Removal of Arsenic (III, V) from Aqueous Solution by Nanoscale Zero-Valent Iron Stabilized with Starch

Abstract

Arsenic is a toxic and carcinogenic pollutant. Contamination of surface and groundwater sources with arsenic (As) is one of the major public health and environmental worries in the world and also in Iran. The most common arsenic removal techniques are: coagulation/precipitation, lime-softening, ion exchange, membrane filtration and adsorption. Most of these methods remove arsenic effectively from water containing high initial arsenic concentration but residual concentrations are still high for the water quality standards. Zerovalent iron technology (ZVI) is a promising method for removal of various pollutants including arsenic from water and soils and Zero-valent iron nanoparticles due to smaller size and larger surface area can be used for efficient removal of As (III), (V) even at very low arsenic concentrations, from aqueous solutions. However the efficiency of this process is reduced by the rapid aggregation of nanoparticles that necessitates the use of stabilizers to improve their stability. In the present study, the mechanism and removal ability of arsenic by nano scale zero-valent iron stabilized with two different polymeric materials were compared. The adsorption process was accomplished in a laboratory- scale batch with emphasis on the effect of various environmental factors on adsorption efficiency. Chemical composition and morphological features of synthetic nanoparticles were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. Starch stabilized nanoparticles displayed∼36.5% greater removal for As (V) and 30% for As (III) in comparison with CMC-stabilized nanoparticles. More than 99% of arsenite and arsenate was removed from aqueous solution using S-nZVI at an initial concentration less than 1000 µg/L within 30 min under the conditions of 0.3 g/L of S-nZVI and pH 7.118 There was an inverse correlation between pH and arsenic feed concentration with removal efficiency, but contact time and nZVI loading have a proximate linear relationship with removal efficiency. The isotherm equilibrium studies confirmed that the Langmuir-1 (qmax=14 mg/g) and Langmuir-2 (qmax=13 mg/g) forms are the highest fitted models for the adsorption process of As (III), (V) respectively. It was also found that adsorption of arsenic species by S-nZVI followed pseudosecond order kinetic model with reaction rate constants (k) of 0.005-0.024 min-1 for arsenite and 0.007-0.089 min-1 for arsenate. The results showed the potential of starched Fe0 nanoparticles for rapid removal of both arsenic species without the need to pre-oxidation from aqueous solutions.