JPH04318134A - Production of metal chromium - Google Patents

Abstract

PURPOSE:To obtain metal chromium by carbon reduction method with little vaporization loss of chromium by mixing and molding chromium oxide and carbon, heating the molded body under specified conditions, pulverizing, molding and then heating under specified conditions. CONSTITUTION:A chromium oxide and carbon or a carbon compd. are mixed and molded to have 0.5-3.0g/cm<3> bulk density. Then the molded body is heated at 1200-1500 deg.C in <=50mmHg vacuum to obtain a reaction product (coarse chromium) having <=7% oxygen content and <=5.3% carbon content. Then successively, the coarse chromium is pulverized into <=20-mesh size, molded to have 2.0-6.0g/cm<3> bulk density, and heated at 1200-1500 deg.C in <=50mmHg vacuum. Thus, metal chromium is obtd. by reduction treatment in a short time.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing metallic chromium from chromium oxide.

0002

BACKGROUND OF THE INVENTION Examples of chromium smelting methods include the thermite method in which chromium oxide is reduced with aluminum or the like, the electrolytic method in which a chromium compound solution is electrolytically reduced, and the carbon reduction method in which chromium oxide is reduced with carbon.

0003

[Problems to be solved by the present invention] Since the thermite process is a batch-type reaction treatment, the quality of the product as metallic chromium varies greatly, and reducing agents such as aluminum and reactor material components are mixed into the product. It has the problem of impurities.

[0004] The electrolytic reduction method can obtain metallic chromium with relatively high purity, but it requires many treatments to purify the chromium compound solution, making the process complicated, the equipment cost is high, and the power consumption is high. There is also a problem that the amount is large.

[0005] Furthermore, in the carbon reduction method, a large amount of oxygen and carbon remain in the metal chromium product, and the obtained metal chromium becomes spongy, which poses problems in subsequent processing.

[0006]

[Means for Solving the Problems] In order to solve the above problems, the present inventors have conducted intensive research on a method for obtaining metallic chromium by reducing chromic acid compounds with carbon.
By carrying out the reduction in stages and specifying the conditions during the reduction, it was discovered that the reduction process could be carried out in a short time and the evaporation loss of chromium could be reduced, and the present invention was completed.

That is, the present invention mixes chromium oxide and carbon or a carbon compound, and has a bulk density of 0.5 to 3.0 g/
After molding to cm3, the degree of vacuum is 50 mmHg or less, 12
The first step is heating at 00 to 1500°C to obtain a reaction product (crude chromium) with an oxygen content of 7% or less and a carbon content of 5.3% or less, followed by pulverizing the crude chromium to a size of 20 mesh or less. , a second step of molding to a bulk density of 2.0 to 6.0 g/cm3 and then heating at 1200 to 1500°C under a degree of vacuum of 50 mmHg or less, with a purity of 99%.
The above metal chromium is manufactured.

[0008]

[Operation] The present invention will be explained in detail below.

The raw material chromium oxide used in the method of the present invention may be any trivalent chromium oxide, for example,
Examples include chromium trioxide and chromium oxyhydroxide, but chromium oxyhydroxide is preferably used. Further, the raw material chromium oxide can contain components that can be volatilized and removed during the process of the present invention, such as carbon, water, and low-temperature volatile or decomposable organic substances, within the limits.

The carbon or carbon compound used as the reducing carbon source in the method of the present invention may be carbonaceous materials such as graphite, carbon black, oil coke, etc., or Cr23
Chrome cars such as C6, Cr7, C3, Cr3C2, etc.
Bide and other carbon compounds can be used.

[0011] The raw material chromium oxide and carbon or carbon compound are preferably in powder form, preferably in fine powder form.

[0012] Examples of the binder used in the present invention include polyvinyl alcohol, polyvinyl acetate, polyvinyl butyral, starch, dextrin, and resin. The mixing ratio when mixing chromium oxide and carbon source in the first step of the method of the present invention is determined by formula (1) or formula (2).
) Cr2 O3 +3C=2Cr+3CO
Formula (1) 2CrOOH+
3C=2Cr+3CO+H2O Formula (2)
It may be 90 to 110% of the stoichiometric value, but preferably 97 to 103%. If it is less than 90%, it will be difficult for the reduction reaction to proceed sufficiently, and if it exceeds 110%, carbon will remain in the product, which is not preferable.

[0013] A binder is added to the mixed powder and kneaded. The amount of binder used varies depending on the particle size and physical properties of the chromium oxide and carbon source, but it is
0.1 to 5% by weight is suitable. For kneading, a commonly used kneader or mixer is used.

[0014] In the first step of molding, the kneaded material is shaped into bricks,
Alternatively, it is molded into a clog-shaped block or a briquette, but in the case of a brick-shaped or clog-shaped block, the molding pressure is 0.
1 to 5 tons/cm2, preferably 0.2 to 3 tons
/cm2, and in the case of briquettes, 10to
It is preferable to mold at n/cm2 or less.

[0015] Also, the bulk density of the obtained molded product is 0.5 to 3.
．． It is preferable to set it to 0 g/cm3.

