Leaching copper-containing ores

Abstract

A method of leaching copper-containing ores, such as chalcopyrite ores, with a leach liquor in the presence of silver and an activation agent that activates silver whereby the silver enhances copper extraction from copper ores.

Claims

1. A method of leaching copper-containing ores with a leach liquor including: (a) forming agglomerates by a step selected from (i) mixing together ore fragments and silver in an agglomeration step, (ii) adding silver to ore fragments and then mixing together ore fragments in an agglomeration step, or (iii) forming agglomerates in an agglomeration step and then adding silver to the agglomerates, with the agglomerates having a low added silver concentration of less than 5 g silver per kg copper in the ore in agglomerates, and (b) leaching agglomerates in the presence of an activation agent that activates silver whereby the silver enhances copper extraction from copper ores, with the activation agent being in the form of any one or more than one of chlorides, iodides, bromides, and thiourea.

2. The method defined in claim 1 wherein the leaching is selected from the group consisting of heap, vat, and tank leaching.

3. The method defined in claim 1 includes providing a selected concentration or concentration range of the activation agent in the leach liquor.

4. The method defined in claim 3 wherein the selected concentration or concentration range of the activation agent in the leach liquor results from any one or more of the following positive steps: (a) addition of the activation agent to the leach liquor; (b) removal of the activation agent from the leach liquor; (c) addition of the activation agent in the agglomeration step; (d) mixing different ore types having regard to the activation agent in the ores; (e) selection and mixing/blending of water source/type regard to the activation agent in the ores; and (f) other human-intervention into one or more inputs to the method of leaching that can affect the activation agent concentrations in the method of leaching.

5. The method defined in claim 1 wherein the leaching is carried out in the presence of a low concentration or concentration range of the activation agent.

6. The method defined in claim 5 wherein the leaching is carried out in the presence of a low concentration of chlorides, iodides, and bromides of up to 5 g/L in the leach liquor.

7. The method defined in claim 6 wherein the low concentration of chlorides is greater than 0.8 g/L.

8. The method defined in claim 5 wherein the leaching is carried out in the presence of a low concentration of chlorides of greater than 0.2 g/L.

9. The method defined in claim 5 wherein the leaching is carried out in the presence of a low concentration of thiourea of less than 10 g/L in the leach liquor.

10. The method defined in claim 5 wherein the low concentration of chlorides, iodides and bromides is up to 4 g/L in the leach liquor.

11. The method defined in claim 1 includes adding the activation agent to the leach liquor during the method to maintain a required concentration.

12. The method defined in claim 1 includes leaching a heap of agglomerates with the leach liquor.

13. The method defined in claim 12 wherein heap leaching includes bioleaching with microorganisms to assist leaching of copper.

14. The method defined in claim 12 wherein heap leaching includes controlling heap temperature to be less than 85 C.

15. The method defined in claim 12 includes controlling oxidation potential of the leach liquor during an active leaching phase of heap leaching to be less than 900 mV versus a standard hydrogen electrode.

16. The method defined in claim 12 includes recovering copper from the leach liquor in downstream copper recovery steps.

17. The method defined in claim 16 includes regenerating the leach liquor and recycling the regenerated leach liquor to the heap of agglomerates.

18. The method defined in claim 12 wherein heap leaching includes controlling the heap temperature to be less than 50 C.

19. The method defined in claim 1 wherein the added silver concentration in agglomerates is less than 2 g silver per kg copper in the ore in agglomerates.

20. The method defined in claim 1 wherein the added silver concentration in agglomerates is less than 1 g silver per kg copper in the ore in the agglomerates.

21. The method defined in claim 1 wherein the added silver concentration in agglomerates is less than 0.5 g silver per kg copper in the ore in the agglomerates.

22. The method defined in claim 1 wherein added silver concentration in agglomerates is greater than 0.02 g silver per kg copper in the ore in agglomerates.

23. The method defined in claim 22 wherein the added silver concentration in agglomerates is greater than 0.2 g silver per kg copper in the ore in agglomerates.

24. The method defined in claim 1 includes steps (a)(i) or (a)(ii) and comprises adding the silver in a solution or in a solid form to chalcopyrite ore fragments.

25. The method defined in claim 1 includes forming agglomerates by also mixing microorganisms that can assist leaching of copper.

