Thermodynamic and Kinetic study of the removal of Cu 2+ and Pb 2+ ions from aqueous solution using Fe 7 S 8 nanomaterial

In the present study, pyrrhotite (Fe S ) was investigated for the removal of Pb and Cu2 ions from aqueous solution. The Fe S material was prepared through a solvothermal method and was characterized using XRD. The average particle size for the nanomaterial was determined to be 29.86 ± 0.87 nm using XRD analysis and Scherrer's equation. Batch studies were performed to investigate the effects of pH, time, temperature, interfering ions, and the binding capacity of Pb and Cu ions to the Fe S nanomaterial. During the pH profile studies, the optimum pH for the binding of Pb and Cu was determined to be pH 5 for both cations. Isotherm studies were conducted from which the thermodynamics and binding capacities for both Cu and Pb were determined. The binding capacity for Pb and Cu binding to the Fe S were determined to be 0.039 and 0.102 mmol/g, respectively at 25°C. The thermodynamic parameters indicated a ΔG for the sorption of Pb ranged from 5.07 kJ/mol to -2.45 kJ/mol indicating a non-spontaneous process was occurring. Whereas, the ΔG for Cu ion binding ranged from 9.78 kJ/mol to -11.23 kJ/mol indicating a spontaneous process at higher temperatures. The enthalpy indicated an endothermic reaction was occurring for the binding of Pb and Cu to the Fe S nanomaterial with ΔH values of 55.8 kJ/mol and 153.5 kJ/mol, respectively. Furthermore, the ΔS values for the reactions were positive indicating an increase in the entropy of the system after metal ion binding. Activation energy studies indicated the binding for both Pb and Cu occurred through chemisorption.