Uranium recovery from phosphoric acid by solvent extraction using a synergistic mixture of di-nonyl phenyl phosphoric acid and tri-n-butyl phosphate

Extraction of uranium from fertiliser-grade phosphoric acid with a novel synergistic mixture of di-nonyl phenyl phosphoric acid (DNPPA) and tri-n-butyl phosphate (TBP) is reported in this paper. The effects of varying the concentrations of phosphoric acid, DNPPA and TBP on the distribution ratio of uranium have been studied. Batch counter-current extraction tests have been carried out. The extracted uranium in the organic phase was efficiently stripped at 65 °C using concentrated phosphoric acid containing ferrous iron. The stability of the solvent was investigated by extended contact testing as well as cyclic extraction and stripping tests. The data on the effect of temperature on the extraction showed that the enthalpy change is −24 kJ/mol when DNPPA-TBP is used as the extractant, more than double when DNPPA alone was used. Uranium extracted by DNPPA-TBP is further subjected to a second cycle of extraction using D2EHPA-TBP and scrubbing impurities. The uranium is finally converted to a high purity UO3 product using precipitation with hydrogen peroxide and heat treatment at 200 °C.