Microbial-assisted Heap Leaching

Abstract

Microbial-assisted heap leaching of fragments or agglomerates of fragments of copper-containing sulfidic ores, such as chalcopyrite ores, and copper-containing sulfidic waste materials is disclosed. A heap leaching method includes controlling the sulfate concentration in a leach liquor. When heap leaching includes using agglomerates, a method of forming agglomerates includes adding the feed materials at, or close to, the inlet end, typically no more than 40%, typically no more than 30%, more typically no more than 20%, of the length from the inlet end of the agglomeration unit.

Claims

1. A method of microbial-assisted heap leaching of base metal-containing sulfidic ores or base metal-containing sulfidic waste materials which includes: supplying an acidic leach liquor containing sulfate to a heap of fragments of base metal-containing sulfidic ores or base metal-containing sulfidic waste materials or agglomerates of fragments and allowing the leach liquor to flow through the heap and leach base metal from fragments, collecting leach liquor from the heap, and processing collected leach liquor and recovering base metal from the leach liquor, with any one or more of the fragments, agglomerates of the fragments (when present), and the leach liquor containing microbes, and the method controlling a sulfate concentration in the leach liquor so that it does not exceed a threshold sulfate concentration.

2. The method defined in claim 1 includes monitoring the sulfate concentration in the leach liquor collected from the heap and controlling the method, as required, so that the sulfate concentration in the leach liquor does not exceed the threshold concentration.

3. The method defined in claim 1 includes indirectly controlling a parameter other than sulfate concentration that influences the sulfate generation rate, such that changing the parameter causes a known change to the sulfate concentration.

4. The method defined in claim 1 wherein the threshold sulfate concentration is 170 g/L sulfate in a leach liquor collected from the heap.

5. The method defined in claim 1 wherein the threshold sulfate concentration is at least 20 g/L in a leach liquor collected from the heap in a start-up stage of the method.

6. The method defined in claim 1 wherein the threshold sulfate concentration is 50-100 g/L in a leach liquor collected from the heap in a later post-start-up leaching stage of the method.

7. The method defined in claim 1 includes controlling the temperature of the heap to be less than 85 C.

8. The method defined in claim 1 includes an agglomeration step for forming agglomerates of fragments of copper-containing sulfidic ores or copper-containing sulfidic waste materials for subsequent heap leaching in the method.

9. A method of forming agglomerates for heap leaching base metal-containing sulfidic ores or base metal-containing sulfidic waste materials that includes agglomerating crushed fragments of base metal-containing sulfidic ores or base metal-containing sulfidic waste materials and other feed materials in an agglomeration unit having an inlet end and an outlet end configured to move material along a length of the agglomeration unit from the inlet end to the outlet end, with the method, including adding the feed materials at, or close to, the inlet end.

10. The method defined in claim 9 includes adding the feed materials a short distance along the length of the agglomeration unit, typically no more than 40%, typically no more than 30%, more typically no more than 20%, of the length from the inlet end of the agglomeration unit.

11. The method defined in claim 9 includes substantially completing formation of agglomerates a short distance along the length of the agglomeration unit, typically no more than 40%, of the length from the inlet end of the agglomeration unit.

12. The method defined in claim 1 wherein, when the base metal is copper, the other feed materials include combinations selected from: (a) silver with catalyst properties to enhance leaching of copper from copper-containing sulfidic ores or copper-containing sulfidic waste materials, (b) sulfuric acid, (c) microbes to oxidise ferrous ions and oxidise solid and soluble sulfur compounds, thereby regenerating ferric ions and protons, (d) optionally, an activation agent to activate silver, selected from thiourea, chlorides, bromides and iodides, (e) optionally, a complexing additive agent to enhance the dissolution of copper from copper minerals in the ores or waste materials by forming a complex between (i) sulfur, that has originated from copper minerals in the ores, and (ii) the additive, (f) pyrite or elemental sulfur to provide a source of ferrous ions (pyrite), acid and heat (both pyrite and elemental sulfur), and (g) one or more of water and/or other water sources, pregnant leach solution from a heap leaching operation, a raffinate formed in a solvent extraction operation on pregnant leach solution.

