Guide · Metals and minerals
Iron ore grades,explained.
An iron ore grade is defined by its iron content (Fe %, on a dry basis), its impurities and its size. Together they decide whether the ore goes to a sinter plant, straight into a blast furnace or into a direct reduction plant, and they are what the contract specifies and the inspector confirms at loading.
The short answer
What grade meansin iron ore.
In the iron ore trade, the grade is the Fe content of the ore, expressed as a percentage of its dry weight, together with limits on the main impurities: silica (SiO2), alumina (Al2O3), phosphorus (P), sulphur (S), loss on ignition (LOI) and moisture. A cargo described only as "62% Fe" is not fully specified: two ores with the same Fe can behave very differently in a furnace if their silica, alumina or phosphorus differ.
The product form matters as much as the chemistry: fines, lump, pellets and concentrate have different buyers, size limits and tests. This guide explains each parameter, why it matters to the steel plant, and how it is checked at loading. For the other ores and base metals we work with, see Metals and minerals; for refined copper, see copper cathode grades, explained.
Product forms
Fines, lump, pelletsand concentrate.
| Form | What it is | Main use |
|---|---|---|
| Fines (sinter feed) | Crushed and screened ore below the lump size | Blended and sintered before the blast furnace |
| Lump | Coarse screened ore | Charged directly into the blast furnace; selected lump in direct reduction furnaces |
| Pellets | Concentrate rolled into balls with a binder and fired | Blast furnace pellets, or DR-grade pellets for direct reduction |
| Concentrate (pellet feed) | Ore ground fine and upgraded by magnetic separation, flotation or gravity | Pelletising; some concentrate goes into sinter blends |
Fe content
How iron contentis quoted.
Fe is reported as a percentage of the dry sample. The bands below are descriptions commonly used in the trade, not fixed classes.
| Band | Typical Fe (dry basis) | Typical products |
|---|---|---|
| Low grade | Below about 58% Fe | Some fines, often blended or beneficiated before use |
| Mid grade | About 58 to 61% Fe | Fines and lump, often with higher LOI or alumina |
| Standard grade | About 62% Fe | Fines and lump; a common reference grade for fines |
| High grade | About 63 to 65% Fe | Fines, lump and blast furnace pellets |
| Premium and DR grade | About 65% Fe and above; DR-grade pellets typically 67% or more | Concentrate, pellet feed and DR-grade pellets |
Dry basis
Why Fe is quoted dryand cargo is weighed wet.
Iron ore is shipped wet. The cargo is weighed at loading, usually by draught survey or belt scales, in wet metric tonnes (wmt). The inspector measures the moisture of each sub-lot and converts the weight to dry metric tonnes (dmt): dmt = wmt x (100 - moisture %) / 100.
Chemistry is reported on the dried sample, so an ore with 62% Fe and 8% moisture carries about 57% Fe as shipped. Stating Fe and quantity on the dry basis keeps lots comparable whatever the weather, stockpile or season. Check that every figure in a specification states its basis: dry, or as received.
Impurities
What the assay showsbeyond Fe.
Typical parameters used in the trade. Limits are set in each contract according to the buyer's process.
| Parameter | What it is | Why it matters |
|---|---|---|
| SiO2 (silica) | Quartz and silicate gangue | More slag and more fuel per tonne of hot metal; in direct reduction it stays in the product |
| Al2O3 (alumina) | Clay and other aluminous gangue | Makes slag more viscous and weakens sinter, which breaks down more in the furnace |
| P (phosphorus) | Phosphorus minerals in the ore | Passes almost entirely into the hot metal and makes steel brittle; removing it costs flux and time at the steel plant |
| S (sulphur) | Sulphide minerals | Makes steel brittle when hot; must be removed in the furnace or by desulphurisation |
| LOI (loss on ignition) | Weight lost when the ore is heated: combined water and carbonates | Less iron per tonne once heated, more energy, lower sinter productivity |
| Moisture | Free water in the cargo as shipped | Freight is paid on the water too; handling problems; liquefaction risk for fines at sea |
| Other elements | TiO2, Mn, alkalis (Na2O, K2O), zinc, copper, arsenic | Alkalis and zinc attack blast furnace linings; some steel grades limit copper and arsenic |
Size fractions
Size is partof the specification.
Typical ranges, measured by sieving (ISO 4701). Contracts set the main range plus limits on oversize and undersize.
| Form | Typical specification | Why it matters |
|---|---|---|
| Fines | 0 to 6.3 mm (some grades up to 10 mm), a limit on oversize, sometimes on ultrafines | Too many ultrafines reduce the permeability of the sinter bed |
| Lump | 6.3 to 31.5 mm, limits on undersize and oversize | Fines in the lump block gas flow through the blast furnace |
| Pellets | Most of the lot within 8 to 16 mm, a limit on undersize fines | Even size keeps the furnace burden permeable |
| Concentrate | % passing a fine sieve (for example 0.045 mm), or specific surface (Blaine) | Grind fineness controls pellet quality |
Pellet and lump tests
How the ore behavesin handling and in the furnace.
