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

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).sub.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.

Claims

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.sub.2O.sub.3 and FeB, and calcium reduction diffusion reaction is conducted using CaH.sub.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.sub.2Fe.sub.14B stoichiometric ratio, Nd.sub.2O.sub.3 is added to make sure that the amount of rare earth was 40 wt. % of the mixed powders of the pretreatment powders, Nd.sub.2O.sub.3 and FeB; FeB is added to make sure that the amount of B in mixed powders of the pretreatment powders, Nd.sub.2O.sub.3 and FeB is in excess 0-10 wt. % of that in stoichiometric RE.sub.2Fe.sub.14B; the quantity of CaH.sub.2 is 1.2-1.3 times as large as the mixed powders; the quantity of CaO is 50 wt. % of CaH.sub.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.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the x-ray diffraction (XRD) pattern of the pretreatment sludge powders.

(2) FIG. 2 shows the XRD pattern of the recycled NdFeB powders.

(3) FIG. 3 shows the demagnetization curve of the recycled sintered NdFeB magnets.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(4) The following examples describe this disclosure, but do not limit the coverage of the disclosure.

EXAMPLE 1

(5) A NdFeB sludge of 30 ml with distilled water of 450 ml in a flask was distilled by rotary evaporator placed in a water bath under vacuum conditions. The procedure started from 30° C. to 80° C. with increments of 5° C. in the intervals of 5 min until the internal liquid had evaporated. The operation was repeated for 3 times. As a result, 26.42 g of distilled powders were obtained. The distillation powders were washed for 3 times by 52 ml of acetone in an ultrasonic vessel, and then were cleaned twice by ethanol in the ultrasonic vessel for 10 min. After removing the liquid, the wet powders were dried in vacuum at 50° C. to obtain the pretreatment powders. The XRD pattern and XRF results of the pretreatment powders are shown in FIG. 1 and TAB. 1, respectively. It was concluded that the pretreatment powders were mainly composed of Fe.sub.3O.sub.4, Nd(CO.sub.3)(OH).sub.4.xH.sub.2O, Fe.sub.2Nd and Fe.sub.2B.

(6) Based on the elemental content, shown in TAB. 1, and calculations in accordance with RE.sub.2Fe.sub.14B stoichiometric ratio, Nd.sub.2O.sub.3 was added to make sure that the amount of rare earth was 40 wt. % of mixed powders including pretreatment powders, Nd.sub.2O.sub.3 and FeB; FeB was added to make sure that the amount of B in the mixed powders was same as that in the RE.sub.2Fe.sub.14B compound; The quantity of CaH.sub.2 was 1.2 times as large as the mixed powders; The quantity of CaO was 50 wt. % of CaH.sub.2. The mixed powders were grinded homogeneously, wrapped in tantalum foil, and placed in a tube furnace. Reduction diffusion reaction was carried out at 1160° C. for 150 min in inert gas. After cooling to room temperature, the reducing product was grinded, ultrasonically rinsed for 3 times with 15% glycerol aqueous solution in a magnetic field of 0.5 T, then rinsed with water until the pH value of the supernatant reached 9.3, and finally was washed by ethanol and ether for 15 min, respectively. After rinsing, the product was dried in vacuum of 10.sup.−3 Pa at 400° C. for 120 min to obtain the recycled NdFeB powders with particle sizes of about 10 μm. The XRD patterns of the recycled NdFeB powders are shown in FIG. 2. The recycled NdFeB powders were mainly composed of Nd.sub.2Fe.sub.14B and a small amount of NdFe.sub.4B.sub.4 phase. The resulting recycled NdFeB powders were milled to about 5 μm, doped by hydrogenated neodymium nanoparticles of 15 wt. %, and mixed evenly; subsequently pressed and aligned in a magnetic field to obtain the compact. The green compact was first dehydrogenated at 900° C. for 120 min, and then sintered at 1100° C. for 180 min, finally annealed at 900° C. for 180 min and 480° C. for 120 min, respectively. The recycled sintered magnets exhibited good magnetic properties with the remanence (B.sub.r) of 12.36 kGs, the coercivity (H.sub.ci) of 13.12 kOe, and maximum energy product [(BH).sub.max] of 35.26 MGOe, as shown in FIG. 3.

EXAMPLE 2

(7) A NdFeB sludge of 30 ml with distilled water of 450 ml in a flask was distilled by rotary evaporator placed in a water bath under vacuum conditions. The procedure started from 30° C. to 80° C. with increments of 5° C. in intervals of 8 min until the internal liquid had evaporated. The operation was repeated for 2 times. As a result, 25.64 g of distilled powders were obtained. The distillation powders were washed for 3 times by 51 ml of acetone in an ultrasonic vessel, and then were cleaned for 1 time by ethanol in the ultrasonic vessel for 12 min. After removing the liquid, the wet powders were dried in vacuum at 50° C. to obtain the pretreatment powders. The XRF results of the pretreatment powders are shown in TAB. 2.

