CN117364177A - Method for preparing metallic iron and ferrosilicon alloy by electrolysis of molten oxide fluoride system - Google Patents

Abstract

The invention belongs to the technical field of metal iron metallurgy, and provides a method for preparing metal iron and ferrosilicon alloy by electrolysis of a molten oxide fluoride system, which comprises the following steps: siO is carried out under the atmosphere of protective gas ₂ 、CaO、CaF ₂ And Fe (Fe) ₂ O ₃ Grinding and drying are sequentially carried out after mixing, so as to obtain a molten oxide electrolyte; and (3) electrolyzing the molten oxide electrolyte by taking a tungsten wire as a cathode and an inert material as an anode to obtain liquid metal iron and ferrosilicon alloy. The method for preparing the metal iron and the ferrosilicon alloy by electrolyzing and melting the oxide electrolyte is simple, strong in operability, green and efficient; the residual mineral components of tailings after iron separation of the bayan obo ores are used as raw materials, and metal iron and ferrosilicon alloy are efficiently prepared from the ores in one step, so that the energy consumption for preparing the whole metal iron is reduced; using a suitable inert anode material, CO is reduced ₂ Even up to CO ₂ Is not discharged.

Description

A method for electrolytically preparing metallic iron and ferrosilicon alloys using a molten oxide fluoride system method

Technical field

The invention relates to the technical field of metallic iron metallurgy, and in particular to a method for electrolytically preparing metallic iron and ferrosilicon alloys using a molten oxide fluoride system.

Background technique

Pure iron has good soft magnetic, corrosion resistance, electrical conductivity, thermal conductivity and other properties, and is widely used in aerospace, automobiles, military manufacturing, electromagnetic components and other fields. At present and for a long time to come, metallic iron and its alloys will remain the most widely used structural materials in industrial production and life. In traditional methods, metallic iron is smelted through carbon thermal reduction of iron ore in a blast furnace or electric arc furnace. In this process, coke is an essential raw material. However, with the continuous development and utilization of fossil energy, its corresponding reserves continue to decrease, which will inevitably impose certain restrictions on the carbon thermal reduction of iron ore. In addition, coke, as a reducing agent, will produce a large amount of carbon dioxide gas during the production of steel. Large-scale emissions of carbon dioxide gas directly lead to global climate warming and have a great impact on the environment.

With the help of electrochemical metallurgical technology using electron transfer as an energy carrier, the reaction process is easy to control and is expected to have high energy efficiency. It has achieved great success in the field of aluminum electrolysis. At present, many researchers have also successfully prepared metallic iron or iron alloys through electrochemical methods. Typically, electrochemical ironmaking is represented by the molten salt electrodeoxidation method, namely the Cambridge process, molten salt electrolysis and molten oxide electrolysis. The Cambridge method is an electrochemical metallurgical process proposed by Fray et al. of Cambridge University. In this method, a graphite electrode is generally used as the anode and solid iron oxide is used as the cathode. Metal iron is obtained at the cathode through direct electrolytic reduction at a temperature lower than the melting point of the metal and a voltage at which the molten salt decomposes. However, molten salt electrodeoxidation iron production still requires relatively pure iron oxide raw materials. The products obtained by electrodeoxidation iron production are clumps composed of tiny iron particles. It is difficult to effectively separate the solidified molten salt and reduce the oxygen content of the product.

Molten salt electrolytic iron production usually uses molten salts such as metal halides or carbonates as electrolytes. Iron oxide is an iron-containing raw material. Iron oxide is dissolved in molten salt, iron is precipitated on the cathode, and oxygen is precipitated on the inert anode. Compared with molten oxide electrolytic iron making, the electrolysis temperature of molten salt electrolytic iron making is lower. However, the solubility of iron oxide in molten salt is low, resulting in low limit current density of the electrolysis process, low iron production efficiency, and low electrolysis efficiency. In addition, the product of molten salt electrolysis is usually powdered iron, which is difficult to separate from the molten electrolyte, making it difficult to achieve continuous production. The above-mentioned preparation methods of common metallic iron all have problems such as complex processes, low electrolysis efficiency, high energy consumption, difficulty in continuous production, and environmental pollution.

