– amphoteric – they contain different groups, are used in narrow areas.
An important place in industrial water treatment is occupied by mixtures of cation exchangers . For example, DOW Amberlite resin . (On the image)
In this case, cation exchange resin absorbs mainly metal ions, replacing them with hydrogen (H +), and anion exchange exchanges anions (sulfates, organic acids, hydrocarbons) with hydroxide ions. Hydroxide and hydrogen mutually neutralize to form water.
Upon contact with water, cation exchange resin absorbs positive metal ions and other ionic substances contained in water, releasing an equivalent amount of hydrogen ions. Anion exchange resin absorbs negative ions (bicarbonates, sulfates, organic acids, etc.), releasing an equivalent amount of hydroxide ions. Such resins are used to desalinate water as a second stage. The resin is not regenerated and discharged after the exhaustion of the resource, or it is separated and regenerated separately.
Equipment
The traditional softening system is a cylinder, inside of which there is a filter material and a tank salt-solvent.
The filter is connected to the cold water supply. It passes through a pre-installed main cartridge filter, which traps impurities larger than 5 microns and enters the filter housing (1). Water seeps through the resin layer (2), which exchanges certain cations or anions from water for ions from its surface. Purified water is supplied to the consumer through the lower distribution device (4) and the central pipe (4).
When the resource of the resin ends, even before the breakthrough of the pollutant, the filter is switched to the washing mode. In modern equipment, automation is capable of producing this process in a fully automatic mode with minimal user involvement.
Typically, regeneration involves 4 stages:
- rinsing with a reverse current of water to remove mechanical impurities;
- Rinsing with a solution of reagents from a tank of a salt solvent.
- Rinsing with direct current of water to remove excess reagents.
- Filling a salt tank with water.
Another common design of such a water filter for home is a compact unit that combines a tank with cation exchange resin and a salt solvent in one housing. It is used preferably in everyday life to soften water.
Water treatment:
1. Steam and hot water boilers;
2. Production of drinks and food;
3. Chemical and pharmaceutical industries, hydrometallurgy.
4. Nuclear and thermal power plants
5. Domestic water softening or water filter for home
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watertreatment 