A method and system for producing ultra-high purity iron using recycled steel feedstock

Abstract

The application provides a method and system for preparing ultra-high purity iron by using recycled steel raw materials, and relates to the field of metallurgy. The method for preparing ultra-high purity iron by using recycled steel raw materials comprises the following steps: pretreating recycled steel raw materials to obtain anode materials of a first electrolysis zone, then performing first electrolysis in the first electrolysis zone by taking first high-purity iron as a cathode and the anode materials as an anode, and obtaining primary iron at the cathode; performing second electrolysis by taking the primary iron as anode materials of a second electrolysis zone and second high-purity iron as a cathode to obtain third high-purity iron with a purity of not less than 99.95wt%; and performing hydrogen plasma smelting on the third high-purity iron to obtain an ultra-high purity iron product. The method and system provided by the application can realize efficient electrolysis and plasma smelting by combining electrolysis and hydrogen plasma smelting, and 4N5 grade ultra-high purity iron can be obtained by using scrap steel materials.

Description

Technical Field

[0001] This application relates to the field of metallurgy, and in particular to a method and system for preparing ultra-high purity iron using recycled steel raw materials. Background Technology

[0002] Ultra-high purity iron is an indispensable key material in fields such as semiconductors, aerospace, and nuclear industry. With the increasing global demand for resource recycling, the direct production of high-purity iron from recycled steel such as scrap steel and stainless steel waste has become an important direction for industry development. However, the residual metallic impurities such as copper (Cu), tin (Sn), lead (Pb), zinc (Zn), and nickel (Ni) as well as non-metallic impurities such as oxygen (O), sulfur (S), and phosphorus (P) in recycled raw materials make it difficult for traditional processes to achieve efficient removal, severely restricting the product quality and production cost of high-purity iron.

[0003] Currently, the main industrial method for producing high-purity iron is electrolytic refining. However, producing high-purity iron with a purity of 4N and above faces significant technical challenges. Because iron has a relatively negative standard electrode potential (-0.44 V), the hydrogen evolution reaction during electrolysis competes with iron deposition. This not only leads to an increased oxygen content in the cathode iron product, reaching up to 1000 ppm, but also makes the iron sheet more susceptible to oxidation due to the microporous structure formed by hydrogen evolution. To suppress the hydrogen evolution reaction, the current density is typically limited to 300 A / m. 2 The following factors contribute to low production efficiency. Furthermore, residual elements such as Cu, Sn, Pb, Zn, and Ni in recycled steel have electrode potentials close to those of iron, making selective removal difficult with traditional electrolytic processes. This forces existing technologies to rely on high-purity raw materials, such as ferrous sulfate, and prevents the effective utilization of recycled resources.

[0004] In view of the above, this application is hereby submitted. Summary of the Invention

[0005] The purpose of this application is to provide a method and system for preparing ultra-high purity iron using recycled steel raw materials, so as to solve the above-mentioned problems.

[0006] To achieve the above objectives, this application adopts the following technical solution:

[0007] A method for preparing ultra-high purity iron using recycled steel raw materials includes:

[0008] The recycled steel raw material is pretreated to obtain the anode material of the first electrolysis zone. Then, the first high-purity iron is used as the cathode and the anode material is used as the anode to perform the first electrolysis in the first electrolysis zone and primary iron is obtained at the cathode. The primary iron is used as the anode material of the second electrolysis zone and the second high-purity iron is used as the cathode to perform the second electrolysis to obtain the third high-purity iron with a purity of not less than 99.95 wt%.

[0009] The third high-purity iron is subjected to hydrogen plasma melting to obtain an ultra-high-purity iron product;

[0010] The purity of the ultra-high purity iron product is not less than 99.995 wt%; the initial electrolytes of the anode chambers of the first electrolysis zone and the second electrolysis zone are each independently aqueous solutions of inorganic acids; the initial electrolyte of the cathode chamber of the first electrolysis zone is the liquid obtained by electrolysis of the initial electrolyte of the anode chamber of the first electrolysis zone and subsequent sulfidation to remove impurities; the cathode chamber of the first electrolysis zone also contains a first additive, a first pH buffer, and iron powder; the initial electrolyte of the cathode chamber of the second electrolysis zone is the liquid obtained by electrolysis of the initial electrolyte of the anode chamber of the second electrolysis zone and subsequent extraction to remove impurities; the cathode chamber of the second electrolysis zone also contains a second additive and a second pH buffer.

[0011] The first additive includes gelatin and / or polyethylene glycol, the first pH buffer includes boric acid, the second additive includes one or more of ascorbic acid, sulfuric acid, and hydrochloric acid, and the second pH buffer includes citric acid and / or sodium citrate.

[0012] The current density in the first electrolysis zone is 1000-1500 A / m 2 The pH value is 1-4; the current density in the second electrolysis zone is 800-1000 A / m. 2 The pH value is 2-3.5.

[0013] Preferably, both the first electrolysis zone and the second electrolysis zone are separated from the cathode chamber and the anode chamber by anion exchange membranes.

[0014] Preferably, the method for preparing ultra-high purity iron from recycled steel raw materials satisfies one or more of the following conditions:

[0015] (1) The inorganic acid is hydrochloric acid or sulfuric acid;

[0016] (2) The sulfiding agent used for sulfidation and impurity removal includes one or more of Na2S, NaHS, Na2S2O3, and Na2SO3;

[0017] (3) The dosage of the first additive is 0.01-1 g / L;

[0018] (4) The amount of the first pH buffer is 1-10 g / L.

[0019] Preferably, the sulfidation impurity removal includes a first stage and a second stage performed sequentially;

[0020] In the first stage, the pH of the system is adjusted to 1-4, then the vulcanizing agent is added, the reaction temperature is 60-80℃, and the time is 30-60min. After the reaction is completed, the first solid-liquid separation is carried out.

[0021] In the second stage, the pH of the liquid obtained in the first stage is adjusted to 3-4.5, and then a sulfiding agent is added to react. After the reaction is completed, a second solid-liquid separation is performed.

[0022] Preferably, the filter membranes used for the first solid-liquid separation and the second solid-liquid separation are made of polyvinylidene fluoride with a pore size of 0.1-10 μm.

[0023] Preferably, in the second additive, the amount of ascorbic acid is 1-10 g / L, and the amount of hydrochloric acid or sulfuric acid is 0.01-1 g / L;

[0024] And / or,

[0025] The dosage of the second pH buffer is 1-10 g / L.

[0026] Preferably, the organic phase used for extraction and impurity removal is a mixture of saponified extractant HBL110 and diluent, wherein the diluent is kerosene and / or sulfonated kerosene, and the volume ratio of the saponified extractant HBL110 to the diluent is 1:(1-5).

[0027] And / or,

[0028] The extraction and impurity removal is carried out using a multi-stage countercurrent extraction method at a temperature of 20-50℃, with a volume ratio of organic phase to aqueous phase of 1:(1-5).

