Iron high-valued and tailing reduction recovery method for multi-source neodymium iron boron secondary resources

Abstract

The invention belongs to the field of iron high-valued treatment and tailing reduction, and relates to an iron high-valued treatment and tailing reduction recovery method for multi-source neodymium iron boron secondary resources. In order to solve the problems of iron tailing treatment and high-value utilization of iron elements in the secondary resource recovery process of the neodymium iron boron waste, the invention develops a new process of'oxidizing roasting, carbonylation method iron extraction and wet process rare earth recovery ', so that effective extraction of rare earth elements is realized, high-value recovery of iron is promoted, and the generation amount of tailings is reduced. According to the technology, 60%-86% of iron elements in the neodymium iron boron magnetic material waste can be prepared into pentacarbonyl iron with the high additional value, then pentacarbonyl iron can be pyrolyzed to prepare a carbonyl iron powder product, the amount of iron tailings obtained after rare earth leaching is 350-600 kg / t of raw materials, and the output of the iron tailings is only 40%-60% of iron tailings generated after rare earth magnetic materials are recycled through a conventional roasting-hydrochloric acid optimal solution method. The new process can provide powerful guarantee for efficient and high-value utilization of neodymium iron boron waste and tailing reduction.

Description

Technical Field

[0001] The invention belongs to the field of iron high value and tailings reduction, and relates to a method for iron high value and tailings reduction and recovery of multi-source NdFeB secondary resources. Background Art

[0002] Neodymium iron boron (NdFeB) magnets play a key role in the field of green energy as powerful permanent magnetic materials. NdFeB magnetic materials mainly contain neodymium, and iron. At present, a small amount of dysprosium (Dy), terbium (Tb), cobalt (Co), niobium (Nb), gallium (Ga), aluminum (Al), copper (Cu) and other elements are added to NdFeB materials to improve the properties of NdFeB magnetic materials. Due to the non-renewable nature of rare earth resources and the limitations of mining, it is particularly important to recover rare earth elements from discarded NdFeB magnets. During the production of NdFeB waste materials, waste or scrap will inevitably be generated in each process from raw material pretreatment to final product testing, which will produce 25%~30% of waste materials; plus the waste magnetic materials recycled by the society, these waste materials contain 20~30% rare earths and 60~70% iron, and have extremely high value. Therefore, effective recovery of rare earths in multi-source NdFeB secondary resources can not only ease the pressure of rare earth supply and demand and reduce risks, but also has very important significance for environmental protection.

[0003] At present, the mainstream multi-source NdFeB secondary resource recovery methods include hydrochloric acid optimal dissolution method, full dissolution method and sulfate complex salt method, among which hydrochloric acid optimal dissolution method is the mainstream recovery technology. According to reports (Kumari A et al., Waste Manage., 2018, 75, 486.), these processes will produce a large amount of iron slag after extracting rare earths (the amount of iron tailings is 760~840 kg / t rare earth secondary dry waste). If these waste slags are directly used for steel smelting, they will not only have poor economic efficiency, but may also cause resource waste and environmental pollution. In addition, it is difficult to achieve high value-added reuse of iron tailings. Therefore, it is urgent to develop new rare earth waste recovery technologies so as to achieve high-value utilization of iron while recovering rare earth elements. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention proposes for the first time a new process of "oxidative roasting + carbonylation method for iron extraction + wet process for rare earth recovery", thereby making the iron high-value of multi-source NdFeB secondary resources and the tailings reduction recovery have industrial use value.

[0005] The present invention discloses a method for increasing the iron value of multi-source NdFeB secondary resources and reducing and recovering tailings, comprising the following steps: Step 1: Activation of raw materials. NdFeB waste materials are used as raw materials. The raw materials are activated by oxidation followed by reduction. First, the initial oxidation roasting is carried out at a temperature of 700-850°C (preferably 720-750°C, more preferably 730°C), and then the subsequent oxidation roasting is carried out at a temperature of 500-600°C (preferably 550°C); then reduction is carried out at a temperature of 300-800°C (preferably 680-730, more preferably 700°C), so that more than 70wt% of the iron oxides generated during the oxidation process are reduced; and an activated material is obtained; Step 2: Carbonylation to extract iron and retain rare earths; using the activated material obtained in step 1 to treat the object, CO is used to react with iron to undergo carbonylation reaction Fe+5CO →Fe(CO)5 to generate pentacarbonyl iron Fe(CO)5 gas, thereby separating iron from the raw material and obtaining carbonyl slag enriched in rare earths; by cooling and condensing the gas containing pentacarbonyl iron Fe(CO)5, liquid pentacarbonyl iron Fe(CO)5 can be obtained, thereby realizing high-value recovery of iron; when CO is used to react with iron to undergo carbonylation reaction, the pressure of the reaction gas containing CO after being introduced into the reactor is controlled to be 5-20 MPa (preferably 8.5 MPa) and the temperature is controlled to be 120-200°C (preferably 150-200°C, and more preferably 160°C); Step 3: extracting rare earth from the rare earth-enriched carbonyl slag; subjecting the rare earth-enriched carbonyl slag to aging treatment and oxidative roasting, so that the iron exists in the form of trivalent oxide.

