Enhancing U(VI) removal from water using nano-Kaolin and nano-Kaolin/MnFe₂O₄ composite adsorbents

Abstract The binding behavior of U(VI) ions onto nano-Kaolin (NK) and nano-Kaolin/MnFe 2 O 4 composite (NK-MF) adsorbents was systematically investigated, focusing on the influence of pH, adsorbent mass, temperature, and contact time. Kinetic analysis, utilizing the pseudo-second-order model, revealed that both NK and NK-MF composites reach their maximum capacity of adsorption (q m ) at pH 3. The maximum adsorption capacities were found to be (8.6) mg g −1 for NK and (14.79) mg g −1 for NK-MF at 25C°, indicating a significant enhancement due to the incorporation of MnFe 2 O 4 . The adsorption isotherms were examined using Langmuir, Freundlich, and Dubinin-Radushkevich models to characterize the adsorption mechanisms. The Langmuir and Freundlich models provided the best fit (R 2 > 0.9), indicating monolayer and multilayer adsorption. Thermodynamics parameters, including enthalpy change (ΔH°), Gibbs free energy change (ΔG°), and entropy change (ΔS°), were derived from adsorption data across different temperatures. The values at 25 °C of ΔH° were (49.67) for NK and (70.97) for NK-MF; ΔG° values were (−5.06) kJ mol −1 for NK and (−7.39) kJ mol −1 for NK-MF; and ΔS° values were 187.36 J (mol·K) −1 for NK and (263.70) J (mol·K) −1 for NK-MF. The results indicate that the adsorption process is endothermic, with conditions that favor adsorption and a positive entropy change. These findings demonstrate the effectiveness and potential of NK and NK-MF composites as viable adsorbents for the uptake of U(VI) ions from water-based solutions. The incorporation of MnFe 2 O 4 into NK improves adsorption capacity, making NK-MF a novel and practical material for uranium removal in environmental applications.