An experimental study of abrupt changes in cake structure during deadend pressure filtration

In a practical study, a computer automated apparatus has been used to obtain experimental data for the dead-end, constant pressure filtration of aqueous zinc sulphide suspensions. The apparatus and particulate/suspension properties are briefly described and filtration data typical of that acquired during the investigation are presented. The conditions under which unexpected changes in cake structure occur are identified. It is shown how filtration parameters such as pressure, filter cell diameter and particle dispersion all influence the onset of both irreversible and reversible changes in cake structure and how these changes induce disturbances in the expected filtrate flow. Analyses of the experimental data and their relation to previous studies suggest that more localised changes in cake structure are responsible for the effects observed. The most probable mechanism is the migration of particle fines within a forming cake leading to the establishment of preferential flow channels; alternative mechanisms are also presented and discussed. It is concluded that an abrupt change in cake form is more likely during the filtration of suspensions containing loosely networked particles and when filter cell dimensions are larger.