[0029] Preferably, the hydrogen plasma melting includes a melting stage, a primary refining stage, a deep refining stage, and a solidification stage;

[0030] The hydrogen plasma melting satisfies one or more of the following conditions:

[0031] (1) The melting stage includes: first, evacuating the furnace to a pressure of 1×10⁻⁶. -1 Up to 1×10 -3 Then argon gas is introduced and melting and stirring begin;

[0032] (2) The temperature of the main refining stage is 1550-1600℃ and the time is 20-40min; the protective gas in the melting stage of the main refining stage is argon, and the flow rate is 5-20L / min; after the melting of the main refining stage is completed, the system gas is switched to hydrogen, the flow rate is 3-4L / min, and the time is 5-20min; after the partial pressure of H2S decreases, the hydrogen flow rate is reduced by 1-2.5 L / min for 15-40min.

[0033] The main refining stage ends when the sulfur content in the molten metal pool is less than 10 ppm.

[0034] (3) During the deep refining stage, the gas supply is stopped, and the temperature is maintained for 15-60 minutes until the total content of hydrogen, oxygen, nitrogen and sulfur is less than 40 ppm.

[0035] (4) The solidification stage is cooled with the furnace in an argon atmosphere.

[0036] This application also provides a system for preparing ultra-high purity iron from recycled steel raw materials, for performing the method for preparing ultra-high purity iron from recycled steel raw materials, the system comprising: a raw material pretreatment device, a first electrolysis zone, a second electrolysis zone, and a hydrogen plasma melting device;

[0037] The raw material pretreatment device is used to pretreat scrap steel raw materials to obtain the anode material of the first electrolysis zone; the first electrolysis zone includes one or more electrolysis cells for electrolysis to obtain the primary iron; the second electrolysis zone includes one or more electrolysis cells for electrolysis to obtain high-purity iron; the hydrogen plasma melting device is used to smelt the high-purity iron obtained in the second electrolysis zone to obtain the ultra-high-purity iron product.

[0038] Preferably, the first electrolysis zone further includes a sulfidation and impurity removal module for treating the electrolyte after electrolysis in its anode chamber, and the second electrolysis zone further includes an extraction and impurity removal module for treating the electrolyte after electrolysis in its anode chamber.

[0039] Compared with the prior art, the beneficial effects of this application include:

[0040] The method and system for preparing ultra-high purity iron from recycled steel raw materials provided in this application employ a combination of staged electrolysis and complementary impurity removal processes to deeply remove Cu. 2+ Sn 2+ Pb 2+ Zn 2+ Ni 2+ By combining hydrogen plasma directional reduction, the total amount of metallic impurities is <20ppm, and the removal rate of non-metallic impurities is >90%. Adding appropriate additives at each electrolysis stage effectively suppresses side reactions, enabling high-current electrolysis, improving current efficiency and cathode deposition quality, and shortening electrolysis time. This significantly reduces the metallic impurity content of the high-purity iron obtained under high-current-density conditions, meeting the requirements of hydrogen plasma melting. Furthermore, subsequent use of hydrogen plasma melting eliminates the need to consider excessive non-metallic impurities during electrolysis, making high-current-density electrolysis possible. The combined use of high-current-density electrolysis and hydrogen plasma melting achieves the dual goals of improved preparation efficiency and guaranteed ultra-high-purity iron quality.

[0041] The method and system for preparing ultra-high purity iron from recycled steel raw materials provided in this application achieve the direct preparation of 4N5 grade high purity iron from recycled steel raw materials, with a total metallic impurity content of <20ppm, a non-metallic impurity removal rate of >90%, and an electrolysis current density increased to 800A / m. 2 above. Attached Figure Description

[0042] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation on the scope of this application.

[0043] Figure 1 A process flow diagram of a method for preparing ultra-high purity iron using recycled steel raw materials, provided in an embodiment;

[0044] Figure 2 This is a photograph of the anode and cathode in the first electrolysis zone of Example 2;

[0045] Figure 3 These are photographs of the anode and cathode after electrolysis in the first electrolysis zone of Example 2.

[0046] Figure 4 SEM image of primary iron obtained in the first electrolysis zone of Example 2;

[0047] Figure 5 A photograph of the high-purity iron (strippings) obtained in the second electrolysis zone of Example 2;

[0048] Figure 6 SEM image of high-purity iron obtained in the second electrolysis zone of Example 2;

[0049] Figure 7 This is a photograph of the ultra-high purity iron obtained in Example 2. Detailed Implementation

[0050] To better illustrate the technical solution provided in this application, the technical solution will be described in its entirety before the embodiments, as follows:

[0051] A method for preparing ultra-high purity iron using recycled steel raw materials includes:

[0052] The recycled steel raw material is pretreated to obtain the anode material of the first electrolysis zone. Then, the first high-purity iron is used as the cathode and the anode material is used as the anode to perform the first electrolysis in the first electrolysis zone and primary iron is obtained at the cathode. The primary iron is used as the anode material of the second electrolysis zone and the second high-purity iron is used as the cathode to perform the second electrolysis to obtain the third high-purity iron with a purity of not less than 99.95 wt%.

[0053] The third high-purity iron is subjected to hydrogen plasma melting to obtain an ultra-high-purity iron product;

[0054] The purity of the ultra-high purity iron product is not less than 99.995 wt%; the initial electrolytes of the anode chambers of the first electrolysis zone and the second electrolysis zone are each independently aqueous solutions of inorganic acids; the initial electrolyte of the cathode chamber of the first electrolysis zone is the liquid obtained by electrolysis of the initial electrolyte of the anode chamber of the first electrolysis zone and subsequent sulfidation to remove impurities; the cathode chamber of the first electrolysis zone also contains a first additive, a first pH buffer, and iron powder; the initial electrolyte of the cathode chamber of the second electrolysis zone is the liquid obtained by electrolysis of the initial electrolyte of the anode chamber of the second electrolysis zone and subsequent extraction to remove impurities; the cathode chamber of the second electrolysis zone also contains a second additive and a second pH buffer.

[0055] The first additive includes gelatin and / or polyethylene glycol, the first pH buffer includes boric acid, the second additive includes one or more of ascorbic acid, sulfuric acid, and hydrochloric acid, and the second pH buffer includes citric acid and / or sodium citrate.

[0056] The current density in the first electrolysis zone is 1000-1500 A / m 2 The pH value is 1-4; the current density in the second electrolysis zone is 800-1000 A / m. 2 The pH value is 2-3.5.

[0057] Using recycled steel as the starting material, this study develops a deep purification technology that efficiently removes impurities with similar electrical potentials, such as Cu, Sn, Pb, Zn, and Ni, and overcomes the current density limitations of traditional electrolysis processes (<400 A / m). 2 The high-efficiency electrolysis technology solves the problems in the purification of recycled resources, and ultimately achieves the stable and efficient preparation of >4N5 high-purity iron products.

