To enhance the fixed carbon content and recovery rate of flotation concentrates from low-grade natural flake graphite (NFG), this study employed synchronous ultrasonic flotation in combination with inorganic salt ion (NaCl) enhancement. Flotation experiments were conducted to investigate the synergistic effects of these two methods. X-ray photoelectron spectroscopy, contact angle analysis, laser particle-size analysis, Raman spectroscopy, infrared spectroscopy, zeta potential measurements, electron microscopy, and Debye length calculations confirmed that ultrasonic cavitation disrupted particle agglomeration and cleaned the graphite surface. This process generated fine micro-/nanobubbles with enhanced hydrophobicity, significantly improving concentrate recovery rates. NaCl addition compressed the double electric layer on particle surfaces and suppressed bubble coalescence, stabilizing the froth and promoting graphite–bubble adhesion, which markedly increased the fixed carbon content of the concentrate. The results demonstrated that through the integrated approach, low-grade NFG with an initial fixed carbon content of 7.98% was upgraded after rough processing to a concentrate containing 79.24% fixed carbon, with a recovery rate of 65.76%. These findings demonstrate that combining ultrasonic flotation with NaCl addition substantially improved both fixed carbon content and recovery rate in the concentrate. Overall, this study provides a novel technical pathway for the efficient utilization of low-grade graphite ore resources.

Synergistic enhancement of low-grade flake graphite flotation via ultrasonic cavitation and ionic-strength modulation
    Abstract
        Graphical abstract
    1 Introduction
    2 Materials and methods
        2.1 Experimental materials
        2.2 Experimental flow
        2.3 Characterization methods
        2.4 Theoretical analysis of ionic strength and Debye length
        2.5 Measurement of cavitation strength
    3 Results and discussion
        3.1 Flotation performance under different conditions
        3.2 XPS analysis and quantification of cavitation intensity
        3.3 Analysis of the mechanism of action between graphite wettability and NaCl
        3.4 Morphology and tailings analysis
        3.5 Raman spectroscopy analysis
        3.6 Zeta potential analysis
        3.7 Infrared spectroscopy analysis
    4 Conclusion
    Acknowledgements 
    References

• Yonghang Zhang(School of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, China, State Key Laboratory of Complex Nonferrous Metal Resources Cleaning Utilization in Yunnan Province, Kunming University of Science and Technology, Kunming 650093, China)
• Shilong Ye(School of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, China, State Key Laboratory of Complex Nonferrous Metal Resources Cleaning Utilization in Yunnan Province, Kunming University of Science and Technology, Kunming 650093, China, National Engineering Research Center of Vacuum Metallurgy, Kunming University of Science and Technology, Kunming 650093, China)
• Zhengjie Chen(School of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, China, State Key Laboratory of Complex Nonferrous Metal Resources Cleaning Utilization in Yunnan Province, Kunming University of Science and Technology, Kunming 650093, China, National Engineering Research Center of Vacuum Metallurgy, Kunming University of Science and Technology, Kunming 650093, China) Corresponding author
• Xiaowei Chen(School of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, China, State Key Laboratory of Complex Nonferrous Metal Resources Cleaning Utilization in Yunnan Province, Kunming University of Science and Technology, Kunming 650093, China, National Engineering Research Center of Vacuum Metallurgy, Kunming University of Science and Technology, Kunming 650093, China)
• Dandan Wu(School of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, China, State Key Laboratory of Complex Nonferrous Metal Resources Cleaning Utilization in Yunnan Province, Kunming University of Science and Technology, Kunming 650093, China, National Engineering Research Center of Vacuum Metallurgy, Kunming University of Science and Technology, Kunming 650093, China)
• Shaoyuan Li(School of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, China, State Key Laboratory of Complex Nonferrous Metal Resources Cleaning Utilization in Yunnan Province, Kunming University of Science and Technology, Kunming 650093, China, National Engineering Research Center of Vacuum Metallurgy, Kunming University of Science and Technology, Kunming 650093, China)
• Wenhui Ma(School of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, China, State Key Laboratory of Complex Nonferrous Metal Resources Cleaning Utilization in Yunnan Province, Kunming University of Science and Technology, Kunming 650093, China, National Engineering Research Center of Vacuum Metallurgy, Kunming University of Science and Technology, Kunming 650093, China, School of Materials and Energy, National Engineering Laboratory for Vacuum Metallurgy, Yunnan University, Kunming 650093, China)
• Xiuhua Chen(School of Materials and Energy, National Engineering Laboratory for Vacuum Metallurgy, Yunnan University, Kunming 650093, China) Corresponding author
• Yaqi Zhao(School of Materials and Energy, National Engineering Laboratory for Vacuum Metallurgy, Yunnan University, Kunming 650093, China)