What to Check Before Buying Quick Lime

Quick lime looks simple to buy. It is calcium oxide; the seller quotes a purity and a price per tonne; the buyer compares two quotations and picks the lower one. Then the first lot arrives, slakes slowly in the dosing tank, carries more fines than the feeder can take, or runs out of specification in the third week because it sat uncovered in the yard. None of that showed on the quotation, because the quotation was never asked the right questions.

This article is the list of those questions. It is written for a purchase or plant engineer buying quick lime for an industrial duty in India, and it stays with what can be checked: a number, a method, a document, a term on the order.

1. Start from the duty, not the datasheet

The grade of quick lime a process needs follows from what the lime has to do, and every other check depends on it.

• A steel melt shop charges lime as a flux. It wants high available lime, low silica and sulphur, a reactivity that suits the furnace, and a lump size the charging system can handle without excess fines.
• A water or effluent plant slakes lime to make milk of lime for pH correction or softening. It wants consistent reactivity so the slaker behaves the same every day, and a size the slaker was designed for.
• A chemical plant making a calcium compound wants the impurity profile — magnesium, silica, iron — controlled, because the impurities end up in the product.
• Soil stabilisation and construction want enough reactive lime per tonne, and a form that can be spread or mixed on site.

Write the duty on the enquiry. A supplier who asks for it before quoting is doing the first check for you; the article on choosing a supplier covers what else that tells you.

2. Agree the chemical numbers — with their methods

A quotation that says "CaO 85%" has not said enough. Decide which of these your process is actually paying for, and ask the seller to quote each against a named test method:

• Available lime — the calcium oxide that will react, as distinct from total calcium. This is the number that governs dosing and flux cost.
• Total CaO, and whether the figure is "on ignited basis" or as received; the two differ.
• MgO, SiO₂, R₂O₃ (iron and aluminium oxides) — the impurities, each against a maximum.
• Loss on ignition — a measure of unburnt carbonate and picked-up moisture; a low figure means well-burnt lime that has been kept dry.
• Sulphur, if the duty is metallurgical.

The method matters as much as the number. In India the reference methods for sampling and testing quicklime and hydrated lime are set out in IS 1514; the specification for quicklime for chemical industries is IS 1540 (Part 1). ASTM C25 covers the chemical analysis of limestone, quicklime and hydrated lime. Two laboratories using two methods can report two different "available lime" figures on the same lot, and a purchase order that names the method settles the argument before it starts. The article on reading a certificate of analysis goes through each parameter.

3. Agree reactivity the same way

Reactivity — how fast the lime slakes — is the property most often argued about and least often specified. There are several ways to measure it: the temperature rise when a set mass of lime is slaked in a set volume of water (the approach in ASTM C110 and EN 459-2), or the volume of acid consumed in a fixed time, which some Indian steel plants use. The results are not interchangeable. Choose the method your laboratory can run, write it on the order, and ask for it on every certificate.

4. Fix the size fraction

Lump quick lime is sold in size bands. Deshwali Minerals, for example, grades quick lime in 0–3 mm, 0–10 mm and 10–50 mm fractions, and supplies ground quick lime powder for duties that want a fine material. The right band is the one your feeder, slaker or furnace was designed for, and the question to ask is how much material outside the band the seller allows. A lot that is "10–50 mm" with a fifth of its weight below 10 mm behaves differently in a charging bucket from one with five percent.

5. Decide the packing against the journey

Quick lime takes up moisture from the air and begins to slake in the bag. Packing therefore depends on how far the material travels, in which season, and what will unload it: small bags where there is no lifting equipment, lined jumbo bags for long or humid journeys, loose tipper loads for a short run into covered storage. The packing, storage and transport article sets out the choice; the point here is that packing is agreed on the order, not left to the seller's default.

6. Understand the quantity and the price basis

Industrial lime moves by the truckload, so minimum orders in the forty-tonne range are normal — Deshwali Minerals' published minimum is 42 to 44 tonnes depending on the product. Prices are usually quoted ex-works, with GST at the applicable rate and freight added, so the delivered cost at your gate is the number to compare, not the ex-works rate. Ask for the quotation to state:

• the product, grade and size fraction;
• the rate, its basis (ex-works or delivered), and the GST treatment;
• packing, and whether it is included;
• the delivery point and the expected dispatch time;
• validity, and the payment terms.

A quotation with all of this is an offer a buyer can accept. One with a price and nothing else is the beginning of a negotiation at best.

7. Settle what happens to an out-of-specification lot

Every lot should be tested before it is loaded, and a lot outside the agreed band should be held at the plant. Write that down: certificate before dispatch, the retained-sample and retest procedure if the buyer's laboratory disagrees, and what happens to a rejected lot. These terms cost nothing to agree while both sides are friendly and a great deal to argue about after a truck has arrived.

8. Check the seller as carefully as the lime

A specification is only as good as the firm behind it. Before money moves, verify the GSTIN on the GST portal, match the beneficiary bank account to the firm's name, and confirm that the plant exists where the seller says it does. The supplier verification article covers this step by step.

9. Test a sample before committing tonnage

A sample drawn from a tested lot, with its certificate, lets your laboratory run the agreed methods on the actual material before a consignment is ordered. It is the cheapest check on this list. Deshwali Minerals will send a sample against the duty you describe, with the parameters it was tested for.

The short version

Decide the duty; agree the numbers and their methods; fix size, packing, quantity and price basis on the order; agree in advance what happens to an off-specification lot; verify the seller; test a sample. Done in that order, buying quick lime is as predictable as buying any other industrial input.

Sources

• Bureau of Indian Standards, IS 1514:1990 — Methods of sampling and test for quicklime and hydrated lime: BIS standards portal
• Bureau of Indian Standards, IS 1540 (Part 1) — Specification for quick lime and hydrated lime for chemical industries, Part 1 quick lime: BIS standards portal
• ASTM C25 (chemical analysis) and ASTM C110 (physical testing) of limestone, quicklime and hydrated lime: ASTM International