A method for high-value utilization of iron from multi-source NdFeB secondary resources and reduction and recovery of tailings.

Abstract

This invention belongs to the field of iron high-value utilization and tailings reduction. It relates to a method for high-value utilization of iron and tailings reduction in the recycling of multi-source NdFeB secondary resources. Addressing the challenges of iron tailings treatment and high-value utilization of iron in the secondary resource recycling process of NdFeB waste, this invention develops a new process of "oxidative roasting + carbonylation iron extraction + hydrometallurgical rare earth recovery" to achieve effective extraction of rare earth elements, promote high-value iron recovery, and reduce tailings generation. This process can prepare high-value-added iron pentacarbonyl from 60% to 86% of the iron in NdFeB magnetic material waste. The pentacarbonyl iron can then be pyrolyzed to prepare carbonyl iron powder. The amount of iron tailings after rare earth leaching is only 350 to 600 kg / t of raw material, which is only 40% to 60% of the iron tailings generated by the conventional roasting-hydrochloric acid optimal dissolution method for rare earth magnetic material recovery. This new process provides a strong guarantee for the efficient and high-value utilization of NdFeB waste and the reduction of tailings.

Description

Technical Field

[0001] This invention belongs to the field of iron value enhancement and tailings reduction. This invention relates to a method for iron value enhancement and tailings reduction and recovery of multi-source neodymium iron boron secondary resources. Background Technology

[0002] Neodymium iron boron (NdFeB) magnets play a crucial role in the field of green energy as powerful permanent magnet materials. NdFeB magnetic materials mainly contain neodymium and iron. Currently, the properties of NdFeB magnetic materials are improved by adding small amounts of elements such as dysprosium (Dy), terbium (Tb), cobalt (Co), niobium (Nb), gallium (Ga), aluminum (Al), and copper (Cu). Due to the non-renewable nature of rare earth resources and the limitations of mining them, recovering rare earth elements from discarded NdFeB magnets has become particularly important. Because the production of NdFeB waste inevitably generates waste or scrap at every stage, from raw material pretreatment to final product testing, it produces 25% to 30% waste materials. In addition, there are recycled waste magnetic materials, which contain 20% to 30% rare earth elements and 60% to 70% iron, and have extremely high value. Therefore, the effective recovery of rare earth elements from multi-source NdFeB secondary resources can not only alleviate the supply and demand pressure of rare earth elements and reduce risks, but also has great significance for environmental protection.

[0003] Currently, mainstream methods for recovering NdFeB secondary resources from multiple sources include hydrochloric acid preferential dissolution, total dissolution, and sulfuric acid double salt methods, with hydrochloric acid preferential dissolution being the dominant recovery technology. It has been reported (Kumari A et al., Waste Manage., 2018, 75, 486.) that these processes generate a large amount of iron slag after rare earth extraction (iron tailings amounting to 760-840 kg / t of rare earth secondary dry waste). Direct use of this waste in steel smelting is not only economically unfeasible but may also lead to resource waste and environmental pollution. Furthermore, iron tailings are difficult to reuse with high added value. Therefore, there is an urgent need to develop new rare earth waste recovery technologies to achieve high-value utilization of iron while recovering rare earth elements. Summary of the Invention

[0004] This invention addresses the shortcomings of existing technologies by proposing a novel process for the first time: "oxidative roasting + carbonylation for iron extraction + wet process for rare earth recovery." This process enables the high-value utilization of iron from multi-source NdFeB secondary resources and the reduction and recovery of tailings to have industrial application value.

[0005] This invention discloses a method for high-value utilization of iron from multi-source neodymium iron boron secondary resources and for reducing and recovering tailings, comprising the following steps:

[0006] Step 1: Raw material activation. Using NdFeB waste as raw material, the raw material is activated through a process of oxidation followed by reduction. First, a preliminary oxidation roasting is performed at a temperature controlled at 700-850℃ (preferably 720-750℃, more preferably 730℃). Then, a subsequent oxidation roasting is performed at a temperature controlled at 500-600℃ (preferably 550℃). Next, reduction is performed at a temperature of 300-800℃ (preferably 680-730℃, more preferably 700℃), so that more than 70 wt% of the iron oxide generated during the oxidation process is reduced, resulting in activated material.

