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.
Properties
Calcium chloride can serve as a source of calcium ions in an aqueous solution, as calcium
chloride is soluble in water. 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:
CaCl2(l) → Ca(s) + Cl2(g) Calcium chloride has a very high enthalpy
change of solution. A considerable temperature rise accompanies its dissolution in water.
The anhydrous salt is deliquescent; it can accumulate enough water in its crystal lattice
to form a solution. 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. A Dow Chemical Company manufacturing facility in Michigan houses about 35% of the
total U.S. production capacity for calcium chloride.
Occurrence Calcium chloride occurs as the rare evaporite
minerals sinjarite and antarcticite. A related mineral chlorocalcite is also very rare.
Uses Desiccant
Drying tubes are frequently packed with calcium chloride. Kelp is dried with calcium chloride
for use in producing sodium carbonate. Adding solid calcium chloride to liquids can remove
dissolved water. Anhydrous calcium chloride has been approved by the FDA as a packaging
aid to ensure dryness. These hygroscopic properties are also applied
to keep a liquid layer on the surface of the roadway, which holds dust down.
Deicing and freezing point depression
By depressing the freezing point of water, calcium chloride is used to prevent ice formation
and to deice. This is particularly useful on road surfaces. Calcium chloride dissolution
is exothermic, and the compound is relatively harmless to plants and soil; however, recent
observations in Washington state suggest it may be particularly harsh on roadside evergreen
trees. 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, making it ideal for filling agricultural implement tires as a liquid ballast,
aiding traction in cold climates. Source of calcium ions
Calcium chloride is used to increase the water hardness in swimming pools. This reduces the
erosion of the concrete in the pool. By Le 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. In marine aquariums, calcium chloride is added
to introduce bioavailable calcium for calcium carbonate-shelled animals such as mollusks
and some cnidarians. Calcium hydroxide 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. Food
As an ingredient, it is listed as a permitted food additive in the European Union for use
as a sequestrant and firming agent with the E number E509. It is considered as generally
recognized as safe by the U.S. Food and Drug Administration. Its use in organic crop production
is generally prohibited under US National Organic Program's National List of Allowed
and Prohibited Substances. The average intake of calcium chloride as food additives has
been estimated to be 160–345 mg/day for individuals.
As a firming agent, calcium chloride is used in canned vegetables, in firming soybean curds
into tofu and in producing a caviar substitute from vegetable or fruit juices. It is commonly
used as an electrolyte in sports drinks and other beverages, including bottled water.
The extremely salty taste of calcium chloride is used to flavor pickles while not increasing
the food's sodium content. Calcium chloride's freezing-point depression properties are used
to slow the freezing of the caramel in caramel-filled chocolate bars.
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 cheeses, such as brie, Pélardon and Stilton. Also, it is frequently added
to sliced apples to maintain texture. Medicine
It is injected to treat internal hydrofluoric acid burns. It can be used to treat 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. Calcium chloride can be used to quickly treat calcium
channel blocker toxicity, from the side effects of drugs such as diltiazem — helping avoid
potential heart attacks. Aqueous calcium chloride is used in genetic
transformation of cells by increasing the cell membrane permeability, inducing competence
for DNA uptake. Animal sterilization
Calcium chloride dihydrate dissolved in ethanol has been used as a sterilant for male animals.
The non surgical procedure consists of the injection of the solution into the testes
of the animal. Within 1 month, necrosis of testicular tissue results in sterilization.
Other Calcium chloride is used in concrete mixes
to help speed up the initial setting, but chloride ions lead to corrosion of steel rebar,
so it should not be used in reinforced concrete. The anhydrous form of calcium chloride may
also be used for this purpose and can provide a measure of the moisture in concrete.
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, and in fabric softener as a thinner.
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. CaCl2 acts as flux material in the Davy process
for the industrial production of Sodium metal, through the electrolysis of molten NaCl.
Calcium chloride is also an ingredient used in ceramic slipware. It suspends clay particles
so that they float within the solution making it easier to use in a variety of slipcasting
techniques. Hazards
Calcium chloride can act as an irritant by desiccating moist skin. Solid calcium chloride
dissolves exothermically, and burns can result in the mouth and esophagus if it is ingested.
Ingestion of concentrated solutions or solid products may cause gastrointestinal irritation
or ulceration. Other possible side effects of taking calcium
chloride include: A chalky taste in the mouth
Hot flushes Lowered blood pressure
Loss of appetite Feeling sick
Being sick Constipation
Stomach pain Feeling weak
Mental disturbances Extreme thirst
Passing a large amount of urine Bone pain
Kidney stones Irregular heart beat
Coma Any of these may be a sign of overly high
calcium blood levels. Calcium chloride salts also tend to contain
a small amount of metals, especially aluminium. Over time these metals can accumulate in the
body and have a toxic effect. See also
Calcium(I) chloride Calcium chloride transformation
References
Greenwood, Norman N.; Earnshaw, Alan. Chemistry of the Elements. Butterworth-Heinemann. ISBN 0080379419.
External links International Chemical Safety Card 1184
Product and Application Information Report on steel corrosion by chloride including
CaCl2 Collection of calcium chloride reports and
articles Calcium chloride, Anhydrous MSDS