Four Iron Ores Beneficiation Methods

Iron ore serves as the cornerstone of steel industries, widely used in steelmaking and machinery manufacturing. Over 300 iron-bearing minerals exist in nature, but only 20+ are commercially viable. The four primary types are magnetite, hematite, limonite, and siderite. Beneficiation methods vary significantly based on ore characteristics and require tailored optimization.

1. Magnetite Beneficiation

Composition: Iron oxide (Fe₃O₄), Fe content 72.36%, black color, cherry-red streak, strong magnetism (Mohs 5.5-6.5, SG 4.6-5.2).
Processes:

1. Single Low-Intensity Magnetic Separation (LIMS): Applied to simple, easily-separable magnetite ores.

• Continuous Grinding-LIMS: Uses 1-2 stage grinding based on disseminated grain size.

• Stage Grinding-LIMS: For fine-grained low-grade ores. Roughing after primary grinding discards tailings; secondary grinding for cleaning.

2. LIMS-Reverse Flotation: Enhances concentrate grade by removing SiO₂:

• Cationic reverse flotation (amine collectors)

• Anionic reverse flotation (starch depressants)

3. Combined Processes:

For polymetallic ores:

• LIMS-Flotation (sulfide removal)

• LIMS-HIMS (hematite recovery from tailings)

• LIMS-HIMS-Flotation (complex associations)

2. Hematite Beneficiation

Composition: Ferric oxide (Fe₂O₃), Fe 69.94%, weak magnetism (Mohs 5.5-6.5, SG 4.8-5.3).
Methods:

1. Gravity Separation:

• Fine-grained: Grinding + spirals/jigs for high-grade concentrate

• Coarse-grained: "Crushing-only" with coarse tailing rejection

2. Flotation:

• Direct flotation: Fatty acids (e.g., oxidized paraffin soap) for simple ores

• Reverse flotation: Cationic (dodecylamine) or anionic collectors for high-grade ores with floatable gangue

3. Combined Processes:

• HIMS-Flotation (complex ores)

• Roasting-LIMS (magnetization of weakly magnetic ores)

• LIMS-HIMS (mixed magnetite-hematite)

3. Limonite Beneficiation

Composition: Hydrated iron oxide (mFe₂O₃·nH₂O), Fe 50%-65%, weak magnetism (Mohs 1-4, SG 2.7-4.3).
Strategies:

1. Gravity Separation:

Scrubbing + heavy media separation for coarse ores

2. High-Intensity Magnetic Separation (HIMS):

Recovers fine particles despite weak magnetism

3. Flotation:

Requires desliming; uses direct (anionic) or reverse (cationic) flotation

4. Integrated Processes:

Gravity-HIMS (heterogeneous ores)

Selective flocculation-flotation (high slimes)

4. Siderite Beneficiation

Composition: Iron carbonate (FeCO₃), Fe 48.2%, non-magnetic (Mohs 3.5-4, SG 3.8)
Techniques:

1. Gravity Separation:

DMS/jigs for coarse-grained ores

2. HIMS:

Upgrades Fe grade after desliming

3. Flotation:

Direct: Acidic/alkaline processes with fatty acids

Reverse: Anionic (quartz flotation) or cationic (carbonate removal)

4. Magnetizing Roasting-LIMS:

Converts siderite to magnetite via roasting (600-800°C), followed by LIMS

Conclusion

Iron ore beneficiation demands rigorous mineralogical analysis (liberation size, associations) and process testing. Key considerations include ore type, scale, and economics. Integrated flowsheets combining grinding, magnetic, gravity, and flotation methods maximize recovery and grade while reducing impurities like SiO₂ and Al₂O₃.

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