Ferrate (VI) is the inorganic anion with the chemical formula [FeO4]2−. It is photosensitive, contributes a pale violet color to compounds and solutions containing it and is one of the strongest water-stable oxidizing species known. Although it is classified as a weak base, concentrated solutions containing ferrate (VI) are corrosive and attack the skin and are only stable at high pH. The ferrate (VI) anion is unstable at neutral or acidic pH values, decomposing to iron. The reduction goes through intermediate species in which iron has oxidation states +5 and +4. These anions are even more reactive than ferrate (VI). In alkaline conditions ferrates are more stable, lasting for about 8 to 9 hours at pH 8 or 9. Ferrates are excellent disinfectants, and are capable of removing and destroying viruses. Fe (VI) is a strong oxidizing agent over the entire pH range, with a reduction potential (Fe (VI)/Fe (III) couple) varying from +2.2 V to +0.7 V versus NHE in acidic and basic media respectively. Sodium ferrate (Na2FeO4) is a useful reagent with good selectivity and is stable in aqueous solution of high pH, remaining soluble in an aqueous solution saturated with sodium hydroxide. Iron usually exists in the +2 and +3 oxidation states; however, in a strong oxidizing environment, higher oxidation states of iron such as +4, +5 and +6 can also be obtained. Ferrate is one of the most powerful, yet environmentally friendly, water treatment chemicals known. The byproduct of ferrate oxidation is the relatively benign iron (III), or ferric oxide. Fe (III) occurs naturally in the human body and plant and animal forms. Ferrate is a tetrahedral ion isostructural with the chromate and permanganate ions.