Project ended 1993; report dated March 1994
Solid-liquid separation operations leading to the concentration and isolation of fine particles dispersed in liquids are important in the chemical and mineral processing industries. In spite of this, the procedures available for the prediction of equipment performance remain crude. Almost all major mineral and chemical processing companies now have a clear priority in R&D budgets to develop new approaches to waste minimization; a major part of the problem faced by these industries relates to the effect of management of waste slurries. The processes that manage final waste slurries are often classical “end-of-pipe” solutions. One of the key aims of the present broad program is to understand’how to manipulate the structure of slurries within the process so that finally it is possible to engineer clear liquor and simultaneously manageable or tractable waste solids. The best way to process such wastes relies on understanding how to control the compressibility and viscosity of these materials.
We have developed a generalized approach to understanding and prediction of solid-liquid separation methods based on the measurement of fundamental material properties. This is of value in designing more efficient methods and ultimately to optimizing the performance of solid-liquid separation methods and the selection of flocculants for any given slurry.
Our model identifies two key parameters, the compressional yield stress P,(Q) and the hindered settling factor r(o) and we have developed laboratory test procedures for the direct measurement of both.
We have demonstrated the application of this model to a variety of thickening and filtration processes and provided a direct relationship between our model parameters and the conventional cake resistance (a) as utilised by current filtration engineers.
We have attempted to compare our model with Terzaghi’s consolidation model with some success but more work is required to perfect this analogy. We also need to investigate the role of a wider particle size distribution and the effects of shear on cake thickening. These remain as future targets in conjunction with the experimental work of Wakeman at al.