KR20030055505A - A method for manufacturing of cerium carbonate from the cerium hydroxide - Google Patents

Abstract

PURPOSE: A method for preparing cerium carbonate from cerium hydroxide is provided, in which cerium chloride aqueous solution is prepared by using trivalent cerium hydroxide and high purity cerium carbonate is prepared by adding ammonium carbonate to the cerium chloride aqueous solution. CONSTITUTION: The method comprises the steps of forming a cerium chloride aqueous solution by dissolving cerium hydroxide into hydrochloric acid; reducing the cerium chloride aqueous solution by adding hydrogen oxide to the cerium chloride aqueous solution; removing Fe constituent contained in the cerium chloride aqueous solution; and adding ammonium carbonate to the cerium chloride aqueous solution, wherein a part of trivalent cerium hydroxide is oxidized to quadrivalent cerium hydroxide when dissolving the trivalent cerium hydroxide into hydrochloric acid so that cerium hydroxide that is not dissolved into hydrochloric acid is reduced into trivalent cerium hydroxide by adding hydrogen hydroxide to the aqueous solution having an appropriate acidity in the step of forming a cerium chloride aqueous solution by dissolving cerium hydroxide into hydrochloric acid, wherein pH of cerium chloride aqueous solution is maintained to 0.5 to 1.5, and addition amount of hydrogen peroxide is 1.0 to 2.0 equivalents in the step of reducing the cerium chloride aqueous solution by adding hydrogen oxide to the cerium chloride aqueous solution, wherein the step of removing Fe constituent contained in the cerium chloride aqueous solution comprises the steps of slowly adding ammonia water so that cerium is maintained to a uniformed phase that is not coprecipitated by cerium hydroxide, and maintaining pH of the cerium chloride aqueous solution to 2.0 to 4.0, and wherein concentration of cerium chloride of the cerium chloride aqueous solution is 50 to 120 g/L, ammonium carbonate concentration of ammonium carbonate aqueous solution added is 0.5 to 2.0 M, and reaction temperature is 30 to 60 deg.C in the step of adding ammonium carbonate to the cerium chloride aqueous solution.

Description

A method for manufacturing of cerium carbonate from the cerium hydroxide}

The present invention relates to a method for producing cerium carbonate from cerium hydroxide, in particular, to prepare a cerium chloride aqueous solution using a trivalent cerium hydroxide, and to add a high-purity cerium carbonate by adding ammonium carbonate to the cerium chloride aqueous solution From a method for producing cerium carbonate from

In general, cerium salts such as cerium chloride are mainly used as starting materials used to prepare cerium carbonate. However, cerium salts have a disadvantage in that raw materials are more expensive than cerium hydroxide.

In addition, when trivalent cerium hydroxide (Ce (OH) ₃ ) is used as a starting material, the cerium hydroxide is oxidatively strong, and part of the cerium hydroxide is oxidized to tetravalent cerium hydroxide (Ce (OH) ₄ ) in the air, and the oxidized tetravalent Cerium hydroxide (Ce (OH) ₄ ) has a disadvantage in that it does not dissolve well in hydrochloric acid when preparing an aqueous solution of cerium chloride which is a raw material of cerium carbonate, causing a decrease in production yield.

In addition, although hydrothermal synthesis using a catalyst such as urea is widely used for the preparation of cerium carbonate smoothly, the reaction conditions must be strictly maintained for accurate crystal preparation of cerium carbonate (Ce ₂ (CO ₃ ) ₃ · nH ₂ O). There is a disadvantage that the manufacturing conditions are difficult.

In addition, when the cerium carbonate is prepared from cerium salts, there is a disadvantage in that strict reaction conditions must be controlled using a catalyst such as urea.

An object of the present invention for solving the above problems is to produce a cerium carbonate from a cerium hydroxide by a continuous process, to improve the production yield, to remove the Fe component to increase the purity of the final cerium carbonate To provide a method for producing cerium carbonate from cerium hydroxide to simplify the manufacturing process when adding ammonium carbonate.

1 is a process chart for the production of cerium carbonate according to the present invention.

Figure 2 is a graph showing the XRD pattern of cerium carbonate according to the change in the initial cerium chloride concentration of the present invention.

Figure 3 is a graph showing the XRD pattern of cerium carbonate prepared according to the change in the concentration of ammonium carbonate added in the present invention.