13. A microbial-assisted heap leaching operation for base metal-containing sulfidic ores or base metal-containing sulfidic waste materials, the heap leaching operation comprising: (a) a heap of fragments of the base metal-containing sulfidic ores or base metal-containing sulfidic waste materials, and microbes; and (b) a system that (i) supplies an acidic leach liquor containing sulfate to the heap so that the leach liquor flows downwardly though the heap and leaches base metal from the base metal-containing sulfide-containing sulfidic ores or base metal-containing sulfidic waste materials, (ii) collects a pregnant leach liquor containing base metal in solution from the heap, with the microbes oxidising ferrous iron to ferric iron, and (iii) controls the system so that the sulfate concentration in the leach liquor does not exceed a threshold concentration.

14. The heap leaching operation defined in claim 13 wherein when the base metal is copper and the fragments are in the form of agglomerates of fragments, the agglomerates comprise: (a) silver with catalyst properties to enhance leaching of copper from copper-containing sulfidic ores or copper-containing sulfidic waste materials, (b) an acid, (c) optionally, an activation agent to activate silver, selected from thiourea, chlorides, bromides and iodides, (d) optionally, a complexing additive agent to enhance the dissolution of copper from copper minerals in the ores or waste materials by forming a complex between (i) sulfur, that has originated from copper minerals in the ores or waste materials, and (ii) the additive, (e) pyrite or elemental sulfur to provide a source of ferrous ions (pyrite), acid and heat (pyrite and elemental sulfur); and (f) water and/or other water sources and/or a pregnant leach solution from a heap leaching operation or a raffinate formed in a solvent extraction operation on pregnant leach solution.

15. A heap of base metal-containing sulfidic ores or base metal-containing sulfidic waste material configured for a microbial-assisted heap leaching operation, the heap comprising: a support surface, a layer of granular material located on the support surface, a layer of base metal-containing sulfidic ores or base metal-containing sulfidic waste materials located on the granular material layer, an irrigation system configured to supply a solution through the granular layer, a collection system configured to collect a pregnant leach liquor containing base metal in solution from the heap, an aeration system configured to blow air to react with the layer of base metal-containing sulfidic ores or base metal-containing sulfidic waste, and a control system to monitor and change one or more operating parameters to maintain a predetermined sulfate concentration.

16. (canceled)

Description

DESCRIPTION OF THE DRAWINGS

[0308] The invention is described further with reference to the accompanying drawings of which:

[0309] FIG. 1 illustrates the steps of a method of microbial-assisted heap leaching agglomerates of fragments of copper-containing sulfidic ores that contains chalcopyrite (CuFeS.sub.2), enargite (Cu.sub.3AsS.sub.4), tetrahedrite (Cu,Fe,Zn,Ag.sub.12Sb.sub.4S.sub.13), tennantite (Cu.sub.12As.sub.4S.sub.13), chalcocite (Cu.sub.2S), covellite (CuS), bornite (CusFeS.sub.4) or any combination thereof, or other copper containing sulfide minerals, with a leach liquor in accordance with an embodiment of the invention,

[0310] FIG. 2 is a schematic diagram of an agglomeration unit for producing agglomerates of fragments of copper-containing sulfidic ores in accordance with an embodiment of the invention,

[0311] FIG. 3 is a graph of microbe count versus sulfate concentration for microbes in pregnant leach liquor and on solids which shows the effect of solution sulfate concentration on the cell population in solution and on ore solids for a 50 C. moderate thermophile microbes,

[0312] FIG. 4 is a graph of microbe count versus sulfate concentration for microbes which shows the maximum bacterial cell concentration vs sulfate concentration for 60 C. extreme thermophile microbes,

[0313] FIG. 5 is a graph of copper extraction versus time with leach solutions having different sulfate concentrations which shows the effect of starting solution sulfate concentrations (first value in the legend) and maximum sulfate operating level (second value) on copper extraction from a primary copper sulfide dominant ore in a column test operated at 60 C.,

[0314] FIG. 6 is a graph of ferric to ferrous ratio versus time for columns inoculated with adapted inoculum solution (C218) and adapted inoculum slurry during agglomeration (C227); and

[0315] FIG. 7 is a graph of ferric to ferrous ratio for columns inoculated with adapted inoculum solution (C221) and adapted inoculum slurry during agglomeration (C226).

