Effect of Sodium Chloride on the Profiles of the IR Spectrum Bands of Kaolinite at Moistures under Plastic Limit

Abstract

This study presents data on the IR spectra of kaolinite at a moisture of 26% and after drying. The preparation of moistened samples was made with distilled water, and the solutions of NaCl with limiting and 50% of limiting concentrations at a temperature of 21 °C. To experimentally evaluate the effect of the interaction between liquid water and sorbing basal surfaces of kaolinite on the profile of the IR spectrum bands, the spectra of distilled water and NaCl solutions were additionally studied. Comparison of the band profiles in the wavenumber range of 2750–4000 cm−1 for kaolinite samples allows the conclusion that, when going from distilled water to the most saline water, the adsorption effect is inferior to the effect of solvation, and it decreases with increasing salinity. During drying of the samples, an increase in the peak intensities of the bands in the wavenumber range of 3550–3750 cm−1 is observed. Observed spectral variations are qualitatively interpreted by the results of calculations performed by the DFT method with the XLYP exchange–correlation potential. The presented data can be used to test theoretical approximations and computer models for calculating the structure and properties of moist minerals and salt adsorption mechanisms.