ABSTRACT
Uranium occurs in nature in low concentrations in soil, rock and water. Uranium-bearing minerals such as uraninite, carnotite, autunite, uranophane, torbernite and cof-finite are the commercial sources of the metal. The impurities of rare-earth metals are separated by increasing the pH in the sulphate solution. The extraction of other metals such as antimony, copper, lead, molybdenum, silver, tin, tungsten and zinc often yields bismuth as a by-product. Production of bismuth is largely in the form of its compounds which are used in cosmetics, pigments and pharmaceuticals, notably Pepto-Bismol, for the treatment of diarrhoea. The processing of crude lead bullion through several stages to a refined product co-produces bismuth. In the course of extracting rare earth metals from monazite, thorium is refined as a byproduct. When nitric acid leaches thorium diphosphate, thorium nitrate is produced which can be treated with tributyl phosphate.
