Electrochemical and spectroscopie behaviour of iron in the molten NaCl-K2SO4 mixture

The chemical and electrochemical dissolving of Armco iron in the NaCl-K2SO4 melt has been studied. In the case of the chemical dissolution, a sample becomes coated, as time goes on, with a dense film consisting of FeO, FeS and Fe3O4; precipitation in the melt is observed, the precipitate consisting mainly of FeS and FeO.

Iron in the dissolved state is most probably in the form of [Fe(II)(SO4)3CL3](7-), a mixed-ligand complex of quasi-octahedral type.In the case of electrochemical dissolution iron oxidizes stepwise, first to Fe(II) and then to Fe(III). This process is reversible, and the Fe(III) is reduced via Fe(II) and then to the metal.

The electrode process as a whole may be represented as follows:Fe(+2e) (-2e)Fe(II)(+e) (-e)Fe(III)Formation of insoluble particles (probably Fe3O4) in the melt is observed. Iron is in the melt as a mixed octahedral bivalent iron sulfate-chloride complex. We did not detect Fe(III) by electronic absorption spectra, possibly due to the superimposition of the charge transfer bands edge on low-intensity Fe(III) bands of the 5d electronic configuration.

The solubility of Fe2O3 in the NaCl-K2SO4 melt is low and was determined to 2 x 10(-3) wt%.