Hard water
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Not to be confused with heavy water.
Hard water caused calcification on this faucet.Hard water is water that has high mineral content (mainly calcium and magnesium ions) (in contrast with soft water). Hard water minerals primarily consist of calcium (Ca2+), and magnesium (Mg2+) metal cations, and sometimes other dissolved compounds such as bicarbonates and sulfates. Calcium usually enters the water as either calcium carbonate (CaCO3), in the form of limestone and chalk, or calcium sulfate (CaSO4), in the form of other mineral deposits. The predominant source of magnesium is dolomite (CaMg(CO3)2). Hard water is generally not harmful to one's health.
The simplest way to determine the hardness of water is the lather/froth test: soap or toothpaste, when agitated, lathers easily in soft water but not in hard water. More exact measurements of hardness can be obtained through a wet titration. The total water 'hardness' (including both Ca2+ and Mg2+ ions) is read as parts per million (ppm) or weight/volume (mg/L) of calcium carbonate (CaCO3) in the water. Although water hardness usually only measures the total concentrations of calcium and magnesium (the two most prevalent, divalent metal ions), iron, aluminium, and manganese may also be present at elevated levels in
[edit] Hardness
Hardness in water is defined as the presence of multivalent cations. Hardness in water can cause water to form scales and a resistance to soap. It can also be defined as water that doesn’t produce lather with soap solutions, but produces white precipitate (scum). For example, sodium stearate reacts with calcium:
2C17H35COONa + Ca2+ → (C17H35COO)2Ca + 2Na+
[edit] Types of hard water
In the 1960s, scientist Chris Gilby Jnr discovered that hard water can be categorized by the ions found in the water.[citation needed] A distinction is also made between 'temporary' and 'permanent' hard water.
[edit] Temporary hardness
Temporary hardness is caused by a combination of calcium ions and bicarbonate ions in the water. It can be removed by boiling the water or by the addition of lime (calcium hydroxide). Boiling promotes the formation of carbonate from the bicarbonate and precipitates calcium carbonate out of solution, leaving water that is softer upon cooling.
The following is the equilibrium reaction when calcium carbonate (CaCO3) is dissolved in water:
CaCO3(s) + H2CO3(aq) ⇋ Ca2+(aq) + 2HCO3-(aq)
Upon heating, less CO2 is able to dissolve into the water (see Solubility). Since there is not enough CO2 around, the reaction cannot proceed from left to right, and therefore the CaCO3 will not dissolve as rapidly. Instead, the reaction is forced to the left (i.e. products to reactants) to re-establish equilibrium, and solid CaCO3 is formed. Boiling the water will remove hardness as long as the solid CaCO3 that precipitates out is removed. After cooling, if enough time passes the water will pick up CO2 from the air and the reaction will again proceed from left to right, allowing the CaCO3 to "re-dissolve" into the water.
For more information on the solubility of calcium carbonate in water and how it is affected by atmospheric carbon dioxide, see calcium carbonate.
[edit] Permanent hardness
Permanent hardness is hardness (mineral content) that cannot be removed by boiling. It is usually caused by the presence of calcium and magnesium sulfates and/or chlorides in the water, which become more soluble as the temperature rises. Despite the name, permanent hardness can be removed using a water softener or ion exchange column, where the calcium and magnesium ions are exchanged with the sodium ions in the column.
Hard water causes scaling, which is the left over mineral deposits that are formed after the hard water had evaporated. This is also known as limescale. The scale can clog pipes, ruin water heaters, coat the insides of tea and coffee pots, and decrease the life of toilet flushing units.
Similarly, insoluble salt residues that remain in hair after shampooing with hard water tend to leave hair rougher and harder to untangle. [1]
In industrial settings, water hardness must be constantly monitored to avoid costly breakdowns in boilers, cooling towers, and other equipment that comes in contact with water. Hardness is controlled by the addition of chemicals and by large-scale softening with zeolite and ion exchange resins.
[edit] Measurement
It is possible to measure the level of hard water by obtaining a free water testing kit. These are supplied by most water softening companies. There are several different scales used to describe the hardness of water in different contexts.
Parts per million (ppm)
Usually defined as one milligram of calcium carbonate (CaCO3) per litre of water (the definition used below)[2].
grains/gallon (gpg)
Defined as 1 grain (64.8 mg) of calcium carbonate per U.S. gallon (3.79 litres), or 17.118 ppm
mmol/L (millimoles per litre)
One millimole of calcium (either Ca2+ or CaCO3) per litre of water corresponds to a hardness of 100.09 ppm or 5.608 dGH, since the molar mass of calcium carbonate is 100.09 g/mol.
Degrees of General Hardness (dGH)
One degree of General Hardness is defined as 10 milligrams of calcium oxide per litre of water, which is the same as one German degree (17.848 ppm).
Various obsolete "degrees":
Clark degrees (°Clark)/English degrees (°E)
One degree Clark is defined as one grain (64.8 mg) of calcium carbonate per Imperial gallon (4.55 litres) of water, equivalent to 14.254 ppm.
German degrees (Deutsche Härte, °dH)
One degree German is defined as 10 milligrams of calcium oxide per litre of water. This is equivalent to 17.848 milligrams of calcium carbonate per litre of water, or 17.848 ppm.
French degrees (°F) (letter to be written in lowercase to avoid confusion with degree Fahrenheit — not always adhered to)
One degree French is defined as 10 milligrams of calcium carbonate per litre of water, equivalent to 10 ppm.
American degrees
One degree American is defined as one milligram of calcium carbonate per litre of water, equivalent to 1 ppm.
