WO2014040140A1

WO2014040140A1 - Removal of radioactive impurities from a copper ore or copper concentrate during or after smelting

Info

Publication number: WO2014040140A1
Application number: PCT/AU2013/001054
Authority: WO
Inventors: Robert Charles West; Anthony Robert Gee; Shouyi SUN; Shafi Jahanshahi
Original assignee: Bhp Billiton Olympic Dam Corporation Pty Ltd
Priority date: 2012-09-13
Filing date: 2013-09-13
Publication date: 2014-03-20
Also published as: AU2013315359A1; AU2013315359B2

Abstract

A process for the removal of one or more radioactive impurities from a copper bearing copper containing material having a radioactivity greater than a predetermined level, including: (a) forming a melt from the copper containing material, (b) treating the molten copper containing material under conditions sufficient to substantially volatilise and separate the impurities from the molten copper containing material, and (c) producing a copper product from the molten copper containing material.

Description

REMOVAL OF RADIOACTIVE IMPURITIES FROM A COPPER ORE OR

COPPER CONCENTRATE DURING OR AFTER SMELTING

TECHNICAL FIELD

The present disclosure relates to a method for the removal of impurities from an ore or ore concentrate. The disclosure is particularly concerned with the removal of radioactive impurities from copper ore or copper concentrate during or after smelting.

BACKGROUND

Some ore deposits are associated with significant levels of radioactive minerals. In particular, certain base metal deposits, such as copper ore deposits, may have high levels of associated uranium mineralization. The process of concentrating the base metal can result in an ore concentrate with a high residual level of radioactivity. Such concentrates may not comply with international legal standards on radioactivity and hence will be problematic to treat.

It would therefore be desirable to develop a process for producing a metal containing product of no or acceptably low radioactivity from a radioactive ore mineral or ore concentrate. It would also be desirable to provide a metal containing product, formed from that process which can be directly traded as a commodity on international markets. It would be further desirable to provide a process for removal of one or more radioactive impurities from a copper containing material that was compatible with existing pyrometallurgical processes and equipment for smelting copper ore concentrate. It would be further desirable to provide a process for removal of one or more radioactive impurities from a copper containing material that complied with safety standards for handling radioactive materials.

SUMMARY OF THE DISCLOSURE

According to the present disclosure, there is provided a process for the removal of one or more radioactive impurities from a copper containing material having a radioactivity greater than a predetermined level, including:

(a) forming a melt from the copper containing material,

(b) treating the molten copper containing material under conditions sufficient to substantially volatilise and separate the impurities from the molten copper containing material, and

(c) producing a copper containing product from the molten copper containing material.

The above process enables the production of copper containing products having a desired level of radioactivity from a copper containing material having an unacceptably high level of radioactivity. The copper containing material may be a copper containing ore (eg a copper sulphide) and/or a copper containing ore concentrate.

The copper containing product may comprise a pure or substantially pure metal. Alternatively the product may be an impure metal containing product, such as a smelting product. In the case of the copper containing material being a sulfide mineral, the smelting product may include a sulfide phase. Examples of smelting products include a matte or a blister product.

In a preferred embodiment, the copper containing material is a copper ore concentrate and the copper containing product is a copper matte.

Accordingly, the process enables the treatment of smelting products to control their radioactivity levels and to thereby produce tradable commodities which to date have not been able to be traded.

The predetermined level of radioactivity may be that determined by IAEA guidelines and/or current government regulations or standards in the particular country of interest. For example, the current IAEA Safety Standards require that ore concentrates containing radionuclides from the U, Th decay series should have a radioactivity less than lBq/gram/radionuclide.

The process can remove and separate a substantial proportion of radionuclides from the copper containing material. The process may remove greater than 85%, such as greater than 90% of the radionuclides, from the copper containing material. In most cases this can result in a radioactivity level of less than 1 Bq/g per radionuclide in the copper containing product. Depending on the intended application of the copper containing product, in some embodiments, the radioactivity of the copper containing product achieved using the process of the disclosure may be less than 0.1 Bq/gram/radionuclide.

