Method for treating rare earth iron slag by carbonylation to produce carbonyl iron powder and rare earth enrichment

Abstract

This invention discloses a method for treating rare earth iron slag using carbonylation to produce carbonyl iron powder and rare earth enriched materials, belonging to the field of metal waste recycling technology. The method includes pretreatment, drying, rare earth catalytic self-activation, fluidized bed reduction, and selective separation of iron via carbonylation. This invention utilizes rare earth catalytic self-activation to construct a metastable oxygen vacancy structure, providing an efficient electron transfer channel for the deep reduction and carbonylation separation of iron. Combined with the selective reaction of the carbonylation method, it achieves molecular-level dissociation of iron and rare earth elements, converting iron into high-value carbonyl iron powder while significantly increasing the enrichment of rare earth elements. This transforms industrial solid waste into a product with both economic value and application potential, significantly improving the comprehensive utilization rate of resources.

Description

Technical Field

[0001] This invention relates to the field of metal waste recycling technology, specifically to a method for treating rare earth iron slag using a carbonylation process to produce carbonyl iron powder and rare earth enrichment. Background Technology

[0002] Rare earth iron slag is the main solid waste generated after acid leaching of rare earth elements in neodymium iron boron permanent magnet materials. Its iron content typically exceeds 50%, rare earth oxide (REO) content is ≥0.5%, and it is accompanied by impurities such as silicon and calcium. my country's annual rare earth production exceeds 200,000 tons, and conservatively estimated, the amount of rare earth iron slag as a byproduct exceeds 100,000 tons per year. If not efficiently utilized, this not only wastes strategic metals such as iron and rare earth elements but also poses environmental risks due to long-term storage—residual radioactive thorium in the slag may migrate into soil and water bodies, and fluorides may leach out and pollute groundwater.

[0003] Currently, the processing technologies for rare earth iron slag are mainly divided into the following three categories:

[0004] Although physical separation methods (magnetic separation / gravity separation) are simple to operate, the complex occurrence state of iron and rare earth elements (such as micron-sized grains) makes it difficult to completely separate them, resulting in insufficient rare earth enrichment.

[0005] Pyrometallurgical processes (high-temperature reduction smelting) require operation at temperatures above 1400℃, consuming 800-1000 kWh / ton of slag; and at high temperatures, rare earth elements are easily dispersed in the slag phase to form silicates, resulting in low recovery rates and poor economic efficiency.

[0006] Although hydrometallurgical processes (acid leaching for iron extraction) can improve the enrichment of rare earth elements, each ton of slag consumes approximately 0.8-1.2 tons of hydrochloric acid, generating a large amount of acidic wastewater containing heavy metals (such as cobalt and manganese).

[0007] To address the aforementioned challenges, there is an urgent need to develop a co-processing technology for rare earth iron slag that balances efficient resource conversion with environmental friendliness. Summary of the Invention

[0008] To address the aforementioned shortcomings of existing technologies, this invention provides a method for treating rare earth iron slag using a carbonylation process to produce carbonyl iron powder and rare earth enrichment, comprising the following steps:

[0009] S1. Preprocessing;

[0010] Fine rare earth iron slag powder with a particle size of ≤50μm was separated from rare earth iron slag.

[0011] S2. Drying;

[0012] The rare earth iron slag powder was dried until the moisture content was reduced to ≤1%;

[0013] S3. Rare earth catalytic self-activation;

[0014] Spray citric acid solution onto the surface of dry rare earth iron slag fine powder;

[0015] The mixture is transferred to a rotary kiln, oxygen-containing gas is introduced, the temperature is raised and held, triggering the valence state transition reaction of cerium.

[0016] The oxygen-containing hot air is switched to an N2 / CO mixture and kept at a constant temperature. CO reacts with high-valence cerium to release oxygen vacancies.

[0017] After activation, the rare earth iron slag fine powder is rapidly cooled to lock the metastable oxygen vacancy structure.

[0018] S4. Fluidized bed reduction;

[0019] The rare earth iron slag fine powder is fed into a circulating fluidized bed reactor, and nitrogen is introduced to replace the air.

[0020] Gradient heating reduces the iron in rare earth iron slag powder to elemental form.

[0021] S5. Selective separation of iron via carbonylation;

[0022] Nano carbon black was added to rare earth iron slag powder, and the mixture was heated and pressurized under CO atmosphere to obtain liquid Fe(CO)5, with the remainder being rare earth enrichment material.

[0023] Liquid Fe(CO)5 pyrolyzes to produce carbonyl iron powder and CO gas.

