The kinetics and thermodynamics of adsorption of heavy metal ions on titanium- pillared and un-pillared bentonite clays

Abstract

Titanium-Pillared and Un-Pillared bentonite clays were studied in order to evaluate the thermodynamics and kinetics of heavy metal ion removal from aqueous solutions. The results showed that the maximum sorption of Cu, Cd, Hg and Pb ions occurred within 30 minutes. A pseudo-second order kinetic model was used to characterize the metal ion transport mechanism and the correlation coefficients (r2) were high, confirming the validity of pseudosecond- order. The rate of adsorption was observed to increase with pillaring and does not only depend on the the metal ion concentration, but may also involve additional adsorbent –adsorbate interaction processes.. The thermodynamic parameter (Go) was found to be negative at all temperatures studied, which indicate that the adsorption process is spontaneous while So values are positive. The positive values of So showed the increasing randomness of the metal ions at the adsorbent – adsorbate interface. The heat of adsorption (enthalpies, Ho) and the
activation enegies (Ea) were both positive and their values lie within the range associated with physisorption. The results are presented and discussed in terms of the mechanism of ion adsorption on solid Ti-pillared and un-pillared bentonite clay minerals.