NEWS CENTER

02

2025

-

09

Zero discharge of nanofiltration concentrate: A key application of electrodialysis

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I. Core Background
Nanofiltration concentrate contains high salt, refractory organic matter and heavy metals. Direct discharge is highly harmful. Zero discharge treatment is an essential need for industrial environmental protection. Electrodialysis, with its characteristic of selective ion migration, has become one of the core technologies for concentrated liquid treatment. It can connect pretreatment and evaporation crystallization, solving the problems of salt separation and concentration.

Ii. Principles and Advantages of Electrodialysis Technology
2.1 Working Principle
By taking advantage of the selective permeability of ion-exchange membranes and the driving force of a direct current electric field, the ions in the concentrated liquid are directed to migrate: monovalent ions (such as Na⁺, Cl⁻) and divalent ions (such as SO₄²⁻) are separated and enter different electrode chambers respectively, achieving precise salt separation and further volume reduction of the concentrated liquid.

2.2 Core Advantages
Precise salt separation: It can efficiently separate ions of different valence states, enhance the purity of subsequent crystalline salts, and lay the foundation for salt resource utilization. In a certain electroplating park case, the purity of sodium chloride and sodium sulfate after treatment reached 95% and over 90%.
Reduce energy consumption: Compared with evaporation crystallization, it has lower energy consumption and can reduce the load on subsequent evaporation equipment, helping the system to cut costs.
Adaptation to high salt: Resistant to the high TDS environment of nanofiltration concentrate, stable operation is not easily affected by high salt concentration.

Iii. Application of Electrodialysis in Treatment Systems
3.1 Process Connection
It is often used in combination with pretreatment (softening and scale removal, oxidation and destabilization), reverse osmosis (RO enhanced concentration), and MVR evaporation and crystallization: pretreatment removes calcium and magnesium ions to prevent membrane scaling, RO first preliminarily concentrates the concentrated liquid, electrodialysis then separates and purifies the salt, and finally evaporation and crystallization obtain reusable salt. A certain coal chemical enterprise adopted the process of "pretreatment + two-stage RO + electrodialysis + MVR", achieving a water recovery rate of 90% and a purity of crystalline salt exceeding 96%.

3.2 Key Supporting Facilities
Pre-treatment guarantee: Calcium and magnesium ions need to be removed through the lime-soda softening method to prevent scaling of the electrodialysis membrane and extend the membrane's lifespan.
Membrane fouling control: Regularly clean the electrodialysis membrane with acid or alkali cleaning agents to prevent the adsorption of organic matter and colloids and maintain the efficiency of ion migration.
Iv. Existing Challenges and Optimization
4.1 Main Challenges
Membrane fouling (organic matter, colloidal deposition) can reduce the efficiency of ion migration, and it is necessary to optimize the pretreatment and cleaning schemes. The membrane life still needs to be improved under a high-salt system.

4.2 Optimization Direction
Develop ion-exchange membranes with stronger anti-pollution capabilities, such as surface-modified membranes;
Combined with the intelligent monitoring system, the membrane operation status is monitored in real time, and the cleaning cycle and parameters are precisely regulated.
V. Future Outlook
Electrodialysis will be further integrated with intelligence. Through the Internet of Things, the ion migration rate and membrane fouling degree will be monitored to achieve automatic parameter adjustment. At the same time, when combined with new membrane materials, it enhances the salt separation efficiency and membrane lifespan, and more deeply meets the resource utilization requirements of zero discharge of nanofiltration concentrate.

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