In an embodiment, the one or more radioactive impurities include isotopes of lead and polonium, such as ²¹⁰Po and ²¹⁰Pb.

The process of the disclosure may comprise a copper smelting process where the copper containing material is smelted to produce a slag and matte phase. Alternatively the smelting process may produce a slag and metal phase or it may produce slag, matte and metal phases. The smelting process may simply comprise melting the copper containing material and allowing the slag and matte phases to form. Alternatively, the process may involve the addition of air or oxygen enriched air to oxidise the sulfides and produce any of the above mentioned products.

Where the process of the disclosure includes formation of a slag phase, step (b) may additionally comprise the preferential deportment of the impurities to the slag phase which further enhances separation of the impurities from the molten copper containing material.

In an embodiment, the product produced from the process may comprise copper matte, blister copper or other impure form of copper containing product. Alternatively, the product may comprise pure or substantially pure metal, such as copper cathode.

The molten copper containing material is treated under controlled conditions sufficient to volatilise and separate the volatile impurities therefrom. The treatment may include subjecting the molten copper containing material to a temperature at least as high as a temperature of volatilisation of one or more impurities. Where the respective impurities have different temperatures of volatilisation, the treatment may comprise subjecting the molten copper containing material to the higher temperature of volatilisation. The temperature may be 1200°C or greater. In one embodiment, the temperature is 1300°C or greater. In another embodiment, the temperature is 1400°C or greater. In a further embodiment, the maximum temperature is 1500°C. Generally, the lower the temperature of treatment, the slower is the rate of volatilisation. Accordingly, temperatures above approximately 1400°C showed good rates of volatisation. The treatment may further include contacting the molten copper containing material with a stream of gas whilst at the volatilisation temperature. The stream of gas entrains the volatilised impurities and carries them from the melt. The gas may be a non-oxidising gas. Examples of suitable non oxidising gases are inert gases such as nitrogen or argon. Alternatively, or in addition, the non oxidising gases may be reducing gases such as gaseous products from combustion of hydrocarbons, eg carbon monoxide, or recycled smelting gases, containing S0₂

Where the process comprises a copper smelting process, the gas may initially be a gas suitable for smelting, such as an oxygen containing gas, eg air. When the desired matte grade has been achieved, the gas is preferably replaced with a non-oxidising gas, such as an inert or reducing gas stream.

The gas stream may have a flow rate of at least 1 NmVtonne matte/min, such as at least

2Nm 3 /tonne matte/min. In an embodiment, the flow rate is at least 10 Nm 3 /tonne matte/min.

Contact with the gas may occur during gentle agitation of the molten copper containing material. The gas may be introduced beneath the surface of the melt, such as through a lance or tuyere, which assists in optimising contact between the gas and melt phases, while effecting gentle agitation and mixing. The degree of agitation is preferably controlled to avoid mixing of matte and slag phases and the attendant loss in matte grade. Further, the increased power levels required for a high level of (e.g. violent) agitation is not cost effective.

In one embodiment, the process takes place in a flash smelter, and non oxidising gases are introduced into the matte bath while effecting gentle agitation and mixing.

If the process is conducted in a rotary furnace, it is preferred that the peripheral speed of rotation is less than 0.5 m/s. Such a speed of rotation would ensure that the process is not subjected to violent agitation.

Additionally or alternatively, the treatment may include processing of the molten copper containing material under reduced pressures (vacuum) whilst at the volatilisation temperature. The processing may, for example, be conducted under a vacuum of 100 Torr or lower, such as less than 75 Torr, preferably less than 50 Torr. In an embodiment, the vacuum may be less than 10 Torr, such as less than 5 Torr. The minimum vacuum may be less than 0.5 Torr. Treatment may be conducted for up to approximately 1 hour. In an embodiment, the reduced pressure processing is conducted at 0.5 Torr, a temperature of 1200°C and a gas flow rate of 0.1 - 0.2 NmVton matte / min for a period of < 60 minutes.

