ABSTRACT
If two liquids, a solvent and a solute, are in a homogeneous solution and a third liquid is introduced into the solution, there will be two liquid layers separated into two homogeneous solutions as shown in Figure 10.1. This type of phenomenon will occur only for certain selected third liquids, which solubilise any one or both of the components, which were formerly in the homogeneous solution. Phase separation occurs due to the difference in density of the resulting solutions. This phenomenon is utilised for separating two miscible liquid components from a solution and such a method is called extraction. If the solute (A), the carrier liquid (B) in the feed mixture, and the pure solvent (C) are brought in intimate contact by thorough mixing, the solute will transfer to the solvent due to the concentration gradient set up between the feed and the solvent. This transfer (mass transfer) process will continue until the equilibrium concentration of the solute between the feed and the solvent is achieved, as long as the feed and the solvent are in intimate contact.
