Liquid–liquid extraction

Liquid–liquid extraction, also known as solvent extraction and partitioning, is a method to separate compounds or metal complexes, based on their relative solubilities in two different immiscible liquids, usually water (polar) and an organic solvent (non-polar).

Liquid–liquid extraction is a basic technique in chemical laboratories, where it is performed using a variety of apparatus, from separatory funnels to countercurrent distribution equipment called as mixer settlers.

The term partitioning is commonly used to refer to the underlying chemical and physical processes involved in liquid–liquid extraction, but on another reading may be fully synonymous with it.

[not verified in body] It is among the most common initial separation techniques, though some difficulties result in extracting out closely related functional groups.

[not verified in body] In solvent extraction, a distribution ratio (D) is often quoted as a measure of how well-extracted a species is.

[2] The partition or distribution coefficient (Kd) is the ration of solute concentration in each layer upon reaching equilibrium.

The data set can then be converted into a curve to determine the steady state partitioning behavior of the solute between the two phases.

A novel settling device, Sudhin BioSettler, can separate an oil-water emulsion continuously at a much faster rate than simple gravity settlers.

In this photo, an oil-water emulsion, stirred by an impeller in an external reservoir and pumped continuously into the two bottom side ports of BioSettler, is separated very quickly into a clear organic (mineral oil) layer exiting via the top of BioSettler and an aqueous (coloured with a red food dye) layer being pumped out continuously from the bottom of BioSettler.

In the multistage countercurrent process, multiple mixer settlers are installed with mixing and settling chambers located at alternating ends for each stage (since the outlet of the settling sections feed the inlets of the adjacent stage's mixing sections).

Mixer-settlers are used when a process requires longer residence times and when the solutions are easily separated by gravity.

Two liquids will be intensively mixed between the spinning rotor and the stationary housing at speeds up to 6000 RPM.

[15] Some solutes such as noble gases can be extracted from one phase to another without the need for a chemical reaction (see absorption).

Some solutes that do not at first sight appear to undergo a reaction during the extraction process do not have distribution ratio that is independent of concentration.

The PUREX process that is commonly used in nuclear reprocessing uses a mixture of tri-n-butyl phosphate and an inert hydrocarbon (kerosene), the uranium(VI) are extracted from strong nitric acid and are back-extracted (stripped) using weak nitric acid.

In this case Another example is the extraction of zinc, cadmium, or lead by a dialkyl phosphinic acid (R2PO2H) into a nonpolar diluent such as an alkane.

This, as well as the absence of solvents or other denaturing agents, makes polymer–polymer extractions an attractive option for purifying proteins.

[citation needed] The PEG–NaCl system has been shown to be effective at partitioning small molecules, such as peptides and nucleic acids.

Amines of sufficiently low molecular weight are rather polar and can form hydrogen bonds with water and therefore will readily dissolve in aqueous solutions.

As such purification steps can be carried out where an aqueous solution of an amine is neutralized with a base such as sodium hydroxide, then shaken in a separatory funnel with a nonpolar solvent that is immiscible with water.

Subsequent processing can recover the amine by techniques such as recrystallization, evaporation or distillation; subsequent extraction back to a polar phase can be performed by adding HCl and shaking again in a separatory funnel (at which point the ammonium ion could be recovered by adding an insoluble counterion), or in either phase, reactions could be performed as part of a chemical synthesis.

Temperature swing solvent extraction is an experimental technique for the desalination of drinking water.

It has been used to remove up to 98.5% of the salt content in water, and is able to process hypersaline brines that cannot be desalinated using reverse osmosis.

For instance, in the case of iodine being distributed between water and an inert organic solvent such as carbon tetrachloride then the presence of iodide in the aqueous phase can alter the extraction chemistry: instead of

[22][23] After use, the organic phase may be subjected to a cleaning step to remove any degradation products; for instance, in PUREX plants, the used organic phase is washed with sodium carbonate solution to remove any dibutyl hydrogen phosphate or butyl dihydrogen phosphate that might be present.

[24][25][26][27] While solvent extraction is often done on a small scale by synthetic lab chemists using a separatory funnel, Craig apparatus or membrane-based techniques,[28] it is normally done on the industrial scale using machines that bring the two liquid phases into contact with each other.

[32] The rare earth element Neodymium is extracted by di(2-ethyl-hexyl)phosphoric acid into hexane by an ion exchange mechanism.

[33] Nickel can be extracted using di(2-ethyl-hexyl)phosphoric acid and tributyl phosphate in a hydrocarbon diluent (Shellsol).

[34] Dialkyl sulfides, tributyl phosphate and alkyl amines have been used for extracting palladium and platinum.

[38] In the modified Zincex process, zinc is separated from most divalent ions by solvent extraction.