CA2032357A1 - Pressure oxidation methods for gold extraction and toxic waste treatment - Google Patents
Pressure oxidation methods for gold extraction and toxic waste treatmentInfo
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- CA2032357A1 CA2032357A1 CA 2032357 CA2032357A CA2032357A1 CA 2032357 A1 CA2032357 A1 CA 2032357A1 CA 2032357 CA2032357 CA 2032357 CA 2032357 A CA2032357 A CA 2032357A CA 2032357 A1 CA2032357 A1 CA 2032357A1
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- 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
- C22B11/00—Obtaining noble metals
- C22B11/08—Obtaining noble metals by cyaniding
-
- 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
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- Treatment Of Sludge (AREA)
Abstract
PRESSURE OXIDATION METHODS FOR
GOLD EXTRACTION AND TOXIC WASTE TREATMENT
Abstract of the Disclosure The present invention provides methods for extracting gold from refractory auriferous material, such as a gold-containing ore, a concentrate thereof, a reclaimed sulphide concentrate or some combination thereof, including the steps of mixing the refractory auriferous material with at least one toxic residue exhibiting a low sulphur content to form a low sulphur content mixture; pressure oxidizing the mixture; and cyaniding the oxidized mixture. Methods for extracting gold while simultaneously decreasing the toxicity of previously generated toxic wastes are also discussed.
The gold extraction/toxic waste treatment methods preferably involve mixing refractory auriferous material with first and second toxic residues of low sulphur content; pressure oxidizing the mixture; and cyaniding the oxidized mixture. In these methods, contaminants in the toxic residues (e.g., iron and arsenic) combine with each other or with other feed components to form inert molecules having a decreased environmental impact.
GOLD EXTRACTION AND TOXIC WASTE TREATMENT
Abstract of the Disclosure The present invention provides methods for extracting gold from refractory auriferous material, such as a gold-containing ore, a concentrate thereof, a reclaimed sulphide concentrate or some combination thereof, including the steps of mixing the refractory auriferous material with at least one toxic residue exhibiting a low sulphur content to form a low sulphur content mixture; pressure oxidizing the mixture; and cyaniding the oxidized mixture. Methods for extracting gold while simultaneously decreasing the toxicity of previously generated toxic wastes are also discussed.
The gold extraction/toxic waste treatment methods preferably involve mixing refractory auriferous material with first and second toxic residues of low sulphur content; pressure oxidizing the mixture; and cyaniding the oxidized mixture. In these methods, contaminants in the toxic residues (e.g., iron and arsenic) combine with each other or with other feed components to form inert molecules having a decreased environmental impact.
Description
2~323~7 PRESSURE OXIDATION METHOD~ FOR
GOLD EXTRACTION AND TOXIC WASTE TREATMENT
Technical Field of the Invention This invention relates to the extraction of gold from feed mixtures of auriferous sulphidic ores, concentrates of such ores or reclaimed sulphide concentrates and previously generated toxic wastes, such as roaster calcine and roaster arsenic sludge.
Backaround Of the Invention Metallic gold is extracted from gold-containing ores or concentrates formed from such ores.
Higher grades of auriferous ores have a higher gold content. Since sources of high-grade ores are rapidly being depleted, the attention of the gold mining industry is becoming more and more focused upon methods of extracting gold from lower-grade ores. The lower-grade ores contain higher amounts of impurities, such as sulphidic minerals. Typical sulphidic minerals present in gold-containing ores are arsenopyrite and/or pyrite, and may also include appreciable amounts of pyrrhotite. Lesser amounts of base metals in sulphide form, such as copper, zinc, and lead may also be present.
Extraction of metallic gold from ores or ore concentrates is conventionally accomplished by cyaniding (i.e., dissolution in cyanide solutions).
The cyaniding extraction of gold from refractory auriferous sulphidic material has been shown to be improved if the material is first subjected to a pressure oxidation treatment. See, for example, U.S.
2~323~7 Patent No. 2,777,764. In the pressure oxidation treatment, maximum gold recovery is obtained through complete oxidation of the sulphide sulphur atoms to sulphate form.
A problem with this pre-cyaniding pressure oxidation treatment is the formation of elemental sulphur as an intermediate or as a primary oxidation product. As a result of the elevated temperature at which the pressure oxidation treatment is conducted, the elemental sulphur so produced will be in molten form. Molten sulphur tends to wet and/or coat many of the sulphides present in the slurry being oxidized.
Such coated sulphides tend to agglomerate. Formation of agglomerates containing molten sulphur and unreacted sulphides limits sulphide oxidation, ultimately resulting in decreased gold recovery. Additional problems arise in continuous operations, because agglomerates may build up to the point where they accumulate in the reaction vessel. Moreover, elemental sulphur detrimentally affects subsequent cyaniding processing, even further decreasing gold recovery.
One method of obviating the molten elemental sulphur problem is described in U.S. Patent No. 4,605,439. That patent discusses the addition of "relatively inert solids" to the feed of iron-containing, refractory auriferous sulphidic material to provide a feed slurry of high pulp density. As a result, the patented pressure oxidation process could be carried out at a lower temperature with less agglomeration. The inventors of this patented technique theorized that the added inert solids promoted the dispersion o~ the elemental sulphur formed in the pressure oxidation reaction (reduc1ng the amount of agglomeration) and suspen~ion of any agglomerates formed (permitting the agglomerates to oxidize more 2 t~3~3 ~ 7 completely). The only example recited in the patent of a relatively inert solid suitable for admixture with the pressure oxidation autoclave refractory feed stream is a recycle stream (i.e., a portion of the process stream constituting material previously passed through the autoclave, either before or after liquid-solid separation and prior to cyaniding).
Other alternatives for overcoming the problems created by the formation of molten elemental sulphur have been suggested. A survey of some of these alternatives and the deficiencies thereof with respect to practical, continuous, industrial-scale gold recovery operations are discussed in U.S. Patent No.
4,605,439.
An additional problem facing the mining industry is an increased emphasis on the environmental impact of both present and past mining and metal recovery processes. Consequently, heightened interest has been shown in processes for removing inorganic contaminants from wastewater generated during gold milling and other industrial processes as well as for removing toxic substances ~rom previously generated waste from such processing.
In the past, refractory auriferous materials were sometimes treated by roasting, a technique that resulted in the production of toxic by-products, such a~ arsenic-containing calcines and sludges. As a result of greater environmental awareness, roasting is being replaced by pressure oxidation in the treatment of auriferous refractory material. Pressure oxidation techniques, utilizing correct feed stoichiometry and followed by appropriate neutralization processing, typically generate waste effluent process streams containing non-directly dischargeable levels of toxic contaminants. The toxic wastes previously produced by the roasting process remain; however, and pressure is ~2~7 being brought to bear upon the mining industry to institute clean up procedures.
Specifically, wastewater from a large percentage of previously conducted roasting processes has been retained in tailings ponds. In fact, retention of wastewater in tailings ponds is the oldest and still a common method for treatment of gold mill wastewater effluent. Natural degradation, photodegradation, precipitation, and volatilization of contaminants are the primary mechanisms of tailings pond wastewater treatment. Many metals are soluble in wastewater as a result of cyanide complexing, however.
These metals therefore do not precipitate out of solution and contribute substantially to the high levels of inorganic contaminants found in tailings ponds. Also, severe climatic conditions limit the efficacy of tailings ponds, since the aforementioned mechanisms of tailings pond wastewater treatment do not occur when that pond is frozen.
Implementation of more strict environmental regulation would appear to limit the use of tailings ponds. Speci~ically, wastewater retention in tailings ponds is ef~ective to reduce wastewater contamination;
however, ~uch wastewater purification is inadequate to permit direct discharge. Oxidized residues of, for example, high iron content constitute toxic byproducts o~ the roasting process. These contaminants are discharged into and remain in tailings ponds in soluble (i.e., toxic) form.
Also, ores containing significant amounts of, for example, arsenopyrite (generally in excess of 1%
arsenic) have been previou~ly subjected to roasting.
Such roasting released oxidized forms of arsenic from the ore, thereby producing effluent having arsenic contaminants. Effluent containing high levels of soluble arsenic was typically stored in underground 2~23~7 vaults dedicated to that purpose. Such storage techniques are susceptible to breach, thereby releasing the toxic residue into the environment. For example, a fissure may develop in the vault structure.
Alternatively, ground water drainage may occur. As a result, methods of treating these previously produced toxic wastes are being sought.
Summary of the Invention The present invention provides methods whereby currently mined refractory auriferous materials, preferably auriferous sulphidic materials, are mixed with koxic waste from old mill tailings to extract gold from both the new ore production and the old production wastes. Gold may also be recovered from reclaimed sulphidic concentrates by the methods of the present invention. These methods also produce an environmentally acceptable, gold extraction waste product.
The methods of the present invention include the steps of: mixing currently mined refractory auriferous material and/or reclaimed sulphidic concentrates with at least one low sulphur content toxic waate generated in p.evious gold mill processing, such as roaster calcine or sludge to produce a low sulphur content mixture; pressure oxidizing the mixture; and cyaniding the oxidized mixture.
Preferably, the mixing step of the methods of the present invention includes the addition of a waste having low sulphur, high iron, and low arsenic content, such as calcine, and a waste having low sulphur, low iron, and high arsenic content, such as arsenic sludge.
In a preferred method, both a reduction in the amount of sulphur present in the pressure oxidation feed mixture and an increase in the formation of insoluble ferric arsenate during pressure oxidation are achieved.
2 ~ 3 2 3 ~ 7 Reduction in feed sulphur content results in a decrease in elemental sulphur and concomitant agglomeration formation in the pressure oxidation step. In addition, the insoluble molecules constitute a more manageable waste product.
If the currently mined refractory auriferous material or a reclaimed sulphidic concentrate contains carbonate compounds, an acidification step can be utilized prior to the pressure oxidation treatment. In this manner, a high level of carbonate conversion to carbon dioxide during the pressure oxidation process can be avoided. Acid liquor generated in the pressure oxidation process is preferably recycled for use in this acidification step.
Brief Description of the Drawing The Figure shows a flow diagram of a gold extraction/toxic waste treatment method of the present invention.
