Recovering Metal from Metal-Bearing Material

Abstract

A method of recovering a metal, such as copper or nickel or zinc or cobalt, from a metal sulfide-containing material in a mined material that is “non-economic” to recover metals from using conventional recovery options before the invention was made is disclosed. The method includes mixing (i) the metal sulfide-containing material and (ii) pyrite and forming agglomerates, leaching agglomerates with a leach liquor and microbes and removing a metal from the metal sulfide-containing material and forming a pregnant leach liquor containing metal, and recovering the metal from the pregnant leach liquor. A heap leaching operation for a metal sulfide-containing material is also disclosed. A flotation circuit for an ore processing plant for a metal sulfide-containing material is also disclosed.

Claims

1. A method of recovering a metal, such as copper or nickel or zinc or cobalt, from a metal sulfide-containing material in a mined material, such as a metal sulfide-containing material that is “non-economic” to recover metals from using conventional recovery options before the invention was made, that includes the steps of: (a) mixing (i) the metal sulfide-containing material and (ii) pyrite and forming agglomerates; (b) leaching agglomerates from step (a) with a leach liquor and microbes and removing a metal from the metal sulfide-containing material and forming a pregnant leach liquor containing metal, with pyrite generating acid and heat facilitating leaching metal from the metal sulfide-containing material, and with the microbes oxidising ferrous iron to ferric iron; and (c) recovering the metal from the pregnant leach liquor.

2. The method defined in claim 1 wherein the metal sulfide-containing material is in the form of as-mined material or stockpiled material that has been processed to be suitable for the agglomeration step (b).

3. The method defined in claim 2 includes comminuting as-mined or stockpiled material and producing a suitable particle size distribution for the agglomeration step (b).

4. The method defined in claim 3 includes crushing as-mined or stockpiled material in one or more than one comminution circuit that reduces the size of the material.

5. The method defined in claim 4 includes crushing as-mined or stockpiled material successively in primary, secondary and tertiary comminution circuits.

6. The method defined in claim 1 wherein the pyrite is in a pyrite-containing slurry, such as mine tailings.

7. The method defined in claim 1 wherein the pyrite is derived from a pyrite-containing slurry, such as mine tailings.

8. The method defined in claim 7 includes removing pyrite from the pyrite-containing slurry and producing pyrite in a concentrate form.

9. The method defined in claim 7 wherein the pyrite removal step (a) includes removing pyrite from the pyrite-containing slurry and forming (i) a pyrite-containing material and (ii) an inert stream.

10. The method defined in claim 1 wherein the mixing step is carried out before the agglomerating step.

11. The method defined in claim 1 wherein the mixing and the agglomerating steps are carried out simultaneously.

12. The method defined in claim 1 wherein the leaching step is a heap leaching step.

13. A heap leaching method for a metal sulfide-containing material that contains a metal, such as copper or nickel or zinc or cobalt, in a mined material that comprises: (a) leaching a heap of agglomerates of the metal sulfide-containing material and pyrite with a leach liquor containing microbes and producing a pregnant leach liquor containing the metal in solution, with the pyrite generating acid and heat that facilitates leaching metal from the metal sulfide-containing material, with the pyrite being in or derived from a slurry containing pyrite, and with the microbes oxidising ferrous iron to ferric iron; and (b) collecting the pregnant leach liquor from the heap.

14. A heap leaching operation for leaching a metal, such as copper or nickel or zinc or cobalt, from a metal sulfide-containing material in a mined material, the heap leaching operation comprising: (a) a heap of agglomerates of the metal sulfide-containing material and pyrite; and (b) a system that (i) supplies a leach liquor and microbes to the heap so that the leach liquor flows downwardly though the heap and leaches the metal from the metal sulfide-containing material and (ii) collects a pregnant leach liquor containing the metal in solution from the heap, with the pyrite generating acid and heat in the heap that facilitates leaching the metal from the metal sulfide-containing material, with pyrite being in or derived from a slurry containing pyrite, and with the microbes oxidising ferrous iron to ferric iron.

15. The heap leaching operation defined in claim 14 wherein pyrite is 1-10 wt. % of the total mass of the agglomerates.

16. A flotation circuit for an ore processing plant for a metal sulfide-containing material, the flotation circuit including: (a) a mill feed flotation circuit for producing a tailings stream and a concentrate stream from a mill feed, with the tailings stream comprising a metal sulfide-containing material; and (b) a pyrite flotation circuit for producing a pyrite concentrate stream, i.e. a pyrite-containing slurry, and a tailings stream.

