Static and dynamic filtration properties of aqueous suspensions of clays and electrolytes

Abstract

Filtration properties of aqueous colloidal suspensions of clays in presence of electrolytes (NaCl, KCl, CaCl2) have been studied in static and dynamic conditions. Filtration experiments combined with cake observation by cryo-SEM and TEM show the influence of the associating mode of clay particles in suspension on the texture, the permeability and the relaxation properties of the cake. These parameters are very much dependent on the nature of the electrolyte added. In dynamic conditions the construction of the cake is related to the state of aggregation of the clay suspension, its polydispersity and the sensitivity of the aggregates to shear rates. In all cases the build up of the cake is slowed down and dynamic filtrate volumes are larger than static filtrate volumes. The shear rate has two effects: first to dissociate loose aggregates in the suspension and second to exert a granulometric sorting of the particles in the case of a polydisperse suspension. At high shear rate a cake of constant thickness is quickly obtained. The thickness of this cake depends on the fraction of small particles present within the initial suspension or that are formed by dissociation of loose aggregates under dynamic conditions. In dynamic like in static the permeability is controlled by the size and shape of particles that constitute the cake.