Method for recovering rare earth elements from rare earth waste residue and application thereof

Abstract

The application discloses a method for recovering rare earth elements from rare earth waste residues and application thereof, and comprises the following steps: stirring and leaching the rare earth waste residues after being crushed with a sulfuric acid solution with pH of 0.7-1 at 15-35 DEG C, and performing solid-liquid separation to obtain a rare earth leaching solution and secondary waste residues; wherein the rare earth waste residues are waste residues generated by sulfuric acid roasting of rare earth concentrate; and the solid-liquid ratio of the rare earth waste residues to the sulfuric acid solution is 1kg:(4-10)L. The method can recover rare earth elements from the rare earth waste residues, greatly separates the rare earth elements from elements such as thorium, phosphorus and iron, improves the relative separation degree, and has mild conditions.

Description

Technical Field

[0001] This invention relates to a method and application for recovering rare earth elements from rare earth waste. Background Technology

[0002] Currently, most of the rare earth concentrate from Bayan Obo is decomposed using a high-temperature roasting process with concentrated sulfuric acid. For every ton of rare earth concentrate containing 50% REO, approximately 0.6 tons of waste residue is generated, known as rare earth waste residue. This waste residue contains approximately 0.25% ThO2 (by mass), 3.51% REO, and 10% total iron. Based on an annual processing capacity of 120,000 tons of mixed rare earth concentrate, this results in 72,000 tons of waste residue, representing a loss of 2,527 tons of REO. This rare earth waste residue can only be stored in designated slag pits, causing environmental pollution and preventing the recovery of valuable rare earth elements, resulting in significant waste. Therefore, reducing the volume of rare earth waste residue and extracting and recovering rare earth elements is of great practical significance.

[0003] There are many methods for recovering rare earth elements, but because iron and rare earth elements have similar properties and mostly exist in the form of phosphates, the separation, extraction and recovery process becomes more difficult.

[0004] CN116676486A discloses a method for recovering iron, phosphorus, and rare earth elements from rare earth waste residue. This method involves dissolving the residue in sulfuric acid and then using P... 204 Iron and phosphoric acid are extracted using tributyl phosphate, and the rare earth sulfate solution is then reused in a water leaching process to recover rare earth elements. This method allows for the enrichment and recovery of iron, phosphorus, and rare earth elements from rare earth waste at different treatment stages. However, the extraction method in the process is a multi-stage countercurrent cascade extraction, which increases the complexity of the actual process operation and is not suitable for industrial production.

[0005] CN103184343A discloses a method for recovering rare earth elements, thorium, and iron from waste residue in a rare earth acid process. The method includes the following steps: mixing the waste residue with an acid solution, leaching with stirring at a temperature from 60°C to boiling, extracting the leachate with a primary amine, and back-extracting with nitric acid to obtain a thorium nitrate solution; adjusting the pH of the remaining thorium extraction solution with alkali to precipitate iron; and obtaining the filtrate as a rare earth feed solution. This recovery method solves the problem of radioactive waste residue in the acid process and achieves comprehensive resource recovery and utilization of the waste residue. However, the leaching temperature in this method is relatively high, which would increase energy consumption in actual industrial production.

[0006] CN106148713A discloses a method for recycling and degrading rare earth slag, comprising the following steps: (1) acid leaching; (2) ion adsorption; (3) catalytic degradation; and (4) deep degradation. This method first acid-leaches the powdered slag slurry to extract some rare earth elements from the slag. The liquid and solid phases are easily separated. Uranium and thorium in the liquid phase are separated and extracted using ion adsorption materials. A moderately acidic and stable transition metal salt is used as a catalyst to carry out alcoholysis on the solid phase. This method still involves simultaneously leaching uranium, thorium, and rare earth elements, and then separating and extracting uranium and thorium using ion adsorption materials.

