Method and system for recovering rare earth elements from neodymium iron boron waste and preparing iron-based alloy

Abstract

The invention discloses a method and system for recovering rare earth elements from neodymium iron boron waste and preparing an iron-based alloy. The method comprises the steps that S01, powder, sludge, acid leaching residues and block materials are separated from the neodymium iron boron waste; s02, the powder, the sludge or the acid leaching residues are subjected to compatibility, then auxiliary materials are added to form a mixed material, then an adhesive and a carbonaceous reducing agent are added, and the material is subjected to pelletizing; s03, feeding the prepared pellets into a solid-state reduction roasting furnace for pre-reduction roasting; s04, the roasted ball material is subjected to secondary burdening, and a block material obtained after neodymium iron boron waste material sorting, an auxiliary material and a carbonaceous reducing agent are added to form a mixture; and S05, the mixture is fed into a non-standard special reduction electric furnace to be subjected to solid-state and molten-state reduction smelting and slag iron dissolution, and rare earth oxide enters a slag phase after separation. According to the scheme, the grade of rare earth elements contained in the neodymium iron boron waste or the oxidation pollution degree of the rare earth elements can be treated at one time at the same time, the applicability is high, the added value of the obtained iron-based alloy product is far higher than that of other single steel products, the rare earth element recovery rate is larger than or equal to 98%, and high-value efficient utilization of the waste is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of comprehensive utilization of solid waste resources, and in particular to a method and system for recovering rare earth elements from NdFeB waste and preparing an iron-based alloy. Background Art

[0002] Neodymium iron boron permanent magnets (REEM) are mainly composed of three elements: neodymium, iron and boron. During the manufacturing process, in order to improve the high-temperature characteristics of the magnet, a small amount of terbium (Tb) or dysprosium (Dy) is added. Sometimes a small amount of praseodymium (Pr) is added to replace neodymium. In order to improve the performance of the magnet, transition metals such as cobalt are also added.

[0003] The wet recovery process is a metallurgical process that separates rare earth elements from transition metal elements by controlling the stability of the elements in the solution, using chemical solvents, and relying on chemical reactions. The purity of rare earth products produced by the wet process is relatively high, and the process is relatively mature. It is currently the mainstream recovery process in China. However, the wet process requires a large amount of chemical agents such as acid, a large amount of waste liquid discharge, a long process flow, serious pollution, and a low recovery rate of transition metal elements. If wet electrolysis is used, the comprehensive energy consumption is high and the cost is high. Fire recovery is adopted. Fire recovery has a large processing capacity and a relatively short process flow. It is environmentally friendly and can select different processes to obtain different rare earth products and corresponding transition metal products. It has a good application prospect. However, the technical difficulties that the fire process needs to overcome are: (1) simultaneous processing of waste materials of different temperatures; (2) reasonable selection of reducing agents and oxidizing agents and accurate control of transition metal products; (3) design and selection of fire metallurgical equipment required for the recovery of rare earth elements and transition metal elements. Only by solving the above technical difficulties can the fire process achieve industrial-scale production.

[0004] The existing typical pyrometallurgical process technology is: Chinese invention patent CN108359798A discloses "A method for rapid and efficient recycling of NdFeB waste". The steps are: collecting NdFeB magnet waste and dividing it into block and powder waste, wherein the oil sludge in the powder waste is pre-treated, the powder waste is pressed into blocks and then loaded into the furnace, and a deoxidizer is added according to the ratio of powder to block. The rare earth metals in the block waste and the deoxidizer are used to smelt, reduce and deoxidize the oxides of other alloy elements in the waste except rare earth. The smelting and reduction can be carried out in a medium frequency induction furnace or an arc furnace. After the smelting is completed, an iron alloy product and slag are obtained; the slag is crushed and then subjected to molten salt electrolysis to obtain mixed rare earth metals or rare earth iron alloys. The main shortcomings of this method are: (1) The powder components of the waste contain some rare earth metals and some oxidized rare earth elements and transition metal Fe oxides, so it is difficult to accurately determine the amount of oxidant added, and the control requirements for the impurity components of the waste are high, and the added value of the iron element after recovery is low. (2) If the powder content exceeds 50%, rare earth metals or calcium or aluminum must be added as deoxidizers, which increases the production cost. (3) The utilization of waste has certain limitations (especially for waste powders with relatively serious oxidation and some sodium iron borate leaching residues with low rare earth content, which are basically unusable); (4) The metallurgical equipment selected by this technology, the medium frequency furnace and the electric arc furnace, both have defects in the smelting redox reaction process. The reason is that the medium frequency furnace and the electric arc furnace are both metal smelting equipment. When the metal oxide content in the waste is high, the amount of smelting furnace slag is large and easy to corrode the furnace lining. In addition, the operation is intermittent open arc operation, which has poor effect on the oxide reduction reaction, low recovery rate, low production efficiency, and is difficult to achieve large-scale continuous production.

[0005] Chinese invention patent CN104087755A discloses a method for recovering rare earth elements from NdFeB waste. The invention comprises the following steps: (1) mixing alumina powder and cryolite powder in a mass ratio of 1:1 to 1:10 to obtain a cryolite-alumina mixture; (2) crushing the NdFeB waste into particles with a particle size of 4 to 6 mm and burying them in the cryolite-alumina mixture; (3) placing the cryolite-alumina mixture buried with the NdFeB waste in an electric furnace and reacting it at a temperature of 900°C to 1200°C for 3 to 12 hours; (4) subjecting the reaction product to solid-liquid separation to obtain a solid residue and a molten salt, respectively. The solid residue is scrap steel, and the molten salt is a mixture of rare earth oxides, cryolite, and alumina. Compared with the above-mentioned invention patent CN108359798A, this method has low requirements for the selection of NdFeB waste materials and can even process NdFeB waste acid leaching residue with low rare earth content and high iron oxide content. However, the main disadvantages are that the utilization value of the transition element iron is low, and the rare earth slag after enrichment is affected by the introduction of aluminum oxide and cryolite impurities, which affects the enrichment effect of rare earth oxides and reduces the content of released earth oxides. Moreover, in order to separate the rare earth oxides from the rare earth slag, it is also necessary to remove oxides such as aluminum and sodium in the mixture, and a high-quality rare earth oxide product cannot be obtained at one time.