[0058] Gelatin and polyethylene glycol are used to refine the cathode deposited grains, inhibit dendrite growth, and obtain a dense primary iron deposition layer. Boric acid is used to stabilize the pH value of the cathode interface region and inhibit Fe... 2+ The hydrolysis reaction provides a stable electrochemical environment for the first additive to function. The role of iron powder is to neutralize the Fe present in the electrolyte. 3+ Ions reduced to Fe 2+ Its main reaction is: 2Fe 3+ +Fe→3Fe 2+ To prevent Fe 3+ Cathodic reduction decreases current efficiency and leads to coarse deposits. The amount of iron powder added is needed to maintain Fe in the electrolyte. 3+ The concentration should be below 1 g / L.

[0059] The initial electrolyte in the cathode chamber of the first electrolysis zone is the liquid obtained by sulfidation and impurity removal after electrolysis of the initial electrolyte in the anode chamber of the first electrolysis zone. In the initial stage, sulfuric acid or hydrochloric acid aqueous solution can be used instead. The electrolyte in the anode chamber of the first electrolysis zone contains various metal ions, including Fe. 2+ Cu 2+ Sn 2+ Pb 2+ Zn 2+ Ni 2+ These substances need to be removed through sulfidation before they can be recycled to the cathode chamber for use.

[0060] The second additive is a reducing agent or an acid regulator, used to inhibit Fe. 2+ The oxidation of Fe is prevented, maintaining the stability of the electrolyte; the second pH buffer is used to inhibit Fe oxidation. 2+ The oxidation and hydrolysis work synergistically to improve the quality of cathode deposition.

[0061] Optionally, the current density in the first electrolysis zone can be 1000 A / m 2 1100A / m 2 1200A / m 2 1300A / m 2 1400A / m 2 1500A / m 2 Or 1000-1500A / m 2 The pH value can be any value between 1, 2, 3, 4, or any value between 1 and 4; the current density in the second electrolysis zone can be 800 A / m. 2 900A / m 2 1000A / m 2 Or 800-1000A / m 2 The pH value can be any value between 2, 2.5, 3, 3.5 or any value between 2 and 3.5.

[0062] The purity of the first, second, and third high-purity irons must all be no less than 99.95 wt%. If necessary, ultra-high-purity iron can be used for the first and second high-purity irons to further reduce the impact of cathode iron on product purity and improve the purity of the final ultra-high-purity iron product.

[0063] In an optional embodiment, both the first electrolysis zone and the second electrolysis zone are separated from the cathode chamber and the anode chamber by an anion exchange membrane.

[0064] In an optional implementation, the method for preparing ultra-high purity iron from recycled steel raw materials satisfies one or more of the following conditions:

[0065] (1) The inorganic acid is hydrochloric acid or sulfuric acid;

[0066] (2) The sulfiding agent used for sulfidation and impurity removal includes one or more of Na2S, NaHS, Na2S2O3, and Na2SO3;

[0067] (3) The dosage of the first additive is 0.01-1 g / L;

[0068] (4) The amount of the first pH buffer is 1-10 g / L.

[0069] Optionally, the dosage of the first additive can be any value between 0.01 g / L, 0.05 g / L, 0.1 g / L, 0.5 g / L, 1 g / L, or 0.01-1 g / L, and the dosage of the first pH buffer can be any value between 1 g / L, 2 g / L, 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L, 10 g / L, or 1-10 g / L.

[0070] In an optional embodiment, the sulfidation impurity removal includes a first stage and a second stage performed sequentially;

[0071] In the first stage, the pH of the system is adjusted to 1-4, preferably 2-3, and then a vulcanizing agent is added. The reaction temperature is 60-80℃ and the time is 30-60 min. After the reaction is completed, the first solid-liquid separation is performed.

[0072] Under these conditions, Cu has an extremely small solubility product constant (Ksp). 2+ Sn 2+ Pb 2+ Zn 2+ Preferential formation of CuS, SnS, PbS, and ZnS sulfide precipitates, while Fe... 2+ and some Ni 2+ Because of its large solubility product, the sulfide remains in the solution; after the reaction, solid-liquid separation is performed to obtain a primary purified liquid and sulfide slag rich in copper, tin, lead, and zinc.

[0073] In the second stage, the pH of the liquid obtained in the first stage is adjusted to 3-4.5, and then a sulfiding agent is added to react. After the reaction is completed, a second solid-liquid separation is performed.

[0074] Within this pH range, the Ksp values ​​of NiS and FeS are close, with NiS being slightly smaller, which allows some Ni to... 2+ Priority over Fe 2+ A precipitation reaction occurs, thereby achieving the selective separation of NiS. The precipitation pH of FeS is 4-7, and the maximum pH should not exceed 5.0 to avoid the loss of Fe ions.

[0075] The amount of sulfiding agent added is determined based on the total mass of Cu, Sn, Pb, Zn, and Ni ions to be removed in the electrolyte, and its theoretical calculation is as follows:

[0076] ;

[0077] ;

[0078] in: This represents the amount of substance of each metal ion, expressed in moles. for The molar mass, expressed in g / mol. This is the reaction coefficient, typically ranging from 1 to 1.5, and is dimensionless. It is the mass fraction of i-ions. This is the molar mass of the i-ion, where i can be Cu, Sn, Pb, Zn, or Ni. This refers to the mass of scrap steel, expressed in grams (g).

[0079] In one optional embodiment, the filter membranes used for the first solid-liquid separation and the second solid-liquid separation are made of polyvinylidene fluoride with a pore size of 0.1-10 μm.

[0080] Optionally, the pore size of the filter membrane can be 0.1 μm, 1 μm, 5 μm, 10 μm or any value between 0.1 and 10 μm.

[0081] After multiple stages of sulfidation reaction, the content of each impurity element in the electrolyte, namely Cu, Sn, Pb, Zn, and Ni, is less than 10 ppm.

[0082] In an optional embodiment, the amount of ascorbic acid in the second additive is 1-10 g / L, and the amount of hydrochloric acid or sulfuric acid is 0.01-1 g / L.

[0083] And / or,

[0084] The dosage of the second pH buffer is 1-10 g / L.

[0085] Optionally, in the second additive, the amount of ascorbic acid can be any value between 1 g / L, 2 g / L, 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L, 10 g / L or 1-10 g / L, and the amount of hydrochloric acid or sulfuric acid can be any value between 0.01 g / L, 0.05 g / L, 0.1 g / L, 0.5 g / L, 1 g / L or 0.01-1 g / L; the amount of the second pH buffer can be any value between 1 g / L, 2 g / L, 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L, 10 g / L or 1-10 g / L.

[0086] In an optional embodiment, the organic phase used for extraction and impurity removal is a mixture of saponified extractant HBL110 and a diluent, wherein the diluent is kerosene and / or sulfonated kerosene, and the volume ratio of the saponified extractant HBL110 to the diluent is 1:(1-5).

