Calcium Hydroxide Uses Across Industries: Complete Guide
From water treatment to steel, sugar, AAC blocks, paper, and chemicals — a comprehensive guide to calcium hydroxide (hydrated lime) uses across every major industry in India, with dosage rates and grade requirements.
Calcium Hydroxide Uses Across Industries: Complete Guide
Frequently Asked Questions
What are the main uses of calcium hydroxide in water treatment?
Calcium hydroxide (hydrated lime) is used in water treatment for: pH correction and alkalinity adjustment (raising pH to prevent pipe corrosion), water softening (lime-soda process to remove hardness), coagulation aid (optimising pH for coagulant performance), fluoride removal (precipitating fluoride as calcium fluoride), heavy metal precipitation (at pH 9–11, dissolved metals precipitate as hydroxides), and sludge conditioning (raising pH above 12 to kill pathogens). IS 712 Class S (90%+ Ca(OH)₂) is the standard specification for water treatment.
How is hydrated lime used in AAC block manufacturing?
In AAC block manufacturing, hydrated lime (15–20% of the mix by weight) reacts with silica (from fly ash or sand) under high-pressure steam curing (autoclaving at 180°C, 10 bar) to form tobermorite — a calcium silicate hydrate that gives AAC blocks their strength. Ultra grade lime (93–95% Ca(OH)₂) with MgO below 1.5% is required. High MgO causes unsoundness (delayed expansion and cracking). Typical consumption is 60–80 kg per cubic metre of AAC blocks.
What is the role of hydrated lime in sugar manufacturing?
In sugar mills, hydrated lime is used for juice clarification (defecation process). Raw sugarcane juice contains impurities — proteins, waxes, gums, and organic acids — that must be removed before crystallisation. Lime is added to raise pH to 8.0–8.5, precipitating impurities as calcium salts. The limed juice is then carbonated (CO₂ added) to precipitate excess lime as calcium carbonate, which carries the impurities down as a floc. Typical consumption is 0.8–1.5 kg of hydrated lime per tonne of sugarcane processed.
Can calcium hydroxide be used in food and pharmaceutical applications?
Yes. Food-grade calcium hydroxide (E526) is approved for use in food processing. It is used in the nixtamalisation of corn (making tortillas and masa), as a firming agent in canned vegetables, as a pH regulator in food processing, and as a calcium supplement in animal feed. For food and pharmaceutical applications, Ultra grade lime (93–95% Ca(OH)₂) with very low heavy metal content is required. A food-grade certificate and compliance with FSSAI regulations are necessary.
Which industries use the most hydrated lime in India?
By volume, the largest consumers of hydrated lime in India are: road construction (soil stabilization and bituminous mixes, driven by Bharatmala and PM Gati Shakti), water treatment (municipal and industrial), sugar mills (juice clarification), and AAC block manufacturing (the fastest-growing segment, growing 15–20% annually). Chemical manufacturing (bleaching powder, calcium carbide, PCC) and paper mills (causticisation) are also significant consumers.
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