Processing Method

Abstract

A method of processing a pyrite-containing slurry is disclosed. The method includes removing pyrite from the pyrite-containing slurry and forming (i) an inert stream and (ii) a pyrite-containing material, with the pyrite-containing slurry including tailings from a tailings dam or an ore processing plant. The method also includes leaching a metal sulfide-containing material and the pyrite-containing material with a leach liquor and microbes. A method of leaching 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 processing a pyrite-containing slurry that comprises: (a) removing pyrite from the pyrite-containing slurry and forming (i) an inert stream and (ii) a pyrite-containing material, with the pyrite-containing slurry including tailings from a tailings dam or an ore processing plant; and (b) leaching a metal sulfide-containing material and the pyrite-containing material 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 the pyrite in the pyrite-containing material generating acid and heat that facilitate leaching metal from the metal sulfide-containing material, and with the microbes oxidising ferrous iron to ferric iron.

2. The method defined in claim 1 wherein the pyrite removal step (a) includes floating pyrite-containing material in the pyrite-containing slurry and producing (i) the inert stream as one flotation output and (ii) the pyrite-containing material as another flotation output.

3. The method defined in claim 2 wherein, before the flotation step, the pyrite removal step (a) includes a size separation step which separates larger particles in the pyrite-containing material from the remaining pyrite-containing slurry, with the remaining pyrite-containing slurry being transferred to the flotation step.

4. The method defined in claim 3 wherein the pyrite removal step (a) includes reducing the size of the larger particles in the pyrite-containing material in a size reduction circuit and returning the reduced-sized particles to the size separation step.

5. The method defined in claim 3 wherein the pyrite removal step (a) includes selecting the operating conditions so that pyrite particles in the pyrite-containing material in the remaining pyrite-containing slurry have a required particle size distribution for the downstream leach step (b).

6. The method defined in claim 1 wherein pyrite particles in the pyrite-containing material have a particle size of P.sub.80 of 1 mm or a value <1 mm.

7. The method defined in claim 6 wherein the pyrite particles in the pyrite-containing material have a particle size of P.sub.80 of 250 μm or a value <250 μm.

8. The method defined in claim 1 wherein the pyrite removal step (a) includes thickening and/or filtering the pyrite-containing material and forming a pyrite-containing concentrate.

9. The method defined in claim 1 includes using the inert stream as a source of water in processing plants for recovering metal from the metal sulfide-containing material.

10. The method defined in claim 1 wherein the metal is copper and the metal sulfide-containing material is a copper sulfide mineral.

11. The method defined in claim 10 wherein pyrite is 1-10 wt. % of the total mass of the copper sulfide-containing material and the pyrite-containing material.

12. The method defined in claim 1 includes mixing together the metal sulfide-containing material and the pyrite-containing material before the leaching step (b).

13. The method defined in claim 12 wherein the leach step (b) includes: i. agglomerating the pyrite-containing material and the metal sulfide-containing material, such as copper sulfide-containing material, and forming agglomerates; and ii. heap leaching the metal, such as copper, from a heap of the agglomerates and producing a pregnant leach liquor containing the metal, such as copper, in solution; iii. recovering the metal, such as copper, from the pregnant leach liquor.

14. A heap leaching method for a mined material that contains a metal, such as copper or nickel or zinc or cobalt, in a metal sulfide-containing material that is characterized by: (a) leaching a heap of agglomerates produced from (i) a pyrite-containing material produced from a pyrite-containing tailings from a tailings dam or an ore processing plant, and (ii) the mined material, such as waste rock, with a leach liquor and microbes, with the pyrite in the pyrite-containing material generating acid and heat that facilitates leaching metal from the mined material, and with the microbes oxidising ferrous iron to ferric iron, and (b) collecting a pregnant leach liquor containing the metal in solution from the heap.

15. A heap that leaches a metal, such as copper or nickel or zinc or cobalt, from a metal sulfide-containing material in a mined material, the heap comprising: (a) a heap of agglomerates produced from (i) a pyrite-containing material produced from a pyrite-containing tailings from a tailings dam or an ore processing plant, and (ii) the mined material, such as waste rock, 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 mined 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 metal from the mined material, and with the microbes oxidising ferrous iron to ferric iron.

