基于润湿膜时空演化的颗粒−气泡间相互作用力数值求解

Numerical calculation of interaction forces between bubbles and particles based on the spatiotemporal evolution of wetting film

  • 摘要: 颗粒−气泡间的相互作用涉及颗粒−气泡碰撞、黏附和脱附,作为泡沫浮选的基本单元直接影响浮选效率。其中,颗粒−气泡黏附伴随着颗粒−气泡间润湿膜的薄化破裂。明晰润湿膜薄化过程中颗粒−气泡间的相互作用,对强化难浮煤/难选矿浮选回收具有重要的理论指导意义。采用动态润湿膜测试系统(DWFA)研究了亲/疏水二氧化硅表面与气泡之间润湿膜的时空演化,基于润湿膜薄化动力学数据数值求解了颗粒−气泡间相互作用力,进一步分析了润湿膜薄化过程中流体力和表面力协同作用机制。结果表明,亲水二氧化硅−气泡间润湿膜最终呈现“U”型平衡轮廓,其中心点厚度为121.0 nm;疏水二氧化硅−气泡间润湿膜不稳定并于0.93 s快速破裂,中心点临界破裂厚度为157.8 nm。颗粒−气泡相互作用力学分析表明,分离距离较远时,马达以6 μm/s给定速度驱动样品接近气泡,流体力是颗粒−气泡润湿膜排液的最主要贡献力。当颗粒−气泡分离距离缩短至约300 nm时,表面力开始作用。亲水二氧化硅−气泡间润湿膜排液速率低、达到平衡所需时间久,在润湿膜稳定前,马达停止驱动,继而流体力减小,表面力增大,排斥性分离压力主导亲水二氧化硅−气泡间润湿膜缓慢排液至平衡。疏水二氧化硅−气泡间流体力持续增大,随着分离距离减小,吸引性范德华力或疏水力等表面力作用,诱发润湿膜快速破裂。因此,对于表面疏水性弱的二氧化硅,其与气泡间排斥作用强,不利于颗粒−气泡黏附;通过表面改性方法提高其表面疏水性,可诱发颗粒−气泡间润湿膜破裂,提高黏附概率,这归因于疏水颗粒−气泡间吸引性分离压力。

     

    Abstract: The bubble-particle interaction, including bubble-particle collision, attachment, and detachment, directly affects flotation efficiency as the basic unit of froth flotation. Among them, bubble-particle attachment is accompanied by the thinning and/or rupture of the wetting film between bubble and particles. Clarifying the interaction forces during the thinning of the wetting film is of great theoretical significance to regulate the flotation recovery of difficult-to-float coal/ore. The spatiotemporal profiles of the wetting film between hydrophilic/hydrophobized silica surface and an air bubble were investigated using the dynamic wetting film apparatus (DWFA). The bubble-particle interaction forces were calculated based on the wetting film thinning kinetics. Furthermore, the synergistic effect of hydrodynamic and surface forces on the wetting film thinning was analyzed. The results show that the wetting film between the hydrophilic silica and the bubble remains stable, eventually showing a “U” profile with a central thickness of 121.0 nm. However, for the hydrophobized silica surface, the wetting film is unstable and ruptures rapidly at 0.93 s, with a critical wetting film of 157.8 nm at the center. The interaction force results indicate that the hydrodynamic force is the most significant contributor to the wetting film drainage when the bubble-particle separation is far and the sample is driven by the motor approaching the bubble at 6 μm/s. When the separation is reduced to approximately 300 nm, surface forces come into play. Due to the low drainage rate of the wetting film between silica and bubbles, and the long time required, the motor stops driving before the wetting film reaches an equilibrium. The hydrodynamic force decreases and the surface force increases, so the repulsive disjoining pressure dominates the wetting film slowly drain to equilibrium. The hydrodynamic force between hydrophobized silica and bubble continuously increases, and as the separation distance decreases, the surface force such as an attractive van der Waals force or hydrophobic force enhances, inducing the rupture of the wetting film. Therefore, for silica with weak surface hydrophobicity, its strong repulsive interaction with bubbles is not conducive to bubble-particle attachment. The improvement of its surface hydrophobicity by surface modification contributes to the rupture of the wetting film as well as to increasing the attachment probability, which is attributed to the attractive disjoining pressure between the hydrophobized surface and the bubble.

     

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