Cake formation and particle rejection in microfiltration of binary mixtures of particles with two different sizes

• Cake formation and pore blocking occurred in microfiltration of binary mixtures.
• Flux decay became marked as smaller particles were trapped into voids of cake.
• Concentration of smaller particles and applied pressure affected rejection behaviors.
• Logistic equation was used to describe variation of rejection of smaller particles.
• Flux decay was described using logistic equation based on resistance-in-series model.

The filtration behaviors were examined in microfiltration of binary mixtures of particles with two different sizes. Dilute suspension of monodisperse polystyrene latexes with particle diameters of 0.522 and 0.091 μm was filtered using the microfiltration membranes with the nominal pore size of 0.3 μm, making them essentially impermeable to larger particles but permeable to smaller particles.The filter cake comprised of larger particles alone initially formed because smaller particles permeate through the membrane. However, the flux decline became gradually marked since smaller particles were trapped into the pores of the filter cake of larger particles. Eventually, smaller particles were fully rejected, and thereafter the binary cake of both larger and smaller particles grew. This filtration behavior was reflected by both data of flux decline and particle rejection.The logistic equation was employed to describe the variation of the rejection of smaller particles with the progress of filtration. The flux decline behaviors were well described using the logistic equation on the basis of the resistance-in-series model that the total cake resistance was represented by adding the increased cake resistance caused by the capture of smaller particles to the cake resistance of larger particles alone.

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