JPH11236633A - How to recover cerium - Google Patents

Abstract

(57) [Summary] [Object] To provide a method for economically recovering cerium by removing dissolved chromium from a chromium etching waste solution containing cerium (IV) ammonium nitrate used for chromium etching. [Constitution] A cerium (IV) ammonium nitrate solution is used for etching a chromium thin film. A method for recovering cerium, which separates and removes chromium in a state in which chromium is dissolved and cerium is precipitated by supplying an oxidizing agent and increasing the pH of a chromium etching waste liquid which is a mixed waste liquid of cerium and chromium, and a recovery method. An etching solution using cerium.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering cerium from a chromium etching solution used for chromium etching or the like, and more particularly to a method for recovering cerium from a chromium etching solution comprising cerium (IV) ammonium nitrate and an acid. And a method for recovering cerium from a solution containing cerium and chromium.

[0002]

2. Description of the Related Art When manufacturing semiconductors and liquid crystal displays, it is necessary to etch metal thin films. In particular, since cerium compounds are used for chromium etching, tetravalent cerium and hexavalent chromium are dissolved in the waste liquid after use. Both substances are strongly oxidizing substances and are harmful, so it is necessary to remove these substances from the waste liquid. For the treatment, sodium bisulfite is added to a waste liquid of cerium (IV) ammonium nitrate containing chromium and cerium as described in JP-A-52-68860 to reduce chromium, and then calcium hydroxide is added. A method of removing chromium in waste liquid by coprecipitation with cerium hydroxide has been widely used. Further, as disclosed in Japanese Patent Application Laid-Open No. 9-85264, a method has been devised in which tetravalent cerium and hexavalent chromium are reduced and then adsorbed and removed by an adsorbent. However, in any case, these methods result in a large amount of expensive cerium being discarded.

A method for purifying cerium is disclosed in
-191422 discloses a method in which trivalent cerium is converted to cerium tetravalent with an oxidizing agent and separated and purified according to the difference in properties from other substances. Cerium and chromium are co-precipitated in the case where chromium is mixed as an impurity, and thus cannot be separated.

[0004]

SUMMARY OF THE INVENTION As described above, the present invention is an improvement of the current waste liquid treatment method in which a large amount of expensive cerium must be discarded when treating a waste liquid containing cerium and chromium. Method, which can recover expensive cerium, reduce waste, and have less environmental impact,
An object of the present invention is to provide a method for treating a waste liquid containing cerium and chromium.

[0005]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems. As a result, a method of recovering cerium by dissolving cerium as a precipitate and chromium as hexavalent chromium in the liquid and performing solid-liquid separation was developed. That is, the gist of the present invention is characterized in that an oxidizing agent and an alkali are supplied to a solution containing cerium and chromium, cerium is precipitated and chromium is dissolved as hexavalent chromium, and cerium is recovered. Cerium recovery method. Note that the recovery of the cerium recovered above as cerium (IV) ammonium nitrate and a chromium etching solution using the cerium recovered by the above method are also included in the gist of the present invention.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The solution containing cerium and chromium used in the present invention may be any solution as long as it contains at least cerium and chromium. Cerium ammonium nitrate (I) used for etching of metals and thin films during production, mainly for etching of chromium
A chromium etching waste solution containing V) is preferably used.

[0007] The pH of the chromium etching waste liquid is generally about 0 because an acid is added. When the pH of the aqueous solution is raised, cerium dissolved in the solution precipitates as a hydroxide. At this time, coexisting chromium is also coprecipitated and cerium and chromium cannot be separated. When the solution is made alkaline and an oxidizing agent for cerium and chromium coexists, cerium and chromium are oxidized. As the oxidizing agent used at this time, any oxidizing agent which does not contaminate the yarn or does not affect the cerium to be recovered can be used. In the present invention, hydrogen peroxide is preferable. Hereinafter, the present invention will be described using hydrogen peroxide as an example, but the present invention is not limited thereto. When hydrogen peroxide is used as an oxidizing agent, tetravalent cerium hydroxide forms a red complex with hydrogen peroxide and remains precipitated, but hexavalent chromium dissolves in the liquid. The pH at this time may be an alkali. However, in order to dissolve chromium efficiently, it is preferable to use a pH of 10 because of speed problems.
The pH is preferably 12 or more. By using such a method, the recovered cerium can be oxidized to tetravalent necessary for use as an etching solution, and chromium can be removed at the same time. If this precipitate is subjected to solid-liquid separation, cerium can be recovered.

Since the alkali used at this time is only for the purpose of raising the pH, any alkali may be used, and the form of supply may be a solid or an aqueous solution.
Examples of the alkali include, but are not limited to, lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, ammonia, and an aqueous solution thereof.

In this treatment, the pH is closely related to the oxidation of cerium and chromium, so that pH control is important. Chromium does not dissolve even when hydrogen peroxide coexists at a low pH. Therefore, when supplying the alkali, it is preferable to perform the measurement while measuring the liquid property using an electrochemical method or a spectroscopic method. As an electrochemical method, there is a method of measuring pH or oxidation-reduction potential, and as a spectroscopic method, there is a method of measuring absorption of hexavalent chromium. However, the measuring method is not limited to these.

In the present invention, precise separation can be performed by repeating the above operation until the concentration of cerium to be recovered reaches a desired concentration. For this purpose, it is necessary to estimate the chromium concentration in the precipitate by quantifying the chromium concentration in the recovered precipitate or measuring the concentration of dissolved chromium. Although there are many methods for measuring the chromium concentration in the precipitate and the chromium concentration in the solution, the measurement is preferably performed using a spectroscopic method or an electrochemical method. Spectroscopic methods include ICP emission, X-ray fluorescence measurement, and absorbance measurement, and electrochemical methods include measurement of oxidation-reduction potential and the like. According to this method, cerium and chromium can be separated from the cerium solution and the precipitate for removing chromium, and cerium can be recovered.

The recovered cerium precipitate is a red hydrogen peroxide addition complex of cerium hydroxide. If this is recovered and dissolved in an acid having a pH of 1 or less, cerium tetravalent is reduced by hydrogen peroxide contained in the precipitate itself,
It becomes a solution of cerium (III). When a solution of trivalent cerium is used, it is necessary to oxidize cerium again in order to use cerium as an etching solution. To avoid this, it is necessary to remove hydrogen peroxide from the hydrogen peroxide addition complex of cerium hydroxide.

As one of the methods for removing hydrogen peroxide,
There is a method of removing hydrogen peroxide from a hydrogen peroxide complex of cerium by self-decomposition. Hydrogen peroxide becomes oxygen and water by self-decomposition and can be removed.
The decomposition product does not cause any problem in the recovery of cerium. When hydrogen peroxide is removed, the cerium precipitate changes from red to yellow of cerium hydroxide, confirming the removal of hydrogen peroxide. This operation may be performed before or after the solid-liquid separation.

The rate of self-decomposition of hydrogen peroxide is quite slow under normal conditions. Therefore, it is conceivable to quickly recover cerium hydroxide by promoting the self-decomposition of hydrogen peroxide. Heating, infrared irradiation, and ultraviolet light irradiation are effective methods for promoting self-decomposition, but the method for promoting self-decomposition is not limited thereto.

When the purity of the recovered cerium is low, the purity can be increased by repeating the above-mentioned operation. That is, when the concentration of the recovered cerium is low, this operation is repeated. By repeating this operation, chromium can be almost completely removed, and cerium and chromium can each be reused.

The cerium hydroxide recovered from the chromium etching solution can be recovered as cerium ammonium nitrate (IV). The recovered cerium hydroxide is dissolved in nitric acid, filtered, charged with ammonium nitrate, and concentrated.
Double-salt and recover the precipitate as cerium (IV) ammonium nitrate. However, the method for recovering ammonium cerium (IV) from cerium hydroxide is not limited to this method.

Recovered cerium (IV) ammonium nitrate
Can be again used as an etchant. The recovered ammonium cerium (IV) nitrate is dissolved in pure water, perchloric acid is supplied, and the concentration is adjusted. For example, cerium ammonium nitrate 13% by weight (wt), perchloric acid 5
The solution can be used as an etching solution by using a solution of wt%. If the etching rate is measured, it can be compared with that adjusted from the reagent. In the present invention, the composition of the chromium etching solution using the recovered cerium and the method for adjusting the same are not limited to the above.

[0017]

EXAMPLES Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to these examples.

