A method for producing niobium-iron alloy by molten salt electrolysis using co-associated niobium-titanium-iron-rare earth-containing ore

Abstract

The present application relates to a kind of niobium, titanium, iron, rare-earth co-associated ore containing molten salt electrolysis production niobium-iron alloy method, comprising: S1, niobium, titanium, iron, rare-earth co-associated ore and molten salt are mixed uniformly, placed in electrolytic cell and heated and are imported into protective gas, molten salt is heated to melting temperature and is kept warm;S2, inert metal is used as cathode, high-purity graphite rod is used as anode, cathode and anode are inserted into the molten salt of electrolytic cell, after being connected to direct current power supply, electrolysis is carried out by strictly controlling electrolysis voltage;Electrolysis voltage is determined according to the temperature and the concentration of co-associated ore in molten salt, and electrolysis voltage is lower than the decomposition voltage of titanium oxide and rare earth oxide but higher than the decomposition voltage of iron oxide and niobium oxide;S3, the product in electrolytic cell is cooled, ground, magnetic separation under protective atmosphere, and niobium-iron alloy is obtained.The present application process flow is simple, can produce niobium-iron alloy without titanium impurity, improve application value, and process CO2 emission is low.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgical refining technology, and particularly relates to a method for producing niobium-iron alloys by molten salt electrolysis of common rare earth minerals containing niobium, titanium, and titanium. Background Technology

[0002] Niobium is a rare metal. Due to the excellent physical, chemical and mechanical properties of niobium and its related compounds, it is widely used in fields such as steel, aviation, aerospace, navigation, chemical industry, construction and medicine. It is an important metallic material for the development of modern industry and cutting-edge science.

[0003] The Bayan Obo mine is a world-renowned polymetallic symbiotic deposit containing important elements such as rare earth, iron, niobium, and titanium. However, the development and utilization of Bayan Obo's mineral resources have historically focused primarily on iron extraction, with rare earth resource utilization rates below 10% and niobium resource utilization rates almost zero. The Bayan Obo mine exhibits a symbiotic relationship between niobium, rare earth, iron, and titanium, and is characterized by low ore grades, diverse mineral types, fine grain size, and intergrowth of mineral phases, resulting in small differences in the selectivity of valuable components and difficulties in separation and extraction. Baogang Group, addressing the characteristics of the Bayan Obo mine, adopted the principle of "group separation and selection, prioritizing easy flotation" to select a rougher concentrate containing more than 3% Nb₂O₅ from the niobium-bearing tailings of the Bayan Obo ore under industrial conditions.

[0004] Advances in niobium beneficiation technology have provided better conditions for the comprehensive development and utilization of niobium resources, leading to the development of multiple pyrometallurgical niobium extraction processes. For example, Chinese patent application CN201310449481.X proposes a process for smelting niobium-titanium ferroalloys using "high-temperature carbon reduction-graphite powder secondary reduction," which involves high-temperature carbon reduction of high-titanium, niobium-rich slag to obtain carbides, followed by secondary smelting. Patent CN201310449614.3 employs a method of high-temperature carbonization and re-oxidation of high-titanium, niobium-rich slag to prepare niobium-titanium ferroalloys. Patent CN201410840076.5 describes a three-step smelting process for niobium-titanium ferroalloys from niobium-titanium concentrate: gas-solid selective reduction, electric furnace melting, and electric furnace smelting. All the existing technologies mentioned above utilize carbon reduction to reduce metallic elements. However, at high temperatures, carbon reacts with elements such as niobium and titanium in the slag to form carbides. Niobium and titanium carbides are high-melting-point compounds, difficult to dissolve in slag, leading to slag viscosity during smelting and even causing splashing accidents, severely impacting niobium yield and process smoothness. Furthermore, the aforementioned technologies all use carbon as a reducing agent to smelt niobium-iron alloys, which typically contain high levels of titanium. Titanium severely limits the application range of niobium-iron alloys, and the difficulty in separating niobium from titanium is a major obstacle in the carbothermic reduction smelting process. In addition, the carbothermic reduction process generates significant CO2 emissions, hindering the implementation of the "carbon peak, carbon neutrality" policy. Existing technologies propose using electrolysis to produce niobium-iron alloys. For example, the scheme in Chinese patent application CN103160863A first selectively and magnetically separates iron from niobium concentrate to obtain a niobium-rich and rare-earth mixture. The molten niobium-rich and rare-earth mixture is then electrolyzed with molten oxides to prepare the niobium-iron alloy. Chinese patent application CN103160864A discloses a method for producing ferroniobium alloy by selectively and magnetically separating iron from niobium concentrate to obtain a niobium-rich and rare earth mixture. This mixture is then added to a binder and briquetted to form a cathode, which is used for molten salt electrolysis. All of these methods require pretreatment of the niobium concentrate through selective reduction, followed by magnetic separation to remove iron, and finally electrolysis to produce the ferroniobium alloy. The smelting process is lengthy and complex. Furthermore, based on the niobium concentrate composition described in the examples of the aforementioned patent application, these methods are not suitable for processing mineral raw materials containing both niobium and titanium. This is mainly because niobium and titanium have similar chemical properties and close ionic radii, often coexisting as isomorphous compounds that are difficult to separate. This results in ferroniobium alloy products containing large amounts of titanium, thus limiting the practical application of ferroniobium alloys. Summary of the Invention