Steps (a) and (b) of the process may be conducted in a single stage. In this manner the copper containing material may be melted under specific conditions to ensure that the radioactive elements are deported to the gas phase leaving a melt with a desired level of radioactivity. For example, the copper containing material may be smelted at a temperature of volatilisation of one or more impurities and simultaneously subjected to a stream of non oxidising gas and/or a vacuum.

The process of the disclosure may further include controlling the grade of copper in the molten copper containing material. In an embodiment, the copper grade is a minimum of 50%, such as 60% or higher. In another embodiment, the copper grade is a minimum of 70%. In a further embodiment, the copper grade is a minimum of 75%.

The copper containing material may also include other radionuclides comprising one or more isotopes of uranium, thorium, radium and bismuth. The process may include one or more further steps of treating the copper containing material to remove the one or more other radionuclides.

In an embodiment, the process includes one or more steps of treating the copper containing material to remove radium. Those steps may include:

• smelting the copper containing material to produce a slag phase and a melt phase, and

• controlling the chemistry of the slag phase to thereby concentrate the radium into the slag phase and produce a radium depleted melt phase.

The step of controlling the chemistry of the slag phase may comprise controlling the ratio of Fe:SiC>2 in the slag phase depending on the level of radium in the copper containing material. In an embodiment, the ratio of Fe:Si0₂ is controlled to be less than 1.4. However, lower minimum ratios may be required where there are relatively higher initial concentrations of radium in the copper containing material. For example, in another embodiment, the Fe:Si0₂ ratio is controlled to a minimum value of 1 : 1. While the inventors have focussed on the range of Fe:Si0₂ from 1.1 to 1.4, compositions beyond this range may also be effective in achieving the level of removal required with appropriate adjustment in other variables such as reaction time and slag volume for example.

The step of controlling the chemistry of the slag phase may further comprise the potential addition of a strongly acidic flux such as B₂C>3 .

BRIEF DESCRIPTION OF THE DRAWINGS

Notwithstanding any other forms which may fall within the scope of the apparatus and method as set forth in the Summary, specific embodiments will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a graph showing the change in copper and iron content of the matte with time during smelting to nominally 60 (triangles), 75 (diamonds) and 80 % Cu (circles) at 1300°C using air at a flow rate of 4 1/min (Tests 1, 2, 3 respectively). Closed symbols Cu, open Fe.

210 210

Figure 2 is a graph showing the activity of Pb and Po in matte with gas purging (41/min N₂) over time for matte grades between -60 and 80% (Tests 1, 2, 3, 6).

Figure 3 is a graph showing the activity of 210 Pb and 210 Po (Tests 1-3) in slag with gas purging (41/min N₂) over time with matte grades between -60 and 80%.

Figure 4 is a series of graphs showing the activity of ²²⁶Ra in matte (a) and slag (c) and activity of 234 U and 238 U in matte (b) and slag (d) with time from experiments with matte grades between 60 and 80% (Testsl to 3).

Figure 5 is a graph showing the change in copper (upper symbols) and iron (lower symbols) content of the matte with time during smelting at 1300°C using air at 4 (Test 2, dashed line) and 8 1/min (Test 7 solid line).

Figure 6 is a graph showing the activity of 210 Pb and 210 Po in matte with time for smelting to a 75% copper matte with 4 or 8 1/min air at 1300°C followed by gas purging with N₂ at the same rate (Tests 2, 7).

Figure 7 is a graph showing the change in copper and iron content of the matte with time during the smelting to ~ 75% at 1300, 1400 and 1500°C (Tests 2,4,5 respectively) at a flow rate of 4 1/min for both smelting and purging with N₂.

