The Preparation Of Inorganic Nanofiltration Membranes By Electrophoretic Deposition And Study On Zero Discharge Technology Of Printing And Dyeing Wastewater Based On The Membranes

The preparation of inorganic membranes by sol-gel technique was complex, with the long-term cycle and difficulty in film quality control. For solving these difficulties, the preparation of inorganic membranes by electrophoretic deposition was studied. The electrophoresis experiments were carried out with industrial ceramics piece as electrophoretic matrix and alumina sol as electrophoretic liquid. The feasibility of preparation of nanofiltration Al2O3 ceramic membranes by electrophoretic deposition was also studied. It was found that aging time of sols, types and amounts of film-forming additive, electrophoresis temperature, voltage, electrophoresis time all affected film quality. The key factors were voltage, electrophoresis time, and film-forming additive. The post-treatments, including dryness and sintering, were roughly the same with sol-gel technique. After 4 to 7 days for Al2O3 sols aging, ceramic substrates were put in the electrophoretic liquid of Al2O3 sols under the temperature of 20～30℃. Under the voltage of 18～30 volts, electrophoretic process lasted for 3～5 minutes. The satisfactory films were prepared after dryness at suitable conditions and sintering according to procedures.The Al2O3 ceramic membrane obtained from our experimental conditions was characterized through SEM, XRD, liquid-liquid displacement method and so on. The results showed that the surface appearance of the Al2O3 ceramic membrane was even. The thickness of the prepared ceramic membrane was 50μm, and the porosity rate of 31.51%, the pore size of 3.1nm and the pore size distribution of 2.88 nm to 5.76 nm. The performance tests showed that the Al2O3 ceramic membrane with great acid and alkaline erosion tolerance, had notable retentions of calcium ions representing hardness components, copper ions representing heavy metal ions and Rhodamine B representing dyestuffs.Based on inorganic membranes obtained from our experimental conditions, a set of zero discharge technology of printing and dyeing wastewater was designed to treat refractory wastewater in printworks. After membrane filtration treatment, the COD removal rate of the printing and dyeing wastewater achieved 92.8%. Combined with electro-catalytic disinfection equipment developed by our groups, the effluent could be used as the supplement water for recirculating cooling. Membrane cleaning methods were studied to solve membrane contamination problems which often occurred in the process of membrane filtration treatment on wastewater. The results showed that the Al2O3 ceramic membrane obtained from our experimental conditions could be washed easily as well as the properties recovering.The preparation of SiO2 ceramic membranes was studied by electrophoretic deposition for further explaining the feasibility of preparation of ceramic membranes by electrophoretic deposition. The results showed it was possible to prepare SiO2 ceramic membranes through electrophoretic deposition.