Quantitative Measurement of Paramagnetic Fe3+ in Kaolinite

Etienne Balan1, Thierry Allard1, Bruno Boizot1, Guillaume Morin1 and Jean-Pierre Muller1, 2
1 Laboratoire de Minéralogie-Cristallographie, UMR 7590, CNRS, Universités Paris 6 et 7 and IPGP, Case 115, 4 Place Jussieu, 75252 Paris cedex 05, France
2 Institut de Recherche pour le Développement (IRD), 213 rue Lafayette, 75480 Paris cedex 10, France
E-mail of corresponding author: balan@lmcp.jussieu.fr

Abstract: A method is proposed to measure the absolute concentration of paramagnetic Fe3+ ions in kaolinite from various geochemical environments using powder X-band electron paramagnetic resonance (EPR) data. An Fe3+-doped corundum sample is used as a concentration standard. The Fe3+ signal is calibrated by calculating the powder EPR spectra of Fe3+ ions in corundum and low-defect kaolinite. The paramagnetic Fe3+ concentration in other samples is obtained by an extrapolation procedure. This study provides a direct assessment of the iron distribution between isolated structural Fe3+ ions and other iron species, such as Fe3+ concentrated phases and Fe2+ ions. The concentration of isolated structural Fe3+ ranges between 200–3000 ppm and represents less than half of the total iron within kaolinite crystals.

Key Words: Electron Paramagnetic Resonance • EPR • Fe3+ • Kaolinite

Clays and Clay Minerals; August 2000 v. 48; no. 4; p. 439-445; DOI: 10.1346/CCMN.2000.0480404
© 2000, The Clay Minerals Society
Clay Minerals Society (www.clays.org)