Method for preparing high-purity nanoscale iron oxide red from neodymium iron boron reclaimed material iron slag

Abstract

The invention belongs to the technical field of recycling of neodymium iron boron reclaimed materials, and relates to a method for preparing high-purity nanoscale iron oxide red from neodymium iron boron reclaimed material iron slag. Adding iron slag into a hydrochloric acid solution for reaction, washing filter residues, adding a sulfuric acid solution for reaction, and adding reduced iron powder and ammonium thiosulfate for a plurality of times; cooling, standing and centrifugally filtering to obtain a light green ferrous sulfate solution. Adding into an ammonium persulfate solution, adding a hexamethylenetetramine solution, stirring for reaction, adding dilute ammonia water, introducing oxygen until a large amount of reddish brown colloidal precipitate appears, and dropwise adding liquid nitrogen; after the suspension reacts, naturally cooling to room temperature, filtering, and washing, drying and grinding filter residues to obtain the high-purity nanoscale iron oxide red. In the preparation process, only extremely few solid wastes are generated, so that the environmental pollution is reduced, two by-products, namely ammonium chloride and ammonium sulfate fertilizer are produced at the same time, and the green cyclic utilization of multiple elements is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of resource utilization of NdFeB recycled materials, and relates to a method for preparing high-purity nano-level red iron oxide from NdFeB recycled material iron slag. Background Art

[0002] The main raw materials of NdFeB permanent magnets are 32% rare earth metal neodymium, 64% metal element iron, 1% non-metallic element boron, and a small amount of cobalt, gallium, copper and other metals. NdFeB is a permanent magnetic material, widely used in the electronics industry, automobile industry, micro motors, permanent magnetic instruments, sensors, magnetic therapy equipment, magnetic suspension systems, etc. While this material is widely used, a large amount of waste materials are generated. During the recycling process of these waste materials, a large amount of iron slag will be generated. At present, there is no more feasible treatment technology for these iron slags, resulting in a huge waste of resources and environmental pollution. Summary of the invention

[0003] Aiming at the problems existing in the treatment of traditional NdFeB recycled iron slag, the present invention proposes a novel method for preparing high-purity nano-level iron oxide red from NdFeB recycled iron slag.

[0004] In order to achieve the above object, the present invention is implemented by adopting the following technical solutions: A method for preparing high-purity nano-grade red iron oxide from NdFeB recycled iron slag, the steps are as follows: (1) Adding iron slag to a hydrochloric acid solution, heating and stirring to react, centrifugally filtering after the reaction is completed, washing the filter residue with deionized water to obtain iron slag; adding ammonia water to the filtrate to adjust the pH to 10 and centrifugally filtering again to obtain a secondary filter residue and a secondary filtrate; and evaporating and concentrating the secondary filtrate to obtain ammonium chloride.

[0005] (2) After adding sulfuric acid solution to the filter residue, heat and stir to react. During the reaction, add reduced iron powder and ammonium thiosulfate several times. After the reaction is completed, cool to room temperature, add deionized water and stir evenly, then leave it at room temperature until no bubbles are generated, centrifuge and filter to obtain a light green ferrous sulfate solution.

[0006] (3) Add the ferrous sulfate solution to the stirred ammonium persulfate solution, add the hexamethylenetetramine solution, stir for reaction, add dilute ammonia water, and then introduce oxygen until a large amount of red-brown colloidal precipitate appears to obtain a suspension, and add liquid nitrogen dropwise.

[0007] (4) The suspension is reacted at 175-185°C for at least 5 hours. After the reaction is completed, it is naturally cooled to room temperature and centrifuged. The filtrate is evaporated and concentrated to obtain fertilizer-grade ammonium sulfate. The filter residue is repeatedly washed with water and ethanol alternately for several times, dried and ground to obtain high-purity nano-grade iron oxide red.

[0008] Preferably, the heating temperature in step (1) is 70-80°C.

[0009] Preferably, in step (2), the concentration of the sulfuric acid solution is 10-11 M, the heating and stirring reaction temperature is 85-88° C., the reaction time is 1.5-3 h, and the mass ratio of iron slag: reduced iron powder: ammonium thiosulfate is (8-15): (4-6): (2-4).

