SHORT-PROCESS METHOD FOR PREPARING SINTERED NDFEB MAGNETS WITH HIGH MAGNETIC PROPERTIES RECYCLING FROM NDFEB SLUDGE

摘要

The present invention discloses a short process preparation technology of sintered NdFeB magnets from the NdFeB sludge, which relates to a field of recycle technology of NdFeB sludge. The present invention comprises the following steps: water bath distillation of organics in sludge, ultrasonic cleaning, calcium reduction and diffusion, ultrasonic rinsing in a magnetic field and drying, powders mixing and sintering. NdFeB sludge as raw materials was directly prepared from recycled sintered magnets with high magnetic properties. Most of the organics in the sludge could be removed by a vacuum distillation process with stepwise heating. The ultrasonic rinsing process in a magnetic field could effectively remove the remaining organics. The recycled sintered magnets exhibited good maximum energy product [(BH)max] of 35.26 MGOe. The present invention has important features, such as the short processing time, efficient environmental protection, high recycling rate and effective utilization rate of rare earth metals.

主权项

1. A short-process method for preparing sintered NdFeB magnets from NdFeB sludge, comprising the following steps: water bath distillation of sludge, ultrasonic cleaning, calcium reduction and diffusion, ultrasonic rinsing in a magnetic field, drying, powders mixing and sintering:
(1) water bath distillation of sludge: wherein distilled water is added into the sludge and stirred, subsequently, water bath distillation with stepwise temperature increase is carried out under vacuum until the internal liquid has evaporated, the operation is repeated for 3 times to obtain distillation powders; (2) ultrasonic cleaning for sludge: wherein the distillation powders of step (1) are washed for 3 times by acetone in an ultrasonic vessel, followed by cleaning by ethanol in the ultrasonic vessel, after removing liquid, wet powders are dried to get pretreatment powders; (3) calcium reduction-diffusion: wherein the pretreatment powders of step (2) is added with appropriate amounts of Nd2O3 and FeB, and calcium reduction diffusion reaction is conducted using CaH2 as reactant and CaO as dispersant; (4) rinsing and drying: wherein reducing product of step (3) is grinded, ultrasonically rinsed in a glass container in a magnetic field, and then dried; (5) mixing powders and sintering: wherein resulting recycled NdFeB powders of step (4) are milled down to 3-5 μm, doped by rare earth hydride nanoparticles of 10-20 wt. %, and mixed; subsequently pressed and aligned in a magnetic field to obtain a green compact; the green compact is first dehydrogenated at 900-1000° C. for 30-180 min, and then sintered at 1050-1150° C. for 120-240 min, and finally annealed at 850-950° C. for 60-180 min and 450-550° C. for 60-180 min, respectively; so as to obtain recycled sintered magnets.