A cationic electrode (used as a potassium specific‐ion electrode and a sodium specific‐ion electrode were used to measure rates of cation exchange on clay minerals. The Ba‐K exchange rates for kaolinite, illite, and montmorillonite were rapid with >75% exchange being measured within 3 sec. Because this time interval represents response time of the specific‐ion electrode, the Ba‐K exchange on these clay minerals occurs at a faster rate than this and may be an instantaneous process. Ba‐K exchange on vermiculitic materials was characterized by both a rapid and a slow rate of exchange. A major part of the Ba‐K exchange in silt‐ and clay‐size vermiculite was found to be diffusion controlled. Ca‐K, Mg‐K, Ca‐Na, and Mg‐Na exchange rates were rapid for all vermiculites and other clay minerals used in the experiment. Only Poole vermiculite exhibited two rates of Ba‐Na exchange similar to those shown by all vermiculites during Ba‐K exchange. Ba‐Na exchange rates on all vermiculites except Poole were rapid.
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Malcolm et al. (1969) studied this question.