[0005] (a) Technical problems to be solved

[0006] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a method for producing niobium-iron alloy by electrolysis of molten salt containing niobium, titanium, iron, and rare earth elements. Specifically, the method involves selectively electrolyzing iron and niobium in the associated minerals by precisely controlling the voltage, so that the niobium-iron alloy is electrolytically extracted, and a molten salt containing rare earth elements and titanium is obtained. The present invention can avoid the generation of carbides and can produce niobium-iron alloys without titanium impurities, thus giving niobium-iron alloys a wider range of applications. At the same time, the method does not require pre-treatment of iron in the associated minerals by carbothermal reduction and magnetic separation, thereby simplifying the process, shortening the process route, reducing production costs, and significantly reducing CO2 emissions.

[0007] (II) Technical Solution

[0008] This invention provides a method for producing ferroniobium alloys by molten salt electrolysis of niobium-titanium-iron rare earth co-existing minerals, comprising the following steps:

[0009] S1. Mix the associated minerals containing niobium, titanium, iron, and rare earth elements with molten salt, place them in an electrolytic cell, heat the electrolytic cell and introduce an inert protective gas, heat the molten salt to its melting temperature and hold it therein so that the molten salt is completely in a molten state.

[0010] S2. An inert metal is used as the cathode, and a high-purity graphite rod is used as the anode. The cathode and anode are inserted into the molten salt of the electrolytic cell. After the inert metal cathode and graphite anode are connected to a DC power supply, the electrolysis voltage is strictly controlled. The electrolysis voltage is determined based on the heat preservation temperature and the dissolution concentration of associated minerals in the molten salt. The electrolysis voltage is lower than the decomposition voltage of titanium oxide and rare earth oxides but higher than the decomposition voltage of iron oxide and niobium oxide. The entire electrolysis process is carried out under the protection of an inert protective gas.

[0011] S3. After electrolysis, the cathode, anode, and molten salt are cooled under the protection of an inert protective gas.

[0012] According to a preferred embodiment of the present invention, in S1, the molten salt is a mixture of cryolite Na3AlF6 and one or more salts selected from NaF, LiF, and KF.

[0013] Preferably, the mixing ratio of cryolite Na3AlF6 with one or more salts selected from NaF, LiF, and KF is 7:3 to 5:5. By mixing cryolite Na3AlF6 with one or more fluoride salts selected from NaF, LiF, and KF, the melting point of the molten salt mixture can be further reduced, the holding temperature can be lowered, and energy consumption can be saved. The melting point of the molten salt increases with the increase of the mass percentage of cryolite and decreases with the increase of the mass percentage of fluoride salt. When the content of cryolite in the molten salt is close to 70%, the holding temperature needs to be controlled at around 1100℃, while reducing the mass percentage of cryolite can lower the melting temperature of the molten salt.

[0014] According to a preferred embodiment of the present invention, in S1, the heat preservation temperature is 900-1100℃; the heat preservation time is 1-3h; and in S2, the electrolysis voltage is 2-5V.

[0015] According to a preferred embodiment of the present invention, in S1, the associated mineral containing niobium, titanium, iron, and rare earth is Bayan Obo mineral, and its mass ratio with molten salt ranges from 2 to 10:100.

[0016] According to a preferred embodiment of the present invention, in S1, the associated mineral containing niobium, titanium, iron, and rare earth elements comprises the following components in mass percentage: Nb₂O₅ 1-30%, TiO₂ 1-20%, TFe 1-40%, CaO 1-20%, SiO₂ 1-30%, Al₂O₃ 1-20%, RE x O y 1-10%, other components ≤10%; its mass ratio with molten salt ranges from 2-10:100.

[0017] According to a preferred embodiment of the present invention, in S1-S3, the inert protective gas is high-purity argon with a purity ≥99%.

