Removal and determination of thorium (IV) ions based on organophosphonic acid/TBP-modified Amberlite XAD-16 by UV-visible analysis: Equilibrium, kinetic, and thermodynamic studies

The performance of solvent-impregnated resin (SIR) technology for extracting pollutants from aqueous solutions has been extensively studied by impregnating macroporous copolymers with organophosphorus extractants. In this study, the adsorption of thorium by XAD-16 resin beads impregnated with (1-Hydroxy-1-phosphonohexadecyl) phosphonic acid/Tributyl phosphate (TBP) as an organophosphorus compound was examined and optimized as a function of pH, equilibrium time, temperature, initial Th (IV) concentration, and ionic strength of the aqueous phase. The validated UV-Visible spectroscopic method for thorium quantification demonstrated high linearity, precision, and accuracy, with an LOD of 0.044 mg L⁻¹ (0.19 μmol L-1), an LOQ of 0.439 mg L⁻¹ (1.89 μmol L-1), and an RSD of 4.9% (n=7, 100 μmol L-1 or 23.2 mg L⁻¹), confirming its sensitivity and reproducibility. It was found that over 90% removal was achieved under optimal conditions. Th(IV) extraction by the functionalized resin is governed by pseudo-second-order kinetics, while the adsorption follows the Langmuir model, with a capacity of 44.84mg g-1. Further, the effect of temperature was realized, and the thermodynamic parameters were calculated. Increasing the temperature increases the reaction rate constant and the diffusivity. Thermodynamic parameters such as ΔG°, ΔH°, and ΔS° indicate that the adsorption of Th(IV) onto impregnated XAD-16 resin was spontaneous, endothermic, and involved an increase in randomness. Desorption experiments proved that the SIR could be reused three times without any significant loss of its initial performance. The results of this study revealed that SIR XAD-16 is a promising, cost-effective material for the removal of metal pollutants in practical environmental remediation.