[0007] Step 2: Carbonylation for Iron Extraction and Rare Earth Retention; Using the activated material obtained in Step 1, the carbonylation reaction Fe + 5CO → Fe(CO)5 is carried out with CO to generate pentacarbonyl iron Fe(CO)5 gas, thereby separating iron from the raw material and obtaining carbonylation slag enriched with rare earth elements; by cooling and condensing the gas containing pentacarbonyl iron Fe(CO)5, liquid pentacarbonyl iron Fe(CO)5 can be obtained, realizing the high-value recovery of iron; when CO reacts with iron, the pressure of the CO-containing reaction gas after entering the reactor is controlled at 5~20 MPa (preferably 8.5 MPa) and the temperature is controlled at 120~200℃ (preferably 150-200℃, more preferably 160℃).

[0008] Step 3: Extract rare earth elements from the carbonyl residue enriched with rare earth elements; age and oxidize the carbonyl residue enriched with rare earth elements so that iron exists in the form of trivalent oxides.

[0009] Preferably, in step one, neodymium iron boron waste is used as raw material, and a preliminary oxidation roasting is carried out: the temperature is controlled at 700~850℃ (preferably 720-750℃, more preferably 730℃), combustion air is introduced and the oxygen partial pressure in the combustion air is controlled at 0.1~0.21 (preferably 0.15), and water mist is continuously sprayed in at a rate of 5~200 kg water / t raw material (preferably 10~50 kg water / t raw material, more preferably 30 kg water / t raw material), and stirring is performed (stirring speed 3~5 rpm, preferably 3 rpm) to prevent sticking or local over-sintering, and the roasting time is 10~45 minutes (preferably 12 minutes).

[0010] Then, the subsequent oxidation roasting is carried out: the oxygen partial pressure of the combustion air is adjusted to 0.1~0.4 (preferably 0.21) and the temperature is lowered to 500~600℃ (preferably 550℃). During the cooling process, the water mist spraying is reduced until the spraying stops at 600℃. The roasting time is controlled at 10~45 minutes (preferably 20 minutes), and the stirring speed of the furnace charge is 5~20 rpm (preferably 5 rpm) to ensure that the rare earth in the raw material is fully oxidized; thus, the oxidation product is obtained.

[0011] Preferably, in step one, the oxidation product is cooled and ground to below 60 mesh, and then reduced using a CO / H2 / NH3 mixed gas at 300~800℃ (preferably 680~730℃, more preferably 700℃) for 50~120 minutes (preferably 50 minutes). During the reduction, stirring is performed (preferably 5~20 rpm, more preferably 7 rpm) to reduce the iron oxide in the calcined product to iron, with a reduction rate of 70%~90%, to obtain rare earth oxides and iron.

[0012] Preferably, in step one, during reduction, the molar ratio of CO, H2, and NH3 in the mixed gas is CO:H2:NH3 = x:y:z, and it is recommended that the content satisfy x = 3.5y + 7z, more preferably x:y:z = 10.5:1:1. In this invention, controlling the proportion of various gases in the mixed gas within this range during reduction ensures system temperature balance. In step one of this invention, the reduction reaction of CO is exothermic, but the reduction reactions of hydrogen and ammonia are endothermic. Considering that heat is released into the air from the reaction vessel, if the reducing gases are not heated, the relationship x = 3.5y + 7z can ensure that the system undergoes a chemical reaction while maintaining a constant temperature.

[0013] Preferably, in step two, when carrying out the carbonylation reaction (Fe+5CO → Fe(CO)5), the CO reaction gas contains 0~10% NH3, preferably 0.5~2% in molar proportion, 0~10% H2, preferably 0.5~2% in molar proportion, and 0~3% H2S, preferably 0.2~0.7% in molar proportion.

