Bioleaching of copper sulphide concentrate using extreme thermophilic bacteria

An extreme thermophilic, iron-sulphur oxidising bacterial culture was isola ted and adapted to tolerate high metal and solids concentrations at 70 degr ees C. Following isolation and adaptation, the culture was used in a contin uous multi-stage pilot plant employing standard mechanically agitated and a erated tanks, for the bioleaching of a mixed secondary copper sulphide-chal copyrite concentrate. The culture exhibited stable leach performance over t he period of pilot plant operation and overall copper extractions of higher than 97% were maintained. It was shown, however, that solids concentration had a significant effect on the copper bioleach kinetics. Increased solids concentrations resulted in a drop in redox potential and copper extraction s in the first stage reactor. Batch chemical ferric leaches, performed at c ontrolled redox potentials, indicated that reduced residence times may be p ossible in bioleach processes, using thermophiles, if high redox potential levels can be maintained. (C) 1999 Elsevier Science Ltd. All rights reserve d.