Description o~ the Preferred Embodiments The present invention is directed to methods o~ extracting gold from a re~ractory auriferous materlal, preferably an auri~erous sulphide material, including mixing, pressure oxidation and cyaniding steps. The present invention is also directed to methods of simultaneously extracting gold and treating (detoxifying) toxic waste.
For the purpose of this description, the values stated as percentages are percentages by weight, unless otherwise indicated. With the exception of usage ln connectlon with gold, the term "content" also re~ers to weight percent, albeit less de~initively than a numerical percentage value. Gold content is expressed in ounces per ton (oz/ton).
2~32~7 For the purpose of this description, the term "refractory auriferous material" encompasses any refractory material containing gold. Exemplary of such materials are auriferous sulphide ores, concentrates 5derived from such ores, concentrates reclaimed from gold mill tailings, or the like. A combination of one or more of these materials might also be used as a refractory auriferous sulphidic material in accordance with the present invention. A "currently mined 10refractory auriferous sulphidic material" encompasses auriferous ores, concentrates thereof or combinations of the two that have not previously been treated to extract gold therefrom.
As mentioned above, typical sulphide minerals 15present in auriferous ores are arsenopyrite, pyrite, pyrrhotite, base metal sulphides, such as copper, zinc, and lead sulphides, and the like. An exemplary ore that might be processed in accordance with the present invention contains from about 0.05 to about 0.8 oz/ton 20gold (Au); from about 0.2 to about 3% arsenic (As);
from about 2 to about 5% iron (Fe); and from about l to about 5% sulphur (S). An exemplary concentrate derived from ~uch an ore contains from about 1 to about 10 oz/ton Au; from about 8 to about 20% As; from about 2520 to about 40% Fe; and from about 15 to about 35% S.
An exemplary concentrate reclaimed from gold mill tailings contains from about 0.2 to about 2 oz/ton Au;
from about 5 to about 15% As; from about 10 to about 35% Fe; and from about 8 to about 30% S.
30The methods of the present invention feature a mixing step, where the refractory auriferous material is blended with at lea~t one toxic residue (i.e., waste) in order to substantially decrease the sulphur content in the pressure oxidation feed stream. Such a 35decrease in sulphur content improves the performance of the pressure oxidation treatment by preventing the 2~3'~7 generation of excessive heat and decreasing the amount of elemental sulphur formed during that treatment. The mixing step may be accomplished in any conventional manner. Exemplary mixing techniques are vibrational agitation, stirring, and the like. This mixing procedure may be conducted using commercially available equipment designed for that purpose.
Preferable toxic wastes useful in the present invention are those that were generated by gold mill processes using techniques such as roasting. One preferred toxic residue for admixture with the refractory auriferous material is a residue exhibiting a low sulphur content, a high iron content, and a low arsenic content. For the purpose of describing such a toxic residue, a low sulphur content indicates a weight percentage of sulphur below about 5%: a high iron content ind~cates a weight percentage of iron in excess of about 30%; and a low arsenic content indicates a weight percentage of arsenic below about 50%.
Exemplary of such a toxic residue is calcine derived ~rom wastee produced in roasting processes. Exemplary ¢al¢lne ¢ompo~itions use~ul in practicing the present invention include from about 0.25 to about l oz/ton Au;
from about 2 to about 12% As~ from about 25 to about 50% Fe; and from about 2 to about 15% S.
A second pre~erred toxic residue for admixture wlth the refractory auriferous material is a residue exhibiting a low sulphur content, a low iron content, and a high arsenic content. For the purposes of describing such a toxic residue, a low sulphur content indicates a weight percentage of sulphur below about 3%; a low iron content indicates a weight percentage of iron below about 10%; and a high ar~enic content indicates a weight percentage of ar~enic in excess of about 50%. Exemplary of such a toxic residue i~ ar~enic-containing sludge derived ~rom wastes ~? ~ 3 ~r~
produced in previous roasting processes. Exemplary arsenic-containing sludge compositions useful in practicing the present invention include from about 0.25 to about l oz/ton Au: from about 45 to about 65%
As; from about 5 to about 10% Fe; and from about l to about 5~ S.
Arsenic sludge is typically derived from precipitators or from dedicated pits, dedicated ponds or underground vaults in which effluent from roaster processing is stored. High iron content calcine is typically derived from the oxidized solid residues resulting from the roasting process.
In order to disperse the sulphur present in the refractory auriferous sulphide material and decrease the sulphur content of the pressure oxidation feed, the mixing step must be conducted with appropriate components in appropriate amounts.
Specifically, an amount of toxic residue(s) sufficient to reduce the sulphur content of the pressure oxidation feed ~i.e., refractory auriferous sulphide material and toxic residue(s)) below about 12% by weight, preferably below about 10% by weight, must be used. Such stoichiometric ad~ustment o~ the pressure oxidation feed to achieve a speci~ied sulphur content is within the purview of a practitioner in the art.
The methods oP the present invention may also feature addition of toxic residues having soluble toxic contaminants capable of reacting with one another or with other components of the pressure oxidatian feed stream under oxidizing conditions to form insoluble molecules having decreased toxicity. When arsenic sludge is used in admixture with a refractory sulphidic material containing iron, some of that iron reacts with the ~oluble arsenic present in the sludge to form ferric arsenate as described more fully below. In addition or in the alternative, iron may be added to _g_ 2~323~
the pressure oxidation feed to react with the soluble arsenic in the sludge as is more fully described below.
Since ferric arsenate is insoluble in water, the amount of soluble arsenic is decreased, and the toxicity of the pressure oxidation effluent is therefore reduced.
In a preferred method, calcine and arsenic sludge are mixed with the refractory auriferous sulphidic material. The soluble iron present in calcine is capable of reacting with the soluble arsenic present in arsenic-containing sludge under oxidizing conditions to form insoluble ferric arsenate and acid.
The reaction proceeds as follows:
2FeS2+ 72 + 2HzO --> 2FeSO4 + 2H2SO4 4FeAsS + 1102 + 2H20 --> 4HAs02 + 4FeSO4 4FeS04 + 2H2S04 + 2 --> 2Fe2(SO4)3 + 2H20 2HAsO~ + 2 + 2H2 --> 2H3As04 Fe2(SO4)3 + 2H3As04 --> 2FeAsO4 + 3H2S04 Preferably, the Fe:As ratio in the pressure oxidation feed is about 1.2:1 or greater. If necessary, iron may be added to the pressure oxidation feed to provide the appropriate component ratio. This iron may be added at any time prior to pressure oxidation, i.e., before, during or after the mixing step. The iron BO added may be in any chemical form sultable ~or this purpose, such as shredded form. The iron i8 pre~erably dissolved in acid prior to admixture with the pressure oxidation feed. Recycled pressure oxidation-produced acid or any other acid capable of dissolving iron may be used for this purpose.
When a decrease in the toxicity of toxic residue(s) contained in the pressure oxidation feed is also desired, the stoichiometry and other parameters of the reaction converting the soluble toxic contaminant(s) into insoluble non-toxic or less toxic molecules must also be taken into account to determine the composition of the pressure oxidation feed stream.
2~323~
For example, a pressure oxidation feed stream composed of 20% sulphide concentrates, which can comprise arsenopyrite, pyrite, pyrrhotite, or a combination thereof and up to about 25% gangue minerals, 40%
calcine (<10% S, 40% Fe, 2% As), and 40% arsenic sludge (2-3% S, 8% Fe, 55% As) is characterized by a total sulphur content of less than 10%. Pressure oxidation of such a feed stream will result in the formation of ferric arsenate. A practitioner in the art would be able to determine an appropriate pressure oxidation feed stream composition to achieve both gold extraction and toxicity reduction.
The pressure oxidation step of the present invention may be conducted in accordance with known techniques. See, for example, U.S. Patent No.
2,777,764. Moreover, toxic wastes generated in alternative gold recovery techniques, such as roasting, contain gold. For example, roaster calcine wastes may contain from about 0.25 to about 1 oz/ton Au.
Similarly, arsenic sludge wastes may contain from about 0.25 to about 1 oz/ton Au. By reprocessing these wastes, some of the gold contained therein may be recovered, thereby increaeing the total amount of gold extracted.
The pressure oxidation feed stream used in the practice of the present invention is a slurry.
Aqueous slurries are preferred. Slurries useful in the methods o~ the present invention are characterized by pulp densities of from about 15 to about 60% solids by weight, with from about 20 to about 40% solids by weight being preferred.
The pressure oxidation step of the present invention may be conducted in commercially available equipment, such as a multi-compartment autoclave, under conventionally accepted sulphide-oxidizing conditions.
For example, a 50 L capacity, 6-stage, equal volume per 3~
stage autoclave may be used in practicing the present invention. The pressure oxidation treatment may be conducted using other reactor types, such as industrial autoclaves of, for example, 3 m diameter and 20 m length. Exemplary equipment useful in continuous operations are tubular reactors, a plurality of reactors arranged in series, and the like. In addition, a batch reaction vessel may be used when the methods of the present invention are employed in a non-continuous fashion.
Oxidation conditions include a temperaturefrom about 150 to about 250C and a total pressure ranging from about 400 to 6000 kPa (50-700 psi). The oxidation will be allowed to proceed for a time sufficient to achieve adequate oxidation of feed sulphides to sulphates. An adequate oxidation may be characterized by the conversion of at least about 98%
sulphides by weight to sulphate form. When toxic waste treatment is also involved, the time required for formation of insoluble molecules from one or more soluble toxic contaminants must also be considered, sincs this reaction will generally require more time.
The time required to sufficiently complete these reactions will vary with feed composition and total feed volume. A practitioner in the art would be able to determine an appropriate pressure oxidation parameters.
The cyaniding step of the present invention may be conducted in accordance with well known conventional techniques. For example, the cyaniding feed stream is mixed with an excess of an alkaline cyanlde solution, such as a NaCN solution, to effectuate gold extraction. Specifically, the cyaniding feed is treated with the alkaline cyanide solution for a time sufficient to dissolve the metal to be extracted (i.~., gold) therein. After filtration ~3'~7 and filter washing, the gold present in the filtrate may be recovered by any conventional method therefor.
Carbon in pulp procPssing or the like may alternatively be used to recover gold.
An exemplary cyaniding process useful in the practice of the present invention is described below.
The pressure oxidation effluent is subjected to a solid/liquid separation step. Solids separated therein are repulped to a pulp density of about 45~ solids.
