Aggregate densification and batch settling

Abstract

The sedimentation behaviour of particulate slurries in laboratory scale batch settling experiments is important to the prediction of full-scale gravity thickening behaviour. However, the material throughput predicted by modelling of thickener performance from material properties derived from conventional batch experiments has been shown to be up to 100 times less than observed (at full-scale). Such discrepancies have been attributed to various shear and compression-induced effects (prevalent at full-scale) that modify flocculated aggregate structure, including aggregate densification. Standard Kynch batch settling analysis has been modified to incorporate the effect of aggregate densification behaviour on material properties. Based on this modification, a semi-analytical method is presented, which provides improved real-time predictions of batch sedimentation behaviour. This method can produce a slurry–liquid interface height versus time profile up to the end of the fan region, based on a functional form of aggregate densification behaviour. Additionally, aggregate densification theory incorporated into the compressive yield stress is used to predict the final equilibrium bed height. A functional form is proposed that incorporates parameters which describe the rate and the extent of densification. Validations of this method are presented against theoretical numerical simulations and experimental data.