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摘要
The extraction behavior of U(VI),Np(V),Pu(IV),Am(III),and TcO_4~- 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 TcO_4~- from aqueous solutions of HNO_3 (0.1 to 4 mol/L).At 25 deg C,the distribution ratio of the actinide ions (D_(An)) generally increased as the concentration of HNO_3 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 HNO_3.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 UO_2L_2(NO_3)_2,NpO_2L_2(NO_3),PuL(NO_3)_4,AmL_3(NO_3)_3,and HL_2(TcO_4) where L = TiBOGA.The enthalpy and entropy of the corresponding extraction reactions,DELTA_rH and DELTA_rS,were calculated from the dependence of D on temperature in the range of 15-55 deg C.For U(VI),Np(V),Am(III) and TcO_4~-,the extraction reactions are enthalpy driven and disfavored by entropy (DELTA_rH < 0 and DELTA_rS < 0).In contrast,the extraction reaction of Pu(IV) is entropy driven and disfavored by enthalpy (DELTA_rH > 0 and DELTA_rS > 0).A test run with 0.2 mol/L TiBOGA in 40/60% 1-octanol/kerosene was performed to separate actinides and TcO_4~- from a simulated acidic high-level liquid waste (HLLW),using tracer amounts of ~(238)U(VI),~(237)Np(V),~(239)Pu(IV),~(241)Am(III) and ~(99)TcO_4~- . The distribution ratios of U(VI),Np(V),Pu(IV),Am(III) and TcO_4~- 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 TcO_4~- 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.
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