Process for preparing 5N-grade ultrapure iron from industrial pure iron

Abstract

A process for preparing 5N-grade ultrapure iron from industrial pure iron is characterized in that 3N-grade industrial pure iron is adopted as an anode to obtain 4N-grade high-purity iron through primary electrolysis, the 4N-grade high-purity iron obtained through primary electrolysis is adopted as an anode to continue secondary electrolysis, pure iron obtained through secondary electrolysis is subjected to tertiary electrolysis or multiple times of electrolysis, and 5N-grade ultrapure iron is obtained. And removing free-state and combined-state gas elements in the pure iron subjected to three times of electrolysis or multiple times of electrolysis by utilizing a rotary vacuum drying furnace and a rotary reduction furnace matched with a proper process, so as to prepare the ultrapure iron with the purity of 5N grade. The method disclosed by the invention has the advantages that industrial pure iron is used as a raw material to be electrolyzed for many times to reduce the content of near iron elements such as Co, Ni, Cu and Zn, and a rotary drying furnace and an atmosphere reduction furnace are matched with a proper process to reduce free-state and combined-state gas elements in electrolytic iron; the preparation of 5N-grade ultrapure iron with low near iron element, low oxygen content and low cost is realized by combining three steps of electrolysis, drying and reduction.

Description

Technical Field

[0001] The invention relates to the technical field of ultrapure iron production, in particular to a process for preparing 5N-grade ultrapure iron using industrial pure iron. Background Art

[0002] As an advanced material used in core components of advanced equipment, high-purity iron has broad application prospects in many industrial fields such as aerospace equipment, marine engineering, and military industry, and has attracted widespread attention. Among them, the electrolytic method for preparing pure iron has been the focus of research by scholars at home and abroad due to its advantages such as low cost, short process flow, and simple equipment structure.

[0003] Internationally, Japan has always been the largest producer and exporter of high-purity electrolytic iron. As early as the 1930s, Japanese factories could produce electrolytic iron with a purity level of 4N to 5N using ferrous sulfate solution and ferrous chloride solution. Japan's Toho Lead Corporation has conducted research and development of high-purity electrolytic iron and achieved independent production of electrolytic iron with a purity close to 5N. In addition, relevant institutions such as the Massachusetts Institute of Technology, the National Bureau of Standards of the United States, the National Physical Laboratory of the United Kingdom, France and Germany have also conducted certain research on the technology of preparing pure iron by electrolysis.

[0004] However, due to the severe 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, there are still technical bottlenecks for the preparation of electrolytic iron with higher purity levels, such as excessive gas element content in electrolytic iron and rapid surface oxidation. At present, the purity level of high-purity metals usually does not consider the gas element content, mainly because the removal of the gas element content is difficult to achieve. The present invention provides a method for reducing the content of near-iron elements and gas elements in electrolytic pure iron. Summary of the invention

[0005] The technical problem to be solved by the present invention is as follows: In view of the technical problem that the purity level of pure iron currently prepared by electrolytic refining technology is generally not high, such as the high content of metal elements such as Co, Ni, Cu, Zn and gas elements such as H and O, the present invention provides a process for preparing 5N grade ultra-pure iron from industrial pure iron, wherein the 5N grade ultra-pure iron is prepared by combining industrial pure iron as a raw material with multiple electrolysis and rotary vacuum drying and a rotary atmosphere reduction furnace; by using 3N grade industrial pure iron as a raw material, it is repeatedly electrolytically refined to achieve a gradual and graded reduction of metal impurity elements such as Co, Ni, Cu, and Zn; the pure iron obtained by multiple electrolysis is subjected to dehydrogenation annealing treatment to reduce the free and combined hydrogen content inside the pure iron, and the pure iron after multiple electrolytic refining is reduced in a reducing atmosphere to reduce the combined oxygen content in the electrolytic iron, thereby achieving the goal of preparing 5N grade ultra-pure iron with a purity of 99.995-99.9995wt% by electrolysis of industrial pure iron.

