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Alkali Metal Cation Exchange on Chambers Montmorillonite
Author(s) -
Gast R. G.
Publication year - 1972
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1972.03615995003600010003x
Subject(s) - chemistry , montmorillonite , bentonite , ion exchange , alkali metal , cation exchange capacity , metal , mole , mole fraction , inorganic chemistry , standard molar entropy , nuclear chemistry , standard enthalpy of formation , ion , geology , organic chemistry , paleontology , soil science , soil water
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.