Progress in salt separation and crystallization technology for zero liquid discharge systems: Principles, applications, and future prospects

In the context of water resource scarcity and increasingly strict environmental protection policies, the zero-discharge technology for industrial wastewater has gained increasing attention. This paper systematically reviews the current development status and engineering applications of the desalination crystallization process in the zero liquid discharge system, clarifying the basic technical path of “pre-treatment-membrane concentration-evaporation crystallization-desalination resource utilization”. It also focuses on analyzing the principles, energy consumption characteristics, and applicable scenarios of three types of desalination technologies: thermal method, freezing crystallization, and membrane method. Subsequently, by combining typical cases of coal chemical and power desulfurization wastewater, it discusses the integration mode and resource utilization effect of the desalination process, while explicitly addressing the underexplored integration strategies between specific industrial wastewater streams and desalination crystallization technologies. The review also points out key challenges such as mixed salt separation bottlenecks, system stability, and high energy consumption. By synthesizing recent engineering practices and comparative technology analyses, this work provides a updated and integrative perspective on system design and optimization for ZLD. In the future, desalination technology will develop towards intelligent control, high-value salt product development, and low-carbon process integration, helping industrial wastewater transition from end-of-pipe treatment to resource recycling.