[0016] The molded body obtained in this way was heated to a degree of vacuum of 50
mmHg or less, preferably 1 to 10 mmHg, temperature 12
The reduction reaction is carried out at a temperature of 00 to 1500°C, preferably 1350 to 1450°C. At this time, it goes without saying that the heat treatment can be carried out continuously up to the reaction temperature in one step, but
Once preheating is performed at 300-500°C to decompose most of the decomposable substances, and if necessary, heating at 800-100°C
A two-step or three-step heat treatment in which the binder is completely decomposed at 000° C. and then reacted is also preferred. There is no particular reason to limit the time for holding and heating during this period, and the time may be set as desired.

In the method of the present invention, the oxygen and carbon contents in the reaction product (crude chromium) obtained by reduction in the first step must be 7% or less and 5.3% or less, respectively. This can be achieved by controlling the reduction time.

Next, when subjecting the crude chromium obtained by the first step reduction reaction to the second step, the crude chromium is ground to 20 mesh or less, and the ratio of residual carbon to oxygen in the ground product is reduced to CO
If the stoichiometric amount is almost equal to the stoichiometric amount that volatilizes as a gas, add a binder as is and mold. If the ratio does not match, add the stoichiometric amount ± (5 g/rough A chromium oxide or a carbon source containing oxygen or carbon in an amount of 1 kg of chromium is added to and mixed with the crushed chromium product, and then a binder is added and molded.

[0019] The amount of binder added is 0.1 to crude chromium.
~2.0% by weight is preferable, and the molding is performed at a molding pressure of 1 to 10 t.
It is preferable to make it into a briquette shape at on/cm2. The bulk density of the molded body is closely related to the bulk density of metal chromium.
The density of the molded body is preferably 2.0 to 6.0 g/cm3, preferably 3.0 to 6.0 g/cm3.

[0020] As the reaction conditions for the second step, conditions within the same range as those for the first step can be used.

The metallic chromium obtained by the method of the present invention is dense with a purity of 99% or more, contains very little non-metallic components such as carbon and oxygen, and is of extremely excellent quality. In addition, when using chromium oxyhydroxide,
Since the reaction time can be made extremely short, almost no volatilization of chromium is observed during the reaction.

[0022]

[Examples] The present invention will be explained below with reference to Examples, but the present invention is not limited thereto.

Example 1 1000 g of Cr2O3 powder with an average particle size of 2 μm and 20
238.8 g of coke powder of 0 mesh or less was mixed in a powder mixer, and further, 100 ml of 10% polyvinyl alcohol aqueous solution was added and kneaded. 0.2t of this kneaded material
/cm2 and 200 x 100 x 25 mm using a hydraulic press.
One piece was molded into a brick-like block. After drying, the resulting molded product having a bulk density of 2.5 g/cm3 was placed in an atmospheric furnace, held at 900°C for 30 minutes, and then further held at 1400°C for 2 hours. At this time, the degree of vacuum in the furnace was 5 mmHg. After cooling, the reaction product obtained was 687 g. When the reaction product was measured by powder X-ray diffraction, it was found that C
Cr2O3 and Cr23C6 were detected in addition to the r peak, and the analytical values for residual carbon and oxygen were 0.98% and 1.65%, respectively.

After pulverizing 65 g of this reaction product to 100 mesh or less, 1.81 g of coke powder and 30 ml of a 40% polyvinyl alcohol aqueous solution were added and kneaded. This kneaded material is molded using a briquetting machine under a pressure of 4 tons.
/cm2 and the maximum length, maximum width, and maximum thickness are each 4
Seven almond-shaped briquettes of 0, 35 and 20 mm were obtained. After that, the bulk density obtained by drying was 4.5 g/cm.
The briquettes of No. 3 were placed in an atmospheric furnace, held at 900°C for 30 minutes, and then held at 1400°C for 4 hours. At this time, the degree of vacuum in the furnace was set to 5 mmHg. After reaction, 627g of metallic chromium
I got it.

When the obtained metallic chromium was analyzed by powder X-ray diffraction, only a Cr peak was detected. In addition, the amount of carbon and oxygen in metal chromium is 0.009% and 0.039%.
Met. The chromium volatilization loss was 0.5% in the first step and 1% in the second step.

Example 2 1,550 g of Cr2O3 powder from Example 1 and 370 g of coke powder were prepared in the same manner as in Example 1 (upper 200 L x 10
0W x 30Hmm, foot 30W x 30H x 100Lmm
) One piece was molded into a clog-shaped block. Thereafter, the dried molded product having a bulk density of 2.5 g/cm 3 was reacted under the same conditions as in Example 1. The reaction product was 1059g. When the reaction product was measured by powder X-ray diffraction,
CrO3 and Cr23C6 were detected in addition to the Cr peak, and the analytical values for residual carbon and oxygen were 0.89% and 1.18%, respectively. Since this was close to the stoichiometric ratio, no blending was performed to adjust carbon and oxygen.

1000 g of powder with a particle size distribution of 20 to 100 mesh 10%, 90% of 100 mesh or less obtained by crushing the reaction product obtained in the first step, and 40%
Add 43 ml of polyvinyl alcohol aqueous solution, Example 1
Ten briquettes of the same shape were obtained under the same conditions. Thereafter, the dried briquettes with a bulk density of 4.7 g/cm3 were reacted under the same conditions as in Example 1, and the metal chromium 97
7g was obtained.

When the obtained metallic chromium was analyzed by powder X-ray diffraction, only the peak of Cr was detected. Further, carbon and oxygen were 0.007% and 0.010%, respectively. The chromium volatilization loss was almost the same as in Example 1.

Example 3 1,550 g of the Cr2O3 powder of Example 1 and 376 g of coke powder were molded into one piece in the same shape as Example 2 by the same operation as in Example 1. After that, the bulk density obtained by drying is 2.5
g/cm3 of the molded body was reacted under the same conditions as in Example 1, and the obtained reaction product was 1073 g. When the reaction product was measured by powder X-ray diffraction, Cr2C3 and Cr23C6 were detected in addition to the Cr peak, and the remaining carbon and oxygen amounts were each 1.76.
%, 1.65%.

Cr2O3 powder 2 was added to 950g of powder of 100 mesh or less obtained by pulverizing this reaction product.
2 g and 41 ml of a 40% polyvinyl alcohol aqueous solution were added thereto and treated in the same manner as in Example 1 to obtain 10 briquettes. Thereafter, the briquettes of 4.5 g/cm3 obtained by drying were reacted under the same conditions as in Example 1, and 918 g of metallic chromium was obtained.
I got it.

When the obtained metallic chromium was analyzed by powder X-ray diffraction, only the peak of Cr was detected. The carbon and oxygen contents of metallic chromium were 0.011% and 0.019%, respectively. The chromium volatilization loss was almost the same as in Example 1.

Example 4 1000 g of hydrated CrOOH fine powder containing 53.1% by weight of chromium and 180 g of coke powder of 200 mesh or less
were mixed using a powder mixer, and 100 ml of a 15% polyvinyl alcohol aqueous solution was added and kneaded. Example 1
Two pieces were molded into the same shape. After drying, the obtained molded body with a bulk density of 1.2 g/cm3 was placed in an atmospheric furnace.
After holding at 900°C for 30 minutes, it was further held at 1400°C for 30 minutes. At this time, the degree of vacuum was 5 mmHg. After cooling,
The product obtained was 550 g. When the reaction product was measured by powder X-ray diffraction, Cr2O3 and Cr23C6 were detected in addition to the Cr peak, and the analytical values for residual carbon and oxygen were 1.15% and 1.1%, respectively.
．． It was 71%.

After pulverizing 500 g of this reaction product to 100 mesh or less, 0.68 g of coke powder and 30 ml of a 40% polyvinyl alcohol aqueous solution were added and kneaded to form briquettes of the same shape under the same conditions as in Example 1. I got 5 pieces. Thereafter, the dried briquettes with a bulk density of 4.5 g/cm3 were placed in an atmospheric furnace and kept at 900°C for 30 minutes.
It was held at 400°C for 3 hours. At this time, the vacuum level inside the furnace is 5m.
It was set as mHg. After the reaction, 480 g of metallic chromium was obtained. When metallic chromium was analyzed by powder X-ray diffraction, Cr peaks were found.
At this time, carbon and oxygen were detected at 0.008%.
,0.021%. Further, chromium volatilization loss was almost non-existent in the first step and 0.7% in the second step.

[0034]

[Effects of the Invention] As explained above, according to the method of the present invention, carbon reduction is carried out in two stages and the conditions at the time of reduction are specified, thereby reducing chromium evaporation loss in a short time. Metallic chromium can be obtained with less carbon reduction.

Claims (7)

[Claims] [Claim 1] Chromium oxide and carbon or carbon compounds are mixed and molded to a bulk density of 0.5 to 3.0 g/cm3, and then heated at 1200 to 1500°C under a vacuum of 50 mmHg or less to reduce the oxygen content. The first step is to obtain a reaction product (crude chromium) with a carbon content of 5.3% or less and a bulk density of 2.0-6.
．． After molding to 0g/cm3, vacuum degree is 50mmHg.
A method for producing metallic chromium with a purity of 99% or more, characterized by comprising a second step of heating at 1200 to 1500°C. Claim 2: Oxygen in an amount of ±(5g/1Kg of crude chromium) of the stoichiometric amount necessary for all of the carbon and/or oxygen in the crushed crude chromium product to become carbon monoxide in the second step. The manufacturing method according to claim 1, characterized in that a chromium oxide containing carbon or a carbon source is added to and mixed with the crushed coarse chromium product, and then molded. 3. The manufacturing method according to claim 1, wherein the chromium oxide is an oxide of trivalent chromium. 4. The manufacturing method according to claim 1, wherein the chromium oxide is chromium oxyhydroxide. 5. The manufacturing method according to claim 1, wherein the molded body in the first step is a brick-like block or a clog-like block. 6. The manufacturing method according to claim 1, wherein the molded product in the first step is in the form of a briquette. 7. The manufacturing method according to claim 1, wherein the molded product in the second step is in the form of a briquette.