[0007] Furthermore, the extracted thorium requires separate, long-term damming for storage, which consumes significant manpower, material resources, and financial resources. Post-extraction stockpiling could also cause greater radioactive contamination. Therefore, given the current restrictions on thorium use, it is more practical to retain it in the leaching residue as much as possible during the leaching process. Summary of the Invention

[0008] In view of this, one object of the present invention is to provide a method for recovering rare earth elements from rare earth waste residue, which facilitates the separation of rare earth elements from elements such as thorium, phosphorus, and iron, thereby improving the relative separation degree, and the method is performed under mild conditions. Another object of the present invention is to provide an application of a sulfuric acid solution with a pH of 0.7-1 in separating rare earth elements from thorium, phosphorus, and iron elements from rare earth waste residue to improve the relative separation degree. The present invention achieves the above objects using the following technical solutions.

[0009] On the one hand, the present invention provides a method for recovering rare earth elements from rare earth waste residue, comprising the following steps:

[0010] The crushed rare earth waste residue was leached with a sulfuric acid solution with a pH of 0.7-1 at 15-35℃, and the solid and liquid were separated to obtain rare earth leachate and secondary waste residue.

[0011] Among them, rare earth waste residue is the waste residue produced by roasting rare earth concentrate with sulfuric acid;

[0012] The solid-liquid ratio of rare earth waste residue to sulfuric acid solution is 1 kg: (4-10) L.

[0013] According to the method of the present invention, preferably, the particle size of the crushed rare earth waste residue is ≤100 mesh.

[0014] According to the method of the present invention, preferably, the pH of the sulfuric acid solution is 0.7 to 0.8.

[0015] According to the method of the present invention, preferably, the temperature of stirring and immersion is 20-30°C.

[0016] According to the method of the present invention, preferably, the stirring and soaking time is 1 to 5 hours.

[0017] According to the method of the present invention, preferably, the solid-liquid ratio of rare earth waste residue to sulfuric acid solution is 1 kg: (6-8) L.

[0018] According to the method of the present invention, preferably, it further includes the following steps: drying the rare earth waste residue, and crushing the dried rare earth waste residue to obtain crushed rare earth waste residue.

[0019] According to the method of the present invention, preferably, the rare earth waste residue contains less than 13.0 wt% REO, more than 10.0 wt% CaO, more than or equal to 0.08 wt% ThO2, more than or equal to 2.5 wt% P, and more than or equal to 4.9 wt% TFe.

[0020] According to the method of the present invention, preferably, the rare earth waste residue is the waste residue generated from the sulfuric acid roasting of rare earth concentrate. The specific steps include: roasting the rare earth concentrate with concentrated sulfuric acid at a temperature above 400°C for 2-3 hours to form sulfuric acid rare earth roasted ore; leaching the sulfuric acid rare earth roasted ore with water to obtain a clear slurry and slurry residue; neutralizing and removing impurities from the clear slurry with magnesium oxide to obtain a water leaching solution and a neutralization residue; the water leaching solution is the sulfuric acid rare earth solution; washing the neutralization residue and slurry residue with sulfuric acid to obtain a slag washing solution and secondary residue; washing the secondary residue with water and neutralizing and removing impurities with magnesium oxide to obtain the discharge residue, which is the rare earth waste residue.

[0021] On the other hand, the present invention also provides an application of a sulfuric acid solution with a pH of 0.7-1 in separating rare earth elements from thorium, phosphorus and iron from rare earth waste to improve the relative separation degree, comprising the following steps:

[0022] The crushed rare earth waste residue was leached with a sulfuric acid solution with a pH of 0.7-1 at 15-35℃, and the solid and liquid were separated to obtain rare earth leachate and secondary waste residue.

[0023] Among them, rare earth waste residue is the waste residue produced by roasting rare earth concentrate with sulfuric acid;

[0024] The solid-liquid ratio of rare earth waste residue to sulfuric acid solution is 1 kg: (4-10) L.