[0006] The technical solution of the present invention is as follows:

[0007] A process for preparing 5N grade ultrapure iron from industrial pure iron, characterized by comprising the following steps:

[0008] Step A, using a first anode formed of 3N grade industrial pure iron as an anode material and a first cathode formed of titanium as a cathode material, the iron element dissolved from the anode 3N grade industrial pure iron into the first electrolyte in the first electrolysis is deposited on the surface of the first cathode titanium as the first electrolysis 4N grade pure iron;

[0009] Step B, using the first electrolytic 4N grade pure iron as the second anode and titanium as the cathode material to form the second cathode, and the iron element dissolved from the anode 4N grade pure iron into the second electrolyte in the second electrolysis is deposited on the second cathode titanium surface as the second electrolytic 4N grade pure iron with less iron element content;

[0010] Step C, shearing the second electrolytic 4N grade pure iron into electrolytic pure iron sheets and placing them in a high-temperature vacuum furnace for dehydrogenation annealing to obtain dry iron sheets with free and combined hydrogen elements removed;

[0011] Step D, placing the dried electrolytic pure iron sheet into a reduction furnace for reduction treatment to remove the combined oxygen element in the dried electrolytic pure iron sheet, thereby preparing 5N grade ultrapure iron with a purity of 99.995 to 99.9995 wt% of iron element;

[0012] Step E: Packing the 5N grade ultrapure iron in a vacuum or nitrogen atmosphere.

[0013] In step A, the first electrolyte contains Fe 2+The concentration is 50-300 g / L, the pH is 1-5, the temperature is 60-100°C, and the cathode current density is 50-500 A / m 2 The sum of the weight contents of near-iron elements Co, Ni, Cu, and Zn in 3N grade industrial pure iron is ≤500ppm, the sum of the weight contents of Cr, Mn, Co, Ni, Cu, and Zn in the first electrolytic 4N grade pure iron is ≤100ppm, and the remaining metal impurity elements are all ≤1ppm.

[0014] The second electrolyte in step B contains Fe 2+ The concentration is 50-100 g / L, the pH is 2-4, the temperature is 80-100°C, and the cathode current density is 50-300 A / m 2 .

[0015] In step C, the high temperature vacuum dehydrogenation annealing treatment is carried out at a temperature of 300-1000°C and a vacuum pressure value of ≤1.0*10 -2 Pa, annealing time is not less than 1h.

[0016] In step D, the reducing medium in the reduction furnace is H2 gas atmosphere, the reduction temperature is 800-1200°C, the reduction time is ≥72h, and the reducing gas medium flow rate is not less than 0.5L / min.

[0017] The sum of the weight contents of the metal elements Cr, Mn, Co, Ni, Cu, and Zn in the 5N grade ultra-pure iron in step D is not higher than 20 ppm, the sum of the weight contents of the gas elements oxygen, nitrogen, and hydrogen is not higher than 20 ppm, and the contents of other elements are all lower than 1 ppm. The sum of the contents of non-ferrous elements in the obtained 5N grade pure iron is not higher than 50 ppm.

[0018] Step B includes a third or more electrolysis for further electrolytic purification.

[0019] Both step A and step B include: during electrolysis, the electrolyte flows out from the bottom of the electrolytic cell and is added to the top, the electrolyte flowing out of the cell is filtered by sedimentation and the pH is adjusted, and finally re-enters the electrolytic cell from the top, thereby forming a circulation flow of electrolyte flowing in from top to bottom.

[0020] Both step A and step B include: during electrolysis, the cathode current density is gradually increased.

[0021] The technical effects of the present invention are as follows: The present invention is a process for preparing 5N grade ultrapure iron from industrial pure iron, which is characterized by using 3N grade industrial pure iron as an anode to obtain 4N grade high-purity iron through a primary electrolysis, using the 4N grade high-purity iron obtained from the primary electrolysis as an anode to continue secondary electrolysis, using the pure iron obtained from the secondary electrolysis to perform three or multiple electrolysis, and using a rotary vacuum drying furnace and a rotary reduction furnace to match an appropriate process to remove free and compound gas elements from the pure iron after the three or multiple electrolysis, thereby preparing ultrapure iron with a purity of 5N grade. The advantages of the method of the present invention are that industrial pure iron is used as a raw material to perform multiple electrolysis to reduce the content of near-iron elements such as Co, Ni, Cu, and Zn, using a rotary drying furnace and an atmosphere reduction furnace matched with an appropriate process to reduce the free and compound gas elements in the electrolytic iron, and using the combination of electrolysis, drying, and reduction to achieve low near-iron elements, low oxygen content, and low-cost preparation of 5N grade ultrapure iron. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a physical picture of the electrolytic preparation of pure iron involved in Example 1 of the present invention.

