Treatment process for removing impurities in neodymium iron boron oil sludge

Abstract

The invention discloses a treatment process for removing impurities in neodymium-iron-boron oil sludge. The treatment process comprises the following steps: step 1, sieving the neodymium-iron-boron oil sludge, washing the neodymium-iron-boron oil sludge in an organic mixed solution, and removing liquid; 2, washing in a weakly acidic mixed aqueous solution, and removing liquid; 3, washing in an alkaline mixed aqueous solution, and removing liquid; 4, washing in water, and removing liquid; and 5, washing in an organic solvent, removing liquid, and drying to obtain purified neodymium iron boron oil sludge powder. According to the treatment process, the neodymium-iron-boron oil sludge is sequentially cleaned through the organic mixed solution, the weakly acidic mixed aqueous solution, the alkaline mixed aqueous solution, the water and the organic solvent, impurity elements such as Si, Mn and Ca and impurity particles in the neodymium-iron-boron oil sludge can be effectively removed, and the treatment process is suitable for the technical field of preparation of regenerated neodymium-iron-boron magnetic powder.

Description

Technical Field

[0001] The invention belongs to the technical field of preparation of regenerated NdFeB magnetic powder, and in particular relates to a treatment process for removing impurities from NdFeB oil sludge. Background Art

[0002] NdFeB magnetic powder is known as the "king of magnets" for its excellent magnetic properties such as high coercivity, high remanence, and high magnetic energy product. It is the most widely used rare earth permanent magnet material in the market. With the rapid development of new energy vehicles, clean energy, consumer electronics and other industries, its market demand has grown rapidly. However, with the increase in market demand, rare earth prices have fluctuated dramatically, and NdFeB magnetic powder is facing great supply pressure. In addition, during the production process of NdFeB magnetic powder, a large amount of waste sludge will be generated in multiple processes such as cutting and grinding. If it is not properly disposed of, it will not only cause waste of resources, but also cause great environmental pollution. Therefore, the green and efficient recycling of NdFeB waste sludge can not only promote the recycling of resources, alleviate the supply pressure of NdFeB magnetic powder, promote the sustainable development of the country and the industry, but also protect the environment, with good economic and social benefits.

[0003] At present, the recycling processes of NdFeB sludge at home and abroad mainly include hydrometallurgical process and reduction diffusion method to prepare regenerated NdFeB magnetic powder. The former mainly includes acid dissolution precipitation process, double salt conversion process, hydrochloric acid optimal dissolution process and full extraction process, etc. The final products of these processes are rare earth oxides, not NdFeB magnetic powder, and the process flow is long, the cost is high, and a large amount of waste liquid is generated, so the economic benefit is low; the latter is to recover and clean the NdFeB sludge, and then prepare the regenerated NdFeB magnetic powder by calcium reduction diffusion, which has the characteristics of short process flow, low cost, green and environmental protection, and high economic benefit. However, in the process of preparing regenerated NdFeB magnetic powder by reduction diffusion method, the presence of impurity elements such as Si, Mn, and Ca in NdFeB sludge will have a very adverse effect on the magnetic properties of the regenerated NdFeB magnetic powder. Therefore, it is very important to remove impurity elements such as Si, Mn, and Ca as much as possible during the cleaning process of NdFeB sludge, which is very important for the subsequent preparation of NdFeB magnetic powder with excellent magnetic properties. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies in the above-mentioned prior art and provide a treatment process for removing impurities from NdFeB sludge. The treatment process uses an organic mixed solution, a weakly acidic mixed aqueous solution, an alkaline mixed aqueous solution, water and an organic solvent to sequentially clean the NdFeB sludge, thereby effectively removing impurity elements and impurity particles such as Si, Mn, and Ca in the NdFeB sludge, and greatly reducing the adverse effects of impurity elements such as Si, Mn, and Ca on the magnetic properties of the regenerated NdFeB magnetic powder.

[0005] To achieve the above object, the technical solution adopted by the present invention is: a treatment process for removing impurities from NdFeB sludge, characterized in that the process comprises the following steps: Step 1, sieving the NdFeB sludge and placing it in an organic mixed solution for washing, and removing the liquid to obtain the first NdFeB sludge; Step 2: washing the first NdFeB oil sludge obtained in step 1 in a weakly acidic mixed aqueous solution, and removing the liquid to obtain a second NdFeB oil sludge; Step 3, washing the second NdFeB oil sludge obtained in step 2 in an alkaline mixed aqueous solution, and removing the liquid to obtain a third NdFeB oil sludge; Step 4, washing the third NdFeB oil sludge obtained in step 3 in water, and removing the liquid to obtain a fourth NdFeB oil sludge; Step 5: Wash the fourth NdFeB sludge obtained in step 4 in an organic solvent, remove the liquid and dry it to obtain purified NdFeB sludge powder.

