Inhibition of Sintering by Si During the Conversion of Si-Rich Ferrihydrite to Hematite

Susan M. Glasauer1, †, Paul Hug2, Peter G. Weidler3 and Andreas U. Gehring3
1 Lehrstuhl für Bodenkunde, Technische Universität München, 85350 Freising-Weihenstephan, Germany
2 Institut für Anorganische Chemie, Universität Zürich, CH-8057 Zürich, Switzerland
3 Institut für Terrestrische Ökologie, ETH Zürich, CH-8952 Schlieren, Switzerland
Present address: Department of Microbiology, University of Guelph, Guelph, Ontario, N1G 2W1, Canada. E-mail of corresponding author: sglasaue@micro.uoguelph.ca

Abstract: The distribution and chemical state of Si in a synthetic 2-line ferrihydrite with a Si/(Si + Fe) molar ratio of 0.11 was studied. Heat treatment under oxidizing conditions shows that Si-rich ferrihydrite is stable to 400°C. The transformation to hematite and the formation of a polymerized amorphous-silica phase occur at 850°C. At this temperature, the specific surface area decreases greatly and the average pore diameter increases, which is indicative of sintering. Heating under severe reducing conditions causes a segregation of Si from Fe and results in a mixture of elemental Fe and SiO2. Surface and structural data suggest that Si is located near the particle surface where it limits the rearrangement of Fe octahedra to form hematite.

Key Words: BET • Ferrihydrite • Si • Sintering • XPS

Clays and Clay Minerals; February 2000 v. 48; no. 1; p. 51-56; DOI: 10.1346/CCMN.2000.0480106
© 2000, The Clay Minerals Society
Clay Minerals Society (www.clays.org)