固-液界面纳米气泡稳定性及其强化浮选黏附机制研究进展

Advances in stability of nano-bubble on solid-liquid interface and mechanismfor enhancing flotation adhesion

颗粒-气泡黏附是浮选核心作用单元,驱动其自发黏附的主要作用为疏水颗粒-气泡间疏水引力。作为长程疏水引力主要来源,界面纳米气泡对浮选界面调控有重要影响。从纳米气泡的基本性质、稳定性机理及浮选强化机制3个方面进行了系统讨论。纳米气泡异常稳定性和接触角一直是近20 a来的研究热点。经典物理学理论预测纳米气泡寿命在微秒尺度,而试验发现纳米气泡寿命通常可达数天以上。针对纳米气泡异常稳定性提出污染物层、动态平衡、三相线钉扎等假说,然而各假说均无法解释所有试验现象,其稳定性机理仍需要深入研究。纳米气泡接触角(气侧)远小于Young接触角,高密度气体导致的固-气界面能降低可能是接触角异常的主要原因。对纳米气泡强化浮选黏附机制进行了探讨,一方面界面纳米气泡可通过边界滑移促进颗粒-气泡碰撞过程中液膜排液,另一方面纳米气泡桥接使颗粒-气泡出现长程引力,同时颗粒-气泡间的DLVO力由排斥力转变为引力,从而促使颗粒-气泡黏附。目前已有试验表明纳米气泡在煤、磷酸盐、白钨矿及铁矿石等多种矿物的浮选中均有显著提升效果。在浮选日益精细化的背景下,纳米气泡强化技术可为浮选界面调控提供新的理论视角与技术手段,是未来浮选领域重点研究方向之一。

The long-range hydrophobic attraction plays an important role in bubble-particle attachment,while the latter is the key sub-process in flotation.As the main origin of the long-range hydrophobic attraction,nano-bubble is significant for interface control in flotation.The basic properties,stability mechanism,and flotation strengthening mechanism of nano-bubbles were systematically discussed.The abnormal stability and contact angle of nano-bubbles have been research hotspots in the past two decades.Classical physics theory predicts the lifetime of nano-bubbles on the microsecond scale,but experiments have found that the life of nano-bubbles usually reaches more than a few days.To explain this,several hypotheses such as contamination theory,dynamic equilibrium theory,and contact line pinning theory have been proposed.However,none of these stability theories can explain all the experimental phenomena,and the stability mechanism still needs to be further studied.The contact angle of nano-bubble is much lower than that of its macroscopic counterpart,and the decrease of solid-gas interface energy caused by high-density gas inside of the nano-bubble may be the main reason for the abnormal contact angle.Next,the enhancement mechanism of nano-bubbles in flotation adhesion was discussed.On the one hand,nano-bubble promotes the drainage of intervening liquid film during particle-bubble collisions through boundary slip,on the other hand,it provides long-range attraction and attractive DLVO force between particle and bubble to promote the particle-bubble adhesion.At present,the experiments have shown that nano-bubbles have a significant improvement effect on the flotation of various minerals such as coal,phosphate,scheelite and iron ore,etc.In the context of flotation becoming increasingly refined,the introduction of nano-bubble enhanced technology can provide a new theoretical perspective and technical means for flotation interface regulation,and is one of the key research directions in the field of flotation in the future.