[0014] In step two of this invention, an appropriate amount of NH3 can promote the carbonyl reaction and eliminate the oxide film on the iron surface. This makes it easier for CO to come into contact with Fe, undergoing a carbonylation synthesis reaction to generate pentacarbonyl iron gas.

[0015] In step two of this invention, a carbon deposition reaction easily occurs: 2CO → CO2 + C. The introduction of an appropriate amount of H2S can suppress this reaction. This prevents carbon buildup on the iron surface and promotes the creation of more active sites on the Fe surface capable of adsorbing CO. It avoids the situation where carbon enrichment on the iron surface occupies active sites on the Fe surface, thus hindering the binding of CO to Fe.

[0016] Preferably, in step two, the reaction time is 24-48 hours (preferably 24 hours), and the CO gas in the reactor is replaced 3-7 times per hour (preferably 7 times / hour). The gas removed from the reactor is condensed to obtain liquid iron pentacarbonyl Fe(CO)5. In a preferred embodiment of the present invention, appropriate amounts of ammonia, hydrogen, and hydrogen sulfide are added to the CO gas to enhance the carbonylation synthesis reaction. The purpose of adding ammonia and hydrogen is to break down the oxide layer on the iron surface, especially rare earth oxides, to increase the contact opportunity between Fe and CO. At the same time, adding hydrogen sulfide to CO mainly inhibits the carbon deposition reaction on the iron surface (2CO = CO2 + C), which also increases the contact opportunity between Fe and CO. Furthermore, the reaction is enhanced by ultrasound, which suspends the furnace charge, increases the reaction area, and promotes the rapid entry of the iron pentacarbonyl product on the iron surface into the gas phase, thereby greatly increasing the chance of Fe and CO and eliminating the 'mass transfer and diffusion resistance' in the carbonylation reaction kinetics. Therefore, the present invention can prepare iron pentacarbonyl with a high synthesis rate even at relatively low pressures of 5-20 MPa, or even 12-15 MPa.

[0017] In industrial applications, whenever the partial pressure of Fe(CO)5 in the gas is about 6-8%, the gas needs to be replaced before it reaches the dew point or before dense fog forms and envelops solids.

[0018] Preferably, in step two, ultrasonic waves with a power of 1-6 kW (preferably 2 kW) are introduced during the reaction process. In this invention, introducing ultrasonic waves with a power of 1-6 kW can suspend the iron powder, resulting in a larger reaction area. At the same time, the ultrasonic waves promote the evaporation of Fe(CO)5 on the iron surface, accelerating the synthesis reaction.

[0019] This invention involves aging the rare earth-enriched carbonyl slag in air for 1-3 days (preferably 1 day), followed by secondary oxidation roasting to ensure the iron exists as trivalent oxides. Simultaneously, the roasting temperature and time are controlled to prevent excessive sintering of the carbonyl slag. The roasting temperature is 550-750℃ (preferably 550-560℃, more preferably 550℃), the oxygen partial pressure of the combustion air is 0.21-0.4, preferably 0.21-0.25 (more preferably 0.21), and the roasting time is 10-45 minutes (preferably 20-30 minutes, more preferably 25 minutes). The stirring speed of the furnace charge is 5-20 rpm (preferably 5 rpm). Next, the material is air-cooled, and the roasted product is ground to below 100 mesh. Then, the rare earth in the enriched slag is leached with hydrochloric acid. The rare earth enters the solution, and the remaining dissolved iron tailings, amounting to 350-600 g / m³, are leached. kg / t dry weight of raw material (far lower than the existing conventional oxidation roasting-wet leaching process. In the existing conventional process, iron is not recovered, and all the iron in the magnetic material waste containing 70% iron is turned into slag, with the amount of iron tailings being 760~840 kg / t of raw material).

[0020] In this invention, the carbonyl residue surface contains liquid or solid Fe(CO)5, which is highly toxic. Once decomposed, it produces a large amount of CO, so contact with humans must be prevented as it can easily cause CO poisoning. Skin contact should also be avoided. Direct combustion could be used, but this is inconvenient for transfer and transportation. Therefore, it is safer to leave it for 1-3 days to allow the CO to dissipate.

