Method for reducing rare earth loss in acid dissolution-impurity removal process of neodymium iron boron waste roasting material through gas oxidation
By combining gas oxidation and alkaline precipitant with seed treatment, the problem of large rare earth loss during the hydrochloric acid dissolution of NdFeB waste roasting materials was solved, low-cost and efficient rare earth recovery was achieved, the production process was simplified and the introduction of sodium impurities was reduced.
Patent Information
- Application Number
- CN202510841307.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-23
- Publication Date
- 2025-09-12
AI Technical Summary
In the hydrochloric acid dissolution process of NdFeB waste roasting materials, the existing technology has problems such as large rare earth loss, introduction of sodium impurities and high production costs. Especially when removing iron and aluminum impurities, the rare earth loss rate is high and the production process is complicated.
This method uses gas oxidation combined with an alkaline precipitant and seed crystals to control the pH and temperature of the oxidation reaction, and reduces rare earth loss through solid-liquid separation and filtration and washing. The specific steps include hydrochloric acid dissolution, solid-liquid separation, the addition of copper chloride and oxidizing gas, an alkaline precipitant, and seed crystal treatment. The bubble size and pH are controlled between 2.5 and 4.0, and the temperature is between 50 and 80°C. Finally, filtration and washing are performed to obtain a decontaminated rare earth solution.
The rare earth loss rate is effectively reduced to less than 0.5%, the production process is simplified, the production cost is reduced, the introduction of sodium impurities is reduced, and the filtering performance is improved.
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Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of resource recycling, and particularly relates to a method for reducing rare earth loss in the acid dissolution-impurity removal process of NdFeB waste roasting materials through gas oxidation. Background Art
[0002] With the rapid development of the new energy sector, demand for NdFeB magnets is rapidly increasing. However, scrap is inevitably generated at every step in the NdFeB magnet production process, from raw material pretreatment to final product testing. Furthermore, as time passes, more and more NdFeB equipment will be scrapped due to end-of-service, generating large amounts of NdFeB scrap. Consequently, the annual production of NdFeB scrap is increasing. According to statistics, approximately 83,000 tons of NdFeB scrap was generated nationwide in 2021, and this figure is expected to exceed 150,000 tons by 2030.
[0003] NdFeB waste contains more than 20% rare earth elements. Currently, the industry mainly uses hydrochloric acid dissolution to recover valuable metals from NdFeB waste. The main process includes oxidation roasting, hydrochloric acid dissolution, extraction separation, precipitation roasting, etc. However, during the hydrochloric acid dissolution process of the NdFeB waste roasted material obtained after oxidation roasting, Fe 2+ and Al 3+ Sodium chlorate needs to be added to dissolve Fe 2+ Oxidized to Fe 3+ At the same time, alkaline compounds are used to adjust the pH and hydrolyze and precipitate to remove impurities such as iron and aluminum. This process results in a significant loss of rare earth elements, causing the rare earth content in the acid slag to exceed 0.5%, resulting in a waste of rare earth resources. Furthermore, the addition of sodium chlorate adds more sodium impurities to the current treatment process, which primarily uses ammonium or calcium salts, hindering the recovery and utilization of salt in the wastewater.
[0004] To reduce rare earth losses during the iron removal process of rare earth solutions, Wang Haibin used the goethite method to remove iron from rare earth solutions, resulting in a rare earth loss of 3.40%. Sun Changyong et al. used phosphoric acid to remove iron, which was also effective in reducing rare earth losses. Li Xiangliang et al. invented a SO2 / O2 segmented catalytic oxidation process for efficient iron removal, which features high efficiency and deep iron removal, effectively reducing primary metal losses without introducing other impurity elements. Furthermore, extraction methods using extractants such as N235 can also effectively remove iron, but they result in significant rare earth losses, and the addition of new organic matter can have a certain impact on the subsequent P507 extraction and separation of rare earths.
