A method for recycling acid-soluble residue from NdFeB waste

Abstract

This paper discloses a method for recycling NdFeB waste acid leaching residue. In this method, the acid leaching solution of the NdFeB waste acid leaching residue is used to separate iron from rare earth / cobalt through selective precipitation, yielding battery-grade iron phosphate and precipitates enriched with rare earth, cobalt, and other metal elements. Compared with other recycling processes, the technical solution presented in this paper yields iron phosphate with higher value, achieves efficient enrichment and recovery of rare earth and cobalt metal elements from NdFeB waste acid leaching residue, improves the overall recycling efficiency of NdFeB waste acid leaching residue in industry, significantly reduces the emission of NdFeB waste acid leaching residue, reduces stockpiling costs, and is a green recycling method that is environmentally friendly.

Description

Technical Field

[0001] This invention belongs to the field of NdFeB waste recycling, specifically relating to a method for recycling acid-soluble residue from NdFeB waste. Background Technology

[0002] During the production and use of NdFeB (neodymium iron boron) materials, approximately 20% NdFeB waste is generated due to various production process factors. NdFeB materials contain about 30% rare earth elements (approximately 90% praseodymium and neodymium, with the remainder being terbium, dysprosium, and other rare earth elements). As the production of NdFeB waste gradually increases, the hydrochloric acid dissolution method is commonly used industrially to extract and recover the rare earth elements. Generally, after the NdFeB waste is roasted, ground, and then dissolved in hydrochloric acid in a container, followed by pressure filtration, rare earth chloride filtrate and filter residue are produced. The filter residue is commonly referred to as NdFeB waste acid dissolution residue. The main component of NdFeB waste acid dissolution residue is Fe2O3 / Fe(OH)3, with 0.5%-1% rare earth elements and cobalt residue. Currently, the acid dissolution residue is generally sent to steel plants for recycling, which is economically inefficient, and the high-value rare earth elements and cobalt in the residue are not recovered, resulting in resource waste.

[0003] Currently, some researchers have begun studying acid-soluble slag to improve its comprehensive utilization value. For example, in their paper "Preparation of Manganese-Zn Ferrite from NdFeB Waste Slag: Research on Preparing Mn-Zn Ferrite Micropowder from Waste Slag After Rare Earth Extraction from NdFeB Waste," Zhong Xiaolin and Song Ning used NdFeB waste acid-soluble slag as raw material and obtained manganese-zinc ferrite micropowder through leaching, impurity removal, and co-precipitation, thus achieving high-value utilization of iron. Patent document CN107055627A uses a combination of hydrochloric acid complete dissolution and extraction / hydrothermal methods to recover iron from NdFeB acid-soluble slag and prepare nano-iron oxide red. However, the above studies only recovered the main element iron from the acid-soluble slag and did not recover the more expensive rare earth elements, thus failing to maximize the benefits of the acid-soluble slag. Furthermore, in his paper "Research on Comprehensive Recycling Technology of Secondary Waste from Neodymium Iron Boron Magnetic Materials," Wu Mian used a hydrochloric acid complete dissolution method to transfer the metal into a solution, then prepared β-FeOOH through Fe hydrolysis, and obtained iron oxide red with a purity of 98.01% after calcination. After hydrolysis, the solution was used as a precipitant to precipitate and recover rare earth elements and cobalt stepwise. Patent publication number CN115074530A describes a method using hydrochloric acid leaching, with sodium sulfide and sodium bicarbonate as precipitants to enrich and recover rare earth elements and cobalt, finally preparing iron oxide red through spray pyrolysis. While these processes achieve comprehensive recovery of iron, cobalt, and rare earth elements, the recovery rates of rare earth and cobalt are not high, and the purity and value of the obtained iron oxide red and other products are not high, indicating that economic benefits need further improvement.

[0004] The comprehensive recovery of acid slag generated during the recycling of NdFeB waste is a pressing technical problem. How to separate rare earth / cobalt and other elements from iron in the acid slag while simultaneously recycling and maximizing the value of iron, and recovering and enriching high-value rare earth and cobalt metals, in order to reduce the accumulation of acid slag and improve the recycling efficiency of industrial waste, has become an urgent technical problem to be solved. Summary of the Invention

[0005] In response to the problems of low value of iron element recycling and inefficient recovery of rare earth / cobalt elements in the acid leaching slag of NdFeB waste mentioned above, this paper will provide a method for recycling NdFeB waste acid leaching slag.

