Understanding superhydrophobization for enhanced fine particle flotation

为了满足不断增长的世界人口和提高的生活水平的需要，易于加工的矿物迅速枯竭，这就要求勘探低品位的矿藏。为了有效地将贵重物品从脉石中解放出来，作为分离的先决条件，必须进行细磨，从而不可避免地进行细颗粒处理。基于表面润湿性的浮选技术仍然是分离细颗粒最通用和最有效的方法。尽管经过几十年的广泛研究，目前的细颗粒浮选技术对于处理小于5µm的颗粒是无效的。细粒浮选的困难很大程度上是由于细粒比表面积大，惯性小。前者在浮选药剂用量较大时选择性吸附较少，导致精矿质量较差；后者细颗粒与浮选气泡碰撞效率较低，导致回收率较低。微泡的使用已被证明可以提高细颗粒的回收率，但细颗粒浮选的最终性能仍受矿物颗粒表面化学性质的控制。

Rapid depletion of easy processing minerals to meet the needs of ever-growing world population and improved life standards calls for exploration of low grade mineral deposits. To effectively liberate valuables from gangues as a prerequisite for separation, fine grinding becomes necessary, leading to inevitable fine particle processing. Surface wettability-based flotation technology remains the most versatile and effective method to separate fine particles. Even with many decades of extensive research, current fine particle flotation technology has been found ineffective to treat particles less than 5 µm in size. The difficulty in fine particle flotation is largely attributed to large surface area and low inertia of fine size particle. The former contributes to poorer quality of the concentrate due to less selective adsorption at a higher flotation chemical dosage while the latter results in lower recovery due to low collision efficiency of the fine particles with flotation bubbles. Use of microbubbles has been shown to improve the recovery of fine particles, but the ultimate performance of fine particle flotation remains to be controlled by the nature of mineral particle surface chemistry. In this discovery project, a new concept based on superhydrophobization of fine particles to enhance bubble-particle attachment and hence fine particle flotation will be studied. Recognizing the extremely low affinity of water to superhydrophobic surfaces such as wings of butterfly or cicada orni, legs of water strider and leafs of lotus, it is hypothesized that making the surface of fine particles superhydrophobic would lead to spontaneous in situ nano bubble formation on superhydrophobized fine particles, leading to enhanced attachment to flotation size bubbles and hence improved fine particle flotation. To test and realize this hypothesis, it is essential to design molecules that could selectively adsorb and self-assemble on target mineral surfaces into nano size domains that promote superhydrophobicity. The morphology of self-assembled collector aggregates or nano domains in the context of collector molecular structure (hydrophobic chain structure and length) will be studied using molecular dynamics simulation and confirmed with existing collector molecules and atomic force microscope imaging. The nano bubble formation on superhydrophobic surfaces will be determined using atomic force microscope and linked to the morphology of self-assembled collector molecule aggregates. The effect of nano bubbles formed on mineral surfaces, on bubble-particle attachment will be studied by measuring interaction forces between the nano bubble-frosted mineral surfaces and air bubbles using our specially designed surface force apparatus. The results from this study will lay a scientific foundation for a revolutionary concept of fine particle flotation.