solventextraction

Solvent extraction, or liquid-liquid extraction, is a separation technique in which a solute partitions between two immiscible liquid phases, typically an aqueous phase and an organic solvent. The distribution of the solute between phases is described by a distribution coefficient, often denoted as Kd, which depends on the solute, solvents, temperature, and pH. The process exploits differences in solubility to concentrate or remove a component from a mixture.

In practice, the feed solution is contacted with the immiscible solvent to transfer the desired component into the extract phase. Phase separation follows, yielding an enriched organic phase and a raffinate phase. Operations can be batch or continuous, and are carried out in equipment such as mixer-settlers, extraction columns, or centrifugal contactors. Multi-stage countercurrent operation enhances separation efficiency by repeatedly redistributing the solute across stages.

Solvent selection is guided by solubility, density, immiscibility with water, chemical compatibility, toxicity, volatility, and environmental impact. Common organic solvents include kerosene, toluene, xylene, and dichloromethane, though greener or specialized solvents are increasingly used. Sometimes the process targets metal ions, organics, or pharmaceutical intermediates, with pH adjustment or complexing agents enabling selective transfer.

Applications span hydrometallurgy (metal refining and recovery), nuclear reprocessing (for example, uranium and plutonium separation), pharmaceutical purification, and environmental analysis or remediation. Advantages of solvent extraction include high selectivity and the ability to operate at ambient conditions, while challenges include solvent management, phase entrainment, emulsification, and safety concerns related to flammability and toxicity.