[0021] Through this invention, iron in rare earth waste can be converted into iron pentacarbonyl Fe(CO)5 with a synthesis rate of 60% to 86%.

[0022] The carbonylation synthesis reaction of this invention takes 24 hours to achieve a conversion rate of Fe to pentacarbon-based iron greater than or equal to 60%.

[0023] The pentacarbonyl iron prepared in this invention is decomposed by heating under low pressure into Fe(CO)5 → Fe+5CO to obtain carbonyl iron powder Fe.

[0024] The rare earth leaching rate obtained by this invention is no less than 99.5%.

[0025] During the activation of the raw materials in this invention, since most of the secondary resources of NdFeB waste are oily sludge-type, an initial oxidation roasting is performed, followed by grinding. A CO / H2 / NH3 mixed gas is then used to reduce the iron oxide in the roasted product to iron (iron reduction rate 70%~90%), preparing for subsequent carbonylation to extract iron and preserve rare earth elements. The purpose of oxidizing and roasting the multi-source NdFeB secondary resources before reduction treatment is to burn the organic matter in the waste and convert it into loose, porous rare earth oxides and iron. Specifically, the initial oxidation roasting is performed at a combustion temperature of 700~850 ℃ (preferably 730 ℃), with an oxygen partial pressure of 0.1~0.21 (preferably 0.15) for the combustion air, and continuous water mist is sprayed (spray volume 5~200 kg water / t raw material, preferably 30 kg water / t raw material). To prevent deflagration, the combustion process requires continuous stirring (stirring speed 3-5 rpm, preferably 3 rpm) to prevent sticking or local over-sintering. The calcination time is 10-45 minutes (preferably 12 minutes). Then, a later oxidation calcination is carried out: the oxygen partial pressure of the combustion air is 0.1-0.4 (preferably 0.21), and the temperature is gradually reduced to 500-600℃ (preferably 550℃). During the cooling process, the water mist spray is gradually reduced until the spraying stops at 600℃. The calcination time is 10-45 minutes (preferably 20 minutes), and the stirring speed of the furnace charge is 5-20 rpm (preferably 5 rpm) to ensure that the rare earth elements of the multi-source NdFeB secondary resources are fully oxidized. Next, the oxidation product is air-cooled and ground to below 60 mesh. Then, a CO / H2 / NH3 mixed gas (gas content CO:H2:NH3 = x:y:z, it is recommended that the content meet x = 3.5y +7z) is used to reduce the iron oxide in the roasted product to iron (iron reduction rate 70%~90%) at 300~800℃ (preferably 700 ℃) for 50~120 minutes (preferably 50 minutes) and a reduction stirring speed of 5~20 rpm, preferably 7 rpm. This transforms the waste into loose and porous rare earth oxides and iron, preparing for subsequent carbonylation to extract iron and preserve rare earths.

[0026] The purpose of this invention, carbonylation for iron extraction and rare earth enrichment, is to remove iron from the raw material to enrich rare earth elements, while simultaneously obtaining gaseous pentahydroxy iron (Fe(CO)5), which is then pyrolyzed to yield hydroxy iron powder. In this step, activated, porous raw materials are placed in a reactor, and CO gas (containing 0-10% NH3, 0.5-2% H2, and 0.2-0.7% H2S) at a temperature of 120-200°C and a pressure of 5-20 MPa is introduced from above. The reaction time is 24-48 hours, with the CO gas being replaced 3-7 times per hour. During the reaction, an ultrasonic device with a power of 1-6 kW is placed inside the reactor to promote the reaction between Fe and CO, generating pentacarbonyl iron (Fe(CO)5) gas. The conversion rate of iron to pentacarbonyl iron is 60%-86%. The CO gas removed from the reactor is then dusted, cooled, and condensed to obtain liquid carbonyl iron. Heating pentacarbonyl iron under low pressure decomposes it into Fe(CO)5 → Fe + 5CO, yielding carbonyl iron powder (Fe) and CO. The CO can be returned to the carbonylation reactor or used in step one for the reduction of rare earth waste. After the carbonylation reaction is complete, rare earth-enriched carbonylation slag is obtained in the reactor.

