AU2004243345B2 - Process of upgrading a copper concentrate - Google Patents

Description

WO 2004/106561 PCT/AU2004/000738 PROCESS OF UPGRADING A COPPER CONCENTRATE Field of the Present Invention The present invention relates to a 5 hydrometallurgical process for upgrading a copper concentrate. Background of the Invention The present invention has been made to enable 10 continued treatment of an ore body such as the ore body at Olympic Dam Operations in South Australia despite the grade and mineralogy of the ore being mined changing over time. At present run-of-mine ore at Olympic Dam 15 Operations is ground and concentrated in flotation vessels to produce a copper concentrate. Copper concentrate can have a particle size distribution with 80 weight percent passing 20-75 microns. The concentrate includes various copper sulphide minerals including chalcocite (Cu2S), 20 chalcopyrite (CuFeS 2 ) and bornite (Cu 5 FeS 4 ) as well as gangue material, which includes compounds containing any one or a combination of iron, uranium, aluminium, and silicon. It is expected that the relative proportions of 25 the copper sulphide minerals in the ore body, and thus in the concentrate will change over time as the ore body is further developed. Specifically, it is expected that the proportion of chalcocite in the concentrate will reduce and the proportion of the chalcopyrite in the concentrate 30 will increase over time. This will result in the production of a lower grade concentrate having a lower Cu:Fe and a lower Cu:S ratio. This is of fundamental importance in smelting. According to present practice, the concentrate, 35 which is fed to the smelter at Olympic Dam Operations undergoes an initial treatment to recover uranium and to at least partially remove hematite and other gangue WO 2004/106561 PCT/AU2004/000738 -2 material using a sulphuric acid leach stage. Although hematite is normally considered difficult to leach using sulphuric acid, under suitable conditions hematite is dissolved to produce a ferrous sulphate solution. Thus, 5 one apparent option to adjust the Cu:Fe ratio is to adjust the acidity of the leach to remove more hematite. However, the oxidation-reduction potential (ORP) of the leaching slurry also increases as acidity increases and some copper minerals would be more susceptible to dissolution and thus 10 would also be removed from the concentrate if the leach conditions were changed. However, the Cu:S ratio is not changed by increased hematite dissolution. An alternative process for upgrading low grade copper concentrate to maintain the Cu:S and Cu:Fe ratio 15 within acceptable limits for smelting is therefore needed. Summary of the Invention According to the present invention there is provided a process for upgrading a copper concentrate 20 suitable for smelting, the concentrate including gangue material containing any one or more of iron, uranium, aluminium, silicon or compounds thereof, the concentrate also including at least one of chalcopyrite and bornite, the process including the stages of: 25 a) leaching at least a portion of the gangue material from the concentrate using an acid solution; and b) reacting chalcopyrite or bornite in the concentrate with ionic copper in a metathesis reaction that replaces iron with copper in the chalcopyrite or 30 bornite and forms copper sulphide minerals. An advantage provided by the present invention is that soluble ionic copper can react with chalcopyrite and bornite to form relatively insoluble copper sulphide minerals and thereby add to the amount of copper in the 35 concentrate. Although it is possible that stages a) and b) can be carried out concurrently, it is preferred that stages WO 2004/106561 PCT/AU2004/000738 -3 a) and b) be carried out consecutively. It is also possible that stage b) occur before stage a) or at least begin before stage a). It has been found that acid leaching gangue 5 material according to stage a) of the process of the present invention can create conditions in which the concentrate is upgraded by a series of redox reactions. In particular, during the acid leaching of stage a), it is possible that conditions may be created in which bornite 10 and/or chalcopyrite are oxidised to copper sulphide minerals and thereby increase the ratio of copper to iron in the concentrate. For example, the oxidation of bornite to produce copper sulphide minerals may occur in stage a) without the addition of a reductant according to the 15 following two half reactions. Reaction 1 Cu 5 FeS 4 -4 4CuS + Fe 2 + + Cu 2 + + 4e~ 20 Reaction 2 Cu 5 FeS 4 -+ 3CuS + Cu 2 S + Fe2+ + 2e~ Reaction 1 suggests the copper may be dissolved during stage a), however, the following half reaction 25 involving the reduction of bornite suggests that any available copper ions are reacted to produce a copper sulphide precipitate. Reaction 3 30 CusFeS 4 + 3Cu2+ + 4e~ - 4Cu 2 S + Fe2+ In the instance when stage a) involves the dissolution of hematite, ferric and sulphate ions are produced. Depending on the mineralogy of the concentrate 35 being upgraded, ferric ions are a relatively strong oxidant and have a propensity to be reduced to ferrous ions in accordance with the following half reaction.

