Calciumis the chemical element with the symbol Ca

Calciumis the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth'scrust. Calcium is also the fifth-most-abundant dissolved ion in seawater by both molarity and mass, after sodium, chloride,magnesium, and sulfate.Sony VAIO VPCW218JC/L Battery

Calcium is essential for living organisms, in particular in cell physiology, where movement of the calcium ion Ca2+ into and out of the cytoplasm functions as a signal for many cellular processes. As a major material used in mineralization of bones and shells, calcium is the most abundant metal by mass in many animals.Sony VAIO VPCW218JC/P Battery

In chemical terms, calcium is reactive and soft for a metal (though harder than lead, it can be cut with a knife with difficulty). It is a silvery metallic element that must be extracted byelectrolysis from a fused salt like calcium chloride. Once produced, it rapidly forms a gray-white oxide and nitride coating when exposed to air. Sony VAIO VPCW218JC/T Battery

In bulk-form (typically as chips or "turnings"), the metal is somewhat difficult to ignite, more so even than magnesium chips; but, when lit, the metal burns in air with a brilliant high-intensity orange-red light. Calcium metal reacts with water, evolving hydrogen gas at a rate rapid enough to be noticeable, but not fast enough at room temperature to generate much heat.Sony VAIO VPCW218JC/W Battery

In powdered form, however, the reaction with water is extremely rapid, as the increased surface area of the powder accelerates the reaction with the water. Part of the slowness of the calcium-water reaction results from the metal being partly protected by insoluble white calcium hydroxide. In water solutions of acids, where this salt is soluble, calcium reacts vigorously.Sony VAIO VPCW219AJ/L Battery

Calcium, with a density of 1.55 g/cm3, is the lightest of the alkaline earth metals; magnesium (specific gravity 1.74) and beryllium (1.84) are more dense, although lighter in atomic mass. From strontium onward, the alkali earth metals become more dense with increasing atomic mass.Sony VAIO VPCW219AJ/P Battery

It has two allotropes.

Calcium has a higher electrical resistivity than copper or aluminium, yet weight-for-weight, due to its much lower density, it is a rather better conductor than either. However, its use in terrestrial applications is usually limited by its high reactivity with air.Sony VAIO VPCW219AJ/W Battery

Calcium salts are colorless from any contribution of the calcium, and ionic solutions of calcium (Ca2+) are colorless as well. As with magnesium salts and other alkaline earth metal salts, calcium salts are often quite soluble in water. Notable exceptions include thehydroxide, the sulfate (unusual for sulfate salts), the carbonate and the phosphates. Sony VAIO VPCW21AAJ Battery

With the exception of the sulfate, even the insoluble ones listed are in general more soluble than itstransition metal counterparts. When in solution, the calcium ion to the human taste varies remarkably, being reported as mildly salty, sour, "mineral like" or even "soothing." Sony VAIO VPCW21AKJ Battery

It is apparent that many animals can taste, or develop a taste, for calcium, and use this sense to detect the mineral in salt licks or other sources.In human nutrition, soluble calcium salts may be added to tart juices without much effect to the average palate.Sony VAIO VPCW21AVJ Battery

Calcium is the fifth-most-abundant element by mass in the human body, where it is a common cellular ionic messenger with many functions, and serves also as a structural element in bone. It is the relatively high-atomic-number calcium in the skeleton that causes bone to be radio-opaque. Sony VAIO VPCY115FGS Battery

Of the human body's solid components after drying and burning of organics (as for example, after cremation), about a third of the total "mineral" mass remaining, is the approximately one kilogram of calcium that composes the average skeleton (the remainder being mostly phosphorus and oxygen).Sony VAIO VPCY115FX/BI Battery

H and K lines

Visible spectra of many stars, including the Sun, exhibit strong absorption lines of singly ionized calcium. Prominent among these are the H-line at 3968.5 Å and the K line at 3933.7 Å of singly ionized calcium, or Ca II. For the Sun and stars with low temperatures, the prominence of the H and K lines can be an indication of strong magnetic activity in thechromosphere. Sony VAIO VPCY115FXBI Battery

Measurement of periodic variations of these active regions can also be used to deduce the rotation periods of these stars.

Compounds

Calcium, combined with phosphate to form hydroxylapatite, is the mineral portion of human and animal bones and teeth. The mineral portion of some corals can also be transformed into hydroxylapatite.Sony VAIO VPCY118EC Battery

Calcium hydroxide (slaked lime) is used in many chemical refinery processes and is made by heating limestone at high temperature (above 825 °C) and then carefully adding water to it. When lime is mixed with sand, it hardens into a mortarand is turned into plaster by carbon dioxide uptake. Mixed with other compounds, lime forms an important part of Portland cement.Sony VAIO VPCY118GX/BI Battery

Calcium carbonate (CaCO3) is one of the common compounds of calcium. It is heated to form quicklime (CaO), which is then added to water (H2O). This forms another material known as slaked lime (Ca(OH)2), which is an inexpensive base material used throughout the chemical industry. Chalk, marble, and limestone are all forms of calcium carbonate.Sony VAIO VPCY119FJ/S Battery

When water percolates through limestone or other soluble carbonate rocks, it partially dissolves the rock and causes cave formation and characteristic stalactites and stalagmites and also forms hard water. Other important calcium compounds arecalcium nitrate, calcium sulfide, calcium chloride, calcium carbide, calcium cyanamide and calcium hypochlorite.Sony VAIO VPCY11AFJ Battery

A few calcium compounds in the oxidation state +1 have also been investigated recently.

Nucleosynthesis

Calcium-40 is created in extremely large and hot (over 2.5 × 109 K) stars, as part of the silicon-burning process in whichalpha particles are added to silicon atoms. The process fuses an atom of argon and an atom of helium:Sony VAIO VPCY11AGJ Battery

36Ar + 4He = 40Ca

Calcium has four stable isotopes (40Ca, 42Ca, 43Ca and 44Ca), plus two more isotopes (46Ca and 48Ca) that have such long half-lives that for all practical purposes they also can be considered stable. The 20% range in relative mass among naturally occurring calcium isotopes is greater than for any element except hydrogen and helium.Sony VAIO VPCY11AHJ Battery

Calcium also has acosmogenic isotope, radioactive 41Ca, which has a half-life of 103,000 years. Unlike cosmogenic isotopes that are produced in the atmosphere, 41Ca is produced by neutron activation of 40Ca. Most of its production is in the upper metre or so of the soil column, where the cosmogenic neutron flux is still sufficiently strong. Sony VAIO VPCY11AVJ Battery

41Ca has received much attention in stellar studies because it decays to 41K, a critical indicator of solar-system anomalies.

Ninety-seven percent of naturally occurring calcium is in the form of 40Ca. 40Ca is one of the daughter products of 40K decay, along with 40Ar. Sony VAIO VPCY11M1E/S Battery

While K-Ar dating has been used extensively in the geological sciences, the prevalence of 40Ca in nature has impeded its use in dating. Techniques using mass spectrometry and a double spike isotope dilution have been used for K-Ca age dating.

The most abundant isotope, 40Ca, has a nucleus of 20 protons and 20 neutrons. Sony VAIO VPCY11S1E Battery

This is the heaviest stable isotope of any element that has equal numbers of protons and neutrons. In supernova explosions, calcium is formed from the reaction of carbon with various numbers of alpha particles (helium nuclei), until the most common calcium isotope (containing 10 helium nuclei) has been synthesized.Sony VAIO VPCY11V9E/S Battery

Isotope fractionation

As with the isotopes of other elements, a variety of processes fractionate, or alter the relative abundance of, calcium isotopes. The best studied of these processes is the mass dependent fractionation of calcium isotopes that accompanies the precipitation of calcium minerals, such as calcite, aragonite and apatite, from solution. Sony VAIO VPCY218EC/BI Battery

Isotopically light calcium is preferentially incorporated into minerals, leaving the solution from which the mineral precipitated enriched in isotopically heavy calcium. At room temperature the magnitude of this fractionation is roughly 0.25‰ (0.025%) per atomic mass unit (AMU). Sony VAIO VPCY218EC/G Battery

Mass-dependent differences in calcium isotope composition conventionally are expressed the ratio of two isotopes (usually 44Ca/40Ca) in a sample compared to the same ratio in a standard reference material. 44Ca/40Ca varies by about 1% among common earth materials.Sony VAIO VPCY218EC/L Battery

Calcium isotope fractionation during mineral formation has led to several applications of calcium isotopes. In particular, the 1997 observation by Skulan and DePaolo that calcium minerals are isotopically lighter than the solutions from which the minerals precipitate is the basis of analogous applications in medicine and in paleooceanography. Sony VAIO VPCY218EC/P Battery

