The Chemical Form of Vanadium (IV) in Kaolinite

A. U. Gehring1, I. V. Fry2, J. Luster1 and Garrison Sposito1
1 Department of Soil Science, University of California Berkeley, California 94720
2 Department of Plant Biology, University of California Berkeley, California 94720

Abstract: A combined application of electron paramagnetic resonance (EPR) and Fourier-transform infrared (FTIR) spectroscopies with thermal methods was used to determine the chemical form of V(IV) in a Georgia kaolinite (KGa-I). Precise values of the EPR spectroscopic g-values and hyperfine coupling constants were obtained for an untreated sample (g = 1.940, A = 18.71 mT; g = 1.966, A = 7.63 mT). Heating the sample to 1000°C in steps while monitoring phase changes with EPR and FTIR spectra led to the following structural interpretations: 1) Vanadium (IV) occurs almost entirely as an isomorphically substituted species in the octahedral sheet of KGa-1 kaolinite; 2) during the dehydroxylation of kaolinite at about 500°C and the subsequent formation of metakaolinite, V(IV)-substituted octahedral sites are readily converted into truncated octahedra exhibiting fourfold coordination; and 3) in these highly distorted four-coordinated sites, V(IV) is metastable, being completely oxidized at about 800°C.

Key Words: Electron paramagnetic resonance • Isomorphic substitution • Kaolinite • Vanadium

Clays and Clay Minerals; December 1993 v. 41; no. 6; p. 662-667; DOI: 10.1346/CCMN.1993.0410604
© 1993, The Clay Minerals Society
Clay Minerals Society (www.clays.org)