[0005] In order to reduce the loss of rare earths in the process of removing aluminum from rare earth solutions, Yang Yang et al. used ammonia water circulation to neutralize and precipitate aluminum ions in praseodymium-neodymium chloride solutions. The aluminum precipitation removal rate reached 88%, and the rare earth precipitation loss rate was only 2.89%. However, the large number of operating steps led to complex production processes and increased production costs. Luo Xianping's research group has explored neutralizing and removing aluminum from low-concentration rare earth solutions by adding organic compounds such as hexamethylenetetramine, decyl glucoside, and dodecyl glucoside as pH regulators. For example, when hexamethylenetetramine was used to neutralize and remove aluminum from leachates, the aluminum removal rate reached 97%, while the rare earth loss rate was only approximately 4%. Xiao Yanfei's research group also proposed that adding a small amount of acetic acid to neutralize and remove aluminum from low-concentration rare earth solutions could reduce the rare earth loss rate from 8% to below 3%. Furthermore, some studies have used organic compounds such as benzoic acid, 8-hydroxyquinoline, and cyclohexanecarboxylic acid to replace inorganic precipitants, reducing the rare earth loss rate to approximately 5% through complexation and precipitation of aluminum ions. However, organic complexing agents can easily cause environmental COD levels to exceed standards and are expensive, making them difficult to control. Wang Dong's research group used solid bases such as hydrotalcite to neutralize and hydrolyze aluminum ions from rare earth solutions, achieving a suspension filtration time of only approximately 20 seconds and a rare earth loss rate of 4.3%. However, the alkalinity of solid alkali is too weak and the required amount is large, which leads to problems such as reduced production efficiency and increased slag volume.
[0006] Neodymium iron boron scrap roasting material contains not only aluminum but also a large amount of iron, which will enter the leachate to varying degrees during the acid dissolution process. How to simultaneously remove iron and aluminum impurities while improving filtration performance and reducing rare earth losses is a technical problem that needs to be solved urgently. On the other hand, the hydrochloric acid dissolution process for neodymium iron boron scrap roasting material uses sodium chlorate as an oxidant, which has been used for a long time. Although air, oxygen, ozone, etc. can be used as alternative oxidants to oxidize divalent iron to trivalent iron without introducing new anionic and cationic impurities, the air oxidation rate is very slow. How to achieve sufficient oxidation, neutralization and removal of ferrous ions in a relatively short period of time is also a technical problem that needs to be solved. Summary of the Invention
[0007] In response to the above problems, the main purpose of the present invention is to develop a method for reducing rare earth loss in the hydrochloric acid dissolution and impurity removal process of NdFeB waste roasting materials, so as to improve the rare earth recovery rate and eliminate the problem of sodium salt wastewater caused by using sodium chlorate as an oxidant.
[0008] In order to achieve the above object, a method for reducing rare earth loss in the acid dissolution-impurity removal process of NdFeB scrap roasting material by gas oxidation is provided, comprising the following steps: S1, dissolving the NdFeB waste roasted material with hydrochloric acid, and performing solid-liquid separation after the dissolution to obtain an acid solution and acid slag; S2, mixing the acid solution with copper chloride and controlling the copper ion concentration to be 50-200 ppm to obtain a mixed solution, adding an alkaline precipitant and a seed crystal while bubbling an oxidizing gas into the mixed solution, controlling the pH value to be 2.5-4.0, the reaction temperature to be 50-80° C., and obtaining a mixed slurry after precipitation reaction; S3. Filtering and washing the mixed slurry to obtain impurity-removed residue and rare earth solution.
[0009] Furthermore, in step S1, the temperature during the hydrochloric acid dissolution process is 60-90° C., and the pH value at the end point of the hydrochloric acid dissolution is less than 1.0.
[0010] Furthermore, in the step S2, a gas dispersion device is used in the process of blowing in the oxidizing gas, and the diameter of the bubbles in the mixed solution is controlled to be less than 0.5 mm.
[0011] Furthermore, the oxidizing gas is any one of air, oxygen or ozone.
[0012] Furthermore, the alkaline precipitant in step S2 is one or more of sodium hydroxide, calcium hydroxide, magnesium hydroxide, and ammonia water, preferably calcium hydroxide.
[0013] Furthermore, in step S2, the seed crystals are FeOOH seed crystals, and the seed crystal coefficient is 20%-50% of the mass of iron in the acid solution.
[0014] Furthermore, the seed crystal in step S2 is the impurity-removed slag obtained in step S3.
[0015] Furthermore, the temperature of water during the water washing process in step S3 is greater than 60°C.
[0016] Furthermore, the rare earth loss rate in step S2 is less than 0.5%, and the rare earth content in the impurity-removed slag obtained in step S3 is less than 5‰.