[0087] And / or,

[0088] The extraction and impurity removal is carried out using a multi-stage countercurrent extraction method at a temperature of 20-50℃, with a volume ratio of organic phase to aqueous phase of 1:(1-5).

[0089] Optionally, the volume ratio of the saponified extractant HBL110 to the diluent can be any value between 1:1, 1:2, 1:3, 1:4, 1:5, or 1:(1-5); the extraction and impurity removal are carried out by multi-stage countercurrent extraction, the temperature can be any value between 20℃, 30℃, 40℃, 50℃, or 20-50℃, and the volume ratio of the organic phase to the aqueous phase can be any value between 1:1, 1:2, 1:3, 1:4, 1:5, or 1:(1-5).

[0090] This module employs solvent extraction to deeply remove Ni from the anolyte. Its core component is an organic phase composed of a specific extractant. The extractant HBL110 requires saponification before use to convert it into a more reactive sodium salt form; the saponification rate should be controlled at approximately 40-80%. Saponification is accomplished by adding NaOH or Na₂CO₃ solution to the organic phase and stirring thoroughly.

[0091] The extraction process employs multi-stage countercurrent extraction, typically requiring 3-7 stages to ensure a nickel ion concentration of <0.05 g / L in the effluent phase. Before feeding the extraction solution, the pH of the electrolyte should generally be maintained between 2 and 4 to optimize the extraction effect of HBL110.

[0092] In one optional implementation, the hydrogen plasma melting includes a melting stage, a primary refining stage, a deep refining stage, and a solidification stage.

[0093] The hydrogen plasma melting satisfies one or more of the following conditions:

[0094] (1) The melting stage includes: first, evacuating the furnace to a pressure of 1×10⁻⁶. -1 Up to 1×10 -3 Then argon gas is introduced and melting and stirring begin;

[0095] Control the pressure to effectively remove residual oxygen in the furnace and prevent metal oxidation.

[0096] (2) The temperature of the main refining stage is 1550-1600℃ (which can be any value between 1550℃, 1560℃, 1570℃, 1580℃, 1590℃, 1600℃ or 1550-1600℃), and the time is 20-40min (which can be any value between 20min, 30min, 40min or 20-40min); the protective gas in the melting stage of the main refining stage is argon, and the flow rate is 5-20L / min (which can be 5L / min, 10L / min). The flow rate is set at 15 L / min, 20 L / min, or any value between 5 and 20 L / min. After melting in the main refining stage, the system gas is switched to hydrogen at a flow rate of 3-4 L / min (which can be any value between 3 L / min, 3.5 L / min, 4 L / min, or 3-4 L / min) for 5-20 min (which can be any value between 5 min, 15 min, 20 min, or 5-20 min). After the H2S partial pressure decreases, the hydrogen flow rate is reduced by 1-2.5 L / min (which can be any value between 1 L / min, 1.5 L / min, 2 L / min, 2.5 L / min, or 1-2.5 L / min) for 15-40 min (which can be any value between 15 min, 20 min, 30 min, 40 min, or 15-40 min).

[0097] The main refining stage ends when the sulfur content in the molten metal pool is less than 10 ppm.

[0098] During the melting stage, argon gas is used for protection and its flow rate is controlled to ensure stirring of the molten pool and removal of reaction gaseous products. After complete melting, the gas is switched to hydrogen. Initially, a reducing atmosphere is quickly established at a high flow rate to enhance stirring of the molten pool. Once the partial pressure of hydrogen sulfide begins to decrease, the flow rate is reduced.

[0099] Towards the end of the main refining stage, hydrogen supply is temporarily stopped for sampling and spectral analysis. Once the sulfur content in the molten metal pool is less than 10 ppm, the main refining stage ends. If the sulfur content does not meet the standard, the hydrogen supply time is extended and the hydrogen flow rate is appropriately increased to continue refining until the sulfur content meets the standard.

[0100] (3) During the deep refining stage, the gas supply is stopped and the temperature is maintained for 15-60 minutes (which can be any value between 15 minutes, 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, 60 minutes or 15-60 minutes) until the total content of hydrogen, oxygen, nitrogen and sulfur is less than 40 ppm.

[0101] The deep refining stage primarily allows the gases produced in the smelting reaction to escape from the melt under static conditions. The larger and deeper the molten pool, the longer it takes for the dissolved gases to diffuse to the surface and escape.

[0102] (4) The solidification stage is cooled with the furnace in an argon atmosphere.

[0103] This method employs a combination of staged electrolysis and impurity removal processes to deeply remove Cu. 2+ Sn 2+ Pb 2+ Zn 2+ Ni 2+ Combined with hydrogen plasma directional reduction, the total amount of metallic impurities is <20ppm, and the removal rate of non-metallic impurities is >90%. Through an independent electrolyte circulation system and specialized additives, the reaction environment at each stage is optimized, effectively suppressing side reactions and improving current efficiency and cathode deposition quality. The electrolysis current density is increased to 800A / m³. 2 Electrolysis time is shortened by 40%; scrap steel is efficiently converted into 4N5 grade ultra-high purity iron, which improves the product value and economic benefits of recycled steel raw materials.

[0104] This application also provides a system for preparing ultra-high purity iron from recycled steel raw materials, for performing the method for preparing ultra-high purity iron from recycled steel raw materials, the system comprising: a raw material pretreatment device, a first electrolysis zone, a second electrolysis zone, and a hydrogen plasma melting device;

[0105] The raw material pretreatment device is used to pretreat scrap steel raw materials to obtain the anode material of the first electrolysis zone; the first electrolysis zone includes one or more electrolysis cells for electrolysis to obtain the primary iron; the second electrolysis zone includes one or more electrolysis cells for electrolysis to obtain high-purity iron; the hydrogen plasma melting device is used to smelt the high-purity iron obtained in the second electrolysis zone to obtain the ultra-high-purity iron product.

[0106] In an optional embodiment, the first electrolysis zone further includes a sulfidation impurity removal module for treating the electrolyte after electrolysis in its anode chamber, and the second electrolysis zone further includes an extraction impurity removal module for treating the electrolyte after electrolysis in its anode chamber.

[0107] The implementation schemes of this application will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating this application and should not be regarded as limiting the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0108] Example 1

[0109] This embodiment provides a system for preparing ultra-high purity iron using recycled steel raw materials, including: a raw material pretreatment device, a first electrolysis zone, a second electrolysis zone, and a hydrogen plasma melting device;

[0110] The raw material pretreatment unit is used to pretreat scrap steel raw materials to obtain anode material for the first electrolysis zone. It includes a crushing unit, an acid washing unit, and a casting unit, used for crushing the scrap steel raw materials, cleaning impurities, and casting into anodes, respectively. The first electrolysis zone includes an electrolytic cell for electrolyzing to obtain primary iron. The second electrolysis zone includes an electrolytic cell for electrolyzing to obtain high-purity iron. Each electrolytic cell includes an anode chamber and a cathode chamber, separated by an anion exchange membrane. The hydrogen plasma melting unit is used to smelt high-purity iron to obtain ultra-high-purity iron products.