Lime is then added as a slurry (e.a., about 20% w/w) to the pulp, and the mixture is agitated until the pH
remains constant at from about 10.5 to about 11Ø An amount of NaCN sufficient to dissolve gold from the repulped solids, as is calculable by a practitioner in the art, is added to the neutralized mixtures.
Optionally, cyanide and/or lime consumption may be monitored to ascertain whether additional material need be added. Also, additional stages of cyanide leaching may be conducted to enhance gold recovery.
Monitoring the level of free cyanide and/or lime may be conducted in accordance with known techniques. An exemplary procedure for making the free cyanide and lime level determinations is set ~orth below. 10 ml of a cyanide-containing solution is transferred by pipette into a 100 ml beaker. 5-6 drops of a cyanide indicator, such as potassium iodide (e.g., 5 g dissolved in 100 ml distilled water), 5 - (p-dimethylamino benzylidene) rhodamine (e.g., 0.02 g dissolved in 100 ml acetone), or the like, are added.
Titration for free cyanide is then conducted to the endpoint (e.a., a cloudy yellow color for potassium iodide) with a silver nitrate solution (e.a., 5.2 g dis~olved in 3 1 distilled water). 2-3 excess drops of the silver nitrate solution are added prior to the addition of 3-4 drops of a lime indicator, such as phenolphthalein (~g~, O.05 g dissolved in 50 ml ethyl 2~23~7 alcohol and followed by the addition of 50 ml distilled water) or the like. Titration for lime is then conducted with oxalic acid (e.a., 6.75 g of oxalic acid dissolved in 3 l distilled water) until the red color disappears. The respective levels may be calculated as follows:
mls silver nitrate . 10 = g/l free cyanide mls oxalic acid . 10 = g/l lime The refractory auriferous material useful in the practice of the present invention may contain additional components, such as carbonates, that exhibit undesirable properties upon oxidation.
Carbonates generate carbon dioxide under pressure oxidation conditions. Excessive venting which results in oxygen loss and decreases the efficiency of the pressure oxidation treatment, is therefore required.
Carbon dioxide formation under oxidizing conditions can be avoided by neutralizing the carbonates prior to oxidation. Addition of an amount of an acid, such as H2S04, sufficient to neutralize substantially all of the carbonates in the refractory auriferous sulphide material will accomplish this objective.
Alternatively, acid liquor produced as a byproduct of the pre~sure oxidation treatment can be recycled to serve this purpose. If an insuf~icient amount o~ acid liquor is produced ~ , substantially all of the carbonate~ in the refractory aurtferous sulphidic material will not be neutralized by admixture with the recycle acid liquor), an amount of fresh acid, such as H2SO4, may be added.
The invention will now be described by way of example with reference to the Figure, which shows a ~low diagram o~ a gold extraction/toxic waste treatment process. Ground currently mined re~ractory auriferous sulphidic ore or concentrate is slurried by 2~323~7 admixture with water in a slurry formation step 10.
If necessitated by the presence of carbonates or like components in the refractory auriferous sulphide material, the slurry may be formed in step 10 with the addition of recycle acid liquor to the slurry components to neutralize those carbonates. In this embodiment of the present invention, slurry formation step 10 must extend for a time period sufficient to permit neutralization of substantially all of the carbonates. This option is indicated by the dashed line in the Figure. Alternatively, the acid may be added in a separate step, either prior or subsequent to slurry formation step lO.
When the slurry is formed, ground calcine and arsenic-containing sludge are blended with the slurry in a mixing step 12 to form the pressure oxidation feed stream. The feed is subjected to a pressure-oxidation step 14. The oxidized slurry resulting from pressure oxidation step 14 proceeds to a liquid/solid separation step 16, including a plurality of thickeners in series. The industry practice of ¢ounter current decantation (CCD) may be utilized to achieve liquid/solid separation. A practitioner in the art would be able to ascertain and employ an appropriate CCD protocol ~or this purpose.
~ portion o~ the liquid (i.e., acid liquor) may be recycled to neutralize carbonates, if necessary. Excess acid liquor is neutralized with alkaline mill ~lotation tailings or with other appropriate alkaline compounds in an acid treatment step 18, and the treated acid is discharged as process ef~luent. After pH ad~ustment with a neutralizing agent in a neutralizing step 20, the solids are ~ub~ected to a cyaniding step 22. One output stream ~rom cyaniding step 22 is the gold product stream.
The waste effluent from cyaniding step 22 may be 2~ ~2~7 directly discharged as a result of the decrease insoluble toxic residues contained therein.
Neutralizing step 20 involves the pH
adjustment of the solid effluent from liquid/solid separation step 16. In neutralizing step 20, a neutralizing agent, such as lime, is added to the solids-containing slurry in an amount sufficient to elevate the pH of the slurry to a level conducive to cyaniding (i.e., a pH from about 8 to about 11).
The results of various tests conducted in connection with the present invention are described by way of example only, and the present invention is therefore not limited thereby.
Conventional cyaniding tests were done on individual materials that are useful as components of pressure oxidation feed streams contemplated for use in methods of the present invention. Batch cyaniding tests may be conducted in accordance with the ~ollowing procedure. If necessary, the test example i~ ground or pulverized. The test sample is then transferred into a suitable container (e.g., a glass bottle) suitable for placement on a set of rolls to achieve agitation thereof. The pulp density o~ the test sample is ad~usted to a preferred value through the addition of water. A "neutralizing amount" of lime and an "extracting amount" of cyanide (i.e., amounts of these reagents necessary to carry out the respective reactions) are added to the test sample.
Preferably, lime is added and admixed with the test sample prior to cyanide addition. The sample container i8 then secured on the rolls and agitated.
A sample of currently mined re~ractory sulphidic concentrate containing 3.9 oz/ton gold (Au), 13.7% arsenic (As), 32.1% iron (Fe), and 29.5% sulphur 2~32~7 (S) was subjected to a 48 hr. cyaniding. The gold extraction was 62.3%, with a residue of 1.47 oz/ton.
A 48 hr. cyaniding of the refractory ore itself gave a gold extraction of 48.1%. A sample of refractory 5 sulphidic concentrate obtained from old tailings contained 0.63 oz/ton AU, 3.12% As, 35.1% Fe, and 38.9% S. The gold extraction after a 48 hr. cyaniding was 57.4%, with a residue of 0.27 oz/ton. Ground calcine, containing 0.40 oz/ton Au, 2.26% As, 43.9%
Fe, and 22.5% S, gave a gold extraction of 26.5%, with a residue of 0.36 oz/ton following a 72 hr. cyaniding.
Conventional cyaniding tests on samples of arsenic sludge containing 0.52 oz/ton Au, 56.2% As, 7.8% Fe, and 2.7% S were unsuccessful, as a result of the toxicity and acidity of the sludge. A total of ~everal hundreds of pounds/ton of lime was added for alkalinity. This treatment was followed by a consumption of at least 100 lb/ton of NaCN. Less than 10% of the gold was extracted after subjecting the treated sludge to 72 hr. of cyaniding.
The materials described in Example 1 were subjected to individual batch pressure oxidation tests at a pulp density of 9%, a total pressure of 2200 kPa, and a temperature of 190C. Samples were taken at pre-determined time intervals and the amount of ~ulphide sulphur oxidation to sulphate form was measured as well as gold extraction obtained in subsequent cyaniding. The results of these tests are summarized in Table 1.
203i2357 TAB~E 1 %S Oxidation Oxidation Time in Minutes to Sulphate 20 40 60 90 120 Refractory Conct. 16.4 46.9 91.6 99.9 99.9 Refractory Tails Conct. 58.1 84.3 99.2 99.9 99.9 Calcine 48.7 88.1 90.8 95.4 98.1 Sludge 94.7 96.1 97.1 97.4 98.1 % Gold Extraction Refractory Conct. 75.3 92.1 94.5 95.3 95.5 Refractory Tails Conct. 74.3 85.8 86.6 90.5 94.2 Calcine 68.9 72.4 72.8 72.8 72.9 Sludge 89.3 90.8 92.3 92.8 95.3 In general, the results, when compared with those obtained in Example 1, confirm that pressure oxidation enhances gold recovery. The results also show increased gold extraction upon increased sulphur oxidation. With respect to calcine, the increase in gold extraction after 20 minutes of oxidation is slight as a result of encapsulation of gold in the iron oxlde matrix o~ calcine.
Batch pressure oxidation tests were conducted on ~eed compo~ites o~ di~erent compositions under the conditions employed in Example 2 (i.e., 9% solids by weight at a temperature 190'C and at a pressure of 2200 kPa ~or 2 hours). The results of these tests are shown in Table 2.
Feed Composite & Total Weight Composite Gold CQnct. Calcine Sludge % S Extraction %
37.0 38.0 25.0 18.2 90.4 30.0 30.0 40.0 12.8 91.2 37.0 38.0 25.0 18.2 89.6 - 50.0 50.0 11.9 86.6 45 50.0 30.0 20.0 17.7 90.5 213323~
These results show that 86.6% of the gold contained in the toxic wastes may be recovered in the practice of the present invention. In addition, decreased percentages of sulphur in the pressure oxidation feed composite appear to result in increased gold extraction. Such results indicate that the process works metallurgically.
Batch pressure oxidation tests were conducted a~ in Example 2 on a feed composite consisting of 27%
refractory sulphidic concentrate, 23% reclaim tailings refractory sulphidic concentrate, 25% calcine, and 25%
sludge by weight. The tested feed composites exhibited pulp densities of either 20 or 25% solids.
Oxidation time and temperature were varied. The results of these tests are shown in Table 3.
Pulp Time % S Gold DensitY % min Temp C Oxidation Extraction %
20 120 190 97.6 85.8 20 60 210 98.4 94.9 25 60 210 97.3 90.9 Thess results appear to indicate that 20~
pulp density and Z10C constitute the preferred pressure oxidation parameters in terms of sulphur oxidation and gold recovery. Such results indicate that the process works metallurgically on different feed composites.
The feed composite tested in Example 4 was used in four continuous runs in a 50 1. capacity, 6-compartment autoclave (Titanium Ltd., Quebec, Canada).
All compartments were of equal volume and eguipped 2032~7 with individual agitators. In each run, the oxygen overpressure was 700 kPa.