[0009] Preferably, in step 1, NdFeB waste is used as raw material, and preliminary oxidation roasting is first performed: the temperature is controlled at 700-850°C (preferably 720-750°C, more preferably 730°C), combustion-supporting wind is introduced and the oxygen partial pressure in the combustion-supporting wind is controlled to be 0.1-0.21 (preferably 0.15), and water mist is continuously sprayed at a spray 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), stirred (stirring speed 3-5 rpm, preferably 3 rpm), to prevent adhesion or local over-sintering, and the roasting time is 10-45 minutes (preferably 12 minutes);

[0010] Then, the post-oxidation roasting is carried out: the oxygen partial pressure of the combustion-supporting air is adjusted to 0.1-0.4 (preferably 0.21) and the temperature is lowered to 500-600°C (preferably 550°C), and the water mist is reduced during the cooling process until the spraying is stopped at 600°C. The roasting time is controlled at 10-45 minutes (preferably 20 minutes), and the stirring speed of the charge is 5-20 rpm (preferably 5 rpm) to fully oxidize the rare earth in the raw material; and an oxidation product is obtained.

[0011] Preferably, in step 1, the oxidation product is cooled and ground to less than 60 mesh, and then reduced using a CO / H2 / NH3 mixed gas at 300-800°C (preferably 680-730°C, more preferably 700°C), with a reduction time of 50-120 minutes (preferably 50 minutes), and the reduction is assisted by stirring (preferably 5-20 rpm, more preferably 7 rpm), to reduce the iron oxide in the calcined product to iron, with an iron reduction rate of 70%-90%, to obtain rare earth oxides and iron.

[0012] Preferably, in step 1, during reduction, the molar ratio of CO, H2, and NH3 in the mixed gas is CO: H2: NH3 = x: y: z, and the recommended content satisfies x = 3.5y + 7z, and further preferably, x: y: z = 10.5: 1: 1. In the present invention, during reduction, the ratio of various gases in the mixed gas is controlled within this ratio range to ensure the temperature balance of the system. During reduction in step 1 of the present invention, CO releases heat during the reduction reaction, but the reduction reaction of hydrogen and ammonia absorbs heat during the reduction reaction. Considering that heat is transferred to the air by the reactor, if the reducing gas is not heated, the relationship of x = 3.5y + 7z can ensure that the system undergoes a chemical reaction and the temperature remains unchanged.

[0013] Preferably, in step 2, when the carbonylation reaction (Fe+5CO → Fe(CO)5) is carried out, the CO reaction gas contains NH3 in a molar ratio of 0-10%, preferably 0.5-2%, H2 in a molar ratio of 0-10%, preferably 0.5-2%, and H2S in a molar ratio of 0-3%, preferably 0.2-0.7%.

[0014] In step 2 of the present invention, an appropriate amount of NH3 can promote the carbonyl reaction and eliminate the oxide film on the surface of iron, making it easier for CO to contact Fe, causing a carbonyl synthesis reaction to generate pentacarbonyl iron gas.

[0015] In step 2 of the present invention, carbon deposition reaction is likely to occur: 2CO → CO2 + C. The introduction of an appropriate amount of H2S can inhibit this reaction. This can prevent carbon deposition on the iron surface and promote more active points on the Fe surface that can adsorb CO. This avoids carbon accumulation on the iron surface, occupying active points on the Fe surface, and affecting the binding of CO with Fe.

