Thermodynamic and Kinetic study of the removal of Cu2+ and Pb2+ ions from aqueous solution using Fe7S8 nanomaterial

摘要

In the present study, pyrrhotite (Fe7S8) was investigated for the removal of Pb²⁺ and Cu2⁺ ions from aqueous solution. The Fe7S8 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 Pb²⁺ and Cu²⁺ ions to the Fe7S8 nanomaterial. During the pH profile studies, the optimum pH for the binding of Pb²⁺ and Cu²⁺ was determined to be pH 5 for both cations. Isotherm studies were conducted from which the thermodynamics and binding capacities for both Cu²⁺ and Pb²⁺ were determined. The binding capacity for Pb²⁺ and Cu²⁺ binding to the Fe7S8 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 Pb²⁺ ranged from 5.07 kJ/mol to −2.45 kJ/mol indicating a non-spontaneous process was occurring. Whereas, the ΔG for Cu²⁺ 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 Pb²⁺ and Cu²⁺ to the Fe7S8 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 Pb²⁺ and Cu²⁺ occurred through chemisorption.