Chlor-alkali membrane cell process for industrial waste salt utilization: Fundamentals and challenges

Zero liquid discharge (ZLD) of industrial wastewater is an important way to achieve the recycling of waste resources. However, the utilization of the concentrated brine or/and waste salt has become one of the crucial bottlenecks restricting the ZLD process. The ion exchange membrane-based chlor-alkali process (termed chloralkali membrane cell process) that reuses industrial waste salt as raw material can close the technology gap between the production lines. However, the ZLD waste salt contains numerous and complex impurities, which can cause membrane fouling, posing a new challenge for the chlor-alkali membrane cell process. To this end, this paper systematically reviews the principles and process flow of waste salt utilization in the chlor-alkali membrane cell process. We have delved into the mechanisms, impacts, and characterization methods of ion exchange membrane fouling caused by anions and dissolved organic matter. Moreover, this paper proposes practical strategies encompassing feed pre-treatment, membrane cleaning and modification, and operating condition optimization to address the membrane fouling issues. We have indicated the future research directions in this domain. These efforts aim to foster the development and implementation of waste salt recycling technology within the context of achieving the sustainable management of industrial wastewater.