Rheology,Sedimentation, and Filtration of TiO2 Suspensions

It is shown that with aqueous suspensions of colloidal oxide and hydroxide particles simple rheometric and sedimentation experiments allow the determination of the optimum pH for filtration and washing. This approach is more practical than zeta potential measurements, as explained by a theoretical review and illustrated by experiments with industrial TiO₂ white pigments of varying surface chemistry. Besides, the solids content of the filter cake and its dependence on pH is correctly predicted from the rheology of the suspension, thus giving an idea of the mechanism of filter cake formation. This follows from a comparison to the results of filtration experiments. There, the influences of filter vacuum as well as of pH and solids content of the pigment feed suspension on filtration capacity and washing efficiency have been studied. The experiments also illustrate an inexpensive method of how to find the optimum set of parameters for an economical drum filter operation in the plant.