Although most of the above measures define hardness in terms of concentrations of calcium in water, any combination of calcium and magnesium cations having the same total molarity as a pure calcium solution will yield the same degree of hardness. Consequently, hardness concentrations for naturally occurring waters (which will contain both Ca2+ and Mg2+ ions), are usually expressed as an equivalent concentration of pure calcium in solution. For example, water that contains 1.5 mmol/L of elemental calcium (Ca2+) and 1.0 mmol/L of magnesium (Mg2+) is equivalent in hardness to a 2.5 mmol/L solution of calcium alone (250.2 ppm).
Because it is the precise mixture of minerals dissolved in the water, together with the water's pH and temperature, that determines the behaviour of the hardness, a single-number scale does not adequately describe hardness. Descriptions of hardness correspond roughly with ranges of mineral concentrations:
Very soft: 0-70 ppm, 0-4 dGH
Soft: 70-140 ppm, 4-8 dGH
Slightly hard: 140-210 ppm, 8-12 dGH
Moderately hard: 210-320 ppm, 12-18 dGH
Hard: 320-530 ppm, 18-30 dGH
Very hard >530 ppm, >30 dGH
[edit] Indices
Several indices are used to describe the behaviour of calcium carbonate in water, oil, or gas mixtures.[3]
[edit] Langelier Saturation Index (LSI)
The Langelier Saturation Index (sometimes Langelier Stability Index) is a calculated number used to predict the calcium carbonate stability of water. It indicates whether the water will precipitate, dissolve, or be in equilibrium with calcium carbonate. Langelier developed a method for predicting the pH at which water is saturated in calcium carbonate (called pHs). The LSI is expressed as the difference between the actual system pH and the saturation pH.
LSI = pH - pHs
If the actual pH of the water is below the calculated saturation pH, the LSI is negative and the water has a very limited scaling potential. If the actual pH exceeds pHs, the LSI is positive, and being supersaturated with CaCO3, the water has a tendency to form scale. At increasing positive index values, the scaling potential increases.
Langelier saturation index is defined as:
LSI = pH (measured) - pHs
For LSI > 0, water is super saturated and tends to precipitate a scale layer of CaCO3
For LSI = 0, water is saturated (in equilibrium) with CaCO3 . A scale layer of CaCO3 is neither precipitated nor dissolved
For LSI < 0, water is under saturated and tends to dissolve solid CaCO3
In practice, water with an LSI between -0.5 and +0.5 will not display enhanced mineral dissolving or scale forming properties. Water with an LSI below -0.5 tends to exhibit noticeably increased dissolving abilities while water with an LSI above +0.5 tends to exhibit noticeably increased scale forming properties.
It is also worth noting that the LSI is temperature sensitive. The LSI becomes more positive as the water temperature increases. This has particular implications in situations where well water is used. The temperature of the water when it first exits the well is often significantly lower than the temperature inside the building served by the well or at the laboratory where the LSI measurement is made.
[edit] Ryznar Stability Index (RSI)
The Ryznar stability index (RSI) uses a database of scale thickness measurements in municipal water systems to predict the effect of water chemistry.
Ryznar saturation index (RSI) was developed from empirical observations of corrosion rates and film formation in steel mains.
Ryznar saturation index is defined as:
RSI = 2 pHs – pH (measured)
For 6,5 < RSI < 7 water is considered to be approximately at saturation equilibrium with calcium carbonate
For RSI > 8 water is under saturated and, therefore, would tend to dissolve any existing solid CaCO3
For RSI < 6,5 water tends to be scale forming
[edit] Puckorius Scaling Index (PSI)
The Puckorius Scaling Index (PSI) uses slightly different parameters to quantify the relationship between the saturation state of the water and the amount of limescale deposited.
[edit] Other indices
Other indices include the Larson-Skold Index[4], the Stiff-Davis Index[5], and the Oddo-Tomson Index[6].
[edit] Health considerations
The World Health Organization says that "there does not appear to be any convincing evidence that water hardness causes adverse health effects in humans."[7]
Some studies have shown a weak inverse relationship between water hardness and cardiovascular disease in men, up to a level of 170 mg calcium carbonate per litre of water. The World Health Organization has reviewed the evidence and concluded the data were inadequate to allow for a recommendation for a level of hardness.[7]
In a review by František Kožíšek, M.D., Ph.D. National Institute of Public Health, Czech Republic there is a good overview of the topic, and unlike the WHO, sets some recommendations for the maximum and minimum levels of calcium (40-80 ppm) and magnesium (20-30 ppm) in drinking water, and a total hardness expressed as the sum of the calcium and magnesium concentrations of 2-4 mmol/L.[8]
Other studies have shown weak correlations between cardiovascular health and water hardness.[9][10][11]
A UK nationwide study, funded by the Department of Health, is investigating anecdotal evidence that childhood eczema may by correlated with hard water.[12]
Very soft water can corrode the metal pipes in which it is carried and as a result the water may contain elevated levels of cadmium, copper, lead and zinc.[7]
[edit] Softening
Main article: water softening
It is often desirable to soften hard water, as it does not readily form lather with soap. Soap is wasted when trying to form lather, and in the process, scum forms. Hard water may be treated to reduce the effects of scaling and to make it more suitable for laundry and bathing.
[edit] Process
A water softener, like a fabric softener, works on the principle of cation or ion exchange in which ions of the hardness minerals are exchanged for sodium or potassium ions, effectively reducing the concentration of hardness minerals to tolerable levels and thus making the water softer and giving it a smoother feeling.[13]
The most economical way to soften household water is with an ion exchange water softener. This unit uses sodium chloride (table salt) to recharge beads made of the ion exchange resins that exchange hardness mineral ions for sodium ions. Artificial or natural zeolites can also be used. As the hard water passes through and around the beads, the hardness mineral ions are preferentially absorbed, displacing the sodium ions. This process is called ion exchange. When the bead or sodium zeolite has a low concentration of sodium ions left, it is exhausted, and can no longer soften water. The resin is recharged by flushing (often back-flushing) with saltwater. The high excess concentration of sodium ions alter the equilibrium between the ions in solution and the ions held on the surface of the resin, resulting in replacement of the hardness mineral ions on the resin or zeolite with sodium ions. The resulting saltwater and mineral ion solution is then rinsed away, and the resin is ready to start the process all over again. This cycle can be repeated many times.
