Characterization for the interaction of nickel(II) and copper(II) from aqueous solutions with natural silicate minerals

This paper describes the interaction and removal of some heavy metal ions such as Ni(II) and Cu(II) from aqueous solution at constant pH (6.0) and 0.01 M NaClO4 ionic strength using raw clay mineral. The experimental results were analysed in terms of Langmuir, Freundlich and Redlich–Peterson isotherms to obtain the characteristic parameters of each model. Both the Langmuir and Redlich–Peterson isotherms were found to represent the measured sorption data. The Langmuir monolayer adsorption capacity was found to range from 48.54 to 60.98 and 58.48 to 69.93 mg metal ion/g clay for Ni(II) and Cu(II) respectively. Also thermodynamic parameters such as enthalpy (ΔH), free energy (ΔG) and entropy (ΔS) were calculated and these values show that adsorption of heavy metal ions on clay was an endothermic, entropically driven with very favorable entropy and spontaneous process. The values of ΔG indicate that the adsorption is characterized by physical adsorption. According to the equilibrium studies, the selectivity sequence can be given as Cu(II) > Ni(II). These results show that natural clay holds great potential to remove cationic heavy metal species from aqueous solutions.