WO2004092690A1 - Determining gas volume, porosity, and intrinsic oxidation rate - Google Patents

Determining gas volume, porosity, and intrinsic oxidation rate Download PDF

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Publication number
WO2004092690A1
WO2004092690A1 PCT/AU2004/000512 AU2004000512W WO2004092690A1 WO 2004092690 A1 WO2004092690 A1 WO 2004092690A1 AU 2004000512 W AU2004000512 W AU 2004000512W WO 2004092690 A1 WO2004092690 A1 WO 2004092690A1
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WO
WIPO (PCT)
Prior art keywords
enclosure
volume
sample
gas
determining
Prior art date
Application number
PCT/AU2004/000512
Other languages
French (fr)
Inventor
John William Bennett
Sreten Askraba
Alan Stanley Boyd
Andrew Mckay Garvie
Original Assignee
Australian Nuclear Science & Technology Organisation
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Filing date
Publication date
Application filed by Australian Nuclear Science & Technology Organisation filed Critical Australian Nuclear Science & Technology Organisation
Priority to AU2004231120A priority Critical patent/AU2004231120B2/en
Publication of WO2004092690A1 publication Critical patent/WO2004092690A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/08—Investigating permeability, pore-volume, or surface area of porous materials
    • G01N15/082—Investigating permeability by forcing a fluid through a sample
    • G01N15/0826—Investigating permeability by forcing a fluid through a sample and measuring fluid flow rate, i.e. permeation rate or pressure change
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B7/00—Working up raw materials other than ores, e.g. scrap, to produce non-ferrous metals and compounds thereof; Methods of a general interest or applied to the winning of more than two metals
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F22/00—Methods or apparatus for measuring volume of fluids or fluent solid material, not otherwise provided for
    • G01F22/02—Methods or apparatus for measuring volume of fluids or fluent solid material, not otherwise provided for involving measurement of pressure
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N7/00—Analysing materials by measuring the pressure or volume of a gas or vapour
    • G01N7/02—Analysing materials by measuring the pressure or volume of a gas or vapour by absorption, adsorption, or combustion of components and measurement of the change in pressure or volume of the remainder
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/08—Investigating permeability, pore-volume, or surface area of porous materials
    • G01N2015/0866—Sorption
    • G01N2015/0873—Dynamic sorption, e.g. with flow control means
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/10—Reduction of greenhouse gas [GHG] emissions
    • Y02P10/122—Reduction of greenhouse gas [GHG] emissions by capturing or storing CO2
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

Definitions

  • a method for determining at least one of internal gas volume in a sealed enclosure and whether there is gas leakage into or from the sealed enclosure comprising: a) measuring a first gas pressure in the sealed enclosure; b) changing the internal volume of the sealed enclosure by a known volume, whereby the gas pressure in the enclosure is less than or greater than the gas pressure outside the enclosure; c) measuring a second gas pressure in the sealed enclosure after said changing as a function of time; d) determining from said second gas pressure as a function of time whether there is gas leakage from or into said sealed enclosure; e) where there is no gas leakage from or into said sealed enclosure, determining the internal gas volume of the sealed enclosure from the first and second gas pressures and the known volume.
  • a method for determining at least one of internal gas volume in a sealed enclosure and whether there is gas leakage into or from a sealed enclosure comprising: a) changing the internal volume of the sealed enclosure by a first known volume whereby the gas pressure in the enclosure is less than or greater than the gas pressure outside the enclosure; b) measuring a first gas pressure in the sealed enclosure after said changing as a function of time; and c) determining from said first gas pressure as a function of time whether there is gas leakage from or into said sealed enclosure.
  • said method further comprises: d) further changing the internal volume of the sealed enclosure by a second known volume; e) measuring a second gas pressure in the sealed enclosure after said further changing; and f) determining the internal gas volume of the sealed enclosure from the first and second gas pressures and the known volumes.
  • the first known volume may be the same as or different from the second known volume.
  • a method for determining whether there is gas leakage into or from a sealed enclosure comprising: a) changing the internal volume of the sealed enclosure whereby the gas pressure in the enclosure is less than or greater than the gas pressure outside the enclosure; b) measuring gas pressure in the sealed enclosure after said changing as a function of time; and c) determining from said gas pressure as a function of time whether there is gas leakage from or into said sealed enclosure. Where there is a gas leak from or into the sealed enclosure, the gas pressure will vary as a function of time.
  • a method for determining the volume of a sample of material comprising: a) placing the sample of material in a closable sealable enclosure; b) closing and sealing said enclosure; c) measuring a first pressure within said enclosure; d) changing the internal volume of said enclosure by a known volume, whereby the gas pressure in the enclosure is less than or greater than the gas pressure outside the enclosure; e) measuring a second pressure within said enclosure as a function of time; f) determining from said second pressure as a function of time whether the enclosure has a leak; and g) where the enclosure has no leak, determining the volume of the sample from the volume of the enclosure, the first and second gas pressures, the known volume and the porosity of the sample.
  • a method for determining the volume of a sample of material comprising: a) placing the sample of material in a closable sealable enclosure; b) closing and sealing said enclosure; c) measuring a first gas pressure in the enclosure; d) changing the internal volume of the enclosure by a known volume, whereby the gas pressure in the enclosure is less than or greater than the gas pressure outside the enclosure; e) measuring a second gas pressure in the enclosure after said changing as a function of time; f) determining from said second gas pressure as a function of time whether there is a gas leak from or into said enclosure; g) where there is no gas leak from or into said enclosure, determining the internal gas volume of the enclosure from the first and second gas pressures and the known volume; and h) determining the volume of the sample from the internal gas volume of the enclosure, the first and second gas pressures, the known volume and the porosity of the sample.
  • porosity is taken to mean the proportion of a material that is gas, and includes interstitial gas and gas in open pores, but excludes gas in totally sealed inclusions in the solid portion of the material as well as gas dissolved in any portion of the sample.
  • the porosity is a gas-filled porosity, and does not include the portion of pores that are filled with liquid.
  • Such liquid-containing pores may be common in waste rock samples.
  • the porosity may be in the range of 0.1 to 0.6, for example, or may be 0.1, 0.2, 0.3, 0.4, 0.5 or 0.6, for example.
  • the porosity may, depending on the nature of the waste rock, be taken to be 0.4, but may be determined independently.
  • the volume of the enclosure may be determined by the method of the first aspect of this invention, or by some other means.
  • a method for determining the density of a sample of material comprising: a) placing a known mass of the sample of material in a closable sealable enclosure; b) closing and sealing said enclosure; c) measuring a first pressure within said enclosure; d) changing the internal volume of said enclosure by a known volume, whereby the gas pressure in the enclosure is less than or greater than the gas pressure outside the enclosure; e) measuring a second gas pressure within said enclosure as a function of time; f) determining from said second gas pressure as a function of time whether the enclosure has a leak; g) where the enclosure has no leak, determining a volume of the sample; and h) determining the density of the sample from the volume of the sample and the mass of the sample.
  • a method for determining a gas-filled porosity of a material that contains both gas phase and solid phase intermingled The gas phase may be included in the solid phase either in the form of open pores or cavities within the solid particles or in the form of interstitial spaces between solid particles or both.
  • the method may include the steps of: a) placing the sample in an openable enclosure capable of holding the sample; b) sealing the enclosure; c) measuring a first gas pressure in the enclosure; d) changing the internal volume of the enclosure by a known volume; e) measuring a second gas pressure in the enclosure after said changing; f) determining a volume occupied by the sample; and g) determining the gas-filled porosity of the sample from the volume occupied by the sample, the volume of the enclosure and the volume of gas in the enclosure when the sample is in the enclosure.
  • the step of measuring a second gas pressure may comprise measuring said second gas pressure as a function of time, and the method may comprise the step of determining whether the enclosure has a leak.
  • V g volume of gas in the enclosure (which may conveniently be expressed in m 3 ) when the sample is in the enclosure. This will include interstitial gas and gas in open pores in the sample.
  • V p the known volume (which may conveniently be expressed in m 3 ), which may conveniently be 140x10 " m
  • P 2 pressure of the gas in the sealed enclosure (which may conveniently be expressed in kPa) when the volume of the enclosure is increased by V p .
  • the porosity ⁇ of in the sample may then be calculated using the equation:
  • the method according to this aspect of the invention may be employed for the determination of the volume of gas in the interstitial spaces and open pores in a particulate material, whereby the particulate material is placed inside the sealed enclosure also containing a gas phase, the internal volume of the enclosure is changed by a known volume, and the pressures of the gas phase in the enclosure before and after the change in volume are used to calculate said volume of gas.
  • the moisture levels in the sample may not be the same as the moisture levels in the bulk of the material from which the sample was talcen. This may lead to some inaccuracy in extrapolating the determined values of density and of porosity for the sample to values of those properties for the bulk of the material, although this inaccuracy is likely to be small in many instances.
  • a method for measuring the intrinsic oxidation rate of a sample comprising: a) placing the sample in an openable enclosure capable of holding the sample; b) sealing the enclosure; c) determining at least one of the volume of the sample and the mass of the sample in the enclosure; d) determining changes in gaseous oxygen mass as a function of time; and e) detennining the intrinsic oxidation rate of the sample.
  • ⁇ m changes in mass of oxygen (kg).
  • M m dry mass of the sample.
  • M m may be determined by weighing the dried sample.
  • V -V m ⁇ — * ⁇ (6)
  • V c volume of enclosure, which may be about 4.1x10 "3 m 3
  • V g volume of gas in enclosure (which may conveniently expressed in m 3 ).
  • a method for measuring the intrinsic oxidation rate of a sample comprising: a) placing the sample of material in a closable sealable enclosure; b) closing and sealing said enclosure; c) measuring a first gas pressure in the enclosure; d) changing the internal volume of the enclosure by a known volume, whereby the gas pressure in the enclosure is less than or greater than the gas pressure outside the enclosure; e) measuring a second gas pressure in the enclosure after said changing as a function of time; f) determining from said second gas pressure as a function of time whether there is a gas leak from or into said enclosure; g) where there is no gas leak from or into said enclosure, determining the internal gas volume of the enclosure from the first and second gas pressures and the known volume; h) determining the volume of the sample from the internal gas volume of the enclosure, the first and second gas pressures, the known volume and the porosity of the sample; i) determining a change in gaseous oxygen mass in the enclosure as a function of time; and
  • the method for measuring the intrinsic oxidation rate of a sample comprises: a) placing the sample in an openable enclosure capable of holding the sample; b) sealing the enclosure; c) measuring a first gas pressure in the sealed enclosure having a first volume; d) changing the internal volume of the sealed enclosure by a known volume; e) measuring a second gas pressure in the sealed enclosure after said changing; f) restoring the internal volume of the sealed enclosure to the first volume; g) measuring gaseous oxygen concentration in the enclosure as a function of time for a time sufficient to enable a determination of intrinsic oxidation rate of the sample; h) determining at least one of the volume of the sample and the mass of the sample in the enclosure; i) determining changes in gaseous oxygen mass as a function of time; and j) determining the intrinsic oxidation rate of the sample from the measuring of the gaseous oxygen concentration, the resultant changes in mass of gaseous oxygen in the enclosure as a function of time, from at least one of the volume of the
  • the measurement of gaseous oxygen concentration may be conducted over a period of less than about 24 hours, preferably less than about 12 hours, more preferably, less than about 10 hours. Still more preferably, individual values of gaseous oxygen concentration are obtained at least once every hour throughout the overall measurement period.
  • Measurement of temperature may be made outside the sample container and may be assumed to be the same as inside the sample container, or it may be measured inside the sample container. Measurements of temperature and/or pressure may be taken once only at the beginning of the test, or they may be measured each time a measurement of oxygen concentration is made or they may be measured a different number of times through the progress of the test. Optionally, during all or a portion of a period in which measurements of gaseous oxygen concentration are taken, gas in the enclosure in which the sample is located may be circulated by means of a pump or other similar means.
  • Each individual value of gaseous oxygen concentration may be calculated from a plurality of separate measurements of oxygen concentration, all of which may be measured within a relatively short period of time, by taking an average of some or all of the separate measurements.
  • each individual value of gaseous oxygen concentration may be calculated from a continuous measurement over a short period of time.
  • the gas from an enclosure is passed through a filter or a plurality of filters before a measurement of gaseous oxygen concentration is made.
  • Said filter(s) may be designed to remove one or more of moisture, carbon dioxide, particulate matter and other material that could damage an oxygen sensor or that could alter its ability to accurately measure a concentration of oxygen in a gas.
  • carbon dioxide may affect the accuracy of the measurement of oxygen concentration.
  • carbon dioxide may be filtered out of the gas before a measurement of oxygen is made.
  • the carbon dioxide concentration in the gas from an enclosure may be measured, and the method may comprise the step of compensating the measurement of oxygen concentration for the concentration of carbon dioxide.
  • the IOR so measured may be used, for example, to make decisions in advance regarding the disposition of waste rock generated during blasting in an open cut mining operation.
  • a method for measuring the intrinsic oxidation rate of a sample comprising: a) placing the sample in an openable enclosure capable of holding the sample; b) sealing the enclosure; c) measuring a first gas pressure in the sealed enclosure; d) changing the internal volume of the sealed enclosure by a known volume; e) measuring a second gas pressure in the sealed enclosure as a function of time, to ascertain whether there is gas leakage from or into the enclosure; f) where there is no gas leakage from the enclosure, determining the intrinsic oxidation rate of the sample.
  • the step of placing the sample in the openable enclosure may, if desired, comprise placing a known mass of the sample in the openable enclosure, or it may comprise placing a quantity of the sample in the openable enclosure and then determining the mass of said quantity of the sample.
  • the step of placing the sample in the openable enclosure may, if desired, comprise the step of placing a known volume of sample in the openable enclosure, or it may comprise the step of placing a quantity of the sample in the openable enclosure and then determining the volume of said quantity of the sample.
  • the step of determining the intrinsic oxidation rate of the sample may include: a) restoring the internal volume of the sealed enclosure to the first volume; b) measuring gaseous oxygen concentration in the enclosure as a function of time for a time sufficient to enable a determination of intrinsic oxidation rate of the sample; c) dete ⁇ nining the volume of the sample in the enclosure; d) determining changes in gaseous oxygen mass as a function of time; and e) determining the intrinsic oxidation rate of the sample from the measuring of the gaseous oxygen concentration, the resultant changes in mass of gaseous oxygen in the enclosure as a function of time and from the volume of the sample.
  • the step of measuring the gaseous oxygen concentration may be repeated, and may be repeated more than once.
  • An oxygen concentration may be determined for each step of determining oxygen mass in said enclosure.
  • the value of the oxygen concentration used in a determination of oxygen mass may be derived from a plurality of measurements of said oxygen concentration or from a continuous measurement thereof, conveniently over a short period of time.
  • the value of oxygen concentration used in the determination of oxygen mass is preferably derived from a plurality of measurements of oxygen concentration by determining an average of some or all of said measurements of oxygen concentration.
  • each value of oxygen mass may be derived from more than one individual measurement of oxygen mass, preferably by taking an average of some or all of said individual values of oxygen mass.
  • Each of said individual values of oxygen mass may be determined from a measurement of oxygen concentration in the gas.
  • a method of estimating a rate of oxygen consumption in a pile of material which is oxygenated comprising: a) determining a volume of a sample of the material from the pile of material; b) determining an IOR of the sample of material; c) determining a volume of the pile of material; and d) estimating the rate of oxygen consumption of the pile of material from the volume of the sample, the IOR of the sample and the volume of the pile of material.
  • the volume of the pile of material may conveniently be determined from the dimensions of said pile.
  • the rate of oxygen consumption of the pile of material may conveniently be calculated using the equation:
  • IOR intrinsic oxidation rate (which may be expressed in kg(oxygen)m "3 s '1 )
  • V p ii e volume of the pile of material (which may be expressed in m 3 )
  • sampie volume of the sample of material (which may be expressed in m 3 )
  • the plurality of samples may be taken from the same location in the waste heap, and the IORs obtained from said plurality of samples may be used to determine an average IOR and optionally, the variation of IOR at such single location.
  • the plurality of samples may be taken from different waste heaps in order to compare the IOR for those different heaps with each other.
  • Yet another alternative is to measure the IOR of samples taken from different locations in an open cut mining operation, in order to make decisions in advance regarding the disposition of waste rock from blasting in those different locations. For example, in one application, samples of rock from different locations in an open cut mine where blasting is planned may be tested to determine their IORs. Waste rock with similar IOR from different areas of the blasting operation may then be grouped into allocated waste piles so that the appropriate management of those piles can be effectively implemented.
  • a method for determination of a spatial distribution of intrinsic oxidation rate within a waste heap comprising the steps of: a) obtaining samples from different locations in the waste heap, b) measuring an intrinsic oxidation rate for at least two of the samples, and c) determining a spatial distribution of intrinsic oxidation rate within the waste heap.
  • a system for determining at least one of an internal gas volume in, and whether there is gas leakage into or from, a sealed enclosure comprising: a) an enclosure selected from the group consisting of a sealable enclosure and a sealed enclosure; b) means for changing the internal volume of the sealed enclosure by a known volume whereby the gas pressure in the enclosure is less than or greater than the gas pressure outside the enclosure; c) means for measuring the gas pressure in the sealed enclosure.
  • the system may include means for determining the internal gas volume of the sealed enclosure from the first and second gas pressures and the known volume.
  • the means for measuring gas pressure in the sealed enclosure may be a means for measuring gas pressure in the sealed enclosure as a function of time.
  • a system for determining the porosity of a sample of material comprising: a) an openable sealable enclosure; b) a volume adjustor for changing the internal volume of the enclosure by a known volume, whereby the gas pressure in the enclosure is less than or greater than the gas pressure outside the enclosure; c) a pressure measuring device for measuring the gas pressure in the enclosure as a function of time; d) a volume calculator for calculating the volume of the sample; and e) a porosity calculator.
  • the volume calculator and the porosity calculator may be the same or they may be different. They may for example comprise a computer or other calculating device.
  • the system may also include means for determining the mass of a sample placed in the enclosure, and may also include a means for calculating at least one of the volume of the sample and the density of the sample.
  • a system for determining the volume of a sample of material comprising: a) an openable sealable enclosure; b) a volume adjustor for changing the internal volume of the enclosure by a known volume, whereby the gas pressure in the enclosure is less than or greater than the gas pressure outside the enclosure; c) a pressure measuring device for measuring the gas pressure in the enclosure as a function of time; and d) a volume calculator for calculating the volume of the sample.
  • a system for 5 measuring the intrinsic oxidation rate of a sample comprising: a) an openable enclosure capable of holding the sample said enclosure being selected from the group consisting of a sealable openable enclosure and a sealed openable enclosure; b) means for changing the internal volume of the sealed enclosure by a known i o volume, said means for changing being coupled to the enclosure; c) means for measuring gas pressure and temperature; and d) means for measuring gaseous oxygen concentration in the enclosure.
  • the means for determining the intrinsic oxidation rate may be an IOR determiner.
  • the means for sealing the enclosure may comprise complementary screw threads on each of two portions of the enclosure and a seal that may be compressed when the two portions are screwed together.
  • the means may comprise some other device for sealing the enclosure.
  • the system for measuring the intrinsic oxidation rate of a sample comprises: a) an openable enclosure capable of holding the sample said enclosure being selected from the group consisting of a sealable openable enclosure and a sealed openable enclosure; b) means for sealing the enclosure; c) means for measuring a first gas pressure in the sealed enclosure having a first volume; d) means for changing the internal volume of the sealed enclosure by a known volume; e) means for measuring a second gas pressure in the sealed enclosure; f) means for restoring the internal volume of the sealed enclosure to the first volume; g) means for measuring gaseous oxygen concentration and measurement gas pressure in the enclosure as a function of time for a time sufficient to enable a detennination of intrinsic oxidation rate of the sample; h) means for determining the volume of the sample in the enclosure; i) means for determining temperature; j) means for determining changes in gaseous oxygen mass as a function of time; and k) means for determining the intrinsic oxidation rate of the sample from the
  • said system may also include means to recirculate a gas within an enclosure containing the sample.
  • Said means may be a gas circulator.
  • the means for measuring gaseous oxygen concentration is not located within the enclosure in which the sample is located and there is a means to transport air from the enclosure to the means for measuring gaseous oxygen concentration.
  • the means to transport may be a transport system.
  • there may also be a filter or a plurality of filters which is (are) capable of removing one or more of moisture, carbon dioxide, particulate matter and other material that could damage an oxygen sensor or that could alter its ability to detect an accurate concentration of oxygen in a gas.
  • Said filter(s) may be located such that gas passes through said filter(s) before reaching the means for measuring gaseous oxygen concentration.
  • the means for measuring gaseous oxygen concentration may be an oxygen meter, or an oxygen sensor.
  • the oxygen sensor may be for example an oxygen fuel cell.
  • the system for measuring the intrinsic oxidation rate may have a carbon dioxide filter for removing carbon dioxide from the gas before it reaches the oxygen sensor, since carbon dioxide is capable of affecting the accuracy of an oxygen sensor.
  • the system may comprise a carbon dioxide meter for measuring the concentration of carbon dioxide in the gas.
  • the oxygen sensor may have a compensator so that the measurement of oxygen is compensated for the concentration of carbon dioxide.
  • a system for measuring the intrinsic oxidation rate of a sample comprising: a) an openable enclosure capable of holding the sample said enclosure being selected from the group consisting of a sealable openable enclosure and a sealed openable enclosure; b) means for sealing the enclosure; c) means for measuring a first gas pressure in the sealed enclosure; d) means for changing the internal volume of the sealed enclosure by a known volume; e) means for measuring a second gas pressure in the sealed enclosure as a function of time to ascertain whether there is gas leakage from or into the enclosure; and f) where there is no gas leakage from the enclosure, means for determining the intrinsic oxidation rate of the sample.
  • the means for determining the intrinsic oxidation rate of the sample may include: a) means for restoring the internal volume of the sealed enclosure to the first volume; b) means for measuring gaseous oxygen concentration and for measuring gas pressure in the enclosure as a function of time for a time sufficient to enable a determination of intrinsic oxidation rate of the sample; c) means for determining the volume of the sample in the enclosure; d) means for determining the temperature; e) means for determining changes in gaseous oxygen mass as a function of time; and f) means for determining the intrinsic oxidation rate of the sample from the measuring of the gaseous oxygen concentration and the resultant changes in mass of oxygen as a function of time and from the volume of the sample.
  • a system for determining an IOR for a plurality of samples comprising: a) a plurality of an openable enclosures capable of holding the samples, said enclosures being selected from the group consisting of a sealable openable enclosures and a sealed openable enclosures; b) means for determining the gas volume of each of said enclosures individually; c) means for determining for each enclosure separately whether that enclosure has a gas leak; and d) means for determining for each enclosure separately the IOR of the sample in said enclosure.
  • the system may also include means to isolate an enclosure. Said means may be for example an isolator.
  • the system may include means to isolate an enclosure, or a portion of an enclosure that contains the sample, or more than one such enclosure or portion of an enclosure, if it is determined that there is a leakage into or from said enclosure or enclosures.
  • All of the enclosures may be connected to a single means for changing the volume of the enclosure, a single means for measuring the pressure in the enclosure and a single means for measuring oxygen concentration, which may be a single oxygen sensor.
  • a single means for changing the volumes of the all of the enclosures separate means for measuring the pressure in each enclosure and single means for measuring oxygen concentration in all of the enclosures
  • separate means for changing the volume of each enclosure single means for measuring the pressures in all of the enclosures and single means for measuring oxygen concentration in all of the enclosures
  • separate means for changing the volume of each enclosure separate means for measuring the pressure in each enclosure and single means for measuring oxygen concentration in all of the enclosures
  • each enclosure may have a separate means for measuring temperature, or there may be one means for measuring temperature.
  • Said means may be a voltage divider circuit incorporating a thermistor as a temperature sensor, or a the ⁇ nocouple or a thermometer or may be some other suitable means for measuring temperature.
  • a system for determining a spatial distribution of intrinsic oxidation rates within a waste heap comprising: a) a sampling system for obtaining samples from different locations within the heap; b) a plurality of openable sealable enclosures capable of holding the samples; c) a volume measuring system for determining the gas volume of each of said enclosures individually; d) a leak detection system for determining for each enclosure separately whether that enclosure has a gas leak; e) an intrinsic oxidation rate detection system for determining for each enclosure separately an intrinsic oxidation rate of the sample in said enclosure; and f) distribution determiner for detennining a spatial distribution of intrinsic oxidation rates.
  • a system for estimating a rate of oxygen consumption of a pile of material which is oxygenated comprising; a) means for determining a volume of a sample from the pile of material; b) means for determining an IOR of said sample; c) means for estimating a volume of the pile of material; and d) means for calculating the rate of oxygen consumption of the pile from the IOR and the volumes of the sample and of the pile.
  • the means for determining the volume of the sample may comprise:
  • an enclosure selected from the group consisting of an openable sealable enclosure and an openable sealed enclosure
  • (iv) means for calculating a volume of the sample.
  • the system may additionally include means to estimate the rate of production of pollutant materials from the pile of material from the rate of oxygen consumption of the pile.
  • a system for estimating a rate of oxygen consumption of a pile of material which is oxygenated comprising; a) an openable sealable enclosure capable of holding a sample of the material; b) a volume adjustor for changing the internal volume of the enclosure by a known volume, said adjustor being coupled to the enclosure; c) a pressure measuring device for measuring gas pressure and a temperature measuring device for measuring temperature; d) an oxygen meter for measuring gaseous oxygen concentration of a gas in the enclosure in order to determine an intrinsic oxidation rate of the sample; e) a volume estimator for estimating a volume of the pile of material; and f) an oxygen consumption calculator for calculating the rate of oxygen consumption of the pile from the intrinsic oxidation rate and the volumes of the sample and of the pile.
  • a system for determining the proportion of a gas phase in a material that contains both gas phase and solid phase intermingled comprising: a) an enclosure selected from the group consisting of a sealable enclosure and a sealed enclosure; b) means for changing the internal volume of the sealed enclosure by a known volume whereby the gas pressure in the enclosure is less than or greater than the gas pressure outside the enclosure; c) means for measuring the gas pressure in the sealed enclosure; and d) means for determining the volume of the sample in the enclosure.
  • the system may include means for determining the internal gas volume of the sealed enclosure from the first and second gas pressures and the known volume.
  • the IOR may be measured at any desired combination of values of oxygen concentration, pressure and temperature.
  • IOR is S ma ⁇ , where S max is the IOR determined at atmospheric oxygen concentration.
  • IOR is determined at the same conditions of atmospheric oxygen concentration, temperature and pressure as pertain outside the enclosure(s) in the vicinity of the system for detennining IOR. These conditions may be 25°C, 101.3kPapressure and 20.95% (v/v) oxygen, or one or more of these conditions may be different from these values, depending on local conditions when and at the location at which the IOR is determined.
  • Measurement of IOR can assist in providing estimates for all of these parameters.
  • the rapidity and sensitivity of the system described herein allows a fast and accurate indication of the IOR of a body of waste material, and enables a timely estimate of the prospective environmental impact of the material tested. This allows a user to make informed decisions concerning waste rock pile management. It is a further advantage of the invention that there is no need to pretreat the sample before testing, although pretreatment of a sample, for example drying of a particularly wet sample, may be practiced within the scope of this invention.
  • the volume of the sample is determined, and the IOR is able to be determined, on the same sample without further processing or manipulation of the sample. This simplifies the test, and helps to minimise the time required to conduct a test, and thereby allows the results of the testing to be made available in a relatively short timeframe.
  • IOR systems and methods described in this invention are designed to measure the oxygen consumption rate of sulfidic waste rock and tailing waste materials for the mining industry
  • this instrument could be easily applied in other applications.
  • determination of IOR is of use in management of biooxidation and bioleach heaps, where IOR is used to determine what improvements may be necessary in the operating conditions of such heaps in order to improve the yield of valuable metals from mining operations, and to predict the effective lifetimes of such heaps.
  • the decision about whether to treat a particular sulfidic material in a biooxidation or bioleach heap may be based on economic criteria that may include the time for a pre-determined amount of material to oxidise.
  • Determining the IOR of materials during mining may provide cost- effective and timely information to be used in choosing suitable materials for use in production heaps.
  • the systems and methods in this invention may also find use in other industries such as the food industry, and the scope of the invention is to be construed as including such applications.
  • Figure 1 is a diagrammatic representation of a voltage divider circuit which may be used to measure temperature
  • Figure 2 is a graph of temperature as a function of calculated voltage in the voltage divider circuit of Figure 1;
  • Figure 3 is a diagrammatic representation of a system in accordance with the invention;
  • Figure 4 is a graph showing mass of oxygen consumed by a sample as a function of time, as determined in the course of the Example;
  • Figure 5 is a diagrammatic representation of a sealing system that may optionally be used to seal plastic (PVC) sample containers forming part of the system of Figure 3;
  • Figure 6 is a diagrammatic representation of a mechanism which may optionally be used to control a force urging an upper edge of a sample container against a foam rubber seal fonning part of the system of Figure 3;
  • PVC plastic
  • Figure 7 shows diagrammatic representations of a variety of systems that may be used in accordance with the invention.
  • Figure 8 is a diagrammatic representation of another system in accordance with the invention, said system being not the same as the system represented in Figure 3.
  • circuit 100 may be used to measure temperature. Circuit
  • thermistor 101 with nominal resistance Rthermisto r of 100 kOhm for use within the range of from 0°C to 70°C.
  • the thermistor is used as a sensor in the voltage divider.
  • the maximum power dissipation of thermistor 101 is 28 ⁇ W in the temperature range from 0°C to 70°C.
  • the excitation voltage (U exc it.) provided by power source 102 and fixed resistor (Rf) 103 were determined to be 1.5V and 20 kOhm, respectively. From the manufacturer's specification for thermistor 101, the voltage U f across terminals 104 and 105 was calculated by using the equation:
  • Equation 10 is used to calculate the temperature co ⁇ esponding to a particular measured voltage U f .
  • a system 300 for determining the intrinsic oxidation rate (IOR) of a plurality of samples of material measures the intrinsic oxidation rate of up to eight different samples. The invention is, however, not limited to the use of up to eight samples. Any number of samples may be used at the same time.
  • System 300 includes cylinder 301 having a piston 302, and a pressure sensor 303.
  • System 300 further includes a manifold of valves 304 which incorporates solenoid valves 305a, 306a, 307a, 308a, 309a, 310a, 311a and 312a, and spare solenoid valves 395 and 396 (which in this description remain closed throughout), as well as a manifold of solenoid valves 313 which incorporates solenoid valves 305b, 306b, 307b, 308b, 309b, 310b, 311b and 312b, and also solenoid valve 391 leading to the atmosphere and solenoid valve 317 leading to the oxygen detection system described below.
  • solenoid valves 304 which incorporates solenoid valves 305a, 306a, 307a, 308a, 309a, 310a, 311a and 312a, and spare solenoid valves 395 and 396 (which in this description remain closed throughout), as well as a manifold of solenoid valves 313 which incorporates solenoid valves
  • System 300 also includes eight air pumps 305c, 306c, 307c, 308c, 309c, 310c, 311c and 312c, and eight sample containers 305d, 306d, 307d, 308d, 309d, 310d, 3 lid and 312d.
  • Each of the sample containers 305d, 306d, 307d, 308d, 309d, 310d, 31 id and 312d is openable to enable a sample to be placed into and/or to be removed from it.
  • System 300 also includes an air pump 314, a moisture filter 315, a CO 2 filter 316, an oxygen analyser 318 (with a resolution better than 0.001% co ⁇ esponding to a mass of oxygen less than 3 x 10 "9 g) and a computer 319.
  • Cylinder 301 having piston 302 is coupled to pressure sensor 303 by lines 320 and 321 and to the manifold of valves 313 by lines 320 and 322.
  • Sample containers 305d to 312d are connected to valves 305b to 312b respectively by lines 325, 328, 331, 334, 337, 340, 343 and 390 respectively.
  • valve 317 The manifold of valves 313 is coupled via valve 317 to moisture filter 315 by line 362, whilst moisture filter 315 is coupled to CO 2 filter 316 by line 364, and CO 2 filter 316 is coupled to the pump 314 by line 365, and pump 314 is coupled to oxygen analyser 318 by line 366, and oxygen analyser 318 is coupled to manifold of valves 304 by line 367.
  • the computer 319 is electrically coupled to air pump 314 by line 368, to oxygen analyser 318 by line 371, to piston 302 by line 372, to the pressure sensor 303 by line 373, to manifold of valves 313 which incorporates valves 305b, 306b, 307b, 308b, 309b, 310b, 311b, 312b, 391 and 317 by a plurality of lines capable of controlling each of the solenoid valves in manifold 313 individually (for the sake of clarity, only one of said lines, 374, is shown in Figure 3), to the manifold of valves 304 which incorporates inlet valves 305a, 306a, 307a, 308a, 309a, 310a, 311a, 312a, 395 and 396 by a plurality of lines capable of controlling each of the solenoid valves in manifold 304 individually (for the sake of clarity, only one of said lines, 375, is shown in Figure 3), and to the air pumps 305c
  • Figure 4 shows experimental data for variation of oxygen content as a function of time, obtained in the Example.
  • the abscissa of the graph represents the time expired since the start of the test, and the ordinate axis represents the mass of oxygen detected in an enclosure containing a sample, individual points on the graph represent individual values of oxygen mass at the co ⁇ esponding time shown on the abscissa.
  • Figure 5 shows a mechanism which may optionally be used for sealing sample containers in the system of Figure 3.
  • Figure 5 only those four sample containers that are located at the front of system 300 of Figure 3 are shown.
  • a similar assembly containing a further four sample containers is located at the rear, behind the assembly shown.
  • individual sample containers 501, 502, 503 and 504 may be located in complementary sample bases 531, 532, 533 and 534, which are attached to a movable sample container holder 506.
  • Sample container holder 506 is located above the fixed base 508 of the system 300.
  • Fixed base 508 is a portion of frame 550.
  • Shelves 551 and 552 are provided for convenient storage of other components of the system, tools, samples or other items.
  • Linear actuators 510, 511 and 512 are used to move the sample container holder 506, and thereby the sample containers 501, 502, 503 and 504, in a vertical direction.
  • the top plate 514 is in a fixed position, and is attached to the sample container lids 516, 517, 518 and 519, each of which is fitted with a 6mm thick closed cell neoprene foam rubber seal 522, 523, 524 and 525 respectively.
  • the force applied by the rims of the sample containers 501, 502, 503 and 504 to the seals 522, 523, 524 and 525 maybe adjusted.
  • Bolts 610, 611 and 612 are fitted with washers 615, 616 and 617, springs 620, 621 and 622 and washers 625, 626 and 627, and connect plates 604 and 606, fitting through both sets of holes in those plates.
  • Bolts 610, 611 and 612 are held in place by nuts 630, 631 and 632, located beneath fixed plate 604. The length of stainless steel springs 620, 621 and 622, and the position of bottom nuts 630, 631 and 632, regulate the distance between plates 604 and 606.
  • Figure 7e is a diagrammatic representation of a further system which may be used in accordance with the eighth aspect of the invention.
  • gas in container 702 may be circulated by means of pump 710.
  • the system of Figure 7e may also be used in accordance with other aspects of the invention, for example the ninth aspect.
  • Figure 7 is not intended to represent all of the possible systems that may be used in accordance with this invention, and should not be taken as in any way limiting the invention to those systems shown diagrammatically in Figure 7.
  • FIG 8 there is represented a system 800, wherein those components of the system that are in common with Figure 3 are described above, and serve the same functions as described for Figure 3.
