An Interpretation of the Sedimentation Behavior of Pharmaceutical Kaolin and Other Kaolin Preparations in Aqueous Environments

Abstract

The effect of flocculant materials on kaolin-water suspensions is reported using two kaolins. One of these is a pharmaceutical-grade kaolin and the other an industrial kaolin. These two systems serve as a model in a broader investigation which will systematically study the ancillary ingredients of pharmaceutical kaolin-based suspensions. These studies are based on concentrated suspensions where fall of particles is hindered and characterized by sedimentation “en bloc” with a sludge line serving as interface between the supernatent liquid and the settling suspension. It is shown that there is an optimum concentration of macromolecular flocculant which causes maximum flocculation. At higher concentrations of flocculant the system is stabilized. Two approaches are used to explain the results. The first represents the phenomenon as a modification of Stokes Law results. A correlation is found between the parameter A used as a characterization constant in Steinour's empirical relationship and the Richardson and Zaki exponent n. A theoretical justification of this relationship is provided. A permeability relationship is used in the second approach based on the application of permeability equations put forward by Kozeny-Carmen. The variable k in the resultant equation is shown in theory and in practice to have a minimum at some value of porosity determined by the nature of the concentrated suspension. This treatment is applied here to flocculated systems. The systems are found in general to show very high hindrance