FerratesVI

Ferrate(VI) refers to chemical species containing iron in the +6 oxidation state, most commonly the ferrate ion [FeO4]2-. In aqueous solutions, this anion is stabilized in strongly alkaline conditions. Related solid ferrate materials, including alkali metal ferrates such as sodium ferrate Na2FeO4, have also been studied.

Ferrate(VI) is a powerful oxidant. It can oxidize a wide range of inorganic and organic substrates and is reduced to Fe(III) species in the process. In water treatment, the oxidation is often accompanied by the formation of iron(III) oxyhydroxide flocs that aid coagulation and subsequent solids removal. Its effectiveness is greatest at high pH and diminishes in acidic media, where the ferrate decomposes more rapidly.

Production and handling: Ferrate(VI) is typically generated electrochemically by oxidizing iron in strongly alkaline solutions, and is most stable in such media. In acidic conditions it decomposes, releasing oxygen and forming iron(III) products. Because it is a strong oxidizer, it must be handled with appropriate precautions to avoid rapid, uncontrolled reactions with reducing materials.

Applications: The principal use is in water and wastewater treatment, where ferrate(VI) serves as an oxidant and coagulant, helping remove color, taste, odor, and various contaminants while forming Fe(III) precipitates that assist solid-liquid separation. Research has also explored solid ferrates as alternative oxidants and potential on-site generation in treatment trains.

History: Ferrate chemistry has been studied since the early 20th century, with renewed interest in recent decades due to environmental and operational advantages for water treatment.