Metal Recovery by Leaching Agglomerates of Metal-Containing Material/Pyrite

Abstract

A method of recovering a metal, such as copper or nickel or zinc or cobalt, from a metal-containing material, such as a metal-containing material that has been categorized by a mine operator as being “non-economic” from the perspective of recovering the metal from the material. Mixing (i) the metal-containing material and (ii) pyrite and forming agglomerates. Leaching agglomerates with a leach liquor, with pyrite generating acid and heat that facilitate recovering the metal from the metal-containing material, and forming a pregnant leach liquor containing metal. Recovering the metal from the pregnant leach liquor.

Claims

1. A method of recovering copper from a low-grade copper-containing material comprising the steps of: (a) obtaining a pyrite-containing slurry from a mine; (b) mixing (i) the low-grade copper-containing material and (ii) pyrite in, or obtained from, the pyrite-containing slurry and forming agglomerates; (c) heap leaching agglomerates from step (b) with a leach liquor and microbes, with pyrite generating acid and heat that facilitate recovering copper from the low-grade copper-containing material, and with the microbes oxidising ferrous iron to ferric iron, and forming a pregnant leach liquor containing copper; and (d) recovering copper in solution from the pregnant leach liquor.

2. The method defined in claim 1 wherein the low-grade copper-containing material is in the form of as-mined material or stockpiled material.

3. The method defined in claim 2 further includes comminuting as-mined or as-stockpiled material.

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

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

6. The method defined in claim 1 further comprising mixing the low-grade copper-containing material and the pyrite-containing slurry in step (b).

7. The method defined in claim 1 wherein the method includes, prior to step (b), removing pyrite from the pyrite-containing slurry.

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

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

10. The method defined in claim 1 wherein the mixing is carried out before forming agglomerates in step (b).

11. The method defined in claim 1 wherein mixing and forming agglomerates are carried out simultaneously in step (b).

12-26. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWING

[0070] The invention is described further below by way of example only with reference to FIG. 1 which is a flow sheet of one embodiment of a method of recovering copper from a metal-containing material, such as a copper-containing material that has been categorized by a mine operator as being “non-economic” from the perspective of recovering copper from the material.

DESCRIPTION OF EMBODIMENT

[0071] The embodiment of the invention described below is described in the context of recovering copper from a metal-containing material.

[0072] It is noted that the invention is not confined to copper and extends to other metals such as nickel or zinc or cobalt.

[0073] The embodiment of the method of recovering copper from a copper-containing material, such as a copper-containing material that has been categorized by a mine operator as being “non-economic” from the perspective of recovering copper from the material, from a copper mine shown in FIG. 1 includes the steps of: [0074] (a) processing a slurry containing pyrite and removing pyrite therefrom; [0075] (b) forming agglomerates of the copper-containing material and pyrite from step (a); [0076] (c) leaching the agglomerates, with pyrite facilitating recovery of copper from the copper-containing material, and forming a copper-containing liquor; and [0077] (d) recovering copper from the copper-containing liquor.

[0078] The embodiment of the method of recovering copper from a copper-containing material in accordance with the invention shown in FIG. 1 is described in the context of the copper-containing material being in the form of waste rock, i.e. material that has been categorized by a mine operator as being “non-economic” from the perspective of recovering copper from the material. The copper-containing material may be as-mined material or stockpiled material.

[0079] In addition, the embodiment of the method of recovering copper from a copper-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.

[0080] 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

[0081] In the flow sheet shown in FIG. 1, the copper-containing material is in the form of waste rock having low grades of copper that has been re-mined from stockpiles 1.

[0082] As noted above, currently, these waste rock stockpiles are considered too low grade to be economically processed for recovering copper by known conventional methods.

[0083] As noted above, the invention is not confined to this source of copper-containing material.

[0084] The stockpiled waste rock 1 is transported in suitable vehicles, such as haul trucks or front-end loaders, for on conveyor belts or 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.

[0085] 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.

[0086] 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).

[0087] The resultant comminuted material is transferred to the agglomeration step 4.

Agglomeration Step 4

[0088] The agglomeration step 4 agglomerates: [0089] (a) the comminuted material produced in steps 2 and 3; and [0090] (b) pyrite that, in this embodiment, is pyrite-containing concentrate obtained from tailings (see below).

