THE MECHANISM OF OXIDATION OF FERROUS HYDROXIDE IN SULFATED AQUEOUS-MEDIA - IMPORTANCE OF THE INITIAL RATIO OF THE REACTANTS

In simulated aqueous corrosion processes of iron in sulphated media, the most important factor is the ratio, R, of the initial concentration of Fe2+ and SO4(2-) to OH- ions which separates the basic and acidic media at a value of 1/2. Mossbauer spectroscopy, coupled with direct recording of the pH and the electrode potential, has identified six characteristic values of R and a basic sulphate, named sulphated ferrous hydroxide (SFH) and also determined the chemical formula of green rust 2 (GR2). Apart from GR2, two other ferrous-ferric intermediate compounds, a basic compound and a hydrated magnetite, the oxidation of which leads to delta FeOOH and magnetite respectively, are suspected. The various mechanisms of oxidation are established based on the rigorous analysis of the evolution of the composition of the end products of oxidation with respect to R.