[0027] The specific operation for extracting rare earths from the carbonyl slag enriched with rare earths according to this invention is as follows: The carbonyl slag enriched with rare earths obtained in the second step is aged in air for 1-3 days (preferably 1 day), and then subjected to secondary oxidation roasting. Simultaneously, the roasting temperature and time are controlled to prevent excessive sintering of the carbonyl slag. The roasting temperature is 550-750℃ (preferably 550-560℃, more preferably 550℃), the oxygen partial pressure of the combustion air is 0.21-0.4 (preferably 0.21-0.25, more preferably 0.21), and the roasting time is 10-45 minutes (preferably 20-30 minutes, more preferably 25 minutes). The stirring speed of the furnace charge is 5-20 rpm (preferably 5 rpm). Next, the material is air-cooled, and the roasted product is ground to below 100 mesh. Then, the rare earths in the enriched slag are leached with hydrochloric acid, with a leaching rate of not less than 99.5%, and the amount of iron tailings after leaching is 350-600 g / m³. The amount of rare earth secondary dry waste generated is only 40% to 60% of the iron tailings generated by the conventional roasting-hydrochloric acid dilution method for recovering rare earth magnetic materials (760~840 kg / t rare earth secondary dry waste). In this invention, the rare earth secondary dry waste is the dry material of NdFeB waste after removing water and oil.

[0028] The present invention discloses a new technology for high-value iron utilization and tailings reduction and recovery of multi-source NdFeB secondary resources. The feature is that the multi-source NdFeB secondary resources are activated by oxidation roasting-reduction treatment. The purpose is to remove organic components from the waste, burn the organic matter in the waste, and convert the waste into loose and porous rare earth oxides and iron, in preparation for subsequent carbonylation iron extraction and rare earth preservation.

[0029] This invention discloses a new technology for the high-value recovery and tailings reduction of secondary NdFeB resources. The key feature is the carbonylation treatment of the activated pretreated raw materials. Under conditions of 150-200℃, 5-20 MPa (preferably 12-15 MPa), and ultrasonic stimulation, CO selectively reacts with iron to generate pentacarbonyl iron (Fe(CO)5) gas, thus removing iron from the raw materials. The CO gas removed from the reactor is then dedusted and cooled to obtain liquid pentacarbonyl iron. Heating the pentacarbonyl iron under low pressure decomposes it, yielding carbonyl iron powder (Fe), achieving high-value recovery of iron.

[0030] The present invention discloses a new technology for high-value utilization of iron and reduction and recovery of tailings from multi-source neodymium iron boron secondary resources. The key feature is that the carbonyl slag enriched with rare earth elements that may contain metallic iron is subjected to secondary oxidation roasting or aging treatment. The purpose is to control the valence state of oxides and remove pentacarbonyl iron, thereby reducing the amount of sodium bicarbonate or acid used in subsequent wet process recovery of rare earth elements.

