Influence of thermally modified clays and inexpensive pore-generating and strength improving agents on the properties of porous ceramic membrane

The effect of the temperature of thermal treatment on the properties of ceramic membranes prepared from raw clays mixed with pore-generating and strength improving agents has been studied. Thermal treatment was performed at 500 degrees C (TC500) and 600 degrees C (TC600) and the properties of the membrance prepared from modified clays were compared with the properties of the membranes prepared from raw clay (NC). Three different additives were applied in the preparation of ceramic membranes; cationic manioc starch (CMS) was used as pore-generating agent, egg shell residue (ES) was used to improve mechanical strength and a mixture of ES/CMS was used to improve both porosity and mechanical strength of the ceramic membranes. Flat membranes were prepared from mixtures of thermally treated clays and additives with compositions of 5-15 wt% via uniaxial compression. The properties of tubular ceramics prepared by extrusion from samples NC and TC500 with ES/CMS of 5 wt% were evaluated in terms of hydraulic permeability, mechanical strength and apparent porosity using crossflow processes. The clays and their membranes were characterized by granulometric analysis, apparent porosity, three-point bending load experiments, X-ray fluorescence analysis, Fourier-transform infrared spectroscopy and X-ray diffraction experiments. The results show that the presence of thermally treated clays, independent of the type of pore-generating and mechanical strength improving agents, significantly improved the apparent porosity and hydraulic permeability, possibly due to opened pore structures. It is also suggested that the final performance is related to the structure of the clays, specifically to the presence of metakaolinite (MKaol). Besides, the addition of eggshell has increased the mechanical strength, possibly due to the increase of anorthite in the structure. Overall, these results demonstrate a potential application of thermally treated clays in development of porous ceramic membranes.