JPH11236632A - 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] Reduce cerium and chromium in chromium etching waste liquid, change to a solution containing trivalent cerium and trivalent chromium, further raise pH, precipitate and remove chromium hydroxide, and recover cerium solution A method for recovering cerium, raising the pH of the recovered cerium solution and supplying an oxidizing agent, oxidizing cerium and chromium remaining in a small amount, and precipitating cerium into hydroxide to convert chromium into hexavalent chromium Cerium recovery method to dissolve and remove
And an etching solution using the recovered 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 a 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.

As a method for purifying cerium, JP-A-62-1
As disclosed in Japanese Patent Publication No. 91422, a method has been proposed in which trivalent cerium is converted to tetravalent with an oxidizing agent and separated and purified according to the difference in properties between cerium tetravalent and other substances. Since cerium and chromium co-precipitate chromium mixed with chromium as an impurity, chromium could not be separated and removed from cerium.

[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, it was found that it was coprecipitation of cerium (IV) and chromium that made the separation of cerium and chromium difficult. In the present invention, it is necessary to supply a reducing agent to a solution containing at least cerium and chromium. To reduce cerium (IV) and hexavalent chromium contained to cerium (III) and chromium (III), respectively, to prevent coprecipitation of cerium (IV) and chromium, and then separate and remove chromium to recover cerium. Was found. As a method of separating chromium, a method of raising the pH and precipitating and removing trivalent chromium as chromium hydroxide was effective.

That is, the gist of the present invention is to supply a reducing agent to a solution containing cerium and chromium, to reduce tetravalent cerium and hexavalent chromium in the solution to trivalent cerium and trivalent chromium, respectively, Cerium is recovered by separating a precipitate containing cerium. An oxidizing agent and an alkali are supplied to the trivalent cerium solution after the chromium has been separated, and the liquid is made alkaline to convert the trivalent cerium to tetravalent cerium. Then, the cerium is recovered. After separation, the separated chromium is supplied to an alkaline solution to make the liquid alkaline, an oxidizing agent is coexisted, and trivalent cerium is added to the solution.
After converting the cerium to valent cerium, the cerium recovered above is converted to cerium ammonium nitrate (IV)
The present invention also includes an etching solution using cerium collected by the above method and an etching solution using cerium collected by the above method.

[0007]

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 (IV) used for etching metal thin films during production, mainly for chromium
A chromium etching waste solution containing is preferably used.

In the treatment method disclosed in Japanese Patent Application Laid-Open No. 52-68860, a reducing agent is supplied to reduce to trivalent chromium. However, substances such as sodium bisulfite currently used as a reducing agent require a system. Dirty, making it virtually impossible to recover cerium. In the present invention, any reducing agent which does not contaminate the system or does not affect the cerium to be recovered can be used, but is generally used in a cerium production method as disclosed in JP-A-62-191422. Hydrogen peroxide, which is used as an oxidizing agent for trivalent cerium,
It has been found that some can be suitably used as a reducing agent for cerium. Hereinafter, the present invention will be described using hydrogen peroxide as an example, but the present invention is not limited thereto. Hydrogen peroxide acts as a reducing agent for tetravalent cerium in a low pH range. From the viewpoint of the reaction rate, this reduction reaction is preferably carried out at a pH of 0.6 or less, more preferably at a pH of 0 or less. Furthermore, in the present invention, it has been found that hydrogen peroxide also works as a reducing agent for hexavalent chromium in a low pH range. Although the range in which hexavalent chromium can be reduced is even lower than the range in which cerium can be reduced, p
H1 or less, preferably pH 0.5 or less, more preferably pH 0 or less.

Here, when the pH of the solution containing cerium and chromium is high, hydrogen peroxide does not act as a reducing agent for cerium and chromium. Before supplying hydrogen peroxide. The pH at this time is 1 or less, preferably 0.5 or less, and more preferably 0 or less. That is, in the present invention, the solution containing cerium and chromium,
It is necessary to have a pH capable of reducing tetravalent cerium and hexavalent chromium by hydrogen peroxide.

At this time, the amount of hydrogen peroxide required is more than the equivalent of reducing cerium and chromium because hydrogen peroxide is decomposed at the time of reduction. However, if hydrogen peroxide is left in the solution, when the pH is increased in a later step, hydrogen peroxide will act as an oxidizing agent, and cerium will be oxidized to tetravalent, and the recovery rate of cerium will decrease. Therefore, the amount of hydrogen peroxide is necessary and sufficient to reduce cerium and chromium, and it is better not to add more hydrogen peroxide. If the supplied hydrogen peroxide is in an amount that reduces the amount of cerium and chromium contained in the processing liquid, it is necessary to supply a substance that is reduced by the hydrogen peroxide to decompose and remove the hydrogen peroxide. For this purpose, a material containing tetravalent cerium may be supplied. As one of the methods, there is a method of supplying the solution containing cerium and chromium again, and a method of supplying a solution containing cerium (IV) ammonium nitrate newly. In addition, it is possible to decompose and remove hydrogen peroxide even if a substance oxidized by hydrogen peroxide is added.