[0006] Chinese invention patent CN118389862A discloses a "process for extracting rare earth elements from NdFeB waste and discarded iron slag". The invention mainly includes the following steps: adding iron slag to a binder, then adding pulverized coal, continuing to use a pelletizing machine to make balls, and then using a sintering machine to sinter the balls to obtain a primary material A, putting the primary material A and coke into an electric furnace for smelting, respectively releasing molten iron and smelting slag during smelting, cooling the molten iron into blocks and sending them to a steel plant, and using the smelting slag as a carrier for enriching rare earths; crushing the smelting slag, then decomposing it with industrial hydrochloric acid, filtering, removing impurities, and precipitating it, and then adding industrial oxalic acid to obtain rare earth oxalate; ... the total recovery rate of rare earths reaches more than 80%. From the patent of this invention, It can be seen from the claims and the invention that the waste material processed by the invention is actually the iron slag discarded during the wet recovery process of NdFeB waste, containing Fe2O3 ≥ 70% and rare earth oxide REO between 0.3 and 1%. The invention pelletizes the iron slag and sintering it at a temperature of 300-400°C, and then directly sends it to a conventional electric furnace for molten reduction to remove iron. The smelting temperature is 1400-1500°C (molten reduction temperature), and the sintering is mixed with coal in a weight ratio of iron slag: pulverized coal = 700-900: 50-70; the electric furnace smelting is mixed with coke in the ratio of initial material A: coke = 40%-50%; the mass ratio of molten iron to smelting slag in the invention is: 1:0.2-0.4, and the iron slag contains iron (Fe2O3) ≥ 70%.

[0007] According to common sense, after each ton of iron slag is smelted in an electric furnace, based on a 90% recovery rate of rare earth oxides and a rare earth oxide content of 0.5% in the iron slag entering the furnace, 9 kg of rare earth oxides can be recovered from two tons of iron slag. After smelting and enrichment, the rare earth slag is 400-800 kg, and the converted percentage of rare earth oxides in the smelting slag is 1.125%-2.25%.

[0008] Obviously, the invention still has several major technical defects as follows:

[0009] (1) Since the REO content of the rare earth slag after the above-mentioned electric furnace smelting enrichment is only 1.125%-2.25%, it would be unprofitable to use wet processing to treat such a low rare earth content. Since the lowest rare earth oxide content REO of the smelting waste slag after wet separation is ≥3.5%, continuing wet separation has no economic value.

[0010] (2) The coke consumption of this scheme is extremely high. In terms of consumption in electric furnace smelting, the initial material A:coke = 40% to 50%, which is 70% higher than the more reasonable coke consumption of 12% to 15% in electric furnace ironmaking. This makes electric furnace smelting costly and unsuitable for production.

[0011] (3) The iron slag used in the invention is actually the acid leaching slag from the wet recovery process of NdFeB waste. The S and P impurities in it exceed the standard. The iron blocks produced can only be sold to steel mills as scrap iron without desulfurization and dephosphorization treatment. Compared with the national standard pig iron, the price is only 40% off, thereby reducing iron revenue by 40%. Therefore, the invention has no practical significance in terms of economic value and process technology.

[0012] The main reason for the high coke consumption in smelting of this invention is that the sintering temperature in the slag sintering stage is only 300-400℃, which wastes coking coal and cannot sinter the ball material, and can only achieve a drying effect. Therefore, the strength of the initial material A is poor, and it is quickly pulverized when sent to the electric furnace for reduction. The permeability of the electric furnace causes the reduction reaction to be incomplete. The main reason why the block iron product of this invention does not meet the standards is that the corresponding auxiliary raw materials or the molten iron are not added according to the requirements of the iron product or the impurity removal and refining treatment are not carried out. The REO recovery rate in the rare earth slag is low, the grade is low, and the smelting power consumption is high. It is simply molten reduction at a high temperature of 1400-1500 in the electric furnace without a scientific formula, resulting in high overall cost and low profit.

[0013] In summary, although the pyrometallurgical process for recovering rare earth elements from NdFeB waste has the advantages of relatively shorter process flow, larger processing capacity and less environmental pollution compared with the hydrometallurgical process, the technical problems that need to be solved in view of the shortcomings of the existing pyrometallurgical process technology are:

[0014] (1) Further reduce energy consumption, especially electricity consumption and coke consumption;

[0015] (2) Improve the recovery rate of rare earth elements. The smelting slag must be enriched to at least 10% REO;

[0016] (3) Rationally and scientifically combine waste materials of different contents and supplement them with corresponding auxiliary materials to prepare transition metal alloy products with higher added value, thereby reducing production costs and increasing benefits. Only by solving the above technical problems can the pyrometallurgical process achieve industrial-scale production. Summary of the Invention

[0017] In view of this, the purpose of the present invention is to provide a technical solution with strong applicability, reliable implementation, high output, high rare earth element recovery rate, low energy consumption, low production cost, and industrial-scale production.

[0018] In order to achieve the above technical objectives, the technical solution adopted by the present invention is:

[0019] A method for recovering rare earth elements from NdFeB waste and preparing an iron-based alloy, comprising:

[0020] S01. Sorting NdFeB waste into powder, sludge, acid leaching residue, block material, etc. and stacking them separately, and detecting the chemical composition of each material respectively;

[0021] S02. First, determine the brand and quality requirements of the iron-based alloy product to be prepared based on the chemical composition of each material. According to the required conditions, mix one or more of the powder, sludge, and acid leaching residue, then add auxiliary materials to form a mixture. Then, add a binder and a carbonaceous reducing agent, and form the materials into balls to obtain balls.

[0022] S03. The prepared pellets are fed into an electric heating solid state reduction roasting furnace or other non-electric heating solid state reduction roasting equipment for solid state reduction roasting at a temperature of 800°C to 1000°C; the roasting time is 1.5 to 4 hours per furnace; and the solid state reduction rate is ≥50%;

[0023] S04, the calcined ball material is subjected to secondary batching, by adding the block material after sorting the NdFeB waste material, the auxiliary material and the carbonaceous reducing agent to obtain a mixed material;

[0024] S05. The prepared mixture is sent into a special electric furnace with non-standard design that can carry out solid, molten, gaseous and melt reduction reactions for smelting. The smelting time is 3 to 8 hours, and finally the slag and iron are tapped.

