The surface properties of intrinsic and activated attapulgite were studied using potentiometric titration. The sorption mechanisms of Th（IV） on intrinsic and activated attapulgite were investigated by employing surface complexation model and FITEQL 3.2 code. The results indicated that the sorption sites of intrinsic attapulgite involved in the sorption process were main ion exchange site （ ≡ XNa/K）, strong site （≡ SsOH） and weak site （ ≡ SwOH）, while only strong site （ ≡SSOH） and weak site （≡SwOH） were predominant for activated attapulgite. At pH 〈 2.5, the species of Th（IV） was main Th4＋ in aqueous solution; then the hydrolysis species of Th（IV） （i.e., Th（OH）22＋, Th（OH）3＋ and Yh（OH）40） gradually formed as pH increasing. For the sorption of Th（IV） on intrinsic attapulgite, both ion exchange species （ ≡ X2Th） and inner-sphere surface complexes （ ≡ SsOTh） were dominant, while only inner-sphere surface complexes （i.e., ≡SSOThOH and ≡ SWOTh） were observed for Th（IV） sorption to activated attapulgite. In the presence of humic acid （HA）, the sorption of Th（IV） on activated attapulgite was obviously enhanced; and both ≡ SsOH-HA-Th and≡ SSOTh were the predominant speciation. It was also interesting to find that the addition of HA obviously provoked the desorption behavior of Th（IV）.
PAN DuoQiang FAN QiaoHui DING KeFei LI Ping LU Yan YU Tao XU Jiang WU WangSuo
The sorption of UO22+ onto ZrP2O7 was studied using the batch technique and the point of zero charge of ZrP2O7 was obtained through mass titration.The results indicated that sorption of UO22+ onto ZrP2O7 was strongly affected by pH,solid-to-liquid ratio (m/V),the species of electrolyte in solution and fulvic acid (FA),but was insensitive to ionic strength.The sorption of UO22+ increased with increasing pH and m/V.The presence of FA enhanced UO22+ sorption onto ZrP2O7 at low pH.The presence of phosphate or sulfate caused opposite effects on the sorption of UO22+ onto ZrP2O7.Addition of citrate also significantly affected UO22+ sorption.The sorption of UO22+ increased as the temperature of the system increased.The Langmuir and Freundlich models were used to simulate the sorption isotherms of UO22+ onto ZrP2O7 at different temperatures.The results indicated that the Freundlich model described UO22+ sorption better than the Langmuir model.Thermodynamic parameters for the sorption process were calculated from the temperature dependent sorption isotherms.The results suggested that the sorption process of UO22+ onto ZrP2O7 is spontaneous and endothermic.The desorption process of UO22+ from ZrP2O7 was also investigated and it was found that sorption onto ZrP2O7 was irreversible.
QIAN LiJuan,HU PeiZhuo,JIANG ZhenJiang,GENG YanXia & WU WangSuo Radiochemistry Laboratory,School of Nuclear Science and Technology,Lanzhou University,Lanzhou 73000,China
