Alkali Metal Cation Exchange on Chambers Montmorillonite1
- R. G. Gast2
Standard free energies of exchange, ΔG°, were determined for the exchange of Na with Li, K, Rb, and Cs on a 0.1–0.5 micron fraction of Chambers montmorillonite having an exchange capacity of 123 ± 2 meq/100 g. The ΔG° values ranged from +80 cal mole-1 for Na→Li exchange to -1886 cal mole-1 for Na→Cs exchange and were approximately twice as large as those found previously for similar exchange reactions on Wyoming bentonite having an exchange capacity of 92 ± 2 meq/100 g. The ΔG° values reflect cation selectivity differences of a factor of two to three between the two clays. In contrast, the standard heats of exchange, determined calorimetrically, were approximately the same for both clays and ranged from + 125 cal mole-1 for Na→Li exchange to -2575 cal mole-1 for Na→Cs exchange. These results indicate that the differences in free energies of exchange between the two clays are due to entropy effects.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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