Mechanism of the synergistic extraction of octahedral Co(II) from nitrate medium by 8-hydroxyquinoline-Db18C6 chloroform mixture

The kinetics of extraction of radioactive octahedral Co(II) by a chloroform mixture of 8-hydroxyquinoline (HOX) and dibenzo-18-crown-6 (Db18C6) from nitrate medium was investigated using a stirred Lewis cell. The effects of the stirring speed, temperature, specific interfacial area and interfacial tension on the extraction rate showed that the extraction process is controlled by a chemical reaction in the bulk aqueous phase rather than at the interface. The results of the effect of [HOX], [Db18C6] and [H-] on the extraction rate indicated that the synergistic extraction of octahedral Co(II) is first-order dependent on HOX concentration, of fractional negative order with respect to H+ while it is nearly independent of the crown ether concentration. The extraction process is expressed by a reaction mechanism in which the formation of the 1:1 cobalt species in the aqueous phase is the rate-controlling step. (orig.)