One-dimensional filtration of pharmaceutical grade phyllosilicate dispersions

The filtration behaviour of some clay-water dispersions was studied. Two Sp anish fibrous phyllosilicates (sepiolite from Vicalvaro and palygorskite fr om Turon) and a commercial bentonite (Bentopharm (C), UK) with similar size s and different morphologies (fibrous and/or laminar) were selected as mode l clays. Sepiolite from Vicalvaro is an almost pure fibrous sample, Bentoph arm (C) presents a high amount of laminar particles and palygorskite from T uron is made up of similar percentages of laminar and fibrous particles. Th e disperse systems were made up using a rotor-stator mixer working at two d ifferent mixing rates (1000 and 8000 rpm), for periods of 1 and 10 min. Fil tration measurements were taken and the corresponding filtration curves obt ained. Finally, the desorptivity (S) of the filtration cakes was calculated and correlated to the textural characteristics of the materials, the solid fraction and mixing conditions. Filtration behaviour of the dispersions de pended on all three of these factors. Laminar dispersions presented lower S values than fibrous dispersions. In the 2% w/v dispersions the bridging fo rces between particles did not permit formation of an interconnected networ k as in 10% w/v dispersions and, consequently, filtration times increased w ith the solid fraction (i.e. S values decreased). Regarding stability to pH changes, the results showed that filtration behaviour was highly sensitive to basic pH in the fibrous clay dispersions and almost insensitive in the laminar clay dispersions. (C) 2001 Elsevier Science B.V. All rights reserve d.