[0010] Compared with the prior art, the advantages and positive effects of the present invention are: The present invention utilizes iron slag in NdFeB recycled materials to prepare high-purity nano-level red iron oxide. The entire preparation process generates only very little solid waste, greatly reducing environmental pollution. At the same time, two by-products, ammonium chloride and ammonium sulfate fertilizers, are produced, realizing green recycling of multiple elements. DETAILED DESCRIPTION

[0011] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described below in conjunction with specific embodiments. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0012] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways than those described herein. Therefore, the present invention is not limited to the specific embodiments of the following disclosure.

[0013] Example 1 Washing process: put 10g iron slag into 60mL 2M HCL solution, heat to 70℃ in a water bath, stir at 200rpm for 0.5h, then centrifuge and filter. Wash the residue with high-purity water for 3 times to obtain iron slag with very little impurity content. Add ammonia water to the filtrate to adjust the pH of the solution to 10, centrifuge and filter again. The residue is solid waste. The filtrate can be prepared into fertilizer-grade ammonium chloride after evaporation and concentration.

[0014] Dissolution process: Use 40mL of 10.8M H2SO4 solution to transfer the filter residue in the centrifuge tube to a beaker after oscillation and ultrasound, heat it in a water bath to 85°C, and stir at 150rpm for 2h. During this period, add reduced iron powder (5g in total) and co-solvent ammonium thiosulfate (2.96g in total) in 6 times. Reduced iron powder and auxiliary agent need to be added at the same time each time, and the amount and interval time of each addition are roughly equal. The last addition time is about 15min left from the end of the reaction. Then, take out the beaker, cool it naturally to room temperature, add 100mL of deionized water, stir it with a glass rod, and then stand at room temperature until no bubbles are generated, then centrifuge and filter, and the light green filtrate obtained is the ferrous sulfate solution.

[0015] Precipitation process: Weigh 24.45g of ammonium persulfate and add it to high-purity water to prepare a 2M solution. Then add the above ferrous sulfate solution to the ammonium persulfate solution while stirring at 100rpm. The solution gradually changes from light green to reddish brown, and the ferrous (‖) ions are converted into iron (Ⅲ) ions. Weigh 1g of hexamethylenetetramine (template) and dissolve it in 5mL of water. Add this solution to the above reddish brown solution, adjust the speed to 200rpm and continue stirring for 20 minutes, then slowly add dilute ammonia water with a mass fraction of 12.5%, and at the same time bubble oxygen from the bottom of the solution (flow rate 2.5m 3 / h, 2min), ammonia water was added until the pH of the solution was 5, then stopped, a large amount of red-brown colloidal precipitation appeared, and it became a suspension state. At this time, 3 drops of liquid nitrogen (temperature was about -180 degrees Celsius) were added. The addition of oxygen made the ferrous ions oxidized more thoroughly. After a large amount of red-brown colloidal precipitation appeared, the addition of liquid nitrogen could make the solution temperature drop sharply, so that the precipitations adhered to each other to form flocs, reducing the loss rate of red iron oxide in the subsequent washing process.

[0016] Crystallization process: The above suspension is transferred to a hydrothermal reactor, which is placed in an oven and heated to 180°C and reacted for 5 hours, then taken out and naturally cooled to room temperature, centrifuged, and the obtained filtrate is evaporated and concentrated to obtain fertilizer-grade ammonium sulfate. The obtained filter residue is repeatedly washed with water and ethanol for 3 times, and kept at 70°C for 10 hours for drying, and finally ground to obtain high-purity nano-scale red iron oxide. After testing, the nano-scale red iron oxide prepared in this embodiment has a particle size of 30-55 nanometers and a purity of 99.8%.

[0017] Example 2 Washing process: 12g iron slag is placed in 65mL of 1.8M HCL solution, heated to 78°C in a water bath, stirred at 200rpm for 0.5h, then centrifuged and filtered. The residue is washed with high-purity water for 3 times to obtain iron slag with very little impurity content. The filtrate is adjusted to pH 10 with ammonia water, and centrifuged again. The residue is solid waste. The filtrate can be prepared into fertilizer-grade ammonium chloride after evaporation and concentration.

