Particle removal from liquid phase using fine gas bubbles

Cold model study was undertaken to investigate the particle removal from the liquid phase using fine gas bubbles. Fine gas bubbles were created by flowing water through a tube in which a constriction was implanted, and injecting air underneath the constriction. The strong turbulent conditions underneath the constriction warranted formation and dispersion of fine bubbles in the tube. It was found that the probability of attachment of particles to bubbles in the tube was unity. When the aggregates of particle/bubble were discharged into the bottom tank where an abrupt change occurred in their relative movements, large particles were detached from the bubbles due to high inertial force and penetrated into the liquid in the tank, while small particles were kept attached to the bubbles and quickly floated up to the free surface of the tank. Under the present experimental conditions, polystyrene particles smaller than 500 x 10(-6) m in diameter were mostly kept attached to the bubbles and floated up to the free surface of the bottom tank, while the ones larger than 500 x 10(-6) m were detached from the bubbles and remained in the tank, circulating with water. This was in good agreement with the results predicted by the mathematical model reported previously. The wettability of a particle with-the liquid was found to be an important factor in determining the removal efficiency of particles by attachment to bubbles. It was demonstrated that the process employed in the present study can be an effective technique for removing non-metallic inclusions from molten metals such as steel.