Extraction of uranium (IV) from wet phosphoric acid with a kerosene solution of nonylphenyl phosphoric acids

A uranium(IV) recovery process from wet phosphoric acid produced by the dihydrate method was elaborated. Decomposition of phosphate rock containing more than 0.01% U is carried out with sulphuric acid, partially applying 10-20% waste sulphuric acid derived from a titanium oxide plant. A solution of this acid containing FeSO4 is introduced into the reactors through the phosphogypsum filter cake, in the washings to the last but one filter zone, applying the countercurrent system. This enables a partial recovery of uranium from phosphogypsum. Crude wet process phosphoric acid is filtered off and then clarified with mineral-carbon adsorbents, in order to reduce the content of organic compounds included in the phosphate rocks and those introduced into the decomposition process to lower the foam stability. After separating the clarified precipitate, the clear phosphoric acid is introduced to extraction cycle I, where U(IV) is effectively extracted using a kerosene solution of equimolar mixture of mono- and di-nonylphenyl phosphoric acids (NPPA). The NPPA process is characterized by a very high distribution coefficient (Ksub(e)=3-50) and a high stability and resistance to deterioration. A three-stage NPPA countercurrent extraction system is followed by five-stage oxidative stripping using 8M H3PO4 containing 0.2% NaClO3. This U-laden acid is not reduced back, but is diluted to 5-6M H3PO4 and U(IV) is directly extracted by a kerosene solution of a mixture of D2EHPA and TOPO. Ammonium uranyltricarbonate is precipitated from this solution by the action of NH3 and CO2. Over 90% uranium recovery is obtained. (author)