What Ions Can Electrodialysis Remove?

Jul 21, 2026

Electrodialysis (ED) is an independent membrane-based desalination pathway distinct from pressure-driven membrane technologies (RO/NF/UF/MF). Driven by an electric field, it achieves ion separation through the selective migration of ion exchange membranes, complementing rather than competing with RO.

The core component of ED is the membrane stack: between the anode and cathode, CEMs (cation exchange membranes, which only allow cations to pass) and AEMs (anion exchange membranes, which only allow anions to pass) are arranged alternately, forming alternating "diluate chambers" and "concentrate chambers." When saline feed water enters the diluate chamber, under the electric field: cations (Na⁺, Ca²⁺, Mg²⁺, K⁺, etc.) migrate toward the cathode, pass through the CEM into the adjacent concentrate chamber, but are blocked by the next AEM and retained in the concentrate chamber; anions (Cl⁻, SO₄²⁻, NO₃⁻, HCO₃⁻, etc.) migrate toward the anode, pass through the AEM into the adjacent concentrate chamber, but are blocked by the next CEM and retained in the concentrate chamber. The result: the ion concentration in the diluate chamber effluent is significantly reduced, while the concentrate chamber effluent is enriched with ions migrated from the diluate chamber. The entire process requires no phase change, no high pressure, and no chemicals.

What ions can electrodialysis remove?

The ion types, common sources, removal mechanisms, and engineering considerations are as follows:

Ion	Common Sources	Removal Mechanism and Engineering Considerations
Na⁺	Salt, seawater, brackish water, industrial wastewater	Monovalent cation with fast migration rate. A core removal target of ED — desalination rate depends on applied current density and number of membrane stack stages. Final effluent Na⁺ can be as low as 5–20 mg/L.
K⁺	Agricultural runoff, food processing wastewater	Chemical behavior highly similar to Na⁺; ED removal efficiency is nearly identical. In whey desalination, K⁺ is effectively removed together with Na⁺.
Fe³⁺/Fe²⁺	Acid mine drainage, groundwater	High retention rate for multivalent cations, but attention must be paid to Fe(OH)₃ precipitation clogging membrane pores. pH needs to be controlled in the acidic range before influent, or pre-oxidation precipitation removal is required.
NH₄⁺	Municipal wastewater, aquaculture wastewater, landfill leachate	Monovalent cation; removal rate depends on competing ion concentrations. NH₄⁺ removal is competitively inhibited in high Na⁺ environments. The form of ammonia nitrogen is pH-controlled (predominantly NH₄⁺ at pH<9, removable by ED; converts to NH₃ molecules at pH>10 → ED cannot remove).
Li⁺	Salt lake brine, lithium battery recycling	Monovalent small ion; faces competition when coexisting with large amounts of Mg²⁺. Requires selective ion exchange membranes or NF pretreatment to first separate Mg²⁺, then use ED to concentrate Li⁺.
NH₄⁺	Municipal wastewater, aquaculture wastewater, landfill leachate	Monovalent cation; removal rate depends on competing ion concentrations. NH₄⁺ removal is competitively inhibited in high Na⁺ environments. The form of ammonia nitrogen is pH-controlled (predominantly NH₄⁺ at pH<9, removable by ED; converts to NH₃ molecules at pH>10 → ED cannot remove).
Cl⁻	Salt, seawater, industrial wastewater	Fastest migration rate among anions. The “primary target anion” for ED desalination.
SO₄²⁻	Groundwater, mine drainage, industrial wastewater	Divalent anion → high charge density → strong electric field driving force → extremely high retention rate. One of the most efficiently removed targets by ED. However, CaSO₄ scaling risk in the concentrate chamber requires special control.
NO₃⁻	Agricultural runoff, fertilizer-contaminated groundwater	Moderate removal rate for monovalent anions. ED is an important technology for nitrate removal from drinking water — compared to RO, ED does not produce high-salinity concentrate and has a higher recovery rate (80–95%).
HCO₃⁻	Natural alkalinity (groundwater)	Removing HCO₃⁻ reduces the buffering capacity of water, leading to a decrease in effluent pH (due to CO₂ dissolution equilibrium shift). ED treatment of high-alkalinity water requires post-treatment pH adjustment.
F⁻	High-fluoride groundwater (endemic disease areas)	ED is one of the WHO-recommended technologies for fluoride removal from drinking water. Removal efficiency is significantly affected by competing ions (Cl⁻, SO₄²⁻) and pH.
Organic acid anions (acetate, lactate, citrate)	Food fermentation broths, industrial wastewater	Organic ions have larger molecular volumes → higher migration resistance in membranes than inorganic small ions → lower removal rates. Polyvalent organic acids (e.g., citrate³⁻) have better removal rates than monovalent organic acids (e.g., acetate⁻).

However, it should be noted that electrodialysis systems are relatively sensitive to certain heavy metal ions, and the water quality entering the ED system has certain requirements. Therefore, pretreatment of the source wastewater is necessary to meet the influent standards. In terms of physical interception, mechanical filtration, ultrafiltration (UF), and cartridge filters are typically used to remove sediment, colloids, and other impurities, keeping suspended solids (SS) strictly at low levels. In terms of chemical and adsorption treatment, activated carbon filters are used to remove free chlorine with oxidative damaging effects, color, and some organic matter, and scale inhibitors are dosed or pH is adjusted based on water quality to prevent inorganic salt scaling. For hardness ions such as calcium and magnesium, as well as high-valence metal ions such as iron and manganese, deep removal through chemical softening or chelating resins is required to significantly reduce the scaling and poisoning burden on the membrane surfaces.

After the above pretreatment, the water quality entering the ED system must meet a series of core control indicators: suspended solids (SS) generally required below 1 mg/L; the sum of divalent and higher-valent cations prone to hydroxide precipitation, such as calcium, magnesium, iron, and zinc, must be <0.3 mg/L; and free chlorine must be reduced below the safety threshold of 0.5 mg/L. In addition, water temperature typically needs to be controlled between 5–40°C. In practical engineering applications, the combination of pretreatment processes (e.g., “pretreatment + softening + ED” or “pretreatment + RO + ED”) is flexibly configured based on raw water quality characteristics and final product water requirements to achieve efficient, long-cycle operation of the system.

FAQ：

1. What is the working principle of electrodialysis?

Driven by an electric field, it uses alternately arranged CEMs and AEMs to realize selective ion migration, to purify water and concentrate ions.

2. What are the advantages of electrodialysis compared with RO?

Electrodialysis requires no high pressure and no chemicals, features higher water recovery rate and no high-salinity concentrate production.

3. What water scenarios is electrodialysis suitable for?

It applies to seawater, brackish water, industrial wastewater, agricultural runoff, groundwater and salt lake brine treatment.

ETIQUETAS CALIENTES : Ion exchange membrane electrodialysis Electric field drive ion migration pretreatment of the source wastewater ED influent pretreatment requirements

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What Ions Can Electrodialysis Remove?