Models for scale-up of liquid-liquid reactors should account for the microscopic problem of defining processes of interphase mass transfer with reaction and the macroscopic problem of extractor design. One aspect of the microscopic problem discussed is that of obtaining kinetic data for the solvent extraction of metals. The role of interphase mass transfer, metal speciation, and reaction kinetics should be accounted for properly in order to describe the interfacial flux. The liquid jet recycle reactor is shown to be a suitable laboratory reactor for this purpose. Kinetic rate models developed with this reactor for two metal chelation reaction systems are presented. Recent work employing classical film theory, penetration theory, and convective-diffusion models is discussed.