  • moisture filter 315 and CO 2 filter 316, together with lines 362, 364 and 365 are omitted, and manifold of valves 313 is connected via valve 317 to pump 314 by line 862.
  • sample containers 305d, 306d, 307d, 308d, 309d, 310d, 31 Id and 312d are connected to valves 305b, 306b, 307b, 308b, 309b, 310b, 311b and 312b respectively by a) line 805a, CO 2 filter 805b, line 805c, moisture filter 805d and lines 805e and 805f; b) line 806a, CO 2 filter 806b, line 806c, moisture filter 806d and lines 806e and 806f; c) line 807a, CO 2 filter 807b, line 807c, moisture filter 807d and lines 807e and 807f; d) line 808a, CO 2 filter 808b, line 808c, moisture filter 808d and lines 808e and 808f; e) line 809a, CO 2 filter 809b, line 809c, moisture filter 809d and lines 809e and 809f; f) line 810a,
  • Moisture filters 805d, 806d, 807d, 808d, 809d, 810d, 81 Id and 812d are connected to air pumps 305c, 306c, 307c, 308c, 309c, 310c, 311c and 312c respectively by lines a) 805e and 805g; b) 806e and 806g; c) 807e and 807g; d) 808e and 808g; e) 809e and 809g; f) 810e and 810g; g) 81 le and 81 lg; and h) 812e and 812g respectively.
  • an enclosure as used in this description, comprises cylinder 301, pressure sensor 303, manifold 313, one of solenoid valves 305b to 312b, the co ⁇ esponding one of pumps 305c to 312c, the co ⁇ esponding one of sample containers 305d to 312d, together with tubing connecting the above to each other and to the co ⁇ esponding solenoid valve of 305 a to 312a, as shown diagrammatically in Figure 3.
  • the enclosure that incorporates sample container 305d will be refe ⁇ ed to as enclosure 1
  • the enclosure that incorporates sample container 306d will be refe ⁇ ed to as enclosure 2 and so forth, such that the enclosure that incorporates sample container 312d will be refe ⁇ ed to as enclosure 8.
  • a program written in Lab VIEW computer language controls the data acquisition device, solenoid valves, air pumps, linear actuators, thermistor, pressure sensor and oxygen analyser.
  • each sample container is placed in a sample container base, represented by the sample bases 501, 502, 503 and 504 of Figure 5, and shown in detail in Figure 6.
  • a sample container base represented by the sample bases 501, 502, 503 and 504 of Figure 5, and shown in detail in Figure 6.
  • the force with which the sample containers represented by the sample containers 501, 502, 503 and 504 of Figure 5) impinge on the seals 522, 523, 524 and 525 ( Figure 5) may be set to an appropriate value.
  • the linear actuators 510, 511 and 512 are then used to raise the movable sample container holder 506 ( Figure 5) so that the sample containers seal against the sample container lids 516, 517, 518 and 519 ( Figure 5) by means of seals 522, 523, 524 and 525.
  • a second pressure P 2 is then measured using pressure sensor 303.
  • the quality of the seal is improved until the procedure described above shows that there is not a leakage into or from enclosure 1.
  • the acceptable amount of the difference between P 2 and P 3 may be chosen to be less than 200, 150, 100, 80, 60, 40, 20, 10, 5 or lPa, or some other acceptable value if required.
  • the above method for determining the internal gas volume of enclosure 1 is then repeated using the appropriate combinations of valves and other elements in order to determine the internal gas volumes of enclosures 2 to 8 in turn, although it is not necessary to measure a new value of the first gas pressure Pi for each enclosure, since Pi is the same as the ambient atmospheric pressure.
  • That value may be stored. The stored value may then be used for subsequent tests, rather than redete ⁇ nining the volume of the enclosure as described above.
  • Enclosures 1 to 8 are then opened by using linear actuators 510, 511 and 512 to lower sample container holder 506.
  • a sample of material to be tested is then placed in each of the sample containers 305d to 312d (although one or more containers may be left empty if desired), the sample containers are located in the co ⁇ esponding sample container bases, and the enclosures are sealed by using linear actuators 510, 511 and 512 to raise the sample container holder 506.
  • a similar procedure is followed to that described above to determine whether there is a gas leakage into or from enclosure 1 and to determine the internal gas volume of enclosure 1 before the sample was loaded into container 305d.
  • the acceptable amount of the difference between P 2 and P 3 may be chosen to be less 200, 150, 100, 80, 60, 40, 20, 10, 5 or lPa, or some other acceptable value if required.
  • the method for determining whether there is a gas leakage into or from an enclosure, and for determimng the volume of gas in an enclosure and for restoring the internal volume of the enclosure to its original value, as described above, is then repeated for each of the enclosures 2 to 8 in turn, although it is not necessary to measure a new value of Pi for each enclosure, since Pi is the same as the ambient atmospheric pressure.
  • the ambient temperature is then measured, using a voltage divider circuit containing a thermistor, as shown diagrammatically in Figure 1.
  • the voltage U f determined by the circuit shown in Figure 1 is used to determine the temperature by use of a calibration curve such as that shown in Figure 2. Alternatively temperature may be measured by some other convenient means. This temperature used in all calculations relating to this invention where temperature is required.
  • valves 305a to 312a and 305b to 312b, and valves 391 and 317 are all closed.
  • the oxygen concentrations in enclosures 2 to 8 are measured individually in turn, using the appropriate combinations of solenoid valves, pumps and other components of system 300 shown diagrammatically in Figure 3.
  • pumps 305c to 312c are started and are used continuously throughout the remainder of the test to circulate gas through containers 305d to 312d respectively.
  • the measurement of oxygen concentration of the gas in the enclosures is performed for each enclosure as described above, at approximately hourly intervals over an approximately ten hour period.
  • the volume of sample in each cylindrical sample container is also determined. This may conveniently be done by measuring the depth of the sample in the sample container, and then applying Equation 1 to determine the volume V m .
  • a program written in Lab VIEW computer language controls the data acquisition device, solenoid valves, air pumps, linear actuators, thermistor, pressure sensor and oxygen analyser.
  • the methods for determining the volume of each sealable container, for determining whether there is a gas leakage into or from each enclosure and for measuring the ambient temperature are the same as was described above for the earlier mode of operation.
  • valves 305a to 312a and 305b to 312b, and valves 391 and 317 are all closed.
  • a gaseous oxygen concentration in enclosure 1 is measured as follows.
  • An IOR meter as shown diagrammatically in Figure 3, was used to measure the IOR of reactive rock samples over a period of approximately 12 hours. Reactive rock samples were placed in eight plastic (PVC) sample containers of volume approximately 4xl0 "3 m 3 , which were then sealed in a reversible manner into the IOR meter.
  • PVC plastic
  • This example describes a process that may be used to control the operation of, and acquire data from, a system for measuring IOR of a plurality of samples in accordance with this invention.
  • the steps of the process are described with reference to Figure 1, Figure 3 and Figure 5.
  • Figure 3 there is a linear actuator, not shown in Figure 3, which may be used to move piston 302 in order to change the internal gas volume of one or more of enclosures 1 to 8.
  • Figure 5 as was described above, a similar assembly containing a further four sample containers is located at the rear, behind the assembly shown. Elements in the rear assembly will be refe ⁇ ed to in tins example with a suffix b.
  • linear actuators 510, 511 and 512 are similar linear actuators 510b, 511b and 512b respectively. This does not apply to any numbers representing components in Figures other than Figure 5.
  • MFC mass flow controller
  • the computer opens communications with the following modules: linear actuators, solenoid valves, pumps, mass flow controller (if present), oxygen sensor, pressure sensor, thermistor, then blanks the display panels and initialises graphs.
  • the operator should then input into the computer program the sample containers that are to be tested.
  • the screen of computer 319 then displays the text "test/no test" for the 8 sample containers 305d, 306d, 307d, 308d, 309d, 310d, 3 l id and 302d.
  • the operator should input the details of the contents of each sample container.
  • the operator is then prompted for a file name.
  • the file is then created, and the file name, date, time, contents of sample containers and file headers are saved to a file for each sample container.
  • the power to linear actuators (510, 511, 512, 510b, 511b and 512b) for the sample container holders (506 and 506b), and the power to piston 302 and linear actuator are turned off.
  • Air valve 391, oxygen pump valve 317 and valves 305b to 312b are then closed, and air pumps 305c to 312c for sample containers are turned off.
  • the operator then places the sample containers on the holders.
  • a prompt appears on the screen of computer 319: "Are the canisters in place on the holders? Press OK when you are ready to begin testing.”
  • the start time is displayed on screen of computer 319 and time is set to t 0 for test.
  • Linear actuators 510, 511, 512, 510b, 511b and 512b are activated. If only testing any or all of sample containers 501 to 504 then only front sample container holder 506 is activated using linear actuators 510, 511 and 512. If only testing any or all of sample containers 501b to 504b then only back sample container holder 506b is activated using linear actuators 510b, 511b and 512b. If testing a plurality of sample containers, at least one of which is one of 501, 502, 503 and 504 and at least one of which is one of 501b, 502b, 503b and 504b, then both sample container holders are activated.
  • the screen of computer 319 displays the text "sealing canister” for each sample container that will be tested. After an 8 second delay to allow for the sample containers to be lifted up, the power to the linear actuators 510, 511, 512, 510b, 511b and 512b is turned off. Air valve 391 and valves 305b to 312b are then opened. This equalises the pressure in all sample containers to atmospheric pressure. The screen of computer 319 displays the text "Equalising Canister” for each sample container to be tested. After waiting 60s for the sample containers and gas lines to equalise to atmospheric pressure, the barometric pressure (ie P atm , atmospheric pressure) is determined and displayed, and the value is saved to file.
  • the barometric pressure ie P atm , atmospheric pressure
  • Solenoid valves 305b to 312b are then closed.
  • the screen of computer 319 displays "measuring pressure in canister/waiting/pressure test completed" for each enclosure that is to be tested.
  • the solenoid valve in manifold 313 that co ⁇ esponds to the enclosure to be tested is opened, and also air valve 391 is opened for 10 seconds to equalise the single enclosure to atmospheric pressure again.
  • air valve 391 is closed.
  • the computer then reads, calculates and stores pressure Pi from pressure sensor 303.
  • the actuator for piston 302 is activated, to withdraw gas from the enclosure. After waiting 40 seconds for the piston to move and for system to stabilise, the power to the linear actuator is turned off.
  • the computer then reads pressure P 2 from the pressure sensor. After waiting a further 40 seconds to check for a leak in the enclosure seal, the computer reads pressure P 3 from pressure sensor and calculates P ⁇ -P 2 and P 3 -P2. If Pi - P2 ⁇ 3 kPa then sample container is not present and this enclosure is not tested any further, and the screen of computer 319 displays the text "canister not present". If P 3 - P 2 ⁇ 0.08 kPa then there is no leak. Otherwise, testing on the enclosure is discontinued and the screen of computer 319 displays the text "leak".
  • thermistor 1.5V is applied to thermistor (see Figure 1) so that the temperature can be read.
  • voltage Uf is read the from the voltage divider of the thermistor, and the temperature is calculated, displayed and stored. The voltage that was applied to the thermistor is then turned off. If present, the MFC is activated and flow rate set to 0.4 L/min. Then, for each cycle the following procedure is followed. Firstly, for each enclosure that is being tested the following operations are conducted, in order to determine a mass of oxygen in each of the enclosures. The two solenoid air valves (one in each of manifolds 304 and 313) co ⁇ esponding to the enclosure being tested, are opened at the same time.
  • Air pump valve 317 is also opened, and air pump 314 is turned on by setting the voltage of the pump to 1.75V.
  • air pump 318 After eight minutes of n ning air pump 318, the output from oxygen analyser 318 is read, calculated and stored every 10 seconds for 60s, and the average reading for the 60s is calculated, display and stored, and the time t X j seconds when the average value was calculated is also recorded. Therefore, air pump 318 runs for nine minutes in total.
  • the mass of oxygen, m X) i is then calculated, displayed and then stored in the file. After each measurement of the mass of oxygen except for the first measurement for each sample, the IOR for the sample is then calculated using a linear fit to the data stored in the file, and is then displayed on the screen of computer 319.
  • IOR is expressed in either units kg(O 2 )kg(material) "1 s "1 or kg(O 2 )m “3 s "1 depending on which units were selected on the main screen of computer 319 by the user. If in kg(material) then user should enter mass of material on the computer 319 before test started and if m "3 then user should have entered volume of material on the computer 319 before test started.) The mean square e ⁇ or to the fit of the IOR is then calculated and stored in the file. Air pump 314 is then turned off by setting the voltage to the pump to 0V, and the air pump valve 317 and solenoid valves in manifolds 304 and 313 co ⁇ esponding to the enclosure being tested are closed.
  • the air pumps in all of the enclosures, 305c to 312c are turned on, and the screen of computer 319 displays the text "Waiting till next oxygen measurement”. After a delay of several minutes (the exact time is set by the user on the computer) for the gas in the sample containers may to circulate and mix, the air pumps, 305c to 312c are turned off.
  • the screen of computer 319 displays the text "Testing completed”.
  • the voltages for thermistor, MFC (if present) and oxygen air pump are set to 0V.
  • Valves 305a to 312a are closed, the linear actuators are reset to the start position, fully extended (turn the relay OFF): Group A (510, 511 and 512) and Group B (510b, 511b and 512b).
  • Valves 305b to 312b and air valve 391 are opened. This ensures that there is no pressure built up inside the sample containers so that they will not get stuck and will move down with the sample container holder.
  • Piston 302 is reset to the start position.

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Abstract

The present invention describes a method for measuring the intrinsic oxidation rate of a sample wherein a sample of material is placed in a closable sealable enclosure, the enclosure is closed and sealed, and a first gas pressure is measured in the enclosure. The internal volume of the enclosure is then changed by a known volume and a second gas pressure is measured in the enclosure after said changing as a function of time. It is then determined from said second gas pressure as a function of time whether there is a gas leak from or into said enclosure. Where there is no gas leak, the internal gas volume of the enclosure is determined from the first and second gas pressures and the known volume. The porosity of the sample may then determined from the volume of gas in the enclosure, the volume of the enclosure and the volume occupied by the sample. A change in gaseous oxygen mass in the enclosure is then determined as a function of time and the intrinsic oxidation rate of the sample determined. The invention further describes methods for determining the intrinsic oxidation rate of a plurality of samples, and for determining a spatial distribution of intrinsic oxidation rate within a waste heap, as well as systems for performing the methods of the invention.

Description

DETERMINING GAS VOLUME, POROSITY, AND INTRINSIC OXIDATION RATE
Technical Field
This invention relates to a method for measuring the oxidation rate of a sample of porous material. In particular, the invention relates to a method for determining the intrinsic oxidation rate (IOR) of waste rock from a mine by measuring changes as a mnction of time in oxygen levels in the gas which has been in contact with a sample of the waste.
Background Art
Pyrite and other sulfidic minerals commonly occur in many of the base metal, precious metal and coal deposits which are mined around the world. Sulfidic materials below cut-off grade are routinely consigned to waste rock dumps and sulfidic wastes from ore processing are piped to tailings storage facilities. In these piles the sulfides may be exposed to air and may undergo oxidation reactions, generating sulfate and iron salts, sulfuric acid and possibly mobilising trace metals present in the wastes such as nickel, copper, cobalt, zinc etc. Such low quality drainage may be referred to as acid mine drainage (AMD) or acid rock drainage (ARD). The presence of metal species in drainage waters from sulfidic waste piles may cause receiving ecosystems to be adversely affected. There is a need for a means to predict whether a particular mine waste might present an ecological risk and, if it does so, to manage the waste in order to reduce the risk to an acceptable level. To meet this need, a numerical model is required which can be used with confidence to predict the chemical composition of drainage waters from a full-sized waste pile.
The intrinsic oxidation rate (IOR) is the rate of oxidation of material at a point in a system (for example a column, stockpile or a dump), under the particular conditions which pertain at that point. The IOR is a function of many parameters, such as oxygen concentration, sulfide sulfur concentration, temperature, pH, sulfide mineral morphology, microbial ecology etc. Since there currently exists no method for predicting the functional dependence of the IOR by measuring individual material characteristics, a reasonable alternative approach uses direct measurements of oxidation rate, either of samples in the laboratory or in-situ.
Field measurements of IOR are usually expressed as mass of oxygen consumed per cubic metre of material per second [kg(O2) m" s" ]. If the mass or bulk density of the material is known, then IOR may be expressed as the mass of oxygen consumed per mass of material per second [kg(O2) kgCrnateriaiyV1].
The use of IOR in predictive modelling of sulfidic piles has been well described by Ritchie (Ritchie, A.I.M, "Bio-oxidation heaps and AMD from waste rock dumps - the importance of the intrinsic oxidation rate", in Proceedings of the AusIMM Annual Conference, Darwin, 5-9 August 1994, pp. 473-476). IOR is the property of the material which enables oxidation and primary pollutant generation rates in a system to be described as a function of space and time.
Various forms of the functional dependence of the IOR have been proposed. Ritchie (Ritchie, A.I.M. "Sulfide oxidation mechanisms: controls and rates of oxygen transport" in Short Course Handbook on Environmental Geochemistry of Sulfide Mine- Wastes, vol. 22, eds. D.W.Blowes and J..L Jambour, pp 201-245, Mineralogical Association of Canada, May 1994, Waterloo) has shown that the overall oxidation rate in a waste rock dump is comparatively insensitive to detailed changes in the intrinsic oxidation rate unless the IOR is very low. It follows that in many situations, knowledge of the detailed dependencies of the IOR are not required for the practical purposes of decision-making in the management of sulfidic wastes.
The management of waste material in the mining industry is expensive. It is believed that characterising and selecting materials with respect to their intrinsic oxidation rate during a mining operation would be a cost-effective element of a strategy for management of waste materials.
There is no conventional instrument available that is capable of determining the IOR of material at an accuracy of the order 10"10 kg O^m' 1 in the time frame of less than about 12 hours. A typical time for laboratory measurements is between 2 and 3 days. The data obtained from an instrument that could accurately measure IOR of waste material in a period of, say, less than about 12 hours, would, if such an instrument were available, be beneficial for characterising and selecting waste material. There is therefore a need for an instrument capable of measuring IOR of mine waste material in a relatively short period of time. A device for measuring the rate of oxygen consumption by waste rock from mining operations has been disclosed in a paper by Anderson, Scharer and Nicholson (Sudbury 1999, Mining and the Environment, Sudbury, Canada pp. 1133 to 1142). The authors specify in that paper that their device requires a measurement time of 1 to 3 days, which is too long to provide the rapid results necessary for efficient management of waste rock piles. In addition, although the authors claim the ability to measure multiple samples simultaneously, to do so using their system has the disadvantage that it would require the use of multiple oxygen sensors. High sensitivity oxygen sensors are required in order to enable accurate measurement of the IOR of samples of a conveniently small size for laboratory testing. Further, the gas within the sample in the device described by Anderson, Scharer and Nicholson is static, since the device has no means to circulate the gas. Consequently, the system must rely on diffusion through a porous mass of rock to the headspace above in order to achieve a representative measurement of gaseous oxygen concentration. In addition, the oxygen sensor is inserted directly into the sample container. This arrangement can allow damage or contamination of the oxygen sensor. The presence of moisture and CO can damage sensitive oxygen sensors, or lead to inaccurate results. Further, in that device there are no means to determine whether the sample container has leaks. Since typical samples for the device are waste rock material, the potential for particulate contamination of the seals is considerable. Such contamination could cause leaks, and consequently allow oxygen diffusion from the outside atmosphere, which would lead to measurement errors.
Objects of the Invention
It is an object of this invention to address the aforementioned need. It is another object of this invention to overcome at least one of the disadvantages of the prior art. It is a further object to provide methods and systems for determining the intrinsic oxidation rate (IOR) of one or more samples of waste material in a period of time sufficiently short to allow for timely characterisation and selection of waste material.
Disclosure of Invention According to a first aspect of this invention, there is provided a method for determining internal gas volume in a sealed enclosure, said method comprising: a) measuring a first gas pressure in the sealed enclosure; b) changing the internal volume of the sealed enclosure by a known volume; c) measuring a second gas pressure in the sealed enclosure after said changing; and d) determining the internal gas volume of the sealed enclosure from the first and second gas pressures and the known volume.
According to a second aspect of this invention, there is provided a method for determining at least one of internal gas volume in a sealed enclosure and whether there is gas leakage into or from the sealed enclosure, said method comprising: a) measuring a first gas pressure in the sealed enclosure; b) changing the internal volume of the sealed enclosure by a known volume, whereby the gas pressure in the enclosure is less than or greater than the gas pressure outside the enclosure; c) measuring a second gas pressure in the sealed enclosure after said changing as a function of time; d) determining from said second gas pressure as a function of time whether there is gas leakage from or into said sealed enclosure; e) where there is no gas leakage from or into said sealed enclosure, determining the internal gas volume of the sealed enclosure from the first and second gas pressures and the known volume.
Where there is a gas leak from or into the sealed enclosure, the second gas pressure will vary as a function of time.
According to a third aspect of this invention there is provided a method for determining at least one of internal gas volume in a sealed enclosure and whether there is gas leakage into or from a sealed enclosure, said method comprising: a) changing the internal volume of the sealed enclosure by a first known volume whereby the gas pressure in the enclosure is less than or greater than the gas pressure outside the enclosure; b) measuring a first gas pressure in the sealed enclosure after said changing as a function of time; and c) determining from said first gas pressure as a function of time whether there is gas leakage from or into said sealed enclosure.
Where there is no gas leakage from or into said sealed enclosure, said method further comprises: d) further changing the internal volume of the sealed enclosure by a second known volume; e) measuring a second gas pressure in the sealed enclosure after said further changing; and f) determining the internal gas volume of the sealed enclosure from the first and second gas pressures and the known volumes.
The first known volume may be the same as or different from the second known volume.
According to a fourth aspect of this invention, there is provided a method for determining whether there is gas leakage into or from a sealed enclosure, said method comprising: a) changing the internal volume of the sealed enclosure whereby the gas pressure in the enclosure is less than or greater than the gas pressure outside the enclosure; b) measuring gas pressure in the sealed enclosure after said changing as a function of time; and c) determining from said gas pressure as a function of time whether there is gas leakage from or into said sealed enclosure. Where there is a gas leak from or into the sealed enclosure, the gas pressure will vary as a function of time.
According to a fifth aspect of this invention, there is provided a method for determining the volume of a sample of material, said method comprising: a) placing the sample of material in a closable sealable enclosure; b) closing and sealing said enclosure; c) measuring a first pressure within said enclosure; d) changing the internal volume of said enclosure by a known volume, whereby the gas pressure in the enclosure is less than or greater than the gas pressure outside the enclosure; e) measuring a second pressure within said enclosure as a function of time; f) determining from said second pressure as a function of time whether the enclosure has a leak; and g) where the enclosure has no leak, determining the volume of the sample from the volume of the enclosure, the first and second gas pressures, the known volume and the porosity of the sample.
In an embodiment there is provided a method for determining the volume of a sample of material, said method comprising: a) placing the sample of material in a closable sealable enclosure; b) closing and sealing said enclosure; c) measuring a first gas pressure in the enclosure; d) changing the internal volume of the enclosure by a known volume, whereby the gas pressure in the enclosure is less than or greater than the gas pressure outside the enclosure; e) measuring a second gas pressure in the enclosure after said changing as a function of time; f) determining from said second gas pressure as a function of time whether there is a gas leak from or into said enclosure; g) where there is no gas leak from or into said enclosure, determining the internal gas volume of the enclosure from the first and second gas pressures and the known volume; and h) determining the volume of the sample from the internal gas volume of the enclosure, the first and second gas pressures, the known volume and the porosity of the sample.
In this specification, porosity is taken to mean the proportion of a material that is gas, and includes interstitial gas and gas in open pores, but excludes gas in totally sealed inclusions in the solid portion of the material as well as gas dissolved in any portion of the sample. The porosity is a gas-filled porosity, and does not include the portion of pores that are filled with liquid. Such liquid-containing pores may be common in waste rock samples. For waste rock samples, the porosity may be in the range of 0.1 to 0.6, for example, or may be 0.1, 0.2, 0.3, 0.4, 0.5 or 0.6, for example. In particular the porosity may, depending on the nature of the waste rock, be taken to be 0.4, but may be determined independently.
The volume of the enclosure may be determined by the method of the first aspect of this invention, or by some other means.
According to a sixth aspect of this invention, there is provided a method for determining the density of a sample of material, comprising: a) placing a known mass of the sample of material in a closable sealable enclosure; b) closing and sealing said enclosure; c) measuring a first pressure within said enclosure; d) changing the internal volume of said enclosure by a known volume, whereby the gas pressure in the enclosure is less than or greater than the gas pressure outside the enclosure; e) measuring a second gas pressure within said enclosure as a function of time; f) determining from said second gas pressure as a function of time whether the enclosure has a leak; g) where the enclosure has no leak, determining a volume of the sample; and h) determining the density of the sample from the volume of the sample and the mass of the sample.
The volume of the sample may be determined from volume of the enclosure, the volume of gas in the enclosure when the sample is present and the porosity of the sample. The volume of gas in the enclosure when the sample is present may be determined from the first and second gas pressures, the known volume. Details of these calculations are provided later in this specification. The sample referred to in this aspect of the invention includes all portions of the sample including solid matter, moisture included in the sample and gaseous material in pores, interstitial spaces, inclusions and other spaces.
Alternatively, the mass of the sample may be determined after it has been placed inside the openable enclosure. This may for example comprise: a) measuring the mass of the openable enclosure or a part thereof capable of holding the sample, before the sample has been placed therein; b) measuring the mass of the openable enclosure or the part thereof after the sample has been placed therein; and c) subtracting the mass of step a) from the mass of step b).
According to a seventh aspect of the invention, there is provided a method for determining a gas-filled porosity of a material that contains both gas phase and solid phase intermingled. The gas phase may be included in the solid phase either in the form of open pores or cavities within the solid particles or in the form of interstitial spaces between solid particles or both. The method may include the steps of: a) placing the sample in an openable enclosure capable of holding the sample; b) sealing the enclosure; c) measuring a first gas pressure in the enclosure; d) changing the internal volume of the enclosure by a known volume; e) measuring a second gas pressure in the enclosure after said changing; f) determining a volume occupied by the sample; and g) determining the gas-filled porosity of the sample from the volume occupied by the sample, the volume of the enclosure and the volume of gas in the enclosure when the sample is in the enclosure. The step of measuring a second gas pressure may comprise measuring said second gas pressure as a function of time, and the method may comprise the step of determining whether the enclosure has a leak.
The volume occupied by the sample may be determined by calculation using a measured depth of the sample and the known geometry and dimensions of the sealed enclosure. For example, if the sealed enclosure is a vertical cylinder of radius R, and the depth of the sample is D, then the volume Vm may be determined from the equation:
Vm = π.R2.D (1)
Alternatively, the volume may be determined by removing the sample from the enclosure and inserting into the enclosure sufficient quantity of a reference material of known density, for example water, to occupy the same volume as had been occupied by the sample. The mass of that quantity of the reference material may then be determined, and the volume of the sample determined from the equation:
Vm - m/d (2) where: m is the mass of the reference material d is the bulk density of the reference material
The total volume of the gas phase in the enclosure may be calculated from the equation: p 2 D =^~^ (3)
Vg = volume of gas in the enclosure (which may conveniently be expressed in m3) when the sample is in the enclosure. This will include interstitial gas and gas in open pores in the sample.
Vp = the known volume (which may conveniently be expressed in m3), which may conveniently be 140x10" m
Pi = pressure of the gas within the enclosure before changing the volume of the container (which may conveniently be expressed in kPa), which may be the same as the pressure outside the enclosure.
P2 = pressure of the gas in the sealed enclosure (which may conveniently be expressed in kPa) when the volume of the enclosure is increased by Vp.
The porosity ε of in the sample may then be calculated using the equation:
Figure imgf000009_0001
Vc = volume of the enclosure
The method according to this aspect of the invention may be employed for the determination of the volume of gas in the interstitial spaces and open pores in a particulate material, whereby the particulate material is placed inside the sealed enclosure also containing a gas phase, the internal volume of the enclosure is changed by a known volume, and the pressures of the gas phase in the enclosure before and after the change in volume are used to calculate said volume of gas.
With reference to the sixth and the seventh aspects of this invention, the moisture levels in the sample may not be the same as the moisture levels in the bulk of the material from which the sample was talcen. This may lead to some inaccuracy in extrapolating the determined values of density and of porosity for the sample to values of those properties for the bulk of the material, although this inaccuracy is likely to be small in many instances. According to an eighth aspect of this invention, there is provided a method for measuring the intrinsic oxidation rate of a sample comprising: a) placing the sample in an openable enclosure capable of holding the sample; b) sealing the enclosure; c) determining at least one of the volume of the sample and the mass of the sample in the enclosure; d) determining changes in gaseous oxygen mass as a function of time; and e) detennining the intrinsic oxidation rate of the sample.
Preferably the enclosure is not opened and the sample is not disturbed after said sealing but before said determining changes in gaseous oxygen mass as a function of time.
The intrinsic oxidation rate (IOR) is the rate at which oxygen is consumed by the sample. It depends on the concentration of oxygen in the gas in which the sample is located. IOR is conveniently measured at atmospheric oxygen concentration, however the actual IOR of a sample will vary with the local oxygen concentration. For example, in the centre of a mineral waste dump, if the oxygen has been depleted by the material in the dump, the IOR of a sample may be considerably lower than it would be if the same sample were located in a region of atmospheric oxygen concentration. IOR may conveniently be expressed as:
Figure imgf000010_0001
where:
IOR = intrinsic oxidation rate (kg(oxygen)m" s" ).
Δm = changes in mass of oxygen (kg).
At = time period (s)
Vm = volume of material (m3). Equation 5 provides a volume based IOR. A similar equation, Equation 5 a, may also be used to determine a mass based IOR, which may be expressed in kg(oxygen)kg_1 (materials'1 :
Figure imgf000010_0002
where Mm = dry mass of the sample. Mm may be determined by weighing the dried sample.
Vm may be calculated using the equation:
V -V m = ^— *■ (6)
1-ε Vc = volume of enclosure, which may be about 4.1x10"3m3
Vg = volume of gas in enclosure (m3). ε = porosity (a typical value for the materials commonly investigated by this instrument is ε=0.4 although it may commonly have a different value, ε may be determined independently).
The mass of oxygen is defined by the equation: m = -^-p x — V (7)
RT 100 s where: m = mass of oxygen (which may conveniently expressed in kg), μ = molar mass of oxygen (μ=32 x 10" kg moi" ), p = pressure, which may be atmospheric pressure (which may conveniently expressed in kPa).
R = universal gas constant (R=8.314 nΛgK^s^mol"1),
T = temperature (K), • C = oxygen concentration in enclosure measured using oxygen analyser
(expressed in molar %),
Vg = volume of gas in enclosure (which may conveniently expressed in m3).
In an embodiment, there is provided a method for measuring the intrinsic oxidation rate of a sample comprising: a) placing the sample of material in a closable sealable enclosure; b) closing and sealing said enclosure; c) measuring a first gas pressure in the enclosure; d) changing the internal volume of the enclosure by a known volume, whereby the gas pressure in the enclosure is less than or greater than the gas pressure outside the enclosure; e) measuring a second gas pressure in the enclosure after said changing as a function of time; f) determining from said second gas pressure as a function of time whether there is a gas leak from or into said enclosure; g) where there is no gas leak from or into said enclosure, determining the internal gas volume of the enclosure from the first and second gas pressures and the known volume; h) determining the volume of the sample from the internal gas volume of the enclosure, the first and second gas pressures, the known volume and the porosity of the sample; i) determining a change in gaseous oxygen mass in the enclosure as a function of time; and j) determining the intrinsic oxidation rate of the sample.
In one particular embodiment of the invention, the method for measuring the intrinsic oxidation rate of a sample comprises: a) placing the sample in an openable enclosure capable of holding the sample; b) sealing the enclosure; c) measuring a first gas pressure in the sealed enclosure having a first volume; d) changing the internal volume of the sealed enclosure by a known volume; e) measuring a second gas pressure in the sealed enclosure after said changing; f) restoring the internal volume of the sealed enclosure to the first volume; g) measuring gaseous oxygen concentration in the enclosure as a function of time for a time sufficient to enable a determination of intrinsic oxidation rate of the sample; h) determining at least one of the volume of the sample and the mass of the sample in the enclosure; i) determining changes in gaseous oxygen mass as a function of time; and j) determining the intrinsic oxidation rate of the sample from the measuring of the gaseous oxygen concentration, the resultant changes in mass of gaseous oxygen in the enclosure as a function of time, from at least one of the volume of the sample and the mass of the sample and from temperature and pressure. The measurement of gaseous oxygen concentration may be conducted over a period of less than about 24 hours, preferably less than about 12 hours, more preferably, less than about 10 hours. Still more preferably, individual values of gaseous oxygen concentration are obtained at least once every hour throughout the overall measurement period.
Measurement of temperature may be made outside the sample container and may be assumed to be the same as inside the sample container, or it may be measured inside the sample container. Measurements of temperature and/or pressure may be taken once only at the beginning of the test, or they may be measured each time a measurement of oxygen concentration is made or they may be measured a different number of times through the progress of the test. Optionally, during all or a portion of a period in which measurements of gaseous oxygen concentration are taken, gas in the enclosure in which the sample is located may be circulated by means of a pump or other similar means.
Each individual value of gaseous oxygen concentration may be calculated from a plurality of separate measurements of oxygen concentration, all of which may be measured within a relatively short period of time, by taking an average of some or all of the separate measurements. Alternatively, each individual value of gaseous oxygen concentration may be calculated from a continuous measurement over a short period of time. Preferably, the gas from an enclosure is passed through a filter or a plurality of filters before a measurement of gaseous oxygen concentration is made. Said filter(s) may be designed to remove one or more of moisture, carbon dioxide, particulate matter and other material that could damage an oxygen sensor or that could alter its ability to accurately measure a concentration of oxygen in a gas. It is known that for some types of oxygen measuring devices, carbon dioxide may affect the accuracy of the measurement of oxygen concentration. Thus carbon dioxide may be filtered out of the gas before a measurement of oxygen is made. Alternatively the carbon dioxide concentration in the gas from an enclosure may be measured, and the method may comprise the step of compensating the measurement of oxygen concentration for the concentration of carbon dioxide.
The IOR so measured may be used, for example, to make decisions in advance regarding the disposition of waste rock generated during blasting in an open cut mining operation.
According to a ninth aspect of this invention, there is provided a method for measuring the intrinsic oxidation rate of a sample comprising: a) placing the sample in an openable enclosure capable of holding the sample; b) sealing the enclosure; c) measuring a first gas pressure in the sealed enclosure; d) changing the internal volume of the sealed enclosure by a known volume; e) measuring a second gas pressure in the sealed enclosure as a function of time, to ascertain whether there is gas leakage from or into the enclosure; f) where there is no gas leakage from the enclosure, determining the intrinsic oxidation rate of the sample. The step of placing the sample in the openable enclosure may, if desired, comprise placing a known mass of the sample in the openable enclosure, or it may comprise placing a quantity of the sample in the openable enclosure and then determining the mass of said quantity of the sample. Alternatively, the step of placing the sample in the openable enclosure may, if desired, comprise the step of placing a known volume of sample in the openable enclosure, or it may comprise the step of placing a quantity of the sample in the openable enclosure and then determining the volume of said quantity of the sample.
