Silver catalyzed IBES process: Application to a Spanish copper–zinc sulphide concentrate. Part 2. Biooxidation of the ferrous iron and catalyst recovery

Abstract

The indirect bioleaching with effect separation process has been applied to a chalcopyrite–sphalerite concentrate from Rio Tinto. In this paper the biooxidation of the ferrous iron generated in the chemical stage (ferric sulphate leaching) and the recovery of the silver used as a catalyst have been studied. The ferrous iron in leaching liquors can be effectively biooxidized both in static batch and packed-bed reactors. The regenerated ferric iron can be recycled to the chemical stage of the process. The recovery of silver from the leach residue requires the previous removal of the elemental sulphur. The effect of variables such as temperature, type of acid, time, acid concentration and composition of the residue on the silver extraction has been examined. It is possible to obtain total recovery of the silver added as a catalyst (2 mg/g concentrate) plus 93% of the silver originally present in the concentrate by leaching a leach residue containing 1.1% Cu with a 200 g/l NaCl–0.5 M H 2SO 4 medium, at 90°C for 2 h.