JPH0684550B2 - Method for producing high-purity electrolytic iron - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing high-purity electrolytic iron, and more particularly to a method for reducing heavy metal impurities such as copper, cobalt and nickel in the method for producing high-purity electrolytic iron.

(Prior art) Electrolytic iron has a much smaller content of various impurities than ordinary mild steel, pure iron, etc., so high quality such as soft magnetic materials, electronic materials, alloy materials, and base metal materials for testing and research are required. It is used in various fields.

As for the needs of high-purity electrolytic iron, there is a demand for high-purity electrolytic iron or those with few specific elements in order to improve the functionality of metal materials. For example, to show the original properties of iron, the residual resistance ratio
RRR _H was set to be 3000 or more, that is, 10 wtppm or less as the total of metal components. For more information, see Iron and Steel Vol.
72 (3) (1986) pp. 361-367, especially 363.

Pure iron having the above RRR _H value can be obtained by a special method such as an electron beam zone melting method in an ultrahigh vacuum, but it cannot be expected to carry out such a method industrially.

As a conventional method for obtaining electrolytic iron, raw material iron such as mild steel and pure iron is used as an anode, and an aqueous sulfuric acid solution such as sodium sulfate, potassium sulfate, and ammonium sulfate, or water-soluble hydrochloric acid such as sodium chloride, potassium chloride, and ammonium chloride. A method is known in which a supporting electrolyte such as an aqueous solution and an aqueous solution containing an iron sulfate and an iron chloride is electrolytically deposited on a cathode such as stainless steel as an electrolytic solution, and for example, a new metal data book (Metal Jikkensha, Issued December 12, 1975, Issue 455
Pp. 457), a flow sheet and an outline of the electrolysis method are described. In this method, the element having a smaller ionization tendency than the target metal in the anode material (crude metal) and the insoluble or sparingly soluble substance in the crude metal do not dissolve but remain attached to the anode or become a precipitate. Collect at the bottom of the tank. On the other hand, those having an ionization tendency higher than that of the target metal are dissolved from the anode, but are not deposited on the cathode and are accumulated in the electrolytic solution. That is, only the target metal is dissolved at the anode and conveniently deposited at the cathode, and other impurities adhere to the anode, precipitate as slime at the bottom of the tank, or remain dispersed in the liquid and do not deposit at the cathode. Therefore, electrolytic iron with high purity can be obtained.

Conventionally, regarding the heavy metal content of pure iron obtained by the electrolysis method,
In the document issued by Metals Co., Ltd., Cu =
0.0001% (1ppm) or less, Ni = 0.020% (200
ppm) or less and Co = 0.006% (60 ppm) or less, internal standards are described. There is a problem that these heavy metal elements are difficult to remove by the conventional electrolytic method as described below.

(Problems to be Solved by the Invention) When high-purity iron is produced by an electrolytic method, a cathode 3 and an anode 4 are placed in an electrolytic solution 2 contained in an electrolytic bath 1 for producing electrolytic iron shown in FIG. Place them in opposition and perform electrolysis. In this example, the cathode 4 is a plate-shaped member, but may be a rotating drum type having a horizontal rotating shaft, or may have another structure. For the cathode on which electrolytic iron is electrodeposited, stainless steel such as SUS304 is preferably used because of its good handling properties such as cost and peelability of the electrodeposit. Generally, an iron material such as mild steel is used for the anode, but it is necessary to use industrial pure iron for the purpose of improving the purity even a little. The electrolytic solution supports electrolysis of ferrous ions and aqueous sulfuric acid solutions of water-soluble sulfates such as sodium sulfate, potassium sulfate, and ammonium sulfate, or aqueous hydrochloric acid solutions of water-soluble hydrochlorides such as sodium chloride, potassium chloride, and ammonium chloride. Use as liquid.

In order to reduce impurities in the above method, there is a method of using relatively high-grade mild steel or pure iron for the anode. But copper,
Since nickel, cobalt, etc. cannot be removed by the ordinary pure iron refining method, they are contained in trace amounts in mild steel, etc. Heavy metals such as copper, cobalt, and nickel contained in a trace amount in the anode material are ionized and dissolved, and a part of them is electrodeposited and always taken into electrolytic iron. Therefore, high-purity electrolytic iron cannot be obtained because contamination from the anode material cannot be prevented.

