Interaction of Cd(II) with acid- and base-saturated montmorillonites

The effect of time, pH and temperature on the interaction of Cd(II) with acid- and base-saturated montmorillonites has been investigated. It has been found that maximum adsorption occurs after 6 hr. Application of kinetic rate laws and the evaluation of rate constants at different concentrations of Cd(II) suggests a first order reaction. The variation of rate constants and half-life periods of the reaction confirm that the dominating reaction is of ion-exchange type. The pH studies show that the adsorption increases with increasing pH upto pH 7.5. These inferences find support from the nature of adsorption isotherms which indicate the order of adsorption to be : H-mont > Na-mont in accordance with their surface areas. The reaction is endothermic. The activation energy of the adsorption of Cd(II) on H- and Na-montmorillonites is 0.60, and 0.98 kcal/mole respectively. The desorption data show almost complete desorption of Cd(II) from its adsorption sites by water or salt solutions. All these evidences indicate that the adsorption of Cd(II) on montmorjllonite is physical in nature involving Van der Wall's and noncoulombic forces. (author)