Effect of micro-bubble size and dynamic characteristics on oil removal efficiency of the flotation

Abstract

The size and dynamic characteristics of micro-bubbles play a crucial role in determining flotation efficiency. However, the detailed study of micro-bubbles in jet flotation remains limited. This study established a high-speed camera system capable of capturing and analyzing the flow behavior of jet flotation bubbles, micro-bubble sizes, bubble size distribution, and dynamic characteristics. The particle diameter and oil concentration were measured using Marvin and Ultraviolet spectroscopy, respectively. Subsequently, the study discussed the oil removal efficiency of the jet flotation system. The results revealed that the flow field of jet flotation could be categorized into three distinct regions: shear crushing region, collision adhesion region, and expansion foam region. Moreover, it was observed that the average bubble diameter (Dab) decreased as the gas mass flow, circulating liquid mass flow, and liquid depth increased, with gas mass flow being the primary influencing factor. Concurrently, high gas mass flow contributed to an increased density of small-scale bubbles. The velocity at which the bubbles rose was found to be influenced by the liquid depth, gas mass flow, circulating liquid mass flow, and the bubble's location. At an oil concentration of 300 mg/L (average diameter of Sauter in oil droplets is 4.787 μm), the jet flotation process in this study achieves an oil removal efficiency of over 80 %. Interestingly, in high gas mass flow conditions, jet flotation exhibited notable oil removal efficiency, even with a relatively low residence time. This study provides valuable empirical evidence to support the optimization of flotation systems.