INTERPRETATION OF FILTERABILITY MEASURED BY THE CAPILLARY SUCTION TIME METHOD

The capillary suction time (CST) method for measuring the filterabilit y of a suspension is described, and its mode of operation is reviewed and discussed. A radial capillary suction time apparatus, and the filt er paper used by it, are investigated in various ways to obtain the ca pillary suction pressure P, the water porosity epsilon of the filter p aper, and the water saturation s(w)(r) in the filter paper as a functi on of the radial distance r from the suspension to be filtered. Air is shown to coexist with water in the wetted filter paper, but P and the effective water porosity are shown to be practically constant in the paper as used in the CST method. Measurements are made of the desorpti vity S of a bentonite suspension using a conventional constant-pressur e filter press, and compared with S obtained from CST measurements.