Method for producing carbonyl iron powder and rare earth enriched material by processing rare earth iron slag through carbonylation method

Abstract

The invention discloses a method for producing carbonyl iron powder and a rare earth enriched material by treating rare earth iron slag through a carbonylation method, and belongs to the technical field of metal waste recovery. Comprising the steps of pretreatment, drying, rare earth catalytic self-activation, fluidization reduction and carbonyl method selective iron separation. A metastable-state oxygen vacancy structure is constructed by means of rare earth catalytic self-activation, an efficient electron transfer channel is provided for deep reduction and carbonylation separation of iron, molecular-level dissociation of iron and rare earth is achieved in cooperation with a selective reaction of a carbonyl method, iron is converted into high-value carbonyl iron powder, meanwhile, the enrichment degree of rare earth elements is greatly increased, and the preparation method is suitable for industrial production. Original industrial solid waste is converted into a product with economic value and application potential, and the comprehensive utilization rate of resources is remarkably increased.

Description

Technical Field

[0001] The present invention relates to the technical field of recycling metal waste, in particular to a method for producing carbonyl iron powder and rare earth enriched material by treating rare earth iron slag with a carbonylation method. Background Art

[0002] Rare earth iron slag is the primary solid waste generated after rare earth extraction from NdFeB permanent magnet materials using acid leaching. Its iron content typically exceeds 50%, its rare earth oxide (REO) content ≥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 conservative estimates suggest the byproduct, rare earth iron slag, exceeds 100,000 tons per year. If not efficiently utilized, this waste of strategic metals like iron and rare earths will also pose environmental risks due to long-term storage. Residual radioactive thorium in the slag can migrate into soil and water, and fluoride leaching can easily contaminate groundwater.

[0003] At present, the treatment processes for rare earth iron slag are mainly divided into the following three categories: Although physical separation (magnetic separation / gravity separation) is simple to operate, it is difficult to completely separate iron and rare earth elements due to their complex occurrence (such as encapsulation in micron-sized grains), resulting in insufficient rare earth enrichment. The pyrometallurgical process (high-temperature reduction smelting) needs to operate at temperatures above 1400°C, with energy consumption reaching 800-1000 kWh per ton of slag. Furthermore, at high temperatures, rare earth elements tend to disperse in the slag phase to form silicates, resulting in low recovery rates and poor economic efficiency. Although the hydrometallurgical process (acid leaching for iron extraction) can increase the enrichment of rare earth elements, it consumes about 0.8-1.2 tons of hydrochloric acid per ton of slag, generating a large amount of acidic wastewater containing heavy metals (such as cobalt and manganese).

[0004] In response to the above challenges, it is urgent to develop a rare earth iron slag collaborative processing process that takes into account both efficient resource conversion and environmental friendliness. Summary of the Invention

[0005] In view of the above-mentioned shortcomings of the prior art, the present invention provides a method for treating rare earth iron slag by carbonylation to produce carbonyl iron powder and rare earth enriched aggregate, comprising the following steps: S1. Pretreatment; Separate rare earth iron slag fine powder ≤50μm from rare earth iron slag; S2. Drying; Dry the rare earth iron slag powder until the moisture content is reduced to ≤1%; S3. Rare earth catalytic self-activation; Spraying the citric acid solution onto the surface of the dry rare earth iron slag fine powder; Transfer to a rotary kiln, introduce oxygen-containing gas, increase the temperature and keep it warm, triggering the valence transition reaction of cerium; Switch the oxygen-containing hot air to a N2 / CO mixture and keep it warm. CO reacts with high-valent cerium to release oxygen vacancies. After activation, the rare earth iron slag fine powder is quenched to lock the metastable oxygen vacancy structure; S4. Fluidized reduction; The rare earth iron slag fine powder is fed into a circulating fluidized bed reactor and nitrogen is introduced to replace the air; The temperature is increased gradually to reduce the iron in the rare earth iron slag fine powder to a single substance; S5. Selective separation of iron by carbonyl method; Add nano-carbon black to rare earth iron slag fine powder, and react at elevated temperature and pressure in a CO atmosphere to obtain liquid Fe(CO)5, with the remainder being rare earth enriched material; Liquid Fe(CO)5 is pyrolyzed to generate carbonyl iron powder and CO gas.

