The study of ion‐exchange kinetics on soils and soil constituents has attracted much interest throughout the last decade. The introduction of a stirred‐flow method to study these reactions, as well as other adsorption‐desorption phenomena, has stimulated this interest. However, the manner in which rate data are interpreted using this technique and other flow methods has been questioned. Accordingly, a numerical solution for various instantaneous equilibrium and kinetic models is presented. It was found that rate data that could be described using an instantaneous equilibrium model could also be interpreted using a kinetic model. Therefore, the validity of kinetic rate coefficients obtained by flow methods is questionable. An analytical approach was developed to outline experimental methods that could be used to distinguish between instantaneous equilibrium and time‐dependent reactions and to differentiate between solution‐concentration‐dependent kinetic models vs. those that are independent of solution concentration. By using this approach, and employing various flow rates and influent concentrations, as well as using a stopped‐flow technique, it is easy to decide whether rates of reactions can be measured using the stirred‐flow method for specific experimental conditions.
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Bar‐Tal et al. (1990) studied this question.