JPH0517158A - Production of chromium (iii) oxide - Google Patents

Abstract

PURPOSE:To produce high-purity chromium III oxide having low contents of impurities from chromium III hydroxide readily, efficiently and effectively. CONSTITUTION:Chromium III hydroxide is heated to >=300 deg.C, dehydrated, washed with water, an acidic aqueous solution, an alkali aqueous solution, etc., and impurities such as alkali metals and alkaline earth metals are removed to produce high-purity chromium III oxide efficiently and effectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a hydrated chromium oxide (II
I) is purified by washing to obtain high-purity chromium oxide (II
I).

Chromium (III) oxide is a useful compound widely used as a raw material for producing pigments and metallic chromium. In this case, a high-purity product is required due to its use.

[0003]

2. Description of the Related Art Conventionally, when producing chromium (III) oxide from hydrated chromium (III) oxide, it is heated and dehydrated as it is, or after hydrated chromium (III) oxide is washed with water,
It was dehydrated by heating.

[0004]

Problem to be Solved by the Invention Chromium (III) oxide hydrate
Is heated and dehydrated as it is to form chromium (III) oxide, impurities mixed during the production of hydrated chromium (III) oxide remain in the chromium (III) oxide as they are, resulting in a decrease in purity.

When the chromium (III) oxide hydrate is washed with water, the chromium (III) oxide hydroxide has a large effect of adsorbing impurities, and it is difficult to remove the impurities. Further, some of the impurities are contained inside the crystal and cannot be removed by washing with water.

[0006]

SUMMARY OF THE INVENTION In order to solve the above problems, the present inventors have made it possible to remove impurities from hydrated chromium (III) oxide easily, efficiently, and effectively by removing impurities of high purity chromium (III) oxide. As a result of earnest studies on the production method of (1), it was found that impurities can be easily removed by heating and dehydrating the hydrated chromium (III) oxide, and finally the present invention was completed.

That is, the present invention relates to hydrated chromium oxide (I
II) is dehydrated by heating at a temperature of 300 ° C. or higher, and then washed to remove impurities.
This is the method I).

[0008]

The present invention will be described in detail below.

The hydrated chromium oxide (II) used in the present invention
I) is represented by [Cr ₂ O ₃ · nH ₂ O: n ≧ 1], in which chromium oxyhydroxide [CrOOH = Cr ₂ O _{3 is included.}
H ₂ O], and hydrates with higher water content, where 1 <n ≦ 9. Here, when n = 9, [Cr (OH) ₃
・ 3H ₂ O]. These hydrated chromium oxides (I
The production method of II) is not particularly limited, but chromium oxyhydroxide is generally produced by hydrothermal treatment of a chromium compound in an alkaline atmosphere, often has needle-like crystals, and has a high water content. (III) is often obtained by a usual neutralization reaction. Hydrated chromium (III) oxide is
Either powder or granulated powder may be used.

The temperature for dehydrating the chromium (III) oxide hydrate by heating is 300 ° C. or higher. When the temperature is lower than 300 ° C, the dehydration by heating does not proceed sufficiently or the dehydration requires a long time.
It is immediately dehydrated at 300 ° C or higher, and the subsequent chromium oxide (II
The impurities can be easily removed by the cleaning of I). The upper limit of the heating dehydration temperature is not particularly limited, but it is preferably 1500 ° C or lower. When the temperature is high, dehydration is easy, but a large amount of heat energy is required, and the equipment materials are limited to expensive ones. More preferable heat dehydration temperature is 400 to 1000 ° C.
Is. Within this temperature range, it can be carried out easily and economically, and the effect of removing impurities by washing is large.

Air is preferable as the heating and dehydrating atmosphere, and it can be carried out efficiently and effectively at a relatively low temperature.
In an atmosphere of an inert gas such as nitrogen or argon, the temperature is relatively high and 600 to 1000 ° C. is preferable.

As the heating and dehydrating machine, a stationary heating machine, a rotary kiln, a flow type heating machine, a belt type heating machine, a muffle furnace and the like which are usually used can be used.

[0013] The heat dehydration gives chromium (III) oxide, but chromium (III) oxide does not have to be completely anhydrous. In the chemical formula Cr ₂ O ₃ · nH ₂ O,
It is preferable that n is 0.5 or less, and in this case, removal of impurities by washing can be effectively and efficiently performed. When n is large, that is, when the water content is high, the cleaning effect is slightly reduced. More preferably, n ≦ 0.05, which is substantially anhydrous. In this case, the effect of cleaning and removing impurities is further improved, and the cleaning time is shortened, which facilitates the operation.

Next, in the present invention, the washing conditions for washing chromium (III) oxide to remove impurities are not particularly limited,
It suffices if the chromium (III) oxide and the cleaning liquid are brought into sufficient contact with each other.

The cleaning liquid may be water, an acidic aqueous solution or an alkaline aqueous solution.

When water is used, alkali metals such as sodium and potassium and alkaline earth metals such as magnesium and calcium can be removed relatively easily.

As the acidic aqueous solution, an aqueous solution of an inorganic acid or an organic acid can be used, and specific examples thereof include aqueous solutions of hydrochloric acid, sulfuric acid, acetic acid and the like. The concentration is 2 mol / l
The following are preferred. As the alkaline aqueous solution, both an inorganic alkaline solution and an organic alkaline aqueous solution can be used, and specific examples thereof include aqueous solutions of sodium hydroxide, potassium hydroxide, ammonia, water-soluble amines and the like. The concentration is preferably 2 mol / l or less. When using an acidic aqueous solution and / or an alkaline aqueous solution, it is preferable to wash again with water later. By doing so, the acidic substance and the alkaline substance used for cleaning can be removed.

