Method for hydrogen-based reduction and stepwise enrichment of iron, niobium and rare earths from low-grade rare earth tailings

Abstract

This application belongs to the field of metallurgical technology, specifically relating to a method for hydrogen-based reduction and stepwise enrichment of iron, niobium, and rare earth elements from low-grade rare earth tailings, comprising the following steps: S1, obtaining low-grade rare earth tailings, and performing hydrogen-based reduction on the low-grade rare earth tailings to obtain a first rare earth ore, wherein, by mass percentage, the composition of the low-grade rare earth tailings includes: Fe: 10%-20%, Nb: 0.01%-0.3%, rare earth: 2%-10%; the mass ratio of iron oxide to niobium oxide in the first rare earth ore is 100:(6-12); S2, performing a first melting separation on the first rare earth ore to obtain metallic iron and a second rare earth ore; S3, mixing the second rare earth ore with a reducing agent and performing a second melting separation to obtain niobium-iron alloy and rare earth-rich ore. This application combines hydrogen-based selective reduction of iron with reduction smelting of ferro-niobium alloys. By controlling the degree of hydrogen reduction, an appropriate amount of FeO is retained in the slag, improving the slag properties and providing an endogenous iron source for ferro-niobium smelting, thereby achieving efficient enrichment and separation of iron, niobium, and rare earth elements.

Description

Technical Field

[0001] This application relates to the field of metallurgical technology, specifically to a method for hydrogen-based reduction and stepwise enrichment of iron, niobium and rare earth elements in low-grade rare earth tailings. Background Technology

[0002] The Bayan Obo mine is a globally rare Fe-Nb-RE polymetallic associated deposit. This deposit is characterized by its complex composition, low grade, fine mineral embedding, and strong dispersion, resulting in low recovery rates of valuable elements such as iron, niobium, and rare earth elements during beneficiation and smelting, and insufficient comprehensive resource utilization. Statistics show that the iron recovery rate at the Bayan Obo mine is only about 70%, the rare earth recovery rate is less than 10%, and niobium resources have not yet been effectively utilized. These metals have accumulated in the tailings pond for a long time, not only causing resource waste but also potentially leading to environmental problems such as heavy metal pollution of soil and groundwater acidification. Therefore, achieving comprehensive utilization of the resources in the Bayan Obo rare earth tailings is of great significance.

[0003] Currently, research on the recovery of low-grade rare earth tailings from Bayan Obo mainly focuses on mineral processing and hydrometallurgical processes. However, due to the fine mineral structure, complex intergrowth relationships, dispersed element occurrence, and low grade of valuable elements in these tailings, traditional mineral processing techniques such as gravity separation, flotation, and magnetic separation are difficult to achieve efficient separation. Iron concentrate recovery rates are generally 70%-80%, rare earth concentrate recovery rates are 40%-60%, and niobium concentrate recovery rates are 30%-50%. Hydrometallurgical recovery processes typically use strong acid / alkali media to decompose the minerals, followed by extraction, purification, washing, and drying to prepare the target product. This approach suffers from high reagent consumption, low decomposition efficiency, and severe environmental pollution, making it difficult to meet the requirements for large-scale industrial recovery. A complete, green, efficient, and economical process system has not yet been established.

[0004] Due to the high iron content in the Bayan Obo mine, other processing methods mainly involve traditional pyrometallurgical processes to smelt niobium-iron alloys. These processes primarily use coal-based reducing agents, but these agents readily react with niobium to form high-melting-point NbC, affecting slag-gold separation and product quality. Furthermore, coal-based reducing agents contain 10%-40% impurities, and the smelting process requires the addition of large amounts of binders, slag-forming agents, and additional metallic iron, further reducing the niobium and rare earth grades in the slag and hindering the comprehensive recovery of resources from low-grade tailings. Traditional pyrometallurgical processes have limited effectiveness in treating such rare earth tailings; therefore, a method suitable for hydrogen-based reduction and stepwise enrichment of iron, niobium, and rare earths in low-grade rare earth tailings is urgently needed. Summary of the Invention

[0005] To solve the above-mentioned technical problems, this application provides a method for hydrogen-based reduction and stepwise enrichment of iron, niobium, and rare earth elements from low-grade rare earth tailings, comprising the following steps: S1, obtaining low-grade rare earth tailings, and performing hydrogen-based reduction on the low-grade rare earth tailings to obtain a first rare earth ore, wherein, by mass percentage, the composition of the low-grade rare earth tailings includes: Fe: 10%-20%, Nb: 0.01%-0.3%, rare earth: 2%-10%; the mass ratio of iron oxide to niobium oxide in the first rare earth ore is 100:(6-12); S2, performing a first melting fractionation on the first rare earth ore to obtain metallic iron and a second rare earth ore; S3, mixing the second rare earth ore with a reducing agent and performing a second melting fractionation to obtain ferroniobium alloy and rare earth-rich ore.

