Demineralization of an oil shale by Bacillus circulans (“siliceous bacteria”)

Abstract

Experiments are presented aimed at removing the silicates from an oil shale by a chemoorganoheterotrophic bacterium, Bacillus circulans. This process was expected to substitute the drastic HF-treatment in the kerogen concentrate preparation procedure. Three Bacillus circulans strains were isolated from siliceous habitats. Tests showed that they were not using the shale organic matter as source of carbon. The substrates were the raw oil shale from Aleksinac, Yugoslavia (-0.063 mm), and the corresponding neutralized HCl- and HCl-kerogen-concentrates. The solid/liquid ratio was 1:10 (w/v), the liquid phase being 2% glycerol in distilled water. In all experiments with the shale concentrates, the pH decreased to ca 3. This resulted in a decrease of the number of bacteria and hence failure in demineralization, the lowest pH limit for the growth being ca 4. The raw shale was shown to be the most favourable substrate due to the buffer effect of the carbonates. The achieved leaching was obviously much better but not yet optimal. So far the total effects were found to be 21.4, 18.7 and 17.2%, respectively. Several possible ways are suggested for improving the efficiency of the process.