In animals with skeletons mineralized with calcium the calcium isotopic composition of soft tissues reflects the relative rate of formation and dissolution of skeletal mineral. In humans changes in the calcium isotopic composition of urine have been shown to be related to changes in bone mineral balance. Sony VAIO VPCY21S1E/L Battery

When the rate of bone formation exceeds the rate of bone resorption, soft tissue 44Ca/40Ca rises. Soft tissue 44Ca/40Ca falls when bone resorption exceeds bone formation. Because of this relationship, calcium isotopic measurements of urine or blood may be useful in the early detection of metabolic bone diseases likeosteoporosis.Sony VAIO VPCY21S1E/P Battery

A similar system exists in the ocean, where seawater 44Ca/40Ca tends to rise when the rate of removal of Ca2+ from seawater by mineral precipitation exceeds the input of new calcium into the ocean, and fall when calcium input exceeds mineral precipitation.Sony VAIO VPCY21S1E/SI Battery

It follows that rising 44Ca/40Ca corresponds to falling seawater Ca2+concentration, and falling 44Ca/40Ca corresponds to rising seawater Ca2+ concentration. In 1997 Skulan and DePaolo presented the first evidence of change in seawater44Ca/40Ca over geologic time, along with a theoretical explanation of these changes. Sony VAIO VPCZ110 Battery

More recent papers have confirmed this observation, demonstrating that seawater Ca2+ concentration is not constant, and that the ocean probably never is in “steady state” with respect to its calcium input and output. This has important climatological implications, as the marine calcium cycle is closely tied to the carbon cycle (see below).Sony VAIO VPCZ110GB/BI Battery

Geochemical cycling

Calcium provides an important link between tectonics, climate and the carbon cycle. In the simplest terms, uplift of mountains exposes Ca-bearing rocks to chemical weathering and releases Ca2+ into surface water. This Ca2+ eventually is transported to the ocean where it reacts with dissolved CO2 to form limestone.Sony VAIO VPCZ112GD/S Battery

Some of this limestone settles to the sea floor where it is incorporated into new rocks. Dissolved CO2, along with carbonate and bicarbonate ions, are referred to as dissolved inorganic carbon (DIC).

The actual reaction is more complicated and involves the bicarbonate ion (HCO3-) that forms when CO2 reacts with water at seawaterpH:Sony VAIO VPCZ112GX/S Battery

Ca2+ + 2HCO?
3 ? CaCO3 (limestone) + CO2 + H2O

Note that at ocean pH most of the CO2 produced in this reaction is immediately converted back into HCO3?. The reaction results in a net transport of one molecule of CO2 from the ocean/atmosphere into the lithosphere.Sony VAIO VPCZ114GX/S Battery

The result is that each Ca2+ ion released by chemical weathering ultimately removes one CO2 molecule from the surficial system (atmosphere, ocean, soils and living organisms), storing it in carbonate rocks where it is likely to stay for hundreds of millions of years. Sony VAIO VPCZ115 Battery

The weathering of calcium from rocks thus scrubs CO2 from the ocean and atmosphere, exerting a strong long-term effect on climate.[14] Analogous cycles involving magnesium, and to a much smaller extent strontium and barium, have the same effect.Sony VAIO VPCZ115FC/B Battery

As the weathering of limestone (CaCO3) liberates equimolar amounts of Ca2+ and CO2, it has no net effect on the CO2 content of the atmosphere and ocean. The weathering of silicate rocks like granite, on the other hand, is a net CO2 sink because it produces abundant Ca2+ but very little CO2.Sony VAIO VPCZ115FC/S Battery

Calcium (from Latin calx, genitive calcis, meaning "lime") was known as early as the first century when the Ancient Romans prepared lime as calcium oxide. Literature dating back to 975 AD notes that plaster of paris (calcium sulfate), is useful for setting broken bones. Sony VAIO VPCZ116 Battery

It was not isolated until 1808 in England whenSir Humphry Davy electrolyzed a mixture of lime and mercuric oxide. Davy was trying to isolate calcium; when he heard that Swedish chemist Jöns Jakob Berzeliusand Pontin prepared calcium amalgam by electrolyzing lime in mercury, he tried it himself. Sony VAIO VPCZ116GX/S Battery

He worked with electrolysis throughout his life and also discovered/isolated sodium, potassium, magnesium, boron and barium. Calcium metal was not available in large scale until the beginning of the 20th century.

Occurrence

Calcium is not naturally found in its elemental state. Sony VAIO VPCZ117 Battery

Calcium occurs most commonly in sedimentary rocks in the minerals calcite, dolomite and gypsum. It also occurs in igneous and metamorphic rocks chiefly in the silicate minerals: plagioclases, amphiboles, pyroxenes and garnets.

Applications

Calcium is used[17]

• as a reducing agent in the extraction of other metals, such as uranium, zirconium, and thorium.Sony VAIO VPCZ117FC/B Battery
• as a deoxidizer, desulfurizer, or decarbonizer for various ferrous and nonferrous alloys.
• as an alloying agent used in the production of aluminium, beryllium, copper, lead, and magnesium alloys.
• in the making of cements and mortars to be used in construction.
• in the making of cheese, where calcium ions influence the activity of rennin in bringing about the coagulation of milk.Sony VAIO VPCZ118 Battery

Calcium compounds

• Calcium carbonate (CaCO3) is used in manufacturing cement and mortar, lime, limestone (usually used in the steel industry) and aids in production in the glass industry. It also has chemical and optical uses as mineral specimens in toothpastes, for example.Sony VAIO VPCZ118GC/B Battery
• Calcium hydroxide solution (Ca(OH)2) (also known as limewater) is used to detect the presence of carbon dioxide by being bubbled through a solution. It turns cloudy where CO2 is present.
• Calcium arsenate (Ca3(AsO4)2) is used in insecticides.Sony VAIO VPCZ118GX/S Battery
• Calcium carbide (CaC2) is used to make acetylene gas (for use in acetylene torches for welding) and in the manufacturing of plastics.
• Calcium chloride (CaCl2) is used in ice removal and dust control on dirt roads, in conditioner for concrete, as an additive in canned tomatoes, and to provide body for automobile tires.Sony VAIO VPCZ119 Battery
• Calcium cyclamate (Ca(C6H11NHSO3)2) was used as a sweetening agent but is no longer permitted for use because of suspected cancer-causing properties.
• Calcium gluconate (Ca(C6H11O7)2) is used as a food additive and in vitamin pills.
• Calcium hypochlorite (Ca(OCl)2) is used as a swimming pool disinfectant, as a bleaching agent, as an ingredient in deodorant, and in algaecide and fungicide.Sony VAIO VPCZ119FJ/S Battery
• Calcium permanganate (Ca(MnO4)2) is used in liquid rocket propellant, textile production, as a water sterilizing agent and in dental procedures.
• Calcium phosphate (Ca3(PO4)2) is used as a supplement for animal feed, fertilizer, in commercial production for dough and yeast products, in the manufacture ofglass, and in dental products.Sony VAIO VPCZ119GC/X Battery
• Calcium phosphide (Ca3P2) is used in fireworks, rodenticide, torpedoes and flares.
• Calcium stearate (Ca(C18H35O2)2) is used in the manufacture of wax crayons, cements, certain kinds of plastics and cosmetics, as a food additive, in the production of water resistant materials and in the production of paints.Sony VAIO VPCZ119L Battery
• Calcium sulfate (CaSO4·2H2O) is used as common blackboard chalk, as well as, in its hemihydrate form better known as Plaster of Paris.
• Calcium tungstate (CaWO4) is used in luminous paints, fluorescent lights and in X-ray studies.Sony VAIO VPCZ119R/B Battery
• Hydroxylapatite (Ca5(PO4)3(OH), but is usually written Ca10(PO4)6(OH)2) makes up seventy percent of bone. Also carbonated-calcium deficient hydroxylapatite is the main mineral of which dental enamel and dentin are comprised.Sony VAIO VPCZ119R/S Battery

Nutrition

Calcium is an important component of a healthy diet and a mineral necessary for life. The National Osteoporosis Foundationsays, "Calcium plays an important role in building stronger, denser bones early in life and keeping bones strong and healthy later in life."Sony VAIO VPCZ11AFJ Battery

Approximately 99 percent of the body's calcium is stored in the bones and teeth. The rest of the calcium in the body has other important uses, such as some exocytosis, especially neurotransmitter release, and muscle contraction. In the electrical conduction system of the heart, calcium replaces sodium as the mineral that depolarizes the cell, proliferating the action potential. Sony VAIO VPCZ11AGJ Battery

In cardiac muscle, sodium influx commences an action potential, but during potassium efflux, the cardiac myocyte experiences calcium influx, prolonging the action potential and creating a plateau phase of dynamic equilibrium. Long-term calcium deficiency can lead to rickets and poor blood clotting and in case of a menopausal woman, Sony VAIO VPCZ11AVJ Battery

it can lead to osteoporosis, in which the bone deteriorates and there is an increased risk of fractures. While a lifelong deficit can affect bone and tooth formation, over-retention can cause hypercalcemia (elevated levels of calcium in the blood), impaired kidney function and decreased absorption of other minerals.Sony VAIO VPCZ11CGX/X Battery

Several sources suggest a correlation between high calcium intake (2000 mg per day, or twice the U.S. recommended daily allowance, equivalent to six or more glasses of milk per day) and prostate cancer. High calcium intakes or high calcium absorption were previously thought to contribute to the development of kidney stones. Sony VAIO VPCZ11DGX/SJ Battery

However, a high calcium intake has been associated with a lower risk for kidney stones in more recent research. Vitamin D is needed to absorb calcium.

