Journal of Environmental Sciences 19(2007) 783–786 Oxidation of As(III) by potassium permanganate LI Na 1,2 , FAN Maohong 1,2, * , Van Leeuwen Johannes 1 , Saha Basudeb 3 , YANG Hongqun 4 , HUANG C. P. 5 1. Department of Civil, Construction and Environmental Engineering, Center for Sustainable Environmental Technology, Iowa State University, Ames, Iowa 50011, USA. E-mail: nali@iastate.edu 2. Center for Sustainable Environmental Technology, Iowa State University, Ames, Iowa 50011, USA 3. Department of Chemistry, Iowa State University, Ames, Iowa 50011, USA 4. Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 2G6, Canada 5. Department of Civil and Environmental Engineering, University of Delaware, Newark, DE 19716, USA Received 20 September 2006; revised 19 December 2006; accepted 5 January 2007 Abstract The oxidation of As(III) with potassium permanganate was studied under conditions including pH, initial As(III) concentration and dosage of Mn(VII). The results have shown that potassium permanganate was an effective agent for oxidation of As(III) in a wide pH range. The pH value of tested water was not a significant factor affecting the oxidation of As(III) by Mn(VII). Although theoretical redox analyses suggest that Mn(VII) should have better performance in oxidization of As(III) within lower pH ranges, the experimental results show that the oxidation efficiencies of As(III) under basic and acidic conditions were similar, which may be due to the adsorption of As(III) on the Mn(OH) 2 and MnO 2 resulting from the oxidation of As(III). Key words: arsenite; arsenate; oxidation; potassium permanganate Introduction Arsenic (As) is a naturally occurring toxic element which exists in both organic and inorganic forms in nature. Organic arsenic species in water supplies are seldom above 1 μg/L (Anderson and Bruland, 1991) and have no significant effect on drinking water treatment. Inorganic arsenic in water mainly exists in two forms, As(III) and As(V). In the normal pH range of natural water, As(V) exists in the form of anions such as H 2 AsO 4 - and HAsO 4 2- while As(III) is in the form of neutral molecular, i.e., H 3 AsO 3 . As(V) and As(III) are present mainly in surface water and anaerobic groundwater. Arsenic contamination of drinking water has received increasingly intensive attention in recent years because of its carcinogenic properties (Smith et al., 1992). Arsenic poisoning has affected millions of people worldwide, espe- cially in Bangladesh (Smith et al., 2000). Accordingly, the Environmental Protection Agency of the United States re- cently reduced the maximum contaminant level of arsenic in drinking water from 50 to 10 μg/L. In order to meet the new stringent standard, different As removal methods have been developed. As(III) is more toxic and mobile than As(V), so its removal efficiency is much lower than that of As(V) when conventional arsenic removal technologies are used. Therefore, oxidation of As(III) to As(V) is necessary to *Corresponding author. E-mail: mfan3@mail.gatech.edu. improve total arsenic removal efficiency. Chlorine is one of the oxidizers so far explored by many researchers. However, harmful Cl-based byproducts could be generated during this oxidation process. The other oxidants reported for oxidation of As(III) include ozone, pure oxygen (Kim and Nriagu, 2000), hydrogen peroxide (Ryu and Choi, 2004), manganese oxides (Manning et al., 2002; Tournassat et al., 2002), UV/iron (Emett and Khoe, 2001; Hug et al., 2001), TiO 2 /UV (Kocar and Inskeep, 2003; Lee and Choi, 2002), and ferrate (Lee et al., 2003). Each oxidant as an As(III) oxidizing agent has its advantages and disadvantages. Potassium permanganate is powerful oxidant. Commer- cial potassium permanganate is in solid form and it does not generate seriously concerned byproducts. Therefore, it can potentially be used to oxidize As(III) in water treatment. This research aims at investigating the oxidation of As(III) by potassium permanganate and examining the factors affecting the oxidation of As(III). 1 Experiments 1.1 Materials and chemicals All solutions used in the research were prepared with deionized water, which was further degassed with purging helium for at least 10 min to exclude oxygen from water. All the chemicals were analytic grade and were used as