Water softening


Water softening

A water softener reduces the dissolved calcium, magnesium, and to some degree manganese and ferrous iron ion concentration in hard water.

These "hardness ions" cause three major kinds of undesired effects. Most visibly, metal ions react with soaps and calcium-sensitive detergents, hindering their ability to lather and forming a precipitate—the familiar "bathtub ring". Presence of "hardness ions" also inhibits the cleaning effect of detergent formulations. Second, calcium and magnesium carbonates tend to adhere to the surfaces of pipes and heat exchanger surfaces. The resulting build-up of scale can restrict water flow in pipes. In boilers, the deposits act as an insulation that impairs the flow of heat into water, reducing the heating efficiency and allowing the metal boiler components to overheat. In a pressurized system, this can lead to failure of the boiler. [cite web |url=http://www.chem1.com/CQ/hardwater.html |title=Hard water and water softening |accessdate=2007-10-08 |author=Stephen Lower |month=July | year=2007 |year= |month= |format= |work= |publisher=] Third, the presence of ions in an electrolyte, in this case, hard water, can also lead to galvanic corrosion, in which one metal will preferentially corrode when in contact with another type of metal, when both are in contact with an electrolyte.

Conventional water-softening devices intended for household use depend on an ion-exchange resin in which "hardness" ions trade places with sodium ions that are electrostatically bound to the anionic functional groups of the polymeric resin. A class of minerals called zeolites also exhibits ion-exchange properties; these minerals were widely used in earlier water softeners. Water softeners may be desirable when the source of water is a well, whether municipal or private.

Chelating agents

Chelators are used in chemical analysis, as water softeners, and are ingredients in many commercial products such as shampoos and food preservatives. Citric acid is used to soften water in soaps and laundry detergents. A commonly used synthetic chelator is EDTA.

Ion-exchange resin devices

How it works

The water to be treated passes through a bed of the resin. Negatively-charged resins absorb and bind metal ions, which are positively charged. The resins initially contain univalent hydrogen, sodium or potassium ions, which exchange with divalent calcium and magnesium ions in the water. This exchange eliminates precipitation and soap scum formation. As the water passes through both kinds of resin, the hardness ions replace the hydrogen, sodium or potassium ions which are released into the water. The "harder" the water, the more hydrogen, sodium or potassium ions are released from the resin and into the water.

Regeneration

As these resins become loaded with hardness ions they gradually lose their effectiveness and must be regenerated by passing a concentrated brine, usually of sodium chloride or potassium chloride, or hydrochloric acid solution through them. Most of the salts used for regeneration gets flushed out of the system and may be released into the soil or sewer. These processes can be damaging to the environment, especially in arid regions.Fact|date=June 2007 Some jurisdictions prohibit such release and require users to dispose of the spent brine at an approved site or to use a commercial service company. Most water softener manufacturers provide metered control valves to minimize the frequency of regeneration. It is also possible on most units to adjust the amount of salt used for each regeneration. Both of these steps are recommended to minimize the impact of water softeners on the environment and conserve on salt use.Fact|date=June 2007 Using acid to regenerate lowers the pH of the regeneration waste.

In industrial scale water softening plants, the effluent flow from re-generation process can be very significant. Under certain conditions, such as when the effluent is discharged in admixture with domestic sewage, the calcium and magnesium salts may precipitate out as hardness scale on the inside of the discharge pipe. This can build up to such an extent so as to block the pipe as happened to a major chlor-alkali plant on the south Wales coast in the 1980s.Fact|date=June 2007

