Treatment of base metal concentrate by a two-step bioleaching process

Abstract

A method of recovering at least one base metal from a concentrate wherein a residue of a primary bioleach of the concentrate, under mesophilic and moderate themophilic conditions, is processed to recover at least one metal, and the base metal is recovered from a solution, produced by a secondary bioleach under thermophilic conditions, of a residue of the metal recovery process.

Description

BACKGROUND OF THE INVENTION [0001] This invention relates to the treatment of a base metal containing concentrate. [0002] The recovery of a base metal such as copper from a concentrate, which contains arsenic, using a bioleaching process, can be problematic for it is necessary to avoid producing a bioleach residue which is contaminated with arsenic. [0003] U.S. Pat. No. 6,461,577 addresses the problem of arsenic toxicity of extremely thermophilic bacterial cultures by means of a two-stage leaching process. In a first mesophilic stage a major part of the arsenic contained in the material being treated is leached from the material and then oxidised from As(III) to As(V). The remaining leachable metal content of the material being treated is leached out in a second thermophilic stage. The concentration of pentavalent arsenic falls quickly and the toxic effect thereof on the thermophilic bacteria thus falls at the same rate. [0004] It is desirable though to remove the soluble arsenic as...

AI Technical Summary

Benefits of technology

[0015] An objective of operating the primary bioleaching process under the aforementioned conditions is to maximise the leaching of the sulphides in the concentrate and to maximise mass loss, and to minimise the precipitation in pentavalent form of arsenic which may be present in solution. The product from the primary bioleach residue may contain high concentrations of elemental sulphur due to the maximised bioleaching conditions.

[0019] An objective of operating the thermophilic secondary bioleaching process under the aforementioned parameters is to maximise the oxidation of sulphides minerals and mass loss, and to minimise the precipitation in pentavalent form of arsenic which may be present in solution.

[0020] Furthermore sulphur oxidation at thermophilic temperature conditions is maximised and thus any elemental sulphur produced during the proceeding preleach and primary bioleach may be fully oxidised. This is very important if further treatment of the thermophilic secondary bioleach residue is required for precious group metals (PGM's) recovery like gold. Elemental sulphur increases cyanide consumption during cyanidation to recover gold and thus contributes significantly to the increase in cyanidation costs. Additionally, elemental sulphur not oxidised decreases the acid produced in the bioleach solution and thus may decrease the effectiveness of any preleach step using recycled bioleach solution.

[0021] As indicated the at least one base metal is recovered from the leach solutions produced by the bioleaching processes. Preferably the pH of the solution produced in the preleaching step is adjusted to maximise recovery of the at least one base metal using solvent extraction techniques.

Problems solved by technology

The recovery of a base metal such as copper from a concentrate, which contains arsenic, using a bioleaching process, can be problematic for it is necessary to avoid producing a bioleach residue which is contaminated with arsenic.

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