Neodymium iron boron secondary waste recycling method

Abstract

The application discloses a neodymium-iron-boron secondary waste recycling method, which comprises the following steps: step 1, reacting neodymium-iron-boron secondary waste with acid solution, controlling the pH of the solution after reaction to be 0.5-1.5, and performing solid-liquid separation to obtain filter liquor A containing Fe 3+ and filter residue A; step 2, reducing Fe 3+ in the filter liquor A into Fe 2+ , performing solid-liquid separation to obtain filter liquor B and filter residue B; step 3, adjusting the pH of the filter liquor B to 2-6, performing solid-liquid separation to obtain filter liquor C and filter residue C; and step 4, reacting the filter liquor C with a precipitant, performing solid-liquid separation to obtain filter residue D and filter liquor D. The present application realizes short-process comprehensive utilization of oxalic acid, hydrochloric acid and iron resources, is friendly to the operation environment, does not need strong-acid and strong-alkali equipment, and can simultaneously realize green and efficient comprehensive utilization of iron-containing waste residue and oxalic acid wastewater.

Description

Technical Field

[0001] This invention belongs to the field of resource recycling, specifically relating to a method for recycling and treating secondary waste of neodymium iron boron. Background Technology

[0002] Neodymium iron boron (NdFeB) secondary waste is generally obtained by roasting, leaching to remove impurities, and separating it from rare earth slurry to obtain iron-containing slag (commonly known as iron slag). Industrially, iron slag is used as a raw material for ironmaking. This method has poor economic efficiency, as high-value elements such as rare earths and cobalt in the slag are not recovered, resulting in a waste of resources.

[0003] Regarding the recycling of NdFeB secondary waste, the existing technology employs four processes: rare earth extraction and recycling separation process, cobalt oxide recycling and separation process, iron oxide recycling process, and effluent recycling process, which can achieve the recycling of rare earth, cobalt, and iron.

[0004] Another method involves mixing the acid leaching residue of NdFeB waste with the acid leaching solution from the acid leaching and separation processes in a neutralization reactor. The neutralized slurry is then filtered to obtain a neutralized liquid and a neutralized residue. The neutralized liquid is used as a raw material for preparing iron oxide red. The neutralized residue is mixed with the acid leaching residue washing solution obtained from the acid leaching process and sulfuric acid is added for acid leaching reaction. After filtration, acid leaching solution and acid leaching residue are obtained. The acid leaching solution is used for neutralization of feed ingredients. The acid leaching residue is mixed with the later washing solution produced in the iron oxide red preparation process and slurryed. Then, it is filtered and washed to dissolve the rare earth sulfates in the acid leaching residue. The filtrate obtained after separation is sent to the rare earth extraction process for the preparation of rare earth products.

[0005] The aforementioned methods suffer from high acid consumption, high production costs, the generation of large quantities of difficult-to-treat high-salt wastewater, long production processes, complex techniques, and difficulty in industrialization. Furthermore, the comprehensive utilization of NdFeB waste generates a large amount of difficult-to-treat, high-COD, acidic wastewater. The industry has been searching for a simple solution to address these issues simultaneously, achieving green environmental protection, comprehensive resource utilization, and the preparation of new materials. Summary of the Invention

[0006] To address the above problems, this invention provides a method for recycling and treating secondary waste of neodymium iron boron magnets, the method comprising the following steps:

[0007] A method for recycling and treating secondary waste of neodymium iron boron includes the following steps:

[0008] Step 1: React the NdFeB secondary waste with acid, controlling the pH of the solution after the reaction to be 0.5-1.5, then perform solid-liquid separation to obtain Fe-containing waste. 3+ Filtrate A and filter residue A;

[0009] Step 2: Remove Fe from filtrate A 3+ Reduced to Fe2+ Solid-liquid separation was performed to obtain filtrate B and filter residue B.

[0010] Step 3: Adjust the pH of filtrate B to 2-6, perform solid-liquid separation, and obtain filtrate C and filter residue C;

[0011] Step 4: React filtrate C with a precipitant to separate the solid and liquid, obtaining filter residue D and filtrate D.

[0012] Optionally, the NdFeB secondary waste is iron-containing waste residue obtained by roasting, leaching, and solid-liquid separation of NdFeB waste.

[0013] Preferably, the iron-boron secondary waste contains 10% to 65% iron, 0.1% to 10% silicon, 0.1% to 5% aluminum, 0.01% to 1% calcium, 0.01% to 3% boron, and 0.01% to 0.5% rare earth elements.

[0014] Optionally, the acid solution in step 1 is at least one of hydrochloric acid, nitric acid, sulfuric acid, and oxalic acid wastewater; and / or

[0015] The acid concentration in the acid solution is 1.5-2 mol / L, and the solid-liquid ratio is 1:5-1:25; and / or

[0016] The oxalic acid wastewater is obtained by precipitating a solution containing rare earth ions with oxalic acid.

[0017] The oxalic acid wastewater contains 1.5-2 mol / L HCl and 0.07-0.15 mol / L oxalic acid; and / or

[0018] The mass ratio of Al / Fe in filtrate A is 0.5-5%, Ca / Fe is 0.05-2%, and Si / Fe is 0.01-1%.

[0019] Optionally, in step 2, filtrate A is reduced using a reducing agent or reduced by light.

