Grinding and roastingThe magnet was rst crushed between two aluminium metalplates by applying a force of 10 tons with a hydraulic press.NdFeB magnets are brittle and break quite easily into smallerpieces. A sieve of 400 mm was used, (Fig. 1B) and part of theundersize particles were milled with a centrifugal mill to obtainparticles <80 mm. Note that we refer to <80 and <400 mm powderas a powder in which the cross section is maximum 80 mm and400 mm, respectively. The roasting temperature and uptake ofoxygen as a function of time and temperature were studied withTGA. The magnet powder was rst heated at 20 C min1 up to950 C and kept at this temperature for another 480 min. Thesample chamber was purged with dry air (60 mL min1) and theinitial sample mass in the alumina crucible was 15.988 mg.The inuence of the temperature on the mass gain of theNdFeB magnet was studied as well on larger scales. A powdersample (5 g) was placed into a ceramic crucible and heated to thedesired temperature without blowing extra air or oxygen into themuffle furnace. The difference and increase in mass was calculatedfrom the mass before and aer the roasting experiments.The mass gain (%) aer the roasting process is dened as: Roasting as a function of time was studied at a temperatureof 650 C. This temperature was chosen to test if also lowertemperatures but longer heating times could be used for theroasting process. The sample was removed from the furnaceaer certain time intervals and allowed to cool down to roomtemperature. Aerwards, it was weighed and then placed againin the furnace. The <400 mm powder used in all leachingexperiments was kept for 15 h at 950 C to obtain full conversionof the metal into the oxides.
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