Hydrated Lime - Lime Trade Turkey - AKAR Lime Trade Consultant and Analysis Company

Hydrated Lime

Calcium hydroxide, traditionally called slaked lime, is an inorganic compound with the chemical formula Ca(OH)2. It is a colorless crystal or white powder and is obtained when calcium oxide (called lime or quicklime) is mixed, or "slaked" with water. It has many names including hydrated lime, builders' lime, slack lime, cal, or pickling lime. Calcium hydroxide is used in many applications, including food preparation. Limewater is the common name for a saturated solution of calcium hydroxide.

When heated to 512 °C, the partial pressure of water in equilibrium with calcium hydroxide reaches 101 kPa (normal atmospheric pressure), which decomposes calcium hydroxide into calcium oxide and water.

Ca(OH)2 → CaO + H2O

A suspension of fine calcium hydroxide particles in water is called milk of lime. The solution is called limewater and is a medium strength base that reacts with acids and attacks many metals. Limewater turns milky in the presence of carbon dioxide due to formation of calcium carbonate, a process called carbonatation:

Ca(OH)2 + CO2 → CaCO3 + H2O

Calcium hydroxide adopts a polymeric structure, as do the related hydroxides of the alkaline earth metals. The packing resembles the cadmium iodide motif with layers of octahedral Ca centres. Strong hydrogen bonds exist between the layers.

The structure of calcium hydroxide, with the hydrogen atoms omitted (purple = O centres).

Calcium hydroxide is produced commercially by treating lime with water:

CaO + H2O → Ca(OH)2

In the laboratory it can be prepared by mixing aqueous solutions of calcium chloride and sodium hydroxide. The mineral form, portlandite, is relatively rare but can be found in some volcanic, plutonic, and metamorphic rocks. It has also been known to arise in burning coal dumps.

One significant application of calcium hydroxide is as a flocculant, in water and sewage treatment. It forms a fluffy charged solid that aids in the removal of smaller particles from water, resulting in a clearer product. This application is enabled by the low cost and low toxicity of calcium hydroxide. It is also used in fresh water treatment for raising the pH of the water so pipes will not corrode where the base water is acidic because it is self-regulating and does not raise the pH too much.

Another large application is in the paper industry, where it is used in the production of sodium hydroxide. This conversion is a component of the Kraft process.

Calcium hydroxide is produced on a large scale, is easily handled and is generally inexpensive. Numerous niche applications are in use. A partial listing follows:

In life support systems as a carbon dioxide scrubber, particularly in closed-circuit diving re-breathers such as the US Navy LAR V or MK-16, where the more caustic lithium hydroxide is deemed too risky due to inhaled dust, combat handling, or generation of caustic "slurry" in flooding events

An ingredient in whitewash, mortar, and plaster

In road construction, to improve the quality of excessively plastic subgrade soils

To fill the root canal for the first stage of endodontic therapy (it is then replaced by rubber)

As an additive to sea water to reduce atmospheric CO2 and mitigate the greenhouse effect

In the production of metals, lime is injected into the waste gas stream to neutralize acids, such as fluorides and chlorides prior to being released to atmosphere.

An alkali used as a lye substitute in no-lye hair relaxers

A chemical depilatory agent found in most hair removal creams (for example Nair)

In Bordeaux mixture to neutralize the solution and form a long-lasting fungicide

In lime-sulfur, it is mixed with sulfur and boiled in water for an hour. The ratio by mass of Ca(OH)2:Sulfur:water is about (1):(1.7):(8.6). Diluted (1:25) lime-sulfur is used as a dip to combat sarcoptic mange. Against fungus on plants it is used in various concentrations.

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 petrochemical industry for manufacturing solid oil of various marks

In the manufacture of brake pads

In manufacturing the trademarked compound "Polikar", an antifungal and antimicrobial preservative for vegetables in storage

For preparation of dry mixes for painting and decorating

In manufacturing mixes for pesticides

In the manufacture of ebonite

As a calcium supplement and pH/carbonate buffer (known as Kalkwasser lit. trans. lime-water) for the aquaculture of corals in reef aquaria.

As a natural "alternative" insecticide, most crawling insects are killed by its touch, including ticks, fleas, beetles and grubs.

Because of its low toxicity and the mildness of its basic properties, slaked lime is widely used in the food industry to:

clarify raw juice from sugarcane or sugar beets in the sugar industry, (see carbonatation)

process water for alcoholic beverages and soft drinks

pickle cucumbers and other foods

make Chinese century eggs

make corn tortillas (it helps the corn flour (masa) bind together) (see nixtamalization)

clear a brine of carbonates of calcium and magnesium in the manufacture of salt for food and pharmaceutical uses

fortify (Ca supplement) fruit drinks, such as orange juice, and infant formula

aid digestion (used in India as paan, a mixture of areca nuts, calcium hydroxide and a variety of seeds wrapped in betel leaves)

substitute for baking soda in making papadam.