AU2007234509A1 - Leaching of copper - Google Patents

Description

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT (Original) APPLICATION NO:

LODGED:

COMPLETE SPECIFICATION LODGED:

ACCEPTED:

PUBLISHED:

RELATED ART: NAME OF APPLICANT: NAME OF INVENTOR: ADDRESS FOR SERVICE: INVENTION TITLE: TENNANT LIMITED FRANK TRASK LORD AND COMPANY, Patent and Trade Mark Attorneys, of 4 Douro Place, West Perth, Western Australia, 6005, AUSTRALIA.

LEACHING OF COPPER DETAILS OF ASSOCIATED PROVISIONAL APPLICATION: Australian Provisional Patent Application Number 2006906485 filed on 21 November 2006 The following Statement is a full description of this invention including the best method of performing it known to us:

TITLE

LEACHING OF COPPER 0 FIELD OF THE INVENTION S 5 The present invention relates to a process for the recovery of copper from metal sulfides.

BACKGROUND TO THE INVENTION It is known to use leaching chemicals to extract soluble metal values from oxide or mixed oxide/sulfide ores. These chemicals are used in a process which includes crushing of ore, the exposure of the crushed ore to leaching chemicals over a period of time (typically ranging from several hours to several days), and then treatment of the leaching chemicals to remove dissolved metal values.

Tests show that known lixiviants used in heap, dump and other types of leaching are only partially successful in extracting significant copper from typical ores derived from the supergene enrichment of copper as chalcocite and covellite. Supergene processes include the presence of meteoric water circulation with concomitant oxidation and chemical weathering. The descending meteoric waters oxidise the primary (hypogene) sulfide ore minerals and redistribute the metallic ore elements. Supergene enrichment occurs at the base of the oxidised portion of an ore deposit at which point the metals are redeposited on hypogene sulfides creating a zone of increased ore content.

0 Previous work has concentrated on the use of dilute sulfuric acid coupled with varying amounts and kinds of air, bacteria, and ferric ion, which has shown only very slow and Z partial recovery of copper as very dilute solutions at ambient temperatures and pressures.

The present invention attempts to overcome at least in part the aforementioned disadvantages of previous leaching methods.

SUMMARY OF THE INVENTION In accordance with one aspect of the present invention there is provided a process for leaching of copper from an ore containing various metal sulfides by treatment of the ore with an oxidising agent generated through the dissolution of a metal oxide in an acidic aqueous solution.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a preferred embodiment of the present invention recovery of metals from deposits containing metal sulfides may be achieved through a leaching process which involves the addition of a suitable oxidising agent in the presence of varying quantities of acidic aqueous media.

The oxidising agent, preferably oxygen generated from the dissolution of a metal oxide in an acidic aqueous solution, reacts with the ore in the presence of an acidic aqueous solution. The ore is preferably an ore containing metal sulfides, more preferably an ore containing one or more of the following: supergene chalcocite; covellite; chalcopyrite; or bomite. The metal oxide is preferably a transition metal oxide and more preferably O manganese (IV) dioxide. The acidic aqueous solution used for the generation of the oxidising agent and the leaching of the ore is preferably a mineral acid, more preferably 0 Z sulfuric acid.

O\ 5 The oxidising agent reacts with the ore in the presence of the acidic aqueous solution to form elemental sulfur and water. The stoichiometric quantity of manganese (IV) dioxide to the metal sulfide in the ore should be in the range of 10:1 to 1:10, preferably in the Srange of 5:1 to 1:5 and more preferably in the range of 2:1 to 1:2. The quantity of acid to be added should be in the range of 25 to 250 kg/ T of ore more preferably 50 to 150 kg/T of ore.

The reaction equation is described below using chalcocite as a model: MnO 2 2H Mn2+ H 2 0 2 0 2 Cu 2 S 4H 0 2 2Cu 2 2H 2 0 S

O

The manganese (IV) dioxide and the acidic aqueous solution may be admixed with heap leach ores during the creation of the heap. The amount of aqueous acidic solution in relation to the ore should be such that there is no continuous liquid phase.

The resultant heat of hydration of the acid and exothermic reaction of the oxidising agent with the ore heats the reactants. The temperatures of the reactants should be maintained below their boiling point and preferably in the range of 15 0 C to 70 0 C, more preferably in the range of 30 0 C to 70 0

C.

The time required for conversion of the metal sulfides to the soluble metal ions, the 0 Z curing time, may be between 1 hour to 10 days, more preferably 8 hours to 10 days.

0\ 5 In an alternative embodiment of this invention, the ore may be admixed with the manganese (IV) dioxide and acidic aqueous solution in a suitable apparatus such as a tumble mixer, in quantities such that there is no continuous liquid phase formed. The O mixtures may then be cured for a period of 1 hour to 10 days. The cured, solubilised and conditioned ore may then be belt leached in order to separate the dissolved metal ions from the ore. The amount of lixiviant solution used is arranged such that a high concentration of the metal is obtained in solution following leaching.

In an alternative embodiment of this invention, existing heap leach dumps that contain metal sulfides may be treated with an acidic aqueous suspension of finely ground manganese (IV) dioxide. The acidic aqueous suspension containing the manganese (IV) dioxide may be dispersed through the heap through the use of drippers, sprinklers and holes drilled in the dump.

In an alternative embodiment of this invention, it may be possible to solubilise copper from metal sulfide containing ores through selective attack. The ore may be processed in such a way that enables attack of the phases containing copper and at the same time minimising the attack on the phases that do not. The ore may be treated in a very concentrated medium in which the quantities of water used are restricted when the properties of the ore make this possible.

