Influence of various factors in the bioleaching of a bulk concentrate with mesophilic microorganisms in the presence of Ag(I)

Various aspects concerning bioleaching of a complex sulphide in the presence of Ag+ cation were studied in order to improve the kinetics of sulphide leaching. The use of 9K medium, 9K medium without chlorides and Norris' medium, together with the addition of Ag(I) in the form of Ag2SO4 or AgNO3, was studied. The use of a second cation (Bi3+, Co2+ Or Sn2+) and a two-stage bioleaching with Ag+ addition in the first or second stage was also evaluated. The bioleaching medium and the form of Ag+ incorporated had no influence on the bulk concentrate leaching kinetics. The addition of a second cation together with the Ag+ cation did not improve the copper and zinc recoveries. Sn2+ favoured bacterial growth and, as a consequence, the dissolution rate of copper and zinc. When a two-stage bioleaching was performed with Ag+ addition in the first stage, copper and zinc yields were not modified and only a slight increase in copper extraction was obtained. When a two-stage bioleaching was performed with. Ag+ addition in the second stage, both chalcopyrite and sphalerite were dissolved in the first stage and in the second stage a preferential chalcopyrite dissolution was produced. The Sn2+ addition helped to leach most of the sphalerite in the first stage.