MATERIALS AND METHODS FOR CERAMIC MEMBRANE SYNTHESIS. SHORT REVIEW

Water and Water Purification Technologies. Scientific and Technical News ISSN 2218-9300 MATERIALS AND METHODS FOR CERAMIC MEMBRANE SYNTHESIS. SHORT REVIEW S. Kyrii1 1 National Technical University of Ukraine "Igor Sikorsky Kyiv Polytechnic Institute", Ukraine, DOI: https://doi.org/10.20535/2218-930012023281034 This article briefly overviews the main types of raw materials used to synthesise ceramic membranes. Traditional materials such as aluminium oxide, silicon dioxide, titanium dioxide, zirconium dioxide, zeolites, and cost-effective materials like various clays and industrial waste are highlighted. Modern methods for producing high-performance ceramic membranes are discussed, including slip casting, tape casting, pressing, extrusion, solid state method etc. The general scheme for preparing a selective layer on a ceramic membrane using various methods for synthesising it is also examined. Furthermore, the cost of commercial ceramic membranes and influencing factors are analysed. Based on contemporary literature, ceramic membranes exhibit distinct advantages over polymer membranes with their potential for application under high temperature, high pressure, and aggressive environments. Additionally, their energy efficiency, compactness, and versatility make them a viable alternative for water purification, replacing more expensive methods like coagulation and adsorption. Ceramic membranes have become a competitive alternative to polymer membranes, showcasing unique material properties and excellent characteristics. Using cost-effective materials for ceramic membrane fabrication allows for utilisation in economically sensitive sectors. Such membranes demonstrate excellent mechanical properties and high permeability, while inexpensive materials can reduce costs. Current scientific research and developments focus on utilising various clays and waste materials to produce ceramic membranes, aiming to create new generations of ceramic membranes for environmentally friendly applications. Key words: ceramic membrane, low-cost membrane material, materials for ceramic membrane, membrane technology, selective layer, synthesis methods Received: 2 June 2023 Revised: 10 June 2023 1. Introduction Recently, membrane separation processes have gained significant importance across various industrial applications. These processes have demonstrated high efficiency in numerous separation processes, particularly in treating industrial effluent water (Issaoui et al., 2019, Issaoui et al., 2015), air purification, food industries, and other environmental applications (M.G. Buonomenna, 2013). Exploring new membrane technologies holds МАТЕРІАЛИ ТА ОБЛАДНАННЯ ДЛЯ ВОДОПІГОТОВКИ Accepted: 12 June 2023 great potential for addressing environmental challenges. However, a critical challenge that remains to be addressed is the cost-benefit aspect and the optimisation of membrane filtration performance. To overcome this challenge, the possibility of using different materials and methods of obtaining ceramic membranes is actively being investigated. Production porous ceramic membranes have been widely adopted in numerous industrial processes due to their distinct advantages over 26 Water and Water Purification Technologies. Scientific and Technical News polymeric membranes (Elaine Fung, 2013). These ceramic membranes offer several wellestablished benefits that make them preferable in industrial applications. Compared to most polymer and inorganic membranes, ceramic membranes offer numerous advantages, including exceptional chemical, thermal, mechanical, and physical stability. Ceramic membranes exhibit remarkable durability, withstanding high temperatures, a wide pH range (0 to 14), and operating pressures up to 10 bar without compaction or swelling. This makes them suitable for applications where polymeric and other inorganic membranes are unsuitable. Ceramic membranes deliver excellent separation capabilities, have a prolonged operational life, and are often more environmentally favourable than alternative separation technologies. In addition, ceramic membranes enable highly selective filtration without phase transformation and can undergo chemical cleaning at high temperatures using caustic, chlorine, hydrogen peroxide, ozone, and inorganic solid acids. Steam sterilisation and backflushing are also possible. Ceramic materials possess exceptional properties that make them highly suitable for demanding water purification processes, including industrial wastewater treatment, oil/water separation, and hazardous waste treatment. Initially, α-Al2O3 was proposed as the primary raw material for ceramic membrane preparation (DeFriend et al., 2003). However, subsequent studies have identified γ-Al2O3, zirconia, titania, and silica as promising materials for membrane synthesis (Yoshino et al., 2005, Sun et al., 2020). More recently, there has been a significant focus on utilising abundant natural minerals and industrial wastes that require lower firing temperatures compared to metal ISSN 2218-9300 oxide materials. Examples of these costeffective starting materials include kaolin, bauxite, diatomite, and dredge sediment, among others. This shift towards low-cost ceramic membranes has opened up new avenues in separation domains. 2. Materials for synthesis of ceramic membranes Ceramic membranes can be fabricated from a wide range of materials. A precise definition of ceramics as inorganic, nonmetallic materials specifies the utilization of metal oxides or zeolites. Notably, alumina and silica are frequently used as membrane precursors, exemplifying this definition (Burggraaf et al., 1996). However, the limited stability of these membranes has prompted the exploration of more stable yet expensive alternatives like titania and zirconia. Presently, a composite ceramic membrane is defined as one that incorporates at least one layer of ceramic material. This encompasses inorganic membranes supported by metal or glass substrates and hybrid membranes featuring an organic-templated top layer. Below, it is discussed several typical materials used to prepare ceramic membranes, highlighting their advantages and drawbacks. 2.1 Traditional materials 2.1.1 Aluminium oxide Aluminium oxide (Al2O3) is the most widely recognized material associated with ceramic membranes. Alumina possesses abundant availability, excellent chemical and thermal stability, reasonable strength, and desirable thermal and electrical insulation properties. Typically, alumina ceramic membranes are manufactured by sintering α- MATERIALS AND EQUIPMENT FOR WATER TREATMENT 27 Water and Water Purification Technologies. Scientific and Technical News alumina and γ-alumina powders at high temperatures (>1300 °C). The primary natural source of aluminium is bauxite ore, which consists of a mixture of minerals such as gibbsite Al(OH)3, boehmite γ-AlO(OH), diaspore α-AlO(OH), Fe2O3, FeO, kaolinite clay, and small amounts of TiO2. Heating this ore (...truncated)