[0025] As a possible implementation method, further, in the present solution S01, the selected block materials are crushed to produce materials with a particle size of 10 to 40 mm.

[0026] As a possible implementation method, further, this solution S02 also includes: sorting out the powder, sludge, and acid leaching residue, and determining the output iron-based alloy product based on chemical composition analysis (based on the analysis data, first calculating the combination of the powder, sludge, and acid leaching residue, and then calculating the amount of auxiliary materials to be added according to the requirements of the iron-based alloy product, and adding the auxiliary materials to form a mixture), and combining one or more of the powder, sludge, and acid leaching residue.

[0027] As a preferred embodiment, preferably, in this solution S02, the carbonaceous reducing agent is coke powder or anthracite, and its fixed carbon content is greater than 80%, and the binder is an organic binder.

[0028] As a preferred embodiment, preferably, in this solution S02, the addition ratio of the mixture, carbonaceous reducing agent and adhesive is 100:3~8:3~5; before making balls, if the moisture content of the material exceeds the standard, the material needs to be dried to control the moisture content between 10% and 15%; the particle size of the ball material is 10~40mm.

[0029] As a preferred embodiment, preferably, in this scheme S04, the dry weight ratio of the added balls, blocks and carbonaceous reducing agent is: balls: blocks: reducing agent 70-115:0-30:8-14; the carbonaceous reducing agent is one or a combination of more than one of coke pellets, blue carbon or anthracite blocks; in this step, auxiliary materials can be added as needed, and the selection and addition amount of auxiliary materials need to be selected and calculated based on the transition metal element composition in the waste and the requirements of the iron-based alloy product.

[0030] As a preferred embodiment, preferably, in this scheme S05, the normal smelting temperature of the non-standard special reduction electric furnace is 700-1500°C, including: 700-1000°C in the solid reduction zone; 1000-1500°C in the "molten reduction" and melting zone (the maximum adjustable temperature range of the molten reduction and melting zone is 1700°C).

[0031] Among them, the prepared materials are sent to the reduction electric furnace for smelting, and solid-state and molten-state reduction reactions of the materials and slag and iron melting are carried out simultaneously in the electric furnace, so that the transition metal elements are reduced to the required iron-based alloy, and the rare earth oxides enter the slag phase.

[0032] In terms of smelting time in S05, the smelting time is determined according to the capacity of the electric furnace, which includes the following:

[0033] (1) For large electric furnaces (capacity ≥ 12500KVA), the smelting time is 3 to 4 hours, the slag is discharged in 2.5 to 3 hours, and the iron is discharged in 3 to 4 hours;

[0034] (2) The smelting time of medium-sized and above electric furnaces (capacity ≥ 6000KVA) is 4 to 6 hours, slag is discharged in 3 to 3.5 hours, and iron is discharged in 4 to 6 hours;

[0035] (3) The smelting time of a small electric furnace (capacity ≤ 6000KVA) is 6 to 8 hours, and slag and iron can be produced at the same time.

[0036] As a preferred embodiment, this solution also preferably includes:

[0037] S06, that is, during the slag discharge operation, after the material is smelted in the electric furnace, the rare earth oxides enter the slag phase, the slag outlet is opened to discharge the slag, and the slag is flushed into the slag pool through the flow channel for water crushing. After water crushing, the slag is ball milled to more than 200 mesh, and after magnetic separation to remove iron, the rare earth slag is packaged and stored.

[0038] The iron-based alloy obtained by tapping is discharged from the tapping hole into the ladle to obtain crude molten iron. The molten iron is decarburized by bottom blowing or fed into the AOD furnace for refining, decarburization and dephosphorization. The product composition can be adjusted according to the preset product standards or index requirements.

[0039] In addition, the refined molten iron is cast into ingots, and the ingot products are cooled, finished, packaged and stored.

[0040] Based on the above process method, this solution also provides a system for recovering rare earth elements from NdFeB waste and preparing iron-based alloys, which includes a waste sorting unit, a waste pretreatment unit, a waste solid-state pre-reduction unit, an electric furnace smelting unit, a rare earth oxide recovery unit, and an iron-based alloy preparation unit connected in sequence.

[0041] As a preferred embodiment, preferably, the waste sorting unit of this solution includes a cleaning machine, a sorting machine, and a crusher connected in sequence.

[0042] The waste pretreatment unit includes a drying machine, a batching machine and a pelletizing machine which are connected in sequence.

[0043] The waste solid-state reduction unit includes: an electrically heated solid-state reduction roasting furnace and its associated supporting facilities, or any other equipment and supporting facilities that can be used for solid-state reduction of materials.

[0044] The electric furnace smelting and melting unit includes: an electric furnace batching machine, a special reduction furnace with non-standard design that can be used for solid, molten, and gaseous carbon thermal reduction and slag iron melting, as well as supporting slag iron separation facilities and flue gas purification and dust removal facilities.

[0045] The rare earth oxide recovery unit includes rare earth slag water crushing and grinding machine, and electromagnetic separation equipment.

[0046] The iron-based alloy preparation unit includes: a tapping device, a molten iron decarburization device, a dephosphorization device and a molten iron conditioning and refining device.

[0047] Furthermore, the special reduction furnace is a special reduction furnace that can be used for solid, molten, gaseous carbon thermal reduction and slag iron smelting, and it should meet the following basic design requirements:

[0048] (1) The current-voltage ratio of the electric furnace is A / V = 230 ~ 400A / V;

[0049] (2) The power density per unit area of ​​the molten high-temperature reduction reaction zone is P1=1200KW / M2;

[0050] (3) Furnace power density per unit area P2 = 230KW ~ 350 / KW / M2;

[0051] (4) Furnace unit volume power density P3 = 80KW ~ 100 / KW / M2;

[0052] (5) The furnace depth should be 1.1 to 1.3 times deeper than the conventional theoretical calculation, taking into account the special characteristics of the product being refined, such as the thicker hot material layer.

[0053] Furthermore, the electric furnace can be either an AC furnace or a DC furnace, provided that the above basic parameters are met. Idle submerged arc furnace equipment can also be modified for use in this system.

