BACKGROUND AND FORMULATION OF WORK
1.5 Formulation of the Work
In view of the importance of ionic microbubble flotation, present research has been undertaken for a systematic study of various aspects of ionic microbubble flotation to separate fines. The term
“ionic microbubble” is used in the present work because microbubble carries charge over it. Based on the background on the possibility of the work in microbubble aided floatation processes, the following work is proposed for the present research:
1.5.1 Microbubble Generation and Stability of Microbubble
Microbubble requires three states of matter to persist for a useful time frame: a gas core, a liquid medium, and a viscoelastic stabilizing shell. The stability and dynamics of a microbubble depend on the properties of all three components. The stability of microbubble is very important aspect in order to use them for fine separation. The transport process associated with microbubble is significantly affected by the microbubble stability. Thus it becomes very essential to study the stability characteristics of microbubbles. In the present work, the stability of microbubble dispersion is analyzed by the drainage mechanism. The stability of microbubble dispersions is also examined by using its electrical properties. Correlations are also developed to interpret the half- life and drainage mechanism of microbubble. The details of work is described in chapter 2.
1.5.2 Rise Velocity and Size Distribution of Microbubble
The collection of particles by rising air bubbles in flotation can be predicted by determining the motion of particles in the path of the bubble rise (Reay and Ratcliff, 1973). The flotation rate also depends on the bubble surface area flux which is inversely proportional to bubble size (Laskowski et al., 2003). The particle recovery depends not only on the solids content of the pulp and the hydraulic regimes in the column, but also on the size, the bubble population and distribution of the bubbles (Lee and Lee, 2002). So the bubble size is an important variable in a flotation process (Tao, 2005). To optimize the flotation process on the basis of surface area flux, it is essential to know the microbubble size, its distribution along with the knowledge of the microbubble rise velocity. This work, hence, intended to examine the microbubble size and its distribution of microbubbles. The effect of physicochemical properties of liquid and gas on motion of microbubble is also enunciate. Correlations are also develop to interpret the size and distribution of microbubble based on its physicochemical properties of liquid. The details of the work is presented in chapter 3.
1.5.3 Hydrodynamics of Microbubble Flow
The microbubble-particle interaction is highly affected by the hydrodynamics and the phenomena associated with microbubble suspension flow. In applications of microbubbles, the microbubbles are pumped through columns, pipes, etc. Therefore the studies on the flow behavior of microbubble suspensions flow, pressure drop, hydrodynamics drag, friction and rheology of microbubble suspension flow is required in this regard. Present work investigates the hydrodynamic characteristics of the flow of a microbubble suspension in a surfactant solution through a pipe. A mechanistic model has been developed to analyze the interfacial stress of microbubble suspension
flow in a pipe by considering bubble formation, drag at the interface, and loss of energy due to wettability. A correlation between the intensity factor of interfacial stress and the friction factor based on energy loss due to wettability has been developed, which are described in details in chapter 4.
1.5.4 Dispersion Characteristic of Ionic Microbubble
The particle-bubble collision is affected by intensity of mixing in the device. The mixing process is affected by all three phases present in a column. However, most attention has been paid to the liquid phase. It is suggested, that the solids and liquid axial dispersion coefficient are equal for fine particles having mean diameters less than 150 µm (Mavros, 1993). Therefore in the present research, the dispersion characteristic of ionic microbubble suspension in continuous plant prototype developed for mineral beneficiation has been investigated. The effects of different operating variables and physiochemical properties of liquid on the dispersion of ionic microbubble suspension are examined. A phenomenological model with consideration of liquid circulation was developed to analyze the dispersion coefficient of the microbubble suspension due to circulation.
Generalized correlations for dispersion coefficient and the time to reach uniform dispersion are also developed based on the physicochemical properties of microbubble suspension. The details of the work is presented in chapter 5.
1.5.5 Fine Particle Separation by Ionic Microbubble
Fine separation is one of the most important application of ionic microbubble (Jauregi et al., 1997).
Industrial applications of flotation moved much faster than scientific understanding of the phenomena involved. It is recognized that the size of the bubbles and its surface potential has an influence on the efficiency of the flotation process (Ahmadi et al., 2014). This work, hence,
intended to explore the separation characteristics of ionic microbubble for fine particle separation.
The effects of different operating variables and physicochemical properties of liquid on the separation characteristics of ionic microbubble are enunciated. A phenomenological kinetic model based on collision, attachment and detachment mechanisms of fine particle is developed to analyze the flotation characteristics of the ionic microbubbles. An analysis of particle recovery based on the mixing of phenomena of microbubble dispersion is also presented. Generalized correlations for flotation rate constant and induction time are also developed based on the physicochemical properties of microbubble particle mixture.The details is enunciated in chapter 6.