Electrolytic Hydrogen Decrepitation of NdFeB Magnets Under Ambient Conditions

We describe an electrolytic process which successfully decrepitates (pulverizes) sintered Nd2Fe14B magnets in preparation for further recycling. Laboratory-scale measurements on magnets that had been removed from end-of-life hard disk drives demonstrate that cm-size magnet fragments, in electrical contact with a titanium cathode in a 2 M KOH solution, can undergo hydrogen decrepitation (HD) into powder with grain size < 50 μm. Electrolysis during 2 h at 4.7 V, 13–15 A, with nickel foil as the anode, was sufficient for complete material pulverization under ambient conditions. As a guide for understanding the reaction thermodynamics of each of the magnet components with hydrogen, the Gibbs energies for two groups of reactions in the temperature range 273–473 K were calculated: (1) reactions with atomic hydrogen radical (i.e., uncharged atom, unpaired electron); (2) reactions with hydrogen gas. As expected for small grain HD powders that have not been degassed at elevated temperatures, only weak remanent magnetic polarization and coercive field are detected in SQUID magnetometer measurements; demagnetization to facilitate powder handling is therefore not required. We expect that the financial cost, time, and safety of a scaled-up version of our electrolytic process should compare favorably with high pressure and/or high-temperature hydrogen gas decrepitation protocols currently in use.