Potassium ferrate(VI) (K 2 FeO 4 ) as the most often applied ferrate or sodium
ferrate(VI) (Na 2 FeO 4 ) can be prepared by a wet chemical synthesis. Iron(III) oxides
or their salts (e.g., ferric chloride or potassium nitrate) are oxidized by hyperchlorite
ion (OCl
À ) in highly alkaline solution, prepared by NaOH resulting in sodium ferrate
(VI) according to the following reaction:
2Fe OH
ð Þ 3 þ 3NaOCl þ 4NaOH ! 2Na 2 Fe
VI O 4 þ 3NaCl þ 5H 2 O
ð8:1Þ
Potassium ferrate(VI) can then be obtained through precipitation from the solution of Na 2 FeO 4 by adding KOH according to the reaction:
Na 2 Fe
VI O 4 þ 2KOH ! K 2 Fe
VI O 4 þ 2NaOH
ð8:2Þ
The purity of ferrates prepared by this method is very high (approx. 98%).
However, it is worth mentioning that this wet chemical method of synthesis is not
environmentally friendly as it results in high concentrations of NaOH and residues of
NaOCl in reaction solutions.
Concerning a wet chemical approach, the electrochemical anodic oxidation of
iron or cast iron in concentrated hydroxide solutions or melts provides much more
Fig. 8.1 Possible approaches to the synthesis of ferrates. (Reprinted with permission from Sharma
et al. (2015). Copyright (2015) American Chemical Society)
8 Ferrates as Powerful Oxidants in Water Treatment Technologies
179