Properties of Goethites of Varying Crystallinity

Udo Schwertmann, Philippe Cambier1 and Enver Murad
Lehrstuhl für Bodenkunde, Technische Universität München D-8050 Freising-Weihenstephan, Federal Republic of Germany
1 On leave from Station de Science du Sol, INRA, F-78000 Versailles, France.

Abstract: Goethites were synthesized from ferrihydrite in 0.7 M KOH between 4° and 90°C. As temperatures increased, the goethite crystals became larger and of less domainic character, and surface areas decreased from 153 to 9 m2/g. Surface area, oxalate-soluble Fe to total Fe ratios, chemisorbed water, Mössbauer parameters, and dissolution rate in 6 M HCl at 25°C are particle-size controlled, whereas mean crystallite dimensions, a-dimension of the unit cell, differences between the two OH-bending modes, and dehydroxylation temperatures suggest the existence of a low-temperature (high-a-dimension) and a high-temperature (low-a-dimension) goethite, with a narrow transition range at a synthesis temperature of 40°–50°C. Hydrothermal treatment at 125°–180°C of a low-temperature goethite led to a healing of the multidomainic, microporous high-a-dimension goethite into a monodomainic low-a-dimension goethite of similar overall crystal size with the properties of a low-a-dimension goethite.

Key Words: Crystallinity • Dissolution • Goethite • Hydrothermal treatment • Iron • Unit-cell dimension • X-ray powder diffraction

Clays and Clay Minerals; October 1985 v. 33; no. 5; p. 369-378; DOI: 10.1346/CCMN.1985.0330501
© 1985, The Clay Minerals Society
Clay Minerals Society (www.clays.org)