Removal of Arsenic from Water by Supported Nano Zero-valent Iron on Activated Carbon

Nano-sized zero-valent iron is an effective adsorbent for arsenic removal from drinking water. However, its application may be limited in public water system and small scale water treatment system due to its tiny particle size. In the present work, nanoscale zero-valent iron was supported onto activated carbon (NZVI/AC) by impregnating carbon with ferrous sulfate followed by chemical reduction with NaBH(4). Approximate 8.2 wt% of iron was loaded onto carbon and SEM analysis showed that the iron particles in the pores of carbon were needle-shaped with the size of 30-500 x 1000-2000 nm. Kinetics study revealed that adsorption of arsenite and arsenate by NZVI/AC was fast in the first 12h and the equilibrium was achieved in approximately 72 h. The adsorption capacity of the synthesized sorbent for arsenite and arsenate at pH 6.5 calculated from Langmuir adsorption isotherms in batch experiments was 18.2 and 12.0mg/g, respectively. Phosphate and silicate markedly decreased the removal of both arsenite and arsenate, while the effect of other anions and humic acid was insignificant. Common metal cations (Ca(2+), Mg(2+)) enhanced arsenate adsorption but ferrous iron (Fe(2+)) was found to suppress arsenite adsorption. NZVI/AC can be effectively regenerated by elution with 0.1M NaOH.