Molten oxide electrolysis is a promising sustainable iron extraction method that directly electrolytically decomposes iron ore to obtain liquid metallic iron and pure oxygen. During electrolysis, an electric current is applied between two electrodes to provide the necessary electromotive force to break down the ore into metallic iron and oxygen. The use of molten oxide electrolyte allows iron ore (usually hematite (Fe ₂ O ₃ )) to be fed directly into the electrolytic cell, and the operating temperature is set above the melting point of iron metal (1811K) without considering volatilization.

Therefore, it is of great significance to study a method for preparing metallic iron and its alloys by electrolysis of molten oxide fluoride that reduces energy consumption, is green and efficient.

Contents of the invention

The object of the present invention is to provide a method for electrolytically preparing metallic iron and ferrosilicon alloys using a molten oxide fluoride system in order to overcome the shortcomings of the prior art.

In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

The invention provides a method for electrolytically preparing metallic iron and ferrosilicon alloys using a molten oxide fluoride system, which includes the following steps:

1) Under a protective gas atmosphere, SiO ₂ , CaO, CaF ₂ and Fe ₂ O ₃ are mixed and then ground and dried in sequence to obtain a molten oxide electrolyte;

2) Using tungsten wire as the cathode and inert material as the anode, the molten oxide electrolyte is electrolyzed to obtain liquid metal iron and ferrosilicon alloy.

Preferably, the mass ratio of SiO ₂ , CaO, CaF ₂ and Fe ₂ O ₃ in step 1) is 40-50:20-30:10-30:5-20.

Preferably, the SiO ₂ , CaO, CaF ₂ and Fe ₂ O ₃ in step 1) are the remaining components of the tailings after iron beneficiation at the Bayan Obo mine; the flow rate of the protective gas is 0.3 to 0.5 m ³ /h.

Preferably, the drying temperature in step 1) is 160-240°C, the drying time is 30-50h, and the heating rate to the drying temperature is 2-6°C/min.

Preferably, the electrolysis temperature in step 2) is 1200-1600°C, and the heating rate to the electrolysis temperature is 4-6°C/min.

Preferably, after being incubated at the electrolysis temperature, current is passed through to perform electrolysis. The incubation time is 30 to 150 minutes, and the electrolysis time is 1 to 15 hours.

Preferably, during the electrolysis process in step 2), the current density is 0.1-2.5A/cm ² , and the area ratio of the anode and the cathode is 5-10:1.

Preferably, the inert material in step 2) is graphite, platinum, platinum rhodium or iridium.

Preferably, when the reduction potential of electrolysis in step 2) is 0.3-0.6V, liquid metal iron is obtained; when the reduction potential of electrolysis is 0-0.3V, ferrosilicon alloy is obtained.

The beneficial effects of the present invention include:

1) The method of the present invention for preparing metallic iron and ferrosilicon alloy by electrolysis of molten oxide electrolyte is simple, highly operable, green and efficient.

2) Using the remaining mineral components of the tailings after iron beneficiation at the Bayan Obo Mine as raw materials, metallic iron and ferrosilicon alloys can be efficiently prepared from the ore in one step, thereby reducing the energy consumption of the entire metallic iron preparation and obtaining good economic benefits.

3) Compared with the traditional method of smelting metallic iron in a blast furnace electric furnace, the present invention uses suitable inert anode materials, which reduces the amount of _CO2 released and even achieves zero emission of _CO2 .

