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Calcium Oxide

Last updated: May 2, 2018

What Does Calcium Oxide Mean?

Calcium oxide (CaO) is a calcium-containing inorganic material in which carbonates, oxides and hydroxides are predominating. It is a white crystalline solid with a melting point of 2572 °C (4662 °F). It is manufactured by heating limestone, coral, seashells or chalk, which are mainly composed of CaCO3, to drive off carbon dioxide.

Calcium oxide (with ferrous sulfate) is used extensively for wastewater treatment and for cement production.

Frequently uses for calcium oxide:

  • Building and engineering materials
  • Producing chemical feed stocks
  • Producing chemicals
  • Refining sugar

Calcium oxide is also known as lime.


Corrosionpedia Explains Calcium Oxide

Calcium oxide, commonly known as lime, has the chemical formula CaO. Hydrated lime is called calcium hydroxide, Ca(OH)2, which is the cement in concrete.

Calcium oxide has an adhesive property with bricks and stones, so it is used as a binding material in masonry works. It is also used in whitewashing as a wall coat so that the white wash adheres to the wall.

Calcium oxide, as used in building products, is broadly classified in three types:

  • Pure – Also known as fat, rich, air, slaked, slack, pickling, hydrated and high-calcium lime. It consists primarily of calcium hydroxide and may contain up to 5% other ingredients.
  • Hydraulic – Also called water lime. It contains lime with silica and/or alumina and sets with exposure to water. It can be set underwater.
  • Poor lime – Also known as lean or meager lime. Poor lime sets and cures very slowly and has weak bonding.

Nearly 45% of lime or calcium oxide is used in the steel industry. It is also used in the production of other metals. For example, it is used to remove silicates from alumina before the alumina is reduced to aluminum metal.

Calcium oxide is used in stack gas scrubbers to reduce sulfur dioxide emissions from power plants. It is also added to sewage to remove phosphates. Lime is used to pretreat water supplies to decrease the acidity and to soften drinking water. A variety of other industrial processes also make extensive use of calcium oxide.


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