Continuous bioleaching of chalcopyrite using a novel extremely thermophilic microbial mixed culture (78 degreesC) was carried out in a laboratory unit using one 50-1 operating capacity tank and two 21-1 total capacity tanks in series. The following operating conditions were studied: solids' concentration, agitation-aeration, oxygen and carbon dioxide requirements, nutrient requirements, residence time and pH regulation. The general operability of the bioleach step was shown to be better than expected, with a copper recovery greater than 90% being achieved in a 5-day residence time using a continuous slurry feed at 12% (w/w) solids' concentration. Nevertheless, some potentially limiting factors, such as bacterial sensitivity, nutrient concentrations, and oxygen transfer efficiency, were also identified. The work formed part of a European project (HIgh-temperature bacterial OXidation, HIOX(R)) for which the final industrial objective was to propose a complete new method for copper recovery on the basis of an economically and environmentally friendly process. (C) 2002 Elsevier Science B.V. All rights reserved.