Heap leaching

Abstract

A method of leaching chalcopyrite ores includes the steps of forming agglomerates of fragments of chalcopyrite ores and silver and leaching the agglomerates with suitable leach liquor.

Claims

1. A method of leaching chalcopyrite ores includes the steps of: (a) forming agglomerates of fragments of chalcopyrite ores and silver, defined herein as added silver, the agglomeration step including adding silver in a solution as a spray or a mist or in a solid form as an aerosol to the chalcopyrite ore fragments while the fragments are being mixed together; and (b) leaching the agglomerates with suitable leach liquor.

2. The method defined in claim 1 wherein the agglomerates formed in the agglomeration step (a) have a low added silver concentration of less than 2 g silver per kg copper in the ore in the agglomerates.

3. The method defined in claim 1 wherein the agglomeration step (a) includes adding silver to the chalcopyrite ore fragments in the aerosol.

4. The method defined in claim 1 wherein the agglomeration step (a) includes adding silver in the mist or the spray.

5. The method defined in claim 1 wherein the agglomeration step (a) includes forming agglomerates by also mixing together an acid with the chalcopyrite ore fragments and the added silver.

6. The method defined in claim 5 wherein the acid is sulfuric acid.

7. The method defined in claim 1 wherein the agglomeration step (a) includes forming agglomerates by also mixing microorganisms that can assist leaching of copper with the chalcopyrite ore fragments and added silver.

8. The method defined in claim 1 wherein the agglomeration step (a) includes simultaneously mixing and agglomerating fragments and the added silver.

9. The method defined in claim 1 wherein the leaching step (b) is a heap leaching step.

10. The method defined in claim 9 wherein the heap leaching step (b) includes controlling the heap temperature to be less than 75 C.

11. The method defined in claim 10 wherein the heap leaching step (b) includes controlling the heap temperature to be less than 65 C.

12. The method defined in claim 10 wherein the heap leaching step (b) includes controlling the heap temperature to be less than 60 C.

13. The method defined in claim 9 includes controlling the oxidation potential of the leach liquor during an active leaching phase of the step to be less than 700 mV versus the standard hydrogen electrode in the heap leaching step (b).

14. The method defined in claim 1 wherein the agglomerates formed in the agglomeration step (a) have an added silver concentration of less than 1 g silver per kg copper in the ore in the agglomerates.

15. A method of leaching chalcopyrite ores includes the steps of: (a) forming agglomerates of fragments of chalcopyrite ores and silver, defined herein as added silver, wherein the agglomerates formed in the agglomeration step (a) have a low added silver concentration of less than 1 g silver per kg copper in the ore in the agglomerates; and (b) heap leaching the agglomerates with suitable leach liquor, wherein the heap leaching step (b) includes controlling the heap temperature to be less than 75 C.

16. The method defined in claim 15 wherein the added silver concentration in the agglomerates is less than 0.5 g silver per kg copper in the ore in the agglomerates.

17. The method defined in claim 16 wherein the added silver concentration in the agglomerates is less than 0.25 g silver per kg copper in the ore in the agglomerates.

18. The method defined in claim 16 wherein the added silver concentration in the agglomerates is less than 0.125 g silver per kg copper in the ore in the agglomerates.

19. The method defined in claim 16 wherein the added silver concentration in the agglomerates is less than 0.075 g silver per kg copper in the ore in the agglomerates.

20. The method defined in claim 15 wherein the heap leaching step (b) includes controlling the heap temperature to be less than 65 C.

21. The method defined in claim 15 includes controlling the oxidation potential of the leach liquor during an active leaching phase of the step to be less than 700 mV versus the standard hydrogen electrode in the heap leaching step (b).

22. The method defined in claim 15 wherein the heap leaching step (b) includes controlling the heap temperature to be less than 60 C.

23. The method defined in claim 15 wherein the heap leaching step (b) includes controlling the heap temperature to be less than 55 C.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The present invention is described further with reference to the accompanying drawings 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 in accordance with the present invention;

(3) FIG. 2 is a graph of copper extraction versus leaching time for a series of column tests (columns 272, 273, and 288) on agglomerates of fragments of chalcopyrite ores and two different concentrations of silver in accordance with the invention and a comparative example;

(4) FIG. 3 is a graph of the copper grades for five different size fractions in the leach residues in two of the column tests (columns 272 and 273);

(5) FIG. 4 is a graph of the mass (g) of copper in the five different size fractions in the leach residues in two of the column tests (columns 272 and 273);

