Extraction of actinide(III, IV, V, VI) ions and TcO4- by N,N,N′,N′-tetraisobutyl-3-oxa-glutaramide

The extraction behavior of U(VI), Np(V), Pu(IV), Am(III), and TcO4- with N,N,N',N'-tetraisobutyl-3-oxa-glutaramide (TiBOGA) were investigated. An organic phase of 0.2 mol/L TiBOGA in 40/60% (V/V) 1-octanol/kerosene showed good extractability for actinides (III, IV, V VI) and TcO4- from aqueous solutions of HNO3 (0.1 to 4 mol/L). At 25 degrees C, the distribution ratio of the actinide ions (D-An) generally increased as the concentration of HNO3 in the aqueous phase was increased from 0.1 to 4 mol/L, while the D-Tc at first increased, then decreased, with a maximum of 3.0 at 2 mol/L HNO3. Based on the slope analysis of the dependence of D-M (M = An or Tc) on the concentrations of reagents, the formula of extracted complexes were assumed to be UO2L2(NO3)(2), NpO2L2(NO3), PuL(NO3)(4), AmL3(NO3)(3), and HL2(TcO4) where L = TiBOGA. The enthalpy and entropy of the corresponding extraction reactions, Delta H-r and Delta S-r, were calculated from the dependence of D on temperature in the range of 15-55 degrees C. For U(VI), Np(V), Am(III) and TcO4-, the extraction reactions are enthalpy driven and disfavored by entropy (Delta H-r < 0 and Delta S-r < 0). In contrast, the extraction reaction of Pu(IV) is entropy driven and disfavored by enthalpy (Delta H-r > 0 and Delta S-r > 0). A test run with 0.2 mol/L TiBOGA in 40/60% 1-octanol/kerosene was performed to separate actinides and TcO4- from a simulated acidic high-level liquid waste (HLLW), using tracer amounts of U-238(VI), Np-237(V), Pu-239(IV), Am-241(III) and (TcO4-)-Tc-99. The distribution ratios of U(VI), Np(V), Pu(IV), Am(III) and TcO4- were 12.4, 3.9, 87, >1000 and 1.5, respectively, confirming that TiBOGA is a promising extractant for the separation of all actinides and TcO4- from acidic HLLW. It is noteworthy that the extractability of TiBOGA for Np(V) from acidic HLLW (D-Np(V) = 3.9) is much higher than that of many other extractants that have been studied for the separation of actinides from HLLW.