17. The flotation circuit defined in claim 16 wherein the pyrite concentrate stream is a source of pyrite for the method of recovering a metal, such as copper, nickel or zinc or cobalt, from a metal sulfide-containing material that includes the steps of: (a) mixing (i) the metal sulfide-containing material and (ii) pyrite and forming agglomerates; (b) leaching agglomerates from step (a) with a leach liquor and microbes and removing a metal from the metal sulfide-containing material and forming a pregnant leach liquor containing metal, with pyrite generating acid and heat facilitating leaching metal from the metal sulfide-containing material, and with the microbes oxidising ferrous iron to ferric iron; and (c) recovering the metal from the pregnant leach liquor.

18. The flotation circuit defined in claim 16 wherein the pyrite flotation circuit is configured to process the pyrite concentrate stream, i.e. the pyrite-containing slurry, in accordance with the pyrite removal step including removing pyrite from a pyrite-containing slurry and forming a pyrite-containing material and an inert stream and produce (i) the tailings stream as the inert stream and (ii) the pyrite concentrate stream as the pyrite-containing material stream.

19. The flotation circuit defined in claim 16 wherein the mill feed flotation circuit includes a rougher/scavenger cell and a bulk cleaner cell, with the rougher/scavenger and the bulk cleaner cells being configured so that: (i) the rougher/scavenger cell processes the mill feed and produces a first tailings stream and a concentrate stream, and (ii) the bulk cleaner cell processes the concentrate stream and produces a second tailings stream and another concentrate stream and transfers the other concentrate stream for further processing, such as metal recovery, and the second tailings stream to the pyrite flotation circuit for processing in that circuit.

20. The flotation circuit defined in claim 16 wherein the metal sulfide-containing material is a copper sulfide-containing material, such as a copper sulfide-containing mineral.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0115] The invention is described further below by way of example only with reference to the following Figures, of which:

[0116] FIG. 1 is a flow sheet of one embodiment of a method of processing, for example by beneficiating, pyrite-containing tailings, i.e. a pyrite-containing slurry, and using the pyrite removed from the tailings in downstream heap leaching of a copper sulfide-containing material;

[0117] FIG. 2 is a graph of copper extraction versus leaching time for a series of column bioleach tests conducted on (i) a sample of ore from a copper mine, (ii) the copper ore augmented with finely pulverised museum grade pyrite and (iii) the copper ore augmented with pyrite concentrate produced by flotation of tailings produced at the copper mine; and

[0118] FIG. 3 is a flow sheet of one embodiment of a flotation circuit for an ore processing plant in accordance with the invention.

DESCRIPTION OF EMBODIMENTS

[0119] One embodiment of the invention described below is described in the context of recovering copper from a copper sulfide-containing material from a mine.

[0120] It is noted that the invention is not confined to copper and extends to other metals such as nickel or zinc or cobalt, in metal sulfide-containing materials from a mine.

[0121] In general terms, the embodiment shown in FIG. 1 is a method of mining comprising: [0122] (a) mining and optionally stockpiling a copper sulfide-containing material, such as a copper sulfide-containing mineral; [0123] (b) processing a copper sulfide-containing ore, as described herein, in the copper sulfide-containing material in an ore processing plant and (i) recovering copper and (ii) producing a pyrite-containing slurry; [0124] (c) processing the pyrite-containing slurry and producing pyrite; and [0125] (d) processing “non-economic” copper sulfide-containing material, as described herein, with pyrite in a heap leaching operation.

[0126] In more specific terms, the heap leaching operation shown in FIG. 1 includes the steps of: [0127] (a) processing a slurry containing pyrite from a tailings dam or the ore processing plant (not shown) of the mine and removing pyrite therefrom; [0128] (b) forming agglomerates of the copper sulfide-containing material and pyrite from step (a); [0129] (c) leaching the agglomerates, with pyrite facilitating recovery of copper from the copper sulfide-containing material, and forming a copper-containing liquor; and [0130] (d) recovering copper from the copper-containing liquor.

[0131] It is noted that the pyrite-containing slurry may be any suitable pyrite-containing slurry, such as tailings, from an ore processing plant. Example 2 and FIG. 3 describe an embodiment of a flotation circuit in accordance with the invention for producing a suitable pyrite-containing slurry.

