Method for preparing high-purity iron from low-grade iron ore

Abstract

The invention discloses a method for preparing high-purity iron from low-grade iron ore, which comprises the following steps: (1) crushing and finely grinding the low-grade iron ore into iron ore powder, then adding iron powder and oxalic acid according to a certain proportion, reacting under a stirring condition, and filtering after the reaction is completed to obtain ferrous oxalate powder; (2) heating the ferrous oxalate powder to obtain anhydrous ferrous oxalate powder; (3) the anhydrous ferrous oxalate powder is placed in molten carbonate electrolyte for electrolysis; and (4) after electrolysis is finished, the cathode material is cleaned and dried, and high-purity iron is obtained. The purity of the high-purity iron prepared through the method is larger than 98%, the current efficiency is larger than 95%, and the technical problem that low-grade iron ore is difficult to utilize at present is solved.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical engineering technology, specifically relating to a method for preparing high-purity iron from low-grade iron ore. Technical Background

[0002] Traditional blast furnace ironmaking processes are facing unprecedented environmental constraints. The steel industry has entered a period of deep adjustment and low-carbon transformation, making the development of efficient and low-carbon ironmaking technologies crucial. Currently, the main technologies include hydrogen-based reduction (vertical shaft furnace and fluidized bed methods) and electrometallurgical reduction. High-quality iron ore resources are increasingly scarce. For iron ores with poor endowment ("lean," "impurity," and "fineness"), fine grinding to the point of individual liberation is required before beneficiation to obtain iron concentrate. Therefore, the content of medium-fine iron concentrate powder with a particle size of less than 100μm is increasing. This concentrate must be sintered into pellets before it can be used for hydrogen-based vertical shaft furnace reduction, resulting in a complex process with high energy consumption and low reduction efficiency. Hydrogen-based fluidized bed reduction can directly use fine ore, eliminating the raw material pelletizing process (reducing energy consumption), but the "loss of flow" phenomenon is a bottleneck limiting its development.

[0003] High-temperature electrometallurgical reduced iron is based on the potential difference between metals. Electrical energy is used to heat and melt oxides or salts into an ionic melt, which then selectively dissolves or precipitates different impurity ions, achieving the separation and purification of metallic iron. The ionic melt, as a conductor, exhibits high stability at high temperatures and can effectively promote the reaction. It boasts advantages such as a simple process flow, low environmental pollution, and low production cost. With the development and maturation of renewable energy power generation technologies such as wind power and nuclear power, the advantages of green and efficient high-temperature electrometallurgical reduced iron technology are becoming increasingly prominent, and it is bound to become the mainstream ironmaking process. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing high-purity iron from low-grade iron ore, the resulting high-purity iron having a purity greater than 98% and a current efficiency greater than 95%, thus solving the current technical problem of the difficulty in utilizing low-grade iron ore.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows: A method for preparing high-purity iron from low-grade iron ore includes the following steps: (1) The low-grade iron ore is crushed and finely ground into iron ore powder, and then iron powder and oxalic acid are added in a certain proportion. The leaching reaction is carried out under stirring conditions. After the reaction is completed, the ferrous oxalate powder is obtained by filtration. (2) The ferrous oxalate powder was heated to obtain anhydrous ferrous oxalate powder; (3) Electrolyze anhydrous ferrous oxalate powder in a molten carbonate electrolyte; (4) After electrolysis, the cathode material is cleaned and dried to obtain high-purity iron.

[0006] Furthermore, in the method for preparing high-purity iron from low-grade iron ore described in this invention, the iron ore powder in step (1) has a particle size of less than 74 μm accounting for ≥80%.

[0007] Furthermore, in the method for preparing high-purity iron from low-grade iron ore described in this invention, the mass ratio of iron ore powder to iron powder in step (1) is 0.5 to 1:1; the mass concentration of oxalic acid is 25 to 60%; the volume of oxalic acid added is 3 to 8 times the sum of the mass of iron ore powder and iron powder; the reaction temperature is 60 to 90°C, and the reaction time is 30 to 120 min.

[0008] In this stage, the reaction between oxalic acid and iron oxide is as follows: Fe2O3+3H2C2O4→2FeC2O4·2H2O +CO2+2H2O Fe2O3+H2C2O4+2Fe+ 5H2O→3FeC2O4·2H2O Furthermore, in the method for preparing high-purity iron from low-grade iron ore described in this invention, the heating temperature in step (2) is 180–200°C; at this temperature, ferrous oxalate decomposes into anhydrous ferrous oxalate and water, and the reaction process is as follows: ; Furthermore, in the method for preparing high-purity iron from low-grade iron ore described in this invention, the carbonate electrolyte in step (3) is composed of two or three of sodium carbonate, potassium carbonate, and lithium carbonate, and the mixing ratio satisfies that the eutectic point of the resulting mixture is below 600°C.