WO 2004/106561 PCT/AU2004/000738 -4 Reaction 4 Fe3+ + e- + Fe2+ 5 However, as can be seen from reactions 1 and 2, the oxidation of bornite produces in addition to copper sulphide minerals, ferrous and cuprous ions. The rate at which reaction 4 can occur depends on the products of reaction 1, 2 and 4. The rate of dissolution of hematite 10 is also affected by the rate at which reaction 4 can occur. In order to favour the dissolution of hematite, a reductant can be supplied to stage a) to facilitate the reduction of the ferric ions which in turn facilitates the 15 dissolution of hematite. Although it is possible that different types of reductants may be supplied to stage a), it is preferred that the reductants be any one or a combination of sulphur dioxide, sodium sulphite, or elemental iron. 20 Ionic copper can be supplied to stage a) which reacts with bornite and/or chalcopyrite to produce copper sulphide minerals by way of reduction and/or metathesis reactions. Ionic copper may be added to stage a) with or without the addition of a reducing agent. In the instance 25 when ionic copper and a reductant are added to stage a), chalcopyrite may be reduced to produce a copper sulphide mineral in accordance with the following half reaction. Reaction 5 30 CuFeS 2 + 3Cu2+ + 4e~ - 2Cu 2 S + Fe 2 + In the event that ionic copper is supplied to stage a) without the addition of a reductant, the dissolution of hematite is likely to reduce on account of 35 the reduced availability of electrons to reduce ferric ions to ferrous ions. In the event that ionic copper is supplied to WO 2004/106561 PCT/AU2004/000738 -5 stage a) during acid leaching without the addition of a reductant, ionic copper is likely to react with bornite and/or chalcopyrite in a metathesis reaction. An overall redox reaction in which no additional 5 reductants and/or ionic copper are added to stage a) may be represented by the following reaction. Reaction 6 CuSFeS 4 + Fe 2 0 3 + 3H 2

SO

4 - 3CuS + Cu 2 S + 3FeSO 4 + 3H 2 0 10 It is preferred that the acid solution used in stage a) be a sulphuric acid solution. Accordingly, stage a) produces a solid phase from which iron oxides (eg hematite) and other gangue material have been partially or 15 wholly removed and a liquid phase containing ferrous, uranium and other ions. It is preferred that the concentration of sulphuric acid range from 20 to 100 g/L. In the situation in which stages a) and b) occur 20 consecutively, it is preferred that the liquid and solid phases produced in stage a) be at least partially separated in a solid/liquid separator prior to the concentrate being further processed according to stage b). It is preferred that stage a) be carried out at a 25 temperature > 70 0 C. Generally speaking, the amount and rate at which gangue material, particularly hematite, is leached from the concentrate increases as the temperature increases. It is preferred that the acid solution and the 30 concentrate in stage a) form a slurry whereby the proportion of solids in the slurry ranges from 35 to 60%. It is preferred that the concentrate be subjected to leaching in stage a) for at least 10 hours. It is even more preferred that the concentrate be 35 subjected to leaching in stage a) for a period ranging from 10 to 25 hours. It is preferred that the oxidation-reduction WO 2004/106561 PCT/AU2004/000738 -6 potential (ORP) of the slurry in stage a) be < 380 mV and in stage b) be < 300mV. The ORP value is reported with reference to Ag/AgCl and 3M KCl. The term "metathesis reaction" throughout this 5 specification means a type of exchange reaction in which cations, preferably provided by a copper sulphate solution, react with chalcopyrite or bornite minerals to form relatively insoluble copper sulphide minerals including: covellite, chalcocite, digenite or derivatives 10 thereof. The copper sulphide minerals formed by metathesis have a tendency to form on the outer surfaces of copper iron sulphide mineral particles in the concentrate. It is preferred that the metathesis reaction in 15 stage b) be based on a reaction between copper sulphate and chalcopyrite or bornite. It is preferred that the copper sulphate be in the form of a solution. Two examples of metathesis reactions involving 20 copper sulphate (provided from an external source) and chalcopyrite and bornite are as follows: Reaction 7 3Cu 5 FeS 4 + 6CuSO 4 + 4H 2 0 + 5Cu 1

.

8 S + 6Cu 2 S + 3FeSO 4 +4H 2 SO4 25 Reaction 8 3CuFeS 2 + 6CuSO 4 + 4H20 + 5Cu..

8 S + 3FeSO 4 +4H 2 SO4 It is preferred that a reducing agent be added to 30 stage b). It has been found that slightly reducing conditions enhance the substitution of copper ions for iron ions in the lattice of chalcopyrite and bornite minerals (ie. increase the metathesis reaction rate). Examples of possible reducing agents include 35 sodium sulphite (Na 2

SO

3 ), sodium metabisulphite (Na 2

S

2 0 5 ), sulphur dioxide (SO 2 ), hydrogen and iron. However, it is preferred that the reducing agent WO 2004/106561 PCT/AU2004/000738 -7 be in the form of sulphur dioxide. When stages a) and b) are carried out concurrently, one of the advantages of a reducing agent is that it can facilitate the dissolution of gangue material 5 such as hematite and create conditions conducive to metathesis reactions. An example of a metathesis reaction involving chalcopyrite and copper sulphate carried out in the presence of a reducing agent (SO 2 ) is as follows; 10 Reaction 9 Cu 5 FeS 4 + 2SO2 + 4H 2 0 + 3Cu 2 + -> 4Cu 2 S + 6H* + 2HS0 4 ~ + Fe2+ It will be appreciated by those skilled in the 15 art of the invention that an embodiment of the present invention may involve carrying out stages a) and b) concurrently whereby both leaching of gangue material and precipitation of copper sulphide minerals occurs. simultaneously. 20 According to an alternative embodiment, stage a) can be carried out before stage b) so that in essence leaching of gangue material from the concentrate proceeds the production of a copper sulphide mineral. However as explained previously, it is possible that redox reactions 25 may to some extent convert bornite and/or chalcopyrite into copper sulphide minerals during stage a). According to yet another embodiment, stage b) may be carried out prior to stage a). Furthermore, when ionic copper is added to the concentrate to facilitate 30 metathesis reactions prior to acid leaching, it is possible that a reductant may also be added to stage b) to facilitate a reduction of bornite and/or chalcopyrite to other copper sulphide minerals. Reaction 5 is an example of a half reaction in which bornite and/or chalcopyrite is 35 reduced to a copper sulphide mineral.

