There are two basic types of Liquid -Liquid extraction columns. For liquids with a significant difference in density, a column consisting of alternating agitated and calm spaces is used. An agitated space is an open space in the column with a spinning impeller. In this state the two liquids are whipped into an emulsion to gain high surface area contact between the two phases. The calm section consists of a sponge-like layered mesh material. In these sections the two phases separate and allow downward movement of the heavy phase and upward movement of the light phase.
The second type of liquid-liquid extraction column is used when the two phases are close in density. This column is designed to aid the upward and downward movement of the light and heavy phases, respectively. This column consists of a series of rapidly spinning disks each with an annulus shaped deflector mounted to the inside of the column. Here the surface of the spinning disk serves as the agitation area. The fluid of greater density will be flung outward into the deflector and directed downward, while the lighter fluid will be directed upwards.
Finally, for batch processes, a liquid-liquid extraction unit simply consists of an agitated vessel containing both phases. After continuous agitation for a period of time, the contents are allowed to settle, and the phase of interest is either poured or otherwise extracted out.
A basic schematic of the three Liquid-Liquid extraction units are shown below:
In the first two columns, the liquid containing impurities and the relatively clean liquid enter the column where they are mixed. A good portion of the impurities are dissolved into the second liquid phase, and the cleaner liquid and dirtier liquid then leave the column as two separate exit streams.
The two liquids are mixed in the tank, and then allowed to settle. The Liquid of interest is
then removed from an extraction port.