liquid extraction (LLE), also known as solvent extraction and partitioning, is a method to separate compounds or metal complexes, based on their relative solubilits in two different immiscible liquids, usually water and an organic solvent. The key elements to successful LLE are solvent selection and effective mass transfer. The solvent needs to be able to extract the desired solute(s) from the feed stream, be immiscible with the other components of the feed stream, and have high recoverability.