Dairy products, such as milk and cheese, are a well-known source of calcium. Sony VAIO VPCZ11FHX/XQ Battery

Some individuals are allergic to dairy products and even more people, in particular those of non Indo-European descent, are lactose-intolerant, leaving them unable to consume non-fermented dairy products in quantities larger than about half a liter per serving. Others, such as vegans, avoid dairy products for ethical and health reasons. Sony VAIO VPCZ11V9R/B Battery

However, many good sources of calcium exist. These include seaweeds such as kelp, wakame and hijiki; nuts and seeds (like almonds and sesame); blackstrap molasses; beans; figs; quinoa; amaranth;collard greens; okra; rutabaga; broccoli; dandelion leaves; kale; and fortified products such as orange juice and soy milk. Sony VAIO VPCZ11X9E/B Battery

An overlooked source of calcium is eggshell, which can be ground into a powder and mixed into food or a glass of water.

The calcium content of most foods can be found in the USDA National Nutrient Database.Sony VAIO VPCZ11Z9E/B Battery

Dietary calcium supplements

Calcium supplements are used to prevent and to treat calcium deficiencies. Most experts recommend that supplements be taken with food and that no more than 600 mg should be taken at a time because the percent of calcium absorbed decreases as the amount of calcium in the supplement increases.Sony VAIO VPCZ125GX/S Battery

It is recommended to spread doses throughout the day. Recommended daily calcium intake for adults ranges from 1000 to 1500 mg. It is recommended to take supplements with food to aid in absorption.

Vitamin D is added to some calcium supplements. Proper vitamin D status is important because vitamin D is converted to a hormone in the body, which then induces the synthesis of intestinal proteins responsible for calcium absorption.Sony VAIO VPCZ127FC Battery

• The absorption of calcium from most food and commonly used dietary supplements is very similar. This is contrary to what many calcium supplement manufacturers claim in their promotional materials.
• Milk is an excellent source of dietary calcium for those whose bodies tolerate it because it has a high concentration of calcium and the calcium in milk is excellently absorbed.Sony VAIO VPCZ128GC Battery
• Soymilk and other vegetable milks are usually sold with calcium added so that their calcium concentration is as high as in milk
• Also different kind of juices boosted with calcium are widely available.
• Calcium carbonate is the most common and least expensive calcium supplement. It should be taken with food. It depends on low pH levels for proper absorption in the intestine.Sony VAIO VPCZ12M9E/B Battery
• Some studies suggests that the absorption of calcium from calcium carbonate is similar to the absorption of calcium from milk. While most people digest calcium carbonate very well, some might develop gastrointestinal discomfort or gas. Taking magnesium with it can help to avoid constipation. Sony VAIO VPCZ13M9E/B Battery
• Calcium carbonate is 40% elemental calcium. 1000 mg will provide 400 mg of calcium. However, supplement labels will usually indicate how much calcium is present in each serving, not how much calcium carbonate is present.Sony VAIO VPCZ13V9E/X Battery
• Antacids frequently contain calcium carbonate, and are a commonly used, inexpensive calcium supplement
• Coral calcium is a salt of calcium derived from fossilized coral reefs. Coral calcium is composed of calcium carbonate and trace minerals.Sony VAIO VPCZ13Z9E/X Battery
• Calcium citrate can be taken without food and is the supplement of choice for individuals with achlorhydria or who are taking histamine-2 blockers or proton-pump inhibitors. It is more easily digested and absorbed than calcium carbonate if taken on an empty stomach and less likely to cause constipation and gas than calcium carbonate. Sony VAIO VPCZZZHJ Battery
• It also has a lower risk of contributing to the formation of kidney stones. Calcium citrate is about 21% elemental calcium. 1000 mg will provide 210 mg of calcium. It is more expensive than calcium carbonate and more of it must be taken to get the same amount of calcium.Sony VAIO VPZ117 Battery
• Calcium phosphate costs more than calcium carbonate, but less than calcium citrate. It is easily absorbed and is less likely to cause constipation and gas than either.
• Calcium lactate has similar absorption as calcium carbonate,[37] but is more expensive. Calcium lactate and calcium gluconate are less concentrated forms of calcium and are not practical oral supplements.Sony VAIO VPZ118 Battery
• Calcium chelates are synthetic calcium compounds, with calcium bound to an organic molecule, such as malate, aspartate, or fumarate. These forms of calcium may be better absorbed on an empty stomach. However, in general they are absorbed similarly to calcium carbonate and other common calcium supplements when taken with food.Sony VAIO VPZ119 Battery
• The 'chelate' mimics the action that natural food performs by keeping the calcium soluble in the intestine. Thus, on an empty stomach, in some individuals, chelates might, in theory, be absorbed better.
• Microcrystalline hydroxyapatite (MH) is marketed as a calcium supplement, and has in some randomized trials been found to be more effective than calcium carbonate.Sony VPCM11M1E/B Battery

In July 2006, a report citing research from Fred Hutchinson Cancer Research Center in Seattle, Washington claimed that women in their 50s gained 5 pounds (2.3 kg) less in a period of 10 years by taking more than 500 mg of calcium supplements than those who did not.Sony VPCM11M1E/W Battery

However, the doctor in charge of the study, Dr. Alejandro J. Gonzalez also noted it would be "going out on a limb" to suggest calcium supplements as a weight-limiting aid.

Prevention of fractures due to osteoporosis

Such studies often do not test calcium alone, but rather combinations of calcium and vitamin D. Randomized controlled trials found both positive and negative effects. Sony VPCM12M1E/L Battery

The different results may be explained by doses of calcium and underlying rates of calcium supplementation in the control groups. However, it is clear that increasing the intake of calcium promotes deposition of calcium in the bones,Sony VPCM12M1E/P Battery

where it is of more benefit in preventing the compression fractures resulting from the osteoporotic thinning of the dendritic web of the bodies of the vertebrae, than it is at preventing the more serious cortical bonefractures that happen at hip and wrist. Sony VPCM12M1E/W Battery

Possible cancer prevention

A meta-analysis[41] by the international Cochrane Collaboration of two randomized controlled trials found that calcium "might contribute to a moderate degree to the prevention of adenomatous colonic polyps".Sony VPCM13M1E/L Battery

More recent studies were conflicting, and one that was positive for effect (Lappe, et al.) did control for a possible anti-carcinogenic effect of vitamin D, which was found to be an independent positive influence from calcium-alone on cancer risk (see second study below).Sony VPCM13M1E/P Battery

• A randomized controlled trial found that 1000 mg of elemental calcium and 400 IU of vitamin D3 had no effect on colorectal cancer
• A randomized controlled trial found that 1400–1500 mg supplemental calcium and 1100 IU vitamin D3 reduced aggregated cancers with a relative risk of 0.402.Sony VPCM13M1E/W Battery
• An observational cohort study found that high calcium and vitamin D intake was associated with "lower risk of developing premenopausal breast cancer."

Hazards and toxicity

Compared with other metals, the calcium ion and most calcium compounds have low toxicity.Sony VAIO VGN-Z11MN/B Battery

This is not surprising given the very high natural abundance of calcium compounds in the environment and in organisms. Calcium poses few serious environmental problems, with kidney stones the most common side-effect in clinical studies. Acute calcium poisoning is rare, and difficult to achieve unless calcium compounds are administered intravenously. Sony VAIO VGN-Z11VN/X Battery

For example, the oral median lethal dose (LD50) for rats for calcium carbonate and calcium chloride are 6.45 and 1.4 g/kg, respectively.