Example 1 A waste liquid obtained by etching a chromium thin film with a chromium etchant having a composition of 13 wt% of cerium (IV) ammonium nitrate and 5 wt% of perchloric acid, and having a hexavalent chromium concentration of 0.017
mol / l, tetravalent cerium concentration 0.164 mol / l,
25 ml of a solution with a trivalent cerium concentration of 0.102 mol / l
Was supplied with 2.5 ml of 35% hydrogen peroxide solution and 250 ml of a 1N aqueous sodium hydroxide solution to adjust the pH to 12 or more. After stirring at room temperature for 1 hour, solid-liquid separation was performed. Further, the recovered substance was mixed with 250 ml of a 1N aqueous sodium hydroxide solution and 35 ml.
The solution was placed in a solution of 2.5% aqueous hydrogen peroxide and stirred at room temperature for 1 hour. Thereafter, the mixture was stirred at 80 ° C. for 2 hours, and then subjected to solid-liquid separation to recover cerium hydroxide. The chromium concentration in the cerium hydroxide was 100 ppm or less. This cerium hydroxide was dissolved in nitric acid, filtered, charged with ammonium nitrate, concentrated and double-chlorinated, and the precipitate was recovered as cerium (IV) ammonium nitrate. The recovery rate of cerium is about 90%
Met. This cerium ammonium nitrate (IV) was dissolved in pure water, perchloric acid was supplied, and the concentration was adjusted.
It was confirmed that 0 ml was usable as an etching solution. When the chromium etching rate of this etching solution was measured, it was almost the same as that adjusted from the reagent.

Comparative Example 1 The same chromium etching waste liquid as in the above example was supplied with sodium hydroxide to raise the pH to 6. A precipitate at that time was obtained. As a result, chromium and cerium co-precipitated, and chromium and cerium could not be separated.

[0020]

According to the present invention, it is possible to recover cerium and chromium from a used effluent of a chromium etching solution, and to remove cerium hydroxide and chromium hydroxide waste which have been discarded up to now. It is possible to reduce the amount of cerium, which is effective as an environmental measure, and contributes to the cost reduction of chromium etching by recovering expensive cerium.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a method for recovering cerium.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C22B 3/44 C23F 1/26 C23F 1/26 1/46 1/46 C22B 3/00 Q

Claims (15)

[Claims] An oxidizing agent and an alkali are supplied to a solution containing cerium and chromium, and cerium is recovered while cerium is precipitated and chromium is dissolved as hexavalent chromium. Collection method. 2. The method for recovering cerium according to claim 1, wherein the oxidizing agent is hydrogen peroxide. 3. The method for recovering cerium according to claim 1, wherein an alkali is supplied to adjust the pH to 10 or more. 4. The method for recovering cerium according to claim 3, wherein the pH is 12 or more. 5. The method for recovering cerium according to claim 1, wherein the supply of the alkali is performed while measuring the liquid property using an electrochemical method or a spectroscopic method. . 6. The method according to claim 1, wherein the recovery of cerium is a recovery of cerium precipitate by solid-liquid separation.
The method for recovering cerium according to any one of the above. 7. The recovery of cerium according to claim 2, wherein the recovery of cerium is a recovery of cerium hydroxide by solid-liquid separation after removing residual hydrogen peroxide. Method. 8. The method for recovering cerium according to claim 6, wherein the method according to claim 6 or 7 is repeated until the chromium content in the recovered cerium precipitate reaches a desired amount. 9. The method according to claim 6, wherein the chromium content in the recovered cerium precipitate is analyzed to determine whether the method according to claim 6 or 7 needs to be repeated. Collection method. 10. The liquid property of a solution is measured using an electrochemical method or a spectroscopic method, and it is determined whether the method according to any one of claims 1 to 7 needs to be repeated. The method for recovering cerium according to claim 1. 11. The method according to claim 7, wherein the removal of the hydrogen peroxide is removal of the hydrogen peroxide by self-decomposition.
0. The method for recovering cerium according to any one of 0. 12. The method for recovering cerium according to claim 11, wherein the self-decomposition of hydrogen peroxide is promoted by heating, infrared irradiation or ultraviolet light irradiation. 13. A method for recovering cerium, comprising recovering the cerium recovered in claim 1 as cerium (IV) ammonium nitrate. 14. A method for recovering cerium, comprising recovering the cerium (IV) ammonium nitrate recovered in claim 13 in a state usable as a chromium etching solution. 15. A chromium etching solution using cerium recovered by the method of claim 1. Description: