Abstract: An improved method for the wet process manufacture of concentrated phosphoric acid is disclosed herein. A mixture of gaseous sulfur trioxide and sulfuric acid now replaces concentrated sulfuric acid as a process reactant which results in a higher heat of reaction and the ability to evaporate out of the reaction slurry increased inputs of water. With this method the increased inputs of water, either from undried phosphate rock, wet grinding of phosphate rock, use of dilute sulfuric acid, or from other sources will not interfere with associated high P.sub.2 O.sub.5 yields, lower concentrations of filtrate phosphoric acid and/or unbalance the zero steam requirements.

Abstract: Phosphoric acid and gypsum are produced from phosphate rock by digesting same with sulfuric acid to produce a high concentration of phosphoric acid and calcium sulfate hemihydrate. The solubilized uranium in the rock is rendered recoverable by reducing same from the +6 valence state to the +4 valence state during the digestion step followed by oxidizing back to the +6 valence state in a subsequent step.