Solvent Extraction

Solvent extraction has always proved itself very helpful as a recovery method for many components. It is a method of separating compounds on the basis of their solubility in two different immiscible liquids like water and organic compound. We can also say that it's a method of separating a compound which is soluble in an immiscible or a partially immiscible liquid which gives you a desired compound either in the form of a solute or in a form of a residue. This forms different layers which facilitates the separation of compounds.

The simplest solvent extraction examples may be derived from water and organic compounds. For example: Benzene is non polar and is immiscible in water as the polarity of water is very high. So, if we want to separate benzene from a liquid which contains a component which dissolves in water then we can mix it with water and the separated layer will be benzene.

Solvent Selection for Solvent Extraction
In a solvent extraction process, it is very important to choose a perfect solvent for the compound to get better results. Following are some of the points which are important while selecting a perfect solvent for separation.

• The solvent should be able to dissolve some components to a larger extent than the rest of the components in the mixture.
• The reaction taking place should be stable and irreversible. Reversible reactions can come back into their previous form and the extraction will not be completed successfully.
• The compound formed after the reaction should be easily separated from the extracted compound so that it can be reused.
• The density of the compound should be different from the required component to help the separation readily.
• It should be inexpensive and cost-effective.
• The solvent should not be toxic or corrosive as it can harm the extraction instruments.
• Other factors important during solvent selection are viscosity, boiling point, flammability, etc.

Conditions for Extraction
Condition under which the reaction or the extraction process takes place also affects the separation. Temperature and pH play a very important role in separating components. So it is very necessary to maintain the temperature and pH of the compound during the extraction process. Pressure does not affect the reaction much, as most of the solvent extractions are carried out under the atmospheric pressure. Other factors may be precipitation of solids, vapor pressure, etc. Apart from these factors, residence time is also important in the reactions like metals separation or short life components like antibiotics.

Various Methods of Solvent Extraction
As solvent extraction is very widely used for the separation, recovery and purification of any component. Various methods under this extraction are:

• Centrifugal Extractions: Centrifugal devices work at very high-speed. They are high-speed rotatory machines which rotate the solvent and due to the density and the centrifugal force, the liquids are separated from each other. This method is usually used in the pharmaceutical industries.
• Aqueous Two Phase Extraction: They are used for organic-water solvent system. They are excellent for the extraction of enzymes and proteins.
• Batchwise Single Stage Extraction: It is used in small-scale chemical industries. The extraction is carried out in a simple separator funnel.
• Multistage Counter-current Continuous Process: This process is helpful in processing metals. It is used for the components which need multistage extraction as in every single step they need materials to be separated.
• Mixer Settlers: This method is used in the metal industry. The mixing is done at a very high-speed and a long residence time is given for the components to settle down.
• Extraction Without Chemical Change: This is the one of the simplest methods. It does not involve any chemical elements which can lead to chemical reactions. Two immiscible liquids are shaken with the mixture. The component dissolves with its relevant liquid and is extracted easily.

So now we can say solvent extraction is very useful for the separation and recovery of important metals and compounds and is an important part in the world of chemistry. Due to cost-effectiveness, it is widely used in various sectors. The most important aspect of this extraction is that it separates the required component without changing its properties and identity.