Same limestone, one extra reaction — and a completely different material to handle, store and dose. How to choose between calcium oxide and calcium hydroxide for your duty.
Both products start as the same stone. Limestone — calcium carbonate, CaCO3 — is burnt in a kiln to drive off carbon dioxide, leaving calcium oxide: quick lime. Add a controlled amount of water to that and it converts to calcium hydroxide: hydrated lime, also called slaked lime. One extra reaction step, and the two materials behave so differently that choosing the wrong one costs money at best and creates a safety problem at worst.
This guide sets out the practical differences a buyer needs, and which product fits which duty.
The chemistry in one paragraph
Quick lime is CaO. It is hungry for water: when the two meet, the reaction releases significant heat — enough to boil the water it is reacting with. That reactivity is exactly what makes it valuable in process industries, and exactly what makes it demanding to store and handle. Hydrated lime is Ca(OH)2 — quick lime that has already had that reaction, carried out deliberately and under control at the plant. What arrives on your site is a dry, stable, free-flowing powder that delivers alkalinity without the heat.
Where quick lime is the right answer
- Steelmaking and metallurgy. Lime is the primary flux: it combines with silica and other impurities in the melt to form slag. The furnace wants the most concentrated, most reactive form of calcium available — that is quick lime, in a size fraction matched to how it is charged. Lime in steelmaking is about consistency of reactivity above all else.
- Processes that use the heat. In sludge conditioning and some soil-stabilisation work, the exothermic slaking reaction is doing useful drying work. Hydrated lime cannot contribute that.
- High-volume neutralisation. Tonne for tonne, quick lime carries more neutralising power than hydrated lime, because the water it will react with is not part of the delivered weight. Where a plant has proper slaking equipment, buying quick lime and slaking on site is usually the more economical route at scale.
Where hydrated lime is the right answer
- Dosing without slaking equipment. If your plant meters lime into a process by hand or with simple equipment, hydrated lime is the practical choice — it can be dosed straight from the bag. Water treatment works frequently run on hydrated lime for exactly this reason.
- Mortars, plasters and construction chemistry. Hydrated lime blends predictably into dry mixes and gives workability that cement alone does not. In construction, it is the lime that goes into the mix; quick lime is the lime that goes under the road.
- Agriculture. Soil pH correction wants a material that can be spread and handled on an open site without heat risk. Hydrated lime acts faster than ground limestone; both are safer to spread than quick lime.
- Sites where handling discipline is limited. Quick lime demands dry storage and trained handling, because any contact with water — rain, humidity, sweat — starts an exothermic reaction. If that discipline is hard to guarantee, specify hydrated lime.
The differences at a glance
- Form: quick lime arrives as lumps or graded granules (also milled, as quick lime powder); hydrated lime is always a fine dry powder.
- Reaction with water: quick lime reacts violently and exothermically; hydrated lime dissolves modestly with no heat problem.
- Neutralising power per tonne: quick lime is higher — you are not paying to transport the water of hydration.
- Handling risk: quick lime is the more hazardous material; both are alkaline and need gloves, goggles and dust control.
- Storage life: both degrade in contact with air — quick lime by picking up moisture and carbon dioxide, hydrated lime by carbonation. Sealed packing and stock rotation matter for both; they matter more for quick lime.
- Slaking equipment: needed to use quick lime as a liquid reagent; not needed for hydrated lime.
What it means commercially
Because hydrated lime has been through an extra process step and weighs more per unit of active lime, the delivered economics differ from the headline price. The honest comparison is cost per tonne of available lime delivered and usable at your plant — including whether you have slaking capacity, how far the material travels, and what packing the journey demands. Lime is supplied ex-works with GST and transport additional, so the delivery point is part of the price question, not an afterthought.
Deshwali Minerals supplies both products from Borunda, Rajasthan, in 10 kg and 40 kg bags, jumbo bags and bulk, with minimum orders from 42 tonnes. If you can tell us the duty — flux, neutralisation, stabilisation, treatment, soil correction — we will recommend the product and the size fraction rather than leaving the choice to you.
The short version
Buy quick lime when your process wants maximum reactive calcium, can handle the material safely, and either uses the heat of slaking or has the equipment to slake. Buy hydrated lime when you dose directly, blend into mixes, spread on land, or want the simplest material to handle and store. If you are unsure, request a quotation and describe the application — recommending the right grade is part of the job.