3. Classification of extraction systems

Schematically, the transfer of a solute from a feed phase to a solvent may or may not require reciprocal material transfer (i.e. from the solvent to the feed phase). We can thus distinguish two main types of extraction process:

• ion exchange extractions, in which the feed phase generally receives a new species or is enriched with a species already present (e.g. H ⁺ ions) in parallel with the extraction of the solute at stake in the process;

• uncompensated extractions, simply transferring a molecule or an aggregate of ions that is neutral overall, and depleting the feed phase.

In fact, each of these two main types of process can be further classified to reflect a variety of situations (figure