[0031] Technical Principles

[0032] Before wet rare earth recovery, a carbonylation synthesis reaction is first performed using CO selectively with iron in the activated raw materials to generate iron pentacarbonyl gas, thus separating iron from the raw materials and obtaining carbonylation slag enriched with rare earth elements. Simultaneously, the CO gas removed from the reactor is cooled and condensed to obtain liquid iron pentacarbonyl Fe(CO)₅. Then, the iron pentacarbonyl is heated under low pressure to decompose it, yielding iron carbonyl powder (Fe). 1) Raw material activation: The raw materials are activated using a process of oxidation followed by reduction to remove organic components from the waste and convert the waste into loose, porous rare earth oxides and iron, preparing for subsequent carbonylation iron extraction and rare earth preservation. 2) Iron extraction by carbonylation: CO reacts with iron to generate iron pentacarbonyl gas, separating iron from the raw materials and obtaining carbonylation slag enriched with rare earth elements. Liquid iron pentacarbonyl is obtained by cooling and condensation, and can be decomposed under low pressure to obtain iron carbonyl powder (Fe), achieving high-value recovery of iron. 3) Hydrometallurgical process for rare earth recovery: After carbonylation, NdFeB-enriched rare earth slag is obtained. The carbonylation slag is first aged and then oxidized and roasted to ensure that iron exists in the form of trivalent oxides. Simultaneously, the roasting temperature and time are controlled to prevent excessive sintering of the carbonylation slag. Selective leaching is performed using hydrochloric acid, allowing the rare earth elements to dissolve in the hydrochloric acid solution, while residual iron and other elements remain in the slag. Because the second step of carbonylation removes some of the iron from the waste (60%~86%), the iron content of the carbonylation-enriched slag is even lower, resulting in less iron tailings remaining after rare earth leaching.

[0033] Advantages of this invention:

[0034] 1. Effectively reduces the generation of iron tailings; compared with the existing advanced roasting-hydrochloric acid optimal leaching method for rare earth recovery, the rare earth leaching rate of this invention is no less than 99.5%, and the amount of iron tailings after leaching is 350~600 kg / t of rare earth secondary dry waste, while the amount of iron tailings of the conventional roasting-hydrochloric acid optimal leaching method is 760~840 kg / t of rare earth secondary dry waste. That is, the amount of iron tailings of this invention is only 40%~60% of that of the conventional roasting-hydrochloric acid optimal leaching method, and can even be lower.

[0035] 2. High-value recycling of iron has been achieved; 60% to 86% of the iron in neodymium iron boron magnet waste can be prepared into high-value pentacarbonyl iron, or carbonyl iron powder (Fe) can be prepared by pyrolysis of pentacarbonyl iron. Attached Figure Description

[0036] Figure 1 Process diagrams for high-value iron extraction and tailings reduction of multi-source NdFeB secondary resources; (a) is a process diagram for iron extraction by oxidative roasting and carbonylation; (b) is a process diagram for rare earth recovery by hydrometallurgical process.

[0037] Figure 2 The image shows the actual carbonyl iron powder obtained in Example 1 and its XRD pattern.

[0038] from Figure 1 As shown in section a, the raw materials are activated using a process of oxidation followed by reduction, removing organic components from the waste and converting it into loose, porous rare earth oxides and iron, preparing for subsequent carbonylation for iron extraction and rare earth preservation. Under specific temperature, pressure, and atmosphere conditions, CO reacts with iron to produce pentacarbonyl iron gas, achieving separation of iron from the raw materials and obtaining carbonylation slag enriched with rare earth elements. Liquid pentacarbonyl iron Fe(CO)5 is obtained through cooling and condensation. Fe(CO)5 is then decomposed under low pressure to yield carbonyl iron powder Fe.

[0039] from Figure 1 As shown in section b, aging and oxidative roasting of the carbonyl slag enriched with rare earth elements ensures that iron exists in the form of trivalent oxides. Simultaneously, controlling the roasting temperature and time prevents excessive sintering of the carbonyl slag, preparing for reducing the amount of hydrochloric acid used and increasing the rare earth leaching rate in the subsequent hydrochloric acid-based optimal leaching process. Next, the leachate undergoes impurity removal and extraction. Ammonium bicarbonate is used to precipitate the back-extraction solution, followed by precipitating the raffinate with oxalic acid or sodium carbonate to obtain rare earth chlorides. Finally, these are calcined to obtain rare earth oxide products.

[0040] Figure 2 In the image, (a) shows the actual Fe carbonyl powder and its particle size distribution, and (b) shows the XRD pattern of the Fe carbonyl powder. Figure 2 It can be seen that the product has extremely high purity and uniform particle size distribution. Detailed Implementation

[0041] The invention will be further described in detail below through specific implementation examples.

