A treatment method for improving the leaching efficiency of neodymium iron boron waste

Abstract

This invention discloses a method for improving the leaching efficiency of NdFeB waste, comprising the following steps: uniformly mixing the NdFeB waste; roasting it in air at 300–600°C for 0.5–6 hours, with intermittent stirring during roasting, and obtaining an oxidized material after cooling; adding the oxidized material to a sulfuric acid solution, and leaching it in stages at 40–50°C, 60–80°C, and 80–90°C; and performing solid-liquid separation after acid leaching to obtain an acid leaching solution rich in rare earth valuable elements and an acid leaching residue. This invention inhibits the formation of insoluble phases such as rare earth ferrites through low-temperature air roasting, promotes uniform oxidation of the material by intermittent stirring, reduces the release of hydrogen gas from acid leaching, and efficiently dissolves rare earths under mild conditions through staged temperature leaching, achieving a single-time leaching rate of rare earth oxides of over 99.0%. It has the advantages of high recovery rate, good safety, and simple process.

Description

Technical Field

[0001] This invention belongs to the field of NdFeB waste recycling technology, specifically involving a roasting-oxidation pretreatment and acid leaching process for NdFeB waste. Background Technology

[0002] In the rare earth element recovery process of NdFeB waste, roasting oxidation and acid leaching are key pretreatment steps. Existing technologies typically use air or an oxygen-enriched atmosphere to roast the waste at high temperatures, aiming to oxidize the metal elements and improve the leaching efficiency of valuable elements such as rare earths.

[0003] However, existing technologies have the following significant drawbacks: during conventional high-temperature calcination (e.g., above 600℃), rare earth ferrites (ReFeO3, where Re represents rare earth elements), neodymium borate (NdBO3), and dense iron spinel phases (Fe3O4 sintered bodies) are easily generated, which are difficult or insoluble substances. These substances can coat rare earth oxides, significantly hindering the acid leaching and dissolution of rare earth elements, leading to a decrease in recovery rate.

[0004] If the roasting temperature is too low or the time is insufficient, the oxidation will be incomplete, resulting in the generation of a large amount of hydrogen gas during acid dissolution, which will lead to safety and efficiency problems.

[0005] Traditional continuous roasting processes result in uneven oxidation of materials, with localized overheating leading to the formation of insoluble substances and localized under-oxidation producing hydrogen gas. It is difficult to strike a balance between suppressing insoluble substance formation and controlling hydrogen production. Therefore, there is an urgent need for a safe and efficient roasting pretreatment method that can effectively suppress insoluble substance formation, improve the dissolution efficiency of valuable elements such as rare earth elements, and enhance overall efficiency. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a treatment method to improve the leaching efficiency of NdFeB waste, so as to solve the technical problems of existing high-temperature roasting easily generating rare earth ferrite and other insoluble phases that hinder rare earth leaching, low-temperature roasting insufficient oxidation to generate hydrogen, and uneven oxidation of materials in continuous roasting.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for improving the leaching efficiency of NdFeB waste includes the following steps:

[0009] S1. Material preparation: Mix the NdFeB waste materials evenly;

[0010] S2. Calcination: The prepared material is calcined in air at 300-600℃ for a total time of 0.5-6 hours. During the calcination process, the material is stirred intermittently. After calcination, the material is cooled to obtain the oxidized material.

[0011] S3. Acid leaching: Add the oxidized material to a sulfuric acid solution and leach it in stages at 40-50℃, 60-80℃, and 80-90℃.

[0012] S4. Separation: After acid dissolution, solid-liquid separation is carried out to obtain acid leaching solution and acid dissolution residue rich in rare earth valuable elements.

[0013] Furthermore, in step S2, the calcination temperature is 400–500°C.

[0014] Furthermore, in step S2, the intermittent stirring frequency is once every 0.5 to 1 hour.

[0015] Furthermore, in step S3, the concentration of the sulfuric acid solution is 2.2–2.5 mol / L, and the solid-liquid ratio of the oxidant to the sulfuric acid solution is 1:1–5.

