Cadmium and nickel adsorption using modified agricultural waste

This study examined the effectiveness and kinetics of Cd and Ni adsorption onto wheat straw treated with succinic anhydride and NaOH. The effects of absorbent dose, degree of succinylation, initial concentration and respective molar ratios of Cd and Ni, and pH on the adsorption efficiency were investigated. The maximum adsorption percentage of Cd (> 99%) was obtained at 5 g/L absorbent dose, 50 mg/L initial Cd concentration, under natural pH. The same conditions yielded maximum Ni adsorption (about 97%). In binary Cd-Ni solutions, a maximum 97.8% of Cd and 88.9% of Ni were adsorbed onto modified wheat straw with a molar ratio of 2:1 (Cd:Ni) under natural pH, absorbent dose of 5 g/L, and initial concentration of 200 mg/L and 52.25 mg/L for Cd and Ni, respectively. Higher initial concentrations of Ni decreased the adsorption percentage of Cd, and higher initial concentrations of Cd decreased adsorption of Ni. Cadmium interfered with Ni adsorption more than Ni interfered with Cd adsorption. Modeling of adsorption percentages with exposure time shows the reaction kinetics for Cd adsorption on modified wheat straw to be pseudo-second-order and the sorption isotherm for Cd to be Langmuir isotherm model.