Ferrate

Ferrate refers to iron compounds in unusually high oxidation states, most commonly the ferrate(VI) ion FeO4^2− and the ferrate(V) ion FeO4^−. In alkali metal salts, such as potassium ferrate (K2FeO4) and sodium ferrate (Na2FeO4), ferrates are powerful oxidizing agents. They are typically stable in strongly basic conditions and are used as convenient solid or concentrated solutions in water treatment and chemistry.

In aqueous solutions, ferrates act as oxidants and, upon reaction, tend to hydrolyze to iron oxyhydroxide species (Fe(OH)3) with release of oxygen. The stability and reactivity of ferrates depend strongly on pH: they are most stable at high pH (often above 12) and rapidly decompose under acidic or moderately alkaline conditions. The redox chemistry of ferrates enables multi-electron oxidation processes, making them useful for both disinfection and the oxidation of organic contaminants.

Production of ferrates is primarily achieved by electrolytic oxidation of iron in hot, concentrated alkaline electrolytes (such as NaOH or KOH), often using an iron anode. Chemical routes in alkaline media and other specialized methods also exist. Due to their sensitivity to pH, ferrate preparations are typically stored and used under alkaline conditions to minimize premature decomposition.

Applications of ferrates include water and wastewater treatment, where they function as oxidants and coagulants to remove organic pollutants, pathogens, and metals. They offer an alternative to chlorine-based disinfection in some cases, as they can reduce the formation of halogenated disinfection byproducts. Limitations include production cost, stability under non-basic conditions, and handling requirements as strong oxidants.