Structural Changes of Minerals in Iron Ores via Aqueous Solution

This paper provides a view of formation pathways of various iron oxides, such as hematite, goethite, lepidocrocite, magnetite etc. via aqueous solution. Formation mechanisms of these iron oxides are important to understand formation processes of iron-relevant minerals in Precambrian banded iron formations (BIF). This is because most of iron ores used in Japanese steel industries are imported from BIFs of Australia, Brazil and so on. The chemical and physical properties of the iron ores considerably dominate their sintering before iron making. Nevertheless, formation processes of the iron ores are still enigmatic, since the iron oxide species are changed by a number of reaction conditions. Various analytical techniques have been used to elucidate oxidation and reduction of the iron oxides in solution from the viewpoint of electrochemical reaction in aqueous solution so far. In those investigations, structural stability of the iron oxides has been studied using the electrochemical potential and pH diagrams of solution. In this paper, formation processes of the iron oxides are discussed as related to the iron ore formation. It is stressed that structural changes of iron oxides including green rusts and oxyhydroxides play an important role in most of iron ore formation.