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Nanobubbles in Mineral Processing: Unlocking the Recovery of Fine Particles
The efficient recovery of fine and ultrafine particles (<20 µm) remains one of the greatest challenges in mineral processing. Traditional flotation is limited by low collision efficiency, reduced bubble–particle attachment probability, and entrainment of gangue minerals. In this context, nanobubbles (NBs) - gas bubbles typically <200 nm in size - are emerging as a promising solution. Their unusual stability, high surface energy, and ability to nucleate selectively on hydrophobic mineral sites offer new strategies to overcome the intrinsic limitations of fine particle flotation.
Unique Features of Nanobubbles in Flotation
- High Stability Unlike conventional microbubbles that collapse within seconds, NBs remain stable for hours or days due to their negative zeta potential and strong interfacial forces. This persistence ensures sustained interaction with mineral surfaces.
- Surface Nanobubbles (SNBs) NBs can nucleate directly on hydrophobic patches of mineral surfaces, forming stable “nano-anchors.” These significantly reduce induction times and provide nucleation sites for the attachment of larger flotation bubbles.
- Agglomeration of Fines NBs induce heterocoagulation, bridging ultrafine particles together into larger aggregates that behave like coarse particles. This enhances collision efficiency and reduces particle slimes loss.
- Surface Cleaning and Activation The collapse of NBs can generate localized shear forces and reactive oxygen species (ROS), which help remove oxidation films or slimes from mineral surfaces, restoring hydrophobicity.
Applications in Mineral Recovery
- Sulfide Minerals and Gold Recovery Nanobubbles have shown remarkable results in the recovery of ultrafine sulfides. In auriferous pyrite flotation, NB conditioning increased both sulfur and gold recoveries by promoting fine particle agglomeration and selective bubble attachment (Xu et al., 2025).
- Silver Minerals Recent work demonstrated that NBs adsorb preferentially on argentite (Ag₂S) surfaces, leading to improved recovery of fine silver particles that are usually lost in tailings (Gupta et al., 2024).
- Base Metals (Copper, Nickel, Zinc) In copper sulfide flotation, the use of NBs improved recovery of <10 µm particles by up to 15%, owing to faster collector adsorption and reduced induction times (Fan et al., 2020). Nickel and zinc systems showed similar trends, especially in feeds dominated by ultrafines.
- Coal Beneficiation Coal fines, known for being highly hydrophobic yet difficult to float due to their low mass, benefit from NB-assisted agglomeration. Studies reported higher combustible recovery and reduced ash content when NBs were introduced in fine coal flotation (Ahmed & Mao, 2019).
- Rare Earth Elements (REEs) REE processing often involves slimes-rich ores, where conventional flotation suffers from entrainment. NBs improve surface hydrophobicity and enhance selectivity against gangue minerals, resulting in higher REE concentrate grades (Liu et al., 2021).
- Industrial Minerals and Oxides In kaolinite and hematite flotation, NBs mitigate slime coatings and restore floatability. This not only increases recovery but also improves selectivity by reducing entrainment of gangue.
Conclusion
Nanobubbles represent a game-changing innovation in flotation technology. They address the long-standing challenge of fine particle recovery by improving both efficiency and selectivity. Early successes in sulfides, gold, silver, coal, and REEs suggest that NBs could unlock significant value from ultrafine-rich ores previously considered uneconomic.
Future work should focus on scaling NB generation, optimizing NB dosage for industrial circuits, and integrating NB systems with existing flotation units. If these hurdles are addressed, nanobubble flotation could become a standard practice in the beneficiation of complex and fine-grained ores.