[0024] Furthermore, S1 specifically involves preparing a slurry of rare earth iron slag at 15-22 wt%, adding it to a hydrocyclone, controlling the feed pressure at 0.15-0.25 MPa, and separating out rare earth iron slag fine powder of ≤50 μm.

[0025] Furthermore, S2 specifically involves: feeding rare earth iron slag fine powder into a circulating fluidized bed, controlling the bed temperature at 120-150℃, the gas velocity at 0.8-1.2m / s, and the drying time at 20-40min, so that the moisture content is reduced to ≤1%.

[0026] Furthermore, S3 specifically involves uniformly spraying a 5-10 wt% citric acid solution (at a temperature of 60-70℃) onto the surface of dry rare earth iron slag fine powder through an atomizing nozzle. The spraying amount is 0.5-1.0 L / kg of rare earth iron slag fine powder. After spraying, the pH is 3.5-4.5, at which point citric acid and cerium form a stable chelate.

[0027] The mixture is transferred to a rotary kiln and introduced with oxygen-containing gas (O2 content 45-48%). The temperature is increased to 150-180℃ at a rate of 10-15℃ / min and held constant for 20-40min to trigger the valence state transition reaction of cerium.

[0028] The oxygen-containing hot air is switched to an N2 / CO mixture (CO content 60-80%), and kept at 150-180℃ for 10-15 minutes. CO reacts with high-valence cerium to release oxygen vacancies.

[0029] After activation, the rare earth iron slag fine powder is rapidly cooled to lock the metastable oxygen vacancy structure.

[0030] Furthermore, the activated rare earth iron slag powder is rapidly cooled to 50-60°C within 8-10 seconds by a water-cooling jacket.

[0031] Furthermore, S4 specifically involves: feeding rare earth iron slag fine powder into a circulating fluidized bed reactor via pneumatics, filling it to 1 / 2 of the reactor volume, and then purging high-purity nitrogen to replace the air.

[0032] Heat to 220-260℃ at a rate of 5-10℃ / min, and replace N2 with CO;

[0033] Heat to 480-520℃ at a rate of 5-10℃ / min and hold for 15-25min to generate a nano-carbon film on the surface of rare earth iron slag fine powder by CO disproportionation reaction, which inhibits subsequent high-temperature bonding.

[0034] The iron in the rare earth iron slag fine powder is reduced to elemental form by heating to 750-950℃ at a rate of 10-15℃ / min and reacting at a constant temperature for 30-90min.

[0035] Furthermore, S5 specifically involves: adding fine rare earth iron slag powder to a high-pressure reactor, simultaneously adding 0.1-0.3wt% nano carbon black with a particle size of 20-50nm as heterogeneous nucleation sites for Fe(CO)5; replacing the air with CO and raising the temperature to 160-180℃, pressurizing to 16-20MPa, and reacting at a constant temperature for 2-3 hours to obtain liquid Fe(CO)5 which is discharged from the bottom of the reactor and condensed by cooling water at 2-5℃; the remainder is rare earth enriched material.

[0036] Liquid Fe(CO)5 undergoes thermal decomposition at 200-280℃ in a mixed N2 / CO / NH3 atmosphere to produce carbonyl iron powder and CO gas.

[0037] Furthermore, in the N2 / CO / NH3 mixture, CO accounts for 10-20% and NH3 accounts for 3-5%.

[0038] Compared with the prior art, the beneficial effects of this invention are as follows:

[0039] 1. This invention uses rare earth iron slag as the treatment target, achieving efficient resource recovery and harmless treatment of solid waste through innovative processes. By utilizing rare earth catalytic self-activation to construct a metastable oxygen vacancy structure, an efficient electron transfer channel is provided for the deep reduction and carbonylation separation of iron. Combined with the selective reaction of the carbonylation method, molecular-level dissociation of iron and rare earth elements is achieved, converting iron into high-value carbonyl iron powder. Simultaneously, the enrichment of rare earth elements is significantly increased, transforming the original industrial solid waste into a product with both economic value and application potential, significantly improving the comprehensive utilization rate of resources.

[0040] 2. This invention employs medium-low temperature reaction conditions. The rare earth catalytic self-activation process achieves self-catalysis through its own valence state cycle, eliminating the need for additional high-temperature drive and reducing energy consumption. The chelate structure formed by rare earth elements during self-activation synergistically works with the subsequent selective adsorption of nano carbon black to promote the directional retention of rare earth elements and improve the recovery efficiency of rare earth resources.

