Transition Metals in Llano Vermiculite Samples: an EPR Study

P. M. Schosseler1 and A. U. Gehring2, †
1 Laboratory for Physical Chemistry, Swiss Federal Institute of Technology, ETH, CH-8092 Zürich, Switzerland
2 Swiss Federal Institute for Forest, Snow and Landscape Research, WSL/ETH CH-8903 Birmensdorf, Switzerland
Present address: Institute of Terrestrial Ecology ETH Zu-rich Grabenstrasse 3 CH 8952 Schlieren Switzerland.

Abstract: Continuous wave and pulsed electron paramagnetic resonance spectroscopies combined with thermal and chemical methods were used to identify and characterize V(IV), Fe(III), Mn(II) and Cr(III) in a multimineral system that consists of vermiculite and impurities of carbonates. All of these transition metals were structure-bound in mineral phases. The V(IV) was located in octahedral layers of the vermiculite and became oxidized to V(V) during the transformation of the host mineral to enstatite at about 800 °C. The Fe(III) was associated with the vermiculite as well as the carbonate impurities. The Fe(III) identified in the vermiculite was transferred into the enstatite structure during the thermal conversion. An indirect proof of Fe(III) and Cr(III) in the impurities was found in the heated samples in which these cations occurred in Ca and/or Mg oxides that were formed by transformation of the carbonates. The Mn(II) in the untreated samples was associated with the impurities and was also detected in oxides formed from the samples heated at 600 °C.

Key Words: Carbonates • Cw and Pulsed Electron Paramagnetic Resonance Spectroscopies • Phase Transformation • Vermiculite

Clays and Clay Minerals; August 1996 v. 44; no. 4; p. 470-478; DOI: 10.1346/CCMN.1996.0440404
© 1996, The Clay Minerals Society
Clay Minerals Society (www.clays.org)