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

17. 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 slurry; and (b) a pyrite flotation circuit for producing a pyrite concentrate stream, i.e. a pyrite-containing slurry, and a tailings stream.

18. The flotation circuit defined in claim 17 wherein the pyrite flotation circuit is configured to process the pyrite concentrate stream, i.e. the pyrite-containing slurry, in accordance with a method of processing a pyrite-containing slurry that comprises: (a) removing pyrite from the pyrite-containing slurry and forming (i) an inert stream and (ii) a pyrite-containing material, with the pyrite-containing slurry including tailings from a tailings dam or an ore processing plant; and (b) leaching a metal sulfide-containing material and the pyrite-containing material 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 the pyrite in the pyrite-containing material generating acid and heat that facilitate leaching metal from the metal sulfide-containing material, and with the microbes oxidising ferrous iron to ferric iron, wherein the pyrite removal step (a) includes floating pyrite-containing material in the pyrite-containing slurry and producing (i) the inert stream as one flotation output and (ii) the pyrite-containing material as another flotation output.

19. The flotation circuit defined in claim 17 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.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0124] The invention is described further below by way of example only with reference to the following Figures, of which:

[0125] 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;

[0126] 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

[0127] 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

[0128] One embodiment of the method of processing, for example by beneficiating, a pyrite-containing slurry in the form of tailings from a tailings dam or an ore processing plant of a mine in accordance with the invention shown in FIG. 1 removes pyrite from the tailings and produces an inert stream that is suitable for use in downstream applications and a pyrite-containing material that is used beneficially, as described below, in downstream heap leaching of a copper sulfide-containing material and, as a consequence, minimizes the adverse environmental impact of pyrite.

[0129] In other words, the embodiment produces two □products □from the pyrite-containing slurry.

[0130] It is understood that the invention is not confined to this embodiment and extends generally to a method of processing, for example by beneficiating, a pyrite-containing slurry, such as a pyrite-containing tailings produced in a mine, that comprises removing pyrite from the slurry and forming two □products □in the form of (a) an inert stream and (b) a pyrite-containing material, typically a solid material, such as a solid concentrate that can be used in an application other than downstream heap leaching of a copper sulfide-containing material.

[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] In general terms, the embodiment shown in FIG. 1 includes a method of removing copper from a low-grade copper-containing material having copper sulfide minerals, with the method including leaching the low-grade copper-containing material and pyrite and producing a pregnat leach liquor and recovering copper form the leach liquor, with the pyrite being produced from a pyrite-containing slurry.

[0133] In general terms, the embodiment shown in FIG. 1 is a method of mining comprising: [0134] (a) mining and optionally stockpiling a copper sulfide-containing material, such as a copper sulfide-containing mineral; [0135] (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 a; [0136] (c) processing the pyrite-containing slurry and producing pyrite; and [0137] (d) processing □non-economic□, low-grade copper sulfide-containing material, as described herein, with pyrite in a heap leaching operation.

[0138] In more specific terms in relation to processing the pyrite-containing slurry and producing pyrite and downstream use of the pyrite, with reference to FIG. 1. the method includes the following steps: [0139] (a) separation steps 15, 16, 17, 18, 19, 20 that process pyrite-containing tailings from a tailings dam or an ore processing plant (not shown in FIG. 1 but shown in part by way of example in FIG. 3) of the mine and produce two □products □in the form of (i) a solid pyrite-containing concentrate stream 20 and (a) an inert stream from the tailings; [0140] (b) an agglomeration step 4 that mixes and agglomerates (i) the pyrite-containing concentrate stream 20 from the separation steps and (ii) at least one copper sulfide-containing solid material that has been processed in steps 1, 2, 3; [0141] (c) a heap leach step 6 that leaches copper from copper sulfide-containing material in a heap of the agglomerates produced in the agglomeration step 4 and produces a pregnant leach liquor; and [0142] (d) copper recovery steps 9, 10 that recover copper from the pregnant leach liquor from the heap.

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

[0143] 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.

[0144] The ore processing plant may be any suitable plant.