The discharge of brine water during this regeneration process has been banned in some jurisdictions (notably California, USA) due to concerns about the environmental impact of the discharged sodium.
Potassium chloride (softener salt substitute) may also be used to regenerate the resin beads. It exchanges the hardness ions for potassium. It also will exchange naturally occurring sodium for potassium resulting in sodium-free soft water.
Some softening processes in industry use the same method, but on a much larger scale. These methods create an enormous amount of salty water that is costly to treat and dispose of.
Temporary hardness, caused by hydrogen carbonate (or bicarbonate) ions, can be removed by boiling. For example, calcium bicarbonate, often present in temporary hard water, may be boiled in a kettle to remove the hardness. In the process, a scale forms on the inside of the kettle in a process known as "furring". This scale is composed of calcium carbonate.
Ca(HCO3)2 → CaCO3 + CO2 + H2O
Hardness can also be reduced with a lime-soda ash treatment. This process, developed by Thomas Clark in 1841, involves the addition of slaked lime (calcium hydroxide — Ca(OH)2) to a hard water supply to convert the hydrogen carbonate hardness to carbonate, which precipitates and can be removed by filtration:
Ca(HCO3)2 + Ca(OH)2 → 2CaCO3 + 2H2O
The addition of sodium carbonate also permanently softens hard water containing calcium sulfate, as the calcium ions form calcium carbonate which precipitates out and sodium sulfate is formed which is soluble. The calcium carbonate that is formed sinks to the bottom. Sodium sulfate has no effect on the hardness of water.
Na2CO3 + CaSO4 → Na2SO4 + CaCO3
[edit] Effects on skin
Some confusion may arise after a first experience with soft water. Hard water does not lather well with soap and leaves a "less than clean" feeling. Soft water lathers better than hard water but leaves a "slippery feeling" on the skin after use with soap. A certain water softener manufacturer contends that the "slippery feeling" after showering in soft water is due to "cleaner skin" and the absence of "friction-causing" soap scum.
However, the chemical explanation is that softened water, due to its sodium content, has a much reduced ability to combine with the soap film on your body and therefore, it is much more difficult to rinse off.[14] Solutions are to use less soap or a synthetic liquid body wash.
[edit] Regional information
[edit] Hard water in Australia
Analysis of water hardness in major Australian cities by the Australian Water Association shows a range from very soft (Melbourne) to very hard (Adelaide). Total Hardness levels of Calcium Carbonate in ppm are: Canberra: 40[15]; Melbourne: 10 - 26[16]; Sydney: 39.4 - 60.1[17]; Perth: 29 - 226[18]; Brisbane: 100[19]; Adelaide: 134 - 148[20]; Hobart: 5.8 - 34.4[21]; Darwin: 31[22].
[edit] Hard water in Canada
Prairie provinces (mainly Saskatchewan and Manitoba) contain high quantities of calcium and magnesium, often as dolomite, which are readily soluble in the groundwater that contains high concentrations of trapped carbon dioxide from the last glaciation. In these parts of Canada, the total hardness in ppm of calcium carbonate equivalent frequently exceed 200 ppm, if groundwater is the only source of potable water. The west coast, by contrast, has unusually soft water, derived mainly from mountain lakes fed by glaciers and snowmelt.
Some typical values are: Montreal 116 ppm[23], Calgary 165 ppm, Regina 202 ppm, Saskatoon < 140 ppm, Winnipeg 77 ppm[24], Toronto 121 ppm[25], Vancouver < 3 ppm[26], Charlottetown PEI 140 - 150 ppm[27].
[edit] Hard water in England and Wales
Information from the British Drinking Water Inspectorate shows that drinking water in England is generally considered to be 'very hard', with most areas of England, particularly the East, exhibiting above 200 ppm for the calcium carbonate equivalent. Wales, Devon, Cornwall and parts of North-West England are softer water areas, and range from 0 to 200 ppm[citation needed]. In the brewing industry in England and Wales, water is often deliberately hardened with gypsum in the process of Burtonisation.
[edit] Hard water in the United States
More than 85% of American homes have hard water.[28] The softest waters occur in parts of the New England, South Atlantic-Gulf, Pacific Northwest, and Hawaii regions. Moderately hard waters are common in many of the rivers of the Tennessee, Great Lakes, Pacific Northwest, and Alaska regions. Hard and very hard waters are found in some of the streams in most of the regions throughout the country. Hardest waters (greater than 1,000 ppm) are in streams in Texas, New Mexico, Kansas, Arizona, and southern California.[29]
[edit] See also
Water portal
Water softener
Water quality
Water treatment
Water purification
Zamzam Well
[edit] References
^ Body And Fitness Healthy Hair Tips
^ Definitions of units of measure for water hardness
^ Corrosion by water
^ T.E., Larson and R. V. Skold, Laboratory Studies Relating Mineral Quality of Water to Corrosion of Steel and Cast Iron, 1958 Illinois State Water Survey, Champaign, IL pp. [43] - 46: ill. ISWS C-71
^ Stiff, Jr., H.A., Davis, L.E., A Method For Predicting The Tendency of Oil Field Water to Deposit Calcium Carbonate, Pet. Trans. AIME 195;213 (1952).
^ Oddo,J.E., Tomson, M.B.,Scale Control, Prediction and Treatment Or How Companies Evaluate A Scaling Problem and What They Do Wrong, CORROSION/92, Paper No. 34, (Houston, TX:NACE INTERNATIONAL 1992).
