Thermal analysis and FT-IR spectroscopy of synthetic clay mineral mixtures

Common clays and especially mixed-layered or interstratified clay minerals are generally mixtures of predominantly clay mineral along with minor quantity of another clay mineral, wherein the ratio of the components will determine the resulting properties of these clay materials. This study focuses on IR spectroscopy and TG/DTA analysis and their contribution to the identification of clay minerals in two-component mixtures. Identifying clay minerals in such mixtures by means of thermal analysis is often complicated by the similarity of the thermal effects of the individual clay components. Similarity in thermal behavior is mainly connected with the origin, chemical variability and crystal structure of phyllosilicates. The main problem is overlapping thermal effects of clay minerals or thermal effects related to accessory minerals (calcite, quartz, etc.) on DTA curve. A similar problem also appears in the identification of mixed clay mineral structures by infrared spectroscopy. There are also more or less overlapping absorption bands in the infrared spectra for the mixtures of clay minerals. In this paper, the prepared clay mixtures were supposed to partially simulate the natural mixed clay structures and a minimum content of detectable minerals in clay mixtures were determined according to characteristic peaks on the DTA curves and absorption bands in FT-IR spectra. The results of both methods showed that kaolinite is the most reliable detectable mineral. The detection limit for thermal analysis corresponds to 3% mass kaolinite in admixture with chlorite or montmorillonite, and 1% mass kaolinite for both of these mixtures is based on IR spectroscopy. In case of montmorillonite and chlorite, the identification by FT-IR spectroscopy shows detection limit only 30% mass in contrast to TG/DTA with the detection limit of 5% mass for montmorillonite and 5% mass or 10% mass for chlorite. The obtained results can be effectively used to solve problems in identification of clay minerals in sedimentary rocks, which is very important for subsequent applications in geotechnical, geothermal, and mining activities.