CFD modelling of simultaneous extraction and stripping of rare earth metals in a hollow fiber supported liquid membrane

Abstract

Nickel Metal Hydride batteries are used in many electronic devices. These batteries contain trace amounts of rare earth metals such as neodymium and lanthanum, which can be extracted from spent batteries and repurposed. Hollow fiber supported liquid membrane (HFSLM) systems have emerged as a promising alternative to the conventional solvent extraction methods, when dealing with low metal concentrations in solution. Hence, a Computational Fluid Dynamics (CFD) model has been developed to study extraction only, and simultaneous extraction-stripping of two rare earth metals (lanthanum and neodymium) in a HFSLM, using Cyanex 272 as the carrier. The equilibrium constants were obtained from experiments, for the extraction only study, and were considered as a fitting parameter for the extraction-stripping study. The metal transport from aqueous to organic solution was modelled based on the distribution coefficient, where it has been incorporated as an evolving parameter, which keeps changing along the length of the membrane. The Navier-Stokes equation and the species transport equation were coupled, and solved simultaneously to obtain the concentration distributions of La⁺³, Nd⁺³, and H⁺. The proposed model has been validated with experiments. During simultaneous extraction-stripping, the overall recovery is governed by the rate at which the complex diffuses through the membrane, and also the rate at which decomplexation takes during the stripping process. The suggested CFD model will be beneficial in both the design and scale-up of HFSLM for the separation of metal ions by modifying the design and process parameters. The model is generic in nature and hence any system with different transport properties can also be simulated using this model.