^ a b c World Health Organization Hardness in Drinking-Water, 2003
^ František Kožíšek Health significance of drinking water calcium and magnesium, February 2003
^ Studies of water quality and cardiovascular diseas...[Sci Total Environ. 1981] - PubMed Result
^ Cardiovascular mortality and calcium and magnesium...[Eur J Epidemiol. 2003] - PubMed Result
^ Magnesium and calcium in drinking water and death ...[Epidemiology. 1999] - PubMed Result
^ BBC News. Water softener eczema relief hope
^ How does a water softener work? at Howstuffworks.com
^ With soft water, why can't we rinse off all the soap?
^ ACTewAGL: Dishwashers and Water Hardness
^ Melbourne Water Public Health Compliance Report - July-September 2006
^ Sydney Typical Drinking Water Analysis
^ Perth Drinking Water Quality Annual report 2005-06
^ Brisbane Drinking Water
^ Adelaide Water Quality
^ Hobart Drinking Water Quality
^ Darwin Water Quality
^ http://www2.ville.montreal.qc.ca/pls/portal/docs/page/eau_potable_en/eau_residence.shtm
^ 2006 Winnipeg drinking water quality test results
^ City of Toronto: Toronto Water - FAQ
^ GVRD Wash Smart - Water Facts
^ http://www.city.charlottetown.pe.ca/allaire/spectra/system/mediastore/Water_Report_2006.pdf
^ Wilson, Amber; Parrott, Kathleen; Ross, Blake (1999-06), Household Water Quality - Water Hardness, http://www.ext.vt.edu/pubs/housing/356-490/356-490.html, retrieved on 2009-04-26
^ Briggs, J.C., and Ficke, J.F.; Quality of Rivers of the United States, 1975 Water Year -- Based on the National Stream Quality Accounting Network (NASQAN): U.S. Geological Survey Open-File Report 78-200, 436 p. (1977)
[edit] External links
Alcoa Chemical, Langelier Saturation Index (LSI) Calculator
Water hardness unit converter, Converter for hardness of water
Retrieved from "http://en.wikipedia.org/wiki/Hard_water"
Categories: Water | Forms of water | Liquid water
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Water softening
Water softening
From Wikipedia, the free encyclopedia
(Redirected from Water softener)
Jump to: navigation, search
A water softener reduces the dissolved calcium, magnesium, and to some degree manganese and ferrous iron ion concentration in hard water. (A common water softener is sodium carbonate; formula Na2CO3.)
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 precipitate out as hard deposits to the surfaces of pipes and heat exchanger surfaces. This is principally caused by thermal decomposition of bi-carbonate ions but also happens to some extent even in the absence of such ions. 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.[1]
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. However the sodium (or potassium) ions released during conventional water softening are much more electrolytically active than the calcium or magnesium ions that they replace and galvanic corrosion would be expected to be substantially increased by water softening and not decreased. Similarly if any lead plumbing is in use, softened water is likely to be substantially more plumbo-solvent than hard water.
[edit] Ion-exchange resin devices
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.
[edit] 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. As the water passes through the resin column, 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.
Resins are also available to remove carbonate, bi-carbonate and sulphate ions which are absorbed and hydroxyl ions released from the resin. Both types of resin may be provided in a single water softener.
[edit] Regeneration
As these resins become loaded with undesirable cations and anions they gradually lose their effectiveness and must be regenerated. If a cationic resin is used (to remove calcium and magnesium ions) then regeneration is usually effected by passing a concentrated brine, usually of sodium chloride or potassium chloride, or hydrochloric acid solution through them.
For anionic resins a solution of sodium or potassium hydroxide (lye) is used. 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.[citation needed] 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 reagent used for each regeneration. Both of these steps are recommended to minimize the impact of water softeners on the environment and conserve on reagent use.[citation needed] 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.[citation needed]
If potassium chloride is used the same exchange process takes place except that potassium is exchanged for the calcium, magnesium and iron instead of sodium. This is a more expensive option and may be unsuited for people on potassium-restricted diets.
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 litres (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."[2] Most people who are concerned with the added sodium in the water generally have one tap (US: 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.
Chelating agents
Main article: Chelation
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.
See also
Ion exchange
Water purification
Descaling agent
Desalination
From Wikipedia, the free encyclopedia
(Redirected from Water softener)
Jump to: navigation, search
A water softener reduces the dissolved calcium, magnesium, and to some degree manganese and ferrous iron ion concentration in hard water. (A common water softener is sodium carbonate; formula Na2CO3.)
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 precipitate out as hard deposits to the surfaces of pipes and heat exchanger surfaces. This is principally caused by thermal decomposition of bi-carbonate ions but also happens to some extent even in the absence of such ions. 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.[1]
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. However the sodium (or potassium) ions released during conventional water softening are much more electrolytically active than the calcium or magnesium ions that they replace and galvanic corrosion would be expected to be substantially increased by water softening and not decreased. Similarly if any lead plumbing is in use, softened water is likely to be substantially more plumbo-solvent than hard water.
[edit] Ion-exchange resin devices
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.
[edit] 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. As the water passes through the resin column, 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.
Resins are also available to remove carbonate, bi-carbonate and sulphate ions which are absorbed and hydroxyl ions released from the resin. Both types of resin may be provided in a single water softener.
[edit] Regeneration
As these resins become loaded with undesirable cations and anions they gradually lose their effectiveness and must be regenerated. If a cationic resin is used (to remove calcium and magnesium ions) then regeneration is usually effected by passing a concentrated brine, usually of sodium chloride or potassium chloride, or hydrochloric acid solution through them.