As another method of removing hydrogen peroxide, there is a method of removing hydrogen peroxide by self-decomposition. Hydrogen peroxide is converted to oxygen and water by self-decomposition and can be removed.
It does not cause any problems. As described above, there are several methods for removing hydrogen peroxide, but the method is not limited to the methods described here. In addition, the rate of self-decomposition of hydrogen peroxide is quite slow at room temperature. Therefore, by promoting self-decomposition of hydrogen peroxide, cerium hydroxide can be recovered quickly. Heating, infrared irradiation, and ultraviolet light irradiation have been effective as methods for promoting self-decomposition, but the method for promoting self-decomposition is not limited thereto.

As described above, it is preferable that the amount of the reducing agent be supplied in an amount sufficient to reduce the liquid. For this purpose, the supply of the treatment liquid may be performed while measuring the liquid property of the treatment liquid using an electrochemical method or a spectroscopic method. The oxidation-reduction state can be known by observing the oxidation-reduction potential as an electrochemical technique and the decrease in absorption of tetravalent cerium or hexavalent chromium as a spectroscopic technique. However, the method for checking the liquid properties of the treatment liquid is not limited to these methods.

The present invention is characterized in that it is removed as a chromium-containing precipitate from the treatment liquid obtained by reducing cerium and chromium as described above. At this time, a preferable example is a method in which alkali is supplied to the treatment liquid to precipitate and remove chromium. The alkali used at this time is p
Since it only raises H, it may be any alkali as long as it is alkali, and the supply form may be a solid or an aqueous solution. Possible alkalis include, but are not limited to, lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, ammonia or their aqueous solutions. At this time, if the pH exceeds 8, the recovery rate decreases.
It is necessary to perform H control accurately. The preferred pH for chromium precipitation is between 5 and 7. When the pH at which the liquid is stopped is lowered, the amount of chromium remaining in the liquid increases, but the cerium recovery rate increases. Increasing the pH decreases the residual chromium content but decreases the cerium recovery.
As described above, the cerium recovery rate and the cerium purity change depending on the liquid conditions. Therefore, in raising the pH of the treatment liquid, an alkali is supplied while measuring the liquid property of the treatment liquid using an electrochemical method or a spectroscopic method, and an optimal amount of alkali is supplied to the treatment liquid. Should be done. At this time, the electrochemical method used is pH or redox potential, and the spectroscopic method is turbidity of the liquid, or the absorption of chromium in the liquid obtained by removing the precipitate using a method such as filtration. Good to do. However, the method for measuring liquid properties is not limited to these methods.

Further, as a method for separating a precipitate containing chromium (hereinafter referred to as "chromium precipitate"), it can be removed by filtration or centrifugation. It is also conceivable to use these methods in combination. However, the method for separating the chromium precipitate is not limited to these methods.

As described above, a method for obtaining an aqueous cerium solution by removing a chromium precipitate from a solution containing cerium and chromium was developed. However, even after the chromium is precipitated and removed in the cerium aqueous solution, a trace amount of chromium remains. In the present invention, a method for removing the residual chromium was further studied.

As a result, a method of recovering only cerium by separating cerium from the aqueous solution of cerium obtained as above, depositing cerium, oxidizing chromium and dissolving it as hexavalent chromium in the liquid, and performing solid-liquid separation. Was developed. The pH of the cerium aqueous solution after the precipitation and removal of the chromium is about 5 to 8. When the pH of the aqueous solution is increased, both cerium and chromium dissolved in the solution precipitate as hydroxides. When hydrogen peroxide coexists in an alkaline state, both cerium and chromium are oxidized. At this time, it was found that tetravalent cerium hydroxide forms a red complex with hydrogen peroxide and precipitates, but hexavalent chromium generated by oxidation dissolves in the liquid. The pH at this time may be an alkali, but in order to actually dissolve the chromium, it is preferably 10 or more from the viewpoint of speed,
More preferably, 12 or more is good. By using such a method, the recovered cerium can be oxidized to a necessary tetravalent as an etching solution and chromium can be removed at the same time. If this precipitate is separated, cerium can be recovered.