[0016] Furthermore, in step S3, the sample is soaked at 40–50°C for 0.2–1 h, at 60–80°C for 0.5–1 h, and at 80–90°C for 3–6 h.

[0017] Furthermore, in step S2, after calcination and cooling, the process also includes ball milling the oxidized material and detecting the oxidation rate.

[0018] Furthermore, in step S4, after solid-liquid separation, the acid-soluble residue is also washed with deionized water.

[0019] The method for improving the leaching efficiency of NdFeB waste provided by this invention has the following beneficial effects:

[0020] (1) Significantly improve rare earth recovery efficiency: By controlling the roasting temperature in the low temperature range of 300 to 600℃, the formation of insoluble substances such as rare earth ferrite (ReFeO3), neodymium borate (NdBO3) and iron spinel phase is effectively suppressed, avoiding the encapsulation of insoluble substances with rare earth oxides, so that the single dissolution rate of rare earth oxides in the treated oxide material is stable at over 99.0%, the single dissolution rate of cobalt is greater than 95.0%, and the residual rare earth oxides in the slag are less than 1%.

[0021] (2) The roasting process adopts intermittent stirring, which makes the material fully and evenly oxidized, avoiding the problems of local overheating to generate insoluble substances and local insufficient oxidation to generate hydrogen. This greatly reduces the release of hydrogen during acid dissolution and significantly improves the safety of the process.

[0022] (3) Using sulfuric acid staged heating leaching, the material reacts slowly and hydrogen release is controlled in the lower temperature range first, and then the temperature is gradually increased to deeply leach rare earth. Under mild acid dissolution conditions, the efficient and stable recovery of valuable elements such as rare earth is achieved, reducing acid consumption and energy consumption. It is also easy to operate and highly operable, requiring no special equipment or harsh atmosphere. Attached Figure Description

[0023] Figure 1 This is a process flow diagram of a method for improving the leaching efficiency of NdFeB waste provided in an embodiment of the present invention. Detailed Implementation

[0024] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0025] like Figure 1 As shown, the method for improving the leaching efficiency of NdFeB waste provided by the present invention includes steps such as material preparation, roasting, cooling, acid leaching, and solid-liquid separation. Preferably, the roasted and cooled oxidized material is ball-milled (ball milling is an optional step). Specifically, the NdFeB waste is uniformly mixed and roasted at 300–600°C in an air atmosphere. During roasting, intermittent stirring ensures uniform oxidation of the material, thereby inhibiting the formation of insoluble phases such as rare earth ferrite (ReFeO3). The cooled (preferably ball-milled) oxidized material is added to a sulfuric acid solution for staged leaching. First, a slow reaction at a low temperature is used to control hydrogen release, and then the temperature is gradually increased to deeply leach rare earth elements.

[0026] Further, in step S1, the NdFeB waste can be scrap, grinding material, chips, or waste NdFeB magnets generated during NdFeB production or processing. When the waste has a high moisture content, it can be dried first and then mixed evenly. In step S2, the roasting can be carried out in a muffle furnace, rotary kiln, or dynamic roasting furnace, and the air atmosphere is natural air. The intermittent stirring can be carried out by manual turning, mechanical stirring, or furnace rotation to ensure that the material is heated evenly and oxidized fully during roasting. After roasting, it can be cooled naturally or cooled to room temperature with the furnace. The oxidation rate can be detected using conventional analytical methods in the art, such as determining the content of incompletely oxidized metallic or low-valence states in the oxidized material by chemical titration, or calculating it by measuring the oxygen content of the oxidized material using an oxygen and nitrogen analyzer.

[0027] In step S3, the sulfuric acid solution can be preheated to the first temperature range, and then the oxidant can be slowly and in batches added to the sulfuric acid solution to control the hydrogen release rate. Stirring can be used during the leaching process to promote sufficient solid-liquid contact. The heating method between adjacent temperature ranges is not particularly limited, but a gradual hydrogen release is preferable. In step S4, the solid-liquid separation can be performed using conventional methods such as vacuum filtration, pressure filtration, or centrifugation. The number of washing cycles for the acid-soluble residue can be appropriately increased or decreased depending on the residual soluble salts in the residue, and the washing liquid and acid leaching liquid are treated together.

