Use of Iron(VI) and Iron(V) as Oxidants and Disinfectants in Water Treatment

Abstract

A technology involving environmentally friendly oxidants, ferrates (Fe(VI), Fe VI O 4 2-and Fe(V), (Fe V O 4 3-)) can meet criteria of water treatment. Fe(VI) and Fe(V) have high oxidizing power, selectivity, and upon decomposition produce a non-toxic by-product, Fe(III). Fe(VI) is easily be prepared by oxidizing Fe(III) by hypochlorite in alkaline medium. Fe(V) is produced by oneelectron reduction of Fe(VI) using three different methods: chemical (e.g. Fe(II)), electron beam (eaq ), and photocatalytic (conduction band electron).Fe(VI) exhibits a multitude of advantageous properties; these include higher reactivity and selectivity as an oxidant, disinfectant, antifoulant, and coagulant. Examples include treatment of cyanides and toxic metals, and inactivation of microorganisms. Rates of oxidation increase with a decrease in pH and are related to protonation of Fe VI O 4 2-. Oxidation of sulfur-and nitrogencontaining pollutants by Fe(VI) can be accomplished in seconds to minutes with formation of non-hazardous products. Fe(VI) can easily oxidize the amino acid components of microcystins and is a suitable disinfectant for detoxifying toxins in water. Fe(V) is more powerful oxidant than is Fe(VI). The oxidation of pollutants and amino acids with Fe(V) is 3-5 orders of magnitude faster than with Fe(VI). Removal of pollutants by Fe(V) can be completed in microseconds to millisecond time scales. The use of ionizing radiation and photocatalytic techniques in the presence of Fe(VI) results in Fe(V) formation and may have synergistic effects on the oxidation of pollutants and removal of toxins in water. Fe(V) can be useful in inactivation of microbial contaminants that are resistant to chlorination, chloramines, and Fe(VI). This paper gives examples of the multi-functional properties of Fe(VI) and Fe(V) to treat water and wastewater.