[0041] 3. This invention uses citric acid coordination coating instead of strong acid leaching, and achieves rare earth activation through a mild coordination reaction, without generating a large amount of acidic waste liquid throughout the process; the carbonylation separation process uses CO as the reaction medium, and in conjunction with the tail gas recycling system, it achieves efficient reuse of raw materials, reduces pollutant emissions from the source, and reflects environmentally friendly characteristics. Attached Figure Description

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

[0043] Figure 1 A process flow diagram of a method for treating rare earth iron slag by carbonylation to produce carbonyl iron powder and rare earth enrichment.

[0044] Figure 2 EPR characterization diagrams of rare earth iron slag fine powder before and after activation in Example 3 of the present invention;

[0045] Figure 3 The XRD characterization diagram of carbonyl iron obtained in Example 3 of this invention;

[0046] Figure 4 This is a carbonyl iron XRD standard card. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0048] Example 1: This example provides a method for processing rare earth iron slag using carbonylation to produce carbonyl iron powder and rare earth enrichment, including the following steps:

[0049] S1. Preprocessing;

[0050] Hydraulic classification: Rare earth iron slag is prepared into a 22wt% slurry and added to a hydrocyclone. The feed pressure is controlled at 0.25MPa to separate the rare earth iron slag fine powder ≤50μm (accounting for about 90%). The remaining coarse particles (accounting for about 10%) appear in the underflow and are recovered after drying.

[0051] S2. Drying;

[0052] Rare earth iron slag fine powder was fed into a circulating fluidized bed, and the bed temperature was controlled at 150℃, the air velocity at 1.2m / s, and the drying time at 40min, so that the moisture content was reduced to ≤1%.

[0053] S3. Rare earth catalytic self-activation;

[0054] Coordination coating: A 10wt% citric acid solution (70℃) was uniformly sprayed onto the surface of dry rare earth iron slag powder through an atomizing nozzle at a spray rate of 1.0 L / kg of rare earth iron slag powder. After spraying, the pH was 4.5. At this point, citric acid (C6H8O7) and cerium (Ce) were co-located. 3+ Forming stable chelates;

[0055] Reaction formula: 2Ce 3+ +3C6H8O7→Ce2(C6H6O7)3+6 H + ;

[0056] Low-temperature oxidation activation: Transfer to a rotary kiln, introduce oxygen-containing gas (O2 content 48%), heat to 180℃ at 15℃ / min, maintain the temperature for 40min, and trigger cerium (Ce) oxidation activation. 3+ Valence transition reactions;

[0057] Reaction formula: 4Ce 3+ +O2→4Ce 4+ +2O 2- ;

[0058] Dynamic reduction and reconstruction: The oxygen-containing hot air is switched to a N2 / CO mixture (CO accounts for 80%) and kept at 180℃ for 15 min. CO reacts with high-valence cerium to release oxygen vacancies (establishing an electron transfer channel and promoting the increase of Fe(CO)5 formation rate).

[0059] Reaction formula: 2Ce 4+ +CO→2Ce 3+ +CO2+V O ;

[0060] After activation, the rare earth iron slag fine powder is rapidly cooled to 60°C within 10 seconds by a water-cooling jacket, locking the metastable oxygen vacancy structure.

[0061] S4. Fluidized bed reduction;

[0062] Charging: The rare earth iron slag fine powder is pneumatically fed into the circulating fluidized bed reactor (with built-in α-Al2O3 inert bed material) and the filling is stopped at 1 / 2 of the reactor volume (50% of the effective volume of the reactor). High-purity nitrogen (explosion-proof and anti-oxidation) is introduced to replace the air.

[0063] Preheating and atmosphere switching: Increase the temperature to 260℃ at a rate of 10℃ / min, switch N2 to CO / N2 mixture (CO concentration gradient increases to 100%), and gradually establish a pure CO atmosphere;

[0064] Low-temperature pre-reduction: The temperature is increased to 520℃ at a rate of 10℃ / min and held for 25min. A nano-carbon film is generated on the surface of rare earth iron slag fine powder by utilizing the CO disproportionation reaction (2CO→C+CO2) to inhibit subsequent high-temperature bonding.

[0065] High-temperature deep reduction: The temperature is increased to 950℃ at 15℃ / min and the reaction is kept at a constant temperature for 90min to reduce the iron in the rare earth iron slag fine powder to elemental form.

[0066] S5. Selective separation of iron via carbonylation;

[0067] Rare earth iron slag fine powder was added to a high-pressure reactor, and 0.3wt% nano carbon black with a particle size of 50nm was added simultaneously as a heterogeneous nucleation site for Fe(CO)5. After replacing the air with CO, the temperature was raised to 180℃ and the pressure was increased to 20MPa. The reaction was carried out at a constant temperature for 3h, and liquid Fe(CO)5 was discharged from the bottom of the reactor and condensed by 5℃ cooling water. The remainder was rare earth enriched material.

