Particle-bubble interaction and attachment in flotation
Particle-bubble interaction and attachment in flotation
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DOI：
10.1016/j.ces.2011.08.016
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发表时间：
2011-12-01
影响因子：
4.7
通讯作者：
Nguyen, Anh V.
中科院分区：
文献类型：
--
作者：
Verrelli, David I.;Koh, Peter T. L.;Nguyen, Anh V.
浮选是矿产工业的重要单元作业之一。目前最先进的浮选模型结合了计算流体力学(CFD)和基于“诱导时间”概念的用户定义算法来描述选择性气泡-颗粒附着以及疏水和亲水颗粒的分离。我们已经进行了实验研究，可以在微观尺度上直接观察颗粒-气泡的相互作用和附着，以提供经验数据以与新的理论预测相比较。相互作用被记录在高速数字视频上，允许直接估计相关参数，如接近速度和粒子在气泡表面上滑动的持续时间。一种新的实验构型使粒子朝向气泡、绕着气泡和离开气泡的路径完全畅通无阻。粒子轨迹在远大于其自身直径的分离物上显示出明显的偏差；这种偏差是由于流体动力学造成的。与理论预测的比较表明，气泡表面的迁移率介于“完全滑移”和“无滑移”之间。对于静止气泡表面的理论预测实际上是关于气泡的赤道对称的，而对于移动气泡表面的理论预测是明显的不对称。然而，在观察到的粒子轨迹和速度中发现了最强的不对称性，粒子落在更中心的位置滑过气泡表面。在一些情况下，滑动的粒子向气泡“跳入”，这被解释为准确的附着时刻。这提供了实现依恋的门槛持续时间的直接估计，即“入职时间”。观察到的事件包括粒子在跳入气泡时的旋转，以及粒子跳入气泡赤道以下。从颗粒性质和流动现象两个方面提出了解释。(C)2011爱思唯尔有限公司。保留所有权利。
Flotation is an important unit operation in the minerals industry, among others. Current state-of-the-art flotation modelling combines computational fluid dynamics (CFD) with user-defined algorithms based on the "induction time" concept to describe selective bubble-particle attachment and separation of hydrophobic and hydrophilic particles.We have undertaken experimental studies permitting direct observation of particle-bubble interaction and attachment at the microscale to provide empirical data for comparison with new theoretical predictions.Observations were made on a model system in which 150 mu m glass particles were dropped onto a captive 1.3 mm air bubble formed in water within a glass cell. The interactions were recorded on highspeed digital video, permitting direct estimation of relevant parameters such as the approach velocity, and the duration of particle sliding over the bubble surface. A new experimental configuration has allowed the particle path toward, around, and away from the bubble to be totally unimpeded.Particle trajectories show a significant deviation at separations much larger than their own diameter; such deviations are due to the hydrodynamics. Comparisons with theoretical predictions indicate that the bubble surface exhibited mobility intermediate between "full slip" and no slip". Theoretical predictions for an immobile bubble surface were practically symmetrical about the bubble's equator, while asymmetry was apparent in the theoretical predictions for a mobile bubble surface. However, the strongest asymmetries were seen in the observed particle trajectories and speeds.Particles dropping more centrally were seen to slide over the surface of the bubble. In several cases the sliding particle 'jumped in' toward the bubble, which is interpreted as the precise moment of attachment. This provides for a direct estimate of the threshold duration to achieve attachment, i.e. "induction time". Among the events observed were rotation of the particle upon jumping in, and particle jump-in below the bubble's equator. Explanations are proposed in terms of particle properties and flow phenomena. (C) 2011 Elsevier Ltd. All rights reserved.