Uses of near-infrared transmission spectra for the identification of hydrothermal kaolinite, dickite and kaolinite-dickite.

Abstract

X-ray diffraction (XRD) patterns and near-infrared (NIR) spectra have been evaluated and compared to differentiate hydrothermal kaolinite, dickite and kaolinite-dickite. The spectral bands were fitted for the first overtone and combination area of the infrared spectra of kaolinite, dickite and kaolinite-dickite, and the characteristic bands of kaolinite, dickite and kaolinite-dickite were obtained. The infrared spectra of kaolinite and dickite have obvious differences in the first overtone and combination area of OH bands. When kaolinite and dickite need to be distinguished from kaolinite-dickite, the first overtone and the combination region need to be analysed together. 7237 cm-1 is a characteristic band of dickite, and 7170 cm-1 is a characteristic band of kaolinite. The ratio of intensity at 7170 cm-1 and 7237 cm-1 can help distinguish kaolinite, dickite, and kaolinite-dickite.