The Transformation of Lepidocrocite to Goethite

U. Schwertmann* and R. M. Taylor
C.S.I.R.O., Division of Soils, Private Bag Glen Osmond, South Australia 5064
* Present address: Institut für Bodenkunde Techn. Univers. München, 8050 Freising-Weihenstephan, West Germany. The research was carried out at the CSIRO, Division of Soils, Adelaide, South Australia, whilst on a visiting fellowship.

Abstract: The conversion of lepidocrocite (γFeOOH) to its more stable polymorph, goethite (αFeOOH) was followed by observing changes in crystal morphology, oxalate solubility, surface area and X-ray diffraction. In conjunction, kinetics were measured as functions of surface area, temperature, alkalinity and seeding with goethite crystals.

The results suggest that the transformation is not topochemical, but proceeds through the solution phase. The main steps governing the rate of transformation are, (1) the dissolution of lepidocrocite, and (2) the formation of goethite nuclei and subsequent growth. Either of these processes can be rate-determining under appropriate conditions.

Clays and Clay Minerals; June 1972 v. 20; no. 3; p. 151-158; DOI: 10.1346/CCMN.1972.0200306
© 1972, The Clay Minerals Society
Clay Minerals Society (www.clays.org)