Method for recycling acid-soluble slag of neodymium-iron-boron waste

Abstract

A method for recycling acid-soluble slag of neodymium-iron-boron waste. The method comprises: separating iron from rare earths / cobalt in an acid leachate of acid-soluble slag of neodymium-iron-boron waste in a selective precipitation manner to obtain a battery-grade iron phosphate product and a precipitate enriched with metal elements such as rare earths and cobalt. Compared with other recycling processes, the value of the recycled iron phosphate product is higher, achieving efficient enrichment and recovery of metal elements such as rare earths and cobalt in the acid-soluble slag of neodymium-iron-boron waste, improving the overall recovery efficiency of the acid-soluble slag of neodymium-iron-boron waste in industry, greatly reducing the discharge of the acid-soluble slag of neodymium-iron-boron waste, and reducing the storage cost; in addition, the method achieves environmentally-friendly recycling and is environmentally friendly.

Description

A method for recycling NdFeB waste acid slag Technical Field

[0001] The invention belongs to the field of recycling of NdFeB waste, and in particular relates to a method for recycling acid slag of NdFeB waste. Background Art

[0002] During the production and use of NdFeB, various factors in the production process generate approximately 20% NdFeB waste. NdFeB material contains approximately 30% rare earth elements (90% of which is praseodymium and neodymium, with the remainder being terbium, dysprosium, and other rare earth elements). With the increasing production of NdFeB waste, the industry often uses hydrochloric acid extraction to recover the rare earths. Typically, the NdFeB waste is roasted, ground, dissolved in hydrochloric acid, and then filtered to produce a rare earth chloride filtrate and a residue, commonly known as NdFeB acid slag. The primary components of this acid slag are Fe₂O₃ / Fe(OH)₃, with 0.5%-1% rare earth elements and cobalt residues. Currently, the acid slag is typically sent to steel mills for recycling, which is economically inefficient. Furthermore, the high-value rare earths, cobalt, and other valuable metals in the slag are not recovered, resulting in a waste of resources.

[0003] At present, in order to improve the comprehensive utilization value of acid-soluble slag, some scientific researchers have conducted research on it. For example, in the paper "Preparation of manganese-zinc ferrite from NdFeB waste slag: Research on the preparation of Mn-Zn ferrite micropowder from waste slag after extracting rare earths from NdFeB waste", Zhong Xiaolin, Song Ning and others used NdFeB waste acid-soluble slag as raw material, and obtained manganese-zinc ferrite micropowder through leaching, impurity removal, co-precipitation and other methods, thereby realizing the high value of iron. In the patent document with publication number CN107055627A, the iron in the NdFeB acid-soluble slag was recovered by combining hydrochloric acid dissolution with extraction and hydrothermal treatment to prepare nano iron oxide red. However, the above research only recycled the main element iron in the acid-soluble slag, and did not recover the more expensive rare earth elements, and did not maximize the benefits of the acid-soluble slag. Furthermore, in his paper "Research on Comprehensive Recycling Technology of Secondary Waste from NdFeB Magnetic Materials," Wu Mian employed a hydrochloric acid dissolution method to transfer metals into solution. The hydrolysis of Fe then produced β-FeOOH, which was then calcined to yield red iron oxide with a purity of 98.01%. The hydrolysis solution was then subjected to step-by-step precipitation using NH₄HCO₃ as a precipitant to recover rare earths and cobalt. Patent publication number CN115074530A describes the enrichment and recovery of rare earths and cobalt through hydrochloric acid leaching using sodium sulfide and sodium bicarbonate as precipitants, followed by spray pyrolysis to produce red iron oxide. While these processes achieve comprehensive recovery of iron, cobalt, and rare earths, the recovery rates of rare earths and cobalt are low, and the resulting products, such as red iron oxide, are of low purity and value, requiring further improvement in economic efficiency.

[0004] Regarding the comprehensive recovery of acid slag generated during the recycling process of NdFeB waste, how to separate rare earth / cobalt and other elements in the acid slag from iron while achieving the recycling of iron elements and high-value recovery and enrichment of high-value metal rare earths and cobalt to reduce the accumulation of acid slag and improve the recycling efficiency of industrial waste has become a technical problem that needs to be solved urgently.

[0005] Summary of the Invention

[0006] In response to the problems mentioned above in the related technologies, such as the low recycling value of iron elements in NdFeB waste acid slag and the inability to efficiently recover rare earth / cobalt elements, this article will provide a method for recycling NdFeB waste acid slag.

