Kinetics of differentially small conversions in contact isotopic and contact ion exchange.

The kinetics of differentially small contact ion exchange processes of two adjacent resin ion exchanger beads in pure water was investigated, using radioactive tracers. Interruption tests and determination of the rates, as a function of the force with which the beads were pressed together, indicate that diffusion of the ions across the aqueous film between the beads was the rate-determining step. The experiments show that the half-times of the exchange Cs+-Na+ and Cs+-H+ decrease, if the initial Cs+ concentration in the particles is increased. With the help of the theory developed, the rate coefficients of these processes can be evaluated from the experiments. It is found that they depend strongly on the ionic composition in the case of the exchange Cs+-H+ but are almost constant when Cs+ is exchanged vs. Na+. The rate coefficients of differentially small contact ion exchange processes were closely related to those of isotopic contact exchange processes. With the help of the rate coefficients of differential exchange processes the rates observed for nondifferential exchange processes are discussed