HOTLINE: +86-13592528737In iron ore processing, the transformation from raw ore to high-grade iron concentrate depends on precise control over four critical stages — crushing, grinding, separation, and purification. Each stage directly affects the concentrate grade and metal recovery rate. Today, Leemay Machinery shares essential operational insights for achieving efficient and stable iron ore beneficiation.
1. Crushing Stage: Controlling Particle Size with “Graded Crushing”
The goal of crushing is to reduce large raw ore blocks (typically 1–1.5 m) to a size suitable for grinding, while avoiding over-crushing or uneven particles that reduce grinding efficiency.
Primary Crushing – Breaking Large Blocks
Raw ore is first fed into a jaw crusher. The feed opening should match the largest ore size (e.g., PE-900×1200, max feed 900 mm) with discharge ≤ 150 mm.
Key Tips:
- Check jaw plates regularly — replace when worn by over 1/3 to prevent “unbroken blocks.”
- Maintain uniform feed to avoid overloading.
Secondary / Fine Crushing – Matching Grinding Requirements
After coarse crushing, ore enters a cone crusher for secondary reduction (20–30 mm output). For softer ores such as limonite, an impact crusher can improve uniformity.
For fine crushing, use a VSI sand maker or high-efficiency fine crusher to reach 5–10 mm particles, ensuring “fine but not muddy” feed that reduces grinding energy consumption.
2. Grinding Stage: Dual Control of Liberation and Classification
Grinding determines the recovery rate — the target is to achieve ≥ 85% monomer liberation between iron minerals and gangue, while preventing excessive fines.
Grinding Equipment & Parameters
Ball mills are commonly used for magnetite and hematite. Example: Φ3.2×13 m ball mill (40–50 t/h).
Operational Tips:
- Maintain 75–80% of critical speed (e.g., Φ3 m → 18–20 r/min) to prevent “empty grinding.”
- Use a mixed steel ball ratio of large : medium : small = 4 : 4 : 2 and replenish regularly.
Classification – Avoiding Over-Grinding
Ground pulp should be classified via spiral classifier or hydrocyclone.
- Magnetite: −200 mesh = 60–70%
- Hematite: −200 mesh = 80–85%
If coarse particles remain, return them for regrinding. If −325 mesh fines exceed 20%, add a desliming stage to prevent slime coating that interferes with separation.
3. Separation Stage: Tailoring the Process by Ore Type
Different iron ores require distinct separation methods to enhance grade and reduce tailings.
(1) Magnetite – Magnetic Separation Dominant
Use a three-stage process: Roughing → Cleaning → Scavenging
- Roughing: Permanent magnetic drum (1200–1500 Gs), yielding 45–50% Fe concentrate.
- Cleaning: High-gradient separator (800–1000 Gs) to upgrade to ≥ 65% Fe.
- Scavenging: Strong magnetic separator (1800–2000 Gs) to recover fine magnetite and reduce tail Fe ≤ 8%.
Tips: - Clean drum surfaces regularly to avoid “magnetic clumping.”
- Control slurry velocity (roughing 1.5–2 m/s; cleaning 0.8–1.2 m/s).
(2) Hematite / Limonite – Magnetic + Flotation Combination
These weakly magnetic ores benefit from a strong magnetic roughing + flotation cleaning process.
- Magnetic Roughing: Strong magnetic separator (2000–2500 Gs).
- Flotation Cleaning: Add collectors (e.g., oleic acid, tall oil) and regulators (e.g., sodium carbonate, pH 8–9) to separate gangue, achieving ≥ 63% Fe.
Tips: - Control pulp concentration (25–30%) for even reagent dispersion.
- Check impeller wear to maintain stable aeration (0.2–0.3 m³/min per m³ pulp).
4. Purification Stage: Dehydration and Impurity Removal
After separation, the iron concentrate slurry (30–40% moisture) must be dehydrated and refined to meet smelting requirements (≤ 12% moisture, S & P ≤ 0.1%).
Dehydration – Layered Dewatering
- Thickening: Feed concentrate into a center-drive thickener to reduce moisture to 50–60%.
- Filtration: Use a filter press or vacuum filter (0.6–0.8 MPa, 15–20 min cycle) to achieve 8–12% moisture.
Tips: Clean filter cloth regularly; add flocculant (PAM) if slime content is high.
Impurity Removal – Lowering S & P
If S > 0.3%, perform flotation desulfurization using xanthate collectors.
If P > 0.1%, add lime (pH 10–11) to form precipitated phosphates for removal.
Dosage Control: 500–800 g/t lime — excess reduces Fe grade.
5. Key Considerations for the Entire Process
- Ore Analysis First: Conduct chemical and mineralogical analysis before production to guide process design.
- Real-Time Monitoring: Install online analyzers (particle size, grade) for continuous control and early anomaly detection.
- Routine Maintenance: Inspect liners, steel balls, and magnetic systems regularly to minimize downtime and extend service life.
Optimize Your Iron Ore Beneficiation Line with Leemay Machinery
Every step — from crushing to purification — requires precise control and process adaptation to ore characteristics. Leemay Machinery provides customized beneficiation line designs and equipment solutions tailored to your ore type and production capacity.
Contact us today to get a professional process flow design and quotation for your magnetite or hematite beneficiation project.
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