GB798189A - Improvements in and relating to the recovery of uranium values - Google Patents

Abstract

Uranium values are precipitated from a liquor obtained by neutralizing the product of reaction of mineral acid on rock phosphate by means of a derivative of sulphoxylic acid with an aliphatic aldehyde or ketone, which also contains an alkali metal, ammonium or zinc. The rock phosphate may be opened up by means of sulphuric, hydrochloric or nitric acid or mixtures of sulphuric and nitric acids or of sulphuric acid and ammonium sulphate. Oxidizing conditions are desirable; when using sulphuric acid alone or with ammonium sulphate a stream of air may be passed through the mixture. Thereafter solids may if desired be removed, and neutrlization is carried out to a point at which the sulphoxylate derivative is an effective reducing precipitant, e.g. to above pH 2, such as pH 3.5-5, with a reagent such as gaseous ammonia, the hydroxides or carbonates of ammonia, an alkali metal or an alkaline earth metal. It is desirable to remove solids, if present, after this neutralization. A filter aid such as kieselguhr, silica, fuller's earth or diatomaceous earth may then be added and the uranium pecipitated (as phosphate) with the sulphoxylate derivative (formaldehyde, acetaldehyde or acetone derivatives being specified), e.g. at 70 DEG C. to the boiling point. The solid may be filtered off and if desired washed; a part of the slurry obtained during the precipitation step may if desired be returned before filtering to a previous stage in the process, e.g. that preceding precipitation, as can the washings, if any. The uranium may be recovered (1) by dissolving the solid in mineral acid, preferably under oxidizing conditions, e.g. with nitric acid or with sulphuric acid and manganese dioxide; and (a) treating with an oxidizing agent such as hydrogen peroxide to precipitate hydrated uranium tetroxide (in this case the reduction precipitate must be well washed); if desired before this treatment the pH of the solution may be increased to 0.5 by dilution or addition of alkali, e.g. aqueous ammonia; or (b) after removal of the filter aid, adjusting the pH value, e.g. with ammonia, to about 1.0 to give after stirring a precipitate probably of uranyl ammonium phosphate (NH4UO2PO4) which may be ignited; or alternatively (2) by proceeding as in Specification 775,119 and extracting the solid with an aqueous alkali metal or ammonium carbonate or bicarbonate, precipitating the phosphate with a suitable cation, e.g. calcium, magnesium or ferric, and recovering the uranium values from the liquid; when using this method the solid must be first oxidized to the hexavalent state, e.g. with hydrogen peroxide or alkali metal dichromate or permanganate. In an example phosphate rock is opened up with sulphuric acid and ammonium sulphate whilst passing in air at 50 DEG C., the mixture filtered, sodium silicofluoride removed conventionally (not described) and the pH adjusted to 4.0 and the liquid filtered. Kieselguhr is added with sodium formaldehyde sulphoxylate and the mixture warmed to 80 DEG C. The solid is then treated as in (1) (b) above. Specification 768,946 also is referred to.