[0054] In terms of the connection between the various units of the system: the waste sorting unit, waste pretreatment unit, waste solid pre-reduction unit, and electric furnace smelting and melting unit are connected in sequence through belt conveyors, and the electric furnace smelting and melting unit is connected to the rare earth oxide recovery unit and the iron-based alloy preparation unit through slag troughs and rail iron-out flat cars respectively.

[0055] Compared with the prior art, the technical solution of the method and system for recovering rare earth elements from NdFeB waste and preparing iron-based alloys has the following beneficial effects:

[0056] (1) This solution is not limited to the rare earth element grade or oxidation contamination degree of NdFeB waste (including transition metal elements) and can be processed at one time, with strong applicability;

[0057] (2) The composition of the iron-based alloy products obtained by this solution can be precisely controlled according to customer needs and national standards. The added value of the iron-based alloy products is much higher than that of other single steel products, achieving high-value utilization of transition metal elements in waste materials;

[0058] (3) Since the temperature of the "solid-state reduction" of metal oxides in the carbon thermal reduction process is about 400°C lower than that of the "molten reduction" reaction, the technical solution system of the present invention adopts a "solid-state reduction" technology unit configured at the front end of the electric furnace smelting, so that about 50% or more of the metal oxides, especially iron oxide, of the material are basically reduced. At the same time, about 30% of the material is "solid-state reduced" by the CO gas generated by the combustion of coke in the electric furnace in the special reduction furnace, and only about 20% of the material actually undergoes the "molten reduction" reduction reaction in the electric furnace. Therefore, the smelting power consumption and coke consumption are greatly reduced, and the smelting cost can be saved by about 40% compared with the existing technology, and industrial-scale production can be carried out;

[0059] (4) Recovery rate of rare earth elements: Since the specially designed reduction furnace is a metallurgical special equipment suitable for enriching rare earth oxides, the temperature can be controlled by controlling the input power, and the temperature condition for the redox of rare earth oxides is greater than 1900°C. The temperature range of the electric furnace for the molten reduction reaction of the present invention is controlled at 1000-1500°C, and the maximum will not exceed 1600°C. With such a large temperature difference, theoretically, 100% of the rare earth oxides will enter the slag phase. However, after deducting the losses in each process link, the recovery rate of rare earth elements is at least 98%, which is much higher than the existing technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the present invention, the drawings required for the embodiments or the technical solutions of the present invention will be briefly described below. Obviously, the drawings are merely some supplementary explanations of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0061] Figure 1 This is a schematic diagram of a simplified implementation process of the method for recovering rare earth elements from NdFeB waste and preparing an iron-based alloy according to the present invention;

[0062] Figure 2 This is a schematic diagram of the unit module connection of the system for recovering rare earth elements from NdFeB waste and preparing iron-based alloys in this scheme;

[0063] Figure 3 This is a schematic diagram of the structural principle of the non-standard reduction electric furnace in this system. DETAILED DESCRIPTION

[0064] The present invention will be described in further detail below with reference to the accompanying drawings and examples. It is particularly noted that the following examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. Similarly, the following examples are only some embodiments of the present invention and are not intended to be exhaustive. All other embodiments obtained by those of ordinary skill in the art without creative effort are intended to fall within the scope of protection of the present invention.

[0065] Figure 1 This is a schematic diagram of a simplified implementation process of the method for recovering rare earth elements from NdFeB waste and preparing an iron-based alloy according to the present invention; Figure 2 This is a schematic diagram of the unit module connection of the system for recovering rare earth elements from NdFeB waste and preparing iron-based alloys in this scheme.

[0066] This invention provides a method for recovering rare earth elements from NdFeB waste and preparing an iron-based alloy, which comprises:

[0067] S01. Sorting NdFeB waste into powder, sludge, acid leaching residue, magnetic blocks, etc. and stacking them separately, while detecting the chemical composition of each material;

[0068] S02. First, determine the brand and quality requirements of the iron-based alloy product to be prepared based on the chemical composition of each material. According to the required conditions, mix one or more of the powder, sludge, and acid leaching residue, then add auxiliary materials to form a mixture. Then, add a binder and a carbonaceous reducing agent, and form the materials into balls to obtain balls.

[0069] S03. The prepared pellets are fed into an electric heating solid-state reduction roasting furnace or other non-electric heating solid-state reduction roasting furnace for solid-state reduction roasting at a temperature of 800°C to 1000°C; the roasting time is 1.5 to 4 hours per furnace; and the solid-state reduction rate is ≥50%;

[0070] S04, the calcined ball material is subjected to secondary batching, by adding the block material after sorting the NdFeB waste material, the auxiliary material and the carbonaceous reducing agent to obtain a mixed material;

[0071] S05. The prepared mixture is sent into a special electric furnace with non-standard design that can carry out solid, molten, gaseous and melt reduction reactions for smelting. The smelting time is 3 to 8 hours, and finally the slag and iron are tapped.

[0072] In the present solution S01, the selected bulk materials are further crushed to produce materials with a particle size of 10 to 40 mm.

[0073] This solution S02 also includes: sorting the powder, sludge, and acid leaching residue, and determining the output iron-based alloy product based on chemical composition analysis (based on the analysis data, first calculating the compatibility of the powder, sludge, and acid leaching residue, and then calculating the amount of auxiliary materials to be added according to the requirements of the iron-based alloy product, and adding the auxiliary materials to form a mixture), and mixing one or more of the powder, sludge, and acid leaching residue.

[0074] In this solution S02, the carbonaceous reducing agent is coke powder or anthracite, and its fixed carbon content is greater than 80%, and the binder is an organic binder.

[0075] In this scheme S02, the addition ratio of the mixture, carbonaceous reducing agent and adhesive is 100:3~8:3~5; before making balls, if the moisture content of the material exceeds the standard, the material needs to be dried to control the moisture content between 10% and 15%; the particle size of the ball material is 10~40mm.

[0076] In this solution S04, the dry weight ratio of the added balls, blocks and carbonaceous reducing agent is: balls: blocks: reducing agent 70-115:0-30:8-14; the carbonaceous reducing agent is one or a combination of more than one of coke pellets, blue carbon or anthracite blocks; in this step, auxiliary materials can be added as needed, and the selection and addition amount of auxiliary materials need to be selected and calculated based on the transition metal element composition in the waste and the requirements of the iron-based alloy product.

