The Characteristics of Filter Pressed Kaolinite-Water Pastes

Richard West
State University of New York, College of Ceramics at Alfred University, Alfred, New York

Abstract: A Georgia kaolin was selected for investigation because of its large, euhedral, platelike particles and mineral composition consisting of 96 per cent kaolinite. The clay was prepared as a suspension and treated with various water-soluble compounds, with or without the addition of an organic colloid, to determine the role of the organic material in the flocculation and deflocculation characteristics of the clay as measured by the rate of filtration under pressure. Although the organic colloid acted as a strong deflocculant alone, 1 per cent of it actually increased the flocculation action of aluminum sulfate and yet increased the deflocculation action of sodium sulfate.

Water-soluble compounds were added to the clay-water slip and then either a cation exchange resin or an anion exchange resin was added to replace either the cation with H+1 or the anion with OH−1. The filtration characteristics of these prepared slips indicated that the anions studied —Cl−1, SO4−2, and PO4−2— play a passive role in the flocculation or the deflocculation of the clay-water slips but that these ions often have a profound effect in combination with the cations. The cations play the active role in flocculation and deflocculation. Al+3 acted as a strong flocculant and Na+1 acted as a strong deflocculant. Small additions of Ca+2 acted as a flocculant by increasing the rate of filtration of the clay-water slip but further additions decreased the rate of filtration.

The ratio of the amount of clay to water in the slip shows an important relationship with rate of filtration. A slip with 25 per cent clay had a relatively low rate of filtration and yielded a filter cake with a higher bulk density in the wet and the dry state thau did a slip with 40 per cent clay. The lower viscosity of the slip with 2S per cent clay may allow a greater freedom for particle orientation as deposited on the filter cake than a slip with 40 per cent clay having a higher viscosity.

Electron micrographs of the top and edge of filter cakes prepared from flocculated and deflocculated clay show that the structure of both is similar with regard to parallelism of plates. However, the deflocculated clay deposits in a close-packed parallel arrangement whereas the flocculated clay deposits with some slight displacement of the plates but in a parallel arrangement.

Clays and Clay Minerals; 1963 v. 12; no. 1; p. 209-221; DOI: 10.1346/CCMN.1963.0120123
© 1963, The Clay Minerals Society
Clay Minerals Society (www.clays.org)