Short-process method for preparing sintered NdFeB magnets with high magnetic properties recycling from NdFeB sludge

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 internal liquid has evaporated, the operation is repeated to obtain distillation powders;
• (2) ultrasonic cleaning for sludge:
• wherein the distillation powders of step (1) are washed 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 pm, 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.