Figure 8 is a graph showing the activity of 210Pb and 210Po in matte with time for smelting to a 75% copper matte with 4 1/min of air at 1300, 1400 and 1500°C followed by purging with N2 at the same rate (Tests 2, 4, 5 respectively).

Figure 9 is a series of graphs showing the changes in activity of ²²⁶Ra in (a) matte and (b) slag with time from experiments at 1300 to 1500°C.

Figure 10 is a graph showing the change in copper and iron content of the matte with time during the smelting and purging at 1300°C at a flow rate of 4 1/min and targeting a slag chemistry with an Fe/Si0₂ ratio of 1.4 or 1.1. Also shown is the result when approximately 1% B2O3 was added to the slag.

Figure 11 is a graph showing the activity of 210 Pb and 210 Po in matte with time for smelting to a 75% copper matte with 4 1/min air at 1300°C followed by gas purging with N₂ at the same rate, with an Fe/Si0₂ ratio of 1.1, 1.4 and 1.4 + B₂0₃ addition.

Figure 12 is a graph showing the activity of 210 Pb and 210 Po in slag with time for smelting to a 75% copper matte with 4 1/min air at 1300°C followed by gas purging with N₂ at the same rate, with an Fe/Si0₂ ratio of 1.1, 1.4 and 1.4 + B₂0₃ addition. Figure 13 is a graph showing the distribution ratio of radioactive lead and polonium between slag and matte from the kilogram scale experiments at 1300°C and 4 1/min gas rate. L is a weight ratio or activity ratio between slag and matte.

Figure 14 is a graph showing the distribution ratio of 226 Ra and 238 U between slag and matte as a function of matte grade at 1300°C from radioisotope measurement and ICP-MS analysis. Circles denote Activity measurements and Squares denote ICP-MS.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Non-limiting Examples of the process of the present disclosure will now be described.

The Examples disclose the results of a number of experiments examining the removal of radionuclides from a copper concentrate.

EXAMPLES

Concentrate Assays

Tests were conducted on dried samples of a copper concentrate having radioactivity levels generally in excess of 1 Bq/g per radionuclide. A representative concentrate sample used in this work had a composition as shown in Table 1. Typical copper concentrates for smelting range from <20% Cu to >45% Cu.

Table I. Average element assay of the dried leached copper concentrate

# Note that radionuclide concentrations in this sample are not in secular equilibrium due to prior treatment of the copper containing material through a leaching process. Impuritv Removal

In this testwork, air was blown through the copper concentrate whilst smelting to a target grade matte. After attaining the target grade, air blowing was replaced with nitrogen blowing under similar injection conditions to examine the removal of the radionuclides by volatilisation under neutral or purging conditions.

Parameters which were varied included gas flow rate, temperature, matte grade and slag chemistry.

Specific variables assessed for their effect on Pb and Po volatilization and the range investigated are given in Table II.

Table II: Experimental conditions and parameters investigated in the combined smelting/purging trials

A 600 g bath of low grade matte having <40% Cu was prepared by melting dried copper concentrate without additional fluxes in magnesia crucibles using a 400 kHz induction furnace. A blanketing cover of nitrogen gas was maintained over the charge in the crucible to prevent oxidation of the matte by exposure to air. A stainless steel cover over the crucible and steel ducting above the crucible mouth under negative pressure collected fumes and hot gases from the crucible. The fumes were drawn through the ducting and collected on large air sampling filter papers.

When the crucible was at ~1250°C, a lance was lowered to within 5 mm of the crucible base with a low flow of nitrogen into the slag over the matte to gently stir and homogenise the matte. When the experimental temperature was attained, the lance was then lifted out of the crucible and a matte sample collected by drawing matte into a silica tube.

