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

In this dissertation,the sorption of U(Ⅵ) and Th(Ⅳ) on the attapulgite was studied as functions of contact time,sorbent content,ionic strength,pH,fulvic acid(FA) and temperature by using a bacth techniqueIt was found that the equilibrium time of U(Ⅵ) sorption on Na-attapulgite is relatively short,the equilibrium is achieved in about 2-3h,suggesting that there is a strong affinity between U(Ⅵ) and the surface of Na-attapulgite.The sorption of U(Ⅵ) increases with the increasing of Na-attapulgite content.The sorption of U(Ⅵ) decreases with the increasing concentrations of NaCl solution in low pH range(＜5.5),whereas increases in high pH range(＞8).The sorption of U(Ⅵ) sharply increases with increasing pH at pH＜6,but decreases at pH＞8.The strong pH-dependent of U(Ⅵ) sorption on attapulgite indicated that surface complexation may be the main sorption mechanism.Sorption-desorption isotherms at variable temperatures indicated that the sorption of U(Ⅵ) on attapulgite is spontaneous and endothermic.The sorption of U(Ⅵ) is reversible at lower concentrations of U(Ⅵ), irreversible at higher concentrations of U(Ⅵ).The sorption of U(Ⅵ) on attapulgite is obviously enhanced in the presence of FA.In compare of the sorption of U(Ⅵ) on Na-attapulgite,the equilibrium time of the sorption of Th(Ⅵ) on purified attapulgite is longer,the equilibrium is achieved at about 8-10.The effects of FA and sorbent content on the sorption of Th(Ⅳ) are positive,whereas ionic strength has negative effect.The sorptions of Th(Ⅳ) increases with increasing pH.The sorption mechanism may be mainly ionic exchange at low pH,and surface complexation maybe dominate at high pH.The sorption of Th(Ⅳ) on attapulgite is a spontaneous and endothermic process.The sorption-desorption isotherms show that the sorption of Th(Ⅳ) is reversible at low concentrations of Th(Ⅳ),and irreversible at high concentrations of Th(Ⅳ).