26. The method defined in claim 1 includes steps (a)(i) or (a)(ii) and comprises adding the silver in a spray or a mist to chalcopyrite ore fragments.

27. The method defined in claim 1 includes steps (a)(i) or (a)(ii) and comprises adding the silver in an aerosol to chalcopyrite ore fragments.

28. A method of leaching copper-containing ores that includes: (a) forming agglomerates of fragments of (i) a copper-containing ore, (ii) silver, (iii) an acid, and (iv) optionally microorganisms, wherein the agglomerate forming step includes any one of (i) mixing together ore fragments and added silver in an agglomeration step, (ii) adding silver to ore fragments and then mixing together ore fragments in an agglomeration step, and (iii) adding silver to the agglomerates after the agglomerates have been formed, and wherein the added silver concentration in the agglomerates is less than 1 g silver per kg copper in the ore in the agglomerates; (b) forming a heap of the agglomerates; (c) leaching the agglomerates in the heap with a leach liquor in the presence of an activation agent that activates silver whereby the silver enhances copper extraction, with the activation agent being any one or more than one of chlorides, iodides, bromides, and thiourea; and (d) recovering copper from the leach liquor.

29. A method of leaching copper-containing ores that includes: (a) forming agglomerates of fragments of (i) a copper-containing ore, (ii) an acid, (iii) optionally silver, and (iv) optionally microorganisms, wherein when addition of silver is required, the agglomerate forming step includes any one of (i) mixing together ore fragments and added silver in an agglomeration step, (ii) adding silver to ore fragments and then mixing together ore fragments in an agglomeration step, and (iii) adding silver to the agglomerates after the agglomerates have been formed, wherein the amount of added silver is determined by taking into account catalyst properties for copper leaching of naturally occurring silver in the ore, and wherein the added silver concentration in the agglomerates is less than 1 g silver per kg copper in the ore in the agglomerates; (b) forming a heap of the agglomerates; (c) leaching the agglomerates in the heap with a leach liquor in the presence of an activation agent that activates silver whereby the silver enhances copper extraction, with the activation agent being any one or more than one of chlorides, iodides, bromides, and thiourea; and (d) recovering copper from the leach liquor.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The present invention is described further with reference to the accompanying Figures, of which:

(2) FIG. 1 illustrates the steps in one embodiment of a method of heap leaching agglomerates of fragments of chalcopyrite ores and silver with a leach liquor containing an activation agent, including any one or more than one of chlorides, iodides, bromides, thiourea and other silver-complexing ligands to activate or mobilise silver in accordance with the present invention;

(3) FIG. 2 is a graph that depicts copper extraction profiles for chalcopyrite-containing ores for a copper leach extraction with chloride addition and/or silver addition; and

(4) FIGS. 3 and 4 are graphs that show copper extraction profiles for chalcopyrite-containing ores for copper leach extractions with thiourea and/or silver addition.

DESCRIPTION OF EMBODIMENT

(5) The following description is in the context of heap leaching agglomerates of copper-containing ore fragments, with the activation agent being added to the leach liquor. However, it is noted that the invention extends to vat and tank leaching copper-containing ores that are in the form of fragments or in the form of agglomerates of fragments. It is also noted that the invention also extends to heap, vat, and tank leaching concentrates of copper-containing ores, with the ore concentrates being in any suitable form, including unagglomerated and agglomerated forms. It is also noted that the activation agent may be present in the method by any suitable option and the invention is not confined to adding the activation agent to the leach liquor. By way of example, the activation agent may be added in an agglomeration step. By way of example, the activation agent may be sprayed or otherwise distributed in a liquid form onto ore fragments or ore concentrates.

(6) With reference to FIG. 1, the following feed materials are transferred to an agglomeration station 3 and are agglomerated as described below:

(7) (a) fragments of chalcopyrite ore that have been crushed to a suitable particle size distribution, identified by the numeral 7 in the Figure;

(8) (b) silver, in this embodiment as a silver solution (but could be in a solid form), typically having an added concentration of silver of less than 5 g silver per kg copper in the ore in the agglomerates, identified by the numeral 9 in the Figure;

(9) (c) an acid, typically sulfuric acid, identified by the numeral 11 in the Figure in any suitable concentration;

(10) (d) microorganisms, identified by the numeral 13 in the Figure, of any suitable type and in any suitable concentration; and

(11) (b) optionally, an activation agent such as silver-complexing ligands including chlorides, iodides, bromides, and thiourea identified by the numeral 15 in the Figure.

