Removal of Silver (I) from Aqueous Solutions by Natural Bentonite

Abstract

The aim of the present work is to investigate the ability of commercial natural bentonite (untreated) (NB) to remove silver ions from aqueous solution. Specific surface area of the sample was determined as a result of N2 adsorption-desorption at 77 K using BET method. X-ray powder diffraction (XRD) was used to characterize the (NB). Towards this aim, batch adsorption experiments were carried out and the effect of various parameters on this removal process has been investigated. The effects of pH, adsorption time, silver ion concentration, bentonite doses, Temperature and the NB treatment (calcinations and washing) on the adsorption process were examined. The optimum pH for adsorption was found to be 4-8. It was found that NB treatment has a substantial effect on the metal uptake. In adsorption studies, residual silver ions concentration reached equilibrium in a short duration of 15 min. The paper discusses the thermodynamic parameters of the adsorption (the Gibbs free energy, entropy, and enthalpy). Adsorption of Ag + on NB appeared to follow Langmuir isotherm. Our results demonstrate that the adsorption process was spontaneous and endothermic under natural conditions. Additionally, a pseudo-second-order rate model was adopted to describe the kinetics of adsorption. In desorption experiment, an approximately (15%) desorption yield was obtained for silver ions.