[0091] The agglomeration step 4 may be any suitable agglomeration step using any suitable apparatus, such as agglomeration drums.

[0092] By way of example, required ratios of the comminuted 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.

[0093] 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.

[0094] 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 material and the pyrite-containing concentrate and the required mechanical properties for the agglomerates.

[0095] The agglomeration step 4 may include any suitable protocol for adding and mixing the comminuted material and the pyrite-containing concentrate and the binder and water, if required.

[0096] The agglomerates are transferred to the heap leach steps described below.

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

[0097] The agglomerates are stored in a stack 5 and are conveyed from the stack 5 and formed into a heap 6 on a leach pad.

[0098] The heap 6 is provided with: [0099] (a) a leach liquor storage and delivery system to supply leach liquor to the heap; [0100] (b) a pregnant leach liquor collection system for collecting leach liquor containing copper in solution that is extracted from agglomerates in the heap; and [0101] (c) optionally, microbes (bacteria and archaea) to oxidise ferrous iron to ferric iron, with the ferric iron being an oxidant in the leaching process.

[0102] 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.

[0103] The copper-containing solution is transferred to an electrowinning plant 10 and copper is recovered from solution.

[0104] 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 in a neutralization residue storage facility 12 or possibly co-impoundment with tailings.

[0105] The pyrite-containing concentrate in the agglomerates provides valuable sources of acid via the pyrite and heat.

[0106] 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.

[0107] In addition, when microbes are present, the microbial oxidation of pyrite produces acid and heat, all of which are beneficial for heap leaching the copper containing material.

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

[0108] As noted above, the pyrite for the agglomeration step 4 is mine tailings.

[0109] 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 suspended in water. Typically, these are pyrite-containing particles and are slow to settle. The particles may also contain some copper.

[0110] The tailings are transferred, for example by being pumped, from a tailings dam or other suitable source of tailings 15 to a series of cyclones 16 or any other suitable size separation option that separates larger solids from the remaining fines-containing tailings.

[0111] The cyclones 16 may be any suitable cyclones.

[0112] The larger solids stream from the cyclones 16 are processed in a size reduction circuit, such as a milling/grinding/polishing circuit 17.

[0113] The output of this circuit is returned to the cyclones 16 for further processing in the cyclones.

[0114] The operating conditions of the cyclones 16 are selected so that the remaining tailings have a required particle size distribution for downstream processing of the tailings.

[0115] The remaining tailings from the cyclones 16 are transferred to a 1.sup.st flotation circuit 18 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.

[0116] The underflow from the 1.sup.st flotation circuit 18 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. In the embodiment of FIG. 1, the underflow stream for the 1.sup.st flotation circuit is transferred to a downstream neutralization step 11 described below

[0117] The floated stream from the 1.sup.st flotation circuit is transferred to and processed in a 2.sup.nd flotation circuit 19.

[0118] 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 particulates.

[0119] The underflow from the 2.sup.nd flotation circuit is transferred back to the 1.sup.st flotation circuit.

[0120] 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.

[0121] The pyrite-containing concentrate is transferred to the agglomeration step 4 described above.

Advantages of the Embodiment Shown in FIG. 1

[0122] The advantages of the above-described embodiment shown in FIG. 1, and the invention generally, include the following advantages: [0123] The method makes it possible to extract copper from a copper-containing material, such as a copper-containing material that has been categorized by a mine operator as being “non-economic” from the perspective of recovering copper from the material. [0124] 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. [0125] 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. [0126] 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. [0127] 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. [0128] 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. [0129] The method can be operated with readily-available and tried and tested equipment. [0130] 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.

[0131] Many modifications may be made to the flow sheet of FIG. 1 without departing from the spirit and scope of the invention.

[0132] By way of example, whilst the embodiment includes steps 1-3 to process waste rock to form the copper-containing material that is one feed for the agglomeration step 4, the invention is not confined to this combination of steps.

[0133] By way of further example, whilst the embodiment includes processing a slurry containing pyrite and removing pyrite therefrom, the invention is not limited to this option and extends to the use of any suitable source of pyrite.

[0134] 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.