[0006] As a preferred embodiment of the method for hydrogen-based reduction and stepwise enrichment of iron, niobium and rare earth elements in low-grade rare earth tailings described in this application, in step S1, the low-grade rare earth tailings consist of: hematite, magnetite, bastnaesite, monazite, columbite, calcite and rutile.

[0007] As a preferred embodiment of the method for hydrogen-based reduction and stepwise enrichment of iron, niobium and rare earth elements in low-grade rare earth tailings described in this application, in step S1, the gas used for hydrogen-based reduction includes at least one of high-purity hydrogen or hydrogen-rich mixed gas; the temperature of hydrogen-based reduction is 600-1000℃, the time of hydrogen-based reduction is 60-120 min, and the gas flow rate of hydrogen-based reduction is 200-500 mL / min.

[0008] As a preferred embodiment of the method for hydrogen-based reduction and stepwise enrichment of iron, niobium and rare earth in low-grade rare earth tailings described in this application, in step S2, the temperature of the first melting fraction is 1500-1600℃.

[0009] As a preferred embodiment of the method for hydrogen-based reduction and stepwise enrichment of iron, niobium and rare earth elements in low-grade rare earth tailings described in this application, in step S2, the purity of the metallic iron is ≥99.9%.

[0010] As a preferred embodiment of the method for hydrogen-based reduction and stepwise enrichment of iron, niobium and rare earth in low-grade rare earth tailings described in this application, in step S3, the reducing agent includes at least one of carbonaceous reducing agent, metallic aluminum and metallic silicon.

[0011] As a preferred embodiment of the method for hydrogen-based reduction and stepwise enrichment of iron, niobium and rare earth in low-grade rare earth tailings described in this application, in step S3, the temperature of the second melting fraction is 1500-1600℃.

[0012] As a preferred embodiment of the method for hydrogen-based reduction and stepwise enrichment of iron, niobium, and rare earth elements in low-grade rare earth tailings described in this application, the niobium content in the niobium-iron alloy is 25 times or more than the niobium content in the low-grade rare earth tailings.

[0013] As a preferred embodiment of the method for hydrogen-based reduction and stepwise enrichment of iron, niobium and rare earth elements in low-grade rare earth tailings as described in this application, the rare earth content in the rich rare earth ore is 1.5 times or more than the rare earth content in the low-grade rare earth tailings.

[0014] As a preferred embodiment of the method for hydrogen-based reduction and stepwise enrichment of iron, niobium and rare earth elements in low-grade rare earth tailings described in this application, the total recovery rate of iron is ≥92% and the recovery rate of niobium is ≥85%.

[0015] This application proposes a method for hydrogen-based reduction and stepwise enrichment of iron, niobium, and rare earth elements in low-grade rare earth tailings. This method addresses the problems of limited recovery efficiency, high cost and low efficiency of existing beneficiation processes for low-grade niobium-containing rare earth tailings from Bayan Obo, as well as poor performance of pyrometallurgical reduction smelting. It combines hydrogen-based selective reduction of iron with reduction smelting of niobium-iron alloys. By controlling the degree of hydrogen reduction to retain an appropriate amount of FeO in the slag, the properties of the slag are improved, and an endogenous iron source is provided for niobium-iron smelting. This avoids NbC formation, reduces the introduction of impurities, and achieves efficient enrichment and separation of iron, niobium, and rare earth elements.

[0016] Low-grade niobium-containing rare earth tailings are fed into a vertical shaft furnace for hydrogen-based reduction to obtain the first rare earth ore. By controlling the degree of reduction, most of the iron is reduced to metallic iron, while a small portion of iron, rare earth elements, and niobium remain in the slag phase as oxides, creating favorable slag conditions for subsequent smelting and providing an iron source for niobium-iron alloy smelting. The first rare earth ore is then fed into an electric furnace for smelting, separating metallic iron and niobium-rich rare earth smelting slag containing a certain amount of FeO. This process completely avoids the formation of niobium carbide, achieving efficient iron recovery and preliminary enrichment of rare earth elements and niobium. The resulting second rare earth ore is mixed with a reducing agent and subjected to deep reduction smelting without the addition of an external iron source to obtain niobium-iron alloy and rich rare earth ore, thereby achieving the recovery of niobium and residual iron, and deeply enriching rare earth elements in the rich rare earth ore.

[0017] The reaction mechanism of hydrogen-based reduction is as follows: Under a hydrogen atmosphere, iron is reduced to elemental iron, while rare earth elements and niobium are not reduced. By adjusting the degree of reduction, most of the iron is reduced, while a small amount of iron, rare earth elements, and niobium are converted into oxides and remain in the slag phase, providing good slag conditions for slag-iron smelting and simultaneously providing an iron source for subsequent smelting of ferro-niobium alloys. The FeO retained in the first rare earth ore helps improve the fluidity of the slag, allowing metallic iron to naturally aggregate and separate from the slag phase, while rare earth elements and niobium are enriched in the second rare earth ore. The reaction mechanism of the second smelting is as follows: niobium and iron oxides in the slag are reduced to form ferro-niobium alloys and recovered, while rare earth oxides remain in the slag, forming rare earth-rich ore, which facilitates subsequent rare earth extraction.

[0018] The beneficial effects of this application are as follows: This application achieves selective and efficient reduction of iron by using hydrogen or hydrogen-rich gas as a clean reducing agent, avoiding the formation of niobium carbide (NbC) at the source, reducing niobium loss, and combining environmental protection with high efficiency. It innovatively couples hydrogen-based reduction with reduction smelting, retaining an appropriate amount of FeO in the slag by controlling the degree of reduction, optimizing slag performance, and providing an endogenous iron source for ferro-niobium smelting without the need for external iron sources or slag-forming agents. This is beneficial for improving the niobium grade in ferro-niobium alloys and allowing rare earth elements to be fully enriched and improved in the slag phase, creating favorable conditions for subsequent extraction. The entire process achieves stepwise and targeted recovery of iron, niobium, and rare earth resources. Iron is produced in the form of direct reduced iron, niobium is recovered together with residual iron to form ferro-niobium alloys, and rare earth elements are deeply enriched in the final slag. This method is particularly suitable for the low-grade, polymetallic associated, and finely embedded rare earth tailings of Bayan Obo, overcoming the shortcomings of traditional processes in terms of recovery efficiency and environmental friendliness, and providing a practical new technological path for the comprehensive utilization of my country's strategic mineral resources. Detailed Implementation

[0019] The technical solutions in the embodiments will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0020] This application provides a method for hydrogen-based reduction and stepwise enrichment of iron, niobium, and rare earth elements in low-grade rare earth tailings, comprising the following steps: S1. Obtain low-grade rare earth tailings, and perform hydrogen-based reduction on the low-grade rare earth tailings to obtain a first rare earth ore, wherein, by mass percentage, the composition of the low-grade rare earth tailings includes: Fe: 10%-20%, Nb: 0.01%-0.3%, rare earth: 2%-10%; the mass ratio of iron oxide to niobium oxide in the first rare earth ore is 100:(6-12). Specifically, the mass ratio of iron oxide to niobium oxide in the first rare earth ore is any one of 100:6, 100:7, 100:8, 100:9, 100:10, 100:11, 100:12 and any range between the two. The composition of the low-grade rare earth tailings includes: hematite, magnetite, bastnaesite, monazite, columbite, calcite, and columbite-rutile; the gas used for the hydrogen-based reduction includes at least one of high-purity hydrogen or a hydrogen-rich mixture; the temperature of the hydrogen-based reduction is 600-1000℃, the time of the hydrogen-based reduction is 60-120 min, and the gas flow rate of the hydrogen-based reduction is 200-500 mL / min; Specifically, the temperature for hydrogen reduction is within the range of any one or any two of 600℃, 700℃, 800℃, 900℃, and 1000℃; the time for hydrogen reduction is within the range of any one or any two of 60min, 70min, 80min, 90min, 100min, 110min, and 120min; and the gas flow rate for hydrogen reduction is within the range of any one or any two of 200mL / min, 300mL / min, 400mL / min, and 500mL / min. S2. Perform a first melting and separation process on the first rare earth ore to obtain metallic iron and a second rare earth ore. The temperature of the first melting fraction is 1500-1600℃; the purity of the metallic iron is ≥99.9%; Specifically, the temperature of the first melting point is any one of 1500℃, 1510℃, 1520℃, 1530℃, 1540℃, 1550℃, 1560℃, 1570℃, 1580℃, 1590℃, and 1600℃, and the range between any two of them. S3. Mix the second rare earth ore and the reducing agent and perform a second melting separation to obtain niobium-iron alloy and rare earth rich ore; The reducing agent includes at least one of carbonaceous reducing agent, metallic aluminum, and metallic silicon; the temperature of the second melting fraction is 1500-1600℃. Specifically, the temperature of the second melting point is any one of 1500℃, 1510℃, 1520℃, 1530℃, 1540℃, 1550℃, 1560℃, 1570℃, 1580℃, 1590℃, and 1600℃, and the range between any two of them. The niobium content in the niobium-iron alloy is 25 times or more than the niobium content in the low-grade rare earth tailings; the rare earth content in the rich rare earth ore is 1.5 times or more than the rare earth content in the low-grade rare earth tailings; the total iron recovery rate is ≥92%, and the niobium recovery rate is ≥85%.

