Ferrate ion, FeO42-, as a Cl2 and MnO4- replacement in water purification

Abstract

A method has been devised by which solid samples of K2FeO4 can be stabilized with respect to decomposition through a double-mixed salt with inexpensive K2SO4. This solid solution is stable over a wide range of compositions and can be prepared directly by electrolysis in a continuous process. The mechanism of stabilization of solutions of FeO2- by IO4- has been studied and it is found to prevent solid oligomers of Fe(III) from forming which are the major catalytic species. This occurs through complexation to form a symmetrical ion which has been isolated and its crystal structure determined. There is a direct correlation between the time of complete removal of IO4- and the start of the catalytic path. It is concluded that the kinetics of decomposition in the presence of metalion complexes is a function of trace impurities in the solvent and that "clean" kinetics cannot be observed. The reaction of CH2O, HCOO-, and N02- with FeO4^2- were studied and the rates shown to be first order in substrate and oxidant, increasing with acidity and are consistent with a 2e- slow step followed by a rapid reaction or reactions. The third oxygen in N03- (from N02- oxidation) comes from Fe04^2- as shown by O^18 measurements. Enhancement of the rates of NH3 reaction were found with traces of oxidizable metal ions. But the products of the reaction were many and the mechanism is not certain. A study of the formation of [Fe{ophen)3]^+2 during CH2O oxidation by FeO4^2- in the presence of ophen shows that it definately forms but we were not able to establish that Fe(II) was generated from Fe(IV).

This material is based upon work supported by the U.S. Geological Survey and the Missouri Water Center under the Grant/Cooperative Agreement.

The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the opinions or policies of the U.S. Geological Survey or Missouri Water Center. Mention of trade names or commercial products does not constitute their endorsement by the U.S. Geological Survey or Missouri Water Center.