GROWTH OF THIOBACILLUS-FERROOXIDANS - A NOVEL EXPERIMENTAL-DESIGN FORBATCH GROWTH AND BACTERIAL LEACHING STUDIES

The concentrations of ferrous and ferric ions change dramatically duri ng the course of the batch experiments usually performed to study the kinetics of the bacterial oxidation of ferrous ions and sulfide minera ls, This change in concentration of the iron species during the course of the experiment often makes it difficult to interpret the results o f these experiments, as is evidenced by the lack of consensus concerni ng the mechanism of bacterial leaching, If the concentrations of ferro us and ferric ions were constant throughout the course of the batch ex periment, then the role of the bacteria could be easily established, b ecause the rate of the chemical leaching should be the same at a given redox potential in the presence and in the absence of bacteria. In th is paper we report an experiment designed to obtain kinetic data under these conditions, The redox potential is used as a measure of the con centrations of ferrous and ferric ions, and the redox potential of the leaching solution is controlled throughout the experiment by electrol ysis, The effects of ferrous, ferric, and arsenite ions on the rate of growth of Thiobacillus ferrooxidans on ferrous ions in this redox-con trolled reactor are presented. In addition, the growth of this bacteri um on ferrous ions in batch culture was also determined, and it is sho wn that the parameters obtained from the batch culture and the redox-c ontrolled batch culture are the same, An analysis of the results from the batch culture indicates that the initial number of bacteria that a re adapted to the solution depends on the concentrations of ferrous an d arsenite ions.