RECOVERY OF METALS FROM PYRITE

Abstract

A process is disclosed for the recovery of a metal from a pyrite-bearing material. The process comprises thermally decomposing the pyrite-bearing material so as to produce a material comprising pyrrhotite (FeS). The process also comprises leaching the material comprising pyrrhotite with an acid such that the iron in the pyrrhotite is oxidised to a +3 oxidation state, elemental sulphur is produced and the metal is released from the pyrite-bearing material.

Claims

1. A process for treating a pyrite-bearing material to enable the recovery therefrom of a metal, elemental sulphur and Fe.sub.2O.sub.3, the process comprising: (a) thermally decomposing the pyrite-bearing material so as to produce a material comprising pyrrhotite (FeS) and a separate elemental sulphur material; (b) leaching the material comprising pyrrhotite from (a) with an acid, the leaching conditions being controlled such that the metal is released from the material comprising pyrrhotite, the iron in the pyrrhotite is oxidised to Fe.sub.2O.sub.3, and the sulphur in the pyrrhotite is oxidised to elemental sulphur in a form that is separate from the metal and that is separable from the Fe.sub.2O.sub.3.

2. A process as claimed in claim 1 wherein oxygen is added to the leaching stage (b) to form the Fe.sub.2O.sub.3, with the Fe.sub.2O.sub.3 being removed from the leaching stage (b) along with elemental sulphur solids.

3. A process as claimed in claim 1, wherein in leaching stage (b) the material comprising pyrrhotite is leached with an acid by mixing it with an acidic aqueous solution, wherein the metal is released into the solution to be recovered therefrom.

4. A process as claimed in claim 3, wherein solution pH in leaching stage (b) is controlled to be in the range of −1 to 3.5 to promote the precipitation of iron as Fe.sub.2O.sub.3.

5. A process as claimed in claim 3, wherein solution temperature in leaching stage (b) is controlled to be in the range of around 95-220° C.

6. A process as claimed in claim 1, wherein when the acid comprises an acidic aqueous halide solution, the solution temperature in leaching stage (b) is controlled to be in the range of around 95-150° C., and is optimally in the range of around 130-140° C.

7. A process as claimed in claim 1, wherein leaching stage (b) is operated at atmospheric pressure.

8. A process as claimed in claim 1, wherein when the acid comprises an acidic aqueous sulphate solution, the solution temperature in leaching stage (b) is controlled to be in the range of around 150-220° C., and is optimally in the range of around 190-210° C.

9. A process as claimed in claim 1, wherein leaching stage (b) is operated at elevated pressures between 1-20 ATM.

10. A process as claimed in claim 1, wherein the residence time of the material passed to leaching stage (b) ranges from 0.1-24 hours, and is optimally around 1-2 hours.

11. A process as claimed in claim 2, wherein the Fe.sub.2O.sub.3 and elemental sulphur solids are recovered and passed to sulphur and iron oxide recovery stages respectively.

12. A process as claimed in claim 3, further comprising passing the solution from (b) to a metal recovery stage in which the metal is separated from the solution and the solution is then recycled back to the leaching stage (b).

13. A process as claimed in claim 12 wherein the acidity of the solution is regenerated by the addition of an acid, such as hydrochloric or sulphuric acid, prior to the solution being recycled to the leaching stage (b).

14. A process as claimed in claim 3, wherein the solution in leaching stage (b) comprises an aqueous halide solution having a concentration in the range 1-10 moles per litre of solution, optimally around 5 moles per litre.

15. A process as claimed in claim 3, wherein the solution in leaching stage (b) comprises a metal halide solution that comprises one or more of: NaCl, NaBr, CaCl.sub.2, and CaBr.sub.2.

16. A process as claimed in claim 1, wherein the elemental sulphur produced in step (a) is recovered and combined with the elemental sulphur produced in leaching step (b).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Notwithstanding any other forms which may fall within the scope of the process as defined in the Summary, specific embodiments will now be described, by way of example only, with reference to the Examples and the accompanying drawings in which:

[0057] FIG. 1 shows a block diagram for an embodiment of the process comprising a number of circuits that are integrated to process pyrite and produce elemental sulphur and iron oxide, and recover base or precious metals that are part of the pyrite mineral lattice;

[0058] FIG. 2 shows a block diagram for an embodiment of the process comprising a number of circuits that are integrated to process pyrite and produce elemental sulphur and iron oxide, and recover cobalt metal that forms a part of the pyrite mineral lattice;

[0059] FIG. 3 which shows the X-ray diffraction profiles at various temperatures for a pyrite concentrate which is thermally treated under an argon atmosphere.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0060] In the following detailed description, reference is made to the accompanying drawings which form a part of the detailed description. The illustrative embodiments described in the detailed description, depicted in the drawings and defined in the claims, are not intended to be limiting. Other embodiments may be utilised and other changes may be made without departing from the spirit or scope of the subject matter presented. It will be readily understood that the aspects of the present disclosure, as generally described herein and illustrated in the drawings can be arranged, substituted, combined, separated and designed in a wide variety of different configurations, all of which are contemplated in this disclosure.

