Evaluation of samarium (III) recovery from aqueous model solutions using chemically activated Salvadora persica biomass

The removal of the rare earth element, samarium, from water has gained close environmental attention due to its recent use in technologies and industries and its toxic effects. Therefore, the potential use of activated Salvadora percia sticks (SPS) as a highly efficient biosorbent for samarium (III) ions in model solutions under controlled experimental conditions was assessed. The raw SPS biomass was separately pre-treated with HCl (SPS-A) and NaOH (SPS-B) to enhance its sorption characteristics. Solution pH plays a substantial role in sorption properties, and pH 5.0 was found to have the best sorption efficiency. The activated SPS materials were characterized using SEM, EDX, XRD, and FTIR analysis. The biosorption process was optimized, and the equilibrium and kinetic data were best fitted to the Sips isotherm and pseudo-second-order models, respectively, based on high correlation coefficient (r²) and low average relative errors. SPS-A and SPS-B biosorption capacities were 137.2 and 208.5 mg g⁻¹, respectively, demonstrating the high efficiency of SPS. The thermodynamics showed that the biosorption process for Sm(III) ions was spontaneous and exothermic (ΔH-137.5 kJ mol⁻¹ for SPS-B). Notably, SPS-B demonstrated a greater propensity for biosorbing Sm(III) ions compared to Th(IV) or U(VI) ions with separation factors exceeding 3.0. SPS showed excellent recyclability, and the desorption efficiency for Sm(III), Th(IV), and U(VI) ions ranged between 94.1 and 96.8% for three consecutive cycles using 1.5 M HNO₃. These results demonstrate the potential of SPS as a promising biosorbent for the effective and selective recovery of Sm(III) from wastewater effluents, especially when considering its recyclability.