A method for recovering rare earth elements from slag based on microwave irradiation assisted crushing
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- XI AN JIAOTONG UNIV
- Filing Date
- 2026-04-28
- Publication Date
- 2026-06-05
AI Technical Summary
In existing technologies, rare earth elements are difficult to fully expose in slag because they are contained in stable mineral lattices, resulting in low leaching rates, high energy consumption and poor selectivity in mechanical crushing, and high energy consumption and large equipment investment in the pretreatment process.
A microwave-assisted crushing method is adopted. After coarse crushing of the slag, microwave irradiation is applied to induce thermal stress at the mineral interface, forming microcracks. Subsequently, selective fine crushing, graded magnetic separation, and rare earth acid leaching are carried out. The residual carbon in the slag is used as a microwave absorption medium, so that the residual carbon and rare earth enriched phases are preferentially heated, generating a temperature difference to form thermal stress, which promotes the dissociation of rare earth from minerals.
It significantly reduces crushing energy consumption, increases rare earth leaching rate, achieves low-energy and high-efficiency recycling with a total recovery rate of 79.4%, and has a simple process that is easy to industrialize, reducing equipment wear and carbon emissions.
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Figure CN122142056A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of slag recycling technology, specifically relating to a method for recovering rare earth elements from slag based on microwave irradiation-assisted crushing. Background Technology
[0002] Coal-fired solid waste (fly ash and slag) has attracted widespread attention from domestic and international research institutions and enterprises as a potential secondary resource of rare earth elements. The rare earth element content in these materials can reach 200ppm to 500ppm, demonstrating enormous resource recovery potential and making them important industrial raw materials for rare earth elements.
[0003] Currently, research on recovering rare earth elements from coal combustion byproducts mainly focuses on the following technical directions: 1. Conventional mechanical crushing + acid leaching process: The slag undergoes multi-stage crushing, followed by fine grinding in a ball mill or stirred mill until the particle size reaches below 200 mesh (approximately 74μm). Then, an acid leaching reaction is carried out under normal or pressurized conditions, resulting in solid-liquid separation and a leachate containing rare earth ions. However, because mechanical crushing cannot destroy the crystal structure of minerals such as mullite and quartz, rare earth elements remain encapsulated within the particles, resulting in an extremely low rare earth leaching rate (generally less than 30%). Furthermore, the high hardness of quartz in the slag leads to extremely high energy consumption in ball milling (accounting for over 60% of the total energy consumption of the entire process), and severe equipment wear and tear, resulting in high maintenance costs.
[0004] 2. High-Temperature Roasting Pretreatment + Acid Leaching Process: Before acid leaching, the slag is roasted at a high temperature of 800℃~1200℃ to utilize the high temperature to cause a phase transformation of stable minerals such as mullite in the slag, decomposing them into more reactive amorphous structures (such as amorphous aluminosilicates), thereby "releasing" the encapsulated rare earth elements. The roasted slag is then ball-milled and acid-leached to extract rare earth elements. However, this process involves high energy consumption and high carbon emissions. More importantly, alkali metals and alkaline earth metals in the slag tend to form low-melting-point eutectics at high temperatures, causing the particle surface to melt and sinter to form a dense shell, which in turn hinders acid penetration. This results in the rare earth leaching rate not only failing to increase but potentially even being lower than that of unroasted samples.
[0005] 3. Microwave-assisted leaching technology: The core of this technology is to directly apply a microwave field to the mixture of slag and acid. Utilizing the "volume heating" characteristic of microwaves, the material is heated simultaneously from the inside out, and the "hot spot effect" accelerates the chemical reaction between rare earth elements and acid at the microscopic level, aiming to shorten leaching time and increase the leaching rate. However, simply applying microwaves to the leaching process cannot increase the exposure ratio of rare earth elements, and the improvement in leaching rate is usually less than 10 percentage points. Furthermore, microwave irradiation in an acidic environment causes acidic vapors from acid volatilization, which severely corrodes the equipment cavity and seals, forcing the use of expensive corrosion-resistant materials and significantly increasing equipment costs.