Flowsheet Descriptions

[0061] FIG. 1 shows a process flowsheet in block diagrammatic form. The flowsheet illustrates a generalised embodiment for the treatment of pyrite bearing material to produce useable forms of sulphur, iron and contained base or precious metals.

[0062] FIG. 2 also shows a process flowsheet in block diagrammatic form. The flowsheet illustrates an embodiment for the treatment of pyrite bearing material to produce useable forms of sulphur, iron and cobalt contained in the pyrite-bearing material.

[0063] Each of the flowsheets of FIGS. 1 and 2 depicts a sequential process whereby thermal decomposition, followed by leaching and precipitation, are integrated into a consolidated process.

[0064] Each flowsheet comprises four main integrated circuits: a thermal treatment circuit 100, followed by leaching the calcine produced in circuit 100 in a leaching circuit 200. The leach residue is processed in sulphur circuit 300 for recovery of elemental sulphur, and the remaining leach residue is beneficiated in iron oxide circuit 400 to produce useable iron oxide.

[0065] Additional circuits for recovery of other base or precious metals can be included, such as further precipitation stages, solvent extraction, and/or ion-exchange resins, as may be the case for recovering leached metals which were leached either simultaneously or in separate stages to the leaching of the calcine from circuit 200.

[0066] Hereafter, reference will be made to each of FIGS. 1 and 2, with specific features of either flowsheet being highlighted as required.

Thermal Treatment (Decomposition)

[0067] Usually the pyrite-bearing material that is passed to the thermal treatment circuit 100 is prepared by flotation, gravity, leaching, or other separation stages for other target metals. For example, the pyrite may be concentrated by froth flotation of the pyrite (or sulphides) from an ore. This prepares a concentrate 101 that is now ready to be thermally treated in circuit 100.

[0068] More specifically, the pyrite-bearing material is thermally decomposed in circuit 100. The pyrite feed 101 is heated in an inert atmosphere (e.g. nitrogen and/or argon) to prevent oxidation of the mineral by interaction with oxygen. The flowsheet of FIG. 2 depicts thermal decomposition as a pyrolysis stage 104.

[0069] In the thermal treatment circuit 100 the pyrite decomposes into pyrrhotite (which has no specific iron to sulphur ratio, but which is commonly simplified as Fe.sub.7 S.sub.8) and elemental sulphur as shown in the following reaction 1:

FeS.sub.2(s).fwdarw.FeS.sub.2-x(s)+xS.sub.(g)  Rn 1

[0070] The temperature must be greater than 450° C. for the reaction to proceed, although an optimal temperature is in the range of around 600-750° C. The reaction duration can be in the range of 1 minute to 240 minutes, and typically takes place over 60 to 90 minutes. The off-gas (stream 102) containing the elemental sulphur is cooled to condense the sulphur S (e.g. in a gas condenser 106), and to ultimately recover the sulphur S in a solid form.

[0071] Next, the calcine (stream 103) is forwarded to the leach circuit 200, where the artificial pyrrhotite is leached while simultaneously precipitating iron oxide. The flowsheet of FIG. 2 depicts leaching occurring in a leaching reactor 205.

[0072] Leaching can take place in a gas phase, optionally in an aqueous gas phase. However, for many pyrite-bearing materials typically the leach circuit 200 employs an aqueous liquid phase for ease of handling and unit operations.

