ESR and IR Evidence for Chromium in Kaolinites
Tóm tắt
Evidence obtained from ESR and IR studies is presented for the presence of structural Cr in two natural kaolinites (MILO and GEY) formed in an hydrothermal environment in Sonoma County, California. The XRD patterns show a greater structural disorder for GEY than for MILO, but both have the usual hexagonal shapes as shown by TEM observations. On the basis of EDX analysis of different particles, GEY, on average, appears to be richer in Cr (2.1% Cr203) than MILO (0.6% Cr203). The presence of Fe oxide particles containing some Cr, Ni and V is also indicated by EDX analysis. By FT-IR observation, the octahedral Cr3+position was easily detected by a well resolved spectral feature at 3586 cm-1. The adsorbed Cr3+kaolinite (KMRXCR) presents no band at 3586 cm-1, but two other bands situated at 3527 and 3477 cm-1. The main features of the ESR spectra of these two kaolinites are a set of resonances near
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