Method for safely oxidizing and roasting neodymium-iron-boron powder and application thereof

Abstract

A method for safely oxidising roasting NdFeB powder material. The method may include: S1: magnetizing and drying the NdFeB powder material; S2: heating the magnetized and dried NdFeB powder material to spontaneous combustion, and then preparing the spontaneous combustion product into a powder; and S3: magnetizing and then oxidising roasting the powder to obtain NdFeB oxide.

Claims

1. A method for safely oxidizing roasting NdFeB powder material, comprising: S1: magnetizing and drying the NdFeB powder material; S2: heating the magnetized and dried NdFeB powder material to spontaneous combustion, and then preparing the spontaneous combustion product into a powder; and S3: magnetizing and then oxidizing roasting the powder to obtain NdFeB oxide; wherein, in step S1, the NdFeB powder material is prepared by wet grinding from NdFeB blocks or is an oil-free NdFeB waste powder; the moisture content of the NdFeB powder material is <0.3% after drying; wherein, in step S2, the process of heating to spontaneous combustion involves: placing the NdFeB powder material in an ignition furnace for ignition and spontaneous combustion, wherein the ignition furnace has a furnace temperature of 150-350? C., and the treatment time is 0.01-1 h; and wherein, in steps S1 and S3, the magnetization refers to direct current magnetization, pulse magnetization or strong magnetization of the NdFeB powder material.

2. The method of claim 1, wherein, in step S1, the NdFeB powder material has a particle size of 50-200 mesh.

3. The method of claim 1, wherein, step S2 further comprises, after preparing the powder, carrying out a sieving process, and taking an undersize powder for the next process, wherein the mesh number of a sieve for the sieving is 50-200.

4. The method of claim 3, wherein, in step S2, the oversize after sieving is subjected to wet grinding and then returned to step S1.

5. The method of claim 1, wherein, in step S3, the temperature of oxidizing roasting is 600-800? C. and a treatment time of 1-3 h.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The present invention will be further illustrated below in conjunction with the accompanying drawings and embodiments, wherein

(2) FIG. 1 is a process flow diagram of an embodiment of the present invention.

DETAILED DESCRIPTION

(3) The concept of the present invention and the technical effects produced thereby will be clearly and completely described in conjunction with examples below in order to fully understand the object, features and effects of the present invention. Obviously, the described examples are merely some, rather than all, of the examples of the present invention, and based on these examples of the present invention, other examples obtained by those skilled in the art without involving any inventive effort all fall within the scope of protection of the present invention.

Embodiment 1

(4) A method for safely oxidizing roasting NdFeB powder material was provided, which comprised the following steps:

(5) At a step of S1: NdFeB powder material (100 mesh) obtained by wet grinding load into a pot at a loading thickness of 6-8 mm, subjecting the loaded NdFeB powder material to pulse magnetization on a magnetization device so as to endow the NdFeB powder material with magnetism, whereby the magnetized NdFeB powder material was in a radial form, and drying the magnetized NdFeB powder material at 80? C. for 1 h so as to control the moisture content to 0.1%;

(6) At a step of S2: the dried NdFeB powder material remaining a fluffy structure as shown after magnetization, and at this point entering an ignition furnace at 150? C., wherein the NdFeB powder material spontaneously ignited within 8 min, and after spontaneous combustion, the NdFeB naturally cooled to room temperature at which the NdFeB powder material was cohered; and grinding the NdFeB powder material by means of a twin roller, passing the ground NdFeB powder material through a 100-mesh sieve with a sieving rate of 99%, returning the oversize to wet grinding, and loading the undersize into a pot at a loading thickness of 8-10 mm; and

(7) At a step of S3: firstly magnetizing the loaded NdFeB powder material, then roasting the NdFeB powder material at 800? C. for 2 h during which air was introduced, wherein during the roasting process, the NdFeB powder material was demagnetized, but could remain the original magnetized cotton-like structure, and the oxidizing roasting NdFeB powder material had an iron oxidation degree is 97.5%, the ferrous iron content is 1.2 wt %, and the total iron content is 48.9 wt %.

Embodiment 2

(8) A method for safely oxidizing roasting NdFeB powder material was provided, which comprised the following steps:

(9) At a step of S1: passing waste powder recovered during the NdFeB production process through a 50-mesh sieve, loading the undersize into a pot at a loading thickness of 6-8 mm, subjecting the loaded NdFeB powder material to pulse magnetization on a magnetization device so as to endow the NdFeB powder material with magnetism, whereby the magnetized NdFeB powder material was in a radial form, and drying the magnetized NdFeB powder material at 80? C. for 1 h so as to control the moisture content to 0.2%;

(10) At a step of S2: the dried NdFeB powder material remaining a fluffy structure as shown after magnetization, and at this point entering an ignition furnace at 300? ? C., wherein the NdFeB powder material spontaneously ignited within 5 min, and after spontaneous combustion, the NdFeB naturally coole to room temperature at which the NdFeB powder material was cohered; and grinding the NdFeB powder material by means of a twin roller, passing the ground NdFeB powder material through a 50-mesh sieve with a sieving rate of 99%, subjecting the oversize to wet grinding, and loading the undersize into a pot at a loading thickness of 8-10 mm; and

(11) At a step of S3: firstly magnetizing the loaded NdFeB powder material, then roasting the NdFeB powder material at 800? C. for 2 h during which air was introduced, wherein during the roasting process, the NdFeB powder material was demagnetized, but could remain the original magnetized cotton-like structure, and the oxidizing roasting NdFeB powder material had an iron oxidation degree is 95.5%, the ferrous iron content is 2.2 wt %, and the total iron content is 48.5 wt %.