[0006] The present invention first removes impurities with larger particle sizes in the NdFeB sludge by screening and preliminarily disperses the NdFeB sludge. Secondly, organic substances and other impurities soluble in organic solvents in the NdFeB sludge are preliminarily removed by washing with an organic mixed solution, and the particle dispersibility of the NdFeB sludge is improved to facilitate subsequent impurity removal treatment. Then, weakly acidic mixed aqueous solution and alkaline mixed aqueous solution are sequentially used for washing to remove acid- and alkali-soluble impurities in the NdFeB sludge. Water is then used for washing to remove residual washing liquid and water-soluble impurities in the aforementioned steps, and organic solvent is used for washing to remove residual water and impurities soluble in organic solvents in the NdFeB sludge. Finally, drying is performed to complete the impurity removal treatment of the NdFeB sludge.

[0007] The specific process of removing liquid in each step of the present invention is: tilting the container to discharge the liquid from the top of the container to prevent the impurity elements dissolved in the upper layer of liquid from contacting the NdFeB oil sludge at the bottom layer again and being re-absorbed by the NdFeB oil sludge.

[0008] The above-mentioned treatment process for removing impurities from NdFeB sludge is characterized in that the screening in step one uses a 400-600 mesh stainless steel screen.

[0009] The present invention can preliminarily disperse the NdFeB oil sludge by controlling the aperture of the stainless steel screen, which is conducive to the mutual contact between the NdFeB oil sludge and the cleaning liquid, thereby improving the impurity removal efficiency.

[0010] The above-mentioned treatment process for removing impurities from NdFeB sludge is characterized in that the washing in steps 1 to 5 is carried out by ultrasonic washing.

[0011] The present invention adopts ultrasonic cleaning in each cleaning step, which can reduce the agglomeration of NdFeB sludge particles, make the impurity elements adsorbed in the NdFeB sludge and the impurity particles with low density more easily enter the cleaning liquid, and then remove the impurity elements and impurity particles by removing the liquid, which is beneficial to improve the cleaning efficiency and quality.

[0012] The above-mentioned treatment process for removing impurities from NdFeB sludge is characterized in that the organic mixed solution in step one includes ethanol, sodium tripolyphosphate and OP-10, the mass concentration of sodium tripolyphosphate in the organic mixed solution is 0.1%~0.5%, and the mass concentration of OP-10 in the organic mixed solution is 1.4%~2.0%.

[0013] The present invention adopts sodium tripolyphosphate and OP-10 (alkylphenol polyoxyethylene ether), and mixes an ionic surfactant (sodium tripolyphosphate) with a non-ionic surfactant (OP-10), so as to further improve the dispersibility of NdFeB sludge particles, facilitate the contact of impurity elements with the cleaning liquid, and thus improve the removal efficiency.

[0014] The present invention uses ethanol to remove organic substances in the NdFeB oil sludge and prevents the organic substances from agglomerating the NdFeB oil sludge particles, thereby improving the dispersibility of the NdFeB oil sludge particles.

[0015] The above-mentioned treatment process for removing impurities from NdFeB sludge is characterized in that the weakly acidic mixed aqueous solution in step 2 is a mixture of water, ammonium chloride, sodium tripolyphosphate and OP-10, the mass concentration of sodium tripolyphosphate in the weakly acidic mixed aqueous solution is 0.2%~0.5%, the mass concentration of OP-10 in the weakly acidic mixed aqueous solution is 1.4%~2.0%, and the concentration of ammonium chloride in the weakly acidic mixed aqueous solution is 1.0 mol / L.

[0016] The invention adopts ammonium chloride to provide a weakly acidic environment, thereby being able to remove oxides in the NdFeB sludge and impurities soluble in the acidic environment.

[0017] The above-mentioned treatment process for removing impurities from NdFeB sludge is characterized in that the alkaline mixed aqueous solution in step three is a mixture of water, sodium hydroxide, sodium tripolyphosphate and OP-10, the concentration of sodium hydroxide in the alkaline mixed aqueous solution is 1.0 mol / L~3.0 mol / L, the mass concentration of sodium tripolyphosphate in the alkaline mixed aqueous solution is 0.2%~0.5%, and the mass concentration of OP-10 in the alkaline mixed aqueous solution is 1.4%~2.0%.

