The efficient conversion of iron ore into high-grade iron concentrate relies on precise control over four core processes: crushing, grinding, separation, and purification. The selection of processes and operational details at each stage directly determines the final product’s grade and cost. This article focuses on the entire workflow, systematically breaking down the core operational points and key parameters for each stage, providing you with a clear, practical guide.
First Stage: Crushing
Crushing serves as the initial stage in iron ore beneficiation, with its core objective being to progressively reduce ore particle size through the “three-stage closed-circuit” process (primary crushing → secondary and tertiary crushing → screening closed-circuit cycle), thereby ensuring efficient subsequent grinding. The key lies in balancing equipment load, strictly controlling the crushing ratio and circulating feed rate, and achieving a final product where over 95% of particles measure ≤12mm. This establishes a uniformly refined raw material foundation for grinding operations.
The “three-stage closed-circuit” configuration is standard for professional processing plants, with key operational points as follows:
1. Primary Crushing
Jaw crushers are the preferred choice. Critical maintenance involves regular inspection and replacement of jaw plates. When wear exceeds one-third, immediate replacement is mandatory to prevent oversize material discharge, which severely impedes downstream process efficiency. For large-scale production lines exceeding 2,000 tons per hour, gyratory crushers offer superior advantages in processing capacity and operational stability.
2. Medium and Fine Crushing
Hydraulic cone crushers (e.g., HST, HPT series) have become the mainstream choice. Their core advantage lies in the “laminar crushing” principle, achieving fragmentation through mutual compression of ore within the crushing chamber. This enhances efficiency while significantly extending liner life and reducing long-term maintenance costs.
3. Closed-Circuit Circulation
This is key to achieving “more crushing, less grinding.” Vibrating screens must be integrated to form a closed-loop system of “crushing-screening-return.” The core control objective is ensuring the final feed size to the grinding mill remains consistently below 10-15mm. Inconsistent feed size is the primary culprit behind soaring energy consumption in subsequent grinding processes.
The essence of the “three-stage closed-circuit” system lies in progressive crushing combined with dynamic cycle optimization—rapid particle size reduction in primary crushing, precise control in secondary and tertiary crushing, and closed-circuit screening to ensure pass rate. These three elements work synergistically to achieve the crushing objective of high efficiency and low consumption. Key control points include balanced crushing ratio, rational refeeding, and equipment stability, ultimately providing uniformly sized, suitable feedstock for grinding.
Second Stage: Grinding and Classification
Grinding and classification are the core processes in iron ore beneficiation. Crushed ore is further reduced to 0.074-0.2mm using grinding equipment (ball mills/semi-autogenous mills), and combined with classification equipment (spiral classifiers/hydrocyclones) to separate qualified particle sizes, providing an ideal particle size distribution for subsequent separation. The key lies in balancing grinding fineness with energy consumption to avoid over-grinding or under-grinding, ensuring maximized classification efficiency.
Core Operational Control Points
1. Grinding Equipment and Efficiency
Basic Configuration: Φ3.2×13m ball mills and equivalent specifications, with rotational speed typically controlled at 75%-80% of critical speed.
High-Efficiency Combination: For hard-to-grind or refractory ores, employ a “high-pressure roller mill + ball mill” combined process to reduce total system energy consumption by 20-30%.
Ball Management: Maintain an optimal ball size ratio of “Large:Medium: Small = 4:4:2” with regular replenishment to sustain grinding efficiency.
2. Classification Control (Critical Success Factor)
Magnetite: Control -200 mesh content at 65%-75%.
Hematite/Limonite: Achieve -200 mesh content of 80%-90%.
Hydraulic cyclones or spiral classifiers must be installed to ensure the timely separation of qualified fine particles.
Target Grinding Fineness
Overgrinding Core Alert: Daily monitor -325 mesh (slime) content in the classification overflow. If exceeding 20%, immediately adjust grinding parameters. Failure to do so will severely degrade separation indicators and increase chemical consumption.
