The Influence of Aluminum on Iron Oxides. VII. Substitution of Al for Fe in Synthetic Lepidocrocite

R. M. Taylor and U. Schwertmann
C.S.I.R.O. Division of Soils, Private Bag 2 Glen Osmond, South Australia 5064, Australia
Institut für Bodenkunde, Technische Universität München 8050 Freising, Germany

Abstract: The presence of Al hydroxy species in solution during the synthesis of lepidocrocite had been previously found to influence the reaction towards goethite formation. However, under certain conditions, which are not unrealistic in terms of the natural soil environment, this influence does not occur, and Al appears to substitute for Fe(III) in the lepidocrocite structure. This substitution causes the unit-cell dimensions to decrease along the “a” direction and to increase along the “b.” From the differential line broadening of X-ray powder diffraction peaks, the incorporation of Al was found to inhibit crystal growth preferentially in the b-axis direction, the hkl peaks being more broadened the higher the value of k relative to h and l. Al-substituted lepidocrocites have been suggested to occur in soils, and although they can be synthesized under conditions approaching those expected in soils, it is considered that their formation in nature is unlikely or restricted to unusual environments.

Key Words: Aluminum • Goethite • Iron • Lepidocrocite • Substitution • Synthesis

Clays and Clay Minerals; August 1980 v. 28; no. 4; p. 267-271; DOI: 10.1346/CCMN.1980.0280404
© 1980, The Clay Minerals Society
Clay Minerals Society (www.clays.org)