[0006] In summary, existing technologies still generally suffer from the following common problems: rare earth elements are difficult to fully expose because they are contained in stable mineral lattices, resulting in low leaching rates; mechanical crushing is energy-intensive and has poor selectivity; and pretreatment processes (such as roasting and mechanical activation) are energy-intensive and require large equipment investments. Summary of the Invention
[0007] To address the aforementioned problems, this invention provides a method for recovering rare earth elements from slag based on microwave-assisted crushing. Based on a process of coarse crushing → microwave pre-irradiation → selective fine crushing → graded magnetic separation → rare earth acid leaching → separation and enrichment, the slag is crushed to a particle size controllable by microwave irradiation. Residual carbon in the slag is used as a microwave absorbing medium, causing preferential heating of the residual carbon and rare earth enriched phases. A temperature difference is generated between the residual carbon, rare earth elements, and aluminosilicates, resulting in thermal stress at the mineral interface and the formation of cracks. The presence of these microcracks allows energy to be preferentially released along the interface during subsequent fine crushing, reducing energy consumption and effectively dissociating rare earth elements from the minerals, thereby improving the rare earth leaching rate.
[0008] The present invention solves the above-mentioned technical problems through the following technical solutions.
[0009] The purpose of this invention is to provide a method for recovering rare earth elements from slag based on microwave irradiation-assisted crushing, comprising the following steps: S1. The slag is first crushed to a particle size of <20mm. The crushed slag is then subjected to microwave irradiation treatment to generate thermal stress at the mineral interface and form microcracks along the interface, thus obtaining the irradiated crushed slag.
[0010] S2. The irradiated crushed slag is crushed a second time to a particle size of <3mm, and then screened, graded, decarburized, and magnetically separated to remove iron-containing components, thus obtaining decarburized crushed slag.
[0011] S3. Acid leaching is performed on the decarburized and crushed slag, and solid-liquid separation is performed to obtain rare earth enrichment.
[0012] Furthermore, during the microwave irradiation treatment, the microwave frequency is 2.45 GHz or 915 MHz, the irradiation time is 30 s to 300 s, and the microwave power density is 10 kW / m². 3 ~100kW / m 3 .
[0013] Furthermore, during the acid leaching process, the solid-liquid ratio of the graded crushed slag to the acid is 1g:2mL~5mL.
[0014] Furthermore, the acid is at least one of hydrochloric acid, sulfuric acid, or nitric acid, with a concentration of 1 mol / L to 4 mol / L.
[0015] Furthermore, the acid leaching temperature is 60℃~95℃, and the time is 1h~4h.
[0016] Furthermore, during the acid leaching process, an oxidizing agent is added, namely hydrogen peroxide, and the amount of hydrogen peroxide used is 0.1% to 1% of the acid volume.
[0017] Furthermore, after acid leaching, solvent extraction or ion exchange is performed to separate and obtain enriched rare earth elements.
[0018] Furthermore, before microwave irradiation treatment, the moisture content of the crushed slag is controlled to be less than 15%.
[0019] Compared with the prior art, the present invention has the following advantages: The method for recovering rare earth elements from slag provided by this invention involves crushing the slag to a particle size controllable by microwave irradiation. Utilizing the selective heating characteristics of microwaves, residual carbon in the slag acts as a microwave absorption medium, causing preferential heating of the residual carbon and rare earth-enriched phases. A temperature difference is generated between the residual carbon, rare earth elements, and aluminosilicates, resulting in thermal stress at the mineral interface and the formation of cracks. The presence of these microcracks allows energy to be preferentially released along the interface during subsequent fine crushing, reducing energy consumption in the later crushing process and effectively dissociating rare earth elements from the minerals, thereby improving the rare earth leaching rate.
[0020] This invention employs microwave irradiation, a process that takes only a few minutes and requires no chemical reagents, achieving a low-energy, green rare earth recovery process. Microwave irradiation disrupts the crystal structure of stable minerals such as mullite, releasing rare earth elements and creating conditions for subsequent acid leaching. The total recovery rate reaches 79.4%. The process is simple and easy to implement industrially. This method only requires embedding a microwave irradiation unit into an existing slag crushing production line, without altering the original acid leaching and extraction processes, making it easy for technological upgrades and widespread application. Attached Figure Description
[0021] Figure 1 This is a flowchart of the method for recovering rare earth elements from slag based on microwave irradiation-assisted crushing according to the present invention. Detailed Implementation
[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0023] It should be noted that the technical terms used in this invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the following embodiments of this invention can be purchased from the market or prepared by existing methods.
[0024] Existing methods for recovering rare earth elements from coal combustion byproducts, such as direct acid leaching, roasting pretreatment + acid leaching, mechanical activation + acid leaching, or microwave-assisted leaching, have made some progress in rare earth recovery. However, they still generally suffer from the following common problems: (1) Rare earth elements are difficult to fully expose due to their presence in stable mineral lattices, resulting in low leaching rates; (2) Pretreatment steps (roasting, mechanical activation) involve high energy consumption and large equipment investment; (3) There is a lack of targeted selective dissociation methods, leading to low energy utilization efficiency. Therefore, developing a new pretreatment method that is low in energy consumption, highly selective, and can effectively destroy mineral lattices is of great significance for achieving efficient recovery of rare earth resources from slag.
[0025] The purpose of this invention is to provide a method for recovering rare earth elements from slag based on microwave irradiation-assisted crushing, comprising the following steps: S1. The slag is first crushed to a particle size of <20mm. The crushed slag is then subjected to microwave irradiation treatment to generate huge thermal stress at the mineral interface, forming microcracks along the interface, thus obtaining the irradiated crushed slag.
[0026] The initial crushing can be performed using a jaw crusher or hammer crusher. After crushing, the slag is screened to control the particle size below 20mm, thus reducing the slag to a size suitable for microwave irradiation. Then, microwave irradiation treatment is carried out. In this invention, residual carbon in the slag is used as a microwave absorbing medium. Due to the significant differences in microwave absorption capacity among the components—for example, residual carbon and rare earth enriched phases preferentially absorb microwave energy and rapidly heat up, while the aluminosilicate matrix (quartz, mullite, etc.) is almost transparent to microwaves and heats up very slowly—this selective heating characteristic allows the temperature of the residual carbon and rare earth enriched phases to rise to 400°C to 600°C within tens of seconds, while the surrounding aluminosilicate matrix only heats up to 150°C to 200°C. This creates a temperature difference of 200°C to 400°C, generating significant thermal stress (up to 50MPa to 100MPa) at the mineral interface. This causes microcracks to preferentially initiate and propagate along the interface, releasing rare earth elements from the crystal lattice.
[0027] In some embodiments, during microwave irradiation treatment, the microwave frequency is 2.45 GHz or 915 MHz, the irradiation time is 30 s to 300 s, and the microwave power density is 10 kW / m². 3 ~100kW / m 3During microwave irradiation treatment, this invention requires no addition of any chemical reagents. The naturally occurring residual carbon in the slag is the best microwave absorption medium, realizing spontaneous selective heating of "waste-to-waste" treatment. The microwave treatment time is significantly reduced, crushing energy consumption is lowered, equipment life is extended, and an energy-saving crushing mode of "heat-for-power" is achieved.
[0028] Understandably, the moisture content of the crushed slag should be controlled to be less than 15% before microwave irradiation treatment. During microwave irradiation, the moisture content in the slag has a significant impact on microwave absorption efficiency. When the moisture content is greater than 15%, the moisture will preferentially absorb microwave energy, reducing the selective heating effect on residual carbon and rare earth phases. Therefore, for slag produced by wet slag removal processes, a drying process needs to be added to ensure that the moisture content is less than 15%.
