SEDIMENTATION AND COMPACTION OF CALCIUM-CARBONATE AGGREGATING SUSPENSIONS - SCALING ANALYSIS OF THE EQUILIBRIUM

Aggregating suspensions generally separate into a clear supernatant an d a Voluminous gelled sediment. The suspension remains homogeneous (i. e. a gel stable under gravity forms) only when the Volume fraction of particles exceeds a given value Phi*. The present study is devoted to the determination of Phi*. A simplified model describing the gel equ ilibrium has been developed and its validity is checked comparing its predictions to systematic measurements of the sediment Volume performe d on calcium carbonate suspensions. Applying this model to the predict ion of Phi*, we show that Phi** is not a characteristic of the physic o-chemical system but depends on the height of the sample, its aspect ratio and friction between the gel and the side wall. For large (respe ctively small) aspect ratios, we find that Phi* is a power law functi on of the width (respectively the height) of the sample involving an e xponent 1/(kappa - 1) which is related to the dependence of the yield stress on the volume fraction of the suspension.