Decantation is a process for the separation of mixtures. This is achieved by carefully pouring a solution from a container in order to leave the precipitate (sediments) in the bottom of the original container. Usually a small amount of solution must be left in the container, and care must be taken to prevent a small amount of precipitate from flowing with the solution out of the container. It is generally used to separate a liquid from an insoluble solid (e.g. in red wine, where the wine is decanted from the potassium bitartrate crystals). For example, to obtain a sample of clear water from muddy water, muddy water is left in a container until the mud settles, and then the clear water is poured into another container.
A mixture of two immiscible liquids can also be separated by decantation. For example, the oil and water extracted from olives may be decanted to obtain the olive oil. A mixture of kerosene and water can also be separated through decantation.
A centrifuge may be useful in successfully decanting a solution. The centrifuge causes the precipitate to be forced to the bottom of the container; if the force is high enough, the precipitate may form a compact solid. Then the liquid can be more easily poured away, as the precipitate will likely remain in its compressed form. A mixture of an insoluble solid in liquid is allowed to stand. The solid being insoluble settles at the bottom if kept undisturbed for some time, this process is called sedimentation. The clear liquid is then poured off carefully, this process is called decantation.
Another example of decantation is the regeneration of used chiral stationary phase (CSP). The CSP to be decanted is gently mixed in a container with a compatible solvent to form a suspension. The suspension is allowed to rest for a period of time, after which the supernatant is carefully poured off. The supernatant contains the undesirable constituents of the former suspension, while the leftover sediment in the container is clean, reusable CSP.