Direct prediction of sediment permeability using 3D tomographic imaging

Separation of solids from suspending liquid plays a crucial role in a variety of processes, from nano-materials synthesis to bio-processing. The problem often involves small, colloidal-type particles that have to be aggregated into more manageable sizes. Characteristics of these aggregates inevitably influence downstream solids recovery. Porosity and density are as important as size in influencing aggregate settling behaviour and fluid transport properties, such as permeability of the aggregate networks or sediments. Most existing data on filtration, sedimentation, and thickening are focused on the macro-scale phenomena, whereas challenges still remain for fundamental understanding at a much smaller length scale. Insights into the micro-properties of aggregate and sediment are important for understanding system behaviour. Correlating the physical properties and hydrodynamic behaviour of these solids poses a significant challenge due to their non-spherical and porous structures. 3D structural imaging of aggregated systems in a relatively non-destructive manner is now possible with a high resolution X-ray microtomography. Data obtained from in-situ measurements could enable direct computation of the properties of solids assembly (shape, size, contact area) and their permeability to fluids. High-resolution X-ray microtomographic method combined with robust fluid simulation is a promising tool to provide invaluable insights into aggregate and sediment microstructures. A specific application relating to the formation of silica aggregates is described here from which the behaviour of sediments containing these materials can be predicted on the basis of a bench-top test and the use of a Lattice Boltzmann simulation. The ability to derive performance information, such as fluid permeability from laboratory based measurements of microstructure coupled with appropriate micro-scale physical simulations has considerable potentials. It is proposed that the method may be used to predict trends such as the filtration behaviour of porous structures under different states of compression. This offers a significant benefit in assisting the formulation design of flocculated materials pertinent to a number of industrial sectors wishing to design optimal filtration or relevant operations.