[0018] According to a preferred embodiment of the present invention, in S2, the inert metal is tungsten, molybdenum, or platinum. Preferably, the electrolytic cell is a graphite electrolytic cell.

[0019] According to a preferred embodiment of the present invention, in S2, the electrolysis time is 4-8 hours.

[0020] According to a preferred embodiment of the present invention, step S3 further includes: crushing, grinding, and magnetically separating the cooled product in the electrolytic cell to obtain niobium-iron alloy and residual molten salt.

[0021] Preferably, the grinding involves grinding the cooled product in the electrolytic cell to a mesh size of 200-500.

[0022] Preferably, the magnetic induction intensity of the magnetic separation is 50-200 mT.

[0023] Preferably, the rare earth elements and titanium are further separated and extracted from the remaining molten salt.

[0024] (III) Beneficial Effects

[0025] This invention provides a method for producing ferroniobium alloy from associated minerals containing niobium, titanium, iron, and rare earth elements via molten salt electrolysis. By precisely controlling the electrolysis voltage, niobium oxide and iron oxide in the associated minerals are selectively electrolytically reduced to ferroniobium alloy, achieving effective separation of iron and niobium from rare earth elements and titanium. Compared to existing electrolysis processes for niobium-containing iron ore, this invention eliminates the need for pre-treatment of iron elements in the ore through carbothermic reduction and magnetic separation. The process is shorter, simpler to operate, and achieves better element separation, especially deep separation of niobium and titanium, preventing titanium impurities from entering the ferroniobium alloy and enhancing its application value.

[0026] The molten salt is preferably a mixture of cryolite and one or more salts selected from NaF, LiF, and KF. Associated minerals containing niobium, titanium, iron, and rare earth elements can be dissolved in the molten salt at 900-1100℃. Electrolytic reduction is carried out under inert gas protection to selectively reduce niobium oxide and iron oxide in the molten salt.

[0027] The method of this invention is applicable to associated minerals containing multiple elements such as niobium, titanium, iron, and rare earth elements, and can effectively solve the problem of difficulty in enriching the numerous elements in associated minerals. Compared with the existing technology that uses carbonaceous reducing agents, this method not only avoids the formation of niobium carbide and titanium carbide in the product, but also produces a titanium-free (undetectable titanium) niobium-iron alloy, expanding the application range of niobium-iron alloys and greatly reducing CO2 emissions from the process. Attached Figure Description

[0028] Figure 1 The theoretical decomposition voltage diagrams for niobium oxide, iron oxide, titanium oxide, and rare earth oxide at different temperatures are shown. Detailed Implementation

[0029] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] like Figure 1 The figure shows the theoretical decomposition voltages of niobium oxide, iron oxide, titanium oxide, and rare earth oxides at different temperatures. Analysis of this figure reveals that the theoretical decomposition voltages of titanium oxide and rare earth oxides are consistently higher than those of niobium oxide and iron oxide. Therefore, this provides theoretically feasible support for the process of separating niobium-iron and rare earth elements from commensurate niobium-titanium-rare earth minerals using molten salt electrolysis.

[0031] It should be noted that, Figure 1The theoretical decomposition voltage is calculated based on pure chemical substances. In practical applications, different oxides in niobium-titanium-iron rare earth associated minerals dissolve in molten salt. The electrolytic characteristics of each oxide differ from those of the pure substance, and their actual activity is much lower than that of the pure substance (the activity of the pure substance is 1). Therefore, the actual electrolysis voltage is higher than that of the pure substance. Experiments have shown that when the mass ratio of niobium-titanium-iron rare earth associated minerals (or other minerals with niobium-titanium-iron rare earth oxide content similar to or comparable to that of Bayan Obo minerals) to molten salt is in the range of 2-10:100, and the molten salt holding temperature is 900-1100℃, selective electrolytic reduction of niobium-iron in niobium-titanium-iron rare earth associated minerals can be achieved by controlling the electrolysis voltage within the range of 2-5V, thus preparing niobium-iron alloys without titanium impurities.

[0032] This invention achieves the effect of preparing niobium-iron alloy by selectively reducing iron and niobium to form niobium-iron alloys through electrolysis between iron oxides and niobium oxides and titanium rare earths (titanium oxides and rare earth oxides) by precisely controlling the voltage. It also obtains molten salts containing rare earths and titanium, thus separating iron and niobium from associated minerals. This invention solves the problems of high titanium impurity content in the product of carbothermic reduction process and the complexity and long process line of existing electrolysis methods.