The step of determining the intrinsic oxidation rate of the sample may include: a) restoring the internal volume of the sealed enclosure to the first volume; b) measuring gaseous oxygen concentration in the enclosure as a function of time for a time sufficient to enable a determination of intrinsic oxidation rate of the sample; c) deteπnining the volume of the sample in the enclosure; d) determining changes in gaseous oxygen mass as a function of time; and e) determining the intrinsic oxidation rate of the sample from the measuring of the gaseous oxygen concentration, the resultant changes in mass of gaseous oxygen in the enclosure as a function of time and from the volume of the sample.
The step of measuring the gaseous oxygen concentration may be repeated, and may be repeated more than once. An oxygen concentration may be determined for each step of determining oxygen mass in said enclosure. The value of the oxygen concentration used in a determination of oxygen mass may be derived from a plurality of measurements of said oxygen concentration or from a continuous measurement thereof, conveniently over a short period of time. The value of oxygen concentration used in the determination of oxygen mass is preferably derived from a plurality of measurements of oxygen concentration by determining an average of some or all of said measurements of oxygen concentration. Alternatively, each value of oxygen mass may be derived from more than one individual measurement of oxygen mass, preferably by taking an average of some or all of said individual values of oxygen mass. Each of said individual values of oxygen mass may be determined from a measurement of oxygen concentration in the gas.
According to a tenth aspect of this invention, there is provided a method of estimating a rate of oxygen consumption in a pile of material which is oxygenated, comprising: a) determining a volume of a sample of the material from the pile of material; b) determining an IOR of the sample of material; c) determining a volume of the pile of material; and d) estimating the rate of oxygen consumption of the pile of material from the volume of the sample, the IOR of the sample and the volume of the pile of material. hi an embodiment of the tenth aspect the method comprises: a) placing a sample of the material in a closable sealable enclosure; b) closing and sealing said enclosure; c) measuring a first gas pressure in the enclosure; d) changing the internal volume of the enclosure by a known volume, whereby the gas pressure in the enclosure is less than or greater than the gas pressure outside the enclosure; e) measuring a second gas pressure in the enclosure after said changing as a function of time; f) determining from said second gas pressure as a function of time whether there is a gas leak from or into said enclosure; g) where there is no gas leak from or into said enclosure, determining the internal gas volume of the enclosure from the first and second gas pressures and the known volume; h) determining the volume of the sample from the internal gas volume of the enclosure, the first and second gas pressures, the known volume and the porosity of the sample; i) determining a change in gaseous oxygen mass in the enclosure as a function of time; j) determining the intrinsic oxidation rate of the sample; k) determining a volume of the pile of material; and
1) estimating the rate of oxygen consumption in the pile of material from the volume of the sample, the intrinsic oxidation rate of the sample and the volume of the pile of material. The volume of the pile of material may conveniently be determined from the dimensions of said pile. The rate of oxygen consumption of the pile of material may conveniently be calculated using the equation:
^(pile) = IOR x Vpi, = ^(sample)x -^*- (8)
At At Vsample where: Am = change in mass of oxygen (which may be expressed in kg)
At = time over which change in mass of oxygen occurs (which may be expressed in s)
IOR = intrinsic oxidation rate (which may be expressed in kg(oxygen)m"3s'1)
Vpiie = volume of the pile of material (which may be expressed in m3) sampie = volume of the sample of material (which may be expressed in m3)
Alternatively, the method of estimating the rate of oxygen consumption in the pile may comprise: a) determining a mass of a sample from the pile of material; b) determining a density of the sample; c) determining a mass-based IOR of the sample; d) estimating a mass of the pile of material; and e) calculating the rate of oxygen consumption in the pile.
The mass-based IOR may be determined by a modification of Equation 5 in which the mass of the sample replaces the volume of the sample, and is conveniently expressed in kg(oxygen)kg (materials'1. The mass of the pile of material may be estimated, for example, from the dimensions of the pile of material and the bulk density of the sample. The rate of oxygen consumption in the pile of material may be used to estimate the rate of production of pollutant materials from the pile, and may be used to predict future rates of production of pollutant materials from the pile. This may be useful in the management of piles such as waste rock dumps from mining operations.
According to an eleventh aspect of this invention, there is provided a method of determining IOR of each of a plurality of samples, wherein the IOR of all of the plurality of samples is measured over the same period of time, comprising: a) loading each of said plurality of samples into the same enclosure, or into a different enclosure, or into an enclosure that shares some regions with other enclosures; b) determining if any one or more of the enclosures have gas leaks; c) for those enclosures with no gas leak, measuring an internal gas volume for each enclosure; and d) for each enclosure with no gas leak, determining an IOR. In an embodiment the method comprises: a) loading said plurality of samples into a plurality of enclosures; b) determining if any of the enclosures has a gas leak; c) for each enclosure with no gas leak, measuring an internal gas volume for said enclosure; and d) for each enclosure with no gas leak, determining an intrinsic oxidation rate of the sample therein. Optionally, the plurality of samples may be obtained from different locations in a waste heap, so that a determination of the spatial distribution of IOR within the waste heap may be derived from the IORs of the samples. Alternatively, the plurality of samples may be taken from the same location in the waste heap, and the IORs obtained from said plurality of samples may be used to determine an average IOR and optionally, the variation of IOR at such single location. As a further alternative, the plurality of samples may be taken from different waste heaps in order to compare the IOR for those different heaps with each other. Yet another alternative is to measure the IOR of samples taken from different locations in an open cut mining operation, in order to make decisions in advance regarding the disposition of waste rock from blasting in those different locations. For example, in one application, samples of rock from different locations in an open cut mine where blasting is planned may be tested to determine their IORs. Waste rock with similar IOR from different areas of the blasting operation may then be grouped into allocated waste piles so that the appropriate management of those piles can be effectively implemented.
In an embodiment, there is provided a method for determination of a spatial distribution of intrinsic oxidation rate within a waste heap comprising the steps of: a) obtaining samples from different locations in the waste heap, b) measuring an intrinsic oxidation rate for at least two of the samples, and c) determining a spatial distribution of intrinsic oxidation rate within the waste heap. According to a twelfth aspect of this invention, there is provided a system for determining at least one of an internal gas volume in, and whether there is gas leakage into or from, a sealed enclosure, said system comprising: a) an enclosure selected from the group consisting of a sealable enclosure and a sealed enclosure; b) means for changing the internal volume of the sealed enclosure by a known volume whereby the gas pressure in the enclosure is less than or greater than the gas pressure outside the enclosure; c) means for measuring the gas pressure in the sealed enclosure. The system may include means for determining the internal gas volume of the sealed enclosure from the first and second gas pressures and the known volume. The means for measuring gas pressure in the sealed enclosure may be a means for measuring gas pressure in the sealed enclosure as a function of time.
In an embodiment there is provided a system for determining an internal gas volume in a sealed enclosure, comprising: a) an openable sealable enclosure; b) a volume adjustor for changing the internal volume of the enclosure by a known volume, whereby the gas pressure in the enclosure is less than or greater than the gas pressure outside the enclosure; c) a pressure measuring device for measuring the gas pressure in the enclosure as a function of time.
In another embodiment there is provided a system for determining the porosity of a sample of material comprising: a) an openable sealable enclosure; b) a volume adjustor for changing the internal volume of the enclosure by a known volume, whereby the gas pressure in the enclosure is less than or greater than the gas pressure outside the enclosure; c) a pressure measuring device for measuring the gas pressure in the enclosure as a function of time; d) a volume calculator for calculating the volume of the sample; and e) a porosity calculator.
The volume calculator and the porosity calculator may be the same or they may be different. They may for example comprise a computer or other calculating device.
According to a thirteenth aspect of this invention, there is provided a system for determining at least one of the volume of a sample and the density of a sample, comprising: a) an enclosure selected from the group consisting of an openable sealable enclosure and an openable sealed enclosure; b) means for changing the internal volume of the enclosure by a known volume whereby the gas pressure in the enclosure is less than or greater than the gas pressure outside the enclosure; and c) means for measuring the gas pressure in the sealed enclosure.
The system may also include means for determining the mass of a sample placed in the enclosure, and may also include a means for calculating at least one of the volume of the sample and the density of the sample. In an embodiment there is provided a system for determining the volume of a sample of material comprising: a) an openable sealable enclosure; b) a volume adjustor for changing the internal volume of the enclosure by a known volume, whereby the gas pressure in the enclosure is less than or greater than the gas pressure outside the enclosure; c) a pressure measuring device for measuring the gas pressure in the enclosure as a function of time; and d) a volume calculator for calculating the volume of the sample.
According to a fourteenth aspect of this invention, there is provided a system for 5 measuring the intrinsic oxidation rate of a sample comprising: a) an openable enclosure capable of holding the sample said enclosure being selected from the group consisting of a sealable openable enclosure and a sealed openable enclosure; b) means for changing the internal volume of the sealed enclosure by a known i o volume, said means for changing being coupled to the enclosure; c) means for measuring gas pressure and temperature; and d) means for measuring gaseous oxygen concentration in the enclosure.
The means for measuring gaseous oxygen concentration may be located outside the openable enclosure, and there may be a means to transport some or all of the gas in the is enclosure to said means for measuring gaseous oxygen concentration. There may additionally be means to prevent access to said means for measuring gaseous oxygen concentration by materials that could damage it or that could alter its ability to accurately measure a concentration of oxygen in a gas. Said means to prevent access may comprise, for example, one or more of a moisture filter, a carbon dioxide filter and a filter for 0 removing particulate matter. The means for measuring temperature may be inside the enclosure or it may be outside the enclosure. According to this aspect of the invention, there may also be a means for determining IOR of the sample from the temperature, the pressure, the volume of the sample and the gaseous oxygen concentration in the enclosure as a function of time. 25 According to a fifteenth aspect of this invention there is provided a system for determining at least one of an internal gas volume in a sealed enclosure and whether there is gas leakage into or from a sealed enclosure, said system comprising: a) an openable enclosure, said enclosure being selected from the group consisting of a sealable openable enclosure and a sealed openable enclosure; 30 b) means for changing the internal volume of the sealed enclosure by a first known volume whereby the gas pressure in the enclosure is less than or greater than the gas pressure outside the enclosure; c) means for measuring a first gas pressure in the sealed enclosure after changing the internal volume of the sealed enclosure by a first known volume whereby the gas pressure in the enclosure is less than or greater than the gas pressure outside the enclosure as a function of time; d) means for determining whether there is gas leakage from or into said sealed enclosure; e) means for further changing the internal volume of the sealed enclosure by a second known volume; f) means for measuring a second gas pressure in the sealed enclosure after said further changing; and g) means for determining the internal gas volume of the sealed enclosure from the first and second gas pressures and the known volumes.
The first known volume may be the same as or different from the second known volume. The means for measuring a first gas pressure may be the same as or different from the means for measuring a second gas pressure. The means for changing the internal volume of the sealed enclosure may be the same as or different from the means for further changing the internal volume of the sealed enclosure.
According to a sixteenth aspect of this invention, there is provided a system for measuring the intrinsic oxidation rate of a sample comprising: a) an openable enclosure capable of holding the sample said enclosure being selected from the group consisting of a sealable openable enclosure and a sealed openable enclosure; b) means for sealing the enclosure; c) means for determining the volume of the sample in the enclosure; d) means for determining changes in gaseous oxygen mass as a function of time; and e) means for determining the intrinsic oxidation rate of the sample.
The means for determining the intrinsic oxidation rate may be an IOR determiner. The means for sealing the enclosure may comprise complementary screw threads on each of two portions of the enclosure and a seal that may be compressed when the two portions are screwed together. Alternatively the means may comprise some other device for sealing the enclosure.
In an embodiment there is provided a system for measuring an intrinsic oxidation rate of a sample comprising: a) an openable sealable enclosure capable of holding the sample; b) a volume adjustor for changing the internal volume of the sealed enclosure by a known volume, said adjustor being coupled to the enclosure; c) a pressure measuring device for measuring gas pressure and a temperature measuring device for measuring temperature; and d) an oxygen meter for measuring gaseous oxygen concentration of a gas in the enclosure. In one particular embodiment, the system for measuring the intrinsic oxidation rate of a sample comprises: a) an openable enclosure capable of holding the sample said enclosure being selected from the group consisting of a sealable openable enclosure and a sealed openable enclosure; b) means for sealing the enclosure; c) means for measuring a first gas pressure in the sealed enclosure having a first volume; d) means for changing the internal volume of the sealed enclosure by a known volume; e) means for measuring a second gas pressure in the sealed enclosure; f) means for restoring the internal volume of the sealed enclosure to the first volume; g) means for measuring gaseous oxygen concentration and measurement gas pressure in the enclosure as a function of time for a time sufficient to enable a detennination of intrinsic oxidation rate of the sample; h) means for determining the volume of the sample in the enclosure; i) means for determining temperature; j) means for determining changes in gaseous oxygen mass as a function of time; and k) means for determining the intrinsic oxidation rate of the sample from the measuring of the gaseous oxygen concentration and the resultant changes in mass of oxygen as a function of time and from the volume of the sample. Optionally said system may also include means to recirculate a gas within an enclosure containing the sample. Said means may be a gas circulator. Preferably the means for measuring gaseous oxygen concentration is not located within the enclosure in which the sample is located and there is a means to transport air from the enclosure to the means for measuring gaseous oxygen concentration. The means to transport may be a transport system. Advantageously there may also be a filter or a plurality of filters which is (are) capable of removing one or more of moisture, carbon dioxide, particulate matter and other material that could damage an oxygen sensor or that could alter its ability to detect an accurate concentration of oxygen in a gas. Said filter(s) may be located such that gas passes through said filter(s) before reaching the means for measuring gaseous oxygen concentration. The means for measuring gaseous oxygen concentration may be an oxygen meter, or an oxygen sensor. The oxygen sensor may be for example an oxygen fuel cell. The system for measuring the intrinsic oxidation rate may have a carbon dioxide filter for removing carbon dioxide from the gas before it reaches the oxygen sensor, since carbon dioxide is capable of affecting the accuracy of an oxygen sensor. Alternatively, the system may comprise a carbon dioxide meter for measuring the concentration of carbon dioxide in the gas. In this case, the oxygen sensor may have a compensator so that the measurement of oxygen is compensated for the concentration of carbon dioxide.
According to a seventeenth aspect of this invention, there is provided a system for measuring the intrinsic oxidation rate of a sample comprising: a) an openable enclosure capable of holding the sample said enclosure being selected from the group consisting of a sealable openable enclosure and a sealed openable enclosure; b) means for sealing the enclosure; c) means for measuring a first gas pressure in the sealed enclosure; d) means for changing the internal volume of the sealed enclosure by a known volume; e) means for measuring a second gas pressure in the sealed enclosure as a function of time to ascertain whether there is gas leakage from or into the enclosure; and f) where there is no gas leakage from the enclosure, means for determining the intrinsic oxidation rate of the sample. The means for determining the intrinsic oxidation rate of the sample may include: a) means for restoring the internal volume of the sealed enclosure to the first volume; b) means for measuring gaseous oxygen concentration and for measuring gas pressure in the enclosure as a function of time for a time sufficient to enable a determination of intrinsic oxidation rate of the sample; c) means for determining the volume of the sample in the enclosure; d) means for determining the temperature; e) means for determining changes in gaseous oxygen mass as a function of time; and f) means for determining the intrinsic oxidation rate of the sample from the measuring of the gaseous oxygen concentration and the resultant changes in mass of oxygen as a function of time and from the volume of the sample.
According to an eighteenth aspect of the invention there is provided a system for determining an IOR for a plurality of samples comprising: a) a plurality of an openable enclosures capable of holding the samples, said enclosures being selected from the group consisting of a sealable openable enclosures and a sealed openable enclosures; b) means for determining the gas volume of each of said enclosures individually; c) means for determining for each enclosure separately whether that enclosure has a gas leak; and d) means for determining for each enclosure separately the IOR of the sample in said enclosure. The system may also include means to isolate an enclosure. Said means may be for example an isolator. In one form the system may include means to isolate an enclosure, or a portion of an enclosure that contains the sample, or more than one such enclosure or portion of an enclosure, if it is determined that there is a leakage into or from said enclosure or enclosures.
All of the enclosures may be connected to a single means for changing the volume of the enclosure, a single means for measuring the pressure in the enclosure and a single means for measuring oxygen concentration, which may be a single oxygen sensor. Alternatively, one of the following options maybe used: a) single means for changing the volumes of the all of the enclosures, separate means for measuring the pressure in each enclosure and single means for measuring oxygen concentration in all of the enclosures; b) separate means for changing the volume of each enclosure, single means for measuring the pressures in all of the enclosures and single means for measuring oxygen concentration in all of the enclosures; c) separate means for changing the volume of each enclosure, separate means for measuring the pressure in each enclosure and single means for measuring oxygen concentration in all of the enclosures; d) single means for changing the volumes of all of the enclosures, single means for measuring the pressures in all of the enclosures and separate means for measuring oxygen concentration in each enclosure; e) single means for changing the volumes of all of the enclosures, separate means for measuring the pressure in each enclosure and separate means for measuring oxygen concentration in each enclosure; f) separate means for changing the volume of each enclosure, single means for measuring the pressures in all of the enclosures and separate means for measuring oxygen concentration in each enclosure; g) separate means for changing the volume of each enclosure, separate means for measuring the pressure in each enclosure and separate means for measuring oxygen concentration in each enclosure. Herein, "single means" indicates that all enclosures are connected to the same means, whereas "separate means" indicates that at least two of the enclosures are connected to one means. In addition, each enclosure may have a separate means for measuring temperature, or there may be one means for measuring temperature. Said means may be a voltage divider circuit incorporating a thermistor as a temperature sensor, or a theπnocouple or a thermometer or may be some other suitable means for measuring temperature.