[0021] The technical solution of this application will be further described below with reference to specific embodiments.

[0022] Example 1 This application provides a method for hydrogen-based reduction and stepwise enrichment of iron, niobium, and rare earth elements in low-grade rare earth tailings, comprising the following steps: S1. Obtain low-grade rare earth tailings, and perform hydrogen-based reduction on the low-grade rare earth tailings to obtain the first rare earth ore. The composition of the low-grade rare earth tailings by mass percentage includes: Fe: 18.8%, Nb: 0.2%, and rare earth: 6.71%. The mass ratio of iron oxide to niobium oxide in the first rare earth ore is 100:7. The composition of low-grade rare earth tailings includes: hematite, magnetite, bastnaesite, monazite, columbite, calcite, and columbite-rutile; the gas used for hydrogen-based reduction is high-purity hydrogen; the temperature of hydrogen-based reduction is 900℃, the time is 100min, and the gas flow rate is 250mL / min. S2. Perform a first melting and separation process on the first rare earth ore to obtain metallic iron and the second rare earth ore. The temperature of the first melting point is 1550℃; the purity of the metallic iron is ≥99.9%; S3. Mix the second rare earth ore and the reducing agent to carry out a second melting separation to obtain niobium-iron alloy and rare earth rich ore; The reducing agent is coke; the temperature of the second melting fraction is 1600℃. The niobium content in ferroniobium alloys is 31 times that in low-grade rare earth tailings; the rare earth content in rich rare earth ores is 1.6 times that in low-grade rare earth tailings; the total iron recovery rate is 96%, and the niobium recovery rate is 90%.

[0023] Example 2 This application provides a method for hydrogen-based reduction and stepwise enrichment of iron, niobium, and rare earth elements in low-grade rare earth tailings, comprising the following steps: S1. Obtain low-grade rare earth tailings, and perform hydrogen-based reduction on the low-grade rare earth tailings to obtain the first rare earth ore. The composition of the low-grade rare earth tailings, by mass percentage, includes: Fe: 15.34%, Nb: 0.09%, and rare earth: 3.53%. The mass ratio of iron oxide to niobium oxide in the first rare earth ore is 100:11. The composition of low-grade rare earth tailings includes: hematite, magnetite, bastnaesite, monazite, columbite, calcite, and columbite-rutile; the gas used for hydrogen-based reduction is a hydrogen-rich mixed gas; the temperature of hydrogen-based reduction is 800℃, the time is 80min, and the gas flow rate is 350mL / min. S2. Perform a first melting and separation process on the first rare earth ore to obtain metallic iron and the second rare earth ore. The temperature of the first melting point is 1600℃; the purity of the metallic iron is ≥99.9%; S3. Mix the second rare earth ore and the reducing agent to carry out a second melting separation to obtain niobium-iron alloy and rare earth rich ore; The reducing agent is metallic aluminum; the temperature of the second melting point is 1550℃; The niobium content in ferroniobium alloys is 70 times that in low-grade rare earth tailings; the rare earth content in rich rare earth ores is 1.5 times that in low-grade rare earth tailings; the total iron recovery rate is 92%, and the niobium recovery rate is 85%.

[0024] Comparative Example 1 The difference between this comparative example and Example 1 is that the mass ratio of iron oxide to niobium oxide in the first rare earth ore is 100:20. The niobium content in ferroniobium alloys is 45 times that in low-grade rare earth tailings; the rare earth content in rich rare earth ores is 1.1 times that in low-grade rare earth tailings; the total iron recovery rate is 79%, and the niobium recovery rate is 54%.

[0025] Comparative Example 2 The difference between this comparative example and Example 1 is that the mass ratio of iron oxide to niobium oxide in the first rare earth ore is 100:5. The niobium content in ferroniobium alloys is 15 times that in low-grade rare earth tailings; the rare earth content in rich rare earth ores is 1.6 times that in low-grade rare earth tailings; the total iron recovery rate is 97%, and the niobium recovery rate is 91%.