[0025] The method for recovering rare earth elements from rare earth waste residue according to this invention does not require additional physicochemical methods for impurity removal, achieving maximum separation of rare earth elements from thorium, phosphorus, and iron, while simultaneously separating rare earth elements from calcium. It essentially focuses on the extraction and recovery of rare earth elements, significantly improving the relative separation degree and separation speed. Furthermore, this method can significantly reduce the amount of secondary waste residue, achieving waste reduction. In addition, the method operates under mild conditions, with no waste gas or waste liquid emissions throughout the process, making it environmentally friendly, simple, and conducive to industrial production. Detailed Implementation

[0026] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0027] The technical concept of this invention differs from existing technologies. The method for recovering rare earth elements from rare earth waste in this invention can achieve maximum separation of rare earth elements from thorium, phosphorus, and iron, while simultaneously achieving separation of rare earth elements from calcium, allowing for the extraction and recovery of rare earth elements essentially independently. The method of this invention is not a conventional approach.

[0028] <Method>

[0029] The method for recovering rare earth elements from rare earth waste according to the present invention includes the following steps: 1) a crushing step; 2) a leaching and solid-liquid separation step. Optionally, it also includes a drying step and a recycling step. A detailed description follows.

[0030] Drying steps

[0031] The rare earth waste residue is dried to obtain the dried rare earth waste residue. The drying temperature can be 100-120℃, and the drying time can be 1-5 hours.

[0032] The rare earth waste residue is the waste residue generated from the sulfuric acid roasting of rare earth concentrate. The specific steps include: roasting the rare earth concentrate with concentrated sulfuric acid at a temperature above 400℃ for 2-3 hours to form sulfuric acid rare earth roasted ore; leaching the sulfuric acid rare earth roasted ore with water to obtain a clear slurry and slurry residue; neutralizing and removing impurities from the clear slurry with magnesium oxide to obtain a water leaching solution and a neutralization residue; the water leaching solution is the sulfuric acid rare earth solution; washing the neutralization residue and slurry residue with sulfuric acid to obtain a slag washing solution and secondary residue; washing the secondary residue with water and neutralizing and removing impurities with magnesium oxide to obtain the discharged residue, which is the rare earth waste residue.

[0033] The preferred roasting temperature is 450–550°C, and the preferred roasting time is 2.5–3 hours. In this step, the concentration of concentrated sulfuric acid used can be 80–95 wt%, preferably 85–95 wt%. Neutralization and leaching can be performed according to those known in the art, and will not be elaborated here.

[0034] In the rare earth waste residue, the REO content is less than 13.0 wt%, preferably less than or equal to 12 wt%, more preferably less than or equal to 11.5 wt%; the CaO content is greater than 10.0 wt%, preferably greater than or equal to 11 wt%, more preferably greater than or equal to 12 wt%, even more preferably greater than or equal to 13 wt%, and even more preferably greater than or equal to 14 wt% and less than 15 wt%; the ThO2 content is greater than or equal to 0.08 wt%, preferably greater than or equal to 0.09 wt%, more preferably greater than or equal to 0.1 wt%; the P content is greater than or equal to 2.5 wt%, preferably greater than or equal to 2.6 wt%, even more preferably greater than or equal to 2.7 wt%; and the TFe content is greater than or equal to 4.9 wt%, preferably greater than or equal to 5.1 wt%, more preferably greater than or equal to 5.2 wt%, and even more preferably greater than or equal to 5.3 wt%.

[0035] Grinding step

[0036] The dried rare earth waste residue is then pulverized. The particle size of the pulverized rare earth waste residue is ≤100 mesh. This facilitates the maximum extraction of rare earth elements. Pulverization can be performed using equipment known in the art.

[0037] Leaching and solid-liquid separation steps

[0038] The crushed rare earth waste residue is leached with a sulfuric acid solution with a pH of 0.7-1 at 15-35°C under stirring, followed by solid-liquid separation to obtain a rare earth leachate and secondary waste residue. This invention surprisingly discovers that, under the conditions of this invention, the separation of rare earth elements from thorium, phosphorus, and iron can be maximized, essentially extracting and recovering only the rare earth elements.

[0039] It should be noted that this invention can also separate rare earth elements from calcium. Although the relative separation degree between rare earth and calcium is slightly lower, the separation of rare earth elements from thorium, phosphorus and iron is more difficult. Therefore, this invention focuses more on the separation of rare earth elements from thorium, phosphorus and iron, while also taking into account the separation of rare earth and calcium.

[0040] In this invention, the pH of the sulfuric acid solution can be 0.7–1, preferably 0.7–0.9, and more preferably 0.7–0.8. When the pH of the sulfuric acid solution is 1, the molar concentration of H₂SO₄ in the sulfuric acid solution is 0.05 mol / L.

[0041] In this invention, the solid-liquid ratio of rare earth waste residue (i.e., pulverized rare earth waste residue) to sulfuric acid solution can be 1 kg:(4-10) L, preferably 1 kg:(5-9) L, and more preferably 1 kg:(6-8) L. For example, the solid-liquid ratio can be 1 kg:6 L, 1 kg:6.5 L, 1 kg:7 L, 1 kg:7.5 L, or 1 kg:8 L.

[0042] In this invention, the temperature for stirring and leaching can be 15-35°C, preferably 20-35°C, more preferably 20-30°C, and even more preferably 20-25°C.

[0043] In this invention, the stirring and soaking time can be 1 to 5 hours, preferably 1.5 to 4 hours, and more preferably 2 to 3 hours.

[0044] Solid-liquid separation can be achieved through centrifugation or filtration, with filtration being the preferred method.

[0045] The rare earth leachate obtained by this invention has a high rare earth content, and the REO yield in the rare earth leachate reaches 35-56%, which can achieve maximum separation of rare earths from other elements. This rare earth leachate can be reused in the water leaching process to leach rare earth elements and obtain a high-concentration rare earth sulfate solution.

[0046] The formula for calculating the rare earth leaching rate is: (mass of REO in the rare earth leachate / mass of REO in the rare earth waste residue) × 100%.

[0047] The formula for calculating the calcium leaching rate is: (mass of CaO in rare earth leachate / mass of CaO in rare earth waste residue) × 100%.

[0048] The formula for calculating the thorium leaching rate is: (mass of ThO2 in rare earth leachate / mass of ThO2 in rare earth waste residue) × 100%.

[0049] The formula for calculating the phosphorus leaching rate is: (mass of P in rare earth leachate / mass of P in rare earth waste residue) × 100%.

[0050] The formula for calculating the iron leaching rate is: (mass of TFe in rare earth leachate / mass of TFe in rare earth waste residue) × 100%.

[0051] The amount of secondary waste residue obtained by this invention is significantly reduced, with a reduction of 22% to 32%.

[0052] The formula for calculating the reduction in slag volume is: [(amount of rare earth waste slag - amount of secondary waste slag) / amount of rare earth waste slag] × 100%.

[0053] The total radioactive emission ratio of Th in the secondary waste residue was detected to be 5.104 × 10⁻⁴. 4 The concentration is around Bq / kg, far below the prescribed storage standards for low-level radioactive waste.

[0054] The process of this invention is simple, does not require physical methods such as adsorption, and the separation speed is correspondingly improved.

[0055] <Application>

[0056] This invention also provides an application of a sulfuric acid solution with a pH of 0.7-1 in separating rare earth elements from thorium, phosphorus, and iron in rare earth waste to improve the relative separation degree, comprising the following steps:

[0057] The rare earth waste residue is crushed, and the crushed rare earth waste residue is leached with sulfuric acid solution with pH 0.7-1 at 15-35℃ by stirring. Solid-liquid separation is performed to obtain rare earth leachate and secondary waste residue.

[0058] The rare earth waste residue is the waste residue produced by roasting rare earth concentrate with sulfuric acid;

[0059] The solid-liquid ratio of the rare earth waste residue to the sulfuric acid solution is 1 kg:(4-10) L. Detailed descriptions are provided above and will not be repeated here.

