As(III) oxidation by different oxidizers

Arsenic (III) is much more toxic and difficult in removal than Arsenic (V) by conventional arsenic removal technologies. However, As(III) may be more prevalent in groundwater than As(V). Furthermore, as of 23 January 2006 the EPA will require all public water facilities to meet the new standard of 10 ppb maximum for arsenic in drinking water. Therefore, a method for removing As(III) is urgently needed. A precondition for better As(III) removal is to oxidize it to As(V). In this study, hydrogen peroxide, air, potassium ferrate, and potassium permanganate were used as oxidizers, and it was found that both Fe(VI) and Mn(VII) are effective As(III) oxidizers. The impacts of pH, As(III) initial concentration, and the amount of oxidizers on the As(III) oxidation efficiency of Fe(VI) and Mn(VII) were also investigated. The results show that the pH value of tested water is a significant factor affecting the As(III) oxidation efficiency of Fe(VI). However, the As(III) oxidation efficiency of Mn(VII) does not depend much on pH. Although theoretical redox analyses suggest that Fe(VI) should be a better oxidizer than Mn(VII) throughout the entire pH range, experimental results show that Mn(VII) performs better than Fe(VI) for As(III) oxidation under acidic conditions due to the acid-catalyzed redox reaction between Fe(VI) and H2O. This study also investigates subsequent As(V) removal efficiency after As(III) oxidation by Fe(VI). The removal efficiency obtained in this research is very low. This is probably because of the low concentration of Fe(VI) in the solution and because the water was not flocculated.