INITIAL AND FINAL STAGES OF COMPRESSIBLE FILTERCAKE COMPACTION

Filtration experiments were performed to dewater bentonite slurries at different filtration pressures. The diffusivity of the cake was then determined as a function of void ratio using the measured filtration r ates, the final void ratios of tile cakes and the theory of compressib le filtercakes. Any filtration process can, in theory, be predicted, o nce the cake diffusivity is known as a function of void ratio and the void ratio as a function of applied pressure, In particular, the final stage of the filtration process can be modeled and offers an alternat ive route to determine the cake properties from the experimental resul ts. The final slow approach to equilibrium is difficult to study exper imentally other techniques to determine cake properties are therefore preferable, Final stages of the cake compaction are also markedly slow er than predictions based on the initial filtration rates. Possible ex planations include a filtercake rheology that is more complicated than assumed in the model or time-dependent effects caused by exclusion of ions from the bentonite filtercake, but such explanations appear unsa tisfactory. Filtration models in which the filtercake void ratio and p ermeability depend solely on the imposed stress, may therefore be too simple for some materials.