Dissolution of Iron Oxides and Oxyhydroxides in Hydrochloric and Perchloric Acids

P. S. Sidhu1, R. J. Gilkes, R. M. Cornell2, A. M. Posner and J. P. Quirk3
Department of Soil Science and Plant Nutrition, University of Western Australia, Nedlands, Western Australia, 6009, Australia
Deceased August 1980.
1 Present address: Department of Soils, Punjab Agricultural University, Ludhiana 141004, India.
2 Present address: Chemistry Department, University of Berne, Berne, Switzerland.
3 Present address: Waite Agricultural Research Institute, University of Adelaide, Glen Osmond, South Australia, 5064, Australia.

Abstract: The dissolution of synthetic magnetite, maghemite, hematite, goethite, lepidocrocite, and akaganeite was faster in HCl than in HClO4. In the presence of H+, the Cl ion increased the dissolution rate, but the ClO4 ion had no effect, suggesting that the formation of Fe-Cl surface complexes assists dissolution. The effect of temperature on the initial dissolution rate can be described by the Arrhenius equation, with dissolution rates in the order: lepidocrocite > magnetite > akaganeite > maghemite > hematite > goethite. Activation energies and frequency factors for these minerals are 20.0, 19.0, 16.0, 20.3, 20.9, 22.5 kcal/mole and 5.8 × 1011, 1.8 × 1010, 7.4 × 107, 5.1 × 1010, 2.1 × 1010, 3.0 × 1011 g Fe dissolved/m2/hr, respectively. The complete dissolution of magnetite, maghemite, hematite, and goethite is well described by the cube-root law, whereas that of lepidocrocite is not.

Key Words: Acid • Akaganeite • Dissolution • Goethite • Hematite • Iron oxide • Lepidocrocite • Maghemite • Magnetite

Clays and Clay Minerals; August 1981 v. 29; no. 4; p. 269-276; DOI: 10.1346/CCMN.1981.0290404
© 1981, The Clay Minerals Society
Clay Minerals Society (www.clays.org)