This process involves crushing the ore relatively coarsely. The leaching agents,

O

Smanganese (IV) dioxide and a solution of sulfuric acid, are then able to solubilise the ore containing the copper value while at the same time the particles that do not contain 5 copper are maintained at a sufficient size that minimises their exposure to the leaching

O

agents. This may result in a more efficient leaching process as less reagent may be used trying to solubilise phases of ore that do not contain the metal value.

O

Preferably there should be a sufficient quantity of the leaching medium to allow all of the constituents of the mixture to be wetted and for the reagents to be diffused, while at the same time preventing a continuous liquid phase from being formed. The mixture may then be allowed to cure before the metal ions are separated into a lixivant solution.

The present invention will now be described, by way of example.

Example 1 A sample of ore was set up in a system with a control column and a test column, in order to simulate heap leaching. The sample had a mineralogical composition comprising: chalcocite/ minor covellite; dioptase; chrysocolla; brochantite; and chalcopyrite. The sample had an assay content of 10.4 per cent total copper and 3.54 per cent acid soluble copper.

The samples in each column were admixed with 25 kg/T of ore sulfuric acid and the test column was dosed with 60 kg/T of ore manganese (IV) dioxide from an impure source.

O Both the control and test columns were then irrigated with their lixiviant solutions, for days. At this 30 day point the performance of the test column compared to the control

\O

Z column was not significantly different, 25 per cent recovery compared to 20 per cent. It was noted at this time point that the pH of the test column was higher than that of the 5 control. This was believed to be due to the consumption of acid through the reduction of the manganese (IV) dioxide to release oxygen. At this point the amount of acid in the test column was increased four fold in order to counter this acid consumption.

The addition of this acid resulted in an increased extraction of the copper from the ore with a 38 per cent recovery achieved in the test column compared to 22 per cent in the control at the 42 day point.

It can be seen that copper may be recovered more efficiently through treatment with manganese (IV) dioxide and acid, compared to treatment with acid alone. It can also be seen that the concentration of the acid can limit the extraction efficiency of the system.

Sufficient acid is required in order to counter the consumption through generation of oxygen from the metal oxide, and dissolution of acid soluble moieties in the ore.

0 Example 2 A sample of ore containing 2.10 per cent total copper and 1.54 per cent acid soluble

O

Z copper was set up in a reactor system. The sample was a representative sample from an oxide tailings dam in Queensland, Australia. The oxide fraction had a mineralogical composition comprising mainly malachite and chrysocolla, the non-oxide fraction Scomprised mainly chalcocite. The sample was subjected to various test conditions, namely: acid concentration; amount of reagent grade manganese (IV) dioxide; and curing Stime. The test conditions and the recovery of the copper are outlined in the table below Test [H 2 S0 4 [MnO 2 Water Curing Recovery (kg/T) Time total copper) 1 30 N/A 12 8 69 2 53 10 11 1 82 3 53 10 11 2 88 4 53 10 11 4 92 53 10 11 8 98 It can be seen that treatment of the oxide tailings with manganese (IV) dioxide and acid may provide far greater recovery of copper than treatment with acid on its own. By increasing the curing time to 8 hours a higher recovery may be achieved compared to curing for a shorter period.

Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.

Claims (12)

1. A process for leaching of copper from an ore containing various metal sulfides by treatment of the ore with an oxidising agent generated through the dissolution of a metal oxide in an acidic aqueous solution.

2. A process as claimed in claim 1, wherein the oxidising agent reacts with the ore in the presence of the acidic aqueous solution to solubilise copper.

3. A process as claimed in claim 1 or 2, wherein the metal oxide is a transition metal oxide.

4. A process as claimed in claim 3, wherein the metal oxide is manganese (IV) dioxide. A process as claimed in any one of the preceding claims, wherein the acidic aqueous solution contains a mineral acid.

6. A process as claimed in claim 5, wherein the mineral acid is sulfuric acid.

7. A process as claimed in any one of the preceding claims, wherein the ore contains one or more of supergene chalcocite, covellite, chalcopyrite or bomrnite.

8. A process as claimed in any one of the preceding claims, wherein the 1 0 stoichiometric quantity of manganese (IV) dioxide to the metal sulfide in the ore is in a range from 10:1 to 1:10. O z

9. A process as claimed in claim 8, wherein the stoichiometric quantity of 5 manganese (IV) dioxide to the metal sulfide in the ore is in a range from 5:1 to tt A process as claimed in claim 9, wherein the stoichiometric quantity of 0manganese (IV) dioxide to the metal sulfide in the ore is in a range from 2:1 to 1:2.

11. A process as claimed in any one of the preceding claims, wherein acid is used in an amount in the range from 25 to 250 kg/T of ore.

12. A process as claimed in claim 11, wherein acid is used in an amount in the range from 50 to 150 kg/T of ore.

13. A process as claimed in any one of claims 1 to 12, wherein an acidic aqueous suspension of finely ground manganese (IV) dioxide is dispersed through existing heap leach dumps in a heap leaching process.

14. A process as claimed in any one of claims 1 to 12, wherein the ore is crushed relatively coarsely, so that a leaching agent, manganese dioxide and a solution of sulfuric acid, is able to solublise copper from metal sulfide containing ores, while at the same time the particles that do not contain copper are maintained at a sufficient size that minimises their exposure to the leaching agent. A process substantially as hereinbefore described with reference to any one of the O Z accompanying Examples. ^-i