For anionic resins a solution of sodium or potassium hydroxide (lye) is used. 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.[citation needed] 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 reagent used for each regeneration. Both of these steps are recommended to minimize the impact of water softeners on the environment and conserve on reagent use.[citation needed] 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.[citation needed]
If potassium chloride is used the same exchange process takes place except that potassium is exchanged for the calcium, magnesium and iron instead of sodium. This is a more expensive option and may be unsuited for people on potassium-restricted diets.
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 litres (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."[2] Most people who are concerned with the added sodium in the water generally have one tap (US: 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.
Chelating agents
Main article: Chelation
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.
See also
Ion exchange
Water purification
Descaling agent
Desalination
biocide
biocide is a chemical substance capable of killing living organisms, usually in a selective way. Biocides are commonly used in medicine, agriculture, forestry, and in industry where they prevent the fouling of water and oil pipelines. Some substances used as biocides are also employed as anti-fouling agents or disinfectants under other circumstances: chlorine, for example, is used as a short-life biocide in industrial water treatment but as a disinfectant in swimming pools. Many biocides are synthetic, but a class of natural biocides, derived from e.g. bacteria and plants[1], includes brassica oleracea, brassica oleracea gemmifera, and clostridium botulinum bacteria.[citation needed][clarification needed]
A biocide can be:
A pesticide: this includes fungicides, herbicides, insecticides, algicides, molluscicides, miticides and rodenticides.
An antimicrobial: this includes germicides, antibiotics, antibacterials, antivirals, antifungals, antiprotozoals and antiparasites. See also spermicide.
Uses
Biocides can be added to other materials (typically liquids) to protect them against biological infestation and growth. For example, certain types of quaternary ammonium compounds (quats) are added to pool water or industrial water systems to act as an algicide, protecting the water from infestation and growth of algae. Chlorine is also added during wastewater treatment to kill micro-organisms, algae, and so on. It is often impractical to store and use poisonous chlorine gas for water treatment, so alternative methods of adding chlorine are used. These include hypochlorite solutions, which gradually release chlorine into the water, and compounds like sodium dichloro-s-triazinetrione (dihydrate or anhydrous), sometimes referred to as "dichlor", and trichloro-s-triazinetrione, sometimes referred to as "trichlor". These compounds are stable while solid and may be used in powdered, granular, or tablet form. When added in small amounts to pool water or industrial water systems, the chlorine atoms hydrolyze from the rest of the molecule forming hypochlorous acid (HOCl) which acts as a general biocide killing germs, micro-organisms, algae, and so on. Halogenated hydantoin compounds are also used as biocides.
Hazards and environmental risks
Because biocides are intended to kill living organisms, many biocidal products pose significant risk to human health and welfare. Great care is required when handling biocides and appropriate protective clothing and equipment should be used. The use of biocides can also have significant adverse effects on the natural environment. Anti-fouling paints, especially those utilising organic tin compounds such as TBT, have been shown to have severe and long-lasting impacts on marine eco-systems and such materials are now banned in many countries for commercial and recreational vessels (though sometimes still used for naval vessels).
Disposal of used or unwanted biocides must be undertaken carefully to avoid serious and potentially long-lasting damage to the environment.
Classification
European Community Classification
The Biocidal Products Directive 98/8/EC (BPD), the classification of biocides, is broken down into 23 product types (i.e. application categories), with several comprising multiple subgroups:[2]
MAIN GROUP 1: Disinfectants and general biocidal products
Product-type 1: Human hygiene biocidal products
Product-type 2: Private area and public health area disinfectants and other biocidal products
Product-type 3: Veterinary hygiene biocidal products
Product-type 4: Food and feed area disinfectants
Product-type 5: Drinking water disinfectants
MAIN GROUP 2: Preservatives
Product-type 6: In-can preservatives
Product-type 7: Film preservatives
Product-type 8: Wood preservatives
Product-type 9: Fibre, leather, rubber and polymerised materials preservatives
Product-type 10: Masonry preservatives
Product-type 11: Preservatives for liquid-cooling and processing systems
Product-type 12: Slimicides
Product-type 13: Metalworking-fluid preservatives
MAIN GROUP 3: Pest control
Product-type 14: Rodenticides
Product-type 15: Avicides
Product-type 16: Molluscicides
Product-type 17: Piscicides
Product-type 18: Insecticides, acaricides and products to control other arthropods
Product-type 19: Repellents and attractants
MAIN GROUP 4: Other biocidal products
Product-type 20: Preservatives for food or feedstocks
Product-type 21: Antifouling products
Product-type 22: Embalming and taxidermist fluids
Product-type 23: Control of other vertebrates
References
^ Natural biocide-term
^ Directive 98/8/EC of the European Parliament and of the Council of 16 February 1998 concerning the placing of biocidal products on the market
Literature
Wilfried Paulus: Directory of Microbicides for the Protection of Materials and Processes. Springer Netherland, Berlin 2006, ISBN 1-4020-4861-0.
Danish EPA (2001): Inventory of Biocides used in Denmark
See also
Non-pesticide management
Ecological pesticides
A biocide can be:
A pesticide: this includes fungicides, herbicides, insecticides, algicides, molluscicides, miticides and rodenticides.
An antimicrobial: this includes germicides, antibiotics, antibacterials, antivirals, antifungals, antiprotozoals and antiparasites. See also spermicide.
Uses
Biocides can be added to other materials (typically liquids) to protect them against biological infestation and growth. For example, certain types of quaternary ammonium compounds (quats) are added to pool water or industrial water systems to act as an algicide, protecting the water from infestation and growth of algae. Chlorine is also added during wastewater treatment to kill micro-organisms, algae, and so on. It is often impractical to store and use poisonous chlorine gas for water treatment, so alternative methods of adding chlorine are used. These include hypochlorite solutions, which gradually release chlorine into the water, and compounds like sodium dichloro-s-triazinetrione (dihydrate or anhydrous), sometimes referred to as "dichlor", and trichloro-s-triazinetrione, sometimes referred to as "trichlor". These compounds are stable while solid and may be used in powdered, granular, or tablet form. When added in small amounts to pool water or industrial water systems, the chlorine atoms hydrolyze from the rest of the molecule forming hypochlorous acid (HOCl) which acts as a general biocide killing germs, micro-organisms, algae, and so on. Halogenated hydantoin compounds are also used as biocides.
