About Calcined Dolomite
Calcined dolomite is dolomite that has been heated at roughly 900–1,100 °C to drive off carbon dioxide, leaving a porous, reactive mixture of calcium oxide and magnesium oxide known as doloma or light-burnt dolomite. Because the structure stays open, it dissolves quickly in molten slag. That speed of dissolution, together with its high magnesia content, is the main reason steel plants specify it.
In basic oxygen and electric arc furnaces, slag that is under-saturated in MgO attacks the magnesia-carbon refractory lining to take up the magnesia it lacks. Adding calcined dolomite with the lime charge supplies that MgO from outside, which reduces chemical wear on the lining and helps build slag suited to slag splashing and foamy slag practice. Its CaO fraction also adds basicity, so it partly replaces burnt lime as a flux. Refractory and lime-product makers use it as a reactive MgO–CaO raw material as well.
Obsidian Minerals supplies calcined dolomite in screened lump sizes for furnace additions, and as fines on request, with chemistry, residual loss on ignition and size agreed with the plant's metallurgy team. Calcined dolomite takes up moisture and carbon dioxide from the air, so it is packed in lined bags and is best used soon after delivery.
Typical specifications
| Parameter | Typical Value | Test Method |
|---|---|---|
| CaO | 55–59 % | ASTM C25 |
| MgO | 36–40 % | ASTM C25 |
| SiO₂ | ≤ 1.5 % | ASTM C25 |
| Fe₂O₃ + Al₂O₃ | ≤ 1.5 % | ASTM C25 |
| Loss on ignition | ≤ 3.0 % | ASTM C25 |
| Sulphur (S) | ≤ 0.05 % | Internal method |
| Size | 10–40 mm or 10–60 mm lump; 0–10 mm fines on request | Sieve analysis |
Typical values for guidance. Guaranteed limits, size fractions and any reactivity requirement are confirmed on the Technical Data Sheet and batch CoA.
Key features & benefits
High MgO for slag saturation
Typical MgO of 36–40 % lets a single addition bring steelmaking slag close to MgO saturation, so the slag draws less magnesia from the magnesia-carbon lining of the converter or furnace.
Fast dissolution in slag
Light-burnt calcination leaves a porous, high-surface-area structure. Calcined dolomite therefore dissolves into slag much faster than raw dolomite and avoids the heat cost of decarbonating stone inside the vessel.
Partial lime substitute
The CaO fraction contributes to slag basicity, so calcined dolomite can replace part of the burnt lime charge. The split between lime and doloma is set by each plant's slag model and targets.
Low residual LOI
Residual loss on ignition is typically 3 % or less, so little carbon dioxide is released in the vessel. That limits extra heat demand and lowers the risk of uncontrolled slag foaming or slopping.
Low sulphur and silica
Selected dolomite feed keeps sulphur and silica low, limiting the impurity load added to each heat and reducing the additional lime needed to neutralise silica in the slag.
Applications
BOF / LD converter slag conditioning
Charged with lime early in the blow to raise slag MgO, supporting slag splashing practice and reducing chemical wear on the magnesia-carbon converter lining between relines.
Electric arc furnace fluxing
Added through the roof or with the scrap charge to build a foamy slag of suitable MgO content, which helps shield sidewall refractories from arc radiation and improves energy use.
Ladle slag practice
Used in ladle and secondary metallurgy slags where a controlled MgO level helps reduce attack on magnesia or dolomite ladle linings during refining and holding.
Refractory and lime-product raw material
A reactive MgO–CaO source for refractory mixes and related products, and a feedstock that can be densified further by high-temperature sintering where dense dolomite grain is required.
Usage & handling
- Addition rates are calculated from slag chemistry; many converter practices aim for slag MgO near saturation, often in the region of 8–12 %, and the plant sets the dose from that target.
- Charge together with lime early in the heat so MgO is in solution before slag aggressiveness peaks.
- Store under cover in sealed bags; calcined dolomite hydrates and recarbonates on contact with humid air.
- Limit re-handling, which breaks lumps and generates fines, and use stock in delivery order.
- Wear dust masks, goggles and gloves; the material is strongly alkaline and releases heat on contact with water.
Packaging & supply
- 1 MT or 1.2 MT jumbo (FIBC) bags with inner liner for lump sizes
- 25 kg or 50 kg lined HDPE bags for fines and trial lots
- TDS, MSDS/SDS and batch CoA supplied with each consignment
Frequently asked questions
What is calcined dolomite used for in steelmaking?
Calcined dolomite is added to basic oxygen and electric arc furnace slags to supply MgO. Slag that already contains enough magnesia is far less aggressive towards the magnesia-carbon lining, so refractory wear falls. The material also contributes CaO as a flux, supports slag splashing in converters and helps form foamy slag in electric arc furnaces.
How does calcined dolomite differ from the burnt dolomite grade?
Calcined dolomite is light-burnt at around 900–1,100 °C and kept porous and reactive so it dissolves fast in slag; its job is chemical. The burnt dolomite grade is dead-burnt at sintering temperature until dense, and its job is to resist slag as a refractory. Choose calcined dolomite for fluxing and burnt dolomite for linings and furnace repair.
What MgO content does your calcined dolomite have?
Typical MgO is 36–40 %, with CaO of 55–59 % and residual loss on ignition of 3 % or less. Exact values depend on the source deposit and degree of calcination. Guaranteed limits for your order are given on the Technical Data Sheet, and every lot is shipped with a batch Certificate of Analysis.
Which lump sizes can you supply?
Common furnace sizes are 10–40 mm and 10–60 mm lump, matched to the plant's bunker and feeding system. Fines of 0–10 mm can be supplied for injection, briquetting or refractory use on request. Tell us your screening limits for oversize and undersize, and the size range will be confirmed on the Technical Data Sheet.
How should calcined dolomite be stored?
Keep it dry, covered and in its lined bags until it is charged. Calcined dolomite reacts with moisture to form hydroxides and slowly takes up carbon dioxide, which raises loss on ignition, creates fines and reduces its value as a flux. Use material in the order it was received and reseal any opened bags.