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

Patent metadata

Field	Value
Publication number	US-9728310-B2
Application number	US-201615133042-A
Country	US
Kind code	B2
Filing date	Apr 19, 2016
Priority date	Mar 8, 2015
Publication date	Aug 8, 2017
Grant date	Aug 8, 2017

Abstract

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.

First claim

What is claimed is:

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 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 Nd 2 O 3 and FeB, and calcium reduction diffusion reaction is conducted using CaH 2 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.

2. The short-process method for preparingsintered NdFeB magnets from NdFeB sludge according to claim 1 , wherein in step (1) the volume ratio between the sludge and the distilled water is 1:15, water bath distillation is carried out under vacuum with stepwise temperature increase, preferably starting from 30° C. and increased to 80° C. with increments of 5° C. in intervals of 5-10 min until the internal liquid has evaporated, the operation is repeated to obtain the distillation powders.

3. The short-process method for preparing sintered NdFeB magnets from NdFeB sludge according to claim 1 , wherein in step (2) every 5 g of the distillation powders corresponds to 10 ml acetone and 10 ml ethanol.

4. The short-process method for preparing sintered NdFeB magnets from NdFeB sludge according to claim 1 , wherein the materials quality in the step (3) of calcium reduction-diffusion are: the pretreatment powders after step (2) are analyzed by XRF, based on XRF results and calculations in accordance with RE 2 Fe 14 B stoichiometric ratio, Nd 2 O 3 is added to make sure that the amount of rare earth was 40 wt. % of the mixed powders of the pretreatment powders, Nd 2 O 3 and FeB; FeB is added to make sure that the amount of B in mixed powders of the pretreatment powders, Nd 2 O 3 and FeB is in excess 0-10 wt. % of that in stoichiometric RE 2 Fe 14 B; the quantity of CaH 2 is 1.2-1.3 times as large as the mixed powders; the quantity of CaO is 50 wt. % of CaH 2 .

5. The short-process method for preparing sintered NdFeB magnets from NdFeB sludge according to claim 1 , wherein in step (3) the reduction diffusion reaction is carried out at 1160-1240° C. for 60-150 min in inert gas.

6. The short-process method for preparing sintered NdFeB magnets from NdFeB sludge according to claim 1 , wherein the reducing product is ultrasonically rinsed with glycerol aqueous solution in a magnetic field of 0.1-0.5 T and, then rinsed with water until the pH value of supernatant reaches 8-10, and finally is washed by ethanol and ether, respectively, after rinsing, the product is dried in vacuum to obtain recycled NdFeB powders.

7. The short-process method for preparing sintered NdFeB magnets from NdFeB sludge according to claim 6 , wherein an optimized rinsing time is 15 min.

8. The short-process method for preparing sintered NdFeB magnets from NdFeB sludge according to claim 1 , wherein the rare earth hydride nanoparticles are made of hydrogenated neodymium, hydrogenated praseodymium, hydrogenated dysprosium, or hydrogenated terbium.

Assignees

• Univ Beijing Technology
• Anhui Earth-Panda Advance Magnetic Mat Co Ltd

Inventors

• Yue Ming
• Liu Weiqiang
• Li Xiantao
• Li Meng
• Liu Min
• Zhang Dongtao
• Yin Xiaowen
• Huang Xiulian
• Chen Jingwu
• Yi Xiaofei

Classifications

• B22F1/00

  Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties · CPC title

• C22C38/60 Primary

  containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur · CPC title

• C22C38/002

  containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60 · CPC title

• B22F1/0003

  Operations & Transport · mapped topic

• B22F2301/355

  Rare Earth - Fe intermetallic alloys · CPC title