(6) FIG. 5 is a graph of copper extraction versus leaching time for a series of column tests (columns 272, 273, 288, 294, and 295) on agglomerates of fragments of chalcopyrite ores in accordance with the invention and a comparative example illustrating the effect of varying silver dosages and a comparative example;

(7) FIG. 6 is a graph of copper extraction versus leaching time for a column test (column 296) on agglomerates of fragments of chalcopyrite ores in accordance with the invention illustrating the effect of the addition of silver during the column test;

(8) FIG. 7 is a graph of copper extraction versus leaching time for a series of column tests (columns 272, 273, 288, 294, and 295) on agglomerates of fragments of chalcopyrite ores in accordance with the invention and two comparative examples illustrating the effect of varying sulfate concentration in solution in the column tests;

(9) FIG. 8 is a graph of copper extraction versus leaching time for a series of column tests (columns 273, 288, 310, and 311) on agglomerates of fragments of chalcopyrite ores in accordance with the invention and two comparative examples illustrating the effect of different particle sizes in the columns; and

(10) FIG. 9 is a graph of copper extraction versus leaching time for a series of column tests (columns 273, 276, 277, 288, 299, and 300) on agglomerates of fragments of chalcopyrite ores in accordance with the invention and two comparative examples illustrating the effect of silver additions at different temperatures in the columns.

DESCRIPTION OF EMBODIMENT

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

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

(13) (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;

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

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

(16) The agglomerates produced in the agglomeration station 3 are subsequently used in the construction of a heap 5, and 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 suitable leach liquor, and the leached copper is recovered from the leach liquor in downstream copper recovery steps and the leach liquor is regenerated and recycled to the heap to leach more copper from the chalcopyrite and other copper-containing minerals in the agglomerates in the heap.

(17) 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.

(18) 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.

(19) 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.

(20) 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.

(21) The applicant has found that adding silver as a solution in a fine mist or spray or as solid particles in an aerosol to fragments of chalcopyrite ores as the ore fragments are being mixed in a suitable mixer, such as a drum mixer, is a particularly suitable way of achieving a desirable dispersion of silver on the ore fragments.

(22) The selection of a mist/spray/aerosol as a medium for adding silver to the chalcopyrite ore fragments makes it possible to maximise the delivery of a small concentration of the silver to a substantially larger mass (and large surface area) and to a substantial proportion of the chalcopyrite ore fragments.

(23) The work carried out by the applicant indicates that adding silver as a fine mist or spray or aerosol facilitates interaction of silver with surfaces of chalcopyrite minerals within ore fragments. Moreover, the applicant believes at this point that dispersing silver to surfaces of chalcopyrite minerals during the agglomeration process makes it possible to achieve high copper recoveries with very low concentrations of added silver compared to the copper concentrations in chalcopyrite ore fragments, that is, g Ag per kg of Cu in the ore fragments, and the very low mass of added silver compared to the overall mass of the agglomerates of chalcopyrite ore fragments and the other feed materials.

(24) In a situation where the mixing is carried out separately, the mixing may include subjecting fragments to impact forces that cause breaking of at least a portion of the fractured fragments. International application PCT/AU2014/000648 in the name of the applicant describes an apparatus for subjecting fragments to impact forces and the disclosure in the specification of the International application is incorporated herein by cross-reference.

(25) The applicant has carried out column leach testing to investigate the impact on bioleaching, i.e. microorganism assisted leaching, of agglomerates of fragments of chalcopyrite ores where the agglomerates contain low concentrations of silver as part of the agglomerates. The column leach tests are described in Examples 1 and 2 below.

Example 1

(26) A selection of the column tests on the following three different agglomerates are described below and the copper extraction results of the column tests are reported in FIGS. 2-4 and in Table 2 below. The experimental procedure is detailed below and the ore composition provided in Table 1.

(27) 1. Experimental Procedure

(28) Ore samples were crushed to <12 mm, with a P.sub.80 of 9 mm (unless specified otherwise) 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 was dissolved in the water prior to agglomeration, and this was added as a mist, 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 commenced.

(29) During leaching, the temperature of the columns was controlled using a heating jacket and the column was aerated at 0.102 Nm.sup.3/h/t. The column was inoculated with ferric ions and sulfur-oxidising microorganisms and the irrigation solution, which can vary from 5-20 g/L ferric iron as ferric sulfate, was pumped into the top of the column through drippers, at 0.079 L/h, and collected at the base of the column.

(30) The pH of the collected leach solution was adjusted to the target of pH 1.2 if required before recycling back to the top of the column.