[0006] Furthermore, S1 is specifically as follows: preparing the rare earth iron slag into a 15-22wt% slurry, adding the slurry into a hydrocyclone, controlling the feed pressure to be 0.15-0.25MPa, and separating the rare earth iron slag fine powder ≤50μm.

[0007] Furthermore, S2 is specifically as follows: feeding rare earth iron slag fine powder into a circulating fluidized bed, controlling the bed temperature at 120-150°C, the gas velocity at 0.8-1.2 m / s, and the drying time at 20-40 min, so as to reduce the moisture content to ≤1%.

[0008] Furthermore, S3 is specifically as follows: 5-10wt% citric acid solution (temperature 60-70°C) is evenly sprayed onto the surface of the dry rare earth iron slag fine powder through an atomizing nozzle, with a spraying amount of 0.5-1.0L / kg rare earth iron slag fine powder, and the pH after spraying is 3.5-4.5, at which time citric acid forms a stable chelate with cerium; Transfer to a rotary kiln, introduce oxygen-containing gas (O2 content 45-48%), raise the temperature to 150-180°C at a rate of 10-15°C / min, and maintain the temperature for 20-40 minutes to trigger the valence transition reaction of cerium; Switch the oxygen-containing hot air to a N2 / CO mixture (CO accounts for 60-80%) and maintain it at 150-180°C for 10-15 minutes. CO reacts with high-valent cerium to release oxygen vacancies. After activation, the rare earth iron slag fine powder is quenched to lock the metastable oxygen vacancy structure.

[0009] Furthermore, the activated rare earth iron slag fine powder is rapidly cooled to 50-60° C. within 8-10 seconds through a water cooling jacket.

[0010] Furthermore, S4 specifically comprises: pneumatically feeding rare earth iron slag fine powder into a circulating fluidized bed reactor, filling the reactor to 1 / 2 of its volume, and introducing high-purity nitrogen to replace the air; Heat to 220-260°C at a rate of 5-10°C / min, and replace N2 with CO; Raise the temperature to 480-520°C at a rate of 5-10°C / min, keep warm for 15-25 minutes, and use the CO disproportionation reaction to form a nano-carbon film on the surface of the rare earth iron slag fine powder to inhibit subsequent high-temperature adhesion; The temperature is raised to 750-950°C at a rate of 10-15°C / min, and the reaction is carried out at a constant temperature for 30-90 minutes to reduce the iron in the rare earth iron slag fine powder to a single substance.

[0011] Furthermore, S5 is specifically as follows: rare earth iron slag fine powder is added to the autoclave, and 0.1-0.3wt% nano carbon black with a particle size of 20-50nm is simultaneously added as the heterogeneous nucleation site of Fe(CO)5; after CO replaces the air, 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 2-3h to obtain liquid Fe(CO)5, which is discharged from the bottom of the autoclave and condensed with 2-5℃ condensed water; the remainder is the rare earth enriched material; Liquid Fe(CO)5 generates carbonyl iron powder and CO gas through thermal decomposition reaction in N2 / CO / NH3 mixed gas atmosphere at 200-280℃.

[0012] Furthermore, in the N2 / CO / NH3 mixed gas, CO accounts for 10-20% and NH3 accounts for 3-5%.

[0013] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention treats rare earth iron slag and achieves efficient resource utilization and harmless treatment of solid waste through innovative processes. By utilizing rare earth catalytic self-activation to construct a metastable oxygen vacancy structure, it provides 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. This significantly increases the enrichment of rare earth elements, transforming the original industrial solid waste into products with both economic value and application potential, significantly improving the comprehensive utilization rate of resources.

[0014] 2. The present invention adopts medium-low temperature reaction conditions. The rare earth catalytic self-activation process achieves self-catalysis through its own valence state cycle, without the need for additional high-temperature drive, thus reducing energy consumption; the chelate structure formed by the rare earth elements during self-activation and the subsequent selective adsorption of nano-carbon black synergistically promote the directional retention of rare earths and improve the recovery efficiency of rare earth resources.

