Method for preparing 5N-grade ultrapure iron

Abstract

The invention belongs to the technical field of high-purity metal preparation, and particularly discloses a method for preparing 5N-grade ultrapure iron. The method is characterized by comprising the following steps: electrolyzing industrial pure iron to prepare liquid; carrying out ion exchange treatment on the solution to reduce near-iron elements such as Co, Ni, Cu and Zn and impurities in the solution, so that ferrous ions are effectively enriched; then, the solution with the near iron element removed serves as electrolyte for electrolysis to prepare pure iron; in the electrolysis process, a ruthenium-coated titanium plate is used as an anode, and a pure titanium plate is used as a cathode; performing high-temperature vacuum annealing treatment and high-temperature atmosphere reduction on a product obtained by electrolysis to remove free-state and combined-state hydrogen and oxygen elements in the product; the 5N-grade ultrapure iron is prepared by matching the steps with a corresponding process. The method has the advantages that the removal of near-iron elements and gas elements is realized by combining solution purification, electrolysis, vacuum annealing and reduction from enrichment and purification of ferrous ions, and the purpose of preparing 5N-grade ultrapure iron through electrolysis is realized.

Description

Technical Field

[0001] The invention relates to the technical field of high-purity metal preparation, and in particular to a method for preparing 5N-grade ultrapure iron. Background Art

[0002] As an important basic material, high-purity iron involves a wide range of fields such as aerospace, electronic information and military industry, and has become an important development direction in the field of new materials. Internationally, the purity of iron is generally represented by N (the first letter of the English word nine) and numbers, such as the purity of industrial pure iron is 2N~3N, 4N is high-purity iron, and 5N~6N is ultra-pure iron; the preparation methods of pure iron generally include pyrometallurgy, hydrometallurgy and combined preparation methods; among them, from the perspective of cost and mass production, the electrolytic preparation of high-purity iron has irreplaceable advantages, and the electrolytic preparation of pure iron has the advantages of simple process, low cost, less pollution and low energy consumption.

[0003] However, due to the serious blockade of the technology of preparing pure iron by electrolysis abroad, compared with foreign countries, my country's independent research and development of electrolytic iron started late, and some technologies still lag behind countries such as Japan that started earlier. The research on the electrolytic preparation of high-purity iron is still in the experimental stage, and its demand mainly relies on imports from Japan. Although in recent years, some small and medium-sized enterprises in China have also begun to develop specific process flows for preparing high-purity iron by electrolysis, among which a domestic electrolytic iron enterprise has an annual production capacity of 1,000 tons, but the purity level is only 3N; Gansu Metal Products Group has achieved the preparation of 4N-grade electrolytic iron at the laboratory level, but it has only achieved a small amount of laboratory preparation; there are still technical bottlenecks for the industrial production of electrolytic iron with higher purity levels, so it is particularly important to break through the technical bottleneck of electrolytic preparation of 5N-grade ultra-pure iron. Summary of the invention

[0004] In view of the current situation that the technology for preparing ultra-high purity iron by electrolysis in China is still immature, and the foreign countries have a serious blockade on electrolysis technology, and there are few reports on the preparation of 5N grade ultra-pure iron, the present invention provides a method for preparing 5N grade ultra-pure iron (99.995-99.9995wt%); by using industrial pure iron to make liquid, and ion exchange the electrolyte to remove near-ferrous elements and enrich ferrous ions; then using titanium-coated ruthenium plates as anodes and pure titanium plates as cathodes to electrolyze and prepare pure iron; finally, by high-temperature vacuum annealing and reduction, the residual gas elements in the electrolytic iron are further removed, so as to achieve the goal of preparing 5N grade ultra-pure iron by electrolysis.

[0005] The key points of the present invention are: (1) electrolysis liquid preparation is required to enrich Fe in industrial pure iron; (2) ion exchange resin is required to remove near-iron elements. If they are not removed in advance, the near-iron elements will be deposited on the cathode plate together with iron during the subsequent electrolysis process and will be difficult to separate; (3) the pure iron obtained after electrolysis of the enriched solution needs to be subjected to high-temperature vacuum annealing and reduction treatment. The higher the temperature during the annealing process, the more conducive it is to the removal of free oxygen.