(31) 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.

(32) 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 leaching of gangue minerals, the solution was diluted to maintain a maximum of 120 g/L sulfate.

(33) The composition of the ore used is shown in Table 1.

(34) TABLE-US-00001 TABLE 1 Ore Composition Cu Cu Fe As S.sub.SO4 S.sub.T CuFeS.sub.2 CuS Cu.sub.2S Arsenides (%) (%) (%) (%) (%) (%) (%) (%) (%) 1.30 5.16 0.076 0.55 5.55 2.1 0.25 0.04 0.37
2. Copper Extraction with and without Added Silver Column 273a control columnwith no added silver in agglomerates of fragments of chalcopyrite ores. Column 272example of the inventionagglomerates of (a) fragments of chalcopyrite ores and (b) 1 g silver added as silver nitrate solution per 1 kg copper in the ore. Column 288example of the inventionagglomerates of (a) fragments of chalcopyrite ores and (b) 0.25 g silver added as silver nitrate solution per 1 kg copper in the ore.

(35) The concentrations of chalcopyrite and other copper-containing minerals in the ores in columns 272 and 273 are set out in Table 2. It is evident from Table 2 that chalcopyrite was the main copper-containing mineral and there were also reasonably significant concentrations of chalcocite/digenite/covellite and enargite.

(36) Therefore, having regard to the above, the only significant difference between the agglomerates in the column tests was the silver concentrations.

(37) FIG. 2 is a graph of copper extraction versus leaching time for columns C272, C273, and C288.

(38) FIG. 2 shows that the addition of low concentrations of silver to the agglomerates of fragments of chalcopyrite ores had a significant impact on (a) copper extraction and (b) the leach times to achieve high copper extractions.

(39) For example, with reference to FIG. 2, it can be seen that after 100 days of leaching (under the same leach conditions), nearly 90% of the copper was leached from the agglomerates in column C288 having 0.25 g silver per kg copper in the agglomerates and only approximately 67% of the copper was leached from the agglomerates in control column C273. It is clear that the low silver concentration in the C288 column had a significant impact on copper extraction. Taking into account the additional cost of the silver, the applicant believes that the use of silver provides a considerable economic benefit.

(40) It is also evident from FIG. 2 that the significant difference in copper extraction after 100 days leach time noted in the preceding paragraph was maintained as the leach time increased to the end of the column tests at 200 days.

(41) It is also evident from FIG. 2 that the leaching rate was faster with the C272 and C288 columns in accordance with the invention compared to that for the control column C273. This finding further reinforces the potential economic advantages arising from the addition of silver to the agglomerates.

(42) FIGS. 3 and 4 provide further data on copper extractions from the agglomerates in column C272 in accordance with the invention and the control column C273.

(43) FIG. 3 provides the copper grades for five different size fractions in the leach residues for columns C272 and C273.

(44) FIG. 4 provides the mass (g) of copper in the five different size fractions in the leach residues for columns C272 and C273.

(45) FIGS. 3 and 4 show that there were significantly lower copper grade and copper mass in each of the column C272 residue size fractions compared to the corresponding control column C273 size fractions, particularly in the finer fractions, i.e. 4 mm.

(46) Finally, Table 2 below compares copper extractions achieved from each of the copper-containing minerals in column C272 in accordance with the invention and control column C273.

(47) The feed ore column in Table 2 shows that only about 60 wt. % of the copper in the feed ore was in the form of chalcopyrite (with a total copper concentration of 1.3 wt. %).

(48) It is evident from Table 2 that silver in the agglomerates made it possible to remove 94.8 wt. % of the copper in the chalcopyritecompared with only 69.7 wt. % of the copper in the chalcopyrite in the control column C273.

(49) It is also evident from Table 2 that silver also had a beneficial impact on the leaching of other copper-containing minerals, including chalcocite/digenite, enargite and other copper minerals.

(50) TABLE-US-00002 TABLE 2 Residue at the end of Leach Period Copper Extraction Copper Feed Ore C272 C273 C272 C273 Mineral Cu Mass (%) Cu, % Chalcocite/ 0.028 0.001 0.006 95.2 79.5 Digenite Covellite 0.167 0.001 0.004 99.4 99.5 Cu Oxides 0.03 0.003 0.003 89.7 89.5 Chalcopyrite 0.712 0.055 0.212 92.6 71.5 Enargite 0.22 0.052 0.113 77.5 51.0 Other Cu 0.03 0.004 0.008 85.7 70.9 Minerals Cu Clays 0.001 0.0001 0.0001 95.5 92.7

(51) In summary, the column tests reported above show that the addition of silver to agglomerates of fragments of chalcopyrite ores, particularly low concentrations of silver, has a significant positive impact on copper recoveries from chalcopyrite minerals in the agglomerates and leach times.

