Estimations on the degradability of ores and bacterial leaching activity using short-time microcalorimetric tests

Abstract: This work is based on calorimetric measurements on batch cultures of ferrous iron-oxidizing thiobacilli and leaching cultures degrading solid substrates in the titration vessel under aerobic conditions. It has been demonstrated that heat-flow levels are a direct measure for oxidation rates of known reactions under non-limiting conditions. The total loss of heat-energy per unit of ferrous iron oxidized is identical under similar incubation conditions with different Thiobacillus ferrooxidans strains and different cell-densities in culture suspension. Under limiting conditions a reduced heat-loss occurred. This may have been due to either a more effective use of the substrate or to a shift to different redox reactions. Oxygen was proved to be a limiting factor in dense bacterial cultures with high substrate concentrations in the titration vessel. The experimental duration decreased significantly with the use of increasing cell densities. Therefore cell densities in degradation experiments with solid substrates were adjusted to between 5X10⁹ and 1x10¹⁰ cells/ml in short-term experiments. T. ferrooxidans is the most important species for short-term leaching experiments. Calorimetric measurements allow the best strains for a degradation of unknown substrates to be found. The calculated heat energy is a measure of the amount of converted substrate. High heat-flow only occurs if catabolic reactions take place and maintenance reactions and phenomena like adhesion of cells to surface do not cause significant loss of heat.