The method of separation of a solid phase from a liquid by a repeating sequence of stages comprising dilution and gravity sedimentation is known as decantation. Most applications of the method involve continuous countercurrent decantation (CCD), with the number of stages ranging from 2 and 10. The equipment selected for CCD may consist of multiple-compartment washing tray thickeners or a train of unit thickeners. Factors which make CCD a preferred choice of separation technique include the following: rapidly settling solids (settlement rate may be assisted by flocculation); a high ratio of solids concentration between the underflow and the feed; the need for high wash ratios during the dilution stage (greater than three times the liquor volume in the thickened underflow); a large quantity of solids to be processed (containing a significant fines fraction, which is otherwise difficult to concentrate).
Decanters is also a generic term used to cover the range of continuous sedimenting Centrifuges which utilize a scrolling mechanism for transport of solids through the machine and their subsequent discharge.