Hazards and environmental risks
Because biocides are intended to kill living organisms, many biocidal products pose significant risk to human health and welfare. Great care is required when handling biocides and appropriate protective clothing and equipment should be used. The use of biocides can also have significant adverse effects on the natural environment. Anti-fouling paints, especially those utilising organic tin compounds such as TBT, have been shown to have severe and long-lasting impacts on marine eco-systems and such materials are now banned in many countries for commercial and recreational vessels (though sometimes still used for naval vessels).
Disposal of used or unwanted biocides must be undertaken carefully to avoid serious and potentially long-lasting damage to the environment.
Classification
European Community Classification
The Biocidal Products Directive 98/8/EC (BPD), the classification of biocides, is broken down into 23 product types (i.e. application categories), with several comprising multiple subgroups:[2]
MAIN GROUP 1: Disinfectants and general biocidal products
Product-type 1: Human hygiene biocidal products
Product-type 2: Private area and public health area disinfectants and other biocidal products
Product-type 3: Veterinary hygiene biocidal products
Product-type 4: Food and feed area disinfectants
Product-type 5: Drinking water disinfectants
MAIN GROUP 2: Preservatives
Product-type 6: In-can preservatives
Product-type 7: Film preservatives
Product-type 8: Wood preservatives
Product-type 9: Fibre, leather, rubber and polymerised materials preservatives
Product-type 10: Masonry preservatives
Product-type 11: Preservatives for liquid-cooling and processing systems
Product-type 12: Slimicides
Product-type 13: Metalworking-fluid preservatives
MAIN GROUP 3: Pest control
Product-type 14: Rodenticides
Product-type 15: Avicides
Product-type 16: Molluscicides
Product-type 17: Piscicides
Product-type 18: Insecticides, acaricides and products to control other arthropods
Product-type 19: Repellents and attractants
MAIN GROUP 4: Other biocidal products
Product-type 20: Preservatives for food or feedstocks
Product-type 21: Antifouling products
Product-type 22: Embalming and taxidermist fluids
Product-type 23: Control of other vertebrates
References
^ Natural biocide-term
^ Directive 98/8/EC of the European Parliament and of the Council of 16 February 1998 concerning the placing of biocidal products on the market
Literature
Wilfried Paulus: Directory of Microbicides for the Protection of Materials and Processes. Springer Netherland, Berlin 2006, ISBN 1-4020-4861-0.
Danish EPA (2001): Inventory of Biocides used in Denmark
See also
Non-pesticide management
Ecological pesticides
Dispersant
A dispersant or a dispersing agent or a plasticizer is either a non-surface active polymer or a surface-active substance added to a suspension, usually a colloid, to improve the separation of particles and to prevent settling or clumping. Dispersants consist normally of one or more surfactants, but may also be gases.
Applications
Automotive
Dispersing agents are added to lubricating oils used in automotive engines to prevent the accumulation of varnishlike deposits on the cylinder walls and to gasoline to prevent the buildup of gummyish residues.
Bio-Dispersing
Dispersants can be used to prevent formation of biofouling or biofilms in industrial processes. It is also possible to disperse bacterial slime and increase the efficiency of biocides.
Concrete
Dispersants/plasticizer are used in the concrete mix (sand, stone, cement and water) to lower the use of water and still keeping the same slump (flow) property. This make the concrete stronger and more impervious to water penetration.[1]
Detergents
Dispersing agents are the principal applications of detergents for which the liquid bath is water. Detergents also are used as emulsifiers in many applications.
Gypsum Wallboard
A dispersant/plasticizer is added to the gypsum wallboard slurry to reduce the amount of water used, while maintaining the same slump as the slurry without dispersant. The lower water usage allows lower energy use to dry the wallboard.[2]
Oil Drilling
Dispersants in oil drilling are chemical that aids in breaking up solids or liquids as fine particles or droplets into another medium. This term is often applied incorrectly to clay deflocculants. Clay dispersants are various sodium phosphates and sodium carbonates aided by heat, mechanical shearing and time. Powdered polymers are dispersed by precoating the particles with a type of glycol to prevent formation of "fish-eye" globules. For dispersing (emulsification) of oil into water (or water into oils), surfactants selected on the basis of hydrophile-lipophile balance (HLB) number can be used. For foam drilling fluids, synthetic detergents and soaps are used, along with polymers, to disperse foam bubbles into the air or gas.
Oil spill
Dispersants can be used to dissipate oil slicks.
When used appropriately, dispersants can be an effective method of response to an oil spill[3]. They may rapidly remove large amounts of certain oil types from the sea surface by transferring it into the sea water. Wave energy will cause the oil slick to break up into small oil droplets that are rapidly diluted and subsequently biodegraded by micro-organisms occurring naturally in the marine environment. They can also delay the formation of persistent water-in-oil emulsions.
A dispersant was used in an attempt to clean up the Exxon Valdez oil spill[4] though their use was discontinued as there was not enough wave action to mix the dispersant with the oil in the water.
Process industry
In the process industry dispersing agents or plasticizers are added to process liquids to prevent unwanted deposits by keeping them finely dispersed. They function in both aqueous and nonaqueous media.
Surface coating
In order to provide optimal performance, pigment particles must act independently of each other in the coating film and thus must remain well dispersed throughout manufacture, storage, application, and film formation. Unfortunately, colloidal dispersions such as the pigment dispersions in liquid coatings are inherently unstable, and they must be stabilized against the flocculation that might occur.
