Kinetics study on supercritical fluid extraction of zinc(II) ion from aqueous solutions

This work studies the kinetics of metal ion extraction using an in situ chelation-SFE method with Cyanex 302 as the chelating agent, which is commercially available, and supercritical carbon dioxide as the solvent, which extracts the metal-chelate complex from aqueous solutions. Zinc(II) ion is studied as a model species. The experiments are conducted in a 1.3-dm3 batch stirred tank. The effects of pressure and stirring rate were investigated. The extraction efficiency at 313 K varies from 50 to 60% when the pressure varies from 8.3 to 13.8 MPa. A simplified model is used to estimate the effective mass-transfer coefficient. The results show that the extraction rate of zinc(II) ion increases with an increase in stirring rate, but decreases with pressure. The effective mass-transfer coefficient at 313 K and 8.3 MPa varies from 0.45 to 2.6×10−3 s−1 when the stirring rate increases from 7.2 to 17.7 s−1.