Biological Leaching of Uranium from Low-grade Uraniferous Black Shale by Acidithiobacillus Ferrooxidans

摘要

The main purpose of present study was to characterize the dissolution of uranium from low-grade black shale with indigenous isolated strain of Acidithiobacillus ferrooxidans (BSAF-01). The nature of shale is quartzite-schistose and contains uranium content of 0.005% U3O8 (50 ppm U3O8). Uranium is present in the tetravalent oxidation state (U4+) in the shale matrix. The main minerals identified are graphite, quartz, pyrite, mica minerals (phlogopite, biotite, sericite, and chlorite), microcline,K-feldspar and kerogen (hydrocarbon-compounds). Bacterial oxidation of pyrite was an acid-generating system and produced sulfuric acid and ferric sulfate during this biological phenomenon.A series of bioleaching experiments were conducted in shake flasks for leaching of uranium from black shale. The leaching experiments were performed at 50% pulp density using indigenous Feand S-oxidizing bacterium (Acidithiobacillus ferrooxidans), Bioleaching data revealed that about 90%～95% U3O8 was leached out from black shale ore. Uranium dissolution from shale depends on pH (pH 1.5～1.9), redox potential (≥500 mev) and the concentration of Fe2+ and Fe3+ ions in the leaching environment. The oxidative leaching of U4+ involves a redox reaction with Fe3+ as an oxidant and bacterial re-oxidation of Fe2+ in acidic leaching environment. Uranium leaching efficiency was attributed to the sulfuric acid and ferric sulfate production during bacterial oxidation of pyrite.