What is Decantation?

What Does Decantation Mean

It is known as decantation to a physical procedure that serves to separate a heterogeneous mixture composed of a solid or liquid of higher density , and a liquid of lower density .

This procedure consists of the separation of the densest component (solid or densest liquid), from the less dense liquid , by the action of gravity . The mixture is allowed to settle in a container (generally separating or separating funnels are used) and, in this way, the denser component descends by gravity towards the bottom of the funnel and the less dense component remains at the top. .

Finally, the densest component is extracted from the bottom . These types of tools for separating mixtures generally have several keys attached in different positions, which can be opened and closed to remove the desired component. An illustrative example is shown in the following figure, where the mixture is colored green, dark blue liquid is the densest component and the liquid light blue is the least dense component

This process is widely used in laboratories and industrial processes , especially using separatory funnels or similar tools. It should not be confused with sedimentation or gravitational separation, which consists of the separation of solid waste suspended in a liquid (such as water and sand) by the mere effect of gravity.

There are two ways in which decantation can be carried out, taking into account the state of aggregation of the substances that make up the mixture:

• Solid-liquid decantation. When solid elements are deposited in a liquid medium.
• Liquid-liquid decantation. When the mixture is formed by two liquids of different densities that cannot dissolve in each other.

It can help you: Filtration

Examples of decantation

• Sewage treatment . The dirty waters of the sewage system of the cities are generally denser than the clean ones, since they are full of organic matter and other substances in suspension. Therefore, an initial process of decanting and filtering the dirt can be carried out before returning the water to the seas and rivers. Thus, the water is returned cleaner to the environment, reducing the pollution of the environment .
• Obtaining natural oils. It is known that fats are not soluble in water and, therefore, during the extraction of vegetable oils, decantation is usually used as a way to separate them from the water. In addition, decantation is also used to extract the solid residues that remain in the oil after crushing the palm, seed or olive.
• Biodiesel and glycerin separation. Glycerin is an unwanted by-product of the biofuel production process that uses vegetable or animal fats. To separate them, the difference in densities is used in a settling stage, which deposits the glycerin at the bottom of the container.
• Purification of the water . In the processes to make water drinkable, various initial settling stages are used, which give time for the clays and other suspended materials to settle to the bottom and be extracted, leaving the waters cleaner for later filtering stages.
• Decantation of wine. The wine is obtained from the fermentation of the grapes, so it is necessary to separate the liquor from the physical residues that remain and that can often re-form in the bottle, after some time of sedimentation. The experts in the field then recommend applying a decantation process to extract the sediments and also oxygenate the wine. It is something usual in long-maturing wines.
• Manufacture of vinegars. The refinement of vinegar of vegetable origin requires decantation stages, in which it is separated from the heavier vegetable oils (also valuable), obtained during the transformation of the raw material .
• Oil refining . The oil must be refined to achieve the necessary degree of purity hydrocarbon which allows obtaining derivatives . Various useful hydrocarbons result from this process , in a gaseous or liquid state , which can be separated from the rest of the mixture by decantation. Thus, the lightest hydrocarbons are extracted and the densest ones continue to be refined in the lower part of the deposits.
• Oil extraction on offshore platforms. When it comes to extracting oil from reservoirs on the seabed, it is often the case that the hydrocarbon mixes with seawater. This is remedied by decanting the mixture, since oil is much denser than water. The latter is stored and instead the water is returned to the ocean .

Mixture separation methods

The methods of separation of mixtures, also called methods of separation of phases, are the different physical procedures (never chemical) that allow to separate the different components of a mixture , using the different physical properties that each one presents.

So for these methods to work, we must be in the presence of mixtures whose components retain their identity in the mixture and no chemical reactions take place that permanently alter their properties as a result of mixing them.