JP4992651B2 - Method for producing indium hydroxide - Google Patents

Description

  The present invention relates to a method for producing indium hydroxide. More specifically, the present invention relates to an inexpensive and high-yield production method of indium hydroxide powder having a chlorine concentration of 50 ppm or less, which is optimal for use as an electronic material.

  Indium oxide powder is widely used for electronic materials as a raw material for a conductive material for kneading a resin, a transparent conductive film paint, a target material for producing a transparent conductive thin film, etc. in addition to a conductive filler for resin kneading.

  Since the conductive filler or transparent conductive film paint is used for electronic materials, it is problematic that impurities, particularly halogen elements, are contained. When a halogen element is present, corrosion and elution of a metal used in an electronic device is likely to occur, and deterioration with time is also likely to occur in a resin mixed with indium oxide powder. For these reasons, in recent years, indium hydroxide used for electronic materials is required to have halogen, specifically chlorine, of 50 ppm or less.

  The indium oxide powder is generally obtained by adding an alkali such as ammonia or an aqueous sodium hydroxide solution to an indium salt aqueous solution to neutralize it, crystallizing indium hydroxide, washing it with water, drying and calcining. Since it is difficult to remove halogen elements by calcination, it is necessary to sufficiently reduce the halogen element quality of indium hydroxide before calcination in order to obtain indium oxide powder having sufficiently low halogen element quality. .

  For example, Patent Document 1 describes an ITO (Indium Tin Oxide) powder in which tin is doped into indium oxide, but describes the removal of chlorine which is a halogen element. Decantation of a coprecipitate precipitate (hydroxide) obtained by neutralizing a mixed aqueous solution of indium chloride and tin chloride with an aqueous ammonium carbonate solution until the conductivity of the washing final solution is 200 Ωcm or higher, preferably 5000 Ωcm or higher. Alternatively, ITO powder is obtained by washing with water by centrifugal separation and heat decomposition.

  However, in this method, in order to reduce the amount of residual chlorine to less than 100 ppm, the hydroxide obtained by coprecipitation is washed with water by decantation or centrifugation, and the conductivity of the filtrate is 2000 Ωcm or more, preferably 5000 Ωcm or more. Therefore, the cost of the washing process is expected to increase. Furthermore, although it is said that the chlorine elution amount in distilled water of ITO powder obtained by thermally decomposing the hydroxide is 6 to 44 ppm by mass, more chlorine than the elution amount usually remains in the powder. Therefore, it can be estimated that the chlorine contained in the powder exceeds 50 ppm, and it is difficult to meet the recent demands of the electronic industry.

    For example, Patent Document 2 describes that when an ITO target is produced, sintering is considered to be inhibited if a component that volatilizes in a sintering temperature range, particularly at a temperature exceeding 800 ° C., particularly the presence of a halogen element. Has been shown to be unfavorable and describes the use of indium nitrate which does not contain chlorine or sulfur which inhibits sintering as the starting indium salt. If this method is diverted to the production of indium hydroxide, it is possible to produce low chlorine grade indium hydroxide for electronic materials.

  However, the indium nitrate as a raw material is expensive and the processing cost of nitrate nitrogen that is contained in the waste liquid is high, resulting in an increase in manufacturing cost.

  For this reason, a process using indium chloride as a starting material is preferable rather than a manufacturing process using indium nitrate as a by-product of nitrate nitrogen, but it is oxidized via indium hydroxide using cheap indium chloride as a raw material. When indium is synthesized, chlorine remains, so that there is a problem that it is difficult to use as an electronic material as described above.

  Furthermore, indium hydroxide after washing is recovered by filtration using a centrifugal separator or centrifugal filter. At this time, fine indium hydroxide passes through the mesh of the mesh, resulting in a loss. As the amount of washing and filtration increases, the loss increases in proportion to this, so improvement of the filtration loss is a major issue.

  In Patent Document 3, as a method for improving the filtration loss, fine indium hydroxide is aggregated by adding sodium hydroxide or ammonium hydroxide aqueous solution to the indium solution and adjusting the pH to 7 to 10, that is, near the isoelectric point. And a method of recovering it is described. However, this method has been made for the purpose of improving the recovery rate of indium hydroxide, and there is no disclosure regarding the low chlorine quality of the resulting indium hydroxide.