Comparative Example 1

(12) The main difference between this comparative example and Embodiment 1 lay in that the NdFeB powder material did not undergo a magnetization treatment during three-stage oxidizing roasting, and comparison was made in terms of drying time, spontaneous combustion phenomenon, sieving rate, and oxidation degree of oxides in the process, specifically as shown in Table 1. The specific process of this comparative example involved: S1: NdFeB powder material (100 mesh) obtained by wet grinding load into a pot at a loading thickness of 6-8 mm, and drying the loaded magnetized NdFeB powder material at 80? C. for 1.5 h so as to control the moisture content to 0.1%; S2: bringing the dried NdFeB powder material into an ignition furnace at 150? C., wherein the NdFeB powder material spontaneously ignited within 8 min, and after spontaneous combustion, the NdFeB naturally cooled to room temperature at which the NdFeB powder material was severely cohered; and grinding the NdFeB powder material by means of a twin roller, passing the ground NdFeB powder material through a 100-mesh sieve with a sieving rate of 95%, returning the oversize to wet grinding, and loading the undersize into a pot at a loading thickness of 8-10 mm; and S3: roasting the loaded NdFeB powder material at 800? C. for 2 h during which air was introduced, wherein the oxidizing roasting NdFeB powder material had an iron oxidation degree of 92.5%, the ferrous iron content is 3.6 wt %, and the total iron content is 48 wt %.

Comparative Example 2

(13) The difference between this comparative example and Embodiment 1 lay in that NdFeB powder material underwent neither three-stage oxidizing roasting nor a magnetization treatment, and comparison was made in terms of drying time, spontaneous combustion phenomenon, sieving rate, and oxidation degree of oxides in the process, specifically as shown in Table 1. The specific process of this comparative example involved:

(14) NdFeB powder material (100 mesh) obtained by wet grinding load into a pot at a loading thickness of 6-8 mm, heating the loaded NdFeB powder material from room temperature 25? C. to 800? C. at a ramp rate of 5? C./min, maintaining the temperature for 2 h, wherein the drying and spontaneous combustion situations of the powder was observed during the heating period, and sieving roasted NdFeB oxide with a sieving rate of only 85%, wherein the oxidation degree of iron in the NdFeB oxide was only 88%.

(15) TABLE-US-00001 TABLE 1 Sieving rate of Spontaneous spontaneous combustion combustion Oxidation Example Drying time phenomenon product degree Embodiment 1 1 h No flame was 99% 97.5% (Three-stage, found, and the time magnetized roasting) for combustion phenomenon to complete was 6 min Comparative 1.5 h No flame was 95% 92.5% Example 1 found, and the time (Three-stage, non- for combustion magnetized roasting) phenomenon to complete was 10 min Comparative Continuous At about 150? C., (NdFeB oxide) .sup.88% Example 2 NdFeB 85% (Non-three-stage, spontaneously non-magnetized ignited and flame roasting) appeared

(16) It could be seen from Table 1 that compared with Embodiment 1, the drying time and the time for spontaneous combustion to complete of Comparative Example 1 were longer, and the sieving rate of the spontaneous combustion product and the oxidation degree were lower, indicating that the magnetization treatment could make the NdFeB powder material in a radial form, thereby speeding up the drying; in addition, the powder was not easy to agglomerate and was fully in contact with air at a high temperature so as to achieve a high degree of oxidation. By observing the spontaneous combustion situation of Comparative Example 2, it could be seen that at about 150? C., the NdFeB powder material reacted with water vapor in the furnace to generate hydrogen by means of displacement and thereby cause flame combustion, which indicates that if no magnetized three-stage treatment was used for the roasting process, the fire and explosion hazard of the NdFeB powder material would be increased. In addition, the sieving rate of NdFeB oxide was relatively low. This was because after the spontaneous combustion of the NdFeB powder material without a magnetization treatment, severe agglomeration occurred and the particles of the powder fused with each other; furthermore, after high-temperature roasting, the structure thereof was denser, making it difficult for the NdFeB inside to come into contact with the air, so the degree of oxidation was not as high as that of Embodiment 1.

(17) FIG. 1 is a process flow diagram of an embodiment of the present invention, wherein NdFeB powder material (a material obtained by wet grinding from NdFeB blocks or an NdFeB waste powder) is loaded into a pot and subjected to magnetization, drying, ignition, grinding and sieving, and the undersieve is further magnetized and roasted to obtain NdFeB oxide, while the oversieve is returned to wet grinding.

(18) The embodiments of the present invention have been described above in detail in conjunction with the accompanying drawings; however, the present invention is not limited to the above-mentioned embodiments, and within the scope of knowledge possessed by those of ordinary skill in the art, various modifications can be made without departing from the gist of the present invention. In addition, without conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.