Hard water is water that has a high mineral content (different from "soft water"). Hard water is formed when water seeps through limestone and limestone deposits composed largely of calcium and magnesium carbonate.
Harsh drinking water may have moderate health benefits, but can pose a critical problem in industrial settings, where water hardness is monitored to avoid costly damage to boilers, cooling towers, and other water-handling equipment. In domestic settings, hard water is often characterized by a lack of foam formation when soap is restless in water, and by the formation of limescale in kettles and water heaters. Wherever water hardness becomes a concern, water softening is usually used to reduce the adverse effects of hard water.
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Water hardness is determined by the concentration of multivalent cations in water. The multivalent cation is a positively charged metal complex with a charge greater than 1. Normally, the cation has a charge of 2. Common cations found in hard water include Ca 2 and Mg 2 . These ions enter the water supply by washing off the mineral in the aquifer. Minerals containing calcium are calcite and gypsum. Common magnesium minerals are dolomite (which also contains calcium). Rainwater and distilled water are soft, because they contain few ions.
The following equilibrium reaction explains the dissolution and formation of calcium carbonate:
- CaCO 3 (s) CO 2 (aq) H 2 O (l)? Ca 2 (aq) 2HCO 3 - (aq)
The reaction could be anywhere. Rain that contains dissolved carbon dioxide can react with calcium carbonate and carry calcium ions with it. Calcium carbonate can be re-stored as calcite because carbon dioxide is lost to the atmosphere, sometimes forming stalactites and stalagmites.
Calcium and magnesium ions can sometimes be removed with water softeners.
Temporary violence
Temporary violence is a type of water hardness caused by the presence of dissolved bicarbonate minerals (calcium bicarbonate and magnesium bicarbonate). When dissolved, these minerals produce calcium and magnesium cations (Ca 2 , Mg 2 ) and carbonate and bicarbonate anions (CO 3 2 - , HCO 3 - ). The presence of metal cations makes water hard. However, unlike the permanent hardness caused by sulfate and chloride compounds, this "temporary" hardness can be reduced either by boiling water, or by adding lime (calcium hydroxide) through a lime softening process. Boiling increases the carbonate formation of the bicarbonate and deposits the calcium carbonate out of the solution, leaving the water softer after cooling.
Permanent violence
Permanent hardness is the hardness (mineral content) that can not be removed by boiling. When this occurs, it is usually caused by the presence of calcium sulfate/calcium chloride and/or magnesium sulfate/magnesium chloride in water, which does not precipitate as the temperature increases. The ions that cause permanent water hardness can be removed using a water softener, or ion exchange column.
Total Permanent Hardness = Permanent Permanent Hardness of Permanent Magnesium Hardness
Maps Hard water
Effects
With hard water, soap solution forms a white precipitate (foam soap) rather than producing foam, since 2 ions destroy the properties of surfactants from the soap by forming a solid sediment (soap foam). The main component of the waste is calcium stearate, derived from sodium stearate, the main component of soap:
Such hardness can be defined as the capacity to consume sample soap water, or soap deposition capacity as a characteristic characteristic of water that prevents soap soap. Synthetic detergents do not form such puncture.
Hard water also forms deposits that clog pipes. These deposits, called "scales", consist mainly of calcium carbonate (CaCO 3 ), magnesium hydroxide (Mg (OH) 2 ), and calcium sulfate (CaSO 4 ). Calcium and magnesium carbonate tend to be stored as white solids on the inner surfaces of pipes and heat exchangers. This rainfall (the formation of insoluble solids) is mainly due to the thermal decomposition of bicarbonate ions but also occurs in cases where the carbonate ions are at saturation concentrations. The resulting scale buildup limits the flow of water in the pipes. In the boiler, the deposit damages heat flow into the water, reduces the heating efficiency and allows the metal boiler component to overheat. In pressurized systems, this heating can cause boiler failure. Damage caused by precipitated calcium carbonate varies in the form of crystals, for example, calcite or aragonite.
The presence of ions in electrolytes, in this case, hard water, can also cause galvanic corrosion, where one metal will rust when in contact with another metal type, when both are in contact with the electrolyte. The softening of hard water by ion exchange does not increase its corrosive properties per se . Similarly, where the plumbing is used, the softened water does not substantially increase the plumbo-solvency.
