Kinetic studies on the adsorption of Cd2+, Cu2+ and Zn2+ ions from aqueous solutions by cassava (Manihot sculenta Cranz) tuber bark waste

The kinetics of Cd2+, Cu2+ and Zn2+ adsorption onto pure and thioglycolic acid treated cassava tuber bark wastes (CTBW) were investigated using a batch sorption technique at 30 °C. Kinetic data suggested that the adsorption process was exothermic, the rate limiting sorption step was physisorption and adsorption rates could be best described by a pseudo-second order model. Rate coefficients were determined to range between 1.39 × 10−2 min−1 and 5.94 × 10−2 min−1, 1.46 × 10−3 min−1 and 5.76 × 10−3 min−1 and 0.69 × 10−3 min−1 and 5.8 × 10−3 min−1 for Cd2+, Cu2+ and Zn2+, respectively. The results from these studies indicated that the sorption process is fast and stable. The adsorption equilibria were evaluated using the Langmuir equation and the monolayer sorption capacity was found to range between 5.88-26.3 mg/g, 33.3-90.9 mg/g and 22.2-83.3 mg/g for Cd2+, Cu2+ and Zn2+, respectively. Negative values of ΔGads0 indicated that the adsorption process was spontaneous and exothermic in nature.