RES³T - Rossendorf Expert System for Surface and Sorption Thermodynamics

U(VI) sorption on goethite was investigated as functions of pH, solid-to-liquid ratio (m/V), ionic strength and U(VI) concentration by a batch experimental method. Effects of phosphate, carbonate and fulvic acid (FA) on U(VI) sorption were examined. It was found that the sorption of U(VI) increases from 0% to 100% over the pH range of 2.5–4.5 and keeps constant in the high pH range. The sorption of U(VI) on goethite is insensitive to ionic strength. Different surface complexes in the framework of double-layer model were examined for fitting the sorption of U(VI) on goethite. A model with two mononuclear inner-sphere surface complexes, ≡SOUO₂⁺ and ≡SOUO₂OH, was found capable of reproducing the pH sorption edges, the sorption isotherms and the sorption data with variable m/V in this study. The proposed model can also interpret the pH sorption edge collected at p_CO2 = 10^−3.58 without considering any ternary surface complexes of carbonate. Moreover, it was found that the presence of phosphate at relatively high concentration (6×10⁻⁴ mol/L) promotes U(VI) sorption. The presence of FA of 20 mg/L has little effect on the sorption of U(VI) on goethite.