Increasing efficiency of solvent extractions of rare earth elements by magnetic fields

A novel method for rare-earth (RE) separation that incorporate magnetic separation into solvent extraction is proposed and validated. Exposing the RE(III) concentration boundary layer to a tailored magnetic field ( B ), solutomagnetic convection is induced by the Kelvin force. The basic hypothesis pursued is the competing RE(III) extraction kinetics to be selectively enhanced consequently. To validate this in a first step, the cation exchange process of dysprosium, Dy(III), inside a Hele-Shaw configuration is studied using a 0.5 g, 4x5 mm sized magnet. The extraction kinetics is quantified in terms of the Sherwood number. Here, a nearly squared dependence is found on the Ra ^* number, generalizing the Rayleigh number by inclusion of the Kelvin force. Laser optics combined with numerical simulations unveil three different flow stages, which conclude with a quasi-steady, large scale recirculation emerging from a symmetry break at a critical value of Ra ^* . This re-circulation replaces depleted Dy(III) solution at the interface by fresh solution from the bulk. Exceptional RE(III) extraction kinetics were demonstrated for this regime, characterized by a reaction rate that increases more than 18-fold when the B intensity is doubled. Thus, a greener technological route towards rare-earth extraction with potentially superior selectivity is opened.