Infra-Red Determination of the Kaolin Group Minerals

Abstract

BY infra-red absorption analysis, it is possible to make a semi-quantitative estimation of the kaolin minerals. In contrast to X-ray diffraction, the infrared spectrum of halloysite is as clearly defined as those of kaolinite and dickite, and the content of these three minerals in mixtures can be determined by a ratio between the depths of their hydroxyl absorptions. The peaks at 2.70µ (A) and 2.75µ (B) are common to all three minerals, and a peak depth ratio A/B of 1.2–1.5 is characteristic of kaolinite, with a ratio A/B of 0.8–0.9 characterizing halloysite. Values of 0.6–0.8 are typical of dickite. If the depth of the band due to physically adsorbed water at 2.9µ (C) is plotted as the abscissa with A/B as the ordinate, the three minerals fall into separate areas.