1989 Volume 22 Issue 2 Pages 168-177
The kinetic mechanism was elucidated for metal extraction with hydroxyoximes. The reaction of the 1:2 metal–chelating agent complex formation determines the rate of copper extraction with the chelating agents, which are surface-active and less soluble in the aqueous phase. It is found from the results about the diluent’s effect on the rate that this complex is formed at the interface through the reactions between the adsorbed 1:1 complex and the chelating agent dissolved in the aqueous phase, and also between the adsorbed chelating agent and the 1:1 complex in the aqueous phase. The overall rate constant of this interfacial reaction can be related to the pKa value of the chelating agent. The 1:1 complex formation in the stagnant film of the aqueous phase controls the rate of copper extraction with the chelating agent, which is surface-inactive and soluble in the aqueous phase. The catalysis of α-hydroxyoxime in the copper extraction with β-hydroxyoxime is caused by the fast reaction between the 1:1 copper–β-hydroxyoxime complex adsorbed at the interface and the α-hydroxyoxime dissolved in the aqueous phase. The question of increasing the rate of extraction is examined by focusing on the physical properties, the partition coefficient of the chelating agent between the aqueous and the organic phases, and the surface activity of the chelating agent. Modification of the substitutional group in the hydroxyoximes is also examined as a means of increasing the rate.
