Chemical Thermodynamic Insights on Rare-Earth Magnet Sludge Recycling
Author(s)Wagner, Mary Elizabeth; Allanore, Antoine
MetadataShow full item record
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.
DepartmentMIT Materials Research Laboratory
Iron and Steel Institute of Japan
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
Final published version