[0006] In order to achieve the above object, the specific technical solution adopted by the present invention is as follows:

[0007] A method for preparing 5N grade ultrapure iron comprises the following steps:

[0008] S1. Electrolysis: Industrial pure iron is used as the anode plate, titanium plate is used as the cathode plate, and high-purity (better than 99.9%) FeCl2·4H2O is used as the electrolyte. Electrolysis is performed in an electrolytic cell without a diaphragm. External power is applied to the anode and cathode plates to promote the precipitation of hydrogen on the cathode plate and the normal dissolution of Fe on the anode, thereby enriching ferrous ions.

[0009] S2. Solution purification: using exchange resin to perform ion exchange on the solution after electrolysis in step S1 to remove near-iron elements (the near-iron elements are metal impurities with a potential difference close to that of ferrous ions in the solution, such as Co, Ni, Cu, Zn, etc.) and impurities (such as non-metallic elements such as P and S) therein, so as to make the electrolyte purer and avoid deposition on the cathode plate together with ferrous ions in the later electrolytic iron making process;

[0010] S3. Electrolysis of pure iron: using a titanium-coated ruthenium plate as an anode and a pure titanium plate as a cathode, removing the near-iron element and impurities in the solution as an electrolyte for electrolysis to obtain an electrolytic iron plate, which is cut to obtain an electrolytic iron sheet;

[0011] S4. High temperature vacuum and reduction treatment: The electrolytic iron sheet is subjected to high temperature vacuum annealing to remove moisture, free oxygen and pre-remove combined oxygen; the treated electrolytic iron sheet is placed in a rotary atmosphere furnace for high temperature reduction treatment to remove combined gaseous elements hydrogen and oxygen to produce 5N grade ultra-pure iron.

[0012] Furthermore, in step S1, the total content of the near-iron elements Co, Ni, Cu, and Zn in the industrial pure iron is not higher than 500 ppm, and the contents of other elements meet the standards of process pure iron.

[0013] Furthermore, in step S2, the purpose of ion exchange is to remove Co, Ni, Cu, and Zn elements in the solution. The sum of the contents of Co, Ni, Cu, and Zn elements in the solution after ion exchange is required to be no higher than 50 ppm, and the contents of other elements meet the process requirements.

[0014] Furthermore, in step S1, hydrochloric acid is added during the electrolytic dissolution of industrial pure iron to control the pH value of the solution to be no higher than 1, ensuring that hydrogen precipitation is the main reaction on the cathode plate. If the pH is higher than 1, iron deposition will begin to appear on the cathode plate. Hydrochloric acid is used to adjust the pH value. Since FeCl2·4H2O is used as the electrolyte, the H + and Cl - The ions will not cause secondary contamination to the electrolyte.

[0015] Furthermore, in step S3, the concentration of ferrous ions in the electrolyte is between 100 and 300 g / L. When it exceeds 200 g / L, the deposition rate of electrolytic iron does not change much under the same conditions. It is preferably between 100 and 150 g / L. If it is lower than 100 g / L, ferrous ions need to be replenished in time.

[0016] Furthermore, in step S3, the temperature of the electrolyte is 80-95°C, preferably 80-90°C; the pH value of the electrolyte is 2-5, preferably 2-4; the cathode current density is 50-500A / m 2 , preferably 100 to 300 A / m 2 .

[0017] Furthermore, in step S3, the size of the titanium-coated ruthenium plate and the pure titanium plate is not less than 500*500*2mm. 3 , which is conducive to industrial production.

[0018] Furthermore, in step S3, the size of the cut electrolytic iron sheet is 1 to 50 mm in width and 1 to 50 mm in length.

[0019] Furthermore, in step S4, the vacuum annealing temperature is 800-1100°C, preferably 1000-1100°C; the annealing time is 1-48h, preferably 5-20h; the vacuum degree is not less than 1.0*10 -3 Pa; During the vacuum annealing process, Ar is first introduced to exclude air and then heating is performed. Necessary measures must be taken during the process to prevent oxygen from entering.

[0020] Furthermore, in step S4, the rotation frequency of the rotary atmosphere furnace is 1 to 30 r / min, preferably 3 to 8 r / min; the reduction temperature is 600 to 1100°C, preferably 700 to 900°C; the reduction time is 1 to 240h, and the reducing gas flow rate is not less than 0.1L / min; during the reduction process, a positive pressure of not less than 0.1MPa must be maintained inside the equipment.

[0021] Furthermore, in step S4, oxygen must be prevented from entering during the heating and cooling processes during the high-temperature reduction process. After the iron sheet is placed in, the reducing gas is first introduced for 1 hour during the heating process and then the temperature is gradually increased. The reducing gas must be continuously introduced during the cooling process after the reduction. After the temperature is lower than 100°C, the furnace can be opened to take out the sample to obtain 5N grade ultra-pure iron.

[0022] Furthermore, in step S4, the electrolytic iron sheet needs to be placed in a grinder for grinding before high-temperature vacuum annealing to remove hydrolysis products and gas elements in the surface layer.

[0023] Furthermore, in step S4, the obtained 5N grade ultrapure iron is packaged in a vacuum or filled with an inert gas such as argon or nitrogen to prevent the 5N grade pure iron from being oxidized due to oxygen absorption during transportation or storage.

[0024] The present invention has the following beneficial effects:

[0025] The method for preparing 5N grade ultrapure iron of the present invention starts from the perspective of purifying electrolyte, selects industrial pure iron for electrolysis and liquid preparation, uses exchange resin for ion exchange to remove impurity elements in the metal with a potential difference close to that of ferrous ions; selects insoluble anode plates for electrolysis, reduces the consumption of anode plates, saves material costs, and shortens the process operation flow; the pure iron obtained by electrolysis is subjected to high-temperature vacuum annealing and reduction treatment, solves the technical problem of high gas element content in electrolytic iron, reduces the content of impurity elements in electrolytic iron, achieves the goal of preparing 5N grade ultrapure iron by electrolysis, and breaks through the technical bottleneck of industrial production of pure iron of this level. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a physical picture of the 5N grade ultrapure iron obtained in Example 1 of the present invention.

[0027] Figure 2 The test results of the chemical composition content of the 5N grade ultrapure iron prepared in Example 1 of the present invention are shown.

[0028] Figure 3 This is a physical picture of 5N grade ultrapure iron prepared in Example 2 of the present invention.

[0029] Figure 4 The test results of the chemical composition content of the 5N grade ultrapure iron prepared in Example 2 of the present invention.

[0030] Figure 5 It is the change of electrolyte concentration in comparative example 1 of the present invention.

[0031] Figure 6 This is the test result of the content of near-iron elements in the 5N grade ultrapure iron prepared in Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0032] The present invention is further described below in conjunction with the specific embodiments of the above method. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0033] Example 1

[0034] A method for preparing 5N grade ultrapure iron, specifically comprising the following steps:

[0035] S1. Electrolysis

[0036] Industrial pure iron (3N grade, purity 99.5-99.95wt%, the total content of near-iron elements Co, Ni, Cu, Zn is not higher than 500ppm) is used as anode, titanium plate is used as cathode, and FeCl2·4H2O with a purity of 99.9% is used as electrolyte. Electrolysis is carried out in an electrolytic cell without a diaphragm, and external power is applied to the anode and cathode plates. Hydrochloric acid is automatically added to control the pH value to be lower than 1, so that hydrogen is preferentially precipitated on the cathode and Fe is normally dissolved on the anode, thereby making Fe in the electrolyte 2+ Ions are enriched.

[0037] S2. Solution purification

[0038] Using a cation exchange resin to perform ion exchange on the solution after electrolysis in step S1, exchanging metal impurities in the solution with a potential difference close to that of ferrous ions, removing near-iron elements and impurities, and purifying the electrolyte;

[0039] S3. Electrolysis of pure iron

[0040] The size is 700*800*2mm 3 The titanium-coated ruthenium plate is the anode plate, with a size of 700*800*2mm 3 The pure titanium plate is used as the cathode plate, and the solution obtained in step S2 to remove the near-iron element is used as the electrolyte for electrolysis. The electrolyte temperature is 80°C, the electrolyte pH value is 2.0-2.4, and the cathode current density is 150A / m 2 After 5 days of electrolysis, the electrolytic iron plate is taken out and cut into electrolytic iron sheets with a cutting machine.