[0018] The invention adopts sodium hydroxide to provide an alkaline environment, thereby being able to remove organic impurities in the NdFeB oil sludge and some impurities soluble in the alkaline environment.

[0019] The above-mentioned treatment process for removing impurities from NdFeB sludge is characterized in that the water in step 4 is ultrapure water.

[0020] The above-mentioned treatment process for removing impurities from NdFeB sludge is characterized in that the organic solvent in step five is anhydrous ethanol.

[0021] The present invention adopts anhydrous ethanol as a cleaning liquid, so as to remove the residual water in the NdFeB sludge in the previous impurity removal step, thereby facilitating subsequent drying and preventing water from corroding and damaging the NdFeB sludge during the drying process.

[0022] The above-mentioned treatment process for removing impurities from NdFeB sludge is characterized in that the drying in step five is vacuum drying, the drying temperature is 50°C~70°C, and the drying time is 16h~24h.

[0023] Compared with the prior art, the present invention has the following advantages: 1. The present invention uses an organic mixed solution, a weakly acidic mixed aqueous solution, an alkaline mixed aqueous solution, water and an organic solvent to clean the NdFeB sludge in sequence, thereby effectively removing impurity elements such as Si, Mn, and Ca from the NdFeB sludge; by selecting a weakly acidic mixed aqueous solution, it is possible to avoid corrosion damage to the NdFeB sludge particles while ensuring the impurity removal effect, which is beneficial to the subsequent preparation of regenerated NdFeB magnetic powder.

[0024] 2. The treatment process of the present invention is simple, stable, and highly operable, and the entire treatment process does not require heating, which can avoid high temperatures during the treatment process, thereby promoting the oxidation of the NdFeB sludge and the reaction between it and the cleaning solution, which will cause corrosion damage to the NdFeB sludge powder.

[0025] 3. The present invention mixes an ionic surfactant with a non-ionic surfactant, which can overcome the dispersion limitation caused by one surfactant, can disperse different types of particles and impurities, and improve the impurity removal efficiency; by controlling the concentration of sodium tripolyphosphate and OP-10, the removal efficiency of impurity elements such as Si, Mn, and Ca in the NdFeB sludge can be controlled; at the same time, sodium tripolyphosphate can also form soluble chelates with some impurity metal ions in the NdFeB sludge, which are removed with the liquid after washing.

[0026] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a SEM image of the purified NdFeB sludge powder obtained in Example 1 of the present invention.

[0028] Figure 2This is the XRD diagram of the purified NdFeB sludge powder obtained in Example 1 of the present invention.

[0029] Figure 3 This is a SEM image of the purified NdFeB sludge powder obtained in Example 2 of the present invention.

[0030] Figure 4 This is the XRD diagram of the purified NdFeB sludge powder obtained in Example 2 of the present invention.

[0031] Figure 5 This is a SEM image of the purified NdFeB sludge powder obtained in Comparative Example 1 of the present invention.

[0032] Figure 6 This is the XRD diagram of the purified NdFeB sludge powder obtained in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0033] Example 1 The processing process of this embodiment includes the following steps: Step 1, weigh 20g of NdFeB sludge sieved through a 500-mesh stainless steel sieve, and then place it in 50mL of an organic mixed solution consisting of ethanol, sodium tripolyphosphate and OP-10 for 5 times of ultrasonic washing, and remove the liquid to obtain a first NdFeB sludge; the mass concentration of sodium tripolyphosphate in the organic mixed solution is 0.5%, and the mass concentration of OP-10 in the organic mixed solution is 1.5%; Step 2: Place the first NdFeB sludge obtained in step 1 in 50 mL of a weakly acidic mixed aqueous solution consisting of ammonium chloride, sodium tripolyphosphate and OP-10, and perform ultrasonic washing for 5 times to remove the liquid to obtain a second NdFeB sludge; the concentration of ammonium chloride in the weakly acidic mixed aqueous solution is 1.0 mol / L, the mass concentration of sodium tripolyphosphate in the weakly acidic mixed aqueous solution is 0.5%, and the mass concentration of OP-10 in the weakly acidic mixed aqueous solution is 1.5%; Step 3: Place the second NdFeB sludge obtained in step 2 in 100 mL of an alkaline mixed aqueous solution consisting of sodium hydroxide, sodium tripolyphosphate and OP-10, perform ultrasonic washing 10 times, and remove the liquid to obtain a third NdFeB sludge; the concentration of sodium hydroxide in the alkaline mixed aqueous solution is 1.0 mol / L, the mass concentration of sodium tripolyphosphate in the alkaline mixed aqueous solution is 0.5%, and the mass concentration of OP-10 in the alkaline mixed aqueous solution is 1.5%; Step 4: Place the third NdFeB oil sludge obtained in step 3 in 100 mL of ultrapure water and perform ultrasonic washing 10 times to remove the liquid to obtain a fourth NdFeB oil sludge; Step 5: Place the fourth NdFeB sludge obtained in step 4 in 50 mL of anhydrous ethanol and perform ultrasonic washing for 5 times. After removing the liquid, place it in a vacuum drying oven and dry it at 50° C. for 24 hours to obtain purified NdFeB sludge powder.

