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Decantation is a process for the
separation of mixture A separation process is a method that converts a mixture or a solution of chemical substances into two or more distinct product mixtures, a scientific process of separating two or more substance in order to obtain purity. At least one product mi ...
s of
immiscible Miscibility () is the property of two substances to mix in all proportions (that is, to fully dissolve in each other at any concentration), forming a homogeneous mixture (a solution). The term is most often applied to liquids but also appli ...
liquids or of a liquid and a solid mixture such as a suspension. The layer closer to the top of the container—the less dense of the two liquids, or the liquid from which the
precipitate In an aqueous solution, precipitation is the process of transforming a dissolved substance into an insoluble solid from a super-saturated solution. The solid formed is called the precipitate. In case of an inorganic chemical reaction leading ...
or
sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand ...
has settled out—is poured off, leaving the other component or the denser liquid of the mixture behind. An incomplete separation is witnessed during the separation of two immiscible liquids. To put it in a simple way, decantation is separating immiscible materials by transferring the top layer to another container. The process does not provide accurate or pure product.


Processes


Immiscible liquid separation

Decantation can be used to separate immiscible liquids that have different densities. For example, when a mixture of water and oil is present in a beaker, after some time a distinct layer between the two liquids is formed, with the oil layer floating on top of the water layer. This separation can be done by pouring oil out of the container, leaving water behind. Generally, this technique gives an incomplete separation as it is difficult to pour off all of the top layer without pouring out some parts of the bottom layer. A separatory funnel is an alternative apparatus for separating liquid layers. It has a valve at the bottom to allow draining off the bottom layer. It can give better separation between the two liquids.


Liquid-solid separation

Decantation can also separate solid and liquid mixtures by allowing
gravity In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...
to pull the solid fragments to settle at the bottom of the container. In laboratory situations, decantation of mixtures containing solids and liquids occur in
test tube A test tube, also known as a culture tube or sample tube, is a common piece of laboratory glassware consisting of a finger-like length of glass or clear plastic tubing, open at the top and closed at the bottom. Test tubes are usually placed in ...
s. To enhance productivity, test tubes should be placed at a 45° angle to allow sediments to settle at the bottom of the apparatus. A
centrifuge A centrifuge is a device that uses centrifugal force to separate various components of a fluid. This is achieved by spinning the fluid at high speed within a container, thereby separating fluids of different densities (e.g. cream from milk) or ...
machine may also be used in decantation as the natural process of settling down is time-consuming and tedious. A centrifuge forces the
precipitate In an aqueous solution, precipitation is the process of transforming a dissolved substance into an insoluble solid from a super-saturated solution. The solid formed is called the precipitate. In case of an inorganic chemical reaction leading ...
to the bottom of the container; if the force is high enough, solids can aggregate to form pellets, making it easier to separate the mixtures. Then the liquid can be more easily poured away, as the precipitate will tend to remain in its compressed form.  A
decanter centrifuge A centrifuge is a device that employs a high rotational speed to separate components of different densities. This becomes relevant in the majority of industrial jobs where solids, liquids and gases are merged into a single mixture and the separation ...
may be used for continuous solid-liquid separation.


Examples

Decantation is frequently used to purify a liquid by separating it from a suspension of
insoluble In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solubi ...
particles (e.g. in red
wine Wine is an alcoholic drink typically made from Fermentation in winemaking, fermented grapes. Yeast in winemaking, Yeast consumes the sugar in the grapes and converts it to ethanol and carbon dioxide, releasing heat in the process. Different ...
, where the wine is decanted from the potassium bitartrate crystals to avoid unsavory taste). This makes the wine more tonic and astringent. Cream accelerates to the top of milk, allowing the separation of milk and cream. This is used in the cheese industry. Fat is determined in butter by decantation. To obtain a sample of clear water from muddy water, muddy water is poured into another container, which separates the water from the mud. In the
sugar industry The sugar industry subsumes the production, processing and marketing of sugars (mostly sucrose and fructose). Globally, most sugar is extracted from sugar cane (~80% predominantly in the tropics) and sugar beet (~ 20%, mostly in temperate cl ...
, the processing of
sugar beets Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. Simple sugars, also called monosaccharides, include glucose, fructose, and galactose. Compound sugars, also called disaccharides or double ...
into granular sugar and many liquid - solid separations are encountered e.g. separation of syrups from crystals. Decantation is also present in
nanotechnology Nanotechnology, also shortened to nanotech, is the use of matter on an atomic, molecular, and supramolecular scale for industrial purposes. The earliest, widespread description of nanotechnology referred to the particular technological goal ...
. In the synthesis of high quality silver nanowire (AgNW) solutions and fabrication process of high performance electrodes, decantation is also being applied which greatly simplifies the purification process. After using a
desiccant A desiccant is a hygroscopic substance that is used to induce or sustain a state of dryness (desiccation) in its vicinity; it is the opposite of a humectant. Commonly encountered pre-packaged desiccants are solids that absorb water. Desiccants ...
to absorb water from an organic liquid, the organic liquid can often be decanted away from the desiccant. The process of deriving vinegar also requires decantation to remove fats and biomolecular antioxidants from the raw substance. Plasma can be separated from blood through decantation by using a centrifuge. Mercury is disposed of in water bodies during mining, turning the water unfit and toxic. The mercury can be removed through decantation.


See also

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Sedimentation Sedimentation is the deposition of sediments. It takes place when particles in suspension settle out of the fluid in which they are entrained and come to rest against a barrier. This is due to their motion through the fluid in response to the ...
*
Centrifugation Centrifugation is a mechanical process which involves the use of the centrifugal force to separate particles from a solution according to their size, shape, density, medium viscosity and rotor speed. The denser components of the mixture migrate ...


References

{{Separation processes Liquid-liquid separation Liquid-solid separation Laboratory techniques Analytical chemistry Alchemical processes