[0020] Preferably, the reducing agent is at least one selected from iron, iron-carbon, hydroxylamine hydrochloride, and ascorbic acid;

[0021] Preferably, Fe in filtrate B 3+ Concentration ≤ 0.5 g / L; further preferred, Fe 3+ Concentration ≤ 0.05 g / L.

[0022] Optionally, step 3 may further include adding a purification agent to the filtrate B;

[0023] Preferably, the impurity remover is at least one of sodium sulfide, organic sulfur, PAC, and PAM.

[0024] Optionally, in step 3, at least one of sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium hydroxide, ammonia, ammonium carbonate, and ammonium bicarbonate is used to adjust the pH of filtrate B to 2-6; and / or

[0025] In step 3, ammonia, ammonium carbonate, and ammonium bicarbonate are used to adjust the pH to 4.5-5.5.

[0026] Optionally, the mass ratio of Al / Fe in the filtrate C is ≤0.061%, Ca / Fe ≤0.040%, and Si / Fe ≤0.026%.

[0027] Optionally, the precipitant is one of carbonate, bicarbonate, oxalate, urea, and ammonia; and / or

[0028] The precipitant is at least one of ammonium bicarbonate, ammonium carbonate, sodium bicarbonate, and sodium carbonate.

[0029] Optionally, the method further includes calcining the filter residue D to obtain iron oxide I; and / or

[0030] Optionally, the purity of the iron oxide I is greater than 96%;

[0031] The calcination temperature is 400℃-700℃; and / or

[0032] Iron oxide I is subjected to a calcium removal post-treatment to obtain iron oxide III; the calcium removal post-treatment includes soaking the iron oxide I in an ammonium chloride solution; and / or

[0033] The purity of the iron oxide III is greater than 98%.

[0034] Optionally, the CO2 in the flue gas produced during the combustion process can be absorbed by alkali to obtain carbonate, which is then returned to step 4.

[0035] Optionally, the solid-liquid separation method may be at least one of filtration, centrifugation, vacuum filtration, and sedimentation.

[0036] Optionally, the acid solution is oxalic acid wastewater, and step 2 further includes calcining filter residue B to obtain iron oxide II; and / or

[0037] The purity of the iron oxide II is greater than 96%.

[0038] Optionally, the filtrate D can be evaporated to obtain recovered salt.

[0039] The present invention has the following beneficial effects:

[0040] This invention utilizes selective leaching and chemical precipitation processes to remove elements such as calcium, silicon, aluminum, and cobalt from waste materials, obtaining high-purity iron-containing products. This achieves efficient iron recovery from waste, forming a diversified resource recycling chain and improving overall resource utilization. This solution offers significant socio-economic benefits, is low-cost, has easily controllable processes, and is readily industrializable, making it highly valuable for widespread application.

[0041] This invention utilizes oxalic acid wastewater to dissolve iron slag, saving acid consumption and significantly reducing production costs. It promotes a green circular economy and has significant socio-economic value. It achieves a short-process comprehensive utilization of oxalic acid, hydrochloric acid, and iron resources, with an environmentally friendly operation that eliminates the need for equipment resistant to strong acids and alkalis. It simultaneously realizes the green and efficient comprehensive utilization of iron-containing waste slag and oxalic acid wastewater. In this scheme, after dissolving the iron slag, the oxalate ions in the acidic wastewater are converted into high-value materials through ferrous oxalate precipitation. After precipitation with carbonates, ferrous carbonate is obtained, transforming the wastewater into easily treatable carbon precipitation wastewater that can be seamlessly integrated with evaporation. Attached Figure Description

[0042] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0043] Figure 1 This is a flowchart of the method of the present invention.

[0044] Figure 2 This is a flowchart of an embodiment of the present invention. Detailed Implementation

[0045] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0046] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0047] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0048] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0049] like Figure 1 As shown, this invention proposes a method for recovering rare earth elements and iron from neodymium iron boron secondary waste, comprising the following steps:

[0050] Step 1: React the neodymium iron boron secondary waste with acid until the pH reaches 0.5-1.5, then separate the solid and liquid components to obtain filtrate A containing ferric ions and filter residue A.

[0051] Step 2: Reduce Fe³⁺ in filtrate A using a reduction method. + Reduced to Fe² + Solid-liquid separation yields filtrate B and filter residue B.

[0052] Step 3: Add alkali to filtrate B, adjust the pH to 2-6, remove impurities, and separate the solid and liquid to obtain filtrate C and filter residue C.

[0053] Step 4: React filtrate C with a precipitant to separate the solid and liquid, obtaining filter residue D and filtrate D.

[0054] The neodymium iron boron secondary waste is obtained by roasting pretreatment, hydrochloric acid leaching, impurity removal and separation from rare earth liquid to obtain iron-containing waste residue (hereinafter referred to as iron slag).

[0055] Furthermore, the acid in step 1 is at least one of hydrochloric acid, nitric acid, sulfuric acid, and oxalic acid in the wastewater.