Calcium metal is hazardous because of its sometimes-violent reactions with water and acids. Sony VAIO VGN-Z11WN/B Battery

Calcium metal is found in some drain cleaners, where it functions to generate heat and calcium hydroxide that saponifies the fats and liquefies the proteins (e.g., hair) that block drains. When swallowed calcium metal has the same effect on the mouth, esophagus and stomach, and can be fatal.Sony VAIO VGN-Z11XN/B Battery

Excessive consumption of calcium carbonate antacids/dietary supplements (such as Tums) over a period of weeks or months can cause milk-alkali syndrome, with symptoms ranging from hypercalcemia to potentially fatal renal failure. What constitutes “excessive” consumption is not well known and, it is presumed, varies a great deal from person to person.Sony VAIO VGN-Z15 Battery

Persons consuming more than 10 grams/day of CaCO3 (=4 g Ca) are at risk of developing milk-alkali syndrome, but the condition has been reported in at least one person consuming only 2.5 grams/day of CaCO3 (=1 g Ca), an amount usually considered moderate and safe.Sony VAIO VGN-Z15N Battery

Oral calcium supplements diminish the absorption of thyroxine when taken within four to six hours of each other.[58] Thus, people taking both calcium and thyroxine run the risk of inadequate thyroid hormone replacement and thence hypothyroidism if they take them simultaneously or near-simultaneously.Sony VAIO VGN-Z17 Battery

Calcium (Ca2+) plays a pivotal role in the physiology and biochemistry of organisms and the cell. It plays an important role in signal transduction pathways, where it acts as a second messenger, in neurotransmitter release from neurons, contraction of all muscle cell types, and fertilization.Sony VAIO VGN-Z17N Battery

Many enzymes require calcium ions as a cofactor, those of the blood-clotting cascade being notable examples. Extracellular calcium is also important for maintaining the potential difference across excitable cell membranes, as well as proper bone formation.

Calcium levels in mammals are tightly regulated, with bone acting as the major mineral storage site.Sony VAIO VGN-Z19 Battery

Calcium ions, Ca2+, are released from bone into the bloodstream under controlled conditions. Calcium is transported through the bloodstream as dissolved ions or bound to proteins such as serum albumin. Parathyroid hormonesecreted by the parathyroid gland regulates the resorption of Ca2+ from bone, Sony VAIO VGN-Z19N Battery

reabsorption in the kidney back into circulation, and increases in the activation ofvitamin D3 to Calcitriol. Calcitriol, the active form of vitamin D3, promotes absorption of calcium from the intestines and the mobilization of calcium ions from bone matrix. Calcitonin secreted from the parafollicular cells of the thyroid gland also affects calcium levels by opposing parathyroid hormone;Sony VAIO VGN-Z21MN/B Battery

however, its physiological significance in humans is dubious.

Calcium storages are intracellular organelles, that constantly accumulate Ca2+ ions and release them during certain cellular events. Intracellular Ca2+ storages include mitochondria and the endoplasmic reticulum.Sony VAIO VGN-Z21VN/X Battery

In vertebrates, calcium ions, like many other ions, are of such vital importance to many physiological processes that its concentration is maintained within specific limits to ensure adequate homeostasis. This is evidenced by human plasma calcium, which is one of the most closely regulated physiological variables in the human body.Sony VAIO VGN-Z21WN/B Battery

Normal plasma levels vary between 1 and 2% over any given time. Approximately half of all ionized calcium circulates in its unbound form, with the other half being complexed with plasma proteins such as albumin, as well as anions including bicarbonate, citrate, phosphate, and sulfate.Sony VAIO VGN-Z21XN Battery

Different tissues contain calcium in different concentrations. For instance, Ca2+ (mostly calcium phosphate and some calcium sulfate) is the most important (and specific) element of bone and calcified cartilage. In humans, the total body content of calcium is present mostly in the form of bone mineral (roughly 99%). Sony VAIO VGN-Z21ZN/X Battery

In this state, it is largely unavailable for exchange/bioavailability. The way to overcome this is through the process of bone resorption, in which calcium is liberated into the bloodstream through the action of bone osteoclasts. The remainder of calcium is present within the extracellular and intracellular fluids.Sony VAIO VGN-Z25 Battery

Within a typical cell, the intracellular concentration of ionized calcium is roughly 100 nM, but is subject to increases of 10– to 100-fold during various cellular functions. The intracellular calcium level is kept relatively low with respect to the extracellular fluid, by an approximate magnitude of 12,000-fold. Sony VAIO VGN-Z25/B Battery

This gradient is maintained through various plasma membrane calcium pumps that utilize ATP for energy, as well as a sizable storage within intracellular compartments.

Effects

The effects of calcium on human cells are specific, meaning that different types of cells respond in different ways. Sony VAIO VGN-Z25TN/B Battery

However, in certain circumstances, its action may be more general. Ca2+ ions are one of the most widespread second messengers used insignal transduction. They make their entrance into the cytoplasm either from outside the cell through the cell membrane via calcium channels (such as Calcium-binding proteins or voltage-gated calcium channels),Sony VAIO VGN-Z26TN/B Battery

or from some internal calcium storagessuch as the endoplasmic reticulum and mitochondria. Levels of intracellular calcium are regulated by transport proteins that remove it from the cell. For example, the sodium-calcium exchanger uses energy from the electrochemical gradient of sodium by coupling the influx of sodium into cell Sony VAIO VGN-Z27 Battery

(and down its concentration gradient) with the transport of calcium out of the cell. In addition, the plasma membrane Ca2+ ATPase (PMCA) obtains energy to pump calcium out of the cell by hydrolysing adenosine triphosphate (ATP). In neurons, voltage-dependent, Sony VAIO VGN-Z27/B Battery

calcium-selective ion channels are important for synaptic transmission through the release of neurotransmitters into the synaptic cleft by vesicle fusionof synaptic vesicles.

Calcium's function in muscle contraction was found as early as 1882 by Ringer. Subsequent investigations were to reveal its role as a messenger about a century later. Sony VAIO VGN-Z27TN/X Battery

Because its action is interconnected with cAMP, they are called synarchic messengers. Calcium can bind to several different calcium-modulated proteins such astroponin-C (the first one to be identified) and calmodulin, proteins that are necessary for promoting contraction in muscle.Sony VAIO VGN-Z29N Battery

Negative effects and pathology

Substantial decreases in extracellular Ca2+ ion concentrations may result in a condition known as hypocalcemic tetany, which is marked by spontaneous motor neurondischarge. In addition, severe hypocalcaemia will begin to affect aspects of blood coagulation and signal transduction.Sony VAIO VGN-Z29N/X Battery

Ca2+ ions can damage cells if they enter in excessive numbers (for example, in the case of excitotoxicity, or over-excitation of neural circuits, which can occur inneurodegenerative diseases, or after insults such as brain trauma or stroke). Excessive entry of calcium into a cell may damage it or even cause it to undergoapoptosis, or death by necrosis. Sony VAIO VGN-Z31MN/B Battery

Calcium also acts as one of the primary regulators of osmotic stress (Osmotic shock). Chronically elevated plasma calcium (hypercalcemia) is associated with cardiac arrhythmias and decreased neuromuscular excitability. One cause of hypercalcemia is a condition known ashyperparathyroidism.Sony VAIO VGN-Z31VN/X Battery

Invertebrates

Some invertebrates use calcium compounds for building their exoskeleton (shells and carapaces) or endoskeleton (echinoderm plates and poriferan calcareous spicules).Sony VAIO VGN-Z31WN/B Battery

Stomata Closing

When ABA signals the guard cells, free Ca2+ ions enter the cytosol from both outside the cell and internal stores, reversing the concentration gradient so the K+ ions begin exiting the cell. The loss of solutes makes the cell flaccid and closes the stomatal pores.Sony VAIO VGN-Z31ZN/X Battery

Cellular Division

Calcium is a necessary ion in the formation of the mitotic spindle. Without the mitotic spindle, cellular division cannot occur. Although young leaves have a higher need for calcium, older leaves contain higher amounts of calcium because calcium is relatively immobile through the plant.Sony VAIO VGN-Z35 Battery

It is not transported through the phloembecause it can bind with other nutrient ions and precipitate out of liquid solutions.

Structural roles

Ca2+ ions are an essential component of plant cell walls and cell membranes, and are used as cations to balance organic anions in the plant vacuole.[4] The Ca2+concentration of the vacuole may reach millimolar levels. Sony VAIO VGN-Z35/B Battery

The most striking use of Ca2+ ions as a structural element in plants occurs in the marine coccolithophores, which use Ca2+ to form the calcium carbonate plates, with which they are covered.

Calcium is needed to form the pectin in the middle lamella of newly formed cells.Sony VAIO VGN-Z35TN/B Battery

Calcium is needed to stabilize the permeability of cell membranes. Without calcium, the cell walls are unable to stabilize and hold their contents. This is particularly important in developing fruits. Without calcium, the cell walls are weak and unable to hold the contents of the fruit.Sony VAIO VGN-Z36GD Battery

Some plants accumulate Ca in their tissues, thus making them more firm. Calcium is stored as Ca-oxalate crystals in plastids.

