Includes: Thickening: Process in which a portion of the liquid of a pulp is removed to thicken the latter. Mostly achieved by decantation, but sometimes by filtration or cycloning. Decantation (clarification, dewatering): (1) Spontaneous separation by gravity of a solid phase in suspension within a liquid (settling), or of non-miscible liquids. (2) When solids are settling out they always retain some trapped liquid. But, as the settled phase has a higher solids percentage than the initial pulp, the end result is a thickening. Filtration: Process of separating solid particles in suspension in a fluid by forcing the latter to pass through some porous material (fabric, diatom layer, ...) that retains the solid particles.