[0056] Preferably, the acid in step 1 is oxalic acid wastewater. Oxalic acid and its salts are widely used in non-ferrous metallurgy, metal processing, pharmaceuticals, printing and dyeing, and plastics industries. The hydrometallurgical industry generates a large amount of wastewater containing oxalic acid (and / or oxalate ions) annually (hereinafter referred to as oxalic acid wastewater). Improper treatment will cause serious environmental pollution and a significant waste of valuable resources. Based on the national production of rare earth elements and neodymium iron boron magnets, the annual production of oxalic acid wastewater is estimated at 3.9 million cubic meters. Oxalic acid wastewater is a highly acidic wastewater with a high COD value; direct discharge without treatment will consume a large amount of dissolved oxygen in the water. Industrially, lime neutralization is commonly used to treat this type of wastewater. This method is simple to operate and has low cost, but it generates a large amount of calcium-containing wastewater. 2+The high-salt wastewater containing impurities also generates a large amount of neutralization residue that requires additional treatment, increasing treatment costs and resulting in the underutilization of various valuable resources. Comprehensive utilization of oxalic acid wastewater resources has not been achieved.

[0057] Traditional treatment processes for oxalic acid wastewater generally include lime neutralization and Fenton oxidation. Lime neutralization generates a large amount of calcium-containing wastewater. 2+ High-salt wastewater containing impurities such as calcium requires further treatment to meet discharge requirements; this type of wastewater is difficult and costly to treat. Furthermore, the lime neutralization method generates a large amount of neutralization residue that requires additional treatment, increasing costs and resulting in the underutilization of valuable resources. Fenton oxidation, as an advanced oxidation technology, produces hydroxyl radicals with high oxidation potentials, enabling indiscriminate oxidation of organic matter. However, the reaction rate of hydroxyl radicals in treating wastewater containing oxalic acid is very slow, resulting in very low treatment efficiency, complex process control, and high costs.

[0058] This method allows iron slag to react with oxalic acid to form ferrous oxalate precipitate, and ferric iron to form ferric oxalate complexes with excellent photochemical activity. Through photodecomposition, a small portion of the oxalate ions leaves the water as CO2, while ferric iron is converted to ferrous iron, further precipitating oxalate ions. This process achieves resource utilization of oxalate ions and reduces carbon emissions.

[0059] Furthermore, this solution can recover high-value salts such as rare earth elements and cobalt while treating oxalic acid wastewater, thus both recovering resources and generating economic value, and improving the purity of the product.

[0060] Furthermore, in step 1, the acid concentration is 1.5-2 mol / L, and the solid-liquid ratio is 1:5-1:25.

[0061] Furthermore, the reduction method in step 2 is at least one of iron reduction, light reduction, and / or a reducing agent.

[0062] Furthermore, the impurity removal agent in step 3 is at least one of alkali and sodium sulfide, organic sulfur, PAC, and PAM.

[0063] Furthermore, the alkali used to adjust the pH in step 3 can be one or more of sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium hydroxide, ammonia, ammonium carbonate, and ammonium bicarbonate.

[0064] Preferably, the alkali mentioned in step 3 can be ammonia, ammonium carbonate, or ammonium bicarbonate. The ammonium ions are easily removed after washing and calcination, resulting in better and more stable product quality control.

[0065] Preferably, the pH in step 3 is 4.5-5.5.

[0066] In step 3, the mass ratio of filtrate C is Al / Fe ≤ 0.061%, Ca / Fe ≤ 0.040%, and Si / Fe ≤ 0.026%.

[0067] Furthermore, in step 3, a purification agent is added to precipitate impurity elements and facilitate solid-liquid separation, making it easy to industrialize and engineer. This achieves technical effects that are unexpected by those skilled in the art.

[0068] Furthermore, the precipitant in step 4 is at least one of ammonium bicarbonate, ammonium carbonate, sodium bicarbonate, and sodium carbonate. Preferably, the precipitant in step 4 is at least one of ammonium bicarbonate and ammonium carbonate.

[0069] Furthermore, the solid-liquid separation method may be one or more of filtration, centrifugation, vacuum filtration, and sedimentation.

[0070] Furthermore, after step 4, the filter residue D is calcined to obtain iron oxide I.

[0071] Furthermore, the burning temperature is 400℃-700℃.

[0072] Furthermore, CO2 is generated during the combustion process. The CO2 in the flue gas is absorbed by an alkali solution to obtain carbonates, which are then returned to step 4. This method utilizes the CO2 generated from the combustion of ferrous oxalate and ferrous carbonate, which, after absorption by an alkali solution, can prepare precipitant carbonates, achieving carbon recycling and significantly reducing carbon emissions.

[0073] Furthermore, the iron reduction method in step 2 is at least one of elemental iron, iron-carbon, and iron alloy.

[0074] The photoluminescence reduction method described in step 2 involves irradiation with visible or ultraviolet light. The light source can be sunlight. Visible light with a wavelength less than 570 nm is preferred, and ultraviolet light is even more preferred.

[0075] The reducing agent in step 2 is hydroxylamine hydrochloride or ascorbic acid.

[0076] Step 2 describes the reduction of C(Fe) 3+ ≤0.5g / L. Preferred C(Fe) 3+ ≤0.05g / L.

[0077] Furthermore, when the acid is oxalic acid wastewater, the filter residue B mentioned in step 2 is ferrous oxalate, which is calcined to iron oxide II.

[0078] Furthermore, the iron oxide I is post-treated to obtain iron oxide III. The purity of the iron oxide III obtained after treatment can reach over 98%.

[0079] Furthermore, in step 1, the mass ratio of Al / Fe in filtrate A is 0.5-5%, Ca / Fe is 0.05-2%, and Si / Fe is 0.01-1%.

