Eick, M.J., Univ. of Delaware, Newark, DE 19717-1303, USA.
Bar-Tal, A., Univ. of Delaware, Newark, DE 19717-1303, USA.
Sparks, D.L., Univ. of Delaware, Newark, DE 19717-1303, USA.
Feigenbaum, S., Univ. of Delaware, Newark, DE 19717-1303, USA.

Potassium-calcium adsorption kinetics on a Llano vermiculite and an Arizona montmorillonite were studied using a stirred-flow technique. Various experiments were conducted to distinguish between instantaneous equilibrium and time-dependent reactions, and solution-concentration-dependent kinetic models, vs. those that are independent of solution concentration. It was found that K-Ca exchange on montmorillonite was too rapid to be measured with the stirred-flow technique, while exchange rates on vermiculite could be ascertained. -from Authors