On the formation of β-FeOOH (akaganéite) in chloride-containing environments

Fe(III) oxyhydroxides were synthesised in chlorinated environments via chemical or electrochemical processes in order to determine the conditions favouring the formation of akaganéite. Corrosion products were characterised using X-ray diffraction, Raman spectroscopy and Fourier transform infrared spectroscopy. The first method produced Fe(III) oxyhydroxides from the aerial oxidation of iron(II) precipitates which were obtained by mixing FeCl2 · 4H2O and NaOH solutions. Depending on the initial amounts of Fe2+, Cl− and OH−, goethite, lepidocrocite or akaganéite were then obtained. When a large excess of dissolved FeCl2 was present, akaganéite was formed independently of the oxygen flow. In the second method, steel electrodes were left in baths containing chloride with [Cl−] = 2 mol L−1, using either FeCl2 · 4H2O or NaCl. Akaganéite was obtained exclusively in the FeCl2 solutions, confirming that to obtain the formation of this compound, both iron(II) and chloride concentrations must be important.