Selective Aggregation of Hydrophilic Gangue Minerals in Froth Flotation
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Selective Aggregation of Hydrophilic Gangue Minerals in Froth Flotation
Qi Liu Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta, Canada T6G 2V4. Email: [email protected]
ABSTRACT In a highly dispersed flotation pulp, ultrafine hydrophilic minerals can entrain into froth products even though they may be perfectly hydrophilic. Therefore, effective depression of the hydrophilic minerals in froth flotation relies not only on rendering the minerals hydrophilic, but also on proper particle size control. In this paper, it will be shown that several depressants in mineral flotation systems indeed not only make the minerals hydrophilic but also cause selective coagulation or flocculation of the hydrophilic minerals. As a result, both the genuine flotation and the hydraulic entrainment of the hydrophilic minerals are reduced. The aforementioned depressants and mineral flotation systems include: zinc sulfate in the depression of sphalerite while copper sulfide and lead sulfide are floated; starch in the depression of iron oxides and phosphates while quartz is floated; polyethylene oxide in the depression of quartz while sulfide minerals such as chalcopyrite is floated. Therefore, in fine and ultrafine particle flotation, the flotation depressants should be able to not only make the to-be-depressed minerals hydrophilic, but also make them selectively aggregate. INTRODUCTION Effective separation of fine and ultrafine mineral particles by froth flotation is a challenge to all mineral processors today. Mineral resources are depleting and most new ore bodies that are found have increasingly lower grades and more complex dissemination, and require an ultrafine grind to achieve mineral liberation. It is known that in mineral flotation, intermediate sized particles have the highest separation efficiency, while neither coarse nor fine/ultrafine particles float well [1-4]. Due to their small masses and high specific surface areas, the ultrafine particles cannot be effectively separated using conventional flotation. For hydrophobic particles, the small masses mean that their chances of colliding and becoming attached to gas bubbles are low, leading to low recovery. For hydrophilic particles, the small masses mean that they do not have enough inertia to overcome water flow and can thus get entrained into the froth product, and their small masses do not allow them to drain back to the pulp by gravity. This lowers the grade of the froth product. Entrainment is believed to happen when particles are below about 30 µm, and becomes predominant with particles smaller than about 10 µm [4-7]. Several technologies have been tested in the past several decades to improve the flotation recovery of ultrafine hydrophobic particles. The majority of these technologies are based on size enlargement of the ultrafine hydrophobic particles, through some form of “hydrophobic forces”, or the generation of micro bubbles. For example, Zhou et al [8] indicated that fine bubbles formed by a cavitation tube in the feed li
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