Further, as a method of reducing impurities, there is a method of previously purifying the iron salt constituting the electrolytic solution by, for example, ion exchange resin purification, solvent extraction purification, preliminary electrolysis, or the like. Even if this method is carried out, the heavy metal in the anode is dissolved to contaminate the electrolytic solution, and these heavy metals are electrodeposited, so that high-purity electrolytic iron cannot be obtained.

Further, since the iron electrolytic solution is generally in an acidic condition, corrosion is unavoidable in the portion in contact with the acidic solution. Therefore, anticorrosion of the cathode is effective in reducing impurities. However, since a current necessary for anticorrosion does not flow in the gas-liquid interface between the electrolyte in contact with the cathode and the generated gas or in the fine gap which is a defect of the cathode constituent material, nickel, chromium, heavy metals such as copper are dissolved from the cathode, Redeposit on the cathode.

Providing electrolytic iron with an extremely low content of impurities such as Co, Ni, and Cu by the electrolytic method is advantageous in terms of cost, and the application of pure iron can be further expanded, but this has not been achieved in the past. .

Further, although it can be said that the heavy metal content of pure iron obtained by the conventional electrolysis method is considerably low, the heavy metal content could not be further reduced even if it was retreated by the conventional electrolysis method. Therefore, in the conventional method, C, which is the five elements of iron impurities,
If it is possible to reduce Si, Mn, P, S, and then reduce heavy metal impurities such as Co, Ni, and Cu by reprocessing, the pure iron manufacturing technology will make remarkable progress.

(Means and Actions for Solving Problems) The present inventors completed the invention of the following electrolysis method as a result of diligent efforts to solve the problems.

That is, the method of the present invention uses an insoluble electrode to reduce the dissolution of impurities from the anode, and a small amount of heavy metal ions present in the electrolyte involved in the anodic reaction reach the cathode and are electrodeposited on the cathode. In order to prevent it, an intermediate chamber separated from each of the cathode chamber and the anode chamber by a diaphragm is provided,
In addition, in order to reduce the electrodeposition of impurities, the heavy metal concentration was set to 20
The gist is to supply the electrolytic solution purified to less than μg / to the cathode chamber.

That is, the method of the present invention comprises a cathode chamber, an anode chamber and an intermediate chamber, the diaphragm between the cathode chamber and the intermediate chamber is an anion exchange membrane, and the diaphragm between the anode chamber and the intermediate chamber is cation exchange membrane. Using an electrolytic cell that is a membrane, the cathode chamber is supplied with an electrolytic solution consisting of an aqueous solution containing iron ion carriers and supporting electrolyte purified to a heavy metal concentration of 20 μg / or less, and the anode chamber is composed of dilute sulfuric acid. An electrolytic solution is supplied, and an insoluble electrode coated with a film made of platinum group and its oxide on a Ti substrate is used as a cathode, and electrolytic solution is supplied while supplying electrolytic solution in an intermediate chamber during electrolytic extraction while supplying pure water. It is a method for producing high-purity electrolytic iron, which is characterized by collecting.

When carrying out this method, it is preferable to use an aqueous solution containing ferrous ions and a supporting electrolyte as main components as an electrolyte to be supplied to the cathode chamber.

Co and N contained as impurities in the ferrous ion carrier material
It is necessary to reduce heavy metals such as i and Cu in advance as much as possible. The upper limit of the content of these impurities is 20 μg /
The upper limit of the content of impurities in electrolytic iron that is less than or equal to (electrolytic solution capacity) can be 1 ppm or less. The impurities can be purified by an ion exchange resin purification method, a solvent extraction purification method, or the like.

The electrolyte supplied to the anode chamber is an electrolyte that discharges anions or water to generate halogen gas or oxygen and protons (H ⁺ ). High-purity sulfuric acid or the like is used as this electrolyte.

The liquid supplied to the intermediate chamber must satisfy the following conditions.

(A) It is a medium for generating electrolyte ions having ionic conductivity necessary for electrolysis.

(B) If the cathode chamber becomes excessively acidic, the cathode will dissolve, the cathode will dissolve, the electrolyte in the cathode chamber will be contaminated, or hydrogen gas will be generated by the discharge of protons (H ⁺ ) and the current efficiency of electrolytic iron deposition Is a medium in which excessive proton (H ⁺ ) transfer does not occur from the electrolytic solution in the intermediate chamber, since it may decrease.

(C) A medium that does not cause precipitation or the like due to pH change due to the progress of electrolytic reaction in the cathode chamber and the anode chamber.

(D) It is a medium that makes the pH higher than that of the cathode chamber after being supplied to the intermediate chamber.

(E) When heavy metals such as Co, Ni, Cu contained in the electrolytic solution in the anode chamber are ionized in the anode chamber and moved to the intermediate chamber and accumulated, these heavy metals are harmless to the electrolytic reaction system in the intermediate chamber. To the state of. As a detoxification measure, dilution or renewal is performed while partially removing the intermediate chamber liquid, and if necessary, the concentration of heavy metals in the intermediate chamber liquid is diluted, or the intermediate chamber liquid is renewed with a new liquid or pure water. .

(F) Substantially free of heavy metal ions.

As the liquid satisfying the above requirements, pure water, a weak acid, a weak base, a supporting salt, and HCl and NH ₄ OH in the cathode supply liquid are preferable.

Further, in the above method, the diaphragm that defines the intermediate chamber does not prevent generation of a necessary bath voltage between the anode and the cathode, and also separates the above-mentioned chamber liquids from each other.

Embodiments of the present invention will be described below with reference to the drawings.

(Example) FIG. 1 shows an example of the method of the present invention.

In this drawing, 1 is an electrolytic cell for producing electrolytic iron, 3 is a cathode, 4 is an anode, 5 is electrolytic iron, 6 is a cathode chamber, 7 is an intermediate chamber,
8 is an anion exchange membrane, 10 is a cation exchange membrane, 11 is a cathode chamber electrolyte, 12 is an intermediate chamber liquid, and 13 is an anode chamber electrolyte.

In FIG. 1, the cathode chamber electrolyte 11 includes, for example, ion exchange resin treatment, solvent extraction treatment, chelate resin treatment, iron powder,
Alternatively, an electrolytic solution composed of a ferrous iron aqueous solution purified by a substitution precipitation treatment with a metal powder such as aluminum or zinc having a higher ionization tendency than iron and a supporting electrolyte is arranged. As this electrolyte, 15-60 g / Fe of Fe ²⁺
In addition to Cl ₂ , 30 g / or less NH ₄ as an optional additive for conductivity adjustment
A solution containing Cl and having a pH of 1.5 to 5.0 is preferable.

Pure water or an acid, preferably a hydrochloric acid solution is used in the intermediate chamber 7. The hydrochloric acid solution has a HCl concentration of 0.3-0.5 g /
Is preferably 5.00 to 1.86. With the progress of electrolysis,
Proton (H ⁺ ) and Cl ⁻ ions are accumulated in the intermediate chamber 7, so pure water is added to cause overflow, and
Drive out. The amount of overflow is the volume of the intermediate chamber of the electrolytic cell 1
Therefore, 5 to 30 times is preferable.

The highly pure dilute sulfuric acid 8 is supplied to the anode chamber 9. By preventing the generation of Cl ₂ gas by changing the form of the cathode ions in the anode chamber and the cathode chamber, the deterioration of the film is prevented and the safety is improved.

For the anode 4, for example, an insoluble electrode having good corrosion resistance as an electrode material, that is, a dimensionally stable electrode made of platinum group and its oxide on a Ti substrate, which has a proven record in salt electrolysis, is used. A specific example of the insoluble electrode is a Ti substrate coated with Pt and IrO ₂ having a thickness of 0.3 to 3.0 μm.

The reaction of the aqueous solution on the insoluble anode is generally performed in hydrochloric acid system.
Chlorine gas is generated as shown by 2Cl ⁻ → Cl ₂ + 2e, and this chlorine gas reacts with water to generate Cl ₂ + H ₂ O → HCl + HClO. In the sulfuric acid system, oxygen gas is generated and protons are generated as shown in 2H ₂ O → 4H ⁺ ＋ O ₂ + 4e. Therefore, in either case, the anode chamber becomes strongly acidic. Therefore, it is necessary to prevent the protons from mixing into the cathode chamber 6 as much as possible by the diaphragm 10 between the anode 4 and the cathode 3 and prevent the current efficiency of the electrolytic iron from lowering due to hydrogen generation. As the diaphragm 8 between the cathode chamber 6 and the intermediate chamber 7, cations such as copper, nickel, and cobalt are mixed in the purified electrolytic solution 11 supplied to the cathode chamber, and ferrous ions escape from the cathode chamber 6. An anion exchange membrane is used to prevent this. Also, a cation exchange membrane is used for the diaphragm 10 between the anode chamber 4 and the intermediate chamber 7.
It suppresses the movement of Cl ^- ions as much as possible. Since the protons move to the cathode chamber through the ion exchange membrane, the intermediate chamber 7
Pure water is supplied to reduce the migration of protons to the cathode chamber 6, prevent the pH from decreasing, and maintain stable electrolysis conditions.

The material used for the insoluble anode 4 is used for the cathode 3.

The electrolysis conditions in the experimental examples described below were as follows.

Diaphragm between cathode chamber and intermediate chamber: Anion exchange membrane (Selemion AMV (Asahi Glass Co., Ltd.) Diaphragm between anode chamber and intermediate chamber: Cation exchange membrane (NAFLON324 (DuPont) Current density: 0.5-2.0A / dm ² Bath temperature: 50-70 ° C Catholyte composition: FeCl ₂ 34-136g / (15-60g / as Fe ²⁺ ) NH ₄ Cl 0-30g / Impurity concentration: Ni 5μg / Co 8μg / Cu 4μg / pH 1.5- 5.5 FeCl ₂ pre-purification method: Ion exchange resin method; (Ni = 7 μg / Co = 11 μg /, Cu = 5 μg /, Mn ≦ 1 μg /) Anolyte composition: H ₂ SO ₄ 20-50 μg / sulfuric acid purity (EL grade) Intermediate chamber liquid composition: HCl 0.3-0.5 μg / hydrochloric acid purity (EL grade) Insoluble anode: Pt.IrO ₂ / Ti (Ti substrate coated with Pt and IrO ₂ to a thickness of 1 μm) Cathode: SUS304 (Effect of the Invention) Since the present invention is configured as described above, the amount of heavy metal mixed into electrolytic iron can be significantly reduced, and high-purity electrolytic iron can be easily obtained. High purity iron according to the present invention
Annealing in H ₂ gas (800 to 900 ° C, 24 to 48H) or electron beam melting treatment will reduce the gas components and make it even more pure. The obtained high-purity iron is used in the fields of magnetic materials and electronic materials, which require ever-increasingly high-purity, and in the basic research field of iron, so that the industrial value of the present invention is extremely high.

[Brief description of drawings]

FIG. 1 is a drawing for explaining an embodiment of an electrolytic extraction method of the present invention and the concept of an electrolytic process, and FIG. 2 is a drawing for explaining a conventional electrolytic method. 1 ... Electrolytic bath for producing electrolytic iron, 3 ... Cathode, 4 ... Anode, 5 ... Electrolytic iron, 6 ... Cathode chamber, 7 ... Intermediate chamber, 8 ...
… Anion exchange membrane, 10 …… Cation exchange membrane, 11 …… Cathode chamber electrolyte, 12 …… Intermediate chamber liquid, 13 …… Anode chamber electrolyte.

Continued Front Page (72) Inventor Susumu Saito Fukushima Prefecture Kawanuma-gun Kato-cho Oji Nagamura Harajuku 180-1 Showa Denko Co., Ltd. Higashi-Nagahara Factory (72) Inventor Fukuoji Toshio Kawanuma-gun Kawato-cho Ogata Nagahara-ji Village Kitaoto 180-1 Showa Denko Co., Ltd. Higashi Nagahara Factory (56) Reference JP 62-161987 (JP, A) JP 59-118892 (JP, A)

Claims (1)

[Claims] 1. A cathode chamber, an anode chamber, and an intermediate chamber, wherein the diaphragm between the cathode chamber and the intermediate chamber is an anion exchange membrane, and the diaphragm between the anode chamber and the intermediate chamber is a cation exchange membrane. Using a certain electrolytic cell, the cathode chamber is supplied with an electrolytic solution consisting of an aqueous solution containing iron ion carrier and supporting electrolyte purified to a heavy metal concentration of 20 μg / or less, and the anode chamber is composed of dilute sulfuric acid. Is supplied, and an insoluble electrode coated with a film of platinum group and its oxide on the Ti substrate is used as the cathode, and electrolytic extraction is performed while supplying pure water while flowing out the electrolytic solution in the intermediate chamber during electrolytic extraction. A method for producing high-purity electrolytic iron characterized by the above.