Electrochemical Behavior of Fe(VI)-Fe(III) System in Concentrated NaOH Solution

摘要

The electrochemical behavior of a Fe(VI)/Fe(III) system was investigated with both a SnO_2-Sb_2O_3/Ti electrode and a powder microelectrode. Results showed that ferrite ion (FeO_2~-), formed in solution and solid phase, was a suitable Fe(III) species for the generation of FeO_4~(2-) and for construction of a Fe(VI)/Fe(III) redox system under strong basic conditions. Solid ferrite was made by the method of molten melting a mixture of Fe_2O_3 and NaOH at 973 ± 2K. The product was confirmed to be NaFeO_2 by X-ray diffraction (XRD) measurements. Ferrate (Fe(VI)) was also synthesized from ferrite (solid), Fe(OH)_3, and Fe_2O_3 using an hypochlorite oxidation method. In this method, it was demonstrated that ferrite was the most suitable material among these Fe(III) compounds for ferrate synthesis. Results also indicated: a) FeO_4 ~(2-)/FeO_2~- is a suitable redoxrnsystem under studied experimental conditions, b) rate and the reversibility of the redox reaction between FeO_4~(2-) and FeO_2~- were promoted markedly with the increase of temperature from 293 K to 333 K, c) the electro-oxidation of FeO_ 2~- is a fast two-electron transfer reaction on both the SnO_2-Sb_2O_3/Ti electrode and the NaFeO_2 powder microelectrode, and d) open-hearth dust of iron and steel industry could be used as a promising and valuable raw material for ferrate synthesis.