WO 2004/106561 PCT/AU2004/000738 -8 Brief Description of the Drawings A detailed description of a copper concentrate upgrading process according to a prior art process and the preferred embodiment of the invention will now be 5 described with reference to: Figure 1 which is a flowsheet of a copper concentrate treatment process presently in use at Olympic Dam Operations in South Australia; Figure 2 which is a flowsheet of a copper concentrate 10 upgrading process according to a preferred embodiment of the present invention; Figures 3 to 5 which are flowsheets of copper concentrate upgrading processes according to alternative embodiments of the present invention; and 15 Tables 1 and 2 provide details of a total of 23 trials carried out on a concentrate presently available at Olympic Dam Operations and a concentrate expected to be produced in the future. 20 Detailed Description The upgrading process shown in Figure 1 is a single stage leaching process presently in use at Roxby Downs mine. The materials fed to the leaching process comprise a copper concentrate slurry and sulphuric acid. 25 The copper concentrate is prepared from a run-of-mine ore that has been ground and then concentrated in froth flotation vessels (not illustrated). Upon completion of the leaching stage, the slurry is transferred to a solid/liquid separator. The upgraded 30 concentrate can then be supplied to a smelter via other unit operations such as driers as necessary. The liquid from the separator contains ferrous sulphate, uranium compounds and possibly small amounts of soluble copper that may be further processed in the tails leaching 35 circuit within the copper refining plant at Olympic Dam Operations. In contrast, the process of the preferred WO 2004/106561 PCT/AU2004/000738 -9 embodiment shown in Figure 2 is essentially a two stage process. A copper concentrate slurry comprising approximately 50 to 55% solids initially undergoes a sulphuric acid leaching stage to remove gangue material. 5 The acid leaching stage may also involve redox reactions to assist the upgrading of concentrate. The concentrate is then transferred to a copper precipitation stage involving metathesis reactions resulting from contacting the concentrate with a copper 10 sulphate solution and carried out in the presence of a reducing agent. The metathesis reactions involve the conversion of solid chalcopyrite and bornite particles to solid compounds containing higher concentrations of copper and sulphur. 15 The process also includes solid/liquid separation after each stage for separating liquid and upgraded concentrate. The slurry concentrate is treated in the leaching stage for a period of approximately 20 hours and at an 20 elevated temperature of approximately 85 0 C. The sulphuric acid solution mixed with the slurry is supplied to produce an acid concentration in the leach solution ranging from 20-100 g/L. The oxidation-reduction potential (ORP) of the 25 slurry is of the order of 300mV, wherein the potential is in reference to Ag/AgCl and 3M KCl. The acidity in the leaching step is maintained initially at 100 g/L but allowed to decrease about half way through the leach time to a lower concentration of 20 30 g/L. The ORP is dependent on the acid addition and the mineral composition of the concentrate. The reaction kinetics under normal operating conditions are such that the concentrate is upgraded by at least partial dissolution of gangue material in the 35 concentrate. The gangue material includes iron oxide compounds and uranium containing compounds. In addition, the dissolution of iron oxide such WO 2004/106561 PCT/AU2004/000738 - 10 as hematite produces ferric ions that readily reduce in accordance with reaction 4. Reaction 4 takes place in association with reactions 1 and 2 and thereby converts bornite to insoluble copper sulphide minerals by way of 5 redox reactions. A reductant may be added to the leach stage for reducing ferric ions to ferrous ions and thereby increase the dissolution of hematite. In addition, ionic copper may also be added to 10 the leaching stage to convert bornite and/or chalcopyrite to copper sulphide minerals in accordance with reactions 3 and 5. Figure 3 is a flowsheet in which iron leaching and copper precipitation are carried out simultaneously in 15 a single stage. In particular a copper concentrate, sulphuric acid, and a soluble copper solution are supplied to the single stage to facilitate the dissolution of iron and produce a copper sulphide mineral from bornite and/or chalcopyrite by metathesis and redox reactions. A 20 reductant is also supplied to assist in the reduction of ferric ions to ferrous ions and thus the dissolution of iron oxide material. The reductant also creates reducing conditions that favour the formation of the copper sulphide minerals by way of the redox and metathesis 25 reactions. An upgraded solid phase is then separated from the liquid phase in a separator. Figure 4 is a flowsheet in which both iron leaching and copper precipitation are carried out simultaneously in a first stage followed by copper 30 precipitation in a second stage. The first stage is the same as flow sheet shown in Figure 3. The liquid and solid phases formed in the first stage are then separated and the solid phase further processed in a second stage that involves metathesis reactions driven by an ionic 35 copper solution and reductant. An upgraded solid phase is then separated from the liquid phase in a further separator.