The first continuous run was conducted at 20%
solids by weight at 190C following acidification of the concentrates with 100 kg/ton of H2SO4. The gold extraction was 84.6~. Cyaniding consumed 9.4 lb/ton of lime and 1.79 lb/ton of NaCN. Over 97% sulphide oxidation to sulphate was achieved. Chemical analyses showed that all of the arsenic dissolved and combined with iron to form ferric arsenate.
The second continuous test was conducted at 20~ solids by weight at 210C following acidification treatment as described above. The gold extraction was 87.9%. Cyaniding consumed 8.96 lb/ton of lime and 2.02 lb/ton of NaCN. Over 98% sulphide oxidation was achieved. Ferric arsenate was formed. An increase in pressure oxidation temperature resulted in increased gold recovery.
The third continuous test was conducted at 25% solids by weight at 210C following acidification treatment as described above. The gold extraction was 88.1%. Cyanidlng consumed 8.96 lb/ton of lime and 2.91 lb/ton o~ NaCN. Over 98% sulphide oxidation was agaln achieved. Chemical analyses showed an exaess o~
~errlc lron ln solution with less than 1 g/L o~ As.
The ~ourth continuous run was conducted at 25% solids by weight at 220C following acidification treatment as described above. The gold extraction was 88.4%. Cyaniding consumed 8.29 lb/ton of lime and 2.24 lb/ton of NaCN. 98% sulphide oxidation was achieved, while ~erric arsenate was formed. Again, an increase in pressure oxidation temperature resulted in lncreased gold recovery. Cyanidlng of composites havlng pulp densities o~ 20% and 25% solids resulted in substantially e~uivalent gold extraction.
2~3~3~7 . .
The process ran smoothly in all four continuous tests. No evidence of agglomeration of solids or elemental sulphur formation inside the autoclave was observed in any of the continuous tests.
Consequently, the tests show that addition of toxic wastes to the pressure oxidation feed composite improves pressure oxidation performance over non-diluted, refractory auriferous sulphidic material, prior art pressure oxidation treatments.
Environmental (EPA-type) testing, i.e., acetic acid extraction was done on selected neutralized products from the autoclave. The environmental testing procedure was as follows:
1. A solid sample was prepared for extraction by crushing, cutting or grinding, until the sample was able to pass through a 9.5 mm mesh sieve.
2. The moisture content of the de-watered sample was determined by drying a suitable aliquot to constant weight at 50~C in an oven.
3. The equivalent of 50 g dry weight of the de-watered, undried material was placed into a 1250 ml wide mouth cylindrical bottle.
GOLD EXTRACTION AND TOXIC WASTE TREATMENT
Technical Field of the Invention This invention relates to the extraction of gold from feed mixtures of auriferous sulphidic ores, concentrates of such ores or reclaimed sulphide concentrates and previously generated toxic wastes, such as roaster calcine and roaster arsenic sludge.
Backaround Of the Invention Metallic gold is extracted from gold-containing ores or concentrates formed from such ores.
Higher grades of auriferous ores have a higher gold content. Since sources of high-grade ores are rapidly being depleted, the attention of the gold mining industry is becoming more and more focused upon methods of extracting gold from lower-grade ores. The lower-grade ores contain higher amounts of impurities, such as sulphidic minerals. Typical sulphidic minerals present in gold-containing ores are arsenopyrite and/or pyrite, and may also include appreciable amounts of pyrrhotite. Lesser amounts of base metals in sulphide form, such as copper, zinc, and lead may also be present.
Extraction of metallic gold from ores or ore concentrates is conventionally accomplished by cyaniding (i.e., dissolution in cyanide solutions).
The cyaniding extraction of gold from refractory auriferous sulphidic material has been shown to be improved if the material is first subjected to a pressure oxidation treatment. See, for example, U.S.
2~323~7 Patent No. 2,777,764. In the pressure oxidation treatment, maximum gold recovery is obtained through complete oxidation of the sulphide sulphur atoms to sulphate form.
A problem with this pre-cyaniding pressure oxidation treatment is the formation of elemental sulphur as an intermediate or as a primary oxidation product. As a result of the elevated temperature at which the pressure oxidation treatment is conducted, the elemental sulphur so produced will be in molten form. Molten sulphur tends to wet and/or coat many of the sulphides present in the slurry being oxidized.
Such coated sulphides tend to agglomerate. Formation of agglomerates containing molten sulphur and unreacted sulphides limits sulphide oxidation, ultimately resulting in decreased gold recovery. Additional problems arise in continuous operations, because agglomerates may build up to the point where they accumulate in the reaction vessel. Moreover, elemental sulphur detrimentally affects subsequent cyaniding processing, even further decreasing gold recovery.
One method of obviating the molten elemental sulphur problem is described in U.S. Patent No. 4,605,439. That patent discusses the addition of "relatively inert solids" to the feed of iron-containing, refractory auriferous sulphidic material to provide a feed slurry of high pulp density. As a result, the patented pressure oxidation process could be carried out at a lower temperature with less agglomeration. The inventors of this patented technique theorized that the added inert solids promoted the dispersion o~ the elemental sulphur formed in the pressure oxidation reaction (reduc1ng the amount of agglomeration) and suspen~ion of any agglomerates formed (permitting the agglomerates to oxidize more 2 t~3~3 ~ 7 completely). The only example recited in the patent of a relatively inert solid suitable for admixture with the pressure oxidation autoclave refractory feed stream is a recycle stream (i.e., a portion of the process stream constituting material previously passed through the autoclave, either before or after liquid-solid separation and prior to cyaniding).
Other alternatives for overcoming the problems created by the formation of molten elemental sulphur have been suggested. A survey of some of these alternatives and the deficiencies thereof with respect to practical, continuous, industrial-scale gold recovery operations are discussed in U.S. Patent No.
4,605,439.
An additional problem facing the mining industry is an increased emphasis on the environmental impact of both present and past mining and metal recovery processes. Consequently, heightened interest has been shown in processes for removing inorganic contaminants from wastewater generated during gold milling and other industrial processes as well as for removing toxic substances ~rom previously generated waste from such processing.
In the past, refractory auriferous materials were sometimes treated by roasting, a technique that resulted in the production of toxic by-products, such a~ arsenic-containing calcines and sludges. As a result of greater environmental awareness, roasting is being replaced by pressure oxidation in the treatment of auriferous refractory material. Pressure oxidation techniques, utilizing correct feed stoichiometry and followed by appropriate neutralization processing, typically generate waste effluent process streams containing non-directly dischargeable levels of toxic contaminants. The toxic wastes previously produced by the roasting process remain; however, and pressure is ~2~7 being brought to bear upon the mining industry to institute clean up procedures.
Specifically, wastewater from a large percentage of previously conducted roasting processes has been retained in tailings ponds. In fact, retention of wastewater in tailings ponds is the oldest and still a common method for treatment of gold mill wastewater effluent. Natural degradation, photodegradation, precipitation, and volatilization of contaminants are the primary mechanisms of tailings pond wastewater treatment. Many metals are soluble in wastewater as a result of cyanide complexing, however.
These metals therefore do not precipitate out of solution and contribute substantially to the high levels of inorganic contaminants found in tailings ponds. Also, severe climatic conditions limit the efficacy of tailings ponds, since the aforementioned mechanisms of tailings pond wastewater treatment do not occur when that pond is frozen.
Implementation of more strict environmental regulation would appear to limit the use of tailings ponds. Speci~ically, wastewater retention in tailings ponds is ef~ective to reduce wastewater contamination;
however, ~uch wastewater purification is inadequate to permit direct discharge. Oxidized residues of, for example, high iron content constitute toxic byproducts o~ the roasting process. These contaminants are discharged into and remain in tailings ponds in soluble (i.e., toxic) form.
Also, ores containing significant amounts of, for example, arsenopyrite (generally in excess of 1%
arsenic) have been previou~ly subjected to roasting.
Such roasting released oxidized forms of arsenic from the ore, thereby producing effluent having arsenic contaminants. Effluent containing high levels of soluble arsenic was typically stored in underground 2~23~7 vaults dedicated to that purpose. Such storage techniques are susceptible to breach, thereby releasing the toxic residue into the environment. For example, a fissure may develop in the vault structure.
Alternatively, ground water drainage may occur. As a result, methods of treating these previously produced toxic wastes are being sought.
Summary of the Invention The present invention provides methods whereby currently mined refractory auriferous materials, preferably auriferous sulphidic materials, are mixed with koxic waste from old mill tailings to extract gold from both the new ore production and the old production wastes. Gold may also be recovered from reclaimed sulphidic concentrates by the methods of the present invention. These methods also produce an environmentally acceptable, gold extraction waste product.
The methods of the present invention include the steps of: mixing currently mined refractory auriferous material and/or reclaimed sulphidic concentrates with at least one low sulphur content toxic waate generated in p.evious gold mill processing, such as roaster calcine or sludge to produce a low sulphur content mixture; pressure oxidizing the mixture; and cyaniding the oxidized mixture.
Preferably, the mixing step of the methods of the present invention includes the addition of a waste having low sulphur, high iron, and low arsenic content, such as calcine, and a waste having low sulphur, low iron, and high arsenic content, such as arsenic sludge.
In a preferred method, both a reduction in the amount of sulphur present in the pressure oxidation feed mixture and an increase in the formation of insoluble ferric arsenate during pressure oxidation are achieved.
2 ~ 3 2 3 ~ 7 Reduction in feed sulphur content results in a decrease in elemental sulphur and concomitant agglomeration formation in the pressure oxidation step. In addition, the insoluble molecules constitute a more manageable waste product.
If the currently mined refractory auriferous material or a reclaimed sulphidic concentrate contains carbonate compounds, an acidification step can be utilized prior to the pressure oxidation treatment. In this manner, a high level of carbonate conversion to carbon dioxide during the pressure oxidation process can be avoided. Acid liquor generated in the pressure oxidation process is preferably recycled for use in this acidification step.
Brief Description of the Drawing The Figure shows a flow diagram of a gold extraction/toxic waste treatment method of the present invention.
Description o~ the Preferred Embodiments The present invention is directed to methods o~ extracting gold from a re~ractory auriferous materlal, preferably an auri~erous sulphide material, including mixing, pressure oxidation and cyaniding steps. The present invention is also directed to methods of simultaneously extracting gold and treating (detoxifying) toxic waste.
