Application of Electrodialysis Technology in Concentration of Salts like Sodium Nitrate and Strategies for Reducing Evaporation Volume

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In industries such as chemical engineering, rare earth catalysts, and refining catalysts, the treatment of wastewater containing salts like sodium nitrate has always been a challenge. Traditional evaporation concentration methods are effective but suffer from high energy consumption, large equipment investment, and scaling issues. As an efficient membrane separation technology, electrodialysis has shown great application potential in concentrating salts like sodium nitrate in recent years, effectively reducing evaporation volume and treatment costs.

1. Principles and Advantages of Electrodialysis Technology

(1) Principles of Electrodialysis Technology

Electrodialysis technology utilizes the selective permeability of ion-exchange membranes, enabling directional migration and selective passage of anions and cations in a solution under an applied direct current electric field. Inside an electrodialysis device, multiple pairs of alternating anion and cation exchange membranes separate the solution into concentrated water chambers and freshwater chambers. Cations pass through cation membranes toward the negative electrode, while anions pass through anion membranes toward the positive electrode, forming a high-concentration salt solution in the concentrated water chambers and low-salinity freshwater in the freshwater chambers.

(2) Advantages of Electrodialysis Technology

2. Application Cases of Electrodialysis Technology in Concentration of Salts like Sodium Nitrate

(1) Treatment of Sodium Nitrate Wastewater in Rare Earth Catalyst Industry

During the production of rare earth oxide catalysts, a large amount of 3%–5% sodium nitrate wastewater is generated. Using a homogeneous membrane electrodialysis device, sodium nitrate can be concentrated to over 20% before entering the evaporation system for further treatment. This process solves the problems of low concentration multiples and poor resistance to metal ion pollution in heterogeneous membranes and some imported homogeneous membranes, achieving zero discharge and resource utilization of sodium nitrate-containing wastewater.

(2) Treatment of Ammonium Nitrate Wastewater in Refining Catalyst Industry

Refining catalyst production generates approximately 3% ammonium nitrate wastewater. Homogeneous membrane electrodialysis is used for concentration and desalination, and the concentrated water with ammonium nitrate reaching 20% enters the evaporation system. The freshwater from electrodialysis is recycled after reverse osmosis treatment, realizing resource utilization and zero discharge of ammonium nitrate-containing wastewater.

(3) Applications in Other Salt Concentrations

Beyond sodium nitrate and ammonium nitrate, electrodialysis can also concentrate salts such as ammonium chloride and sodium bromide. For example, in the nano-zirconium industry, a homogeneous membrane electrodialysis device treats ammonium chloride wastewater. The concentrated water with 17% ammonium chloride enters the MVR (mechanical vapor recompression) evaporation system to produce solid ammonium chloride for sale, while the electrodialysis freshwater is reprocessed and recycled to the workshop.

3. Strategies for Reducing Evaporation Volume

(1) Optimizing Electrodialysis Process Parameters

By optimizing electrodialysis operation parameters (e.g., current, voltage, flow rate), concentration efficiency can be improved, reducing the volume of wastewater entering the evaporation system. For instance, appropriately increasing the operation current and voltage accelerates ion migration and enhances the concentration multiple.

(2) Adopting Multi-stage Electrodialysis in Series

Multi-stage electrodialysis in series gradually increases the concentration of salts like sodium nitrate, reducing the final wastewater volume entering the evaporation system. Each stage of the electrodialysis device further concentrates the salts, alleviating the burden on subsequent evaporation treatment.

(3) Combining with Other Separation Technologies

Integrating electrodialysis with other separation technologies (e.g., diffusion dialysis, reverse osmosis) achieves more efficient salt concentration and wastewater recycling. For example, diffusion dialysis first removes most free acids from wastewater, followed by electrodialysis to further concentrate the dialyzed residue, and finally, the concentrated water is sent to the evaporation system.

(4) Enhancing Evaporation System Efficiency

Although electrodialysis reduces evaporation volume, the evaporation system remains critical for treating high-concentration salt solutions. Advanced evaporation technologies (e.g., MVR evaporation, multi-effect evaporation) can improve evaporation system efficiency, reducing energy consumption and operating costs.

4. Conclusion and Prospect

Electrodialysis technology holds significant application value in concentrating salts like sodium nitrate, effectively reducing evaporation volume and treatment costs. Strategies such as optimizing electrodialysis process parameters, adopting multi-stage electrodialysis in series, combining with other separation technologies, and enhancing evaporation system efficiency can further improve the treatment effect and economy of electrodialysis.

In the future, with continuous optimization of membrane materials and development of electrodialysis technology, its application in concentrating salts like sodium nitrate will become broader, promising more efficient and environmentally friendly solutions for wastewater treatment in industries such as chemical engineering, rare earth catalysts, and refining catalysts.