[0017] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: The present invention first preferentially dissolves the calcined NdFeB scrap material in hydrochloric acid. After the reaction, solid-liquid separation and washing are performed to produce an acid solution and acid-dissolved slag. To address the problem of iron and aluminum impurities in the acid solution, a small amount of cupric chloride is first added to catalyze the oxidation of ferrous ions. An oxidizing gas is then bubbled through the acid solution to fully oxidize the ferrous iron in the solution. Simultaneously, an alkaline precipitant such as sodium hydroxide or calcium oxide is introduced. The oxidation reaction pH is controlled between 2.5 and 4.0, the reaction temperature is 50-80°C, and seed crystals are added. Under these conditions, the speed of ferrous iron oxidation and neutralization and hydrolysis are balanced, resulting in a cleaned slag with improved crystallization properties and reduced rare earth adsorption. Finally, the reaction is terminated when the iron and aluminum precipitation rate exceeds 99%. At this point, the rare earth loss rate during the cleaned slag is less than 0.5%. The mixed slurry after gas oxidation is filtered and washed with hot water to produce a cleaned slag and a rare earth solution. The cleaned slag contains less than 5‰ of rare earths and can be used as seed crystals for the air oxidation cleaned slag. The process is simple, the raw materials and reagents used are cheap and easily available, and it is easy to industrialize. BRIEF DESCRIPTION OF THE DRAWINGS
[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.
[0019] Figure 1 The present invention provides a process flow chart for reducing rare earth loss in the hydrochloric acid dissolution and impurity removal process of NdFeB waste roasting materials. DETAILED DESCRIPTION
[0020] To facilitate understanding of the present invention, the present invention will be described in more comprehensive and detailed form below in conjunction with the accompanying drawings and preferred embodiments. However, the protection scope of the present invention is not limited to the following specific embodiments.
[0021] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.
[0022] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.
[0023] At present, sodium chlorate is used in industry to oxidize and neutralize the iron and aluminum impurities in the acid dissolution process of NdFeB waste roasting materials. However, there are problems such as large loss of rare earths and the introduction of sodium impurities, which leads to poor quality of products such as calcium chloride or ammonium chloride obtained from subsequent wastewater evaporation treatment. Although scientific and technological workers have proposed the goethite method, staged catalysis, organic complexation and other methods to remove iron or aluminum in the solution, there are still problems such as high cost and large loss of rare earths. It has not yet been promoted and applied in the acid dissolution-impurity removal process of NdFeB waste roasting materials.
[0024] The present invention provides a method for reducing rare earth loss during the acid dissolution and impurity removal process of NdFeB scrap roasting material by using gas oxidation, replacing sodium chlorate to achieve oxidation of ferrous ions. Simultaneously, by adding seed crystals and changing the precipitant, the co-precipitation of rare earths and the adsorption of rare earths by the precipitated products are reduced. Specifically, the method comprises the following steps: (1) Hydrochloric acid preferential dissolution: The NdFeB waste roasted material is preferentially dissolved in hydrochloric acid, and the acid dissolution temperature is controlled at 60-90℃, and the dissolution end point pH is less than 1.0. After the reaction is completed, solid-liquid separation and washing are performed to obtain acid solution and acid slag. In actual industrial operation, hydrochloric acid preferential dissolution and air oxidation impurity removal are carried out continuously without solid-liquid separation step. However, experiments have found that after solid-liquid separation, the adsorption sites in the gas oxidation impurity removal process can be effectively reduced, thereby reducing the adsorption loss of rare earth.
