Influences of pH and ionic strength on ceramic microfiltration of TiO2 suspensions

The surface properties of both suspensions and membranes vary with solution environments in the microfiltration of mineral particulate suspensions using ceramic membranes. It remained uncertain which one might be more important in determining the filtration flux. In this paper the influences of pH and ionic strength on ceramic microfiltration of TiO2 suspensions were studied. Special attention was given to the changes of the surface properties of both the ceramic membranes and the suspensions. The filtration behaviors were analyzed based on the measurements of particle size distribution of the TiO2 suspension, the zeta potential of the ceramic membrane and the TiO2 particle. Results showed that the influence of solution environments on the dispersity of the TiO2 suspension played a major role in the filtration flux. When the particles were well dispersed, changes in the surface charge of the membrane are important in determining membrane performance.

The permeate flux of the ceramic membrane in the microfiltration of TiO2 suspension was affected significantly by the solution environment including pH and ionic strengths. The steadystate flux increased with increasing ionic strength and decreasing pH in the NaCl solution environment. This was mainly due to the influences of ionic strength and pH on the dispersity of the TiO2 suspensions. While there was little change in the TiO2 particle size from pH 8 to 10, a decrease in the steady flux was observed. This could be due to the electroviscous effect caused by the change in the membrane zeta potential. The results suggested that the influences of inorganic salts on the micro-filtration of TiO2 suspension were related to changes in the surface properties of both the ceramic membrane and TiO2 particle. The influence of solution environment on the dispersity of the TiO2 suspension played a major role in the filtration flux. When the particles were well dispersed, changes in the surface charge of the membrane would be important in determining membrane performance.