Fundamental Understanding on the Inception of Hydrodynamic Cavitation and its Generated Microbubbles in Fine Particle Flotation
Creators: Li, Mingda
Publisher: name: University of Alberta Library
Year: 2022

<p>Hydrodynamic cavitation is a frequently occurring phenomenon with positive and negative implications. Research has been mostly conducted to avoid cavitation in the last century because it is the major cause of corrosion in the marine industry. With the progress of science and technology, hydrodynamic cavitation is now used as an innovative process for enhancing chemical reactions and water disinfection. Most importantly, it has shown great potential in improving the flotation recovery of fine mineral particles. With the pros and cons, understanding the promotion and prevention mechanisms and controlling the inception of hydrodynamic cavitation become essential for industrial applications. <br>
In this thesis, Venturi tubes were used as the hydrodynamic cavitation devices by inducing low static pressure in the throat region. In contrast to the visualization techniques used in the previous research, the cavitation inceptions were measured by detecting the high magnitude energy at the instant of bubble burst. The addition of NaCl was shown to promoted cavitation inceptions. And the results were explained by the increase in air saturation level with lowered water solubility. Based on this idea, an innovative control method of cavitation inception was proposed by modifying the CO2 solubility by changing the pH of carbonated water. The reversibility of the process was also demonstrated.<br>
In mineral flotation, the hydrodynamic cavitation-generated microbubbles act as an efficient aid for improving fine particle recovery. The process involving particles and tube walls is considered three-phase hydrodynamic cavitation. Experimental studies were performed to better understand the cavitation behavior in the presence of solids with different surface hydrophobicity and surface structure. Results demonstrated that hydrodynamic cavitation was promoted by particles with low wettabilities but was barely affected by the particle size and roughness. Tests performed using Venturi tubes of different materials demonstrated the similar effect of the wall as particles. Hydrodynamic cavitation was promoted by a more hydrophobic Venturi tube which screened the effect of particle surface properties. <br>
The different behaviors of hydrodynamic cavitation with particles of various wettabilities suggested its potential to achieve not only high recovery but also high grade in particle flotation. This effect of hydrodynamic cavitation on the selective flotation of fine particles was further investigated from a detailed mechanism. The single-bubble flotation experiment indicated that the bubble-particle collection efficiencies of hydrophobic fine silica particles were improved significantly after hydrodynamic cavitation compared to the hydrophilic ones. The results were explained from three perspectives: (1) The strong attachment between microbubble and hydrophobic particles after hydrodynamic cavitation was demonstrated using zeta potential measurements; (2) The formation of large aggregates of hydrophobic fine particles after cavitation was revealed by slurry turbidity and particle size measurements; (3) The attachment efficiency between solid and flotation bubbles was enhanced with cavitation-generated microbubbles on solid surfaces. In the end, the beneficial effect of hydrodynamic cavitation in fine particle flotation was demonstrated in bench-scale flotation tests.</p>