Separation by Extraction

There are two types of extraction, liquid-liquid extraction also known as solvent extraction as well as solid-liquid extraction. Both extraction types are based on the same principle, the separation of compounds, based on their relative solubilities in two different immiscible liquids or solid matter compound.

Liquid-liquid extraction

A mixture of two immiscible liquids is feeded with a solvent to separate one or several compounds. It is an extraction of a substance from one liquid phase into another liquid phase.

There are three different procedures known as

  • Mixer-Settler-Extraction
  • This type of extraction is especially applicable for preliminary experiments for the scale up of the parameters received.
  • Spinning Band Extraction
  • This extraction method is preferably applied for small quantities due to their low column laod and hold up. The main application is for micro extractions with small throughputs for expensive solvents.
  • Pulsating Sieve Tray or Packed Columns Extraction Systems

Pulsating extraction columns are operated continuously countermovement-wise for a very intensive mixing of the liquid phases. Generally use for larger throughput.


The principle for the solid-liquid extraction is that the soluble compounds of a solid matter, existing of an inert matrix and the active agent, are extracted by a solvent. The extract can be included in the extraction matter in solid or liquid form. It can be included in cells like oil in oil seeds or as fine dispersion on the solid matter like caffeine in coffee.


Extraction processes are specially recommended for separation of

  • nonvolatile components
  • mixtures, which cannot be separated by other procedures
  • mixtures, whose vapour-liquid-phase equilibria show azeotropic features
  • temperature–sensitive components

Important applications of extraction procedures can be found in

  • chemical industry (anorganics, organics)
  • chemical metallurgy (extraction of metallic salts from diluted brines)
  • nuclear technology (reprocessing of nuclear fuels)
  • environmental technology (waste water treatment)
  • food technology (edible oil refining)
  • pharmaceutical industry (extraction of agents)