[0016] Preferably, in step 2, the reaction time is 24 to 48 hours (preferably 24 hours), and the reactor changes CO gas 3 to 7 times per hour (preferably 7 times per hour) during the reaction; the gas replaced by the reactor is condensed to obtain liquid pentacarbonyl iron Fe(CO)5. In the preferred embodiment of the present invention, it is proposed to add appropriate amounts of ammonia, hydrogen and hydrogen sulfide gas to the CO gas to strengthen the carbonyl synthesis reaction. The purpose of adding ammonia and hydrogen is to destroy the oxide layer on the surface of iron, especially the oxide of rare earth, so as to increase the contact opportunity between Fe and CO; at the same time, adding hydrogen sulfide to CO is mainly to inhibit the carbon deposition reaction on the surface of iron (2CO = CO2 + C), and also to increase the contact opportunity between Fe and CO; and ultrasonic wave is used to strengthen the reaction, so that the furnace charge is suspended, the reaction area is increased, and the pentacarbonyl iron product on the surface of iron is promoted to quickly enter the gas phase, thereby greatly increasing the opportunity of Fe and CO, and removing the "mass transfer and diffusion resistance" of the carbonyl reaction kinetic process. Therefore, the present invention can prepare pentacarbonyl iron at a high synthesis rate at a relatively low pressure of 5 to 20 MPa, or even at 12-15 MPa.

[0017] In industrial applications, whenever the partial pressure of Fe(CO)5 in the gas is about 6~8%, the gas must be replaced before it reaches the dew point / before fog appears and wraps the solid.

[0018] Preferably, in step 2, during the reaction, ultrasonic waves with a power of 1 to 6 kW (preferably 2 kW) are introduced. In the present invention, the introduction of ultrasonic waves with a power of 1 to 6 kW can suspend the iron powder, increase the reaction area, and promote the evaporation of Fe(CO)5 on the iron surface, thereby accelerating the synthesis reaction.

[0019] The method comprises placing the obtained rare earth-enriched carbonyl slag in air for aging for 1 to 3 days (preferably 1 day), and then performing secondary oxidation roasting to make iron exist in the form of trivalent oxide, and controlling the roasting temperature, time, etc. to prevent excessive sintering of the carbonyl slag; the roasting temperature is 550 to 750°C (preferably 550 to 560°C, and more preferably 550°C), the oxygen partial pressure of the combustion-supporting air is 0.21 to 0.4, preferably 0.21-0.25 (more preferably 0.21), the roasting is 10 to 45 minutes (preferably 20 to 30 minutes, and more preferably 25 minutes), and the stirring speed of the furnace charge is 5 to 20 rpm (preferably 5 rpm); then the material is air-cooled, and the roasted product is ground to less than 100 meshes; 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 after leaching are 350 to 600 rpm. kg / t dry weight of raw materials (much lower than the existing conventional oxidation roasting-wet leaching process. In the existing conventional process, iron is not recovered, and the iron in the magnetic waste containing 70% iron is all converted into slag, and the amount of iron tailings is 760~840 kg / t raw materials).

[0020] In the present invention, the surface of carbonylation slag contains liquid or solid Fe(CO)5, which is very toxic. Once decomposed, a large amount of CO will be produced. It is necessary to prevent people from contacting it, as it is easy to get CO poisoning and to avoid skin stickiness. It can be burned directly, but it is inconvenient to transfer and transport. Therefore, it is safe to choose to leave it for 1-3 days and wait for it to be released.

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

[0022] The carbonylation synthesis reaction of the present invention takes 24 hours to achieve a conversion rate of Fe to pentacarbonyl iron greater than or equal to 60%.

[0023] The pentacarbonyl iron prepared by the present invention is heated under low pressure to decompose Fe(CO)5→Fe+5CO to obtain carbonyl iron powder Fe.

[0024] The rare earth leaching rate of the present invention is not less than 99.5%.

