Solving the pain points of the zirconia industry: Electrodialysis technology enables the concentration, desalination and zero discharge of 3.5% ammonium chloride wastewater

In the production process of high-end ceramic material zirconia, ammonium salt precipitation is a key purification step, which subsequently generates a large amount of complex wastewater containing high concentrations of ammonium nitrogen (NH₄⁺) and chloride ions (Cl⁻), with a typical concentration of approximately 3.5%. If this kind of wastewater is discharged directly, it will cause serious eutrophication of water bodies and put huge pressure on environmental protection. If simple evaporation is adopted, it will face many problems such as extremely high energy consumption, severe equipment corrosion, low recovery value of crystalline ammonium salts and easy secondary pollution. Electrodialysis (ED) technology, with its unique advantages, provides a perfect answer to the pain points of this industry.

I. Core Challenges and Objectives of the Project

The treatment goal of zirconia wastewater is not only to meet the discharge standards, but also to achieve "zero discharge" and "resource utilization". The core challenge lies in:
1. High-efficiency desalination: Effectively separate ammonium chloride (NH₄Cl) from wastewater.
2. Concentration and reduction: Significantly reduce the volume of wastewater, lowering the load and cost of subsequent evaporation or crystallization.
3. Resource recycling: Obtain pure water and high-purity NH₄Cl solution that can be reused in the production process.
4. Economic and energy-saving: The entire process must have more economic and energy consumption advantages than traditional thermal evaporation.

Ii. Principles and System Composition of Electrodialysis Technology

Electrodialysis is a membrane separation process that, under the action of a direct current electric field, utilizes the selective permeability of ion-exchange membranes to direct the migration of ions from one liquid flow to another, thereby achieving the concentration, desalination and refinement of solutions.

For 3.5% ammonium chloride wastewater, a complete electrodialysis system typically consists of an electrodialyzer (membrane stack), a water pump, a rectifier power supply, a pretreatment system and an automatic control system. Its core - the membrane stack, is composed of alternately arranged anion exchange membranes (allowing only anions such as Cl⁻ to pass through) and cation exchange membranes (allowing only cations such as NH₄⁺ to pass through), forming the concentrated water chamber and the fresh water chamber.

Iii. Process Flow and Advantages of Electrodialysis in This Project

Brief description of the process flow: The 3.5% ammonium chloride wastewater, after precise pretreatment (such as filtration to remove suspended solids and anti-scaling treatment), enters the electrodialysis system. Under the drive of an electric field, NH₄⁺ and Cl⁻ ions respectively pass through the corresponding ion-exchange membranes and migrate towards the concentrated water chamber. Ultimately, the system produced two products:
Desalinated liquid (produced from the fresh water chamber) : The ammonium salt content is significantly reduced (can be lowered to below 500mg/L), the water quality is pure, and it can be directly reused in the washing process of zirconia production or as process water, achieving the recycling of water resources.
Concentrated liquid (produced in the concentrated water chamber) : The concentration of ammonium chloride is significantly increased (it can be concentrated from 3.5% to 15% or even higher). This high-concentration ammonium salt solution has doubled in value and can be directly reused in the previous precipitation process, replacing fresh ammonium salts purchased from outside and saving a large amount of raw material costs.

Its significant advantages are reflected in:
Energy-saving and highly efficient: The separation process involves no phase change, and the electrical energy is directly used for ion migration, with energy consumption far lower than that of evaporation and concentration.
Environmentally friendly: The entire process does not involve the addition of chemicals, causing no secondary pollution and truly achieving clean production.
High degree of resource utilization: Water and ammonium salts are recovered simultaneously, turning waste into treasure, creating direct economic benefits and reducing operating costs.
Easy operation: Modular design, high degree of automation, stable operation and easy maintenance.

Iv. Conclusion

Electrodialysis technology is not merely a simple wastewater treatment unit, but a strategic process link for achieving the "resource utilization" and "zero discharge" of ammonium chloride wastewater in the zirconia industry. It has perfectly solved the problem of treating high-salt wastewater in this industry, transformed environmental protection burdens into economic benefits, and greatly enhanced the green manufacturing level and core competitiveness of enterprises. For zirconia production enterprises committed to sustainable development, investing in a zero-discharge project for electrodialysis wastewater is a wise choice that brings both environmental and economic benefits.