Effects of sodium

For people on a low-sodium diet, the increase in sodium levels (for systems releasing sodium) in the water can be significant, especially when treating very hard water. A paper by Kansas State University gives an example: "A person who drinks two liters (2L) of softened, extremely hard water (assume 30 gpg) will consume about 480 mg more sodium (2L x 30 gpg x 8 mg/L/gpg = 480 mg), than if unsoftened water is consumed." This is a significant amount, as they state: "The American Heart Association (AHA) suggests that the 3 percent of the population who must follow a severe, salt-restricted diet should not consume more than 400 mg of sodium a day. AHA suggests that no more than 10 percent of this sodium intake should come from water. The EPA’s draft guideline of 20 mg/L for water protects people who are most susceptible." [cite web |url=http://www.oznet.ksu.edu/library/H20QL2/MF1094.PDF |title=Sodium in Drinking Water |accessdate=2007-04-03 |author=Michael H. Bradshaw, G. Morgan Powell|month=October | year=2002 |year= |month= |format= |work= |publisher=Kansas State University] Most people who are concerned with the added sodium in the water generally have one faucet in the house that bypasses the softener, or have a reverse osmosis unit installed for the drinking water and cooking water, which was designed for desalinisation of sea water.

See also

* Ion exchange
* Water purification
* Descaling agent
* Desalination

References

External links

* [http://www.water-research.net/hardness.htm Wilkes University hard water site]
* [http://www.riversideca.gov/municipal_code/Title_14/12/245.html Riverside County CA water softener restrictions]
* [http://www.pwgazette.com/howsoftenerswork.htm Water softener diagram]
* [http://www.uwsp.edu/cnr/gndwater/privatewells/Water%20Softener%20Use%20Raises%20Questions%20for%20System%20Owners.htm#SofteningProcess Water softener regeneration]
* [http://www.chem1.com/CQ/gallery.html Gallery of water-related pseudoscience] - Chemist's site providing explanations of how alternatives to water softening, such as catalytic water conditioning, are not scientifically grounded


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • water softening — vandens minkštinimas statusas T sritis chemija apibrėžtis Vandenyje ištirpusių Ca ir Mg druskų šalinimas. atitikmenys: angl. water softening rus. водоумягчение; умягчение …   Chemijos terminų aiškinamasis žodynas

  • water softening — vandens minkštinimas statusas T sritis ekologija ir aplinkotyra apibrėžtis Vandenyje ištirpusio kalcio ir magnio druskų šalinimas. atitikmenys: angl. water softening vok. Wasserenthärtung, f; Wasserweichmachen, f rus. смягчение воды, n; умягчение …   Ekologijos terminų aiškinamasis žodynas

  • water softening — noun The removal of calcium and magnesium ions from water, or their replacement with sodium, either by chemical reaction or by ion exchange. See Also: water softener …   Wiktionary

  • Water purification — This article is about large scale, municipal water purification. For portable/emergency water purification, see portable water purification. For industrial water purification, see deionized water. For distilled water, see distilled water. Water… …   Wikipedia

  • water softener — any of a group of substances that when added to water containing calcium and magnesium ions cause the ions to precipitate or change their usual properties: used in the purification of water for the laboratory, and for giving water more efficient… …   Universalium

  • water softener — noun a device which reduces the calcium and magnesium concentration of hard water by passing it through an ion exchange resin See Also: water softening …   Wiktionary

  • water softener — n. 1. a chemical compound added to hard water to soften it, as by precipitating out the minerals 2. a tank or other container in which water is filtered through any of various chemicals or ion exchange media for softening …   English World dictionary

  • Water quality — A rosette sampler is used to collect samples in deep water, such as the Great Lakes or oceans, for water quality testing. Water quality is the physical, chemical and biological characteristics of water.[1] It is a measure of the condition of… …   Wikipedia

  • water-supply system — Facilities for the collection, treatment, storage, and distribution of water. Ancient systems included wells, storage reservoirs, canals and aqueducts, and water distribution systems. Highly advanced systems appeared с 2500 BC and reached their… …   Universalium

  • water — n. & v. n. 1 a colourless transparent odourless tasteless liquid compound of oxygen and hydrogen. Usage: Chem. formula: H2O 2 a liquid consisting chiefly of this and found in seas, lakes, and rivers, in rain, and in secretions of organisms. 3 an… …   Useful english dictionary