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What Is Solvent Extraction?

2023-12-29
Liquid-liquid extraction (LLE), also known as solvent extraction or partitioning, is a widely used separation technique in the chemical, pharmaceutical, and environmental industries. The technique involves the separation of a mixture of two or more liquids, based on their relative solubilities in two immiscible liquids, typically an organic solvent and an aqueous solution.
LLE can be used for a variety of purposes, including the removal of impurities, the concentration of a desired product, or the isolation of specific compounds from a complex mixture.
Principles of Liquid-Liquid Extraction
The principle of liquid-liquid extraction is based on the different solubilities of the components of a mixture in two immiscible liquids. The two liquids used in LLE are typically a polar solvent, such as water, and a nonpolar solvent, such as an organic solvent.
When the mixture is added to the two-phase system, the components with higher solubility in the polar solvent will remain in the aqueous phase, while those with higher solubility in the nonpolar solvent will transfer to the organic phase.
The extent of the partitioning of a component between the two phases depends on several factors, including the solubility of the component in each phase, the relative amounts of the two solvents, and the nature of the solvents themselves.
The partition coefficient, which is defined as the ratio of the concentration of a component in the organic phase to its concentration in the aqueous phase, is a key parameter in liquid-liquid extraction.
The partition coefficient depends on the chemical nature of the solvents and the components being extracted. For example, polar components are generally more soluble in water, while nonpolar components are more soluble in organic solvents. In addition, the partition coefficient is affected by the pH of the aqueous phase, the temperature of the system, and the presence of other solutes.