Preparation Of Geopolymer Ultrafiltration Membrane And Its Application In Wastewater Treatment

The problem of water pollution has always been a problem brought about by economic development.Membrane separation technology is regarded as an ideal means of water treatment because of its low energy consumption and small footprint.However,the preparation of inorganic ceramic membranes in current applications has problems such as the need for multiple sintering,high energy consumption and high raw material costs,which make it difficult to popularise them on an industrial scale.Therefore,there is an urgent need to develop a new inorganic membrane with low raw material cost,no multiple sintering,low energy consumption and simple preparation process.The low raw material cost and simple preparation process of geopolymers make them more suitable for the preparation of cost-effective inorganic membranes.In this study,geopolymer ultrafiltration membranes were prepared on stainless steel perforated mesh supports and Al₂O₃ ceramic supports using geopolymer chemistry instead of the traditional high temperature sintering process,which not only reduces the raw material cost of membrane preparation,but also avoids multiple sintering and reduces energy consumption in the preparation process.The lignin and other pollutants in the black liquor can be effectively retained in the black liquor.The main findings of the study are as follows:In the preparation of the geopolymer ultrafiltration membrane,the optimum conditions for the preparation of metakaolin geopolymer membrane（MGM）were determined after ratio optimisation experiments:modified water glass modulus of1.3,metakaolin:slag:sand:water glass mass ratio of=10:1:5:11.55,and a mass ratio of all solid components to deionised water of 0.60.The metakaolin-based geopolymer membrane（MGM-10）had the best performance.The compressive strength and water flux of MGM-10 were 23.9 MPa and 2866.2 kg·h^-1·m^-2·MPa^-1,respectively.The retention rate was 98.84%for TSS,91.75%for COD and98.97%for lignin extracted from the black liquor.In order to further optimize the membrane material performance,two processes,spraying and brushing,were used to coat the geopolymer slurry onto different supports to prepare ultrafiltration membranes;it was found that the pore structure and performance of the filter layers of the membranes prepared by the spraying and brushing methods on the Al₂O₃ supports respectively did not differ significantly,and the pore size and separation effect of the membranes prepared by the brushing method were slightly better.The effect of curing temperature and brush coating thickness on the membrane was also investigated.The results showed that when the curing temperature was 40℃and the brush coating mass per unit area was 47.10 mg·cm^-2,the geopolymer ultrafiltration membrane had a breaking strength of 0.14 MPa,a peak pore size distribution of 50 nm,a retention rate of 94.46%for TSS and a filtration flux of 460.2 kg·h^-1·m^-2·MPa^-1.The membrane showed excellent performance in the separation of TSS from black liquor.The membrane was subjected to repeated 5 h test experiments and the water flux recovery rate was 92.23%,demonstrating the membrane’s good resistance to contamination.In addition,the membrane was tested for long-term stability over a continuous period of 74 h.It was found that the retention rate of TSS by the membrane was maintained above 90.00%in all cases,proving its good stability.