WO 2004/106561 PCT/AU2004/000738 - 11 Figure 5 is a flowsheet in which copper precipitation involving metathesis and redox reactions occurs in a first stage followed by an iron leaching in a second stage. Copper concentrate, a soluble copper 5 solution and a reductant are supplied to a first stage. The solid and liquid phases formed in the first stage are then separated and the solid phase treated in a second stage with sulphuric acid to leach iron. An upgraded solid phase is then separated from the liquid phase in a further 10 separator. Table 1 provides the results of 16 trials, of which trials 1 to 13 are upgrading processes carried out on a concentrate expected to be produced from ore mined at Olympic Dam Operations in the future ("future 15 concentrate") and trials 14 to 16 are upgrading processes carried out on the concentrate presently available at Olympic Dam Operations ("present concentrate"). Table 1 includes data that shows the proportions of copper and iron in the feed concentrate, the liquid 20 phase, and the upgraded concentrate, and the conditions under which the trials were conducted. The upgrading processes in trials 6 to 13 were carried out in accordance with the present invention. However, unlike the preferred embodiment described above 25 in relation to Figure 2, the upgrading processes in trials 6 to 13 were carried out so that the leaching and precipitation stages occurred concurrently. The upgrading processes conducted in the other trials 1 to 5 and 14 to 16 were carried out in accordance with the prior art and 30 involved a leaching stage without soluble copper addition for metathesis of bornite (< 100*C). An operating condition that had a notable impact on the leaching stage of both present and future concentrates was the temperature at which the leaching 35 stage was operated. Specifically for the trials that only involved leaching without precipitation (trials 1 to 5 and 14 to 16), the percentage of the copper in the upgraded WO 2004/106561 PCT/AU2004/000738 - 12 solid phase was noticeably higher when the trials were conducted at higher temperatures. In the case of trials 7 and 8 moderate amounts of an aqueous solution containing copper sulphate were added 5 to the slurry in an attempt to facilitate copper precipitation into the concentrate and to create conditions in which precipitation of copper compounds may occur by means of metathesis reactions. However, although copper was precipitated in these trials, the proportion of 10 copper in the upgraded solids was not as high as that achieved in comparable trials 1 and 4 where no soluble copper was added. This is attributed to the higher iron extraction in trials 1 and 4. This suggests that the addition of an aqueous copper solution to the leaching 15 stage has a detrimental effect on the dissolution of iron compounds from the concentrate. This leads to a conclusion that preventing the dissolution of copper and creating conditions that encourage the precipitation of copper by metathesis 20 reactions may be less feasible when the leaching and copper precipitation stages are carried out concurrently when an aqueous solution of copper sulphate is used as the exchange reactant and when the ORP is high. Trials 9, 10 and 12 involved the addition of a 25 reducing agent in the form sodium sulphite and trials 9 and 10 also involved the addition of an aqueous copper solution for the purposes of precipitating dissolved copper. Precipitation of soluble copper was 52%, 95% and 100% in trials 9, 10 and 12. 30 Table 2 provides the results of 7 trials numbered 17 to 23, all of which are upgrading processes carried out on a concentrate expected to be produced from ore mined at Olympic Dam Operations in the future. Trials 17 to 21 were carried out in accordance with the flowsheet shown in 35 Figure 2, namely an iron leaching stage followed by copper precipitation stage. Trials 22 and 23 were carried out in accordance WO 2004/106561 PCT/AU2004/000738 - 13 with the flowsheet shown in Figure 5, namely a copper precipitation stage followed by an iron leaching stage. The results of the trials show that the optimal process for upgrading the concentrate involves a 2 stage 5 process in which gangue material leaching and copper precipitation are carried out at different optimum conditions. A summary of the optimal process operating conditions for a flowsheet shown in Figure 2 is as set out 10 below: Stage 1 - Leach stage Temperature: > 80 0 C Acidity: 100 g acid per L for 8-12 h 15 Duration: 12 - 24 h Slurry density: > 50 wt% solids ORP: < 380 mV Stage 2 - Copper precipitation stage 20 Temperature: > 70 *C Acidity: > 20 g acid per L Duration: > 5 h Slurry density: > 50 wt% solids ORP: < 300 mV 25 Reductant: sodium sulphite Copper Concentration: < 100 g Cu per L Many modifications may be made to the preferred embodiment of the present invention described above 30 without departing from the spirit and scope of the invention.