[0015] 3. The present invention uses citric acid coordination coating instead of strong acid leaching, and realizes 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 cooperates with the tail gas circulation system to achieve efficient reuse of raw materials, reduce pollutant emissions at the source, and embody environmentally friendly characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort.

[0017] Figure 1 A process flow chart of a method for producing carbonyl iron powder and rare earth enriched aggregate by treating rare earth iron slag by carbonylation; Figure 2 The EPR characterization diagram of rare earth iron slag fine powder before and after activation in Example 3 of the present invention; Figure 3 This is the XRD characterization diagram of carbonyl iron prepared in Example 3 of the present invention; Figure 4 This is the carbonyl iron XRD standard card. DETAILED DESCRIPTION

[0018] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0019] Example 1: This example provides a method for producing carbonyl iron powder and rare earth enriched aggregate by treating rare earth iron slag by carbonylation, comprising the following steps: S1. Pretreatment; Hydraulic classification: The rare earth iron slag is prepared into a 22wt% slurry and fed into a hydrocyclone. The feed pressure is controlled at 0.25MPa to separate the rare earth iron slag fine powder (about 90%) with a size of ≤50μm. The remaining coarse particles (about 10%) appear in the underflow and are recovered after drying. S2. Drying; The rare earth iron slag powder was put into a circulating fluidized bed, and the bed temperature was controlled at 150°C, the air velocity was 1.2m / s, and the drying time was 40min to reduce the moisture content to ≤1%. S3. Rare earth catalytic self-activation; Coordination coating: 10wt% citric acid solution (temperature 70℃) is evenly sprayed onto the surface of dry rare earth iron slag fine powder through an atomizing nozzle. The spraying volume is 1.0L / kg rare earth iron slag fine powder. The pH after spraying is 4.5. At this time, citric acid (C6H8O7) and cerium (Ce 3+ ) form a stable chelate; Reaction formula: 2Ce 3++3C6H8O7→Ce2(C6H6O7)3+6 H + ; Low temperature oxidation activation: transfer to rotary kiln, introduce oxygen-containing gas (O2 content 48%), heat up to 180℃ at 15℃ / min, keep constant temperature for 40min, trigger cerium (Ce 3+ ) valence transition reaction; Reaction formula: 4Ce 3+ +O2→4Ce 4+ +2O 2- ; Dynamic reduction and reconstruction: The oxygen-containing hot air is switched to a N2 / CO mixture (CO accounts for 80%) and maintained at 180°C for 15 minutes. CO reacts with high-valent cerium to release oxygen vacancies (establishing electron transfer channels and promoting the increase in the Fe(CO)5 generation rate). Reaction formula: 2Ce 4+ +CO→2Ce 3+ +CO2+V O ; After activation, the rare earth iron slag fine powder was quenched to 60°C in a water-cooling jacket within 10 seconds to lock the metastable oxygen vacancy structure; S4. Fluidized reduction; Charging: Pneumatically feed rare earth iron slag fine powder into a circulating fluidized bed reactor (with built-in α-Al2O3 inert bed material), and stop filling until the reactor volume reaches 1 / 2 (50% of the reactor's effective volume). Then introduce high-purity nitrogen (explosion-proof and oxidation-proof) to replace the air. Preheating and atmosphere switching: Raise the temperature to 260°C at a rate of 10°C / min, switch from N2 to a CO / N2 mixed gas (CO concentration gradient increases to 100%), and gradually establish a pure CO atmosphere; Low-temperature pre-reduction: Raise the temperature to 520°C at a rate of 10°C / min and keep warm for 25 minutes. Use the CO disproportionation reaction (2CO→C+CO2) to form a nano-carbon film on the surface of the rare earth iron slag fine powder to inhibit subsequent high-temperature bonding. High-temperature deep reduction: heating at 15°C / min to 950°C, and maintaining constant temperature for 90 minutes to reduce the iron in the rare earth iron slag powder to its elemental form; S5. Selective separation of iron by carbonyl method; Fine powder of rare earth iron slag was added to an autoclave, and 0.3 wt% nano-carbon black with a particle size of 50 nm was added simultaneously as heterogeneous nucleation sites for Fe(CO)5. After the air was replaced by CO, the temperature was raised to 180°C, the pressure was increased to 20 MPa, and the reaction was carried out at a constant temperature for 3 hours. Liquid Fe(CO)5 was discharged from the bottom of the autoclave and condensed with 5°C condensed water. The remainder was a rare earth enriched material. Reaction formula: Fe+5CO→Fe(CO)5; Liquid Fe(CO)5 undergoes thermal decomposition at 280°C to generate carbonyl iron powder and CO gas (the generated CO gas can be used in the synthesis of Fe(CO)5 and other steps). At the same time, a N2 / CO / NH3 mixed gas (CO accounts for 20%, NH3 accounts for 5%) is introduced to reduce the risk of Fe oxidation and inhibit the CO disproportionation reaction. S6. Exhaust gas recirculation; The unreacted CO is adsorbed on 13X molecular sieve (1.5MPa) to remove CO2 → dehydrated on 3A molecular sieve (dew point ≤-70℃) → returned to the synthesis kettle to complete the cycle.