[0029] S2. The irradiated crushed slag is crushed a second time to a particle size of <3mm, and then screened, graded, decarburized, and magnetically separated to remove iron-containing components, thus obtaining decarburized crushed slag.
[0030] After irradiation, the slag is finely crushed using a roller crusher or impact crusher. Large cracks have already formed inside the slag particles, allowing energy to be preferentially released along the interface during subsequent fine crushing. This reduces energy consumption in later crushing processes and effectively dissociates rare earth elements from the minerals, thereby increasing the rare earth leaching rate. This achieves the goals of energy conservation and reduced equipment wear. The coarse material after screening and grading undergoes further microwave irradiation treatment, followed by crushing again.
[0031] In some embodiments, the screening and grading method is coarse grading using a vibrating screen followed by airflow classification for decarburization. Specifically, coarse grading using a vibrating screen removes fine particles with a diameter less than 3 mm, while coarse particles larger than 3 mm are returned for a second crushing. Airflow classification for decarburization utilizes the difference in settling velocity of different particles in the airflow to separate carbon particles from mineral particles. Finally, decarburized mineral particles with a diameter less than 3 mm are obtained. Magnetic separation separates the iron-containing components, which can be recycled as raw material for ironmaking, while the unburned carbon separated can be returned to the boiler for co-firing, achieving resource utilization and avoiding the adsorption of rare earth ions by residual carbon during acid leaching, as well as the consumption of acid and impact on extraction selectivity by iron, thus improving subsequent leaching efficiency.
[0032] S3. The decarburized and crushed slag is subjected to acid leaching under normal pressure, followed by solvent extraction (such as P507 extractant) or ion exchange to separate rare earth enrichment. The raffinate after solvent extraction can be recycled after neutralization.
[0033] Acid leaching selectively dissolves rare earth elements in the slag into the liquid phase, thereby separating rare earth elements from gangue minerals. Finally, rare earth elements are extracted and enriched from the leachate by solvent extraction or ion exchange to obtain rare earth concentrates. In some embodiments, during acid leaching, the solid-liquid ratio of the graded crushed slag to acid is 1g:2mL–5mL, and the acid is at least one of hydrochloric acid, sulfuric acid, or nitric acid, with a concentration of 1mol / L–4mol / L. The acid leaching temperature is 60℃–95℃, and the time is 1h–4h. As a preferred embodiment of the invention, an oxidizing agent, hydrogen peroxide, can be added during acid leaching at a concentration of 0.1%–1% of the acid volume. The addition of hydrogen peroxide primarily acts as an oxidizing agent, improving rare earth leaching efficiency by altering the valence state of elements, disrupting mineral structures, or preventing secondary precipitation.
[0034] The following specific examples will provide further explanation.
[0035] Example 1 A method for recovering rare earth elements from slag based on microwave-assisted crushing, such as... Figure 1 As shown, it includes the following steps: S1. Coarse crushing: A jaw crusher is used to screen and coarsely crush the slag discharged from the coal-fired boiler, so that the particle size of the coarse crushed slag is <20mm.
[0036] S2. Microwave Radiation: The coarsely crushed slag is transported to a microwave resonant cavity and irradiated for 200 seconds using microwaves at a frequency of 2.45 GHz under an oxygen-rich or inert atmosphere. The microwave power density is 10 kW / m². 3 .
[0037] S3. Selective fine crushing: The coarsely crushed slag after microwave irradiation is fed into a double roll crusher or impact crusher for fine crushing to a particle size of less than 3mm to obtain finely crushed slag.
[0038] S4. Grading and Magnetic Separation: The finely crushed slag is screened and graded using a combination of coarse grading with vibrating screens and decarburization with airflow classification. First, fine particles smaller than 3mm in diameter are screened out using a circular vibrating screen, while larger particles are returned for a second crushing. Then, airflow classification decarburization utilizes the difference in settling velocity of different particles in the airflow to separate carbon particles from mineral particles, resulting in decarburized mineral particles smaller than 3mm in diameter. Magnetic separation equipment is then used to separate iron-containing components and unburned carbon, yielding decarburized crushed slag fine powder. The screened coarse material undergoes further microwave irradiation treatment; the iron-containing components can be recovered as raw material for ironmaking, and the unburned carbon can be returned to the boiler for co-firing.