[0073] In this latter case, the contained base and/or precious metals are solubilised into the liquor media. The sulphur component of the pyrrhotite is oxidised to elemental sulphur, and is not oxidised to sulphuric acid (as would be the case for prior art processes which leach the sulphur component of pyrite). As a consequence, the net reaction of the disclosed process requires a small consumption of oxygen compared to the leaching of pyrite. Further, there is no generation of free acid requiring neutralisation, as is the case when leaching pyrite. The reactions, when an aqueous halide solution is employed, are as follows:

Leaching 2FeS.sub.(s)+1.5O.sub.2(g)+6HCl.fwdarw.2FeCl.sub.3+2S.sub.(g)+3H.sub.2O  Rn 2

Precipitation FeCl.sub.3+3H.sub.2O.fwdarw.Fe.sub.2O.sub.3+6HCl  Rn 3

Overall 2FeS.sub.(s)+1.5O.sub.2(g).fwdarw.Fe.sub.2O.sub.3(s)+2S.sub.(s)  Rn 4

{In the above reactions FeS is used for simplicity in the nomenclature, however, here it should be understood that FeS stands for Fe.sub.xS.sub.(2-x)}

[0074] In the process as depicted, the concentration of the halide solution can be in the range of 1-10 moles per litre of solution, and is optimally around 5 moles per litre. A typical halide solution employed is sodium-halide (although the solution can contain mixtures of magnesium or calcium halides). Copper may also be present in the feed pyrite-bearing material or added as copper salts (see below).

[0075] The temperature of the leach and precipitation step/stage can be controlled to be in the range of 95-150° C., and is optimally controlled to be around 130-140° C. This optimal temperature range promotes the simultaneous formation of hematite and liquefies the elemental sulphur. Upon cooling, the sulphur freezes and can be separated by physical or chemical processes in sulphur circuit 300.

[0076] The pH of the leach and precipitation step can be controlled to be <7, with the optimal range being somewhere between −1 and 3.5.

[0077] The net reactions consume oxygen for the oxidation of the pyrrhotite. This can be supplied by sparging air or oxygen directly into a leach and precipitation reactor. Alternatively, the leaching solution can contain ferric cations which oxidise the pyrrhotite. The ferric ions can be produced by oxidising ferrous ions inside or outside of the main leach reactor. Similarly, other oxidation couples can be employed, such as cupric/cuprous. The reaction for ferrous/ferric oxidation is as follows:

Oxidation FeCl.sub.2+HCl+0.25O.sub.2(g).fwdarw.FeCl.sub.3+0.5H.sub.2O  Rn 5

[0078] The resultant leach solution (stream 201) containing base and/or precious metals is forwarded to metal recovery unit operations such as precipitation, electrowinning, ion-exchange, solvent extraction, etc. The flowsheet of FIG. 2 depicts the metal recovery unit operations occurring as cobalt ion-exchange 207 followed by a cobalt sulphate crystallisation stage 208, to produce a cobalt sulphate product C.

[0079] In most instances, a return stream 204 of solution will be recycled back to the leach circuit 200 in a closed-loop fashion to minimise emissions to the environment.

[0080] Thirdly, the leach residue stream 203 from circuit 200 is forwarded to sulphur circuit 300 for recovery of the elemental sulphur. The elemental sulphur can be separated from the iron oxide in the leach residue by any of the known processes, including, but not limited to, particle size separation, gravity techniques, froth flotation, distillation, melting or remelting. The flowsheet of FIG. 2 depicts sulphur recovery occurring as a sulphur screening stage 304, which produces a stream 301 representing a further sulphur product S.

[0081] Fourthly, the remaining iron oxide (stream 302) from circuit 300 is forwarded to an iron oxide beneficiation circuit 400. In this circuit the iron oxide is thermally treated to remove any remaining sulphur. The flowsheet of FIG. 2 depicts iron oxide recovery occurring in an Fe.sub.2O.sub.3 beneficiation furnace 404, which produces a hematite product H.

[0082] An oxidising atmosphere is used in the furnace to promote the oxidation of the sulphur to sulphur dioxide. The furnace temperature is in the range of 300-1400° C., more typically around 1250-1350° C. The sulphur dioxide that is produced can be captured in a wet scrubber and recycled to the leach circuit 200 as a weak sulphurous acid stream 402.

[0083] Each of the circuits 100, 200, 300, and 400 can comprise one or more recycle streams to allow for control of solids residence time to improve yield/recovery. Each recycle stream can be from a given reactor stage to a previous reactor stage; a so-called “internal” recycle (for example the slurry from one reactor is recycled back to a previous reactor). Alternatively or additionally, each recycle stream can be from a separation stage (for example off-gas from one circuit to another circuit) to a given reactor stage; a so-called “external” recycle.