The gas was changed to air at the required flow rate for the experiment and the lance lowered back to within 5 mm of the crucible base. After 40 minutes, silica was added at the desired rate to the bath, while air was being injected into the bath. After either 15 minutes or 30 minutes of blowing time, the lance was raised from the bath, and the bath was allowed a short time (1/2 to 1 min) to settle. Three to four grams of slag were quenched onto a steel dip rod, and matte was collected as described before.

Once the samples were collected, the lance was lowered back into the bath, with continuing air and flux addition. The sampling occurred at regular intervals (15 or 30 minutes) until a predetermined time (for a target matte grade) was attained. The lance was removed from the crucible and samples of matte and slag were collected.

The gas was then changed to nitrogen for the start of the purging period and the lance lowered back into the bath. Samples were then collected at 60 minute intervals for a further 3 to 5 hours. After the final samples were collected, the lance was lifted and the crucible was allowed to cool under a blanket cover of nitrogen.

Once the furnace was cold, the bag house was weighed to determine the mass of fume collected. The steel ducting was also swept clean and the fume collected. The crucible was then weighed and separated from the matte and slag with a hammer. The matte and slag were weighed and then separated. Representative samples of each were collected for chemical analysis. In some tests where the final matte grade was at the white metal composition, a layer of copper was observed underneath the matte. The copper, the matte and the slag were crushed and separated, samples of each product were collected for chemical analysis.

The samples were analysed by conventional methods, such as inductively coupled plasma atomic emission spectroscopy (ICP-OES) and the lead and other minors at low concentrations analysed by inductively coupled plasma mass spectrometry (ICP-MS). The matte and slag samples were digested and the prepared solutions were then analysed for the radionuclides:™Pb,™Po, ²²⁶Ra,^«U,™U and ²³°Th as required.

The volume of air required to smelt the concentrate to the target matte grade was determined by calculations using a concentrate assay and the target matte grade, and the predicted slag and gas volume using thermodynamic calculations.

The smelting conditions and the matte copper and lead contents at the end of smelting and purging and the slag chemistry are summarised in Table III.

Conditions Analytical Results

τ Smelting conditions Purge conditions Matte Matte (end Matte (final Slag

E (t=0) smelting) chemistry) (final chemistry) S T Temp Flux* Air Duration Fe/ N₂ Duration (Cu),wt.% (Cu)_s wt.% (Cu)_f wt.% Fe/Si0₂ (Cu)_fwt.% °C g/min l/min min Si0₂ l/min min

Table III: Smelting/purging trials and the matte chemistries during the test including the initial (t=0); the end-of-smelting and the final matte (and slag) indicated by subscripts "i, s and f".

The plot of the changes in the copper and iron content of the matte with time for Tests 1, 2 and 3 are shown in Figure 1. The target matte grades were 55, 65 and 75%, and the actual matte grades obtained were 57, 67, 78%, respectively, at the end of smelting (as shown in Table III). After purging, the matte copper contents were 59, 75 and 74% respectively. In Test 3 a small quantity of copper metal was produced. For all three experiments, the rate at which the copper content of the matte increased with blowing time was nearly identical. During the nitrogen purging period, the copper content of the matte remained fairly constant.

The determined activities of™Po and™Pb at the end of smelting and purging as a function of matte grade are summarised in Table IV.

Table IV. Measured RN activities in the matte after the smelting and purging periods for Tests 1, 6, 2 and 3.

# Short 58 minute purge, compared with the typical 4 hour purge.

## The excessive high count of ²²⁶Ra for this matte sample is due to slag contamination, as indicated by consistently higher assays of typical slag components like Al, Ca and Mg. For the same reason the analysis of U is also affected.