DESCRIPTION OF EMBODIMENT

[0316] The following description is in the context of heap leaching agglomerates of fragments of copper-containing sulfidic ROM material in the form of ores.

[0317] The following description is in the context of microbial-assisted heap leaching copper-containing sulfidic ores with a leach liquor.

[0318] The flow sheet of FIG. 1 shows the steps in one embodiment of a method of microbial-assisted heap leaching agglomerates of fragments of copper-containing sulfidic ores that contain chalcopyrite and/or enargite with a leach liquor.

[0319] With reference to FIG. 1, copper-containing sulfidic ROM ores 5, such as ore containing chalcopyrite and/or enargite, from a mine 3 is crushed in a crusher 7. The ore is crushed to fragments having a suitable particle size distribution for downstream processing of the fragments. Crushed ore fragments 9 are transferred to an agglomeration unit 11 and formed into agglomerates 25 of fragments of crushed copper containing ore. The agglomerates 25 are transferred to a heap 27. A leach liquor 39 is supplied to an upper surface of the heap 27 and allowed to percolate through the heap 27 and take copper into solution. A pregnant leach liquor 29 containing copper in solution is collected from the heap and processed in a copper recovery circuit 31. The circuit 31 may be a solvent extraction and electrowinning circuit. A copper product 33 is produced in the circuit 31. A spent leach liquor 35, i.e., a raffinate in situations where the circuit 31 is a SX circuit, is transferred to a regeneration circuit 37. Any one or more of water, acid, microbes, and other additives are added as required to produce a regenerated leach liquor 39, which is returned to the heap 27.

[0320] With reference to FIGS. 1 and 2, in this embodiment, the following feed materials are transferred to the agglomeration unit 11 and are mixed together and form agglomerates in the unit 11, with the feed materials being added at, or close to, an inlet of the unit 11 and forming agglomerates a short distance along the length of the unit, typically within 40% of the length of the unit 11: [0321] (a) the above-mentioned crushed fragments 9 of copper-containing sulfidic ores, [0322] (b) silver 13 with catalyst properties to enhance leaching of copper from copper-containing sulfidic ores, in this embodiment provided 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, where added concentration means the concentration of silver in addition to the concentration of naturally occurring silver in the ores, [0323] (c) acid 15, typically sulfuric acid in any suitable concentration, [0324] (d) microbes 17 of any suitable type and in any suitable concentration to oxidise ferrous ions and oxidise solid and soluble sulfur compounds, thereby regenerating ferric ions and protons, [0325] (e) an activation agent 19 for silver, typically thiourea, chlorides, bromides or iodides, [0326] (f) an additive 21 to enhance the dissolution of copper from copper minerals in the ores by forming a complex between (a) sulfur, that has originated from copper minerals in the ores, and (b) the additive, [0327] (g) pyrite 23 (or any other suitable material) to provide a source of ferrous ions and heat, in this embodiment, is tailings-derived pyrite-containing concentratetypically a concentration range of 1-20% pyrite in the agglomerates 25, and [0328] (h) water from any suitable water source (not shown).

[0329] As is described further below, the feed materials may be added at the same time or in any suitable order.

[0330] Typically, the microbes are added last.

[0331] In some embodiments, the microbes are added last and furthest from the inlet of the agglomeration unit 11.

[0332] It is noted that the invention is not confined to the use of all of the above additives.

[0333] In addition, it is noted that the invention extends to the use of other additives.