[0080] Furthermore, the filtrate D is wastewater, which can be prepared into salt after evaporation; the filter residue D is ferrous carbonate, which can be prepared into pigments, magnetic materials, and catalysts.

[0081] The mass ratio of Al / Fe in filtrate A in step 1 is 0.5-5%, Ca / Fe is 0.05-2%, and Si / Fe is 0.01-1%.

[0082] The iron reduction method described in step 2 is at least one of elemental iron, iron-carbon, or iron alloy.

[0083] The photoluminescence reduction method described in step 2 involves irradiation with visible or ultraviolet light. The light source can be sunlight. Visible light with a wavelength less than 570 nm is preferred, and ultraviolet light is even more preferred.

[0084] The reducing agent in step 2 is hydroxylamine hydrochloride or ascorbic acid.

[0085] Step 2 describes the reduced filter residue B Fe 3+ Concentration ≤ 0.5 g / L. Fe is preferred. 3+ Concentration ≤ 0.05 g / L.

[0086] The filter residue B mentioned in step 2 is ferrous oxalate, which is calcined to obtain iron oxide II. The purity of iron oxide II is greater than 96%, which can be used as a ferrite precursor raw material and meets the standard (GB / T 24244-2009, YHT5).

[0087] This solution utilizes a novel green chemistry method to treat high-salt, high-COD oxalic acid wastewater. Simultaneously, it prepares ferrous oxalate from the oxalate ions in the wastewater, realizing the resource utilization and productization of oxalic acid wastewater. Furthermore, it achieves the comprehensive utilization of resources such as iron, rare earth elements, and cobalt, as well as the preparation of new materials.

[0088] Compared to existing extraction processes, this method omits traditional extraction and separation steps, reducing processing costs and significantly shortening the production cycle. Furthermore, the process is stable, control is significantly reduced, and automation is easily achieved. Impurities are controllable, ensuring product quality and facilitating recycling. The equipment is simple, promoting industrialization. The process is highly adaptable, capable of handling high-impurity raw materials, and is easy to promote.

[0089] This solution achieves a short-process, comprehensive utilization of iron resources, hydrochloric acid, and oxalic acid. It is environmentally friendly, requiring no equipment resistant to strong acids and alkalis, and avoids other environmental problems while comprehensively utilizing waste residue and wastewater. It can fundamentally solve the comprehensive treatment problems of iron slag and oxalic acid wastewater in the hydrometallurgical industry in one go. Based on the characteristics of impurities, this solution effectively separates various impurities from iron, while simultaneously recovering high-value elements. This solution can simultaneously produce ferrous oxalate and ferrous carbonate, achieving product diversification.

[0090] This solution utilizes low-value iron resources such as iron slag (approximately 500 yuan / ton) to treat oxalic acid wastewater. This not only achieves the goal of treating waste with waste but also produces high-value new iron oxide materials for ferrite applications (such as ferrous oxalate at approximately 5000 yuan / ton and ferrous carbonate at 7000 yuan / ton). This achieves high-value utilization of iron resources, significantly increasing the value per unit of iron and resulting in significant economic benefits.

[0091] Neodymium iron boron (NdFeB) secondary waste is produced by roasting, leaching, and solid-liquid separation (traditional process) of NdFeB waste to obtain iron-containing slag (hereinafter referred to as iron slag). This material has a complex composition, mainly containing iron, silicon, aluminum, calcium, and boron. Due to the variety and large fluctuations in impurities, it has not been utilized for high-value purposes and has only been used as a raw material for iron smelting. In industrial applications, based on the high-value elements it contains, it can generally be divided into cobalt-containing and cobalt-free types.

[0092] Oxalic acid wastewater is produced from NdFeB waste through roasting pretreatment, leaching, and solid-liquid separation to obtain rare earth feed solution. This feed solution is then subjected to traditional extraction separation, precipitation, and calcination to obtain rare earth oxides (traditional process). When oxalic acid is selected for precipitation, a large amount of oxalic acid-containing wastewater is generated. This wastewater has a complex composition, with anions mainly consisting of chloride ions, oxalate ions, and boron, and cations mainly consisting of hydrogen ions, aluminum ions, and zinc ions. The high chloride content results in high salinity, and the presence of oxalate ions results in high COD, classifying this wastewater as high-salt, high-COD wastewater. To meet discharge standards, COD and salt content need to be reduced, making treatment difficult and costly.

[0093] The comprehensive utilization of oxalic acid wastewater has always been a pressing but unresolved problem in the industry. Due to the high levels of oxalate and aluminum ions in the wastewater, it cannot be easily reused in traditional processes and the preparation of new materials. On the one hand, oxalate readily precipitates with rare earth elements, cobalt, and calcium, affecting the quality of various products; on the other hand, it easily introduces large amounts of impurities such as aluminum and zinc into the system, causing fatal damage to various precipitation systems.

[0094] Both iron slag and oxalic acid wastewater contain a large number of impurities. The removal of these impurities is a core issue in the material preparation process for those skilled in the art. Either the impurity removal process is complex and lengthy, or pure raw materials are selected from the source.

[0095] Example 1

[0096] like Figure 2 As shown, in this embodiment, neodymium iron boron waste (Fe 39.83%, Al 0.35%, Ca 0.15%, Si 0.30%, REO 20.38%) is first pretreated by roasting. Then, it is leached with hydrochloric acid to obtain rare earth solution and iron-containing waste residue (hereinafter referred to as iron slag). After traditional extraction and separation, oxalic acid is added to the rare earth solution for precipitation, generating a large amount of oxalic acid wastewater containing hydrochloric acid.

