SORINELA DANIELA CANTEA*, EUGEN PINCOVSCHI, ANA-MARIA S. OANCEA EFFECTS OF THE MATRIX OF A MACRONET SULFONATED POLYSTYRENIC RESIN ON H+/MG2+ AND H+/CA2+ ION EXCHANGE KINETICS
A new polymeric resin with styrene-divinylbenzene hyper-reticulated matrix and sulfonic functional groups designated as a macronet resin was evaluated from the kinetic point of view for magnesium and calcium ions removal by ion exchange in the demineralization process. The ion exchanger contains macro-, meso- and micropores. The ion exchange rate was measured at 298 K with a potetiometric method in conditions favouring a particle diffusion controlled mechanism. The results were modeled using both quasi-homogeneous resin phase and bidisperese pore kinetic models. The H+/Mg2+ and H+/Ca2+ integral interdiffusion coefficients were computed and compared. It was shown that the matrix of the macronet resin produced a retarding effect on ion diffusion compared to dilute aqueous solution of about two orders of magnitude. The bidisperese pore kinetic model allowed the evaluation of the upper limit of the ratio between the ion exchange capacity due to the sulfonic groups bound on micropores and macropores walls, for three hypotheses: a) the ion interdiffusion takes place step-by-step in macropores and micropores; b) the ion interdiffusion in macro- and micropores is competitive, but ten times faster in macropores; c) the ions diffuse in parallel in macro- and micropores with the same rate. The plausible ratio between the micropores an macropores uptake at equilibrium of the macronet resin for H+/Mg2+ and H+/Ca2+ ion exchange was evaluated as 1/30, 2/1 and 10/1 in cases a), b) and c), respectively.
Keywords: ion exchange kinetics; magnesium ion; calcium ion; macronet resin; hypercrosslinked polymer; polystyrenic resin; interdiffusion coefficient; porous ion exchangers