Enhanced dissolution of oil shale by bioleaching with thiobacilli

Oil shale was subjected to bioleaching by cultures of thiobacilli. From X-ray, electron microprobe, and thin-section petrographic analysis, the shale matrix was found to contain tightly bonded carbonate minerals. When subjected to the bioproduced acids, these carbonate minerals were removed successively from the shale matrix. This process created pits and cavities which were gradually enlarged as indicated by scanning electron micrographs of samples subjected to leaching for varying lengths of time. At the end of 14 days, essentially all available carbonates had been depleted from the solid matrix. The effected increase in porosity and permeability of the oil shale then enhanced the exposure of fuel precursors, thus facilitating their production and conversion.