See also
Plasticizer
Deflocculant
Detergent
Surfactant
Applications
Automotive
Dispersing agents are added to lubricating oils used in automotive engines to prevent the accumulation of varnishlike deposits on the cylinder walls and to gasoline to prevent the buildup of gummyish residues.
Bio-Dispersing
Dispersants can be used to prevent formation of biofouling or biofilms in industrial processes. It is also possible to disperse bacterial slime and increase the efficiency of biocides.
Concrete
Dispersants/plasticizer are used in the concrete mix (sand, stone, cement and water) to lower the use of water and still keeping the same slump (flow) property. This make the concrete stronger and more impervious to water penetration.[1]
Detergents
Dispersing agents are the principal applications of detergents for which the liquid bath is water. Detergents also are used as emulsifiers in many applications.
Gypsum Wallboard
A dispersant/plasticizer is added to the gypsum wallboard slurry to reduce the amount of water used, while maintaining the same slump as the slurry without dispersant. The lower water usage allows lower energy use to dry the wallboard.[2]
Oil Drilling
Dispersants in oil drilling are chemical that aids in breaking up solids or liquids as fine particles or droplets into another medium. This term is often applied incorrectly to clay deflocculants. Clay dispersants are various sodium phosphates and sodium carbonates aided by heat, mechanical shearing and time. Powdered polymers are dispersed by precoating the particles with a type of glycol to prevent formation of "fish-eye" globules. For dispersing (emulsification) of oil into water (or water into oils), surfactants selected on the basis of hydrophile-lipophile balance (HLB) number can be used. For foam drilling fluids, synthetic detergents and soaps are used, along with polymers, to disperse foam bubbles into the air or gas.
Oil spill
Dispersants can be used to dissipate oil slicks.
When used appropriately, dispersants can be an effective method of response to an oil spill[3]. They may rapidly remove large amounts of certain oil types from the sea surface by transferring it into the sea water. Wave energy will cause the oil slick to break up into small oil droplets that are rapidly diluted and subsequently biodegraded by micro-organisms occurring naturally in the marine environment. They can also delay the formation of persistent water-in-oil emulsions.
A dispersant was used in an attempt to clean up the Exxon Valdez oil spill[4] though their use was discontinued as there was not enough wave action to mix the dispersant with the oil in the water.
Process industry
In the process industry dispersing agents or plasticizers are added to process liquids to prevent unwanted deposits by keeping them finely dispersed. They function in both aqueous and nonaqueous media.
Surface coating
In order to provide optimal performance, pigment particles must act independently of each other in the coating film and thus must remain well dispersed throughout manufacture, storage, application, and film formation. Unfortunately, colloidal dispersions such as the pigment dispersions in liquid coatings are inherently unstable, and they must be stabilized against the flocculation that might occur.
See also
Plasticizer
Deflocculant
Detergent
Surfactant
Detergent
A detergent (as a noun) is a material intended to assist cleaning. The term is sometimes used to differentiate between soap and other surfactants used for cleaning. As an adjective pertaining to a substance, it (or "detersive") means "cleaning" or "having cleaning properties"; "detergency" indicates presence or degree of cleaning property.
Components
Detergents, especially those made for use with water, often include different components such as:
Surfactants to 'cut' (Emulsify) grease and to wet surfaces
Abrasive to scour
Substances to modify pH or to affect performance or stability of other ingredients, acids for descaling or caustics to break down organic compounds
Water softeners to counteract the effect of "hardness" ions on other ingredients
oxidants (oxidizers) for bleaching, disinfection, and breaking down organic compounds
Non-surfactant materials that keep dirt in suspension
Enzymes to digest proteins, fats, or carbohydrates in stains or to modify fabric feel
Ingredients that modify the foaming properties of the cleaning surfactants, to either stabilize or counteract foam
Ingredients to increase or decrease the viscosity of the solution, or to keep other ingredients in solution, in a detergent supplied as a water solution or gel
Ingredients that affect aesthetic properties of the item to be cleaned, or of the detergent itself before or during use, such as optical brighteners, fabric softeners, colors, perfumes, etc.
Ingredients such as corrosion inhibitors to counteract damage to equipment with which the detergent is used
Ingredients to reduce harm or produce benefits to skin, when the detergent is used by bare hand on inanimate objects or used to clean skin
Preservatives to prevent spoilage of other ingredients
Sometimes materials more complicated than mere mixtures of compounds are said to be detergent. For instance, certain foods such as celery are said to be detergent or detersive to teeth.
Types
There are several factors that dictate what compositions of detergent should be used, including the material to be cleaned, the apparatus to be used, and tolerance for and type of dirt. For instance, all of the following are used to clean glass. The sheer range of different detergents that can be used demonstrates the importance of context in the selection of an appropriate glass-cleaning agent:
a chromic acid solution—to get glass very clean for certain precision-demanding purposes such as analytical chemistry
a high-foaming mixture of surfactants with low skin irritation—for hand-washing of dishware in a sink or dishpan
any of various non-foaming compositions—for dishware in a dishwashing machine
other surfactant-based compositions—for washing windows with a squeegee, followed by rinsing
an ammonia-containing solution—for cleaning windows with no additional dilution and no rinsing
ethanol or methanol in windshield washer fluid—used for a vehicle in motion, with no additional dilution
glass contact lens cleaning solutions, which must clean and disinfect without leaving any eye-harming material that would not be easily rinsed
Terminology
Sometimes the word detergent is used to distinguish a cleaning agent from soap. During the early development of non-soap surfactants as commercial cleaning products, the term syndet, short for synthetic detergent was promoted to indicate the distinction. The term never became popular and is incorrect, because most soap is itself synthesized (from glycerides). The term soapless soap also saw a brief vogue. There is no accurate term for detergents not made of soap other than soapless detergent or non-soap detergent.
