Solvent Extraction of Thorium Nitrate and Nitric Acid by Tributyl Phosphate

The extraction equilibrium of Th(NO3)4 and HNO3 in the system Th(NO3)4–HNO3–H2O–TBP was studied. The concentrations of Th(NO3)4 and HNO3 in aqueous solution were maintained at relatively higher levels. The infrared absorption spectra and physico-chemical properties of the equilibrated organic phase were measured in addition to the equilibrium distribution of Th(NO3)4 and HNO3. The H2O concentration in the organic phase was also measured. The extraction equations of HNO3 and Th(NO3)4 were summarized as 2[TBP·H2O](O)+HNO3(A)=[2TBP·HNO3·2H2O](O) and 4[TBP·H2O](O)+Th(NO3)4(A)=[Th(NO3)4·4TBP](O)+4H2O(A) respectively. Using the Redlich-Kister equation, the equilibrium constants of the above extraction equations were calculated to be 17.3 and 0.79, respectively. The activity coefficients of the extracted species positively deviate from ideality.