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Limestone when heated starts decomposing into lime (CaO) and carbon di-oxide (CO2) at 810 deg C. The process is called calcination of limestone. It is a thermal treatment process which is carried out for the thermal decomposition of the raw limestone for the removal of LOI (loss on ignition) or carbon di-oxide (CO2) part of its composition. The product of calcination of limestone is Quicklime which mainly consists of CaO. During the calcination of limestone, since CO2 is removed, the lime (i) is porous (ii) has higher surface area, (iii) has high reactivity, and (iv) is hygroscopic. CaCO3 + around 42.5 kcal of heat = CaO + CO2 Around 1.8 t of limestone is required to produce 1 t of Quicklime. The quicklime is not stable. In the presence of moisture, lime reacts slowly with carbon dioxide in the air, reforming calcium carbonate. Further because of its hygroscopic nature, it absorbs moisture from the ambient air. With the absorption of moisture, it starts losing its reactivity. Since Quicklime has a high affinity for water it is an efficient desiccant. The reaction of Quicklime with water is associated with an increase in volume by a factor of at least 2.5. As Quicklime is a chemically active material, it is desirable to reduce its atmospheric exposure during handling and storage to a minimum. Quicklime, also known as Calcined Lime is expected normally to show high reactivity. A large number of pores exist on the surface when the Quicklime has high reactivity and when it is very porous. Temperature and time of calcination play an important role in the reactivity of Quicklime. The reactivity of Quicklime is also dependent on the homogeneity of lime, the degree of thermal decomposition of limestone, and the specific surface area the Quicklime.

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