Bioleaching of a chalcopyrite concentrate with moderate thermophilic microorganisms in a continuous reactor system

The metal extraction efficiency of bioleaching processes can be greatly improved by using stirred-tank reactors. However, owing to the high cost of acquiring and maintaining these, their use is restricted to the treatment of high-grade ores and concentrates. Unlike gold, the copper industry is not far from achieving commercial implementation of stirred processes on an industrial scale. Recent research has focused on the development of continuous bioleaching processes for the treatment of copper flotation concentrates. The aim of the present work was to optimize a process for continuous bioleaching of chalcopyrite concentrates using moderate thermophilic microorganisms and silver ions. The best results were obtained using a series of three reactors under the following experimental conditions: 45 degrees C, 14 days residence time, 2 g Ag/kg of concentrate (silver deposition stage at 35 degrees C), stirring rate adjusted to 350 rpm, pH between 1.2 and 1.4 and redox potential between 400 and 500 mV vs. Ag/AgCl. The optimized continuous bioleaching system was able to dissolve copper steadily at a concentration higher than 11 g/L. (c) 2007 Elsevier B.V. All rights reserved.