mineral dressing of iron ore

Mineral Dressing of Iron Ore

Mineral dressing (also called ore beneficiation) is the process of separating commercially valuable minerals from their ores. For iron ore, the goal is to remove impurities (gangue minerals) and increase the iron content to make it suitable for steel production.

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Key Steps in Iron Ore Mineral Dressing

1. Crushing & Screening

– Large iron ore lumps are crushed (primary, secondary, and tertiary crushing) using jaw crushers, cone crushers, or impact crushers.
– Screening separates ore into different size fractions for further processing.

2. Grinding

– Crushed ore is ground (ball mills, rod mills, SAG mills) to liberate iron oxide particles from gangue (silica, alumina).
– Produces a fine powder (~45–150 microns).

3. Beneficiation Techniques

Different methods are used depending on ore type:

(a) Magnetic Separation

– Used for magnetite (Fe₃O₄) ores.
– Low-intensity magnetic separators (LIMS) remove ferromagnetic materials.
– High-intensity magnetic separators (HIMS) recover weakly magnetic hematite.

(b) Gravity Separation

– Used for coarse-grained hematite (Fe₂O₃) or goethite ores.
– Techniques:
– Spiral concentrators
– Jigging machines
– Shaking tables

(c) Froth Flotation

– Used for fine-grained ores with silica/alumina impurities.
– Collectors (fatty acids, amines) attach to iron particles while depressants inhibit gangue flotation.

(d) Reverse Flotation

– Silica/alumina is floated away while iron sinks.
– Common in hematite beneficiation.

(e) Heavy Media Separation (Dense Media Separation – DMS)

– Uses a dense liquid (ferrosilicon suspension) to separate high-density iron from low-density gangue.

4. Dewatering & Tailings Management

– Concentrated slurry is dewatered using:
– Thickeners
– Vacuum filters
– Pressure filters
– Tailings (waste material) are stored safely in tailings ponds or reprocessed.

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Final Products

• Iron Ore Concentrate (~60–70% Fe)
• Pellets (~65–72% Fe, made by agglomerating fines)
• Sinter (~55–65% Fe, produced by sintering fines)

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Common Iron Ore Types & Their Processing Routes

| Ore Type | Main Mineral | Beneficiation Method |
|———-|————-|———————-|
| Magnetite | Fe₃O₄ | Magnetic separation → Grinding → Magnetic separation |
| Hematite | Fe₂O₃ | Gravity separation → Flotation / Reverse flotation |
| Goethite/Limonite | FeO(OH)·nH₂O | Roasting → Magnetic separation |

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Conclusion

Iron ore mineral dressing improves quality by removing impurities and increasing iron content. The choice of method depends on the ore type (magnetite vs. hematite) and impurity levels (silica, alumina, phosphorus). Modern plants often combine multiple techniques for optimal recovery.

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