Enabling separation intensification of a lanthanide pair with closely similar kinetics based on droplet microfluidics: hydrodynamic and kinetic approaches

Abstract

Microfluidics has been proved a promising way for highly efficient lanthanide extraction and separation benefiting from the astounding mass transfer characteristics. Efforts have been devoted by us previously to provide a clear understanding of the separation intensification mechanism of lanthanide pairs with distinguished extraction kinetics in microfluidics, such as Eu³⁺/La³⁺. However, for those lanthanide pairs with closely similar extraction kinetics, the working principles of separation intensification are different, which could not be explained by our former proposed theory of nonequilibrium separation intensification. In this study, a numerical model considering nonlinear extraction kinetics was presented to comprehend the separation characteristics of Eu³⁺/Sm³⁺, a lanthanide pair with very similar extraction kinetics, in microfluidics. The hydrodynamic and kinetic approaches, i.e. flow rate, initial concentration of metal ions and extractant, pH and temperature, were studied to manipulate separation performance. Analyses on dimensionless number (Damköhler number) were conducted to unveil the working mechanism of such approaches. The numerical study provides a mechanistic understanding of lanthanide separation in microfluidics and offers manipulating principles for further optimization.