Ferrate(VI)

Nomenclature

The term ferrate is normally used to mean ferrate(VI), although it can refer to other iron-containing anions, many of which are more commonly encountered than salts of [FeO4]2−.{{cite book

In battery electrochemistry, ferrate(VI) is sometimes called "super-iron".

Synthesis

Ferrate(VI) salts are formed by oxidizing iron in an aqueous medium with strong oxidizing agents under alkaline conditions, or in the solid state by heating a mixture of iron filings and powdered potassium nitrate.{{cite book

For example, ferrates are produced by heating iron(III) hydroxide with sodium hypochlorite in alkaline solution:

:2 + 3 + 4 → 2 + 5 + 3

The anion is typically precipitated as the barium(II) salt, forming barium ferrate.

Properties

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 SHE in acidic and basic media respectively.

: + 8 + 3 e− + 4 ; E0 = +2.20 V (acidic medium) : + 4 + 3 e− + 5 ; E0 = +0.72 V (basic medium)

Because of this, the ferrate(VI) anion is unstable at neutral or acidic pH values, decomposing to iron(III):{{cite book

Aqueous solutions of ferrates are pink when dilute, and deep red or purple at higher concentrations.{{cite book

The ferrate(VI) ion has two unpaired electrons and is thus paramagnetic. It has a tetrahedral molecular geometry, isostructural with the chromate and permanganate ions.

Applications

Ferrates(VI) are potentially an environmentally-friendly water treatment chemical, as the byproduct of ferrate oxidation is the relatively benign iron(III). The strong oxidativity makes them excellent disinfectants, capable of removing and destroying viruses{{cite book

Sodium ferrate () 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.

References

References

1. (1999-08-13). "Energetic Iron(VI) Chemistry: The Super-Iron Battery". Science.
2. (2001-10-15). "Analysis of ferrate(VI) compounds and super-iron Fe(VI) battery cathodes: FTIR, ICP, titrimetric, XRD, UV/VIS, and electrochemical characterization". Journal of Power Sources.
3. Karlis Svanks. (June 1976). "Oxidation of Ammonia in Water by Ferrates(VI) and (IV)". Water Resources Center, Ohio State University.
4. (2015). "Ferrates: Greener Oxidants with Multimodal Action in Water Treatment Technologies". Accounts of Chemical Research.
5. (2005-10-01). "Electrochemical Alkaline Fe(VI) Water Purification and Remediation". Environmental Science & Technology.