[0077] In this scheme S05, the normal smelting temperature of the non-standard special reduction electric furnace is 700-1500℃, including: 700-1000℃ in the solid reduction zone; 1000-1500℃ in the "molten reduction" and melting zone (the maximum adjustable temperature range of the molten reduction and melting zone is 1600℃).

[0078] Among them, the prepared materials are sent to the reduction electric furnace for smelting, and solid-state and molten-state reduction reactions of the materials and slag and iron melting are carried out simultaneously in the electric furnace, so that the transition metal elements are reduced to the required iron-based alloy, and the rare earth oxides enter the slag phase.

[0079] In terms of smelting time in S05, the smelting time is determined according to the capacity of the electric furnace, which includes the following:

[0080] (1) For large electric furnaces (capacity ≥ 12500KVA), the smelting time is 3 to 4 hours, the slag is discharged in 2.5 to 3 hours, and the iron is discharged in 3 to 4 hours;

[0081] (2) The smelting time of medium-sized and above electric furnaces (capacity ≥ 6000KVA) is 4 to 6 hours, slag is discharged in 3 to 3.5 hours, and iron is discharged in 4 to 6 hours;

[0082] (3) The smelting time of a small electric furnace (capacity ≤ 6000KVA) is 6 to 8 hours, and slag and iron can be produced at the same time.

[0083] As a preferred embodiment, this solution also preferably includes:

[0084] S06, that is, during the slag discharge operation, after the material is smelted in the electric furnace, the rare earth oxides enter the slag phase, the slag outlet is opened to discharge the slag, and the slag is flushed into the slag pool through the flow channel for water crushing. After water crushing, the slag is ball milled to more than 200 mesh, and after magnetic separation to remove iron, the rare earth slag is packaged and stored.

[0085] The iron-based alloy obtained by tapping is discharged from the tapping hole into the ladle to obtain crude molten iron. The molten iron is decarburized by bottom blowing or fed into the AOD furnace for refining, decarburization and dephosphorization. The product composition can be adjusted according to the preset product standards or index requirements.

[0086] In addition, the refined molten iron is cast into ingots, and the ingot products are cooled, finished, packaged and stored.

[0087] Combine Figure 2 Based on the above process method, this solution also provides a system for recovering rare earth elements from NdFeB waste and preparing iron-based alloys, which includes a waste sorting unit, a waste pretreatment unit, a waste solid-state pre-reduction unit, an electric furnace smelting unit, a rare earth oxide recovery unit, and an iron-based alloy preparation unit connected in sequence.

[0088] The waste sorting unit described in this solution includes a cleaning machine, a sorting machine, and a crusher connected in sequence.

[0089] The waste pretreatment unit includes a drying machine, a batching machine and a pelletizing machine which are connected in sequence.

[0090] The waste solid-state reduction unit includes: an electrically heated solid-state reduction roasting furnace and its associated supporting facilities, or any other equipment and associated facilities that can be used for solid-state reduction of materials.

[0091] The electric furnace smelting and melting unit includes: an electric furnace batching machine, a special reduction furnace with non-standard design that can be used for solid, molten, and gaseous carbon thermal reduction and slag iron melting, as well as supporting slag iron separation facilities and flue gas purification and dust removal facilities.

[0092] The rare earth oxide recovery unit includes rare earth slag water crushing and grinding machine, and electromagnetic separation equipment.

[0093] The iron-based alloy preparation unit includes: a tapping device, a molten iron decarburization device, a dephosphorization device and a molten iron conditioning and refining device.

[0094] Furthermore, the special reduction furnace is a special reduction furnace that can be used for solid, molten, gaseous carbon thermal reduction and slag iron smelting, and it should meet the following basic design requirements:

[0095] (1) The current-voltage ratio of the electric furnace is A / V = 230 ~ 400A / V;

[0096] (2) The power density per unit area of ​​the molten high-temperature reduction reaction zone is P1=1200KW / M2;

[0097] (3) Furnace power density per unit area P2 = 230KW ~ 350 / KW / M2;

[0098] (4) Furnace unit volume power density P3 = 80KW ~ 100 / KW / M2;

[0099] (5) The furnace depth should be 1.1 to 1.3 times deeper than the conventional theoretical calculation, taking into account the special characteristics of the product with a thick hot material layer.

[0100] Furthermore, the electric furnace can be either an AC furnace or a DC furnace, provided that the above basic parameters are met. Idle submerged arc furnace equipment can also be modified for use in this system.

[0101] Figure 3 This is a schematic diagram of the structural principle of the non-standard reduction electric furnace in this scheme system; it can be seen that the reduction reaction of the charge in the furnace can be divided into a molten iron layer, a rare earth smelting slag layer, a coke layer, a solid reduction layer, and a charge preheating layer from bottom to top, and the temperature can be divided into: a molten iron layer of 1450°C, a slag layer of 1400°C, and a coke combustion molten reduction layer of 1000-1500°C. The molten reduction reaction of the material and the gasification of the coke combustion produce carbon monoxide and slag-iron fusion, and the carbon monoxide rises to the charge hot zone to participate in the solid reduction reaction at a temperature of 700-1000°C. The high-temperature flue gas generated by the solid-state reduction in the hot zone rises to the charge preheating zone, and the preheated charge temperature is 200-700°C.

[0102] The following further illustrates this solution with reference to a number of examples.

[0103] Example 1

[0104] This embodiment takes the resource recovery of several common NdFeB waste materials as an example, the amount of which is 100 tons, including 40% grinding sludge (including oil sludge), 35% magnet powder, and 25% magnet block material, to recover rare earth elements, so as to further illustrate the present invention and the system. The main chemical components and proportions of several common NdFeB waste materials are shown in Table 1 below.

[0105] Table 1 Main chemical composition and proportion of several common NdFeB waste materials

[0106]

[0107]

[0108] According to the chemical composition characteristics of the transition metal elements in the waste in Table 1, the production of ferroboron alloy products from this waste is most efficient, so the brand of ferroboron alloy products and the national standard quality requirements are determined first.

