VIEW ARTICLE    DOI: 10.1094/ASBCJ-45-0048

The Determination of the "True" Filtration Characteristics of Diatomaceous Earth. Robert J. R. Reed and Mark A. Picksley, Brewing Research Foundation, Nutfield, Redhill, Surrey, England RH1 4HY. J. Am. Soc. Brew. Chem. 45:0048, 1987.

The flow through any filter bed is directly related to the permeability of the bed, which may be calculated from the size of particles comprising the bed and the void volume (or voidage) between the particles. Conventional measurement by Coulter Counter of the particle size of diatomaceous earth and void volume by displacement of volume leads to unrealistically high values of permeability. This is because the influence of the porosity (internal void volume) of the diatomaceous earth particles is not accounted for in the straight application of conventional measurements to the calculation of permeability. A method was developed whereby the particle size and bed void volume relevant to filtration may be determined by the analysis of data on the volumes of beds comprising mixtures of diatomaceous earths and particles of known filtration characteristics. The diatomaceous earths Celite 578, Standard Supercel, and Hyflo Supercel have total void volumes of 83, 86, and 86%, respectively; the effective bed void volumes for filtration, however, are only 27, 33, and 58%. These results imply that true sizes of diatomaceous earth particles are some 1.7 times greater than indicated by the Coulter Counter. The method also gives an indication of the size of the voids in a bed of filter aid. Effective bed void volume and true particle size give reasonable predictions of permeability.

Keywords: Diatomaceous earth, Filtration, Filter-bed permeability, Void volume, Particle size, Particle shape