Structural recovery behaviour of kaolin, bentonite and K-montmorillonite slurries

When the interparticle attractive force of a flocculated slurry is very strong then both its shear and compressive yield stress will be very high. This slurry will be less compressible in terms of the volume fraction reached for a given applied pressure. Thus the magnitude of the shear yield stress of a feed slurry can be used as an indication of its compressibility in a thickener. If this yield stress is high a lower solids underflow is expected except when it is operated under permeability limited condition. This is undesirable for thickening operations. Clay, a major component in tailing slurries, is known to display time-dependent shear yield stress behaviour. Some clay tailing slurries cannot be thickened to more than 10 wt.% solids. Structural recovery leading to a large yield stress may be responsible. In this study, the shear yield stress of kaolin, K-montmorillonite and bentonite clay slurries was evaluated as a function of rest time. Kaolin clay slurries were not found to display significant time-dependent behaviour. In contrast bentonite and K-montmorillonite clay slurries showed very pronounced time-dependent behaviour, where the yield stress increases significantly with time of aging. The Nguyen–Boger and Leong models were used to describe the structural recovery behaviour of these slurries.

The structural recovery behaviour in terms of yield stress versus aging time, of bentonite suspension at various pH levels is shown below. The so-called Leong model predicted the recovery behaviour well.Figure optionsDownload as PowerPoint slideHighlights
► Kaolin clay slurry did not displayed time-dependent behaviour.
► Bentonite and K-montmorillonite slurries showed very significant time dependent behaviour.
► K-montmorillonite slurries exhibit very high yield stress and significant structural recovery at high pH (> 11) even in the presence of triphosphate dispersants due to high dissolution rate and swelling.
► The so-called Leong model was found to describe the recovery behaviour of the bentonite and K-montmorillonite slurries with triphosphate additives very well.
► The time-scale of structural recovery in the order of hours.