Neodymium, dysprosium and terbium in neodymium–iron–boron (NdFeB) magnets will be recovered from the existing stock of used magnets collected from industrial waste products in the near future owing to the shortage of these elements. Therefore, a method to distinguish NdFeB from various kinds of magnets is required. Here, we report methods to distinguish NdFeB magnets from samarium–cobalt (Sm–Co) magnets from their cathodoluminescence (CL) spectra and images using a portable CL spectrometer that we previously realized because Sm–Co magnets are used in similar products to NdFeB magnets. CL spectra and images of vacuum-dried residues of hydrochloric acid solutions dissolving NdFeB or Sm–Co magnets were obtained using the portable CL spectrometer. Iron in the solution dissolving the NdFeB magnet was extracted using methyl isobutyl ketone before vacuum-drying the solution without changing the concentration ratios of the rare-earth elements in the solution. Peaks due to neodymium chloride (878, 892 nm) and samarium chloride (565, 600, 647, 708 nm) were detected in the CL spectra of the vacuum-dried residues of the NdFeB and Sm–Co magnets, respectively. Thus, we can distinguish NdFeB and Sm–Co magnets from the difference in the wavelengths of the peaks in their CL spectra. Luminescent colors due to neodymium chloride (blue or purple) and samarium chloride (orange) were detected by capturing CL images of the vacuum-dried residues of the NdFeB and Sm–Co magnets with a camera whose infrared filter was removed, respectively.
- cathodoluminescence spectrometer
- neodymium–iron–boron magnet
- portable analyzer
- samarium–cobalt magnet