1. Although rarely studied, ferrate(V) 3− and ferrate(IV) 4− oxyanions of iron also exist.

2. Ferrate(VI) is the inorganic anion with the chemical formula 2−.

3. Disclosed is an aqueous dispersion for chemical mechanical polishing, which is characterized by containing abrasive grains, ferrate ions (FeO42-) and a dispersion medium.