[0334] For example, an optional additive is a surfactant to facilitate contact of additives with solids.

[0335] The agglomeration unit 11 may be any suitable agglomeration unit, such as a drum having an inlet end and an outlet end that is mounted at an inclined angle for rotation about an elongate axis of the drum with the inlet at a higher level than the outlet so that the material added to the drum tends to move downwardly along the drum to the outlet.

[0336] The above-mentioned agglomeration unit feed materials, namely crushed ore fragments 9, silver 13, acid 15, microbes 17, activation agent 19, and complexing additive 21, pyrite 23 and water (as requiredtypically raffinate or fresh water) are added at or close to the inlet end of the agglomeration unit 11, typically no more than 40%, typically no more than 30%, more typically no more than 20%, along the length of the drum.

[0337] Typically, the above addition of feed material results in substantially complete formation of agglomerates a short distance, typically no more than 40%, along the length of the drum.

[0338] In one embodiment, the addition order along a section of the length of the agglomeration unit 3 is as follows: [0339] a mixture of ore/waste material fragments and silver nitrate (or other suitable form of silver), [0340] then water, typically in a raffinate but could be fresh water, [0341] then acid, optionally at multiple locations, [0342] then, pyrite or elemental sulfur, [0343] then, microbes.

[0344] The addition order may be varied, as required. For example, pyrite and microbes may be added together in the agglomeration unit 3.

[0345] The agglomeration unit feed materials may be added to the agglomeration unit 11 in any suitable way.

[0346] For example, silver 13 may be added as a solution in a fine mist or spray or as solid particles in an aerosol. The applicant has found that this is a particularly suitable way of achieving a desirable dispersion of silver on the ore fragmentssee International publication WO2017/070747 in the name of the applicant and the disclosure is incorporated herein by cross-reference. 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 (or other copper sulfide minerals) ore fragments.

[0347] The agglomeration unit feed materials may be added to the agglomeration unit 11 in any suitable concentrations having regard to a range of factors including, for example, mineralogy of the ore, the particle size distribution of the ore fragments, the dimensions (length and diameter of the drum), the target throughput for the agglomeration unit 3, the anticipated attrition of agglomerates in the drum, and the required mechanical properties of the agglomerates.

[0348] For example, the complexing additive 21 may be added to the drum or to the leach liquor 39 in concentrations up to 10 g/L, up to 5 g/L, up to 2.5 g/L, up to 1.5 g/L, up to 1.25 g/L, or up to 1 g/L, in the leach liquor. When the additive is a polymer-like additive, such as longer chain organic substances, such as polyethyleneimine (PEI), it may be preferred to add the additive while forming agglomerates in the agglomeration station 3 rather than adding the additive to leach liquor.

[0349] Mixing and agglomerating the feed materials for the agglomerates 25 may occur simultaneously.

[0350] Alternatively, mixing the feed materials may be carried out first and agglomerating (for example initiated by the addition of the acid 15) may be carried out after mixing has been completed to a required extent.

[0351] Moreover, the timing of adding and then mixing and agglomerating feed materials may be selected to meet the end-use requirements for the agglomerates 25. For example, it may be preferable in some situations to start mixing fragments containing chalcopyrite 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 containing chalcopyrite 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.

[0352] The feed materials may be added at the same location or at different locations along the short distance along the length of the agglomeration unit, typically no more than 40%, of the length from the inlet end of the agglomeration unit. For example, typically acid 15 is added at one location and microbes 17 are added at another location further along the length of the agglomeration unit to minimise impact of acid on microbes. By way of further example, pyrite 23 is added close to the end of the short distance so that pyrite is more likely to form on exposed surfaces of the agglomerates 25. In addition, there may be multiple locations for adding portions of the same additive.

[0353] Some of the additives may be premixed with ore just prior to agglomeration. This provides more thorough mixing. In one example, ore is mixed with pyrite concentrate thickener underflow slurry ahead of agglomeration.