Example 2

(52) Another selection of the column tests on the different agglomerates are described below and the copper extraction results of the column tests are reported in FIGS. 5-9 and in Table 3 below. The composition of the ore used for these tests is shown in Table 1 and the experimental procedure for these tests is as described in Example 1.

(53) 1. Silver Dosage

(54) The following five column leach tests were carried out and the results of the leach tests are presented in FIG. 5 and summarised in Table 3: Column 273a control columnwith no added silver in agglomerates of fragments of chalcopyrite ores. Column 295example of the inventionagglomerates of (a) fragments of chalcopyrite ores and (b) 0.0625 g silver added as silver nitrate solution per 1 kg copper in the ore. Column 294example of the inventionagglomerates of (a) fragments of chalcopyrite ores and (b) 0.125 g silver added as silver nitrate solution per 1 kg copper in the ore. Column 288example of the inventionagglomerates of (a) fragments of chalcopyrite ores and (b) 0.25 g silver added as silver nitrate solution per 1 kg copper in the ore. Column 272example of the inventionagglomerates of (a) fragments of chalcopyrite ores and (b) 1 g silver added as silver nitrate solution per 1 kg copper in the ore

(55) In FIG. 5, copper extraction with time is shown with the varying silver dosages in the five column leach tests. At all silver dosages tested, there was a significant improvement in copper extraction compared to leaching without silver.

(56) Table 3 summarises the final copper and chalcopyrite extractions obtained from the five column leach tests.

(57) TABLE-US-00003 TABLE 3 Column Test Summary for Varying Silver Dosage Column tests conducted at P.sub.80 9 mm, 50 C., pH 1.2. Chalcopyrite Extractions were determined by Scanning Electron Microscope. Leach Cu Chalcopyrite Silver Dosage Time Extraction Extraction Column # (g Ag/kg Cu) (days) (%) (%) C273 0.0 200 73.9 71.5 C295 0.0625 280 81.7 74.7 C294 0.125 244 81.8 77.3 C288 0.25 200 84.2 84.3 C272 1.0 200 91.1 92.6

(58) 2. Silver Addition Method

(59) In other column tests, extra silver was added later in the leach by adding it to the irrigation solution. This was conducted first using silver chloride (0.04 g Ag/kg Cu), and later using a silver thiourea solution (0.25 g Ag/kg Cu). The results of one of these column leach tests (column 296), including details of the column, is shown in FIG. 6. This Figure shows copper extraction versus time. No increase in the copper extraction rate was observed after either addition, as shown in FIG. 6. But it does show an approximately 6% increase after the AgCl addition. This demonstrates that the application method of silver to the ore during agglomeration is far more effective than adding silver to the leach solution.

(60) 3. Effect of Other Leach Variables

(61) In other column leach tests, the effect of sulfate concentration in solution was investigated. FIG. 7 is a graph of copper extraction versus sulfate concentration in solution in these column leach tests, with the Figure including details of the columns. In FIG. 7 it is evident that even with varying solution composition (i.e. variations in sulfate salt concentration), silver addition benefits copper extraction. It is noted that that the sulfate concentration stated is the value at the beginning of the leach. Solution collected at the base of the column contained a higher sulfate concentration due to leaching of gangue minerals, and this solution is recycled as leach liquor. The total sulfate concentration was allowed to increase to a maximum of value of 120 g/L over the course of the leach.

(62) In other column leach tests, the effect of different particle size distributions was investigated. FIG. 8 is a graph of copper extraction versus time for these column leach tests, with the Figure including details of the columns. FIG. 8 shows that silver addition benefits copper extraction from ore at different particle size distributions (P.sub.80 of 9 mm and 25 mm).

(63) In other column leach tests, the effect of temperature was investigated. FIG. 9 is a graph of copper extraction versus time for these column leach tests, with the Figure including details of the columns. FIG. 9 shows that silver addition is beneficial to copper extraction at a range of temperatures. In fact, when leaching at 40 C. with 0.25 g Ag/kg Cu, the copper extraction rate was very similar to leaching at 50 C. without silver. This shows that silver addition is an effective alternative to increasing temperature as a means of accelerating copper extraction.

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

(65) 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.

(66) 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.

(67) 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:

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

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

(70) 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.