Dynamics of Transition Metal Ion Transport in High-Gradient Magnetic Fields

Magnetic separation has emerged as an eco-friendly and sustainable technique with applications in water purification, chemical separation, biochemistry, medicine, and mining. In this study, we present a combined experimental and theoretical investigation of the transport of transition metal ions using high-gradient magnetic fields. Experiments were conducted on aqueous solutions containing either paramagnetic manganese chloride (MnCl₂) or diamagnetic zinc chloride (ZnCl₂) ions, with concentrations ranging from 1 to 100 mM under a non-uniform magnetic field of an electromagnet. Our results demonstrate that while paramagnetic MnCl₂ is captured by the mesh wool in the magnetic field, diamagnetic ZnCl₂ remains unaffected by the presence of a magnetic field. The capture efficiency of paramagnetic MnCl₂ increases with both the initial ion concentration and the applied magnetic field strength. Furthermore, in binary mixtures, the capture rate of MnCl₂ is reduced compared with single-ion solutions, highlighting the role of ion interactions in magnetic separation. Our theoretical modeling indicates that magnetic capture is governed by a balance between magnetic forces and viscous forces. Additionally, the magnetic separation process is enhanced by the field-induced cluster formation of paramagnetic metal ions, which are predicted to be 2 orders of magnitude larger than individual hydrated ion units. These findings provide insights into the mechanisms of magnetic transport of metal ions and offer potential pathways for improving separation efficiency in complex ion mixtures that contain critical materials.