The term detergent by itself is sometimes used to refer specifically to clothing detergent, as opposed to hand soap or other types of cleaning agents.
Plain water, if used for cleaning, is a detergent. Probably the most widely-used detergents other than water are soaps or mixtures composed chiefly of soaps. However, not all soaps have significant detergency and, although the words "detergent" and "soap" are sometimes used interchangeably, not every detergent is a soap.
The term detergent is sometimes used to refer to any surfactant, even when it is not used for cleaning. This terminology should be avoided as long as the term surfactant itself is available.
History
The earliest detergent substance was undoubtedly water; after that, oils, abrasives such as wet sand, and wet clay. For the history of soap, see the entry thereon. Other detergent surfactants came from saponins and ox bile.
The detergent effects of certain synthetic surfactants were noted in 1913 by A. Reychler, a Belgian chemist. The first commercially available detergent taking advantage of those observations was Nekal,[1] sold in Germany in 1917, to alleviate World War I soap shortages. Detergents were mainly used in industry until World War II. By then new developments and the later conversion of USA aviation fuel plants to produce tetrapropylene, used in household detergents, caused a fast growth of household use, in the late 1940s.[2] In the late 1960s biological detergents, containing enzymes, better suited to dissolve protein stains, such as egg stains, were introduced in the USA by Procter & Gamble.[3]
See also
Laundry detergent
Cleavable detergent
Dispersant
External links
About.com: How Do Detergents Clean
US Patent 6472364: Detergent compositions or components
Components
Detergents, especially those made for use with water, often include different components such as:
Surfactants to 'cut' (Emulsify) grease and to wet surfaces
Abrasive to scour
Substances to modify pH or to affect performance or stability of other ingredients, acids for descaling or caustics to break down organic compounds
Water softeners to counteract the effect of "hardness" ions on other ingredients
oxidants (oxidizers) for bleaching, disinfection, and breaking down organic compounds
Non-surfactant materials that keep dirt in suspension
Enzymes to digest proteins, fats, or carbohydrates in stains or to modify fabric feel
Ingredients that modify the foaming properties of the cleaning surfactants, to either stabilize or counteract foam
Ingredients to increase or decrease the viscosity of the solution, or to keep other ingredients in solution, in a detergent supplied as a water solution or gel
Ingredients that affect aesthetic properties of the item to be cleaned, or of the detergent itself before or during use, such as optical brighteners, fabric softeners, colors, perfumes, etc.
Ingredients such as corrosion inhibitors to counteract damage to equipment with which the detergent is used
Ingredients to reduce harm or produce benefits to skin, when the detergent is used by bare hand on inanimate objects or used to clean skin
Preservatives to prevent spoilage of other ingredients
Sometimes materials more complicated than mere mixtures of compounds are said to be detergent. For instance, certain foods such as celery are said to be detergent or detersive to teeth.
Types
There are several factors that dictate what compositions of detergent should be used, including the material to be cleaned, the apparatus to be used, and tolerance for and type of dirt. For instance, all of the following are used to clean glass. The sheer range of different detergents that can be used demonstrates the importance of context in the selection of an appropriate glass-cleaning agent:
a chromic acid solution—to get glass very clean for certain precision-demanding purposes such as analytical chemistry
a high-foaming mixture of surfactants with low skin irritation—for hand-washing of dishware in a sink or dishpan
any of various non-foaming compositions—for dishware in a dishwashing machine
other surfactant-based compositions—for washing windows with a squeegee, followed by rinsing
an ammonia-containing solution—for cleaning windows with no additional dilution and no rinsing
ethanol or methanol in windshield washer fluid—used for a vehicle in motion, with no additional dilution
glass contact lens cleaning solutions, which must clean and disinfect without leaving any eye-harming material that would not be easily rinsed
Terminology
Sometimes the word detergent is used to distinguish a cleaning agent from soap. During the early development of non-soap surfactants as commercial cleaning products, the term syndet, short for synthetic detergent was promoted to indicate the distinction. The term never became popular and is incorrect, because most soap is itself synthesized (from glycerides). The term soapless soap also saw a brief vogue. There is no accurate term for detergents not made of soap other than soapless detergent or non-soap detergent.
The term detergent by itself is sometimes used to refer specifically to clothing detergent, as opposed to hand soap or other types of cleaning agents.
Plain water, if used for cleaning, is a detergent. Probably the most widely-used detergents other than water are soaps or mixtures composed chiefly of soaps. However, not all soaps have significant detergency and, although the words "detergent" and "soap" are sometimes used interchangeably, not every detergent is a soap.
The term detergent is sometimes used to refer to any surfactant, even when it is not used for cleaning. This terminology should be avoided as long as the term surfactant itself is available.
History
The earliest detergent substance was undoubtedly water; after that, oils, abrasives such as wet sand, and wet clay. For the history of soap, see the entry thereon. Other detergent surfactants came from saponins and ox bile.
The detergent effects of certain synthetic surfactants were noted in 1913 by A. Reychler, a Belgian chemist. The first commercially available detergent taking advantage of those observations was Nekal,[1] sold in Germany in 1917, to alleviate World War I soap shortages. Detergents were mainly used in industry until World War II. By then new developments and the later conversion of USA aviation fuel plants to produce tetrapropylene, used in household detergents, caused a fast growth of household use, in the late 1940s.[2] In the late 1960s biological detergents, containing enzymes, better suited to dissolve protein stains, such as egg stains, were introduced in the USA by Procter & Gamble.[3]
See also
Laundry detergent
Cleavable detergent
Dispersant
External links
About.com: How Do Detergents Clean
US Patent 6472364: Detergent compositions or components
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