Electrochemistry and dissolution kinetics of magnetite and ilmenite

Natural samples of magnetite and ilmenite were experimentally weathered in pH 1–7 anoxic solutions at temperatures of 2–65 °C. Reaction of magnetite is described as [Fe²⁺Fe₂³⁺]O_4(magnetite) + 2H⁺ → γ[Fe₂³⁺]O_3(maghemite) + Fe²⁺ + H₂O. Dynamic polarization experiments using magnetite electrodes confirmed that this reaction is controlled by two electrochemical half cells, 3[Fe²⁺Fe₂³⁺]O⁴(magnetite) → 4γ[Fe₂³⁺]O₃(maghemite) + Fe²⁺ + 2e⁻ and [Fe²⁺Fe₂³⁺]O_4(magnetite) + 8 H⁺ + 2e⁻ → 3Fe²⁺ + 4H₂O, which result in solid state Fe³⁺ reduction, formation of an oxidized layer and release of Fe(II) to solution. XPS data revealed that iron is present in the ferric state in the surfaces of reacted magnetite and ilmenite and that the TiFe ratio increased with reaction pH for ilmenite.

Short-term (