Characterization of multiphase flow during air-sparged hydrocyclone flotation of quartz as revealed by x-ray computed tomography.

摘要

Air sparged hydrocyclone (ASH) flotation is a new particle separation technology that has been developed at the University of Utah. This technology combines froth flotation principles with the flow characteristics of a hydrocyclone such that the ASH system can perform flotation separations in less than a second. This feature provides the ASH with a high specific capacity, 100 to 600 times greater than the specific capacity of conventional flotation machines. In an effort to develop a more detailed understanding of ASH flotation, multiphase flow characteristics of the air sparged hydrocyclone were studied and the relationship of these characteristics with flotation performance was investigated.; This investigation was divided into four phases. In the first phase, the time-averaged multiphase flow characteristics of the ASH during its steady state operation were studied using x-ray computed tomography (x-ray CT). In this regard, a model system, mono-sized quartz flotation with dodecyl amine as collector, using a 2" diameter ASH unit (ASH-2C), was selected for study. Various flow regimes, namely, the air core, the froth phase, and the swirl layer, were identified and their spatial extent established for different experimental conditions by x-ray CT analysis.; In the second phase, a detailed parametric study of flotation response of the ASH for the same system was carried out in order to establish the effect of various operating variables on flotation response. The findings of this phase of investigation were then correlated with the multiphase flow characteristics as revealed by x-ray CT in the first phase. Thus, the impact of various operating variables on the flow regimes, and hence, on flotation response was established.; In the third phase, the axial flow reversal characteristics of the ASH under steady state operation, were studied using a tracer injection technique. In this regard, the surface of zero axial velocity, which essentially determines the fraction of the froth being carried to the overflow, was located for various operating conditions. The results were reviewed and the importance of the surface of zero axial velocity with respect to flotation recovery was established.; In the final phase of this research, the flow characteristics and flotation response were examined from first principles and valuable information regarding bubble trajectory, flotation rate and bubble attachment mechanism is discussed. The findings from these fundamental studies support earlier speculations about the residence time of air bubbles in the swirl layer, air split, and flotation rate. Finally, based on all of the results mentioned above, a phenomenological description of the ASH flotation process was offered.; All the studies in this research were carried out for the first time and have improved our understanding of the ASH flotation technology from a fundamental standpoint. Based on this understanding, certain operational considerations were suggested. It is expected that the results of this research will be of great use in the future design and operation of the air-sparged hydrocyclone and help achieve better separation efficiency.