[0023] Figure 2 This is a physical picture of 5N grade pure iron involved in Example 1 of the present invention.

[0024] Figure 3 for Figure 2 Chemical composition weight content ppm result chart of 5N grade pure iron. Figure 3 The weight content of iron element in 5N grade pure iron products is 99.9992%, that is, the purity is 5N2 level. The weight content of non-iron elements in ppm is as follows: P=0.75, S=0.5, B<0.01, Na=0.07, Mg<0.01, Al=0.04, Pb=0.06, Bi<0.005, Co=1.75, Si=0.02, Cl=0.05, K<0.05, Ca<0.05, Sc<0.05, Ti<0.01, V<0.01, Cr=0.06, Mn<0.05, Ni=1.13, Cu=2.25, Zn=0.25, Ga=0.09, Ge=0.32, As=0.15, Nb<0.05, Mo=0.08, Sn<0.05.

[0025] Figure 4 This is a physical picture of 5N grade pure iron obtained in Example 2 of the present invention.

[0026] Figure 5 for Figure 4 Chemical composition weight content ppm result chart of 5N grade pure iron. Figure 5The weight content of iron element in 5N grade pure iron products is 99.9993%, that is, the purity is 5N3 level. The weight content of non-iron elements in ppm is as follows: P=0.63, S=0.45, B<0.01, Na=0.07, Mg<0.01, Al=0.02, Pb=0.08, Bi<0.005, Co=1.3, Si=0.06, Cl=0.02, K<0.05, Ca<0.05, Sc<0.05, Ti<0.01, V<0.01, Cr=0.03, Mn<0.05, Ni=1.08, Cu=2.5, Zn=0.14, Ga=0.03, Ge=0.27, As=0.21, Nb<0.05, Mo=0.04, Sn<0.05. DETAILED DESCRIPTION

[0027] Below is the attached figure ( Figure 1-Figure 5 ) and Examples illustrate the present invention.

[0028] Figure 1 This is a physical picture of the electrolytic preparation of pure iron involved in Example 1 of the present invention. Figure 2 This is a physical picture of 5N grade pure iron involved in Example 1 of the present invention. Figure 3 for Figure 2 Chemical composition weight content ppm result chart of 5N grade pure iron. Figure 4 This is a physical picture of 5N grade pure iron obtained in Example 2 of the present invention. Figure 5 for Figure 4 The chemical composition weight content ppm result chart of 5N grade pure iron. Figures 1 to 5 , a process for preparing 5N grade ultrapure iron from industrial pure iron, comprising the following steps: step A, using a first anode formed of 3N grade industrial pure iron as an anode material, and a first cathode formed of titanium as a cathode material, and the iron elements dissolved from the anode 3N grade industrial pure iron into the first electrolyte in the first electrolysis are deposited on the surface of the first cathode titanium as the first electrolysis 4N grade pure iron; step B, using the first electrolysis 4N grade pure iron as a second anode, and a second cathode formed of titanium as a cathode material, and the iron elements dissolved from the anode 4N grade pure iron into the second electrolyte in the second electrolysis are deposited on the surface of the second cathode titanium The surface is deposited with second electrolytic 4N grade pure iron with less iron content; step C, shearing the second electrolytic 4N grade pure iron into electrolytic pure iron sheets and placing them in a high-temperature vacuum box furnace for dehydrogenation annealing to obtain dry electrolytic pure iron sheets with free and combined hydrogen removed; step D, placing the dry electrolytic pure iron sheets into a reduction furnace for reduction treatment to remove free and combined oxygen elements in the dry electrolytic pure iron sheets, thereby preparing 5N grade ultra-pure iron with a purity of 99.995 to 99.9995wt% of iron elements; step E, packaging the 5N grade ultra-pure iron in a vacuum or nitrogen atmosphere.

[0029] In step A, the first electrolyte contains Fe 2+ The concentration is 50-300 g / L, the pH is 1-5, the temperature is 60-100°C, and the cathode current density is 50-500 A / m 2 The sum of the weight contents of the near-iron elements Co, Ni, Cu, and Zn in 3N grade industrial pure iron is ≤500ppm, the sum of the weight contents of Cr, Mn, Co, Ni, Cu, and Zn in the first electrolysis 4N grade pure iron is ≤100ppm, and the remaining metal impurity elements are ≤1ppm. 2+ The concentration is 50-100 g / L, the pH is 2-4, the temperature is 80-100°C, and the cathode current density is 50-300 A / m 2 In step C, the high temperature vacuum dehydrogenation annealing temperature is 300-1000°C, and the vacuum pressure value is ≤1.0*10 -2 Pa, annealing time is not less than 1h. In step D, the reducing medium in the reduction furnace is H2, the reduction temperature is 800-1200°C, the reduction time is ≥72h, and the reducing gas medium flow rate is not less than 0.5L / min.

[0030] The sum of the weight contents of the metal elements Cr, Mn, Co, Ni, Cu, and Zn in the 5N grade ultrapure iron in step D is not more than 20ppm, the sum of the weight contents of the gas elements oxygen, nitrogen, and hydrogen is not more than 20ppm, the contents of other elements are all less than 1ppm, and the sum of non-iron elements is not more than 50ppm. Step B includes a third or more electrolysis for further electrolytic purification. Step A and step B both include: during electrolysis, the electrolyte flows out from the bottom of the electrolytic cell and is added to the upper part, and the electrolyte flowing out of the cell is filtered by sedimentation and acid is added to adjust the pH, and finally re-enters the electrolytic cell from the upper part, thereby forming an electrolyte circulation flow from top to bottom. Step A and step B both include: during electrolysis, the cathode current density adopts a step-by-step increase mode.

[0031] The present invention discloses a process and method for preparing 5N grade (99.995-99.9995wt%) ultrapure iron using industrial pure iron as raw material. The process is characterized in that 3N grade (99.5-99.95wt%) industrial pure iron is used as an anode to obtain 4N grade (99.95-99.995wt%) high-purity iron through a primary electrolysis, the 4N grade high-purity iron obtained through the primary electrolysis is used as an anode to continue the secondary electrolysis, the pure iron obtained through the secondary electrolysis is subjected to a third electrolysis or multiple electrolysis, and the pure iron after the third electrolysis or multiple electrolysis is subjected to a vacuum annealing furnace and a rotary reduction furnace with appropriate processes to remove free and compound gas elements therein, thereby preparing ultrapure iron with a purity of 5N grade. The advantages of the method of the present invention are that industrial pure iron is used as raw material for multiple electrolysis to reduce the content of near-iron elements such as Co, Ni, Cu, and Zn therein, a rotary vacuum annealing furnace and an atmosphere reduction furnace are used in combination with appropriate processes to reduce free and combined gas elements in the electrolytic iron, and a three-step combination of electrolysis, drying, and reduction is used to achieve the preparation of 5N grade ultra-pure iron with low near-iron elements, low oxygen content, and low cost.

[0032] A process and method for preparing 5N grade (99.995-99.9995wt%) ultrapure iron using industrial pure iron as raw material, belonging to the field of electrochemical refining in hydrometallurgy. It is characterized in that it discloses a method of using 3N grade industrial pure iron as an anode to perform a primary electrolysis to obtain 4N grade pure iron, and the obtained 4N grade pure iron is subjected to secondary electrolysis or multiple electrolysis to gradually reduce the near-iron elements in the pure iron; and the electrolytic pure iron obtained by multiple electrolysis is subjected to high-temperature vacuum drying and high-temperature reducing atmosphere reduction treatment to reduce the content of free and combined gas elements therein, thereby obtaining 5N grade ultrapure electrolytic iron. The electrolyte for the primary electrolysis is 50-300g / L Fe 2+ Solution, pH 1-5; electrolyte temperature 60-100°C; cathode current density 50-500A / m 2 The electrolyte for secondary electrolysis and subsequent electrolysis is 50-100 g / L Fe 2+ Solution, pH 2-4, electrolyte temperature 80-100°C, cathode current density 50-300A / m 2 The electrolytic iron obtained by multi-stage electrolysis is dried in a rotary high-temperature vacuum drying furnace at a drying temperature of 300-1000°C and a vacuum degree of not less than 10 -2 Pa; the high-temperature reducing atmosphere reduction temperature is 800-1200°C; the reduction time is not less than 72h, and the gas flow rate is not less than 0.5L / min.

[0033] 3N grade industrial pure iron is used as raw material, wherein the sum of the near-iron elements Co, Ni, Cu, and Zn in the industrial pure iron raw material is required to be less than 500ppm, and the content of other elements in the industrial pure iron is not required.

