Efficient arsanilic acid removal from water via reversible phase transition in a cyclic adsorption process based on reactivated MgO

Abstract MgO possesses efficient adsorption property on arsenate removal from wastewater. However, its performance on adsorbing organoarsenic pollutants is still unknown. MgO nanoparticles was found to possess a very high adsorption capacity of 617 mg/g to arsanilic acid, which is much higher than most of reported adsorbents and even comparable to metal organic framework (621 mg/g). More importantly, the used sorbent, Mg(OH)2/ASA, can be reactivated by annealing at 400 °C without the need of desorption while ASA is transformed into arsenate and dispersed uniformly in MgO/Mg(OH)2. MgO was successfully reactivated for 5 cycles, and the arsenic content was increased up to 5 times than traditional one-off adsorption process and the amount of used sorbent and generated hazardous sludge will be decreased by 80%. The reversible phase transition attribute of MgO/Mg(OH)2 is the main reason for its extremely high and reactivatable adsorption properties. This new MgO-circulation strategy provides a more environmentally friendly and cost-effective way for the treatment of aromatic organoarsenic wastewater, especially when sludge incineration or annealing is already included as a terminal procedure in existing wastewater treatment process.