(461b) Rapid Particle Agglomeration Using Permeable Films

Flotation has been a common process for removing hydrophobic particles and oil droplets from wastewater for over 50 years (Beychok, 1967). In froth floatation, millimeter-sized air bubbles are introduced in an aqueous suspension and selectively scavenge hydrophobic particles or droplets as they rise into a foam or froth layer at the top. However, very fine particles and droplets tend to follow streamlines around the rising air bubbles and not be captured (Miettinen, Ralston, & Fornasiero, 2010; Lowenberg & Davis, 1994). Instead, this paper presents a fundamental analysis of a promising new technology, rapid agglomeration by permeable films. It was invented for mining applications by a collaborator, Professor Kevin Galvin at the University of Newcastle, and utilizes a novel hydrophobic binder formed by a high-internal-phase, water-in-oil emulsion, which is dispersed by mixing in an aqueous suspension to selectively collect hydrophobic particles and droplets (Galvin & van Netten, 2017). The binder contains salt-water drops surrounded by thin oil layers with surfactant stabilization. By using salt water for the internal phase, there is osmotic flow of fresh (or lower osmolality) water across the surfactant-stabilized oil film into the drops, thus allowing for rapid collection of even submicron materials.

This paper presents a hydrodynamic analysis to predict the collection rates of solid particles by a drop covered with a thin, permeable layer, with particles driven toward the drop interface by a uniaxial extensional flow and by osmotic flow. A bispherical-coordinate solution along with modified lubrication theory (Ramon et al., 2013) were used to describe the hydrodynamic interactions via two-sphere mobility functions. In the absence of permeation and molecular attractive forces, the drop collection rate is zero. In contrast, with even small permeabilities, a significant collection rate is achieved, even for small particles and in the absence of molecular attractions. Greater capture rates occur in the presence of osmotic flow.

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Galvin K.P. and van Netten K., 2017. A new method for ultr-fast concentration of hydrophobic particles. Chem. Eng. Sci. 158, 439-444.

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Miettinen T., Ralston J. and Fornasiero D., 2010. The limits of fine particle flotation. Miner. Eng. 23, 420−437.

Ramon, G.Z., Huppert, H.E., Lister, J.L., and Stone, H.A., 2013. On the hydrodynamic interaction between a particle and a permeable surface. Phys. Fluids 25, 073103.