Abstract:
Low cost ceramic membranes were prepared by paste casting followed by sintering at various temperatures using natural clay (- 150 mesh) of IIT Guwahati as the main raw material. The mechanical strength of the membrane was successfully increased by addition of small amount of sodium carbonate, sodium metasilicate and boric acid. The pore size of the prepared membrane was found to be 4.58 Dm (for the membrane sintered at 1000 DC). For decreasing the pore size of the membrane, kaolin was mixed with the natural clay in different proportions which resulted in various microfiltration (MF) membranes with a wide range of pore size (4.58 Dm to 0.31 Dm). The membrane pore size and pore density were predicted directly from the particle size distribution of the clay and kaolin and were suitably represented by second-order polynomials. These microfiltration membranes were successfully applied in hybrid processes such as Micellar Enhanced Microfiltration (MEMF) for removal of chromate ions and Advanced Oxidation Process (AOP) followed by MF for the removal of crystal violet dye. With an aim to reduce the pore size of these membranes to Ultrafiltration (UF) range, polymers such as chitosan and polyvinyl acetate were used to coat a thin layer over it using dip-coating method. The glutaraldehyde cross-linked chitosan membrane resulted in a pore size of 14 nm and was successfully applied for the removal of heavy metals (As and Hg) from synthetic groundwater using polymer enhanced UF. Almost 100 % removals were observed for both 500 g LD1 mercury and 1000 g LD1 arsenic. A modified dip coating method was used for preparing the polyvinyl acetate coated membrane whose pore size was found to be 9 nm. This membrane was successfully applied to fractionate lysozyme and ovalbumin from chicken egg white. An overall rejection of 94 % ovalbumin and transmission of 95% lysozyme was achieved. Another mixed matrix membrane was prepared using one polymer (cellulose acetate) and one inorganic precursor (LTA zeolite) with a pore size of 10 nm and the membrane efficiency was tested by rejection of bovine serum albumin (BSA). An overall BSA rejection of more than 95% was obtained....
