calcium and water in boilers

Calcium - Ca
Chemical properties of calcium - Health effects of calcium - Environmental effects of calcium
Atomic number 20
Atomic mass 40.08 g.mol -1
Electronegativity according to Pauling 1.0
Mass volume 1.6 g.cm-3 at 20°C
Melting point 840 °C
Boiling point 1484 °C
Vanderwaals radius 0.197 nm
Ionic radius 0.099 nm
Isotopes 10
Electronic configuration [ Ar ] 4s2
Energy of first ionisation 589.6 kJ.mol -1
Energy of second ionisation 1145 kJ.mol -1
Standard potential - 2.87 V
Discovered Sir Humphrey Davy in 1808


Calcium
The chemical element Calcium (Ca), atomic number 20, is the fifth element and the third most abundant metal in the earth’s crust. The metal is trimorphic, harder than sodium, but softer than aluminium. A well as beryllium and aluminium, and unlike the alkaline metals, it doesn’t cause skin-burns. It is less chemically reactive than alkaline metals and than the other alkaline-earth metals.
Calcium ions solved in water form deposits in pipes and boilers and when the water is hard, that is, when it contains too much calcium or magnesium. This can be avoided with the water softeners. In the industry, metallic calcium is separated from the melted calcium chloride by electrolysis. This is obtained by treatment of carbonated minerals with chlorhydric acid, or like a sub product of the carbonates Solvay process.
In contact with air, calcium develops an oxide and nitride coating, which protects it from further corrosion. It burns in the air at a high temperature to produce nitride.
The commercially produced metal reacts easily with water and acids and it produces hydrogen which contains remarkable amounts of ammonia and hydrocarbides as impurities.
Applications
The metal is used in aluminium alloys for bearings, as a helper in the bismuth removal form lead, as well as in controlling graphitic carbon in melted iron. It is also used as a deoxidizer in the manufacture of many steels; as a reducing agent in the preparation of metals as chromium, thorium, zirconium and uranium, and as separating material for gaseous mixtures of nitrogen and argon. Calcium is an alloying used in the production of alluminium, beryllium, copper, lead and magnesium alloys. It is also used in making cements and mortar that are used in builldings.
The calcium oxide, CaO, is produced by thermal decomposition of carbonated minerals in furnaces, applying a continuous bed process. The oxide is used in high intensity light arcs (lime light) for its unusual spectral characteristics and as dehydrating industrial agent. The metallurgic industry extensively uses the oxide during the reduction of ferrous alloys.
The calcium oxide, Ca(OH)2, has many applications in which the hydroxyl ion is necessary. In the process of calcium hydroxide quenching, the volume of blown out lime [Ca(OH)2] expends to double the initial quantity of quick lime (CaO), fact that makes it useful to break down rocks or wood.
The quick lime is an excellent absorbent for the carbon dioxide, because it produces carbonate, which is very insoluble.
The calcium silicate, CaSi, prepared in an electric oven from lime, silica and reducing carbonated agents, is useful as a steel-deoxidizing agent. Calcium carbide, CaC2, is produces when heating up a mixture of lime and carbon at 3000ºC in an electric oven and it is an acetylate which produces acetylene by hydrolysis. The acetylene is the base material of a great number of important chemicals for the organic industrial chemistry.
The pure calcium carbonate occurs in two crystalline forms: calcite, hexagonal shaped, which possesses birrefringent properties, and aragonite, rhombohedric. The natural carbonates are the most abundant calcium minerals. The Iceland spar and the calcite are essentially pure carbonate forms, whilst the marble is impure and much more compact, reason why it can be polished. It’s very demanded as construction material. Although the calcium carbonate is very little soluble in water, it is quite soluble if the water contains dissolved carbon dioxide, for in these solutions it forms bicarbonate when dissolving. This fact explains the cave formation, where the lime stone deposits have been in contact with acid waters.
The calcium halogenures include phosphorescent fluoride, which is the calcium compound more abundant and with important applications in spectroscopy. The calcium chloride possesses, in the anhydric form, great deliquescence capacity, which makes it useful as industrial dehydrating agent and as sand whirl control factor in roads. Calcium hypochlorite (whitening powder) is produced in the industry when passing chlorine through a lime solution, and has been used as a whitening agent and as water purifier.
The dehydrated calcium sulphate is the mineral gypsum, constitutes the bigger portion of Portland concrete, and has been used to reduce the alkalinity of soils. Heating gypsum at high temperatures produces a calcium sulphate hemihydrate, which is sold with the commercial name of Parisian stucco.
Calcium in the environment
Calcium is the fifth element and the third most abundant metal in the earth’s crust. The calcium compounds account for 3.64% of the earth’s crust. The distribution of calcium is very wide; it is found in almost every terrestrial area in the world. This element is essential for the life of plants and animals, for it is present in the animal’s skeleton, in tooth, in the egg’s shell, in the coral and in many soils. Seawater contains 0.15% of calcium chloride.
Calcium cannot be found alone in nature. Calcium is found mostly as limestone, gypsum and fluorite. Stalagmites and stalactites contain calcium carbonate.
Calcium is always present in every plant, as it is essential for its growth. It is contained in the soft tissue, in fluids within the tissue and in the structure of every animal’s skeleton. The vertebrate’s bones contain calcium in the form of calcium fluoride, calcium carbonate and calcium phosphate.