[0097] Step 1: Dissolve 100g of iron slag (Fe 39.81%, Al 0.30%, Ca 0.075%, Si 0.29%, REO 0.20%) in oxalic acid wastewater with an oxalate concentration of 0.13mol / L and an acid value of 1.68mol / L. Raise the pH to 0.5 and filter to obtain 1.18L of filtrate A containing ferric ions [C(Fe) = 27.03g / L], and filter residue A.

[0098] Step 2: Add iron powder to filtrate A and expose it to sunlight to react the Fe... 3+ Reduced to Fe 2+ Bubbles and precipitates are produced. Fe 3+ When the concentration decreased to 0.05 g / L, solid-liquid separation was performed, yielding filtrate B (Fe 34.37 g / L, Al 0.235 g / L, Ca 0.020 g / L, Si 0.006 g / L) and filter residue B. The obtained filter residue B, ferrous oxalate, was calcined at 400℃ for 1.5 h to obtain ferric oxide II with a purity of 96.95%. This achieves high-value comprehensive utilization of oxalate.

[0099] Step 3: Slowly pump 81 g / L ammonium bicarbonate solution into filtrate B until the pH is 5-5.5, and perform solid-liquid separation to obtain filtrate C (Fe 30.93 g / L, Al 0.019 g / L, Ca 0.013 g / L, Si 0.0084 g / L) and filter residue C.

[0100] Step 4: Add filtrate C to an 81 g / L ammonium bicarbonate solution. Heat in a water bath at 45°C, rotating at 100 rpm. The filtrate C is pumped in at a rate of 0.03-0.1 ml / min, resulting in a tea-colored precipitate. Control the final pH to 8-8.5. Separate the solid and liquid components to obtain filter residue D and filtrate D (Fe 2.15 mg / L, REO < 1.0 mg / L). Filter residue D is mainly ferrous carbonate. Drying yields 98% ferric oxide I, weighing 53.13 g (impurities included Al 0.042%, Ca 0.028%, Si 0.018%, MnO 0.01%, and sulfates in the form of SO42-). 2- 0.01% of chloride as Cl -(0.20%), can be used as a ferrite precursor raw material, conforming to the standard (GB / T 24244-2009, YHT5).

[0101] Filtrate D is ammonium-containing carbon precipitation wastewater with a COD of 150 mg / L. It can be seamlessly integrated with evaporation and crystallization to obtain ammonium chloride byproduct (product standard GB / T 2946-2018, conforming to agricultural standards).

[0102] Compared to traditional acid leaching methods, this technical solution uses acidic wastewater to dissolve iron slag, saving on acid consumption. Simultaneously, it transforms difficult-to-treat, high-salt, high-COD oxalic acid wastewater into easily treatable carbon precipitation wastewater, allowing for seamless integration with evaporation. Production costs are significantly reduced. This approach is conducive to achieving a green circular economy and has significant socio-economic value. This solution uses oxalic acid wastewater to leach low-value iron slag (approximately 500 RMB / ton) from rare earth recovery from NdFeB waste, not only achieving the goal of waste-to-waste treatment but also producing a high-value ferrous oxalate byproduct (approximately 5000 RMB / ton). This achieves high-value utilization of iron resources, increasing the value per unit of iron by at least 15 times. Compared to traditional iron smelting methods, this not only improves the utilization of iron resources and broadens their application scope but also yields significant economic benefits.

[0103] The iron powder and ammonium bicarbonate used in this embodiment have advantages such as wide availability, safety, stability, and easy acquisition. The process is flexible, stable, and easy to industrialize and engineer. This embodiment can recover high-value oxalates, rare earth oxalates, and other valuable elements while utilizing iron slag, thus both recovering resources and generating economic value, and improving the purity of by-products.

[0104] Example 2

[0105] Step 1: Dissolve 50g of iron slag (Fe 32.86%, Al 1.59%, Ca 0.59%, Si 4.67%, REO 0.24%) in oxalic acid wastewater with an oxalate concentration of 0.07mol / L and an acid value of 1.50mol / L. Raise the pH to 0.5 and filter to obtain 0.58L of filtrate A containing ferric ions (Fe 22.00g / L, Al 0.45g / L, Ca 0.022g / L, Si 0.20g / L, REO 0.12g / L) and filter residue A.

[0106] Step 2: Add an appropriate amount of iron and carbon to filtrate A and place it in sunlight to allow the Fe... 3+ Reduced to Fe 2+ Bubbles and precipitates are produced. Fe 3+When the concentration decreased to 0.5 g / L, solid-liquid separation was performed, yielding filtrate B (Fe 29.84 g / L, Al 0.40 g / L, Ca 0.020 g / L, Si 0.18 g / L, REO 0.11 g / L) and filter residue B. The obtained filter residue B was dried to obtain iron oxide II with a purity of 96.25%.

[0107] Step 3: Slowly pump 6 mol / L sodium hydroxide solution into filtrate B until the pH is 3.8-4, and perform solid-liquid separation to obtain filtrate C (Fe 23.87 g / L, Al 0.30 g / L, Ca 0.019 g / L, Si 0.12 g / L) and filter residue C.

[0108] Step 4: Add 81 g / L ammonium bicarbonate solution to filtrate C, heat in a water bath at 40°C, rotate at 100 r / min, and pump at a rate of 0.03-0.1 ml / min to obtain a gray precipitate. Control the endpoint pH to be 8-8.5, and separate the solid and liquid to obtain filter residue D and filtrate D (Fe 5.14 mg / L).

[0109] The filter residue D is mainly ferrous carbonate. After drying and calcining at 500℃ for 1 hour, 20.45g of 96% iron oxide I is obtained (the impurity content, as tested, includes Al 0.85%, Ca 0.056%, Si 0.033%, and REO 0.22%). It can be used as polishing paste and other industrial raw materials, and meets the standard (HG / T 2574-2009, Class II).

[0110] Filtrate D is ammonium-containing carbon precipitation wastewater with a COD of 140 mg / L. It can be seamlessly integrated with evaporation and crystallization to obtain ammonium chloride byproduct (product standard GB / T 2946-2018, conforming to agricultural standards).

[0111] Example 3

[0112] Step 1: Dissolve 54g of iron slag (Fe 49.88%, Al 0.25%, Ca 0.37%, Si 0.15%, REO 0.41%, Co 0.65%) in oxalic acid wastewater with an oxalate concentration of 0.13mol / L and an acid value of 1.68mol / L. Raise the pH to 0.3 and filter to obtain 0.94L of filtrate A containing iron ions (Fe 27.68g / L, Al 0.57g / L, Ca 0.058g / L, Si 0.085g / L, REO 0.23g / L, Co 0.42g / L).

[0113] Step 2: Add iron and carbon to filtrate A, and expose the Fe to sunlight. 3+ Reduced to Fe 2+ Bubbles and black precipitate are produced. Fe 3+When the concentration dropped to 1.06 g / L (the yellow color faded), solid-liquid separation was performed to obtain filtrate B (Fe 37.42 g / L, Al 0.56 g / L, Ca 0.067 g / L, Si 0.14 g / L, REO 0.25 g / L, Co 0.39 g / L) and filter residue B.

[0114] Step 3: Slowly pump 6 mol / L ammonia solution into filtrate B until the pH is 4-4.5. Add PAC and PAM to perform solid-liquid separation, and obtain filtrate C (Fe 31.81 g / L, Al 0.0073 g / L, Ca 0.10 g / L, Si 0.036 g / L, REO 0.18 g / L, Co 0.32 g / L) and filter residue C.

[0115] Step 4: Prepare an 81 g / L ammonium bicarbonate solution with tap water, add it to filtrate C, heat in a water bath at 40°C, rotate at 100 r / min, and pump at a rate of 0.1 ml / min to obtain a gray precipitate (easily settles). Control the final pH to 6-6.5, separate the solid and liquid, and obtain filter residue D and filtrate D (Fe 2 g / L).

[0116] The filter residue D is mainly ferrous carbonate. After drying and calcining at 700℃ for 1 hour, 18.78 g of ferrous oxide I with a purity of 98.01% was obtained. (The impurities were found to be Al 0.045%, Ca 0.13%, Si 0.027%, REO 0.41%, and Co 0.61%). It can be used as polishing paste and other industrial raw materials and meets the standard (HG / T 2574-2009, Class II).

[0117] Filtrate D is ammonium-containing carbon precipitation wastewater with a COD of 55 mg / L. It can be seamlessly integrated with evaporation and crystallization to obtain ammonium chloride byproduct (product standard GB / T 2946-2018, conforming to agricultural standards).

[0118] Example 4

[0119] Step 1: Dissolve 50g of iron slag (Fe 63.64%, Al 2.12%, Ca 0.03%, Si 1.00%, REO 0.33%, Co 0.73%) in 2mol / L hydrochloric acid, raise the pH to 0.5, and filter to obtain 0.80L of filtrate A containing iron ions [C(Fe) = 31.43g / L], and filter residue A (Fe 47.73%, Al 6.95%, Ca 0.018%, Si 3.22%, REO 0.011%, Co 11.71%).

[0120] Step 2: Slowly add filtrate A to the ascorbic acid solution, while simultaneously adding 6 mol / L ammonia water to maintain the pH at 2-3. Add Fe... 3+Reduced to Fe 2+ (m(Fe) 3+ (≤0.05g / L).

[0121] Step 3: Continue adding 6 mol / L ammonia solution to the filtrate until the pH reaches 4.5-5. Then add organic sulfur (diethyl dithiocarbamate DDTC), PAC, and PAM for solid-liquid separation, yielding filtrate C (Fe 23.57 g / L, Al 0.010 g / L, Ca 0.0051 g / L, Si 0.0051 g / L, REO 0.065 g / L, Co 0.015 g / L) and filter residue C. After adding DDTC, Co is removed as organic sulfur precipitate.

[0122] Step 4: Prepare an 81 g / L ammonium bicarbonate solution with pure water, add it to filtrate C, heat in a water bath at 40°C, rotate at 100 r / min, and pump at a rate of 0.1 ml / min to obtain a gray precipitate. Control the final pH to be 8-8.5, and separate the solid and liquid to obtain filter residue D and filtrate D (Fe 2 mg / L).

[0123] The filter residue D mainly consisted of ferrous carbonate. After drying, 27.5g of ferric oxide (I) with a purity of 98.03% was obtained. (Imperfections were detected, including Al 0.031%, Ca 0.015%, Si 0.015%, REO 0.19%, Co 0.45%, MnO 0.10%, and sulfates in the form of SO42-). 2- It contains 0.02% total content and 0.05% chloride, which can be used as a ferrite precursor raw material and meets the standard (GB / T 24244-2009, YHT5).

