Decantation is a process for the separation of mixtures of

immiscible Miscibility () is the property of two chemical substance, substances to mix in all mixing ratio, proportions (that is, to fully dissolution (chemistry), dissolve in each other at any concentration), forming a homogeneity and heterogeneity, homoge ...

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 Density (volumetric mass density or specific mass) is the ratio of a substance's mass to its volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' (or ''d'') can also be use ...

of the two liquids, or the liquid from which the

precipitate In an aqueous solution, precipitation is the "sedimentation of a solid material (a precipitate) from a liquid solution". The solid formed is called the precipitate. In case of an inorganic chemical reaction leading to precipitation, the chemic ...

sediment Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...

has settled out—is poured off, leaving denser liquid or the solid behind. The process typically is unable to remove all of the top layer, meaning the separation is incomplete or at least one of the two separated components is still contaminated by the other one.

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 A separatory funnel, also known as a separation funnel, separating funnel, or colloquially sep funnel, is a piece of laboratory glassware used in liquid-liquid extractions to separate (''partition'') the components of a mixture into two miscible, i ...

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 (), also known as gravitation or a gravitational interaction, is a fundamental interaction, a mutual attraction between all massive particles. On Earth, gravity takes a slightly different meaning: the observed force b ...

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 ...

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 subject a specimen to a specified constant force - for example, to separate various components of a fluid. This is achieved by spinning the fluid at high speed within a container, thereby ...

machine may also be used in decantation as the natural process of settling down is time-consuming and tedious. A centrifuge forces the

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 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 solub ...

particles (e.g. in red

wine Wine is an alcoholic drink made from Fermentation in winemaking, fermented fruit. Yeast in winemaking, Yeast consumes the sugar in the fruit and converts it to ethanol and carbon dioxide, releasing heat in the process. Wine is most often made f ...

, where the wine is decanted from the

potassium bitartrate Potassium bitartrate, also known as potassium hydrogen tartrate, with formula K C4 H5 O6, is the potassium acid salt of tartaric acid (a carboxylic acid)—specifically, l-( + )-tartaric acid. Especially in cooking, it is also known as cream o ...

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, Sugar refinery, processing and marketing of sugars (mostly sucrose and fructose). Globally, about 80% of sugar is extracted from sugar cane, grown predominantly in the tropics, and 20% from sugar beet, ...

, the processing of sugar beets into granular sugar involves many liquid–solid separations; e.g. separation of syrups from crystals. Decantation is also present in

nanotechnology Nanotechnology is the manipulation of matter with at least one dimension sized from 1 to 100 nanometers (nm). At this scale, commonly known as the nanoscale, surface area and quantum mechanical effects become important in describing propertie ...

. 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. Desiccant ...

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.

References

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

Processes

Immiscible liquid separation

Liquid-solid separation

Examples

See also

References