[0109] The product composition control of the ferroboron alloy in this embodiment is shown in Table 2 below.

[0110] Table 2 Product composition control table of ferroboron alloy

[0111]

[0112] According to the requirements of Table 1 and Table 2, and based on the waste material ratio in Table 1, it is calculated that 40 kg of boric anhydride (all on dry basis) is required as an auxiliary material for every 100 kg of mixed waste.

[0113] Among them, the boric anhydride content: B2O3≧96% (boric anhydride is added compared with boron ore mainly to reduce the impurity content, so as to better ensure the content grade of REO in the recovered slag).

[0114] The specific process steps of this embodiment are:

[0115] Step 1: sort the NdFeB waste into sludge, powder, block (magnetic block), acid leaching residue, and then prepare auxiliary materials such as boric anhydride, reducing agent coke and adhesive, and send them into special storage bags according to their classification. Among them, the magnet block is crushed into 10-40mm to prepare for electric furnace feeding;

[0116] Step 2: The waste materials, except for the lumps, and the auxiliary materials are batched for the first time in a ratio of sludge: powder: boric anhydride: coke powder: adhesive = 40 (t): 35 (t): 40 (t): 6 (t): 3 (t), and the mixture is automatically batched by a PLC computer. The moisture content of the prepared mixture is about 25% (30% sludge moisture, 20% powder, and 10% boric anhydride).

[0117] Step 3: The prepared mixture is sent to a drying equipment and dried to a moisture content of about 12%;

[0118] Step 4: The baked mixture is sent to a ball making machine for ball making, and the ball size is 20-40 mm;

[0119] In step 5, the prepared pellets are sent to an electrically heated roasting furnace for pre-reduction roasting at a temperature of 800°C to 1000°C (to a metallization ratio of 40% to 65%, 60% in this embodiment) for 2 hours per furnace. After the reduction step in step 5, the chemical composition of the roasted pellets is shown in Table 3 below.

[0120] Table 3 Main chemical composition of calcined balls %

[0121]

[0122] Note: Unit: %

[0123] (1) Step 6: According to the composition of the roasted balls, the second batching (adding lump materials and reducing agent) is carried out, and the batching ratio is: roasted balls: lump materials: coke = 115:25:12 (sent to the PLC electric furnace batching system for batching), and the prepared mixture is sent to the electric furnace for smelting;

[0124] (2) Step 7: Electric furnace smelting: The electric furnace smelting uses a metallurgical special non-standard design of the buried arc furnace, through which uninterrupted continuous production is carried out, the temperature is 1250 ~ 1650 ° C, the electric furnace capacity is 16500KVA (large electric furnace), and the smelting time is 4 hours, of which 2.5 to 3 hours are for slag discharge operation and 4 hours for iron discharge operation;

[0125] (3) Step 8: Furnace tapping operation: The furnace tapping operation is divided into slag tapping and iron tapping operation:

[0126] ① After 2.5 hours of smelting, the slag is discharged. After the slag outlet is opened, the slag flows from the slag chute through high-pressure water crushing and then enters the water slag pool;

[0127] ② After 4 hours of smelting, the taphole is opened to discharge the iron, and the molten iron is put into the iron contract on the track flat car for slag and iron separation;

[0128] (4) Step 9: The pulverized slag is ground to a size of 200 mesh or more to produce rare earth oxide products, which are then packaged and stored or sent to a separation plant for wet separation or electrolytic separation. The molten iron-encased ferroboron product is crude ferroboron, which is then subjected to product conditioning and oxygen-blowing decarburization refining treatment according to the composition of the molten iron to obtain a low-carbon ferroboron alloy product.

[0129] In this embodiment, 100 tons of NdFeB waste and 40 tons of boric anhydride were used for continuous production for 8 hours. Slag and iron were produced in two furnaces. The chemical composition and quantity of the obtained products are shown in Table 4 below.

[0130] Table 4 Main components of products and quantity of waste input products

[0131]

[0132]

[0133] Recovery calculation:

[0134] (1) Waste rare earth element recovery rate = output rare earth amount / input rare earth amount = 25 × 0.857 × 80.15% / 17.43 = 98.54% (rare earth oxide Nd3O3 conversion factor 0.857);

[0135] (2) Iron recovery rate in waste = Iron content of ferroboron product ÷ Iron content of waste input = 74 × 80.02% ÷ 63.47 = 62.175 ÷ 63.47 × % = 98%

[0136] This embodiment further illustrates that the present invention has a high rare earth element recovery rate, low requirements for NdFeB waste, and that the iron-based alloy products can be accurately controlled according to national standards for industrial-scale production, which is green and environmentally friendly.

[0137] Example 2

[0138] This embodiment uses NdFeB waste and acid-leached iron slag obtained by wet leaching of NdFeB waste to recover rare earth elements and prepare iron-based alloys, further illustrating the application and applicability of the present invention.

[0139] This embodiment uses 30 tons of magnetic blocks from NdFeB waste and 70 tons of acid-leached iron slag produced in the wet recovery process of NdFeB waste (hydrochloric acid preferential dissolution method), totaling 100 tons, as an example to further illustrate the present invention. The main chemical components and proportions of the waste used in this embodiment are shown in Table 5 below.

[0140] Table 5 Main chemical composition and proportion of waste materials

[0141]

[0142]

[0143] The operation steps of this embodiment are as follows:

[0144] Step 1: sort the NdFeB waste, classify the iron slag (acid leaching residue) and NdFeB blocks into bags and stack them, and crush the magnet blocks into 20-40mm for standby use;

[0145] Step 2: Send the iron slag (acid leaching residue) into the dryer to dry the moisture to about 12%;

[0146] Step 3: Mix the baked iron slag in the following ratio: iron slag: coke powder: binder = 100:8:3, wherein the coke powder can be a type of anthracite with a calorific value of ≥ 6000 kcal, and the binder is an organic binder;

[0147] Step 4: Send the mixed iron slag to the disc ball making machine to make iron slag balls with a particle size of 20 to 40 mm;

[0148] Step 5: Send the iron slag pellets to an electric heating roasting furnace for solid-state reduction roasting at a temperature of 800°C to 1000°C; after solid-state reduction roasting, the metallization rate is 55%, and the roasting time is 2.5 hours per furnace;

[0149] Step 6: Send the roasted pellets and lumps to the PLC batching system of the electric furnace unit for the second batching. The batching ratio is: roasted pellets: lumps: carbonaceous reducing agent = 70:30:8 (the carbonaceous reducing agent is one or a combination of coke particles, blue carbon or smokeless block smoke, and the fixed carbon is ≥82%).

