In a liquid-liquid Column Extractor, a liquid carrier containing the component(s) to be recovered (solute) is fed into an extractor, where it contacts a solvent. The two liquids must be immiscible or only slightly miscible; this allows them to form a dispersion, with one liquid dispersed as droplets in the other. Mass transfer occurs between the droplets and the liquid carrier. In order for the two liquids to be subsequently separated, they must have different densities. Column extractor or extraction column can be separated in two different categories Non-agitated column extractors and Mechanically-agitated columns extractor.
Non-agitated column extractor have no moving internal parts. Non-agitated column extractors are the simplest extractor columns. They contain no mechanical parts to induce mixing or droplet formation. Mass transfer is dictated by the column internals. Despite their low efficiency, unagitated columns are widely used in the industry because of their simplicity and low cost. They are particularly suited for processes requiring few theoretical stages and for corrosive systems where the absence of mechanical moving parts is advantageous. The three main types of unagitated column extractor are:
Mechanically-agitated column extractor contain some type of mechanical device to agitate the liquids as they pass through the column. Rotating and reciprocating mechanisms are the most common methods for creating and maintaining dispersion throughout the column.
Mechanically-agitated column extractor can be divided into two main classes according to mechanical motion patterns: