A study of the physiology of sulphur-oxidizing bacteria and its effect on uranium mobilization and leaching at Udaisagar, Udaipur District, Rajasthan

Abstract

An area of 6.14 sq km lying between latitude 24° 34¢ and 24° 36¢N and longitude 73° 46¢ and 73° 48¢ E in the vicinity of Udaisagar Uranium Prospecting shaft, north of the Udaisagar Lake, was investigated to study the role of sulphur-oxidizing bacteria on the deposition of uranium in the breccia zone and on the solubilization of uranium with dilute H2SO4 during leaching tests. The ore is a brecciated granite which has intrided into the carbonaceous phyllite. The ore in the vicinity of the shaft, analysed 0.7% FeO, 2.31% Fe2O3, 6.3% C, 2.97% sulphate, 0.85% moisture and 0.03% U3O8 and has a bacterial population of 2.3 x 106/g of dry solids, a pH of 2.2 to 4.5, Eh of -300 to -600mv. The carbonaceous phyllite provides a zone of reduction near its contact with calcareous phyllites. It analyses 0.0005 to 0.0027% U3O8, 3.04% FeO, 2.96% Fe2O3, 11.2% C, 3.1% sulphides, 0.11% sulphate and 0.15% moisture, with a pH of 7.0 to 8.5 and a redox potential of -200 to -290 mv. Thiobacillus ferrooxidans and Thiobacillus thiooxidans were identified in this zone and isolated. A study of the behaviour of the bacteria with the use of sulphur, sulphite, thio-sulphite and ferrous sulphite, as electron donors, showed that the sulphur and iron-oxidizing bacteria are active oxidants. This is borne out by the fact that leaching of uranium from the ore analysing 0.03% U3O8 showed that 43.3% of the contained uranium could be leached only with the help of normal water in as little as 6 hours time. With the addition of a small quantity of H2SO4, leachability rises to 80.0% in the same leaching time. (S.C. Kulshrestha, K.M.V. Jayaram & K.K. Dar, Atomic Minerals Division, New Delhi)