[0034] The purified NdFeB oil sludge powder obtained in this example was subjected to microscopic analysis. Figure 1 As shown in FIG. 1 , the purified NdFeB oil sludge powder has small particles and good dispersibility; XRD analysis of the purified NdFeB oil sludge powder is performed, as shown in FIG. Figure 2 As shown, the NdFeB phase in the purified NdFeB sludge powder is well preserved and is not significantly corroded or oxidized.

[0035] After testing, the purified NdFeB sludge powder obtained in this embodiment contains the following mass fractions of impurity elements: Si 0.044%, Mn 0.078%, and Ca 0.018%.

[0036] Example 2 The processing process of this embodiment includes the following steps: Step 1, weigh 20g of NdFeB sludge sieved through a 400-mesh stainless steel sieve, and then place it in 50mL of an organic mixed solution consisting of ethanol, sodium tripolyphosphate and OP-10 for 5 times of ultrasonic washing, and remove the liquid to obtain a first NdFeB sludge; the mass concentration of sodium tripolyphosphate in the organic mixed solution is 0.1%, and the mass concentration of OP-10 in the organic mixed solution is 1.4%; Step 2: Place the first NdFeB sludge obtained in step 1 in a weakly acidic mixed aqueous solution consisting of ammonium chloride, sodium tripolyphosphate and OP-10, perform ultrasonic washing for 5 times, and remove the liquid to obtain a second NdFeB sludge; the concentration of ammonium chloride in the weakly acidic mixed aqueous solution is 1.0 mol / L, the mass concentration of sodium tripolyphosphate in the weakly acidic mixed aqueous solution is 0.4%, and the mass concentration of OP-10 in the weakly acidic mixed aqueous solution is 1.4%; Step 3: Place the second NdFeB sludge obtained in step 2 in an alkaline mixed aqueous solution consisting of sodium hydroxide, sodium tripolyphosphate and OP-10, and perform ultrasonic washing 10 times to remove the liquid to obtain a third NdFeB sludge; the concentration of sodium hydroxide in the alkaline mixed aqueous solution is 2.0 mol / L, the mass concentration of sodium tripolyphosphate in the alkaline mixed aqueous solution is 0.4%, and the mass concentration of OP-10 in the alkaline mixed aqueous solution is 1.4%; Step 4: placing the third NdFeB oil sludge obtained in step 3 in 100 mL of ultrapure water for 10 times of ultrasonic washing, and removing the liquid to obtain a fourth NdFeB oil sludge; Step 5: Place the fourth NdFeB sludge obtained in step 4 in 50 mL of anhydrous ethanol and perform ultrasonic washing for 5 times. After removing the liquid, place it in a vacuum drying oven and dry it at 60° C. for 20 hours to obtain purified NdFeB sludge powder.

[0037] The purified NdFeB oil sludge powder obtained in this example was subjected to microscopic analysis. Figure 3 As shown in FIG. 1 , the purified NdFeB oil sludge powder has small particles and good dispersibility; XRD analysis of the purified NdFeB oil sludge powder is performed, as shown in FIG. Figure 4 As shown, the NdFeB phase in the purified NdFeB sludge powder is well maintained and is not significantly corroded or oxidized. After testing, the purified NdFeB sludge powder obtained in this embodiment contains the following mass fractions of impurity elements: Si 0.095%, Mn 0.168%, and Ca 0.024%.

