What is decantation?

November 1, 2021

Decantation is one of the methods used in laboratories to separate heterogeneous mixtures. Separates a denser solid or liquid from a less dense fluid.

What is it?

It is a physical method used to separate heterogeneous mixtures. It separates a less dense fluid from a higher density one and that therefore is located in the lower part of the mixture, this type of liquids are known as immiscible liquids or that cannot be mixed in a homogeneous way.

Decantation is also often considered to be the process where a solid is separated from a liquid in a heterogeneous mixture, although some authors differ from this opinion.

Types of decantation

Solid-liquid decantation

Also known as sedimentation, it is used when a solid is heterogeneously mixed with a liquid and when the mixture is left to rest, the solid particles accumulate in the lower part of the container. This process is measured by Stokes’ law for sedimentation, it establishes that the time necessary for the sedimentation of a sand particle of 1 mm in diameter is 10 seconds and for a clay particle of 10 µm, the time would be 2 hours. A 1 µm bacterium sediments in 8 days and colloidal particles of 100 nm and 1 nm would take between 2 and 200 years to sediment.

Liquid-liquid decantation

Immiscible liquids or liquids that cannot be mixed due to their different densities are separated. The densest liquid always collects at the bottom of the system. To separate them, a bromine funnel or separatory funnel is used.

How is the Settling Funnel used?

To use the funnel you must first make sure that the tap at the bottom is closed so that the mixture does not come out when pouring it. Pour in the mixture and let it sit so that the liquids separate well.

Place a beaker under the funnel and turn on the tap. The densest liquid will come out first because it collects at the bottom of the mixture. When all the liquid passes, close the tap. The less dense liquid should be extracted from the top to avoid contaminating it with the remains of the dense liquid.

Decantation a Solid

If a solid is dense and thick it is deposited at the bottom of the container. Depending on the type of solid you can determine the time it will take to completely settle. Then, you just have to carefully tilt the glass and extract the liquid.

Dr. Loony Davis5
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Born and raised in Brussels in an English family, I have always lived in a multicultural environment. After several work experiences in marketing and communication, I came to Smart Water Magazine, which I describe as the most exciting challenge of my career.
I am a person with great restlessness and curiosity to learn, discover what I do not know, as well as reinvent myself daily, someone who is curious about life and wants to know. I enjoy sharing knowledge.
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