[0009] Furthermore, in the method for preparing high-purity iron from low-grade iron ore described in this invention, the cathode material used for electrolysis in step (3) is a nickel alloy, titanium alloy, or stainless steel, and the anode material is a graphite rod; the electrolysis temperature is 600-700℃, the voltage is 1.2-3V, and the electrolysis time is 2-5h.

[0010] The cathode reaction of the electrolysis is: Fe 2+ +2e→Fe; The anode reaction is: C2O4 2- -2e→2CO2; The overall reaction is: FeC2O4→Fe+2CO2.

[0011] Furthermore, in the method for preparing high-purity iron from low-grade iron ore described in this invention, the cleaning in step (4) specifically involves sequentially cleaning with distilled water and ultrasonic waves.

[0012] Furthermore, in the method for preparing high-purity iron from low-grade iron ore described in this invention, the drying temperature in step (4) is 100-180°C and the drying time is 1-2 hours.

[0013] Furthermore, the high-purity iron prepared by the method of the present invention has an iron purity greater than 98% and a current efficiency greater than 95%.

[0014] Furthermore, in the method for preparing high-purity iron from low-grade iron ore described in this invention, the oxalic acid that did not participate in the reaction after the oxalic acid reaction in step (1) can be purified and recycled.

[0015] The technical solution of this invention has the following beneficial technical effects: (1) For low-grade iron ore powder that is difficult to process and utilize, the method of the present invention does not require beneficiation to obtain iron concentrate, but directly performs oxalic acid leaching-molten salt electrolysis to obtain high-purity iron. This shortens the process flow and reduces process energy consumption, and the obtained iron product has high purity, providing technical support for the development and utilization of a large number of low-grade iron ores in China.

[0016] (2) After the reaction solution obtained by the iron ore powder reacts with oxalic acid is purified, it can be returned to the system to continue to react with the iron ore powder. The solution is recycled and no wastewater is generated, which is economical and environmentally friendly. Detailed Implementation

[0017] The technical solution of the present invention will be further described in detail below through specific examples.

[0018] The iron ore in each embodiment was sourced from Peru, and its main components and their mass percentages were: Al2O3: 4.62%, V2O5: 0.43%, SiO2: 18.06%, CaO: 2.56%, MgO: 1.96%, TiO2: 5.46%, and TFe: 44.75%. Example 1

[0019] A method for preparing high-purity iron from low-grade iron ore includes the following steps: (1) The iron ore is crushed and finely ground into iron ore powder, wherein 80% of the iron ore powder has a particle size of less than 74 μm; iron powder and oxalic acid with a mass concentration of 25% are added to the iron ore powder, wherein the mass ratio of the iron ore powder to the iron powder is 0.5:1, and the volume of oxalic acid added is 5 times the sum of the mass of the iron ore powder and the iron powder; then a leaching reaction is carried out under stirring conditions, with a stirring rate of 300 rpm, a reaction temperature of 75°C, and a reaction time of 30 min; after the reaction is completed, the mixture is filtered to obtain ferrous oxalate powder.

[0020] (2) The ferrous oxalate powder was heated at 200°C to obtain anhydrous ferrous oxalate powder; (3) Anhydrous ferrous oxalate powder is placed in a molten carbonate electrolyte for electrolysis. The molten carbonate electrolyte is composed of lithium carbonate and potassium carbonate in a 4:6 ratio and has a melting point of about 500°C. The cathode material used for electrolysis is a nickel alloy, the anode material is a graphite rod, the electrolysis temperature is 600°C, the voltage is 3V, and the electrolysis time is 3.5h.

[0021] (4) After electrolysis, the cathode material is cleaned with distilled water and ultrasonic waves in sequence, and then dried at 100°C for 1.5 h to obtain high-purity iron.

[0022] The obtained high-purity iron has an iron purity of 98.5% and a current efficiency of 95.8%. Comparative Example 1

[0023] A comparative experiment was conducted using the same mineral without oxalic acid leaching, and directly performing molten salt electrolysis. The purity of iron was 85%, and the current efficiency was 52%.

[0024] A comparative experiment was conducted using the same mineral without molten salt electrolysis, directly leaching and filtering with oxalic acid. The purity of iron in the obtained ferrous oxalate solid was 66%. Example 2

[0025] The difference between this embodiment and Embodiment 1 is that: (1) The mass ratio of iron ore powder to iron powder is 1:1; the mass concentration of oxalic acid is 45% and the volume of oxalic acid added is 3 times the sum of the mass of iron ore powder and iron powder; the stirring speed is 400 rpm; the reaction temperature is 90℃ and the reaction time is 120 min.

[0026] (2) The heating temperature of ferrous oxalate powder is 190℃.

