| Abstract: | The affinity for water of a kaolinite-type clay (kaolin) and a montmorillonite-type clay (bentonite), saturated with hydrogen, calcium, sodium, and potassium, was studied by three methods, namely, heat of wetting as determined by calorimetric measurements, sorption of water from the vapor phase by weighing, and desorption or removal of water by differential-thermal analysis. It was shown that hydrogen and calcium clays had a greater affinity for water than sodium and potassium clays. Although the bentonite evolved more heat and sorbed more water per gram of clay, it evolved less heat and sorbed less water per milliequivalent of exchangeable cation than did the kaolin; the differences in the effects of various cations were more pronounced in bentonite than in kaolin. The results may be explained as follows from considerations of the mineral structures: (1) A greater amount of water hydrates the surface of kaolinite in proportion to that hydrating the exchangeable cations than is the case in montmorillonite and (2) the exchangeable cations may be hydrated to a greater degree (i.e., less strongly held) on kaolinite than on montmorillonite. |
