Extraction of Uranium and Thorium from Nitric Acid Solution by TODGA in Ionic Liquids

Abstract

Extraction of uranium (UO22+) and thorium (Th4+) from a nitric acid solution into an imidazolium-type ionic liquids (ILs) of 1-alkyl-3-methylimidazolium hexafluorophosphate ([Cnmim][PF6], n = 6 or 8) was carried out using N,N,N′,N′-tetraoctyl-3-oxapentanediamide (TODGA) as an extractant. It was found that the extraction efficiencies of UO22+ and Th4+ ions are higher in comparison with that done in n-dodecane. The extraction mechanism was deduced by the slope analysis and extraction experiment. Transfer of both ions is assumed to proceed predominantly through the neutral solvation mechanism from nitric acid solution into ILs. The UO22+ ion forms a 1:2 complex with TODGA in ILs at lower acidity, and a 1:1 complex in ILs and in n-dodecane at higher acidity. The Th4+ ion forms a 1:2 complex with TODGA in C6mimPF6 IL or a 1:1 complex in C8mimPF6 IL at lower acidity and a 1:1 complex in both ILs, and n-dodecane at higher acidity. Stripping studies were conducted using sodium salt of EDTA as a stripping ligand. The thermodynamics of extracting UO22+ ions and Th4+ ions from a 3 M HNO3 solution was also studied. The results indicated that the extraction reactions are spontaneous and go through an exothermic process.