Health effects of calcium
Calcium is the most abundand metal in the human body: is the main constituent of bones and theets and it has keys metabolic functions.
Calcium is sometimes referred to as lime. It is most commonly found in milk and milk products, but also in vegetables, nuts and beans. It is an essential component for the preservation of the human skeleton and teeth. It also assists the functions of nerves and muscles. The use of more than 2,5 grams of calcium per day without a medical necessity can lead to the development of kidney stones and sclerosis of kidneys and blood vessels.

A lack of calcium is one of the main causes of osteoporosis. Osteoporosis is a disease in which the bones become extremely porous, are subject to fracture, and heal slowly, occurring especially in women following menopause and often leading to curvature of the spine from vertebral collapse.
Unlike most of the people think, there is an intense biological activity inside our bones. They are being renewed constantly by new tissue replacing the old one. During childhood and adolescence, there’s more production of new tissue than destruction of the old one, but at some point, somewhere around the 30 or 35 years of age, the process is inverted and we start to loose more tissue than what we can replace. In women the process is accelerated after the menopause (he period marked by the natural and permanent cessation of menstruation, occurring usually between the ages of 45 and 55); this is because their bodies stop producing the hormone known as estrogen, one of which functions is to preserve the osseous mass.
Evidence suggests that we need a daily intake of 1,000 milligrams of calcium in order to preserve the osseous mass in normal conditions. This is both for man and pre-menopausic women. The recommended daily intake rises to 1,500 for menopausic woman.
The main calcium sources are the dairy products, but also nuts, some green vegetables like spinach, and cauliflower, beans, lentils…
Calcium works together with magnesium to create new osseous mass. Calcium should be taken together with magnesium in a 2:1 rate, that is to say, if you ingest 1000 mg of calcium, you should also ingest 500 mg of magnesium. Some magnesium sources in the diet are seafood, whole-grains, nuts, beans, wheat oats, seeds and green vegetables.
Other important measures to prevent osteoporosis are:
• Doing regular exercise (at least three times a week)
• Taking adequate amounts of manganese, folic acid, vitamin B6, vitamin B12, omega 3 (it aids calcium absorption and stimulates new osseous mass production) and vitamin D (it aids calcium absorption in the small intestine).
• Not abusing of sugar, saturated grease and animal proteins
• Not abusing of alcohol, caffeine, nor gaseous drinks
• Not smoking
Other triggers for osteoporosis are the hereditary factor and the stress.
Environmental effects of calcium
Calcium phosphide is very toxic to aquatic organisms.

Calcium (Ca) and water
Calcium and water: reaction mechanisms, environmental impact and health effects
Calcium occurs in water naturally. Seawater contains approximately 400 ppm calcium. One of the main reasons for the abundance of calcium in water is its natural occurrence in the earth's crust. Calcium is also a constituent of coral. Rivers generally contain 1-2 ppm calcium, but in lime areas rivers may contains calcium concentrations as high as 100 ppm.
Examples of calcium concentrations in water organisms: seaweed luctuca 800-6500 ppm (moist mass), oysters approximately 1500 ppm (dry mass).
In a watery solution calcium is mainly present as Ca2+ (aq), but it may also occur as CaOH+ (aq) or Ca(OH)2 (aq), or as CaSO4 in seawater.
Calcium is an important determinant of water harness, and it also functions as a pH stabilizer, because of its buffering qualities. Calcium also gives water a better taste.
In what way and in what form does calcium react with water?

Contrary to magnesium placed directly above calcium in the periodic chart, elementary calcium reacts with water at room temperature, according to the following reaction mechanism:
Ca (s) + 2H2O (g) -> Ca(OH)2 (aq) + H2 (g)

This reaction forms calcium hydroxide that dissolves in water as a soda, and hydrogen gas.
Other important calcium reaction mechanisms are erosion reactions. These usually occur when carbon dioxide is present. Under normal conditions calcium carbonate is water insoluble. When carbon dioxide is present carbonic acid is formed, affecting calcium compounds.
The reaction mechanism for carbon weathering is:

H2O + CO2 -> H2CO3 and CaCO3 + H2CO3 -> Ca(HCO3)2

And the total reaction mechanism:

CaCO3 (s) + CO2 (g) + 2H2O (l) -> Ca2+ (aq) + 2 HCO3- (aq)

The product is calcium hydrogen carbonate.
Solubility of calcium and calcium compounds

Elementary calcium reacts with water. Calcium compounds are more or less water soluble. Calcium carbonate has a solubility of 14 mg/L, which is multiplied by a factor five in presence of carbon dioxide. Calcium phosphate solubility is 20 mg/L, and that of calcium fluoride is 16 mg/L. Calcium chromate solubility is 170 g/L, and at 0oC calcium hypo chlorate solubility is 218 g/L. Solubility of other calcium compounds lies between the levels of these examples, for example calcium arsenate 140 mg/L, calcium hydroxide 1.3 g/L and calcium sulphate 2.7-8.8 g/L.
Why is calcium present in water?

