We report a method for preparing rare earth oxides (Re_xO_y) from the recycling process for spent Ni-metal hydride (Ni-MH) batteries. This process first involves a leaching of spent Ni-MH powders with sulfuric acid at 90°C, resulting in rare earth precipitates (i.e., NaRE(SO₄)₂·H₂O, RE = La, Ce, Nd), which are converted into rare earth oxides via two different approaches: i) simple heat treatment in air, and ii) metathesis reaction with NaOH at 70°C. Not only the morphological features but also the crystallographic structures of all products are systematically investigated using field-emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD); their thermal behaviors are also analyzed. In particular, XRD results show that some of the rare earth precipitates are converted into oxide form (such as La₂O₃, Ce₂O₃, and Nd₂O₃) with heat treatment at 1200°C; however, secondary peaks are also observed. On the other hand, rare earth oxides, Re_xO_y can be successfully obtained after metathesis of rare earth precipitates, followed by heat treatment at 1000°C in air, along with a change of crystallographic structures, i.e., NaRE(SO₄)₂·H₂O → RE(OH)₃ →Re_xO_y.

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• Recycling of Rechargeable Batteries: Insights from a Bibliometrics‐Based Analysis of Emerging Publishing and Research Trends
  Jiao Lin, Xiaodong Zhang, Li Cai, Ersha Fan, Shumeng Wu, Su Ma, Feng Wu, Renjie Chen, Li Li
  Advanced Energy and Sustainability Research.2022;[Epub]     CrossRef
• Synthesis of Rare Earth Oxide from NaREE(SO4)2·H2O by Ion Substitution Reaction
  Dae-Weon Kim, Bo-Ram Kim, Hee-Lack Choi
  Journal of the Korean Society of Mineral and Energy Resources Engineers.2020; 57(5): 405.     CrossRef