[0132] The “non-economic” copper sulfide-containing material is described in relation to FIG. 1 in the context of waste rock, i.e. material that is “non-economic” to recover metals from using conventional recovery options, i.e. processing options used in commercial mines before the invention was made. The material may be as-mined material or stockpiled material. Typically, the copper concentration of the waste rock is ≤1.5% by weight, typically ≤1.2 wt. %, more typically ≤1.0 wt. %, even more typically ≤0.7 wt. %, even more typically ≤0.5 wt. %, even more typically ≤0.3 wt. %, even more typically ≤0.1 wt. %.

[0133] In addition, the embodiment of the method of recovering copper from a copper sulfide-containing material in accordance with the invention shown in FIG. 1 is described in the context of the pyrite being a pyrite concentrate extracted from mine tailings.

[0134] It is understood that the invention is not confined to this embodiment and extends generally to any suitable copper-containing material and to any suitable source of pyrite.

Processing the Copper-Containing Material Prior to Forming Agglomerates—Steps 1, 2, 3

[0135] In the flow sheet shown in FIG. 1, the copper sulfide-containing material is in the form of waste rock 1 that has been re-mined from stockpiles 1.

[0136] As noted above, currently, these waste rock stockpiles are considered too low grade to be economically processed for recovering copper by known conventional methods.

[0137] As noted above, the invention is not confined to this source of copper sulfide-containing material.

[0138] For example, the copper sulfide-containing material may be material that is considered too low grade to be economically processed for recovering copper by known conventional methods in test work carried out on a section of a mine before being mined (for example by drilling and blasting) and then, after mining, is transferred directly from the mine (without being stockpiled) for processing in steps 2 and 3.

[0139] The stockpiled waste rock 1 is transported in suitable vehicles, such as haul trucks or front-end loaders, for crushing and milling successively in primary, secondary and tertiary comminution circuits 2, 3 to the extent required to produce a suitable particle size distribution for the agglomeration step 4.

[0140] The comminution circuits 2, 3 may include single or multiple crushing steps delivering crushed copper-containing material to single or multiple milling and sizing steps to produce the comminution product stream having a desired particle size distribution for the agglomeration step 4.

[0141] The crushing steps 2, 3 may be carried out using any suitable combination of gyratory, cone and high pressure grinding roll (HPGR) crushers (not shown in the Figures).

[0142] The resultant comminuted copper sulfide-containing material is transferred to the agglomeration step 4.

Agglomeration Step 4

[0143] The agglomeration step 4 agglomerates: [0144] (a) the comminuted copper sulfide-containing material produced in steps 2 and 3; and [0145] (b) pyrite that, in this embodiment, is tailings-derived pyrite-containing concentrate (see below).

[0146] The agglomeration step 4 may be any suitable agglomeration step using any suitable apparatus, such as agglomeration drums.

[0147] By way of example, required ratios of the comminuted copper sulfide-containing material and the pyrite-containing concentrate are added to a mixing device and are mixed together, with or without a binder, with or without an acid, and with or without added water, and with or without recycled leach solution.

[0148] The required ratios depend on factors such as the amount of pyrite in the rock. Typically, a broad pyrite concentration range for the mixed product is from 1-10% pyrite.

[0149] The selection of the binder and the acid and the addition of water and/or recycled leaching solution are a function of a number of factors, including the characteristics of the comminuted copper sulfide-containing material and the pyrite-containing concentrate and the required mechanical properties for the agglomerates.

[0150] The agglomeration step 4 may include any suitable protocol for adding and mixing the comminuted copper sulfide-containing material and the pyrite-containing concentrate and the binder and water, if required.

[0151] The agglomerates are stored in a stack 5 and are transferred to the heap leach steps described below.

Heap Leach and Downstream Solvent Extraction and Electrowinning Steps 5, 6, 9, 10, 11, 12

[0152] The agglomerates from the stack 5 are formed into a heap 6 on a leach pad.

[0153] The heap 6 may be any suitable heap construction and is provided with: [0154] (a) a leach liquor storage and delivery system to supply leach liquor to an upper surface of the heap; [0155] (b) a pregnant leach liquor collection system for collecting leach liquor containing copper in solution that is extracted from copper sulfide-containing materials in agglomerates in the heap; and [0156] (c) microbes (such as bacteria or archaea) or other suitable oxidants to oxidise ferrous iron to ferric iron, with the ferric iron being an oxidant in the leaching process.

