ABSTRACT

The phase diagram of the oxygen/iron binary system shows that only three oxides are thermodynamically stable within certain limits of pressure and temperature: wustite, magnetite and hematite. Iron is a very active element, in the sense that large global fluxes characterize its mobilization between different natural reservoirs. This movement of iron implies phase transformations, many of which have been characterized and studied both in nature and in the laboratory. This chapter illustrates the complex manifold of reactions involved in these phase transformations. Of these reactions, dissolution-reprecipitation processes constitute an important fraction. The solubility of iron oxides can be strongly altered by changing the redox potential of the solution. Complexing agents other than water or hydroxyl ions drastically change the solubility of iron oxides. The increase in solubility due to complexation is very important in practical cases, as it allows the total concentration of aqueous iron to rise substantially.