Batch Analysis of Slurries in Zone Settling Regime

Abstract

An integrated model for computing the height variation of the mudline and sediment-suspension interfaces of a slurry exhibiting zone settling behavior is proposed. The model accounts for the dynamic interaction of the two dominant components of a batch test, the settling of solids in the suspension region, and the compression of the material that has already been deposited at the bottom of the cylinder. The settling of solids is modeled by the Kynch theory, while the compression process is represented by a self-weight nonlinear finite strain model. A graphical procedure that involves use of the slurry flux curve in conjunction with the Kynch model is developed to calculate the flux of the solids that settle atop the sediment layer. The equation governing the compression process, which is a nonlinear transient partial differential equation of the parabolic type, is solved numerically by using the finite-element method for the spatial domain, while for the time domain a finite-difference scheme is used. Its solution provides the compaction rate and the velocity of the upward moving liquid that is squeezed out from the sediment layer. The coupling of the two components is accomplished by continuously accounting for the effect of the newly deposited sediment on the thickness of the sediment layer and the attendant release of upward moving liquid and its influence on the settling of solids within the suspension. The validity of the model is illustrated by using data reported in the literature for a mineral clay.