Solvent extraction studies on the extraction of U(VI) from nitric acid medium with DIDPA dissolved in dodecane

Full text: Di-isodecyl phosphoric acid (DIDPA) an organophosphorous class of extractant, is a close analog of D2EHPA. The feasibility of using DIDPA for the partitioning of actinides from high level liquid waste generated from the reprocessing of spent fuel has been established. The reports on the extraction of radionuclides such as Am(III), Cm(III), Np(V) with DIDPA from nitric acid medium are available in literature. However, this extractant has not been studied thoroughly for the extraction of uranium. Accordingly, in the present investigation the extraction behavior of U(VI) from nitric acid medium with DIDPA has been examined under different experimental conditions. The effect of different experimental variables such as nitric acid concentration, extractant concentration, temperature, stripping agent etc has been carried out on extraction of U(VI). The results obtained indicated the cation exchange mechanism in the lower acid concentration range (upto 3.5M) and salvation mechanism in the higher range (upto 6.0M). Further increase in acid concentration in aqueous phase showed the decreasing trend in D value. With increase in DIDPA concentration in the organic phase extraction of U(VI) was found to increase. The slope analysis of the data suggested the formation of neutral complex of the type UO2(NO3).(HA2)(H2A2) in the organic phase. The decrease in D value with increase in temperature indicated the exothermic nature of the extraction reaction. Stripping of uranium from loaded DIDPA with various reagents followed the order: 8M HCl > 5% (NH4)2CO3 > 8M HNO3 > citric acid > water. Synergism was observed when extraction of U(VI) was performed with DIDPA in the presence of TBP