Relative liquid removal in filtration and expression

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Abstract
A strong relationship exists among the nature of particles in a suspension, properties of the particulate structures forming cakes and sediments, and the best operating procedure for reducing liquid content. Matrices of particles can be crudely classified into (1), super-compactible flocs, (2), highly compressible cakes formed from substances having bound water (clays), (3), moderately compressible, and (4), nearly incompressible materials. Super flocs with little internal strength filter easily by gravity or low pressure and do not respond to increased pump pressure. They require a squeezing process. Highly compressible materials such as attapulgite clay or colloidal silica filter with great difficulty, and high pressure pumps are not effective. They also require expression for substantial reduction of porosity. Moderately compressible cakes exhibit more favourable behaviour with increasing pressure. Incompressible cakes cannot be deliquored by expression. However, if the particles are large enough, suction, blowing, or centrifugal filtration are generally successful for liquor removal. The applied pressure must be greater than the capillary suction. A simple experimental technique for evaluating cake behaviour is provided.