Calcium metabolism or calcium homeostasis is the mechanism by which the body maintains adequate calcium levels. Derangements of this mechanism lead to hypercalcemia or hypocalcemia, both of which can have important consequences for health.Sony VAIO VGN-Z36GD/B Battery

Calcium location and quantity

Calcium is the most abundant mineral in the human body. The average adult body contains in total approximately 1 kg, 99% in the skeleton in the form of calcium phosphate salts. The extracellular fluid (ECF) contains approximately 22.5 mmol, of which about 9 mmol is in the serum.Sony VAIO VGN-Z36GD/J Battery

Approximately 500 mmol of calcium is exchanged between bone and the ECF over a period of twenty-four hours.

Normal ranges

The serum level of calcium is closely regulated with a normal total calcium of 2.2-2.6 mmol/L (9-10.5 mg/dL) and a normal ionized calcium of 1.1-1.4 mmol/L (4.5-5.6 mg/dL). Sony VAIO VGN-Z36TD/B Battery

The amount of total calcium varies with the level of serum albumin, a protein to which calcium is bound. The biologic effect of calcium is determined by the amount of ionized calcium, rather than the total calcium. Ionized calcium does not vary with the albumin level, and therefore it is useful to measure the ionized calcium level when the serum albumin is not within normal ranges, or when a calcium disorder is suspected despite a normal total calcium level.Sony VAIO VGN-Z36TD/J Battery

Corrected calcium level

One can derive a corrected calcium level when the albumin is abnormal. This is to make up for the change in total calcium due to the change in albumin-bound calcium, and gives an estimate of what the calcium level would be if the albumin were within normal ranges.Sony VAIO VGN-Z37D Battery

Corrected calcium (mg/dL) = measured total Ca (mg/dL) + 0.8 (4.0 - serum albumin [g/dL]), where 4.0 represents the average albumin level in g/dL.

in other words, each 1 g/dL decrease of albumin will decrease 0.8 mg/dL in measured serum Ca and thus 0.8 must be added to the measured Calcium to get a corrected Calcium value.Sony VAIO VGN-Z37D/B Battery

Or: Corrected calcium (mmol/L) = measured total Ca (mmol/L) + 0.02 (40 - serum albumin [g/L]), where 40 represents the average albumin level in g/L

in other words, each 1 g/L decrease of albumin, will decrease 0.02 mmol/L in measured serum Ca and thus 0.02 must be added to the measured value to take this into account and get a corrected calcium.Sony VAIO VGN-Z37GD Battery

When there is hypoalbuminemia (a lower than normal albumin), the corrected calcium level is higher than the total calcium.

Absorption

About 25 mmol of calcium enters the body in a normal diet. Of this, about 40% (10 mmol) is absorbed in small intestine, and 5 mmol leaves the body in feces, netting 5 mmol of calcium a day.Sony VAIO VGN-Z37GD/X Battery

Calcium is absorbed across the intestinal brush border membrane, passing through ion channels such as TRPV6. Calbindin is a vitamin D-dependent calcium-binding protein inside intestinal epithelial cells which functions together with TRPV6 and calcium pumps (PMCA1) in the basal membrane to actively transport calcium into the body.Sony VAIO VGN-Z39D Battery

The active transport occurs primarily in the duodenum when calcium intake is low, and passive paracellular diffusion occurs in the ileum and jejunum, independent of Vitamin D, when calcium intake is high. Sony VAIO VGN-Z39D/X Battery

Excretion

The kidney excretes 250 mmol a day in pro-urine, and resorbs 245 mmol, leading to a net loss in the urine of 5 mmol/d. In addition to this, the kidney processes Vitamin D into calcitriol, the active form that is most effective in assisting intestinal absorption. Both processes are stimulated by parathyroid hormone.Sony VAIO VGN-Z41MD/B Battery

The role of bone

Although calcium flow to and from the bone is neutral, about 5 mmol is turned over a day. Bone serves as an important storage point for calcium, as it contains 99% of the total body calcium. Calcium release from bone is regulated by parathyroid hormone. Calcitonin stimulates incorporation of calcium in bone, although this process is largely independent of calcitonin.Sony VAIO VGN-Z41WD/B Battery

Low calcium intake may also be a risk factor in the development of osteoporosis. In one meta-analysis, the authors found that fifty out of the fifty-two studies that they reviewed showed that calcium intake promoted better bone balance.[5] With a better bone balance, the risk of osteoporosis is lowered.Sony VAIO VGN-Z45GD/B Battery

Primarily calcium is regulated by the actions of 1,25-Dihydroxycholecalciferol, parathyroid hormone (PTH) and calcitonin and direct exchange with the bone matrix. Plasma calcium levels are regulated by hormonal and non-hormonal mechanisms. After ingestion of substantial amounts of calcium the short term control that prevents calcium spiking in the serum is absorption by the bone matrix. After about an hour, PTH will be released and not peak for about 8 hours.Sony VAIO VGN-Z45TD/B Battery

The PTH is, over time, a very potent regulator of plasma calcium, and controls the conversion of vitamin D into its active form in the kidney. The parathyroid glands are located behind the thyroid, and produce parathyroid hormone in response to low calcium levels.

The parafollicular cells of the thyroid produce calcitonin in response to high calcium levels, but its significance is much smaller than that of PTH.Sony VAIO VGN-Z46GD/B Battery

Pathology

Hypocalcemia and hypercalcemia are both serious medical disorders.

Renal osteodystrophy is a consequence of chronic renal failure related to the calcium metabolism.

Osteoporosis and osteomalacia have been linked to calcium metabolism disorders.Sony VAIO VGN-Z46GD/U Battery

Research into cancer prevention

The role that calcium might have in reducing the rates of colorectal cancer has been the subject of many studies. However, given its modest efficacy, there is no current medical recommendation to use calcium for cancer reduction. Several epidemiological studies suggest that people with high calcium intake have a reduced risk of colorectal cancer.Sony VAIO VGN-Z46MD/B Battery

These observations have been confirmed by experimental studies in volunteers and in rodents. One large scale clinical trial shows that 1.2 g calcium each day reduces, modestly, intestinal polyps recurrence in volunteers. Data from the four published trials are available.Sony VAIO VGN-Z46SD/B Battery

Some forty carcinogenesis studies in rats or mice, reported in the Chemoprev.Database, also support that calcium could prevent intestinal cancer.

Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Sony VAIO VGN-Z46TD/B Battery

Calcium carbonate is the active ingredient in agricultural lime, and is usually the principal cause of hard water. It is commonly used medicinally as a calcium supplement or as an antacid, but excessive consumption can be hazardous.

The vast majority of calcium carbonate used in industry is extracted by mining or quarrying. Pure calcium carbonate (e.g. for food or pharmaceutical use), can be produced from a pure quarried source (usually marble).Sony VAIO VGN-Z46TD/R Battery

Alternatively, calcium carbonate is prepared by calcining crude calcium oxide. Water is added to give calcium hydroxide, andcarbon dioxide is passed through this solution to precipitate the desired calcium carbonate, referred to in the industry as precipitated calcium carbonate (PCC):Sony VAIO VGN-Z47GD/X Battery

Carbonate is found frequently in geologic settings and constitute an enormous carbon reservoir. Calcium carbonate occurs as thepolymorphs aragonite and calcite. A polymorph is a mineral with the same chemical formula but different chemical structure. The carbonate minerals form the rock types: limestone, chalk, marble, travertine, tufa, and others. Sony VAIO VGN-Z48GD/X Battery

Calcite commonly occurs as sediments in marine settings. Calcite is typically found around the warm tropic environments. Calcite precipitates in warmer shallow environments more than it does under colder environments because warmer environments do not favor the dissolution of CO2. Sony VAIO VGN-Z48TD/X Battery

This is analogous to CO2 being dissolved in soda. When you take the cap off of a soda bottle, the CO2 rushes out. As the soda warms up, carbon dioxide is released. This same principle can be applied to calcite in the ocean. Cold-water carbonates do exist at higher latitudes but have a very slow growth rate.Sony VAIO VGN-Z51WG/B Battery

In tropic settings, the waters are warm and clear. Corals are more abundant in this environment than towards the poles where the waters are cold. Calcium carbonate contributors, including plankton (such as coccoliths and planktic foraminifera), coralline algae, sponges, brachiopods, echinoderms, bryozoa and mollusks, Sony VAIO VGN-Z51XG/B Battery

are typically found in shallow water environments where sunlight and filterable food are more abundant. The calcification processes are changed by the ocean acidification.

Where the oceanic crust is subducted under a continental plate sediments will be carried down to warmer zones in the astenosphere and mesosphere where the calcium carbonate is decomposed to carbon dioxide which will give rise to explosive vulcanic eruptions.Sony VAIO VGN-Z530N/B Battery

Carbonate compensation depth

The carbonate compensation depth (CCD) is the point in the ocean where the rate of precipitation of calcium carbonate is balanced by the rate of dissolution due to the conditions present. Deep in the ocean, the temperature drops and pressure increases. Calcium carbonate is unusual in that its solubility increases with decreasing temperature. Sony VAIO VGN-Z540EBB Battery

Increasing pressure also increases the solubility of calcium carbonate. The CCD can range from 4–6 km below sea level.

