Understanding of Ion Transport in a Na-Mordenite Membrane: Use of Numerical Modeling To Estimate Surface-Solute Interactions in the Pore

A mordenite membrane was prepared and surface characterizations were performed on the synthesized mordenite (as powder form). The surface charge remained constant when mordenite powder was in contact with the studied solutions. A pore diameter of 5.8 x 10(-9) m was estimated. Filtration tests of single salt-water solutions (NaCl, NaF, and Na2SO4) were carried with the mordenite membrane. No rejection was observed. After an alkaline treatment, the rejections were observed: NaF = Na2SO4 = 5-6%, while NaCl = 0%. New filtration tests of mixed salt-water solutions were carried out (Na2SO4 + NaCl and Na2SO4 + NaF). The sulfate ion was retained by a majority (up to 16%) whatever the halide ion in solution. The rejection rate of sulfate ion in mixtures decreases with the applied pressure, which actually cannot be explained (no observable polarization layer effect). A preferential transport is observed for chloride ions and the rejection rate of the fluoride ions remained constant. A numerical modeling (Nernst-Planck approach) was used to understand the modifications due to the alkaline treatment. A significant modification of dielectric effects is observed, which completely modified the filtration properties of the Na-mordenite membrane.