In a process for the recovery of uranium from a wet-process phosphoric acid, comprising treating in an extraction step the preliminarily oxidized acid first with an organic solvent consisting essentially of a dialkylphosphoric acid and a trialkyphosphine oxide dissolved in an inert and unreactive organic solvent whereby there are obtained a uranium-free phosphoric acid and an organic extract consisting essentially of the solvent containing the major portion of uranium; then, in a reextraction step, separating the uranium from the organic extract as ammonium uranyl tricarbonate by reacting the organic extract with ammonium hydroxide and ammonium carbonate; and recycling the uranium-free solvent to the extraction step; an improvement comprises treating the organic extract in a reextraction apparatus having at least two stages, by (a) introducing the extract at the head of the first stage; (b) countercurrently introducing ammonia or ammonium hydroxide solution at the bottom of the first stage; the pH of the first stage being controlled and maintained at a value of 8.0 to 8.5; (c) introducing an ammonium carbonate aqueous solution at the bottom of the last stage; the amount of ammonium carbonate employed being 50-80 percent by weight of the theoretical molar quantity which is necessary to neutralize the dialkylphosphoric acid contained in the solvent and to convert the uranium to ammonium uranyl tricarbonate; and (d) regenerating the ammoniated solvent obtained after the reextraction step by treating it with an acid before recycling it to the extraction step.

An otherwise unusable western sandstone uranium ore is blended with uranium-containing phosphate rock. The mixture is then digested with sulfuric acid to produce a wet process phosphoric acid solution containing higher levels of uranium. Recovery of the uranium values from this solution can be effected by various known processes such as solvent extraction.

In the reductive stripping of uranium from an organic extractant in a uranium recovery process, the use of phosphoric acid having a molarity in the range of 8 to 10 increases the efficiency of the reductive stripping and allows the strip step to operate with lower aqueous to organic recycle ratios and shorter retention time in the mixer stages. Under these operating conditions, less solvent is required in the process, and smaller, less expensive process equipment can be utilized. The high strength H.sub.3 PO.sub.4 is available from the evaporator stage of the process.

An improved method and apparatus for effecting a substantial reduction in retention time of oxidation processes by the autoclave oxidation of ion species dissolved in aqueous solutions. In one embodiment, the invention provides for oxidation of dissolved reduced ion species including ferrous iron (Fe.sup.+2), uranium (U.sup.+4) and vanadium (V.sup.+3) from wet process phosphoric acids, or for conditioning of aqueous solutions for other uses, such as corrosion control, by raising the valence state of dissolved ion species. In accordance with the present invention, pure oxygen, present in quantity of at least 94% by volume, is utilized as an oxidizing agent with specified process parameters: temperature, pressure and mixing conditions in an autoclave reaction vessel. In a presently preferred embodiment, the following specified parameters have achieved optimum results with regard to a significant decrease of retention time of the aqueous solution treated in the autoclave vessel: temperature range of from about 120.degree. F. to about 160.degree. F., pressure range of from about 120 psi to about 150 psi and effecting agitation by the use of an impeller located near the interface of the liquid and gas mixture in the vessel to provide a dispersion of the liquid solution in the gaseous phase. In accordance with such embodiment, a reduction of retention time for oxidation of uranium (U.sup.+4 .fwdarw.U.sup.+6) and vandanium (V.sup.+3 .fwdarw.V.sup.+4) metals from wet process phosphoric acid has been found to be less than two minutes, whereas, prior processes for effecting the same oxidation results have taken at least one hour.

In a solvent extraction method a contactor comprises a forward extraction section comprising sub-sections thereof and a back extraction section comprising sub-sections thereof. To enable higher concentrations of solute to be obtained in the backwash liquor, the contactor is operated with recycle of partially-loaded solvent, via a line from a back extraction sub-section to a forward extraction sub-section.