[0157] The pregnant leach liquor is processed in a solvent extraction system 9 that extracts copper from the liquor in an organic medium and then strips copper from the organic medium and produces a copper-containing solution.

[0158] The copper-containing solution is transferred to an electrowinning plant 10 and copper is recovered from solution.

[0159] The raffinate from the solvent extraction system 9 is regenerated and returned to returned to the heap as leach liquor. The leach liquor regeneration system includes a raffinate bleed limestone/lime neutralization 11 to control the build-up of impurities, generating neutralized solids for separate impoundment or possibly co-impoundment with tailings.

[0160] The pyrite-containing concentrate in the agglomerates provides valuable sources of acid via the pyrite and heat.

[0161] The acid-generating properties of the pyrite mean that the amount of acid that has to be added to the leach liquor can be reduced to maintain a given leaching acid requirement.

[0162] In addition, the microbial oxidation of pyrite produces acid and heat, all of which are beneficial for heap leaching the copper sulfide-containing material.

Separation Steps 15, 16, 17, 18, 19, 20 for Pyrite-Containing Tailings

[0163] As noted above, the pyrite for the agglomeration step 4 is mine tailings.

[0164] Typically, the tailings are an output of an ore processing plant for recovering copper from a copper sulfide-containing ore that contains copper sulfide-containing material, such as copper sulfide minerals.

[0165] The ore processing plant may be any suitable plant.

[0166] One example of an ore processing plant is one that includes comminution of mined ore involving a series of crushing and grinding stages and one or more than one flotation circuit for floating copper sulfide minerals from the comminuted ore (described above and in Example 2 as a “mill feed”) and producing a valuable concentrate output and a tailings output (a pyrite-containing slurry).

[0167] Typically, the solids in the tailings are in the form of a slurry of (a) fines, with low concentrations of copper, typically less than 0.4 wt. %, more typically less than 0.3 wt. %, and (b) pyrite-containing particles suspended in water. Typically, these fines and pyrite-containing particles are slow to settle. The pyrite-containing particles may also contain some copper.

[0168] The tailings are transferred, for example by being pumped, from a tailings dam or other suitable source of tailings 15, such as directly from the ore processing plant, to a series of cyclones 16 or any other suitable size separation option that separates larger solids from the remaining fines-containing tailings.

[0169] The cyclones 16 may be any suitable cyclones.

[0170] The larger solids stream from the cyclones are processed in a size reduction circuit, such as a milling/grinding/polishing circuit 17.

[0171] The output of this circuit is returned to the cyclones 16 for further processing in the cyclones.

[0172] The operating conditions of the cyclones are selected so that the remaining tailings have a required particle size distribution for the heap leach step 5. In this regard, typically pyrite-containing particles in the remaining tailings have a particle size of P.sub.80 of 1 mm or a value <1 mm. More typically, pyrite particles in the remaining tailings have a particle size of P.sub.80 of 250 μm or a value <250 μm.

[0173] The remaining tailings from the cyclones 16 are transferred to a 1.sup.st flotation circuit 18 (described in Example 2 in relation to FIG. 3 as a “pyrite flotation cell”) and are processed in the circuit. Suitable flotation reagents are added to the circuit as required. The operating conditions, including reagents, are selected to float pyrite-containing particles. Typically, these operating conditions will also float copper particles.

[0174] The underflow from the P t flotation circuit forms the abovementioned inert stream. As noted above, the term “inert” means that the stream is less reactive than the input slurry to the method in terms of the amount of pyrite in the stream. In the context of FIG. 1 this means that the underflow stream is less reactive than the pyrite-containing tailings supplied to the method in terms of the amount of pyrite in the stream. As noted above, this is beneficial because pyrite in tailings is an environmental problem because pyrite makes the tailings “acid generating tailings” and this is an issue for disposal of the tailings. The method provides an opportunity to produce an output that is environmentally safe for use in downstream applications, such as in copper ore processing plants, and can reduce the oxidant (ferric iron) requirements. The ferric iron (produced by microbial oxidation of the ferrous iron that dissolves from the pyrite concentrate and iron-bearing minerals in the waste rock) oxidizes the pyrite and the copper sulfide minerals. In the embodiment of FIG. 1, the underflow stream for the 1.sup.st flotation circuit is transferred to a downstream neuralization step 11 described below.

[0175] The overflow, i.e. the floated stream from the 1.sup.st flotation circuit is transferred to and processed in a 2.sup.nd flotation circuit 19 (described in Example 2 in relation to FIG. 3 as a “pyrite flotation cell”).

[0176] The 2.sup.nd flotation circuit 19 processes the floated stream from the 1.sup.st flotation circuit. Suitable flotation reagents are added to the circuit as required. The operating conditions, including reagents are selected to float pyrite-containing particles.

[0177] The underflow from the 2.sup.nd flotation circuit is transferred back to the 1.sup.st flotation circuit.

[0178] The pyrite-containing floated stream from the 2.sup.nd flotation circuit is transferred to thickeners 20 and de-watered and forms a pyrite-containing concentrate.

[0179] The pyrite-containing concentrate is transferred from the thickeners 20 to the agglomeration steps 4, 5 described above.

[0180] It is noted that, whilst the described embodiment has two flotation circuits 18, 19, the invention is not confined to this number of circuits.

[0181] It is also noted that, whilst the described embodiment includes cyclones 16 and a milling/grinding/polishing circuit 17 and returns material to the cyclones 16, the invention is not confined to this arrangement.

[0182] For example, the combination of the cyclones 16 and the milling/grinding/polishing circuit 17 would not be necessary if the particle size distribution in the tailings supplied from the tailings dam or other suitable source of tailings 15 is suitable for downstream processing after the separation steps.

[0183] By way of further example, the combination of the cyclones 16 and the milling/grinding/polishing circuit 17 would not be necessary where there are downstream steps to optimize the particle size distribution of pyrite particles in the pyrite-containing concentrate.

Advantages of the Embodiment Shown in FIG. 1

[0184] The advantages of the above-described embodiment shown in FIG. 1, and the invention generally, include the following advantages: [0185] The method makes it possible to extract copper from a copper sulfide-containing material, such as a copper sulfide-containing material that has been categorized by a mine operator as being “non-economic” from the perspective of recovering copper from the material. [0186] The method makes it possible to process tailings and thereby reduce the volumes of existing tailings dams. This is an important environmental outcome. Tailings present significant environmental and safety risks during the lives of mines. There are substantial issues involved in maintaining tailings dams and remediating tailings dams at the end of the lives of mines. In addition, there are potential issues with structural integrity of tailings dams. From time to time, there are catastrophic collapses of tailings dams that have caused loss of life and considerable damage to areas downstream of the dams. Also, tailings often contain contaminants (such as pyrite) which present challenges for mine remediation. Pyrite in tailings poses a potential environmental hazard because the tailings can oxidize to produce an acidic effluent that requires treatment to neutralize the acidity and remove contaminants before it can be discharged. [0187] The acid and heat generating capacity of pyrite is an advantage in leaching, such as heap leaching, and, for example, can reduce the amount of added acid that is required in the leach liquor. [0188] Moreover, the acid-generating capacity of pyrite means that the pyrite is used beneficially in the leach step and results in a net reduction in pyrite, which is significant from an environmental perspective. [0189] It is noted that any amounts of copper in the pyrite-containing material is a bonus—it is taken into the heap with pyrite and can be recovered in the heap leaching step. [0190] In addition to producing the abovementioned pyrite, removing pyrite from tailings produces an inert stream—i.e. a stream that is less reactive than the input tailings to the pyrite removal method in terms of the amount of pyrite in the inert stream. This is beneficial because pyrite in tailings is an environmental problem because pyrite makes the tailings “acid generating tailings” and this is an issue for disposal of the tailings. [0191] The method can be operated with readily-available and tried and tested equipment. [0192] The method makes it possible to process what has been previously classified as waste materials, such as low-grade copper-containing material or waste rock and tailings, and reduce the environmental impact of these materials as well as optimising the recovery of value from the originally-mined material.

Example 1

[0193] The applicant has carried out column bioleach tests to investigate the impact of pyrite augmentation on bioleaching of a copper ore.

[0194] The column bioleach tests evaluated copper extraction versus leaching time for (i) a sample of ore from a copper mine, (ii) the copper ore augmented with finely pulverised museum grade pyrite and (iii) the copper ore augmented with pyrite concentrate produced by flotation of tailings produced at the copper mine.

[0195] A sample of ore from a copper mine was 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 sulfuric acid.