[0025] When the raw material of the present invention is activated, since there are many sludge-type secondary resources of NdFeB waste materials, an oxidation roasting is first carried out, and then ground, and a CO / H2 / NH3 mixed gas is used to reduce the iron oxide in the roasting product to iron (the iron reduction rate is 70%~90%), in preparation for the subsequent carbonylation to extract iron and retain dilute. The multi-source NdFeB secondary resources are first oxidized and roasted and then reduced, aiming to burn the organic matter in the waste and convert it into loose and porous rare earth oxides and iron. The specific operation is: firstly, a preliminary oxidation roasting is carried out: the combustion temperature is in the range of 700~850 ℃ (preferably 730 ℃), the oxygen partial pressure of the combustion-supporting wind is 0.1~0.21 (preferably 0.15), and water mist is continuously sprayed (the water spraying amount is 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 roasting time is 10~45 minutes (preferably 12 minutes); then the post-oxidation roasting is carried out: the oxygen partial pressure of the combustion-supporting air is 0.1~0.4 (preferably 0.21), the temperature is gradually reduced to 500~600℃ (preferably 550℃), the water mist is gradually reduced during the cooling process, until the spraying is stopped at 600℃, the roasting is 10~45 minutes (preferably 20 minutes), the stirring speed of the charge is 5~20 rpm (preferably 5 rpm), so that the rare earth of the multi-source NdFeB secondary resources is fully oxidized. Next, the oxidation product is air-cooled and ground to less than 60 mesh, and then reduced using a CO / H2 / NH3 mixed gas (gas content CO:H2:NH3 = x:y:z, with a recommended content of x = 3.5y +7z) at 300-800°C (preferably 700°C), with a reduction time of 50-120 minutes (preferably 50 minutes) and a reduction stirring speed of 5-20 rpm, preferably 7 rpm) to reduce the iron oxide in the roasted product to iron (iron reduction rate 70%-90%), thereby converting the waste into loose and porous rare earth oxides and iron, in preparation for subsequent carbonylation to extract iron and retain rare earth metals.

[0026] The purpose of the present invention is to remove iron from the raw material to enrich rare earths, and at the same time obtain gaseous pentahydroxy iron Fe(CO)5, and then pyrolyze Fe(CO)5 to obtain hydroxy iron powder. In this step, the activated loose and porous raw material is 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 into the reactor from above. The reaction time is 24-48 hours. During the reaction, the reactor changes CO gas 3-7 times per hour. During the reaction, an ultrasonic device with a power of 1-6 kW is placed in the reactor to promote the reaction of Fe and CO to generate pentacarbonyl iron Fe(CO)5 gas, and the conversion rate of iron element to pentacarbonyl iron is 60%-86%. The CO gas replaced from the reactor is dusted and cooled and condensed to obtain liquid carbonyl iron. Heating pentacarbonyl iron under low pressure conditions decomposes it into Fe(CO)5→ Fe+5CO, and carbonyl iron powder Fe and CO can be obtained, wherein CO can be returned to the carbonylation reactor or used for reduction treatment of rare earth waste in step 1. After the carbonylation reaction is completed, carbonylation slag enriched with rare earth will be obtained in the reactor.

[0027] The specific operation of extracting rare earth from the rare earth-enriched carbonyl slag of the present invention is: aging the rare earth-enriched carbonyl slag obtained in the second step in the air for 1 to 3 days (preferably 1 day), and then performing secondary oxidation roasting, while controlling the roasting temperature, time, etc. to prevent excessive sintering of the carbonyl slag, the roasting temperature is 550 to 750 ° C (preferably 550 to 560 ° C, more preferably 550 ° C), the oxygen partial pressure of the combustion-supporting air is 0.21 to 0.4 (preferably 0.21-0.25, more preferably 0.21), roasting for 10 to 45 minutes (preferably 20 to 30 minutes, more preferably 25 minutes), and the stirring speed of the furnace charge is 5 to 20 rpm (preferably 5 rpm); then the material is air-cooled, and the roasted product is ground to less than 100 mesh; then the rare earth in the enriched slag is leached with hydrochloric acid, the rare earth leaching rate is not less than 99.5%, and the amount of iron tailings after leaching is 350 to 600 kg / t rare earth secondary dry waste, the amount of iron tailings produced is only 40% to 60% of the iron tailings (760 to 840 kg / t rare earth secondary dry waste) generated by the conventional roasting-hydrochloric acid dissolution method to recover rare earth magnetic materials. The rare earth secondary dry waste in the present invention is the dry material after the water and oil are removed from the NdFeB waste.

[0028] The new technology for high-value iron and tailings reduction and recovery of multi-source NdFeB secondary resources described in the present invention is characterized by: activating the multi-source NdFeB secondary resources through oxidative roasting-reduction, with the aim of removing organic components in the waste, burning organic matter in the waste, and converting the waste into loose and porous rare earth oxides and iron, in preparation for subsequent carbonylation to extract iron and retain rare earth.