[0025] (2) Gas oxidation and impurity removal: Add a small amount of copper chloride to control the copper ion concentration in the acid solution to 50-200ppm, then blow oxidizing gas into the acid solution and introduce alkaline precipitant at the same time to control the pH of the oxidation reaction to 2.5-4.0 and the reaction temperature to 50-80℃. The reaction is terminated when the iron and aluminum precipitation rate exceeds 99%. Generally, there are impurities such as copper in the roasted NdFeB scrap. After acid dissolution, the copper ion concentration in the acid solution can reach 50-200ppm. If it cannot be reached, less copper chloride can be added. The addition of copper ions can catalyze the oxidation of ferrous ions, accelerate the oxidation rate, and improve production efficiency. The oxidizing gas is preferably blown using a gas dispersion device to control the bubbles in the solution to be less than 0.5mm. The smaller the bubbles, the higher the efficiency of air oxidation and the faster the reaction rate. If the bubbles are too large, the reaction time will be too long. The oxidizing gas can use air, oxygen or ozone. Oxygen and ozone have strong oxidizing properties and can enhance the oxidation process, but the hydrolysis and precipitation of iron and aluminum are more difficult to control. An alkaline precipitant is introduced to control the pH of the oxidation reaction to be 2.5-4.0. The alkaline precipitant is selected to be one or more of sodium hydroxide, calcium hydroxide, magnesium hydroxide, and ammonia water. The higher the pH of the oxidation reaction, the faster the precipitation, but the poorer the crystallization of the precipitated product obtained, the more rare earths are adsorbed and wrapped. If the pH is too low, the precipitation rate is too slow, and iron and aluminum cannot be completely removed, affecting production efficiency. Therefore, how to control the size of the gas-added bubbles and the pH of the solution is the key to achieving crystal precipitation of the precipitated product and the key to controlling the precipitation rate, requiring a dialectical balance. In addition, the selection of the alkaline precipitant requires that the alkalinity cannot be too high, otherwise, due to the influence of local supersaturation, more rare earths will be taken away by co-precipitation, but the alkalinity cannot be too low, such as hydrotalcite, which will produce more slag. At the same time, its impact on wastewater treatment must also be considered. Therefore, calcium hydroxide is preferred, which can well balance the problem of alkalinity and impurity introduction. Compared with sodium hydroxide, the alkalinity is low, which prevents the loss of rare earths from local supersaturation co-precipitation. Compared with magnesium hydroxide, the alkalinity is high, the reaction rate is fast, and the slag production is small. At the same time, much of today's wastewater is calcium-based, and calcium hydroxide does not introduce new impurities, thus benefiting wastewater utilization. Furthermore, temperature significantly influences the crystal form and precipitation rate of the precipitated product, so a reaction temperature of 50-80°C is preferred. Seedlings also play a crucial role in the precipitation process, effectively controlling the crystallization properties of the precipitated product. Therefore, FeOOH seed crystals are preferably added, with a seed coefficient of 20%-50% of the mass of iron in the acid solution. Ultimately, through these controlled conditions, the rare earth loss rate during air oxidation impurity removal is reduced to less than 0.5%.
[0026] (3) Filtration and washing: The mixed slurry after gas oxidation is filtered and washed with water above 60°C to obtain impurity removal slag and rare earth solution. Warm water washing helps to reduce the loss of rare earths, and the rare earth content in the impurity removal slag is less than 5‰. In addition, the acid soluble slag is mainly FeOOH, which can be added as a seed to the air oxidation impurity removal process; or in actual industrial practice, a static method is adopted to siphon the supernatant into the extraction section, and the slag at the bottom is left in the reactor to continue the next round of oxidation impurity removal reaction. In this way, the impurity removal slag can be recycled as a seed, reducing the input of seed crystals while the recycled impurity removal slag has better crystallization, which can more effectively reduce adsorption losses.
[0027] The above introduces the specific implementation methods of the present application. In order to objectively illustrate the technical effects produced by the present application, the following will further illustrate a method provided by the present invention for reducing rare earth loss in the acid dissolution-removal process of NdFeB waste roasting materials by air oxidation with reference to examples.
[0028] Example 1 (1) Hydrochloric acid dissolution: 10 g of NdFeB waste calcined material with a rare earth content of 25.4% was slurried, and then 6.0 mol / L hydrochloric acid was slowly added to dissolve it. The acid dissolution temperature was controlled at 65 °C by heating in a water bath, and the reaction was kept warm for 3 h. When the pH value at the end point of the dissolution reaction was less than 1.0, the reaction was completed and filtered for solid-liquid separation and washed to obtain an acid solution and acid slag.
[0029] (2) Air oxidation and impurity removal: Determine the copper ion concentration in the acid solution and add a small amount of copper chloride to the acid solution. At this time, the copper ion concentration in the acid solution is 100 ppm. Then, use a gas dispersion device to blow air with a bubble diameter of less than 0.5 mm into the acid solution. At the same time, add a 1.0 mol / L NaOH solution as an alkaline precipitant to control the pH of the oxidation reaction system to about 3.0. Add FeOOH seeds and control the seed coefficient to 20%. Heat the reaction system in a water bath to 50°C. Monitor the iron and aluminum ion concentrations. When the iron and aluminum precipitation rate exceeds 99%, terminate the reaction to obtain a mixed slurry.
