Study On The Adsorption Of U(Ⅵ) And Th(Ⅳ) Onto Kaolinite

The adsorption of uranium U(â…¥) on kaolinite was studied as a function of contact time, pH, ionic strength, U(VI) concentration, solid-to-liquid ratio (m/V), and the presence of oxyanions (phosphate and sulfate) by batch method. It was found that the adsorption of U(â…¥) on kaolinite could be interpreted kinetically by a pseudo-second-order model. The adsorption of U(â…¥) was pH depended but not sensitive to ionic strength. The adsorption data of U(â…¥) were reasonably described by a surface complexation model, which includes a cation exchange reaction of UO22+ on the structural negatively charged site X2UO2 and two surface complexation reactions on edge sites=SOUO2 and=SO(UO2)3(OH)5 in combination with a double-layer model. Furthermore, it was found that the presence of SO42- did not cause significant influence on the U(â…¥) adsorption, whereas the presence of PO43- increases the adsorption percentage of U(â…¥) to some extent.The adsorption of Th(â…£) on kaolinte was also studied by batch experiments. The kinetic experiments show that the adsorption of Th(â…£) on kaolinte could be interpreted by a pseudo-second-order model. The adsorption of Th(â…£) on kaolinte is significantly pH-dependent, and the adsorption edge is at pH=3-4.5. However, the adsorption of Th(â…£) on kaolinte is not sensitive to ionic strength, which indicates the formation of inner-sphere surface complexes. The adsorption isotherms of Th(â…£) on kaolinte can be interpreted by the Freundlich model.