Method for ammoniacal leaching of copper from oxidised copper ores

Abstract

A method for leaching copper from an oxidized copper ore, wherein at least 5% of the copper present in the oxidized copper ore is an oxidized copper compound, the method comprising the method steps of: applying an aqueous solution of a curing agent to the oxidized copper ore to produce a cured ore; forming a leach solution by applying an ammoniacal solution that has an ammonium carbonate content of less than 5 g/L to the cured ore to produce a pregnant leach solution containing copper; and passing the pregnant leach solution to a means for recovering copper.

Claims

1. A method for leaching copper from an oxidized copper ore, wherein at least 5% by weight of the copper present in the oxidized copper ore is in the form of an oxidized copper compound, the method comprising the method steps of: applying an aqueous solution of a curing agent to the oxidized copper ore; producing a cured ore; forming a leach solution by applying an ammoniacal solution that has an ammonium carbonate content of less than 0.75 g/L to the cured ore; producing a pregnant leach solution containing copper; and passing the pregnant leach solution to a means for recovering copper.

2. The method for leaching copper from an oxidized copper ore according to claim 1, wherein the leach solution maintains a pH between 8 and 11 during the leach process.

3. The method of leaching copper from an oxidized copper ore according to claim 1, wherein the copper is present in the ore as one, or more, compounds from the group: oxide, hydroxide, carbonate, silicate, sulfate, halide, arsenate, and phosphate including combinations thereof.

4. The method for leaching copper from an oxidized copper ore according to claim 1, wherein the oxidized copper ore has a carbonate content of at least 10 weight percent.

5. The method for leaching copper from a oxidized copper ore according to claim 1, wherein the oxidized copper ore contains sufficient carbonate to neutralize at least 5 kg of sulfuric acid, per ton.

6. The method for leaching copper from an oxidized copper ore according to claim 1, wherein the oxidized copper ore comprises one or more of the minerals selected from the group comprising: calcite, quartz, malachite, azurite, chrysocolla, dioptase, atacamite, and brochantite.

7. The method for leaching copper from an oxidized copper ore according to claim 1, wherein the ore comprises one or more minerals selected from the group comprising: malachite, azurite, and chrysocolla.

8. The method according claim 1, wherein the step of forming a leach solution by applying an ammoniacal solution to the cured ore is performed at atmospheric pressure.

9. The method according to claim 1, wherein the step of curing the ore to be leached through the application of an aqueous solution of a curing agent comprises substantially retaining the curing agent in contact with the ore to be leached when the ammoniacal solution is added.

10. The method according to claim 1, wherein the curing agent is selected from the group: acid, base, oxidizing agent, and metal complexing agent.

11. The method according to claim 1, wherein the step of curing the ore to be leached takes place at atmospheric pressure.

12. The method according to claim 1, wherein the step of curing the ore to be leached takes place at ambient temperature.

13. The method according to claim 1, wherein the step of curing the ore to be leached through the application of an aqueous solution of a curing agent saturates at least 50% of the pore space of the ore with the aqueous solution of the curing agent.

14. The method according to claim 1, wherein the step of leaching the cured ore at atmospheric pressure through the application of an ammoniacal solution, and producing a pregnant leach solution takes place at ambient temperature.

15. A method for leaching copper from an oxidized copper ore, wherein at least 5% by weight of the copper present in the oxidized copper ore is in the form of an oxidized copper compound, the method comprising the method steps of: applying an aqueous solution of a curing agent to the oxidized copper ore; producing a cured ore; forming a leach solution by applying an ammoniacal solution that has an ammonium carbonate content of less than 0.75 g/L to the cured ore, wherein the leach solution maintains a pH between 6 and 13; producing a pregnant leach solution; and passing the pregnant leach solution to a means for recovering copper.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will now be described, by way of example only, with reference to one embodiment thereof and the accompanying drawing, in which:

(2) FIG. 1 is a schematic flow sheet of a method for leaching copper from an ore in accordance with the present invention;

(3) FIG. 2 is a graphical representation of the copper recovery as a function of the ammonium carbonate concentration for the samples of Example 2; and,

(4) FIG. 3 is a graphical representation of the copper recovery as a function of the ammonium carbonate concentration for the samples of Example 3.