When compared to the average radionuclide assay in Table I, it is evident from Table IV that the amounts of radioactive lead, polonium and radium removed during smelting may not be significant (eg, the reduction in ²¹°Pb in Tests 1 and 6 were only 25% and 17%, respectively), and that consequently, the lead, polonium and radium activities remaining in the matte can be greater than 1 Bq/g. However, significantly higher overall amounts may be removed after subsequent purging (eg 97% and 88% overall removal of ²¹°Pb after purging in Tests 1 and 6, respectively). Table IV indicates that after purging with N2 for a period of 120 min or more, the activities of isotopes in the matte were mostly reduced by at least about 90%, resulting in a radioactivity of less than 1 Bq/g (with the exception of Test 6 which was only purged for 58 mins). In the case of Tests 1 and 2, the activities of ²¹°Po were reduced to below 0.1 Bq/g.

The change in activities of ²¹⁰Po and ²¹⁰Pb as a result of both blowing time and matte grade, in the matte and slag, are shown in Figure 2 and Figure 3. The first order rate constants (for the equation c=a*e^bt where c is the chemical or the radioactivity concentration and a and b are rate parameters) that describe the volatilization rates of™Pb and™Po for these experiments are shown in Table V.

Table V. Values of the first order rate constants to describe the removal rates of volatile species from matte of nominally 60 (Test 1), 75 (Test 2) and 80% (Test 3) Cu.

The slopes of the lines of best fit (b) are very close for™Pb, and ²¹°Po. It is also worth noting that, although the starting™Po in the concentrate was over 20 Bq/g based on analysis of the supplied concentrate, the first matte sample taken after the bath reached temperature showed activities of only a fraction of it (< lOBq/g). These results indicate substantial volatilisation during preheating. Once molten, however, the remaining Po in the matte volatilised as a first order process, as shown in Figure 2.

The concentration of ²²⁶Ra, ^23SU and ²³⁴U in matte and slag are shown in Figure 4. Although there is some scatter in the results for the plots of activity with time, it is clear that the concentration in the matte does not vary significantly with time and matte grade, but during the smelting period, the activity of Ra increases in the slag and then remains constant during the purging period.

The effect of the air flow rate at 4 and 8 1/min on the smelting of the concentrate is shown in Figure 5. The time to approach the target matte grade was halved with the doubling of the air flow rate.

The change in activities of ²¹°Po and ²¹°Pb in the matte with blowing time are shown in Figure 6 for Tests 2 and 7. The first order equations that describe the volatilization rates of ²¹°Pb and ²¹°Po for these experiments are shown in Table VI.

Table VI. Values of the first order rate constants (b) for the removal of volatile species from matte from the experiments at 4 and 8 1/niiii gas flow rate for a matte grade of 75% (Tests 1 and 7).

For within the results of each trial, the slopes of the lines of best fit (b) are very close for ²¹°Pb and ™Po, with a slightly greater than doubling of the removal rate with the doubling of the gas flow rate.

The effect of temperature on the smelting of the concentrate is shown in Figure 7. The time to approach the target matte grade was not significantly influenced by temperature. The determined activities of™Po,™Pb, ²²⁶Ra, ⁴U and ^23SU at the end of smelting and purging as a function of temperature are summarised in Table VII.

Table VIL Measured RN activities in the matte after the smelting (82-85 min) and purging

# This out-of-trend high value was due to slag contamination of the matte sample as noted in Table IV. ## This result was much lower for no apparent reason, perhaps more a reflection of expremental error.

The mattes after purging had low levels (< 1 Bq/g) of these elements. The change in concentration of ²¹⁰Pb and ²¹⁰Po in matte are shown in Figure 8. For volatile radionuclides, the residual level of radioactivity after purging showed a decreasing trend with increasing smelting/purging temperature. The change in activity of ²²⁶Ra with time and temperature in the matte and slag is shown in Figure 9. Within the scatter of the results, the concentration of Ra in the matte did not vary significantly with temperature, and was on average less than 1 Bq/g. The activity of Ra in the slag was much higher, and after 60 minutes appeared to have attained a constant activity in the slag.

