Monovalent selective ion exchange membranes: A review on preparation processes, applications, performance criteria and sustainability aspects

The increasing world-wide demand for clean water, the rising fresh water scarcity and saltwater intrusion into fresh water resources are the driving forces to find innovative solutions for desalination and water purification. However, in many cases the partial removal of monovalent ions such as sodium or chloride is sufficient. For this purpose, electrochemical processes like electrodialysis (ED) or membrane capacitive deionization (MCDI) are seen as more beneficial than pressure driven desalination techniques like reverse osmosis (RO). However, highly monovalent selective ion exchange membranes are needed for this application. Besides drinking water treatment, such membranes are also needed for metal recovery, e.g., of lithium. The strongly increasing number of publications in the field of monovalent selective ion exchange membranes in the last two decades indicate a huge interest and an ongoing research and development in this field. This review article will provide an overview of the current state-of-the-art in the area of monovalent selective ion exchange membranes and their use in electro membrane processes and especially economic and sustainability aspects.