(12) The agglomerates produced in the agglomeration station 3 are subsequently used in the construction of a heap 5.

(13) The agglomerates produced in the agglomeration station 3 may be transferred directly to a heap construction site. Alternatively, the agglomerates may be stockpiled and used as required for a heap. The agglomeration station 3 and the heap 5 may be in close proximity. However, equally, the agglomeration station 3 and the heap 5 may not be in close proximity.

(14) The method of agglomerating mined ore fragments illustrated in FIG. 1 is suitable for forming agglomerates that can be used in standard heaps. More specifically, the present invention does not extend to particular shapes and sizes of heaps and to particular methods of constructing heaps from the agglomerates and to particular operating steps of the heap leaching processes for the heaps.

(15) By way of example only, the heap may be a heap of the type described in International publication WO2012/031317 in the name of the applicant and the disclosure of the heap construction and leaching process for the heap in the International publication is incorporated herein by cross-reference.

(16) In a heap leaching operation, copper in the chalcopyrite and other copper-containing minerals in the agglomerates are leached from the agglomerates in the heap 5 via the supply of a leach liquor 23 containing a low concentration, typically up to 5 g/L, typically up to 4 g/L, typically up to 2.5 g/L, typically up to 1.5 g/L, typically up to 1.25 g/L, more typically up to 1 g/L, of any one or more than one activation agent such as silver-complexing ligands including chlorides, iodides, bromides, and thiourea to the leach liquor.

(17) As described above, silver-complexing ligands such as chlorides, iodides, bromides, and thiourea mobilise silver to the chalcopyrite surface and/or enhance the reactivity of the silver on the chalcopyrite surface.

(18) The low concentration of any one or more than one silver-complexing ligands such as chlorides, iodides, bromides, and thiourea may be the result of any one or more of the following positive steps:

(19) (a) addition chlorides, iodides, bromides, and thiourea to the leach liquor, as described above;

(20) (b) removal of chlorides, iodides, bromides, and thiourea from the leach liquor;

(21) (c) addition of chlorides, iodides, bromides, and thiourea in the agglomeration step as described above as an optional step;

(22) (d) mixing different ore types having regard to the soluble chlorides, iodides, bromides, and thiourea s in the ores;

(23) (e) selection and blending/mixing of water source/type regard to the soluble chlorides, iodides, bromides, and thiourea in the ores;

(24) (f) other human-intervention into one or more inputs to the heap leach process that can affect the soluble chlorides, iodides, bromides, and thiourea concentrations in the heap.

(25) The leached copper is recovered from the leach liquor in downstream copper recovery steps 17.

(26) The recovered copper 19 is transferred for further processing and the leach liquor is regenerated in a regeneration circuit 21 and recycled to the heap 5 with make-up leach liquor as may be required as the leach liquor 23.

(27) The chlorides, iodides, bromides, and thiourea may be added to the leach liquor 23 continuously or periodically to maintain the required low concentration in the leach liquor.

(28) The method includes monitoring the concentration of chlorides, iodides, bromides, and thiourea in the leach liquor 23 and adjusting addition rates as may be required to maintain the required low concentration.

(29) The agglomeration station 3 may be any suitable construction that includes a drum, conveyor (or other device) for mixing the feed materials for the agglomerates and agglomerating the feed materials. Mixing and agglomerating the feed materials for the agglomerates may occur simultaneously. Alternatively, mixing the feed materials may be carried out first and agglomerating (for example initiated by the addition of the acid) may be carried out after mixing has been completed to a required extent. Moreover, the timing of adding and then mixing and agglomerating feed materials may be selected to meet the end-use requirements for the agglomerates. For example, it may be preferable in some situations to start mixing fragments of chalcopyrite ores and then adding silver in a solution or in a solid form of silver, acid, and microorganisms progressively in that order at different start and finish times in the agglomeration step. By way of particular example, it may be preferable in some situations to start mixing fragments of chalcopyrite ores and then adding silver in a solution or in a solid form and acid together, and then adding microorganisms at different start and finish times in the agglomeration step.

(30) As noted above, the applicant has carried out: (a) column leach testing to investigate the impact of chlorides and thiourea in leach liquors on bioleaching, i.e. microorganism assisted leaching, of agglomerates of fragments of (a) chalcopyrite ores and (b) silver; and (b) reactor leach testing to investigate the impact of thiourea in leach liquors on leaching of agglomerates of fragments of (a) chalcopyrite ores and (b) silver.