[0026] As can be seen from the above examples and comparative examples: Example 1, combined with Comparative Example 1, shows that excessive reduction of elemental iron results in a low mass ratio of iron oxide to niobium oxide in the first rare earth ore. This leads to poor slag fluidity during the first and second melting processes, making slag-gold separation difficult and causing rare earth loss. Consequently, the rare earth grade improvement effect in the rich rare earth ore is poor, and the recovery rates of niobium and iron are reduced. Example 1, combined with Comparative Example 2, shows that insufficient reduction of elemental iron results in an excessively high iron content during the second melting process. This reduces the niobium content in the niobium-iron alloy, lowering its grade. Examples 1-2 and Comparative Examples 1-2 show that retaining an appropriate amount of FeO in the first rare earth ore, while ensuring the grade of the obtained niobium-iron alloy, helps improve the slag fluidity during the first and second melting processes. This allows metallic iron to naturally aggregate and separate from the slag phase, which is beneficial for the full enrichment of rare earth in the slag phase and for improving its grade.

[0027] The above description is only a preferred embodiment of this application and does not limit the patent scope of this application. All equivalent structural transformations made using the content of this application's specification under the inventive concept of this application, or direct / indirect applications in other related technical fields, are included within the patent protection scope of this application.

Claims

1. A method for hydrogen-based reduction and stepwise enrichment of iron, niobium, and rare earth elements in low-grade rare earth tailings, characterized in that, Includes the following steps: S1. Obtain low-grade rare earth tailings, and perform hydrogen-based reduction on the low-grade rare earth tailings to obtain a first rare earth ore, wherein, by mass percentage, the composition of the low-grade rare earth tailings includes: Fe: 10%-20%, Nb: 0.01%-0.3%, rare earth: 2%-10%; the mass ratio of iron oxide to niobium oxide in the first rare earth ore is 100:(6-12). S2. Perform a first melting and separation process on the first rare earth ore to obtain metallic iron and a second rare earth ore. S3. The second rare earth ore and the reducing agent are mixed and subjected to a second melting separation to obtain niobium-iron alloy and rare earth rich ore.

2. The method for hydrogen-based reduction and stepwise enrichment of iron, niobium, and rare earth elements in low-grade rare earth tailings according to claim 1, characterized in that, In step S1, the low-grade rare earth tailings consist of: hematite, magnetite, bastnaesite, monazite, columbite, calcite, and rutile.

3. The method for hydrogen-based reduction and stepwise enrichment of iron, niobium, and rare earth elements in low-grade rare earth tailings according to claim 1, characterized in that, In step S1, the gas used for hydrogen-based reduction includes at least one of high-purity hydrogen or hydrogen-rich mixed gas; the temperature of hydrogen-based reduction is 600-1000℃, the time of hydrogen-based reduction is 60-120min, and the gas flow rate of hydrogen-based reduction is 200-500mL / min.

4. The method for hydrogen-based reduction and stepwise enrichment of iron, niobium, and rare earth elements in low-grade rare earth tailings according to claim 1, characterized in that, In step S2, the temperature of the first melting fraction is 1500-1600℃.

5. The method for hydrogen-based reduction and stepwise enrichment of iron, niobium, and rare earth elements in low-grade rare earth tailings according to claim 1, characterized in that, In step S2, the purity of the metallic iron is ≥99.9%.

6. The method for hydrogen-based reduction and stepwise enrichment of iron, niobium, and rare earth elements in low-grade rare earth tailings according to claim 1, characterized in that, In step S3, the reducing agent includes at least one of carbonaceous reducing agent, metallic aluminum, and metallic silicon.

7. The method for hydrogen-based reduction and stepwise enrichment of iron, niobium, and rare earth elements in low-grade rare earth tailings according to claim 1, characterized in that, In step S3, the temperature of the second melting fraction is 1500-1600℃.

8. The method for hydrogen-based reduction and stepwise enrichment of iron, niobium, and rare earth elements in low-grade rare earth tailings according to claim 1, characterized in that, The niobium content in the niobium-iron alloy is 25 times or more than the niobium content in the low-grade rare earth tailings.

9. The method for hydrogen-based reduction and stepwise enrichment of iron, niobium, and rare earth elements in low-grade rare earth tailings according to claim 1, characterized in that, The rare earth content in the rich rare earth ore is 1.5 times or more than the rare earth content in the low-grade rare earth tailings.

10. A method for hydrogen-based reduction and stepwise enrichment of iron, niobium, and rare earth elements in low-grade rare earth tailings according to claim 1, characterized in that, The total recovery rate of iron is ≥92%, and the recovery rate of niobium is ≥85%.