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

Abstract

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 FeCl 2 · 4H 2O and NaOH solutions. Depending on the initial amounts of Fe 2+, Cl − and OH −, goethite, lepidocrocite or akaganéite were then obtained. When a large excess of dissolved FeCl 2 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 FeCl 2 · 4H 2O or NaCl. Akaganéite was obtained exclusively in the FeCl 2 solutions, confirming that to obtain the formation of this compound, both iron(II) and chloride concentrations must be important.