[0111] It is understood that in other implementations, each electrolysis zone may include multiple electrolysis cells.

[0112] In an optional embodiment, the first electrolysis zone further includes a sulfidation impurity removal module for treating the electrolyte after electrolysis in its anode chamber, and the second electrolysis zone further includes an extraction impurity removal module for treating the electrolyte after electrolysis in its anode chamber.

[0113] The sulfidation impurity removal module includes a sulfidation reaction tank and a solid-liquid separation device. The former performs the sulfidation reaction to remove impurities, while the latter is used for solid-liquid separation. The resulting liquid is transported to the cathode chamber of the first electrolysis zone through a circulation system, achieving the goals of saving reagents, reducing costs, and making the overall process more environmentally friendly. The extraction impurity removal module includes an extraction device. After extraction, the organic phase and aqueous phase are allowed to separate (after extraction, the impurity metal ion Ni is extracted into the organic phase, while the ferrous ion remains in the aqueous phase). The aqueous phase is either recycled or transported to the cathode chamber of the second electrolysis zone for reuse through a circulation system.

[0114] It should be noted that the circulating liquid requires necessary treatment such as pH adjustment. Meanwhile, the electrolyte in the cathode chamber can also be returned to the anode chamber through a separate circulation system after necessary treatment.

[0115] The hydrogen plasma melting apparatus includes a plasma generator, a water-cooled crucible, a multi-channel spectral monitoring module, and a tail gas analysis module. The multi-channel spectral monitoring device is used to acquire plasma spectral data in real time, and the tail gas analysis module is used to monitor the tail gas composition in real time. This application uses an existing plasma melting apparatus and requires no modification.

[0116] Example 2

[0117] like Figure 1 As shown, this embodiment provides a method for preparing ultra-high purity iron using recycled steel raw materials, using the system provided in Example 1. The method includes the following steps:

[0118] 1. The recycled steel raw materials are pretreated by crushing, pickling, washing, drying, and smelting to obtain the anode material for the first electrolysis zone;

[0119] 2. Using high-purity iron as the cathode and the anode material as the anode (e.g.) Figure 2 As shown (left side is high-purity iron, right side is anode material), the first electrolysis is performed in the first electrolysis zone, and primary iron is obtained at the cathode; the purity of the ultra-high-purity iron is not less than 99.995 wt%; the initial electrolyte in the anode chamber is an aqueous solution of hydrochloric acid, and the electrolyte for the initial reaction in the cathode chamber is an aqueous solution of hydrochloric acid. During continuous electrolysis, the liquid obtained after sulfidation and impurity removal from the initial electrolyte in the anode chamber is recycled to the cathode chamber for use; the cathode chamber of the first electrolysis zone also contains 0.01 g / L of polyethylene glycol as the first additive, 5 g / L of boric acid as the first pH buffer, and iron powder; the current density in the first electrolysis zone is 1000 A / m. 2 The pH was 2.5; the sulfiding agent used for impurity removal was Na2S; the sulfidation impurity removal consisted of a first stage and a second stage performed sequentially; in the first stage, the pH of the system was adjusted to 2, then the sulfiding agent was added, the reaction temperature was 60℃, and the time was 60 min. After the reaction was completed, the first solid-liquid separation was performed; in the second stage, the pH of the liquid obtained in the first stage was adjusted to 4, then the sulfiding agent was added to react, and after the reaction was completed, the second solid-liquid separation was performed; the filter membrane used for the first and second solid-liquid separations was made of polyvinylidene fluoride with a pore size of 0.1 μm;

[0120] Photos of the anode and cathode materials after the first electrolysis zone is completed are shown below. Figure 3 As shown (left side is cathode, right side is anode). The SEM image of primary iron obtained from the first electrolysis zone is as follows. Figure 4 As shown.

[0121] 3. Using the product from the first cathode as the anode material in the second electrolysis zone and high-purity iron as the cathode, a second electrolysis is performed to obtain high-purity iron with a purity of not less than 99.95 wt%. The initial electrolyte in the anode chamber is an aqueous solution of hydrochloric acid, and the electrolyte for the initial reaction is also an aqueous solution of hydrochloric acid. During continuous electrolysis, the liquid obtained after extraction and impurity removal from the initial electrolyte in the anode chamber is recycled to the cathode chamber for use. The cathode chamber of the second electrolysis zone also contains a second additive (2 g / L ascorbic acid), 0.2 g / L hydrochloric acid, and a second pH buffer (2 g / L sodium citrate). The current density in the second electrolysis zone is 800 A / m. 2 The pH was 2.5; the organic phase used for extraction and impurity removal was a mixture of saponified extractant HBL110 and diluent, with kerosene as the diluent, and the volume ratio of saponified extractant HBL110 to diluent was 1:5; the extraction and impurity removal was carried out using a 7-stage countercurrent extraction method at a temperature of 30℃, with the volume ratio of organic phase to aqueous phase being 1:5.

[0122] A photograph of the high-purity iron (strippings) obtained in the second electrolysis zone is shown below. Figure 5 As shown, the SEM image is as follows Figure 6 As shown.

[0123] The composition of the recycled steel raw materials and the high-purity iron obtained from the first and second electrolysis zones is shown in Table 1 below:

[0124] Table 1 Ingredients Table

[0125]

[0126] 4. High-purity iron is smelted using hydrogen plasma to obtain ultra-high-purity iron products;

[0127] Hydrogen plasma smelting includes the melting stage, the main refining stage, the deep refining stage, and the solidification stage;

[0128] The melting stage includes: high-purity iron is crushed and loaded into a water-cooled crucible of a hydrogen plasma melting system; the plasma generator is started under an Ar-H2 mixed atmosphere for melting; and a vacuum is first applied to bring the furnace pressure to 1×10⁻⁶. -3 Then argon gas is introduced and melting and stirring begin;

[0129] The temperature of the main refining stage is 1550℃ and the time is 40 min; the protective gas in the melting stage of the main refining stage is argon, and the flow rate is 20 L / min; after the melting of the main refining stage is completed, the system gas is switched to hydrogen, the flow rate is 4 L / min, and the time is 20 min; after the partial pressure of H2S decreases, the hydrogen flow rate is reduced by 2.5 L / min, and the time is 40 min.

[0130] The hydrogen supply was suspended, and the molten iron was sampled and subjected to rapid spectral analysis for the first time. Once the sulfur content in the molten metal pool was less than 10 ppm, the main refining stage was completed.