[0039] S5. Rare earth leaching: The decarburized and crushed slag fine powder and acid leaching solution are mixed with a solid-liquid ratio of 1g:4mL. The acid leaching solution is a hydrochloric acid solution with a concentration of 2.5mol / L. 0.6% of the volume of the acid leaching solution is added as an oxidizing agent. The mixture is stirred and leached for 2 hours under normal pressure and 80℃ to obtain the leaching solution.
[0040] S6. Separation and Enrichment: Rare earth elements are separated and enriched from the leachate using solvent extraction (such as P507 extractant) or ion exchange methods to obtain rare earth concentrates. The raffinate can be recycled after neutralization.
[0041] Example 2 A method for recovering rare earth elements from slag based on microwave-assisted crushing, such as... Figure 1 As shown, it includes the following steps: S1. Coarse crushing: A jaw crusher is used to screen and coarsely crush the slag discharged from the coal-fired boiler, so that the particle size of the coarse crushed slag is <20mm.
[0042] S2. Microwave Radiation: The coarsely crushed slag is transported to a microwave resonant cavity and irradiated for 200 seconds using microwaves at a frequency of 2.45 GHz under an oxygen-rich or inert atmosphere. The microwave power density is 20 kW / m². 3 .
[0043] S3. Selective fine crushing: The coarsely crushed slag after microwave irradiation is fed into a double roll crusher or impact crusher for fine crushing to a particle size of less than 3mm to obtain finely crushed slag.
[0044] S4. Grading and Magnetic Separation: The finely crushed slag is screened and graded using a combination of coarse grading with vibrating screens and decarburization with airflow classification. First, fine particles smaller than 3mm in diameter are screened out using a circular vibrating screen, while larger particles are returned for a second crushing. Then, airflow classification decarburization utilizes the difference in settling velocity of different particles in the airflow to separate carbon particles from mineral particles, resulting in decarburized mineral particles smaller than 3mm in diameter. Magnetic separation equipment is then used to separate iron-containing components and unburned carbon, yielding decarburized crushed slag fine powder. The screened coarse material undergoes further microwave irradiation treatment; the iron-containing components can be recovered as raw material for ironmaking, and the unburned carbon can be returned to the boiler for co-firing.
[0045] S5. Rare earth leaching: The decarburized and crushed slag fine powder and acid leaching solution are mixed with a solid-liquid ratio of 1g:4mL. The acid leaching solution is a hydrochloric acid solution with a concentration of 2.5mol / L. 0.6% of the volume of the acid leaching solution is added as an oxidizing agent. The mixture is stirred and leached for 2 hours under normal pressure and 80℃ to obtain the leaching solution.
[0046] S6. Separation and Enrichment: Rare earth elements are separated and enriched from the leachate using solvent extraction (such as P507 extractant) or ion exchange methods to obtain rare earth concentrates. The raffinate can be recycled after neutralization.
[0047] Example 3 A method for recovering rare earth elements from slag based on microwave-assisted crushing, such as... Figure 1 As shown, it includes the following steps: S1. Coarse crushing: A jaw crusher is used to screen and coarsely crush the slag discharged from the coal-fired boiler, so that the particle size of the coarse crushed slag is <20mm.
[0048] S2. Microwave Radiation: The coarsely crushed slag is transported to a microwave resonant cavity and irradiated for 200 seconds using microwaves at a frequency of 2.45 GHz under an oxygen-rich or inert atmosphere. The microwave power density is 50 kW / m². 3 .
[0049] S3. Selective fine crushing: The coarsely crushed slag after microwave irradiation is fed into a double roll crusher or impact crusher for fine crushing to a particle size of less than 3mm to obtain finely crushed slag.