[0038] Comparative Example 1 The processing technology of this comparative example comprises the following steps: Step 1, weigh 20g of NdFeB sludge sieved through a 200-mesh stainless steel sieve, and then place it in 50mL of an organic mixed solution consisting of ethanol and OP-10 for 5 times of ultrasonic washing, and remove the liquid to obtain a first NdFeB sludge; the mass concentration of OP-10 in the organic mixed solution is 2.0%; Step 2: Place the first NdFeB sludge obtained in step 1 in 50 mL of an acidic aqueous solution consisting of acetic acid and OP-10 and perform ultrasonic washing 5 times to remove the liquid to obtain a second NdFeB sludge; the volume concentration of acetic acid in the acidic aqueous solution is 1.0%, and the mass concentration of OP-10 in the acidic aqueous solution is 2.0%; Step 3: Place the second NdFeB sludge obtained in step 2 in 100 mL of an alkaline aqueous solution consisting of sodium hydroxide and OP-10, perform ultrasonic washing 10 times, and remove the liquid to obtain a third NdFeB sludge; the concentration of sodium hydroxide in the alkaline aqueous solution is 3.0 mol / L, and the mass concentration of OP-10 in the alkaline aqueous solution is 2.0%; Step 4: placing the third NdFeB oil sludge obtained in step 3 in 100 mL of ultrapure water for 10 times of ultrasonic washing, and removing the liquid to obtain a fourth NdFeB oil sludge; Step 5: Place the fourth NdFeB sludge obtained in step 4 in 50 mL of anhydrous ethanol and perform ultrasonic washing for 5 times. After removing the liquid, place it in a vacuum drying oven and dry it at 80° C. for 12 hours to obtain purified NdFeB sludge powder.

[0039] The purified NdFeB oil sludge powder obtained in this comparative example was subjected to microscopic analysis. Figure 5As shown, the purified NdFeB sludge powder has larger particles and poorer dispersibility than the purified NdFeB sludge powder obtained in Example 1; the purified NdFeB sludge powder obtained in this comparative example was subjected to XRD analysis, as shown Figure 6 As shown, the NdFeB phase in the purified NdFeB sludge powder is obviously corroded and oxidized; after testing, the purified NdFeB sludge powder obtained in this comparative example contains the following mass fractions of impurity elements: Si 0.186%, Mn 0.272%, Ca 0.044%.

[0040] In this comparative example, a 200-mesh stainless steel screen with a larger aperture is used for screening, resulting in the presence of larger impurity particles in the NdFeB sludge after screening. The 200-mesh stainless steel screen has a larger aperture, and the effect of preliminary dispersion of the agglomerated NdFeB sludge is not good, resulting in some impurities being wrapped in the NdFeB sludge and not easy to remove; at the same time, the large particles of the NdFeB sludge reduce the contact area with the cleaning solution, which is not conducive to the removal of impurity elements; sodium tripolyphosphate is not added to the solution of each step, resulting in a decrease in the dispersibility of the NdFeB sludge particles, thereby resulting in poor removal of impurity elements; in addition, acetic acid is used for impurity removal in step 2 of this comparative example, and the acidity of acetic acid is stronger than that of ammonium chloride used in Example 1, which can easily cause corrosion and destruction of the NdFeB phase.

[0041] Example 3 The processing process of this embodiment includes the following steps: Step 1, weigh 20g of NdFeB sludge sieved through a 600-mesh stainless steel sieve, and then place it in 50mL of an organic mixed solution consisting of ethanol, sodium tripolyphosphate and OP-10 for 5 times of ultrasonic washing, and remove the liquid to obtain a first NdFeB sludge; the mass concentration of sodium tripolyphosphate in the organic mixed solution is 0.2%, and the mass concentration of OP-10 in the organic mixed solution is 2.0%; Step 2: Place the first NdFeB sludge obtained in step 1 in 50 mL of a weakly acidic mixed aqueous solution consisting of ammonium chloride, sodium tripolyphosphate and OP-10, and perform ultrasonic washing for 5 times to remove the liquid to obtain a second NdFeB sludge; the concentration of ammonium chloride in the weakly acidic mixed aqueous solution is 1.0 mol / L, the mass concentration of sodium tripolyphosphate in the weakly acidic mixed aqueous solution is 0.2%, and the mass concentration of OP-10 in the weakly acidic mixed aqueous solution is 2.0%; Step 3: Place the second NdFeB sludge obtained in step 2 in 100 mL of an alkaline mixed aqueous solution consisting of sodium hydroxide, sodium tripolyphosphate and OP-10, and perform ultrasonic washing 10 times to remove the liquid to obtain a third NdFeB sludge; the concentration of sodium hydroxide in the alkaline mixed aqueous solution is 3.0 mol / L, the mass concentration of sodium tripolyphosphate in the alkaline mixed aqueous solution is 0.2%, and the mass concentration of OP-10 in the alkaline mixed aqueous solution is 2.0%; Step 4: placing the third NdFeB oil sludge obtained in step 3 in 100 mL of ultrapure water for 10 times of ultrasonic washing, and removing the liquid to obtain a fourth NdFeB oil sludge; Step 5: Place the fourth NdFeB sludge obtained in step 4 in 50 mL of anhydrous ethanol and perform ultrasonic washing for 5 times. After removing the liquid, place it in a vacuum drying oven and dry it at 70° C. for 16 hours to obtain purified NdFeB sludge powder.

