EXTRACTION OF NEPTUNIUM WITH DI-ISODECYL PHOSPHORIC ACID FROM NITRIC ACID SOLUTION CONTAINING HYDROGEN PEROXIDE

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Abstract
Extraction of Np with di-isodecyl phosphoric acid (DIDPA) from HN03 solution containing H2O2> was studied from the aspect of the extraction mechanism and the enhancement of the extraction rate. Neptunium initially in the pentavalent oxidation state can be extracted into DIDPA even without any redox agents, but the extraction rate is rather slow. In the present work, H2O2 was found to accelerate the extraction. The rate was almost proportional to the 1/2-power of H2O2 concentration. Dependence of the extraction rate on HN03 concentration was also examined. Neptunium extracted into DIDPA from 0.5 M HN03 solution containing H2O2 was found to be in the tetravalent state in the organic phase, whereas neptunium in aqueous phase was in the pentavalent state. Reduction of Np(V) with H2O2 occurs rapidly in the presence of DIDPA. When the concentration of HNO3 was 4 M. the neptunium extracted was also tetravalent, but the reduction of NP(V) in an aqueous solution was also observed.