(381k) Surface Functionalization of Magnetite for Selective Recovery of Dysprosium (Dy+3) from Permanent Magnet Waste

Dysprosium (Dy) belongs to the REEs in the lanthanide series, and its unique physical and chemical properties make it among the most indispensable heavy rare earth elements. Given its low concentration in ores, its recovery from secondary waste such as waste electrical and electronic equipment is highly needed. Herein, a magnetic nanoparticle (Fe₃O₄ NP)-based adsorbent for selective recovery of Dy is developed for its retrieval from permanent magnet waste. The Fe₃O₄ NPs was synthesized by co-precipitation and functionalized with diglycolic acid (DGA-NH₂-SiO₂@Fe₃O₄), a ligand with good affinity towards Dy³⁺. Before diglycolic acid attachment, the surface of bare Fe₃O₄ NPs was coated with tetraethyl orthosilicate to ensure its stability in harsh condition. N-[(3-trimethoxysily) propyl] ethylene diamine was subsequently functionalized as a linker for DGA. The XRD analysis of the bare Fe₃O₄ NPs confirmed its structure, which remained unaltered after coating and functionalization of the linker and DGA ligand. The adsorbent was characterized thoroughly by SEM, BET, TGA, and VSM. The successful synthesis of DGA-NH₂-SiO₂@Fe₃O₄ was confirmed through FTIR and elemental analysis. The adsorption behavior of Dy⁺³ on DGA-NH₂-SiO₂@Fe₃O₄ was studied in batch equilibrium experiment, which was found optimum at pH 5. The isotherm equilibrium study shows that the material has a maximum adsorption capacity of 75 mg g^-1 and fitted well with the Langmuir adsorption model. The model indicates that the adsorption is monolayer and that there is no interaction among the adsorbates. Kinetics study of the Dy⁺³ adsorption on DGA-NH₂-SiO₂@Fe₃O₄ is fitted well by Elovich model, which suggests the chemical interaction between the adsorbent and adsorbate with slow adsorption rate. Furthermore, the selectivity study shows that DGA-NH₂-SiO₂@Fe₃O₄ has good affinity towards Dy⁺³ ion over competing neodymium ion in permanent magnet waste. Overall results demonstrate the potential of DGA-NH₂-SiO₂@Fe₃O₄ for selective Dy³⁺ recovery from secondary waste.

This work was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (No. 2017R1D1A1B03028102 and No. 22A20130012051 (BK21Plus)) and by the Ministry of Science and ICT (No. 2017R1A2B2002109).