[0131] (3) Deep refining stage: Stop the gas supply and maintain a vacuum of 10. -1 -10 -2 Pa, keep warm for 15 minutes until the total hydrogen, oxygen, nitrogen and sulfur content is less than 40 ppm and then stop;

[0132] (4) During the solidification stage, the furnace is cooled in an argon atmosphere.

[0133] The non-metallic element contents of high-purity iron obtained by electrolysis and ultra-high-purity iron obtained by hydrogen plasma melting are shown in Table 2 below:

[0134] Table 2 Non-metallic element content (ppm)

[0135]

[0136] The actual image of the obtained ultra-high purity iron is shown below. Figure 7 As shown.

[0137] Example 3

[0138] This embodiment provides a method for preparing ultra-high purity iron using recycled steel raw materials, employing the system provided in Example 1. The method includes the following steps:

[0139] 1. The recycled steel raw materials are pretreated by crushing, pickling, washing, drying, and smelting to obtain the anode material for the first electrolysis zone;

[0140] 2. High-purity iron is used as the cathode and the anode material is used as the anode material for the first electrolysis in the first electrolysis zone, and primary iron is obtained at the cathode; the purity of the ultra-high-purity iron is not less than 99.995 wt%; the initial electrolyte in the anode chamber is an aqueous solution of sulfuric acid, and the electrolyte for the initial reaction in the cathode chamber is an aqueous solution of sulfuric acid. During continuous electrolysis, the liquid obtained after sulfidation and impurity removal from the initial electrolyte in the anode chamber is recycled to the cathode chamber for use; the cathode chamber in the first electrolysis zone also contains 1 g / L of gelatin as the first additive, 10 g / L of boric acid as the first pH buffer, and iron powder; the current density in the first electrolysis zone is 1500 A / m 2 The pH is 3; the sulfiding agent used for impurity removal is Na2S2O3; the sulfidation impurity removal includes a first stage and a second stage performed sequentially; in the first stage, the pH of the system is adjusted to 1, then the sulfiding agent is added, the reaction temperature is 80℃, and the time is 30min. After the reaction is completed, the first solid-liquid separation is performed; in the second stage, the pH of the liquid obtained in the first stage is adjusted to 4.5, then the sulfiding agent is added to react, and after the reaction is completed, the second solid-liquid separation is performed; the filter membrane used for the first and second solid-liquid separations is made of polyvinylidene fluoride with a pore size of 1μm;

[0141] 3. Using the product from the first cathode as the anode material in the second electrolysis zone and high-purity iron as the cathode, a second electrolysis is performed to obtain high-purity iron with a purity of not less than 99.95 wt%. The initial electrolyte in the anode chamber is an aqueous solution of sulfuric acid, and the electrolyte for the initial reaction is also an aqueous solution of sulfuric acid. During continuous electrolysis, the liquid obtained after extraction and impurity removal from the initial electrolyte in the anode chamber is recycled to the cathode chamber for reuse. The cathode chamber in the second electrolysis zone also contains a second additive (10 g / L ascorbic acid), 0.01 g / L sulfuric acid, and a second pH buffer (10 g / L citric acid). The current density in the second electrolysis zone is 1000 A / m. 2 The pH was 3.5; the organic phase used for extraction and impurity removal was a mixture of saponified extractant HBL110 and diluent, with kerosene as the diluent, and the volume ratio of saponified extractant HBL110 to diluent was 1:4; the extraction and impurity removal was carried out using a 3-countercurrent extraction method at a temperature of 50℃, with the volume ratio of organic phase to aqueous phase being 1:3.

[0142] 4. High-purity iron is smelted using hydrogen plasma to obtain ultra-high-purity iron products;

[0143] Hydrogen plasma smelting includes the melting stage, the main refining stage, the deep refining stage, and the solidification stage;

[0144] The melting stage includes: high-purity iron is crushed and loaded into a water-cooled crucible of a hydrogen plasma melting system; the plasma generator is started under an Ar-H2 mixed atmosphere for melting; and a vacuum is first applied to bring the furnace pressure to 1×10⁻⁶. -2 Then argon gas is introduced and melting and stirring begin;

[0145] The temperature of the main refining stage is 1600℃ and the time is 20 min; the protective gas in the melting stage of the main refining stage is argon, and the flow rate is 5 L / min; after the melting of the main refining stage is completed, the system gas is switched to hydrogen, the flow rate is 3 L / min, and the time is 15 min; after the H2S partial pressure decreases, the hydrogen flow rate is reduced by 1 L / min for 30 min.

[0146] The hydrogen supply was suspended, and the molten iron was sampled and subjected to rapid spectral analysis for the first time. Once the sulfur content in the molten metal pool was less than 10 ppm, the main refining stage was completed.

[0147] (3) Deep refining stage: Stop the gas supply and maintain a vacuum of 10. -1 -10 -2 Pa, keep warm for 60 minutes until the total hydrogen, oxygen, nitrogen and sulfur content is less than 40 ppm and then stop;

[0148] (4) During the solidification stage, the furnace is cooled in an argon atmosphere.

[0149] Example 4

[0150] This embodiment provides a method for preparing ultra-high purity iron using recycled steel raw materials, employing the system provided in Example 1. The method includes the following steps:

[0151] 1. The recycled steel raw materials are pretreated by crushing, pickling, washing, drying, and smelting to obtain the anode material for the first electrolysis zone;

[0152] 2. High-purity iron is used as the cathode and the anode material is used as the anode in the first electrolysis zone to perform the first electrolysis, and primary iron is obtained at the cathode; the purity of the ultra-high-purity iron is not less than 99.995 wt%; the initial electrolyte in the anode chamber is an aqueous solution of hydrochloric acid, and the electrolyte for the initial reaction in the cathode chamber is also an aqueous solution of hydrochloric acid. During continuous electrolysis, the liquid obtained after sulfidation and impurity removal from the initial electrolyte in the anode chamber is recycled to the cathode chamber for use; the cathode chamber in the first electrolysis zone is also equipped with the first additive gelatin and 0.05 g / L polyethylene glycol, the first pH buffer boric acid 1 g / L, and iron powder; the current density in the first electrolysis zone is 1200 A / m 2The pH was 4; the sulfiding agent used for impurity removal was Na2SO3; the sulfidation impurity removal consisted of a first stage and a second stage performed sequentially; in the first stage, the pH of the system was adjusted to 4, then the sulfiding agent was added, the reaction temperature was 70℃, and the time was 40 min, after which the first solid-liquid separation was performed; in the second stage, the pH of the liquid obtained in the first stage was adjusted to 3, then the sulfiding agent was added and the reaction was carried out, after which the second solid-liquid separation was performed; the filter membrane used for the first and second solid-liquid separations was made of polyvinylidene fluoride with a pore size of 10 μm;

[0153] 3. Using the product from the first cathode as the anode material in the second electrolysis zone and high-purity iron as the cathode, a second electrolysis is performed to obtain high-purity iron with a purity of not less than 99.95 wt%. The initial electrolyte in the anode chamber is an aqueous solution of hydrochloric acid, and the electrolyte for the initial reaction is also an aqueous solution of hydrochloric acid. During continuous electrolysis, the liquid obtained after extraction and impurity removal from the initial electrolyte in the anode chamber is recycled to the cathode chamber for use. The cathode chamber in the second electrolysis zone also contains a second additive (1 g / L ascorbic acid), a second additive (1 g / L hydrochloric acid), and a second pH buffer (1 g / L citric acid). The current density in the second electrolysis zone is 900 A / m. 2 The pH was 2; the organic phase used for extraction and impurity removal was a mixture of saponified extractant HBL110 and diluent, with sulfonated kerosene as the diluent, and the volume ratio of saponified extractant HBL110 to diluent was 1:1; the extraction and impurity removal was carried out using a 5-stage countercurrent extraction method at a temperature of 20℃, with the volume ratio of organic phase to aqueous phase being 1:1.