[0006] To achieve the above objectives, the following technical solutions are specifically included:

[0007] A method for recycling acid-soluble residue from NdFeB waste includes the following steps:

[0008] Acid leaching: The acid-soluble residue of NdFeB waste is leached countercurrently using hydrochloric acid solution. After solid-liquid separation, the leachate is obtained.

[0009] First iron precipitation: Add ferric hydroxide to the leachate to adjust the pH of the leachate to 1-2, add organic acid, and then add phosphate for precipitation and aging. After solid-liquid separation, ferric phosphate and primary filtrate are obtained.

[0010] Second iron precipitation: The pH of the primary filtrate is adjusted to 3.5-4 under an oxidizing atmosphere and precipitation is carried out. After solid-liquid separation, precipitate residue and secondary filtrate are obtained.

[0011] Enrichment of cobalt and rare earth elements: The pH of the secondary filtrate is adjusted to 4-6 using sodium carbonate and / or sodium bicarbonate to induce precipitation. After solid-liquid separation, a precipitate enriched with cobalt and rare earth elements is obtained.

[0012] The technical solution provided in this paper utilizes the pH difference between iron ions and other metal ions in the presence of phosphate to produce phosphate precipitates, thereby achieving efficient separation of iron, cobalt / rare earth elements from the acid leaching solution of NdFeB waste slag. This yields high-purity iron phosphate and precipitates enriched with cobalt and rare earth elements. This high-purity iron phosphate can be used as a precursor for the preparation of lithium iron phosphate, possessing high value. Furthermore, the precipitate enriched with cobalt and rare earth elements is a carbonate precipitate, which is easily redissolved by acid, facilitating subsequent re-separation and recovery. It also benefits subsequent sales and transportation. Therefore, the form of this precipitate enriched with cobalt and rare earth elements (praseodymium, neodymium, terbium, dysprosium, etc.) is more conducive to the recycling of rare earth elements.

[0013] Adding a certain amount of ferric hydroxide to the leachate serves two purposes: firstly, to control the pH, and secondly, to increase the concentration of iron in the leachate, thereby widening the concentration gap between the main Fe element and the impurity elements.

[0014] Separating trivalent iron from rare earth elements / cobalt is relatively difficult. Adding ferric hydroxide to the leachate to control the pH of the system to 1-2 is necessary. If the pH exceeds this range, not only will ferric phosphate be produced, but also ferric hydroxide precipitate, forming a mixture of ferric phosphate and ferric hydroxide. This reduces the purity of the ferric phosphate, making separation of the two even more difficult, rendering it unusable as a commercially viable product. Further processing is required to obtain an economically valuable iron product. Simultaneously, this results in a significant loss rate of rare earth elements / cobalt, exceeding 20%, reducing the content of valuable metals in the enriched rare earth / cobalt precipitate and lowering its value.

[0015] In the second iron precipitation, the pH of the solution system is adjusted to 3.5-4.5. At this time, the iron in the filtrate can completely precipitate with the phosphate ions and hydroxide ions in the solution in the form of iron phosphate and goethite, respectively, which can fully recover and remove the remaining iron elements in the filtrate. After filtration, the filter residue is returned to the acid leaching process, which can make full use of hydrochloric acid and reduce the acidity of the leachate to leach the iron source.

[0016] In the enrichment of cobalt and rare earth elements, adjusting the pH of the solution system to 4-6 using sodium bicarbonate and / or sodium carbonate can better enrich and precipitate cobalt and rare earth elements.

[0017] In acid leaching, the countercurrent leaching of NdFeB waste acid-soluble residue using hydrochloric acid solution specifically includes the following steps:

[0018] First leaching: The acid-soluble residue of NdFeB waste is leached countercurrently using hydrochloric acid solution. After solid-liquid separation, the first leaching residue and the first leaching solution are obtained.

[0019] First leaching: The first leaching solution is then mixed with new NdFeB waste acid leaching residue for countercurrent leaching. After solid-liquid separation, a second leaching residue and a second leaching solution are obtained.

[0020] A typical single leaching process leaves a large amount of residual acid in the leachate. However, by using a double leaching process and adding fresh NdFeB waste acid leaching residue, the acid in the first leaching solution is consumed until the pH is around 0.1-0.3. At the same time, the iron concentration in the leachate can be increased from about 80-90 g / L to about 110-150 g / L. This not only makes full use of the acid, allowing the metal elements in the NdFeB waste acid leaching residue to be fully leached out, but also results in the leachate mainly containing FeCl3 and small amounts of Co and rare earth elements. Furthermore, it makes it easier to adjust the pH of the leachate to a pH value that is conducive to subsequent precipitation, without the need to add excessive pH adjustment reagents.