[0196] In tests with added pyrite, either nearly pure museum grade pyrite, or fine pyrite concentrate produced by flotation of tailings produced at a copper mine, was mixed with the ore in the agglomerating drum to increase, or augment, the pyrite content of the agglomerated material from 0.86 wt. % pyrite naturally present in the ore to 4.0% pyrite. Both pyrite samples used were very fine with a P.sub.100 of 150 μm. The samples were subjected to elemental and mineralogical analysis.

[0197] It is noted that the term “museum grade pyrite” is understood herein to mean a pyrite content of greater than 90 wt. %, typically greater than 95 wt. %, typically greater than 97 wt. %, or more typically greater than 99 wt. %. Museum grade pyrite may have a silver content of less than 1 mg/kg, typically less than 0.5 mg/kg, typically less than 0.2 mg/kg, or more typically less than 0.1 mg/kg.

[0198] Table 1 summarises the elemental and mineralogical compositions of the ore, the museum grade pyrite and the pyrite concentrate used in the tests.

TABLE-US-00001 TABLE 1 Major elements and sulfide minerals in the ore and pyrite samples. Element or Museum Grade Pyrite Mineral Ore Pyrite Concentrate Copper, % 0.63 0.15 1.1 Iron, % 1.19 46.1 41.1 Sulfur, % 0.90 52.9 47.4 Silver, ppm 1.20 0.05 14.2 Chalcopyrite, % 1.10 0.40 1.5 Chalcocite, % — — 0.18 Covellite, % 0.11 — 0.06 Bornite, % 0.11 — 0.53 Nukundamite, % 0.10 — 0.03 Pyrite, % 0.86 99 85

[0199] Once mixed, the agglomerated material 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. During leaching, the temperature of the columns was controlled at 50° C. using a heating jacket and the column was aerated at 0.102 Nm.sup.3/h/tonne ore. The column was inoculated with ferrous iron-oxidising and sulfur-oxidising microorganisms and the irrigation solution, which initially contained 5 g/L ferric iron as ferric 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.

[0200] The pH of the collected leach solution was adjusted to the target pH of 1.2 with sulfuric acid if required before recycling back to the top of the column. Solution samples were regularly taken for analysis of their metals and sulfate concentrations.

[0201] The irrigation solution had a sulfate concentration of about 20 g/L at the beginning of the leach. If the sulfate concentration in solution exceeded 120 g/L, due to addition of sulfuric acid and oxidation of the sulfide minerals, the solution was diluted to maintain a maximum of 120 g/L sulfate.

[0202] 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.

[0203] The column tests were under leach for 350 days. Upon completion of leaching, the columns were rinsed first with dilute sulfuric acid and then with water to remove dissolved metals and sulfate contained in the entrained leach solution. The columns were then emptied and the solids dried and assayed along with the final leach solution. Mass balances were conducted and the copper extraction reported on the basis of the calculated copper head assay.

[0204] FIG. 2 is a graph depicting copper extraction versus leaching time for the three column tests and Table 2 summarises the copper and sulfide mineral extractions achieved.

TABLE-US-00002 TABLE 2 Column test extraction results. Ore + Museum Ore + Pyrite Parameter Ore Grade Pyrite Concentrate Pyrite content, % 0.86 4.0 4.0 Silver content, 0.17 0.16 0.20 g Ag/kg CuFeS.sub.2 Copper extraction, % Overall 59.7 71.2 74.1 From the −150 μm fraction 87.1 90.2 92.0 Chalcopyrite extraction, % 63.2 62.0 70.5 Chalcocite extraction, % — — 79.0 Covellite extraction, % 57.7 64.9 66.8 Bornite extraction, % 89.7 91.6 93.8 Nukundamite extraction, % 44.2 78.4 88.1 Pyrite extraction, % 50.0 90.2 89.4

[0205] The beneficial effect of augmenting the ore with pyrite on copper extraction is clearly evident from FIG. 2 and Table 2.

[0206] Copper extraction was increased by 11.5% and 14.4% by adding museum grade pyrite and pyrite concentrate respectively. The enhanced copper extraction is believed to be attributable to the increased availability of ferric iron provided by the oxidation and leaching of the added pyrite, which reacted rapidly due to its fine particle size (P.sub.100 of 150 μm). This is evident from the pyrite extraction results shown in Table 2. Extraction of pyrite in the ore was only 50.0% whereas extraction of pyrite from the ore augmented with the museum grade pyrite and pyrite concentrate was much higher, reaching 90.2% and 89.4% respectively.

