GB768282A - Leaching uranium from sulphidic materials - Google Patents

Abstract

Uranium is extracted from uranium bearing materials by forming a slurry thereof in an aqueous medium with at least one of the group consisting of mineral sulphides and elemental sulphur in an amount sufficient to produce in the aqueous medium after oxidation, a pH less than 3 and heating the pulp produced to a temperature above 80 DEG C. in the presence of an oxygen bearing oxidizing gas and continuing the oxidation reaction to dissolve the uranium in the leach solution as uranyl sulphate and thereafter separting the leach solution from the undissolved residue. The aqueous medium employed may be water or an acid aqueous sulphate solution such as recycled sulphate-sulphuric acid solution. Uranium ores such as pitchblende, torbernite, metatorbernite, and autunite may be so treated and the required mineral sulphide may be associated naturally with such ores or added in the form of pyrite or pyrrhotites or as elemental sulphur. Oxygen partial pressures are preferably from 5 to 10 lbs. per sq. inch and air, enriched or not with oxygen, pure oxygen, or oxygen containing gaseous diluents such as nitrogen may be employed. According to an example, an ore containing sulphur was ground and mixed with water and charged to an autoclave where it was heated to about 125 DEG C. in the presence of oxygen having a partial pressure of 30 p.s.i. under a total pressure of 45 lbs. gauge p.s.i. The leach solution had a final pH of 1.4 and this was treated after separation from the undissolved residue with ammonia to raise the pH to 8 whereupon the uranium precipitated as ammonium diuranate, leaving a solution containing ammonium sulphate which may be recovered by evaporation. In the preferred operation the leach solution from a previous operation is recycled to slurry a further batch of ore and thus the concentration of uranium can be increased before it is precipitated. In a continuous operation, the pulp leaving the leaching stage is filtered and part of the leach solution is recycled to the leaching stage and part treated to recover uranium. The ammonium uranate contaminated by coprecipitated hydroxides of Fe, Al and Mn, may be ignited to form impure U3O8 or purified by leaching with a carbonate solution to dissolve the uranium and separate it from iron, aluminium and manganese. Dissolution of the latter contaminants in the initial leaching may be minimized by leaching at 100-150 DEG C.