Selection of Isolation Methods for Micron Sized Particles

Solid-liquid separations are commonly used in industrial processes and are approached in a distinctive way based on the desired component- solid or liquid. The separation technique is dependent on a combination of factors- how the feed suspension was prepared, total volume, solid concentration, and particle shape and size distribution of the solids. Investigating the performance of various separation equipment is time consuming and this search can be narrowed down by utilizing specific laboratory scale tests to predict the behavior of a separation technique before scale-up. Herein, the processes of technology selection for situations where solids are the desired fraction with particle size < 10 µm are discussed. The choice of cake filtration methods such as vacuum and pressure filtration is often based on the average flux, which indicates the time required for filtration. Filter media with small channel sizes are required to isolate the micron sized particles. The cake deposited always exhibits high resistance and the small particles may block the channels leading to unacceptably long filtering time. Sedimenting centrifuges such as tubular, or stacked disc can be used for isolating sub-micron particles since they do not use a filter medium for separation and avoid the challenges of media fouling. The selection of sedimenting centrifuge can be based on laboratory scale feasibility tests performed with a benchtop centrifuge by varying the centrifugal force and residence time and observing the sediment compactness and supernatant clarity. Other filtration methods including thin cake filtration and cross-flow filtration can also be considered for systems with small particles.