[0354] The agglomerates 25 produced in the agglomeration unit 11 may be transferred directly to a construction site for the heap 27. Alternatively, the agglomerates 25 may be stockpiled and used as required for the heap 27for example, added to successive lifts of the heap 27. The agglomeration unit 11 and the heap 27 are typically in close proximity. However, this is not essential and may not be the case.

[0355] The method of agglomerating mined ore fragments described above is suitable for forming agglomerates that can be used in standard heaps.

[0356] The invention is not confined 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.

[0357] By way of example only, the heap 27 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.

[0358] The heap 27 may be any suitable heap construction and is provided with: [0359] (a) a leach liquor storage and delivery system to supply leach liquor 39 to an upper surface of the heap; [0360] (b) a pregnant leach liquor collection system for collecting leach liquor 29 containing copper in solution that is extracted from copper sulfide-containing materials in agglomerates 25 in the heap 27; and [0361] (c) additional microbes (such as bacteria or archaea) or other suitable oxidants to oxidise ferrous iron to ferric iron, with the ferric iron and protons breaking down the mineral matrix and solubilising copper.

[0362] In one example, the heap 27 comprises a support surface, a layer of granular material comprising crushed rock having a P80 particle size ranging from 30 mm to 2000 mm and a layer of chalcopyrite-containing feed material. The purpose of the crushed rock is to allow drainage of leach liquor. The feed material comprises the above-described agglomerates. The feed material may also comprise tailings produced by processing of the chalcopyrite feed material in another copper-recovery method.

[0363] The layer of chalcopyrite-containing feed material forms an initial lift of feed material to be leached.

[0364] In use, when leaching of the initial lift reaches a selected point, a new layer of the feed material is added to the heap to form a new lift that is subsequently leached, and so on.

[0365] An aeration system located on the support surface is used to blow ambient air through each lift at or near the base of the first lift and optionally at the base of subsequent lifts to react with the feed material. In addition, an irrigation system located on top of the heap is configured to supply an irrigation solution which can include nutrients for the microbes and pyrite to facilitate the leaching process and to maintain the heap at a temperature ranging from 40-70 C.

[0366] A control system monitors and changes one or more operating parameters to maintain a predetermined sulfate concentration in the leach liquor. The operating parameters may be controlled to ensure that the sulfate concentration in the leach liquor does not exceed a threshold concentration of 170 g/L sulfate in leach liquor collected from the heap. The irrigation solution may be dosed with a carbon source such as carbon dioxide, carbonate, or yeast. A cover comprised of a plastic sheet or a biofilm may be applied on top of the heap to reduce air and heat loss and minimise temperature gradient across the heap.

[0367] A drainage system is also installed on the support surface to avoid phreatic build up.

[0368] The heap operation includes controlling the operation so that the sulfate concentration in the leach liquor does not exceed a threshold concentration.

[0369] As noted above, the applicant has found that it is possible to operate a microbially-assisted heap leach of agglomerates of fragments of copper-containing sulfidic ores or copper-containing sulfidic waste materials with high sulfate concentrations in the acidic leach liquor.

[0370] The sulfate concentration can be controlled in a number of ways.

[0371] One way is to control the aeration rate of the heap. Doing so regulates the amount of oxygen into the heap and consequently, the amount of oxygen supplied to the microbes. The aeration rate was controlled to provide a microbial population that is sufficient to ensure that the leach liquor collected from the heap does not exceed a threshold concentration of 170 g/L sulfate.

[0372] The above finding is indicated by the results of experimental work summarised in FIGS. 3 to 7.

[0373] FIG. 3 is a graph of microbe count versus sulfate concentration for microbes in pregnant leach liquor and on solids which shows the effect of solution sulfate concentration on the cell population in solution and on ore solids for 50 C. moderate thermophile microbial cultures, typically containing up to 20 different species of microbes. The Figure, noting the logarithmic y-axis shows that the cell count for this culture declined more slowly with increasing sulfate concentration for microbes on solids. There was a steeper decline in cell count for microbes in pregnant leach liquor. This indicates that microbes attached to solids are more sulfate tolerant than microbes in solution. Attachment of microbes on solids is important in terms of maintaining high enough cells count at higher sulfate concentrations to enable heap leaching to take place at commercially practical rates.

