JP2639567B2 - Production method of high purity chromium sulfate - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing chromium sulfate, and more particularly, to a high-purity chromium sulfate obtained by reacting a chromic acid solution with a mixture of sulfuric acid and an organic reducing agent. And a method for producing the same.

[Conventional technology]

BACKGROUND ART Conventionally, as an industrial production method of chromium sulfate, there is known a method of dissolving chromium ore in sulfuric acid, adding lime to precipitate as a basic salt, and recrystallizing the salt from diluted sulfuric acid (Chemical Dictionary, vol.9, p701-702, published by Kyoritsu Shuppan Co., Ltd. Further, there is a method in which chromium hydroxide or chromium oxide is substantially dissolved in sulfuric acid and then precipitated from an alcoholic solution. As another method, there is a method of producing an aqueous solution of chromic anhydride and sulfuric acid by adding an alcohol or an ether. (JW Mellor, A COMPREHENSIVE TRE-ATISE AND
THEORETICAL CHEMISTRY vol.X1, p435).

[Problems to be solved by the invention]

Among the conventional methods, the method using chromium hydroxide as a raw material uses a solution obtained by adding an alkali such as ammonia or caustic soda to an aqueous solution of chromium nitrate or chromium chloride, but it is very difficult to wash the obtained chromium hydroxide precipitate with water. There is a disadvantage that impurities such as sodium or chlorine in chromium oxide cannot be removed, and it is difficult to obtain a high-purity chromium solution.

In addition, dehydrated chromium hydroxide often does not readily dissolve in acids.

Furthermore, in the method using a mixed solution of chromic anhydride and sulfuric acid as a starting material, the oxidizing power is extremely large due to the characteristics of the composition of the mixed solution of chromic anhydride and sulfuric acid. Not only is it dangerous, but the reaction is too intense than necessary, and the added reducing agent decomposes without effectively reducing chromium.

These conventional chromium sulphates are unavoidable due to their properties, and are not satisfactory in purity.

In fact, no high-purity chromium sulphate containing extremely low contents of Na and Fe has been known.

[Means and actions for solving the problem]

In view of the above points, the present invention has been intensively studied and found that a high-purity chromium sulfate solution can be industrially advantageously produced by reacting a mixed solution of sulfuric acid and an organic reducing agent with a chromic acid solution. Was completed.

That is, the present invention relates to a method for producing high-purity chromium sulfate, which comprises reacting a chromic acid solution with a mixture of sulfuric acid and an organic reducing agent.

Normally, chromium sulfate is used in industrial production of chromium raw materials.
Further, since the hexavalent chromium compound is erosive and oxidizing, impurity metal ions, particularly Na, Cl and Fe, are inevitably mixed in a large amount. It is characterized by an extremely small number.

In addition, as can be understood from the examples described later, the present invention is characterized in that other metal ions are substantially free of high purity.

In the above description, the fact that other metals are substantially absent means that metal ions such as Ca, Mg, and Al are converted to Cr ₂ (SO ₄ ) _{3 by} 40%.
It is 1 ppm or less in terms of wt% concentration, which means that it is substantially undetectable.

The high-purity chromium sulfate according to the present invention is often
Cr ₂ (SO ₄ ) ₃ from the solubility of chromium sulfate in water
It is an aqueous solution of 40 wt% or less, and the lower limit of the concentration can be appropriately selected depending on the conditions to be used and the like, and is not particularly limited.

If necessary, this can be concentrated to obtain crystals.

Such high-purity chromium sulfate can be produced by the above-described method, but this method has several aspects in terms of operation as described below.

First, the chromic acid solution used as a chromium raw material in the present invention is obtained by using sodium chromate obtained by oxidizing and roasting chromium ore as a starting material, and starting from high-purity chromic anhydride obtained by performing various purification treatments. It is in the place. This raw material chromic acid has a very small amount of impurities such as Fe, Cl, Ni, Mg, Al, and Ca as compared with a method using chromium hydroxide obtained by adding ammonium or caustic soda to chromium nitrate or chromium chloride. .

The chromic acid solution may be any solution in the reaction system, and it is possible to use chromic anhydride at the time of the initial reaction.However, in many cases, water was added thereto and dissolved to prepare a solution. And its concentration is not particularly limited.

Next, the sulfuric acid used in the present invention is for industrial use, and usually has an H ₂ SO ₄ concentration of 98 wt% and a specific gravity of 1.86, but the concentration is not particularly limited.

Further, as the organic reducing agent used in the present invention,
In the reduction reaction described below, it is completely decomposed into carbon dioxide and water,
Substantially no organic decomposition products remain, and there is no particular limitation as long as it is such a substance.

For example, monohydric alcohols such as methyl alcohol, ethyl alcohol and propyl alcohol, and dihydric alcohols such as ethylene glycol and propylene glycol can be suitably used. As another thing, a polysaccharide such as glucose can be used.

The reaction of mixing a chromic acid solution, sulfuric acid, and an organic reducing agent to form chromium sulfate can be represented by the following equation if, for example, ethyl alcohol is used as the organic reducing agent.

