Effect of zeta potentials of oil droplets and bubbles on flotation of oil‐in‐water mixtures

Abstract

AbstractThe effects of surface charges of oil droplets and bubbles in the oil‐in‐water flotation process were studied by a zeta potential apparatus which was specially designed to measure the zeta potential of bubbles. To measure the electrophoretic velocity of bubbles accurately, small bubbles whose rising velocities were less than 1 mm/s were introduced into an electrophoresis cell by a method of pressure reduction of a solution containing dissolved air, and the movement of the bubble in the cell was followed by moving the cell vertically at the same velocity as that of the rising bubble. It was found that the separation efficiency, n, for the flotation was strongly dependent on the zeta potentials of both the oil droplets and the bubbles. n increased as the zeta potentials of both the oil droplets and the bubbles decreased. Also n became the largest when the oil droplets were negatively charged and the bubbles were positively charged. Furthermore, a critical adhesion parameter, m=4πϵζpζb/kA, between oil droplets and bubbles was calculated by the heterocoagulation theory, using the value of the experimentally determined Hamaker constant, A=3.38x 10−20J, and the dependence of n on m was examined.