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

The adsorption of Cd2+ 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 Cd2+ 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 Cd2+ 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(ΔH) and the entropy changes(ΔS) were positive,while the free energy changes(ΔG) were negative.