Flotation and Sedimentation Properties in Centrifugal Separation of Emulsion–Slurry

Abstract

The centrifugal separation of an emulsion–slurry containing oil droplets and colloidal SiO₂ particles was investigated using the microprocessor-controlled analytical photocentrifuge, LUMiFuge. The oil droplets and SiO₂ particles were completely separated after centrifugation due to the flotation of the oil droplets and the sedimentation of the SiO₂ particles, as a result of the density difference. The flotation velocity of the oil droplets and the settling velocity of the SiO₂ particles were larger than those of the single dispersions (oil-in-water (O/W) emulsion and SiO₂ suspension) with the corresponding volume fractions. The acceleration effects of flotation and sedimentation were examined using the flotation and sedimentation coefficients, in which the effect of centrifugal acceleration on the flotation and sedimentation velocities was cancelled. The flotation and sedimentation coefficients increased with increasing SiO₂ particle or oil droplet volume fractions in the emulsion–slurry, and the acceleration effect of the flotation coefficient was noteworthy due to the marked increase in the density difference between the oil droplets and the emulsion–slurry with increasing SiO₂ particle volume fractions. The flotation and sedimentation coefficients were experimentally described using two types of void functions, and accurately described the acceleration effect in the centrifugal separation of the emulsion–slurry.