Methods of Separation

Separation technique is a method in which mass transfer takes place and converts a mixture of substances into two or more substances. For example: handpicking, winnowing, threshing, sedimentation, filtration etc.

Methods Of Separating

  1. Separation of solid from solids
    • Handpicking
    • Threshing
    • Winnowing
    • Sieving
    • Magnetic Separation
  2. Separation of insoluble solids from liquids
    • Sedimentation and Decantation
    • Filtration
  3. Separation of soluble solids from liquids
    • Evaporation and Condensation
  4. Separation of miscible liquids
    • Distillation
  5. Separation of immiscible liquids
    • Separating Funnel
  6. Fat-in-water emulsion (milk) to a water-in-fat emulsion (butter)
    • Churning

Let us discuss them in detail below.

A. Separation of solid from solids


Separation method in which components of a mixture can be separated by just picking them out by hands is called handpicking.

This method involves simply picking out all the unwanted substances by hand and separating them from useful ones. The separated substances may be an impurity that has to be thrown away or maybe that both the separated substances are useful. For example – if you separate black grapes from green ones from a mixture of the two.

Examples :

  • For separating the mixture of chillies and lady’s finger. (on the basis of size)
  • For separating stones from rice, pulses and wheat. (on the basis of size and color)
  • For separating rotten potatoes from fresh ones. (on the basis of shape, color and smell)
  • For separating different kinds of vegetables from the mixture of vegetables in the basket. (on the basis of shape, color, size)
  • For separating the mixture of yellow dal and rice. (on the basis of color)

Threshing :

Threshing is the process of separating the grain from the straw. It can be either done by hand, by using a treadle thresher or mechanized.

This method is mostly done during the harvesting of crops. Normally, the stalks of the wheat are dried once it is harvested. The grain is then separated from the stalks and grounded into the floor by beating the dry stalks to shake off the dried grains.

Winnowing :

The process of separating heavier and lighter components of a mixture by wind or by blowing air is called winnowing.

When the grains are collected from the process of threshing, it needs to be cleared out of husks and chaffs before it is turned into flour. Normally the separation of the mixture is carried out with the help of wind or blowing air. The husk and chaff are blown away by the strong wind when the farmers drop the mixture from a certain height to the ground. The heavier grains are collected at one place.

Sieving :

The process of separating fine particles from the larger particles by using a sieve, is called sieving.

It is done to separate mixtures that contain substances mostly of different sizes. The mixture is passed through the pores of the sieve. All the smaller substances pass through easily while the bigger components of the mixture are retained.

Magnetic Separation :

Magnetic separation is the process of separating components of mixtures by using magnets to attract magnetic materials.

The process that is used for magnetic separation detaches non-magnetic material with those that are magnetic.

When one substance in the mixture has some magnetic properties then this method is quite useful. Strong magnets are commonly used to separate magnetic elements.

B. Separation of insoluble solids from liquids

Sedimentation and Decantation or Filtration


Sedimentation is the process of allowing particles in suspension in water to settle out of the suspension under the effect of gravity.

In this process heavier impurities present in liquid normally water settle down at the bottom of the container containing the mixture. The process takes some amount of time.


Decantation is the process of separation of liquid from solid and other immiscible (non-mixing) liquids, by removing the liquid layer at the top from the layer of solid or liquid below.

The process can be carried out by tilting the mixture after pouring out the top layer. This process can also be used to separate two liquids that do not mix with each other for e.g., oil and water. When we leave the mixture of oil and water, two separate layers are formed, with water at the bottom and oil, being lighter, at the top. We can remove the oil layer from the top by pouring it into another vessel, which leaves us with the water layer at the bottom.

Filtration :

Filtration is a method for separating an insoluble solid from a liquid.

The most common method of separating a liquid from an insoluble solid is the filtration. Take, for example, the mixture of sand and water. Filtration is used here to remove solid particles from the liquid. Various filtering agents are normally used like filtering paper or other materials.

Filter paper:

In addition to the above method Osmosis also use to separation through Semipermeable membrane.

[Osmosis: Osmosis is the spontaneous net movement or diffusion of solvent molecules through a selectively permeable membrane from a region of high water potential to a region of low water potential, in the direction that tends to equalize the solute concentrations on the two sides.]
[Semipermeable membrane: It is a type of biological or synthetic, polymeric membrane that will allow certain molecules or ions to pass through it by osmosis.]
Examples :
Synthetic versions of a semipermeable membrane like filter paper are those used for water filtration or desalination.
A biological example of a semipermeable membrane is kidney tissue. Kidneys allow for some molecules to pass through them while blocking others such as human waste products.

Filter paper is a semi-permeable paper barrier placed to a liquid or air flow. It is used to separate fine substances from liquids or air. Mud water separation through filter paper give more pure water than sedimentation and decantation process.

C. Separation of soluble solids from liquids

Evaporation and Condensation:

Use to separate soluble solid from liquid by evaporating the liquid and then condensing it in separate container.

Evaporation is a process that is used in separating a mixture usually a solution of a solvent and a soluble solid. In this method, the solution is heated until the organic solvent evaporates where it turns into a gas and mostly leaves behind the solid residue.

Example :

  • Salt and water can be separated by evaporation
  • Sugar and water can be separated by evaporation
  • Copper sulphate crystals from copper sulphate solutions

D. Separation of miscible liquids

Distillation :

Distillation is the process of separating components of a mixture based on different boiling points.

When mixtures consist of two or more pure liquids than distillation is used. Here the components of a liquid mixture are vaporized, condensed and then isolated. The mixture is heated and the component which is volatile vaporizes first. The vapour moves through a condenser and is collected in a liquid state.

Examples : Purification of alcohol, crude oil refining and making liquefied gases from air.

E. Separation of immiscible liquids

Separating Funnel:

Separating funnel is used mainly to segregate two immiscible liquids.

The mechanism involves taking advantage of the unequal density of the particles in the mixture. Oil and water can be easily separated using this technique.

F. fat-in-water emulsion (milk) to a water-in-fat emulsion (butter).


Churning process is used to separate the butter from the milk. Moving the milk or curd continuously with skimmers produces butter.

Changing whole milk to butter is a process of transforming a fat-in-water emulsion (milk) to a water-in-fat emulsion (butter). Whole milk is a dilute emulsion of tiny fat globules surrounded by lipoprotein membranes that keep the fat globules separate from one another.

By : Ramakant Verma

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