AbstractA zinc sulfide concentrate was leached microbiologically byThiobacillus ferrooxidansin a continuous stirred tank reactor. A model was developed to predict, the leaching kinetics when the bacterial growth rate was not limited by any substrate other than the zinc concentrate, and it was modified to explain the observed results.Stable steady sates were obtained over a range of dilution rates from 0.0171 to 0.1038 hr−1. Because a solid substrate was used, the specific growth rate of the bacaeria was not a unique function of the subastrate concentration, and conventional contnuous culture theory based on the Monod equation did not apply to this system. The leaching rates and bacterial growth rates were first order in mineral surface area cocentratio