[0030] (3) Filtration and washing: The mixed slurry after air oxidation was filtered and washed with hot water at 65°C to obtain impurity-removed slag and rare earth solution. The rare earth content in the impurity-removed slag was determined to be 0.40 wt%; the rare earth loss rate in the impurity removal process was calculated to be 0.38%.
[0031] Example 2 (1) Hydrochloric acid dissolution: 10 g of NdFeB waste roasted material with a rare earth content of 25.4% is slurried, and then 6.0 mol / L hydrochloric acid is slowly added to dissolve it. The acid dissolution temperature is controlled at about 75 ° C by heating in a water bath, and the reaction is kept warm for 3 hours. When the pH value at the end point of the dissolution reaction is less than 1.0, solid-liquid separation is performed after the reaction is completed and washed to obtain acid solution and acid slag.
[0032] (2) Air oxidation and impurity removal: Determine the copper ion concentration in the acid solution and add a small amount of copper chloride to the acid solution. At this time, the copper ion concentration in the acid solution is 150 ppm. Then, use a gas dispersion device to blow air with a bubble diameter of less than 0.5 mm into the acid solution. At the same time, add 1.0 mol / L ammonia water as an alkaline precipitant. Control the pH of the oxidation reaction system to about 4.0. Add FeOOH seeds and control the seed coefficient to 30%. Heat the reaction system in a water bath to 75°C. Monitor the iron and aluminum ion concentrations. When the iron and aluminum precipitation rate exceeds 99%, terminate the reaction to obtain a mixed slurry.
[0033] (3) Filtration and washing: The mixed slurry after air oxidation was filtered and washed with hot water at 68°C to obtain impurity-removed slag and rare earth solution. The rare earth content in the impurity-removed slag was determined to be 0.45 wt%; the rare earth loss rate in the impurity removal process was calculated to be 0.41%.
[0034] Example 3 (1) Hydrochloric acid dissolution: 10 g of NdFeB waste roasted material with a rare earth content of 25.4% is slurried, and then 6.0 mol / L hydrochloric acid is slowly added to dissolve it. The acid dissolution temperature is controlled at about 85 °C by heating in a water bath, and the reaction is kept warm for 3 hours. When the pH value at the end point of the dissolution reaction is less than 1.0, solid-liquid separation is performed after the reaction is completed and washed to obtain an acid solution and acid slag.
[0035] (2) Oxygen oxidation and impurity removal: Determine the copper ion concentration in the acid solution and add a small amount of copper chloride to the acid solution. At this time, the copper ion concentration in the acid solution is 50 ppm. Then, use a gas dispersion device to blow oxygen with a bubble diameter of less than 0.5 mm into the acid solution. At the same time, add 1.0 mol / L ammonia water as an alkaline precipitant. Control the pH of the oxidation reaction system to about 2.5. Add FeOOH seeds and control the seed coefficient to 50%. Heat the reaction system in a water bath to 60°C. Monitor the iron and aluminum ion concentrations. After the iron and aluminum precipitation rate exceeds 99%, terminate the reaction to obtain a mixed slurry.
[0036] (3) Filtration and washing: The mixed slurry after oxygen oxidation was filtered and washed with hot water at 62°C to obtain impurity-removed slag and rare earth solution. The rare earth content in the impurity-removed slag was determined to be 0.37 wt%; the rare earth loss rate in the impurity removal process was calculated to be 0.33%.
[0037] Example 4 (1) Hydrochloric acid dissolution: 10 g of NdFeB waste calcined material with a rare earth content of 25.4% was slurried, and then 6.0 mol / L hydrochloric acid was slowly added to dissolve it. The acid dissolution temperature was controlled at 65 °C by heating in a water bath, and the reaction was kept warm for 3 h. When the pH value at the end point of the dissolution reaction was less than 1.0, the reaction was completed and filtered for solid-liquid separation and washed to obtain an acid solution and acid slag.
[0038] (2) Air oxidation and impurity removal: Determine the copper ion concentration in the acid solution and add a small amount of copper chloride to the acid solution. At this time, the copper ion concentration in the acid solution is 100 ppm. Then, use a gas dispersion device to blow air with a bubble diameter of less than 0.5 mm into the acid solution. At the same time, add a 1.0 mol / L calcium hydroxide solution as an alkaline precipitant to control the pH of the oxidation reaction system to about 3.0. Add FeOOH seeds and control the seed coefficient to 20%. Heat the reaction system in a water bath to 50°C. Monitor the iron and aluminum ion concentrations. When the iron and aluminum precipitation rate exceeds 99%, terminate the reaction to obtain a mixed slurry.
[0039] (3) Filtration and washing: The mixed slurry after air oxidation was filtered and washed with hot water at 65°C to obtain impurity-removed slag and rare earth solution. The rare earth content in the impurity-removed slag was determined to be 0.26wt%; the rare earth loss rate in the impurity removal process was calculated to be 0.17%.
[0040] Example 5 (1) Hydrochloric acid dissolution: 10 g of NdFeB waste roasted material with a rare earth content of 25.4% is slurried, and then 6.0 mol / L hydrochloric acid is slowly added to dissolve it. The acid dissolution temperature is controlled at about 85 °C by heating in a water bath, and the reaction is kept warm for 3 hours. When the pH value at the end point of the dissolution reaction is less than 1.0, solid-liquid separation is performed after the reaction is completed and washed to obtain an acid solution and acid slag.
[0041] (2) Air oxidation and impurity removal: The copper ion concentration in the acid solution was determined, and a small amount of copper chloride was added to the acid solution. At this time, the copper ion concentration in the acid solution was 50 ppm. Then, oxygen with a bubble diameter of less than 0.5 mm was blown into the acid solution using a gas dispersion device. At the same time, 1.0 mol / L of calcium hydroxide as an alkaline precipitant was added. The pH of the oxidation reaction system was controlled to be about 2.5. The impurity removal slag obtained in Example 1 was added as a seed crystal, and the seed coefficient was controlled to be 50%. The reaction system was heated in a water bath so that the temperature was 60°C. The iron and aluminum ion concentrations were monitored. The reaction was terminated after the iron and aluminum precipitation rate exceeded 99%, and a mixed slurry was obtained.
[0042] (3) Filtration and washing: The mixed slurry after air oxidation was filtered and washed with hot water at 62°C to obtain impurity-removed slag and rare earth solution. The rare earth content in the impurity-removed slag was determined to be 0.44 wt%; the rare earth loss rate in the impurity removal process was calculated to be 0.45%.
[0043] Comparative Example 1 (1) Hydrochloric acid dissolution: 10 g of NdFeB waste calcined material with a rare earth content of 25.4% was slurried, and then 6.0 mol / L hydrochloric acid was slowly added to dissolve it. The acid dissolution temperature was controlled at 65 °C by heating in a water bath, and the reaction was kept warm for 3 h. When the pH value at the end point of the dissolution reaction was less than 1.0, the reaction was completed and filtered for solid-liquid separation and washed to obtain an acid solution and acid slag.
[0044] (2) Air oxidation and impurity removal: Use a gas dispersion device to blow air with a bubble diameter of less than 0.5 mm into the acid solution, and at the same time add a 1.0 mol / L calcium hydroxide solution as an alkaline precipitant to control the pH of the oxidation reaction system to about 3.0, add FeOOH seeds and control the seed coefficient to 20%, heat the reaction system in a water bath to make the temperature of the reaction system 50°C, monitor the iron and aluminum ion concentrations, and terminate the reaction when the iron and aluminum precipitation rate exceeds 99% to obtain a mixed slurry.
[0045] (3) Filtration and washing: The mixed slurry after air oxidation was filtered and washed with hot water at 65°C to obtain impurity-removed slag and rare earth solution. The rare earth content in the impurity-removed slag was determined to be 0.58 wt%; the rare earth loss rate in the impurity removal process was calculated to be 0.65%.
[0046] Comparative Example 2 (1) Hydrochloric acid dissolution: 10 g of NdFeB waste calcined material with a rare earth content of 25.4% was slurried, and then 6.0 mol / L hydrochloric acid was slowly added to dissolve it. The acid dissolution temperature was controlled at 65 °C by heating in a water bath, and the reaction was kept warm for 3 h. When the pH value at the end point of the dissolution reaction was less than 1.0, the reaction was completed and filtered for solid-liquid separation and washed to obtain an acid solution and acid slag.
[0047] (2) Sodium chlorate oxidation and impurity removal: Sodium chlorate is added to the acid solution to make Fe 2+ Converted to Fe 3+ , determine the copper ion concentration in the acid solution, and add a small amount of copper chloride to the acid solution. At this time, the copper ion concentration in the acid solution is 100 ppm. Add 1.0 mol / L calcium hydroxide solution as an alkaline precipitant to control the pH of the oxidation reaction system to about 3.0, add FeOOH seeds and control the seed coefficient to 30%. Heat in a water bath to make the reaction system temperature 50°C, monitor the iron and aluminum ion concentrations, and terminate the reaction after the iron and aluminum precipitation rate exceeds 99% to obtain a mixed slurry.
