Thermodynamics of Copper Adsorption-Desorption by Ca-Kaolinite

The temperature effect on Cu adsorption and desorption on kaolinite has been investigated at four temperatures (8°C, 25°C, 30°C and 40°C). The clay sample was saturated with Ca. Copper was sorbed from solutions containing eleven Cu concentrations between 0.0010 and 0.0211 M, equilibrated for 2 days. Cu adsorption decreased, but desorption increased with increasing temperature, indicating that adsorption is an exothermic process while desorption is endothermic. These conclusions are confirmed by the values of H ⁰ estimated for adsorption and desorption.The initial copper concentration is a significant factor influencing mainly the adsorption process, which is spontaneous (G ⁰ < 0) only for low initial Cu concentrations. The desorption process is spontaneous for all Cu concentrations. S ⁰ values have also been calculated. Experimental adsorption data were successfully fitted to the Freundlich isotherm and to the Gouy-Chapman model in order to express the process quantitatively.