Liquid–liquid extraction

Liquid–liquid extraction, also known as solvent extraction and partitioning, is a method to separate compounds or <a href="/facts/Metal_complex/1tCyeQUm">metal complexes</a>, based on their relative <a href="/facts/Solubility/kLE9h3Jb">solubilities</a> in two different <a href="/facts/Miscibility/HwQaolbQ">immiscible</a> liquids, usually water (polar) and an organic solvent (non-polar). There is a net transfer of one or more <a href="/facts/Chemical_species/A8BxM3oW">species</a> from one liquid into another liquid phase, generally from aqueous to organic. The transfer is driven by chemical potential, i.e. once the transfer is complete, the overall system of chemical components that make up the solutes and the solvents are in a more stable configuration (lower free energy). The solvent that is enriched in solute(s) is called extract. The feed solution that is depleted in solute(s) is called the <a href="/facts/Raffinate/9StXUMTD">raffinate</a>. Liquid–liquid extraction is a basic technique in chemical laboratories, where it is performed using a variety of apparatus, from <a href="/facts/Separatory_funnels/xYwLz3dA">separatory funnels</a> to <a href="/facts/Countercurrent_distribution/JVmcEtMu">countercurrent distribution</a> equipment called as <a href="/facts/Mixer-settler/Bt6fKU5n">mixer settlers</a>.[not verified in body] This type of process is commonly performed after a chemical reaction as part of the <a href="/facts/Work-up_(chemistry)/LURlLf4C">work-up</a>, often including an acidic work-up.
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. The term solvent extraction can also refer to the separation of a substance from a mixture by preferentially dissolving that substance in a suitable solvent. In that case, a soluble compound is separated from an insoluble compound or a complex matrix.[not verified in body]
From a <a href="/facts/Hydrometallurgy/RUW4cffs">hydrometallurgical</a> perspective, solvent extraction is exclusively used in separation and purification of uranium and plutonium, zirconium and hafnium, separation of cobalt and nickel, separation and purification of rare earth elements etc., its greatest advantage being its ability to selectively separate out even very similar metals. One obtains high-purity single metal streams on 'stripping' out the metal value from the 'loaded' organic wherein one can precipitate or deposit the metal value. Stripping is the opposite of extraction: Transfer of mass from organic to aqueous phase.
Liquid–liquid extraction is also widely used in the production of fine <a href="/facts/Organic_compound/gqCNaN45">organic compounds</a>, the processing of <a href="/facts/Perfume/prN8beWz">perfumes</a>, the production of <a href="/facts/Vegetable_fats_and_oils/70v8uQMH">vegetable oils</a> and <a href="/facts/Biodiesel/M6FkfJXH">biodiesel</a>, and other industries.[not verified in body] It is among the most common initial separation techniques, though some difficulties result in extracting out closely related functional groups.
Liquid-Liquid extraction can be substantially accelerated in <a href="/facts/Microfluidic/UW3LnTdE">microfluidic</a> devices, reducing extraction and separation times from minutes/hours to mere seconds compared to conventional extractors.
Liquid–liquid extraction is possible in non-aqueous systems: In a system consisting of a molten metal in contact with <a href="/facts/Molten_salt/b1vjSkwP">molten salts</a>, metals can be extracted from one phase to the other. This is related to a <a href="/facts/Mercury_(element)/WlxfoHva">mercury</a> <a href="/facts/Electrode/251PaKX8">electrode</a> where a metal can be reduced, the metal will often then dissolve in the mercury to form an <a href="/facts/Amalgam_(chemistry)/5dRXJyt3">amalgam</a> that modifies its electrochemistry greatly. For example, it is possible for <a href="/facts/Sodium/eYuSPu2V">sodium</a> <a href="/facts/Cation/wrbwhF3z">cations</a> to be reduced at a mercury <a href="/facts/Cathode/tqdlGayU">cathode</a> to form <a href="/facts/Sodium_amalgam/NlTRR9eq">sodium amalgam</a>, while at an inert electrode (such as platinum) the sodium cations are not reduced. Instead, water is reduced to hydrogen. A <a href="/facts/Detergent/4FLKXR6p">detergent</a> or fine <a href="/facts/Solid/hj5UsXno">solid</a> can be used to stabilize an <a href="/facts/Emulsion/YMSqSCuH">emulsion</a>, or <a href="/facts/Third_phase/nI6f60PG">third phase</a>.[not verified in body]

Liquid–liquid extraction open-in-new

Liquid–liquid extraction