[0021] In one embodiment, during acid leaching, the mass concentration of the NdFeB waste acid-soluble residue in hydrochloric acid is 50-300 g / L.

[0022] In one embodiment, during acid leaching, the temperature of the countercurrent leaching is 60-100°C, and the time of the countercurrent leaching is 1-10 hours.

[0023] In one embodiment, before adding organic acid, the concentration of iron in the leaching is adjusted to 0.5-1.5 mol / L during the first iron precipitation process, wherein the adjustment is performed by dilution or concentration.

[0024] The iron concentration in the leachate is adjusted to 0.5-1.5 mol / L by dilution or concentration. At this concentration, the iron ion concentration is suitable, which is more conducive to the precipitation of iron in the form of ferric phosphate.

[0025] In one embodiment, before adding phosphate for precipitation, the first iron precipitation process further includes adding iron dihydrate seed crystals to the leachate, wherein the mass concentration of the iron dihydrate seed crystals in the leachate is 5-10%.

[0026] Before adding phosphate for precipitation, the process also includes adding ferric phosphate dihydrate seed crystals to the leachate. These seed crystals can induce the formation of ferric phosphate precipitate, improve crystallinity, and induce the ferric phosphate precipitate to form a specific morphology, thereby achieving the purpose of controlling the growth of ferric phosphate.

[0027] In one embodiment, during the first iron precipitation, the concentration of the organic acid in the leachate is 0.004-0.02 mol / L.

[0028] In one embodiment, during the first iron deposition, the organic acid includes at least one of sulfosalicylic acid, histidine, oxalic acid, and triammonium citrate.

[0029] Organic acids can complex with impurity ions to increase the pH of phosphoric acid precipitation, which can effectively prevent the introduction of impurity ions into ferric phosphate.

[0030] In one embodiment, during the first iron precipitation, the phosphate includes at least one of ammonium hydrogen phosphate and ammonium dihydrogen phosphate.

[0031] In one embodiment, during the first iron precipitation, the molar concentration of phosphate is 1.1-1.3 times the molar concentration of iron.

[0032] In one embodiment, the aging time in the first immersion iron is 3-6 hours.

[0033] Aging increases the precipitation rate of iron and improves the crystal form of the precipitate. At the same time, it allows ferric ions to exchange with some of the impurity ions adsorbed by ferric phosphate dihydrate, thereby reducing the impurity content in ferric phosphate dihydrate and improving the purity of ferric phosphate precipitation.

[0034] In one embodiment, the ferric phosphate contains water of crystallization in the first iron precipitation, and the ferric phosphate is further calcined at 550-800°C for 1-3 hours.

[0035] In one embodiment, the calcined iron phosphate comprises the following elements in mass percentage: Fe 35.7-36.7%, P 20.0-21.1%, Ca ≤0.01%, Mg ≤0.06%, Na ≤0.02%, Al ≤0.05%, S ≤0.03%, Co ≤0.006%, rare earth elements ≤0.03%, and the molar ratio of Fe to P is Fe / P = 0.96-1.0.

[0036] The elemental composition of the calcined anhydrous iron phosphate is within the range mentioned above. This purity meets the purity requirements for use as a precursor raw material for lithium iron phosphate, and it can be used to prepare lithium iron phosphate, resulting in high product application value.

[0037] In one embodiment, during the second iron deposition, the oxidizing atmosphere is an oxygen-containing gas; the oxygen-containing gas is air.

[0038] In one embodiment, during the second iron precipitation, the reagent used to adjust the pH of the first filtrate is at least one of sodium hydroxide, potassium hydroxide, and sodium carbonate.

[0039] In one embodiment, during the second iron precipitation, the precipitation time is 2-5 hours, and the precipitation is carried out while stirring.

[0040] In one embodiment, the cobalt and rare earth elements are enriched, and the precipitation time is 0.5-5 hours, while the precipitation is being carried out with stirring.

[0041] Compared with related technologies, this invention has the following advantages: By selectively precipitating the acid leaching solution of NdFeB waste acid leaching residue, iron is separated from rare earth / cobalt to obtain battery-grade iron phosphate product. Compared with other recycling processes, the recovered iron phosphate product has a higher value. At the same time, it achieves efficient enrichment and recovery of rare earth and cobalt metal elements in NdFeB waste acid leaching residue, improves the overall recycling efficiency of NdFeB waste acid leaching residue in industry, greatly reduces the emission of NdFeB waste acid leaching residue, reduces stockpiling costs, and is a green recycling method that is environmentally friendly. Attached Figure Description

[0042] Figure 1 This is a flowchart illustrating the recycling and utilization of NdFeB waste acid leaching residue.

[0043] Figure 2 The image shows the XRD pattern of anhydrous iron phosphate from Example 1.

[0044] Figure 3This is a particle size distribution diagram of anhydrous ferric phosphate in Example 1.

[0045] Figure 4 This is a SEM image of anhydrous iron phosphate from Example 1, magnified 5000 times.

[0046] Figure 5 The image shown is a SEM image of anhydrous iron phosphate from Example 1, magnified at 50,000x.

[0047] Figure 6 The image shows the XRD pattern of anhydrous iron phosphate in Example 3.

[0048] Figure 7 This is a particle size distribution diagram of anhydrous ferric phosphate in Example 3.

[0049] Figure 8 This is a SEM image of anhydrous iron phosphate from Example 3, magnified 5000 times.

[0050] Figure 9 This is a SEM image of anhydrous iron phosphate from Example 3, magnified at 50,000x. Detailed Implementation

[0051] The technical solutions in the embodiments of this article will be clearly and completely described below. Obviously, the described embodiments are only some of the embodiments in this article, and not all of the embodiments.

[0052] The NdFeB waste acid dissolution residue used below all comes from a NdFeB waste recycling company in Ganzhou, Jiangxi.

[0053] The following solutions and precipitates were tested using ICP to determine the content of iron, cobalt, Al, Si, and rare earth elements. The precipitates needed to be completely dissolved in an acidic solution before measurement. The iron content in the solution was determined by potassium dichromate titration. The phosphorus content in the iron phosphate precipitate was determined using the quinomolybdate-limonene gravimetric method, and the molar ratio of Fe to P was calculated.

[0054] The rare earth elements referred to in this article include praseodymium, neodymium, terbium, and dysprosium.

[0055] Example 1

[0056] The specific steps of the method for recycling acid-soluble residue from NdFeB waste in this embodiment are as follows, and the flowchart is attached. Figure 1 :

[0057] (1) First leaching: 50g of NdFeB waste acid leaching residue was leached countercurrently using 250ml of 7mol / L hydrochloric acid solution. The countercurrent leaching temperature was 70℃ and the countercurrent leaching time was 4h. The mass concentration of NdFeB waste acid leaching residue in hydrochloric acid was 200g / L. After solid-liquid separation, the first leaching residue and the first leaching solution were obtained. The contents of iron, cobalt and rare earth elements in the NdFeB waste acid leaching residue raw material and the first leaching solution were tested, and the leaching rates of iron, cobalt and rare earth elements were calculated. The results are shown in Table 1.

[0058] (2) Second leaching: The first leaching solution is then mixed with new NdFeB waste acid leaching residue for countercurrent leaching. The mass concentration of the NdFeB waste acid leaching residue in hydrochloric acid is 500 g / L. The countercurrent leaching temperature is 80℃ and the countercurrent leaching time is 6 h. After solid-liquid separation, the second leaching residue and the second leaching solution are obtained. The second leaching residue can be recycled for further leaching of metal elements in the second leaching residue.

[0059] (3) First sinking of iron:

[0060] (3-1) Dilute the second leachate to 200 mL, and use ferric hydroxide to control the pH of the solution system so that the Fe element content of the diluted leachate is 0.9 mol / L and the pH is 1.0; then add sulfosalicylic acid to ensure that the concentration of sulfosalicylic acid in the solution system is 0.012 mol / L.

[0061] (3-2) Add ferric phosphate dihydrate as seed crystals. The mass content of the seed crystals in the leachate system is 8%. Then, raise the temperature of the leachate system to 90℃ and add 2.0 mol / L ammonium dihydrogen phosphate solution for precipitation. The amount of ammonium dihydrogen phosphate added is based on the number of moles of phosphate ions. The amount added is 1.2 times the number of moles of iron in the leachate system. After aging for 5 hours, ferric phosphate dihydrate and primary filtrate are obtained after solid-liquid separation.

[0062] (3-3) After drying, ferric phosphate dihydrate was calcined at 600℃ for 2h to obtain anhydrous ferric phosphate. The contents of iron, cobalt and rare earth elements in the anhydrous ferric phosphate were detected, as well as the contents of iron, cobalt and rare earth elements measured in the above leaching solution system. The precipitation rate of iron, cobalt and rare earth elements in this stage was calculated, and the results are shown in Table 1.

[0063] Meanwhile, the composition, morphology, and particle size of the anhydrous iron phosphate obtained above were characterized using X-ray diffraction (XRD), Malvern 3000 laser particle size analyzer, and scanning electron microscopy (SEM). The results are shown in Table 2 and Appendix. Figure 2-5 ;

[0064] (4) Second iron precipitation: Air is continuously introduced from the bottom of the container to form an oxidizing atmosphere. The pH value of the first filtrate is then adjusted to 3.5 using sodium hydroxide. The precipitate is allowed to settle for 3 hours with stirring. After solid-liquid separation, the precipitate residue and the second filtrate are obtained.

[0065] (5) Enrichment of cobalt and rare earth: The pH of the secondary filtrate was adjusted to 6 using sodium bicarbonate and precipitated for 1 hour. After solid-liquid separation, cobalt and rare earth precipitates were obtained. After drying, the cobalt and rare earth element content in the cobalt and rare earth precipitates was measured. Combined with the cobalt and rare earth element content in the leachate, the precipitation rate of cobalt and rare earth elements was calculated. The results are shown in Table 1.

[0066] Example 2

[0067] The specific steps of the method for recycling acid-soluble residue from NdFeB waste in this embodiment are as follows, and the flowchart is attached. Figure 1 :

[0068] (1) First leaching: 50g of NdFeB waste acid leaching residue was leached countercurrently using 200ml of 5mol / L hydrochloric acid solution. The countercurrent leaching temperature was 100℃ and the countercurrent leaching time was 1h. The mass concentration of NdFeB waste acid leaching residue in hydrochloric acid was 50g / L. After solid-liquid separation, the first leaching residue and the first leaching solution were obtained. The contents of iron, cobalt and rare earth elements in the NdFeB waste acid leaching residue raw material and the first leaching solution were tested, and the leaching rates of iron, cobalt and rare earth elements were calculated. The results are shown in Table 1.

[0069] (2) Second leaching: The first leaching solution is then mixed with new NdFeB waste acid leaching residue for countercurrent leaching. The mass concentration of the NdFeB waste acid leaching residue in hydrochloric acid is 250 g / L. The countercurrent leaching temperature is 80℃ and the countercurrent leaching time is 4 h. After solid-liquid separation, the second leaching residue and the second leaching solution are obtained. The second leaching residue can be recycled for further leaching of metal elements in the second leaching residue.

[0070] (3) First sinking of iron:

[0071] (3-1) Dilute the second leachate to 200 mL, and use ferric hydroxide to control the pH of the solution system so that the Fe element content of the diluted leachate is 0.5 mol / L and the pH is 1.0; then add sulfosalicylic acid to ensure that the concentration of sulfosalicylic acid in the solution system is 0.012 mol / L;

[0072] (3-2) Add ferric phosphate dihydrate as seed crystals. The mass content of the seed crystals in the leachate system is 5%. Then raise the temperature of the leachate system to 90℃ and add 2.0 mol / L ammonium hydrogen phosphate solution for precipitation. The amount of ammonium hydrogen phosphate added is based on the number of moles of phosphate ions. The amount added is 1.1 times the number of moles of iron in the leachate system. After aging for 6 hours, ferric phosphate dihydrate and primary filtrate are obtained after solid-liquid separation.

[0073] (3-3) After drying, ferric phosphate dihydrate was calcined at 800℃ for 2h to obtain anhydrous ferric phosphate. The contents of iron, cobalt and rare earth elements in the anhydrous ferric phosphate were detected, as well as the contents of iron, cobalt and rare earth elements measured in the above leaching solution system. The precipitation rate of iron, cobalt and rare earth elements in this stage was calculated, and the results are shown in Table 1.

[0074] Meanwhile, the crystal form and particle size of the anhydrous iron phosphate obtained above were characterized by X-ray diffraction (XRD) and Malvern 3000 laser particle size analyzer. The results are shown in Table 2.

[0075] (4) Second iron precipitation: Air is continuously introduced from the bottom of the container to form an oxidizing atmosphere. The pH value of the first filtrate is then adjusted to 4 using sodium hydroxide. The precipitate is allowed to settle for 1 hour with stirring. After solid-liquid separation, the precipitate residue and the second filtrate are obtained.

[0076] (5) Enrichment of cobalt and rare earth elements: The pH of the secondary filtrate was adjusted to 5.5 with sodium bicarbonate and precipitated for 5 hours. After solid-liquid separation, cobalt and rare earth elements were obtained. After drying, the cobalt and rare earth element content in the cobalt and rare earth elements precipitate was measured. Combined with the cobalt and rare earth element content in the leachate, the precipitation rate of cobalt and rare earth elements was calculated. The results are shown in Table 1.