Taphonomy

Calcium carbonate can preserve fossils through permineralization. Most of the vertebrate fossils of the Two Medicine Formation, known for its duck-billed dinosaur eggs, are preserved by CaCO3 permineralization.Sony VAIO VGN-Z540NLB Battery

This type of preservation preserves high levels of detail, even down to the microscopic level. However, it also leaves specimens vulnerable to weathering when exposed to the surface.

Industrial applications

The main use of calcium carbonate is in the construction industry,Sony VAIO VGN-Z540NMB Battery

either as a building material or limestone aggregate for roadbuilding or as an ingredient of cement or as the starting material for the preparation of builder's lime by burning in a kiln. However, due to weathering mainly caused by acid rain, calcium carbonate (in limestone form) is no longer used for building purposes on its own, and only as a raw/primary substance for building materials.Sony VAIO VGN-Z550N/B Battery

Calcium carbonate is also used in the purification of iron from iron ore in a blast furnace. The carbonate is calcined in situ to give calcium oxide, which forms a slag with various impurities present, and separates from the purified iron.

In the oil industry, calcium carbonate is added to drilling fluids as a formation-bridging and filtercake-sealing agent;Sony VAIO VGN-Z55F Battery

it is also a weighting material which increases the density of drilling fluids to control the downhole pressure. Calcium carbonate is added to swimming pools, as a pH corrector for maintaining alkalinityand offsetting the acidic properties of the disinfectant agent.Sony VAIO VGN-Z55TG/B Battery

Calcium carbonate has traditionally been a major component of blackboard chalk. However, modern manufactured chalk is mostly gypsum, hydrated calcium sulfateCaSO4·2H2O. Calcium carbonate is a main source for growing Seacrete, or Biorock.Sony VAIO VGN-Z56GG/B Battery

Precipitated calcium carbonate (PCC), pre-dispersed in slurry form, is a common filler material for latex gloves with the aim of achieving maximum saving in material and production costs. Sony VAIO VGN-Z56GG/E Battery

Fine ground calcium carbonate (GCC) is an essential ingredient in the microporous film used in babies' diapers and some building films as the pores are nucleated around the calcium carbonate particles during the manufacture of the film by biaxial stretching. GCC or PCC is used as a filler in paper because they are cheaper than wood fiber.Sony VAIO VGN-Z56GGX Battery

Printing and writing paper can contain 10–20% calcium carbonate. In North America, calcium carbonate has begun to replace kaolin in the production of glossy paper. Europe has been practicing this as alkaline papermaking or acid-free papermaking for some decades. Sony VAIO VGN-Z56TG/B Battery

PCC has a very fine and controlled particle size, on the order of 2 micrometres in diameter, useful in coatings for paper.

Calcium carbonate is widely used as an extender in paints, in particular matte emulsion paint where typically 30% by weight of the paint is either chalk or marble. It is also a popular filler in plastics.Sony VAIO VGN-Z56TG/E Battery

Some typical examples include around 15 to 20% loading of chalk in unplasticized polyvinyl chloride (uPVC) drain pipe, 5 to 15% loading of stearate coated chalk or marble in uPVC window profile. PVC cables can use calcium carbonate at loadings of up to 70 phr (parts per hundred parts of resin) to improve mechanical properties (tensile strength and elongation)Sony VAIO VGN-Z56TG/R Battery

and electrical properties (volume resistivity). Polypropylene compounds are often filled with calcium carbonate to increase rigidity, a requirement that becomes important at high use temperatures. It also routinely used as a filler inthermosetting resins (sheet and bulk molding compounds) and has also been mixed with ABS,Sony VAIO VGN-Z570N/B Battery

and other ingredients, to form some types of compression molded "clay" poker chips. Precipitated calcium carbonate, made by dropping calcium oxide into water, is used by itself or with additives as a white paint, known as whitewashing.

Calcium carbonate is added to a wide range of trade and do it yourself adhesives, sealants, and decorating fillers.Sony VAIO VGN-Z57G Battery

Ceramic tile adhesives typically contain 70 to 80% limestone. Decorating crack fillers contain similar levels of marble or dolomite. It is also mixed with putty in setting stained glass windows, and as a resist to prevent glass from sticking to kiln shelves when firing glazes and paints at high temperature.Sony VAIO VGN-Z57GG/X Battery

In ceramics/glazing applications, calcium carbonate is known as whiting, and is a common ingredient for many glazes in its white powdered form. When a glaze containing this material is fired in a kiln, the whiting acts as a flux material in the glaze. Ground calcium carbonate is an abrasive (both as scouring powder and as an ingredient of household scouring creams), Sony VAIO VGN-Z57GGX Battery

in particular in its calcite form, which has the relatively low hardness level of 3 on the Mohs scale of mineral hardness, and will therefore not scratch glass and most other ceramics, enamel, bronze, iron, and steel, and have a moderate effect on softer metals like aluminiumand copper. Sony VAIO VGN-Z57TG/X Battery

A paste made from calcium carbonate and deionized water can be used to clean tarnish on silver .

Health and dietary applications

Calcium carbonate is widely used medicinally as an inexpensive dietary calcium supplement or gastric antacid.Sony VAIO VGN-Z58GG/X Battery

It may be used as a phosphate binder for the treatment of hyperphosphatemia (primarily in patients with chronic renal failure). It is also used in the pharmaceutical industry as an inert filler for tablets and other pharmaceuticals.

Calcium carbonate is known among IBS sufferers to help reduce diarrhea. Some individuals report being symptom-free since starting supplementation. Sony VAIO VGN-Z58GGX Battery

The process in which calcium carbonate reduces diarrhea is by binding water in the bowel, which creates a stool that is firmer and better formed. Calcium carbonate supplements are often combined with magnesium in various proportions. This should be taken into account as magnesium is known to cause diarrhea.Sony VAIO VGN-Z590NJB Battery

Calcium carbonate is used in the production of toothpaste and has seen a resurgence as a food preservative and color retainer, when used in or with products such as organic apples or food.

Excess calcium from supplements, fortified food and high-calcium diets, can cause the milk-alkali syndrome, which has serious toxicity and can be fatal. Sony VAIO VGN-Z590UAB Battery

In 1915, Bertram Sippy introduced the "Sippy regimen" of hourly ingestion of milk and cream, and the gradual addition of eggs and cooked cereal, for 10 days, combined with alkaline powders, which provided symptomatic relief for peptic ulcer disease. Over the next several decades, the Sippy regimen resulted in renal failure, alkalosis, and hypercalcemia, mostly in men with peptic ulcer disease.Sony VAIO VGN-Z591U/B Battery

These adverse effects were reversed when the regimen stopped, but it was fatal in some patients with protracted vomiting. Milk alkali syndrome declined in men after effective treatments for peptic ulcer disease arose. During the past 15 years, it has been reported in women taking calcium supplements above the recommended range of 1.2 to 1.5 g daily, Sony VAIO VGN-Z59G Battery

for prevention and treatment of osteoporosis, and is exacerbated by dehydration. Calcium has been added to over-the-counter products, which contributes to inadvertent excessive intake. Excessive calcium intake can lead to hypercalcemia, complications of which include vomiting, abdominal pain and altered mental status.Sony VAIO VGN-Z620D Battery

As a food additive it is designated E170 ; INS number 170. Used as an acidity regulator, anticaking agent, stabiliser or colour it is approved for usage in the EU, USA and Australia and New Zealand. It is used in some soy milk products as a source of dietary calcium; one study suggests that calcium carbonate might be as bioavailable as the calcium in cow's milk.Sony VAIO VGN-Z620N/B Battery

Calcium carbonate is also used as a firming agent in many canned or bottled vegetable products.

Environmental applications

In 1989, a researcher, Ken Simmons, introduced CaCO3 into the Whetstone Brook in Massachusetts. His hope was that the calcium carbonate would counter the acid in the stream from acid rain and save the trout that had ceased to spawn. Sony VAIO VGN-Z650N/B Battery

Although his experiment was a success, it did increase the amounts of aluminium ions in the area of the brook that was not treated with the limestone. This shows that CaCO3 can be added to neutralize the effects of acid rain in river ecosystems. Currently calcium carbonate is used to neutralize acidic conditions in both soil and water.Sony VAIO VGN-Z670N/B Battery

Since the 1970s, such liming has been practiced on a large scale in Sweden to mitigate acidification and several thousand lakes and streams are limed repeatedly.

