The effect of pH, and the concentration of KNO3 and LiNO3 on the electrophoretic mobility and zeta potential of fine silica particles having a different median particle size were studied in order to classify submicron silica particles by electrophoretic phenomenon. The silica particles of 0.05 μm or abradant silica particles (median diameter: 0.067 μm) and silica particles of 0.5 μm were classified by a batch and continuous classification equipment designed in our laboratory.
The absolute values of electrophoretic mobility and zeta potential of silica particles are found to be increased with increasing pH. Electrolytes containing cations with different hydration number were added to the particles of 0.05 and 0.5 μm. The electrophoretic mobility of 0.05 μm particles in KNO3 solution is higher than that in LiNO3. On the other hand, electrophoretic mobility of 0.5 μm particles has almost the same value by the addition of two kinds of electrolytes. These results imply that electrophoretic effect works to smaller particles, while do not act large particles. The electrophoretic mobility decreases when the particle size becomes smaller because of strongly acting asymmetric effect and electrophoretic effect. On the other hand, the electrophoretic mobility decreases with increasing a particle size due to the resistance force with viscosity, when the particle size is larger than 1 μm. It is found that the electrophoretic mobility of particles mainly depends on the particle size.
In the case of a batch type classification equipment, classification of fine and coarse particles is advanced by applying weak electric field for long period. Classification of fine and coarse particles with a continuous classification equipment shows the possibility of classification using electrophoretic phenomenon.