[0041] It should be noted that before electrolysis, the surfaces of the positive and negative plates should be pickled, rusted, polished, impurities removed, and rinsed with clean water to ensure that the state of the plates themselves will not pollute the electrolyte. During the electrolysis process, it is necessary to always observe the concentration of ferrous ions and the content of other metal impurities in the electrolyte. When the concentration of ferrous ions is lower than 100g / L, high-purity FeCl2·4H2O needs to be added in time; when the content of other metal impurities such as Co, Ni, Cu, and Zn is too high and exceeds the limit value, it is necessary to promptly perform ion exchange to adsorb the metal impurities or use industrial pure iron to re-liquid to ensure the purity of the electrolyte.

[0042] S4. High temperature vacuum and reduction treatment

[0043] The electrolytic iron sheet was put into a grinder and ground for 6 hours to remove the hydrolysis products and gas elements on the surface; then placed in a vacuum of 10 -3 Pa high temperature vacuum drying oven for 3h, annealing temperature is 1000℃, remove moisture, free oxygen and pre-removal of combined oxygen in the iron sheet; during vacuum annealing, first introduce Ar to remove air and then heat, and necessary measures should be taken to prevent oxygen from entering during the process. Put the small iron sheet after annealing into a rotary atmosphere furnace for reduction treatment, start the furnace tube rotation button, and the rotation frequency is 3r / min; open the nitrogen valve to introduce nitrogen for 30 minutes, and then slowly introduce reducing gas, the reducing medium is CH4, the gas flow rate is controlled at more than 0.5L / min, and continue to introduce during the reduction process; set the reduction temperature to 800℃, the reduction time is set to 120h, and during the heating process, introduce reducing gas for 1h and then gradually increase the temperature to the reduction temperature. During the reduction process, the equipment must maintain a positive pressure of not less than 0.1MPa; after the reduction is completed, cool it down to below 100℃ and take it out. During the cooling process, continue to introduce reducing gas to prevent the electrolytic iron sheet from absorbing oxygen during the cooling process, and vacuum storage after cooling.

[0044] 5N grade ultrapure iron after vacuum storage Figure 1 As shown, its chemical composition was tested by GDMS, and the results are as follows Figure 2 As shown, the purity reaches 5N3 level.

[0045] Example 2

[0046] A method for preparing 5N grade ultrapure iron, specifically comprising the following steps:

[0047] S1~S2: Same as Example 1.

[0048] S3. The difference from Example 1 is that the electrolyte temperature is 90°C.

[0049] S4. The difference from Example 1 is that the rotation frequency of the rotary atmosphere furnace is 7 r / min, the reduction temperature is 700° C., and the reduction time is set to 150 h.

[0050] The 5N grade ultrapure iron obtained after reduction treatment in this embodiment is as follows Figure 3 Its chemical composition is shown in Figure 4 As shown, the purity reaches 5N3 level.

[0051] Comparative Example 1

[0052] Compared with Example 1, the comparative example changes the requirement that the pH value in step S1 is not higher than 1, and adjusts the pH value to above 1. As a result, iron deposition is found on the cathode plate during the liquid making process, but the Fe 2+ The ion concentration did not increase, e.g. Figure 5 As shown, the effect of electrolysis and liquid formation cannot be achieved.

[0053] Comparative Example 2

[0054] Compared with Example 1, this comparative example changes the method of using ion exchange resin to purify the electrolyte in step S2, and chooses not to place cation exchange resin, and directly electrolyzes to prepare pure iron, as follows: After the electrolysis liquid is completed, a titanium-coated ruthenium plate is directly used as an anode plate and a pure titanium plate is used as a cathode plate for electrolysis preparation, and then the prepared pure iron is subjected to high-temperature vacuum annealing and reduction, and vacuum storage. The results showed that after GDMS was used to detect the reduced electrolytic iron, the content of near-iron elements (Co, Ni) in the electrolytic iron was high, accounting for the largest proportion of the remaining impurity elements, and was difficult to remove, such as Figure 6 shown.