Description of the drawings

Figure 1 is a schematic structural diagram of a high-temperature furnace used for electrolysis with molten oxide electrolyte of the present invention, in which 1 is a boron nitride crucible, 2 is a tube furnace, 3 is a refractory brick, 4 is a water-cooled flange, and 5 is corundum. tube, 6 is the working electrode, 7 is the reference electrode, 8 is the counter electrode, 9 is the air outlet, and 10 is the air inlet;

Figure 2 is a diagram of the product prepared in Example 1;

Figure 3 is the XRD pattern of the product prepared in Example 1;

Figure 4 is a diagram of the product prepared in Example 2;

Figure 5 is the XRD pattern of the product prepared in Example 2;

Figure 6 is an EDX pattern of the ferrosilicon alloy prepared in Example 3;

Figure 7 is an EDX pattern of the ferrosilicon alloy prepared in Example 4.

Detailed ways

The invention provides a method for electrolytically preparing metallic iron and ferrosilicon alloys using a molten oxide fluoride system, which includes the following steps:

1) Under a protective gas atmosphere, SiO ₂ , CaO, CaF ₂ and Fe ₂ O ₃ are mixed and then ground and dried in sequence to obtain a molten oxide electrolyte;

2) Using tungsten wire as the cathode and inert material as the anode, the molten oxide electrolyte is electrolyzed to obtain liquid metal iron and ferrosilicon alloy.

In the present invention, the mass ratio of SiO ₂ , CaO, CaF ₂ and Fe ₂ O ₃ in step 1) is preferably 40-50:20-30:10-30:5-20, and further preferably 42-48:23 ~28:15~25:8~15, more preferably 45:25:20:10~13.

In the present invention, the SiO ₂ , CaO, CaF ₂ and Fe ₂ O ₃ in step 1) are preferably the remaining components of the tailings after iron beneficiation at the Bayan Obo mine; the flow rate of the protective gas is preferably 0.3 to 0.5 m ³ / h, more preferably 0.35 to 0.45 m ³ /h, more preferably 0.4 m ³ /h; the protective gas is preferably nitrogen or argon.

After the iron and rare earth elements are extracted from the Bayan Obo mineral resources, the remaining tailings are piled as waste in a waste warehouse. However, the tailings still contain a large amount of valuable elements such as niobium, titanium, and iron that cannot be fully utilized and have become potential secondary resources. The valuable elements cannot be extracted using traditional smelting methods. By performing molten salt electrolysis on the valuable elements of the tailings after iron beneficiation in the Bayan Obo Mine, the iron and ferrosilicon alloys can be fully extracted, and the calcium fluoride content in the tailings is high, which can be used as a co-solvent to improve electrolyte performance and reduce electrolyte Viscosity, improve ionic conductivity.

In the present invention, the drying temperature in step 1) is preferably 160-240°C, more preferably 170-220°C, more preferably 180-200°C; the drying time is preferably 30-50h, further preferably 35-45h , more preferably 40 h; the heating rate to the drying temperature is preferably 2 to 6°C/min, more preferably 3 to 5°C/min, and more preferably 4°C/min.

In the present invention, the temperature of the electrolysis in step 2) is preferably 1200-1600°C, further preferably 1350-1500°C, more preferably 1400-1450°C; the temperature rise rate to the electrolysis temperature is preferably 4-6°C/min. , more preferably 4.5 to 5.5°C/min, more preferably 5°C/min.

In the present invention, it is preferable to insulate at the electrolysis temperature and then pass in current to perform electrolysis. The insulation time is preferably 30 to 150 min, further preferably 50 to 140 min, and more preferably 70 to 120 min; the electrolysis time is preferably 1 ~15h, more preferably 5-12h, more preferably 6-8h.

In the present invention, during the electrolysis process in step 2), the current density is preferably 0.1~2.5A/cm ² , more preferably 0.5~2A/cm ² , and more preferably 0.8~1.5A/cm ² ; the anode and The area ratio of the cathode is preferably 5 to 10:1, more preferably 6 to 9:1, and even more preferably 7 to 8:1.

In the present invention, electrolysis is preferably performed under a protective atmosphere.

In the present invention, the inert material in step 2) is preferably graphite, platinum, platinum-rhodium or iridium.