[0050] S4. Grading and Magnetic Separation: The finely crushed slag is screened and graded using a combination of coarse grading with vibrating screens and decarburization with airflow classification. First, fine particles smaller than 3mm in diameter are screened out using a circular vibrating screen, while larger particles are returned for a second crushing. Then, airflow classification decarburization utilizes the difference in settling velocity of different particles in the airflow to separate carbon particles from mineral particles, resulting in decarburized mineral particles smaller than 3mm in diameter. Magnetic separation equipment is then used to separate iron-containing components and unburned carbon, yielding decarburized crushed slag fine powder. The screened coarse material undergoes further microwave irradiation treatment; the iron-containing components can be recovered as raw material for ironmaking, and the unburned carbon can be returned to the boiler for co-firing.
[0051] S5. Rare earth leaching: The decarburized and crushed slag fine powder and acid leaching solution are mixed with a solid-liquid ratio of 1g:4mL. The acid leaching solution is a hydrochloric acid solution with a concentration of 2.5mol / L. 0.6% of the volume of the acid leaching solution is added as an oxidizing agent. The mixture is stirred and leached for 2 hours under normal pressure and 80℃ to obtain the leaching solution.
[0052] S6. Separation and Enrichment: Rare earth elements are separated and enriched from the leachate using solvent extraction (such as P507 extractant) or ion exchange methods to obtain rare earth concentrates. The raffinate can be recycled after neutralization.
[0053] Example 4 A method for recovering rare earth elements from slag based on microwave-assisted crushing, such as... Figure 1 As shown, it includes the following steps: S1. Coarse crushing: A jaw crusher is used to screen and coarsely crush the slag discharged from the coal-fired boiler, so that the particle size of the coarse crushed slag is <20mm.
[0054] S2. Microwave Radiation: The coarsely crushed slag is transported to a microwave resonant cavity and irradiated for 300 seconds using microwaves at a frequency of 2.45 GHz under an oxygen-rich or inert atmosphere. The microwave power density is 50 kW / m². 3 .
[0055] S3. Selective fine crushing: The coarsely crushed slag after microwave irradiation is fed into a double roll crusher or impact crusher for fine crushing to a particle size of less than 3mm to obtain finely crushed slag.
[0056] S4. Grading and Magnetic Separation: The finely crushed slag is screened and graded using a combination of coarse grading with vibrating screens and decarburization with airflow classification. First, fine particles smaller than 3mm in diameter are screened out using a circular vibrating screen, while larger particles are returned for a second crushing. Then, airflow classification decarburization utilizes the difference in settling velocity of different particles in the airflow to separate carbon particles from mineral particles, resulting in decarburized mineral particles smaller than 3mm in diameter. Magnetic separation equipment is then used to separate iron-containing components and unburned carbon, yielding decarburized crushed slag fine powder. The screened coarse material undergoes further microwave irradiation treatment; the iron-containing components can be recovered as raw material for ironmaking, and the unburned carbon can be returned to the boiler for co-firing.
[0057] S5. Rare earth leaching: Fine powder of decarburized and crushed slag is mixed with acid leaching solution at a solid-liquid ratio of 1g:4mL. The acid leaching solution is hydrochloric acid solution with a concentration of 2.5mol / L. Hydrogen peroxide is added at 0.6% of the volume of the acid leaching solution as an oxidizing agent. The mixture is stirred and leached for 2 hours under normal pressure and 80℃ to obtain the leaching solution.
[0058] S6. Separation and Enrichment: Rare earth elements are separated and enriched from the leachate using solvent extraction (such as P507 extractant) or ion exchange methods to obtain rare earth concentrates. The raffinate can be recycled after neutralization.
[0059] Comparative Example 1 A method for recovering rare earth elements from slag includes the following steps: S1. Coarse crushing: A jaw crusher is used to screen and coarsely crush the slag discharged from the coal-fired boiler, so that the particle size of the coarse crushed slag is <20mm.