[0055] This specific implementation is only an explanation of the present invention, not a limitation of the present invention. Any changes made by those skilled in the art after reading the specification of the present invention will be protected by the patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A method for preparing 5N grade ultrapure iron, characterized in that: The following steps are involved: S1. Electrolysis: Industrial pure iron is used as anode, titanium plate is used as cathode, and high-purity FeCl2·4H2O is used as electrolyte. Electrolysis is carried out in an electrolytic cell with a diaphragm. External power is applied to the anode and cathode plates to promote the precipitation of hydrogen on the cathode plate and the normal dissolution of Fe on the anode, so that ferrous ions are enriched. S2 solution purification: using ion exchange resin to perform ion exchange on the solution after electrolysis in step S1 to remove the iron-like elements and impurities; S3. Electrolysis of pure iron: using a titanium-coated ruthenium plate as an anode and a pure titanium plate as a cathode, removing the near-iron element and impurities in the solution as an electrolyte for electrolysis to obtain an electrolytic iron plate, which is cut to obtain an electrolytic iron sheet; S4. High temperature vacuum and reduction treatment: The electrolytic iron sheet is subjected to high temperature vacuum annealing treatment to remove moisture, free oxygen and pre-remove combined oxygen; the electrolytic iron sheet subjected to high temperature vacuum treatment is placed in a rotary atmosphere furnace for high temperature reduction treatment to remove combined gas elements hydrogen and oxygen to obtain 5N grade ultra-pure iron.

2. The method for preparing 5N grade ultrapure iron according to claim 1, characterized in that: In step S1, the total content of the near-iron elements Co, Ni, Cu, and Zn in the industrial pure iron is not higher than 500 ppm, and the contents of other elements meet the standards of process pure iron.

3. The method for preparing 5N grade ultrapure iron according to claim 1, characterized in that: In step S1, hydrochloric acid is added during the electrolytic dissolution of industrial pure iron to control the pH value of the solution to be no higher than 1.

4. The method for preparing 5N grade ultrapure iron according to claim 1, characterized in that: In step S2, the total content of Co, Ni, Cu and Zn in the solution after ion exchange is required to be no higher than 50 ppm.

5. The method for preparing 5N grade ultrapure iron according to claim 1, characterized in that: In step S3, the concentration of ferrous ions in the electrolyte is 100-300 g / L.

6. The method for preparing 5N grade ultrapure iron according to claim 1, characterized in that: In step S3, the temperature of the electrolyte is 80-95°C, the pH value of the electrolyte is 2-5, and the cathode current density is 50-500A / m 2 .

7. The method for preparing 5N grade ultrapure iron according to claim 1, characterized in that: In step S3, the size of the titanium-coated ruthenium plate and the pure titanium plate is not less than 500*500*2mm 3 .

8. The method for preparing 5N grade ultrapure iron according to claim 1, characterized in that: In step S4, the vacuum annealing temperature is 800-1100°C, the annealing time is 1-48 hours, and the vacuum degree is not less than 1.0*10 -3 Pa, during vacuum annealing, Ar is first introduced to exclude air and then heating is performed. During the process, oxygen must be prevented from entering.

9. The method for preparing 5N grade ultrapure iron according to claim 1, characterized in that: In step S4, the rotation frequency of the rotary atmosphere furnace is 1-30 r / min, the reduction temperature is 600-1100° C., the reduction time is 1-240 h, the reducing gas flow rate is not less than 0.1 L / min, and a positive pressure of not less than 0.1 MPa is maintained in the equipment during the reduction process.

10. The method for preparing 5N grade ultrapure iron according to claim 1, characterized in that: In step S4, the electrolytic iron sheet needs to be put into a grinder for grinding before high-temperature vacuum annealing to remove hydrolysis products and gas elements in the surface layer.

11. The method for preparing 5N grade ultrapure iron according to claim 1, characterized in that: In step S4, oxygen must be prevented from entering during the heating and cooling processes during the high-temperature reduction process. After the iron sheet is placed in, the reducing gas is first introduced for 1 hour during the heating process and then the temperature is gradually increased. The reducing gas must be continuously introduced during the cooling process after the reduction. After the temperature is lower than 100°C, the furnace can be opened to take out the sample to obtain 5N grade ultra-pure iron.

12. The method for preparing 5N grade ultrapure iron according to claim 1, characterized in that: In step S4, the obtained 5N grade ultrapure iron is packaged in a vacuum or in an inert gas atmosphere.

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