Uranium sorption onto mullite: Characteristics of isotherms, kinetics and thermodynamics

The sorption of uranium onto mullite influenced by pH, initial adsorbate concentration, sorption dose and reaction duration was probed utilising batch techniques. X-ray powder diffraction was used to characterise mullite. Sorption isotherms, sorption kinetics and thermodynamic characteristics were also investigated. The Freundlich isotherm model could best depict experimental data, suggesting that the sorption mechanism of uranium onto mullite may be multi-layer adsorption. The E value obtained from the Dubinin–Radushkevich model implied that uranium sorption onto mullite is a chemical process. The pseudo-second-order model successfully depicted uranium sorption onto mullite, indicating that the sorption rate is mainly controlled by chemical sorption. The thermodynamic parameters computed showed that entropy and enthalpy under the trial conditions were positive and that values of ΔGϴ were negative. Thermodynamics illustrated that the sorption process was endothermic and spontaneous. The results achieved in this study are intended to further a deeper comprehension of uranium migration in silicate minerals.