[0042] Example 1

[0043] 100 kg of oily NdFeB waste (i.e., raw material) was burned at a high temperature of 730 ℃ using air and flue gas as combustion air with an oxygen partial pressure of 0.15, and water mist was continuously sprayed in (30 kg water / t raw material). During the combustion process, it was necessary to stir continuously (stirring speed 3 rpm) to prevent sticking or local over-sintering. The roasting time was 12 minutes. Then, in the later roasting stage, the oxygen partial pressure of the combustion air was 0.21, and the temperature was gradually reduced to 550 ℃. During the cooling process, the water mist was gradually reduced until the spraying was stopped at 600 ℃ (the spraying water volume was 1 kg water / t rare earth waste). The roasting time was 20 minutes, and the stirring speed of the furnace charge was 5 rpm. Secondly, the oxidation products are air-cooled and ground to below 60 mesh. Then, a CO / H2 / NH3 mixed gas (CO:H2:NH3 = 10.5:1:1) is used for reduction treatment at 700 ℃ for 50 minutes with a stirring speed of 7 rpm. This reduces the iron oxide in the calcined products to iron (80% metallization rate), thus converting the waste into loose and porous rare earth oxides and iron. The activated loose and porous raw materials are placed in a reactor, and CO gas (containing 1.5% NH3 + 1.5% H2 + 0.5% H2S) at a temperature of 170 ℃ and a pressure of 15 MPa is introduced from top to bottom. The reaction time is 36 hours, with the CO gas being replaced 3 times per hour. During the reaction, a power of 2 A kW ultrasonic device generates ferric pentacarbonyl gas, achieving a 69% conversion rate of iron in rare earth waste to ferric carbonyl. The CO gas removed from the reactor is cooled and condensed to obtain liquid ferric pentacarbonyl; the ferric pentacarbonyl is then heated under low pressure to decompose it, yielding... Figure 2 The carbonyl iron powder Fe (shown in a) Figure 2 b represents the XRD characterization of carbonyl iron powder (XRD, Rigaku TTR III, Japan); and its particle size distribution (LS13 320, Beckman Coulter, Brea, CA, USA) and CO. After the carbonylation reaction, rare earth-enriched carbonyl slag is obtained in the reactor. The obtained rare earth-enriched carbonyl slag is aged in air for 1 day, and then subjected to secondary oxidation roasting at a temperature of 550 °C, an oxygen partial pressure of 0.21 in the combustion air, and roasting for 35 minutes with a furnace charge stirring speed of 5 rpm. Then, the material is cooled by air, and the roasted product is ground to below 100 mesh. Next, the rare earth in the enriched slag is leached with hydrochloric acid, with a rare earth leaching rate of not less than 99.5%, and the amount of iron tailings after leaching is 450 kg / t dry raw material.

Claims

1. A method for high-value utilization of iron from multi-source NdFeB secondary resources and for reducing and recovering tailings, characterized in that... Includes the following steps: Step 1: Raw material activation. Using NdFeB waste as raw material, the raw material is activated by a process of oxidation followed by reduction. The oxidation temperature is controlled at 700~850 ℃, and the reduction temperature is 300~800 ℃, so that more than 70 wt% of the iron oxide generated during the oxidation process is reduced; thus obtaining activated material. Step 2: Carbonylation for Iron Extraction and Rare Earth Preservation. Using the activated material obtained in Step 1 as the treatment target, CO reacts with iron to generate iron pentacarbonyl gas, achieving separation of iron from the raw material and obtaining carbonylation slag enriched with rare earth elements. Liquid iron pentacarbonyl is obtained through cooling and condensation, realizing the high-value recovery of iron. When CO reacts with iron to form a carbonylation reaction, the pressure of the CO-containing reaction gas after entering the reactor is controlled at 5~20 MPa and the temperature at 120~200℃. Step 3: Extract rare earth elements from the carbonyl residue enriched with rare earth elements, and then age and oxidize the carbonyl residue to allow iron to exist in the form of trivalent oxides.