[0027] (3) The electrolyte is a mixture of molten sodium carbonate and lithium carbonate in a 1:1 ratio, with a melting point of about 530°C; the cathode material used for electrolysis is titanium alloy, the electrolysis temperature is 650°C, the voltage is 1.2V, and the electrolysis time is 5h.

[0028] (4) After electrolysis, dry at 130°C for 2 hours.

[0029] The obtained high-purity iron has an iron purity of 99.5% and a current efficiency of 96.5%. Comparative Example 2

[0030] A comparative experiment was conducted using the same mineral without oxalic acid leaching, and directly performing molten salt electrolysis. The purity of iron was 87%, and the current efficiency was 54%.

[0031] A comparative experiment was conducted using the same mineral without molten salt electrolysis, directly leaching and filtering with oxalic acid. The purity of iron in the obtained ferrous oxalate solid was 65%. Example 3

[0032] The difference between this embodiment and Embodiment 1 is that: (1) The mass ratio of iron ore powder to iron powder is 0.8:1; the mass concentration of oxalic acid is 60% and the volume of oxalic acid added is 8 times the sum of the mass of iron ore powder and iron powder; the stirring speed is 600 rpm; the reaction temperature is 60℃ and the reaction time is 90 min.

[0033] (2) The heating temperature of ferrous oxalate powder is 180℃; (3) The electrolyte is a mixture of molten sodium carbonate, potassium carbonate and lithium carbonate in a ratio of 2:5:3, with a melting point of about 400℃; the cathode material used for electrolysis is stainless steel, the electrolysis temperature is 700℃, the voltage is 2.5V, and the electrolysis time is 2h.

[0034] (4) After electrolysis, dry at 180°C for 1 hour.

[0035] The obtained high-purity iron has an iron purity of 99.0% and a current efficiency of 95.8%. Comparative Example 3

[0036] A comparative experiment was conducted using the same mineral without oxalic acid leaching, and directly performing molten salt electrolysis. The purity of iron was 88%, and the current efficiency was 55%.

[0037] A comparative experiment was conducted using the same mineral without molten salt electrolysis, directly leaching and filtering with oxalic acid. The purity of iron in the obtained ferrous oxalate solid was 62%.

Claims

1. A method for preparing high-purity iron from low-grade iron ore, characterized in that, Includes the following steps: (1) The low-grade iron ore is crushed and finely ground into iron ore powder, and then iron powder and oxalic acid are added in a certain proportion. The reaction is carried out under stirring conditions. After the reaction is completed, the mixture is filtered to obtain ferrous oxalate powder. (2) The ferrous oxalate powder was heated to obtain anhydrous ferrous oxalate powder; (3) Electrolyze anhydrous ferrous oxalate powder in a molten carbonate electrolyte; (4) After electrolysis, the cathode material is cleaned and dried to obtain high-purity iron.

2. The method for preparing high-purity iron from low-grade iron ore according to claim 1, characterized in that, The iron ore powder in step (1) has a particle size of less than 74μm accounting for ≥80%.

3. The method for preparing high-purity iron from low-grade iron ore according to claim 1, characterized in that, In step (1), the mass ratio of iron ore powder to iron powder is 0.5 to 1:1; the mass concentration of oxalic acid is 25 to 60%; the volume of oxalic acid added is 3 to 8 times the sum of the mass of iron ore powder and iron powder; the reaction temperature is 60 to 90°C and the reaction time is 30 to 120 min.

4. The method for preparing high-purity iron from low-grade iron ore according to claim 1, characterized in that, The heating temperature in step (2) is 180-200℃.

5. The method for preparing high-purity iron from low-grade iron ore according to claim 1, characterized in that, The carbonate electrolyte in step (3) is composed of two or three of sodium carbonate, potassium carbonate and lithium carbonate, and the mixing ratio satisfies that the eutectic point of the resulting mixture is below 600°C.

6. The method for preparing high-purity iron from low-grade iron ore according to claim 1, characterized in that, The cathode material used in step (3) for electrolysis is a nickel alloy, titanium alloy or stainless steel, and the anode material is a graphite rod.

7. The method for preparing high-purity iron from low-grade iron ore according to claim 1, characterized in that, The electrolysis temperature in step (3) is 600-700℃, the voltage is 1.2-3V, and the electrolysis time is 2-5h.

8. The method for preparing high-purity iron from low-grade iron ore according to claim 1, characterized in that, The cleaning process in step (4) specifically involves sequentially cleaning with distilled water and ultrasonic waves.

9. The method for preparing high-purity iron from low-grade iron ore according to claim 1, characterized in that, The drying temperature in step (4) is 100-180℃ and the time is 1-2h.

10. A method for preparing high-purity iron from low-grade iron ore according to claim 1, characterized in that, The high-purity iron prepared by the method has a purity greater than 98% and a current efficiency greater than 95%.