For the purpose of this description, the values stated as percentages are percentages by weight, unless otherwise indicated. With the exception of usage ln connectlon with gold, the term "content" also re~ers to weight percent, albeit less de~initively than a numerical percentage value. Gold content is expressed in ounces per ton (oz/ton).
2~32~7 For the purpose of this description, the term "refractory auriferous material" encompasses any refractory material containing gold. Exemplary of such materials are auriferous sulphide ores, concentrates 5derived from such ores, concentrates reclaimed from gold mill tailings, or the like. A combination of one or more of these materials might also be used as a refractory auriferous sulphidic material in accordance with the present invention. A "currently mined 10refractory auriferous sulphidic material" encompasses auriferous ores, concentrates thereof or combinations of the two that have not previously been treated to extract gold therefrom.
As mentioned above, typical sulphide minerals 15present in auriferous ores are arsenopyrite, pyrite, pyrrhotite, base metal sulphides, such as copper, zinc, and lead sulphides, and the like. An exemplary ore that might be processed in accordance with the present invention contains from about 0.05 to about 0.8 oz/ton 20gold (Au); from about 0.2 to about 3% arsenic (As);
from about 2 to about 5% iron (Fe); and from about l to about 5% sulphur (S). An exemplary concentrate derived from ~uch an ore contains from about 1 to about 10 oz/ton Au; from about 8 to about 20% As; from about 2520 to about 40% Fe; and from about 15 to about 35% S.
An exemplary concentrate reclaimed from gold mill tailings contains from about 0.2 to about 2 oz/ton Au;
from about 5 to about 15% As; from about 10 to about 35% Fe; and from about 8 to about 30% S.
30The methods of the present invention feature a mixing step, where the refractory auriferous material is blended with at lea~t one toxic residue (i.e., waste) in order to substantially decrease the sulphur content in the pressure oxidation feed stream. Such a 35decrease in sulphur content improves the performance of the pressure oxidation treatment by preventing the 2~3'~7 generation of excessive heat and decreasing the amount of elemental sulphur formed during that treatment. The mixing step may be accomplished in any conventional manner. Exemplary mixing techniques are vibrational agitation, stirring, and the like. This mixing procedure may be conducted using commercially available equipment designed for that purpose.
Preferable toxic wastes useful in the present invention are those that were generated by gold mill processes using techniques such as roasting. One preferred toxic residue for admixture with the refractory auriferous material is a residue exhibiting a low sulphur content, a high iron content, and a low arsenic content. For the purpose of describing such a toxic residue, a low sulphur content indicates a weight percentage of sulphur below about 5%: a high iron content ind~cates a weight percentage of iron in excess of about 30%; and a low arsenic content indicates a weight percentage of arsenic below about 50%.
Exemplary of such a toxic residue is calcine derived ~rom wastee produced in roasting processes. Exemplary ¢al¢lne ¢ompo~itions use~ul in practicing the present invention include from about 0.25 to about l oz/ton Au;
from about 2 to about 12% As~ from about 25 to about 50% Fe; and from about 2 to about 15% S.
A second pre~erred toxic residue for admixture wlth the refractory auriferous material is a residue exhibiting a low sulphur content, a low iron content, and a high arsenic content. For the purposes of describing such a toxic residue, a low sulphur content indicates a weight percentage of sulphur below about 3%; a low iron content indicates a weight percentage of iron below about 10%; and a high ar~enic content indicates a weight percentage of ar~enic in excess of about 50%. Exemplary of such a toxic residue i~ ar~enic-containing sludge derived ~rom wastes ~? ~ 3 ~r~
produced in previous roasting processes. Exemplary arsenic-containing sludge compositions useful in practicing the present invention include from about 0.25 to about l oz/ton Au: from about 45 to about 65%
As; from about 5 to about 10% Fe; and from about l to about 5~ S.
Arsenic sludge is typically derived from precipitators or from dedicated pits, dedicated ponds or underground vaults in which effluent from roaster processing is stored. High iron content calcine is typically derived from the oxidized solid residues resulting from the roasting process.
In order to disperse the sulphur present in the refractory auriferous sulphide material and decrease the sulphur content of the pressure oxidation feed, the mixing step must be conducted with appropriate components in appropriate amounts.
Specifically, an amount of toxic residue(s) sufficient to reduce the sulphur content of the pressure oxidation feed ~i.e., refractory auriferous sulphide material and toxic residue(s)) below about 12% by weight, preferably below about 10% by weight, must be used. Such stoichiometric ad~ustment o~ the pressure oxidation feed to achieve a speci~ied sulphur content is within the purview of a practitioner in the art.
The methods oP the present invention may also feature addition of toxic residues having soluble toxic contaminants capable of reacting with one another or with other components of the pressure oxidatian feed stream under oxidizing conditions to form insoluble molecules having decreased toxicity. When arsenic sludge is used in admixture with a refractory sulphidic material containing iron, some of that iron reacts with the ~oluble arsenic present in the sludge to form ferric arsenate as described more fully below. In addition or in the alternative, iron may be added to _g_ 2~323~
the pressure oxidation feed to react with the soluble arsenic in the sludge as is more fully described below.
Since ferric arsenate is insoluble in water, the amount of soluble arsenic is decreased, and the toxicity of the pressure oxidation effluent is therefore reduced.
In a preferred method, calcine and arsenic sludge are mixed with the refractory auriferous sulphidic material. The soluble iron present in calcine is capable of reacting with the soluble arsenic present in arsenic-containing sludge under oxidizing conditions to form insoluble ferric arsenate and acid.
The reaction proceeds as follows:
2FeS2+ 72 + 2HzO --> 2FeSO4 + 2H2SO4 4FeAsS + 1102 + 2H20 --> 4HAs02 + 4FeSO4 4FeS04 + 2H2S04 + 2 --> 2Fe2(SO4)3 + 2H20 2HAsO~ + 2 + 2H2 --> 2H3As04 Fe2(SO4)3 + 2H3As04 --> 2FeAsO4 + 3H2S04 Preferably, the Fe:As ratio in the pressure oxidation feed is about 1.2:1 or greater. If necessary, iron may be added to the pressure oxidation feed to provide the appropriate component ratio. This iron may be added at any time prior to pressure oxidation, i.e., before, during or after the mixing step. The iron BO added may be in any chemical form sultable ~or this purpose, such as shredded form. The iron i8 pre~erably dissolved in acid prior to admixture with the pressure oxidation feed. Recycled pressure oxidation-produced acid or any other acid capable of dissolving iron may be used for this purpose.
When a decrease in the toxicity of toxic residue(s) contained in the pressure oxidation feed is also desired, the stoichiometry and other parameters of the reaction converting the soluble toxic contaminant(s) into insoluble non-toxic or less toxic molecules must also be taken into account to determine the composition of the pressure oxidation feed stream.
2~323~
For example, a pressure oxidation feed stream composed of 20% sulphide concentrates, which can comprise arsenopyrite, pyrite, pyrrhotite, or a combination thereof and up to about 25% gangue minerals, 40%
calcine (<10% S, 40% Fe, 2% As), and 40% arsenic sludge (2-3% S, 8% Fe, 55% As) is characterized by a total sulphur content of less than 10%. Pressure oxidation of such a feed stream will result in the formation of ferric arsenate. A practitioner in the art would be able to determine an appropriate pressure oxidation feed stream composition to achieve both gold extraction and toxicity reduction.
The pressure oxidation step of the present invention may be conducted in accordance with known techniques. See, for example, U.S. Patent No.
2,777,764. Moreover, toxic wastes generated in alternative gold recovery techniques, such as roasting, contain gold. For example, roaster calcine wastes may contain from about 0.25 to about 1 oz/ton Au.
Similarly, arsenic sludge wastes may contain from about 0.25 to about 1 oz/ton Au. By reprocessing these wastes, some of the gold contained therein may be recovered, thereby increaeing the total amount of gold extracted.
The pressure oxidation feed stream used in the practice of the present invention is a slurry.
Aqueous slurries are preferred. Slurries useful in the methods o~ the present invention are characterized by pulp densities of from about 15 to about 60% solids by weight, with from about 20 to about 40% solids by weight being preferred.
The pressure oxidation step of the present invention may be conducted in commercially available equipment, such as a multi-compartment autoclave, under conventionally accepted sulphide-oxidizing conditions.
For example, a 50 L capacity, 6-stage, equal volume per 3~
stage autoclave may be used in practicing the present invention. The pressure oxidation treatment may be conducted using other reactor types, such as industrial autoclaves of, for example, 3 m diameter and 20 m length. Exemplary equipment useful in continuous operations are tubular reactors, a plurality of reactors arranged in series, and the like. In addition, a batch reaction vessel may be used when the methods of the present invention are employed in a non-continuous fashion.
Oxidation conditions include a temperaturefrom about 150 to about 250C and a total pressure ranging from about 400 to 6000 kPa (50-700 psi). The oxidation will be allowed to proceed for a time sufficient to achieve adequate oxidation of feed sulphides to sulphates. An adequate oxidation may be characterized by the conversion of at least about 98%
sulphides by weight to sulphate form. When toxic waste treatment is also involved, the time required for formation of insoluble molecules from one or more soluble toxic contaminants must also be considered, sincs this reaction will generally require more time.
The time required to sufficiently complete these reactions will vary with feed composition and total feed volume. A practitioner in the art would be able to determine an appropriate pressure oxidation parameters.
The cyaniding step of the present invention may be conducted in accordance with well known conventional techniques. For example, the cyaniding feed stream is mixed with an excess of an alkaline cyanlde solution, such as a NaCN solution, to effectuate gold extraction. Specifically, the cyaniding feed is treated with the alkaline cyanide solution for a time sufficient to dissolve the metal to be extracted (i.~., gold) therein. After filtration ~3'~7 and filter washing, the gold present in the filtrate may be recovered by any conventional method therefor.
Carbon in pulp procPssing or the like may alternatively be used to recover gold.
An exemplary cyaniding process useful in the practice of the present invention is described below.
The pressure oxidation effluent is subjected to a solid/liquid separation step. Solids separated therein are repulped to a pulp density of about 45~ solids.