Preferably, the volume of the system, excluding the sample containers in which the samples are placed, is kept to a minimum in order to minimise dilution of the sample container air during measurement of oxygen content. In an embodiment there is provided a system for determining an intrinsic oxidation rate for a plurality of samples comprising: a) a plurality of openable sealable enclosures capable of holding the samples; b) a volume measuring system for determining the gas volume of each of said enclosures individually; c) a leak detection system for determining for each enclosure separately whether that enclosure has a gas leak; and d) an intrinsic oxidation rate detection system for determining for each enclosure separately the intrinsic oxidation rate of the sample in said enclosure.
In another embodiment there is provided a system for determining a spatial distribution of intrinsic oxidation rates within a waste heap comprising: a) a sampling system for obtaining samples from different locations within the heap; b) a plurality of openable sealable enclosures capable of holding the samples; c) a volume measuring system for determining the gas volume of each of said enclosures individually; d) a leak detection system for determining for each enclosure separately whether that enclosure has a gas leak; e) an intrinsic oxidation rate detection system for determining for each enclosure separately an intrinsic oxidation rate of the sample in said enclosure; and f) distribution determiner for detennining a spatial distribution of intrinsic oxidation rates.
According to a nineteenth aspect of the invention, there is provided a system for estimating a rate of oxygen consumption of a pile of material which is oxygenated, comprising; a) means for determining a volume of a sample from the pile of material; b) means for determining an IOR of said sample; c) means for estimating a volume of the pile of material; and d) means for calculating the rate of oxygen consumption of the pile from the IOR and the volumes of the sample and of the pile. The means for determining the volume of the sample may comprise:
(i) an enclosure selected from the group consisting of an openable sealable enclosure and an openable sealed enclosure;
(ii) means for changing the internal volume of the enclosure by a known volume whereby the gas pressure in the enclosure is less than or greater than the gas pressure outside the enclosure;
(iii) means for measuring a gas pressure in the sealed enclosure; and
(iv) means for calculating a volume of the sample.
The system may additionally include means to estimate the rate of production of pollutant materials from the pile of material from the rate of oxygen consumption of the pile.
In an embodiment there is provided a system for estimating a rate of oxygen consumption of a pile of material which is oxygenated, comprising; a) an openable sealable enclosure capable of holding a sample of the material; b) a volume adjustor for changing the internal volume of the enclosure by a known volume, said adjustor being coupled to the enclosure; c) a pressure measuring device for measuring gas pressure and a temperature measuring device for measuring temperature; d) an oxygen meter for measuring gaseous oxygen concentration of a gas in the enclosure in order to determine an intrinsic oxidation rate of the sample; e) a volume estimator for estimating a volume of the pile of material; and f) an oxygen consumption calculator for calculating the rate of oxygen consumption of the pile from the intrinsic oxidation rate and the volumes of the sample and of the pile.
According to a twentieth aspect of the invention, there is provided a system for determining the proportion of a gas phase in a material that contains both gas phase and solid phase intermingled, comprising: a) an enclosure selected from the group consisting of a sealable enclosure and a sealed enclosure; b) means for changing the internal volume of the sealed enclosure by a known volume whereby the gas pressure in the enclosure is less than or greater than the gas pressure outside the enclosure; c) means for measuring the gas pressure in the sealed enclosure; and d) means for determining the volume of the sample in the enclosure.
The system may include means for determining the internal gas volume of the sealed enclosure from the first and second gas pressures and the known volume.
With reference to the eighth, ninth, tenth, eleventh, fourteenth, sixteenth, seventeenth, eighteenth and nineteenth aspects of the invention, the IOR may be measured at any desired combination of values of oxygen concentration, pressure and temperature. Conveniently, IOR is Smaχ, where Smax is the IOR determined at atmospheric oxygen concentration. Conveniently also, IOR is determined at the same conditions of atmospheric oxygen concentration, temperature and pressure as pertain outside the enclosure(s) in the vicinity of the system for detennining IOR. These conditions may be 25°C, 101.3kPapressure and 20.95% (v/v) oxygen, or one or more of these conditions may be different from these values, depending on local conditions when and at the location at which the IOR is determined.
In assessing management options for AMD it is useful for the mining industry to quantify the following: a) the time between dumping waste materials and the time for AMD to appear, b) the time for all sulfide material in waste piles to be used up, and c) magnitude of pollution load in drainage as a function of time.
Measurement of IOR can assist in providing estimates for all of these parameters.
It is an advantage of the present invention that the rapidity and sensitivity of the system described herein allows a fast and accurate indication of the IOR of a body of waste material, and enables a timely estimate of the prospective environmental impact of the material tested. This allows a user to make informed decisions concerning waste rock pile management. It is a further advantage of the invention that there is no need to pretreat the sample before testing, although pretreatment of a sample, for example drying of a particularly wet sample, may be practiced within the scope of this invention. In addition, the volume of the sample is determined, and the IOR is able to be determined, on the same sample without further processing or manipulation of the sample. This simplifies the test, and helps to minimise the time required to conduct a test, and thereby allows the results of the testing to be made available in a relatively short timeframe.
Whereas the IOR systems and methods described in this invention are designed to measure the oxygen consumption rate of sulfidic waste rock and tailing waste materials for the mining industry, this instrument could be easily applied in other applications. For example, determination of IOR is of use in management of biooxidation and bioleach heaps, where IOR is used to determine what improvements may be necessary in the operating conditions of such heaps in order to improve the yield of valuable metals from mining operations, and to predict the effective lifetimes of such heaps. The decision about whether to treat a particular sulfidic material in a biooxidation or bioleach heap may be based on economic criteria that may include the time for a pre-determined amount of material to oxidise. Determining the IOR of materials during mining may provide cost- effective and timely information to be used in choosing suitable materials for use in production heaps. The systems and methods in this invention may also find use in other industries such as the food industry, and the scope of the invention is to be construed as including such applications.
Brief Description of Drawings
The invention will now be described, by way of example, with reference to the accompanying drawings wherein:
Figure 1 is a diagrammatic representation of a voltage divider circuit which may be used to measure temperature;
Figure 2 is a graph of temperature as a function of calculated voltage in the voltage divider circuit of Figure 1; Figure 3 is a diagrammatic representation of a system in accordance with the invention;
Figure 4 is a graph showing mass of oxygen consumed by a sample as a function of time, as determined in the course of the Example;
Figure 5 is a diagrammatic representation of a sealing system that may optionally be used to seal plastic (PVC) sample containers forming part of the system of Figure 3; Figure 6 is a diagrammatic representation of a mechanism which may optionally be used to control a force urging an upper edge of a sample container against a foam rubber seal fonning part of the system of Figure 3;
Figure 7 shows diagrammatic representations of a variety of systems that may be used in accordance with the invention; and
Figure 8 is a diagrammatic representation of another system in accordance with the invention, said system being not the same as the system represented in Figure 3.
Best Mode And Other Modes For Carrying Out The Invention Referring to Figure 1, circuit 100 may be used to measure temperature. Circuit
100 comprises thermistor 101 with nominal resistance Rthermistor of 100 kOhm for use within the range of from 0°C to 70°C. The thermistor is used as a sensor in the voltage divider. The maximum power dissipation of thermistor 101 is 28μW in the temperature range from 0°C to 70°C. To satisfy this manufacturer requirement, the excitation voltage (Uexcit.) provided by power source 102 and fixed resistor (Rf) 103 were determined to be 1.5V and 20 kOhm, respectively. From the manufacturer's specification for thermistor 101, the voltage Uf across terminals 104 and 105 was calculated by using the equation:
Figure imgf000028_0001
Figure 2 shows the temperature on the ordinate axis as a function of voltage Uf on the abscissa. For calculated data, the fourth order polynomial fit was obtained and it is given by: T = -56.429 (Uf)4+ 185.39 (Uf)3 - 216.5 (Uf)2 + 177.46 (Uf) - 8.4761 (10)
Equation 10 is used to calculate the temperature coπesponding to a particular measured voltage Uf. Referring to Figure 3, there is shown a system 300 for determining the intrinsic oxidation rate (IOR) of a plurality of samples of material. System 300 measures the intrinsic oxidation rate of up to eight different samples. The invention is, however, not limited to the use of up to eight samples. Any number of samples may be used at the same time. System 300 includes cylinder 301 having a piston 302, and a pressure sensor 303. System 300 further includes a manifold of valves 304 which incorporates solenoid valves 305a, 306a, 307a, 308a, 309a, 310a, 311a and 312a, and spare solenoid valves 395 and 396 (which in this description remain closed throughout), as well as a manifold of solenoid valves 313 which incorporates solenoid valves 305b, 306b, 307b, 308b, 309b, 310b, 311b and 312b, and also solenoid valve 391 leading to the atmosphere and solenoid valve 317 leading to the oxygen detection system described below. System 300 also includes eight air pumps 305c, 306c, 307c, 308c, 309c, 310c, 311c and 312c, and eight sample containers 305d, 306d, 307d, 308d, 309d, 310d, 3 lid and 312d. Each of the sample containers 305d, 306d, 307d, 308d, 309d, 310d, 31 id and 312d is openable to enable a sample to be placed into and/or to be removed from it. System 300 also includes an air pump 314, a moisture filter 315, a CO2 filter 316, an oxygen analyser 318 (with a resolution better than 0.001% coπesponding to a mass of oxygen less than 3 x 10"9g) and a computer 319. Cylinder 301 having piston 302 is coupled to pressure sensor 303 by lines 320 and 321 and to the manifold of valves 313 by lines 320 and 322. Sample containers 305d to 312d are connected to valves 305b to 312b respectively by lines 325, 328, 331, 334, 337, 340, 343 and 390 respectively. Air pumps 305c, 306c, 307c, 308c, 309c, 310c, 311c and 312c are coupled to the sample containers 305d, 306d, 307d, 308d, 309d, 310d, 31 Id and 312d respectively by lines (a) 346, 347, 324; (b) 348, 349, 327; (c) 350, 351, 330; (d) 352, 353, 333; (e) 354, 355, 336; (f) 356, 357, 339; (g) 358, 359, 342; (h) 360, 361, 345; respectively. During measurement of intrinsic oxygen rate each of the sample containers 305d, 306d, 307d, 308d, 309d, 310d, 3 lid and 312d is sealably connected into the system 300 by lines (a) 323, 324, 325; (b) 326, 327, 328; (c) 329, 330, 331; (d) 332, 333, 334; (e) 335, 336, 337; (f) 338, 339, 340; (g) 341, 342, 343; (h) 344, 345, 390; respectively. The manifold of valves 313 is coupled via valve 317 to moisture filter 315 by line 362, whilst moisture filter 315 is coupled to CO2 filter 316 by line 364, and CO2 filter 316 is coupled to the pump 314 by line 365, and pump 314 is coupled to oxygen analyser 318 by line 366, and oxygen analyser 318 is coupled to manifold of valves 304 by line 367. The computer 319 is electrically coupled to air pump 314 by line 368, to oxygen analyser 318 by line 371, to piston 302 by line 372, to the pressure sensor 303 by line 373, to manifold of valves 313 which incorporates valves 305b, 306b, 307b, 308b, 309b, 310b, 311b, 312b, 391 and 317 by a plurality of lines capable of controlling each of the solenoid valves in manifold 313 individually (for the sake of clarity, only one of said lines, 374, is shown in Figure 3), to the manifold of valves 304 which incorporates inlet valves 305a, 306a, 307a, 308a, 309a, 310a, 311a, 312a, 395 and 396 by a plurality of lines capable of controlling each of the solenoid valves in manifold 304 individually (for the sake of clarity, only one of said lines, 375, is shown in Figure 3), and to the air pumps 305c, 306c, 307c, 308c, 309c, 310c, 311c and 312c by lines 376, 377, 378, 379, 380, 381, 382, and 383 respectively.
Figure 4 shows experimental data for variation of oxygen content as a function of time, obtained in the Example. The abscissa of the graph represents the time expired since the start of the test, and the ordinate axis represents the mass of oxygen detected in an enclosure containing a sample, individual points on the graph represent individual values of oxygen mass at the coπesponding time shown on the abscissa.
Figure 5 shows a mechanism which may optionally be used for sealing sample containers in the system of Figure 3. In Figure 5, only those four sample containers that are located at the front of system 300 of Figure 3 are shown. A similar assembly containing a further four sample containers is located at the rear, behind the assembly shown. With reference to Figure 5, individual sample containers 501, 502, 503 and 504 may be located in complementary sample bases 531, 532, 533 and 534, which are attached to a movable sample container holder 506. Sample container holder 506 is located above the fixed base 508 of the system 300. Fixed base 508 is a portion of frame 550. Shelves 551 and 552 are provided for convenient storage of other components of the system, tools, samples or other items. Linear actuators 510, 511 and 512 are used to move the sample container holder 506, and thereby the sample containers 501, 502, 503 and 504, in a vertical direction. The top plate 514 is in a fixed position, and is attached to the sample container lids 516, 517, 518 and 519, each of which is fitted with a 6mm thick closed cell neoprene foam rubber seal 522, 523, 524 and 525 respectively. The sample container lids 516, 517, 518 and 519 are located above the sample bases 531, 532, 533 and 534 in such positions that, when the sample containers 501, 502, 503 and 504 are located in the bases 531, 532, 533 and 534, and when the linear actuators 510, 511 and 512 are operated so as to move the sample container holder 506 upwards, the sample containers 501, 502, 503 and 504 are sealed against the sample container lids 516, 517, 518 and 519 by means of seals 522, 523, 524 and 525. By adjusting the height of the linear activators 510, 511 and 512, and by adjusting the force applied by the sample container bases (shown in Figure 6), the force applied by the rims of the sample containers 501, 502, 503 and 504 to the seals 522, 523, 524 and 525 maybe adjusted.
Figure 6 shows a diagrammatic representation of a spring loaded system located in sample container bases 531, 532, 533 and 534 of Figure 5 in order to allow for adjustment of the force applied by the rim of sample containers 501, 502, 503 and 504 of Figure 5 to the seals 522, 523, 524 and 525 of Figure 5. As is shown in Figure 6, sample container 601 fits into sample container base 602. Located within base 602 is fixed cylindrical plate 604 with 3 holes 642, 644 and 646. Above fixed plate 604 is located movable plate 606, with 3 holes 652, 654 and 656, located so that when plate 604 is placed above plate 606, the two sets of holes in the two plates can be aligned. Bolts 610, 611 and 612 are fitted with washers 615, 616 and 617, springs 620, 621 and 622 and washers 625, 626 and 627, and connect plates 604 and 606, fitting through both sets of holes in those plates. Bolts 610, 611 and 612 are held in place by nuts 630, 631 and 632, located beneath fixed plate 604. The length of stainless steel springs 620, 621 and 622, and the position of bottom nuts 630, 631 and 632, regulate the distance between plates 604 and 606.
Figure 7 shows a variety of diagrams representing systems that may be used in accordance with the invention. In all of the diagrams in Figure 7, there may additionally be means for collecting and optionally for processing data, and there may be means to control one or more of the components in the system. Such means are commonly a computer, connected to the relevant components of the system, however, for the sake of simplicity, said means are not shown. Openable container 702 may have a means for sealing so that the enclosure is sealed. Piston 706 is used to alter the volume of the enclosure by a known volume, and may additionally be capable of altering the volume of the enclosure by a second known volume. The pressure in the enclosure may be measured using manometer 704. Oxygen meter 708 may be used to determine the concentration of oxygen in container 702. The oxygen probe, which forms a part of meter 708 (but is not shown separately in these diagrams) may be located in container 702, as shown in diagrams 7a, 7b and 7c, or it may be located outside container 702, as shown in diagrams 7d and 7e. Recirculation pump 710 may be used to ensure that the gas within the container is approximately homogeneous. If the oxygen probe is located outside container 702, pump 714 is provided to transfer gas from container 702 to the oxygen probe. One or more filters 712 may be provided such that the gas from the container passes through the filters 712 before reaching the oxygen probe, in order to remove materials such as CO2, moisture and dust which might damage the probe or cause it to be inaccurate. Thus Figure 7a is a diagrammatic representation of a system which may be used in accordance with the first aspect of the invention. When using the system in accordance with the first aspect, container 702 is sealed. Manometer 704 may be used for measuring a first pressure and also for measuring a second gas pressure, and piston 706 can be used for changing the internal volume of the sealed enclosure. In this system, the enclosure comprises the internal portions of container 702, manometer 704, the cylinder in which piston 706 moves and the tubing that connects those components. The system of Figure 7a may also be used in accordance with other aspects of the invention, for example the second aspect.
Figure 7b is a diagrammatic representation of a system which may be used in accordance with the eighth aspect of the invention. When using the system in accordance with the eighth aspect, container 702 is openable and sealable, using a system that may be similar to that shown in Figure 5. The volume of the sample may be determined using the method of the fifth aspect of this invention (which may include using manometer 704 to measure a first and a second pressure, and using piston 706 to change the internal volume of the enclosure by a known volume), and changes in oxygen mass as a function of time may be determined using the oxygen meter 708. In this system, the enclosure comprises the internal portions of container 702, manometer 704, the cylinder in which piston 706 moves and the tubing that connects those components. The system of Figure 7b may also be used in accordance with other aspects of the invention, for example the ninth aspect. Figure 7c is a diagrammatic representation of another system which may be used in accordance with the eighth aspect of the invention. When using the system in accordance with the eighth aspect, it is used in a manner similar to that described for Figure 7b, however during all or a portion of the period in which measurements of gaseous oxygen concentration are taken using oxygen meter 708, gas in container 702 may be circulated by means of pump 710. The system of Figure 7c may also be used in accordance with other aspects of the invention, for example the ninth aspect.
Figure 7d is a diagrammatic representation of yet another system which may be used in accordance with the eighth aspect of the invention. When using the system in accordance with the eighth aspect, it is used in a manner similar to that described for Figure 7b, however the gas from container 702 is passed through filter or plurality of filters 712 using pump 714 before a measurement of gaseous oxygen concentration is made by oxygen meter 708. Said filter(s) may be designed to remove one or more of moisture, carbon dioxide, particulate matter and other material that could damage an oxygen sensor or that could alter its ability to accurately measure a concentration of oxygen in a gas. The system of Figure 7d may also be used in accordance with other aspects of the invention, for example the ninth aspect.
Figure 7e is a diagrammatic representation of a further system which may be used in accordance with the eighth aspect of the invention. When using the system in accordance with the eighth aspect, it is used in a manner similar to that described for Figure 7d, however during all or a portion of the period in which measurements of gaseous oxygen concentration are taken using oxygen meter 708, gas in container 702 may be circulated by means of pump 710. The system of Figure 7e may also be used in accordance with other aspects of the invention, for example the ninth aspect. Figure 7 is not intended to represent all of the possible systems that may be used in accordance with this invention, and should not be taken as in any way limiting the invention to those systems shown diagrammatically in Figure 7.
Referring to Figure 8, there is represented a system 800, wherein those components of the system that are in common with Figure 3 are described above, and serve the same functions as described for Figure 3. In Figure 8, moisture filter 315 and CO2 filter 316, together with lines 362, 364 and 365 are omitted, and manifold of valves 313 is connected via valve 317 to pump 314 by line 862. Also sample containers 305d, 306d, 307d, 308d, 309d, 310d, 31 Id and 312d are connected to valves 305b, 306b, 307b, 308b, 309b, 310b, 311b and 312b respectively by a) line 805a, CO2 filter 805b, line 805c, moisture filter 805d and lines 805e and 805f; b) line 806a, CO2 filter 806b, line 806c, moisture filter 806d and lines 806e and 806f; c) line 807a, CO2 filter 807b, line 807c, moisture filter 807d and lines 807e and 807f; d) line 808a, CO2 filter 808b, line 808c, moisture filter 808d and lines 808e and 808f; e) line 809a, CO2 filter 809b, line 809c, moisture filter 809d and lines 809e and 809f; f) line 810a, CO2 filter 810b, line 810c, moisture filter 810d and lines 810e and 81 Of; g) line 811a, CO2 filter 811b, line 811c, moisture filter 81 Id and lines 81 le and 81 If; and h) line 812a, CO2 filter 812b, line 812c, moisture filter 812d and lines 812e and 812f respectively. Moisture filters 805d, 806d, 807d, 808d, 809d, 810d, 81 Id and 812d are connected to air pumps 305c, 306c, 307c, 308c, 309c, 310c, 311c and 312c respectively by lines a) 805e and 805g; b) 806e and 806g; c) 807e and 807g; d) 808e and 808g; e) 809e and 809g; f) 810e and 810g; g) 81 le and 81 lg; and h) 812e and 812g respectively.
A prefeπed mode of operation of an IOR meter is described below with reference to the Figures 1 to 3, 5 and 6. In this description, when reference is made to Figure 5, it is understood that there is a similar assembly of four sample containers and housings behind the four shown in the diagram. Similarly, when reference is made to Figure 6, it is understood that the system shown in Figure 6 is representative of all of the eight sample container bases. In addition, an enclosure, as used in this description, comprises cylinder 301, pressure sensor 303, manifold 313, one of solenoid valves 305b to 312b, the coπesponding one of pumps 305c to 312c, the coπesponding one of sample containers 305d to 312d, together with tubing connecting the above to each other and to the coπesponding solenoid valve of 305 a to 312a, as shown diagrammatically in Figure 3. The enclosure that incorporates sample container 305d will be refeπed to as enclosure 1, the enclosure that incorporates sample container 306d will be refeπed to as enclosure 2 and so forth, such that the enclosure that incorporates sample container 312d will be refeπed to as enclosure 8.
A program written in Lab VIEW computer language controls the data acquisition device, solenoid valves, air pumps, linear actuators, thermistor, pressure sensor and oxygen analyser.
In order to seal each sealable enclosure, the following procedure is followed. Each sample container is placed in a sample container base, represented by the sample bases 501, 502, 503 and 504 of Figure 5, and shown in detail in Figure 6. By selecting appropriate springs 620, 621 and 622 (Figure 6), by adjusting nuts 630, 631 and 632 (Figure 6) and by adjusting linear actuators 510, 511 and 512 (Figure 5), the force with which the sample containers (represented by the sample containers 501, 502, 503 and 504 of Figure 5) impinge on the seals 522, 523, 524 and 525 (Figure 5) may be set to an appropriate value. The linear actuators 510, 511 and 512 (Figure 5) are then used to raise the movable sample container holder 506 (Figure 5) so that the sample containers seal against the sample container lids 516, 517, 518 and 519 (Figure 5) by means of seals 522, 523, 524 and 525.
In order to determine the volume of each sealable enclosure, and whether it has a leak, the following procedure is followed. Initially the sealable containers are sealed into system 300 as described above. Then solenoid valves 305a to 312a, 305b to 312b and 317 (Figure 3) are closed. In order to detennine the internal gas volume in enclosure 1 and whether there is a gas leakage into or from enclosure 1, solenoid valves 305b and 391 are opened, and the system is allowed to equilibrate with atmospheric pressure for 60 seconds. A first gas pressure Pi is then measured using pressure sensor 303, after which solenoid valve 391 is closed. Piston 302 is then used to change the internal volume of enclosure 1 by a known volume Vp. The system is then allowed to equilibrate for 60 seconds.
A second pressure P2 is then measured using pressure sensor 303. A third pressure P3 is measured after a further 40 seconds, using pressure sensor 303. If the difference between P2 and P3 is less than or equal to 80Pa, and if Pι≠P2, then there is not a leakage into or from enclosure 1. In that case, the internal gas volume of sealed enclosure 1, Vc, is calculated using a modification of Equation 3 in which Vc replaces Vg. Using piston 302, the internal volume of the enclosure is then restored to its original value. If the difference between P2 and P3 is greater than 80Pa, or if P1=P2> then there is a leakage into or from enclosure 1. In this case, by adjusting the position of seal (522 or similar in Figure 5) and of the linear actuators 510, 511 and 512 (Figure 5) and of the nuts 630, 631 and 632 (Figure 6) or by other appropriate actions, the quality of the seal is improved until the procedure described above shows that there is not a leakage into or from enclosure 1. The acceptable amount of the difference between P2 and P3 may be chosen to be less than 200, 150, 100, 80, 60, 40, 20, 10, 5 or lPa, or some other acceptable value if required.
The above method for determining the internal gas volume of enclosure 1 is then repeated using the appropriate combinations of valves and other elements in order to determine the internal gas volumes of enclosures 2 to 8 in turn, although it is not necessary to measure a new value of the first gas pressure Pi for each enclosure, since Pi is the same as the ambient atmospheric pressure. Once the internal gas volume of each enclosure has been determined, that value may be stored. The stored value may then be used for subsequent tests, rather than redeteπnining the volume of the enclosure as described above.
Enclosures 1 to 8 are then opened by using linear actuators 510, 511 and 512 to lower sample container holder 506. A sample of material to be tested is then placed in each of the sample containers 305d to 312d (although one or more containers may be left empty if desired), the sample containers are located in the coπesponding sample container bases, and the enclosures are sealed by using linear actuators 510, 511 and 512 to raise the sample container holder 506. In order to determine whether there is a gas leakage into or from enclosure 1 and to determine the volume of gas in enclosure 1, a similar procedure is followed to that described above to determine whether there is a gas leakage into or from enclosure 1 and to determine the internal gas volume of enclosure 1 before the sample was loaded into container 305d. If the difference between P2 and P3 is less than or equal to 80Pa, and Pι≠P2, then there is not a leakage into or from enclosure 1. In that case, the volume of gas in sealed enclosure 1, Vg, is calculated using Equation 3. Using piston 302, the internal volume of the enclosure is then restored to its original value. If the difference between P2 and P3 is greater than 80Pa, or if P1=P2, then there is a leakage into or from enclosure 1. In that case, solenoid valves 305 a and 305b are used to isolate the portion of enclosure 1 between those solenoid valves, and no data is acquired for the sample in sample container 305d, since the results may be inaccurate due to diffusion of oxygen into or out of the container. The acceptable amount of the difference between P2 and P3 may be chosen to be less 200, 150, 100, 80, 60, 40, 20, 10, 5 or lPa, or some other acceptable value if required. The method for determining whether there is a gas leakage into or from an enclosure, and for determimng the volume of gas in an enclosure and for restoring the internal volume of the enclosure to its original value, as described above, is then repeated for each of the enclosures 2 to 8 in turn, although it is not necessary to measure a new value of Pi for each enclosure, since Pi is the same as the ambient atmospheric pressure. For the purpose of the remainder of this description, it is assumed that all of the enclosures 1 to 8 are found not to have a gas leakage into or from the enclosure and not to have any other unacceptable defects, although this will not always be the case.
The ambient temperature is then measured, using a voltage divider circuit containing a thermistor, as shown diagrammatically in Figure 1. The voltage Uf determined by the circuit shown in Figure 1 is used to determine the temperature by use of a calibration curve such as that shown in Figure 2. Alternatively temperature may be measured by some other convenient means. This temperature used in all calculations relating to this invention where temperature is required. After determining whether there is a gas leakage into or from enclosures 1 to 8, and determining the volume of gas in enclosures 1 to 8, and restoring the internal volume of enclosures 1 to 8 to their original values, as described above, valves 305a to 312a and 305b to 312b, and valves 391 and 317 are all closed.
A gaseous oxygen concentration in enclosure 1 is measured as follows. Solenoid valves 305a, 305b and 317 are opened, while solenoid valves 306a to 312a, 306b to 312b and 391 are closed. Air is then circulated for approximately 5 minutes from sample container 305d through moisture and carbon dioxide filters 315 and 316 respectively to oxygen sensor 318 using pump 314 at a rate of approximately 4xl0"4m3/min. A representative value of oxygen concentration of the air so circulated is determined, and the time of said determination is recorded. Solenoid valves 305a and 305b are then closed. In a similar manner to that described above for enclosure 1, the oxygen concentrations in enclosures 2 to 8 are measured individually in turn, using the appropriate combinations of solenoid valves, pumps and other components of system 300 shown diagrammatically in Figure 3. After an initial value of gaseous oxygen concentration is measured for each enclosure, pumps 305c to 312c are started and are used continuously throughout the remainder of the test to circulate gas through containers 305d to 312d respectively. The measurement of oxygen concentration of the gas in the enclosures is performed for each enclosure as described above, at approximately hourly intervals over an approximately ten hour period. The volume of sample in each cylindrical sample container is also determined. This may conveniently be done by measuring the depth of the sample in the sample container, and then applying Equation 1 to determine the volume Vm. Alternatively, if the porosity ε is known, then the volume Vm may be calculated using Equation 6. If ε is not known, it may be determined from known values of Vm (determined by the first method described above) and of Vc and Vg by applying Equation 4.
The data acquired as described above is stored in computer 319 (Figure 3) or similar data processing device.
Once all of the data has been acquired and stored in computer 319 (Figure 3), values of oxygen concentration for each enclosure at each measurement time are converted to a value of oxygen mass using Equation 7. Alternatively, these calculations can be performed during the time that data is being acquired, and the results then stored in the computer. Curves of mass of oxygen against time are then constructed. An example of such a curve is shown in Figure 4. The slope of this curve, , is then determined for
At each enclosure, and the IOR of the material in each enclosure is calculated using Equation 5.
An alternative instrument that may also be used in accordance with the invention is showed diagrammatically in Figure 8. In the following description of the operation of the alternative instrument, an enclosure comprises cylinder 301, pressure sensor 303, manifold 313, one of solenoid valves 305b to 312b, the coπesponding one of pumps 305c to 312c, the coπesponding one of sample containers 305d to 312d, the coπesponding one of CO2 filters 805b to 812b, the coπesponding one of moisture filters 805d to 812e together with tubing connection the above to each other and to the coπesponding solenoid valve of 305a to 312a, as shown diagrammatically in Figure 3. The enclosure that incorporates sample container 305d will be refeπed to as enclosure 1, the enclosure that incorporates sample container 306d will be refeπed to as enclosure 2 and so forth, such that the enclosure that incorporates sample container 312d will be refeπed to as enclosure 8.
A program written in Lab VIEW computer language controls the data acquisition device, solenoid valves, air pumps, linear actuators, thermistor, pressure sensor and oxygen analyser. The methods for determining the volume of each sealable container, for determining whether there is a gas leakage into or from each enclosure and for measuring the ambient temperature are the same as was described above for the earlier mode of operation. After determining whether there is a gas leakage into or from enclosures 1 to 8, and determining the volume of gas in enclosures 1 to 8, and restoring the internal volume of enclosures 1 to 8 to their original values, as described above, valves 305a to 312a and 305b to 312b, and valves 391 and 317 are all closed. A gaseous oxygen concentration in enclosure 1 is measured as follows. Solenoid valves 305a, 305b and 317 are opened, while solenoid valves 306a to 312a, 306b to 312b and 391 are closed. Air is then circulated for approximately 5 minutes from sample container 305d through moisture and CO2 filters 805d and 805b respectively to oxygen sensor 318 using pump 314 at a rate of approximately 4xl0"4m3/min. A representative value of oxygen concentration of the air so circulated is determined, and the time of said determination is recorded. Solenoid valves 305a and 305b are then closed. In a similar manner to that described above for enclosure 1, the oxygen concentrations in enclosures 2 to 8 are measured individually in turn, using the appropriate combinations of solenoid valves, pumps and other components of system 800 shown diagrammatically in Figure 8. After an initial value of gaseous oxygen concentration is measured for each enclosure, pumps 305c to 312c are started and are used continuously throughout the remainder of the test to circulate gas through containers 305d to 312d and moisture filters 805d to 812d and CO2 filters 805b to 812b respectively. The measurement of oxygen concentration of the gas in the enclosures is performed for each enclosure as described above, at approximately hourly intervals over an approximately ten hour period.
The determination of the volume of sample in each cylindrical container and the data acquisition and calculations are the same as was described for the earlier mode of operation.
An advantage of the alternative instrument, as described above and as represented in Figure 8, is that the volume of the system that is not within any of the enclosures is reduced relative to the instrument represented in Figure 3. This reduces the contamination of gases between enclosures when switching from measurement of oxygen concentration in a particular enclosure to measurement of oxygen concentration in another enclosure. However, the choice of which mode of operation is used may depend on the nature of the sample. Samples with very low initial moisture levels may dry out to the point where their IOR is affected if the alternative instrument of Figure 8 is used, whereas the drying effect is less severe when using the instrument of Figure 3. Example 1
An IOR meter, as shown diagrammatically in Figure 3, was used to measure the IOR of reactive rock samples over a period of approximately 12 hours. Reactive rock samples were placed in eight plastic (PVC) sample containers of volume approximately 4xl0"3m3, which were then sealed in a reversible manner into the IOR meter.
Data in this example is provided for the sample in only one representative enclosure of the IOR meter, although similar data might be obtained from the other seven samples.
By means of changing the internal volume of a sealed enclosure by a known volume (using piston 302), measuring a pressure in the enclosure after said changing (using pressure sensor 303), and measuring a pressure in the enclosure at a time 40 seconds after the initial measuring, it was determined that there was no leakage from or into the enclosure. This procedure was conducted for each of the enclosures in the IOR meter, hi addition, after measurement of the ambient atmospheric pressure, the volume of gas in the representative enclosure was determined to be 3.2x10" m using Equation 3. The volume of material placed into the sample container of the representative enclosure was calculated to be 1.48 xlO" m using Equation 6. Pumps 305c to 312c, with flow of 4xl0"4m3/min, were then used to continuously circulate gas through the enclosures, which had been shown to be coπectly sealed. At regular intervals of approximately 5000 seconds, the gas from each enclosure was circulated through moisture and carbon dioxide filters to an oxygen analyser which had a resolution better than 0.001% (coπesponding to a mass of oxygen less than 3xl0"9g) and then back to the enclosure, at a constant flow of 4xl0"4m3/min. The ambient temperature was measured using a thermistor, forming part of a voltage divider circuit shown diagrammatically in Figure 1, and the pressure was measured using a pressure sensor. The mass of oxygen in an enclosure was then calculated for each measurement time, using Equation 7. The values of temperature, oxygen concentration and mass of oxygen for the representative enclosure are shown in Table 1.
Table 1: Measured temperature and oxygen concentrations and calculated mass of oxygen at each measurement time.
Time (s) Temperature (°C) Oxygen concentration Mass of oxygen (kg) (molar %)
1487 25.9 20.54 8.63xl0"4
6115 25.68 20.29 8.53X10"4
10783 25.28 20.07 8.44xl0"4 15478 24.88 19.86 8.35x10"
20162 24.49 19.67 8.26x10"
24882 24.17 19.48 8.18x10 ,-4
29602 23.87 19.31 8.11x10"'
34322 23.62 19.14 8.04x10"
39043 23.39 18.99 7.97x10"
43763 23.64 18.81 7.89x10"
The values of mass of oxygen in the representative enclosure, obtained from the IOR meter, are shown graphically in Figure 4 as a function of time. This data was used to determine the rate of change of the oxygen mass with time, in the representative
At enclosure. Using Equation 5, the value of IOR for the sample in the representative enclosure was calculated to be 1.17x10" kg(oxygen)m" s" . Example 2
This example describes a process that may be used to control the operation of, and acquire data from, a system for measuring IOR of a plurality of samples in accordance with this invention. The steps of the process are described with reference to Figure 1, Figure 3 and Figure 5. With regard to Figure 3, there is a linear actuator, not shown in Figure 3, which may be used to move piston 302 in order to change the internal gas volume of one or more of enclosures 1 to 8. With regard to Figure 5, as was described above, a similar assembly containing a further four sample containers is located at the rear, behind the assembly shown. Elements in the rear assembly will be refeπed to in tins example with a suffix b. Thus, for example, behind linear actuators 510, 511 and 512 are similar linear actuators 510b, 511b and 512b respectively. This does not apply to any numbers representing components in Figures other than Figure 5. In this example there may optionally be a mass flow controller (MFC) which may be inserted into line 366 (Figure 3), between pump 314 and oxygen detector 318. The sequences of operation for startup commence with opening are as follows.