[0028] Example 1:

[0029] The NdFeB waste was mixed evenly and calcined at 450℃ for 3.5 hours, with stirring every 0.5 hours during the calcination. After calcination, it was naturally cooled to room temperature, and the resulting oxide was ball-milled and the oxidation rate was monitored and tested.

[0030] Under 40℃ water bath conditions, the oxidant was slowly added to a 2.2 mol / L sulfuric acid solution at a solid-liquid ratio of 1:5 and reacted for 1 hour. A small amount of hydrogen gas was released during the acid dissolution process. The system was then heated to 80℃ and maintained for 1 hour, and finally heated to 90℃ and continued to react for 4 hours.

[0031] After the reaction, solid-liquid separation was performed. The filter residue was washed twice with deionized water, and the filtrate and washing liquid were collected and retained for analysis of the distribution of valuable elements. The washed acid-soluble residue was dried and weighed. The analysis showed that the REO leaching rate was 99.51%, the Co leaching rate was 98.5%, and the residual REO in the residue was 0.48%.

[0032] Example 2:

[0033] The NdFeB waste was mixed evenly and calcined at 300℃ for 6 hours, with stirring once every 1 hour during the calcination. After calcination, it was naturally cooled to room temperature, and the resulting oxide was ball-milled.

[0034] Under 50℃ water bath conditions, the oxidant was slowly added to a 2.5 mol / L sulfuric acid solution at a solid-liquid ratio of 1:1, and the reaction was allowed to proceed for 0.6 h; subsequently, the system was heated to 60℃ and maintained for 0.7 h.

[0035] Finally, the temperature was raised to 80℃ and the reaction continued for 4 hours. After the reaction was completed, solid-liquid separation was performed, and the filter residue was washed twice with deionized water. Testing showed that in this example, the REO leaching rate was 99.06%, the Co leaching rate was 95.37%, and the residual REO in the residue was 0.94%.

[0036] Example 3:

[0037] The NdFeB waste was mixed evenly and calcined at 600℃ for 0.5h, with stirring once every 0.5h during the process. After calcination, it was naturally cooled to room temperature, and the resulting oxide was ball-milled.

[0038] Under 45℃ water bath conditions, the oxidant was slowly added to a 2.35mol / L sulfuric acid solution at a solid-liquid ratio of 1:3 and the reaction was allowed to proceed for 0.5h. Subsequently, the system was heated to 70℃ and maintained for 0.8h, and finally heated to 85℃ and the reaction continued for 5h.

[0039] After the reaction was completed, solid-liquid separation was performed, and the filter residue was washed twice with deionized water. Testing showed that in this example, the REO dissolution rate was 99.37%, the Co dissolution rate was 97.10%, and the residual REO in the residue was 0.63%.

[0040] Comparative Example 1 (intermittent stirring omitted):

[0041] The NdFeB waste was uniformly mixed and calcined at 450℃ for 3.5 hours without stirring (continuous static calcination). After cooling and ball milling, leaching was performed under the same acid leaching conditions as in Example 1. Due to uneven oxidation of the material, local overheating resulted in the formation of insoluble rare earth ferrite phases, while local under-oxidation led to a significant release of hydrogen during acid leaching. Testing showed that the REO leaching rate was 98.14%, the Co leaching rate was 94.64%, and the residual REO in the residue was 1.86%.

[0042] Comparative Example 2 (high-temperature roasting at 800℃):

[0043] The NdFeB waste was mixed evenly and calcined at 800℃ for 3.5 hours, stirring every 0.5 hours. After cooling and ball milling, leaching was carried out under the same acid leaching conditions as in Example 1. Due to the excessively high calcination temperature, a large amount of insoluble rare earth ferrite (ReFeO3) phase was generated, which coated the rare earth oxides and hindered the dissolution of rare earths. Testing showed that the REO leaching rate was 90.89%, the Co leaching rate was 79.27%, and the residual REO in the slag was 9.11%.

