Synthesis and modification of selectivity performances of an ultrafiltration ceramic membrane: Study of retention of pure salt water solutions
The structural characteristics of zeolites are well-known, and they are often used for the specific adsorption of molecules, ion exchange or their catalytic properties. Also, in recent years, these materials have been used to manufacture ultrafiltration membranes. In this work, a ceramic membrane (low cut-off ultrafiltration membrane) has been made using Mordenite as the active phase. The sol-gel preparation is impregnated onto a ceramic tubular support (alumina) and the zeolite is synthesized by a hydrothermal process. The structural and physical properties of this membrane were studied using X-ray diffraction, BET / BJH (Brunauer-Emmett-Teller and Brunauer-Joyner-Hallenda) experiments, and scanning electron microscopy (SEM). Zeta potential measurements and streaming induced potential measurements were carried out on Mordenite powder (prepared under the same conditions) with different salt solutions and at different ionic strengths, to obtain a qualitative and quantitative estimate of the surface charge density of the active layer. The tubular membrane was then conditioned in a laboratory ultrafiltration pilot unit (stabilisation of pure water hydraulic permeability), and its selectivity was studied by the filtration of a 5•10-3 M sodium chloride-water solution. No retention was observed. In regard to the electrical properties of the membrane active layer surface, a new filtration experiment (aqueous sodium carbonate, 10-2 M) was investigated and a significant retention was observed (around 25% at 5 bar). After cleaning with pure water, the membrane slightly retained a sodium chloride-water solution (around 10%). This seems to be due to a modification of the Mordenite surface chemistry. After cleaning the membrane with an acid solution, it recovered its initial surface properties. To conclude, a mineral ultrafiltration membrane has been synthesized, the filtration properties of which can be reversibly modified by chemical treatment.