[0060] S2. Selective fine crushing: The coarse slag is fed into a double roll crusher or impact crusher for fine crushing to a particle size of less than 3mm to obtain fine slag.
[0061] S3. Grading and Magnetic Separation: The finely crushed slag is screened and graded using a combination of coarse grading with vibrating screens and decarburization with airflow classification. First, fine particles smaller than 3mm in diameter are screened out using a circular vibrating screen, while larger particles are returned for a second crushing. Then, airflow classification decarburization utilizes the difference in settling velocity of different particles in the airflow to separate carbon particles from mineral particles, resulting in decarburized mineral particles smaller than 3mm in diameter. Magnetic separation equipment is then used to separate iron-containing components and unburned carbon, yielding decarburized crushed slag fine powder. The screened coarse material undergoes further microwave radiation treatment; the iron-containing components can be recovered as raw material for ironmaking, and the unburned carbon can be returned to the boiler for co-firing.
[0062] S4. Rare earth leaching: The decarburized and crushed slag fine powder and acid leaching solution are mixed with a solid-liquid ratio of 1g:4mL. The acid leaching solution is a hydrochloric acid solution with a concentration of 2.5mol / L. 0.6% of the volume of the acid leaching solution is added as an oxidizing agent. The mixture is stirred and leached for 2 hours under normal pressure and 80℃ to obtain the leaching solution.
[0063] S5. Separation and Enrichment: Rare earth elements are separated and enriched from the leachate using solvent extraction (such as P507 extractant) or ion exchange methods to obtain rare earth concentrates. The raffinate can be recycled after neutralization.
[0064] The rare earth content of the slag, the concentration of rare earth elements in the leaching solutions of the examples and comparative examples were measured, and the leaching rate was calculated. The results are shown in Table 1.
[0065] Table 1. Leaching rates of rare earth elements enriched in Examples and Comparative Example 1 As shown in Table 1, the leaching rate increases with increasing microwave power density and irradiation time. The core reason lies in the selective heating effect of microwaves on residual carbon and rare earth enriched phases in the slag. Higher power density means more microwave energy is absorbed by the residual carbon and rare earth phases per unit time, leading to a faster heating rate and a wider temperature difference with the aluminosilicate matrix. This generates stronger thermal stress at the mineral interface, promoting the initiation and propagation of microcracks, resulting in more thorough subsequent crushing and improved leaching efficiency. However, further extending the irradiation time does not significantly increase the leaching rate. When the power density exceeds a certain threshold, the excessively high heating rate may cause the residual carbon to oxidize and be consumed in a short time, weakening its role as a microwave absorption medium. Simultaneously, local melting or sintering may occur on the particle surface, forming a dense shell that hinders the exposure of rare earth elements and the penetration of acid. After a certain irradiation time, the microcrack network is essentially fully developed, and further extending the irradiation time only increases the thermal stress effect to a limited extent, while the increase in rare earth leaching rate becomes extremely gradual, exhibiting a clear diminishing marginal benefit. Therefore, from an economic perspective, it is not advisable to use excessively high microwave power density and microwave irradiation time. Examples 1 to 4 only reflect the general trend of microwave irradiation on rare earth leaching rate. For different application scenarios, the optimal parameters of power and irradiation time can be obtained through further experiments.
[0066] In summary, the recycling method provided by this invention preferentially heats the residual carbon and rare earth enriched phases in the slag through microwave pre-irradiation. The residual carbon and rare earth elements generate a temperature difference with the aluminosilicates, thus creating thermal stress at the mineral interface and forming cracks. The presence of these microcracks allows energy to be preferentially released along the interface during subsequent fine crushing, reducing energy consumption in the subsequent crushing process. Furthermore, the rare earth elements are effectively dissociated from the minerals, thereby improving the rare earth leaching rate. This method offers the following advantages:
[0067] 1. Significantly reduces crushing energy consumption and extends equipment life: Selective microcracks generated by microwave pre-irradiation reduce subsequent fine crushing energy consumption by 38.4%, reduce equipment wear, and extend the liner replacement cycle by 60%. This effect stems from the concentrated release of thermal stress generated by microwave heating along the mineral interface, realizing an energy-saving crushing mode of "using heat instead of power".
