Application of portable total-reflection X-ray fluorescence spectrometer to analysis of dysprosium in neodymium-iron-boron magnet

Dysprosium (Dy) is expected to be recovered from end-of-life neodymium-iron-boron (NdFeB) magnets in the near future because of its worldwide shortage. Therefore, the rapid on-site elemental analysis of dysprosium in end-of-life NdFeB magnets is required. Here, we report a method of measuring the dysprosium composition in a NdFeB magnet on-site using a portable total-reflection X-ray fluorescence (TXRF) spectrometer. This method leads to drastic reduction of dysprosium loss caused by dissolving a NdFeB magnet because the portable TXRF spectrometer requires a small sample volume for measurement and its detection limit is as low as the ppb level. A NdFeB magnet was dissolved into hydrochloride acid and then iron in the solution was extracted using 4-methyl-2-pentanone (methyl isobutyl ketone: MIBK). Yttrium oxide (Y₂O₃) and a diluted standard solution of rubidium (Rb) were added to the solution as internal standards. We measured the X-ray intensities of dried residue of the solution using a portable TXRF spectrometer. Dy Lα line was clearly detected in the solution, whereas it overlapped with Fe Kα line in the solution before the MIBK extraction process. The dysprosium composition in the NdFeB magnet was determined from the measured intensities of Dy Lα, Y Kα, and Rb Kα, the relative sensitivities of dysprosium and yttrium to rubidium for the portable TXRF spectrometer, and the weights of the dissolved NdFeB magnet and yttrium oxide. The calculated dysprosium composition was in good agreement with that obtained by conventional ICP-AES.