天然凹凸棒石对水中镉的吸附行为

通过静态实验探讨了天然凹凸捧石吸附水中镉（Cd^2＋）时的影响因素、动力学、等温式和热力学。结果表明，在实验条件下吸附90min后天然凹凸捧石对Cd^2＋的吸附量为6.07-13.15（mg·g^-1），吸附量随着温度或Cd^2＋初始浓度的增加而增加，但天然凹凸棒石用量增加，吸附量却减少。在pH值为5-7时随着pH值的增加而增加。此外，天然凹凸捧石吸附Cd^2＋的速度较快，吸附60min后基本达到平衡。吸附动力学规律符合Lagergren准二级反应模型，不同温度下的吸附等温式都与Freundlich方程符合很好。热力学分析表明，吸附过程吸热，吸附焓变△H和熵变△s都为正值，吸附自由能变△G为负值。

Adsorption of Cd~(2+) in Aqueous Solution by Natural Attapulgite

The adsorption of Cd^2＋ in aqueous solutions by natural attapulgite was investigated through batch experiments, including the affecting factors, kinetics, isotherms and thermodynamics of the adsorption. The adsorption capacity of Cd^2＋ was 6.07-13.15 （mg·g^-1） after 90 min under the experiment conditions, and this capacity was increased with the increasing temperature or Cd^2＋ initial concentration, but decreased with the increasing amounts of natural attapulgite. Also, increasing pH would enhance the adsorption capacity when pH was between 5 and 7. The adsorption speed was rapid before 5 min, and the adsorption process approximately reached equilibrium in 60 min, and the adsorption kinetics followed pseudo-second order reaction models. Besides, the adsorption isotherms in different temperature in accordance with the Freundlich equation and thermodynamics evaluation showed that the adsorption process was endothermic. The enthalpy changes （△H） and the entropy changes （△S） were positive, while the free energy changes （△G） were negative.