Kinetics and mechanism of arsenic removal using sulfide-modified nanoscale zerovalent iron

Sulphur modified nano zerovalent iron (S–nZVI) has shown considerable promise for removal of various aqueous contaminants. However studies utilizing S–nZVI for removal of aqueous inorganic arsenic (As) is relatively rare, which was studied in this work. Characterization of the synthesized S–nZVI showed typical core-shelled structure with distorted outer shell consisting of iron oxide and FeS. The removal rate of both As(III) and As(V) by S–nZVI was considerably enhanced compared to nZVI and highest As removal was observed at S/Fe ratio of 0.1 under acidic condition. Results showed slight decrease in As removal efficiencies for S–nZVI aged upto 48 h, with obvious drop in As removal efficiencies for longer aging time which although still exhibited higher reactivity than bare nZVI. Spectroscopic investigation showed sulphur amendment of nZVI completely altered the As sequestration mechanism compared to nZVI. While reduction of the adsorbed As(III) and As(V) was observed for bare nZVI, in contrast, uptake of As(III) and As(V) by S–nZVI involves adsorption as As(III) and As(V) oxyanion respectively with additional precipitation of As2S3. Overall, the study shows that incorporation of FeS on the surface of nZVI can be an effective modification strategy for efficient sequestration of As from contaminated water.