Comparative and competitive adsorption of copper, lead, and nickel using chitosan immobilized on bentonite

The comparative and competitive adsorption of Cu(II), Ni(II), and Pb(II) from aqueous solution using chitosan immobilized on bentonite (CHB) was investigated. The adsorption data of single and binary systems indicated that Cu(II) and Pb(II) best fits Freundlich isotherm while Ni(II) follows Langmuir. In binary systems, a decrease in adsorption capacities and isotherm constants was observed, showing preference of adsorption in the order of Pb(II) > Cu(II) > Ni(II). Kinetic studies of single system indicated that the pseudo-second order is the best fit with high correlation coefficients (R2 > 0.99) and low sum of error values (SE = 0.13–0.46%). Thermodynamic studies illustrated that adsorption of CHB are exothermic and causes a decrease in the entropy. The adsorption of Pb(II) is spontaneous while Ni(II) is non-spontaneous at 25–55 °C. Cu(II) adsorption is only spontaneous at 25 °C.