Fast agglomeration of ultrafine hydrophobic particles using a high-internal-phase emulsion binder comprising permeable hydrophobic films

A novel hydrophobic binder consisting of tightly packed drops of aqueous salt solution, stabilized by thin films of oil, in the form of a high-internal-phase water-in-oil emulsion was used to agglomerate ultrafine hydrophobic particles in seconds to a size sufficient for their capture on a 150-µm screen. Almost complete recovery of the particles, extending from sizes of more than 100 µm to less than 500 nm, was achieved. Examination of the process revealed that the agglomeration appears to be governed primarily by the length scale of the thin oil films, on the order of 30 nm, and their ability to quickly and efficiently deliver organic liquid to the particles. Moreover, it appears that the hydrodynamic resistance that develops when a particle is driven toward an interface is reduced because of the permeability of the films. Water permeation driven by osmosis also appears to assist the transport of the particles toward the interface.