The processing of ores to recover valuable minerals, the production and recycling of paper, and the treatment of wastewater all require processes that remove small solid particles from an aqueous slurry. Allowing the small particles to settle by gravitational forces alone would require prohibitively large settling basins. Thus, the industrial standard is to bubble air through the slurry, so that the particles adhere to the bubbles and rise to the surface where they can be easily skimmed off. This froth flotation process is best suited for removal of hydrophobic (oil-loving) particles, but is less effective for hydrophilic (water-loving) particles, as the latter have less proclivity to leave the aqueous phase and cling to the air bubble. Yet, a trend to replace oil-based chemicals with benign water-based substitutes has challenged effective removal via traditional froth flotation methods. As one example, the increasing use of environmentally friendly water-based printing inks leads to difficulty in recycling this paper. As new separation strategies are developed, there is an arguable advantage in adapting existing equipment and processes. This project will develop a method to coat the air bubble with environmentally benign and recyclable bio-based oils to increase the improve the efficiency of froth flotation in removing hydrophobic particles.
The central hypothesis of this project is that an oil coating on the bubble will positively affect froth flotation by removing energy barriers for particles to adhere to the bubble surface, thereby improving particle-bubble adhesion, and increasing the separation efficiency. The oil coat is also expected to alter both the bubble shape and its rise dynamics. These hypotheses will be probed experimentally in a flotation column, comparing coated to uncoated bubbles, using a combination of optical, gravimetrical, and chemical analyses. Model particles allow for systematic variations in wettability, particle type, and the oil composition, and will be used to develop a theoretical framework. The theory will be extended and validated with hydrophilic inks from an actual paper pulp. The project will lead to a fundamental understanding of the three-phase oil-water-bubble interactions responsible for the performance of flotation separations, allowing customization of the engineering design of flotation devices for a specific separation task. One graduate student and one or two undergraduate researchers will conduct the laboratory experiments. Outreach efforts will include hands-on demonstrations using table top flotation columns, with a target audience of elementary and middle school students.
