Selective recovery of Th(IV) from radioactive rare earth waste residue by utilizing MoS2-modified ion-absorbed type rare earth tailings

Abstract

In the process of extracting ion-absorbed rare earth ore (IREO), the production of radioactive waste is a major environmental concern. To address this issue, MoS2 was used to modify ion-absorbed rare earth tailings (RET) to synthesize a novel MoS2@RET composite material for the effective handling of radioactive waste generated in IREO separation industry. The composite material was thoroughly characterized using various analytical techniques, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetry (TG), Fourier-transform infrared (FTIR), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) and energy dispersive spectroscopy (EDS). By optimizing the operating parameters, the optimal experimental conditions were determined to be pH = 3, contact time = 60 min, liquid-solid ratio = 6 g/L, and initial concentration = 150 mg/L. The adsorption data fitted well with the pseudo second-order rate model. The thermodynamic parameters concerning the adsorption of Th(IV) were analyzed and computed. Langmuir isotherm model is a more fitting choice for the adsorption process compared to the Freundlich isotherm model. MoS2@RET was used in the acid leachate of IREO waste residue, achieving the separation of Th and rare earth successfully. The mechanism of Th(IV) adsorption by MoS2@RET was investigated, revealing that the adsorption process involves electrostatic interactions, chemical bonding, and redox reactions. The above research results indicate that MoS2@RET composite materials have application potential in the sustainable treatment of IREO radioactive waste.