Selective adsorption of Th(IV) using novel MoX2 (X = S, Se)-α-zirconium phosphate composites from simulated monazite and bastnaesite leachates

The mining, processing, and refining of rare-earth ores generate Th-rich radioactive wastewater, making its effective treatment critical for environmental protection and public health. In this study, mesoporous MoX 2 -α-ZrP (X = S, Se) composite powders were synthesized for Th(IV) adsorption from aqueous solutions. Under the conditions of [Th(IV)] initial = 50 ± 2 mg·L −1 , pH initial = 3, temperature = 298 K, and a contact time = 1440 min, the larger pore volume and pore width of the composites, compared with α-ZrP, enhanced the adsorption capacity ( q e ) of MoSe 2 -α-ZrP and MoS 2 -α-ZrP to 146.3 ± 7.4 mg·g −1 and 143.7 ± 2.5 mg·g −1 , respectively. Higher pH, [Th(IV)] initial, and temperature further enhanced Th(IV) adsorption. Notably, MoX 2 -α-ZrP removed Th(IV) from simulated leaching solution of monazite or bastnaesite and selectively adsorbed Th(IV) in the presence of co-existing ions. Thermodynamic and kinetic analyses confirmed a spontaneous, endothermic, and homogeneous chemisorption behavior. The Thomas and Yoon-Nelson models accurately described dynamic column Th(IV) adsorption, and increases in adsorbent mass, together with decreases in influent Th(IV) concentration, and reduced flow rate extended both breakthrough and saturation times. Mechanistic studies revealed Th(IV) coordination with oxygen-containing groups, ion exchange with -OH, and electrostatic interaction with phosphate groups. Results from our study can help explore the adsorption behaviors and mechanisms of Th(IV) on potential MoX 2 (X = O, S, Se)-based or α-ZrP-based materials for treating Th-rich radioactive wastewater.