A highly efficient solvent system containing functionalized diglycolamides and an ionic liquid for americium recovery from radioactive wastes
作者:Arijit Sengupta、Prasanta K. Mohapatra、Mudassir Iqbal、Jurriaan Huskens、Willem Verboom
DOI:10.1039/c2dt12364a
日期:——
Three room temperature ionic liquids (RTILs), viz. C4mim+·PF6−, C6mim+·PF6− and C8mim+·PF6−, were evaluated as diluents for the extraction of Am(III) by N,N,N′,N′-tetraoctyl diglycolamide (TODGA). At 3 M HNO3, the DAm-values by 0.01 M TODGA were found to be 102, 34 and 74 for C4mim+·PF6−, C6mim+·PF6− and C8mim+·PF6−, respectively. The extraction of Am(III) decreased with increasing feed acidity for all three diluents, indicating an ion exchange mechanism for the extraction. The stoichiometry of the extracted species suggested that two TODGA molecules were associated with Am(III) during the extraction for all three RTILs and the conditional extraction constants have been determined. The DM-values for different metal ions followed the order: 75 (Am(III)) > 30.7 (Pu(IV)) > 3.9 (Np(IV)) > 1.19 (Pu(VI)) > 0.52 (U(VI)) > 0.12 (Cs(I)) > 0.024 (Sr(II)). The distribution behaviour of Am(III) was also studied with a recently synthesized calix[4]arene-4DGA (C4DGA) extractant dissolved in C8mim+·PF6−. Using this extractant diluent combination, the DAm-value was 194 at 3 M HNO3 using 5 × 10−5 M C4DGA, suggesting a very high distribution coefficient at very low extractant concentrations. The stoichiometry of the extracted species containing Am was found to be 1 : 2 (M : L) in C8mim+·PF6−. The thermodynamics of the extraction was also studied for both extractants in C8mim+·PF6−. The use of RTILs gives rise to significantly improved extraction properties than the commonly used n-dodecane and an unusual increase in separation factor values was seen for the first time which can lead to selective separation of Am from wastes containing a mixture of U, Pu and Am.
评估了三种室温离子液体(RTILs),即 C4mim+-PF6-、C6mim+-PF6- 和 C8mim+-PF6-,作为 N,N,N′,N′-四辛基二乙二醇酰胺(TODGA)萃取 Am(III)的稀释剂。在 3 M HNO3 条件下,0.01 M TODGA 对 C4mim+-PF6-、C6mim+-PF6- 和 C8mim+-PF6- 的 DAm 值分别为 102、34 和 74。在所有三种稀释剂中,Am(III)的萃取率随着进样酸度的增加而降低,这表明萃取过程中存在离子交换机制。萃取物的化学计量学表明,在所有三种 RTIL 的萃取过程中,都有两个 TODGA 分子与 Am(III) 结合,并确定了条件萃取常数。不同金属离子的 DM 值依次为75 (Am(III))> 30.7(Pu(IV)> 3.9 (Np(IV)1.19 (Pu(VI)) > 0.52 (U(VI))> 0.52(U(VI)> 0.12(铯(I)>0.024(Sr(II))。我们还利用最近合成的溶于 C8mim+-PF6- 的钙[4]炔-4DGA(C4DGA)萃取剂研究了 Am(III) 的分布行为。使用这种萃取剂稀释剂组合,在3 M HNO3中使用5 × 10-5 M C4DGA时,DAm值为194,这表明在萃取剂浓度很低的情况下,分布系数非常高。在 C8mim+-PF6- 中,含有 Am 的萃取物的化学计量为 1 : 2 (M : L)。还研究了 C8mim+-PF6- 中两种萃取剂的萃取热力学。与常用的正十二烷相比,RTILs 的使用大大提高了萃取性能,分离因子值也首次出现了不寻常的增长,从而可以从含有铀、钚和镅混合物的废物中选择性地分离出镅。