[0124] Filtrate D is ammonium-containing carbon precipitation wastewater with a COD of 145 mg / L. It can be seamlessly integrated with evaporation and crystallization to obtain ammonium chloride byproduct (product standard GB / T 2946-2018, conforming to agricultural standards).

[0125] Example 5

[0126] This embodiment is basically the same as Embodiment 4, except that hydroxylamine hydrochloride is used instead of ascorbic acid. After impurity removal, precipitation, and calcination, 98.01% iron oxide I is obtained, which meets the standard (GB / T 24244-2009, YHT5).

[0127] Example 6

[0128] Step 1: Dissolve 54 kg of iron slag (Fe 49.88%, Al 0.25%, Ca 0.37%, Si 0.15%, REO 0.41%, Co 0.65%) in oxalic acid wastewater with an oxalate concentration of 0.13 mol / L and an acid value of 1.68 mol / L. Raise the pH to 0.3 and filter to obtain 980 L of filtrate A containing iron ions [C(Fe) = 27.60 g / L], and filter residue A.

[0129] Step 2: Add iron and carbon to filtrate A and expose it to sunlight to react the Fe... 3+ Reduced to Fe 2+ Bubbles and black precipitate are produced. Fe 3+ When the concentration dropped to 0.92 g / L, solid-liquid separation was performed, yielding filtrate B (Fe 37.38 g / L, Al 0.53 g / L, Ca 0.062 g / L, Si 0.13 g / L, REO 0.22 g / L, Co 0.35 g / L) and filter residue B.

[0130] Step 3: Slowly pump 6 mol / L ammonia solution into filtrate B until the pH is 4-4.5. Add PAC and PAM, and perform solid-liquid separation to obtain filtrate C (Fe 31.78 g / L, Al 0.0070 g / L, Ca 0.10 g / L, Si 0.032 g / L, REO 0.16 g / L, Co 0.30 g / L) and filter residue C.

[0131] Step 4: Prepare an 81 g / L ammonium bicarbonate solution with pure water, add it to filtrate C, heat in a water bath at 40°C and rotate at 100 r / min to obtain a gray precipitate. Control the final pH to be 6-6.5, and separate the solid and liquid to obtain filter residue D and filtrate D (Fe 2.11 g / L).

[0132] The filter residue D is mainly ferrous carbonate. After drying, it yields iron oxide I with a purity of 98.03%, weighing 20.8 kg (the impurity content, as tested, includes Al 0.043%, Ca 0.12%, Si 0.023%, REO 0.39%, and Co 0.58%). It can be used as polishing paste and other industrial raw materials, and meets the standard (HG / T 2574-2009, Class II).

[0133] Filtrate D is ammonium-containing carbon precipitation wastewater with a COD of 60.5 mg / L. It can be seamlessly integrated with evaporation and crystallization to obtain ammonium chloride byproduct (product standard GB / T 2946-2018, conforming to agricultural standards).

[0134] The filter residue D was ignited at 600°C for 2 hours. The CO2 produced during the ignition process was absorbed with ammonia water to obtain an ammonium bicarbonate solution. The obtained ammonium bicarbonate solution was then returned to step 4.

[0135] Example 7

[0136] This embodiment is basically the same as Embodiment 2, except that 84 g / L sodium bicarbonate solution is used to replace all ammonium bicarbonate, and the endpoint pH is controlled to be 8-8.5 to obtain 96% iron oxide I.

[0137] Example 8

[0138] The iron oxide I obtained in Example 3 was ground, passed through a 300-mesh sieve, and soaked in a 1 mol / L ammonium chloride solution to obtain iron oxide (Ca 0.09%). This step significantly reduced the Ca content from 0.13% to 0.09%. Hydrochloric acid was then added for optimal solubility, controlling the pH at 2-2.5. Solid-liquid separation and calcination were performed to obtain 98.28% iron oxide III (Al 0.025%, Ca 0.013%, Si 0.016%, REO 0.28%, Co 0.50%, MnO 0.05%, sulfate in SO42-). 2- (Total: 0.01%, Chloride: 0.22%).

[0139] The test results show that the levels of Ca, REO, and Co in iron oxide are significantly reduced after post-treatment, thus not affecting product quality and meeting the standard (GB / T 24244-2009, YHT5). High-value elements such as REO and Co are enriched in the solution and can be returned to the main rare earth separation process to prepare rare earth oxides, cobalt oxides, and other products, thereby improving the recovery rate of high-value elements.

[0140] Example 9

[0141] Step 1: Dissolve 50g of iron slag (Fe 63.64%, Al 2.12%, Ca 0.03%, Si 1.00%, REO 0.33%, Co 0.73%) in 2mol / L nitric acid, raise the pH to 1.5, and filter to obtain 1L of filtrate A containing iron ions [C(Fe) = 32.33g / L].

[0142] Step 2: Slowly add filtrate A to the ascorbic acid solution, while simultaneously adding 6 mol / L sodium hydroxide to maintain the pH at 2.5-3. Add Fe... 3+ Reduced to Fe 2+ (m(Fe) 3+ (≤0.05g / L).