[0077] Example 3

[0078] The specific steps of the method for recycling acid-soluble residue from NdFeB waste in this embodiment are as follows, and the flowchart is attached. Figure 1 :

[0079] (1) First leaching: 50g of NdFeB waste acid leaching residue was leached countercurrently using 250ml of 9mol / L hydrochloric acid solution. The countercurrent leaching temperature was 60℃ and the countercurrent leaching time was 10h. The mass concentration of NdFeB waste acid leaching residue in hydrochloric acid was 500g / L. After solid-liquid separation, the first leaching residue and the first leaching solution were obtained. The contents of iron, cobalt and rare earth elements in the NdFeB waste acid leaching residue raw material and the first leaching solution were tested, and the leaching rates of iron, cobalt and rare earth elements were calculated. The results are shown in Table 1.

[0080] (2) Second leaching: The first leaching solution is then mixed with new NdFeB waste acid leaching residue for countercurrent leaching. The mass concentration of the NdFeB waste acid leaching residue in hydrochloric acid is 250 g / L. The countercurrent leaching temperature is 80℃ and the countercurrent leaching time is 4 h. After solid-liquid separation, the second leaching residue and the second leaching solution are obtained. The second leaching residue can be recycled for further leaching of metal elements in the second leaching residue.

[0081] (3) First sinking of iron:

[0082] (3-1) Dilute the second leachate to 200 mL, and use ferric hydroxide to control the pH of the solution system so that the Fe element content of the diluted leachate is 1.5 mol / L and the pH is 1.5; then add triammonium citrate and sulfosalicylic acid, and ensure that the concentrations of triammonium citrate and sulfosalicylic acid in the solution system are 0.008 mol / L and 0.004 mol / L, respectively;

[0083] (3-2) Add ferric phosphate dihydrate as seed crystals. The mass content of the seed crystals in the leachate system is 10%. Then raise the temperature of the leachate system to 80℃ and add 2.0 mol / L ammonium hydrogen phosphate solution for precipitation. The amount of ammonium hydrogen phosphate added is based on the number of moles of phosphate ions. The amount added is 1.3 times the number of moles of iron in the leachate system. After aging for 3 hours, ferric phosphate dihydrate and primary filtrate are obtained after solid-liquid separation.

[0084] (3-3) After drying, ferric phosphate dihydrate was calcined at 550℃ for 3h to obtain anhydrous ferric phosphate. The contents of iron, cobalt and rare earth elements in the anhydrous ferric phosphate were detected, as well as the contents of iron, cobalt and rare earth elements measured in the above leaching solution system. The precipitation rate of iron, cobalt and rare earth elements in this stage was calculated, and the results are shown in Table 1.

[0085] Meanwhile, the composition, morphology, and particle size of the anhydrous iron phosphate obtained above were characterized using X-ray diffraction (XRD), Malvern 3000 laser particle size analyzer, and scanning electron microscopy (SEM). The results are shown in Table 2 and Appendix. Figure 6-9 ;

[0086] (4) Second iron precipitation: Air is continuously introduced from the bottom of the container to form an oxidizing atmosphere. The pH value of the first filtrate is then adjusted to 3.5 using sodium hydroxide. The precipitate is allowed to settle for 3 hours with stirring. After solid-liquid separation, the precipitate residue and the second filtrate are obtained.

[0087] (5) Enrichment of cobalt and rare earth elements: The pH of the secondary filtrate was adjusted to 4 using sodium bicarbonate and precipitated for 5 hours. After solid-liquid separation, cobalt and rare earth elements were obtained as precipitates. After drying, the cobalt and rare earth element content in the precipitates was measured. Combined with the cobalt and rare earth element content in the leachate, the precipitation rate of cobalt and rare earth elements was calculated. The results are shown in Table 1.

[0088] Example 4

[0089] The difference between this embodiment and Embodiment 1 is that in step (3-1), the pH value of the solution system is controlled to be 2.

[0090] Example 5

[0091] The difference between this embodiment and Embodiment 1 is that in step (5), sodium bicarbonate is used to adjust the pH of the secondary filtrate to 4 for precipitation.

[0092] Example 6

[0093] The difference between this embodiment and Embodiment 1 is that in step (3-1), the concentration of sulfosalicylic acid is 0.004 mol / L.

[0094] Example 7

[0095] The difference between this embodiment and Embodiment 1 is that in step (3-1), the concentration of sulfosalicylic acid is 0.02 mol / L.

[0096] Example 8

[0097] The difference between this embodiment and Embodiment 1 is that in step (3-1), histidine is used to replace sulfosalicylic acid, and the concentration is the same.

[0098] Example 9

[0099] The difference between this embodiment and Embodiment 1 is that in step (3-1), oxalic acid is used instead of sulfosalicylic acid, and the concentration is the same.

