Biosorption of cadmium (II) onto loquat leaves (Eriobotrya japonica) and their ash from aqueous solution, equilibrium, kinetics, and thermodynamic studies

Biosorption of Cd(II) onto loquat leaves (LL) powder and loquat leaves ash (LA) from aqueous solution has been investigated. The extent of biosorption of Cd(II) ions was found to be dependent on the solution pH, biosorbent dose, initial cadmium ions concentration, contact time, and temperature. The experimental equilibrium biosorption data were analyzed by three widely used two-parameter Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherm equations. The Langmuir isotherm model provided a better fit with the experimental data than Freundlich and Dubinin- Radushkevich (D-R) isotherm models by high correlation coefficients R^2. The biosorption capacity of LL and LA was found to be 29.240 mg g^−1 and 21.322 mg g^−1 for Cd(II) ions, respectively. The mean adsorption energies evaluated using the D–R model indicated that the adsorption of Cd(II) onto loquat leaves and their ash mainly proceeds through binding surface functional groups, i.e., were taken place by physisorption. The thermodynamic analysis indicated that the biosorption behavior of cadmium ions onto LL and LA biosorbents was an endothermic process. The negative sign values of ΔGo and positive values of ΔHo revealed that the biosorption process was spontaneous and endothermic. Adsorption mechanisms were also investigated using the pseudo-first-order and pseudo-second-order kinetics models. The kinetic results showed that the adsorption of Cd(II) onto LL and LA followed well pseudo-second order kinetics.