Adsorption kinetics and equilibrium of arsenic onto an iron-based adsorbent and an ion exchange resin

Arsenic is commonly present in many groundwater sources. To remove arsenic from groundwater, several advanced techniques, including adsorption and ion exchange, are often employed in drinking water treatment processes. In this study, the transport and adsorption of arsenate within one iron-based adsorbent (Bayoxide E33 from Bayer) and one anion exchange resin (Arsenex from Purolite) is elucidated. A batch reactor with temperature control was used to determine the kinetic and equilibrium uptake of arsenate onto the two media. The experimental results revealed that the adsorption equilibrium was established within 4 to 5 hours for both E33 and Arsenex. After fitting the arsenate uptake data, the Freundlich isotherm equation was able to describe the experimental uptake data for both media. The uptake of arsenate decreased as pH increased for E33, since the surface of E33 became more negatively charged at higher pH. However, the arsenate uptake increased as pH increased due to the fact that more divalent arsenate ions formed at higher pH. A pore diffusion model, combined with the Freundlich isotherm parameters, was used to simulate the kinetic uptake data. The models conforms closely to the experimental data, and the extracted pore diffusion coefficients of arsenate were obtained. The model with the extracted diffusion coefficients was able to predict the kinetic adsorption curves for other experimental conditions, indicating that the model is appropriate for the systems tested in this study.