[0068] Reaction formula: Fe + 5CO → Fe(CO)5;

[0069] Liquid Fe(CO)5 undergoes thermal decomposition at 280℃ to generate carbonyl iron powder and CO gas (the generated CO gas can be used in Fe(CO)5 synthesis and other steps). At the same time, a mixture of N2 / CO / NH3 gas (20% CO and 5% NH3) is introduced to reduce the risk of Fe oxidation and inhibit CO disproportionation reaction.

[0070] S6. Exhaust gas recirculation;

[0071] Unreacted CO is adsorbed by 13X molecular sieve (1.5MPa) to remove CO2 → dehydrated by 3A molecular sieve (dew point ≤ -70℃) → returned to the synthesis reactor to achieve recycling.

[0072] Example 2: This example provides a method for processing rare earth iron slag using carbonylation to produce carbonyl iron powder and rare earth enrichment, including the following steps:

[0073] S1. Preprocessing;

[0074] Hydraulic classification: Rare earth iron slag is prepared into a 15wt% slurry and added to a hydrocyclone. The feed pressure is controlled at 0.15MPa to separate the rare earth iron slag fine powder ≤50μm (accounting for about 90%). The remaining coarse particles (accounting for about 10%) appear in the underflow and are recovered after drying.

[0075] S2. Drying;

[0076] Rare earth iron slag fine powder was fed into a circulating fluidized bed, and the bed temperature was controlled at 120℃, the air velocity at 0.8m / s, and the drying time at 20min, so that the moisture content was reduced to ≤1%.

[0077] S3. Rare earth catalytic self-activation;

[0078] Coordination coating: A 5 wt% citric acid solution (temperature 60℃) was uniformly sprayed onto the surface of dry rare earth iron slag fine powder through an atomizing nozzle. The spraying volume was 0.5 L / kg of rare earth iron slag fine powder. After spraying, the pH was 3.5. At this point, citric acid (C6H8O7) and cerium (Ce) were co-located. 3+ Forming stable chelates;

[0079] Reaction formula: 2Ce 3+ +3C6H8O7→Ce2(C6H6O7)3+6 H + ;

[0080] Low-temperature oxidation activation: Transfer to a rotary kiln, introduce oxygen-containing gas (O2 content 45%), heat to 150℃ at 10℃ / min, maintain the temperature for 20min, and trigger cerium (Ce) oxidation activation. 3+ Valence transition reactions;

[0081] Reaction formula: 4Ce 3+ +O2→4Ce 4++2O 2- ;

[0082] Dynamic reduction and reconstruction: The oxygen-containing hot air is switched to a N2 / CO mixture (CO accounts for 60%) and kept at 150℃ for 10 min. CO reacts with high-valence cerium to release oxygen vacancies (establishing an electron transfer channel and promoting the increase of Fe(CO)5 formation rate).

[0083] Reaction formula: 2Ce 4+ +CO→2Ce 3+ +CO2+V O ;

[0084] After activation, the rare earth iron slag fine powder is rapidly cooled to 50°C within 8 seconds by a water-cooling jacket, locking the metastable oxygen vacancy structure.

[0085] S4. Fluidized bed reduction;

[0086] Charging: The rare earth iron slag fine powder is pneumatically fed into the circulating fluidized bed reactor (with built-in α-Al2O3 inert bed material) until it reaches 1 / 2 of the reactor volume, and then high-purity nitrogen (explosion-proof and anti-oxidation) is introduced to replace the air.

[0087] Preheating and atmosphere switching: Increase the temperature to 220℃ at a rate of 5℃ / min, switch N2 to CO / N2 mixture (CO concentration gradient increases to 100%), and gradually establish a pure CO atmosphere;

[0088] Low-temperature pre-reduction: The temperature is increased to 480℃ at a rate of 5℃ / min and held for 15min. A nano-carbon film is generated on the surface of rare earth iron slag fine powder by utilizing the CO disproportionation reaction (2CO→C+CO2) to inhibit subsequent high-temperature bonding.

[0089] High-temperature deep reduction: The temperature is increased to 750℃ at 10℃ / min and the reaction is kept at a constant temperature for 30min to reduce the iron in the rare earth iron slag fine powder to elemental form.

