[en] Ferrates are a general name for compounds with the iron in higher oxidation states, i.e. Fe(IV), Fe(V) and Fe(VI). In recent years, the ferrates attract increased attention due to their potential for water treatment and environmental remediation technologies. Ferrates alone can transform under high temperature, humid air or in water. These transformation processes limit the applicability of ferrates from the point of view of storage and effectiveness of their oxidative reactions with other species in water. Kinetics and mechanism of ferrates transformation depend on many parameters such as temperature, humidity of air, presence of CO₂ in air, presence of inorganic buffering ions in water. ⁵⁷Fe Moessbauer spectroscopy has been applied as a powerful experimental technique for studying the transformation mechanisms under various physicochemical conditions. The both ex-situ and in-situ approaches were used. The transformation mechanisms in liquids were studied by Moessbauer spectroscopy of frozen solutions. While thermal decomposition of potassium ferrate(VI) leads to reduction of Fe atoms ending by the formation of KFeO₂, the transformation of ferrates in solution is based on the both reduction of Fe atoms and charge disproportionation caused by electron transfers. Kinetics and and mechanism of transformation of ferrate(IV), ferrate(V), and ferrate(VI) differ significantly. (authors)