Adsorption characteristics of copper(II) onto spent activated clay

This study was to investigate the adsorption characteristics of Cu(II) onto spent activated clay (SAC) or so-called spent bleaching earth, a waste produced from an edible oil refinery company. Results of kinetic experiments showed that the Cu(II) adsorption rate was fast and more than 90% of Cu adsorption occurred within 5 min. Among the kinetic models tested, the adsorption kinetics was best described by the pseudo-second-order equation. The rate of adsorption decreased with increasing surface loadings. Results of equilibrium experiments showed that the solution pH was the key parameter affecting the adsorption characteristics. The adsorption of Cu(II) ions onto SAC occurs up to the precipitation pH, and then the precipitation of Cu ions starts. The Langmuir adsorption isotherm properly describes the equilibrium adsorption and the maximum adsorption capacities of SAC towards Cu(II) were determined to be 10.9, 11.5, and 13.2 mg/g, respectively at pH 5.0, 5.5, and 6.0. As temperature was increased from 4 to 50 °C, the adsorption capacity increased from 9.5 to 12.8 mg/g for solution pH of 5.0. Values of ΔG° ranging from −5.73 to −7.26 kcal/mol suggest that the adsorption process is spontaneous and mainly governed by specific surface interaction mechanism. The values of ΔH° and ΔS° were 3.47 kcal/mol and 33.2 cal/(mol K), respectively. Results of this study will be useful for future scale up for using this material as a low-cost adsorbent for the removal of Cu(II) from wastewater.