[0048] (3) Filtration and washing: The mixed slurry after air oxidation was filtered and washed with hot water at 65°C to obtain impurity-removed slag and rare earth solution. The rare earth content in the impurity-removed slag was determined to be 0.93 wt%; the rare earth loss rate was calculated to be 1.05%.
[0049] Comparative Example 3 (1) Hydrochloric acid dissolution: 10 g of NdFeB waste calcined material with a rare earth content of 25.4% was slurried, and then 6.0 mol / L hydrochloric acid was slowly added to dissolve it. The acid dissolution temperature was controlled at 65 °C by heating in a water bath, and the reaction was kept warm for 3 h. When the pH value at the end point of the dissolution reaction was less than 1.0, the reaction was completed and filtered for solid-liquid separation and washed to obtain an acid solution and acid slag.
[0050] (2) Air oxidation and impurity removal: Determine the copper ion concentration in the acid solution and add a small amount of copper chloride to the acid solution. At this time, the copper ion concentration in the acid solution is 100 ppm. Then, use a gas dispersion device to blow air with a bubble diameter of less than 0.1 mm into the acid solution. At the same time, add a 1.0 mol / L NaOH solution as an alkaline precipitant to control the pH of the oxidation reaction system to about 3.0. Heat the reaction system in a water bath to 50°C. Monitor the iron and aluminum ion concentrations. When the iron and aluminum precipitation rate exceeds 99%, terminate the reaction to obtain a mixed slurry.
[0051] (3) Filtration and washing: The mixed slurry after air oxidation was filtered and washed with hot water at 65°C to obtain impurity-removed slag and rare earth solution. The rare earth content in the impurity-removed slag was determined to be 0.67 wt%. The rare earth loss rate was calculated to be 0.72%.
[0052] Comparative Example 4 (1) Hydrochloric acid dissolution: 10 g of NdFeB waste calcined material with a rare earth content of 25.4% was slurried, and then 6.0 mol / L hydrochloric acid was slowly added to dissolve it. The acid dissolution temperature was controlled at 65 °C by heating in a water bath, and the reaction was kept warm for 3 h. When the pH value at the end point of the dissolution reaction was less than 1.0, the reaction was completed and filtered for solid-liquid separation and washed to obtain an acid solution and acid slag.
[0053] (2) Air oxidation and impurity removal: Determine the copper ion concentration in the acid solution and add a small amount of copper chloride to the acid solution. At this time, the copper ion concentration in the acid solution is 100 ppm. Then, use a gas dispersion device to blow air with a bubble diameter of less than 0.1 mm into the acid solution. At the same time, add an alkaline precipitant 1.0 mol / L calcium hydroxide solution to control the pH of the oxidation reaction system to about 5.0. Add FeOOH seed crystals and heat the reaction system in a water bath to 50°C. Monitor the iron and aluminum ion concentrations. When the iron and aluminum precipitation rate exceeds 99%, terminate the reaction to obtain a mixed slurry.
[0054] (3) Filtration and washing: The mixed slurry after air oxidation was filtered and washed with hot water at 65°C to obtain impurity-removed slag and rare earth solution. The rare earth content in the impurity-removed slag was determined to be 1.07wt%; the rare earth loss rate was calculated to be 1.14%.
[0055] Comparative Example 5 (1) Hydrochloric acid dissolution: 10 g of calcined NdFeB waste with a rare earth content of 25.4% was slurried, and then 6.0 mol / L hydrochloric acid was slowly added to dissolve it. The acid dissolution temperature was controlled at 65 °C by heating in a water bath, and the reaction was kept warm for 3 h. When the pH at the end point of the dissolution reaction was less than 1.0, a mixed suspension was obtained after the reaction was completed.
[0056] (2) Air oxidation to remove impurities: Determine the copper ion concentration in the mixed suspension and add a small amount of copper chloride to the acid solution. At this time, the copper ion concentration in the acid solution is 100 ppm. Then, use a gas dispersion device to blow air with a bubble diameter of less than 0.5 mm into the acid solution. At the same time, add a 1.0 mol / L calcium hydroxide solution as an alkaline precipitant to control the pH of the oxidation reaction system to about 3.0. Add FeOOH seeds and control the seed coefficient to 20%. Heat the reaction system in a water bath to 50°C. Monitor the iron and aluminum ion concentrations. When the iron and aluminum precipitation rate exceeds 99%, terminate the reaction to obtain a mixed slurry.
