oa South African Journal of Chemistry - The effect of pH on the ion-exchange properties of hydrated alumina : part II. kinetics of exchange



The effect of pH upon the kinetics of cation- and anion-exchange on hydrated alumina has been investigated. It has been found that in the pH range 6-9 exchange proceeds rapidly, and there are strong indications that film diffusion is the rate-determining step here. As the pH rises from 9 to 11 the rates of cation-exchange processes become slower, and appear to be influenced by particle diffusion to an increasing extent. The same is observed in the case of anion-exchange as the pH falls from 6 to 4. To account for these results it is suggested that hydroxyl groups both on and beneath the surface take part in ion-exchange processes on hydrated alumina, the latter coming into operation to an increasing extent as exchange progresses.


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