U(VI) adsorption mechanisms and behavior of red soil aggregates in typical uranium tailings mining areas in Jiangxi, China

This study investigated the adsorption behavior and mechanisms of uranium on red soil aggregates of different particle sizes from a typical uranium tailings area in Jiangxi Province. Static adsorption experiments were conducted to examine the interaction between uranium and soil aggregates, with the aim of elucidating the characteristics of exogenous uranium contamination. The adsorption kinetics followed a pseudo-second-order kinetic model, indicating chemisorption-dominated processes at equilibrium. Isothermal adsorption analysis revealed that aggregates S1 and S3 adhered to the Langmuir model, suggesting monolayer adsorption, whereas S2 and S4 followed the Freundlich model, implying heterogeneous multilayer adsorption. Scanning electron microscopy (SEM) and spectroscopic analyses demonstrated that the surface morphology of the aggregates remained largely unchanged after adsorption, and their aggregated structure was maintained. Further characterization indicated that uranium adsorption primarily occurred through (i) complexation with surface functional groups (–OH, Si–O, Si–O–Fe, Si–O–Al, Fe–O) and (ii) redox reactions with iron-bearing minerals in the aggregate. These findings provide critical insights into the immobilization mechanisms of uranium in red soils, which are relevant for environmental remediation strategies in uranium-contaminated areas.