Loss of Adsorbed Water
At temperatures below 150°C, water that is physically attached to clays evaporates. Physically attached water can be present as water adsorbed onto the surface of particles or between the layers of the clay structure. The loss of water is endothermic and results in measurable weight loss. For kaolinite, the weight loss is usually minor, on the order of a percent or less. However, other clays, particularly those that swell when exposed to water such as bentonite can have considerable weight loss in this temperature regime (4-8 wt%) . For kaolinite, the changes due to loss of physical water do not alter the structure as determined by X-ray diffraction.