Maghemite nanoparticles for As(V) removal: Desorption characteristics and adsorbent recovery

Maghemite (-Fe₂O₃) nanoparticles are potential adsorbents for arsenate removal from drinking water. Arsenate, As(V) oxoanion, removal is crucial due to arsenate's serious effects on health and its existence in water worldwide. The aim of the present study was to investigate the adsorbent properties of maghemite nanoparticles by observing their stability, desorption and regeneration ability. Arsenate batch desorption and regeneration experiments were carried out with two different kinds of maghemite - a commercial product and a laboratory-synthesized one using the sol-gel process. The best alkaline desorption solution was determined from five different alkaline solutions: NaOH, Na₂CO₃, Na₂HPO ₄, NaHCO₃ and CH₃COONa3H₂O (NaAc). Desorption kinetics were also examined. NaOH was observed to be the best desorption solution at a concentration of 1M with>95% desorption efficiency achieved for both adsorbents. The arsenate adsorption-desorption process was reversible and maghemite recovery was efficient at successive cycles. The laboratory-synthesized maghemite maintained more than 95% of its initial uptake capacity after six cycles for initial As(V) concentrations of 500 and 1000g/l, while the achievement with the commercial product was two to four cycles. In addition, iron dissolution from adsorbents was negligible. Thus, it is possible to regenerate the maghemite nanoparticles for repeated adsorption of As(V).