Basic knowledge of water treatment
1. The traditional preparation method of pure water
Distillation method, this method is the early, traditional preparation method of laboratory water, in order to obtain higher quality water, sometimes need to adopt multiple distillation methods. In addition, in order to remove some special impurities, special measures need to be taken. For example, adding some potassium permanganate in advance can remove easy oxides; adding a little phosphoric acid can remove ferric iron; adding a little non-volatile acid can make ammonia-free water. As we all know, not only does a large amount of water consumption and electricity consumption be required for the production of water by distillation, but distilled water can only meet the requirements of ordinary analytical experiments.
2. Modern technology for preparing purified water and ultrapure water
1. Due to the high cost and low efficiency of producing pure water by traditional distillation methods, the water quality does not meet the I and II standards in the National Laboratory Water Specification GB6680-2000, and cannot meet the water quality requirements of high-precision analysis experiments. With the advancement of science and technology, the problems of water purification and ultra-purification have been fundamentally solved: purification technologies such as reverse osmosis, ion exchange, EDI, ultraviolet oxidation, and terminal filtration have been comprehensively applied.
Reverse osmosis method (ReverseO, currently it is the most widely used desalination technology. The pore size of the membrane is 0.0001-0.001μm, it can remove inorganic salts, organic matter (molecular weight> 500), bacteria, heat sources, viruses, etc .. Removal of impurities The rate is generally between 95-99.7%. Usually when the conductivity of the source water is less than or equal to 200us / cm, the conductivity of the first-grade RO pure water is less than or equal to 5us / cm, which meets the laboratory third-grade water standard. When the raw water conductivity is high, Users need to choose enhanced pretreatment and secondary reverse osmosis to reduce machine operating costs.
Common reverse osmosis membranes include: cellulose acetate membrane, polyamide membrane and polysulfone membrane.
2. Ion exchange (IX)
The structure of the ion exchange resin is a porous spherical structure of fine particles, with H + and OH- functional groups on the surface, which can quickly and efficiently exchange anions and cations in water, producing high-purity water or ultra-pure water with high resistivity!
3. EDI device
Continuous deionization EDI (Electrodeionization) technology uses mixed bed ion exchange resin to adsorb anions and cations in water. At the same time, these adsorbed anions and cations pass through the anion and cation exchange membrane under the action of DC voltage and are continuously removed. process. The biggest advantage of the EDI device is that it can be operated stably for a long time without regeneration with strong acids and bases, it is easy to maintain, and the operating cost is greatly reduced. It is generally used in water systems with a water production of more than a few hundred liters.
4. Ultraviolet oxidation: choose a UV lamp with a wavelength of 185nm / 254nm in order to sterilize and degrade organic components, and improve the comprehensive index of water production.
5. Filtration: Use terminal filtration devices without pores (pore size 0.1 / 0.2 / 0.05 / 0.03 / 0.01um), ultrafiltration membranes, etc. to remove heat sources and fine particles in ultrapure water.
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