[0044] Comparative Example 3 (segmented heating parameters changed):

[0045] The NdFeB waste was treated under the same roasting conditions as in Example 1. After cooling and ball milling, the oxidant was slowly added to a 2.2 mol / L sulfuric acid solution at a solid-liquid ratio of 1:5 in a 35°C water bath and reacted for 3 hours. A small amount of hydrogen gas was released during the acid dissolution process. Subsequently, the system was heated to 90°C and the reaction continued for another 3 hours. Due to the change in parameters during the staged heating leaching, the REO leaching rate was 94.55%, the Co leaching rate was 92.49%, and the residual REO in the residue was 5.45%.

[0046] Table 1 summarizes the effect data of the above embodiments and comparative examples to visually compare the advantages of the method of the present invention.

[0047] Table 1 Summary of Effect Data for Examples and Comparative Examples

[0048]

[0049] As shown in Table 1, the REO leaching rate of each embodiment of the present invention is above 99%, the Co leaching rate is above 95%, and the residual REO in the slag is below 1%, which is significantly better than that of the comparative examples. Comparing Example 1 and Comparative Example 1, it can be seen that intermittent stirring ensures uniform oxidation of the material, avoiding the formation of insoluble phases and the large-scale release of hydrogen, increasing the REO leaching rate by approximately 1.37 percentage points. Comparing Example 1 and Comparative Example 2, it can be seen that controlling the roasting temperature in the low-temperature range of 300–600℃ effectively inhibits the formation of insoluble rare earth ferrite phases, increasing the REO leaching rate by approximately 8.62 percentage points. Comparing Example 1 and Comparative Example 3, it can be seen that segmented heating leaching achieves efficient rare earth leaching while controlling hydrogen release. The above results indicate that the three features of the present invention—low-temperature roasting, intermittent stirring, and segmented heating leaching—work synergistically to achieve a comprehensive effect of inhibiting the formation of insoluble substances, promoting uniform oxidation, and controlling hydrogen release.

[0050] The foregoing descriptions have outlined some exemplary embodiments of the present invention. It is understood that these embodiments are merely illustrative and do not constitute a limitation on the scope of protection of the present invention. Features in these embodiments can be rearranged in suitable ways, and the resulting solutions remain within the scope of protection claimed by the present invention. All other embodiments obtained by those skilled in the art based on the foregoing embodiments without inventive effort, i.e., all modifications, equivalent substitutions, and improvements made within the spirit and principles of this application, fall within the scope of protection claimed by the present invention.

Claims

1. A method for improving the leaching efficiency of NdFeB waste, characterized in that, Includes the following steps: S1. Material preparation: Mix the NdFeB waste materials evenly; S2. Calcination: The prepared material is calcined in air at 300-600℃ for a total time of 0.5-6 hours. During the calcination process, the material is stirred intermittently. After calcination, the material is cooled to obtain the oxidized material. S3. Acid leaching: The oxidized material is added to a sulfuric acid solution and leached in stages at 40-50°C, 60-80°C, and 80-90°C. S4. Separation: After acid dissolution, solid-liquid separation is carried out to obtain acid leaching solution and acid dissolution residue rich in rare earth valuable elements.

2. The processing method according to claim 1, characterized in that, In step S2, the calcination temperature is 400–500°C.

3. The processing method according to claim 1, characterized in that, In step S2, the intermittent stirring frequency is once every 0.5 to 1 hour.

4. The processing method according to claim 1, characterized in that, In step S3, the concentration of the sulfuric acid solution is 2.2 to 2.5 mol / L, and the solid-liquid ratio of the oxidant to the sulfuric acid solution is 1:1 to 5.

5. The processing method according to claim 1, characterized in that, In step S3, the sample is soaked at 40–50°C for 0.2–1 h, at 60–80°C for 0.5–1 h, and at 80–90°C for 3–6 h.

6. The processing method according to claim 1, characterized in that, In step S2, after calcination and cooling, the process also includes ball milling the oxidized material and detecting the oxidation rate.

7. The processing method according to claim 1, characterized in that, In step S4, after solid-liquid separation, the acid-soluble residue is also washed with deionized water.

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