Calcium hydroxide

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Calcium hydroxide, traditionally called slaked lime, hydrated lime, or pickling lime, is a chemical compound with the chemical formula Ca(OH)₂. It is a colourless crystal or white powder, and is obtained when calcium oxide (called lime or quicklime) is mixed, or "slake" with water. It can also be precipitated by mixing an aqueous solution of calcium chloride and an aqueous solution of sodium hydroxide. The name of the natural, mineral form is portlandite. It is relatively rare mineral, known from some volcanic, plutonic and metamorphic rocks. Sometimes it arises on burning coal dumps, too.

When heated to 512 °C, the partial pressure of water in equilibrium with calcium hydroxide reaches 101 kPa and decomposes into calcium oxide and water. A suspension of fine calcium hydroxide particles in water is called milk of lime. The solution is called lime water and is a medium strength base that reacts violently with acids and attacks many metals in presence of water. It turns milky if carbon dioxide is passed through, due to precipitation of calcium carbonate.

Uses

Because of its strong basic properties, calcium hydroxide has many and varied uses:

• A flocculant, in water and sewage treatment and improvement of acid soils
• An ingredient in whitewash, mortar, and plaster
• An alkali used as a lye substitute in no-lye hair relaxers
• A chemical depilatory agent found in Nair
• An ingredient in baby formula milk
• A chemical reagent
• In the reef aquarium hobby for adding bio-available calcium in solution for calcium-using animals such as algae, snails, hard tube worms, and Corals (often referred to as Kalkwasser mix), and also to increase the alkalinity of the water.
• In the tanning industry for neutralization of acid, the liming of hides and skins and the flocculation of wastewater.
• In the petroleum refining industry for the manufacture of additives to oils (salicatic, sulphatic, fenatic)
• In the chemical industry for manufacture of calcium stearate
• In the food industry for processing water (for alcoholic and soft drinks)
• For clearing a brine of carbonates of calcium and magnesium in the manufacture of salt for food and pharmacopoeia
• In Native American and Latin American cooking, calcium hydroxide is called "cal". Corn cooked with cal becomes nixtamal which significantly increases its nutrition value, and is also considered tastier and easier to digest.
• In chewing Betel nut or coca leaves, calcium hydroxide is usually chewed alongside to keep the alkaloid stimulants chemically available for absorption by the body
• Similarly, Native Americans traditionally chewed tobacco leaves with calcium hydroxide derived from burnt shells to enhance the effects
• A filler
• In the petrochemical industry for manufacturing solid oil of various marks
• In the manufacture of brake pads
• In the manufacture of ebonite
• For preparation of dry mixes for painting and decorating
• In manufacturing mixes for pesticides
• In manufacturing the trademarked compound "Polikar", an antifungal and antimicrobial preservative for vegetables in storage
• In Dentistry, it is used as dressing in paste form used for anti-microbial effect during a dental root canal procedure. Calcium hydroxide is known to have a strong anti-microbial effect and is a bone-regeneration stimulant.
• It has been proposed to add it to sea water in great quantities to reduce atmospheric CO₂ and fight the greenhouse effect
• Used as an acid suppressor in the production of metals. Lime is injected into the waste gas stream to neutralise acids such as fluorides and chlorides prior to being released to atmosphere

Health risks

An overexposure to calcium hydroxide can have life threatening effects:

• Difficulty in breathing
• Internal bleeding
• Hypotension
• Skeletal muscle paralysis, interference with actin-myosin system.
• An increase in blood pH, which is damaging to the internal organs.

References

External links

• National Organic Standards Board Technical Advisory Panel "NOSB TAP Review: Calcium Hydroxid". Organic Materials Review Institute. Retrieved on 2008-02-05..
• MSDS Data Sheet
• Lime production process