[0020] Example 2: This example provides a method for producing carbonyl iron powder and rare earth enriched aggregate by treating rare earth iron slag by carbonylation, comprising the following steps: S1. Pretreatment; Hydraulic classification: The rare earth iron slag is prepared into a 15wt% slurry and fed into a hydrocyclone. The feed pressure is controlled at 0.15MPa to separate the rare earth iron slag fine powder (about 90%) with a size of ≤50μm. The remaining coarse particles (about 10%) appear in the underflow and are recovered after drying. S2. Drying; Put rare earth iron slag powder into a circulating fluidized bed, control the bed temperature at 120℃, the air velocity at 0.8m / s, and the drying time at 20min to reduce the moisture content to ≤1%; S3. Rare earth catalytic self-activation; Coordination coating: 5wt% citric acid solution (temperature 60℃) is evenly sprayed onto the surface of dry rare earth iron slag fine powder through an atomizing nozzle. The spraying volume is 0.5L / kg rare earth iron slag fine powder. The pH after spraying is 3.5. At this time, citric acid (C6H8O7) and cerium (Ce 3+ ) form a stable chelate; Reaction formula: 2Ce 3+ +3C6H8O7→Ce2(C6H6O7)3+6 H + ; Low temperature oxidation activation: transfer to rotary kiln, introduce oxygen-containing gas (O2 content 45%), increase the temperature to 150℃ at 10℃ / min, keep constant temperature for 20min, trigger cerium (Ce 3+ ) valence transition reaction; Reaction formula: 4Ce 3+ +O2→4Ce 4+ +2O 2- ; Dynamic reduction and reconstruction: The oxygen-containing hot air is switched to a N2 / CO mixture (CO accounts for 60%) and maintained at 150°C for 10 minutes. CO reacts with high-valent cerium to release oxygen vacancies (establishing electron transfer channels and promoting the increase in the Fe(CO)5 generation rate). Reaction formula: 2Ce4+ +CO→2Ce 3+ +CO2+V O ; After activation, the rare earth iron slag fine powder was quenched to 50°C in a water-cooling jacket within 8 seconds to lock the metastable oxygen vacancy structure; S4. Fluidized reduction; Charging: Pneumatically feed rare earth iron slag fine powder into a circulating fluidized bed reactor (with built-in α-Al2O3 inert bed material), and stop filling until the reactor volume reaches 1 / 2. Then introduce high-purity nitrogen (explosion-proof and oxidation-proof) to replace the air. Preheating and atmosphere switching: Raise the temperature to 220°C at a rate of 5°C / min, switch from N2 to a CO / N2 mixed gas (CO concentration gradient increases to 100%), and gradually establish a pure CO atmosphere; Low-temperature pre-reduction: Raise the temperature to 480°C at a rate of 5°C / min and keep warm for 15 minutes. Use the CO disproportionation reaction (2CO→C+CO2) to form a nano-carbon film on the surface of the rare earth iron slag fine powder to inhibit subsequent high-temperature adhesion. High-temperature deep reduction: heating at 10°C / min to 750°C, and keeping the temperature constant for 30 minutes to reduce the iron in the rare earth iron slag fine powder to a single substance; S5. Selective separation of iron by carbonyl method; Fine powder of rare earth iron slag was added to an autoclave, and 0.1 wt% nano-carbon black with a particle size of 20 nm was added simultaneously as heterogeneous nucleation sites for Fe(CO)5. After the air was replaced by CO, the temperature was raised to 160°C, the pressure was increased to 16 MPa, and the reaction was carried out at a constant temperature for 2 hours. Liquid Fe(CO)5 was discharged from the bottom of the autoclave and condensed with 2°C condensed water. The remainder was a rare earth enriched material. Reaction formula: Fe+5CO→Fe(CO)5; Liquid Fe(CO)5 generates carbonyl iron powder and CO gas through thermal decomposition reaction at 200℃. At the same time, N2 / CO / NH3 mixed gas (CO accounts for 10%, NH3 accounts for 3%) is introduced to reduce the risk of Fe oxidation and inhibit the CO disproportionation reaction. S6. Exhaust gas recirculation; The unreacted CO is adsorbed on 13X molecular sieve (1.5MPa) to remove CO2 → dehydrated on 3A molecular sieve (dew point ≤-70℃) → returned to the synthesis kettle to complete the cycle.

