JPS6247436A - Manufacture of high purity metal chromium - Google Patents

Abstract

PURPOSE:To manufacture high purity metallic chromium, by reducing ore contg. chromium to high carbon ferrochromium, applying a specified treatment to remove silica, iron content, etc., in order. CONSTITUTION:Ore contg. chromium is reduced in electric furnace to high carbon ferrochromium under existence of carbon material reducing material. The ferrochromium is dissolved with sulfuric acid, ammonium sulfate is added to filter and remove undissolved material such as silica. Next filtrate is cooled to precipitate and separate ferrous ammonium sulfate, mother liquor is aged for a long time to transform chromium from hardly crystallizable green form to violet form and to precipitate and separate it as ammonium chromium alum. The crystal is further dissolved into water to oxidize iron ion contained in soln. to trivalent iron ion, and iron content is extracted by using extracting agent (di-2-ethylhexylphosphoric acid, etc.). Next chromium in remaining liquid is adjusted to a prescribed concn. and while using this as electrolyte, the titled chromium is obtd. by electrolysis.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing high-purity metallic chromium from chromium-containing ore.

When metal chromium is used as an alloy component, it has a remarkable effect on imparting wear resistance, corrosion resistance, heat resistance, and toughness to the alloy, so nickel and cobalt.

It is often used as an additive to iron, etc.

Recently, it has also been widely used as a material for semiconductors and dry plating, but for semiconductors in particular, high purity metal chromium is used to improve the etching characteristics of masks and prevent disconnection of IC circuits. A significantly lower content of metallic chromium is needed.

[Conventional technology]

On the other hand, there are two methods for producing metallic chromium: the electrolytic method in which an aqueous solution of trivalent chromium salt is electrolytically reduced, and the thermite method in which chromium oxide such as chromium trioxide is reduced using aluminum, but both methods are suitable for titration for use in semiconductors. I haven't reached the point where I can do it.

In general, high-purity metallic chromium can be obtained by (refuronic acid electrolysis method, (2) method of halogenating metallic chromium with iodine etc. and then separating and purifying it by sublimation, (3) electron beam melting method, (4) anhydrous chlorination method. There are methods such as chromium molten salt electrolysis method.However, method (1) reduces the state of hexavalent ions to metal, which has extremely poor flow efficiency and uses hexavalent chromium, which is harmful. All other methods use metallic chromium as a starting material, but they are not only difficult to operate on an industrial scale, but also have not yet achieved sufficient purity.

[Problem that the invention seeks to solve]

The inventors of the present invention completed their invention as a result of intensive research aimed at obtaining gold-rich chromium with a particularly low iron content using an electrolytic method using a chromium sulfate bath.

[Means for solving problems]

That is, in the present invention, high carbon ferrochrome obtained by reducing chromium ore in an electric furnace in the presence of carbon is dissolved in sulfuric acid, ammonium sulfate is added to remove insoluble substances such as silica, and then ferrous sulfate is dissolved. The dissolved iron is cooled to crystallize ferrous ammonium sulfate, which is then filtered to obtain a crude chromium sulfate solution.

Furthermore, by aging the aqueous solution for a long time, the chromium was transformed from a green form that is difficult to crystallize to a violet form, and then crystallized and separated using ammonium chromium alum. Furthermore, a chromium salt with low iron content was obtained, and this was dissolved in water. After that, the coexisting divalent iron ions are oxidized to trivalent iron ions by adding an oxidizing agent, and then the iron content in the solution is extracted using an extractant, and the chromium in the residual liquid after iron extraction is adjusted to a predetermined concentration. This is then electrolyzed as an electrolyte.

High carbon ferrochrome and ammonium chromium alum can be obtained by already known methods, the latter being generally CLO1
% of iron, and the metal chromium 9 obtained by electrolyzing this solution contains 0.1 to 12% of iron, which hinders high purity.

Therefore, ammonium chromium alum solution Or 8
0~150! A, F@α05~α2%, pHn, o
Ammonia or caustic soda within a range from 5 to α2 that does not cause precipitation of chromium hydroxide, preferably pH 2.5.

Neutralize with an alkali such as soda carbonate, then add an oxidizing agent such as chromic anhydride, chromate, permanganate, hydrogen peroxide, or sodium peroxide to the chemical equivalent or slight excess required for divalent iron to trivalent iron. Add enough amount to completely oxidize the iron.

Extractants used to separate iron and chromium include di-2-ethylhexyl phosphate, trioctyl phosphate, tributyl phosphate, tributylphosphine oxide, trioctylphosphine oxide and triplekylmethylamine, and N-dode. Cenyltrialkylmethylamine, N-dodecyltrialkylmethylamine, triisooctylamine, trinormaloctylamine, tricaprylamine, tricaprylmethylammonium salt.

Included are primary, secondary, tertiary and quaternary amines such as methylbenzylammonium salts and the like.

Note that in this extraction, not only these extractants and trivalent iron are directly extracted, but also a complex salt forming agent such as thiocyanic acid is added, and extraction and separation with methyl isobutyl ketone is also possible.

Kerosene is also used as a diluent for these solvents.

Hydrocarbons such as n-hexane, trichloroethylene, chloroform, carbon tetrachloride, etc. or 15fx aromatic hydrocarbons such as xylene, toluene, benzenato are used.

When diluting the extractants with diluents, the concentration of these extractants is between 5 and 50 inches, preferably between 10 and 20 inches.

In order to extract the iron content in the ammonium chromium alum solution, this solution and the extractant are brought into contact at 10 to 80°C, preferably 20 to 40°C, and it is preferable to use a countercurrent extraction device. .

The extractant used to extract iron is an acidic solution, preferably a sulfuric acid solution of 11 to 10
The iron contained in this extractant is transferred to the aqueous phase as ferric sulfate, and the organic solvent from which the iron has been removed is separated from the aqueous phase and then transferred to the ammonium Recycled for extraction of iron from chromium alum solution.

In order to electrolyze chromium sulfate well, it is necessary to adjust the pH of the catholyte, and an electrolytic cell is used in which the two electrodes are separated by a diaphragm to prevent sulfuric acid and chromic acid, which are produced as by-products at the anode, from mixing with the catholyte.

Electrolysis conditions are not particularly limited, but the chromium ion concentration is 30 to 80!4. Cathode current density 6-8A//υ,
Electrolysis temperature: 45-60°C, electrolyte pH (2.1-2.4.
The cathode is stainless steel and the anode is lead-silver (1T).

The metallic chromium obtained by the method of the present invention is characterized by an extremely low iron content as an impurity.

〔Effect of the invention〕

The metallic chromium obtained in the present invention includes iron 1lumi, silicon,
It is low in impurity of metals such as lead and copper, and can be used for semiconductors.

Next, the present invention will be explained with examples.

Example-1 Ammonium chromium alum purified by high carbon ferrochloride from chromium-containing ore is dissolved in water to produce 0r12
2.5%, NHs 7 [lL9%, Fal100
Obtained 150 tons of 54% solution, and further added 102 tons of chromic anhydride.
After adding 1 liter of ammonia water (NH, 18%) to adjust the pH to 2.48, the chromium supernatant liquid was heated at 100 m/min using a 3-stage mixer-settler type extractor. Ethylhexyl phosphate-kerosine solution (
20 iron) was countercurrently extracted at 200 ml/min.
Iron was back-extracted into the aqueous phase using sulfuric acid (50%) at 80 sd/min, and the iron-removed eluent was washed with water and recycled to the iron extraction step. Note that the back extraction temperature was 25 to 40°C.

The chromium solution purified by removing iron was further mixed with 320 watts of activated carbon, the mixed extractant was removed by inhalation, and water was added.
A replenishment solution containing 0.02%, NH3 70%, Fe (LQOO 1% or less) was obtained.

The purified chromium solution thus obtained was adjusted to pH 0.45 by adding sulfuric acid (98%), and the amount of replenishment liquid was 13 to 15 m
e/min, current density 7.4 A/dy/,
Table 1 shows the composition of the metallic chromium obtained by electrolysis at pH 2, temperature SO"C, and electrolysis time for 48 hours. In Table 1, the values for the conventional electrolytic method are those obtained without the purification as in the method of the present invention. This figure shows the composition of metallic chromium obtained by electrolyzing a chromium solution according to the method of the present invention.

Claims (1)

[Claims] 1. High carbon ferrochrome obtained by reducing chromium-containing ore in an electric furnace in the presence of a carbonaceous reducing agent is dissolved in sulfuric acid,
After adding ammonium sulfate to remove insoluble substances such as silica, the filtrate is cooled and ferrous ammonium sulfate is crystallized and separated, the mother liquor is aged to precipitate ammonium chromium alum, and then dissolved in water. The method is characterized in that iron ions contained in the solution are oxidized to trivalent iron ions, then the iron content in the solution is extracted and removed using an extractant, and the remaining solution is electrolyzed to obtain metallic chromium. A method for producing ultra-low iron-containing chromium metal.