Mercury removal from water by ion exchange resins adsorption

Abstract

In this paper a detailed experimental and theoretical analysis of the adsorption process of mercury by ion exchange resins is presented. Experiments have been performed to study adsorption efficiency, the effect of pH on the uptake of mercury and the adsorption kinetics. The experimental apparatus was a batch mechanically stirred reactor (volume 1.5 dm 3), under almost isothermal conditions (±0.1°C). The resin used in this study is Duolite GT-73, a chelating resin, macroreticular with thiol (S-H) functional groups. The studied resin has a very high adsorption efficiency, reaching 30–40% in weight and the efficiency decreases, decreasing pH, due to competition between ions H + and Hg 2+. Such a high efficiency confirms previous results and justifies the great interest for the application of ion exchange resins in water treatment plants. As in previous works, measurements of process kinetics show that the adsorption rate decreases as the initial mercury concentration is increased. This fact suggests that intraparticle diffusion rate can be the controlling step for the adsorption process. To verify this, a simplified mathematical model has been identified, accounting for a diffusional resistance inside solid particles and where the equilibrium relationship between Hg concentration in the liquid and in the solid is described by the Freundlich isotherm, neglecting H + competition: this model is very effective in the prediction of the change in the adsorption kinetics with the initial Hg concentration. Hence this preliminary approach can be held as the reference starting point for the adsorption model: further developments will concern the equilibrium thermodynamics (H + competition).