Analysis of the chromium precipitate in the process described above indicated that it was a mixture of chromium and cerium hydroxide and contained a significant amount of cerium. This is considered to be because the pH range in which chromium and cerium form a precipitate is close and co-precipitation of chromium and cerium has occurred. From now on, a method for precisely separating chromium and cerium was studied. As a result, it was found that the method for removing residual chromium described here can be used. By allowing the recovered precipitate to coexist with hydrogen peroxide in an alkaline state, chromium is oxidized and dissolved. Cerium is also oxidized, but since tetravalent cerium hydroxide forms a complex with hydrogen peroxide and precipitates, cerium is not observed in the liquid.
The pH at this time may be an alkali, but preferably 10 or more, more preferably 12
That is all. By repeating this operation until the required cerium concentration is reached, precise separation can be performed. For this purpose, it is necessary to estimate the chromium content in the precipitate by quantifying the chromium content in the recovered material or measuring the dissolved chromium content. Although there are many methods for measuring the chromium content in the precipitate and the chromium content in the solution, it is preferable to use 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. In this way,
Cerium and chromium can be separated from the chromium precipitate, and cerium can be recovered.

In the above-described method for removing residual chromium, since pH is closely related to chromium oxidation, pH control becomes important. Even if hydrogen peroxide coexists in a low pH state, oxidation of chromium does not occur and chromium does not dissolve. 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 and 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.

The cerium precipitate that can be recovered by these methods is a red hydrogen peroxide addition complex of cerium hydroxide.
Therefore, if solid-liquid separation is carried out as it is and dissolved in an acid such as nitric acid, cerium tetravalent is reduced by hydrogen peroxide contained in the precipitate itself, resulting in a trivalent cerium solution.
In order to use this solution as an etching solution, it is necessary to oxidize cerium again. 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 may be before or after the solid-liquid separation.

The rate of self-decomposition of hydrogen peroxide is quite slow at room temperature. Therefore, by promoting self-decomposition of hydrogen peroxide, cerium hydroxide can be recovered quickly.
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.

The cerium hydroxide recovered as described above can be recovered as cerium (IV) ammonium nitrate. That is, the recovered cerium hydroxide is dissolved in nitric acid, and after filtration, ammonium nitrate is added, 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 was dissolved in pure water, perchloric acid was supplied, and the concentration was adjusted. For example, cerium ammonium nitrate 13% by weight (wt), perchloric acid 5 wt.
% Solution so that it can be used as an etching solution. If the etching rate is measured, it can be compared with that adjusted from the reagent. The composition of the chromium etching solution using cerium recovered in the present invention and the method for adjusting the composition are not limited to this method.

[0024]

EXAMPLES Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to these examples. Example 1 Cerium (IV) ammonium nitrate 13 wt%, perchloric acid 5
A waste liquid obtained by etching a chromium thin film with a chromium etchant having a wt% composition.
28 ml of 1.2% hydrogen peroxide solution was supplied to 100 ml of a 1 / l, 0.164 mol / l tetravalent cerium concentration and 0.102 mol / l trivalent cerium concentration to reduce cerium and chromium. Thereafter, the pH was raised to 6.2 using a sodium hydroxide solution to precipitate chromium hydroxide. The precipitate was further removed, and hydrogen peroxide and sodium hydroxide were supplied to the filtrate to raise the pH to 12.5. After stirring for 1 hour, the mixture was stirred at 80 ° C. for 2 hours, and then solid-liquid separated to recover cerium hydroxide. 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. At this time, the recovery rate as cerium was 89 wt%, and the concentration of chromium in the mixture was 100 wt ppm or less. This cerium ammonium nitrate (IV) was dissolved in pure water, perchloric acid was supplied, and the concentration was adjusted. A solution containing 13 wt% of ammonium cerium (IV) nitrate and 5 wt% of perchloric acid was added.
0 ml was made. For the chromium film, a substrate was prepared by sputtering chromium on a glass substrate at 1500 °, and the substrate was applied to an etching solution prepared from the recovered cerium, and the chromium was etched with slow stirring. The end of the etching was determined by measuring the light transmitted through the glass substrate. The etching rate at this time was 30 ° / s, which was almost the same as that prepared from the reagent. Comparative Example 1 Sodium hydroxide was supplied to 100 ml of the same etching solution waste liquid as in the above example to raise the pH to 6.2, and a precipitate at that time was obtained. As a result, most of chromium and cerium co-precipitated, and chromium and cerium could not be separated.

[0025]

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 drawing showing an example of a method for recovering cerium.

