Abstract

This study used batch adsorption techniques to evaluate the potential suitability of spent coffee grounds as an environmentally friendly adsorbent for the removal of indium ions from aqueous solutions. In addition, we also investigated the effects of process parameters, such as, the solution pH, adsorbent dose, initial concentration of indium ions and the temperature on adsorption performance. The experimental data were fitted with several adsorption isotherm models to describe the adsorption process of indium ions onto the coffee grounds. The predictions of the Langmuir isotherm model satisfactorily matched the experimental observations. Besides, the kinetic data obtained at different initial concentrations were analyzed using pseudo-first-order and pseudo-second-order kinetic models. A pseudo-second-order model provided a good fit to the experimental results with correlation coefficients greater than 0.99. Thermodynamic parameters, including the Gibbs free energy, enthalpy and entropy, indicated that the indium adsorption of aqueous solutions onto coffee grounds was feasible, spontaneous and endothermic in the temperature range of 288 to 318 K.

Key words: Adsorption, indium ions, coffee grounds, isotherms, kinetics.