Calcination equilibrium

Calcination of limestone using charcoal fires to produce quicklime has been practiced since antiquity by cultures all over the world.Sony VAIO VGN-Z690CTO Battery

The temperature at which limestone yields calcium oxide is usually given as 825 °C, but stating an absolute threshold is misleading. Calcium carbonate exists in equilibrium with calcium oxide and carbon dioxide at any temperature. At each temperature there is a partial pressure of carbon dioxide that is in equilibrium with calcium carbonate. Sony VAIO VGN-Z690NAX Battery

At room temperature the equilibrium overwhelmingly favors calcium carbonate, because the equilibrium CO2 pressure is only a tiny fraction of the partial CO2 pressure in air, which is about 0.035 kPa.

At temperatures above 550 °C the equilibrium CO2 pressure begins to exceed the CO2 pressure in air.Sony VAIO VGN-Z690PAB Battery

So above 550 °C, calcium carbonate begins to outgas CO2 into air. However, in a charcoal fired kiln, the concentration of CO2 will be much higher than it is in air. Indeed if all the oxygen in the kiln is consumed in the fire, then the partial pressure of CO2 in the kiln can be as high as 20 kPa.Sony VAIO VGN-Z690PCB Battery

The table shows that this equilibrium pressure is not achieved until the temperature is nearly 800 °C. For the outgassing of CO2 from calcium carbonate to happen at an economically useful rate, the equilibrium pressure must significantly exceed the ambient pressure of CO2.Sony VAIO VGN-Z690PDB Battery

And for it to happen rapidly, the equilibrium pressure must exceed total atmospheric pressure of 101 kPa, which happens at 898 °C.

Calcium carbonate is poorly soluble in pure water (47 mg/L at normal atmospheric CO2 partial pressure as shown below).

The equilibrium of its solution is given by the equation (with dissolved calcium carbonate on the right):Sony VAIO VGN-Z690PEB Battery

CaCO3 Ca2+ + CO32– Ksp = 3.7×10?9 to 8.7×10?9 at 25 °C

where the solubility product for [Ca2+][CO32–] is given as anywhere from Ksp = 3.7×10?9 to Ksp = 8.7×10?9 at 25 °C, depending upon the data source.Sony VAIO VGN-Z690PFB Battery

What the equation means is that the product of molar concentration of calcium ions (moles of dissolved Ca2+ per liter of solution) with the molar concentration of dissolved CO32– cannot exceed the value of Ksp. This seemingly simple solubility equation, however, must be taken along with the more complicated equilibrium of carbon dioxide with water (see carbonic acid). Sony VAIO VGN-Z690YAD Battery

Some of the CO32– combines with H+ in the solution according to:

HCO3– H+ + CO32– Ka2 = 5.61×10?11 at 25 °C

HCO3– is known as the bicarbonate ion. Calcium bicarbonate is many times more soluble in water than calcium carbonate—indeed it exists only in solution.Sony VAIO VGN-Z691Y/B Battery

Some of the HCO3– combines with H+ in solution according to:

H2CO3 H+ + HCO3– Ka1 = 2.5×10?4 at 25 °C

Some of the H2CO3 breaks up into water and dissolved carbon dioxide according to:Sony VAIO VGN-Z691Y/X Battery

H2O + CO2(dissolved) H2CO3 Kh = 1.70×10?3 at 25 °C

And dissolved carbon dioxide is in equilibrium with atmospheric carbon dioxide according to:

where kH = 29.76 atm/(mol/L) at 25 °C (Henry constant), being the CO2 partial pressure.Sony VAIO VGN-Z698Y/X Battery

For ambient air, is around 3.5×10?4 atmospheres (or equivalently 35 Pa). The last equation above fixes the concentration of dissolved CO2 as a function of , independent of the concentration of dissolved CaCO3. At atmospheric partial pressure of CO2, dissolved CO2 concentration is 1.2×10?5 moles/liter.Sony VAIO VGN-Z699JAB Battery

The equation before that fixes the concentration of H2CO3 as a function of [CO2]. For [CO2]=1.2×10?5, it results in [H2CO3]=2.0×10?8 moles per liter. When [H2CO3] is known, the remaining three equations together with

H2O H+ + OH– K = 10?14 at 25 °C

(which is true for all aqueous solutions), and the fact that the solution must be electrically neutral,Sony VAIO VGN-Z70B Battery

2[Ca2+] + [H+] = [HCO3–] + 2[CO32–] + [OH–]

make it possible to solve simultaneously for the remaining five unknown concentrations (note that the above form of the neutrality equation is valid only if calcium carbonate has been put in contact with pure water or with a neutral pH solution; in the case where the origin water solvent pH is not neutral, the equation is modified).Sony VAIO VGN-Z71JB Battery

The table on the right shows the result for [Ca2+] and [H+] (in the form of pH) as a function of ambient partial pressure of CO2(Ksp = 4.47×10?9 has been taken for the calculation).

• At atmospheric levels of ambient CO2 the table indicates the solution will be slightly alkaline with a maximum CaCO3 solubility of 47 mg/L.Sony VAIO VGN-Z73FB Battery
• As ambient CO2 partial pressure is reduced below atmospheric levels, the solution becomes more and more alkaline. At extremely low , dissolved CO2, bicarbonate ion, and carbonate ion largely evaporate from the solution, leaving a highly alkaline solution of calcium hydroxide, which is more soluble than CaCO3. Sony VAIO VGN-Z790DKX Battery
• Note that for = 10?12 atm, the [Ca2+][OH?]2 product is still below the solubility product of Ca(OH)2 (8×10?6). For still lower CO2 pressure, Ca(OH)2 precipitation will occur before CaCO3 precipitation.
• As ambient CO2 partial pressure increases to levels above atmospheric, pH drops, and much of the carbonate ion is converted to bicarbonate ion, which results in higher solubility of Ca2+.Sony VAIO VGN-Z790DMR Battery

The effect of the latter is especially evident in day-to-day life of people who have hard water. Water in aquifers underground can be exposed to levels of CO2 much higher than atmospheric. As such water percolates through calcium carbonate rock, the CaCO3dissolves according to the second trend.Sony VAIO VGN-Z790DND Battery

When that same water then emerges from the tap, in time it comes into equilibrium with CO2 levels in the air by outgassing its excess CO2. The calcium carbonate becomes less soluble as a result and the excess precipitates as lime scale. This same process is responsible for the formation of stalactites and stalagmites in limestone caves.Sony VAIO VGN-Z820DB Battery

Two hydrated phases of calcium carbonate, monohydrocalcite, CaCO3·H2O and ikaite, CaCO3·6H2O, may precipitate from water at ambient conditions and persist as metastable phases.

With varying pH

Consider the problem of the maximum solubility of calcium carbonate in normal atmospheric conditions ( = 3.5 × 10?4 atm) when the pH of the solution is adjusted. Sony VAIO VGN-Z820G/B Battery

This is for example the case in a swimming pool where the pH is maintained between 7 and 8 (by addition of sodium bisulfate NaHSO4to decrease the pH or ofsodium bicarbonate NaHCO3 to increase it). From the above equations for the solubility product, the hydration reaction and the two acid reactions, the following expression for the maximum [Ca2+] can be easily deduced:Sony VAIO VGN-Z890GLX Battery

• decreasing the pH from 8 to 7 increases the maximum Ca2+ concentration by a factor 100. Water with a pH maintained to 7 can dissolve up to 15.9 mg/L of CaCO3. This explains the high Ca2+ concentration in some mineral waters with pH close to 7.
• note that the Ca2+ concentration of the previous table is recovered for pH = 8.27Sony VAIO VGN-Z890GMR Battery
• keeping the pH to 7.4 in a swimming pool (which gives optimum HClO/ClO? ratio in the case of "chlorine" maintenance) results in a maximum Ca2+ concentration of 1010 mg/L. This means that successive cycles of water evaporation and partial renewing may result in a very hard water before CaCO3 precipitates (water with a Ca2+concentration above 120 mg/L is considered very hard). Addition of a calcium sequestering agent or complete renewing of the water will solve the problem.Sony VAIO VGN-Z898H/X Battery

Solubility in a strong or weak acid solution

Solutions of strong (HCl), moderately strong (sulfamic) or weak (acetic, citric, sorbic, lactic, phosphoric) acids are commercially available. They are commonly used as descaling agents to remove limescale deposits. The maximum amount of CaCO3 that can be "dissolved" by one liter of an acid solution can be calculated using the above equilibrium equations.Sony VAIO VGN-Z90FS Battery

• In the case of a strong monoacid with decreasing acid concentration [A] = [A?], we obtain (with CaCO3 molar mass = 100 g):

where the initial state is the acid solution with no Ca2+ (not taking into account possible CO2 dissolution) and the final state is the solution with saturated Ca2+. Sony VAIO VGN-Z90NS Battery

For strong acid concentrations, all species have a negligible concentration in the final state with respect to Ca2+ and A? so that the neutrality equation reduces approximately to 2[Ca2+] = [A?] yielding . When the concentration decreases, [HCO3?] becomes non-negligible so that the preceding expression is no longer valid. Sony VAIO VGN-Z90PS Battery

For vanishing acid concentrations, one can recover the final pH and the solubility of CaCO3 in pure water.

