BIOLEACHING OF PYRITE BY ACIDIANUS-BRIERLEYI IN A CONTINUOUS-FLOW STIRRED-TANK REACTOR

Bioleaching of pyrite (FeS2) by the thermophilic bacterium Acidianus b rierleyi was studied experimentally and theoretically in a stirred-tan k reactor operated continuously with respect to both mineral particles and liquid medium. Continuous bioleaching experiments were performed at 65 degrees C and pH 1.5 over the range of dilution rates (0.4-5 d(- 1)) and feed pyrite-liquid loading ratios (5 and 20 kg/m(3)). A mathem atical model was developed to describe quantitatively the bioleaching process in the continuous-flow mode of operation. The reactor model as sumed that the growth rate of adsorbed bacteria on the mineral surface is proportional to the product of the adsorbed-cell concentration and the fracton of adsorption sites by unoccupied by cells, and took into account a distribution of residence time for the mineral particles le aving the reactor. The model developed here and the parameter values d etermined previously in separate batch tests gave good predictions of the mean leaching fraction and the free cell concentration in the reac tor. The present model was also consistent with previous rate data for the bioleaching of zinc sulfide by the mesophilic bacterium Thiobacil lus ferrooxidans in a continuous-flow reactor. (C) 1997 Elsevier Scien ce Ltd.