Liquid–liquid extraction

Liquid–liquid extraction separates a dissolved substance by contacting two immiscible liquids, allowing the substance to distribute between them according to its relative solubility.

Partition coefficient: The ratio of a solute’s equilibrium concentrations in two phases. It quantifies the solute’s preference for the extracting phase.
Liquid–liquid phase diagram: A diagram showing the phase states and compositions of a multicomponent liquid system. It identifies compositions that split into two liquid phases.
Separatory funnel: A laboratory vessel with a stopcock used to separate immiscible liquid layers. It is the standard apparatus for batch-scale extraction.
Solid-phase extraction: A separation method that retains target compounds on a solid sorbent before elution. It uses a solid stationary material rather than two immiscible liquid phases.
Distribution ratio: The ratio of total solute concentrations in two phases under specified conditions. Unlike a partition coefficient, it can include multiple chemical forms of the solute.
Immiscibility: The inability of two substances to mix into a single homogeneous phase over a given composition range. Two distinct liquid phases are required for conventional extraction.
Hydrometallurgy: The extraction of metals from ores using aqueous chemistry. Solvent extraction selectively transfers dissolved metals from leach solutions.
Distillation: A separation process that uses differences in volatility through vaporization and condensation. It separates by vapor–liquid behavior rather than liquid-phase solubility.
Nernst distribution law: A relation stating that a solute’s equilibrium concentration ratio between two phases is constant under specified conditions. It describes the equilibrium basis of simple extraction.
Chemical equilibrium: A state in which forward and reverse reaction rates are equal and macroscopic composition remains constant. Solute distribution between phases is evaluated at equilibrium.

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