[0145] 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).

[0146] 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.

[0147] 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 and forms two separate streams.

[0148] The cyclones 16 may be any suitable cyclones.

[0149] The larger solids from the cyclones 16 are processed in a size reduction circuit, such as a milling/grinding/polishing circuit 17, that reduces the particle sizes of the larger solids.

[0150] The output of this circuit is returned to the cyclones 16 for further processing in the cyclones.

[0151] The operating conditions of the cyclones 16 are selected so that the pyrite-containing particles in 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.

[0152] 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.

[0153] The underflow from the 1.sup.st 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.

[0154] The overflow, i.e. 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).

[0155] Suitable flotation reagents are added to the 2.sup.nd flotation circuit 19 as required. The operating conditions, including reagents are selected to float pyrite-containing particles.

[0156] The underflow from the 2.sup.nd flotation circuit is transferred back to the 1.sup.st flotation circuit.

[0157] The pyrite-containing overflow from the 2.sup.nd flotation circuit is transferred to thickeners 20 and de-watered and forms a pyrite-containing concentrate.

[0158] The pyrite-containing concentrate is transferred from the thickeners 20 to the agglomeration step 4 described below.

[0159] It is noted that, whilst the described embodiment has two flotation circuits 18, 19, the invention is not confined to this number of circuits.

[0160] It is also noted that, whist 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.

[0161] 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.

[0162] 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 optimise the particle size distribution of pyrite particles in the pyrite-containing concentrate.

Agglomeration Step 4

[0163] The agglomeration step 4 agglomerates: [0164] (a) the tailings-derived pyrite-containing concentrate described above; and [0165] (b) a copper sulfide-containing material produced in steps 2 and 3.

[0166] The copper sulfide-containing material in this embodiment of the method of the invention includes copper sulfide-containing waste rock and is discussed in the following section.

[0167] It is noted that the copper sulfide-containing material may be any suitable copper sulfide-containing material having regard to the characteristics, such as particle size distribution, of the tailings-derived concentrate and the requirements for downstream processing of the agglomerates.

[0168] The agglomeration step 4 may be any suitable agglomeration step using any suitable apparatus, such as agglomeration drums.

[0169] By way of example, required ratios of the pyrite-containing concentrate and the copper sulfide-containing material 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.

[0170] 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 1 □10 wt. % pyrite.

[0171] 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 pyrite-containing concentrate and the copper sulfide-containing feed materials and the required mechanical properties of the agglomerates.

[0172] The agglomeration step 4 may include any suitable protocol for adding and mixing the pyrite-containing concentrate, the copper sulfide-containing solid feed materials and the binder and water, if required.

[0173] The agglomerates are stored in a stack 5 and are transferred to the heap leach steps described below.

Processing the Copper-Containing Material Steps-1, 2, 3

[0174] In the flow sheet shown in FIG. 1, the copper sulfide-containing material is in the form of waste rock having low grades of copper that has been re-mined from stockpiles 1.

[0175] As noted above, currently, these stockpiles are considered too low-grade to be economically processed in flotation and other ore processing systems for recovering copper from copper sulfide-containing ores and concentrates.

[0176] As noted above, the invention is not confined to this source of copper sulfide-containing material.

[0177] 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.

[0178] The stockpiled waste rock 1 is transported in suitable vehicles, such as haul trucks or front-end loaders, or on conveyor belts to comminution circuits and crushed and milled 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.

[0179] 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 steb 4.

[0180] The crushing steps 2, 3 may be carried out using a combination of gyratory, cone and high pressure grinding roll (HPGR) crushers (not shown in the Figures).

[0181] The resultant comminuted copper sulfide-containing material is transferred to the agglomeration step 4.

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

[0182] The agglomerates from the stack 5 and formed into a heap 6 of agglomerates on a leach pad.

[0183] The heap 6 may be any suitable heap construction and is provided with: [0184] (a) a leach liquor storage and delivery system to supply leach liquor to an upper surface of the heap; [0185] (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 [0186] (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.

[0187] 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.

[0188] The copper-containing solution is transferred to an electrowinning plant 10 and copper is recovered from solution.

