Conductivity stopped-flow study of the kinetics of solutes uptake by colloidal particles of synthetic resins.

The uptake rates of acids (hydrochloric acid, sulfuric acid, perchloric acid and acetic acid) by colloidal solid particles (mean diameter 0.35 microm) of DEAE (diethylaminoethyl Sephadex) resin was studied by the means of the stopped flow technique equipped with a conductivity detection. This original experimental approach allows to avoid hydrodynamics perturbations during data acquisition. For the sake of comparison NaOH uptake or K(+)/H(+) exchange by sulfonic Dowex resin particles experiments have also been performed. As stated in the literature we observed that the uptake rate limiting step is the solute diffusion in the solution layer surrounding the particles. To fit the experimental conductivity versus time curves on the basis of solutes diffusion concepts a simple mathematical equation fitting perfectly well the experimental data is proposed. The mathematical modeling of kinetic data obtained in non-stationary diffusion proposed here can substitute to the empiric pseudo-first- and -second-order models often used in environmental research.