GB760191A - Sulphur dioxide leaching of uranium containing material - Google Patents

Abstract

Uranium is recovered from iron-free finely divided material containing uranium at least in part in the tetravalent form by leaching the material with an aqueous solution containing sulphur dioxide in the presence of a soluble ferric or ferrous salt, and/or a soluble manganese salt, the solution being aerated during the leaching. The solution should contain 1-2 grams of iron per litre as a soluble salt or 0.5-1 grams of manganese sulphate per litre. After separation from the undissolved residue the uranium may be precipitated from the solution by adjusting the pH to 1.25 and adding iron powder in the presence of a soluble phosphate, arsenate or fluoride. The uranium material employed which may contain hexavalent uranium, such as pitch blende and may be constituted by uranium ore or mill tailings, is first freed of free iron by magnetic separation and thereafter formed into a pulp having a liquid solid ratio of from 1:1 to 2:1 with an aqueous sulphur dioxide solution made from water or barren recycled solution by introducing sulphur dioxide from a sulphur burner or roaster or from return processed gas, thereinto. The pulp is agitated with air at atmospheric temperature and pressure in the presence of the soluble iron or manganese salt preferably as sulphate, and the pH of the solution maintained at 1-2 by the addition preferably intermittently, of sulphur dioxide gas. The aeration should be controlled to avoid excessive removal of sulphur dioxide. If desired the leaching may be effected by percolating an aqueous solution containing sulphur dioxide with aeration through a bed of the material. In either event the resulting solution, after filtration if necessary, is adjusted to pH 1.25 by the addition of sulphur dioxide gas, and the soluble phosphate fluoride or arsenate is added together with finely divided iron powder. The precipitated slurry is treated to remove magnetically the excess metallic iron and the resulting slurry is vacuum filtered to recover excess sulphur dioxide which may be recycled to the precipitation step.