Aqueous phase adsorption of aromatic organoarsenic compounds : a review

Abstract

Aromatic organoarsenic compounds (AOCs) are synthetic arsenic-based compounds released into the environment through anthropogenic activities. Due to their high solubility and mobility in aqueous media, AOCs as well as their degradation products can exist for a long time in the environment. This study is a review of published literature that discusses the sequestration of AOCs from aqueous media through the technique of adsorption. Key components related to the adsorption of AOCs such as adsorbent performance, adsorption mechanism, isotherm, kinetic as well as thermodynamic modelling, and desorption/regeneration of adsorbents were discussed in this paper. It was observed that the highest reported adsorption capacities for the AOCs were 975 mg/g for Roxarsone using nano-zerovalent iron/sludge-based biochar, 791 mg/g for p-arsanilic acid using a mesoporous zeolitic imidazolate framework, and 139 mg/g for Phenyl arsonic acid using a hydroxy-functionalized Chromium-based MOF. Adsorption mechanisms were dominated by hydrogen bonding, complexation reactions, electrostatic interactions, and electron donor-acceptor interactions. The Langmuir or Freundlich classical isotherm models were the best-fit in most cases to describe AOCs' adsorption equilibrium, while the pseudo-second-order model was the best-fit for the modelling of AOCs' uptake kinetics. Thermodynamic studies revealed that AOCs' uptake is usually spontaneous (with a few exceptions). This suggests that adsorption can be economical on an industrial scale for the removal of AOCs from aqueous solutions. For future work, the utilization of column systems for AOCs adsorption should be encouraged together with the proper disposal or recycling of used adsorbents.