###### Abstract  
Potassium ferrate(VI) (K\({}_{2}\)FeO\({}_{4}\)) as a particularly strong oxidant represents an effective and environmentally friendly waste water treatment material. When produced by anodic oxidation in highly alkaline aqueous solution, the K\({}_{2}\)FeO\({}_{4}\) product is separated and sealed in inert plastic bags with the retention of some liquid phase with high pH. This method proved to be excellent for long-term storage at moderately low temperature (5 \({}^{\circ}\)C) for industrial applications. It is still imperative to check the ferrate(VI) content of the product whenever it is to be used. Fe-57 Mossbauer spectroscopy is an excellent tool for checking the ratio of ferrate(VI) to the degradation product iron(III) in a sample. For this purpose, normally the spectral areas of the corresponding subspectra are considered; however, this approximation neglects the possible differences in the corresponding Mossbauer-Lamb factors. In this work, we have successfully determined the Mossbauer-Lamb factors for the ferrate(VI) and for the most common iron(III) degradation products observed. We have found superparamagnetic behavior and low-temperature phase transformation for another iron(III) degradation product that made the determination of the Mossbauer-Lamb factors impossible in that case. The identities of a total of three different iron(III) degradation products have been confirmed. potassium ferrite(VI); waste water treatment; anodic oxidation; Mossbauer spectroscopy; Debye temperature 2024 202  
compound--being thermodynamically stable but sensitive to humidity and carbon dioxide in air--involves three different procedures. It is possible to reach the oxidation state (VI) of iron by reaction with hypochlorite in highly alkaline aqueous solution (wet method). This synthesis requires chlorine gas to start with which, from the environmental point of view, is not preferred. The hypochlorite forms in the reaction of water and chlorine. The final reaction is summarized by Equation (1). \[2\text{Fe(OH)}_{3}+3\text{ClO}^{-}+4\text{OH}^{-}=2\text{FeO}_{4}{}^{2}+3 \text{Cl}^{-}+5\text{H}_{2}\text{O} \tag{1}\]  
This is normally conducted in concentrated KOH solution at controlled temperature (\(<\)30 \({}^{\circ}\)C), and to obtain a dry and stable final product, several steps, including washing with benzene, n-hexane, isopropanol, and diethyl ether, are needed. The dry product is reported to be found stable over a one-year period [15]. Solid-state synthesis of potassium ferrate is possible by reacting potassium superoxide and iron oxide powder. An alternative route is the reaction of iron salts with some oxidizing chlorine-containing solid in highly alkaline potash (K\({}_{2}\)CO\({}_{3}\)) [16]. Separation of pure and stable ferrate from such reaction mixtures with good yield is not simple. This is not optimal for industrial applications. The electrochemical synthesis route of K\({}_{2}\)FeO\({}_{4}\) is an attractive method regarding industrial production and environmental issues. For the latter one, it is crucial that there is no need to use chlorine gas in this technology. For industry, the practically one-step synthesis (not counting a simple conversion from Na-ferrate(VI) to K-ferrate(VI)) is a great advantage. In addition, from the pure (chlorine-free) ferrate, the coagulated Fe(OH)\({}_{3}\) is the only, and a non-harmful, product of the oxidation treatment, serving as an adsorbent removing more pollutants from waste water. The stability of potassium ferrate(VI) is important for industrial production since storage from production to selling is a straightforward necessity. The product should have long-term stability, i.e., not suffer substantial decomposition over several months. We have studied the stability of electrochemically produced potassium ferrite(VI) in our recent work using Mossbauer spectroscopy [17]. Mossbauer spectroscopy is an excellent technique for such a study since iron(VI) and the degradation product iron(III) give well-separated spectral contributions in the Mossbauer spectra.