[0042] After testing, the purified NdFeB sludge powder obtained in this embodiment has small particles, good dispersibility, and is not significantly corroded or oxidized; the purified NdFeB sludge powder obtained in this embodiment contains the following mass fractions of impurity elements: Si 0.048%, Mn 0.084%, and Ca 0.026%.

[0043] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent structural transformation made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A process for removing impurities from NdFeB sludge, characterized in that: The process includes the following steps: Step 1, sieving the NdFeB sludge and placing it in an organic mixed solution for washing, and removing the liquid to obtain the first NdFeB sludge; Step 2: washing the first NdFeB oil sludge obtained in step 1 in a weakly acidic mixed aqueous solution, and removing the liquid to obtain a second NdFeB oil sludge; Step 3, washing the second NdFeB oil sludge obtained in step 2 in an alkaline mixed aqueous solution, and removing the liquid to obtain a third NdFeB oil sludge; Step 4, washing the third NdFeB oil sludge obtained in step 3 in water, and removing the liquid to obtain a fourth NdFeB oil sludge; Step 5: Wash the fourth NdFeB sludge obtained in step 4 in an organic solvent, remove the liquid and dry it to obtain purified NdFeB sludge powder.

2. A process for removing impurities from NdFeB sludge according to claim 1, characterized in that: The sieving in step 1 uses a stainless steel sieve of 400-600 mesh.

3. A process for removing impurities from NdFeB sludge according to claim 1, characterized in that: The washing in step 1 to step 5 is all done by ultrasonic washing.

4. A process for removing impurities from NdFeB sludge according to claim 1, characterized in that: The organic mixed solution in step 1 includes ethanol, sodium tripolyphosphate and OP-10, the mass concentration of sodium tripolyphosphate in the organic mixed solution is 0.1% to 0.5%, and the mass concentration of OP-10 in the organic mixed solution is 1.4% to 2.0%.

5. A process for removing impurities from NdFeB sludge according to claim 1, characterized in that: The weakly acidic mixed aqueous solution in step 2 is a mixture of water, ammonium chloride, sodium tripolyphosphate and OP-10, the mass concentration of sodium tripolyphosphate in the weakly acidic mixed aqueous solution is 0.2% to 0.5%, the mass concentration of OP-10 in the weakly acidic mixed aqueous solution is 1.4% to 2.0%, and the concentration of ammonium chloride in the weakly acidic mixed aqueous solution is 1.0 mol / L.

6. A process for removing impurities from NdFeB sludge according to claim 1, characterized in that: The alkaline mixed aqueous solution in step 3 is a mixture of water, sodium hydroxide, sodium tripolyphosphate and OP-10, the concentration of sodium hydroxide in the alkaline mixed aqueous solution is 1.0 mol / L~3.0 mol / L, the mass concentration of sodium tripolyphosphate in the alkaline mixed aqueous solution is 0.2%~0.5%, and the mass concentration of OP-10 in the alkaline mixed aqueous solution is 1.4%~2.0%.

7. A process for removing impurities from NdFeB sludge according to claim 1, characterized in that: The water described in step 4 is ultrapure water.

8. The process for removing impurities from NdFeB sludge according to claim 1, characterized in that: The organic solvent in step 5 is anhydrous ethanol.

9. A process for removing impurities from NdFeB sludge according to claim 1, characterized in that: The drying in step 5 is vacuum drying, the drying temperature is 50° C. to 70° C., and the drying time is 16 h to 24 h.

Images