What is Hydrated Lime? Definition, Production, Properties & Uses
A complete guide to hydrated lime (calcium hydroxide) — what it is, how it is made, its chemical properties, available grades, and why it is one of the most widely used industrial minerals in India.
What is Hydrated Lime? Definition, Production, Properties & Uses
Frequently Asked Questions
What is hydrated lime and how is it different from quicklime?
Hydrated lime (calcium hydroxide, Ca(OH)₂) is produced by adding water to quicklime (calcium oxide, CaO) in a process called slaking. Quicklime is a highly reactive, caustic material that generates intense heat when it contacts water. Hydrated lime is a fine white powder that is safer to handle, easier to dose, and is the standard form used in most industrial applications. The chemical reaction is: CaO + H₂O → Ca(OH)₂ + Heat.
What is the chemical formula of hydrated lime?
The chemical formula of hydrated lime is Ca(OH)₂. Its IUPAC name is calcium hydroxide. It has a molecular weight of 74.09 g/mol, a density of 2.21 g/cm³, and forms a strongly alkaline solution (pH ~12.4) when dissolved in water. It is also known as slaked lime, builder's lime, and milk of lime (when mixed with water).
What is the IS 712 standard for hydrated lime?
IS 712 is the Bureau of Indian Standards specification for hydrated lime. It defines two classes: Class C (minimum 65% Ca(OH)₂, for construction and general industrial use) and Class S (minimum 90% Ca(OH)₂, for water treatment and food-grade applications). IS 712 certification is mandatory for hydrated lime used in NHAI highway projects, municipal water treatment, and other regulated applications.
What purity grades of hydrated lime are available in India?
Hydrated lime is available in multiple purity grades in India. Shree Ram Lime & Chemical manufactures six grades: Standard (70–75% Ca(OH)₂), Industrial (80–85%), Premium (88–92%), and Ultra (93–95%). The right grade depends on your application — water treatment and AAC blocks require 90%+ purity, while general construction can use lower grades.
How is hydrated lime produced from limestone?
Hydrated lime is produced in three stages. First, high-quality limestone (CaCO₃) is quarried and selected. Second, the limestone is calcined (burned) in a kiln at 900–1,000°C to produce quicklime (CaO): CaCO₃ → CaO + CO₂. Third, water is added to the quicklime in a controlled hydrator to produce hydrated lime (Ca(OH)₂): CaO + H₂O → Ca(OH)₂. The quality of each stage — limestone purity, calcination control, and hydration process — determines the quality of the final product.
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