2. The method for high-value utilization of iron and reduction and recovery of tailings from multi-source NdFeB secondary resources according to claim 1, characterized in that: In step one, neodymium iron boron waste is used as raw material, and the raw material undergoes pre-oxidation roasting and post-oxidation roasting; specifically including: First, perform preliminary oxidation roasting: control the temperature at 700~850℃, introduce combustion air and control the oxygen partial pressure in the combustion air to 0.1~0.21, and continuously spray water mist with a spray volume of 5~200 kg water / t raw material, stir to prevent sticking or local over-sintering, and roast for 10~45 minutes. Then, the subsequent oxidation roasting is carried out: the oxygen partial pressure of the combustion air is adjusted to 0.1~0.4 and the temperature is lowered to 500~600℃. During the cooling process, the water mist spraying is reduced until the water mist spraying is stopped at 600℃. The roasting time is controlled at 10~45 minutes and the stirring speed of the furnace charge is 5~20 rpm to ensure that the rare earth in the raw material is fully oxidized; and the oxidation product is obtained.

3. The method for high-value utilization of iron and reduction and recovery of tailings from multi-source NdFeB secondary resources according to claim 1, characterized in that: In step one, the oxidation product is cooled and ground to below 60 mesh, and then reduced using a CO / H2 / NH3 mixed gas at 300~800℃ for 50~120 minutes. Stirring is used during the reduction to reduce the iron oxide in the calcined product to iron. The reduction rate of iron is 70%~90%, resulting in rare earth oxides and iron.

4. The method for high-value utilization of iron and reduction and recovery of tailings from multi-source NdFeB secondary resources according to claim 3, characterized in that: In step one, during reduction, the molar ratio of CO, H2, and NH3 in the mixed gas is CO:H2:NH3 = x:y:z, where x = 3.5y +7z.

5. The method for high-value utilization of iron and reduction and recovery of tailings from multi-source NdFeB secondary resources according to claim 1, characterized in that: In step two, during the carbonylation reaction, the CO reaction gas contains 0-10% NH3, 1-5% H2, and 0-3% H2S in molar proportion.

6. The method for high-value utilization of iron and reduction and recovery of tailings from multi-source NdFeB secondary resources according to claim 1, characterized in that: In step two, the reaction time for the carbonylation reaction to synthesize iron pentacarbonyl is 24-48 hours, and the CO gas in the reactor is changed 3-7 times per hour during the reaction.

7. The method for high-value utilization of iron and reduction and recovery of tailings from multi-source NdFeB secondary resources according to claim 1, characterized in that: During the carbonylation reaction to synthesize iron pentacarbonyl, ultrasonic waves with a power of 1-6 kW are introduced.

8. The method for high-value utilization of iron and reduction and recovery of tailings from multi-source NdFeB secondary resources according to claim 1, characterized in that: The obtained rare earth-enriched carbonyl slag is aged in air for 1-3 days, and then oxidatively roasted to allow iron to exist in the form of trivalent oxides. At the same time, the roasting temperature and time are controlled to prevent the carbonyl slag from over-sintering. The roasting temperature is 550-750℃, the oxygen partial pressure of the combustion air is 0.21-0.4, the roasting time is 10-45 minutes, and the stirring speed of the furnace charge is 5-20 rpm. Then, the material is cooled by air, and the roasted product is ground to below 100 mesh. Next, the rare earth in the enriched slag is leached with hydrochloric acid. The rare earth enters the solution, and the remaining dissolved product after leaching is iron tailings, with a slag volume of 350-600 kg / t of raw material.

9. A method for high-value utilization of iron and reduction and recovery of tailings from multi-source NdFeB secondary resources according to claim 1, characterized in that: The conversion rate of iron in the raw materials to iron pentacarbonyl is 60%~86%.

10. A method for high-value utilization of iron and reduction and recovery of tailings from multi-source NdFeB secondary resources according to claim 8, characterized in that: The rare earth leaching rate is not less than 99.5%.

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