Claims (41)

1. A process for upgrading a copper concentrate suitable for smelting, the concentrate including gangue 5 material containing any one or more of iron, uranium, aluminium, silicon or compounds thereof, the concentrate also including at least one of chalcopyrite and bornite, the process including the stages of: a) leaching at least a portion of the gangue 10 material from the concentrate using an acid solution while substantially retaining the chalcopyrite and bornite in solid phase; and b) reacting chalcopyrite or bornite in the concentrate with ionic copper in a metathesis reaction 15 that replaces iron with copper in the chalcopyrite or bornite and forms copper sulphide minerals, wherein said concentrate is upgraded according to both stages a) and b). 20

2. The process according to claim 1, wherein acid leaching gangue material according to stage a) creates conditions in which redox reactions produce copper sulphide minerals from bornite and/or chalcopyrite. 25

3. The process according to claim 2, wherein bornite and/or chalcopyrite are oxidized to copper sulphide minerals.

4. The process according to claim 2, wherein ionic 30 copper is supplied to stage a) which reacts with bornite and/or chalcopyrite to produce copper sulphide minerals by way of reduction reactions or metathesis reactions.

5. The process according to claim 4, wherein a 35 reducing agent is supplied to stage a) so that the reducing agent and ionic copper react with bornite and/or chalcopyrite in a reduction reaction to produce copper H:\Pcabral\Keep\speci\FP19797.Claims.doc 1/08/05 Received 1 August 2005 - 15 sulphide minerals.

6. The process according to claim 5, wherein the reductant supplied to stage a) also reduces ferric ions 5 which in turn facilitates an increased rate of dissolution of iron oxide gangue material.

7. The process according to claim 6, wherein the reductant is any one or a combination of sulphur dioxide, 10 sodium sulphite, or elemental iron or sodium metabisulphite.

8. The process according to any one of claims 1 to 7, wherein the acid solution used in stage a) is a 15 sulphuric acid solution.

9. The process according to claim 8, wherein the concentration of sulphuric acid solution ranges from 20 to 100 g/L. 20

10. The process according to any one of claims 1 to 9, wherein stages a) and b) are carried out consecutively.

11. The process according to claim 10, wherein liquid 25 and solid phases produced in stage a) are at least partially separated in a solid/liquid separator prior to the concentrate being further processed according to stage b). 30

12. The process according to claims 1 to 11, wherein stage a) is carried out at a temperature > 70*C.

13. The process according to any one of claims 1 to 12, wherein the acid solution and the concentrate in stage 35 a) form a slurry whereby the proportion of solids in the slurry ranges from 35 to 60% H:\Pcabral\Keep\speci\FP19797.Claims.doc 1/08/05 Received 1 August zuuD - 16

14. The process according to any one of claims 1 to 13, wherein the concentrate be subjected to leaching in stage a) for at least 4 hours. 5

15 The process according to claim 13, wherein the concentrate is subjected to leaching in stage a) for a period up to 25 hours.

16 The process according to claim 10 or 11, wherein 10 the oxidation-reduction potential (ORP) of the slurry in stage a) is < 380 mV and in stage b) is < 300mV with reference to Ag/AgCl and 3M KCl.

17 The process according to any one of claims 1 to 15 16, wherein stage b) is carried out at a temperature greater than 100 0 C if chalcopyrite is present in the concentrate.

18 The process according to any one of claims 1 to 20 17, wherein the ionic copper is supplied in the form of a copper sulphate solution.

19 The process according to any one of claims 1 to 18, wherein a reducing agent is supplied to stage b) to 25 enhance the substitution of copper ions for iron ions in chalcopyrite and/or bornite minerals.

20 The process according to claim 19, wherein the reducing agent supplied to stage b) is in the form of 30 sulphur dioxide.