In the pool, hard water is manifested by a cloudy appearance, or cloudy (like milk) into the water. Calcium and magnesium hydroxide are both soluble in water. The solubility of hydroxides from alkaline earth metals containing calcium and magnesium (group 2 of the periodic table) increases the move down the column. This aqueous metal hydroxide solution absorbs carbon dioxide from the air, forming an insoluble carbonate, causing turbidity. This is often the result of too high pH (pH & gt; 7.6). Therefore, a common solution to this problem is, while maintaining chlorine concentrations at appropriate levels, to decrease the pH by adding hydrochloric acid, the optimum value is in the range of 7.2 to 7.6.
Softening
Often desired to soften hard water. Most detergents contain ingredients that counteract the effects of hard water on surfactants. For this reason, water softening is often unnecessary. Where softening is done, it is often recommended to soften only the water delivered to the domestic hot water system to prevent or delay inefficiency and damage due to scale formation in the water heater. The common method for water softening involves the use of ion exchange resins, which replace ions such as Ca 2 by twice the amount of monocations such as sodium or potassium ions.
Soda washing (sodium carbonate - Na 2 CO 3 ) is easy to obtain and has long been used as a water softener for domestic laundry, along with regular soaps or detergents.
Health considerations
The World Health Organization says that "there is no convincing evidence that water hardness causes adverse health effects on humans". In fact, the National Research Council of the United States has found that hard water actually serves as a dietary supplement for calcium and magnesium.
Some studies show a weak inverse association between water hardness and cardiovascular disease in men, to 170 mg of calcium carbonate per liter of water. The World Health Organization has reviewed the evidence and concluded that the data is inadequate to allow recommendations for levels of violence.
Recommendations have been made for the maximum and minimum levels of calcium (40-80 ppm) and magnesium (20-30 ppm) in drinking water, and total hardness is expressed as quantities of calcium and magnesium concentrations of 2-4 mmol/L.
Other studies have shown a weak correlation between cardiovascular health and water hardness.
Several studies correlate the use of domestic hard water with increased eczema in children.
The Soft Melting Eczema Experiment (SWET), a controlled, randomized multicenter test of an ion exchange softener to treat eczema in children, was performed in 2008. However, there was no significant difference in relieving symptoms found among children with access to home water softeners and those who do not have.
Measurement
Hardness can be measured by instrumental analysis. Total water hardness is the amount of molar concentration of Ca 2 and Mg 2 , in units of mole/L or mmol/L. Although water hardness usually only measures the total concentration of calcium and magnesium (two most commonly divalent metal ions), iron, aluminum, and manganese can also be present at higher levels in some locations. The presence of iron typically confers a brownish color (like rust) to calcification, not white (the color of most other compounds).
Water hardness is often not expressed as molar concentration, but in various units, such as the degree of generalized violence (dGH), German degree (Ã, Â ° dH), parts per million (ppm, mg/L, or American degree), grains per gallon (gpg), English degree (Ã, Â ° e, e, or Ã, Â ° Clark), or French degrees (Ã, Â ° FH, Ã, Â ° F or Ã, Â ° HF; lowercase f is used to prevent confusion with Fahrenheit degrees). The table below shows the conversion factors between the various units.
Alternative units represent equal masses of calcium oxide (CaO) or calcium carbonate (CaCO 3 ) which, when dissolved in units of pure water volume, will result in the same total Molar molar concentration. 2 and Ca 2 . Different conversion factors arise from the fact that the equivalent mass of calcium oxide and calcium carbonate are different, and that different units of mass and volume are used. The units are as follows:
- Parts per million (ppm) are usually defined as 1Ã, mg/L CaCO 3 (the definitions used below). This is equivalent to mg/L without the specified chemical compound, and for American degree .
- Seed per Gallon (gpg) is defined as 1 grain (64.8 mg) of calcium carbonate per US gallon (3.79 liters), or 17,118 ppm.
- a mmol/L is equivalent to 100.09 mg/L CaCO 3 or 40.08 mg/L Ca 2 .
- The generalized hardness level (dGH or 'German degree (Â ° dH, deutsche HÃÆ'¤rte ))' is defined as 10 mg/L CaO or 17,848 ppm.
