Principle and operation
Liquid-liquid extraction is used to transfer a solute (dissolved in a diluent and forming the solution) into a solvent with which it has more affinity; the diluent and the solvent are immiscible. The light phase is introduced at the bottom of the column and then goes back to the upper decanter of the column. The heavy phase introduced at the top of the column goes down to the settling zone located at the bottom. The piston pump, positioned at the lower decanter, generates pulsations throughout the column; this agitation allows a mixture of the two phases circulating against the current and causes the transfer of the solute to be extracted in the solvent. Decanters are used for the separation of immiscible phases; the solute enriched extract phase and the solute depleted raffinate phase are continuously withdrawn from these settlers.