Lime is then added as a slurry (e.a., about 20% w/w) to the pulp, and the mixture is agitated until the pH
remains constant at from about 10.5 to about 11Ø An amount of NaCN sufficient to dissolve gold from the repulped solids, as is calculable by a practitioner in the art, is added to the neutralized mixtures.
Optionally, cyanide and/or lime consumption may be monitored to ascertain whether additional material need be added. Also, additional stages of cyanide leaching may be conducted to enhance gold recovery.
Monitoring the level of free cyanide and/or lime may be conducted in accordance with known techniques. An exemplary procedure for making the free cyanide and lime level determinations is set ~orth below. 10 ml of a cyanide-containing solution is transferred by pipette into a 100 ml beaker. 5-6 drops of a cyanide indicator, such as potassium iodide (e.g., 5 g dissolved in 100 ml distilled water), 5 - (p-dimethylamino benzylidene) rhodamine (e.g., 0.02 g dissolved in 100 ml acetone), or the like, are added.
Titration for free cyanide is then conducted to the endpoint (e.a., a cloudy yellow color for potassium iodide) with a silver nitrate solution (e.a., 5.2 g dis~olved in 3 1 distilled water). 2-3 excess drops of the silver nitrate solution are added prior to the addition of 3-4 drops of a lime indicator, such as phenolphthalein (~g~, O.05 g dissolved in 50 ml ethyl 2~23~7 alcohol and followed by the addition of 50 ml distilled water) or the like. Titration for lime is then conducted with oxalic acid (e.a., 6.75 g of oxalic acid dissolved in 3 l distilled water) until the red color disappears. The respective levels may be calculated as follows:
mls silver nitrate . 10 = g/l free cyanide mls oxalic acid . 10 = g/l lime The refractory auriferous material useful in the practice of the present invention may contain additional components, such as carbonates, that exhibit undesirable properties upon oxidation.
Carbonates generate carbon dioxide under pressure oxidation conditions. Excessive venting which results in oxygen loss and decreases the efficiency of the pressure oxidation treatment, is therefore required.
Carbon dioxide formation under oxidizing conditions can be avoided by neutralizing the carbonates prior to oxidation. Addition of an amount of an acid, such as H2S04, sufficient to neutralize substantially all of the carbonates in the refractory auriferous sulphide material will accomplish this objective.
Alternatively, acid liquor produced as a byproduct of the pre~sure oxidation treatment can be recycled to serve this purpose. If an insuf~icient amount o~ acid liquor is produced ~ , substantially all of the carbonate~ in the refractory aurtferous sulphidic material will not be neutralized by admixture with the recycle acid liquor), an amount of fresh acid, such as H2SO4, may be added.
The invention will now be described by way of example with reference to the Figure, which shows a ~low diagram o~ a gold extraction/toxic waste treatment process. Ground currently mined re~ractory auriferous sulphidic ore or concentrate is slurried by 2~323~7 admixture with water in a slurry formation step 10.
If necessitated by the presence of carbonates or like components in the refractory auriferous sulphide material, the slurry may be formed in step 10 with the addition of recycle acid liquor to the slurry components to neutralize those carbonates. In this embodiment of the present invention, slurry formation step 10 must extend for a time period sufficient to permit neutralization of substantially all of the carbonates. This option is indicated by the dashed line in the Figure. Alternatively, the acid may be added in a separate step, either prior or subsequent to slurry formation step lO.
When the slurry is formed, ground calcine and arsenic-containing sludge are blended with the slurry in a mixing step 12 to form the pressure oxidation feed stream. The feed is subjected to a pressure-oxidation step 14. The oxidized slurry resulting from pressure oxidation step 14 proceeds to a liquid/solid separation step 16, including a plurality of thickeners in series. The industry practice of ¢ounter current decantation (CCD) may be utilized to achieve liquid/solid separation. A practitioner in the art would be able to ascertain and employ an appropriate CCD protocol ~or this purpose.
~ portion o~ the liquid (i.e., acid liquor) may be recycled to neutralize carbonates, if necessary. Excess acid liquor is neutralized with alkaline mill ~lotation tailings or with other appropriate alkaline compounds in an acid treatment step 18, and the treated acid is discharged as process ef~luent. After pH ad~ustment with a neutralizing agent in a neutralizing step 20, the solids are ~ub~ected to a cyaniding step 22. One output stream ~rom cyaniding step 22 is the gold product stream.
The waste effluent from cyaniding step 22 may be 2~ ~2~7 directly discharged as a result of the decrease insoluble toxic residues contained therein.
Neutralizing step 20 involves the pH
adjustment of the solid effluent from liquid/solid separation step 16. In neutralizing step 20, a neutralizing agent, such as lime, is added to the solids-containing slurry in an amount sufficient to elevate the pH of the slurry to a level conducive to cyaniding (i.e., a pH from about 8 to about 11).
The results of various tests conducted in connection with the present invention are described by way of example only, and the present invention is therefore not limited thereby.
Conventional cyaniding tests were done on individual materials that are useful as components of pressure oxidation feed streams contemplated for use in methods of the present invention. Batch cyaniding tests may be conducted in accordance with the ~ollowing procedure. If necessary, the test example i~ ground or pulverized. The test sample is then transferred into a suitable container (e.g., a glass bottle) suitable for placement on a set of rolls to achieve agitation thereof. The pulp density o~ the test sample is ad~usted to a preferred value through the addition of water. A "neutralizing amount" of lime and an "extracting amount" of cyanide (i.e., amounts of these reagents necessary to carry out the respective reactions) are added to the test sample.
Preferably, lime is added and admixed with the test sample prior to cyanide addition. The sample container i8 then secured on the rolls and agitated.
A sample of currently mined re~ractory sulphidic concentrate containing 3.9 oz/ton gold (Au), 13.7% arsenic (As), 32.1% iron (Fe), and 29.5% sulphur 2~32~7 (S) was subjected to a 48 hr. cyaniding. The gold extraction was 62.3%, with a residue of 1.47 oz/ton.
A 48 hr. cyaniding of the refractory ore itself gave a gold extraction of 48.1%. A sample of refractory 5 sulphidic concentrate obtained from old tailings contained 0.63 oz/ton AU, 3.12% As, 35.1% Fe, and 38.9% S. The gold extraction after a 48 hr. cyaniding was 57.4%, with a residue of 0.27 oz/ton. Ground calcine, containing 0.40 oz/ton Au, 2.26% As, 43.9%
Fe, and 22.5% S, gave a gold extraction of 26.5%, with a residue of 0.36 oz/ton following a 72 hr. cyaniding.
Conventional cyaniding tests on samples of arsenic sludge containing 0.52 oz/ton Au, 56.2% As, 7.8% Fe, and 2.7% S were unsuccessful, as a result of the toxicity and acidity of the sludge. A total of ~everal hundreds of pounds/ton of lime was added for alkalinity. This treatment was followed by a consumption of at least 100 lb/ton of NaCN. Less than 10% of the gold was extracted after subjecting the treated sludge to 72 hr. of cyaniding.
The materials described in Example 1 were subjected to individual batch pressure oxidation tests at a pulp density of 9%, a total pressure of 2200 kPa, and a temperature of 190C. Samples were taken at pre-determined time intervals and the amount of ~ulphide sulphur oxidation to sulphate form was measured as well as gold extraction obtained in subsequent cyaniding. The results of these tests are summarized in Table 1.
203i2357 TAB~E 1 %S Oxidation Oxidation Time in Minutes to Sulphate 20 40 60 90 120 Refractory Conct. 16.4 46.9 91.6 99.9 99.9 Refractory Tails Conct. 58.1 84.3 99.2 99.9 99.9 Calcine 48.7 88.1 90.8 95.4 98.1 Sludge 94.7 96.1 97.1 97.4 98.1 % Gold Extraction Refractory Conct. 75.3 92.1 94.5 95.3 95.5 Refractory Tails Conct. 74.3 85.8 86.6 90.5 94.2 Calcine 68.9 72.4 72.8 72.8 72.9 Sludge 89.3 90.8 92.3 92.8 95.3 In general, the results, when compared with those obtained in Example 1, confirm that pressure oxidation enhances gold recovery. The results also show increased gold extraction upon increased sulphur oxidation. With respect to calcine, the increase in gold extraction after 20 minutes of oxidation is slight as a result of encapsulation of gold in the iron oxlde matrix o~ calcine.
Batch pressure oxidation tests were conducted on ~eed compo~ites o~ di~erent compositions under the conditions employed in Example 2 (i.e., 9% solids by weight at a temperature 190'C and at a pressure of 2200 kPa ~or 2 hours). The results of these tests are shown in Table 2.
Feed Composite & Total Weight Composite Gold CQnct. Calcine Sludge % S Extraction %
37.0 38.0 25.0 18.2 90.4 30.0 30.0 40.0 12.8 91.2 37.0 38.0 25.0 18.2 89.6 - 50.0 50.0 11.9 86.6 45 50.0 30.0 20.0 17.7 90.5 213323~
These results show that 86.6% of the gold contained in the toxic wastes may be recovered in the practice of the present invention. In addition, decreased percentages of sulphur in the pressure oxidation feed composite appear to result in increased gold extraction. Such results indicate that the process works metallurgically.
Batch pressure oxidation tests were conducted a~ in Example 2 on a feed composite consisting of 27%
refractory sulphidic concentrate, 23% reclaim tailings refractory sulphidic concentrate, 25% calcine, and 25%
sludge by weight. The tested feed composites exhibited pulp densities of either 20 or 25% solids.
Oxidation time and temperature were varied. The results of these tests are shown in Table 3.
Pulp Time % S Gold DensitY % min Temp C Oxidation Extraction %
20 120 190 97.6 85.8 20 60 210 98.4 94.9 25 60 210 97.3 90.9 Thess results appear to indicate that 20~
pulp density and Z10C constitute the preferred pressure oxidation parameters in terms of sulphur oxidation and gold recovery. Such results indicate that the process works metallurgically on different feed composites.
The feed composite tested in Example 4 was used in four continuous runs in a 50 1. capacity, 6-compartment autoclave (Titanium Ltd., Quebec, Canada).
All compartments were of equal volume and eguipped 2032~7 with individual agitators. In each run, the oxygen overpressure was 700 kPa.
The first continuous run was conducted at 20%
solids by weight at 190C following acidification of the concentrates with 100 kg/ton of H2SO4. The gold extraction was 84.6~. Cyaniding consumed 9.4 lb/ton of lime and 1.79 lb/ton of NaCN. Over 97% sulphide oxidation to sulphate was achieved. Chemical analyses showed that all of the arsenic dissolved and combined with iron to form ferric arsenate.
The second continuous test was conducted at 20~ solids by weight at 210C following acidification treatment as described above. The gold extraction was 87.9%. Cyaniding consumed 8.96 lb/ton of lime and 2.02 lb/ton of NaCN. Over 98% sulphide oxidation was achieved. Ferric arsenate was formed. An increase in pressure oxidation temperature resulted in increased gold recovery.
The third continuous test was conducted at 25% solids by weight at 210C following acidification treatment as described above. The gold extraction was 88.1%. Cyanidlng consumed 8.96 lb/ton of lime and 2.91 lb/ton o~ NaCN. Over 98% sulphide oxidation was agaln achieved. Chemical analyses showed an exaess o~
~errlc lron ln solution with less than 1 g/L o~ As.
The ~ourth continuous run was conducted at 25% solids by weight at 220C following acidification treatment as described above. The gold extraction was 88.4%. Cyaniding consumed 8.29 lb/ton of lime and 2.24 lb/ton of NaCN. 98% sulphide oxidation was achieved, while ~erric arsenate was formed. Again, an increase in pressure oxidation temperature resulted in lncreased gold recovery. Cyanidlng of composites havlng pulp densities o~ 20% and 25% solids resulted in substantially e~uivalent gold extraction.
2~3~3~7 . .
The process ran smoothly in all four continuous tests. No evidence of agglomeration of solids or elemental sulphur formation inside the autoclave was observed in any of the continuous tests.
Consequently, the tests show that addition of toxic wastes to the pressure oxidation feed composite improves pressure oxidation performance over non-diluted, refractory auriferous sulphidic material, prior art pressure oxidation treatments.
Environmental (EPA-type) testing, i.e., acetic acid extraction was done on selected neutralized products from the autoclave. The environmental testing procedure was as follows:
1. A solid sample was prepared for extraction by crushing, cutting or grinding, until the sample was able to pass through a 9.5 mm mesh sieve.
2. The moisture content of the de-watered sample was determined by drying a suitable aliquot to constant weight at 50~C in an oven.
3. The equivalent of 50 g dry weight of the de-watered, undried material was placed into a 1250 ml wide mouth cylindrical bottle.
4. 800 ml tless the moisture content of the sample in ml) of reagent water was added to the bottle.
5. The bottle was capped and agitated in a commercially available rotary extractor for 15 minutes.
6. The pH of the solution was measured with a commercially available pH meter, and calibration was undertaken with buffers at pH 7.00 and pH 4.00. The solution was stirred during pH measurement.
7. If the pH was less than 5.2, step lOa was next conducted.
2~32~7 8. If the pH was greater than 5.2, a sufficient volume of 0.5 N acetic acid was added to bring the pH to 5.0 + 0.2.
2~32~7 8. If the pH was greater than 5.2, a sufficient volume of 0.5 N acetic acid was added to bring the pH to 5.0 + 0.2.
9. The bottle was capped and placed in a commercially available tumbling apparatus and rotated at 10 rpm for 24 hours at room temperature end for end.
10. The pH was monitored and manually adjusted during the course of the extraction in accordance with the following procedures.
a. The pH of the solution was measured when 1 hour, 3 hours and 6 hours had elapsed from the extraction starting time. If the pH was above 5.2, it was reduced to 5.0 + 0.2, with no adjustments being made.
b. If the pH was below 5.0 + 0.2 after 6 hoùrs, the volume of the solution was adjusted to 1000 ml with reagent water.
c. The pH was measured and reduced to 5.0 + 0.2, if required, after 22 hours, and the extraction was continued for an additional 2 hours.
a. The pH of the solution was measured when 1 hour, 3 hours and 6 hours had elapsed from the extraction starting time. If the pH was above 5.2, it was reduced to 5.0 + 0.2, with no adjustments being made.
b. If the pH was below 5.0 + 0.2 after 6 hoùrs, the volume of the solution was adjusted to 1000 ml with reagent water.
c. The pH was measured and reduced to 5.0 + 0.2, if required, after 22 hours, and the extraction was continued for an additional 2 hours.
11. Sufficient reagent water was added at the end of the extraction period so that the total volume of the liquid was 1000 ml.
12. The material was separated into its component liquid and solld pha~es by filtering through a 0.45 ~ filter.
13. The ~olution from Step 12 wa6 analyzed for the contaminants listed in Schedule 4 that are likely to be present.
14. Concentrations in the combined leachate and the free liquid solution at pH 5.0 i 0.2 were obtained.
~B32~7 Criteria (ma/L) Results (mq/L) Arsenic 0.05 <0.05 Barium 1.0 0.06 Boron 5.0 not tested Cadmium 0.005 0.02 Chromium 0.05 <0.05 Cyanide (free~ 0.2 not tested Lead 0.05 ~0.05 Mercury 0.001 not tested Selenium 0.01 <0.01 Silver 0.05 not tested Uranium 0.02 not tested TABLE 4 - Semi-Ouantitative ICP Scan Detection Detection Limit Results Limit Results Element (ma/L) (ma/L) Element (ma/L) (mq/L) Al 0.2<0.50 Na 0.05230 As 0.1<0.05 Ni 0.050.11 Ba 0.050.06 P 0.2<0.02 Bo 0 01<0.001 Pb 0.1<0.05 Ca 0 2500 S 2.02400 Cd 0.050.02 Sb 0.1<0.10 Co 0.050.08 Sc [?~ 0.5<0.05 Cr 0.05<0.02 Se 0.5~0.20 Cu 0.050.81 Si 0.10.45 Fe 0.05<0.02 Sn 0.2<0.10 Mg 0.051700 Te 0.1<0.05 Mo 0.1<0.05 Zn 0.050.84 TABLE 5 - Ion Chromatoaraph Scan Results IonDetection Limit (mg/L)(ma/L) Br 0.02 F 0.02 NO3 0.02 S04 0.02 Cl 0.02 NO2 0.02 PO4 0.1 2~3~3~7 TABLE 6 - Leachate Ouality Criteria Element Acceptable Registerable Hazardous Results (mg/L) (ma/L~ (mq/L) (ma/L) Arsenic <0.5 >0.5 <5 ~5 <0.05 Barium <10 >10 <100 >100 <0.10 Boron <50 >50 <500 >500 <5.0 Cadmium <0.05 >0.05 <0.5 >0.5 0.38 Chromium <0.5 >0.5 <5 >5 <0.02 Lead <0.5 >0.5 <5 >5 ~0.05 Mercury <0.01 >0.01 <0.1 >0.1 <0.001 Selenium <0.1 >0.1 <l >l <0.01 Silver <0.5 >0.5 <5 >5 <0.03 Uranium <0.2 >0.2 <2 >2 <0.01 NOTE: For each series of tests a "blank" is run for quality control purposes, using the same reagents and procedure.
In all cases, soluble arsenic was present at less than 0.10 ppm, well below the maximum allowable environmental discharge of 1 ppm. The addition of toxic wastes to the pressure oxidation feed composite therefore also resulted in a reduction in the level of toxic contaminants present in those wastes to acceptable discharge levels. These results confirm that a 9 hour continuous run duplicated the batch results.
A fifth continuous test was conducted on a different feed composite (15% re~ractory sulphide concentrates, and 42.5% each by weight calcine and sludge). The test was run at 20% solids by weight at 210'C following acidification as described above, with the exception of the use of 100 kg/ton recycle acid liquor instead of H2S04. The gold extraction was 83.6%.
Cyaniding consumed 3.14 lb/ton of lime and 1.57 lb/ton of NaCN. 98% sulphide oxidation was achieved. 95% of the arsenic was converted to ferric arsenate, thereby 20323~7 indicating that additional iron was required in the pressure oxidation feed.
This test also ran very smoothly. No formation of agglomerates or elemental sulphur was observed, indicating that no excessive heat was generated in the autoclave. Consequently, this test also shows that the addition of toxic wastes to the pressure oxidation feed composite improves pressure oxidation performance over non-diluted, refractory auriferous sulphidic material, prior art pressure oxidation treatments. The gold extraction obtained for this feed composite was lower (when compared with the second continuous run of Example 5); however, the amount of lime and NaCN consumed was considerably reduced.
While in the foregoing specification this invention has been described in relation to certain preferred embodiments thereof, and many details have been set forth for the purpose of illustration, it will be apparent to those skilled in the art that the lnvention is susceptible to additional embodiments and that certain details described herein may be varied con~iderably without departing from the basic principles of the invention.
~B32~7 Criteria (ma/L) Results (mq/L) Arsenic 0.05 <0.05 Barium 1.0 0.06 Boron 5.0 not tested Cadmium 0.005 0.02 Chromium 0.05 <0.05 Cyanide (free~ 0.2 not tested Lead 0.05 ~0.05 Mercury 0.001 not tested Selenium 0.01 <0.01 Silver 0.05 not tested Uranium 0.02 not tested TABLE 4 - Semi-Ouantitative ICP Scan Detection Detection Limit Results Limit Results Element (ma/L) (ma/L) Element (ma/L) (mq/L) Al 0.2<0.50 Na 0.05230 As 0.1<0.05 Ni 0.050.11 Ba 0.050.06 P 0.2<0.02 Bo 0 01<0.001 Pb 0.1<0.05 Ca 0 2500 S 2.02400 Cd 0.050.02 Sb 0.1<0.10 Co 0.050.08 Sc [?~ 0.5<0.05 Cr 0.05<0.02 Se 0.5~0.20 Cu 0.050.81 Si 0.10.45 Fe 0.05<0.02 Sn 0.2<0.10 Mg 0.051700 Te 0.1<0.05 Mo 0.1<0.05 Zn 0.050.84 TABLE 5 - Ion Chromatoaraph Scan Results IonDetection Limit (mg/L)(ma/L) Br 0.02 F 0.02 NO3 0.02 S04 0.02 Cl 0.02 NO2 0.02 PO4 0.1 2~3~3~7 TABLE 6 - Leachate Ouality Criteria Element Acceptable Registerable Hazardous Results (mg/L) (ma/L~ (mq/L) (ma/L) Arsenic <0.5 >0.5 <5 ~5 <0.05 Barium <10 >10 <100 >100 <0.10 Boron <50 >50 <500 >500 <5.0 Cadmium <0.05 >0.05 <0.5 >0.5 0.38 Chromium <0.5 >0.5 <5 >5 <0.02 Lead <0.5 >0.5 <5 >5 ~0.05 Mercury <0.01 >0.01 <0.1 >0.1 <0.001 Selenium <0.1 >0.1 <l >l <0.01 Silver <0.5 >0.5 <5 >5 <0.03 Uranium <0.2 >0.2 <2 >2 <0.01 NOTE: For each series of tests a "blank" is run for quality control purposes, using the same reagents and procedure.