(8) Based on the elemental content, shown in TAB. 2, and calculations in accordance with RE.sub.2Fe.sub.14B stoichiometric ratio, Nd.sub.2O.sub.3 was added to make sure that the amount of rare earth was 40 wt. % of mixed powders including the pretreatment powders, Nd.sub.2O.sub.3 and FeB; FeB was added to make sure that the amount of B in mixed powders was in excess of 5 wt. % of that in the RE.sub.2Fe.sub.14B compound; The quantity of CaH.sub.2 was 1.25 times as large as the mixed powders; The quantity of CaO was 50 wt. % of CaH.sub.2. The mixed powders were grinded homogeneously, wrapped in tantalum foil, and placed in a tube furnace. Reduction diffusion reaction was carried out at 1180° C. for 110 min in inert gas. After cooling to room temperature, the reducing product was grinded, ultrasonically rinsed for 3 times with 15% glycerol aqueous solution in a magnetic field of 0.3 T, then rinsed with water until the pH value of the supernatant reached 10, and finally was washed by ethanol and ether for 15 min, respectively. After rinsing, the product was dried in vacuum of 10.sup.−3 Pa at 400° C. for 120 min to obtain the recycled NdFeB powders with particle sizes of about 10 μm. The resulting recycled NdFeB powders were milled down to about 3 μm, doped by hydrogenated praseodymium nanoparticles of 10 wt. %, and mixed evenly; subsequently pressed and aligned in a magnetic field to obtain the compact. The green compact was first dehydrogenated at 950° C. for 100 min, and then sintered at 1050° C. for 240 min, finally annealed at 850° C. for 120 min and 450° C. for 180 min, respectively. The recycled sintered magnets exhibited good magnetic properties with remanence (B.sub.r) of 12.32 kGs, coercivity (H.sub.ci) of 12.08 kOe, and maximum energy product [(BH).sub.max] of 35.45 MGOe.

EXAMPLE 3

(9) A NdFeB sludge of 30 ml with distilled water of 450 ml in a flask was distilled by rotary evaporator placed in a water bath under vacuum conditions. The procedure started from 30° C. to 80° C. with increments of 5° C. in intervals of 10 min until the internal liquid had evaporated. The operation was repeated for 3 times. As a result, 25.26 g of distilled powders were obtained. The distillation powders were washed 3 times by 50.5 ml of acetone in an ultrasonic vessel, and then were cleaned for 2 times by ethanol in the ultrasonic vessel for 15 min. After removing the liquid, the wet powders were dried in vacuum at 50° C. to obtain the pretreatment powders. The XRF results of the pretreatment powders were shown in TAB. 3.

(10) Based on the elemental content, shown in TAB. 3, and calculations in accordance with RE.sub.2Fe.sub.14B stoichiometric ratio, Nd.sub.2O.sub.3 was added to make sure that the amount of rare earth was 40 wt. % of the mixed powders including the pretreatment powders, Nd.sub.2O.sub.3 and FeB; FeB was added to make sure that the amount of B in mixed powders was in excess of 8 wt. % of that in the RE.sub.2Fe.sub.14B compound; The quantity of CaH.sub.2 was 1.3 times as large as in the mixed powders; The quantity of CaO was 50 wt. % of CaH.sub.2. The mixed powders were grinded homogeneously, wrapped in tantalum foil, and placed in a tube furnace. Reduction diffusion reaction was carried out at 1240° C. for 60 min in inert gas. After cooling to room temperature, the reducing product was grinded, ultrasonically rinsed for 3 times in a 15% glycerol aqueous solution in a magnetic field of 0.1 T, then rinsed with water until the pH value of supernatant reached 8, and finally was washed by ethanol and ether for 15 min, respectively. After rinsing, the product was dried in a vacuum of 10.sup.−3 Pa at 400° C. for 120 min to obtain the recycled NdFeB powders with particle sizes of about 10 μm. The resulting recycled NdFeB powders were milled down to 4 μm, doped by hydrogenated dysprosium nanoparticles of 20 wt. %, and mixed evenly; subsequently pressed and aligned in a magnetic field to obtain the compact. The green compact was first dehydrogenated at 1000° C. for 30 min, then sintered 1150° C. for 120 min, and finally annealed at 950° C. for 60 min and 550° C. for 60 min, respectively. The recycled sintered magnets exhibited good magnetic properties with remanence (B.sub.r) of 11.15 kGs, coercivity (H.sub.ci) of 18.36 kOe, and maximum energy product [(BH).sub.max] of 31.66 MGOe.

