Extraction by Solvation:

During the discussion on the different classes of extractants, it has been pointed out that a large number of solvent extraction systems are based on the solvation of neutral inorganic molecules or complexes by electron donor containing extractants. The basic role of a solvating molecule is to increase the solubility of the inorganic species in the organic phase. Instead, the solvating molecule makes the extracting species more hydrophobic; therefore, promoting its transfer to the organic phase. As already known, there are two well-known distinct categories of solvating extractants.

i) Extractants with oxygen bonded to carbon such as alcohols, ethers and ketones.

ii) Extractants with oxygen or sulphur bonded to phosphorus such as alkyl phosphates or alkylthiophates.

It may be important to point out here that some of the acidic extractants play a dual role of neutralizing the charge on the metal ion and simultaneously solvating the species. This is true with carboxylic acids and acidic organophosphorus compounds.