Application and challenges of recycling waste salt in the ionic membrane-based Chlor-alkali industry

Under the guidance of China′s ecological civilization policy, while the utilization of industrial water has been improved, the total wastewater discharge still cannot be neglected. Therefore, zero liquid discharge (ZLD) of industrial wastewater has been highlighted as an essential path to realize the utilization of waste. However, waste salt and high-concentration brine are generated during the zero liquid discharge process. The disposal of waste salt is challenging in China, and there is little progress in its utilization, which has become one of the bottlenecks restricting the ZLD process. Compared with the conventional process employing pure salt, the ionic membrane-based Chlor-alkali system using industrial waste salt would be influenced by the presence of impurity components in the feed, which may lead to new challenges such as membrane fouling. To address the limitations, this review paper will introduce the principle and process of recycling waste salt in the ionic membrane-based Chlor-alkali industry, discuss the process mechanism and characterization methods of membrane fouling caused by anions/cations and dissolved organic matter, put forward reasonable countermeasures such as feed control, membrane cleaning and process optimization, and explore future research prospects on adjustment of the feed water quality and the development of high-performance cation exchange membranes. This review aims to promote the development and application of waste salt recycling technology in the process of zero liquid discharge of industrial wastewater.