(31) The column and reactor leach tests are described in the Examples below.

(32) 1 Summary

(33) As described above, testwork conducted by a Group company of the applicant has shown that various silver-complexing agents, including chlorides and thiourea, can be used to activate silver (as this term is described above) in, or added to, chalcopyrite ores, and hence, enhance the catalytic effect of silver in the leaching of chalcopyrite.

(34) The testwork has shown that chlorides have a synergistic effect with silver in enhancing copper extraction from chalcopyrite-containing copper ores. This was an unexpected result, as the literature indicates that chloride in a leach liquor would in fact tend to precipitate silver, as silver chloride, and thus, reduce or eliminate the catalytic effect of silver.

(35) The testwork has shown that thiourea is another reagent that has a synergistic effect with silver in enhancing copper extraction from chalcopyrite-containing copper ores through the activation of silver.

(36) It is expected that other complexants, in particular other sulfur containing ligands and silver-complexing ligands, would have the same effect.

(37) Testwork using chloride-containing and thiourea-containing liquors has been conducted in leaching columns. Testwork using thiourea-containing liquor has been conducted in small scale leaching stirred reactors.

(38) 2 Column Testwork

(39) 2.1 Experimental Procedure

(40) Ore samples were crushed to <12 mm, with a P.sub.80 of 9 mm and around 10 kg of this material was added to an agglomerating drum with water and concentrated acid. In tests with added silver, silver nitrate or silver sulfate was dissolved in the water used in agglomeration, and this was added as a mist, being sprayed onto the ore during agglomeration. Once mixed, the agglomerated ore was loaded into 1 m high, 0.1 m diameter columns and allowed to cure for 2-5 days at room temperature before leaching commences. During leaching, the temperature of a column was controlled at 50 C. using a heating jacket and the column was aerated at 0.102 Nm.sup.3/h/t. The column was inoculated with ferrous and sulfur-oxidising microorganisms. An irrigation solution, initially containing around 15 g/L ferric iron as ferric sulfate, 5 to 7 g/L aluminium as aluminium sulfate and 0.1 to 0.5 g/L magnesium as magnesium sulfate, was pumped into the top of the column through drippers, at 10 L/h/m.sup.2, and collected at the base of the column. The pH of the collected leach solution was adjusted to a target pH of 1.2, if required, before recycling back to the top of the column. If the solution copper concentration exceeded 8 g/L, due to copper leaching, the solution was subjected to ion exchange to remove copper and reduce the solution copper concentration to maintain it at less than 8 g/L. The irrigation solution had a total sulfate concentration of between 20 and 80 g/L at the beginning of the leach. If the total sulfate concentration in solution exceeded 120 g/L, due to the addition of sulfuric acid as a consequence of the leaching of gangue minerals, or the oxidation of sulfide minerals, the solution was diluted to maintain a maximum sulfate concentration of 120 g/L. When used, sufficient chloride to achieve a solution concentration of 1 g/L was added to the leach solution as lithium chloride, or sufficient thiourea to achieve a solution concentration of 1 g/L was added to the leach solution.

(41) The composition of the ore used is shown in Table 1. The copper was predominantly present as chalcopyrite. The ore contained 0.5 g Ag/kg Cu as naturally occurring silver.

(42) TABLE-US-00001 TABLE 1 Ore Composition Cu Cu Fe As Ag S.sub.SO4 S.sub.T CuFeS.sub.2 CuS Cu.sub.2S Arsenides (%) (%) (%) (ppm) (%) (%) (%) (%) (%) (%) 1.30 5.0 0.1 7 0.55 5.4 2.4 0.25 0.05 0.38

(43) 2.2 Impact of Chloride Addition with SilverFIG. 2

(44) FIG. 2 shows copper extraction profiles obtained when the ore was leached at 50 C. with a solution having an initial sulfate concentration of 80 g/L. The figure shows that addition of either 0.25 g Ag/kg Cu (to the ore in agglomeration, C296) and/or 1 g/L chloride (to the leach solution, C335) significantly accelerated copper extraction compared to the control test where neither silver nor chloride was added (C274). However, after 100 days, the addition of both 0.25 g Ag/kg Cu and 1 g/L chloride (C334) gave the highest copper extraction, with approximately 87% extraction after 100 dayscompared with approximately 80%, 75% and 60% with chloride, silver, and the control, respectively after the same time period.

