On the formation and transformation of Fe(III)-containing chukanovite, FeII2-xFeIIIx(OH)2-xOxCO3

Abstract

Aqueous suspensions of Fe(II)-chukanovite were obtained by mixing FeSO4 and (Na2CO3 + NaOH) solutions and studied by X-ray diffraction, vibrational spectroscopy (Raman and infrared) and Mössbauer spectroscopy. After 1 week of ageing in suspension in anoxic conditions, the Fe(II)-chukanovite particles remained poorly crystallized. A partial oxidation by air led to the formation of Fe(III)-containing chukanovite, i.e. FeII2-xFeIIIx(OH)2-xOxCO3, with a Fe(III) proportion about 11–13%. The lattice parameters of the monoclinic structure varied with the Fe(III) content, in particular the b parameter decreased significantly with increasing oxidation time. Fe(III)-containing chukanovite proved metastable in anoxic conditions and transformed upon ageing at room temperature into a mixture of Fe(II)-chukanovite and magnetite Fe3O4. Finally, trying to form Fe(III)-containing chukanovite by co-precipitation from Fe(II) and Fe(III) dissolved species led to a mixture of Fe(II)-chukanovite, i.e. FeII2(OH)2CO3, and sulfated green rust.