- The title Clark (Ã, Â ° Clark) or English (Ã, Â ° e or e) is defined as one item (64.8Ã, mg) CaCO 3 per Imperial gallon (4.55 liters) of water, equivalent to 14,254 ppm.
- The French title (Ã, Â ° FH or Ã, Â ° f) is defined as 10Ã, mg/L CaCO 3 , equivalent to 10 ppm.
Hard/soft standings
Since this is the right mixture of minerals dissolved in water, along with the pH and water temperature, which determines violent behavior, the single-digit scales do not adequately describe violence. However, the United States Geological Survey uses the following classification into hard and soft water,
Sea water is considered very hard because the various salts dissolved. Usually the hardness of sea water is in the range of 6630 ppm. In contrast, fresh water has a hardness in the range of 15 - 375 ppm.
Index
Some indices are used to describe the behavior of calcium carbonate in water, oil, or gas mixtures.
Langelier saturation index (LSI)
The Langelier saturation index (sometimes the Langelier stability index) is a calculated number used to predict the stability of calcium carbonate water. This indicates whether the water will settle, dissolve, or be in equilibrium with calcium carbonate. In 1936, Wilfred Langelier developed a method to predict the pH in which water is saturated in calcium carbonate (called pH). LSI is expressed as the difference between actual pH system and pH saturation:
- LSI = pH (measured) - pH
- For LSI & gt; 0, the water is super saturated and tends to precipitate the CaCO scale layer 3 .
- For LSI = 0, water is saturated (in equilibrium) with CaCO 3 . The layer of CaCO scale 3 is not precipitated or dissolved.
- For LSI & lt; 0, water is below saturated and tends to dissolve solid CaCO 3 .
If the actual pH of water is below the calculated saturation pH, the negative LSI and water have very limited scaling potential. If the actual pH exceeds pH, LSI is positive, and becomes saturated with CaCO 3 , water has a tendency to form a scale. On the increase of positive index value, scaling potential increases.
In practice, water with an LSI between -0.5 and 0.5 will not show mineral dissolution properties or enhanced scales. Water with LSI below -0.5 tends to show an increase in water dissolution capability with LSI above 0.5 tends to show a significant increase in scale formation properties.
LSI is sensitive to temperature. LSI becomes more positive when water temperature increases. This has particular implications in situations where well water is used. The water temperature at the exit of the well was first significantly lower than the temperature inside the building served by the well or in the laboratory where the LSI measurements were made. This increase in temperature can cause scaling, especially in cases such as hot water heaters. In contrast, systems that reduce water temperatures will have fewer scales.
- Water Analysis:
- pH = 7.5
- TDS = 320Ã, mg/L
- Calcium = 150Ã, mg/L (or ppm) as CaCO 3
- Alkalinity = 34Ã, mg/L (or ppm) as CaCO 3
- The LSI formula:
- LSI = pH - pH
- pH = (9.3 A B) - (C D) where:
- A = (Enter 10 [TDS] - 1)/10 = 0.15
- B = -13.12 x Log 10 (Ã, Â ° C 273) 34.55 = 2.09 at 25 Ã, Â ° C and 1.09 at 82Ã, Â ° C
- C = Log 10 [Ca 2 as CaCO 3 ] - 0.4 = 1.78
- (Ca 2 as CaCO 3 is also called Calcium Hardness and is calculated as = 2.5 (Ca 2 ))
- D = Entrance 10 [alkalinity as CaCO 3 ] = 1.53
The Ryznar stability index (RSI) uses a scale thickness measurement database in a municipal water system to predict the water chemistry effect.
The Ryznar saturation index (RSI) is developed from empirical observations of corrosion rates and film formation in the mother armor. This is defined as:
- RSI = 2 pH - pH (measured)
- For 6.5 & lt; RSI & lt; 7 water is considered to be approximately at saturation equilibrium with calcium carbonate
- For RSI & gt; 8 waters below saturation and, therefore, will tend to dissolve the existing solid CaCO3
- For RSI & lt; 6.5 water tends to form a scale Puckorius Scaling Index (PSI)
The Puckorius Scaling Index (PSI) uses slightly different parameters to measure the relationship between the water saturation state and the number of stored limestone.
Other indexes
Other indices include the Larson-Skold Index, the Stiff-Davis Index, and the Oddo-Tomson Index.