[0018] Dissolution process: Use 40mL of 10.5M H2SO4 solution to transfer the filter residue in the centrifuge tube to a beaker after oscillation and ultrasound, heat it in a water bath to 88°C, and stir at 150rpm for 1.5h. During this period, add reduced iron powder (6g in total) and co-solvent ammonium thiosulfate (3.74g in total) in 6 times. Reduced iron powder and auxiliary agent need to be added at the same time each time, and the amount and interval time of each addition are roughly equal. The last addition time is about 15min left from the end of the reaction. Then, take out the beaker, cool it naturally to room temperature, add 100mL of deionized water, stir it with a glass rod, and then stand at room temperature until no bubbles are generated, then centrifuge and filter, and the light green filtrate obtained is the ferrous sulfate solution.

[0019] Precipitation process: Weigh 26.85g of ammonium persulfate and add it to high-purity water to prepare a 2M solution. Then add the above ferrous sulfate solution to the ammonium persulfate solution while stirring at 100rpm. The solution gradually changes from light green to reddish brown, and the ferrous (‖) ions are converted into iron (Ⅲ) ions. Weigh 1g of hexamethylenetetramine (template) and dissolve it in 5mL of water. Add this solution to the above reddish brown solution, adjust the speed to 200rpm and continue stirring for 20 minutes, then slowly add dilute ammonia water with a mass fraction of 12.5%, and at the same time bubble oxygen from the bottom of the solution (flow rate 2.5m 3 / h, 2min), ammonia water is added until the solution pH = 5, then stopped, a large amount of red-brown colloidal precipitation appears, and it becomes a suspension state. At this time, 4 drops of liquid nitrogen (temperature is about -180 degrees Celsius) are added. Crystallization process: The above suspension is transferred to a hydrothermal reactor, which is placed in an oven and heated to 180°C and reacts for 5 hours, then taken out and naturally cooled to room temperature, centrifuged and filtered, and the filtrate obtained can be evaporated and concentrated to obtain fertilizer-grade ammonium sulfate. The obtained filter residue is repeatedly washed 3 times with water and ethanol, and kept at 70°C for 10 hours for drying, and finally ground to obtain high-purity nano-grade iron oxide red.

[0020] Comparative Example 1 The difference between this comparative example and Example 1 is that liquid nitrogen is not added in the last step of the precipitation process, and the other steps are consistent with Example 1. The test of Example 1 and this comparative example was repeated 3 times, and the average value was taken for comparison. As a result, it was found that the mass of the prepared nano iron oxide red was reduced by 4.89%.

[0021] The above description is only a preferred embodiment of the present invention and does not limit the present invention in other forms. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes and apply it to other fields. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing high-purity nano-grade red iron oxide from NdFeB recycled iron slag, characterized in that: Here are the steps: (1) adding iron slag to a hydrochloric acid solution, heating and stirring to react, centrifugally filtering after the reaction is completed, washing the filter residue with deionized water to obtain iron slag; adding ammonia water to the filtrate to adjust the pH to 10 and centrifugally filtering again to obtain a secondary filter residue and a secondary filtrate; evaporating and concentrating the secondary filtrate to obtain ammonium chloride; (2) adding sulfuric acid solution to the filter residue, heating and stirring to react, adding reduced iron powder and ammonium thiosulfate several times during the reaction; cooling to room temperature after the reaction, adding deionized water and stirring evenly, and then standing at room temperature until no bubbles are generated, centrifuging and filtering to obtain a light green ferrous sulfate solution; (3) Add the ferrous sulfate solution to the stirred ammonium persulfate solution, add the hexamethylenetetramine solution, stir for reaction, add dilute ammonia water, and then introduce oxygen until a large amount of red-brown colloidal precipitate appears to obtain a suspension, and then add liquid nitrogen dropwise; (4) The suspension is reacted at 175-185°C for at least 5 hours. After the reaction is completed, it is naturally cooled to room temperature and centrifuged. The filtrate is evaporated and concentrated to obtain fertilizer-grade ammonium sulfate. The filter residue is repeatedly washed with water and ethanol alternately for several times, dried and ground to obtain high-purity nano-grade iron oxide red.

2. The method for preparing high-purity nano-grade iron oxide red from NdFeB recycled iron slag according to claim 1, characterized in that: The heating temperature in step (1) is 70-80°C.

3. The method for preparing high-purity nano-grade iron oxide red from NdFeB recycled iron slag according to claim 1, characterized in that: In step (2), the concentration of the sulfuric acid solution is 10-11M, the heating and stirring reaction temperature is 85-88°C, the reaction time is 1.5-3h, and the mass ratio of iron slag: reduced iron powder: ammonium thiosulfate is (8-15): (4-6): (2-4).