THE CHEMICAL FORM OF VANADIUM(IV) IN KAOLINITE

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