DISSOLUTION OF COBALTIFEROUS PYRITE BY THIOBACILLUS-FERROOXIDANS AND THIOBACILLUS-THIOOXIDANS - FACTORS INFLUENCING BACTERIAL LEACHING EFFICIENCY

A cobaltiferous pyrite was bioleached by a mixed bacterial population. Batch tests were carried out with an air-lift culture system. Several factors that might affect bacterial oxidising capacities were studied. The optimal medium composition for arsenopyrite bioleaching determined by Collinet-Latil (1989) with the same bacterial culture is quite suitable for the biological treatment of pyrite. During batch cultivation, the acidity must be maintained at pH between 1.1 and 2 to obtain the highest efficiency. The dissolution of pyrite is noticeably depressed when the concentration of ferric iron reaches 35 g l-1 and is slightly affected by ferrous iron up to 27 g l-1 or cobalt up to 15 g l-1. The inoculum size does not influence the rate of dissolution of cobalt.