Removal of metallic coatings from rare-earth permanent magnets by solutions of bromine in organic solvents

Abstract

Successful direct recycling routes are known for both Nd-Fe-B permanent magnets and Sm-Co permanent magnets. Often the magnets are coated by a nickel-copper-nickel coating to prevent corrosion of Nd-Fe-B magnets and chipping of Sm-Co magnets. However, this coating does not contribute to the magnetic properties and only ends up as a contamination in the recycled magnet powder, which in turn dilutes the magnet alloy and reduces the magnetic performance. One solution is the addition of virgin magnet alloy to the recycled powder, but this is not the best option from a sustainable point of view. Another option is to remove the coating prior to the magnet recycling. We developed a solvometallurgical process for removal of the metallic coating prior to direct recycling. In particular, a mixture of bromine in organic solvents was found to be very selective in the removal of the nickel-copper-nickel coating from both Nd-Fe-B permanent magnets and Sm-Co permanent magnets, without codissolution of the magnet alloy.