Decantation is a process for the separation of mixtures of immiscible liquids or of a liquid and a solid mixture such as a

suspension Suspension or suspended may refer to: Science and engineering * Suspension (topology), in mathematics * Suspension (dynamical systems), in mathematics * Suspension of a ring, in mathematics * Suspension (chemistry), small solid particles suspende ...

. The layer closer to the top of the container—the less

dense Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematically ...

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 ...

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, sa ...

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 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 immiscib ...

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

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 solubil ...

particles (e.g. in red

wine Wine is an alcoholic drink typically made from fermented grapes. Yeast consumes the sugar in the grapes and converts it to ethanol and carbon dioxide, releasing heat in the process. Different varieties of grapes and strains of yeasts are m ...

, where the wine is decanted from the

potassium bitartrate Potassium bitartrate, also known as potassium hydrogen tartrate, with formula K C4 H5 O6, is a byproduct of winemaking. In cooking, it is known as cream of tartar. It is processed from the potassium acid salt of tartaric acid (a carboxylic ac ...

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 processing of sugar beets into granular sugar and many liquid - solid separations are encountered e.g. separation of syrups from crystals. Decantation is also present in nanotechnology. 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 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