TRANSFORMATION OF FE(II)-FE(III) HYDROXYSULPHITE INTO HYDROXYSULPHATEGREEN RUSTS

Fe(II)-Fe(III) hydroxysulphite Green Rust 1, GR1(SO32-), can be obtain ed by oxidation of Fe(OH)(2) precipitates in aqueous solution and char acterised by X-ray diffraction and Mossbauer spectroscopy. In contrast to other Green Rusts (GRs) which then oxidise directly into ferric ox yhydroxides and magnetite, GR1(SO32-) first oxidises into a Green Rust two compound, as identified by X-ray diffraction. Mossbauer analysis reveals that this GR2 is the Fe(II)-Fe(III) hydroxysulphate, GR2(SO42- ). Such an oxidation process, GR1(SO32-) --> GR2(SO42-) confirms that the average oxidation number of Fe increases according to the chemical formulae previously proposed, [(Fe6Fe2III)-Fe-II(OH)(16)](2+)[SO3 . m H(2)O](2-), and [(Fe4Fe2III)-Fe-II(OH)(12)](2+)[SO4 . nH(2)O](2-) for GR1(SO32-) and GR2(SO42-) with oxidation numbers of 2.25 and 2.33, res pectively. The process implies likely the presence of sulphate ions in herent to the oxidation of sulphite in the solution.