1. General

The main purpose of the equipment used to implement an extraction process is to ensure efficient transfer of the solute across the interface of two immiscible liquids in intimate contact. When designing a column-type extractor in particular, a compromise is often sought (figure 1 ) between efficiency and capacity, without being able to guarantee the stability and reproducibility of the contactor's performance at a later date.

The mass flow rate Q of solute, transferred across an interfacial surface area, is given by the general relationship : $Q=k\mathcal{A}V\left(c-c^{\ast }\right)$