[0029] The invention discloses a new technology for high-value iron and tailings reduction and recovery of multi-source NdFeB secondary resources, characterized in that: the activated pre-treated raw materials are subjected to carbonylation treatment, and CO is selectively reacted with iron to generate pentacarbonyl iron Fe(CO)5 gas at a temperature of 150-200°C and a pressure of 5-20 MPa, preferably 12-15 MPa, and under the action of ultrasound, to achieve iron removal from the raw materials. The CO gas replaced from the reactor is subjected to dust removal and cooling condensation to obtain liquid pentacarbonyl iron, and the pentacarbonyl iron is heated under low pressure to decompose it, to obtain carbonyl iron powder Fe, and to achieve high-value iron recovery.

[0030] The invention discloses a new technology for increasing the iron value and reducing the tailings recovery of multi-source NdFeB secondary resources, characterized in that the rare earth-enriched carbonyl slag that may contain metallic iron is subjected to secondary oxidation roasting or aging treatment, the purpose of which is to regulate the oxide valence state and remove pentacarbonyl iron, so as to reduce the amount of sodium bicarbonate or acid used in the subsequent wet process for recovering rare earths.

[0031] Technical principle

[0032] Before the wet process of rare earth recovery, CO is first selectively reacted with iron in the activated raw material to generate pentacarbonyl iron gas, so as to separate iron from the raw material and obtain carbonyl slag enriched with rare earth elements. At the same time, the CO gas replaced from the reactor is cooled and condensed to obtain liquid pentacarbonyl iron Fe(CO)5. Then the pentacarbonyl iron is heated under low pressure to decompose it and obtain carbonyl iron powder Fe. 1) Activation treatment of raw materials: The raw materials are activated by oxidation and then reduction to remove organic components in the waste, and the waste is converted into loose and porous rare earth oxides and iron, in preparation for the subsequent carbonylation of iron and rare earth. 2) Carbonylation method for iron extraction: CO is used to react with iron to generate pentacarbonyl iron gas, so as to separate iron from the raw material and obtain carbonyl slag enriched with rare earth. Liquid pentacarbonyl iron is obtained by cooling and condensing, and can be heated and decomposed under low pressure to obtain carbonyl iron powder Fe, so as to achieve high-value recovery of iron. 3) Wet process to recover rare earths: After carbonylation, NdFeB-enriched rare earth slag is obtained. The carbonylation slag is first aged and then oxidized and roasted to make iron exist in the form of trivalent oxides. At the same time, the roasting temperature and time are controlled to prevent excessive sintering of the carbonylation slag. The hydrochloric acid solution method is used for selective leaching to dissolve the rare earth elements in the hydrochloric acid solution, and the residual iron and other elements remain in the slag. Since the second step of carbonylation iron extraction removes part of the iron in the waste (60%~86%), the iron content of the carbonylation enriched slag is lower, and the amount of iron tailings left after leaching the rare earth will be less.

[0033] Advantages of the present invention:

[0034] 1. Effectively reduce the generation of iron tailings; compared with the existing advanced roasting-hydrochloric acid excellent dissolution method for recovering rare earths, the rare earth leaching rate of the present invention is not less than 99.5%, and the amount of iron tailings after leaching is 350-600 kg / t rare earth secondary dry waste, while the amount of iron tailings in the conventional roasting-hydrochloric acid excellent dissolution method is 760-840 kg / t rare earth secondary dry waste, that is, the amount of iron tailings in the present invention is only 40%-60% of that in the conventional roasting-hydrochloric acid excellent dissolution method, or even lower.

[0035] 2. High-value recovery of iron elements has been achieved; 60%~86% of the iron elements in NdFeB magnetic waste can be prepared into high-value-added pentacarbonyl iron, or carbonyl iron powder Fe can be prepared by pyrolysis of pentacarbonyl iron. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0038] from Figure 1 It can be seen from a that the raw materials are activated by oxidation followed by reduction, the organic components in the waste are removed, and the waste is converted into loose and porous rare earth oxides and iron, in preparation for the subsequent carbonylation of iron and rare earth; under specific temperature, pressure and atmosphere, CO is used to react with iron to form pentacarbonyl iron gas, which separates iron from the raw materials and obtains carbonyl slag enriched in rare earths. Liquid pentacarbonyl iron Fe(CO)5 is obtained by cooling and condensing, and Fe(CO)5 is heated and decomposed under low pressure to obtain carbonyl iron powder Fe.

