Reverse flotation is a process used to separate unwanted minerals from valuable ore by floating the undesired minerals and leaving the desired minerals in the underflow. In the case of iron ore containing sulfur, reverse flotation can be employed to remove sulfur-bearing minerals (such as pyrite, FeS₂) to improve the quality of the iron concentrate.
Reverse Flotation of Iron Ore for Sulfur Removal
Here’s a step-by-step breakdown of the process:
1. Grinding (Liberation of Sulfur Minerals)
- The iron ore is ground to a fine size (typically below 100 µm) to liberate sulfur-bearing minerals (e.g., pyrite) from iron oxides (hematite/magnetite).
- Over-grinding should be avoided to prevent sliming and poor flotation selectivity.
- Grinding media and conditions should be optimized to minimize iron losses.
2. Conditioning & Reagent Addition
- Depressants (e.g., starch, dextrin, or sodium silicate) are added to selectively depress iron oxides, allowing sulfur minerals to float.
- Activators (e.g., copper sulfate) may be used if pyrite is not naturally floatable.
- Collectors (e.g., xanthates like potassium amyl xanthate or dithiophosphates) are added to make sulfur minerals hydrophobic.
- Frothers (e.g., MIBC – Methyl Isobutyl Carbinol) help stabilize the froth for effective separation.
3. Flotation Process
- The conditioned slurry is fed into a flotation cell where air bubbles are introduced.
- Hydrophobic sulfur minerals attach to air bubbles and rise to form a froth layer, which is skimmed off as tailings.
- The iron-rich underflow (concentrate) remains in the pulp and is further processed.
4. Concentrate Dewatering & Tailings Disposal
- The iron concentrate undergoes thickening and filtration before being sent for pelletizing or sintering.
- Sulfur-rich tailings may undergo further treatment or disposal based on environmental regulations.
Key Challenges & Solutions
- Low Pyrite Liberation: If grinding is insufficient, locked particles reduce efficiency. Solution: Optimize grind size via mineralogical studies.
- Iron Losses in Froth: Overuse of collectors can float iron oxides. Solution: Adjust depressant dosage carefully.
- High Sulfur Content in Concentrate: Poor selectivity may require pH adjustment (~pH 9–10 for better pyrite depression).
Alternative Approaches
- Magnetic separation can pre-concentrate iron before flotation if magnetite is present.
- Roasting or leaching may be needed for refractory sulfur ores.
Would you like details on specific reagents or a case study from an industrial operation?