4CrO ₃ + 6H ₂ SO ₄ + C ₂ H ₅ OH → 2Cr ₂ (SO ₄ ) ₃ + 2CO ₂ + 9H ₂ O (1) In this reaction, organic reduction is carried out to the mixed solution of chromic acid solution and sulfuric acid in the above-mentioned prior art example. As a method of reacting the agent, a chromic acid solution obtained by mixing a chromic acid solution as an oxidizing agent and sulfuric acid as a strong acid is an extremely strong oxidizing agent as can be seen from its characteristics. In the conventional method in which an organic reducing agent is added thereto, the oxidation-reduction reaction is extremely large, the reaction is intense, and the reaction itself is dangerous.

In addition, since the reaction is unnecessarily violent, the amount of the organic reducing agent that volatilizes before it is used for the reduction of chromium becomes a nonnegligible amount and cannot be controlled. Furthermore, when preparing a mixed solution of a chromic acid solution and sulfuric acid, it is conceivable that chromic anhydride crystals may precipitate due to the remarkable decrease in the solubility of chromic acid in the sulfuric acid solution. There is a danger of burning.

However, when the mixed solution of sulfuric acid and the organic reducing agent is reacted with chromic acid, the above-mentioned disadvantages can be solved and the production can be carried out industrially. It is completely unexpected that the process according to the invention can be advantageously produced without the above-mentioned problems, while basically being based on the reaction of formula (1).

The reason is considered to be that the reaction of the formula (1) proceeds instantaneously in the conventional method, whereas the reactions of the formulas (2) and (3) occur in the method of the present invention.

10CrO ₃ + C ₂ H ₅ OH → 2Cr ₂ (CrO ₄ ) ₃ + 3H ₂ O + 2CO ₂ … (2) Cr ₂ (CrO ₄ ) ₃ + 3H ₂ SO ₄ → Cr ₂ (SO ₄ ) ₃ + 3CrO ₃ + 3H ₂ O… (3 That is, by mixing the sulfuric acid and the organic reducing agent calculated by the formula (1) and adding the mixture to the chromic acid solution, the added organic reducing agent reduces the chromic acid by the reaction of the formula (2) to form chromium. Chromic acid (Cr ₂ (CrO ₄ ) ₃ ) is produced, which becomes chromium sulfate by the reaction of sulfuric acid with the formula (3). At this time, chromic acid is released.

Since the reactions (2) and (3) proceed sequentially, the reaction proceeds gently as compared with the conventional method, thereby eliminating the danger of the reaction operation. The reaction is performed by adding the calculated amount of the organic reducing agent. Can be completed.

In the present invention, such a mild reaction for forming chromium sulfate is characterized by a reaction between chromic acid and a mixture of sulfuric acid and an organic reducing agent, but industrially, sulfuric acid and an organic reducing agent are added to a chromic acid solution. A method in which a mixed liquid is gently added and reacted is generally preferable.

As another method, there is a method in which a chromic acid solution is gradually added to the mixed solution to cause a reaction, or a method in which the chromic acid solution and the mixed solution are simultaneously added to cause a reaction.

Since this reaction is a typical oxidation-reduction reaction, it generates heat. However, the reaction may be performed according to the change in heat, and it is not particularly necessary to employ heating or cooling.

However, in order to control the removal of water vapor accompanying the heat generation to the outside of the system and to adjust the concentration, it is preferable to use a reaction vessel with a condenser.

After this reaction, the product can be directly used as a high-purity aqueous solution of chromium sulfate, but it can be crystallized as necessary to obtain a crystalline product.

The high-purity chromium sulfate solution obtained by the method of the present invention is suitable as a raw material for plating, metal surface treatment, catalyst, pigment and the like.

〔Example〕

 Hereinafter, the present invention will be further described with reference to examples.

Example 1 98 wt% sulfuric acid 306 kg, water 374 kg, 95 wt% ethyl alcohol
705kg of a mixture of sulfuric acid and ethyl alcohol consisting of 25kg
Agitation materials, jackets, was prepared in a glass-lined 1 m ³ tank with a capacitor.

99.7wt% 60wt% consisting of 205kg of chromic anhydride and 135kg of water
Chromic acid aqueous solution 340 kg, stirring member, jacket, placed in a glass lined 2m ³ reactor with condenser, using a metering pump with stirring at 30 rpm, the sulfuric acid - a ethyl alcohol mixed solution was added over 5 hours went.

The reaction was mild with continuous microfoaming without any danger. The temperature during the reaction was 100-120 ° C.

After the addition, steam was passed through the jacket, and the mixture was kept at 100 to 120 ° C and aged for 1 hour.

After completion of the ripening, the remaining hexavalent chromium in the reaction solution was checked by coloring with a diphenylcarbazite solution in sulfuric acid. No color was detected, and hexavalent chromium was completely reduced to trivalent chromium.

Water is passed through the jacket and cooled to room temperature.
1000 kg of a% solution were obtained.

The analysis results are shown in Table 1. As a result, a chromium sulfate solution containing very few impurities was obtained.