[0039] from Figure 1 It can be seen from b that the carbonyl slag enriched with rare earth is aged and oxidized and roasted to make iron exist in the form of trivalent oxides. At the same time, the roasting temperature and time are controlled to prevent excessive sintering of the carbonyl slag, so as to prepare for reducing the amount of leaching hydrochloric acid and improving the rare earth leaching rate when recovering rare earths by the subsequent hydrochloric acid optimal solution process. Then, the leachate is impurity-removed and extracted. The stripping solution is precipitated with ammonium bicarbonate, and then the raffinate is precipitated with oxalic acid or sodium carbonate to obtain rare earth chlorides, which are then calcined to obtain rare earth oxide products.

[0040] Figure 2 In the figure, (a) is the carbonyl iron powder Fe and particle size distribution diagram, and (b) is the XRD of carbonyl iron powder. Figure 2 It can be seen that the product has extremely high purity and uniform particle size distribution. DETAILED DESCRIPTION

[0041] The present invention is further described in detail below through specific implementation cases.

[0042] Example 1

[0043] 100 kg of oily NdFeB waste (i.e. raw material) is burned at a high temperature of 730 °C in the high temperature stage. Air and flue gas are used as combustion air with an oxygen partial pressure of 0.15, and water mist is continuously sprayed (the amount of water sprayed is 30 kg water / t raw material). The combustion process requires constant stirring (stirring speed is 3 rpm) to prevent sticking or local over-sintering. The roasting time is 12 minutes; then it enters the later roasting stage, the oxygen partial pressure of the combustion air is 0.21, the temperature is gradually reduced to 550 °C, and the water mist is gradually reduced during the cooling process until the spraying is stopped at 600 °C (the amount of water sprayed is 1 kg water / t rare earth waste), and the roasting is for 20 minutes, and the stirring speed of the charge is 5 rpm. Secondly, the oxidation product was air-cooled and ground to less than 60 mesh, and then reduced at 700 °C using a CO / H2 / NH3 mixed gas (gas content CO: H2: NH3 = 10.5: 1: 1), the reduction time was 50 minutes, and the reduction stirring speed was 7 rpm, so that the iron oxide in the roasted product was reduced to iron (metallization rate of iron was 80%), thereby converting the waste into loose porous rare earth oxides and iron. The activated loose porous raw material was placed in a reactor, and CO gas (containing 1.5% NH3 + 1.5% H2 + 0.5% H2S in the gas) with a temperature of 170 °C and a pressure of 15 MPa was introduced into the reactor from top to bottom. The reaction time was 36 hours, and the CO gas was replaced 3 times per hour during the reaction. During the reaction, a power of 2 kW ultrasonic device to generate pentacarbonyl iron gas, and the conversion rate of iron in rare earth waste to carbonyl iron is 69%. The CO gas replaced from the reactor is cooled and condensed to obtain liquid pentacarbonyl iron; the pentacarbonyl iron is heated under low pressure to decompose it, and the following is obtained: Figure 2 a Carbonyl iron powder Fe ( Figure 2 b is 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 is completed, the reactor will obtain carbonyl slag enriched with rare earth. The obtained carbonyl slag enriched with rare earth is placed in air for aging for 1 day, and then subjected to secondary oxidation roasting, the roasting temperature is 550 ℃, the oxygen partial pressure of the combustion air is 0.21, the roasting time is 35 minutes, and the stirring speed of the charge is 5 rpm; then the material is air-cooled, and the roasting product is ground to less than 100 mesh; then the rare earth in the enriched slag is leached with hydrochloric acid, the rare earth leaching rate is 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 increasing the iron value of multi-source NdFeB secondary resources and reducing tailings recovery, characterized in that The steps include: Step 1: Activation of raw materials: using NdFeB waste as raw materials, the raw materials are activated by oxidation followed by reduction, the oxidation temperature is controlled at 700-850°C, and the reduction temperature is 300-800°C, so that more than 70wt% of the iron oxides generated during the oxidation process are reduced to obtain activated materials; Step 2: Carbonylation to extract iron and retain rare earth; using the activated material level treatment object obtained in step 1, using CO to react with iron to generate pentacarbonyl iron gas, achieving separation of iron from raw materials, and obtaining carbonyl slag enriched in rare earth; obtaining liquid pentacarbonyl iron by cooling and condensing, achieving high-value recovery of iron; when using CO to react with iron to react with carbonylation, controlling the pressure of the reaction gas containing CO after being introduced into the reactor to be 5-20 MPa and the temperature to be 120-200°C; Step 3: extracting rare earth from the rare earth-enriched carbonyl slag; subjecting the rare earth-enriched carbonyl slag to aging treatment and oxidative roasting, so that the iron exists in the form of trivalent oxide.