[0021] Example 3: This example provides a method for producing carbonyl iron powder and rare earth enriched aggregate by treating rare earth iron slag by carbonylation, comprising the following steps: S1. Pretreatment; Hydraulic classification: The rare earth iron slag is prepared into a 20wt% slurry and fed into a hydrocyclone. The feed pressure is controlled at 0.22MPa to separate the rare earth iron slag fine powder (about 90%) with a size of ≤50μm. The remaining coarse particles (about 10%) appear in the underflow and are recovered after drying. S2. Drying; The rare earth iron slag powder was put into a circulating fluidized bed, and the bed temperature was controlled at 130°C, the air velocity was 1.1m / s, and the drying time was 35min, so that the moisture content was reduced to ≤1%; S3. Rare earth catalytic self-activation; Coordination coating: 8wt% citric acid solution (temperature 64℃) is evenly sprayed onto the surface of dry rare earth iron slag fine powder through an atomizing nozzle. The spraying volume is 0.8L / kg rare earth iron slag fine powder. The pH after spraying is 4.2. At this time, citric acid (C6H8O7) and cerium (Ce 3+ ) form a stable chelate; Reaction formula: 2Ce 3+ +3C6H8O7→Ce2(C6H6O7)3+6 H + ; Low temperature oxidation activation: transfer to rotary kiln, introduce oxygen-containing gas (O2 content 46%), heat up to 170℃ at 12℃ / min, keep constant temperature for 32min, trigger cerium (Ce 3+ ) valence transition reaction; Reaction formula: 4Ce 3+ +O2→4Ce 4+ +2O 2- ; Dynamic reduction and reconstruction: The oxygen-containing hot air was switched to a N2 / CO mixture (CO accounted for 72%) and maintained at 160°C for 14 minutes. CO reacted with high-valent cerium to release oxygen vacancies (establishing electron transfer channels and promoting the increase in the Fe(CO)5 generation rate). Reaction formula: 2Ce 4+ +CO→2Ce 3+ +CO2+V O ; After activation, the rare earth iron slag fine powder was quenched to 58°C in a water-cooling jacket within 8 seconds to lock the metastable oxygen vacancy structure; S4. Fluidized reduction; Charging: Pneumatically feed rare earth iron slag fine powder into a circulating fluidized bed reactor (with built-in α-Al2O3 inert bed material), and stop filling until the reactor volume reaches 1 / 2. Then introduce high-purity nitrogen (explosion-proof and oxidation-proof) to replace the air. Preheating and atmosphere switching: Raise the temperature to 232°C at a rate of 6°C / min, switch from N2 to a CO / N2 mixed gas (CO concentration gradient increases to 100%), and gradually establish a pure CO atmosphere; Low-temperature pre-reduction: Raise the temperature to 510°C at a rate of 6°C / min and keep warm for 22 minutes. Use the CO disproportionation reaction (2CO→C+CO2) to form a nano-carbon film on the surface of the rare earth iron slag fine powder to inhibit subsequent high-temperature adhesion. High-temperature deep reduction: heating to 820°C at a rate of 12°C / min, and maintaining the reaction temperature for 50 minutes to reduce the iron in the rare earth iron slag fine powder to its elemental form; S5. Selective separation of iron by carbonyl method; Fine powder of rare earth iron slag was added to an autoclave, and 0.2 wt% nano-carbon black with a particle size of 40 nm was added simultaneously as heterogeneous nucleation sites for Fe(CO)5. After CO replaced the air, the temperature was raised to 166°C and the pressure was increased to 19 MPa. The reaction was carried out at a constant temperature for 3 hours, and liquid Fe(CO)5 was discharged from the bottom of the autoclave and condensed with 4°C condensed water. The remainder was a rare earth enriched material. Reaction formula: Fe+5CO→Fe(CO)5; Liquid Fe(CO)5 generates carbonyl iron powder and CO gas through thermal decomposition reaction at 220℃. At the same time, N2 / CO / NH3 mixed gas (CO accounts for 16%, NH3 accounts for 5%) is introduced to reduce the risk of Fe oxidation and inhibit the CO disproportionation reaction; S6. Exhaust gas recirculation; The unreacted CO is adsorbed on 13X molecular sieve (1.5MPa) to remove CO2 → dehydrated on 3A molecular sieve (dew point ≤-70℃) → returned to the synthesis kettle to complete the cycle.