[0154] 4. High-purity iron is smelted using hydrogen plasma to obtain ultra-high-purity iron products;

[0155] Hydrogen plasma smelting includes the melting stage, the main refining stage, the deep refining stage, and the solidification stage;

[0156] The melting stage includes: high-purity iron is crushed and loaded into a water-cooled crucible of a hydrogen plasma melting system; the plasma generator is started under an Ar-H2 mixed atmosphere for melting; and a vacuum is first applied to bring the furnace pressure to 1×10⁻⁶. -1 Then argon gas is introduced and melting and stirring begin;

[0157] The temperature of the main refining stage is 1570℃ and the time is 30 min. The protective gas in the melting stage of the main refining stage is argon with a flow rate of 10 L / min. After the melting of the main refining stage is completed, the system gas is switched to hydrogen with a flow rate of 3.5 L / min for 5 min. After the partial pressure of H2S decreases, the hydrogen flow rate is reduced by 2 L / min for 15 min.

[0158] The hydrogen supply was suspended, and the molten iron was sampled and subjected to rapid spectral analysis for the first time. Once the sulfur content in the molten metal pool was less than 10 ppm, the main refining stage was completed.

[0159] (3) Deep refining stage: Stop the gas supply and maintain a vacuum of 10. -1 -10 -2 Pa, keep warm for 40 minutes until the total hydrogen, oxygen, nitrogen and sulfur content is less than 40 ppm and then stop;

[0160] (4) During the solidification stage, the furnace is cooled in an argon atmosphere.

[0161] Comparative Example 1

[0162] Unlike Example 2, hydrogen plasma melting was not performed; only electrolysis was performed. The purity of the high-purity iron obtained was 97%, and the main impurities and their contents were [O]: 2.8093%, [H]: 0.1362%, and [N]: 400.91ppm.

[0163] Simple electrolysis cannot effectively remove gaseous impurities (O, H, N). Hydrogen plasma melting, conducted under high temperature, high vacuum, and hydrogen / vacuum conditions, can remove these elements through chemical reactions (such as H2 reacting with O to form H2O and volatilizing) and deep vacuum degassing. Without this crucial step, a large amount of gaseous impurities remain, leading to a significant decrease in purity.

[0164] Comparative Example 2

[0165] Unlike Example 2, no electrolysis was performed; instead, hydrogen plasma smelting was carried out using scrap steel as raw material. The purity of the resulting product was 99.55%, and the main impurities and their contents were [Cu]: 0.35%, [Sn]: 300ppm, and [Ni]: 200ppm.

[0166] Hydrogen plasma melting has limited ability to remove residual metallic elements such as Cu, Sn, and Ni. These elements have vapor pressures similar to iron, making them difficult to remove through vacuum volatilization, and they do not react effectively with hydrogen. Two-stage electrolytic refining is designed specifically to selectively dissolve and separate these metallic impurities.

[0167] Comparative Example 3

[0168] Unlike Example 2, no first additive is added to the first electrolysis zone.

[0169] The purity of the obtained product was reduced, failing to reach 99.95%. The lack of additives led to a deterioration in the cathode deposition morphology. The absence of grain refiners and leveling agents resulted in a coarse, dendritic, and nodular iron deposition layer. This loose structure easily traps electrolyte, leading to chemical impurities in the product and potentially causing electrode short circuits, thus compromising production stability and product consistency.

[0170] Comparative Example 4

[0171] Unlike Example 2, no first pH buffer is added to the first electrolysis zone.

[0172] Unstable pH levels lead to side reactions and impurity precipitation. The inability to stabilize the pH in the cathode region results in a tendency for localized pH increases, causing iron and other metal ions to hydrolyze and form hydroxide precipitates that become trapped within the iron deposition layer. Simultaneously, the hydrogen evolution side reaction is exacerbated, wasting electrical energy and reducing the current efficiency of iron production.

[0173] Comparative Example 5

[0174] Unlike Example 2, no second additive is added to the second electrolysis zone.

[0175] Ascorbic acid, as an antioxidant, inhibits the activity of Fe. 2+ Oxidized by air to Fe 3+ Without this additive, Fe 3+ Increased concentration will cause Fe to occur at the cathode. 3+ →Fe 2+ The reduction reaction will increase current consumption, reduce efficiency, and may affect the quality of deposited iron.

[0176] Comparative Example 6

[0177] Unlike Example 2, no second pH buffer is added to the second electrolysis zone.

[0178] The deep refining stage is more sensitive to pH. The second electrolysis zone aims to obtain extremely high-purity iron; even slight pH fluctuations can lead to the co-deposition of trace impurities or affect the quality of the deposits. The lack of buffer narrows the process control window, making it difficult to maintain optimal conditions and resulting in product purity falling short of expectations.

[0179] Comparative Example 7

[0180] Unlike Example 2, the sulfidation and impurity removal process is not divided into stages. The pH is directly adjusted to 4.5, and the same amount of sulfiding agent as used in Example 2 is added at once.

[0181] Fe 2+ Zn 2+ Ni 2+ Co-deposition occurs, leading to increased Fe loss and reduced selectivity and efficiency in impurity removal. Single-stage treatment at high pH results in mixed precipitates; some precipitated sulfides may redissolve, and iron ions may form colloidal precipitates, causing iron loss and incomplete impurity removal.

[0182] Comparative Example 8

[0183] Unlike Example 2, equal volumes of P204 and P507 extractants were used instead.

[0184] The purity of the product from the second electrolysis zone decreased by approximately 99.9%, with a high co-extraction rate for the impurity element Ni and poor selectivity of the extractant. Compared to the dedicated HBL110 extractant, P204 and P507 have some extraction ability for iron itself, but their selectivity for Fe and Ni impurities in terms of separation coefficient is not as good as HBL110, resulting in insufficient impurity removal rate, iron loss, and affecting the final high-purity iron purity.

[0185] Comparative Example 9

[0186] Unlike Example 2, hydrogen plasma melting does not include a deep refining stage.

