Bubbles and flotation

浮选是大多数矿产资源回收中的分选过程。矿石被磨成粉末，分散在水中形成浆液，通过浆液分散气泡。疏水性矿物颗粒附着在气泡上，并被携带（漂浮）到容器（浮选池）表面，作为浮子产品溢出。大多数研究都是关于如何改变粒子的疏水性。在最近的发展中，申请人发挥了主要作用，这促使人们对泡沫进行了研究。对气泡的研究可分为生成和运动两部分。气泡的产生是气体分散装置和溶液组成的相互作用。申请人团队开发的气体分散技术有助于揭示泡沫表面活性剂在浮选机气泡产生中的重要作用。当气泡尺寸达到最小值时，加入起泡剂使气泡尺寸迅速减小到临界聚结浓度CCC。申请人将CCC与泡沫结构测量相关联，即亲水-亲脂平衡HLB，作为确定泡沫性质-结构关系的总体目标的一部分。申请人拟以两种方式扩展研究：探索用氢核磁共振（H-NMR）谱确定的氢比作为HLB的替代；并将其应用于起泡剂的另一个特性，即减缓泡沫上升的能力。介绍了一种新的测量方法，即达到最小流速的浓度CMV，并确定了它与HLB和h比的关系。性质与结构的联系并不能解释泡沫减小气泡大小的机制。起泡剂可能有两种作用方式：聚结、防止和/或促进泡沫破裂。一个新的实验装置，分离分手事件已被设计，并将用于确定泡沫对分手的影响。加入起泡剂后气泡尺寸的减小，似乎是在气体分散装置传递的机械能之外引入了一种“化学”能量成分，以实现破碎。这一能源概念将被纳入预测泡沫功能的模型中，并可能通过最大化泡沫的贡献来更有效地利用能源。本文还将考虑用无机盐代替起泡剂的作用。在过去的十年里，人们对气泡运动的理解发生了革命性的变化。对于与浮选有关的直径为1 ~ 5mm的气泡，给定大小的气泡的上升速度会有很大的变化。通常归因于“污染”，气泡形状现在被认为是原因。形状的作用是明显的，可以通过调节生成体积相同但形状不同的气泡；球形气泡的上升速度比扁圆形气泡慢，且存在形状-速度关系。申请人通过证明溶质与类型、表面活性剂或无机盐无关，具有相同的形状-速度关系，为这一发现做出了贡献。将建立一个测试柱，用两个直角摄像机跟踪气泡的产生和3D运动。将确定连接形状和速度的机理。对单个气泡的研究是理解气泡群行为的一步。漂移通量分析（DFA）提供了一个可能的联系。DFA是一系列由粒子沉降得到的方程，它已经适应了气泡。计划是发展气泡群的关系。在该计划下，HQPs将通过课程和设备齐全的现代实验室的研究技术培训，接触到矿物加工方面的最新技术。这将为他们进入这个去年为加拿大GDP贡献了630亿美元的行业做好准备。

Flotation is the separation process in recovery of most mineral resources. Ores are ground to powder and dispersed in water to form slurry through which bubbles are dispersed. Hydrophobic mineral particles attach to bubbles and are carried (floated) to the surface of the vessel (flotation cell) to overflow as the float product. Most research has been on how to modify particle hydrophobicity. Recent developments, in which the applicant has played a major role, have prompted research into the bubble.Research into the bubble can be divided into generation and motion. Bubble generation is an interplay of the gas dispersion device and the solution composition. The gas dispersion technology developed by the applicant’s team helped reveal the essential role of the frother surfactant in bubble generation in flotation machines. The addition of frother rapidly decreases bubble size to a critical coalescence concentration CCC when bubble size reaches a minimum. The applicant has correlated the CCC with a measure of frother structure, the hydrophilic-lipophilic balance HLB, as part of a general objective to determine the frother property-structure relationship. The applicant proposes to extend the study in two ways: to explore the H-ratio determined from H-NMR (proton nuclear magnetic resonance) spectra as a substitute for HLB; and to apply to another property of frothers, the ability to slow bubble rise. A novel measure, the concentration to reach minimum velocity CMV is introduced and the relationship to HLB and H-ratio will be determined.The property-structure link does not explain the mechanism by which frothers reduce bubble size. There are two ways frothers may act: coalescence prevention and/or promotion of bubble breakup. A novel experimental setup to isolate the breakup event has been devised and will be used to determine the impact of frothers on breakup. The reduction in bubble size upon frother addition appears to introduce a ‘chemical’ energy component to the mechanical energy imparted by the gas dispersion device to effect breakup. This energy notion will be incorporated into models to predict frother function and may lead to more efficient use of energy by maximizing the contribution of frother. The work will also consider the action of inorganic salts which can substitute for frothers. The last ten years has seen a revolution in understanding bubble motion. For bubbles 1 to 5 mm diameter relevant to flotation, rise velocity of a given size of bubble can vary significantly. Commonly ascribed to ‘contamination’, bubble shape is now argued as the cause. The role of shape is evident by adjusting generation to yield bubbles of same volume but different shape; spherical bubbles rise slower than oblate bubbles and there appears to be a shape-velocity relationship. The applicant has contributed to this finding by showing that solutes give the same shape-velocity relationship independent of type, surfactant or inorganic salt. A test column will be built to follow bubble generation and motion in 3D with two cameras at right angles. The mechanism linking shape and velocity will be determined. Research into single bubbles is a step towards understanding the behaviour of bubble swarms. Drift flux analysis (DFA) provides a possible link. DFA is series of equations derived from sedimentation of particles that has been adapted to bubbles. The plan is to develop the relationships for bubble swarms. The HQPs under this program will be exposed to the latest technology in mineral processing through courses as well as training in research techniques in well instrumented modern labs. The will ready them to enter the industry that last year contributed $63b to Canada’s GDP.