[0374] FIG. 4 is a graph of microbe count versus sulfate concentration for microbes which shows the maximum bacterial cell concentration vs sulfate concentration for a 60 C. extreme thermophile microbial culture. The FIG. 4 culture has a higher cell in solution population over the entire sulfate concentration range compared to the FIG. 3 culture. Comparing Figures, and taking into account that tests were done using differing samples and growth techniques, shows that the cells in solution of FIG. 4 are more sulfate tolerant than the 50 C. cells in solution of FIG. 3.

[0375] FIG. 5 is a graph of copper extraction versus time in column tests operated on a chalcopyrite dominant copper ore at 60 C. using an extremely thermophilic microbial culture with leach solutions having different starting (first value in the legend) and maximum operating level (second value) sulfate concentrations. Similar high copper extractions (86-89%) were achieved for all three tests. The results demonstrate the excellent performance of this culture over a broad sulfate operating range and high sulfate threshold concentrations.

[0376] FIG. 6 is a graph of ferric to ferrous ratio versus time for columns operated on a copper ore inoculated with adapted inoculum solution (C218) and adapted inoculum solution plus slurry added during agglomeration (C227). The columns were leached with a ferric iron containing starting solution. The ferric to ferrous ratio declined initially due to reaction of ferric with sulfide minerals, followed by a lag period, after which the ferric to ferrous ratio increased rapidly due to the onset of high microbial activity. The column inoculated with adapted inoculum solution plus slurry exhibited a shorter lag period, indicative of high microbial activity occurring sooner, than in the column inoculated with adapted inoculum solution.

[0377] FIG. 7 is a graph of ferric to ferrous ratio for another set of columns operated on a different copper ore, inoculated with adapted inoculum solution (C221) and adapted inoculum slurry during agglomeration (C226). The results obtained were similar to those depicted in FIG. 6.

[0378] Many modifications may be made to the embodiment of the invention as described above with reference to the Figures without departing from the spirit and scope of the invention.

[0379] By way of example, whilst the embodiment is described in the context of intermediate processing of fragments of copper-containing sulfidic ROM ores 5 by crushing and then agglomerating in the crusher 7 and the agglomeration unit 15, the invention also extends to other intermediate processing steps, such as grade sorting or size separation (for example on screens).

[0380] By way of example, whilst the embodiment is described in the context of heap leaching agglomerates of fragments of copper-containing sulfidic ROM material in the form of ores, the invention also extends to heap leaching non-agglomerated ore fragments.

[0381] By way of example, whilst the embodiment is described in the context of heap leaching agglomerates of fragments of copper-containing sulfidic ROM material in the form of ores, the invention also extends to heap leaching agglomerated or non-agglomerated fragments of ROM material in the form of waste materials.

[0382] By way of example, whilst the embodiment is described in the context of fragments of copper-containing sulfidic ROM ores 5 being transferred directly for intermediate processing by crushing and then agglomerating in the crusher 7 and the agglomeration unit 15 respectively, the invention also extends to embodiments in which fragments of copper-containing sulfidic ROM ores 5 are transferred first to a stockpile (not shown) and held in the stockpile until being transferred (a) directly to a heap or (b) to intermediate processing, such as crushing and then agglomerating in the crusher 7 and the agglomeration unit 15 respectively, before being transferred to a heap.

[0383] By way of example, the invention also extends to embodiments in which (a) there is intermediate processing (for example crushing) of fragments of copper-containing sulfidic ROM ores 5, (b) the intermediate processed ROM ores are transferred to and stored in a stockpile, (c) there is intermediate processing (such as agglomeration) of the stockpiled intermediate processed ROM ores and (d) the agglomerates are transferred to a heap and leached in the heap.