Kinetic studies on the interfacial reaction in solvent extraction

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Interfacial reactions in chelate extraction, ion-association extarction and synergistic extraction were investigated experimentally :1) Chelate extraction system : The relationship between the extraction rate of Ni(II) with 5-nonylsalicyl aldoxime(P50) and the interfacial concentration of P50 was studied by means of the high-speed stirring apparatus instuled with a photodiode-array spectrophotometer. The rate determining step in the extraction was found to be the formation rate of the 1 : 1 complex at the interface and the rate process was interpreted in terms of the Eigen mechanism. On the other hand, the extraction rate of Ni(II) with 5-Br-PADAP was shown to be much slower than the P50 system, suggesting the rate determining step to be the ring-closure.2) Ion-association extraction system : The extraction of acid with tetraphenylporphyrin(TPP)in toluene and the interfacial ion-association adsorption were studied by means of an optical stirr cell method, a Teflon capillary method and a membrane filter method as well as the high-speed stirring method. Interfacial ion-association adsorption was found also in the systems of water-soluble porphyrin and ionic surfactant paris. The adsorption of ion-pair was affected by an external electric field.3) Synergistic extraction : The extraction of Ni(II) with buthyldithizone was enhanced by the addition of 1,10-phenanthroline. In the course of the extraction, the existance of an interfacial complex was concluded.