Calcium is naturally present in water. It may dissolve from rocks such as limestone, marble, calcite, dolomite, gypsum, fluorite and apatite. Calcium is a determinant of water hardness, because it can be found in water as Ca2+ ions. Magnesium is the other hardness determinant.
Calcium is present in various construction materials, such as cement, brick lime and concrete. It is present in batteries, and is applied in plaster as calcium sulphate. The metal is applies for zirconium and thorium production. In steal industries calcium is applied as a blotter, and is added to aluminium, copper and lead alloys. Calcium can extract sulphur dioxide from industrial exhaust, and neutralize sulphuric acids before discharge. Other examples of calcium applications are calcium hypo chloride as bleach and for disinfection, calcium phosphate in glass and porcelain industries, calcium polysulphide and hydroxide as flocculants in wastewater treatment, and calcium fluoride as turbidity agent in enamel industries, in UV-spectroscopy, and as a raw material for fluid acid production. Calcium may also be applied for removal of carbon and sulphur from iron and iron alloys, and for dewatering oil. Limestone is applied as a paper filler, causing paper to colour whiter, and in plastics to improve stability.
Calcium often positively affects soil quality and various compounds are applied as a fertilizer. For example, CaCl2- or Ca(NO)3 solutions are applied in horticulture. Calcium oxide is a dehydrating molluscicide.

What are the environmental effects of calcium in water?
Calcium is a dietary requirement for all organisms apart from some insects and bacteria. Calcium carbonate is a building stone of skeletons of most marine organisms, and eye lenses. Calcium phosphate is required for bone structure and teeth structure of terrestrial organisms. Plants mainly contain calcium oxalate. Calcium storage in plants is about 1% of dry mass.
Calcium is largely responsible for water hardness, and may negatively influence toxicity of other compounds. Elements such as copper, lead and zinc are much more toxic in soft water.
In limed soils calcium may immobilize iron. This may cause iron shortages, even when plenty of iron is present in the soil.
Water hardness influences aquatic organisms concerning metal toxicity. In softer water membrane permeability in the gills is increased. Calcium also competes with other ions for binding spots in the gills. Consequently, hard water better protects fishes from direct metal uptake. pH values of 4.5-4.9 may harm salmon eggs and grown salmons, when the calcium, sodium and chlorine content is low.
Various calcium compounds may be toxic. The LD50 of rats for calcium arsenite is 20 mg/ kg body weight. Calcium carbide forms flammable ethyn when it comes in contact with water and is therefore considered hazardous.
Some environmental effects of water hardness include hardening of domestic equipment, because high temperatures cause carbonate hardness. This may dramatically decrease the lifespan of equipment, and causes an increase of domestic waste. Calcium carbonate interacts with detergents and cleansing agents. Complex formation causes a decrease in detergent efficiency, resulting in requirement for increased detergent application and softener purchases (see also magnesium and water).
Softening is often carried out by means of ion exchangers. These must be regenerates with kitchen salt, and therefore burden wastewater.
There are six stable calcium isotopes. Today, we know of eight instable calcium isotopes. 45Ca is highly radioactive and toxic.

What are the health effects of calcium in water?

Calcium is a dietary mineral that is present in the human body in amounts of about 1.2 kg. No other element is more abundant in the body. Calcium phosphate is a supporting substance, and it causes bone and tooth growth, together with vitamin D. Calcium is also present in muscle tissue and in the blood. It is required for cell membrane development and cell division, and it is partially responsible for muscle contractions and blood clotting. Calcium regulates membrane activity, it assists nerve impulse transfer and hormone release, stabilizes the pH of the body, and is an essential part of conception. In order to stimulate these body functions a daily intake of about 1000 mg of calcium is recommended for adults. This may be achieved by consuming dairy, grains and green vegetables.
Calcium carbonate works as a stomach acid remedy and may be applied to resolve digestive failure. Calcium lactate may aid the body during periods of calcium deficiency, and calcium chloride is a diuretic.
Hard water may assist in strengthening bones and teeth because of its high calcium concentration. It may also decrease the risk of heart conditions. Drinking water hardness must be above 8.4 odH. Caclium carbonate has a positive effect on lead water pipes, because it forms a protective lead(II)carbonate coating. This prevents lead from dissolving in drinking water, and thereby prevents it from entering the human body.
When one takes up large amounts of calcium this may negatively influence human health. The lethal dose of oral uptake is about 5-50 mg/ kg body weight. Metallic calcium corrodes the skin when it comes in contact with skin, eyes and mucous membranes.

Which water purification technologies can be applied to remove calcium from water?

Removing calcium and magnesium ions from water is carried out by water softeners. These are ion exchangers that usually contain Na+ ions, which are released and substituted by Ca2+ and Mg2+ ions.
Calcium compounds may be applied for wastewater treatment. Drinking water pH and hardness may be altered by means of calcium carbonate and calcium hydroxide.