[0068] 2. Significantly improves rare earth leaching rate and achieves efficient recovery: Microwave irradiation disrupts the crystal structure of stable minerals such as mullite, while selective dissociation fully exposes the rare earth enriched phase. The rare earth leaching rate is increased from less than 30% in traditional processes to 82.3%, with a total recovery rate of 79.4%. This effect stems from the dual mechanism of microwave "selective heating + thermal stress destruction," solving the industry problem of rare earth elements being difficult to leach due to their presence in the crystal lattice of stable minerals.
[0069] 3. Green and low-carbon, environmentally friendly: The process does not require high-temperature roasting (800℃~1200℃), and the energy consumption per ton of residue is only 13.3% of that of the roasting process, reducing CO2 emissions by 86.7%. At the same time, it has low acid consumption and low waste liquid generation, which meets the requirements of green manufacturing under the "dual carbon" background.
[0070] 4. The process is simple and easy to implement industrially. This method only requires embedding a microwave irradiation unit in an existing slag crushing production line (occupying an area of approximately 50m²). 2 ~100m 2 It does not require changes to the original acid leaching and extraction processes, the equipment investment is controllable, and it is easy for existing enterprises to carry out technological transformation and promotion.
[0071] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of the invention have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this invention.
[0072] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.
Claims
1. A method for recovering rare earth elements from slag based on microwave irradiation-assisted crushing, characterized in that, Includes the following steps: The slag is first crushed to a particle size of <20mm, and then microwave irradiation is applied to the crushed slag to generate thermal stress at the mineral interface and form microcracks along the interface, thus obtaining the irradiated crushed slag. The irradiated crushed slag is crushed a second time to a particle size of <3mm, and then screened, graded, decarburized, and magnetically separated to remove iron-containing components, thus obtaining decarburized crushed slag. Acid leaching and solid-liquid separation were performed on decarburized and crushed slag to obtain rare earth enrichment.
2. The method for recovering rare earth elements from slag based on microwave irradiation-assisted crushing according to claim 1, characterized in that, During microwave irradiation treatment, the microwave frequency is 2.45 GHz or 915 MHz, the irradiation time is 30 s to 300 s, and the microwave power density is 10 kW / m². 3 ~100kW / m 3 .
3. The method for recovering rare earth elements from slag based on microwave irradiation-assisted crushing according to claim 1, characterized in that, During the acid leaching process, the solid-liquid ratio of the graded crushed slag to the acid is 1g:2mL~5mL.
4. The method for recovering rare earth elements from slag based on microwave irradiation-assisted crushing according to claim 1, characterized in that, The acid is at least one of hydrochloric acid, sulfuric acid, or nitric acid, with a concentration of 1 mol / L to 4 mol / L.
5. The method for recovering rare earth elements from slag based on microwave irradiation-assisted crushing according to claim 1, characterized in that, The acid leaching temperature is 60℃~95℃, and the time is 1h~4h.
6. The method for recovering rare earth elements from slag based on microwave irradiation-assisted crushing according to claim 1, characterized in that, During the acid leaching process, an oxidizing agent is added, which is hydrogen peroxide. The amount of hydrogen peroxide used is 0.1% to 1% of the acid volume.
7. The method for recovering rare earth elements from slag based on microwave irradiation-assisted crushing according to claim 1, characterized in that, After acid leaching, solvent extraction or ion exchange is performed to separate and obtain enriched rare earth elements.
8. The method for recovering rare earth elements from slag based on microwave irradiation-assisted crushing according to claim 1, characterized in that, Before microwave irradiation treatment, the moisture content of the crushed slag is controlled to be less than 15%.