As described above, in order to obtain low halogen element grade indium hydroxide, it is necessary to use indium nitrate as a raw material, but the cost becomes high. Even when inexpensive indium chloride is used, there is a problem in that the manufacturing cost increases due to the difficulty of removing chlorine.
JP 5-201731 A JP-A-10-182150 JP 2002-201025 A

  The present invention has been made in view of such problems, and provides a method for producing indium hydroxide powder having a residual chlorine quality of 50 ppm or less at low cost even when indium chloride is used as a raw material. Objective.

  In order to achieve the above object, the present inventor conducted research on a method for producing indium hydroxide with low residual chlorine quality using indium chloride as a raw material, and obtained hydroxylation obtained under specific neutralization crystallization conditions. It has been found that indium can be easily removed from chlorine, and that indium hydroxide having a low chlorine quality can be obtained by holding the indium hydroxide in an alkaline solution, leading to the present invention.

That is, in the method for producing indium hydroxide provided by the present invention, an alkaline solution is added to a solution containing indium chloride and neutralized to obtain an indium hydroxide suspension, and then the indium hydroxide is filtered, washed, and washed with low chlorine. In the method for obtaining high grade indium hydroxide, an aqueous ammonia solution is used as the alkaline solution, and the amount of ammonia to be added exceeds 0.8 times in terms of the amount of indium ions in the solution and less than 1.0 times. Thereafter, the pH of the obtained indium hydroxide suspension is controlled to 8.5 to 9.5 , followed by filtration. The obtained indium hydroxide is converted into a basic aqueous solution having a concentration of 0.08 to 1.0 mol / L. dispersing the suspension was kept at least 0.25 hours the suspension liquid temperature of 60 to 100 [° C., filtered and washed it It is an feature. In another preferred embodiment of the present invention, in addition to the above-mentioned invention, the pH of the indium hydroxide suspension obtained by adding an aqueous ammonia solution to the indium solution is controlled to 6 or more at one end, and then the pH is adjusted to 8.5-9. .5 , and then filtered to obtain indium hydroxide.

And another preferable aspect of the present invention includes, in addition to the above aspect,
The obtained indium hydroxide is dried and then washed with water. In another preferred embodiment of the present invention, the obtained indium hydroxide is dried and mixed with an ammonium nitrate solution to obtain a suspension, and the pH of the suspension is adjusted to 8.0 to 10.0 prior to filtration. Thereafter, filtration is performed to obtain indium hydroxide, and the obtained indium hydroxide is further washed with water.

According to the present invention, low chlorine grade indium hydroxide suitable for electronic materials, particularly for target materials and materials for producing transparent conductive thin films can be obtained efficiently and at low cost . Indium oxide obtained by calcining indium hydroxide obtained according to the present invention meets the recent demands of the electronic industry and has an extremely high industrial value.

  The indium hydroxide production method provided by the present invention will be described in detail.

  In the production method of the present invention, an aqueous solution containing indium chloride is used to obtain indium hydroxide by neutralization by adding an alkaline solution, and an aqueous ammonia solution is used as the alkaline solution, and the added ammonia is equivalent to the indium ions. Is over 0.8 times and less than 1.0 times.

  A sodium hydroxide solution or a potassium hydroxide solution can be used as the alkaline solution. However, when these solutions are added in an amount less than 1.0 times equivalent to the indium ions, the indium ions in the solution are completely removed. The neutralized crystallization does not occur, and the yield of indium hydroxide is deteriorated.

  Although it is possible to completely neutralize and crystallize indium ions by adding 1.0 times or more sodium hydroxide or potassium hydroxide in equivalent to indium ions, the pH after neutralization is high, Since the deposited indium hydroxide is fine, the filtration loss increases because it passes through the eyes of the filter cloth. In addition, fine indium hydroxide has poor filterability, and the filtration time is significantly increased.

By using an aqueous ammonia solution as the alkali, the indium ions in the aqueous solution can be completely neutralized and crystallized even if the amount of ammonia added is less than 1.0 times equivalent to the indium ions. It is considered that when an aqueous ammonia solution is used, a part of indium hydroxide crystallizes in the form of In (OH) ₂ .

  Although there is no particular problem with neutralization crystallization of indium hydroxide even if the amount of ammonia added is 1.0 times or more equivalent, the pH after neutralization is high, the crystals of indium hydroxide are fine, and the filtration loss As the amount increases, the filterability deteriorates.