The success of grinding and classification hinges on achieving the “golden balance between fineness and energy efficiency.” Grinding mills must operate stably to ensure particle size compliance, while classification systems must precisely separate qualified particles to prevent energy waste. The core operational focus lies in scientifically proportioning grinding media, controlling the classification return ratio, and adjusting cyclone pressure. This ultimately produces an optimal pulp with high recovery rates and low energy consumption, laying the foundation for subsequent separation processes.
Third Stage: Separation
Separation is central to determining concentrate grade and metal recovery rates. No single process can handle all ores; the most cost-effective technical approach must be selected based on mineral magnetic properties, occurrence characteristics, and other factors.
Mainstream Iron Ore Separation Process Decision-Making and Operational Guidelines:
| Ore Properties | Recommended Core Process | Key Equipment and Operating Parameters | Expected Targets and Precautions |
| Magnetite (ferromagnetic) | Stage Grinding – Stage Magnetic Separation (Roughing – Scouring – Sweeping) | Roughing: Permanent magnet drum separator (magnetic field strength 1200-1800 Gs) Scouring: Magnetic separation column/high-gradient magnetic separator Sweeping: High-intensity magnetic separator (magnetic field strength 1800-2000 Gs) | Target: Concentrate grade ≥66%, Tailings grade ≤8%. Key points: Regularly clean magnetic drums to prevent magnetic inclusions; control pulp flow velocity. |
| Hematite/Limonite (ferrimagnetic) | Strong Magnetic Pre-Dewatering Tailings – Reverse Flotation Concentration | Roughing: Vertical Ring High-Gradient Magnetic Separator (magnetic field strength must reach 8000-12000 Gs) Fining: Reverse Flotation (pH adjusted to 8-9, using collectors) | Objective: Overcome recovery bottlenecks, achieve a concentrate grade ≥63%. Key Points: Strictly control flotation concentration (~30%) and reagent dosage. |
| Complex polymetallic ore | Combined Process of Re-selection-Magnetic Separation-Floating Separation | Based on mineral property differences, this process integrates spiral chutes, various magnetic separators, and flotation machines. | Objective: Achieve comprehensive recovery of iron and associated elements. Key Points: The process is complex and requires precise control of concentration and flow balance at each stage. |
Fourth Stage: Purification (Dehydration and Impurity Removal)
The separated concentrate remains in slurry form and may contain impurities. It must undergo purification treatment to become a qualified commercial product.
1. Key Points for Advanced Dehydration Operations
Concentration: Utilize high-efficiency thickeners with added flocculants (e.g., polyacrylamide) to accelerate solid settling, increasing slurry concentration to 50-60%.
Filtration: Employ high-pressure filter presses (e.g., plate-and-frame type), controlling feed pressure at 0.6-0.8 MPa to ensure final filter cake moisture remains below 12%. Regular filter cloth cleaning is critical for maintaining efficiency.
2. Impurity Removal Key Points
Desulfurization: If sulfur content exceeds standards, flotation is typically used with xanthate-type selective collectors.
Phosphorus Reduction: Chemical precipitation is commonly employed. Lime is added to adjust the slurry pH to 10-11, causing phosphorus to precipitate for separation. Precise control of lime dosage (typically 500-800 g/t) is essential to avoid excess, which increases costs and contaminates the concentrate.
Conclusion
The journey from raw iron ore to high-grade concentrate is a meticulously orchestrated process, driven by precision engineering and operational excellence. Each stage—crushing, grinding, separation, and purification—must be optimized to balance efficiency, cost, and product quality. By mastering key parameters such as particle size control, energy-efficient grinding, targeted magnetic separation, and advanced impurity removal, producers can achieve maximum concentrate recovery while minimizing waste and operating expenses. Ultimately, success hinges on adaptive process selection, real-time monitoring, and continuous optimization, ensuring that every ton of ore delivers its full economic potential.