(45) 3 Stirred Reactor TestworkFIG. 3

(46) 3.1 Experimental Procedure

(47) Stirred reactor tests were conducted on ore samples that were crushed to 2 mm and agglomerated with 2 kg/t sulfuric acid and the added silver, if being used. The agglomerated ore samples were left to cure for two days prior to being mixed with sufficient solution containing 80 g/L sulfate (liquor composition as described in Section 2.1) to achieve a 10% slurry. This slurry was stirred, and was maintained at 50 C. in a water bath, with the pH and E.sub.h controlled to 1.2 and 700 mV, respectively.

(48) In selected tests, sufficient thiourea to achieve a solution concentration of 1 g/L was added to the leach slurry after two weeks of leaching.

(49) The ore sample used for these tests was the same as in Table 1.

(50) 3.2 Impact of Thiourea with Silver

(51) FIG. 3 shows copper extraction profiles for the copper leach extraction with thiourea and/or silver addition during a 50 days period. The addition of 1.0 g Ag/kg Cu in agglomeration clearly benefited copper extraction (LR024) compared to the control test where neither silver nor thiourea was added (LR029). Addition of 1 g/L thiourea after two weeks of leaching also benefited copper extraction (LR028). The highest copper extraction was achieved when both 1.0 g Ag/kg Cu silver and 1 g/L thiourea were added to the leach (LR025)approximately 98%, compared with approximately 85%, 78% and 45% with silver, chloride, and the control, respectively after the same time period.

(52) 4 Column TestworkFIG. 4

(53) 4.1 Experimental Procedure

(54) The experimental procedure used to generate the results depicted in FIG. 4 is the same as FIG. 2, except that thiourea replaced chloride, a lower initial sulfate solution was used, 20 g/L sulfate (made up with ferric sulfate), and a lower temperature was used, 30 C.

(55) The ore sample used for these tests was the same as that summarized in Table 1.

(56) 4.2 Impact of Thiourea with Silver

(57) FIG. 4 shows that addition of either 0.25 g Ag/kg Cu (to the ore in agglomeration, C276) or 1 g/L thiourea (to the leach solution, C429) only slightly improves copper extraction compared to the control test where neither silver nor thiourea was added (C278)50%, 40% and 37% with thiourea, silver, and the control, respectively after the same time period. However, the addition of both 0.25 g Ag/kg Cu and 1 g/L thiourea (C428) gave the highest copper extractionapproximately 78%. This extraction improvement is significantly above the additive impacts of these additives.

(58) It is evident from the results of the testwork reported in FIGS. 2-4 that the combinations of silver/chloride and silver/thiourea greatly improved leaching of chalcopyrite ores.

(59) Many modifications may be made to the embodiment of the present invention described above without departing from the spirit and scope of the invention.

(60) By way of example, the embodiment is described in relation to FIG. 1 as a series of successive steps with fragments being transferred directly to the agglomeration station 3 and thereafter directly to form a heap 5. The invention is not limited to this embodiment and there may be stockpiling of agglomerates after the station 3. In addition, the station 3 and the heap 5 may not be located in the same area and it may be necessary to transport agglomerates between station 3 and heap 5 that are in different locations.

(61) By way of further example, whilst the embodiment is described in relation to FIG. 1 in the context of mixing ore fragments and silver and forming agglomerates of ore fragments and silver and then forming heaps of the agglomerates, the invention is not so limited and extends to mixing run-of-mine ore and silver and then forming heaps from the run-of-mine ore.

(62) By way of further example, whilst the embodiment is described in relation to FIG. 1 in the context of forming agglomerates by mixing together ore fragments and silver in the agglomeration step, the invention also extends to the following options:

(63) (a) forming agglomerates by adding silver to ore fragments and then mixing together ore fragments in an agglomeration step; and

(64) (b) forming agglomerates of ore fragments in an agglomeration step and then adding silver to the agglomerates.

(65) By way of further example, whilst the embodiment is described in relation to FIG. 1 in the context of forming agglomerates by mixing together ore fragments, silver, acid, and microorganisms in an agglomeration step, the invention is not limited to forming agglomerates with acid and microorganisms. In other words, acid and microorganisms are optional additions in the agglomerates.