[0022] Comparative Example 1: This comparative example differs from Example 3 in that the rare earth catalytic self-activation of the rare earth iron slag fine powder is not performed.

[0023] Comparative Example 2: This comparative example differs from Example 3 in that no nano-carbon black is added to S5.

[0024] Comparative Example 3: This comparative example differs from Example 3 in that the rare earth catalytic self-activation of the rare earth iron slag fine powder is not performed, and nano-carbon black is not added to S5.

[0025] Test Description: Figure 2 The electron paramagnetic resonance (EPR) spectra of rare earth iron slag fine powder before and after activation. The test conditions are: The instrument model was Bruker EMXplus electron paramagnetic resonance spectrometer, with a test temperature of 25°C (room temperature), a microwave frequency of 9.8 GHz (X-band), a microwave power of 10 mW, a modulation frequency of 100 kHz, a modulation amplitude of 0.5 mT, a scanning range of 1.8-2.3 (g value), and a scanning time of 40 s; the cumulative number of times was 3.

[0026] Figure 3This is the X-ray diffraction (XRD) spectrum of the carbonyl iron powder prepared in Example 3 of the present invention. The test conditions are: The instrument model is Bruker D8 Advance X-ray diffractometer, target material is CuKα (λ=1.5406Å), tube voltage is 40 kV, tube current is 40 mA, scanning range 2θ=20-90°, step size is 0.02°, scanning speed is 2° / min, divergence slit is 0.6 mm, and receiving slit is 0.1 mm.

[0027] It should be noted that Figure 4 It is the XRD standard card of carbonyl iron powder, used for Figure 3 The experimental spectrum was compared to confirm that the product phase was pure carbonyl iron powder.

[0028] Experimental example: 1. Product characterization (taking Example 3 as an example); (1) EPR characterization of rare earth iron slag fine powder before and after activation in S3 was performed. The results are as follows: Figure 2 As shown; 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.

[0029] (2) The carbonyl iron powder prepared in S5 was characterized by XRD. The results are as follows: Figure 3 As shown; Comparison with carbonyl iron XRD standard card ( Figure 4 ), the diffraction peaks of 2θ=44.7°(110), 65.0°(200), and 82.3°(211) in the spectrum completely match those of the standard card, indicating that the main phase is α-Fe (body-centered cubic structure); Verification of no impurity peaks: There are no diffraction peaks of impurity phases such as Fe3O4 (2θ≈30.1°, 35.5°), Fe2O3 (2θ≈33.1°, 57.0°), and CeO2 (2θ≈28.5°) in the spectrum, indicating that the carbonyl iron powder is of high purity (very little rare earth residue or oxidation products).

[0030] 2. Determine the iron yield; The iron content of rare earth iron slag fine powder was determined to be 56.49% according to GB / T 26416.4-2022 "Chemical analysis methods of rare earth iron alloys Part 4: Determination of iron content - Potassium dichromate titration method"; Accurately weigh the mass M of carbonyl iron powder obtained by activation, reduction and separation of every 100g of rare earth iron slag fine powder, and calculate the iron content P; .

[0031] 3. Determine the rare earth element enrichment rate REO; The rare earth iron slag fine powder (m 样品 ) and rare earth enriched aggregates (m 样品 ) was dissolved in nitric acid-hydrofluoric acid, and a masking agent triethanolamine-EGTA mixed solution (triethanolamine: 50 g / L; EGTA: 0.05 mol / L) was added. 2+ 、Sr 2+ Form stable complexes to correct interfering elements such as calcium and strontium; Ammonia water was added to adjust the pH to 1.8, and saturated oxalic acid was added to precipitate the rare earth (when no more precipitate was formed, the addition of oxalic acid was stopped); the precipitate was filtered, ashed, and then burned in a muffle furnace at 850 ° C to constant weight, and the total mass of rare earth oxide (REO) (m REO ), the 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 enriched material were measured.

[0032] .

[0033] The results are shown in the following table:

[0034] It can be seen from the above table that the iron yield can be effectively improved by subjecting rare earth catalytic self-activation treatment to rare earth iron slag fine powder; the rare earth element enrichment rate can be significantly improved by adding nano-carbon black during the pyrolysis of Fe(CO)5; the combination of the above two processes has a synergistic effect in improving the iron yield.

[0035] The principle is as follows: citric acid and Ce 3+ Forming chelates to achieve uniform dispersion of rare earth elements and avoid the loss of active sites caused by their agglomeration; low-temperature oxidation activation makes Ce 3+ Oxidized to Ce 4+ , complete the valence jump; in the dynamic reduction and reconstruction, Ce 4+ Reduced to Ce by CO 3+ , accompanied by the generation of oxygen vacancies, which serve as electron transfer channels, can accelerate the electron transfer between Fe and CO and promote the synthesis reaction of Fe(CO)5; the quenching treatment locks the metastable oxygen vacancies by rapid cooling, preventing their annihilation at high temperatures and continuously maintaining high catalytic activity, thereby accelerating the rate of iron conversion to Fe(CO)5 and improving the iron yield.

[0036] The addition of nanocarbon black during the pyrolysis of Fe(CO)5 increases rare earth enrichment due to its role as a heterogeneous nucleation site. Nanocarbon black's small particle size and large specific surface area provide a large number of 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 surface of rare earth particles. Furthermore, the presence of nanocarbon black reduces the interfacial binding energy between the Fe(CO)5 decomposition products and the rare earth phase, preventing secondary binding of iron and rare earth elements. This makes it easier for rare earth components to separate from iron, thereby increasing the relative content of rare earth elements in the rare earth enrichment material.

[0037] Rare earth catalytic self-activation accelerates the generation rate of Fe(CO)5 through oxygen vacancies, providing sufficient reactants for subsequent separation. Nanocarbon black, acting as a heterogeneous nucleation site, accelerates the decomposition of Fe(CO)5 and the precipitation rate of iron, preventing its accumulation in the system. According to Le Chatelier's principle, the rapid removal of the product further drives the forward Fe(CO)5 generation reaction, improving the iron conversion efficiency. Furthermore, the nanocarbon film formed during the self-activation process synergizes with the nanocarbon black to inhibit particle adhesion, maintain system dispersion, and ensure that both the catalytic activity of oxygen vacancies and the separation efficiency of nucleation sites are optimal, ultimately achieving a synergistic increase in iron yield.

