The extractant and the solvent in the original solution are incompatible; the solubility of the extractant to the solute is much more excellent than that of the original solvent; the extractant is not easy to volatilize. Extraction, also known as solvent extraction or liquid-liquid extraction, also known as extraction, is a unit operation that uses the different solubility of the components in the system to separate the mixture.
The conditions that the extractant should have (1) The extraction capacity should be large, that is, the unit concentration of the extractant has a greater extraction capacity for the extracted substance; (2) The selectivity is better. That is, there is a more significant separation coefficient for the separated related substances; (3) Good chemical stability, that is, the extractant is not easy to be hydrolyzed, is not easy to decompose when heated, can withstand the action of acid, alkali, salt, oxidant, or reducing agent, is less corrosive to equipment, and has high radiation resistance; (4) The water solubility should be negligible, and the oil solubility should be significant, that is, the solubility in the water phase is slight, and the solubility in the diluent is substantial, and it is easy to layer with the water phase, and does not generate the third phase, and does not emulsify; (5) Easy to back-extract, that is, when the extraction conditions are changed, the extracted substances can be transferred from the organic phase to the aqueous phase more easily; (6) Safe operation, that is, the extractant is non-toxic, non-irritating, non-flammable (high flash point), hard to volatile (high boiling point, low vapor pressure); (7) It is easy to prepare, rich in raw materials, and cheap. However, there are very few extractants that fully meet these conditions. When selecting extractants, we can only consider comprehensively, grasp the main issues, and decide according to specific requirements.
The primary method of extraction An extractant that is not mutually soluble (at most partially mutually soluble) is added to the solution to be separated (material liquid) to form two coexisting liquid phases. Using the difference between the solubility of the original solvent and the extractant for each component (including the dissolution after chemical reaction), make them unequally distributed in the two liquid phases, and then separate the details through the separation of the two liquid phases.