[0057] (3) Filtration and washing: The mixed slurry after air oxidation was filtered and washed with hot water at 65°C to obtain impurity-removed slag and rare earth solution. The rare earth content in the impurity-removed slag was determined to be 1.63wt%; the rare earth loss rate was calculated to be 0.85%.
[0058] From the above results, it can be seen that the method of reducing rare earth loss in the acid dissolution-impurity removal process of NdFeB scrap roasting material by gas oxidation of the present invention is adopted, and the rare earth loss rate in the impurity removal process is less than 0.5%. For Comparative Examples 1 to 5, when some steps are omitted, such as not adding copper chloride, not adding seed crystals, changing the oxidation conditions or having a higher pH value, and omitting the filtration step after hydrochloric acid dissolution, the rare earth element loss rate in the impurity removal process will be affected. The reason is that the change in the impurity removal process conditions changes the speed of ferrous iron oxidation and neutralization hydrolysis, resulting in poor crystallization performance of the impurity removal slag, more adsorption of rare earth elements, and an increase in the loss rate.
[0059] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, and all of these should be considered to fall within the scope of protection of the present invention.
Claims
1. A method for reducing rare earth loss in the acid dissolution-impurity removal process of NdFeB waste roasting material by gas oxidation, characterized in that: The following steps are involved: S1, dissolving the NdFeB waste roasted material with hydrochloric acid, and performing solid-liquid separation after the reaction to obtain an acid solution and acid slag; S2, mixing the acid solution with copper chloride and controlling the copper ion concentration to be 50-200 ppm to obtain a mixed solution, adding an alkaline precipitant and a seed crystal while bubbling an oxidizing gas into the mixed solution, controlling the pH value to be 2.5-4.0, the reaction temperature to be 50-80° C., and obtaining a mixed slurry after precipitation reaction; S3. Filtering and washing the mixed slurry to obtain impurity-removed residue and rare earth solution.
2. The method for reducing rare earth loss in the acid dissolution-impurity removal process of NdFeB scrap roasting material by gas oxidation according to claim 1, characterized in that: In step S1, the temperature during the hydrochloric acid dissolution process is 60-90° C., and the pH value at the end point of the hydrochloric acid dissolution is less than 1.
0.
3. The method for reducing rare earth loss in the acid dissolution-impurity removal process of NdFeB scrap roasting material by gas oxidation according to claim 1, characterized in that: In the step S2, a gas dispersion device is used in the process of blowing in the oxidizing gas to control the diameter of the bubbles in the mixed solution to be less than 0.5 mm.
4. The method for reducing rare earth loss in the acid dissolution-impurity removal process of NdFeB scrap roasting material by gas oxidation according to claim 1, characterized in that: The oxidizing gas is any one of air, oxygen or ozone.
5. The method for reducing rare earth loss in the acid dissolution-impurity removal process of NdFeB scrap roasting material by gas oxidation according to claim 1, characterized in that: In step S2, the alkaline precipitant is one or more of sodium hydroxide, calcium hydroxide, magnesium hydroxide, and ammonia water.
6. The method for reducing rare earth loss in the acid dissolution-impurity removal process of NdFeB scrap roasting material by gas oxidation according to claim 1, characterized in that: In step S2, the seed crystals are FeOOH seed crystals, and the seed coefficient is 20%-50% of the mass of iron in the acid solution.
7. The method for reducing rare earth loss in the acid dissolution-impurity removal process of NdFeB scrap roasting material by gas oxidation according to claim 1, characterized in that: The seed crystal in step S2 is the impurity-removed slag obtained in step S3.
8. The method for reducing rare earth loss in the acid dissolution-impurity removal process of NdFeB scrap roasting material by gas oxidation according to claim 1, characterized in that: During the water washing process in step S3, the temperature of water is greater than 60°C.
9. The method for reducing rare earth loss in the acid dissolution-impurity removal process of NdFeB scrap roasting material by gas oxidation according to claim 1, characterized in that: The rare earth loss rate in step S2 is less than 0.5%, and the rare earth content of the impurity-removed slag obtained in step S3 is less than 5‰.