In the present invention, when the reduction potential of the electrolysis in step 2) is 0.3-0.6V (excluding 0.3V), liquid metal iron is obtained, preferably 0.4-0.5V; when the reduction potential of the electrolysis is 0-0.3V, liquid metal iron is obtained Ferrosilicon alloy, preferably 0.1 to 0.2V.

In the present invention, the diameter of the tungsten wire is preferably 1 to 3 mm, more preferably 1.5 to 2.5 mm, and more preferably 2 mm; the purity of the tungsten wire is preferably 98 to 99.99%, further preferably 98.5 to 99.95%, and more preferably 99 ~99.9%.

In the present invention, the tungsten wire in step 2) is preferably a tungsten wire that has been polished, soaked in acid, and cleaned in sequence. The polishing is preferably done by sequentially using 200 mesh, 400 mesh, 600 mesh, 800 mesh, 1000 mesh, and 1200 mesh sandpaper. Polishing; the acid soaking time is preferably 2 to 3 hours, more preferably 2.5 hours; cleaning is preferably ultrasonic cleaning, and the cleaning reagent is preferably water or absolute ethanol; the power of ultrasonic cleaning is preferably 100 to 500 W, and further preferably 200 to 200 W. 400W, more preferably 300W; the ultrasonic cleaning time is preferably 15 to 60 minutes, more preferably 25 to 50 minutes, more preferably 35 to 40 minutes.

In the present invention, ultrasonic cleaning is used to remove organic matter and other impurities on the surface of the tungsten wire electrode.

The structural schematic diagram of the high-temperature furnace used for electrolysis of the molten oxide electrolyte of the present invention is shown in Figure 1, in which 1 is a boron nitride crucible, 2 is a tube furnace, 3 is a refractory brick, 4 is a water-cooled flange, 5 is the corundum tube, 6 is the working electrode, 7 is the reference electrode, 8 is the counter electrode, 9 is the air outlet, and 10 is the air inlet.

The technical solutions provided by the present invention will be described in detail below with reference to the examples, but they should not be understood as limiting the protection scope of the present invention.

In the embodiment, SiO ₂ , CaO, CaF ₂ and Fe ₂ O ₃ are the remaining components of the tailings after iron beneficiation at the Bayan Obo mine.

Example 1

42g SiO ₂ , 25g CaO, 20g CaF ₂ and 13g Fe ₂ O ₃ were mixed under an argon atmosphere (the flow rate of argon gas was 0.4m ³ /h), then fully ground in an agate mortar, and then ground at 4°C/ The temperature was raised to 200°C at a rate of min, and dried at 200°C for 32 hours for dehydration treatment to obtain a molten oxide electrolyte.

The end of a tungsten wire with a diameter of 2 mm and a purity of 98.5% is polished with 200 mesh, 400 mesh, 600 mesh, 800 mesh, 1000 mesh and 1200 mesh sandpaper in sequence, and then soaked in 15% mass fraction of dilute hydrochloric acid. 2.5h, and finally ultrasonic cleaning with absolute ethanol for 50 minutes. The power of ultrasonic cleaning is 300W. Use the treated tungsten wire as the cathode and graphite as the anode (the area ratio of the anode to the cathode is 8:1).

The high-temperature furnace is heated to 1400°C at a rate of 5°C/min, the molten oxide electrolyte is kept warm at 1400°C for 40 minutes, and then a cathode current with a density of 0.6A/cm ² is passed through to electrolyze the molten oxide electrolyte for 5 hours. The reduction potential was 0.45V, and the electrolysis was performed under an argon atmosphere. After the electrolysis is completed, the melt is slowly cooled in the furnace. After the temperature drops to room temperature, the solidified electrolyte in the boron nitride crucible is taken out, and metallic iron is obtained at the bottom of the electrolyte.

The product prepared in this embodiment is shown in Figure 2. It can be seen from Figure 2 that the metallic iron is spherically gathered at the bottom of the melt, indicating that the obtained metallic iron has a uniform texture.

The XRD pattern of the product prepared in this embodiment is shown in Figure 3. It can be seen from Figure 3 that metallic iron was successfully prepared in this embodiment.

Example 2

45g SiO ₂ , 23g CaO, 22g CaF ₂ and 10g Fe ₂ O ₃ were mixed in a nitrogen atmosphere (the flow rate of nitrogen was 0.35m ³ /h), then fully ground in an agate mortar, and then ground at 3°C/min. The temperature was increased to 170°C, and dried at 170°C for 40 hours to perform dehydration treatment to obtain a molten oxide electrolyte.

The end of the tungsten wire with a diameter of 1.5mm and a purity of 99.95% was polished with 200 mesh, 400 mesh, 600 mesh, 800 mesh, 1000 mesh and 1200 mesh sandpaper in sequence, and then in 12% mass fraction of dilute hydrochloric acid. Soak for 3 hours, and finally use ultrasonic cleaning with absolute ethanol for 30 minutes. The power of ultrasonic cleaning is 400W. Use the treated tungsten wire as the cathode and graphite as the anode (the area ratio of the anode to the cathode is 7:1).

The high-temperature furnace is heated to 1320°C at a rate of 4.5°C/min, the molten oxide electrolyte is kept warm at 1320°C for 80 minutes, and then a cathode current with a density of 1.2A/cm ² is passed through to electrolyze the molten oxide electrolyte for 7 hours. The reduction potential was 0.5V, and the electrolysis was performed under a nitrogen atmosphere. After the electrolysis is completed, the melt is slowly cooled in the furnace. After the temperature drops to room temperature, the solidified electrolyte in the boron nitride crucible is taken out, and metallic iron is obtained at the bottom of the electrolyte.

The product prepared in this embodiment is shown in Figure 4. It can be seen from Figure 4 that the metallic iron is spherically gathered at the bottom of the melt, indicating that the obtained metallic iron has a uniform texture.

The XRD pattern of the product prepared in this embodiment is shown in Figure 5. It can be seen from Figure 5 that metallic iron was successfully prepared in this embodiment.

Example 3

Mix 40g SiO ₂ , 25g CaO, 30g CaF ₂ and 5g Fe ₂ O ₃ in an argon atmosphere (the flow rate of argon gas is 0.45m ³ /h), then grind them fully in an agate mortar, and then grind them at 5℃/ The temperature was raised to 220°C at a rate of min, and dried at 220°C for 30 hours for dehydration treatment to obtain a molten oxide electrolyte.

The end of the tungsten wire with a diameter of 2.5mm and a purity of 99.99% was polished with 200 mesh, 400 mesh, 600 mesh, 800 mesh, 1000 mesh and 1200 mesh sandpaper in sequence, and then in dilute hydrochloric acid with a mass fraction of 17% Soak for 2 hours, and finally clean ultrasonically with water for 40 minutes. The power of ultrasonic cleaning is 200W. Use the treated tungsten wire as the cathode and platinum as the anode (the area ratio of the anode to the cathode is 7.5:1).

The high-temperature furnace is heated to 1450°C at a rate of 4.5°C/min, the molten oxide electrolyte is kept warm at 1450°C for 90 minutes, and then a cathode current with a density of 0.8A/cm ² is passed through to electrolyze the molten oxide electrolyte for 8 hours. The reduction potential was 0.2V, and the electrolysis was performed under an argon atmosphere. After the electrolysis is completed, the melt is slowly cooled in the furnace. After the temperature drops to room temperature, the solidified electrolyte in the boron nitride crucible is taken out, and a ferrosilicon alloy is obtained at the bottom of the electrolyte.

The EDX pattern of the ferrosilicon alloy prepared in this example is shown in Figure 6.

Example 4

43g SiO ₂ , 22g CaO, 27.5g CaF ₂ and 7.5g Fe ₂ O ₃ were mixed under an argon atmosphere (the flow rate of argon gas was 0.4m ³ /h), then fully ground in an agate mortar, and then ground with 4 The temperature was raised to 220°C at a rate of ℃/min, and dried at 220°C for 35 hours for dehydration treatment to obtain a molten oxide electrolyte.

