Construction and mechanism investigation of three-product gravity-magnetic combined separation columns

To enhance the separation efficiency of magnetite, a three-product gravity-magnetic combined separation column was developed by utilising the differences in density and magnetism between magnetite and gangue minerals. Its separation and underlying mechanism were investigated through experiments, hydrodynamic simulations and gravity-magnetic coupling force field simulations. The equipment integrates multiple functions, including gravity separation, cyclonic classification, cyclonic separation and magnetic field cleaning and scavenging. Classification occurs in the column section above the feed inlet, where fine particles experience centrifugal forces, move upward and are discharged as tailings. Gravity separation primarily takes place in the middle and lower sections, where the tangential middling pipe and cylinder act as a vortex finder, enabling centrifugal gravity separation. The underflow discharges the concentrate, while the middling pipe removes the middlings. An axial magnetic field at the bottom of the cone promotes magnetite sinking, thereby improving both concentrate recovery and grade, while another magnetic field below the overflow port restricts upward movement of fine magnetite, reducing losses. At a feed flow rate of 0.8 m³/h, the total Fe content (TFe) of the concentrate, middlings and tailings was 68.25 %, 67.9 % and 67.84 %, respectively, with a concentrate recovery of 47.58 %. When the bottom magnetic field current was increased to 8 A, the concentrate TFe rose to 69.12 %, with recovery improving to 76.57 %. Applying an additional magnetic field at the overflow outlet further increased the TFe to 69.36 % and recovery to 86 %, thereby significantly enhancing separation efficiency. The results of the two-phase flow simulation were consistent with the experimental findings. Using COMSOL Multiphysics, the effect of magnetic fields on magnetite and quartz movement trajectories was simulated, clarifying the migration behaviour of magnetic particles under a gravity-magnetic coupling force field. Overall, the three-product gravity-magnetic combined separation column improves recovery and separation efficiency, simplifies the process flow and provides new insights for fine magnetite separation.