Key Takeaways & Executive Findings
- •• Nanobubble-enhanced flotation significantly improves the grade and recovery of auriferous pyrite from low-grade gold ores. • Surface nanobubbles (SNBs) and bulk nanobubbles (BNBs) both contribute to enhanced flotation, with SNBs playing a critical role in surface hydrophobicity and agglomeration. • Increased surface hydrophobicity, flow rate, and cavitation time promote nanobubble coverage and particle agglomeration, leading to better flotation performance. • The study provides mechanistic insights into nanobubble-assisted flotation, offering a promising approach for upgrading refractory gold ores.
Abstract
Gold ores in the Jiaozhou region of China are characterized by their abundant reserves, low grade, fine dissemination, and challenges in upgrading. Froth flotation, with xanthate as the collector, is a commonly employed method for enriching auriferous pyrite from these ores. This study aimed to develop a more efficient flotation process by utilizing cavitation nanobubbles for a low-grade gold ore. Batch flotation tests demonstrated that nanobubbles significantly enhanced the flotation performance of auriferous pyrite, as evidenced by improved concentrate S and Au grades and their recoveries. The mechanisms underlying this enhancement were explored by investigating surface nanobubble (SNB) formation, bulk nanobubble (BNB) attachment to hydrophobic pyrite surfaces, and nanobubble-induced agglomeration using atomic force microscopy (AFM) and focused beam reflectance measurement (FBRM). The results revealed that nanobubble coverage on the pyrite surface is a critical factor influencing surface hydrophobicity and agglomeration. SNBs exhibited higher coverage on pyrite surfaces with increased surface hydrophobicity, flow rate, and cavitation time. Similarly, BNB attachment on pyrite surfaces was significantly increased with surface hydrophobicity and cavitation time. Enhanced surface hydrophobicity, along with higher flow rates and cavitation times, promoted pyrite particle agglomeration owing to the increased nanobubble coverage, ultimately leading to improved flotation performance.
1. Introduction
Gold, as an important strategic mineral resource, is widely used in the military industry, electronic products, jewelry, and other sectors. China possesses approximately 14000 tons of gold resources, representing about 15% of the global reserve [1]. Gold ore deposits in China are mainly distributed in the Jiaozhou region, where auriferous minerals are predominantly pyrite [2]. In most flotation plants, natural gold is concentrated within pyrite [3], primarily existing as a solid solution or as nanoparticles embedded in pyrite particles [4].
With the rapid depletion of high-grade gold ore, reliance on lower-grade ore has increased. Consequently, the challenges associated with refractory gold ore, such as complex structures, fine dissemination grain sizes, and difficulty in mineral liberation, have become more pronounced [5]. The beneficiation process for refractory gold ores typically involves closed-circuit fine grinding followed by multiple flotation steps. Refractory gold ores are ground to finer particle sizes to liberate auriferous minerals. However, this process often generates fine particles, with sizes as small as a few micrometers, leading to significantly lower flotation efficiency. Furthermore, auriferous minerals tend to accumulate in the grinding circuit due to their high density compared to gangue minerals [6]. Particles smaller than the target grinding fineness (e.g., 20 μm compared to the expected 57 μm) frequently enter the cyclone underflow and remain in the grinding mill until sufficiently reduced in size to enter the cyclone overflow, increasing energy consumption and reducing gold recovery [7].
Previous studies indicate that surface nanobubbles (SNBs) selectively form on hydrophobic surfaces [8–13]. Tao [10] reported that hydrophobic particles coated with SNBs exhibit stronger interactions and more pronounced coalescence due to the formation of vapor capillary bridges. These concave capillary bridges produce attractive forces that bring particles into contact. Wu et al. [14] demonstrated the superior efficacy of hydrodynamic cavitation nanobubble flotation in floating pure pyrite particles compared to conventional flotation methods. Cavitation significantly enhances pyrite flotation recovery and kinetics while reducing sodium amyl xanthate (SAX) consumption. Additionally, hydroxyl radicals generated during bulk nanobubble (BNB) collapse do not markedly increase pyrite oxidation, as SNBs rapidly form on hydrophobic pyrite surfaces, limiting surface oxidation. Azevedo et al. [15] provided micrographs illustrating that nanobubbles on pyrite surfaces significantly enhance macrobubble attachment, primarily due to the adhered nanobubbles. Although extensive research has explored the beneficial effects of SNBs on fine particle flotation, studies on the role of BNBs in fine particle flotation remain limited.
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Zhongxian Wu, Youjun Tao, Jincheng Ran, Hongliang Dong, Dongping Tao (2025). Nanobubble-enhanced flotation of auriferous pyrite in gold ore: Behavior and mechanisms. Int. Journal of Minerals, Metallurgy and Materials (矿物冶金与材料学报). https://doi.org/10.1007/s12613-025-3097-7
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Frequently Asked Questions
What is the main finding of this study?
The study demonstrates that cavitation nanobubbles significantly enhance the flotation performance of auriferous pyrite in low-grade gold ores, improving concentrate grades and recoveries of sulfur and gold.
How do nanobubbles improve flotation?
Nanobubbles increase surface hydrophobicity and promote particle agglomeration through increased nanobubble coverage on pyrite surfaces, which enhances bubble-particle attachment and flotation kinetics.
What methods were used to investigate the mechanisms?
Atomic force microscopy (AFM) and focused beam reflectance measurement (FBRM) were used to study surface nanobubble formation, bulk nanobubble attachment, and nanobubble-induced agglomeration.
What are the practical implications of this research?
The findings suggest that nanobubble-enhanced flotation could be a more efficient and sustainable method for processing refractory gold ores, potentially reducing reagent consumption and improving gold recovery.
What is the significance of surface hydrophobicity in nanobubble flotation?
Surface hydrophobicity is a critical factor influencing nanobubble coverage and attachment, which in turn affects particle agglomeration and flotation efficiency. Higher hydrophobicity leads to greater nanobubble coverage and better flotation performance.
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