The effect of slag chemistry was investigated by making the slag more acidic, either by adding more or less silica so that the target Fe/SiC ratio was either 1.4 or 1.1. The effect of adding other acidic fluxes was also investigated by addition of B2O3 to the slag fluxed with a Fe/SiCh ratio of 1.4. The changes in the copper and iron content in the matte as a function of combined smelting and purging time are shown in Figure 10. The time to approach the target matte grade was not significantly influenced by Fe/SiCh ratio of the slag.

The change in concentration of ²¹⁰Pb and ²¹⁰Po in matte and slag are shown in Figure 11 and Figure 12 respectively. Within the range covered, neither the Fe/Si0₂ ratio, nor the addition of B2O3, showed a significant effect on the rate of Pb or Po volatilisation.

The distribution ratios of Pb and Po between slag and matte as a function of matte grade are shown in Figure 13 and compared with equilibrium conditions where pSC = 0.15 and 0.01 atm for Po. Between matte grades of 50 to 70 percent copper, the deportment ratio slightly favours the matte, but at higher copper content, the ratio becomes more in favour of the slag, as shown also in Figure 3.

The distribution ratios of ²²⁶Ra, ^{2 8}U and ^{2 4}U between slag and matte during the purging period are shown as a function of the matte grade in Figure 14. The concentration of these elements in the matte and slag did not vary with time and the distribution ratios for Ra and U do not vary (within the scatter) with matte grade.

Deportments of key elements were calculated at the end of smelting and at the end of nitrogen purging. During the smelting of the copper concentrate to a high grade matte (60-80% Cu), the deportment of ²¹⁰Pb, ²¹⁰Po and other Pb isotopes was mainly to the gas during smelting with air from low grade (47%Cu) to high grade matte. As the matte grade increased, the deportment to the slag increased and to matte decreased. As the matte grade increased, the deportment to the gas also increased and for an 80% copper matte, 80% of the lead deported to the gas, 7% of the lead to the matte and 14% to the slag. During the purging period where nitrogen gas was injected into the matte and slag, the deportment of these elements to the gas increased and to the condensed phases decreased. After purging, lead deportment to the gas was estimated to be >98%, with less than 1.5% remaining in the matte.

The deportment of™Pb and™Po during the purging of the copper matte and slag was dependent on temperature, gas flow rate, matte grade and slag chemistry. In general terms, the deportment to the gas phase increased with temperature. The rate increased with gas injection rate broadly in proportion. The effect of slag chemistry was weak within the compositional range covered.

Polonium (²¹⁰Po), at the end of smelting deported mainly to the gas, with between 3 and 1% remaining in the matte phase, and less than 1% in the slag. At the end of purging, the ²¹⁰Po deportment in both matte and slag was less than 1%.

Radium was assumed to be non-volatile and deported between matte and slag only with less than 5% remaining in the matte phase.

Uranium distributed mainly to slag. The calculated deportment indicates that 1 to 9 % of ²³⁴U and ^23SU remain in the matte after purging.

Summary

The results of the Examples indicate:

1. Smelting followed by gas purging can remove and separate a substantial proportion of ²¹⁰Pb (such as greater than 90%, preferably greater than 95%, under the particular conditions of the Examples) from the molten copper containing material. This can result in a radioactivity level below 1 Bq/g. Removal and separation is effected largely through volatilisation. The required total gas rate is up to 2 Nm³/kg-conc per minute at 1300 °C; 2. ²¹⁰Po follows similar paths as lead but with much more early removal during heat-up. A substantial proportion of ²¹⁰Po can also be removed and separated largely through volatilisation. Under the conditions of the Examples, the radioactivity for the matte can be reduced by >90%, such as >95%, following bubbling with up to 2Nm³/kg-conc per minute (i.e. to below 0.1 Bq/g);

3. Increased temperature has significant benefit for the removal of ²¹°Pb and ²¹°Po. At 1500 °C the rate roughly doubled, or the required gas volume per unit mass of concentrate halved compared to 1300 °C.

