Bubbles and flotation

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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.