Method of treating a sulphide mineral
A copper bioleaching process which makes use of a consortium which contains Leptospirillum ferriphilum and a sulphur oxidising microorganism which is halophilic or halotolerant.
1. A method of treating a sulphide mineral or mixed sulphide and oxide mineral comprising bioleaching the mineral in a chloride ion solution with a mixed culture consortium wherein:
a) the chloride ion content is in the range of about 5,000 ppm to about 30,000 ppm;
b) the chloride ion solution contains at least one of the following:
aluminium, magnesium and sodium;
c) the temperature of the solution is in excess of about 10° C.;
d) the pH of the solution is in the range of about 1 to about 3; and
e) the mixed culture consortium contains at least a salt tolerant strain of Leptospirillum ferriphilum which is strain Sp-Cl deposited at the DSMZ under the accession number DSM22399, and a sulphur oxidising microorganism which is halophilic or halotolerant, which consortium enhances the rate of ferrous iron oxidation.
2. A method according to claim 1 wherein the temperature is in the range of about 25° C. to about 45° C.
3. A method according to claim 1 wherein at least one microorganism in the consortium is cultured in at least one build-up reactor.
4. A method according to claim 1 wherein the mineral is inoculated with an inoculant which has a cell concentration of the consortium of between about 10 7 cells/ml and about 10 9 cells/ml to maintain a cell count in the mineral of from about 10 6 to about 10 11 cells per ton of ore.
5. A method according to claim 3 wherein an inoculum from the reactor is directed to a pond which is aerated and in which the inoculum is stored and maintained, and inoculum from the pond is added to the mineral.
6. A method according to claim 3 wherein inoculum from the reactor is added to crushed ore together with acid to form inoculated ore that is added to the mineral.
7. A method according to claim 1 wherein the consortium is produced in an inoculum generator and ore, to which microorganisms of the consortium is attached, is added to the mineral.
8. A method according to claim 1 wherein the sulphide mineral or the mixed sulphide and oxide mineral includes copper and wherein the method further comprises: extracting an intermediate leach solution from the mineral wherein the intermediate leach solution is not subjected to a metal recovery process, passing a pregnant leach solution draining from the mineral through a metal recovery process to define a raffinate and recirculating the intermediate leach solution and the raffinate to the mineral to increase the active cell count in the mineral.
9. A method according to claim 1 wherein sulphide mineral or the mixed sulphide and oxide mineral includes copper and wherein the microorganisms in the consortium have a tolerance to copper in excess of about 0.5 g/l.
10. A method according to claim 1 wherein at least one of the microorganisms included in the mixed culture consortium is adapted to increase tolerance of the consortium to chloride and to copper.