[0207] Notably, copper extraction was very high from the minus 150 μm fines fraction in all three tests; 87.1% in the test on the ore, 90.2% in the test on the ore augmented with museum grade pyrite, and 92.0% in the test on the ore augmented with pyrite concentrate. The results demonstrate that very high copper extraction was achieved from the copper minerals contained in the ore fines as well as the copper minerals in the two pyrite augments, both of which had a P.sub.100 particle size of minus 150 μm. The natural silver content of the column feed samples, expressed in Table 2 as g Ag/kg CuFeS.sub.2, is believed to have had a beneficial catalytic effect and enhanced the recovery of copper from chalcopyrite (as taught in International application PCT/AU2018/050316 (WO 2018/184071) in the name of the applicant), particularly from the chalcopyrite in the fines fractions.

[0208] Thus, the invention provides a means of achieving very high copper extraction from copper minerals contained in the pyrite augment as well has high copper extraction from copper minerals contained in an ore.

Example 2

[0209] The purpose of Example 2 is to show the effectiveness of removing pyrite from a pyrite-containing slurry produced in a flotation circuit in an ore processing plant.

[0210] FIG. 3 is a flow sheet of one embodiment of a flotation circuit 23 for an ore processing plant in accordance with the invention.

[0211] The ore processing plant may include any suitable upstream comminution circuits and downstream recovery and tailings storage or other options (not shown).

[0212] The flotation circuit 22 shown in FIG. 3 includes a rougher/scavenger cell 25 and a bulk cleaner cell 27. These may be standard rougher/scavenger and bulk cleaner cells. These may be existing cells in an ore processing plant. They may be cells in a greenfield plant.

[0213] The flotation circuit 22 shown in FIG. 3 also includes a pyrite flotation cell 29 of the type described above in relation to FIG. 1, noting that FIG. 1 includes two cells 18, 19 and FIG. 3 shows a single cell 29. It is noted that the invention extends to any suitable number of pyrite flotation cells, with size separation and re-grind options 16, 17 and other options for processing a feed material to the cells for example as illustrated in FIG. 1, as may be required.

[0214] In use, a mill feed 31 is transferred to the rougher/scavenger cell 25, and the cell produces a concentrate stream 33 and a first tailings stream 35. The mill feed 31 may be any suitable mill feed, produced for example by combinations of crushing and grinding and size separation steps, which may be existing comminution circuits in an ore processing plant or purpose-designed circuits in a greenfield plant.

[0215] The first tailings stream 35 is transferred to an impoundment location 37. This may be a tailings dam or other tailings treatment options.

[0216] The concentrate stream 33 from the rougher/scavenger cell 25 is transferred to the bulk cleaner cell 27, and the cell produces a plant concentrate stream 39 and a second tailings stream 41.

[0217] The plant concentrate stream 39 from the bulk cleaner cell 27 is transferred for recovery of copper and other metals such as molybdenum. The recovery options may be any suitable options.

[0218] The second tailings stream 41 from the bulk cleaner cell 27 is transferred to the pyrite flotation cell 29, and the cell produces a pyrite-containing concentrate stream 43 and a third tailings stream 45.

[0219] The first and third tailings streams 35, 45 and, optionally, a part of the second tailings stream 41, are transferred to the impoundment location, such as tailings storage or other tailings treatment options.

[0220] The pyrite-containing concentrate stream 43 is transferred for further processing, such as agglomeration, and use in the above-described heap leaching circuit as shown in FIG. 1.

[0221] The applicant carried out large-scale flotation testwork on a sample of a scavenger/cleaner tailings, i.e. the second tailings stream, in the pyrite flotation cell shown in FIG. 3. The results are described below.

[0222] Table 3 summarises the composition of the pyrite concentrate obtained from a feed of scavenger/cleaner tailings, i.e. the second tailings stream, in the pyrite flotation cell.

[0223] The table shows the effectiveness of recovering of pyrite (and copper minerals—which is a considerable advantage) in the pyrite concentrate stream (see rows 1-10) from tailings using flotation.

[0224] The process produced a pyrite concentrate at a grade of 83% pyrite, 2.2% Cu and a rougher/scavenger tails at a pyrite grade less than 0.8% pyrite.