[0007] To achieve the above objectives, the following technical solutions are specifically included:

[0008] A method for recycling NdFeB waste acid slag comprises the following steps:

[0009] Acid leaching: Use hydrochloric acid solution to countercurrently leach the acid slag of NdFeB waste, and obtain the leachate after solid-liquid separation;

[0010] First iron precipitation: add ferric hydroxide to the leachate to adjust the pH value of the leachate to 1-2, add organic acid, and then add phosphate for precipitation and aging, and obtain iron phosphate and primary filtrate after solid-liquid separation;

[0011] Second iron precipitation: adjusting the pH value of the primary filtrate to 3.5-4 under an oxidizing atmosphere and performing precipitation, and obtaining precipitate residue and secondary filtrate after solid-liquid separation;

[0012] Enrichment of cobalt and rare earth: adjusting the pH value of the secondary filtrate to 4-6 with sodium carbonate and / or sodium bicarbonate for precipitation, and obtaining a precipitate enriched in cobalt and rare earth after solid-liquid separation.

[0013] In the technical solution provided herein, the difference in pH values ​​of phosphate precipitates produced by iron ions and other metal ions in the presence of phosphate is utilized to achieve efficient separation of iron, cobalt, and rare earths in the acid leaching solution of NdFeB waste acid slag, thereby obtaining high-purity iron phosphate and a precipitate enriched in cobalt and rare earths. The high-purity iron phosphate can be used as a precursor for the preparation of lithium iron phosphate and has high value. The precipitate enriched in cobalt and rare earths is a carbonate precipitate, which is easily redissolved by acid, which is conducive to subsequent re-separation and recovery, and is also conducive to later sale and transportation. Therefore, the form of the precipitate enriched in cobalt and rare earths (praseodymium, neodymium, terbium, dysprosium, etc.) is more conducive to the recycling of rare earths.

[0014] Adding a certain amount of ferric hydroxide to the leachate can achieve the purpose of controlling the pH on the one hand, and at the same time increase the iron concentration in the leachate to widen the concentration gap between the main Fe element and the impurity elements.

[0015] The separation of trivalent iron from rare earth / cobalt is relatively difficult. Ferric hydroxide is added to the leachate to control the pH value of the system to 1-2. If the pH value exceeds the above value, the pH value is too high, which will not only produce iron phosphate but also produce iron hydroxide precipitation, forming a mixture of iron phosphate and iron hydroxide, resulting in reduced purity of the iron phosphate. The separation of iron phosphate and iron hydroxide is more difficult, and it cannot be used as iron phosphate with application value. Further processing is required to obtain an iron product with economic value. At the same time, the loss rate of rare earth / cobalt will be very large, reaching more than 20%, reducing the content of valuable metals in the rare earth / cobalt-enriched precipitate and reducing its value.

[0016] In the second iron precipitation, the pH value of the solution system is adjusted to 3.5-4.5. At this time, the iron in the filtrate can be completely precipitated with the phosphate ions and hydroxide ions in the solution in the form of iron phosphate and goethite, respectively, and the remaining iron element in the filtrate can be fully recovered and removed; 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 leaching solution to leach the iron source.

[0017] In the enrichment of cobalt and rare earth, sodium bicarbonate and / or sodium carbonate are used to adjust the pH value of the solution system to 4-6, which can better enrich and precipitate cobalt and rare earth.

[0018] In acid leaching, the use of hydrochloric acid solution to countercurrently leach the acid slag of NdFeB waste includes the following steps:

[0019] First leaching: using hydrochloric acid solution to countercurrently leach the acid-soluble residue of NdFeB waste, and after solid-liquid separation, obtain the first leaching residue and the first leachate;

[0020] First leaching: New NdFeB waste acid slag is added to the first leaching solution for countercurrent leaching, and after solid-liquid separation, second leaching slag and second leaching solution are obtained.

[0021] Conventional leaching will leave a large amount of acid residue in the leachate after one leaching. However, after two leaching, new NdFeB waste acid slag is added, and the acid in the first leaching solution is consumed to a pH of about 0.1-0.3. At the same time, the iron concentration in the leachate can be increased from about 80-90g / L to about 110-150g / L. This not only makes full use of the acid to fully leach the metal elements in the NdFeB waste acid slag, but also makes it easy to adjust the pH of the leachate to a pH value that is conducive to subsequent precipitation without adding too much pH adjusting reagent.

[0022] In one embodiment, during the acid leaching, the mass concentration of the NdFeB waste acid slag in the hydrochloric acid is 50-300 g / L.