[0090] S5. Selective separation of iron via carbonylation;

[0091] Rare earth iron slag fine powder was added to a high-pressure reactor, and 0.1 wt% nano carbon black with a particle size of 20 nm was added simultaneously as a heterogeneous nucleation site for Fe(CO)5. After replacing the air with CO, the temperature was raised to 160℃ and the pressure was increased to 16 MPa. The reaction was carried out at a constant temperature for 2 hours, and liquid Fe(CO)5 was discharged from the bottom of the reactor and condensed by 2℃ cooling water. The remainder was rare earth enriched material.

[0092] Reaction formula: Fe + 5CO → Fe(CO)5;

[0093] Liquid Fe(CO)5 undergoes thermal decomposition at 200℃ to generate carbonyl iron powder and CO gas. Simultaneously, a mixture of N2 / CO / NH3 gas (10% CO and 3% NH3) is introduced to reduce the risk of Fe oxidation and inhibit CO disproportionation.

[0094] S6. Exhaust gas recirculation;

[0095] Unreacted CO is adsorbed by 13X molecular sieve (1.5MPa) to remove CO2 → dehydrated by 3A molecular sieve (dew point ≤ -70℃) → returned to the synthesis reactor to achieve recycling.

[0096] Example 3: This example provides a method for treating rare earth iron slag using carbonylation to produce carbonyl iron powder and rare earth enrichment, including the following steps:

[0097] S1. Preprocessing;

[0098] Hydraulic classification: Rare earth iron slag is prepared into a 20wt% slurry and added to a hydrocyclone. The feed pressure is controlled at 0.22MPa to separate the rare earth iron slag fine powder ≤50μm (accounting for about 90%). The remaining coarse particles (accounting for about 10%) appear in the underflow and are recovered after drying.

[0099] S2. Drying;

[0100] Rare earth iron slag fine powder was fed into a circulating fluidized bed, and the bed temperature was controlled at 130℃, the air velocity at 1.1m / s, and the drying time at 35min, so that the moisture content was reduced to ≤1%.

[0101] S3. Rare earth catalytic self-activation;

[0102] Coordination coating: An 8 wt% citric acid solution (temperature 64℃) was uniformly sprayed onto the surface of dry rare earth iron slag powder through an atomizing nozzle at a spray rate of 0.8 L / kg of rare earth iron slag powder. After spraying, the pH was 4.2. At this point, citric acid (C6H8O7) and cerium (Ce) were present. 3+ Forming stable chelates;

[0103] Reaction formula: 2Ce 3+ +3C6H8O7→Ce2(C6H6O7)3+6 H + ;

[0104] Low-temperature oxidation activation: Transfer to a rotary kiln, introduce oxygen-containing gas (O2 content 46%), heat to 170℃ at 12℃ / min, maintain the temperature for 32min, and trigger cerium (Ce) oxidation activation. 3+ Valence transition reactions;

[0105] Reaction formula: 4Ce 3+ +O2→4Ce 4+ +2O 2- ;

[0106] Dynamic reduction and reconstruction: The oxygen-containing hot air was switched to a N2 / CO mixture (CO content 72%) and kept at 160℃ for 14 min. CO reacted with high-valence cerium to release oxygen vacancies (establishing an electron transfer channel and promoting the increase of Fe(CO)5 formation rate).

[0107] Reaction formula: 2Ce 4+ +CO→2Ce 3+ +CO2+V O ;

[0108] After activation, the rare earth iron slag fine powder is rapidly cooled to 58°C within 8 seconds by a water-cooling jacket, locking the metastable oxygen vacancy structure.

[0109] S4. Fluidized bed reduction;

[0110] Charging: The rare earth iron slag fine powder is pneumatically fed into the circulating fluidized bed reactor (with built-in α-Al2O3 inert bed material) until it reaches 1 / 2 of the reactor volume, and then high-purity nitrogen (explosion-proof and anti-oxidation) is introduced to replace the air.

[0111] Preheating and atmosphere switching: Increase the temperature to 232℃ at a rate of 6℃ / min, switch N2 to CO / N2 mixture (CO concentration gradient increases to 100%), and gradually establish a pure CO atmosphere;

[0112] Low-temperature pre-reduction: The temperature is increased to 510℃ at a rate of 6℃ / min and held for 22min. A nano carbon film is generated on the surface of rare earth iron slag fine powder by CO disproportionation reaction (2CO→C+CO2) to inhibit subsequent high-temperature bonding.

[0113] High-temperature deep reduction: The temperature is increased to 820℃ at 12℃ / min and the reaction is kept at a constant temperature for 50min to reduce the iron in the rare earth iron slag fine powder to elemental form.