Thermal Decomposition Circuit 100 (in Detail)

[0084] The thermal decomposition circuit 100 usually comprises a furnace connected to a feed hopper. An inert atmosphere is provided by blanketing the solids with an inert gas (e.g. nitrogen, argon, etc.). The feed material is heated to a temperature in the range of 450° C. to 900° C., optimally 600° C. to 800° C. The off-gas from the furnace is collected, and cooled, with elemental sulphur subsequently condensing and freezing. A particulate filter can be used to minimise any carry-over of solids into the off-gas stream. Once the elemental sulphur is collected, the inert gas can be recycled to the furnace. The calcine (solids product containing pyrrhotite) is discharged from the furnace, and typically cooled to below 100° C. while still under an inert atmosphere. This step is to prevent any unwanted oxidation reactions taking place. The number of ancillary items of process equipment in addition to the furnace, and the furnace design, will vary depending on the throughput, and feed material characteristics such as moisture content and particle size.

Leach Circuit 200 (in Detail)

[0085] In leach circuit 200, the calcine material (stream 103) is mixed with an acidic aqueous halide solution. The slurry density range is typically from 0.5-60% w/w, and is often adjusted to minimise process plant equipment size. The oxidation-reduction potential is typically maintained at >450 mV (versus Ag/AgCl) to ensure oxidation of the pyrrhotite. More specifically, the oxidation-potential is sufficient to oxidise any ferrous cations into ferric cations for subsequent precipitation of iron oxide.

[0086] Additional, subsequent reactors can employ oxidative leaching conditions to target other minerals once the artificial pyrrhotite has been leached (e.g. in a first or early stages of leach circuit 200).

[0087] In leach circuit 200, leaching is carried out at a temperature in the range of 95-220° C., optimally at around 130-140° C. for aqueous halide solutions, and typically for a residence time of 0.1-24 hours under atmospheric pressure or elevated pressures of 1-20 ATM. Often the artificial pyrrhotite leaches rapidly, and a residence time of <2 hours (i.e. around 1-2 hours) can be sufficient.

[0088] The precipitated elemental sulphur and iron oxide, along with the un-leached gangue minerals are separated as stream 203, while the solution advances as stream 201 to a metal recovery circuit. The brine is recycled as stream 204 back to the start of leach circuit 200 once the target metals have been recovered. The pH of the recycled solution stream is adjusted to be <7, and preferably between −1 and 3.5, before being mixed with incoming calcine material from stream 103. Usually stream 203 is filtered to recover the brine solution for return to the start of leach circuit 200, before the solids advance to the sulphur recovery circuit 300.

Sulphur Recovery Circuit 300 (in Detail)

[0089] The leach residue produced in leach circuit 200 contains elemental sulphur. The sulphur recovery circuit 300 usually comprises a series of vessels where the elemental sulphur is separated using particle size separation (e.g. cyclones), gravity separation (e.g. concentrators, spirals, tables), froth flotation (e.g. flotation cells), a melting or remelting stage, etc. The optimum method is selected based on the physical characteristics of the elemental sulphur, such as particle size. The residual leach residue, after elemental sulphur is recovered, is forwarded to the iron oxide recovery circuit 400.

[0090] The collected sulphur often contains some trapped leach residue, and thus a secondary circuit can be utilised to improve the purity of the sulphur. Non-limiting examples include distillation, chemical dissolution and re-precipitation, etc.

Iron Oxide Recovery Circuit 400 (in Detail)

[0091] The iron oxide recovery circuit 400 usually comprises a furnace where the iron oxide is thermally treated. The treatment is typically under oxidising conditions designed to reduce the amount of sulphur in the iron oxide. Elemental sulphur is oxidised to sulphur dioxide, which is captured and directed to the leach circuit 200. If a wet scrubber is employed, then the sulphur dioxide gas can be solubilised as sulphurous acid. The temperature of the treatment furnace is in the range of 300-1400° C., and is optimally operated at 1200-1300° C. Often, the iron oxide is first pelletised or converted from fines into lumps prior to thermal treatment. The number of ancillary items of process equipment in addition to the furnace, and the furnace design, will vary depending on the throughput, and feed material characteristics such as moisture content and particle size.

Solids-Liquid Separation

[0092] Appropriate flocculants and coagulants can be added to the slurries throughout the process to improve the efficiency of the solid-liquid separation stages. Typically, each separation stage comprises a thickener and a filter, but alternatives can be a counter-current decantation stage, a single stage filter, or similar equipment. The thickening stage can make use of high rate thickeners, low rate thickeners, clarifiers and similar devices for solid-liquid separation. The filtration stage can make use of pressure filters, pan filters, belt filters, press filters, centrifuge filters and similar devices for solid-liquid separation.

