sonochemical enhanced micro bubble flotation

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The development of fractionation processes for fine particle systems is the focus of the priority program 2045. Those processes are supposed to respect more than one property for the separation. The established separation process column flotation is modified through the use of micro-bubbles and the application of ultrasound with the aim to shift the application window to the size range of 100 nm - 10 µm. The two modifications do not act independently, they have a potential for synergies. Since the resonance frequency of the microbubbles fits to the frequency band of technical ultrasound, the ultrasound is supposed to create intense oscillations of the bubbles in this concept. The oscillation of the bubbles leads to an increased contact probability with the particles. The contact probability is further enhanced due to the fact that the inertia forces of the microbubbles are reduced, which leads to a higher relative mobility. Since the buoyancy decreases with the bubble size, the rising velocity as well as the transport capacity of the microbubbles decreases, too. Furthermore the effort to generate high concentrations of microbubbles is high. Therefore a hybrid approach is chosen, which is the application of a bi-modal bubble size distribution. A defined concentration of micro bubbles is mixed with the conventional bubble size of column flotation. The research work focuses on the selective coupling of particles to the (micro-)bubble system and the stability of the microbubbles regarding coalescence. An Atomic-Force-Microscope is used with a particle or a bubble as probe (CP-AFM). It determines the interaction force, especially the potential boundary at the contact between particle and bubble as well as between bubble and bubble. Since this process is a function of the physico-chemistry, the flotation chemistry has to be optimized. The CP-AFM-measurements are also conducted with superimposed high frequent oscillations, which allows in the AFM to simulate the microscopic behavior due to ultrasound. The engineering approach uses a flotation column in the mini-plant-scale, which is modified for the application of both ultrasound and microbubbles. The production of the microbubbles uses a rotating membrane device. The influence of the flotation chemistry on bubble formation is quantified, too. The experiments in the mini-plant focus on the determination of the multi-dimensional separation curve (size / material composition) as well as on the impact of the bi-odal bubble size distribution on the structure, stability and separation properties of the froth. The particle system for the bench mark experiments is a mixture of functional materials, which is carbon black/graphite and a metal-oxide. This challenge derives from the specifications of the mechanical recycling of electrode materials from batteries. In the second period the focus is on the collection of technological process data and the morphological separation.