[0114] S5. Selective separation of iron via carbonylation;

[0115] Rare earth iron slag fine powder was added to a high-pressure reactor, and 0.2wt% nano carbon black with a particle size of 40nm was added simultaneously as a heterogeneous nucleation site for Fe(CO)5. After replacing the air with CO, the temperature was raised to 166℃ and the pressure was increased to 19MPa. The reaction was carried out at a constant temperature for 3h, and liquid Fe(CO)5 was discharged from the bottom of the reactor and condensed by 4℃ cooling water. The remainder was rare earth enriched material.

[0116] Reaction formula: Fe + 5CO → Fe(CO)5;

[0117] Liquid Fe(CO)5 undergoes thermal decomposition at 220℃ to generate carbonyl iron powder and CO gas. Simultaneously, a mixture of N2 / CO / NH3 gas (16% CO and 5% NH3) is introduced to reduce the risk of Fe oxidation and inhibit CO disproportionation.

[0118] S6. Exhaust gas recirculation;

[0119] Unreacted CO is adsorbed by 13X molecular sieve (1.5MPa) to remove CO2 → dehydrated by 3A molecular sieve (dew point ≤ -70℃) → returned to the synthesis reactor to achieve recycling.

[0120] Comparative Example 1: The difference between this comparative example and Example 3 is that the rare earth iron slag fine powder was not subjected to rare earth catalytic self-activation.

[0121] Comparative Example 2: The difference between this comparative example and Example 3 is that no nano carbon black was added in S5.

[0122] Comparative Example 3: The difference between this comparative example and Example 3 is that neither rare earth catalytic self-activation of rare earth iron slag powder was performed, nor was nano carbon black added in S5.

[0123] Test instructions:

[0124] Figure 2 The electron paramagnetic resonance (EPR) spectra of rare earth iron slag fine powder before and after activation were obtained under the following test conditions:

[0125] The instrument model was a Bruker EMXplus electron paramagnetic resonance spectrometer. The test temperature was 25℃ (room temperature), the microwave frequency was 9.8GHz (X-band), the microwave power was 10mW, the modulation frequency was 100kHz, the modulation amplitude was 0.5mT, the scanning range was 1.8-2.3 (g value), the scanning time was 40s, and the total number of scans was 3.

[0126] Figure 3 The X-ray diffraction (XRD) pattern of the carbonyl iron powder prepared in Example 3 of this invention is shown below. The test conditions were as follows:

[0127] The instrument model is Bruker D8 Advance X-ray diffractometer, the target material is CuKα (λ=1.5406Å), the tube voltage is 40kV, the tube current is 40mA, the scanning range is 2θ=20-90°, the step size is 0.02°, the scanning speed is 2° / min, the divergence slit is 0.6mm, and the receiving slit is 0.1mm.

[0128] It should be noted that, Figure 4 XRD standard card for carbonyl iron powder, used in conjunction with Figure 3 By comparing the experimental spectra, it was confirmed that the product phase was pure carbonyl iron powder.

[0129] Experimental Example: 1. Product Characterization (taking Example 3 as an example);

[0130] (1) The rare earth iron slag fine powder in S3 before and after activation was characterized by EPR, and the results are as follows: Figure 2 As shown;

[0131] Depend on Figure 2 It can be seen that the oxygen vacancy signal is usually located between g≈2.00-2.03. Comparing the EPR signals of the samples before and after S3 treatment, the signal intensity is significantly enhanced after activation, indicating that the oxygen vacancy concentration increases.

[0132] (2) The carbonyl iron powder prepared in S5 was characterized by XRD, and the results are as follows: Figure 3 As shown;

[0133] Comparison of carbonyl iron XRD standard cards ( Figure 4 The diffraction peaks at 2θ = 44.7° (110), 65.0° (200), and 82.3° (211) in the spectrum match the standard card perfectly, indicating that the main phase is α-Fe (body-centered cubic structure).

[0134] Verification of no impurity peaks: The spectrum did not show diffraction peaks of impurity phases such as Fe3O4 (2θ≈30.1°, 35.5°), Fe2O3 (2θ≈33.1°, 57.0°), CeO2 (2θ≈28.5°), indicating that the carbonyl iron powder has high purity (very few rare earth residues or oxidation products).

[0135] 2. Determine the iron yield;

[0136] According to GB / T 26416.4-2022 "Chemical Analysis Methods for Rare Earth Ferroalloys Part 4: Determination of Iron Content by Potassium Dichromate Titration", the iron content in the rare earth iron slag fine powder was determined to be 56.49%.

