CAPTURE - Capture of mineral particles by rising bubbles
Froth flotation is a versatile separation process which plays a major role in the mining industry. It is employed to recover a vast array of different valuable commodities such as copper, zinc, nickel, phosphates and rare earth minerals essential to the manufacture of high-tech products. In the flotation process the valuable hydrophobic particles attach to the fluidic interface of rising bubbles while the undesired hydrophilic particles settle down to eventually be discharged. The simulation of the entire particle attachment process is complex. Current attachment models are still at an early stage of development. Aiming at an efficient capture of hydrophobic mineral particles by rising gas bubbles, the research project pursues the following objectives: (a) development of a three-phase flow model to simulate the particle capture, (b) microscale experiments on the attachment of particles to the surface of a gas bubble.
Direct numerical simulations
In an attempt to develop numerical tools which will find future applications in the flotation process the direct numerical simulation of a particle attachment to a fluidic interface was performed. The “Smooth Profile Method” , originally developed at the University of Kyoto in Japan for the direct numerical simulation of colloidal particles in monophasic fluids, was combined with a newly-defined binary fluid model. In this numerical extension of the Smooth Profile Method , the two fluid-particle boundaries and the fluidic boundary were replaced with smoothly spreading interfaces, i.e. with diffuse interfaces. Application of the method to simulate the attachment of a colloidal particle to the surface of an immersed bubble is seen below.
Using the in-house optical process microscope developed at the Helmholtz-Zentrum Dresden-Rossendorf, the sliding and the adhesion of micron milled glass fibres on the surface of a stationary air bubble immersed in stagnant water was thoroughly investigated. It was found that the fibre orientation during the sliding motion largely depended on the collision area. Upon collision near the upstream pole of the gas bubble, the major axis of the fibre aligned with the local bubble surface (tangential fibre alignment). If collision occurred at least 30° further downstream only the head of the fibre was in contact with the gas–liquid interface (radial fibre alignment). The results matched very well those obtained numerically with spheres as long as the collision angle remained lower than 50°.
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- Lecrivain G., Petrucci G., Rudolph M., Hampel U., and Yamamoto R., Attachment of solid elongated particles on a gas bubble surface. International Journal of Multiphase Flow 71, p. 83-93, 2015
- Lecrivain G., Yamamoto R., Hampel U., and Taniguchi T., Direct numerical simulation of a particle attachment to an immersed bubble. Physics of Fluids 28, 083301, 2016
This work was supported by a Marie Curie International Outgoing Fellowship with the European Union Seventh Framework Program for Research and Technological Development (2007–2013) under the grant agreement number 623518.