Adsorptive Removal of Lead and Zinc Ions From Aqueous Solution using Thiolated Tea (Camellia sinensis) Seed Shell

This study aims at investigating the adsorption of Zinc and lead ions onto thiolated tea (Camellia sinensis) seed shell (TTSS) in batch process. Equilibrium data were fitted into Langmuir, Freundlich and Dubinin–Radushkevich isotherm models. The equilibrium data favored the Langmuir adsorption isotherm with maximum adsorption monolayer coverage of 397.6 and 475 mg/g for Pb (II) and Zn (II), respectively. In order to fit the kinetic data, three kinetic models; Lagergren first-order, pseudo-second-order and intraparticle diffusion models were used. The adsorption behavior was best described by pseudo-second-order with qe value of 76.61and 97.19 mg/g for Pb (II) and Zn (II), respectively. Thermodynamic parameters such as changes in Gibbs free energy ΔGo, enthalpy ΔHo, and entropy ΔSo were calculated. Adsorption process was found to be feasible, endothermic, and spontaneous. The energy of adsorption values of the metal ions (0.717 and 0.759 kJ/mol) and the large negative value of ΔGo confirm the physiosorption nature of the adsorption of Pb (II) and Zn (II) onto TTSS.