Advanced solid-phase extraction of tetravalent actinides using a novel hierarchically porous functionalized silica monolith

Abstract

Separation of actinides is of great concern from the perspective of nuclear energy development and environmental issues, and the development of a highly efficient solid-phase extraction (SPE) process holds significant promise for actinide separation. However, the slow mass transfer kinetics in the currently available SPE separation media limited the throughput and efficiency, rendering the separation process more challenging. Hierarchically porous structures with well-organized and highly interconnected pore systems have been shown to provide efficient mass transfer and enhanced performance in nature. Herein, this paper reports the synthesis of a crack-free diglycolamic acid-functionalized silica monolith with hierarchical macro and meso porous structure for SPE. The hierarchically porous structures were retained upon mild modifications, which favored the convective mass transport and provided more binding sites, resulting in fast kinetics and high throughput. The separation ability was evaluated based on the separation and recovery of Th(IV) from a complex matrix. A superior Th(IV) separation performance (Kd > 2.6 × 104 mL/g) was achieved in the presence of alkaline earth metals, rare earth elements, and uranium within 1 min by batch sorption, and the maximum separation coefficients of Th(IV)/Ln(III) and Th(IV)/U(VI) exceed 1000 and 140, respectively. Particularly, the synthesized material allowed the separation of Th from monazite leachates with highly efficient recovery (> 96%) at a high flow rate (5 mL/min) by column study. Investigation of the binding mechanism revealed the formation of a stable coordination complex (Th(NO3)L3) via Th−O bonds. The material was also employed for the extraction of Pu(IV), and satisfactory sorption was achieved. Thus, this new functionalized material has potential application prospects for an improved actinide separation process.