Extraction

Extraction, selective removal of a substance or substances from a mixture by use of carefully selected solvents. The solvent is chosen so that the desired material dissolves more readily than the rest of the mixture. When the mixture is composed of solids, the process is known as leaching. Salt can be removed from a mixture of sand and salt by leaching with water, and metals can be separated from their ores by leaching with other solvents. Extraction can also be used to separate liquid and gaseous mixtures. The technique is widely used in the petroleum and chemical industries and in metallurgy. It is also used to obtain oil from oil seeds and sugar from sugar beet.