4 is a graph showing an XRD pattern of cerium carbonate prepared according to the reaction temperature change of the present invention.

In order to achieve the above object, the present invention comprises the steps of dissolving cerium hydroxide in hydrochloric acid to form a cerium chloride aqueous solution;

Reducing the cerium chloride aqueous solution using hydrogen peroxide;

Removing the Fe component contained in the cerium chloride aqueous solution:

It provides a method for producing cerium carbonate from cerium hydroxide comprising the step of adding ammonium carbonate to an aqueous solution of cerium chloride.

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

As shown in FIG. 1, a highly oxidizable trivalent cerium hydroxide (Ce (OH) ₃ ) is prepared and then washed with water and exposed to air to oxidize to tetravalent cerium hydroxide (Ce (OH) ₄ ).

The trivalent cerium hydroxide (Ce (OH) ₃ ) is dissolved in hydrochloric acid near pH 3, and the tetravalent cerium hydroxide (Ce (OH) ₄ ) begins to dissolve near pH 0.5 and is not completely dissolved and is oxidized hydroxide. Cerium is reduced to trivalent cerium hydroxide by a reducing agent.

In addition, many cerium chloride aqueous solutions are used as a starting material of cerium carbonate which is a cerium oxide raw material used as a semiconductor substrate abrasive.

Therefore, the cerium carbonate is composed of a trivalent cerium compound, the conversion of the cerium carbonate is not made by the tetravalent cerium compound, so the reduction process of the present invention is very important when preparing an aqueous solution of cerium chloride.

Accordingly, the reduction of some oxidized tetravalent cerium hydroxide is dissolved in hydrochloric acid while being reduced to trivalent cerium hydroxide by adding hydrogen peroxide at an appropriate pH of the aqueous solution of cerium chloride.

In addition, a small amount of Fe component is present in the cerium chloride aqueous solution prepared by the above method, and in order to manufacture cerium carbonate with high purity, the Fe component must be removed.

For this purpose, paying attention to the fact that the pH of the solution in which the trivalent cerium and Fe ions are precipitated as hydroxide is different, the Fe component is removed by using an acidity control method.

Cerium carbonate is prepared by adding ammonium carbonate at an appropriate temperature to an aqueous solution of cerium chloride prepared by the above method.

The manufacturing method of cerium carbonate manufactured by the above manufacturing method is demonstrated in detail by the Example of this invention.

Example 1

(Production of Aqueous Cerium Chloride Solution From Cerium Hydroxide)

Trivalent cerium hydroxide (Ce (OH) ₃ ) is highly oxidizable and is oxidized to Ce (OH) ₄ when washed or exposed to air.

At this time, the trivalent cerium hydroxide (Ce (OH) ₃ ) is dissolved in hydrochloric acid near pH 3, and the tetravalent cerium hydroxide (Ce (OH) ₄ ) begins to dissolve near pH 0.5 and is not completely dissolved. .

Therefore, the oxidized cerium hydroxide is reduced to trivalent cerium hydroxide by the reducing agent.

At this time, the manufacturing process of the cerium chloride aqueous solution formed by adding the cerium hydroxide to hydrochloric acid is prepared by Scheme 1.

Ce (OH) ₃ + 3HCl → CeCl ₃ + 3H ₂ O

In the method for preparing cerium chloride formed by the above reaction formula, the amount of hydrochloric acid added is almost 1.0 trivalent by adding a chemical reaction formula, and the trivalent cerium hydroxide is almost dissolved. Cerium is also dissolved.

In addition, as a result of analyzing the content of trivalent and tetravalent cerium through wet titration, it was found that tetravalent cerium is present in about 18% of the total cerium, thereby reducing the additive added to the tetravalent cerium as in Scheme 2. The amount of hydrogen peroxide added was calculated.

Ce ⁴⁺ + 1 / 2H ₂ O ₂ → Ce ³⁺ + H ⁺ + 1 / 2O ₂

Since the hydrogen peroxide solution is generally used for reducing at pH 2 or less, tetravalent cerium was reduced to trivalent while changing the pH and the amount of hydrogen peroxide added at pH 2 or less of the solution. The results are shown in Tables 1 and 2.

In addition, according to Table 1, as the pH of the solution is lowered, the reducing effect of cerium increases, and it can be seen that the pH is less affected by 1 or less.

And, according to Table 2, as a result of changing the addition amount of hydrogen peroxide while maintaining the pH of the solution to 1, it can be seen that only about 1.5 equivalents of tetravalent cerium content is added to complete reduction.

* The degree of cerium reduction according to the pH change of the solution at a certain amount of hydrogen peroxide Acidity of solution 2.0 1.5 1.0 0.5 Reduction degree (%) 92.7 98.3 99.9 -

The degree of reduction of cerium with the addition of hydrogen peroxide (H ₂ O ₂ ) at a constant pH (1.0) of the solution * Amount of H ₂ O ₂ 1.0 1.2 1.5 2.0 Reduction degree (%) 98.7 99.3 99.9 -

Example 2

(Removal of Iron from Aqueous Cerium Chloride Solution)

A small amount of Fe component (4 to 5 ppm) is present in the cerium chloride solution prepared as described above, and the acidity control method according to Scheme 3 is applied to remove the Fe component.

^{Fe 3+ + 3OH - → Fe (} OH) 3 ↓ (> pH 3.0)

^{Ce 4+ + 4OH - → Ce (} OH) 4 ↓ (> pH 3.5)

^{Ce 3+ + 3OH - → Ce (} OH) 3 ↓ (> pH 7.0)

^{Re 3+ + 3OH - → Re (} OH) 3 ↓ (> pH 7.5)

Where Re means other trivalent rare earth elements except cerium.

As in Scheme 3, trivalent rare earth elements including cerium are precipitated as hydroxide near pH 7.0 of the solution, and Fe is precipitated near pH 3.0 so that the Fe component can be removed by adjusting the pH of the solution.

Accordingly, the process of removing iron by adjusting the acidity (pH) to the aqueous solution of cerium chloride is shown in Scheme 4, and diluted ammonia water was added to adjust the acidity.

_{^{Ce 3+ + 3Cl - + 3NH 4}} OH + Fe 3+ → Ce 3+ + 3Cl - + 3NH 4 - + Fe (OH) 3 ↓

In the reaction, it is desirable to maintain a homogeneous phase by slowly adding ammonia water so that cerium is not co-precipitated with cerium hydroxide when Fe (OH) ₃ is precipitated.

Cerium fraction and Fe content in solution according to pH change of solution Acidity of the solution (pH) 3.0 4.0 4.5 5.0 Cerium fraction (%) 99.7 99.3 98.9 92.4 Iron content (ppm) 0.42 0.39 0.47 0.41

And, Table 3 shows the change in cerium and iron content in the solution after removing the Fe component in accordance with the pH change of the solution.

According to the result, it can be seen that the iron content is well removed to 0.4 to 0.5 ppm regardless of the pH of the solution.

However, at pH 5 or above, it can be seen that some cerium is co-precipitated with cerium hydroxide, and therefore, the pH of the solution is preferably maintained at 3-4.

Example 3

(Production of Cerium Carbonate from Aqueous Cerium Chloride)

Cerium carbonate is prepared by adding ammonium carbonate to the aqueous solution of cerium chloride prepared as above, wherein the crystal state of cerium carbonate formed by the initial concentration of cerium chloride, the reaction temperature and the method of adding ammonium carbonate is as follows.

FIG. 2 shows XRD analysis results of cerium carbonate prepared by the initial concentration of cerium chloride at a reaction temperature of 95 ° C., which shows that cerium carbonate hydrate (Ce ₂₎ has an initial concentration of 90 g / l. It can be seen that the main peak of the crystal structure of (CO ₃ ) ₃ nH ₂ O appears. On the basis of this, when the concentration of cerium chloride is low or large, cerium carbonate hydroxide (Ce ₂ OH (CO _{3) is used.} ) _2, it can be seen that constitute the crystal structure of nH ₂ O).

In addition, Figure 3 shows the XRD analysis of the cerium carbonate prepared according to the change in the concentration of ammonium carbonate contained in the aqueous solution of ammonium carbonate, according to which the concentration of ammonium carbonate is cerium carbonate (Ce ₂ (CO ₃ The main peak appears in the crystal structure of ₃ ) nH ₂ O), and at a higher ammonium carbonate concentration, the crystal structure of cerium hydroxide (Ce ₂ OH (CO ₃ ) ₂ nH ₂ O) is obtained.

In addition, Figure 4 shows the results of XRD analysis of cerium carbonate according to the reaction temperature at a constant cerium chloride concentration, the crystal structure is changed from cerium carbonate hydrate to cerium hydroxide structure as the reaction temperature increases based on the reaction temperature 50 ℃ It can be seen that.

