The acid leaching of a pyrite-rich black shale concentrate (7% S) was tested in this study. The experiments were performed at 5-30% pulp densities and with inoculations of Fe-and S-oxidizing thiobacilli (Thiobacillus ferrooxidans and Thiobacillus thiooxidans). Cultures supplemented with S° showed strong acid production, with final pH values of 0.9 in T. ferrooxidans cultures and 0.4-0.5 in the presence of T. thiooxidans. Fe dissolution was pronounced in the T. ferrooxidans culture whereas T. thiooxidans did not dissolve Fe from the black shale. Total dissolved Fe concentrations were 3 to 50 times higher in the cultures inoculated with T. § TASA ET AL.ferrooxidans when compared to T. thiooxidans and sterile controls. The dissolution of Mo was enhanced in the inoculated cultures as compared with the chemical controls.With V, Si, and Al this effect was not as pronounced but was still discernible in solutions acidified by bacterial oxidation of S°. The leaching experiments suggested that the black shale was inhibitory to the inocula. The inhibition was related to the pulp density and was associated with the leach solution. The inhibition could be completely alleviated by replacing the leach solution.

Sulfur removal from oil shales through bioprocessing can substantially reduce SO; emissions from thermal power plants that combust oil shales for energy production. Iron sulfides constitute the most significant inorganic sulfur fraction in shales. There are several Fe-and S-oxidizing microorganisms that have potential for oxidizing iron sulfides 10 soluble products in acid sulfate-containing solutions.Environmental factors that influence the activities of these organisms are discussed. The organic sulfur compounds in shale matrix are variable and complex. Microbiological transformations of the organic sulfur fraction are poorly understood and it is not clear whether they are amenable to shale bioprocessing.The paper summarizes previously published experimental studies where shales were contacted with bacteria for iron sulfide oxidation. Shales constitute a complex system of study because they contain several phases such as clay minerals, sulfides, organic matter, and carbonates that interact with each other