Kinetic, isotherm and thermodynamic investigations of the adsorption of Ag+ and Cu2+ on vermiculite

Vermiculite was used as a low-cost adsorbent for the removal of silver and copper ions from aqueous solutions. The raw material and acid- or base-treated adsorbents were characterised by SEM, BET, XRD and FTIR analysis. The effect of the pH and temperature of the solution, dose and average size of adsorbent particles, contact time, stirring rate and initial of metal ions concentration on the adsorption efficiency was studied systematically. The maximum adsorption capacity of vermiculite was determined (for Ag(I) as about 73 mg/g and for Cu(II) 117 mg/g). In this study, the four isotherm models (Langmuir, Freundlich, Temkin and Sips) were employed to correlate experimental adsorption isotherm data, which were obtained by batch tests. The linear and non-linear isotherm models were compared. The pseudo-first-order, pseudo-second-order, and Elovich models were used to describe the kinetic data. The kinetics of adsorption indicates that the process followed pseudo-second order kinetics well, which suggests the chemical character of adsorption. Finally, the thermodynamic parameters (ΔG°, ΔH° and ΔS°) were determined. The parameters indicated that, in the studied temperature range, the adsorption of Ag(I) and Cu(II) by vermiculite had a spontaneous and endothermic nature. Based on all of the results, vermiculite can be evaluated as a potentially cost-effective sorbent for the removal of Ag(I) and Cu(II) from aqueous solutions.