The temperature at the time of washing is not particularly limited, but it can be sufficiently carried out at room temperature. When heating, the cleaning time is short and preferable, but heat energy for heating is required. In addition, the chromium (III) oxide obtained by heating and dehydrating is added to 50 to 20
If the cleaning is performed at the time of cooling to 0 ° C., there is an advantage that the cleaning effect can be improved in addition to the effective use of thermal energy.

Although there are various operations, chromium (III) oxide is placed on a filter, and a washing liquid is applied to the filter to perform washing and solid-liquid separation simultaneously. Chromium (III) oxide and the washing liquid are suspended in advance. After that, a method of solid-liquid separating the cleaning liquid and the chromium (III) oxide with a filter can be mentioned as an example.

As the filter, there are a centrifugal filter, a pressure filter, a vacuum filter and the like which are usually used for solid-liquid separation.

The thus-obtained impurity-free chromium (III) oxide is usually preferably dried to remove the attached water.

The mechanism of action of the present invention cannot be clearly explained, but is presumed as follows.

That is, the chromium (III) oxide hydrate has a very large effect of adsorbing impurities, and the impurities cannot be removed by a normal washing operation. However, when the hydrated chromium (III) oxide hydrate is heated and dehydrated, it changes to another crystalline form, chromium (III) oxide. At this time, it is considered that the affinity between the impurities and chromium (III) oxide was reduced, and the cleaning removal effect was improved.

Further, it is considered that the impurities contained inside the crystal of chromium (III) oxide hydrate are moved to the outside of the crystal of chromium (III) oxide due to the change in crystal form, and the cleaning and removing effect thereof is improved.

[0025]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited thereto.

Example 1 Chromium (III) oxide hydrate obtained by hydrothermal synthesis was dehydrated by heating in air at 400 ° C. for 4 hours and then washed with water. Table 1 shows the chemical analysis results of the sample which was suction filtered and dried after washing with water. The analysis results in Table 1 are wt with respect to chromium pure content
Shown in%. 0.26 wt% of Na, 0.005 wt% of Mg, and C in hydrated chromium (III) oxide before heat dehydration
a was 0.005%.

Hydrated chromium (III) oxide before heat dehydration
Was determined by powder X-ray diffraction to be chromium oxyhydroxide (CrO).
OH) peak was observed. The water content of this sample was determined by evaporating the water at 1000 ° C. with a Cal-Fisher type water content measuring instrument equipped with a water evaporation device.
3% by weight, which is converted into CrOO
It can be expressed as H · 0.44H ₂ O or Cr ₂ O ₃ · 1.89H ₂ O.

In the sample after heat dehydration, only weak peaks of chromium dioxide (Cr ₂ O ₃ ) were recognized, and a part of the peak
It was confirmed that it was chromium dioxide. It was also confirmed by electron microscope observation that the needle-shaped crystals before treatment were collapsed after heating and dehydration. The water content of the heat dehydrated sample was 2.95 wt%, and Cr ₂ O ₃ .0.26H ₂ O was used.
Can be expressed as

The washing operation was carried out by adding 100 parts of distilled water to 10 parts of hydrated chromium oxide at room temperature, stirring with a stirrer for 15 minutes, allowing to stand for 60 minutes, and then suction filtering.

From Table 1, it can be seen that Na is remarkably reduced as compared with the comparative example.

Example 2 The same chromium (III) hydrate oxide as in Example 1 was added in nitrogen,
Table 1 shows the results of the same washing operation as in Example 1 except that the mixture was heated and dehydrated at 800 ° C. for 1 hour.

In the sample after heat dehydration, only a strong peak of chromium trioxide (Cr ₂ O ₃ ) was observed, and it was confirmed that the sample was chromium trioxide. It was also confirmed by electron microscope observation that the needle-shaped crystals before treatment were collapsed after heating and dehydration. The water content of the heated dehydrated sample was 0.
It is 21 wt% and can be expressed as Cr ₂ O ₃ .0.02H ₂ O.

From Table 1, it can be seen that in addition to Na, Mg and Ca are also reduced as compared with the comparative example.

Carbon was mixed with a sample obtained by repeating the washing with water 5 times to form a briquette, and a vacuum carbon reduction reaction was carried out. Na ≦ 5 ppm, K ≦ 5 ppm, Mg: 1 p
High-purity metallic chromium with pm and Ca of 20 ppm was easily obtained.

Comparative Example The same results as in Example 1 in which the same hydrated chromium (III) oxide was washed as it is, are shown in Table 1, but no remarkable washing effect was observed.

[0036]

[Table 1]

[0037]

According to the method of the present invention, high-purity chromium (III) oxide containing a small amount of impurities can be easily, efficiently and effectively produced from hydrated chromium (III) oxide.

To list the specific effects, the efficiency of removing impurities is high, the operation is extremely simple, no chemicals are used or only a very small amount is used, and the economy is high.
It can be said that.

The chromium (III) oxide obtained by the method of the present invention can be effectively used as a pigment and a raw material for producing high-purity metallic chromium.

Claims (4)

[Claims] 1. A method for producing chromium (III) oxide, which comprises removing dehydrated impurities by heating and dehydrating chromium (III) hydrate oxide at a temperature of 300 ° C. or higher. 2. The method according to claim 1, wherein the chromium (III) oxide hydrate is chromium oxyhydroxide [CrOOH]. 3. The method according to claim 1, wherein the impurities are Group Ia alkali metal elements and / or Group IIa alkaline earth metal elements. 4. The method according to claim 1, wherein the heat dehydration is performed at a temperature of 400 ° C. or higher and 1000 ° C. or lower.