For pellets and lump, buyers also set limits on physical and metallurgical tests, commonly to these ISO methods.
| Test | ISO method | What it shows |
|---|---|---|
| Crushing strength (cold compression) | ISO 4700 | Resistance to crushing in handling and under the furnace burden |
| Tumble and abrasion indices | ISO 3271 | How much fines the material generates in handling |
| Reduction degradation index (RDI) | ISO 4696 | Breakdown during reduction at low temperature |
| Reducibility | ISO 7215 | How readily the iron oxides give up their oxygen |
End use
How the grade decideswhere the ore goes.
In a blast furnace, gangue leaves with the slag. In direct reduction the ore is never melted, so silica and alumina stay in the DRI and end up in the electric arc furnace. That is why DR grade is the strictest.
| Route | Typical feed | What the buyer looks for |
|---|---|---|
| Sinter plant, then blast furnace | Fines, some concentrate | Consistent Fe, controlled alumina and LOI, a size that granulates well |
| Blast furnace, direct charge | Lump and blast furnace pellets | Strength, few fines, good reducibility, low P, S and alkalis |
| Pellet plant | Concentrate and pellet feed | High Fe, low silica, the right grind fineness |
| Direct reduction (DRI or HBI) | DR-grade pellets and selected lump | Fe typically 67% or more, combined SiO2 and Al2O3 typically below about 3%, low P and S |
Sampling and assay
How quality is confirmedat loading.
Independent sampling and assay at loading are standard practice for iron ore, and part of how BGI works.
- Moisture limit for finesUnder the IMSBC Code the shipper gives the master a certificate of moisture content and Transportable Moisture Limit (TML) before loading. Fines above their TML must not be loaded, as they can liquefy at sea.
- Sampling during loadingIncrements are taken from the moving stream on the conveyor, usually by an automatic sampler, to ISO 3082. The cargo is divided into sub-lots.
- Moisture and weightMoisture is determined on each sub-lot (ISO 3087), and the wet weight from the draught survey is converted to dry tonnes.
- Chemical analysis and sizeA dried composite sample is assayed for Fe and impurities, for example by XRF (ISO 9516-1) and titration for total iron (ISO 2597), and sized by sieving.
- Certificates and reserve samplesThe inspector issues certificates of weight, moisture and quality. Sealed reserve samples are kept for umpire analysis if results differ.
Your checklist
What to put inyour specification.
- 01Product form: fines, lump, pellets (blast furnace or DR grade) or concentrate
- 02Minimum Fe on a dry basis, and the rejection limit
- 03Maximum SiO2, Al2O3, P, S and LOI, and any other element your process limits
- 04Maximum moisture, and the TML certificate for fines
- 05Size distribution, with oversize and undersize limits
- 06For pellets and lump: the strength and metallurgical tests and their limits
- 07Quantity in wmt or dmt with its tolerance, and single cargo or regular supply
- 08Loading or destination port, and preferred Incoterm (for example FOB, CFR or CIF)
- 09Sampling and assay: standards, inspector, whether load port or discharge port results are final, and the umpire laboratory
Questions
Common questionsabout iron ore grades.
What is the difference between iron ore fines and lump?
Fines are ore below the lump size, typically 0 to 6.3 mm, and are sintered before they go into a blast furnace. Lump, typically 6.3 to 31.5 mm, is charged directly into the furnace, so buyers also check its strength and undersize.
What does 62% Fe mean in iron ore?
It means the ore contains 62% iron by weight on a dry basis, measured on a dried sample. It describes the iron content only, so a full specification also sets limits for silica, alumina, phosphorus, sulphur, LOI, moisture and size.
Why is iron ore quoted on a dry basis?
Because moisture varies with weather and handling, and water carries no iron. Quality and quantity are usually stated in dry metric tonnes (dmt), converted from the wet weight measured at loading.
What are DR-grade iron ore pellets?
DR-grade pellets are made for direct reduction plants that produce DRI or HBI. They typically carry 67% Fe or more, with combined silica and alumina typically below about 3%, because in direct reduction the gangue is not removed as slag and ends up in the electric arc furnace.
How is iron ore sampled and assayed at loading?
An independent inspector takes increments from the conveyor during loading to ISO 3082, measures moisture on each sub-lot and assays a dried composite sample for Fe and impurities. Certificates of weight, moisture and quality are issued, and sealed reserve samples are kept for umpire analysis.
Please note
Typical parameters only.
This guide explains parameters commonly used in international trade, for orientation. It is not a specification, an offer or a statement of available goods. Every deal sets its own specification in the written contract.
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