Colloidal particle

Colloidal particle - small amount of matter having size typical for colloids and with a clear phase boundary (phase colloids), a group of such particles (aggregate, agglomerate) or being a macromolecule (eg. solution of polymer molecules is a molecular colloid) or a molecular aggregate (e.g. micelle).

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“Restructuring of colloidal aggregates during dewatering”

J.B. Madeline, M. Meireles, C. Bourgerette, R. Botet, R. Schweins, B. Cabane

Langmuir 23 (2007) 1645

Introduction

Dispersions of fine solid particles in a liquid are used to manufacture coatings (paints, inks, paper coatings), composite materials (reinforced elastomers) and ceramics. They are also found in food (milk, cheese), pharmaceuticals, and biotechnology processes (fermentation broths). Lastly, they form the bulk of industrial and city effluents. In most cases, it is at some point necessary to separate the particles from the liquid: ceramic pastes must be consolidated, clays and sludge must be dewatered, and paper coatings must be drained and dried. At this point major technical problems occur.

The solid/liquid separation may be achieved through a variety of processes including mechanical compression, drying, membrane filtration, and centrifugation. In all these processes, the particles are pre-aggregated to form a flocculated suspension, and the liquid phase that separates the aggregates is removed until the aggregates connect to each other and form a wet cake. Some stress is then applied to the cake in order to remove more of the liquid phase and achieve an optimal solid/liquid separation. This stress is an osmotic pressure (it moves the liquid with respect to the particles), which is applied through the processes listed above. The efficiency of the separation depends on the way in which the wet cake responds to osmotic pressure.

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