Decantation

Decantation - Difference and Process of Decantation

We all have observed that if we leave a bucket full of water mixed with sand or mud undisturbed for a short amount of time most of the insoluble particles settle down at the bottom of the bucket due to the effect of gravity. If we pour the water out by tilting the bucket, the settled precipitate will remain at the bottom of the bucket while the relatively clean water can be poured out. Decantation is the process of separating insoluble solid particles from a liquid or separating two immiscible with different densities. In simpler words, decantation is a process where liquid can be separated from sediments or another immiscible liquid with different density manually.

Difference between filtration and decantation:

While both filtration and decantation can be used to separate impurities from liquids, there are differences between them.
Filtration is the direct separation of the entire solution through a filter, where the solid is trapped by the filter allowing the liquid to pass through. It cannot be used to separate two liquids.

Decantation is pouring away a liquid from solid impurities which have settled at the bottom of the container. Two liquids with a different density which have separated into two layers can similarly be separated by pouring the less dense liquid out.

Procedure for decantation:

It can be categorized into two types.

1. Immiscible liquid separation

Decantation can be used to separate two liquids that have different densities as long as they are immiscible. For example, water and oil form two separate layers when mixed together. Water being denser settles at the bottom and oil floats on water, forming two distinct layers. The separation can be done by pouring oil out into a different container, leaving behind the denser water in the original container. Generally, this type of separation is flawed, because it is difficult to pour out the top layer without pouring out some part of the bottom layer.

An alternate method of separating two immiscible liquid is via a separatory funnel. This apparatus has a valve with a stopcock to allow the effective separation of the two immiscible liquids.



2. Liquid-Solid separation

Decantation can also separate insoluble solids from liquids. This involves first allowing the particles to be settled via the action of gravity and the pouring out the clear liquid. This method is widely used in laboratories, the test tube is placed at a 45 ° to allow effective sedimentation before performing the decantation process. A centrifuge can be utilized if the natural settling process feels time-consuming or tedious.

Loading is a process by which tiny suspended impurities are made heavier by adding chemicals that stick o them and make them heavier. While separating sand and water for example, even after removing the particles that were sedimented, the water still looks muddy due to tiny suspended impurities. By adding alum to this muddy water, the suspended muddy water settles down and clear water is left.



Examples for solutions where decantation can be used include mud in the water, grease on top of the soup, liquid from mustard, and a mixture of oil and water.

Advantages and disadvantages of decantation:

Advantages:

Decantation is a relatively easy process. It can be performed manually. It can thus easily separate insoluble sediments or immiscible liquids with relative ease.

Disadvantages:

It cannot separate solids or liquids that dissolve in the mixture. It cannot separate salt from water, for example. It also cannot separate light solid impurities like chalk powder from water since they are too light and hence do not settle at the bottom for a long time. It is not possible to recover all of the constituents of the mixture since it is difficult to perfectly separate them manually. Unless you are using a centrifuge, it is time-consuming to wait for the sediments to settle down due to gravity.

Uses of decantation:

Decantation is frequently used to purify a liquid by separating it from suspension or sediment of insoluble particles. While it is sometimes not ideal to do so, due to the fact that any solution can be decanted manually as long as it is allowed to settle for some time, it is quite popular. Decantation procedure is commonly used for the following:

1. Decantation is used to separate potassium bitartrate crystals from red wine. Potassium bitartrate is a mono-salt of tartaric acid, the grape’s principle acid, and it is less soluble than tartaric acid and ca precipitate after the wine process. These potassium bitartrate crystals give an unsavory taste to the wine. Hence it is decanted before serving for the best taste. This is also known to make the wine more tonic and astringent. A specially made container exclusive to wine, with a long and narrow neck and wide opening, called the decanter is used for this purpose.

2. Cream floats on top of milk, and this allows the separation of milk and cream via decantation. The same thing applies to butter and buttermilk.

3. Clearwater can be obtained from muddy water via decantation. If there are more suspended impurities, loading can be used to settle those impurities down. This way clear water can be separated from the impurities at the bottom. All water treatment plants, including those for sewage water, use decantation to separate sediments.

4. In sugar industries, while the processing of sugar beets or sugarcanes into granular sugar takes place, many liquid-solid mixtures are obtained. An example of this would be syrups and crystals. Decantation is an ideal separation method

5. Decantation finds its use even in nanotechnology. Decantation is used during the synthesis of high-quality silver nanowire solutions, or the fabrication process of high-performance electrodes, as it greatly simplifies the purification process.

6. After using a desiccant to absorb water and dry an organic liquid, the now separated and dry organic liquid can be often decanted away from the desiccant.

7. The process of deriving grape vinegar or malt vinegar requires decantation process to remove fats from the raw substance.

8. Plasma can be separated from blood by using a centrifuge through decantation while performing diagnostic tests.

9. While mining, mercury is sometimes disposed of off in water bodies, turning this water toxic and unfit for use and consumption. The mercury can be eliminated from water by the process of decantation.

10. Froth flotation is a process of separating hydrophobic and hydrophilic materials from each other. It finds application in mineral industries, paper recycling plants, and wastewater treatment industries. The ultimate separation of materials in this process is done via decantation.