[0060] The testing method is described below:

[0061] The contents of REO, CaO and TFe were determined by full-spectrum direct-reading plasma atomic emission spectrometry.

[0062] The ThO2 content was determined by plasma atomic emission mass spectrometry.

[0063] The phosphorus (P) content was determined by spectrophotometry.

[0064] The following describes the raw materials used:

[0065] The rare earth waste used in the following examples and comparative examples is the waste generated from the sulfuric acid roasting of rare earth concentrate. The specific steps include: roasting rare earth concentrate with concentrated sulfuric acid at 500°C for 3 hours to form sulfuric acid rare earth roasted ore; the concentration of concentrated sulfuric acid is 85 wt%; the mass ratio of concentrated sulfuric acid to rare earth concentrate is 3:1; leaching the sulfuric acid rare earth roasted ore with water to obtain slurry clear liquid and slurry residue; neutralizing and removing impurities from the slurry clear liquid with magnesium oxide to obtain water leaching liquid and neutralization residue; the water leaching liquid is the sulfuric acid rare earth solution; washing the neutralization residue and slurry residue with sulfuric acid to obtain slag washing clear liquid and secondary residue; washing the secondary residue with water and neutralizing and removing impurities with magnesium oxide to obtain discharge residue, which is the rare earth waste.

[0066] The composition analysis of the rare earth waste residue is shown in Table 1.

[0067] Table 1

[0068] 11.28 14.15 0.11 2.72 5.39

[0069] Example 1

[0070] The rare earth waste residue is dried, and the dried rare earth waste residue is crushed. The particle size of the crushed rare earth waste residue is ≤100 mesh.

[0071] At a solid-liquid ratio of 1 kg: 8 L, the pulverized rare earth waste residue was leached with a sulfuric acid solution at pH 0.8 at 20°C with stirring for 1 hour. The solution was then filtered to obtain a rare earth leachate and secondary waste residue. Analysis of the rare earth leachate revealed its main components, as shown in Table 2 (unit: g / L). The leaching rates of rare earth elements, calcium, thorium, phosphorus, and iron were calculated and are shown in Table 3.

[0072] Example 2

[0073] The only difference between Example 2 and Example 1 is that the solid-liquid ratio is 1kg:6L; the pH of the sulfuric acid solution is 0.7; and the stirring and soaking process lasts for 2 hours.

[0074] The rare earth leachate was analyzed, and the main components are shown in Table 2, with units of g / L. The leaching rates of rare earth elements, calcium, thorium, phosphorus, and iron were calculated and are shown in Table 3.

[0075] Example 3

[0076] The only difference between Example 3 and Example 1 is that the solid-liquid ratio is 1kg:6L and the stirring and leaching temperature is 30℃.

[0077] The rare earth leachate was analyzed, and the main components are shown in Table 2, with units of g / L. The leaching rates of rare earth elements, calcium, thorium, phosphorus, and iron were calculated and are shown in Table 3.

[0078] Comparative Example 1

[0079] The only difference between Comparative Example 1 and Example 1 is that the solid-liquid ratio is 1 kg: 6 L and the pH of the sulfuric acid solution is 0.2.

[0080] The rare earth leachate was analyzed, and the main components are shown in Table 2, with units of g / L. The leaching rates of rare earth elements, calcium, thorium, phosphorus, and iron were calculated and are shown in Table 3.

[0081] Comparative Example 2

[0082] The only difference between Comparative Example 2 and Example 1 is that the solid-liquid ratio is 1 kg: 6 L; a 4 mol / L sulfuric acid solution is used; and the stirring and leaching temperature is 80 °C.

[0083] The rare earth leachate was analyzed, and the main components are shown in Table 2, with units of g / L. The leaching rates of rare earth elements, calcium, thorium, phosphorus, and iron were calculated and are shown in Table 3.

[0084] Table 2

[0085]

[0086] Table 3

[0087]

[0088] Table 4

[0089]

[0090] Note: In Table 4, the relative separation degree between rare earth elements and thorium is the leaching rate of rare earth elements / the leaching rate of thorium, and so on for the others.

