Simultaneous elimination and detoxification of arsenite in the presence of micromolar hydrogen peroxide and ferrous and its environmental implications

Abstract

Experiments for simultaneous elimination and detoxification of microgram level of As(Ⅲ) in the presence of micromolar H2O2 and Fe(Ⅱ) which are frequently encountered in natural water were conducted. The results showed that the molar ratio of oxidant to As(III) plays important role in As(III) oxidation under the experimental conditions. The extent of As(Ⅲ) oxidation with single H2O2 or Fe(Ⅱ) ranged from 7.9 % to 60.3 % and 22.2–46.6 %, respectively. Treatments with H2O2/As(Ⅲ) molar ratios in the range 150: 1–750: 1 or Fe(Ⅱ)/As(Ⅲ) molar ratios in the range 37.5: 1–375: 1 were more favor for As(Ⅲ) oxidation respectively, and increasing oxidant concentration did not result in complete As(Ⅲ) oxidation. As(Ⅲ) was completely oxidized and eliminated following the precipitation of ferric hydroxides in 5 reaction minutes when H2O2 and Fe(Ⅱ) coexisted in the reaction system. The interface characterization for the reacted precipitates after the experiment were conducted by using a high-resolution field emission scanning electron microscopy (SEM) coupled with an EX-350 energy dispersive X-ray spectrometer (EDX) and X-ray photoelectron spectroscopy (XPS), respectively. The results showed that As(Ⅴ) was the merely arsenic species and As oxide primary situated in the subsurface layer of the reacted precipitates, whereas Fe was more concentrated in the outermost surface layer. Our research showed that H2O2 and Fe(Ⅱ) at natural level may exert significant influence on arsenic mobilization in natural water. Considering the much more toxic of As(Ⅲ) than that of As(Ⅴ), the research also provide us an environmental friendly choice in the elimination and detoxification of microgram As(Ⅲ) in drinking water.