How to Produce Deionized Water

In industrial production, the raw water (tap water or groundwater) often contains large amounts of dissolved ions (such as calcium, magnesium, sodium, and chloride). These ions can cause significant problems:

Scale: Calcium and magnesium ions will precipitate under high temperature and pressure, forming scale deposits, which reduces the efficiency of heat exchangers and boilers, increases energy consumption, and causes equipment failure.
Corrosion: Some ions (e.g., chlorides and sulfates) may react with the metals in equipment, causing corrosion and accelerating damage to critical machinery.
Impact on chemical reactions: Dissolved ions can interfere with chemical reactions in industrial processes, leading to reduced efficiency and lower product purity.
Contamination of electronic components: In the electronics industry, ion residues from water can remain on product surfaces, causing short circuits or degrading performance, especially in semiconductor and optical device production.
Microbial contamination: Organic matter and microbes in water can form biofilms, contaminating production processes and final products, which is particularly detrimental in pharmaceutical and food industries.

To avoid these issues, many industries require deionized water. Deionized water removes dissolved ions (e.g., sodium, calcium, magnesium, iron) and other impurities, leading to higher water purity.

Production Methods of Deionized Water

There are three main methods to produce deionized water: ion exchange, reverse osmosis, and electrodeionization (EDI). Each method has its own advantages and is suited to different applications.

Ion Exchange Method

The ion exchange method uses ion exchange resins to remove dissolved ions from water. The resin is composed of cation and anion exchange materials. When water passes through the resin bed, cations (e.g., sodium, calcium) are exchanged with hydrogen ions, and anions (e.g., chloride, sulfate) are exchanged with hydroxide ions, producing deionized water.

Reverse Osmosis (RO) Method

Reverse osmosis uses a semi-permeable membrane that allows water molecules to pass through while retaining dissolved ions, microbes, and particulates. Under pressure, water is forced through the membrane, and the ions and other contaminants are retained on the other side, producing high-purity deionized water.

Electrodeionization (EDI) Method

EDI combines reverse osmosis and ion exchange, using electric fields to remove ions via ion exchange membranes. The resin is continuously regenerated by the electric current, eliminating the need for chemical regeneration. EDI is typically used in combination with reverse osmosis to produce ultrapure water.

Comparison of Production Methods

Here is the comparison of the three deionized water production methods—Ion Exchange (IX), Reverse Osmosis (RO), and Electrodeionization (EDI)—based on factors like working principle, removed substances, water purity, regeneration and maintenance, energy consumption and operation, application scenarios, and water recovery rate.

Comparison Criteria	Ion Exchange (IX)	Reverse Osmosis (RO)	Electrodeionization (EDI)
Working Principle	Cation and anion exchange resins Exchange dissolved ions with H⁺ and OH^-	Semi-permeable membranes Water is pushed through by pressure, separating ions and contaminants	Combines ion exchange with electrodialysis Continuously regenerates resins under electronics without chemical agents
Removed Substances	Removes cations (e.g. Na⁺, Ca²⁺) and anions (e.g. Cl^-, SO₄^2-).	Removes ions, particles, microorganisms, and organic matter.	Removes almost all ions, with high purity, can also handle trace organics and CO₂.
Water Purity	1-10 μS/cm, Suitable for lower-purity water needs.	1-10 μS/cm Limited with single-stage RO.	0.1-0.055 μS/cm Ideal for ultra-pure water applications.
Regeneration & Maintenance	Requires frequent chemical regeneration with acids and bases, high chemical consumption.	Requires periodic membrane cleaning to prevent fouling and clogging.	No chemical regeneration needed; resin is continuously regenerated by electric field, low maintenance.
Energy Consumption & Operation	Low energy consumption Simple operation, but chemical management is required.	High energy consumption due to high-pressure requirements More complex operation.	Moderate energy consumption Highly automated Suitable for continuous operation.
Application Scenarios	Laboratories, food & beverage industries, pharmaceuticals, general industrial water.	Large-scale water treatment, industrial applications (e.g., boiler feed water), drinking water.	Semiconductor manufacturing, pharmaceuticals, biotechnology, ultra-pure water for laboratories.
Water Recovery Rate	High recovery rate Typically over 90% Stable output.	Lower recovery rate Usually 50%-75%	High recovery rate, Often over 90% Combined with RO, efficiency can exceed 95%.

Grades of Deionized Water & Applications

Deionized water is classified based on its conductivity and purity, with different grades suited to specific applications. Commonly recognized water quality levels include:

Water Quality	Conductivity	Application Areas
Low-Purity Deionized Water	1-10 μS/cm	Laboratory operations, industrial cooling, food and beverage production, and processes where moderate purity is necessary
Medium-Purity Deionized Water	0.1-1 μS/cm	Used in laboratory operations, industrial cooling, food and beverage production, and processes where moderate purity is necessary
High-Purity Deionized Water	Below 0.1 μS/cm	Required for semiconductor manufacturing, pharmaceutical production (e.g., for injections), and optical device cleaning, where extremely high water quality is needed.
Ultrapure Water	0.055 μS/cm or lower, with resistivity of 18.2 MΩ·cm at 25°C	Essential for semiconductor fabrication, nuclear power industries, nanotechnology, genetic engineering, and high-precision laboratory analysis.

Deionized water plays a critical role in various industries, ranging from low-purity uses like industrial cleaning to ultrapure applications in semiconductor manufacturing. By selecting the appropriate production method (such as ion exchange, reverse osmosis, or electrodeionization), industries can produce the required grade of deionized water to meet specific needs. With advancements in technology, the production of deionized water will continue to become more efficient and environmentally friendly, fulfilling the demands of diverse sectors for high-purity water.