Chemical Thermodynamic Insights on Rare-Earth Magnet Sludge Recycling
Author(s)
Wagner, Mary Elizabeth; Allanore, Antoine
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Recycling rare-earth magnets poses a metallurgical challenge due to their high reactivity and the difficulty in separating individual rare-earth elements. These challenges are compounded when considering magnet machining sludge, which is more heavily oxidized and contains more contaminants than typical end-of-life magnets. If recycled, these materials are sent back to the primary smelter, where they are separated and purified to make new feedstocks which are often re-mixed into a new magnet. Here, a thermodynamic study is presented, assessing the oxidation behavior of rare-earth magnets. The theoretical minimum energy to reduce the whole magnet sludge, without separation and purification, is also presented. A comprehensive model including 25 elements is provided, using a hybrid CALPHAD-classical method. Oxygen distribution in a rare-earth magnet, with a total O content ranging between 0.09% to 5.4 wt%, is assessed. The results predict a final distribution of 40 wt% rare-earth in the oxide phase, with 60 wt% still remaining in the metallic phase. The model performance with respect to published experimental data is used to shed light into the possible processing methods for recycling.
Date issued
2020-11Department
MIT Materials Research LaboratoryJournal
ISIJ International
Publisher
Iron and Steel Institute of Japan
Citation
Wagner, Mary-Elizabeth and Antoine Allanore. "Chemical Thermodynamic Insights on Rare-Earth Magnet Sludge Recycling." ISIJ International 60, 11 (November 2020): 2339-2349. © 2020 The Iron and Steel Institute of Japan
Version: Final published version
ISSN
0915-1559
1347-5460