21 A plant for upgrading a copper concentrate suitable for smelting, the concentrate including gangue material containing any one or more of iron, uranium, 35 aluminium, silicon or compounds thereof, the concentrate also including at least one of chalcopyrite and bornite, the plant including one or more than one vessel in which H:\Pcabral\Keep\speci\FP19797.Claims.doc 1/08/05 Received I August zUUJ - 17 the following stages may be carried out simultaneously, consecutively or disjunctively: a) leaching at least a portion of the gangue material from the concentrate using an acid solution while 5 substantially retaining the chalcopyrite and bornite in solid phase; and b) reacting chalcopyrite or bornite in the concentrate with ionic copper in a metathesis reaction that replaces iron with copper in the chalcopyrite or bornite and forms 10 copper sulphide minerals, wherein said concentrate is upgraded according to both stages a) and b).

22. The plant according to claim 21, wherein acid 15 leaching gangue material creates conditions in which redox reactions produce copper sulphide minerals from bornite and/or chalcopyrite.

23. The plant according to claim 22, wherein bornite 20 and/or chalcopyrite are oxidized to copper sulphide minerals.

24. The plant according to claim 22, wherein ionic copper is supplied to the or each vessel which reacts with

25. bornite and/or chalcopyrite to produce copper sulphide minerals by way of reduction reactions or metathesis reactions. 25. The plant according to claim 24, wherein a 30 reducing agent is supplied to the or each vessel so that the reducing agent and ionic copper react with bornite and/or chalcopyrite in a reduction reaction to produce copper sulphide minerals. 35

26. The plant according to claim 25, wherein the reductant supplied to the or each vessel also reduces ferric ions which in turn facilitates an increased rate of H:\Pcabral\Keep\speci\FP1 9797 .Claims.doc 1/08/05 % - Receivea I AUgUSt zuU:> - 18 dissolution of iron oxide gangue material.

27. The plant according to claim 26, wherein the reductant is any one or a combination of sulphur dioxide, 5 sodium sulphite, or elemental iron or sodium metabisulphite.

28. The plant according to any one of claims 21 to 27, wherein the acid solution used in stage a) is a 10 sulphuric acid solution.

29. The plant according to claim 28, wherein the concentration of sulphuric acid solution ranges from 20 to 100 g/L. 15

30. The plant according to any one of claims 21 to 29, wherein stages a) and b) are carried out consecutively. 20

31. The plant according to claim 30, further including a solid/liquid separator for separating the liquid and solid phases produced in stage a) prior to the concentrate being further processed according to stage b). 25

32. The plant according to claims 21 to 31, wherein stage a) is carried out at a temperature > 70 0 C.

33. The plant according to any one of claims 21 to 32, wherein the acid solution and the concentrate in stage 30 a) form a slurry whereby the proportion of solids in the slurry ranges from 35 to 60%.

34. The plant according to any one of claims 21 to 23, wherein the concentrate is subjected to leaching in 35 stage a) for at least 4 hours.

35. The plant according to claim 33, wherein the H:\Pcabral\Keep\speci\FP1 9797 .Claims.doc 1/08/05 Received 1 August zuu. - 19 concentrate is subjected to leaching in stage a) for a period up to 25 hours.

36. The plant according to claim 30 or 31, wherein 5 the oxidation-reduction potential (ORP) of the slurry in stage a) is < 380 mV and in stage b) is < 300mV with reference to Ag/AgCl and 3M KCl.

37. The plant according to any one of claims 21 to 10 36, wherein stage b) is carried out at a temperature greater than 100*C if chalcopyrite is present in the concentrate.

38. The plant according to any one of claims 21 to 15 37, wherein the ionic copper is supplied in the form of a copper sulphate solution.

39. The plant according to any one of claims 21 to 38, wherein a reducing agent is supplied to stage b) to 20 enhance the substitution of copper ions for iron ions in chalcopyrite and/or bornite minerals.

40. The plant according to claim 39, wherein the reducing agent supplied to stage b) is in the form of 25 sulphur dioxide.

41. An upgraded concentrate produced by the process or plant described above in any one of the preceding claims. 30 H:\Pcabral\Keep\speci\FP1 9797 .Claims.doc 1/08/05