The adsorption of Thiobacillus ferrooxidans on coal surfaces

The adsorption of Thiobacillus ferrooxidans to coal surfaces has been studied. Adsorption experiments were conducted on coal samples from eight different Eastern coal fields. In all cases the adsorption process was at least 90% complete within the first two minutes following inoculation. The results of these experiments were used to test the validity of two proposed adsorption models. The first model assumes that bacterial adsorption follows second-order irreversible kinetics of the second kind with respect to the concentration of bacteria and substratum surface area in the system. The second model allows for the contribution of reversible adsorption detected in desorption experiments. It was found that the combined reversible-irreversible model more accurately describes the initial stages of adsorption. Rate constants in both models were calculated for each coal sample. The relation of each of these constants to the pyrite concentration in coal is presented and the significance of these relations is discussed. Scanning electron micrographs of inoculated coal samples show that Thiobacillus ferrooxidans selectively adsorb to exposed pyrite phases dispersed throughout the organic coal matrix. Preferential attachment was also observed along topographical faults in the coal surface. Mercury contact angle measurements on coal indicate that the selective adsorption of Thiobacillus ferrooxidans may be attributable to the lower surface free energy of pyrite relative to the organic coal matrix.