[0038] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for producing carbonyl iron powder and rare earth enriched aggregate by treating rare earth iron slag by carbonylation, characterized in that: The following steps are involved: S1. Pretreatment; Separate rare earth iron slag fine powder ≤50μm from rare earth iron slag; S2. Drying; Dry the rare earth iron slag powder until the moisture content is reduced to ≤1%; S3. Rare earth catalytic self-activation; Spraying the citric acid solution onto the surface of the dry rare earth iron slag fine powder; Transfer to a rotary kiln, introduce oxygen-containing gas, increase the temperature and keep it warm, triggering the valence transition reaction of cerium; Switch the oxygen-containing hot air to a N2 / CO mixture and keep it warm. CO reacts with high-valent cerium to release oxygen vacancies. After activation, the rare earth iron slag fine powder is quenched to lock the metastable oxygen vacancy structure; S4. Fluidized reduction; The rare earth iron slag fine powder is fed into a circulating fluidized bed reactor and nitrogen is introduced to replace the air; The temperature is increased gradually to reduce the iron in the rare earth iron slag fine powder to a single substance; S5. Selective separation of iron by carbonyl method; Add nano-carbon black to rare earth iron slag powder, and heat and pressure are increased in a CO atmosphere to produce liquid Fe(CO)5, with the remainder being rare earth enriched material. Liquid Fe(CO)5 is pyrolyzed to generate carbonyl iron powder and CO gas.

2. The method for producing carbonyl iron powder and rare earth enriched aggregate by treating rare earth iron slag by carbonylation according to claim 1, characterized in that: S1 is specifically as follows: rare earth iron slag is prepared into a 15-22wt% slurry, added into a hydrocyclone, the feed pressure is controlled at 0.15-0.25MPa, and rare earth iron slag fine powder of ≤50μm is separated.

3. The method for producing carbonyl iron powder and rare earth enriched aggregate by treating rare earth iron slag by carbonylation according to claim 1, characterized in that: S2 is specifically as follows: fine powder of rare earth iron slag is put into a circulating fluidized bed, the bed temperature is controlled at 120-150°C, the gas velocity is 0.8-1.2m / s, and the drying time is 20-40min, so that the moisture content is reduced to ≤1%.

4. The method for producing carbonyl iron powder and rare earth enriched aggregate by treating rare earth iron slag by carbonylation according to claim 1, characterized in that: S3 is specifically as follows: 5-10wt% citric acid solution is evenly sprayed onto the surface of the dry rare earth iron slag fine powder through an atomizing nozzle, the spraying amount is 0.5-1.0L / kg rare earth iron slag fine powder, and the pH after spraying is 3.5-4.5; Transfer to a rotary kiln, introduce oxygen-containing gas, raise the temperature to 150-180°C at a rate of 10-15°C / min, and maintain the temperature for 20-40 minutes to trigger the valence transition reaction of cerium; Switch the oxygen-containing hot air to a N2 / CO mixture and maintain it at 150-180°C for 10-15 minutes. CO reacts with high-valent cerium to release oxygen vacancies. After activation, the rare earth iron slag fine powder is quenched to lock the metastable oxygen vacancy structure.

5. The method for producing carbonyl iron powder and rare earth enriched aggregate by treating rare earth iron slag by carbonylation process according to claim 1, characterized in that: The activated rare earth iron slag fine powder is rapidly cooled to 50-60° C. within 8-10 seconds through a water cooling jacket.

6. The method for producing carbonyl iron powder and rare earth enriched aggregate by treating rare earth iron slag by carbonylation according to claim 1, characterized in that: S4 specifically comprises: pneumatically feeding rare earth iron slag fine powder into a circulating fluidized bed reactor, introducing high-purity nitrogen to replace the air; Heat to 220-260°C at a rate of 5-10°C / min, and replace N2 with CO; Heat to 480-520°C at a rate of 5-10°C / min and keep warm for 15-25 minutes; The temperature is raised to 750-950°C at a rate of 10-15°C / min, and the reaction is carried out at a constant temperature for 30-90 minutes to reduce the iron in the rare earth iron slag fine powder to a single substance.

7. The method for producing carbonyl iron powder and rare earth enriched aggregate by treating rare earth iron slag by carbonylation process according to claim 1, characterized in that: S5 specifically comprises the following steps: adding rare earth iron slag fine powder into an autoclave, and 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 air with CO, heating to 160-180℃, increasing the pressure to 16-20MPa, and reacting at a constant temperature for 2-3h to obtain liquid Fe(CO)5, which is discharged from the bottom of the autoclave and condensed with 2-5℃ condensed water; the remainder is rare earth enriched material; Liquid Fe(CO)5 generates carbonyl iron powder and CO gas through thermal decomposition reaction in N2 / CO / NH3 mixed gas atmosphere at 200-280℃.

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

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