Estimation of floc size in highly concentrated calcium carbonate suspension obtained by filtration with dispersant

This paper deals with the preparation of concentrated calcium carbonate suspensions at 72 wt% by filtration–compression in presence of chemical dispersants. A quantitative analysis of the disaggregating of filter cakes under shear into concentrated suspensions is proposed. Two rheological models were used: an Herschel–Bulkley model to relate the relative viscosity to the shear rate, a modified Krieger and Dougherty model to relate the relative viscosity to the solid concentration at given shear rate. The maximum packing fraction of particles in the cakes was estimated as well as the ratio between the aggregates and the particle size rf/rp. This ratio logically declines with the intensity of shear. It shows that an advanced cake disaggregating was obtained for low shear rates of 10 s−1. Two processes of filtration–compression were also compared: a filtration of deflocculated suspension (FDS) and an innovative precoat filtration of deflocculated suspension (PFDS). The results showed that PFDS improved the cake dryness and specific resistance as well as the flowability of the final concentrated suspension.