Removal of methylated arsenic using a nanostructured zirconia-based sorbent: Process performance and adsorption chemistry

A readily prepared nanostructured zirconia-based sorbent was developed and demonstrated to be effective on adsorption of monomethylarsonic acid (MMA) from water with a capacity of 1.43mmolMMA/gsorbent, which is much higher than that of sorbents reported. It was found that the MMA uptake is highly pH-dependent. Better adsorption is obtained at lower pH, and the optimal pH is from 2.5 to 3.5. Most of the MMA uptake occurs rapidly in the first 48h, followed by a relatively slow process. The adsorption kinetics and isotherm can be well described by pseudo-first order rate model and Langmuir equation, respectively. The temperature does not great influence on the adsorption isotherm. The MMA adsorption is independent on background electrolyte concentration, which implies the MMA forms inner-sphere complexes on the sorbent. The presence of humic acid does not pose noticeable effect on the adsorption. The coexisting HCO3- or F ^- obviously hinders the adsorption of MMA; however, the existence of PO43- slightly enhances the adsorption. FTIR and XPS analyses demonstrated that hydroxyl and sulfur-containing functional groups are involved in the uptake of MMA. Based on the adsorption experimental results and spectroscopic analysis, an anion exchange mechanism is proposed for the adsorption of MMA.