[0189] The raffinate from the solvent extraction system 9 is regenerated and returned to the heap as leach liquor. The leach liquor regeneration system includes a raffinate bleed limestone/lime neutralization step 11 to control the build-up of impurities, generating neutralized solids for separate impoundment in a neutralization residue storage facility 12 or possibly co-impoundment with tailings.

[0190] The pyrite-containing concentrate in the agglomerates provides valuable sources of acid and heat via the pyrite.

[0191] The acid-generating properties of the pyrite mean that the amounts of acid that have to be added to the leach liquor can be reduced to maintain a given leaching acid requirement.

[0192] In addition, the microbial oxidation of pyrite produces acid and heat, all of which are beneficial for heap leaching the copper sulfide-containing material.

Advantages of the Embodiment Shown in FIG. 1

[0193] The advantages of the above-described embodiment shown in FIG. 1, and the invention generally, include the following advantages: [0194] The embodiment makes it possible to produce two output □products □from pyrite-containing tailings. [0195] One product is an inert stream. [0196] The second product is a pyrite concentrate that can be used beneficially in a downstream heap leaching method for a copper-containing material. In this application, the primary focus is on the beneficial use of pyrite to generate acid and heat in a heap to reduce the added acid requirements for heap leaching and to generate elevated temperatures which increase the rate and extent of copper extraction from the copper containing material. [0197] The embodiment makes it possible to reduce the environmental impact of pyrite-containing tailings and to use at least the extracted pyrite beneficially. [0198] The embodiment makes it possible to optimise the recovery of copper from a mined material at low cost, with minimal environmental impact and minimal use of resources. [0199] The embodiment uses readily-available and tried and tested equipment.

Example 1

[0200] The applicant has carried out column bioleach tests to investigate the impact of pyrite augmentation on bioleaching of a copper ore.

[0201] 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.

[0202] 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.

[0203] 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.

[0204] 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.

[0205] 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. Museum Grade Pyrite Element or 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

[0206] 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.3h/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.

[0207] 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.

[0208] 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.

[0209] 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.

[0210] 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.

[0211] 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

[0212] The beneficial effect of augmenting the ore with pyrite on copper extraction is clearly evident from FIG. 2 and Table 2.

[0213] 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.

[0214] 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.

[0215] 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

[0216] The purpose of Example 2 was to show the effectiveness of removing pyrite from a pyrite-containing slurry produced in a flotation circuit in an ore processing plant.

[0217] FIG. 3 is a flow sheet of one embodiment of a flotation circuit 23 for an ore processing plant in accordance with the invention.

[0218] The ore processing plant may include any suitable upstream comminution circuits and downstream recovery and tailings storage or other options (not shown).

[0219] 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.

[0220] 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. 2 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.

[0221] 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.

[0222] The first tailings stream 35 is transferred to an impoundment location 37. This may be a tailings dam or other tailings treatment options.

[0223] 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.

[0224] 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.

[0225] 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.

[0226] 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.

[0227] 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.

[0228] 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.

[0229] 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.

[0230] 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.

[0231] 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.

[0232] 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-00003 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

[0233] 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-00004 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 carbonate equivalent per 1,000 tons of solids.

[0234] The ABA results indicate a reduction in pyrite reporting to the tails (lower AP), i.e. the second and third tailing 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.

[0235] 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.

[0236] Many modifications may be made to the flow sheet of FIG. 1 without departing from the spirit and scope of the invention.

[0237] By way of example, whilst the embodiment includes a □cycloning □step 16, the invention extends to the use of any suitable size separation step.

[0238] In addition, 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 and the waste rock may be processed in any suitable steps to produce a suitable feed material for the agglomeration step 4.

[0239] In addition, whilst the embodiment is described in the context of recovering copper, it is noted that the invention is not confined to copper and extends to recovering metals such as nickel or zinc or cobalt from waste rock containing at least one of these metals in a metal-sulfide containing material.

[0240] In addition, whilst the embodiment focuses on tailings from wet processing plants for copper sulfide-containing ores, the invention also extends to tailings derived from processing ores containing other metals, such as cobalt, nickel and zinc.