EXAMPLE 4

(11) A NdFeB sludge of 30 ml with distilled water of 450 ml in a flask was distilled by rotary evaporator in water bath under vacuum conditions. The procedure started from 30° C. to 80° C. with increments of 5° C. in intervals of 10 min until the internal liquid had evaporated. The operation was repeated for 2 times. As a result, 25.64 g of distilled powders were obtained. The distilled powders were washed for 4 times by 51 ml of acetone in an ultrasonic vessel, and then cleaned for 2 times by ethanol in the ultrasonic vessel for 15 min. After removing the liquid, the wet powders were dried in vacuum at 50° C. to obtain the pretreatment powders. The XRF results of the pretreatment powders are shown in TAB. 4.

(12) Based on the elemental content, shown in TAB. 4, and calculations in accordance with RE.sub.2Fe.sub.14B stoichiometric ratio, Nd.sub.2O.sub.3 was added to make sure that the amount of rare earth was 40 wt. % of the mixed powders including the pretreatment powders, Nd.sub.2O.sub.3 and FeB; FeB was added to make sure that the amount of B in mixed powders was in excess of 10 wt. % of that in the RE.sub.2Fe.sub.14B compound; The quantity of CaH.sub.2 was 1.2 times as large as the mixed powders; The quantity of CaO was 50 wt. % of CaH.sub.2. The mixed powders were grinded homogeneously, wrapped in tantalum foil, and placed in a tube furnace. Reduction diffusion reaction was carried out at 1200° C. for 100 min in inert gas. After cooling to room temperature, the reducing product was grinded, ultrasonically rinsed for 3 times with 15% glycerol aqueous solution in a magnetic field of 0.1 T, then rinsed with water until the pH value of supernatant reached 9, and finally was washed by ethanol and ether for 15 min, respectively. After rinsing, the product was dried in a vacuum of 10.sup.−3 Pa at 400° C. for 120 min to obtain the recycled NdFeB powders with particle sizes of about 10 μm. The resulting recycled NdFeB powders were milled down to 4 μm, doped by hydrogenated terbium nanoparticles of 10 wt. %, and mixed evenly; subsequently pressed and aligned in a magnetic field to get the compact. The green compact was first dehydrogenated at 1000° C. for 60 min, and then sintered at 1100° C. for 180 min, and finally annealed at 900° C. for 180 min and 480° C. for 120 min, respectively. The recycled sintered magnets exhibited good magnetic properties with remanence (B.sub.r) of 11.68 kGs, coercivity (H.sub.ci) of 20.65 kOe, and maximum energy product [(BH).sub.max] of 32.25 MGOe.

(13) TABLE-US-00001 TABLE 1 XRF results of the pretreatment powders (Example 1) Element Content (wt. %) Fe 67.3135 Nd 20.6406 Pr 6.4564 Dy 2.5889 Co 1.1343 Na 0.3221 Ho 0.2905 Cu 0.2837 Al 0.2339 Si 0.2044 Nb 0.1916 Ga 0.1667 S 0.0656 Zr 0.0531 Ca 0.053 W 0.0018

(14) TABLE-US-00002 TABLE 2 XRF results of the pretreatment powders (Example 2) Element Content (wt. %) Fe 67.7794 Nd 20.5665 Pr 6.5391 Dy 2.4912 Co 1.1563 Cu 0.3022 Ho 0.2975 Al 0.2209 Nb 0.1953 Ga 0.1781 Si 0.1389 Ca 0.0609 Zr 0.0441 S 0.0296

(15) TABLE-US-00003 TABLE 3 XRF results of the pretreatment powders (Example 3) Element Content (wt. %) Fe 66.9291 Nd 20.6427 Pr 6.5183 Dy 2.4626 Co 1.1642 Tb 0.7997 Ho 0.2820 Cu 0.2702 Al 0.2381 Si 0.2093 Nb 0.1873 Ga 0.1598 Ca 0.0567 Zr 0.0544 S 0.0256

(16) TABLE-US-00004 TABLE 4 XRF results of the pretreatment powders (Example 4) Element Content (wt. %) Fe 66.3840 Nd 20.9083 Pr 6.6052 Dy 2.5265 Co 1.1398 Tb 0.8582 Cu 0.3107 Ho 0.2898 Si 0.2554 Al 0.2425 Nb 0.1867 Ga 0.1781 Ca 0.0611 Zr 0.0538