Biooxidation of a gold concentrate in a continuous stirred tank reactor: mathematical model and optimal configuration

A model was developed to represent the biooxidation by Acidithiobacillus ferrooxidans of a refractory gold concentrate in a continuous stirred tank reactor (CSTR). The model accounts for the growth of attached and planktonic cells, their role in mineral solubilisation, and the contribution of ferric ions to the process. Predicted solubilisation rates increase with increasing solids dilution rates until a maximum, in agreement with the experimental results. Concentration of suspended cells was more affected by changes in solids dilution rates than attached cells did, behaviour well represented by the model. The model was also able to predict the observed increase in cell growth and mineral solubilisation due to the decrease in particle size and the enrichment of the air with CO2. Finally, the model was used to predict the optimal configuration of a continuous biooxidation system that minimises the residence time required to attain a defined degree of mineral solubilisation. This configuration was found to be a two-stage system consisting of a CSTR followed by a plug flow reactor. The latter can be replaced by a series of smaller equal-size CSTRs. (C) 2003 Elsevier B.V. All rights reserved.