4. ^23SU- reports predominantly to the slag and the radioactivity for the matte is reduced by

>95%;

5. For most part of the smelting and purging process ²²⁶Ra removal from the matte remained around 90 - 95% . Under some "favourable" conditions (e.g. at higher temperature, lower Fe/Si0₂ ratio), >95% of ²²⁶Ra is removed from the matte;

6. The application of a vacuum can significantly enhance the rate of ²¹°Pb and ²¹°Po removal from the matte or reduce the amount of gas required per tonne of matte; Under a vacuum of 10 kPa, for instance, the equivalent amount of gas required may be reduced by a factor of 10 and at 0.05kPa the amount of gas required is reduced by a factor of 10,000.

7. Analysis indicated that the activity for ²³°Th and for ²³⁵U can also be significantly reduced, such as by >95% in the matte.

These results demonstrate the feasibility of using the process of the present disclosure in achieving a high degree of removal of ^23SU, ²²⁶Ra, ²¹°Pb and ²¹°Po. The process can enable greater than 90%, and in some cases >95% removal of radionuclides.

The similar kinetic behaviour for the removal of ²¹°Pb and ²¹°Po during the smelting stage and during the post treatment stage suggests that these radionuclides may be sufficiently removed using a one-step process under specific conditions to ensure the radioactive elements are deported to the slag and gas phases leaving a matte phase with less than the desired level of radioactivity. Such a process would require that sufficient volume of gas is injected during smelting the concentrate to a target matte grade, possibly increased temperature and high slag volume plus high matte grade.

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

It is to be understood that, if any prior art information is referred to herein, such reference does not constitute an admission that the information forms a part of the common general knowledge in the art, in Australia or any other country.

Finally, it is to be understood that various other modifications and/or alterations may be made without departing from the spirit of the present invention as outlined herein.

Claims

1. A process for the removal of one or more radioactive impurities from a copper bearing copper containing material having a radioactivity greater than a predetermined level, including:

(a) forming a melt from the copper containing material,

(c) producing a copper product from the molten copper containing material.

2. The process of claim 1, wherein the product comprises copper matte, blister copper or other impure form of copper containing product.

3. The process of claim 1 or 2, wherein the product comprises pure or substantially pure copper metal.

4. The process of any one of claims 1 to 3, wherein the treatment step (b) includes subjecting the molten copper containing material to a temperature at least as high as a temperature of volatilisation of one or more of the impurities.

5. The process of claim 4, wherein the temperature is 1200°C or greater, such as 1300°C or greater, for example 1400°C or greater.

6. The process of any preceding claim, wherein the treatment step (b) further includes contacting the molten copper containing material with a stream of non oxidising gas, such as nitrogen, whilst at the volatilisation temperature.

7. The process of any preceding claim, wherein the treatment step (b) further includes vacuum treatment of the molten copper containing material whilst at the volatilisation temperature.

8. The process of any preceding claim, wherein steps (a) and (b) are conducted in a single stage.

9. The process of any preceding claim, wherein the one or more volatile radioactive impurities include isotopes of lead and polonium, such as 210 Po and 210 Pb.

10. The process of any preceding claim, wherein the copper containing material further includes radionuclides comprising one or more isotopes of uranium, thorium and radium and the process includes one or more further steps of treating the copper containing material to remove one or more of these radionuclides.

11. The process of claim 10, wherein the further steps include:

• controlling the chemistry of the slag phase to thereby concentrate the radionuclides into the slag phase and produce a radionuclide depleted melt phase.

12. The process of claim 11, wherein the radionuclide is radium and/or uranium and/or thorium.

13. The process of claim 11, wherein the step of controlling the chemistry of the slag phase comprises controlling the ratio of Fe:SiC>2 in the slag phase, preferably to less than 1.4.

14. A method of smelting copper concentrate including the process of claim 1.

15. A product produced by the process of claim 1 or the method of claim 14.