[0023] In one embodiment, during acid leaching, the countercurrent leaching temperature is 60-100° C., and the countercurrent leaching time is 1-10 h.

[0024] In one embodiment, the first iron precipitation process further includes adjusting the iron concentration in the leached product to 0.5-1.5 mol / L before adding the organic acid, and the adjustment is carried out by dilution or concentration.

[0025] The iron concentration in the leachate is adjusted to 0.5-1.5 mol / L by dilution or concentration. At this concentration, the ion concentration of the iron element is appropriate, which is more conducive to the precipitation of iron in the form of ferric phosphate.

[0026] In one embodiment, the first iron precipitation further includes adding ferric phosphate dihydrate seed crystals to the leachate before adding phosphate for precipitation, wherein the mass concentration of the ferric phosphate dihydrate seed crystals in the leachate is 5-10%.

[0027] Before adding phosphate for precipitation, dihydrate ferric phosphate seeds are also added to the leachate. The seeds can be used to induce the formation of ferric phosphate precipitation, improve the crystallinity, and induce the ferric phosphate precipitation to form a specific morphology, so as to achieve the purpose of controlling the growth of ferric phosphate.

[0028] In one embodiment, during the first iron precipitation, the concentration of the organic acid in the leachate is 0.004-0.02 mol / L.

[0029] In one embodiment, in the first iron precipitation, the organic acid includes at least one of sulfosalicylic acid, histidine, oxalic acid, and triammonium citrate.

[0030] The organic acid complexes with the impurity ions to increase the pH of its phosphoric acid precipitation, which can effectively avoid the introduction of impurity ions in the iron phosphate.

[0031] In one embodiment, in the first iron precipitation, the phosphate includes at least one of ammonium monohydrogen phosphate and ammonium dihydrogen phosphate.

[0032] In one embodiment, in the first iron precipitation, the molar concentration of phosphate is 1.1-1.3 times the molar concentration of iron.

[0033] In one embodiment, during the first iron precipitation, the aging time is 3-6 hours.

[0034] Aging is performed to increase the precipitation rate of iron, improve the crystal form of the precipitate, and simultaneously exchange the trivalent iron ions with some of the impurity ions adsorbed by ferric phosphate dihydrate, thereby achieving the purpose of reducing the impurity content in ferric phosphate dihydrate and improving the purity of the ferric phosphate precipitation.

[0035] In one embodiment, in the first iron precipitation, the ferric phosphate contains crystal water, and the ferric phosphate needs to be calcined at 550-800° C.; the calcination time is 1-3 hours.

[0036] In one embodiment, the calcined iron phosphate includes the following elements in percentage by mass: 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.

[0037] The element component content of the anhydrous ferric phosphate after calcination is within the above range, and the purity can meet the purity requirements of the raw material for lithium iron phosphate precursor, and can be used to prepare lithium iron phosphate, and the product has high application value.

[0038] In one embodiment, during the second iron precipitation, the oxidizing atmosphere is a gas containing oxygen; the gas containing oxygen is air.

[0039] In one embodiment, in the second iron precipitation, the reagent for adjusting the pH of the first filtrate is at least one of sodium hydroxide, potassium hydroxide, and sodium carbonate.

[0040] In one embodiment, in the second iron precipitation, the precipitation time is 2-5 hours, and the precipitation is also carried out under stirring.

[0041] In one embodiment, in the enrichment of cobalt and rare earth, the precipitation time is 0.5-5 hours, and the precipitation is carried out while stirring.

[0042] Compared with the related art, this article has the following beneficial effects: the present invention separates iron from rare earth / cobalt by selective precipitation of the acid leaching liquid of NdFeB waste acid slag to obtain a battery-grade iron phosphate product. Compared with other recycling processes, the recovered iron phosphate product has higher value, and at the same time, it realizes the efficient enrichment and recovery of metal elements such as rare earth and cobalt in NdFeB waste acid slag, improves the overall recovery efficiency of NdFeB waste acid slag in industry, greatly reduces the emission of NdFeB waste acid slag, reduces storage costs, and is green and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] FIG1 is a flow chart of the recycling and utilization of NdFeB waste acid slag in this paper.

[0044] FIG2 is an XRD spectrum of anhydrous ferric phosphate of Example 1.

[0045] FIG3 is a particle size distribution diagram of anhydrous ferric phosphate of Example 1.

[0046] FIG4 is a SEM image of the anhydrous ferric phosphate of Example 1 at a magnification of 5000 times.

[0047] FIG5 is a SEM image of anhydrous ferric phosphate of Example 1 at a magnification of 50,000 times.

[0048] FIG6 is an XRD spectrum of anhydrous ferric phosphate of Example 3.

[0049] FIG7 is a particle size distribution diagram of anhydrous ferric phosphate of Example 3.

[0050] FIG8 is a SEM image of anhydrous ferric phosphate of Example 3 at a magnification of 5000 times.

[0051] FIG9 is a SEM image of anhydrous ferric phosphate of Example 3 at a magnification of 50,000 times. DETAILED DESCRIPTION

[0052] The technical solutions in the embodiments of this article will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of this article, rather than all the embodiments.

[0053] The NdFeB waste acid slag used below all comes from a NdFeB waste recycling company in Ganzhou, Jiangxi.

[0054] ICP was used to test the contents of iron, cobalt, Al, Si, and rare earth elements in the following solutions and precipitates. The precipitate needed to be completely dissolved in an acidic solution before measurement. The iron content in the solution was titrated with potassium dichromate. The phosphorus content in the ferric phosphate precipitate was tested using the quinoline gravimetric method, and the molar ratio of Fe to P was calculated.

[0055] The rare earth elements referred to herein include praseodymium, neodymium, terbium, and dysprosium.

[0056] Example 1

[0057] The specific steps of the method for recycling NdFeB waste acid slag of this embodiment are as follows, and the flow chart is shown in Figure 1:

[0058] (1) First leaching: 50 g of NdFeB waste acid slag was subjected to countercurrent leaching using 250 ml of 7 mol / L hydrochloric acid solution. The countercurrent leaching temperature was 70° C., the countercurrent leaching time was 4 h, and the mass concentration of NdFeB waste acid slag in hydrochloric acid was 200 g / L. After solid-liquid separation, the first leaching slag and the first leachate were obtained. The contents of iron, cobalt, and rare earth elements in the NdFeB waste acid slag raw material and the first leachate were tested, and the leaching rates of iron, cobalt, and rare earth elements were calculated. The results are shown in Table 1.

[0059] (2) Second leaching: New NdFeB waste acid slag is added to the first leachate for countercurrent leaching. The mass concentration of the NdFeB waste acid slag in hydrochloric acid is 500 g / L, the countercurrent leaching temperature is 80° C., and the countercurrent leaching time is 6 h. After solid-liquid separation, a second leaching slag and a second leachate are obtained. The second leaching slag can be circulated for leaching to further extract the metal elements in the second leaching slag.

[0060] (3) First iron sinking:

[0061] (3-1) diluting the second leachate to 200 mL, and controlling the pH of the solution system with ferric hydroxide so that the Fe content of the diluted leachate is 0.9 mol / L and the pH is 1.0; then adding sulfosalicylic acid to ensure that the concentration of sulfosalicylic acid in the solution system is 0.012 mol / L;

[0062] (3-2) adding ferric phosphate dihydrate as seed crystals, wherein the mass content of the seed crystals in the leachate system is 8%, then raising the temperature of the leachate system to 90° C., adding a 2.0 mol / L ammonium dihydrogen phosphate solution for precipitation, wherein the amount of ammonium dihydrogen phosphate added is 1.2 times the molar number of iron element in the leachate system, calculated as the number of moles of phosphate ion, and aging for 5 hours. After solid-liquid separation, ferric phosphate dihydrate and a primary filtrate are obtained;

[0063] (3-3) The dried ferric phosphate dihydrate was calcined at 600°C for 2 h to obtain anhydrous ferric phosphate. The iron, cobalt, and rare earth elements contents in the anhydrous ferric phosphate were measured, as well as the iron, cobalt, and rare earth elements contents measured in the above-mentioned leaching solution system. The precipitation rates of iron, cobalt, and rare earth elements at this stage were calculated. The results are shown in Table 1.

[0064] At the same time, X-ray diffraction (XRD), Malvern 3000 laser particle size analyzer, scanning electron microscopy (SEM), etc. were used to characterize the composition, morphology, particle size, etc. of the anhydrous ferric phosphate obtained above. The results are shown in Table 2 and Figures 2-5;

[0065] (4) Second iron precipitation: Air is continuously introduced from the bottom of the container to form an oxidizing atmosphere, and then the pH value of the primary filtrate is adjusted to 3.5 using sodium hydroxide. The precipitation is carried out for 3 hours under stirring. After solid-liquid separation, a precipitate residue and a secondary filtrate are obtained;

[0066] (5) Enrichment of cobalt and rare earth elements: The pH value of the secondary filtrate was adjusted to 6 using sodium bicarbonate, and precipitation was carried out for 1 hour. After solid-liquid separation, a precipitate enriched in cobalt and rare earth elements was obtained. After drying, the cobalt and rare earth element contents in the precipitate enriched in cobalt and rare earth elements were measured. Combined with the cobalt and rare earth element contents in the leachate, the precipitation rates of cobalt and rare earth elements were calculated. The results are shown in Table 1.

[0067] Example 2

[0068] The specific steps of the method for recycling NdFeB waste acid slag of this embodiment are as follows, and the flow chart is shown in Figure 1:

[0069] (1) First leaching: 50 g of NdFeB waste acid slag was subjected to countercurrent leaching using 200 ml of 5 mol / L hydrochloric acid solution. The countercurrent leaching temperature was 100° C., the countercurrent leaching time was 1 h, and the mass concentration of NdFeB waste acid slag in hydrochloric acid was 50 g / L. After solid-liquid separation, a first leaching slag and a first leachate were obtained. The contents of iron, cobalt, and rare earth elements in the NdFeB waste acid slag raw material and the first leachate were tested, and the leaching rates of iron, cobalt, and rare earth elements were calculated. The results are shown in Table 1.

[0070] (2) Second leaching: New NdFeB waste acid slag is added to the first leachate for countercurrent leaching. The mass concentration of the NdFeB waste acid slag in hydrochloric acid is 250 g / L, the countercurrent leaching temperature is 80° C., and the countercurrent leaching time is 4 h. After solid-liquid separation, a second leaching slag and a second leachate are obtained. The second leaching slag can be circulated for leaching to further extract the metal elements in the second leaching slag.

[0071] (3) First iron sinking:

[0072] (3-1) diluting the second leachate to 200 mL, and controlling the pH of the solution system with ferric hydroxide so that the Fe content of the diluted leachate is 0.5 mol / L and the pH is 1.0; then adding sulfosalicylic acid to ensure that the concentration of sulfosalicylic acid in the solution system is 0.012 mol / L;

[0073] (3-2) adding ferric phosphate dihydrate as seed crystals, wherein the mass content of the seed crystals in the leachate system is 5%, then raising the temperature of the leachate system to 90° C., adding a 2.0 mol / L ammonium monohydrogen phosphate solution for precipitation, wherein the amount of ammonium monohydrogen phosphate added is 1.1 times the molar number of iron element in the leachate system, calculated as the number of moles of phosphate ion, and aging for 6 hours. After solid-liquid separation, ferric phosphate dihydrate and a primary filtrate are obtained;

[0074] (3-3) The dried ferric phosphate dihydrate was calcined at 800° C. for 2 h to obtain anhydrous ferric phosphate. The iron, cobalt, and rare earth elements contents in the anhydrous ferric phosphate were determined, along with the iron, cobalt, and rare earth elements contents measured in the aforementioned leaching solution system. The precipitation rates of iron, cobalt, and rare earth elements during this stage were calculated. The results are shown in Table 1.

[0075] At the same time, X-ray diffraction (XRD), Malvern 3000 laser particle size analyzer, etc. were used to characterize the crystal form and particle size of the anhydrous ferric phosphate obtained above. The results are shown in Table 2;

[0076] (4) Second iron precipitation: Air is continuously introduced from the bottom of the container to form an oxidizing atmosphere, and then the pH value of the primary filtrate is adjusted to 4 using sodium hydroxide. The precipitation is carried out for 1 hour under stirring. After solid-liquid separation, a precipitate residue and a secondary filtrate are obtained;

[0077] (5) Enrichment of cobalt and rare earth elements: The pH value of the secondary filtrate was adjusted to 5.5 using sodium bicarbonate, and precipitation was carried out for 5 hours. After solid-liquid separation, a precipitate enriched in cobalt and rare earth elements was obtained. After drying, the cobalt and rare earth element contents in the precipitate enriched in cobalt and rare earth elements were measured. Combined with the cobalt and rare earth element contents in the leachate, the precipitation rates of cobalt and rare earth elements were calculated. The results are shown in Table 1.

[0078] Example 3

[0079] The specific steps of the method for recycling NdFeB waste acid slag of this embodiment are as follows, and the flow chart is shown in Figure 1:

[0080] (1) First leaching: 50 g of NdFeB waste acid slag was subjected to countercurrent leaching using 250 ml of 9 mol / L hydrochloric acid solution. The countercurrent leaching temperature was 60° C., the countercurrent leaching time was 10 h, and the mass concentration of NdFeB waste acid slag in hydrochloric acid was 500 g / L. After solid-liquid separation, a first leaching slag and a first leachate were obtained. The contents of iron, cobalt, and rare earth elements in the NdFeB waste acid slag raw material and the first leachate were tested, and the leaching rates of iron, cobalt, and rare earth elements were calculated. The results are shown in Table 1.

[0081] (2) Second leaching: New NdFeB waste acid slag is added to the first leachate for countercurrent leaching. The mass concentration of the NdFeB waste acid slag in hydrochloric acid is 250 g / L, the countercurrent leaching temperature is 80° C., and the countercurrent leaching time is 4 h. After solid-liquid separation, a second leaching slag and a second leachate are obtained. The second leaching slag can be circulated for leaching to further extract the metal elements in the second leaching slag.

[0082] (3) First iron sinking:

[0083] (3-1) diluting the second leachate to 200 mL, and controlling the pH of the solution system with ferric hydroxide so that the Fe content of the diluted leachate is 1.5 mol / L and the pH is 1.5; then adding triammonium citrate and sulfosalicylic acid to 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;

[0084] (3-2) adding ferric phosphate dihydrate as seed crystals, wherein the mass content of the seed crystals in the leachate system is 10%, then raising the temperature of the leachate system to 80° C., adding a 2.0 mol / L ammonium monohydrogen phosphate solution for precipitation, wherein the amount of ammonium monohydrogen phosphate added is 1.3 times the molar number of iron element in the leachate system, calculated as the number of moles of phosphate ion, and aging for 3 hours. After solid-liquid separation, ferric phosphate dihydrate and a primary filtrate are obtained;

[0085] (3-3) The dried ferric phosphate dihydrate was calcined at 550°C for 3 h to obtain anhydrous ferric phosphate. The iron, cobalt, and rare earth elements contents in the anhydrous ferric phosphate were measured, as well as the iron, cobalt, and rare earth elements contents measured in the above-mentioned leaching solution system. The precipitation rates of iron, cobalt, and rare earth elements at this stage were calculated. The results are shown in Table 1.

[0086] At the same time, X-ray diffraction (XRD), Malvern 3000 laser particle size analyzer, scanning electron microscopy (SEM), etc. were used to characterize the composition, morphology, particle size, etc. of the anhydrous ferric phosphate obtained above. The results are shown in Table 2 and Figures 6-9;

[0087] (4) Second iron precipitation: Air is continuously introduced from the bottom of the container to form an oxidizing atmosphere, and then the pH value of the primary filtrate is adjusted to 3.5 using sodium hydroxide. The precipitation is carried out for 3 hours under stirring. After solid-liquid separation, a precipitate residue and a secondary filtrate are obtained;

[0088] (5) Enrichment of cobalt and rare earth elements: The pH value of the secondary filtrate was adjusted to 4 using sodium bicarbonate, and precipitation was carried out for 5 hours. After solid-liquid separation, a precipitate enriched in cobalt and rare earth elements was obtained. After drying, the cobalt and rare earth element contents in the precipitate enriched in cobalt and rare earth elements were measured. Combined with the cobalt and rare earth element contents in the leachate, the precipitation rates of cobalt and rare earth elements were calculated. The results are shown in Table 1.

[0089] Example 4

[0090] 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.

[0091] Example 5

[0092] The difference between this embodiment and embodiment 1 is that in step (5), sodium bicarbonate is used to adjust the pH value of the secondary filtrate to 4 for precipitation.

[0093] Example 6

[0094] The difference between this embodiment and embodiment 1 is that in step (3-1), the concentration of sulfosalicylic acid is 0.004 mol / L.

[0095] Example 7

[0096] The difference between this embodiment and embodiment 1 is that in step (3-1), the concentration of sulfosalicylic acid is 0.02 mol / L.

[0097] Example 8

[0098] The difference between this embodiment and embodiment 1 is that in step (3-1), histidine is used instead of sulfosalicylic acid, and the concentrations are the same.

[0099] Example 9

[0100] The difference between this embodiment and embodiment 1 is that in step (3-1), oxalic acid is used instead of sulfosalicylic acid, and the concentrations are the same.

[0101] Example 10

[0102] The difference between this embodiment and embodiment 1 is that in step (3-2), the amount of ammonium dihydrogen phosphate added is calculated as the number of moles of phosphate, and the number of moles of phosphate of the ammonium dihydrogen phosphate used is 1.1 times the number of moles of iron in the solution system.

[0103] Example 11

[0104] The difference between this embodiment and embodiment 1 is that in step (3-2), the amount of ammonium dihydrogen phosphate added is calculated as the molar number of phosphate, and the molar number of phosphate of the ammonium dihydrogen phosphate used is 1.3 times the molar number of iron element in the solution system.

[0105] Comparative Example 1

[0106] 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 2.5, and the precipitate obtained after solid-liquid separation is a mixture of ferric phosphate dihydrate and ferric hydroxide.

[0107] Comparative Example 2

[0108] 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.

[0109] Comparative Example 3

[0110] The difference between this comparative example and Example 1 is that in step (3-1), sodium hydroxide is used instead of ferric hydroxide, the hydroxide content of sodium hydroxide is equal to that of ferric hydroxide, and the pH value in the system is also controlled at 1.

[0111] Comparative Example 4

[0112] The difference between this comparative example and Example 1 is that in step (3-1), sulfosalicylic acid is not added.

[0113] Comparative Example 5

[0114] The difference between this comparative example and Example 1 is that in step (5), sodium bicarbonate is used to adjust the pH value of the secondary filtrate to 3 for precipitation.

[0115] Comparative Example 6

[0116] (1) First leaching: 50 g of NdFeB waste acid slag was subjected to countercurrent leaching using 250 ml of 7 mol / L hydrochloric acid solution. The countercurrent leaching temperature was 70 ° C. The countercurrent leaching time was 4 h. The mass concentration of NdFeB waste acid slag in hydrochloric acid was 200 g / L. After solid-liquid separation, the first leaching slag and the first leachate were obtained. The contents of iron, cobalt, and rare earth elements in the NdFeB waste acid slag raw material and the first leachate were tested, and the leaching rates of iron, cobalt, and rare earth elements were calculated. The results are shown in Table 1.

[0117] (2) Second leaching: New NdFeB waste acid slag is added to the first leachate for countercurrent leaching. The mass concentration of the NdFeB waste acid slag in hydrochloric acid is 200 g / L. The countercurrent leaching temperature is 70° C. and the countercurrent leaching time is 4 h. After solid-liquid separation, a second leaching residue and a second leachate are obtained.

[0118] (3) adding sodium hydroxide to the second leachate to consume excess acid to control the pH, and controlling the pH of the solution system to 2, controlling the reaction temperature to 90° C., and adding 1.0 mol / L Na2SO4 solution, wherein the amount of Na2SO4 solution is based on the molar amount of sulfate ions, and the molar number of sulfate ions in the Na2SO4 solution is 1.1 times the molar number of iron elements obtained in the solution system;

[0119] (4) After solid-liquid separation, yellow sodium iron vanadium precipitate with no economic value is obtained, and the filtrate is adjusted to pH 6 using sodium bicarbonate to achieve precipitation enrichment of cobalt and rare earth.

[0120] A large amount of sodium sulfate, potassium sulfate and other salt substances are added to the sodium iron vanadium precipitation to form a precipitate. At this time, the precipitate product is easy to filter, and the loss of rare earth and cobalt is relatively less than that of ferric hydroxide. However, the sodium iron vanadium precipitation residue can only be sold as slag in industry and has basically no economic value. Iron phosphate can be used as a precursor of lithium iron phosphate and has higher economic value.

[0121] Table 1

[0122] Table 2

[0123] As can be seen from the above examples, the scheme of this article can produce high-purity iron phosphate and precipitates enriched in metals such as cobalt and rare earths, which can achieve high-value utilization of iron and enrichment and recovery of rare earths and cobalt.

[0124] It can be seen from Examples 1-11 and Comparative Examples 1-6 that the leaching rate of Fe, Co and rare earth elements leached by hydrochloric acid leaching is higher than 90%, which basically enables efficient leaching. At the same time, the first iron precipitation step is used to precipitate the iron element in the form of dihydrate iron phosphate. The precipitation rate of the iron element is as high as more than 96%, and the precipitation rate of Co and rare earth in dihydrate iron phosphate is relatively low, among which the precipitation rate of Co is less than 3%, and the precipitation rate of rare earth is less than 2%. A higher purity iron phosphate product can be obtained, and the product quality of the iron phosphate meets the requirements of the HG / T4701-2021 standard; by enriching Co and rare earth elements by carbonate precipitation, the precipitation rate of Co reaches more than 99%, and the precipitation rate of rare earth reaches more than 92%, which can achieve efficient recovery of Co and rare earth elements.

Claims

1. A method for recycling acid-soluble slag from NdFeB waste materials, characterized in that, It includes the following steps: Acid leaching: Use hydrochloric acid solution to carry out countercurrent leaching on the acid leaching residue of neodymium iron boron waste. After solid-liquid separation, the leaching solution is obtained. First iron precipitation: Add iron hydroxide to the leaching solution to adjust the pH value of the leaching solution to 1-2. Add organic acid, and then add phosphate for precipitation and aging. After solid-liquid separation, iron phosphate and the first filtrate are obtained. Second iron precipitation: Adjust the pH value of the first filtrate to 3.5-4 under an oxidizing atmosphere for precipitation. After solid-liquid separation, the precipitation residue and the second filtrate are obtained. Enrichment of cobalt and rare earths: Use sodium carbonate and / or sodium bicarbonate to adjust the pH value of the second filtrate to 4-6 for precipitation. After solid-liquid separation, the precipitation rich in cobalt and rare earths is obtained.

2. The method for recycling acid leaching slag of neodymium iron boron waste as claimed in claim 1, wherein In acid leaching, the mass concentration of the acid leaching residue of neodymium iron boron waste in hydrochloric acid is 50-300 g / L.

3. The method for recycling acid-soluble slag from neodymium iron boron waste as claimed in claim 1, characterized in that, In acid leaching, the temperature of the countercurrent leaching is 60-100 °C, and the time of the countercurrent leaching is 1-10 h.

4. The method for recycling the acid leaching slag of neodymium iron boron waste as claimed in claim 1, wherein, In the first iron precipitation, before adding organic acid, it also includes adjusting the iron element concentration in the leaching to 0.5-1.5 mol / L.

5. The method for recycling acid-soluble slag of neodymium-iron-boron waste as claimed in claim 1, wherein In the first iron precipitation, before adding phosphate for precipitation, it also includes adding iron phosphate dihydrate crystal seeds to the leaching solution, and the mass concentration of the iron phosphate dihydrate crystal seeds in the leaching solution is 5-10%.

6. The method for recycling the acid-soluble slag of neodymium-iron-boron waste as claimed in claim 1, wherein In the first iron precipitation, the concentration of the organic acid in the leaching solution is 0.004-0.02 mol / L.

7. The method for recycling acid-soluble slag of neodymium iron boron waste as claimed in claim 1, wherein, In the first iron precipitation, the organic acid includes at least one of sulfosalicylic acid, histidine, oxalic acid, and ammonium citrate.

8. The method for recycling the acid-soluble slag of neodymium-iron-boron waste materials according to claim 1, characterized in that, In the first iron precipitation, the phosphate includes at least one of ammonium monohydrogen phosphate and ammonium dihydrogen phosphate.

9. The method for recycling and utilization of acid-soluble slag from neodymium-iron-boron waste as claimed in claim 1, wherein In the first iron precipitation, based on the phosphate radical added with phosphate and the iron element in the leaching solution, the molar concentration of the phosphate radical is 1.1-1.3 times that of the iron element.

10. The method for recycling the acid-soluble slag of neodymium iron boron waste as claimed in claim 1, wherein, In the first iron precipitation, the aging time is 3-6 h.

11. The method for recycling acid-soluble slag from neodymium-iron-boron waste materials according to claim 1, characterized in that, In the second iron precipitation, the precipitation time is 1-5 h.

12. The method for recycling the acid leaching slag of neodymium iron boron waste as claimed in claim 1, wherein, In the second iron precipitation, the oxidizing atmosphere is to introduce a gas containing oxygen.

13. The method for recycling acid-soluble slag from neodymium-iron-boron waste as claimed in claim 1, wherein, In the enrichment of cobalt and rare earths, the precipitation time is 0.5-5 h.

14. The method for recycling the acid leaching slag of neodymium-iron-boron waste materials according to claim 1, characterized in that, In the first iron precipitation, the iron phosphate contains crystal water, and the iron phosphate also needs to be calcined at 550-800 °C; the calcination time is 1-3 h.

15. The method for recycling the acid-soluble slag of neodymium-iron-boron waste as described in claim 14, characterized in that, The iron phosphate after calcination includes elements with the following mass percentages: 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 therein is Fe / P = 0.96-1.0.

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