THE EFFECT OF AS(III) ON THE GROWTH OF THIOBACILLUS-FERROOXIDANS IN AN ELECTROLYTIC CELL UNDER CONTROLLED REDOX POTENTIALS

Thiobacillus ferrooxidans oxidises ferrous ions in solution during the bacterial leaching process. In batch experiments that are usually per formed to determine the kinetics of the bacterial oxidation of ferrous ions, the concentrations of both the ferrous and ferric ions change a s a result of the bacterial activity. This change in concentration mak es it difficult to interpret the data from these experiments, particul arly if the concentrations vary through reaction regimes where differe nt mechanisms govern the bacterial activity. In this study the concent rations of ferrous and ferric ions are maintained at their initial val ues by controlling the redox potential of the solution in which the re action occurs. The redox potential is controlled by reducing the ferri c ions produced by the bacteria. In order to achieve this, the bacteri a are grown in the cathode compartment of an electrolysis cell. The cu rrent to the cell is varied by the controller, depending on whether mo re or less reduction of ferric ions is required. The current required to reduce the ferric ions in order to maintain the redox potential at a constant value is a measure of the bacterial activity and the rate o f bacterial growth. The effect of ferrous, ferric and arsenite concent rations on the rate of bacterial growth are presented. It is shown tha t growth rate is strongly dependent on the concentration of both the f erric and the arsenite ions in solution. Copyright (C) 1996 Elsevier S cience Ltd.