[0187] The purity of the obtained product is approximately 99.98%. The total amount of gaseous impurities such as [H], [O], and [N] is greater than 50 ppm, indicating insufficient removal of gaseous impurities. The main refining stage introduces hydrogen primarily to remove sulfur and some oxygen. The high-vacuum environment of the deep refining stage is crucial for removing hydrogen, nitrogen, and any remaining oxygen. Without this stage, the dissolved gases in the melt cannot escape sufficiently, resulting in an excessive total amount of gaseous impurities and preventing the achievement of an ultra-high purity of over 99.995%.

[0188] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application 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 therein. Such 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 this application.

Claims

1. A method for preparing ultra-high purity iron using recycled steel raw materials, characterized in that, include: The recycled steel raw material is pretreated to obtain the anode material of the first electrolysis zone. Then, the first high-purity iron is used as the cathode and the anode material is used as the anode to perform the first electrolysis in the first electrolysis zone and primary iron is obtained at the cathode. The primary iron is used as the anode material of the second electrolysis zone and the second high-purity iron is used as the cathode to perform the second electrolysis to obtain the third high-purity iron with a purity of not less than 99.95 wt%. The third high-purity iron is subjected to hydrogen plasma melting to obtain an ultra-high-purity iron product; The purity of the ultra-high purity iron product is not less than 99.995 wt%; the initial electrolytes of the anode chambers of the first electrolysis zone and the second electrolysis zone are each independently aqueous solutions of inorganic acids; the initial electrolyte of the cathode chamber of the first electrolysis zone is the liquid obtained by electrolysis of the initial electrolyte of the anode chamber of the first electrolysis zone and subsequent sulfidation to remove impurities, and in the initial stage, sulfuric acid or hydrochloric acid aqueous solution is used instead; the cathode chamber of the first electrolysis zone also contains a first additive, a first pH buffer, and iron powder; the initial electrolyte of the cathode chamber of the second electrolysis zone is the liquid obtained by electrolysis of the initial electrolyte of the anode chamber of the second electrolysis zone and subsequent extraction to remove impurities; the cathode chamber of the second electrolysis zone also contains a second additive and a second pH buffer. The sulfidation impurity removal process includes a first stage and a second stage performed sequentially. In the first stage, the pH of the system is adjusted to 1-4, then a sulfiding agent is added, the reaction temperature is 60-80℃, and the reaction time is 30-60 min. After the reaction is completed, a first solid-liquid separation is performed. In the second stage, the pH of the liquid obtained in the first stage is adjusted to 3-4.5, then a sulfiding agent is added to carry out the reaction. After the reaction is completed, a second solid-liquid separation is performed. The organic phase used for extraction and impurity removal is a mixture of saponified extractant HBL110 and diluent, wherein the diluent is kerosene and / or sulfonated kerosene, and the volume ratio of the saponified extractant HBL110 to the diluent is 1:(1-5). The extraction and impurity removal is carried out using a multi-stage countercurrent extraction method at a temperature of 20-50℃, with a volume ratio of organic phase to aqueous phase of 1:(1-5). The hydrogen plasma melting process includes a melting stage, a primary refining stage, a deep refining stage, and a solidification stage. The hydrogen plasma melting meets the following conditions: (1) The melting stage includes: first, evacuating the furnace to a pressure of 1×10⁻⁶. -1 Up to 1×10 -3 Then argon gas is introduced and melting and stirring begin; (2) The temperature of the main refining stage is 1550-1600℃ and the time is 20-40min; the protective gas in the melting stage of the main refining stage is argon, and the flow rate is 5-20L / min; after the melting of the main refining stage is completed, the system gas is switched to hydrogen, the flow rate is 3-4L / min, and the time is 5-20min; after the partial pressure of H2S decreases, the hydrogen flow rate is reduced by 1-2.5 L / min for 15-40min. The main refining stage ends when the sulfur content in the molten metal pool is less than 10 ppm. (3) During the deep refining stage, the gas supply is stopped, and the temperature is maintained for 15-60 minutes until the total content of hydrogen, oxygen, nitrogen and sulfur is less than 40 ppm. (4) The solidification stage is cooled with the furnace in an argon atmosphere; The first additive includes gelatin and / or polyethylene glycol, the first pH buffer includes boric acid, the second additive includes one or more of ascorbic acid, sulfuric acid, and hydrochloric acid, and the second pH buffer includes citric acid and / or sodium citrate. The current density in the first electrolysis zone is 1000-1500 A / m 2 The pH value is 1-4; the current density in the second electrolysis zone is 800-1000 A / m. 2 The pH value is 2-3.

5.

2. The method for preparing ultra-high purity iron from recycled steel raw materials according to claim 1, characterized in that, Both the first electrolysis zone and the second electrolysis zone are separated from the cathode chamber and the anode chamber by anion exchange membranes.

3. The method for preparing ultra-high purity iron using recycled steel raw materials according to claim 1, characterized in that, One or more of the following conditions must be met: (1) The inorganic acid is hydrochloric acid or sulfuric acid; (2) The sulfiding agent used for sulfidation and impurity removal includes one or more of Na2S, NaHS, Na2S2O3, and Na2SO3; (3) The dosage of the first additive is 0.01-1 g / L; (4) The amount of the first pH buffer is 1-10 g / L.

4. The method for preparing ultra-high purity iron from recycled steel raw materials according to claim 1, characterized in that, The filter membranes used in the first solid-liquid separation and the second solid-liquid separation are made of polyvinylidene fluoride with a pore size of 0.1-10 μm.

5. The method for preparing ultra-high purity iron from recycled steel raw materials according to claim 1, characterized in that, In the second additive, the amount of ascorbic acid is 1-10 g / L, and the amount of hydrochloric acid or sulfuric acid is 0.01-1 g / L; And / or, the amount of the second pH buffer is 1-10 g / L.

6. A system for preparing ultra-high purity iron using recycled steel raw materials, characterized in that, The system for performing the method for preparing ultra-high purity iron from recycled steel raw materials according to any one of claims 1-4, the system comprising: a raw material pretreatment device, a first electrolysis zone, a second electrolysis zone, and a hydrogen plasma melting device; The raw material pretreatment device is used to pretreat scrap steel raw materials to obtain the anode material of the first electrolysis zone; the first electrolysis zone includes one or more electrolysis cells for electrolysis to obtain the primary iron; the second electrolysis zone includes one or more electrolysis cells for electrolysis to obtain high-purity iron; the hydrogen plasma melting device is used to smelt the high-purity iron obtained in the second electrolysis zone to obtain the ultra-high-purity iron product. The first electrolysis zone further includes a sulfidation and impurity removal module for treating the electrolyte after electrolysis in its anode chamber, and the second electrolysis zone further includes an extraction and impurity removal module for treating the electrolyte after electrolysis in its anode chamber.

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