Selective extraction of thorium to directly form self-assembly solid from HNO3 solution

Abstract

Based on ions exchange between [DMDSA]⁺[Cl]^- (Dimethyl distearyl ammonium chloride) and N,N-dialkyl-succinamide acid (SCA), three novel bifunctional [DMDSA]⁺[SCA]^- ionic liquids (ILs) were firstly synthesized for extraction of thorium (IV) by self-assembly strategy. The simultaneous extraction and solidification of Th(IV) were unexpectedly realized in one-step operation using the present ILs in HNO₃ solution, and more than 99% thorium (IV) was enriched and immediately aggregated into self-assembly solid at the biphasic interface. The self-assembly solid was further identified by FT-IR, SEM with element mapping EDS and XPS analysis, and revealing that the self-assembly extraction (SAE) was triggered by the amphiphilic [DMDSA]⁺ cations. A three-step extraction mechanism dominated by [SCA·Th(NO₃)₄]^- was proposed based on the slope analysis method and HRMS analysis. The self-assembly extraction of Th(IV) exhibited the extremely excellent selectivity in the presence of U(VI) and typical lanthanide elements including La(III), Eu(III) and Lu(III), and the separation factors reached 2516 for Th/U, 1885 for Th/La, 1512 for Th/Eu and 558 for Th/Lu, respectively. The proposed SAE strategy was proved to be an efficient method for one-step separation and solidification of thorium ions from U(VI) and/or lanthanides.