[0150] It should be noted that in this step, due to the rare earth metal elements in the block under certain temperature conditions, the RE in the block reacts with Fe2O3 in the iron slag to replace part of the reducing agent to reduce metallic iron, and the iron slag can act as an oxidant to oxidize the rare earth elements to rare earth oxides and enter the slag phase. Therefore, the carbonaceous reducing agent can be saved by about 35% in the ingredient calculation;

[0151] Step 7: The second mixed material is sent to the electric furnace for smelting. The electric furnace equipment is still a 16500KVA capacity (large electric furnace) special electric furnace; the smelting time is 4 hours, of which 2.5 to 3 hours are for slag tapping and 4 hours for iron tapping. The smelting temperature is controlled between 600℃ and 1400℃ (the reduction temperature is slightly lower in this example because of the use of lump materials);

[0152] Step 8: The slag removal operation is the same as that in Example 1 and will not be described in detail.

[0153] Step 9: This step is the same as Example 1 except that oxygen blowing and decarburization refining are not required.

[0154] The input-output and main chemical composition of the product of this embodiment are shown in Table 6 below.

[0155] Table 6 Product chemical composition and input-output table

[0156]

[0157] Recovery calculation:

[0158] (1) Rare earth element recovery rate = output rare earth metal amount ÷ input rare earth metal amount × % = 0.275 × 0.857 × 31.67% ÷ 100 × 7.58% y rare earth = 7.46 ÷ 7.58 × % = 98.47%

[0159] (2) Pig iron recovery rate = Pig iron produced ÷ Input iron = 56.38 × 93.8 ÷ 100 × 53.97% = 52.88 × 53.97 = 98%

[0160] This example demonstrates that this solution can also replace the acid-solution iron removal step in the wet recovery process. Acid-solution iron removal in wet recovery processes not only requires a long process, is highly polluting, and results in a low iron recovery value, but more importantly, the rare earth element recovery rate is only around 93%. The rare earth elements remaining in the acid-leached iron slag are worthless for further wet recovery. The present process can only enrich and convert the iron slag into pig iron products, generating their value. Combining the present process with the wet process can overcome the low rare earth element recovery rate associated with acid-solution iron removal.

[0161] This embodiment also fully illustrates that the recycling and reuse of NdFeB waste is a comprehensive recycling technology route combining pyrolysis and wet processing, and has broad application prospects.

[0162] Example 3

[0163] This example uses Baotou hydrometallurgical slag and NdFeB waste to recover rare earth elements and prepare a ferrophosphorus alloy product. A total of 100 tons of this material is used, with a ratio of 80:20 (metallurgical slag: NdFeB waste sludge). The main chemical compositions and ratios are shown in Table 7 below.

[0164] Table 7 Main chemical composition and proportion of implementation materials

[0165]

[0166] According to the proportions in Table 7, the national standard FeP16 ferrophosphorus alloy product can be directly produced without adding steel scraps as an auxiliary material. Therefore, the iron-based alloy product in this embodiment is determined to be a FeP16 ferrophosphorus alloy.

[0167] The specific process steps are as follows:

[0168] Step 1: Dry the sludge and waste residue separately until the moisture content is between 12% and 15%;

[0169] Step 2: The first mixing ratio is: sludge: waste residue: coke powder: binder = 20:80:5:3. After mixing evenly, send to the pelletizing machine to make pellets. The pellets are 20-40 mm in size.

[0170] Step 3: The pellets are sent to an electric heating roasting furnace for oxidation roasting and desulfurization, and solid-state reduction at a temperature of 850° C. to 1100° C. (solid-state reduction rate of 50%); the roasting time is 4 hours per furnace, wherein: due to the high sulfur content of the material, oxidation roasting is required for 1.5 hours for desulfurization and then solid-state reduction roasting for 2.5 hours, and the roasting time is higher than that of Example 2;

[0171] Step 4: The roasted balls are sent to the electric furnace batching system for secondary batching, with the batching ratio being: roasted balls: coke = 100: 12-14;

[0172] Step 5: The prepared mixture is sent to the electric furnace for smelting. The electric furnace equipment still uses a 16500KVA large electric furnace. 100 tons of powder is smelted in two furnaces for a total of 8 hours. The smelting temperature is: 600℃~1400℃;

[0173] Step 6, the slag and iron tapping operations are the same as those in Example 2 and will not be described in detail.

[0174] The main chemical components and input-output of the product obtained in this example are shown in Table 8 below.

[0175] Table 8 Main chemical composition and input-output of products

[0176]

[0177] Recovery calculation:

[0178] Rare earth element recovery rate = tons of rare earth gold produced ÷ tons of rare earth gold input = 25 × 0.857 × 39.17% ÷ 100 × 8.54% = 8.39 ÷ 8.54 = 98.24%

[0179] Iron recovery rate = tons of iron metal output ÷ tons of iron metal input = 26 × 79.26% ÷ 100 × 21.26 = 20.14 ÷ 21.26 = 97.6%

[0180] Phosphorus recovery rate = output P metal tons ÷ input P metal tons = 26 × 16.21% ÷ 100 × 5.21 = 4.22 ÷ 5.21 × 100% = 81%

[0181] This embodiment further illustrates that, in addition to being able to be recycled alone using the present invention, NdFeB waste can also be used in combination with other difficult-to-process smelting waste slags due to its high iron content, thereby reducing production costs and achieving high-value and efficient utilization of waste slags.

[0182] It should be noted that the iron-based alloy product described in the above embodiment is only determined based on the composition characteristics of the above-mentioned waste and waste slag. When using the technology of the present invention to prepare iron-based alloys, it should be reasonably determined based on the actual waste slag and waste characteristics, and is not limited to the products described in this embodiment.

