Sorption Of U(Ⅵ) And Th(Ⅳ) On Goethite

The sorption of U(â…¥) and Th(â…£) on goethite in the presence of phosphate and FA was studied by using a batch technique.The objectives of the present dissertation were to(1) collect sorption data of U(â…¥) and Th(â…£) on goethite over wide experimental conditions and(2) to set up a proper surface complexation model capable of quatitative description of the sorption data collected.It was found that the sorption of U(â…¥) is influenced strongly by pH and weakly by ionic strength.A hysteresis was found for desorption isotherms.The presence of CO₂ has little effects on U(â…¥) sorption on goethite at pH＜8.2.However,the sorption decreases with pH very rapidly at pH＞8.2.A double-layer model with two mononuclear inner-sphere surface complxes,≡SOUO₂⁺ and≡SOUO₂OH was used to quantitatively describe the sorption of U(â…¥) on goethite.It was found that the sorption of Th(â…£) is influenced strongly by pH and weakly by ionic strength.A hysteresis was found for desorption of Th(â…£) in NaCl solution whereas the sorption and desorption isotherms were on the same line in NaNO₃ solution.The presence of CO₂ has little effects on Th(â…£) sorption on goethite. The sorption isotherm of Th(â…£) can be fitted by aFreundlich equation.The sorption of U(â…¥) and Th(â…£) on goethite in the presence of phosphate(4.6×10^-4mol/L) and FA(20mg/L) was studied.The presence of phosphate can promote the sorption of U(â…¥) and Th(â…£) on goethite.The presence of FA at low pH can promote the sorption of U(â…¥) and Th(â…£).The sorption of U(â…¥) and Th(â…£) was promoted obviously in the presence of both phosphate and FA.