Potassium ferrate(VI): an environmentally friendly oxidant

Abstract

The iron(VI) derivative, potassium ferrate(VI) (Fe(VI)) has properties such as high stability, oxidizing power, selectivity, and a non-toxic by-product Fe(III), that make potassium ferrate(VI) an environmentally friendly oxidant for natural waters. This paper presents a review of its properties and its role in environmental and industrial removal of contaminants. Fe(VI) is a powerful oxidizing agent throughout the entire pH range with a reduction potential varying from +2.2 V to +0.7 V in acidic and basic solutions, respectively. Fe(VI) ion reduces rapidly and exothermally to Fe(III) and oxygen in strong acids, while the oxygen ligands of Fe(VI) exchange very slowly with water at pH 10. In dilute solutions, the lowest rate of reduction of Fe(VI) by water occurs between pH 9.4 and 9.7. Fe(VI) is also a selective oxidant for a large number of organic compounds with Fe(III) as a by-product. Fe(VI) therefore has a role in cleaner (‘greener’) technology for organic synthesis. Other applications of Fe(VI) include production of ferrate(V) by pulse radiolysis, ‘super-iron’ batteries, and wastewater treatment processes. Many of the contaminants in wastewater can be removed by Fe(VI) in seconds to minutes with formation of non-hazardous products. Fe(VI) is also a disinfectant, antifoulant, and coagulant, and therefore a promising multi-purpose wastewater treatment chemical.