BEST MODE(S) FOR CARRYING OUT THE INVENTION

(5) A method for leaching copper from an ore in accordance with one embodiment of the present invention is now described. A copper oxide ore is used as the basis for this disclosure, metal recovery is by solvent extraction and electrowinning. The flowsheet is shown in FIG. 1.

(6) The ore 11 is mixed with the cure 10 and heaped in order to allow the mixture to rest 12. After an appropriate time the rested ore 13 is irrigated in the leach step 14 using copper-depleted raffinate 15 from the solvent extraction unit 23. The pregnant leach solution 16 is sent to a storage pond 22 from which it I sent to solvent extraction 23 where the copper is selectively removed using, for example, a ketoxime or aldoxime such as LIX841. The copper is stripped into an acid solution 24 which passes to electrowinning 25 where copper cathodes 26 are produced. The leached solids 17 are irrigated with water 19 in order to recover any entrained copper and ammonia, the solution 20 being fed into the pregnant leach solution (PLS) pond 22. The barren solids 21 are disposed of in an appropriate manner.

EXAMPLE 1 (PROSPECTIVE)

(7) A copper ore comprising malachite can be cured by contacting the ore with a volume of 70 g/L ammonia solution sufficient to fill 90% of the pore volume in the particles and resting for 24 h to produce a cured ore. After resting, the cured ore (along with any solution run off) is leached in a 30 g/L ammoniacal solution containing 0-50 g/L of ammonium carbonate for 24 h at which time a solution sample is taken for analysis. It is expected that the extent of leaching of copper will be unaffected by the concentration of ammonium carbonate.

EXAMPLE 2

(8) A dolomite-hosted oxidised copper ore consisting of a mixture of the copper carbonates malachite and azurite was obtained. The head assay of the ore was 1.26% Cu. The acid neutralisation capacity at pH 1.5 was in excess of 200 kg H.sub.2SO.sub.4, which is economically too high for standard acid-based extraction processes.

(9) Ground samples of the above ore (P.sub.80 of 100 um) were divided into 10 g subsamples each of which were cured by mixing the ore with 2.5 mL of 70 g/L NH.sub.3. After 24 h of curing, each cured sample was mixed with 50 mL of 70 g/L NH.sub.3 with increasing concentrations of ammonium carbonate. After agitating for 24 h, the solution was analysed for copper to determine the recovery.

(10) The recovery as a function of the ammonium carbonate concentration is shown in FIG. 2. The run without any added ammonium carbonate is shown at 0.1 g/L. From this, it is clear that the concentration of ammonium carbonate is of low importance for this particular ore sample.

(11) Without wishing to be bound by theory, it is believed that the carbonate minerals in the ore are dissolving and providing sufficient carbonate ion concentration in solution to aid dissolution. There appears to be a decrease in recovery at the highest ammonium carbonate concentrations. Again, without wishing to be bound by theory, it is believed that this is due to Le Chatelier's principle, whereby the high carbonate content in solution is beginning to limit the dissolution of the copper carbonate minerals.

EXAMPLE 3

(12) A dolomite-hosted oxidised copper ore containing 0.92% copper primarily as chrysocolla was ground to a P.sub.80 of 75 um. Subsamples were cured in 1 g/L sulphuric acid for 24 h and then leached in 30 g/L NH.sub.3 with increasing amounts of ammonium carbonate. After 24 h of agitation, the solution was analysed to determine the copper recovery which is shown in FIG. 3. The data point shown at 0.1 g/L on the x-axis did not have any ammonium carbonate added.

(13) The extent of copper leaching is unaffected by the concentration of ammonium carbonate. Without wishing to be bound by theory, it is believed that the carbonate minerals in the ore are dissolving and providing sufficient carbonate ion concentration in solution to aid copper dissolution.

(14) Although it is expected that the leaching behaviour will be specific to each combination of ore mineralogy and cure composition the inventors have demonstrated that providing there is sufficient carbonate ion obtained by dissolution of the minerals in the ore, the addition of ammonium carbonate can be reduced or even eliminated whilst maintaining similar recoveries. Clearly, the reduction or elimination of any reagent improves the economics and also simplifies the copper extraction process.

(15) Modifications and variations such as would be apparent to the skilled addressee are considered to fall within the scope of the present invention.