Uranium leaching

TABLE 15-6 Settling of Aqueous Uranium Leach Liquors with Kerosine-Alkyl Phosphate Solvent ... 

Molybdenum can also be recovered economically from some uranium leach liquors, particularly those of the USA. When uranium is stripped from amine extractants by solutions of sodium chloride, any molybdenum present remains in the organic phase, and can be subsequently recovered by being stripped into a solution of sodium carbonate. A process has been operated in which the strip liquor is acidified to a pH value of 4.5 and the molybdenum is reextracted into a solution of quaternary amine chloride in kerosene.218 The extracted metal is stripped into a solution containing sodium hydroxide and sodium chloride to produce liquors containing 30-40 g of molybdenum per litre, from which calcium molybdate can be precipitated by the addition of calcium chloride. 

Surgical removal of fragments attempts to remove as many fragments as possible, but often there will be residual fragments that cannot be removed due to location and/or size. Over time the fragment sizes will decrease as the uranium leaches from these fragments the body has no other way to effectively remove such embedded fragments. 

In-situ leaching in the seams themselves proceeds with sulfuric acid or carbonate solutions. The leaching agent is fed in via injection tubes into the rock seam and brought to the surface via a central tube. In situ uranium leaching efficiency is 60 to 85%. Currently ca. 5000 t of uranium are extracted in this way. 

In addition to an energy source, the bacteria require a carbon source which may be universally available carbon dioxide or, in some instances, simple organic compounds. Lowson (1975) quotes a number of cases which suggest that bacterial activity is not greatly hindered by lack of available carbon or of trace elements since the addition of nutrients provided little or no increase in uranium leaching rates. 

J. L. Uhrie, J. I. Drever, P. J. S. Colberg, and C. C. Nesbitt, In Situ Immobilization of Heavy Metals Associated with Uranium Leach Mines by Bacterial Sulfate Reduction, Hydrometallurgy, 43 231-239 (1996). 

Small amounts of fission products leaking from faulty fuel pins or generated from uranium (leached from damaged fuel or initially present as inqiurity) deposited on the surfaces in the core (so called tramp uranium) and small amounts of activation products (most troublesome... 

The uranium industry, which has developed during and since the 1939-45 war, has given a great impetus to add leaching and in fact many of the techniques and much of the plant have been developed specially for this industry. It is of interest therefore to outline the chemistry of uranium leaching as the prime example of add leaching, since it is anticipated that many of the problems will be paralleled by similar ones in other ore leaching processes. The chemical problems are frequently the result of side reactions in which common minerals play a predominant role, and these minerals are associated with ores of the other rare metals just as frequently as with uranium ores. 

Rosenbaum, J. B. and Clemmer, J. B. Accelerated thickening and filtering of uranium leach pulps. Proc. 1st Int. Corf, on the Peaceful Uses of Atomic Energy, Geneva, 1955. Paper 528. 

Pinkney, E. T. A review of uranium leaching practice in South Africa, Symposium Uranium in South Africa. The Associated Sdentific Technical Societies of South Africa (1957). 

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