The size of iron ore required for beneficiation depends on the type of ore and the beneficiation process used. Generally, iron ore is crushed and ground to liberate the iron-bearing minerals (hematite, magnetite, etc.) from the gangue (waste material). Here are the typical size ranges for different beneficiation methods:
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1. Crushing & Grinding (Liberation Size)
– Coarse Crushing: 100–250 mm (for primary crushing)
– Intermediate Crushing: 25–50 mm (for secondary crushing)
– Fine Grinding: Below 0.5–1 mm (for liberation of iron minerals)
2. Beneficiation Processes & Required Feed Size
# a) Gravity Separation (Jigging, Spirals, Heavy Media Separation)
– Feed size: 0.5–30 mm
– Coarser particles (>1 mm) work better for jigs and heavy media separation.
– Finer particles (<1 mm) may require spirals or shaking tables.
# b) Magnetic Separation (Low & High Intensity)
– For magnetite ores:
– Coarse: 1–10 mm (for drum magnetic separators)
– Fine: <0.5 mm (for wet high-intensity magnetic separation – WHIMS)
– For hematite/goethite ores:
– Requires fine grinding (<0.15 mm) for effective separation.
# c) Froth Flotation
– Requires very fine grinding (<0.15 mm or 150 microns) to liberate iron minerals from silica/alumina.
# d) Scrubbing & Desliming
– Used for removing clay and ultrafines before beneficiation.
– Feed size: Typically below 1–3 mm.
3. Pellet Feed vs. Sinter Feed
– Pellet Feed: Ultra-fine (<0.15 mm or 150 .jpg)
h) for pelletizing.
– Sinter Feed: Coarser (~6–10 mm for sintering).
Key Considerations:
– The optimal size depends on the ore type (magnetite vs. hematite) and gangue mineralogy.
– Over-grinding increases energy costs and slimes generation.
– Liberation analysis helps determine the best grind size.
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