2. The method for increasing the iron value and reducing the tailings recovery of multi-source NdFeB secondary resources according to claim 1 is characterized by: Using NdFeB waste as raw material, the raw material is subjected to early oxidation roasting and late oxidation roasting; specifically including: First, the preliminary oxidation roasting is carried out: the temperature is controlled at 700-850℃, combustion-supporting air is introduced and the oxygen partial pressure in the combustion-supporting air is controlled to be 0.1-0.21, and water mist is continuously sprayed at a rate of 5-200 kg water / t raw material, and stirring is performed to prevent adhesion or local over-sintering, and the roasting time is 10-45 minutes; Then, the post-oxidation roasting is carried out: the oxygen partial pressure of the combustion-supporting air is adjusted to 0.1-0.4 and the temperature is lowered to 500-600°C. During the cooling process, the water mist spraying is reduced until the water mist spraying is stopped at 600°C. The roasting time is controlled at 10-45 minutes, and the stirring speed of the charge is 5-20 rpm, so that the rare earth in the raw material is fully oxidized; and an oxidation product is obtained.

3. The method for increasing the iron value and reducing the tailings recovery of multi-source NdFeB secondary resources according to claim 1 is characterized by: The oxidation product is cooled and ground to less than 60 mesh, and then reduced using a CO / H2 / NH3 mixed gas at 300-800°C for 50-120 minutes with stirring to reduce the iron oxide in the calcined product to iron with a reduction rate of 70%-90%, thereby obtaining rare earth oxides and iron.

4. The method for increasing the iron value and reducing tailings recovery of multi-source NdFeB secondary resources according to claim 1, characterized in that: In step 1, 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 increasing the iron value and reducing the tailings recovery of multi-source NdFeB secondary resources according to claim 1 is characterized by: In step 2, when the carbonylation reaction is carried out, the CO reaction gas contains NH3 at a molar ratio of 0-10%, H2 at a molar ratio of 1-5%, and H2S at a molar ratio of 0-3%.

6. The method for increasing the iron value and reducing the tailings recovery of multi-source NdFeB secondary resources according to claim 1 is characterized by: In step 2, the reaction time for synthesizing pentacarbonyl iron by carbonyl reaction is 24 to 48 hours, and the CO gas in the reactor is replaced 3 to 7 times per hour during the reaction.

7. The method for increasing the iron value and reducing the tailings recovery of multi-source NdFeB secondary resources according to claim 1 is characterized by: During the process of synthesizing pentacarbonyl iron by carbonyl reaction, ultrasonic waves with a power of 1 to 6 kW are introduced.

8. The method for increasing the iron value and reducing the tailings recovery of multi-source NdFeB secondary resources according to claim 1 is characterized by: The obtained rare earth-enriched carbonyl slag is placed in the air for aging for 1 to 3 days, and then subjected to secondary oxidation roasting to make iron exist in the form of trivalent oxides, while controlling the roasting temperature, time, etc. to prevent excessive sintering of the carbonyl slag; the roasting temperature is 550 to 750°C, the oxygen partial pressure of the combustion-supporting air is 0.21 to 0.4, the roasting time is 10 to 45 minutes, and the stirring speed of the charge is 5 to 20 revolutions per minute; the material is then air-cooled, and the roasted product is ground to less than 100 meshes; the rare earth in the enriched slag is then leached with hydrochloric acid, and the rare earth enters the solution. After leaching, the remaining dissolved iron tailings are 350 to 600 kg / t of raw material.

9. The method for increasing the iron value and reducing the tailings recovery of multi-source NdFeB secondary resources according to claim 1 is characterized by: The conversion rate of iron in the raw material into pentacarbonyl iron is 60%~86%.

10. The method for increasing the iron value and reducing the tailings recovery of multi-source NdFeB secondary resources according to claim 7, characterized in that: The rare earth leaching rate is not less than 99.5%.

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