Kinetics of Metal Extraction by Chelate Formation: Part I: Mass Transfer with a Fast Reversible Chemical Reaction and Product Extraction

Abstract

The description of the rate of extraction of a bivalent metal sets out from the assumption that the mass transfer process consists of the diffusion of the active component from the organic into the aqueous phase, accompanied by its instantaneous dissociation, a fast reversible reaction with the metal ion leading to the 1—1 complex, a consecutive instantaneous formation of the extractable 1—2 complex, and the transfer of this complex into the organic phase. This description reduces after the introduction of suitable simplifying assumptions to the model of component transfer with a fast reversible second-order reaction followed by product extraction. An approximate solution has been elaborated for this model based on the film theory of mass transfer, resulting in a dependence of the reaction factor on dimensionless parameters. The approximation suggested becomes the exact solution in the cases of an instantaneous reversible reaction and of a reversible reaction of the pseudo-first order. The accuracy of the approximation has been checked by a numerical solution. A computational algorithm for the extraction rates is given, including diffusion resistances on both sides of the interface.