Magnetophoresis of Metal ions in Porous Media: Effects of Magnetic Susceptibility and Magnetic Field Gradients

Magnetophoresis is the movement of magnetic particles driven by a non-uniform magnetic field in a fluid medium. It is a simple and effective way for solute transport, with various applications in chemicals separation, environmental remediation, and biotechnology. In this study, we report on the magnetophoresis of metal ions with varying magnetic susceptibility, specifically, paramagnetic ions (MnSO₄, NiSO₄, CoSO₄) and diamagnetic ions (LiSO₄), within a silica-based porous medium under the influence of a non-uniform magnetic field. It is expected that under an applied magnetic field, paramagnetic ions move towards the region of high field gradient, while diamagnetic ions are repelled from high magnetic field regions. Our experiments reveal a clear correlation between the extent of magnetophoresis of metal ions, and the magnetic susceptibility of the respective species. Paramagnetic ions with higher magnetic susceptibilities exhibited greater enrichment levels in regions of high magnetic field gradient, whereas the diamagnetic ions, with a lower susceptibility, showed more pronounced depletion in high field regions. Furthermore, applying a stronger magnetic field gradient resulted in a greater extent of migration, as evidenced by an increased concentration enrichment for paramagnetic metal ions, and enhanced depletion levels for diamagnetic metal ions. We hypothesize that applying a stronger magnetic field gradient increases the magnetic force experienced by the magnetic solutes, thereby driving more significant transport through magnetophoresis in the porous medium.