[0033] The present invention and its technical effects are described below with reference to specific embodiments. Unless otherwise specified, the associated minerals containing niobium, titanium, iron, and rare earth elements in the following embodiments are obtained by Baogang from the Bayan Obo mine; cryolite, sodium fluoride, lithium fluoride, and potassium fluoride are commercially available products; and argon gas is commercially available high-purity argon gas of ≥99%.

[0034] Example 1

[0035] In this embodiment, a mixture of NaF and Na3AlF6 at 42wt% and 58wt% respectively was used as the molten salt. A co-existing mineral containing niobium, titanium, iron, and rare earth elements was added at 4% of the molten salt mass. The co-existing mineral contained (by mass percentage): Nb2O5 5.4%, TiO2 14.6%, Tfe 26.7%, CaO 13.5%, SiO2 18.8%, Al2O3 2.7%, RE x O y 3.2%.

[0036] The aforementioned associated minerals were thoroughly mixed with the molten salt. The mixture was then placed in a high-purity graphite electrolytic cell, heated to 900°C and held for 3 hours, with 99% pure argon gas introduced as a protective gas. Using inert molybdenum (Mo) as the cathode and high-purity graphite as the anode, constant voltage electrolysis was performed at 900°C with the cell voltage set to 3.0V. After 4 hours of electrolysis, a niobium-iron alloy was deposited near the cathode of the electrolytic cell, yielding a molten salt block.

[0037] The molten salt block was thoroughly crushed and ground to 300 mesh. The niobium-iron alloy was then magnetically separated in a magnetic separator using a magnetic field strength of 150 mT. After rinsing several times with distilled water and drying at low temperature, X-ray fluorescence spectroscopy analysis showed that the mass fraction of Nb in the niobium-iron alloy was 10.2%, and no titanium was detected. This yielded a niobium-iron alloy free of titanium impurities, achieving selective electrochemical separation of iron and niobium in complex associated minerals with good niobium-titanium separation effect.

[0038] Example 2

[0039] A mixture of 50 wt% LiF and 50 wt% Na3AlF6 was used as the molten salt. A co-existing mineral containing niobium, titanium, iron, and rare earth elements was added at 6% of the molten salt mass. The co-existing mineral contained (by mass percentage): Nb2O5 6.8%, TiO2 16.6%, TFe 17.8%, CaO 14.8%, SiO2 15.7%, Al2O3 3.9%, RE x O y 3.7%.

[0040] The aforementioned associated minerals were thoroughly mixed with the molten salt. The mixture was then placed in a high-purity graphite electrolytic cell, heated to 920°C and held at that temperature for 1.5 hours, with 99% pure argon gas introduced as a protective gas. Using inert platinum (Pt) as the cathode and high-purity graphite as the anode, constant voltage electrolysis was performed at 920°C with the cell voltage set to 3.5V. After 5 hours of electrolysis, a niobium-iron alloy was deposited near the cathode of the electrolytic cell, yielding a molten salt block.

[0041] The molten salt block was thoroughly crushed and ground to 300 mesh. The niobium-iron alloy was then magnetically separated in a magnetic separator using a magnetic field strength of 200 mT. After rinsing several times with distilled water and drying at low temperature, the niobium-iron alloy contained 18.3% Nb by weight and no titanium was detected. This yielded a niobium-iron alloy free of titanium impurities, achieving selective electrochemical separation of iron and niobium in complex associated minerals with good niobium-titanium separation effect.

[0042] Example 3

[0043] A mixture of KF and Na3AlF6 at 36wt% and 64wt% respectively was used as molten salt. An associated mineral containing niobium, titanium, iron, and rare earth elements was added at 8% of the molten salt mass. The associated mineral contained (by mass percentage): Nb2O5 8.3%, TiO2 16.7%, TFe 10.8%, CaO 15.1%, SiO2 19.6%, Al2O3 4.6%, RE x O y 5.7%.

[0044] The aforementioned associated minerals were thoroughly mixed with the molten salt. The mixture was then placed in a high-purity graphite electrolytic cell, heated to 1000℃ and held for 2 hours, with 99.99% pure argon gas introduced as a protective gas. Using inert tungsten (W) as the cathode and high-purity graphite as the anode, constant voltage electrolysis was performed at 1000℃ with the cell voltage set to 4.0V. After 6 hours of electrolysis, a niobium-iron alloy was deposited near the cathode of the electrolytic cell, yielding a molten salt block.

[0045] The molten salt block was thoroughly crushed and ground to 250 mesh. The niobium-iron alloy was then magnetically separated in a magnetic separator using a magnetic field strength of 100 mT. After rinsing several times with distilled water and drying at low temperature, the niobium-iron alloy contained 30.6% Nb by weight and no titanium was detected. This yielded a niobium-iron alloy free of titanium impurities, achieving selective electrochemical separation of iron and niobium in complex associated minerals with good niobium-titanium separation effect.

[0046] Example 4

[0047] A mixture of NaF and Na3AlF6 at 30wt% and 70wt% respectively was used as molten salt. An associated mineral containing niobium, titanium, iron, and rare earth elements was added at 8% of the molten salt mass. The associated mineral contained (by mass percentage): Nb2O5 11.4%, TiO2 14.8%, TFe 5.8%, CaO 15.2%, SiO2 20.1%, Al2O3 5.2%, RE x O y 3.3%.

[0048] The aforementioned associated minerals were thoroughly mixed with the molten salt. The mixture was then placed in a high-purity graphite electrolytic cell, heated to 1100℃ and held for 1 hour, while 99.95% pure argon gas was introduced. Using inert molybdenum (Mo) as the cathode and high-purity graphite as the anode, electrolysis was performed at 1100℃ with a constant voltage of 4.0V. After 8 hours of electrolysis, a niobium-iron alloy was deposited near the cathode of the electrolytic cell, yielding a molten salt block.

[0049] The molten salt block was thoroughly crushed and ground to 400 mesh. The niobium-iron alloy was then magnetically separated in a magnetic separator using a magnetic field strength of 150 mT. After rinsing several times with distilled water and drying at low temperature, the niobium-iron alloy contained 51.8% Nb by weight and no titanium was detected. This yielded a niobium-iron alloy free of titanium impurities, achieving selective electrochemical separation of iron and niobium in complex associated minerals with good niobium-titanium separation effect.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for producing ferroniobium alloys by molten salt electrolysis of associated minerals containing niobium, titanium, iron, and rare earth elements, characterized in that, Includes the following steps: S1. Mix the associated minerals containing niobium, titanium, iron, and rare earth elements with molten salt, place the mixture in an electrolytic cell, heat the electrolytic cell and introduce an inert protective gas, raise the temperature of the molten salt to its melting temperature and hold it therein, so that the molten salt is completely in a molten state; the molten salt is a mixture of cryolite Na3AlF6 and one or more salts selected from NaF, LiF, and KF. S2. An inert metal is used as the cathode, and a high-purity graphite rod is used as the anode. The cathode and anode are inserted into the molten salt of the electrolytic cell. After the inert metal cathode and graphite anode are connected to a DC power supply, the electrolysis voltage is strictly controlled for electrolysis. The electrolysis voltage is determined based on the heat preservation temperature and the dissolution concentration of the associated minerals in the molten salt. The electrolysis voltage is lower than the decomposition voltage of titanium oxide and rare earth oxides but higher than the decomposition voltage of iron oxide and niobium oxide. The inert metal used for the inert metal cathode is tungsten, molybdenum, or platinum. The entire electrolysis process is carried out under the protection of an inert protective gas. S3. After electrolysis, the cathode, anode, and molten salt are cooled under the protection of an inert protective gas.

2. The method according to claim 1, characterized in that, In S1, the heat preservation temperature is 900-1100℃; the heat preservation time is 1-3h; and in S2, the electrolysis voltage is 2-5V.

3. The method according to claim 1 or 2, characterized in that, In S1, the associated mineral containing niobium, titanium, iron, and rare earth elements is Bayan Obo mineral, and its mass ratio with molten salt ranges from 2 to 10:

100.

4. The method according to claim 1 or 2, characterized in that, In S1, the associated mineral containing niobium, titanium, iron, and rare earth elements comprises the following components by mass percentage: Nb₂O₅ 1-30%, TiO₂ 1-20%, TFe 1-40%, CaO 1-20%, SiO₂ 1-30%, Al₂O₃ 1-20%, RE x O y 1-10%, other components ≤10%; its mass ratio with molten salt ranges from 2-10:

100.

5. The method according to claim 1, characterized in that, In S1-S3, the inert protective gas is high-purity argon with a purity ≥99%.

6. The method according to claim 1, characterized in that, In S2, the electrolysis time is 4-8 hours.

7. The method according to claim 1, characterized in that, Step S3 also includes: crushing, grinding, and magnetically separating the cooled product in the electrolytic cell to obtain niobium-iron alloy and residual molten salt.

8. The method according to claim 7, characterized in that, The grinding process involves grinding the cooled product in the electrolytic cell to a mesh size of 200-500; the magnetic induction intensity of the magnetic separation is 50-200 mT. The remaining molten salt was further used to separate and extract rare earth elements and titanium.

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