Highly Selective Separation of Thorium Using an Extraction Resin by Encapsulating an Amine-Based Ionic Liquid In Situ within a Porous Silica–Polymer Matrix Instead of Conventional Impregnation Method

Abstract

The separation of thorium from uranium and rare earths is of great significance for a thorium molten salt reactor nuclear energy system. Herein, a novel Aliquat 336@SiO₂–P extraction resin, prepared by the in situ encapsulation of an amine-based ionic liquid (Aliquat 336) into a porous silica–polymer matrix at the same time as the polymerization, was developed for the highly selective separation of Th(IV) over U(VI) and rare earth ions. Batch adsorption studies showed that the prepared Aliquat 336@SiO₂–P extraction resin has excellent selectivity, strong adsorption affinity, and high adsorption capacity for Th(IV). The adsorption process of Th(IV) follows pseudo-second-order kinetics and the Langmuir model, and the adsorption of Th(IV) is a monolayer-type, chemical, exothermic, and spontaneous process with increased entropy, achieving a maximum Th(IV) adsorption capacity (q_max) of 52.4 mg/g. Thorium is adsorbed as a complex anion in an HNO₃ solution, and its adsorption conforms to the anion exchange mechanism. Furthermore, column experiments indicated that Th(IV) can be selectively separated from simulated monazite HNO₃ leach liquor with a recovery rate as high as 97.7%, and the prepared extraction resin has good reusability. Compared to the conventional impregnation method, the Aliquat 336 extractant encapsulated in a porous silica–polymer matrix has significantly lower loss during the adsorption process. Overall, this new extraction resin demonstrates great application potential for the highly efficient separation and recovery of Th(IV) from monazite HNO₃ leach liquor.