Th(IV) and U(VI) removal by TODGA in ionic liquids: extraction behavior and mechanism, and radiation effect

Extraction behavior of thorium(IV) and uranium( VI) from nitric acid (HNO3) was studied using N,N,N0,N0-tetraoctyldiglycolamide (TODGA) as extractant in different ionic liquids, and isooctane as comparison.Slope analyses with varying HNO3 concentrations and diluents revealed the extraction mechanism. With increasing length of alkyl chain and HNO3 concentration, the extraction mechanism of TODGA/IL system changed from cation exchange to neutral complex and/or anion exchange,and the molar ratio between TODGA and metal ions varied gradually from 2:1 to 1:1 for Th(IV) and 3:1 to 1:1 for U(VI). The kinetics and thermodynamic studies of Th(IV) and U(VI) by the best TODGA/[C2mim][NTf2] system showed that the extraction equilibrium was reached within 2 h and extraction reactions were endothermic. Compared to TODGA/isooctane system, TODGA/[C2mim][NTf2] system presented higher radiation stability under cirradiation.Therefore, it would have a promising application in spent fuel reprocessing.