Selective separation and preconcentration of Th(iv) using organo-functionalized, hierarchically porous silica monoliths

Abstract

The potential application of thorium (Th) as nuclear fuel, as well as the environmental and public health concerns associated with it, promotes the development of economic and sustainable materials for the separation and removal of Th(iv) from minerals and environmental samples. In this work, centimeter-size, porous silica monoliths exhibiting hierarchical macroporosity-mesoporosity and a robust silica skeleton were prepared using a sol-gel process combined with post-synthetic hydrothermal treatment in ammonium hydroxide. Upon functionalization with diglycolamide (DGA), the resulting monolithic hybrid material was used as a column-type fixed bed sorbent for continuous flow extraction. An enhanced Th(iv) uptake from aqueous solution was achieved with a high enrichment factor and selectivity in the presence of competitive ions such as rare earth elements (REEs) and uranium (U). Systematic mechanistic studies show that the hierarchical pore system is crucial for enhanced adsorption kinetics and capacity. Two mineral leachates were used to assess the performances of the hybrid material, and despite the complex ion matrix and high ionic composition, the sorbent shows highly efficient recovery of Th(iv). The material was able to undergo 10 extraction-stripping-regeneration cycles, which bodes well for potential industrial applications.