Process for producing phosphoric acid

A process for rendering uranium readily recoverable in a process for producing phosphoric acid and gypsum by (1) digesting phosphate rock containing small amounts of uranium with sulfuric acid and phosphoric acid to produce a high concentration of phosphoric acid and calcium sulfate hemihydrate, (2) filtering the resulting mixture to separate the concentrated phosphoric acid, (3) reslurrying the calcium sulfate hemihydrate and hydrating to produce calcium sulfate dihydrate in a low concentration phosphoric acid, (4) filtering the resulting mixture to obtain the calcium sulfate dihydrate as a by-product and the low concentration phosphoric acid as effluent, and (5) recycling the low concentration phosphoric acid effluent to an earlier process step, the improvement which comprises reducing the uranium in the digestion step (1) from the +6 valence state to the +4 valence state and thereby rendering said uranium insoluble in the wet process acid solution and causing same to precipitate with the calcium sulfate hemihydrate, and oxidizing said uranium during the reslurrying step (3) from the +4 valence state to the +6 valence state and thereby rendering said uranium soluble in the low concentration phosphoric acid and recoverable therefrom.