This is the ammonium carbonate in the preparation of cerium carbonate may be accompanied by the following reaction scheme 5, the ammonia water produced is reacted with cerium chloride to combine the hydroxyl group and cerium to form cerium carbonate.

△

NH ₄ HCO ₃ ------- → NH ₄ OH + CO ₂ ↑

> 30 ℃

Accordingly, it is necessary to suppress the reaction scheme, and it can be seen that the following reaction scheme 6 occurs when ammonium carbonate is present in the solution at a high concentration, which is more likely to occur as the temperature increases.

△

NH ₄ HCO ₃ ------- → NH ₃ + CO ₂ ↑ + H ₂ O

_{NH 3 + H 2 O → NH} 4 + + OH -

Therefore, before the reaction takes place, the precipitation of cerium carbonate should occur preferentially, and this reaction induces the production of cerium carbonate preferentially by locally adding ammonium carbonate upon stirring while heating the aqueous solution of cerium chloride at 50 ° C. It is desirable to.

In addition, when the reaction proceeded completely, the continuous addition of ammonium carbonate reduced the acidity of the solution, and the reaction of cerium carbonate was terminated at pH> 7 of the solution.

As described above, in the present invention, when trivalent cerium hydroxide is dissolved in hydrochloric acid to prepare an aqueous solution of cerium chloride, the tetravalent cerium hydroxide present in the aqueous solution is adjusted to about 1.0 by adding pH of the aqueous solution to trivalent Reduction of cerium hydroxide can reduce the loss of cerium in the preparation of aqueous solution of cerium chloride.

In addition, high purity cerium carbonate is prepared by adding ammonium carbonate under a low temperature reaction condition after removing a trace amount of Fe by acidity control.

In addition, compared with the conventional hydrothermal synthesis method using urea as a catalyst, the process is simplified and the process time can be shortened.

While the invention has been shown and described with respect to specific embodiments thereof, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit or scope of the invention as provided by the following claims. I would like to clarify that those who have knowledge of this can easily know.

Claims (6)

Dissolving cerium hydroxide in hydrochloric acid to form an aqueous solution of cerium chloride; Reducing the peroxide solution by adding hydrogen peroxide; Removing the Fe component contained in the cerium chloride aqueous solution: A method for producing cerium carbonate from cerium hydroxide, comprising the step of adding ammonium carbonate to an aqueous solution of cerium chloride. The method of claim 1, wherein dissolving the cerium hydroxide in hydrochloric acid to form an aqueous solution of cerium chloride, the aqueous solution of cerium hydroxide which is not dissolved in hydrochloric acid is partially oxidized to tetravalent when the hydrochloric acid of trivalent cerium hydroxide is dissolved. A method for producing cerium carbonate from cerium hydroxide, characterized in that hydrogen peroxide is added to reduce trivalent cerium hydroxide. According to claim 1 or 2, wherein the step of dissolving the cerium hydroxide in hydrochloric acid to form a cerium chloride aqueous solution, characterized in that the hydrochloric acid of 1 to 1.5 equivalents of the cerium content is added while maintaining the pH 1-2. Method for producing cerium carbonate from cerium hydroxide. The method of claim 1, wherein the step of adding hydrogen peroxide to the aqueous solution of cerium chloride to reduce the pH of the aqueous solution of cerium chloride is maintained at 0.5 to 1.5, and the amount of hydrogen peroxide added is 1.0 to 2.0 equivalents. Method for producing cerium carbonate. The method of claim 1, wherein the removing of the Fe component contained in the aqueous solution of cerium chloride is performed by slowly adding ammonia water to maintain a uniform phase in which cerium is not precipitated with cerium hydroxide, and adjusting the pH of the aqueous solution of cerium chloride to 2.0 to 4.0. A method for producing cerium carbonate from cerium hydroxide, which is characterized in that it is retained. According to claim 1, wherein the step of adding ammonium carbonate to the aqueous solution of cerium chloride, the cerium chloride concentration of the aqueous solution of cerium chloride is 50-120g / L, the ammonium carbonate concentration of the aqueous solution of ammonium carbonate added is 0.5-2.0M and the reaction temperature C is a cerium carbonate production method from cerium hydroxide, It is 30-60 degreeC.