The computer opens communications with the following modules: linear actuators, solenoid valves, pumps, mass flow controller (if present), oxygen sensor, pressure sensor, thermistor, then blanks the display panels and initialises graphs. The operator should then input into the computer program the sample containers that are to be tested. The screen of computer 319 then displays the text "test/no test" for the 8 sample containers 305d, 306d, 307d, 308d, 309d, 310d, 3 l id and 302d. The operator should input the details of the contents of each sample container. The operator is then prompted for a file name. The file is then created, and the file name, date, time, contents of sample containers and file headers are saved to a file for each sample container.
In order to reset all channels to the OFF state, the following sequence of operations is followed. The voltages for thermistor, MFC (if present) and oxygen air pump to are set to 0V. Valves 305a to 312a are closed and the linear actuators are reset to the start position, fully extended (relay OFF): Group A (510, 511 and 512) and Group B (510b, 511b and 512b). Valves 305b to 312b and air valve 391 are then opened. This ensures that there is no pressure built up inside the sample containers so that they will not get stuck and will move down with the sample container holder. Piston 303 is then reset to the start position. After an 8 second delay, the power to linear actuators (510, 511, 512, 510b, 511b and 512b) for the sample container holders (506 and 506b), and the power to piston 302 and linear actuator are turned off. Air valve 391, oxygen pump valve 317 and valves 305b to 312b are then closed, and air pumps 305c to 312c for sample containers are turned off. The operator then places the sample containers on the holders. A prompt appears on the screen of computer 319: "Are the canisters in place on the holders? Press OK when you are ready to begin testing." The start time is displayed on screen of computer 319 and time is set to t0 for test.
To establish a starting pressure, the following procedure is followed. Linear actuators 510, 511, 512, 510b, 511b and 512b are activated. If only testing any or all of sample containers 501 to 504 then only front sample container holder 506 is activated using linear actuators 510, 511 and 512. If only testing any or all of sample containers 501b to 504b then only back sample container holder 506b is activated using linear actuators 510b, 511b and 512b. If testing a plurality of sample containers, at least one of which is one of 501, 502, 503 and 504 and at least one of which is one of 501b, 502b, 503b and 504b, then both sample container holders are activated. This operation lifts up and seals the sample containers. The screen of computer 319 displays the text "sealing canister" for each sample container that will be tested. After an 8 second delay to allow for the sample containers to be lifted up, the power to the linear actuators 510, 511, 512, 510b, 511b and 512b is turned off. Air valve 391 and valves 305b to 312b are then opened. This equalises the pressure in all sample containers to atmospheric pressure. The screen of computer 319 displays the text "Equalising Canister" for each sample container to be tested. After waiting 60s for the sample containers and gas lines to equalise to atmospheric pressure, the barometric pressure (ie Patm, atmospheric pressure) is determined and displayed, and the value is saved to file. Solenoid valves 305b to 312b are then closed. In order to check if there is a leak in each sample container to be tested, and to calculate the volume of gas (Vg) in each sample container to be tested, the following procedure is followed. First, the screen of computer 319 displays "measuring pressure in canister/waiting/pressure test completed" for each enclosure that is to be tested. Then, for each enclosure that is being tested, the following procedure is performed. The solenoid valve in manifold 313 that coπesponds to the enclosure to be tested is opened, and also air valve 391 is opened for 10 seconds to equalise the single enclosure to atmospheric pressure again. Then air valve 391 is closed. The computer then reads, calculates and stores pressure Pi from pressure sensor 303. The actuator for piston 302 is activated, to withdraw gas from the enclosure. After waiting 40 seconds for the piston to move and for system to stabilise, the power to the linear actuator is turned off. The computer then reads pressure P2 from the pressure sensor. After waiting a further 40 seconds to check for a leak in the enclosure seal, the computer reads pressure P3 from pressure sensor and calculates Pι-P2 and P3-P2. If Pi - P2 < 3 kPa then sample container is not present and this enclosure is not tested any further, and the screen of computer 319 displays the text "canister not present". If P3 - P2 < 0.08 kPa then there is no leak. Otherwise, testing on the enclosure is discontinued and the screen of computer 319 displays the text "leak". If the sample container is present and the enclosure has no leak, then gas volume, Vg is calculated and stored, and the piston returned to its starting position. After waiting a further 8 seconds, the solenoid valve in manifold 313 that coπesponds to the enclosure is closed. The screen of computer 319 then displays either the text "Leak" or the text "No Leak" for each enclosure. If all of the enclosures have a leak or they are not present the system will shutdown. Otherwise it proceeds to determine IOR for those enclosures that have no leak. In order to determine the air temperature, measure oxygen concentration, determine change in mass of oxygen and determine the IOR the following procedure is followed. First the text "Waiting" is displayed for the sample containers that are being tested. 1.5V is applied to thermistor (see Figure 1) so that the temperature can be read. After waiting for 5 seconds, voltage Uf is read the from the voltage divider of the thermistor, and the temperature is calculated, displayed and stored. The voltage that was applied to the thermistor is then turned off. If present, the MFC is activated and flow rate set to 0.4 L/min. Then, for each cycle the following procedure is followed. Firstly, for each enclosure that is being tested the following operations are conducted, in order to determine a mass of oxygen in each of the enclosures. The two solenoid air valves (one in each of manifolds 304 and 313) coπesponding to the enclosure being tested, are opened at the same time. Air pump valve 317 is also opened, and air pump 314 is turned on by setting the voltage of the pump to 1.75V. After eight minutes of n ning air pump 318, the output from oxygen analyser 318 is read, calculated and stored every 10 seconds for 60s, and the average reading for the 60s is calculated, display and stored, and the time tXj seconds when the average value was calculated is also recorded. Therefore, air pump 318 runs for nine minutes in total. The mass of oxygen, mX)i is then calculated, displayed and then stored in the file. After each measurement of the mass of oxygen except for the first measurement for each sample, the IOR for the sample is then calculated using a linear fit to the data stored in the file, and is then displayed on the screen of computer 319. (IOR is expressed in either units kg(O2)kg(material)"1s"1 or kg(O2)m"3s"1 depending on which units were selected on the main screen of computer 319 by the user. If in kg(material) then user should enter mass of material on the computer 319 before test started and if m"3 then user should have entered volume of material on the computer 319 before test started.) The mean square eπor to the fit of the IOR is then calculated and stored in the file. Air pump 314 is then turned off by setting the voltage to the pump to 0V, and the air pump valve 317 and solenoid valves in manifolds 304 and 313 coπesponding to the enclosure being tested are closed. Then the air pumps in all of the enclosures, 305c to 312c are turned on, and the screen of computer 319 displays the text "Waiting till next oxygen measurement". After a delay of several minutes (the exact time is set by the user on the computer) for the gas in the sample containers may to circulate and mix, the air pumps, 305c to 312c are turned off.
After all cycles are complete, separate graphs of the mass of oxygen vs time are displayed for each of the enclosures that are being tested.
In order to shut down the system, the following process is followed. The screen of computer 319 displays the text "Testing completed". The voltages for thermistor, MFC (if present) and oxygen air pump are set to 0V. Valves 305a to 312a are closed, the linear actuators are reset to the start position, fully extended (turn the relay OFF): Group A (510, 511 and 512) and Group B (510b, 511b and 512b). Valves 305b to 312b and air valve 391 are opened. This ensures that there is no pressure built up inside the sample containers so that they will not get stuck and will move down with the sample container holder. Piston 302 is reset to the start position. After waiting for 8 seconds, power to linear actuators 510, 511, 512, 510b, 511b and 512b for the sample container holders and power to piston 302 and linear actuator are turned off. Then air valve 391, oxygen pump valve 317 and valves 305b to 312b are closed. Air pumps 305c to 312c are turned off, and communications to linear actuators, solenoid valves, pumps, mass flow controller (if present), oxygen sensor, pressure sensor, thermistor are then closed.

Claims

Claims:
1. A method for determining an internal gas volume in a sealed enclosure comprising: a) measuring a first gas pressure in the sealed enclosure; b) changing the internal volume of the sealed enclosure by a known volume, whereby the gas pressure in the enclosure is less than or greater than the gas pressure outside the enclosure; c) measuring a second gas pressure in the sealed enclosure after said changing as a function of time; d) determining from said second gas pressure as a function of time whether there is a gas leak from or into said sealed enclosure; e) where there is no gas leak from or into said sealed enclosure, determining the internal gas volume of the sealed enclosure from the first and second gas pressures and the known volume.
2. A method for determining a gas-filled porosity of a sample of material, said method comprising: a) placing the sample in an openable sealable enclosure capable of holding the sample; b) sealing the enclosure; c) measuring a first gas pressure in the enclosure; d) changing the internal volume of the enclosure by a known volume; e) measuring a second gas pressure in the enclosure after said changing; f) determining a volume occupied by the sample; and g) determining the gas-filled porosity of the sample from the volume occupied by the sample, the volume of the enclosure and the volume of gas in the enclosure when the sample is in the enclosure.
3. A method for measuring an intrinsic oxidation rate of a sample comprising: a) placing the sample of material in a closable sealable enclosure; b) closing and sealing said enclosure; c) measuring a first gas pressure in the enclosure; d) changing the internal volume of the enclosure by a known volume, whereby the gas pressure in the enclosure is less than or greater than the gas pressure outside the enclosure; e) measuring a second gas pressure in the enclosure after said changing as a function of time; f) determining from said second gas pressure as a function of time whether there is a gas leak from or into said enclosure; g) where there is no gas leak from or into said enclosure, determining the internal gas volume of the enclosure from the first and second gas pressures and the known volume; h) determining the volume of the sample from the internal gas volume of the enclosure, the first and second gas pressures, the known volume and the porosity of the sample; i) determining a change in gaseous oxygen mass in the enclosure as a function of time; and j) detennining the intrinsic oxidation rate of the sample.
4. The method of claim 3 wherein the intrinsic oxidation rate is determined using a formula selected from the group consisting of:
and
Figure imgf000046_0001
where:
IOR = intrinsic oxidation rate Am = change in gaseous oxygen mass
Δt = time period
Vm = volume of the sample
Mm = dry mass of the sample, wherein equation 5 is used to determine a volume based intrinsic oxidation rate and equation 5a is used to determine a mass based intrinsic oxidation rate.
5. The method of claim 3 wherein the step of determining a change in gaseous oxygen mass comprises measurement of gaseous oxygen concentration.
6. The method of claim 5 wherein the measurement of gaseous oxygen concentration is conducted over a period of less than about 24 hours.
7. The method of claim 5 wherein individual values of gaseous oxygen concentration are obtained at least once every hour throughout an overall measurement period.
8. The method of claim 5 further comprising measuring a concentration of carbon dioxide in the enclosure
9. The method of claim 8 comprising compensating the measurement of gaseous oxygen concentration for the concentration of carbon dioxide.
10. The method of claim 5 wherein gas from the enclosure is passed through a filter before a measurement of gaseous oxygen concentration is made.
11. The method of claim 3 wherein a gas in the enclosure is circulated.
12. A method of estimating a rate of oxygen consumption in a pile of material which is oxygenated, comprising: a) placing a sample of the material in a closable sealable enclosure; b) closing and sealing said enclosure; c) measuring a first gas pressure in the enclosure; d) changing the internal volume of the enclosure by a known volume, whereby the gas pressure in the enclosure is less than or greater than the gas pressure outside the enclosure; e) measuring a second gas pressure in the enclosure after said changing as a function of time; f) determining from said second gas pressure as a function of time whether there is a gas leak from or into said enclosure; g) where there is no gas leak from or into said enclosure, determining the internal gas volume of the enclosure from the first and second gas pressures and the known volume; h) determining the volume of the sample from the internal gas volume of the enclosure, the first and second gas pressures, the known volume and the porosity of the sample; i) determining a change in gaseous oxygen mass in the enclosure as a function of time; j) determining the intrinsic oxidation rate of the sample; k) determining a volume of the pile of material; and
1) estimating the rate of oxygen consumption in the pile of material from the volume of the sample, the intrinsic oxidation rate of the sample and the volume of the pile of material.
13. A method of determining intrinsic oxidation rates of a plurality of samples, wherein the intrinsic oxidation rates are measured over the same period of time, comprising: a) loading said plurality of samples into a plurality of enclosures; b) determining if any of the enclosures has a gas leak; c) for each enclosure with no gas leak, measuring an internal gas volume for said enclosure; and d) for each enclosure with no gas leak, determining an intrinsic oxidation rate of the sample therein.
14. The method of claim 13 wherein the intrinsic oxidation rate of each sample in an enclosure with no gas leak is determined using a formula selected from the group consisting of:
Δm
IOR (5)
V„. Δt and
Figure imgf000048_0001
where: IOR intrinsic oxidation rate
Δm change in gaseous oxygen mass Δt time period
Vm volume of the sample Mm dry mass of the sample wherein equation 5 is used to determine a volume based intrinsic oxidation rate and equation 5a is used to determine a mass based intrinsic oxidation rate.
15. A method for determination of a spatial distribution of intrinsic oxidation rate within a waste heap comprising the steps of: a) obtaining samples from different locations in the waste heap, b) measuring an intrinsic oxidation rate for at least two of the samples, and c) detennining a spatial distribution of intrinsic oxidation rate within the waste heap.
16. A system for determining an internal gas volume in a sealed enclosure, comprising: a) an openable sealable enclosure; b) a volume adjustor for changing the internal volume of the enclosure by a known volume, whereby the gas pressure in the enclosure is less than or greater than the gas pressure outside the enclosure; and c) a pressure measuring device for measuring the gas pressure in the enclosure as a function of time.
17. A system for determining a gas-filled porosity of a sample of material comprising: a) an openable sealable enclosure; b) a volume adjustor for changing the internal volume of the enclosure by a known volume, whereby the gas pressure in the enclosure is less than or greater than the gas pressure outside the enclosure; c) a pressure measuring device for measuring the gas pressure in the enclosure as a function of time; d) a volume calculator for calculating the volume of the sample; and e) a porosity calculator.
18. A system for measuring an intrinsic oxidation rate of a sample comprising: a) an openable sealable enclosure capable of holding the sample; b) a volume adjustor for changing the internal volume of the sealed enclosure by a known volume, said adjustor being coupled to the enclosure; c) a pressure measuring device for measuring gas pressure and a temperature measuring device for measuring temperature; and d) an oxygen meter for measuring gaseous oxygen concentration of a gas in the enclosure.
19. The system of claim 18 wherein the oxygen meter is capable of measuring gaseous oxygen concentration as a function of time.
20. The system of claim 19 additionally comprising an intrinsic oxidation rate determiner for determining the intrinsic oxidation rate of the sample from the measuring of gaseous oxygen concentration and the resultant change in gaseous oxygen mass as a function of time and from the volume of the sample.
21. The system of claim 18 additionally comprising a gas circulator for circulating the gas.
22. The system of claim 18 wherein the oxygen meter is located outside the enclosure, and there is a transport system to fransport some or all of the gas in the enclosure to said oxygen meter.
23. The system of claim 18 additionally comprising a carbon dioxide meter for measuring a concentration of carbon dioxide in the gas.
24. The system of claim 18 having a compensator for compensating the measurement of gaseous oxygen concentration for the concentration of carbon dioxide.
25. The system of claim 18 additionally comprising a filter to prevent access to said oxygen meter by a material that is capable of damaging said meter or of altering its ability to accurately measure a concenfration of oxygen in a gas.
26. A system for determining an intrinsic oxidation rate for a plurality of samples comprising: a) a plurality of openable sealable enclosures capable of holding the samples; b) a volume measuring system for determining the gas volume of each of said enclosures individually; c) a leak detection system for determining for each enclosure separately whether that enclosure has a gas leak; d) an intrinsic oxidation rate detection system for determining for each enclosure separately the intrinsic oxidation rate of the sample in said enclosure.
27. The system of claim 26 wherein the intrinsic oxidation rate detection system comprises an oxygen meter for measurement of a gaseous oxygen concentration.
28. The system of claim 27 wherein more than one of the enclosures is connected to the oxygen meter, said oxygen meter being located outside the enclosures.
29. The system of claim 26 additionally comprising a carbon dioxide meter for measuring a concentration of carbon dioxide in each enclosure.
30. The system of claim 29 having a compensator for compensating the measurement of gaseous oxygen concentration for the concentration of carbon dioxide.
31. The system of claim 26 additionally including an isolator to isolate an enclosure.
32. A system for determining a spatial distribution of intrinsic oxidation rates within a waste heap comprising: a) a sampling system for obtaining samples from different locations within the heap; b) a plurality of openable sealable enclosures capable of holding the samples; c) a volume measuring system for determining the gas volume of each of said enclosures individually; d) a leak detection system for determining for each enclosure separately whether that enclosure has a gas leak; e) an intrinsic oxidation rate detection system for determining for each enclosure separately an intrinsic oxidation rate of the sample in said enclosure; and f) distribution determiner for determining a spatial distribution of intrinsic oxidation rates.
33. A system for estimating a rate of oxygen consumption of a pile of material which is oxygenated, comprising; a) an openable sealable enclosure capable of holding a sample of the material; b) a volume adjustor for changing the internal volume of the enclosure by a known volume, said adjustor being coupled to the enclosure; c) a pressure measuring device for measuring gas pressure and a temperature measuring device for measuring temperature; d) an oxygen meter for measuring gaseous oxygen concentration of a gas in the enclosure in order to determine an intrinsic oxidation rate of the sample; e) a volume estimator for estimating a volume of the pile of material; and f) an oxygen consumption calculator for calculating the rate of oxygen consumption of the pile from the intrinsic oxidation rate and the volumes of the sample and of the pile.
PCT/AU2004/000512 2003-04-16 2004-04-16 Determining gas volume, porosity, and intrinsic oxidation rate WO2004092690A1 (en)

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