[0137] Accurately weigh the mass M of carbonyl iron powder obtained from 100g of rare earth iron slag fine powder after activation, reduction and separation, and calculate the iron ratio P;

[0138] .

[0139] 3. Determine the rare earth element enrichment rate (REO%).

[0140] Rare earth iron slag fine powder (m) 样品 ) and rare earth enriched materials (m 样品 Dissolved in nitric acid-hydrofluoric acid, a masking agent triethanolamine-EGTA mixed solution (triethanolamine: 50 g / L; EGTA: 0.05 mol / L) was added. The masking agent reacted with Ca... 2+ 、Sr 2+ It forms stable complexes, thereby correcting interfering elements such as calcium and strontium;

[0141] Adjust the pH to 1.8 with ammonia, then add saturated oxalic acid to precipitate rare earth elements (stop adding oxalic acid when no more precipitate forms); filter the precipitate, ashing it and then calcining it in a muffle furnace at 850℃ to constant weight, and weigh the total mass (m) of rare earth oxides (REO). REOThe initial rare earth oxide content (0.39%) in the rare earth iron slag fine powder and the rare earth element enrichment rate in the rare earth enrichment material were measured.

[0142] .

[0143] The results are shown in the table below:

[0144]

[0145] As shown in the table above, rare earth catalytic self-activation treatment of rare earth iron slag fine powder can effectively improve the iron yield; adding nano carbon black during Fe(CO)5 pyrolysis can significantly improve the rare earth element enrichment rate; the combination of the above two processes has a synergistic effect on improving the iron yield.

[0146] The principle is as follows: Citric acid and Ce 3+ The formation of chelates achieves uniform dispersion of rare earth elements, avoiding the loss of active sites caused by their aggregation; low-temperature oxidation activation enables Ce... 3+ Oxidized to Ce 4+ The price state jump is completed; in the dynamic restoration and reconstruction, Ce 4+ Reduced to Ce by CO 3+ With the generation of oxygen vacancies, these oxygen vacancies act as electron transfer channels, accelerating electron transfer between Fe and CO and promoting the synthesis reaction of Fe(CO)5. The rapid cooling process locks the metastable oxygen vacancies by rapidly cooling down, preventing them from annihilating at high temperatures and maintaining high catalytic activity, thereby accelerating the rate of iron conversion to Fe(CO)5 and increasing the iron yield.

[0147] The addition of nano-carbon black during the pyrolysis of Fe(CO)5 enhances the rare earth enrichment rate due to its role as a heterogeneous nucleation site. The small particle size and large specific surface area of ​​nano-carbon black provide numerous low-energy nucleation centers for the thermal decomposition of Fe(CO)5, causing Fe to preferentially precipitate on the carbon black surface to form carbonyl iron powder, reducing Fe residue on the rare earth particle surface. Simultaneously, the presence of nano-carbon black lowers the interfacial bonding energy between the Fe(CO)5 decomposition products and the rare earth phase, preventing secondary bonding between iron and rare earth elements, making it easier for rare earth components to separate from iron, thereby increasing the relative content of rare earth elements in the enriched material.

[0148] Rare earth catalytic self-activation accelerates the formation rate of Fe(CO)5 through oxygen vacancies, providing sufficient reactants for subsequent separation. Meanwhile, nano-carbon black, acting as heterogeneous nucleation sites, accelerates the decomposition of Fe(CO)5 and the precipitation rate of iron, preventing the accumulation of Fe(CO)5 in the system. According to Le Chatelier's principle, the rapid removal of products further promotes the forward reaction of Fe(CO)5 formation, improving iron conversion efficiency. Furthermore, the nano-carbon film formed during self-activation synergistically works with nano-carbon black to inhibit particle adhesion, maintain system dispersibility, and ensure that the catalytic activity of oxygen vacancies and the separation efficiency of nucleation sites are both optimal, ultimately achieving a synergistic improvement in iron yield.