[0034] The electrolyte for one electrolysis is 50-300 g / L Fe 2+ Solution, pH 1-5; electrolyte temperature 60-100°C; cathode current density 50-500A / m 2 .

[0035] The electrolyte in the secondary electrolysis and subsequent electrolysis process is 50-100 g / L Fe 2+ Solution, pH 2-4, electrolyte temperature 80-100°C, cathode current density 50-300A / m 2 .

[0036] Improve the electrolysis efficiency and purity, reduce the content of near-iron elements and oxygen elements in the obtained electrolytic iron, and the pH value and electrolyte temperature of the subsequent electrolysis should be higher than those of the first electrolysis, and the current density should be slightly lower.

[0037] The purity of the electrolytic pure iron obtained after one electrolysis reaches 4N grade, wherein the sum of the contents of Cr, Mn, Co, Ni, Cu and Zn is not higher than 100ppm, and the contents of other metal impurity elements are not higher than 1ppm.

[0038] Through good matching of electrolyte pH value, current density and temperature, the single purification efficiency of near-iron elements Co, Ni, Cu and Zn reaches more than 90%.

[0039] The sum of the contents of Cr, Mn, Co, Ni, Cu and Zn in the pure iron prepared by multiple electrolysis is not higher than 20 ppm, the sum of the contents of oxygen, nitrogen and hydrogen is not higher than 20 ppm, and the contents of other elements are all lower than 1 ppm.

[0040] The pure iron prepared by multiple electrolysis is dried in a high-temperature vacuum rotary drying furnace to remove the free gas element content inside the pure iron.

[0041] The high temperature vacuum dehydrogenation annealing temperature is 300~1000℃ and the vacuum degree is not less than 10 -2 Pa, annealing time is not less than 1h.

[0042] The pure iron obtained by multiple electrolysis uses a cyclonic atmosphere reduction furnace to remove the chemical gas elements in the pure iron.

[0043] The reducing medium of the rotary atmosphere reduction furnace can be a reducing atmosphere such as H2.

[0044] A process and method for preparing 5N grade ultrapure iron using industrial pure iron as raw material, wherein the reduction temperature is 800-1200°C and the reduction time is not less than 72 hours.

[0045] The ultra-pure iron after multiple electrolysis, vacuum drying and reduction treatments is packaged in a vacuum or nitrogen atmosphere to isolate it from oxygen.

[0046] The total content of major metal impurities (Cr, Mn, Co, Ni, Cu, Zn) does not exceed 20ppm, the content of gaseous elements oxygen, nitrogen and hydrogen does not exceed 20ppm, the sum of non-ferrous elements does not exceed 50ppm, and the purity reaches 5N (99.995~99.9995wt%) level.

[0047] The technical solution provided by the present invention has the following significant effects: the process and method of the present invention for preparing 5N grade (99.995-99.9995wt%) ultrapure iron using industrial pure iron as raw material selects low-cost industrial pure iron as raw material, saves material cost and expands the basic theory of pure iron manufacturing; the pure iron obtained by multiple electrolysis is dried and reduced, which solves the technical problem of high content of free and combined gas elements in the electrolytic iron, and multiple electrolysis, drying and reduction treatment are used to reduce the content of near-iron elements and gas elements in the electrolytic iron, thereby realizing the electrolytic preparation of 5N grade ultrapure iron.

[0048] The present invention provides the following technical solutions:

[0049] (1) A method for preparing 5N grade ultrapure iron from industrial pure iron, wherein the anode material is low-cost industrial pure iron and the cathode material is titanium plate; and the electrolytic pure iron obtained by the first electrolysis is electrolyzed for a second or multiple times.

[0050] (2) A method for preparing 5N grade ultrapure iron from industrial pure iron, by reasonably controlling the electrolyte temperature, current density and electrolyte pH value to achieve the purpose of gradually purifying Cr, Mn, Co, Ni, Cu and Zn.

[0051] (3) A method for preparing 5N grade ultrapure iron from industrial pure iron, wherein the pure iron after multiple electrolysis is subjected to high temperature vacuum dehydrogenation annealing treatment to remove free and combined hydrogen elements in the electrolytic iron, thereby creating conditions for the next reduction treatment.