[0143] Step 3: Continue adding 6 mol / L sodium hydroxide solution to the filtrate until the pH is 5.5-6. Then add sodium sulfide, PAC, and PAM. Perform solid-liquid separation to obtain filtrate C (Fe 28.85 g / L, Al 0.005 g / L, Ca 0.0041 g / L, Si 0.0046 g / L, REO 0.063 g / L, Co 0.013 g / L) and filter residue C.

[0144] Step 4: Prepare an 81 g / L sodium bicarbonate solution with pure water, add it to filtrate C, heat in a water bath at 40°C and rotate at 100 r / min to obtain a gray precipitate, control the endpoint pH to 8-8.5, separate the solid and liquid to obtain filter residue D and filtrate D (Fe 0.5 mg / L).

[0145] The filter residue D is mainly ferrous carbonate, which can be used as a raw material for pigments, magnetic materials, and catalysts.

[0146] Filtrate D is ammonium-containing carbon precipitation wastewater with a COD of 103 mg / L. It can be seamlessly integrated with evaporation and crystallization to obtain sodium chloride as a byproduct.

[0147] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for recycling and treating secondary waste of neodymium iron boron, characterized in that, Includes the following steps: Step 1: React the NdFeB secondary waste with acid, controlling the pH of the solution after the reaction to be 0.5-1.5, then perform solid-liquid separation to obtain Fe-containing waste. 3+ The filtrate A and filter residue A are present; the acid solution is oxalic acid wastewater, which is obtained by precipitating a solution containing rare earth ions with oxalic acid; the acid concentration in the acid solution is 1.5-2 mol / L, and the solid-liquid ratio is 1:5-1:25; the oxalic acid wastewater contains 1.5-2 mol / L HCl and 0.07-0.15 mol / L oxalic acid; Step 2: Remove Fe from filtrate A 3+ Reduced to Fe 2+ Solid-liquid separation yields filtrate B and filter residue B; the Fe in filtrate A is removed... 3+ Reduced to Fe 2+ The reduction is carried out using a reducing agent or light irradiation; the reducing agent is at least one of iron, iron-carbon, hydroxylamine hydrochloride, and ascorbic acid; Step 3: Adjust the pH of filtrate B to 2-6, perform solid-liquid separation, and obtain filtrate C and filter residue C; the mass ratio of Al / Fe in filtrate C is ≤0.061%, Ca / Fe ≤0.040%, and Si / Fe ≤0.026%; Step 4: React filtrate C with a precipitant to separate the solid and liquid, obtaining filter residue D and filtrate D.

2. The method for recycling and treating secondary waste of NdFeB according to claim 1, characterized in that, The NdFeB secondary waste is iron-containing waste residue obtained by roasting, leaching, and solid-liquid separation of NdFeB waste; and / or The iron-boron secondary waste contains 10% to 65% iron, 0.1% to 10% silicon, 0.1% to 5% aluminum, 0.01% to 1% calcium, 0.01% to 3% boron, and 0.01% to 0.5% rare earth elements.

3. The method for recycling and treating secondary waste of NdFeB according to claim 1, characterized in that, The mass ratio of Al / Fe in filtrate A is 0.5-5%, Ca / Fe is 0.05-2%, and Si / Fe is 0.01-1%.

4. The method for recycling and treating secondary waste of NdFeB according to claim 1, characterized in that, Step 3 also includes adding a purification agent to the filtrate B; The impurity removal agent is at least one of sodium sulfide, organic sulfur, PAC, and PAM.

5. The method for recycling and treating NdFeB secondary waste according to claim 4, characterized in that, In step 3, at least one of sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium hydroxide, ammonia, ammonium carbonate, and ammonium bicarbonate is used to adjust the pH of filtrate B to 2-6.

6. The method for recycling and treating secondary waste of NdFeB according to claim 5, characterized in that, In step 3, ammonia, ammonium carbonate, and ammonium bicarbonate are used to adjust the pH to 4.5-5.

5.

7. The method for recycling and treating secondary waste of NdFeB iron boron according to claim 1, characterized in that, The precipitant is one of carbonate, bicarbonate, oxalate, urea, or ammonia.

8. The method for recycling and treating secondary waste of NdFeB according to claim 1, characterized in that, The method further includes calcining the filter residue D to obtain iron oxide I; The purity of the iron oxide I is greater than 96%; the calcination temperature is 400℃-700℃.

9. The method for recycling and treating secondary waste of NdFeB according to claim 8, characterized in that, Iron oxide I is subjected to a calcium removal process to obtain iron oxide III; the calcium removal process includes soaking the iron oxide I in an ammonium chloride solution; the purity of the iron oxide III is greater than 98%.

10. The method for recycling and treating secondary waste of NdFeB according to claim 8, characterized in that, The CO2 in the flue gas produced during the combustion process is absorbed by alkali to obtain carbonate, which is then returned to step 4.

11. The method for recycling and treating secondary waste of NdFeB according to claim 1, characterized in that, The solid-liquid separation method is at least one of filtration, centrifugation, vacuum filtration, and sedimentation.

12. The method for recycling and treating secondary waste of NdFeB according to claim 1, characterized in that, Step 2 also includes calcining filter residue B to obtain iron oxide II; The purity of the iron oxide II is greater than 96%.

13. The method for recycling and treating secondary waste of NdFeB according to claim 1, characterized in that, The filtrate D is evaporated to obtain recovered salt.

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