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Detailed explanation of the process principle of laboratory ultrapure water equipment
Date: 2025-10-09Read: 7
The laboratory ultrapure water equipment is a professional device that uses a multi-stage treatment process to remove various impurities from water, ultimately producing ultrapure water with a resistivity of up to 18.2 M Ω· cm. The process principle is mainly based on technologies such as physical filtration, membrane separation, and ion exchange. The working principles of each stage will be described in detail below.
1、 Overview of Basic Working Principles
Laboratory ultrapure water equipment usually adopts a multi-stage treatment process, which mainly includes four main stages: pretreatment, reverse osmosis, ion exchange, and terminal treatment. Tap water is first treated by a pre-treatment unit to remove larger particles, suspended solids, and some organic matter. It then enters a reverse osmosis unit to intercept and remove ions and macromolecules from the water. The remaining trace ions are purified and ultrapurified by an ion exchange unit. Finally, UV, ultrafiltration, and other technologies are used to ensure that the microorganisms, organic matter, and pyrogen in ultrapure water meet various experimental application requirements.
2、 Detailed explanation of the principles of each process stage
1. Preprocessing stage
Pre treatment is the first process in the preparation of ultrapure water, mainly aimed at removing sediment, rust, colloidal substances, suspended solids, color, odor, and biochemical organic matter contained in the raw water. The common preprocessing system consists of quartz sand filter, activated carbon filter, and precision filter. When the hardness of the raw water is high, a fully automatic water softener is also used to reduce the hardness of the water, which can effectively protect the subsequent reverse osmosis membrane and extend its service life.
2. Reverse osmosis (RO) stage
Reverse osmosis is the core processing unit of ultrapure water equipment, and its basic principle is to apply a pressure greater than the natural osmotic pressure (usually 6-20 kilograms) on the raw water side, so that water molecules reverse osmosis from the high concentration side to the low concentration side. The pore size of reverse osmosis membrane is extremely small (about 0.0001 microns), which can efficiently intercept bacteria, viruses, heavy metals and organic matter, and the desalination rate is usually ≥ 98%. Due to the fact that the pore size of reverse osmosis membranes is much smaller than that of viruses and bacteria by hundreds or even thousands of times, various viruses, bacteria, heavy metals, solid soluble substances, polluted organic matter, calcium and magnesium ions, etc. cannot pass through reverse osmosis membranes to achieve the goal of water purification.
3. Ion exchange stage
Ion exchange technology is used to further remove trace ions remaining after reverse osmosis treatment. The principle is to use cation exchange resin to remove cations from water and release H ⁺, anion exchange resin to remove anions and release OH ⁻, and H ⁺ combines with OH ⁻ to generate pure water. Cation exchange resins (such as sulfonic acid type) adsorb cations such as Ca ² ⁺ and Mg ² ⁺ in water, releasing H ⁺; Anion exchange resins (such as quaternary ammonium type) adsorb anions such as Cl ⁻, SO ₄ ² ⁻, release OH ⁻, and ultimately combine H ⁺ and OH ⁻ to form H ₂ O, achieving deionization.
4. Electrodeionization (EDI) technology
EDI is an advanced technology that combines electrodialysis membrane separation technology with ion exchange technology. The EDI membrane stack is mainly composed of alternating cation exchange membranes, concentrated water chambers, anion exchange membranes, fresh water chambers, and positive and negative electrodes. Under the action of a direct current electric field, cations and anions in the ion exchange resin in the freshwater chamber migrate along the channels formed by the resin and membrane towards the negative and positive directions, respectively. Cations pass through the cation exchange membrane, anions pass through the anion exchange membrane, and enter the concentrated water chamber to form concentrated water. At the same time, the cations and anions in the EDI inlet are exchanged with the hydrogen ions and hydroxide ions in the ion exchange resin to form ultrapure water. The excessive current causes a large amount of hydrogen ions and hydroxide ions generated by water electrolysis to continuously regenerate the ion exchange resin.
3、 Terminal processing technology
After the above main process treatments, ultrapure water still needs to undergo terminal treatment to meet laboratory usage standards. Common terminal processing techniques include:
1. Ultraviolet (UV) sterilization: Utilizing the bactericidal effect of ultraviolet radiation to kill microorganisms in water and improve the biological safety of ultrapure water.
2. Ultrafiltration: Use filters with a pore size of 0.1 μ m or smaller to remove potential particles and heat sources.
3. Polishing mixed bed: further remove residual ions to achieve a water resistance rate of 15-18.2 M Ω· cm for the produced water.
4. TOC (Total Organic Carbon) removal: By using special technology to reduce the organic content in water.
4、 Comparison of Technical Features
The three core technologies commonly used in laboratory ultrapure water equipment each have their own characteristics:
1. Reverse osmosis (RO): It can remove over 99% of soluble salts, colloids, microorganisms, and organic matter, but cannot completely remove all ions.
2. Ion exchange: The water produced has high purity, but requires regular resin regeneration, resulting in high operating costs and inability to remove non electrolytes and microorganisms.
3. EDI technology: Without the need for chemical regeneration, it can continuously and stably produce high-purity ultrapure water, reducing operating costs and environmental impact.
Modern laboratory ultrapure water equipment typically combines multiple technologies, such as the 'pretreatment reverse osmosis EDI terminal treatment' process route, to fully leverage the advantages of each technology and achieve efficient, stable, and low-cost ultrapure water production.
