Solvent extraction studies on U(VI), Pu(IV),and fission products using N,N-dihexyloctanamide

The extraction behaviour of nitric acid, uranium(VI), and plutonium(IV) has been investigated using N,N-dihexyloctanamide (DHOA) in n-dodecane. Result s indicate that, similar to TBP, the amide extracts HNO3, U(VI), and Pu(IV) as HNO3.DHOA UO2(NO3)(2).2DHOA and Pu(NO3)(4).2DHOA respectively, from mod erately acidic solutions (3.5 M HNO3). On the other hand at higher aciditie s (8.5 M HNO3), similar to tertiary amines, anionic species, UO2(NO3)(3)- a nd PU(NO3)(6)(2-) are extracted as [UO2(NO3)(3)(-)] [HDHOA(+)] and [Pu(NO3) (6)(2-)] [HDHOA(+)](2) respectively, by ion-pair formation. The basicity of the amide (K-H= 0.188), indicated by the equilibrium constant for the upta ke of nitric acid is marginally larger than that of TBP (0.160). The third phase formation in H2O-HNO3-0.5 M DHOA-n-dodecane system occurs when nitric acid concentration in the aqueous phase approaches a value of 9 M. The equ ilibrium constant values(log K-ex) for the formation of UO2(NO3)(2).2DHOA a nd Pu(NO3)(1).2DHOA solvates are evaluated as 1.49 +/- 0.01 and 3.55+/- 0.0 2 respectively. Preliminary data on temperature effect, extraction and stri pping from fission products are also included.