Adsorption kinetics of As (III) from groundwater by nanoscale zero-valent iron

Abstract

Artificial synthesized nanoscale zero-valent iron (NZVI) was used in the laboratory for the removal of As (III). The average BET surface area of particles was 49.16 m 2/g, with a diameter in the range of 20-40 nm. Batch experiments were carried out to study the efficiency of inorganic arsenic removal and adsorption kinetics by NZVI. The results show that As (III) can be removed efficiently by NZVI at pH 7, 20°C. The removal rate for As (III) is over 99% within 60 minutes by reacting 910 μg/L As (III) with 0.1 g NZVI. The As (III) adsorption process follows the pseudo-first-order kinetic expression. The surface-area-normalized rate coefficient k SA is 2.6 mL·m -2·min -1 for As (III). The equilibrium adsorption data fit Langmuir and Freundlich adsorption model well, with values of the constants at the regression coefficient (R 2>0.95) for both models. The monolayer adsorption capacity of the sorbent, as obtained from the Langmuir isotherm, 76.3 mg/g is of NZVI. 21% As (III) adsorpted on NZVI was found to desorption by sodium hydroxide solution (0.1 M). The effect of competing anions shows SiO 32- and H 2PO 4- markedly decrease with the removal of As (III), while the effect of other anions is insignificant. The mechanism of As removal is adsorption and coprecipitation.