Laboratory cake filtration testing using constant rate

A precipitated calcium carbonate with Sauter mean diameter of 7.5 μm was filtered under conditions of constant rate and constant pressure in a comparative laboratory investigation. The specific cake resistance to filtration was found to vary between 1 × 109 and 1 × 1011 m kg−1, depending on the applied pressure, and the corresponding filter cake volume concentrations were between 0.42 and 0.54 (v/v). The calculated specific resistance, from the particle size distribution data and the Kozeny–Carman equation is one order of magnitude lower than that measured, even though the solids were extremely robustly characterised. Practical filter testing rather than design based on size distributions is known to be essential. However, the conventional approach is to use constant pressure laboratory tests, the results presented here demonstrate that constant rate filtration is a more reliable method for data acquisition, especially when determining the filter medium resistance, and readily available laboratory equipment is adequate for use.

► Constant rate proposed as standard laboratory test system.
► Robust particle characterisation used to determine Sauter mean diameter.
► All data required for resistance constitutive equation can be obtained from a single test.
► Resistance predicted from Kozeny still an order of magnitude lower than measured value.