[0100] Example 10

[0101] The difference between this embodiment and Embodiment 1 is that in step (3-2), the amount of ammonium dihydrogen phosphate added is calculated in terms of the number of moles of phosphate ions, and the number of moles of phosphate ions in the ammonium dihydrogen phosphate used is 1.1 times the number of moles of iron in the solution system.

[0102] Example 11

[0103] The difference between this embodiment and Embodiment 1 is that in step (3-2), the amount of ammonium dihydrogen phosphate added is calculated in terms of the number of moles of phosphate ions, and the number of moles of phosphate ions in the ammonium dihydrogen phosphate used is 1.3 times the number of moles of iron in the solution system.

[0104] Comparative Example 1

[0105] The difference between this comparative example and Example 1 is that in step (3-1), the pH value of the system is controlled at 2.5, and the precipitate obtained after solid-liquid separation is a mixture of ferric phosphate dihydrate and ferric hydroxide.

[0106] Comparative Example 2

[0107] The difference between this comparative example and Example 1 is that, in step (3-1), the pH value of the system is controlled to be 0.5.

[0108] Comparative Example 3

[0109] The difference between this comparative example and Example 1 is that in step (3-1), sodium hydroxide is used instead of iron hydroxide, the hydroxide content of sodium hydroxide is equal to that of iron hydroxide, and the pH value of the system is also controlled at 1.

[0110] Comparative Example 4

[0111] The difference between this comparative example and Example 1 is that sulfosalicylic acid is not added in step (3-1).

[0112] Comparative Example 5

[0113] The difference between this comparative example and Example 1 is that in step (5), sodium bicarbonate is used to adjust the pH of the secondary filtrate to 3 for precipitation.

[0114] Comparative Example 6

[0115] (1) First leaching: 50g of NdFeB waste acid leaching residue was subjected to countercurrent leaching using 250ml of 7mol / L hydrochloric acid solution at a temperature of 70℃ for 4h. The mass concentration of NdFeB waste acid leaching residue in hydrochloric acid was 200g / L. After solid-liquid separation, the first leaching residue and the first leaching solution were obtained. The contents of iron, cobalt, and rare earth elements in the NdFeB waste acid leaching residue raw material and the first leaching solution were tested, and the leaching rates of iron, cobalt, and rare earth elements were calculated. The results are shown in Table 1.

[0116] (2) Second leaching: The first leaching solution is then added with new NdFeB waste acid soluble residue for countercurrent leaching. The mass concentration of the NdFeB waste acid soluble residue in hydrochloric acid is 200 g / L. The countercurrent leaching temperature is 70℃ and the countercurrent leaching time is 4 h. After solid-liquid separation, the second leaching residue and the second leaching solution are obtained.

[0117] (3) Add sodium hydroxide to the second leachate to consume excess acid to control pH and control the pH of the solution system to 2. Control the reaction temperature to 90℃ and add 1.0 mol / L Na2SO4 solution. The amount of Na2SO4 solution is calculated based on the molar amount of sulfate ions. The number of moles of sulfate ions in the Na2SO4 solution is 1.1 times the number of moles of iron obtained in the solution system.

[0118] (4) After solid-liquid separation, a non-economically valuable sodium iron vanadium precipitate is obtained. The pH of the filtrate is adjusted to 6 with sodium bicarbonate to achieve precipitation and enrichment of cobalt and rare earth elements.

[0119] When sodium ferrovanadium precipitate is formed by adding large amounts of sodium sulfate, potassium sulfate and other salts, the precipitate is easy to filter and the loss of rare earth and cobalt is relatively less than that of iron hydroxide. However, the sodium ferrovanadium precipitate residue can only be sold as slag in industry and has no economic value. Iron phosphate, on the other hand, can be used as a precursor for lithium iron phosphate and has higher economic value.

[0120] Table 1

[0121]

[0122]

[0123] Table 2

[0124]

[0125]

[0126] As can be seen from the above embodiments, the proposed method can produce iron phosphate with high purity and precipitates enriched with metals such as cobalt and rare earth elements, enabling high-value utilization of iron and enrichment and recovery of rare earth elements and cobalt.

[0127] As shown in Examples 1-11 and Comparative Examples 1-6, the leaching rate of Fe, Co, and rare earth elements by hydrochloric acid leaching is higher than 90%, which is basically efficient. At the same time, the first iron precipitation step allows the iron element to precipitate in the form of ferric phosphate dihydrate, with a precipitation rate of over 96%. The precipitation rates of Co and rare earth elements in ferric phosphate dihydrate are low, with the precipitation rate of Co being <3% and the precipitation rate of rare earth elements being less than 2%. This yields a high-purity ferric phosphate product, and the quality of the ferric phosphate product meets the requirements of the HG / T4701-2021 standard. By enriching Co and rare earth elements through carbonate precipitation, the precipitation rate of Co reaches over 99% and the precipitation rate of rare earth elements reaches over 92%, which can achieve efficient recovery of Co and rare earth elements.