[0093] Typically, each slurry is first sent to a thickener; with the resulting underflow slurry then forwarded to a filter for recovery of solids. The overflow can comprise process solution, or may be further filtered.

[0094] Washing of the solids during recovery is employed to minimise any losses of process solutions and salts from the circuit. Fresh water is required for washing, and this is evaporated in the process reactors in the leach circuits. The resulting water vapour is discharged through the off-gas scrubber system or condensed and recycled as fresh wash waters.

Off-Gas Handling and Scrubbing

[0095] Off-gases are transferred from the various process reactors. The thermal decomposition circuit 100 off-gas contains elemental sulphur and is condensed for recovery of solid or liquid sulphur. The leach circuit 200 off-gas contains water and acidic vapours which is collected in a scrubber for water recovery and recovery of the acid. The iron oxide circuit 400 off-gas contains sulphur dioxide, which is collected in a scrubber and directed back to the leach circuit 200.

EXAMPLES

[0096] Non-limiting Examples of various stages (circuits) of the process for treating pyrite to recover useable forms of sulphur, iron, and base or precious metals (such as cobalt) contained in the pyrite mineral lattice will now be described.

Example 1: Determination of Temperature for Thermal Decomposition of Pyrite

[0097] A sulphide concentrate sample was shown to contain a pyrite mineral where cobalt had substituted into the crystal lattice for iron atoms. No other cobalt bearing minerals were detected in the sample by QEMSCAN analysis, scanning electron microscopy, or x-ray diffraction.

[0098] Samples of the cobalt-pyrite concentrate were determined to contain 90% pyrite, 7% albite, 3% silica, and <1% miscellaneous gangue. The samples were treated under argon for 2 hours. A range of temperatures were used, from 450° C. to 700° C. The ratio of pyrite to pyrrhotite was measured by x-ray diffraction. At temperatures between 450° C. and 600° C., the decomposition was partially complete. Above 650° C. all of the pyrite had transformed to pyrrhotite. The x-ray diffraction profiles for thermally treated pyrite concentrate at various temperatures under argon are shown in FIG. 3.

[0099] As expected, the main phase transition was the decomposition of pyrite into pyrrhotite. The transition began at 500° C. and was complete by 650° C. In contrast to a prior art roasting reaction with oxygen, the decomposition of pyrite into pyrrhotite was observed to be a thermal phase transition.

Example 2: Thermal Decomposition of Pyrite to Produce Elemental Sulphur

[0100] A 500 g sample of the same cobalt-pyrite concentrate used in Example 1, was thermally decomposed at 650° C. for 2 hours under nitrogen. The off-gas was cooled, resulting in the freezing of gases into a solid residue. The composition of the residue from the off-gas was measured by x-ray diffraction, and shown to be 97.3% elemental sulphur, and 2.7% pyrite. The pyrite in the off-gas residue was a result of particulate carryover from the furnace reactor, and was able to be minimised by passing the off-gas through a filter. In total, 41% of the sulphur present in the pyrite was evolved from the concentrate by thermal decomposition.

Example 3: Effect of Residence Time on Thermal Decomposition of Pyrite to Pyrrhotite

[0101] A second batch of cobalt-pyrite concentrate was obtained, and used in a series of tests to illustrate the effect of time on the thermal decomposition of pyrite into pyrrhotite. Three, 2 kg samples of the concentrate were heated to 750° C., with the residence time varied from 15 minutes, 30 minutes, and 45 minutes. An inert atmosphere was obtained by purging the reaction vessel with 99% nitrogen. The resulting calcine product was analysed by x-ray diffraction. The results are given in Table 1, and show that the pyrite was progressively converted into pyrrhotite with increasing residence time.

TABLE-US-00001 TABLE 1 Mineral Content of Calcine Product Mineral Units Start 15 minutes 30 minutes 45 minutes Mass g 2000 1809 1739 1690 Pyrite % 66.8 25.9 10.7 1.9 Pyrrhotite % 5.6 46.1 55.4 67 Albite % 10.6 12.6 14.1 10.7 Quartz % 9.7 9.6 11.5 10.7

[0102] The off-gas from the kiln, was directed to a chamber, for recovery of elemental sulphur by condensation and freezing (the chamber was cooled externally by ambient air flow). The sulphur was analysed by elemental analysis, and was shown to contain >99% elemental sulphur.

