Clays and Clay Minerals · 1986 · 11 citations · 8 references
Abstract The reaction of kaolin with NaCl was followed by dynamic thermal analysis and mass spectrometry under N 2 , CO 2 , and air atmospheres and in a 10 −5 -torr vacuum. The weight loss was a function of the atmosphere used and, according to mass spectrometry, was due to the evolution of H 2 O, HCl, and very small amounts of H 2 . HCl was formed only after the release of 85% of the hydroxyl content of the kaolin. When the clay was pretreated with saturated salt solution, H 2 O and HCl evolved in more or less the same temperature range, indicating that only some of the OH groups reacted with the chloride ion. High-temperature X-ray powder diffraction patterns showed that the sodium ion reacted with the noncrystalline metakaolin to give NaAlSiO 4 . Chemical analysis showed that the reaction of kaolinite and sodium chloride started below 400°C. The rate of the reaction increased at higher water vapor concentration. From mass spectrometric data, the NaCl-treated kaolin appeared to adsorb CO 2 . Desorption at several distinct temperatures suggests that CO 2 was adsorbed by different parts of the structure, i.e., holes and channels. X-ray powder diffraction and infrared absorption data indicate that the kaolinite structure persisted even after it had been heated with NaCl in a CO 2 atmosphere to as high as 800°C.
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