[0183] The above descriptions are only some embodiments of the present invention and do not limit the scope of protection of the present invention. Any equivalent device or equivalent process transformation made by using the contents of the description and drawings of the present invention, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for recovering rare earth elements from NdFeB waste and preparing an iron-based alloy, characterized in that: It includes: S01, sorting NdFeB waste to separate powder, sludge, acid leaching residue and lump; S02. According to preset conditions, one or more of the powder, sludge, and acid leaching residue are mixed, and then auxiliary materials are added to form a mixture, and then a binder and a carbonaceous reducing agent are added, and the materials are pelletized to obtain pellets; S03, sending the prepared ball material to the solid pre-reduction facility for solid reduction roasting, the roasting temperature is 800℃~1000℃, and the roasting time is 1.5~4 hours / furnace; S04, the calcined ball material is subjected to secondary batching, by adding the block material after sorting the NdFeB waste material, the auxiliary material and the carbonaceous reducing agent to obtain a mixed material; S05. Send the prepared mixture into a non-standard design reduction electric furnace for solid-state and molten-state reduction smelting and melting. The smelting time is 3 to 8 hours, and finally the slag and iron are tapped.

2. The method for recovering rare earth elements from NdFeB waste and preparing an iron-based alloy according to claim 1, wherein: In S01, the selected blocks are further crushed to produce materials with a particle size of 10 to 40 mm for later use.

3. The method for recovering rare earth elements from NdFeB waste and preparing an iron-based alloy according to claim 1, wherein: S02 also includes: chemically analyzing the sorted powder, sludge, acid leaching residue, and lump materials, then determining the requirements for the output iron-based alloy product, and blending one or more of the powder, sludge, and acid leaching residue according to the requirements.

4. The method for recovering rare earth elements from NdFeB waste and preparing an iron-based alloy according to any one of claims 1 to 3, characterized in that: In S02, the auxiliary material is an auxiliary raw material that needs to be supplemented according to the chemical composition of the waste materials after matching and the requirements of the alloy product. The carbonaceous reducing agent is coke powder or anthracite, and its fixed carbon content is greater than 80%. The adhesive is an organic adhesive.

5. The method for recovering rare earth elements from NdFeB waste and preparing an iron-based alloy according to claim 4, wherein: In S02, the weight ratio of the added parts of the mixture, carbonaceous reducing agent and adhesive is 100:3~8:3~5; if the moisture content of the material is ≥15% before ball making, the material needs to be dried to make its moisture content between 10% and 15%; the particle size of the ball material is 10~40mm.

6. The method for recovering rare earth elements from NdFeB waste and preparing an iron-based alloy according to claim 5, characterized in that: In S04, the dry weight ratio of the added parts of the pellets, blocks and carbonaceous reducing agent is: pellets: blocks: reducing agent = 70-115: 0-30: 8-14; the carbonaceous reducing agent is one or a combination of coke, blue carbon or anthracite blocks.

7. The method for recovering rare earth elements from NdFeB waste and preparing an iron-based alloy according to claim 1, wherein: In S05, the temperature of the reduction electric furnace smelting is 700-1500°C, of ​​which: the solid-state reduction reaction temperature is 700-1000°C, and the molten reduction reaction and melting temperature is 1000-1500°C.

8. The method for recovering rare earth elements from NdFeB waste and preparing an iron-based alloy according to any one of claims 1 to 3, characterized in that: It also includes: S06. The slag obtained from the slag discharge is flushed into the slag pool through a chute for water crushing. The crushed slag is ball-milled to a size of 200 mesh or more, and then subjected to magnetic separation to remove iron. The rare earth slag is then packaged and stored; The iron-based alloy obtained by tapping is discharged from the tap hole into the ladle to obtain crude molten iron. The molten iron is then decarburized by bottom blowing or sent to the AOD furnace for refining, decarburization and dephosphorization. The product composition can then be adjusted according to the preset product standards or index requirements. In addition, the refined molten iron is cast into ingots, and the ingot products are cooled, finished, packaged and stored.

9. A system for recovering rare earth elements from NdFeB waste and preparing an iron-based alloy, which uses the method for recovering rare earth elements from NdFeB waste and preparing an iron-based alloy as claimed in any one of claims 1 to 8, characterized in that: It includes a waste sorting unit, a waste pretreatment unit, a waste solid pre-reduction unit, and an electric furnace smelting and melting unit which are connected in sequence; the reduction electric furnace smelting and melting unit is also connected to a rare earth oxide recovery unit and an iron-based alloy preparation unit.

10. The system for recovering rare earth elements from NdFeB waste and preparing iron-based alloys according to claim 9, characterized in that: The waste sorting unit includes a cleaning machine, a sorting machine and a crusher connected in sequence; The waste pre-processing unit includes a drying machine, a batching machine, and a pelletizing machine connected in sequence; The waste solid-state pre-reduction unit includes: an electrically heated solid-state reduction roasting furnace or other non-electrically heated solid-state reduction facilities and supporting facilities connected thereto; The electric furnace smelting and separation unit includes: an electric furnace batching machine, a non-standard design reduction furnace, and supporting slag and iron separation facilities and flue gas purification and dust removal facilities; Among them: the non-standard reduction furnace should meet the following basic design parameter requirements: (1) The current-voltage ratio of the electric furnace is A / V = 230 ~ 400A / V; (2) The power density per unit area of ​​the molten high-temperature reduction reaction zone is P1=1200KW / M2; (3) Furnace power density per unit area P2 = 230KW ~ 350 / KW / M2; (4) Furnace unit volume power density P3 = 80KW ~ 100 / KW / M2; (5) The furnace depth H is 1.1 to 1.3 times that of a conventional buried electric furnace. The rare earth oxide recovery unit includes one or more equipment selected from the group consisting of a rare earth slag water crushing device, a grinding mill, and an electromagnetic separator; The iron-based alloy preparation unit includes a tapping device, which includes one or more of a molten iron decarburization device, a dephosphorization device, and a refining device; Among them, the waste sorting unit, waste pretreatment unit, waste solid pre-reduction unit, and electric furnace smelting and melting unit are connected in sequence through belt conveyors, and the electric furnace smelting and melting unit is connected with the rare earth oxide recovery unit and the iron-based alloy preparation unit through slag troughs and rail iron-out flat cars respectively.

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