The Chemical Form of Vanadium (IV) in Kaolinite
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 WordsElectron paramagnetic resonance Isomorphic substitution Kaolinite Vanadium
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- Angel, B. R. and Hall, P. L. (1973) Electron spin resonance studies of kaolins: in Proceedings 1972 International Clay Conference, B. R. Serratosa, ed., C.S.I.R., Madrid, 47–60.Google Scholar
- Beinert, H. (1972) Flavins and flavoproteins, including iron-sulfur proteins: in Biological Applications of Electron Spin Resonance, H. Swartz, J. R. Bolton, and D. C. Borg, eds., Wiley-Interscience, New York, 351–410.Google Scholar
- Clark, R. J. H. (1968) The Chemistry of Titanium and Vanadium: Elsevier, Amsterdam, 329 pp.Google Scholar
- Cotton, F. A. and Wilkinson, G. (1989) Advanced Inorganic Chemistry: 5th ed., John Wiley, New York, 1455 pp.Google Scholar
- MCBRIDE, M. B. (1990) Electron spin resonance spectroscopy: in Instrumental Surface Analysis of Geological Materials, D. L. Perry, ed., VCH Publ., New York, 233–281.Google Scholar
- Van Olphen, H. and Fripiat, J. J. (1979) Data Handbook for Clay Materials and Other Nonmetallic Minerals: Per-gamon, Oxford, 346 pp.Google Scholar