A Study on Adsorption of Pb, Cu, Zn and Cd Onto Natural Clay

The effect of temperature on the adsorption of heavy metals on not only natural bulk clay, but also for the individual phases that composed the bulk clay sample, was investigated. Combined Adsorption- Sequential extraction Analysis (CASA) for Pb, Cu, Zn and Cd were conducted under various temperatures that ranged from 150 C to 550 C. As a result, it was found that heavy metals adsorption for bulk clay increased about 12% when the temperature increased from 150 C to 550 C. The effect of temperature on the individual phases was mainly observed in oxide, including Fe-and Mn-oxide, and the organic phases of all of the metals. As for the Phase Concentration Factors (PCFs) of the metals, the largest increase of the values was observed in the oxide phase. Based on the thermodynamic parameters of the individual phases, the adsorption of metals on natural clay was an endothermic reaction with the exception of exchangeable phase adsorption. This shows that adsorption affinity and capacity tend to increase when the temperature increase for all adsorption phases of soil, except for adsorption in the exchangeable phase. In the case of Pb, Zn, and Cu adsorption, the considerable enthalpy changes were observed in carbonates, Fe-oxides, and organic phases, which means the adsorption affinity for those phases were largely affected by temperature change. On the other hand, relatively small enthalpy changes in the Cd adsorption were observed in bulk and all individual phases when it was compared with the other metals enthalpy changes for the same phases. This means that Cd adsorption mainly occurred in the exchangeable phase, which was affected a little by temperature change.