Sol–gel-derived thiocyanato-functionalized silica gel sorbents for adsorption of Fe(III) ions from aqueous solution: kinetics, isotherms and thermodynamics

Adsorption characteristics of Fe(III) ions onto thiocyanato-functionalized silica gel sorbent were investigated under various conditions of contact time, initial metal concentration and temperature. The equilibrium isotherms, kinetics and thermodynamics of Fe(III) ions adsorption onto the surface of thiocyanato-functionalized silica gel from aqueous solution were investigated. Batch kinetic studies showed that an equilibrium time of 30 min was required for the adsorption of Fe(III) ions onto thiocyanato-functionalized silica gel. The estimated maximum capacities of Fe(III) ions adsorbed by thiocyanato-functionalized silica gel were 112.2 mg g−1. The equilibrium adsorption data of thiocyanato-functionalized silica gel for Fe(III) ions best fitted to the Langmuir isotherm since the correlation coefficients for the Langmuir isotherm were higher than that for the Freundlich and Dubinin–Radushkevich isotherms. The kinetic data were well described by the pseudo-second-order model. Spontaneous, endothermic and random characteristics of the process were confirmed by thermodynamic analysis.