Electrochemical formation of a new Fe(II)/Fe(III) hydroxy-carbonate green rust: characterisation and morphology
Résumé
Electrochemical behaviour of iron in deaerated 0.2 M carbonate/bicarbonate solution pH 9.6 and T=25°C was investigated. Oxidation of iron leads to the formation of green rust as intermediate product and ferrihydrite as ultimate product. Characterisation of green rust was done through FTIR, TEM, XRD and Mössbauer spectroscopy. Results point out differences in the structure and morphology, such as size of hexagonal crystal lattice, parameter c and Fe(II)/Fe(III) ratio, between our electrochemically formed GR and GR1(CO32−) obtained by oxidation of Fe(OH)2. Co-precipitation of Fe(II) and Fe(III) species during the electrochemical procedure leads to a new GR. We propose the following chemical formula for this GR, [Fe(II)2Fe(III)2(OH)8]2+·[CO3]2−. However, the possibility that incorporation of both CO32− and Cl− ions could occur is not ruled out.