TABLE-US-00003 TABLE 3 QEMSCAN bulk mineralogy of Cleaner Scavenger Tails sample (the second tailings stream 41) and Pyrite Concentrate from the pyrite flotation cell 29 Product Scav Cl Tails Pyrite Con Mineral % % Chalcocite/Digenite 0.04 0.30 Covellite 0.01 0.08 Cu Oxides 0.01 0.01 Chalcopyrite 0.16 1.42 Bornite 0.08 1.30 Cu Arsenides 0.01 0.03 Nukundamite *— 0.02 Other Cu Minerals 0.13 0.31 CU Clays 0.00 0.00 Pyrite 8.63 83.0 Sphalerite — 0.02 Sulphur 0.03 0.16 Molybdenite 0.27 1.27 Other Sulphides 0.07 0.24 Quartz 45.2 5.82 K-Feldspar 20.2 1.10 Muscovite 2.27 0.17 Plagioclase Feldspar 1.85 0.03 Scolecite 0.01 — Biotite/Phlogopite 8.71 0.91 Chlorite_(K) 0.05 0.01 Chlorites 0.81 0.05 Talc 0.54 1.32 Garnet 0.40 — Epidote 0.07 — Amphibole 1.28 0.18 Pyroxene (Diopside) 0.21 0.02 Andalusite — — Kaolinite (clay) 1.40 0.12 Pyrophyllite 0.02 — Smectite 2.25 0.08 Sphene 0.05 — FeOx/Hydrox 0.30 0.08 Diaspore 0.01 — Carbonates 1.15 0.07 Siderite — — Jarosite — — Alunite 0.07 0.05 Zircon 0.03 — Rutile/Anatase 0.27 0.15 Phosphates 0.66 0.08 Ca-sulphate 0.03 0.02 Other Silicates 0.75 0.20 Others 1.95 1.38 ΣClay 3.67 0.20 ΣSkarn 3.66 1.66

[0225] Table 4 provides a summary of key results from the large-scale pyrite flotation testwork and shows that 78 wt. % of the pyrite originally contained in the tailings sample was recovered to the pyrite concentrate.

TABLE-US-00004 TABLE 4 Pyrite Balance from Flotation Tests Combine pyrite balance T #4-T #7 kg wt. % % pyrite Pyrite dist % Combine rougher (RO) + 138.7 6.76 45.8 78.1 Scavenger concentrate Scavenger Tails 1912 93.24 0.9 21.9 Head Calculated 2051 100 4 100

[0226] A grab sample of pyrite flotation feed, i.e. the second tailings stream 41, and pyrite flotation cell tails, i.e. the third tailings stream 45, was subjected to Acid/Base Accounting (ABA) testing. A summary of results is shown in Table 5.

TABLE-US-00005 TABLE 5 ABA Tests on Pyrite Flotation Feed and Tails % S = % C in Calc Calc Sulfur CO3 AP NP NNP Ratio Pyrite Flotation Feed 1.2 0.23 33 16 −17 0.48 Pyrite Flotation Tails 0.12 0.24 2.8 18 15.2 6.42 AP & NP units tons calcium carbanate equivalent per 1,000 tons of solids.

[0227] The ABA results indicate a reduction in pyrite reporting to the tails (lower AP), i.e. the second and third tailings streams, 41, 45. A negative NNP (net neutralisation potential) indicates that the pyrite flotation cell feed, i.e. the second tailings stream 41, is a net acid generator and the greater than 1 ratio (6.42) for the pyrite flotation cell tails, i.e. the third tailings stream 45, indicates that the inert stream (i.e. flotation tails) can be used as ground cover/fill material.

[0228] It is evident from the above that the flotation circuit shown in FIG. 3 is an effective circuit for producing a pyrite concentrate stream, i.e. pyrite containing slurry that can be used for example in the heap leaching operation described above in relation to FIG. 1.

[0229] Many modifications may be made to the flow sheet of FIG. 1 without departing from the spirit and scope of the invention.

[0230] By way of example, whilst the embodiment includes steps 1-3 to process waste rock to form the copper sulfide-containing material that is one feed for the agglomeration step 4, the invention is not confined to this combination of steps.

[0231] By way of further example, whilst the embodiment includes processing a slurry containing pyrite from a mine tailings and removing pyrite therefrom, the invention is not limited to this option and extends to the use of any suitable source of pyrite.

[0232] For example, the invention extends to adding pyrite-containing tailings directly in agglomeration if they contain sufficient pyrite so that a pyrite removal step is not necessary, is an efficient use of these tailings.