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Regional information
The local water supply hardness depends on the water source. Water in the river that flows over volcanic rocks (frozen) will become soft, while water from drill holes drilled into porous rocks is usually very hard.
In Australia
Analysis of water hardness in major Australian cities by the Australian Water Association shows the range from very soft (Melbourne) to hard (Adelaide). Total Hardness levels of calcium carbonate in ppm are: Canberra: 40; Melbourne: 10-26; Sydney: 39,4-60,1; Perth: 29-226; Brisbane: 100; Adelaide: 134-148; Hobart: 5,8-34,4; Darwin: 31.
In Canada
The Prairie Province (mainly Saskatchewan and Manitoba) contains high amounts of calcium and magnesium, often as a water-soluble dolomite, which contains high concentrations of carbon trapped dioxide from the last glacial. In this part of Canada, total hardness in ppm equivalent of calcium carbonate often exceeds 200 ppm, if ground water is the only source of potable water. The west coast, on the other hand, has incredibly soft water, derived mainly from mountain lakes fed by glaciers and snowmelt.
Some typical values ​​are: Montreal 116 ppm, Calgary 165 ppm, Regina 496 ppm, Saskatoon 160-180 ppm, Winnipeg 77 ppm, Toronto 121 ppm, Vancouver & lt; 3 ppm, Charlottetown, PEI 140-150 ppm, Waterloo Region 400 ppm, Guelph 460 ppm, Saint John (West) 160-200 ppm.
In England and Wales
Information from the British Drinking Water Inspectorate shows that drinking water in the UK is generally considered 'very hard', with most of Britain, especially east of the line between Severn and Tees estuaries, showing above 200 ppm for equivalent calcium carbonate. Water in London, for example, is mostly obtained from the Thames and Lea Rivers, both of which earn a significant proportion of their dry weather flow from springs in limestone and lime aquifers. Wales, Devon, Cornwall and parts of North-West England are softer water areas, and range from 0 to 200 ppm. In the brewing industry in England and Wales, water is often deliberately hardened with gypsum in the Burtonization process.
Generally water is very difficult in urban areas in the UK where soft water sources are not available. A number of cities built a source of water supply in the 18th century when the industrial revolution and urban population increased. Manchester is a famous city in North West England and its rich company built a number of reservoirs in Thirlmere and Haweswater in the Lake District in the north. There is no lime or lime exposure in their upstream and consequently the water in Manchester is rated as 'very soft'. Similarly, tap water in Birmingham is also soft because it is sourced from the Elan Valley Valley in Wales.
In Ireland
The EPA has published a standard handbook for interpreting water quality in Ireland where the definition of water hardness is given. In this section, references to original EU documentation are provided, which do not set limits for violence. In turn, this handbook also does not provide "Suggested or Compulsory Boundaries" for Violence. The handbooks do not show that above the midpoint of the range defined as "Moderately Enough", the effect is seen increasingly: "The major drawback of hard water is that they neutralize the power of soap soap.... and, more importantly, that they can cause blockage of the pipe and greatly reduces the efficiency of the boiler due to scale formation.This effect will increase when the hardness rises to and exceeds 200 mg/l CaCO3. "
In the United States
Data sets from the United States found that about half of the tested water stations had more than 120 m per liter of calcium carbonate equivalent, placing them in the "hard" or "very hard" category. The other half is classified as soft or hard enough. More than 85% of homes in America have hard water. The softest water occurs in parts of New England, South Atlantic-Gulf, Pacific Northwest, and Hawaii. Pretty hard water is common in many rivers in Tennessee, Great Lakes and Alaska. Hard and very hard water is found in several rivers in most parts of the country. The loudest waters (over 1,000 ppm) are in rivers in Texas, New Mexico, Kansas, Arizona, Utah, parts of Colorado, southern Nevada, and southern California.
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See also
- Carbonate violence
- Fouling
- dGH
- Limestone
- Water softener
- Water quality
- Water treatment
- Water purification
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References
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External links
- "Langelier Saturation Index (LSI) Calculato". Akzo Nobel . Retrieved August 29 2017
- "Water hardness modifiers unit" . Retrieved August 29 2017
- "UK Hard Water Map" . Retrieved 12 Jan 2018
Source of the article : Wikipedia
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