Liquid extraction is an operation used to separate the components of a liquid mixture of two or more species.

In the simplest case, the mixture contains two components: a solute $($A$)$ and a liquid solvent $($B$).$

The mixture is contacted in an agitated vessle with a second liquid solvent $(C)$ that has two key properties: A dissolves in it$,$ and $B$ is immiscible or nearly immiscible with it$.$

$($For example, B may be water, $C$ a hydrocarbon oil, and $A$ a species that has significant solubility in both water and oil.$)$ Some of the A transfers from $B$ to $C,$ and then the $B-$rich phase $($the raffinate$)$ and the $C-$rich phase $($the extract$)$ separate from each other in a settling tank.

If the raffinate is then contacted with fresh $C$ in another stage, more A will be transferred from it$.$ This process can be repeated until essentially all of the A has been extracted from the B$.$

Shown below is a flowchart of a process in which acetic acid $($aa$)$ is extracted from a mixture of acetic acid and water $(w)$ into $1-$hexanol $($h$),$ a liquid immiscible with water.

Stream Compositions $($mass fractions$)$

$\backslash$table$[[$Stream$/$Component$,$Solvent $($C$),$Feed $(F),$Raffinate $(R),$Extract $($E$)],[\backslash$table$[[$Acetic Acid $($aa$)],[C{H}_3\frac{C}{O}OH$