The end of a tungsten wire with a diameter of 2mm and a purity of 99.9% is polished with 200 mesh, 400 mesh, 600 mesh, 800 mesh, 1000 mesh and 1200 mesh sandpaper in sequence, and then soaked in 15% mass fraction of dilute hydrochloric acid. 2.5h, and finally ultrasonic cleaning with absolute ethanol for 60 minutes. The power of ultrasonic cleaning is 300W. Use the treated tungsten wire as the cathode and iridium as the anode (the area ratio of the anode to the cathode is 9:1).

The high-temperature furnace is heated to 1470°C at a rate of 5.5°C/min, the molten oxide electrolyte is kept warm at 1470°C for 100min, and then a cathode current with a density of 1.6A/cm ² is passed through to electrolyze the molten oxide electrolyte for 10h. The reduction potential was 0.1V, and the electrolysis was performed under an argon atmosphere. After the electrolysis is completed, the melt is slowly cooled in the furnace. After the temperature drops to room temperature, the solidified electrolyte in the boron nitride crucible is taken out, and a ferrosilicon alloy is obtained at the bottom of the electrolyte.

The EDX pattern of the ferrosilicon alloy prepared in this example is shown in Figure 7.

The present invention uses the remaining components of the tailings after iron beneficiation in the Bayan Obo mine as raw materials, tungsten wire as the cathode, and the inert material as the anode. It deeply extracts the remaining iron ore in the tailings, and can further directly extract the remaining iron ore in the tailings. extract. The method of the present invention not only has high deposition efficiency, but also has a short process and low energy consumption; the entire process is protected by protective gas, which greatly improves the safety of the process, reduces greenhouse gas emissions, and is relatively environmentally friendly.

The above are only preferred embodiments of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principles of the present invention. These improvements and modifications can also be made. should be regarded as the protection scope of the present invention.

Claims (9)

1. A method for electrolytically preparing metallic iron and ferrosilicon alloys using a molten oxide fluoride system, which is characterized by comprising the following steps: 1) Under a protective gas atmosphere, SiO ₂ , CaO, CaF ₂ and Fe ₂ O ₃ are mixed and then ground and dried in sequence to obtain a molten oxide electrolyte; 2) Using tungsten wire as the cathode and inert material as the anode, the molten oxide electrolyte is electrolyzed to obtain liquid metal iron and ferrosilicon alloy. 2. The method according to claim 1, characterized in that the mass ratio of _SiO2 , CaO, _CaF2 and _Fe2O3 in step 1) is 40~50:20~30:10~ ₃₀ :5~ 20. 3. The method according to claim 1 or 2, characterized in that, in step 1), the SiO ₂ , CaO, CaF ₂ and Fe ₂ O ₃ are the remaining components of the tailings after iron beneficiation at the Bayan Obo mine; The flow rate of protective gas is 0.3～0.5m ³ /h. 4. The method according to claim 1 or 2, characterized in that the drying temperature in step 1) is 160-240°C, the drying time is 30-50h, and the heating rate to the drying temperature is 2-6 ℃/min. 5. The method according to claim 4, characterized in that the electrolysis temperature in step 2) is 1200-1600°C, and the heating rate to the electrolysis temperature is 4-6°C/min. 6. The method according to claim 4, characterized in that, after being incubated at the electrolysis temperature, current is passed through to perform electrolysis, the incubation time is 30 to 150 min, and the electrolysis time is 1 to 15 h. 7. The method according to claim 5 or 6, characterized in that, during the electrolysis process in step 2), the density of the current is 0.1~2.5A/ ^cm2 , and the area ratio of the anode and the cathode is 5~10: 1. 8. The method according to claim 7, wherein the inert material in step 2) is graphite, platinum, platinum-rhodium or iridium. 9. The method according to claim 8, characterized in that, when the reduction potential of electrolysis in step 2) is 0.3-0.6V, liquid metal iron is obtained; when the reduction potential of electrolysis is 0-0.3V, ferrosilicon alloy is obtained .