The core objective of the iron tailings re-selection and recovery process is to further extract residual trace iron minerals (such as magnetite, hematite, and limonite) from tailings using single or combined physicochemical methods—such as magnetic separation, flotation, gravity separation, and roasting—to convert them into high-grade iron concentrates.
Common iron tailings re-selection and recovery processes are mainly divided into the following four categories based on the characteristics of the tailings (such as mineral composition, dissemination particle size, and magnetic intensity):
1. Combined Weak Magnetic-Strong Magnetic Re-selection Process (Most Common)
Suitable for mixed iron tailings containing both magnetite (strongly magnetic) and hematite/limonite (weakly magnetic).
- Weak Magnetic Separation Stage: Tailings slurry first passes through a low-intensity magnetic separator (such as a drum magnetic separator) to preferentially recover strongly magnetic minerals (magnetite, pseudo-hematite).
- Strong Magnetic Separation Stage: Tailings from the weak magnetic separation enter a high-gradient magnetic separator (such as a vertical ring pulsating high-gradient magnetic separator) to capture weakly magnetic hematite, limonite, and specularite, while discarding non-magnetic gangue (quartz, feldspar, etc.).
2. Combined Magnetic Separation-Flotation Re-selection Process
Suitable for highly complex, difficult-to-select tailings with extremely fine dissemination particle sizes and high silicate impurity content (such as quartz and amphibole).
- Magnetic Separation Pre-concentration: Strong magnetic separation is used first to remove most coarse-grained, iron-free gangue, obtaining a rough concentrate and significantly reducing the volume of material entering the flotation stage.
- Reverse Flotation Cleaning: Cationic collectors (such as amines) or anionic collectors are added to the rough concentrate. Through reverse flotation, gangue minerals like quartz are scraped out as foam, leaving high-grade iron concentrate in the flotation cell.
3. Combined Gravity-Magnetic Separation Re-selection Process
Suitable for coarse-grained iron tailings with coarser dissemination particle sizes, especially those containing significant amounts of hematite or pseudo-hematite.
- Gravity Pre-roughing: Spiral chutes, shaking tables, or centrifugal separators are used to perform a preliminary separation based on the density difference between iron minerals (high density) and gangue minerals (low density), discarding a large amount of light gangue.
- Magnetic Separation Cleaning: The rough concentrate obtained from gravity separation is sent to a magnetic separator for cleaning to improve the final grade of the iron concentrate.
4. Magnetization Roasting-Magnetic Separation Process (For Extremely Difficult Tailings)
Suitable for extremely difficult-to-select, ultra-fine iron tailings that have a relatively high iron grade but consist of red iron ore, siderite, or limonite.
- Reduction Roasting: Material is roasted at high temperatures (700°C–900°C) in a rotary kiln or fluidized bed reactor with reducing agents like pulverized coal. This converts weakly magnetic hematite (\(\text{Fe}_2\text{O}_3\)) or siderite into strongly magnetic magnetite (\(\text{Fe}_3\text{O}_4\)).
- Conventional Magnetic Separation: After cooling and grinding, the roasted material can be easily separated into high-grade iron concentrate using simple weak magnetic separation.
Key Supporting Technologies for Iron Tailings Re-selection
To ensure re-selection efficiency, the process usually requires coordination with the following two key steps:
- Stage Grinding Technology: Many iron minerals in tailings exist as “interlocked aggregates.” Secondary fine grinding via ball mills or stirred mills is required to fully achieve “liberation” between iron minerals and gangue.
- Efficient Desliming Technology: Tailings often contain large amounts of secondary ultra-fine slime, which interferes with magnetic separation and flotation. Hydrocyclones or inclined plate thickeners are typically used for pre-desliming before re-selection.