Continued on the front page (51) Int.Cl. ⁶ Identification code FI C02F 1/72 C02F 1/72 Z C22B 3/44 C23F 1/26 C23F 1/26 1/46 1/46 C22B 3/00 Q

Claims (32)

[Claims] 1. A reducing agent is supplied to a solution containing cerium and chromium, and tetravalent cerium and hexavalent chromium in the solution are reduced to trivalent cerium and trivalent chromium, respectively. A method for recovering cerium, comprising recovering cerium by separating. 2. The method for recovering cerium according to claim 1, wherein the chromium is separated by raising the pH of the solution to convert chromium into a precipitate containing chromium hydroxide. 3. The method for recovering cerium according to claim 1, wherein the reducing agent is hydrogen peroxide. 4. A solution containing cerium and chromium,
4. The method for recovering cerium according to claim 3, wherein the pH has a range in which tetravalent cerium and hexavalent chromium can be reduced by hydrogen peroxide. 5. A solution containing cerium and chromium,
4. The method for recovering cerium according to claim 3, wherein an acid is supplied to adjust the pH to a range in which tetravalent cerium and hexavalent chromium can be reduced by hydrogen peroxide. 6. The method for recovering cerium according to claim 3, wherein the hydrogen peroxide is supplied only for reducing cerium and chromium contained in the processing solution. 7. The recovery of cerium according to claim 3, wherein the excess is removed after hydrogen peroxide reduces cerium and chromium contained in the processing solution. Method. 8. The method for recovering cerium according to claim 7, wherein the removal of the hydrogen peroxide is performed by supplying a substance reduced by the hydrogen peroxide. 9. The method for recovering cerium according to claim 8, wherein the substance reduced by hydrogen peroxide is a substance containing cerium (IV). 10. The method for recovering cerium according to claim 7, wherein the removal of hydrogen peroxide is performed by supplying a substance oxidized by hydrogen peroxide. 11. The method for recovering cerium according to claim 7, wherein the removal of hydrogen peroxide is performed by self-decomposition of hydrogen peroxide. 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 irradiation. 13. The method according to claim 1, wherein the reducing agent is supplied to the solution containing cerium and chromium while measuring the liquid property of the solution using an electrochemical method.
The method for recovering cerium according to any one of the above. 14. The method for recovering cerium according to claim 2, wherein the increase in the pH of the solution is stopped at a pH of 8 or less. 15. The method for recovering cerium according to claim 2, wherein the increase in the pH of the solution is stopped between pH 5 and pH 7. 16. The method according to claim 2, wherein the pH of the solution is increased by supplying alkali while measuring the liquidity using an electrochemical method or a spectroscopic method. The method for recovering cerium according to any one of the above. 17. The method according to claim 1, wherein an oxidizing agent and an alkali are supplied to the trivalent cerium solution from which chromium has been separated, and the liquid is made alkaline to convert the trivalent cerium to tetravalent cerium. A method for recovering cerium, comprising recovering. 18. The method according to claim 1, wherein after separating the precipitate containing chromium, the separated precipitate containing chromium is
A method for recovering cerium, comprising supplying an alkaline solution to make the solution alkaline, coexisting with an oxidizing agent, converting trivalent cerium to tetravalent cerium, dissolving chromium, and then recovering cerium. 19. The method for recovering cerium according to claim 17, wherein the oxidizing agent is hydrogen peroxide. 20. The solution according to claim 17, wherein the liquid property after the supply of the alkali or the alkali solution is pH 10 or more.
20. The method for recovering cerium according to any one of claims to 19. 21. The liquid property after the supply of an alkali or an alkaline solution is pH 12 or more.
20. The method for recovering cerium according to any one of claims to 19. 22. The cerium according to claim 17, wherein the alkali or the alkali solution is supplied while measuring the liquid property using an electrochemical method or a spectroscopic method. Collection method. 23. The method for recovering cerium according to claim 17, wherein the recovery of cerium is performed by recovering a cerium precipitate by solid-liquid separation. 24. The method according to claim 19, wherein the cerium is recovered by removing cerium hydroxide by solid-liquid separation after removing residual hydrogen peroxide.
24. The method for recovering cerium according to any one of claims to 23. 25. The method according to claim 1, wherein the chromium content in the recovered cerium precipitate or cerium hydroxide becomes a desired amount.
The method for recovering cerium according to any one of claims 17 to 24, wherein the method according to any one of claims 7 to 24 is repeated. 26. The method according to claim 17, wherein the chromium content is analyzed.
26. The method for recovering cerium according to claim 25, wherein it is determined whether the method according to any one of the items 4 needs to be repeated. 27. The method for recovering cerium according to claim 26, wherein the analysis of the chromium content is performed by measuring a liquid property using an electrochemical method or a spectroscopic method. 28. The method for recovering cerium according to claim 24, wherein the removal of the hydrogen peroxide is performed by self-decomposition of the hydrogen peroxide. 29. The method for recovering cerium according to claim 28, wherein the self-decomposition of hydrogen peroxide is promoted by heating, infrared irradiation or ultraviolet irradiation. 30. A method for recovering cerium, comprising recovering the cerium recovered in claim 1 as cerium ammonium nitrate (IV). 31. A method for recovering cerium, wherein the recovered cerium (IV) ammonium nitrate is recovered in a state usable as a chromium etching solution. 32. A chromium etching solution using cerium recovered by the method of claim 1. Description: