ABSTRACT
I. Introduction ................................................................ 456 II. Aim of this Survey...................................................... 459
III. Fluid Mechanics of Bubbles ....................................... 460
A. Stokes Flow ...................................................... 461 B. Potential Flow.................................................. 463 C. Intermediate Reynolds Number Flow............. 463
IV. Probability of Particle-Bubble Collision................. 463 V. Probability of Particle Adhesion ............................. 468
A. Probability of Adhesion by Sliding, Pasl....................................................... 469
B. Probability of Adhesion by Particle Impact ............................................................... 475
VI. Rupture of the Intervening thin Liquid Film......... 476 1. Equilibrium Films on Hydrophilic
Silica .................................................................. 481 2. Metastable Wetting Films on
Methylated Silica .............................................. 482 3. Electrostatically Destabilized
Wetting Films on Recharged Silica (Due to Al3þ Ions) ................................... 486
VII. Probability of Extension of the Three-Phase Contact ..................................................................... 489
VIII. Probability of Aggregate Stability........................... 493 IX. Modelling of a Semibatch Process on the
Basis of the Microprocess Probabilities .................. 498 A. Model development........................................... 500 B. Experimental Methods ..................................... 504 C. Model Validation............................................... 505 D. Model Parametric Variations........................... 506
X. Summary.................................................................. 509 References............................................................................ 511 List of Symbols .................................................................... 515
I. INTRODUCTION
Flotation is a separation process, in which one component of a heterogeneous mixture of solid or liquid particles in an aqueous medium selectively attaches to gas bubbles or oil droplets, forming aggregates of lower specific gravity, which in turn rise to the surface of liquid in a flotation cell and
form a froth layer there. Thus, it can be separated from the remaining components. Flotation is therefore a macro process composed of a very large number of individual physical, hydrodynamic, and physicochemical (adsorption) micro processes taking place simultaneously in space and in time. Recovery of particles by flotation is most successful in the 10 to 200mm particle size range. However, a number of flotation-related techniques are available below and above this size range. Some of these are as follows:
. Carrier or ultra flotation
. Oil or emulsion flotation
. Agglomerate or flocculation flotation
. Liquid-liquid or two-liquid extraction.