• In the case of a weak monoacid (here we take acetic acid with pKA = 4.76) with decreasing total acid concentration [A] = [A?]+[AH], we obtain:Sony VAIO VGN-Z90S Battery

For the same total acid concentration, the initial pH of the weak acid is less acid than the one of the strong acid; however, the maximum amount of CaCO3 which can be dissolved is approximately the same. This is because in the final state, the pH is larger than the pKA, so that the weak acid is almost completely dissociated, yielding in the end as many H+ ions as the strong acid to "dissolve" the calcium carbonate.Sony VAIO VGN-Z90US Battery

• The calculation in the case of phosphoric acid (which is the most widely used for domestic applications) is more complicated since the concentrations of the four dissociation states corresponding to this acid must be calculated together with [HCO3?], [CO32?], [Ca2+], [H+] and [OH?]. Sony VAIO VGN-Z91DS Battery
• The system may be reduced to a seventh degree equation for [H+] the numerical solution of which gives

where [A] = [H3PO4] + [H2PO4?] + [HPO42?] + [PO43?] is the total acid concentration. Thus phosphoric acid is more efficient than a monoacid since at the final almost neutral pH, the second dissociated state concentration [HPO42?] is not negligible (see phosphoric acid).Sony VAIO VGN-Z91JS Battery

Calcium chloride, CaCl2, is a salt of calcium and chlorine. It behaves as a typical ionic halide, and is solid at room temperature. Common applications include brine for refrigeration plants, ice and dust control on roads, and desiccation. Because of its hygroscopic nature, anhydrous calcium chloride must be kept in tightly-sealed air-tight containers.Sony VAIO VGN-Z91PS Battery

Calcium chloride can serve as a source of calcium ions in a solution as calcium chloride is soluble. This property can be useful for displacing ions from solution. For example, phosphate is displaced from solution by calcium:

3 CaCl2 (aq) + 2 K3PO4 (aq) ? Ca3(PO4)2 (s) + 6 KCl (aq)

Molten calcium chloride can be electrolysed to give calcium metal and chlorine gas:Sony VAIO VGN-Z91YS Battery

CaCl2 (l) ? Ca (s) + Cl2 (g)

Calcium chloride has a very high enthalpy change of solution.

The anhydrous salt is deliquescent; it can accumulate enough water in its crystal lattice to form a solution.Sony VAIO VGN-Z92DS Battery

Preparation

Calcium chloride can be produced directly from limestone, but large amounts are also produced as a by-product of the Solvay process. North American consumption in 2002 was 1,687,000 tons (3.7 billion pounds). A Dow Chemical Company manufacturing facility in Michigan, houses about 35% of the total U.S. production capacity for calcium chloride.Sony VAIO VGN-Z92JS Battery

Occurrence

Calcium chloride occurs as the rare evaporite minerals sinjarite (dihydrate) and antarcticite (hexahydrate). A related mineral chlorocalcite (potassium calcium chloride, KCaCl3) is also very rare.Sony VAIO VGN-Z92PS Battery

Desiccant

Drying tubes are frequently packed with calcium chloride. Kelp is dried with calcium chloride for use producing sodium carbonate. Adding solid calcium chloride to liquids can remove dissolved water. Calcium chloride is also used in products such as DampRid and Dri-Z-Air which is advertised as an air moisture absorber.Sony VAIO VGN-Z92YS Battery

Anhydrous calcium chloride has been approved by the FDA as a packaging aid to ensure dryness (CPG 7117.02).

These hygroscopic properties are also applied to keep a liquid layer on the surface of the roadway, which holds dust down.Sony VAIO VGN-Z93FS Battery

Deicing and freezing point depression

By depressing the freezing-point calcium chloride is used to prevent ice formation and to deice. This is particularly useful on road surfaces. Calcium chloride dissolution is exothermic, and is relatively harmless to plants and soil; however, recent observations in Washington state suggest it may be particularly harsh on roadside evergreen trees.Sony VAIO VGN-Z93GS Battery

It is also more effective at lower temperatures than sodium chloride. When distributed for this use, it usually takes the form of small white balls a few millimeters in diameter, called prills. Solutions of calcium chloride can prevent freezing at temperature as low as ?52 °C (?62 °F), making it ideal for filling agricultural implement tires as a liquid ballast, aiding traction in cold climates.Sony VAIO VGN-Z93HS Battery

Source of calcium ions

Calcium chloride is used to increase the hardness in swimming pools. This reduces the erosion of the concrete in the pool. ByLe Chatelier's principle and the common ion effect, increasing the concentration of calcium in the water will reduce the dissolution of calcium compounds essential to the structure of concrete.Sony VAIO VGN-Z93VS Battery

In marine aquariums calcium chloride is added to introduce bioavailable calcium for calcium carbonate shelled animals such asmollusks and cnidarians. Calcium hydroxide (kalkwasser mix) or a calcium reactor can also be used to introduce calcium, however calcium chloride addition is the fastest method and has minimal impact on pH.Sony A1258274A Battery

Food

As an ingredient, it is listed as a permitted food additive in the European Union for use as a sequestrant and firming agentwith the E number E509, and considered as generally recognized as safe (GRAS) by the U.S. Food and Drug Administration. The average intake of calcium chloride as food additives has been estimated to be 160–345 mg/day for individuals.Sony VGP-BPL10 Battery

As a firming agent calcium chloride is used in canned vegetables, in firming soy bean curds into tofu and in producing acaviar substitute from vegetable or fruit juices .It is commonly used as an electrolyte in sports drinks and other beverages including Smartwater and Nestle bottled water.Sony VGP-BPS10 Battery

The extremely salty taste of calcium chloride is used to flavorpickles while not increasing the food's sodium content. Calcium chloride's freezing-point depression properties are used, for example, in Cadbury Caramilk chocolate bars to slow the freezing of the caramel.Sony VGP-BPS10/S Battery

In brewing beer, calcium chloride is sometimes used to correct mineral deficiencies in the brewing water. It affects flavor and chemical reactions during the brewing process, and can also affect yeast function during fermentation. Calcium chloride is sometimes added to processed milk to restore the natural balance between calcium and protein in casein for the purposes of making cheese such as brie, Pélardon and stilton.Sony VGP-BPS10A/B Battery

Medicine

Calcium chloride can be injected as intravenous therapy for the treatment of hypocalcaemia. It can be used for magnesium intoxication. Calcium chloride injection may antagonize cardiac toxicity as measured by electrocardiogram. It can help to protect the myocardium from dangerously high levels of serum potassium in hyperkalemia.Sony VGP-BPS10B Battery

Calcium chloride can be used to quickly treat Calcium Channel Blocker toxicity, from the side effects of drugs such as Cardizem — helping avoid potential heart attacks. [11]

Aqueous calcium chloride is used in genetic transformation of cells by increasing the cell membrane permeability, inducingcompetence for DNA uptake (allowing DNA fragments to enter the cell more readily).Sony VGP-BPS10A Battery

Other

Calcium chloride is used in concrete mixes to help speed up the initial setting, but chloride ion leads to corrosion of steelrebar, so it should not be used in reinforced concrete.[12] The anhydrous form of calcium chloride may also be used for this purpose and can provide a measure of the moisture in concrete.Sony VGP-BPS11 Battery

Calcium chloride is used in swimming pool water as a pH buffer and to adjust the calcium hardness of the water.

Calcium chloride is included as an additive in plastics and in fire extinguishers, in wastewater treatment as a drainage aid, in blast furnaces as an additive to control scaffolding (clumping and adhesion of materials that prevent the furnace charge from descending), and in fabric softener as a thinner.Sony VGP-BPL11 Battery

The exothermic dissolution of calcium chloride is used in self-heating cans and heating pads.

In the oil industry calcium chloride is used to increase the density of solids free brines. It is also used to provide inhibition of swelling clays in the water phase of invert emulsion drilling fluids.Sony VGP-BPL12 Battery

Toxicology

Calcium chloride can act as an irritant by desiccating moist skin. Solid calcium chloride dissolves exothermically and burnscan result in the mouth and esophagus if calcium chloride is ingested. Ingestion of concentrated solutions or solid calcium chloride products may cause gastrointestinal irritation or ulceration.Sony VGP-BPS12 Battery,Sony VGP-BPL13 Battery,Sony VGP-BPS13 Battery,Sony VGP-BPS13/B Battery,Sony VGP-BPS13/S Battery