Example 4: Leaching Calcine from Thermal Decomposition in Sulphate Media

[0103] The calcine from Example 2 was analysed by x-ray diffraction and shown to contain 81.6% pyrrhotite, 9.6% albite, 3.6% silica, and 5.2% miscellaneous gangue (<0.1% pyrite). The major elements were 50.4% iron, 33.2% sulphur, and 0.49% cobalt. A subsample of the calcine was leached in sulphuric acid at 130° C. in an autoclave for 2 hours. The pressure was 4 bars, and oxygen was sparged into the reactor at an over pressure of 2 bars. The resulting leach solubilised >99% of the cobalt, and oxidised >99% of the sulphur in the pyrrhotite to elemental sulphur. Only 33% of the iron in the pyrrhotite was precipitated as hematite, with the other 67% precipitating as jarosite. The formation of jarosite was able to be prevented by using higher autoclave temperatures, e.g. temperatures in the range of 180° C. to 200° C.

Example 5: Leaching Calcine from Thermal Decomposition in Chloride Media

[0104] A further 28 kg of cobalt-pyrite concentrate was thermally decomposed to prepare calcines for leach experiments. Each batch was between 2-3 kg, and the temperature was varied between 700° C.-750° C., with the residence time being varied between 15 minutes, 30 minutes, 45 minutes and 60 minutes.

[0105] The resulting calcines were blended into various feed samples, to obtain different pyrite to pyrrhotite ratios. A calcine containing 55% pyrrhotite and 18% pyrite was selected for leaching, to illustrate the difference in leachability of pyrrhotite versus pyrite.

[0106] A 250 g subsample of the calcine was leached in an autoclave with a solution containing 150 g/L NaCl and 150 g/L CaCl.sub.2, and 5 g/L FeCl.sub.3. The temperature was 130° C., and the starting solution pH was adjusted to 0.5 using HCl. The natural internal pressure from heating the slurry to 130° C. in the autoclave was 3 ATM, and oxygen was sparged in the reactor with an overpressure of 7 ATM, bringing the total pressure to 10 ATM. The leach proceeded until no further oxygen was consumed, with this occurring at approximately 60 minutes.

[0107] The resulting leach solubilised 73.6% of the cobalt, and produced a leach residue containing predominantly elemental sulphur and hematite. The mineral content was measured using x-ray diffraction, and is shown in Table 2. In contrast to Example 4, where a sulphate leaching media was used, no jarosites were identified in the leach residue produced from a chloride leaching media. The remaining pyrite content, indicated that this mineral was not leached under the conditions, and hence the leach conditions were selective for pyrrhotite. The cobalt extraction was limited to the destruction of pyrrhotite, with the remaining 26.4% of the cobalt being hosted in the unreacted pyrite fraction.

TABLE-US-00002 TABLE 2 Mineral Content of Leach Residue Mineral Units Feed Leach Residue Mass g 253 279 Pyrite % 18.1 12.92 Pyrrhotite % 53.6 0.15 Hematite % Not present 46.02 Goethite % Not present 1.36 Elemental Sulphur % Not present 21.95 anhydrite % Not present 0.66

[0108] The resulting leach solution contained 920 ppm cobalt, and was forwarded to a separate metal recovery circuit using ion-exchange and crystallisation to produce cobalt sulphate.

Example 6: Leaching of Pyrrhotite Calcine from Thermal Decomposition Using Chloride Media

[0109] A separate subsample of calcine produced in Example 5, was leached using the same conditions described in Example 5. In contrast to Example 5, this subsample contained 0.1 wt. % pyrite and 92.6 wt. % pyrrhotite. The resulting cobalt extraction was 97.5%, as indicated in the metal content of the feed and leach residue shown in Table 3.

TABLE-US-00003 TABLE 3 Metal Content of Leach Residue Mineral Units Feed Leach Residue Mass g 1000 1272 Fe % 55.4 42.3 S % 37.9 25.1 Co % 0.51 0.01 SiO.sub.2 % 3.56 2.93 Ca % Not present 0.84

[0110] The resulting leach residue was processed to separate the elemental sulphur from the precipitated hematite using known methods. This example demonstrated that excellent recovery of cobalt could be achieved with a high conversion of the pyrite into pyrrhotite.

[0111] Whilst a number of specific process embodiments have been described, it should be appreciated that the process may be embodied in other forms.

[0112] In the claims which follow, and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word “comprise” and variations such as “comprises” or “comprising” are 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 process as disclosed herein.