Mechanism Study of Removing Sealing Aluminum Contaminates from Waste Packaging High-Density Polyethylene by Eddy Current Separation

Recycling of high-density polyethylene (HDPE) packaging waste plastics is necessary for ending white pollution. Existing recycling technologies generally require high purity of polymers before treatment. However, the sealing aluminum film contamination in crushed bottle flakes hinders recycling works. Eddy current separation (ECS) was first applied for the removal of aluminum-containing flakes from crushed HDPE bottles in this study. Through finite element analysis, the formation of rotating magnetic fields, eddy currents, and Lorentz forces are analyzed. It reveals, different from the traditional theory of eddy current forces, that the factors influencing the flake trajectories are attributed to the Lorentz force, whose horizontal component aligns with the tangential direction of the rotor's rotation, while its vertical component is directed upward. The magnitude of the Lorentz force is affected by the magnetic field intensity and the spatial positioning of the flakes. The variation cycle of the force is primarily influenced by the size of the magnetic poles. This model accounts for the unique motion behaviors observed during the separation process. After parameter optimization, the removal efficiency of aluminum foil was 97.38 wt %. This study enhances the mechanical theoretical framework of the ECS process and extends the application scope of the ECS technologies.