Adsorption Of U(Ⅵ) And Th(Ⅳ) On Jinchuan Bentonite

Bentonite has been considered to be back-filling material for high level radioactive waste repository for many countries. In this context, it is of great significance for design and security assessment of the repository to study the interaction between radionuclides and bentonite. In this thesis, the adsorption of U(VI) and Th(IV) on Jinchuan bentonite as a function of pH, contect time, ionic strength, solid-to-liquid ratio, temperature and the partial pressure of CO2(PCO2) was studied by using a batch adsorption method. A surface complexation model was proposed and some experimental results of U(VI) was quantitatively interpreted by the model.It was found that the pH and U(VI) concentration affected U(VI) adsorption significantly; The adsorption of U(VI) decreases with ionic strength; The adsorption of U(VI) at Pco2=0 and 10-3.58 atm are almost indential in the low pH range (pH<6), whereas in the high pH range (pH>7.5) the adsorption of U(VI) decreases sharply with pH in the presence of CO2(PCO2=10-3.58 atm); Temperature incease is favorable to the adsorption of U(VI). A surface complexation model (SCM) with four surface complexation reactions was proposed and the adsorption of U(VI) at ionic strength of 0.1 M was quantitatively interpreted. The standard enthalphy change(ΔrHmθ) of each surface complexation reaction was evaluated from the intrinsic equilibrium constants (Kint) obtained at three temperatures(298±2K,333±2K,353±2K) via the van't Hoff equation.It was found that the adsorption of Th(IV) obviously affected by the solid-to-liquid ratio and increased from 20%to 90%over the pH range of 2-4.5. At pH<4, the adsorption of Th(IV) decreased slightly with increasing ionic strength; The adsorption of Th(IV) on bentonite was increased with increasing temperature; Furthermore, the adsorption of Th(IV) was promoted by the presence of fulvic acid (FA), which was more obvious as the concentration of FA increased. Keywords:U(Ⅵ); Th(Ⅳ); Bentonite; adsorption; Surface complexation model...