[0149] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for treating rare earth iron slag using carbonylation to produce carbonyl iron powder and rare earth enrichment, characterized in that, Includes the following steps: S1. Preprocessing; Fine rare earth iron slag powder with a particle size of ≤50μm was separated from rare earth iron slag. S2. Drying; The rare earth iron slag powder was dried until the moisture content was reduced to ≤1%; S3. Rare earth catalytic self-activation; Spray citric acid solution onto the surface of dry rare earth iron slag fine powder; The mixture is transferred to a rotary kiln, oxygen-containing gas is introduced, the temperature is raised and held, triggering the valence state transition reaction of cerium. The oxygen-containing hot air is switched to an N2 / CO mixture and kept at a constant temperature. CO reacts with high-valence cerium to release oxygen vacancies. After activation, the rare earth iron slag fine powder is rapidly cooled to lock the metastable oxygen vacancy structure. S4. Fluidized bed reduction; The rare earth iron slag fine powder is fed into a circulating fluidized bed reactor, and nitrogen is introduced to replace the air. Gradient heating reduces the iron in rare earth iron slag powder to elemental form. S5. Selective separation of iron via carbonylation; Nano carbon black was added to rare earth iron slag powder, and the reaction was carried out under CO atmosphere with increased temperature and pressure to obtain liquid Fe(CO)5, the remainder being rare earth enrichment material. Liquid Fe(CO)5 pyrolyzes to produce carbonyl iron powder and CO gas.

2. The method for producing carbonyl iron powder and rare earth enrichment by carbonylation of rare earth iron slag according to claim 1, characterized in that, S1 specifically involves preparing a slurry of rare earth iron slag at 15-22 wt%, adding it to a hydrocyclone, controlling the feed pressure at 0.15-0.25 MPa, and separating out fine rare earth iron slag powder of ≤50 μm.

3. The method for producing carbonyl iron powder and rare earth enrichment by carbonylation of rare earth iron slag according to claim 1, characterized in that, S2 specifically involves feeding rare earth iron slag fine powder into a circulating fluidized bed, controlling the bed temperature at 120-150℃, the gas velocity at 0.8-1.2m / s, and the drying time at 20-40min, so that the moisture content is reduced to ≤1%.

4. The method for producing carbonyl iron powder and rare earth enrichment by carbonylation of rare earth iron slag according to claim 1, characterized in that, S3 specifically involves uniformly spraying a 5-10 wt% citric acid solution onto the surface of dry rare earth iron slag fine powder through an atomizing nozzle. The spraying amount is 0.5-1.0 L / kg of rare earth iron slag fine powder, and the pH after spraying is 3.5-4.

5. The mixture is transferred to a rotary kiln, oxygen-containing gas is introduced, and the temperature is increased to 150-180℃ at a rate of 10-15℃ / min. The temperature is then maintained for 20-40 min to trigger the valence state transition reaction of cerium. Switch the oxygen-containing hot air to a N2 / CO mixture and maintain it at 150-180℃ for 10-15 minutes. CO reacts with high-valence cerium to release oxygen vacancies. After activation, the rare earth iron slag fine powder is rapidly cooled to lock the metastable oxygen vacancy structure.

5. The method for producing carbonyl iron powder and rare earth enrichment by carbonylation of rare earth iron slag according to claim 1, characterized in that, The activated rare earth iron slag powder is rapidly cooled to 50-60℃ within 8-10 seconds by a water-cooling jacket.

6. The method for producing carbonyl iron powder and rare earth enrichment by carbonylation of rare earth iron slag according to claim 1, characterized in that, S4 specifically involves: feeding rare earth iron slag fine powder into a circulating fluidized bed reactor via pneumatic input, and then replacing the air with high-purity nitrogen. Heat to 220-260℃ at a rate of 5-10℃ / min, and replace N2 with CO; Heat to 480-520℃ at a rate of 5-10℃ / min, and hold for 15-25min; The iron in the rare earth iron slag fine powder is reduced to elemental form by heating to 750-950℃ at a rate of 10-15℃ / min and reacting at a constant temperature for 30-90min.

7. The method for producing carbonyl iron powder and rare earth enrichment by carbonylation of rare earth iron slag according to claim 1, characterized in that, S5 specifically involves adding fine rare earth iron slag powder to a high-pressure reactor, simultaneously adding 0.1-0.3wt% nano carbon black with a particle size of 20-50nm as heterogeneous nucleation sites for Fe(CO)5; after replacing the air with CO, the temperature is raised to 160-180℃, the pressure is increased to 16-20MPa, and the reaction is carried out at a constant temperature for 2-3 hours to obtain liquid Fe(CO)5 which is discharged from the bottom of the reactor and condensed by cooling water at 2-5℃; the remainder is rare earth enriched material. Liquid Fe(CO)5 undergoes thermal decomposition at 200-280℃ in a mixed N2 / CO / NH3 atmosphere to produce carbonyl iron powder and CO gas.

8. The method for producing carbonyl iron powder and rare earth enrichment by carbonylation of rare earth iron slag according to claim 7, characterized in that, In the N2 / CO / NH3 mixture, CO accounts for 10-20% and NH3 accounts for 3-5%.

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