Claims

1. A method for recycling acid-soluble residue from NdFeB waste, characterized in that, Includes the following steps: Acid leaching: The acid-soluble residue of NdFeB waste is leached countercurrently using hydrochloric acid solution. After solid-liquid separation, the leachate is obtained. First iron precipitation: Add ferric hydroxide to the leachate to adjust the pH of the leachate to 1-2, add organic acid, and then add phosphate for precipitation and aging. After solid-liquid separation, ferric phosphate and primary filtrate are obtained. Second iron precipitation: The pH of the primary filtrate is adjusted to 3.5-4 under an oxidizing atmosphere and precipitation is carried out. After solid-liquid separation, precipitate residue and secondary filtrate are obtained. Enrichment of cobalt and rare earth elements: The pH of the secondary filtrate is adjusted to 4-6 using sodium carbonate and / or sodium bicarbonate to induce precipitation. After solid-liquid separation, a precipitate enriched with cobalt and rare earth elements is obtained.

2. The method for recycling NdFeB waste acid leaching residue as described in claim 1, characterized in that, During acid leaching, the mass concentration of NdFeB waste acid-soluble residue in hydrochloric acid is 50-300 g / L.

3. The method for recycling and utilizing NdFeB waste acid-soluble residue as described in claim 1, characterized in that, In acid leaching, the temperature of the countercurrent leaching is 60-100℃, and the time of the countercurrent leaching is 1-10h.

4. The method for recycling and utilizing NdFeB waste acid-soluble residue as described in claim 1, characterized in that, In the first iron precipitation process, before adding organic acids, the concentration of iron in the leaching is adjusted to 0.5-1.5 mol / L.

5. The method for recycling NdFeB waste acid leaching residue as described in claim 1, characterized in that, In the first iron precipitation process, before adding phosphate for precipitation, iron phosphate dihydrate seed crystals are added to the leachate, and the mass concentration of the iron phosphate dihydrate seed crystals in the leachate is 5-10%.

6. The method for recycling and utilizing NdFeB waste acid-soluble residue as described in claim 1, characterized in that, In the first iron precipitation, the concentration of the organic acid in the leachate is 0.004-0.02 mol / L.

7. The method for recycling NdFeB waste acid leaching residue as described in claim 1, characterized in that, In the first iron precipitation process, the organic acid includes at least one of sulfosalicylic acid, histidine, oxalic acid, and triammonium citrate.

8. The method for recycling NdFeB waste acid leaching residue as described in claim 1, characterized in that, In the first iron precipitation process, the phosphate includes at least one of ammonium hydrogen phosphate and ammonium dihydrogen phosphate.

9. The method for recycling NdFeB waste acid leaching residue as described in claim 1, characterized in that, In the first iron precipitation, the molar concentration of phosphate is 1.1-1.3 times that of iron, based on the added phosphate and the iron in the leachate.

10. The method for recycling NdFeB waste acid-soluble residue as described in claim 1, characterized in that, In the first iron immersion process, the aging time is 3-6 hours.

11. The method for recycling NdFeB waste acid leaching residue as described in claim 1, characterized in that, In the second iron precipitation, the precipitation time is 1-5 hours.

12. The method for recycling NdFeB waste acid-soluble residue as described in claim 1, characterized in that, In the second iron immersion process, the oxidizing atmosphere is achieved by introducing a gas containing oxygen.

13. The method for recycling and utilizing NdFeB waste acid-soluble residue as described in claim 1, characterized in that, In the enrichment of cobalt and rare earth elements, the precipitation time is 0.5-5 hours.

14. The method for recycling NdFeB waste acid leaching residue as described in claim 1, characterized in that, In the first iron precipitation process, the ferric phosphate contains water of crystallization, and the ferric phosphate also needs to be calcined at 550-800℃ for 1-3 hours.

15. The method for recycling NdFeB waste acid-soluble slag as described in claim 14, characterized in that, The calcined iron phosphate contains the following elements by mass percentage: Fe 35.7-36.7%, P 20.0-21.1%, Ca≤0.01%, Mg≤0.06%, Na≤0.02%, Al≤0.05%, S≤0.03%, Co≤0.006%, rare earth elements≤0.03%, and the molar ratio of Fe to P is Fe / P=0.96-1.0.

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