Preparation, properties and uses of quick lime

Calcium oxide is commonly called Quick Lime. Quick lime has always been a cheap commodity because limestone deposits are readily available. Lime manufacturing and application dates back to the Roman, Greek and Egyptian civilizations.

Raw Materials

Calcium carbonate and magnesium carbonate obtained from deposits of limestone, chalk, marble, dolomite, oyster shells, stalactites and stalagmites. Vertical or horizontal kilns are used to burn limestone. The kilns have steel shells line with refracting bricks.

Calcium oxide or lime is prepared by the calcination process. Limestone or calcium carbonate is heated to a temperature between 1200^oC and 1300^oC in Kilns and it decomposes to quicklime and carbon dioxide.

A Vertical Lime Kiln

This is a reversible reaction. It is exothermic in the forward direction. To ensure that the limestone is completely converted to lime, carbon dioxide is allowed to escape from the Kiln. This makes carbon dioxide unavailable for the reverse reaction.

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Properties of Quick Lime

• Lime is a white amorphous solid.

• It has a high melting point of 2600^oC.

• It is highly stable and even fusion cannot decompose it.

Chemical Properties

• On hydration, quick lime forms slaked lime or lime water. When water is added to lime it becomes hot and cracks to form a white powder. This is called slaking of lime.

• Calcium oxide is a basic oxide. It can react with acids to give calcium salts.

• With acidic oxides like silicon dioxide and phosphorus pentoxide, it forms silicates and phosphates. This property makes lime useful as a flux in metallurgy to remove impurities.

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Uses of Lime

• Lime is indispensable for use with mortar and plaster.

• Lime is used for medicinal purposes, insecticides and plant and animal food.

• It is used as a laboratory reagent for gas absorption, precipitation, dehydration etc.

• It is used as a reagent in the manufacture of paper, high grade steel and cement.

• If finds use in dehairing hides.

• It can be used for water softening and in the recovery of ammonia (by-product of Solvay process).

• It finds enormous use in the manufacture of soap, rubber, varnish, refractories and lime bricks.

• It also finds use in the preparation of calcium carbide, basic calcium nitrate and calcium bisulphite.

• Improves the quality of soil.