Example 2 A mixture of sulfuric acid and ethylene glycol consisting of 230 kg of 98 wt% sulfuric acid, 527 kg of water and 29 kg of 98.5 wt% ethylene glycol 78
Stirring member to 6 kg, jacket, it was prepared in a glass-lined 1 m ³ tank with a capacitor.

99.7wt% 60wt% consisting of 154kg of chromic anhydride and 102kg of water
Stirring member chromic acid solution 256Kg, jacket, placed in a glass lined 2m ³ reactor with condenser, using a metering pump with stirring at 30 rpm, the sulphate - was added over ethylene glycol mixture for 5 hours, the reaction went.

The reaction was mild with continuous microfoaming without any danger. The temperature during the reaction was 100-120 ° C.

After the addition, steam was passed through the jacket and kept at 100 to 120 ° C., and aging was performed for 1 hour.

After completion of the ripening, the remaining hexavalent chromium in the reaction solution was checked by coloration with a diphenylcarbazide solution in sulfuric acid acid. No color was detected, and hexavalent chromium was completely reduced to trivalent chromium.

Water is passed through the jacket and cooled to room temperature.
1000 kg of solution were obtained.

The analysis results are shown in Table 2, and a chromium sulfate solution containing very few impurities was obtained.

Comparative Example 1 18.5 kg of 10 wt% chromium (III) chloride was heated with a stirrer 50
Place in an enameled container and heat stir at 60 ° C, 10wt%
Caustic soda solution (14.0 kg) was added over 30 minutes using a metering pump, and the mixture was aged at the same temperature for 1 hour to obtain a chromium hydroxide slurry.

The obtained slurry was subjected to liquid separation using a 300 mmφ suction filter, and then re-pulp and repeated twice using 10 times the weight of the cake to obtain 3 kg of a chromium hydroxide cake. Na, Cl, Fe content in cake is 290, 450, 38pp respectively
m. The time required for cleaning and washing was 22 hours.

In a 10 glass flask equipped with a stirrer and a condenser, set the amount to be 40 wt% chromium sulfate.
5 kg of 98 wt% sulfuric acid was added, the mixture was heated to 100 ° C. with a mantle heater, and a slurry composed of 2.5 kg of the above chromium hydroxide cake and 0.8 kg of water was gradually added thereto over 30 minutes. After completion of the addition, the mixture was aged at 100 ° C. for 1 hour. Since undissolved chromium hydroxide remained, the mixture was further aged for 2 hours, but did not dissolve.

After cooling at room temperature and removing unreacted chromium hydroxide, the amount was 500 g corresponding to 20 wt% of the charged amount.
Table 3 shows the analysis results of the liquid.

Comparative Example 2 When 98 wt% sulfuric acid was added to a 60 wt% chromic acid solution, a large amount of chromic anhydride crystals precipitated due to the solubility of chromic acid in the sulfuric acid solution, and there was a risk that explosive combustion would occur with ethyl alcohol added later. Therefore, an amount of water required to suppress the solubility to below the solubility was added to obtain a mixed solution of chromic sulfate.

That is, 306 kg of 98 wt% sulfuric acid, 510 kg of water, 205 k of chromic anhydride
consisting g, a sulfuric chromic acid mixture, a stirrer, was placed a jacket, a glass lined 2m ³ reactor with condenser, using a metering pump with stirring at 30 rpm, 95 wt%
25 kg of ethylene alcohol was added dropwise over 5 hours to carry out the reaction.

However, the reaction was violent, sounded and foamed, and the droplets reached the looking glass at the top of the reaction tank, and felt dangerous during the reaction. The temperature during the reaction was 100-120 ° C.

After the addition, steam was passed through the jacket and kept at 100 to 120 ° C. for aging for 1 hour.

After the aging, the remaining hexavalent chromium in the reaction solution was checked by coloring with a diphenylcarbazide solution in sulfuric acid, and a large amount of hexavalent chromium remained.

 The analysis values of the obtained reaction solution are shown in Table-4.

10 wt% of the total chromium was not reduced as calculated from the residual hexavalent chromium, and 10 wt% of ethyl alcohol volatilized during the reaction, and did not participate in the reaction.

〔The invention's effect〕

Chromium sulfate according to the present invention is particularly
It has a high purity, in which Na, Fe and Cl are extremely low and other metal ions are substantially absent.

Therefore, such chromium sulfate can be effectively used as a high-purity chromium source required for plating agents, catalysts, pigments and the like.

Further, according to the production method of the present invention, high-purity chromium sulfate can be industrially advantageously obtained under safe operation.

 ──────────────────────────────────────────────────続 き Continuation of front page (56) References W. MELLOR, "A COM PREHENSIVE TREATES EON INORGANIC AND THEORETICAL CHEMI STRY" Vol. XI (1931) Longmans, Green and Co. (US) 435

Claims (1)

(57) [Claims] 1. A method for producing high-purity chromium sulfate, comprising reacting a chromic acid solution with a mixture of sulfuric acid and an organic reducing agent.