[0091] In Examples 1-3, the amount of secondary waste residue was significantly reduced, with reductions of 31%, 29%, and 28%, respectively.

[0092] This invention is not limited to the above-described embodiments. Any modifications, improvements, or substitutions that can be conceived by those skilled in the art without departing from the essential content of this invention fall within the scope of this invention.

Claims

1. A method for recovering rare earth elements from rare earth waste residue, characterized in that, Includes the following steps: The crushed rare earth waste residue was leached with a sulfuric acid solution with a pH of 0.7-1 at 15-35℃, and the solid and liquid were separated to obtain rare earth leachate and secondary waste residue. The rare earth waste residue is the waste residue generated from the sulfuric acid roasting of rare earth concentrate. The specific steps include: roasting the rare earth concentrate with concentrated sulfuric acid at a temperature above 400℃ for 2-3 hours to form sulfuric acid rare earth roasted ore; leaching the sulfuric acid rare earth roasted ore with water to obtain a clear slurry and slurry residue; neutralizing and removing impurities from the clear slurry with magnesium oxide to obtain a water leaching solution and a neutralization residue; the water leaching solution is the sulfuric acid rare earth solution; washing the neutralization residue and slurry residue with sulfuric acid to obtain a slag washing solution and secondary residue; washing the secondary residue with water and neutralizing and removing impurities with magnesium oxide to obtain the discharge residue, which is the rare earth waste residue. The solid-liquid ratio of rare earth waste residue to sulfuric acid solution is 1 kg: (4-10) L.

2. The method according to claim 1, characterized in that, The particle size of the crushed rare earth waste residue is ≤100 mesh.

3. The method according to claim 1, characterized in that, The pH of sulfuric acid solution is 0.7 to 0.

8.

4. The method according to claim 1, characterized in that, The temperature for stirring and soaking is 20–30℃.

5. The method according to claim 1, characterized in that, The stirring and soaking time is 1 to 5 hours.

6. The method according to claim 1, characterized in that, The solid-liquid ratio of rare earth waste residue to sulfuric acid solution is 1 kg: (6-8) L.

7. The method according to any one of claims 1 to 6, characterized in that, It also includes the following steps: The rare earth waste residue is dried, and then crushed to obtain crushed rare earth waste residue.

8. The method according to claim 7, characterized in that, In rare earth waste residue, the REO content is less than 13.0 wt%, the CaO content is greater than 10.0 wt%, the ThO2 content is greater than or equal to 0.08 wt%, the P content is greater than or equal to 2.5 wt%, and the TFe content is greater than or equal to 4.9 wt%.

9. The application of a sulfuric acid solution with a pH of 0.7-1 in separating rare earth elements from thorium, phosphorus, and iron in rare earth waste to improve relative separation, characterized in that... Includes the following steps: The crushed rare earth waste residue was leached with a sulfuric acid solution with a pH of 0.7-1 at 15-35℃, and the solid and liquid were separated to obtain rare earth leachate and secondary waste residue. The rare earth waste residue is the waste residue generated from the sulfuric acid roasting of rare earth concentrate. The specific steps include: roasting the rare earth concentrate with concentrated sulfuric acid at a temperature above 400℃ for 2-3 hours to form sulfuric acid rare earth roasted ore; leaching the sulfuric acid rare earth roasted ore with water to obtain a clear slurry and slurry residue; neutralizing and removing impurities from the clear slurry with magnesium oxide to obtain a water leaching solution and a neutralization residue; the water leaching solution is the sulfuric acid rare earth solution; washing the neutralization residue and slurry residue with sulfuric acid to obtain a slag washing solution and secondary residue; washing the secondary residue with water and neutralizing and removing impurities with magnesium oxide to obtain the discharge residue, which is the rare earth waste residue. The solid-liquid ratio of rare earth waste residue to sulfuric acid solution is 1 kg: (4-10) L.

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