In all cases, soluble arsenic was present at less than 0.10 ppm, well below the maximum allowable environmental discharge of 1 ppm. The addition of toxic wastes to the pressure oxidation feed composite therefore also resulted in a reduction in the level of toxic contaminants present in those wastes to acceptable discharge levels. These results confirm that a 9 hour continuous run duplicated the batch results.
A fifth continuous test was conducted on a different feed composite (15% re~ractory sulphide concentrates, and 42.5% each by weight calcine and sludge). The test was run at 20% solids by weight at 210'C following acidification as described above, with the exception of the use of 100 kg/ton recycle acid liquor instead of H2S04. The gold extraction was 83.6%.
Cyaniding consumed 3.14 lb/ton of lime and 1.57 lb/ton of NaCN. 98% sulphide oxidation was achieved. 95% of the arsenic was converted to ferric arsenate, thereby 20323~7 indicating that additional iron was required in the pressure oxidation feed.
This test also ran very smoothly. No formation of agglomerates or elemental sulphur was observed, indicating that no excessive heat was generated in the autoclave. Consequently, this test also shows that the addition of toxic wastes to the pressure oxidation feed composite improves pressure oxidation performance over non-diluted, refractory auriferous sulphidic material, prior art pressure oxidation treatments. The gold extraction obtained for this feed composite was lower (when compared with the second continuous run of Example 5); however, the amount of lime and NaCN consumed was considerably reduced.
While in the foregoing specification this invention has been described in relation to certain preferred embodiments thereof, and many details have been set forth for the purpose of illustration, it will be apparent to those skilled in the art that the lnvention is susceptible to additional embodiments and that certain details described herein may be varied con~iderably without departing from the basic principles of the invention.
Claims (20)
1. A method of extracting gold from refractory auriferous material, comprising:
mixing the refractory auriferous material with at least one toxic residue having low sulphur content to form a low sulphur content pressure oxidation feed;
pressure oxidizing the feed to form an oxidized slurry; and cyaniding the oxidized slurry.
mixing the refractory auriferous material with at least one toxic residue having low sulphur content to form a low sulphur content pressure oxidation feed;
pressure oxidizing the feed to form an oxidized slurry; and cyaniding the oxidized slurry.
2. A method according to claim 1 wherein the refractory auriferous material comprises an ore.
3. A method according to claim 1 wherein the refractory auriferous material comprises a sulphide concentrate from an ore, old mill tailings, or a combination thereof.
4. A method according to claim 1 wherein the toxic residue has a high iron content and a low arsenic content.
5. A method according to claim 4 wherein the toxic residue is calcine and exhibits an iron content of from about 25 to about 50% and an arsenic content of from about 2 to about 12%.
6. A method according to claim 1 wherein the toxic residue has a low iron content and a high arsenic content.
7. A method according to claim 6 wherein the toxic residue is arsenic sludge and exhibits an iron content of from about 5 to about 10% and an arsenic content of from about 45 to about 65%.
8. A method for decreasing toxicity of toxic residues and extracting gold from refractory auriferous material and toxic residues, said method comprising:
mixing the refractory auriferous material comprising an ore, a concentrate thereof, a reclaimed sulphide concentrate or a combination thereof with a first toxic residue and a second toxic residue to form a pressure oxidation feed;
pressure oxidizing the feed to form an oxidized slurry; and cyaniding the oxidized slurry, wherein a soluble inorganic contaminant in at least one of the first and second toxic residues combines with another soluble inorganic contaminant in at least one of the first and second toxic residues or with another feed component to form insoluble molecules, thereby producing waste streams having a decreased environmental impact.
mixing the refractory auriferous material comprising an ore, a concentrate thereof, a reclaimed sulphide concentrate or a combination thereof with a first toxic residue and a second toxic residue to form a pressure oxidation feed;
pressure oxidizing the feed to form an oxidized slurry; and cyaniding the oxidized slurry, wherein a soluble inorganic contaminant in at least one of the first and second toxic residues combines with another soluble inorganic contaminant in at least one of the first and second toxic residues or with another feed component to form insoluble molecules, thereby producing waste streams having a decreased environmental impact.
9. A method according to claim 8 wherein the first toxic residue exhibits a low iron content and a high arsenic content and the second toxic residue exhibits a high iron content and a low arsenic content.
10. A method according to claim 8 wherein the first toxic residue is arsenic sludge and exhibits an iron content of from about 5 to about 10% and an arsenic content of from about 45 to about 65% and the second toxic residue is calcine and exhibits an iron content of from about 25% to about 50% and an arsenic content of from about 2 to about 12%.
11. A method according to claim g wherein the first and second toxic residues are added in amounts sufficient to form a feed having an iron:
arsenic ratio is about 1.2:1 or greater.
arsenic ratio is about 1.2:1 or greater.
12. A method according to claim 9 further comprising an iron addition step prior to the pressure oxidation step to achieve an iron:arsenic ratio of about 1.2:1 or greater.
13. A method according to claim 8 wherein the pulp density of the feed is between about 15 to about 60% solids by weight.
14. A method of claim 8 wherein the pulp density of the feed is between about 20 to about 40%
solids by weight.
solids by weight.
15. A method according to claim 8 wherein the feed is subjected to pressure oxidation at a temperature of from about 150°C to 250°C under a total pressure of from about 60 to about 700 psi.
16. A method according to claim 8 further comprising an acidification treatment of the feed, including mixing the feed with an acidifying medium selected from the group comprising H2SO4 or recycled acid liquor prior to the pressure oxidation step.
17. A method according to claim 8 further comprising to an acidification treatment of the refractory auriferous material, including mixing the material with an acidifying medium selected from the group comprising H2SO4 or recycled acid liquor prior to the mixing step.
18. A method according to claim 8 further comprising a liquid-solid separation step prior to cyaniding.
19. A method of claim 18 further comprising a neutralization step, wherein the solids resulting from the liquid/solid separation step are treated with lime, prior to cyaniding.
20. A method of claim 8 wherein the steps are carried out in a continuous manner.
Priority Applications (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2032357 CA2032357A1 (en) | 1990-12-14 | 1990-12-14 | Pressure oxidation methods for gold extraction and toxic waste treatment |
| AU88888/91A AU649750B2 (en) | 1990-12-14 | 1991-12-05 | Pressure oxidation methods for gold extraction and toxic waste treatment |
| SE9103692A SE9103692L (en) | 1990-12-14 | 1991-12-13 | PRESSURE OXIDIZATION METHODS FOR EXTRACTION OF GOLD AND TREATMENT OF TOXIC WASTE |
| MX9102549A MX9102549A (en) | 1990-12-14 | 1991-12-13 | PRESSURE OXIDATION METHODS FOR GOLD EXTRACTION AND TOXIC WASTE TREATMENT. |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2032357 CA2032357A1 (en) | 1990-12-14 | 1990-12-14 | Pressure oxidation methods for gold extraction and toxic waste treatment |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2032357A1 true CA2032357A1 (en) | 1992-06-15 |
Family
ID=4146660
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2032357 Abandoned CA2032357A1 (en) | 1990-12-14 | 1990-12-14 | Pressure oxidation methods for gold extraction and toxic waste treatment |
Country Status (4)
| Country | Link |
|---|---|
| AU (1) | AU649750B2 (en) |
| CA (1) | CA2032357A1 (en) |
| MX (1) | MX9102549A (en) |
| SE (1) | SE9103692L (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2017004694A1 (en) * | 2015-07-06 | 2017-01-12 | Sherritt International Corporation | Recovery of copper from arsenic-containing process feed |
| US11118244B2 (en) | 2017-04-14 | 2021-09-14 | Sherritt International Corporation | Low acidity, low solids pressure oxidative leaching of sulphidic feeds |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA1228483A (en) * | 1984-09-19 | 1987-10-27 | Donald R. Weir | Process for the pressure oxidation acid leaching of non-ferrous metal and iron-containing sulphidic material |
| CA1234991A (en) * | 1984-09-27 | 1988-04-12 | Donald R. Weir | Recovery of gold from auriferous refractory iron- containing sulphidic ore |
| US4729788A (en) * | 1987-01-23 | 1988-03-08 | Advanced Mineral Technologies, Inc. | Thermophilic microbial treatment of precious metal ores |
-
1990
- 1990-12-14 CA CA 2032357 patent/CA2032357A1/en not_active Abandoned
-
1991
- 1991-12-05 AU AU88888/91A patent/AU649750B2/en not_active Ceased
- 1991-12-13 SE SE9103692A patent/SE9103692L/en not_active Application Discontinuation
- 1991-12-13 MX MX9102549A patent/MX9102549A/en unknown
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2017004694A1 (en) * | 2015-07-06 | 2017-01-12 | Sherritt International Corporation | Recovery of copper from arsenic-containing process feed |
| US10544482B2 (en) | 2015-07-06 | 2020-01-28 | Sherritt International Corporation | Recovery of copper from arsenic-containing process feed |
| US11118244B2 (en) | 2017-04-14 | 2021-09-14 | Sherritt International Corporation | Low acidity, low solids pressure oxidative leaching of sulphidic feeds |
Also Published As
| Publication number | Publication date |
|---|---|
| MX9102549A (en) | 1992-06-01 |
| SE9103692D0 (en) | 1991-12-13 |
| AU649750B2 (en) | 1994-06-02 |
| AU8888891A (en) | 1992-06-18 |
| SE9103692L (en) | 1992-06-15 |
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