Properties and Acid Dissolution of Metal-Substituted Hematites

M.A. Wells1, R.J. Gilkes2 and R.W. Fitzpatrick3
1 CSIRO Exploration and Mining, Wembley, Perth, Western Australia, 6913, Australia
2 Department of Soil Science and Plant Nutrition, University of Western Australia, Perth, Western Australia, 6907, Australia
3 CSIRO, Land and Water, Glen Osmond, Adelaide, South Australia, 5064, Australia
E-mail of corresponding author: m.wells@per.dem.csiro.au

Abstract: The dissolution in 1 M HCl of Al-, Mn-, and Ni-substituted hematites and the influence of metal substitution on dissolution rate and kinetics of dissolution were investigated. The inhomogeneous dissolution of most of the hematites investigated was well described by the Avrami-Erofe'ev rate equation, kt = √[−ln(1 − α)], where k is the dissolution rate in time, t, and α is the Fe dissolved. Dissolution of Al-substituted hematite occurred mostly by edge attack and hole formation normal to (001), with the rate of dissolution, k, directly related to surface area (SA). Dissolution of rhombohedral Mn- and Ni-bearing hematites occurred at domain boundaries, crystal edges, and corners with k unrelated to SA. The morphology of Mn- and Ni-substituted hematites changed during dissolution with clover-leaf-like forms developing as dissolution proceeded, whereas the original plate-like morphology of Al-bearing hematite was generally retained. Acid attack of platy and rhomboidal hematite is influenced by the direct (e.g., metal-oxygen bond energy, hematite crystallinity) and indirect (e.g., crystal size and shape) affects associated with incorporation of foreign ions within hematite.

Key Words: Acid Dissolution • Activation Energy • Frequency Factor • Hematite • Iron Oxide • Metal Substitution

Clays and Clay Minerals; February 2001 v. 49; no. 1; p. 60-72; DOI: 10.1346/CCMN.2001.0490105
© 2001, The Clay Minerals Society
Clay Minerals Society (www.clays.org)