[0052] (4) A method for preparing 5N grade ultrapure iron from industrial pure iron, wherein the electrolytic iron after dehydrogenation annealing is subjected to reduction treatment to further reduce the content of solid solution gas element oxygen in the electrolytic iron, and a cyclonic atmosphere reduction furnace is selected for the reduction treatment, with a reducing gas as a reducing agent.

[0053] (5) A method for preparing 5N grade ultrapure iron from industrial pure iron, wherein the electrolyte for primary electrolysis is 50 to 300 g / L of Fe 2+ The solution has an initial pH value of 1 to 5, preferably 2.2 to 3.2; the electrolyte temperature is 60 to 100°C, preferably 60 to 80°C; the cathode current density is 100 to 500 A / m 2 , preferably 150 to 250 A / m 2 .

[0054] (6) A method for preparing 5N grade ultrapure iron from industrial pure iron, wherein the electrolyte for secondary electrolysis and multiple electrolysis is 50 to 100 g / L Fe 2+ solution, pH 2-4, preferably 2.8-3.2; electrolyte temperature 80-100°C, preferably 85-95°C, cathode current density 50-300A / m 2 , preferably 50 to 150 A / m 2 .

[0055] (7) A method for preparing 5N grade ultrapure iron from industrial pure iron. Since the anode material will be gradually consumed during the electrolysis process, it needs to be replaced in time when the dissolution is completed to ensure that the electrolysis process is not interrupted; when the electrolytic iron on the surface of the cathode plate collapses during the electrolysis process, it needs to be removed in time to avoid short circuit and blackening of the electrolytic iron surface.

[0056] (8) A method for preparing 5N grade ultrapure iron from industrial pure iron, wherein the dehydrogenation annealing temperature is 300-1000°C, preferably 200-600°C; the reduction temperature is 800-1200°C, preferably 800-1000°C; and the reduction time is not less than 72 hours, preferably 72-120 hours.

[0057] (8) A method for preparing 5N grade ultrapure iron from industrial pure iron, wherein the electrolytic iron after electrolysis and reduction is packaged in a vacuum or nitrogen atmosphere.

[0058] Example 1

[0059] In this embodiment, a process and method for preparing 5N grade ultrapure iron from industrial pure iron is mainly introduced, and the specific process parameters are set as follows:

[0060] (1) The anode plate is made of industrial pure iron with a size of 600*700mm, and the cathode plate is made of mechanically polished titanium plate with a size of 700*700mm. Before electrolysis, an isolation film bag needs to be placed on the anode and cathode plates. During electrolysis, the electrolyte adopts a "top-in, bottom-out" liquid circulation mode. The electrolyte flowing out of the tank is filtered, acidified and adjusted for pH, and then re-enters the electrolytic cell from the top. Fe 2+ The electrolyte concentration is 200g / L, the initial pH value of electrolysis is 2.2-2.4, the electrolyte temperature is 80℃, and the cathode current density is 150A / m 2 After 5 days of electrolysis, the electrolytic iron is taken out and used as an anode plate to repeat electrolysis several times according to the same process parameters. Figure 1(2) The electrolytic iron plate finally obtained is sheared and cut into small electrolytic iron sheets of uniform size, and then placed in a vacuum drying oven for drying. The dehydrogenation annealing temperature is 400°C, and then taken out and placed in a rotary kiln for reduction treatment. A reducing atmosphere is selected as the reducing agent, the reduction temperature is set to 700°C, the reducing agent is ammonia, and the reduction time is 72h. After the reduction is completed, the electrolytic iron sheet is vacuum treated and stored. The obtained 5N grade ultrapure iron is as shown in FIG. Figure 2 As shown, its chemical composition is tested by GDMS. Figure 3 As shown (GDMS, glow discharge mass spectrometry).

[0061] Example 2

[0062] This embodiment is basically the same as embodiment 1, except that Fe 2+ The electrolyte concentration is 150g / L, the initial pH value of electrolysis is 2.0-2.2, the electrolyte temperature is 90℃, and the cathode current density is 150A / m 2 , taken out after 5 days of electrolysis; the dehydrogenation annealing temperature is 500℃, the reduction temperature is set to 800℃, the reducing agent is ammonia, and the reduction time is 144h. Figure 4 Its chemical composition is shown in Figure 5 shown.

[0063] The contents not described in detail in the specification of the present invention belong to the prior art known to the professional and technical personnel in the field. It is pointed out here that the above description helps those skilled in the art to understand the invention, but does not limit the protection scope of the invention. Any equivalent replacement, modification and / or simplification of the above description without departing from the essence of the invention falls within the protection scope of the invention.

Claims

1. A process for preparing 5N grade ultrapure iron from industrial pure iron, characterized in that: The following steps are involved: Step A, using a first anode formed of 3N grade industrial pure iron as an anode material and a first cathode formed of titanium as a cathode material, the iron element dissolved from the anode 3N grade industrial pure iron into the first electrolyte in the first electrolysis is deposited on the surface of the first cathode titanium as the first electrolysis 4N grade pure iron; Step B, using the first electrolytic 4N grade pure iron as the second anode and titanium as the cathode material to form the second cathode, and the iron element dissolved from the anode 4N grade pure iron into the second electrolyte in the second electrolysis is deposited on the second cathode titanium surface as the second electrolytic 4N grade pure iron with less iron element content; Step C, shearing the second electrolytic 4N grade pure iron into electrolytic pure iron sheets and placing them in a high-temperature vacuum annealing furnace for dehydrogenation annealing to obtain dry electrolytic pure iron sheets with free and combined hydrogen elements removed; Step D, placing the dried electrolytic pure iron sheet into a reduction furnace for reduction treatment to remove free and combined gaseous oxygen elements in the dried electrolytic pure iron sheet, thereby preparing 5N grade ultrapure iron with a purity of 99.995 to 99.9995 wt% of iron; Step E: Packing the 5N grade ultrapure iron in a vacuum or nitrogen atmosphere.

2. The process for preparing 5N grade ultrapure iron from industrial pure iron according to claim 1, characterized in that: In step A, the first electrolyte contains Fe 2+ The concentration is 50-200 g / L, the pH is 1-4, the temperature is 60-100°C, and the cathode current density is 50-300 A / m 2 The sum of the weight contents of near-iron elements Co, Ni, Cu, and Zn in 3N grade industrial pure iron is ≤500ppm, the sum of the weight contents of Cr, Mn, Co, Ni, Cu, and Zn in the first electrolytic 4N grade pure iron is ≤100ppm, and the remaining metal impurity elements are all ≤1ppm.

3. The process for preparing 5N grade ultrapure iron from industrial pure iron according to claim 1, characterized in that: The second electrolyte in step B contains Fe 2+ The concentration is 50-100 g / L, the pH is 2-4, the temperature is 80-100°C, and the cathode current density is 50-200 A / m 2 .

4. The process for preparing 5N grade ultrapure iron from industrial pure iron according to claim 1, characterized in that: In step C, the high temperature vacuum dehydrogenation annealing temperature is 300-1000°C, and the vacuum pressure value is ≤1.0*10 -2 Pa, drying time is not less than 1h.

5. The process for preparing 5N grade ultrapure iron from industrial pure iron according to claim 1, characterized in that: In step D, the reducing medium in the reduction furnace is H2, the reduction temperature is 800-1200°C, the reduction time is ≥72h, and the reducing gas medium flow rate is not less than 0.5L / min.

6. The process for preparing 5N grade ultrapure iron from industrial pure iron according to claim 1, characterized in that: The sum of the weight contents of the metal elements Cr, Mn, Co, Ni, Cu, and Zn in the 5N grade ultrapure iron in step D is not higher than 20 ppm, the sum of the weight contents of the gas elements oxygen, nitrogen, and hydrogen is not higher than 20 ppm, the contents of other elements are all lower than 1 ppm, and the total content of non-ferrous elements is lower than 50 ppm.

7. The process for preparing 5N grade ultrapure iron from industrial pure iron according to claim 1, characterized in that: Step B includes a third or more electrolysis for further electrolytic purification.

8. The process for preparing 5N grade ultrapure iron from industrial pure iron according to claim 1, characterized in that: Both step A and step B include: during electrolysis, the electrolyte flows out from the bottom of the electrolytic cell and is added to the top, the electrolyte flowing out of the cell is filtered by sedimentation and acid is added to adjust the pH, and finally re-enters the electrolytic cell from the top, thereby forming a circulation flow of electrolyte entering from the top and exiting from the bottom.

9. The process for preparing 5N grade ultrapure iron from industrial pure iron according to claim 1, characterized in that: Both step A and step B include: during electrolysis, the cathode current density is gradually increased.

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