Effect of solid loading on thermophilic bioleaching of sulfide minerals

The effect of solid loading (mineral pulp density) on thermophilic bioleach ing of pyrite by Sulfolobus metallicus (BC) was investigated in a batch rea ctor. Different mineral pulp densities in the range 3-18% (w/v) were tested . With mineral pulp densities ranging from 3 to 9% the bioleaching proceede d in a single stage with a relatively constant rate. The bioleaching rates calculated for pulp densities of 3, 6 and 9% were 0.10, 0.11 and 0.09 kg ir on m(-3) h(-1) respectively. By contrast the bioleaching of pyrite at pulp densities of 12 and 15% proceeded in two distinct stages. During the expone ntial phase of microbial growth a sharp and linear increase in concentratio n of released iron was achieved. This increasing trend levelled off in the presence of non-growing cells and the second stage of bioleaching continued with a slower rate. For the pulp density of 12% the bioleaching rates of t he first and the second stages were 0.09 and 0.02 kg iron m(-3) h(-1) respe ctively, whereas the calculated rates in the presence of 15% mineral were 0 .07 and 0.017 kg iron m(-3) h(-1) for the first and the second stages. Appl ication of 18% mineral adversely influenced the activity of the cells and t he extent of bioleaching in this case was insignificant. (C) 2000 Society o f Chemical industry.