On the other hand, even if the amount of ammonia to be added is 0.8 times or less in terms of equivalent, indium ions in the aqueous solution can be neutralized and crystallized, but chlorine in indium hydroxide cannot be sufficiently reduced. In the production method of the present invention, indium chloride is used as a raw material, and chlorine is reduced by washing with water, aging and the like after being in the form of ammonium chloride (NH ₄ Cl). Therefore, if the amount of ammonia added is too small, chlorine in indium hydroxide cannot be reduced sufficiently.

  The amount of ammonia added for neutralization is more preferably 0.85 to 0.95 times as an equivalent.

Usually, if the amount of ammonia added exceeds 0.8 times in terms of equivalent to indium ions, the pH of the resulting indium hydroxide suspension will be on the alkali side, but depending on the raw materials used, the pH may be less than 6. is there. In such a case, it is preferable that the pH of the indium hydroxide suspension is 6 or more. This is because if the pH is less than 6, indium hydroxide cannot be sufficiently crystallized and the yield may deteriorate. In the present invention, the pH of the indium hydroxide suspension is controlled to 8.5 to 9.5 before filtering indium hydroxide from the indium hydroxide suspension.

  By controlling the pH of the indium hydroxide suspension obtained by adding the aqueous ammonia solution to 8.0 to 10, the indium hydroxide in the suspension is agglomerated to greatly improve the filtration loss and filterability. It is. If the pH of the indium hydroxide suspension is less than 8.0 or exceeds 10, the effect of improving the filtration loss and filterability may not be sufficient. Aggregation of indium hydroxide occurs most in the vicinity of the isoelectric point (pH 8.8) of indium hydroxide, so that the pH is more preferably controlled to 8.5 to 9.5.

  For controlling the pH, it is preferable to use ammonia or nitric acid. Although hydrochloric acid or sulfuric acid can be used instead of nitric acid, when hydrochloric acid or sulfuric acid is used, chlorine or sulfur remains in the resulting indium hydroxide, which is not suitable for electronic materials. In particular, when used as a target material for producing a transparent conductive thin film, the sinterability is hindered and a high-density target cannot be obtained.

  By using nitric acid, it is possible to prevent harmful elements such as chlorine or sulfur from remaining in indium hydroxide, but as the use of nitric acid increases, nitrate nitrogen is produced as a by-product in the waste liquid, resulting in higher wastewater treatment costs. Therefore, it is preferable to reduce the amount of nitric acid used as much as possible. For this reason, in the present invention, the equivalent of the base of the aqueous ammonia solution used for neutralization is 1.0 times or less with respect to indium ions so that the pH does not become higher than necessary.

As a preferred embodiment of the present invention, when washing indium hydroxide obtained by the above-described method, indium hydroxide is dispersed in an aqueous ammonia solution having a concentration of 0.08 to 1.0 mol / L to form a suspension. It is preferable to maintain the liquid temperature at 100 ° C. for at least 0.25 hours and then filter and wash the resulting indium hydroxide with water. .
When the ammonia water concentration is less than 0.08 mol / L, the amount of chlorine remaining in the indium hydroxide may not be sufficiently reduced. There is no problem even if the concentration of the basic aqueous solution exceeds 1.0 mol / L, but the effect of removing chlorine is not increased and only the cost is increased.

The liquid temperature of the suspension in this washing is preferably maintained at 60 to 100 ° C. When the liquid temperature is lower than 60 ° C., the amount of chlorine remaining in indium hydroxide may not be sufficiently reduced. More preferably, it is kept at 80 ° C. or higher. In addition, when the liquid temperature exceeds 100 ° C., the amount of chlorine cannot be reduced sufficiently because the diffusion of ammonia becomes violent and the handling risk increases, and the base component concentration decreases. There is. Moreover, even if it exceeds 100 degreeC, the effect of chlorine removal does not become large.
It is possible to use an aqueous solution of sodium hydroxide, an aqueous solution of potassium hydroxide or the like in place of the aqueous ammonia solution, but the chlorine removal effect is inferior to the case of using an aqueous ammonia solution, and the impurities in the resulting indium hydroxide may increase. There is also.
The reason for maintaining the temperature at 60 to 100 ° C. for 0.25 hours is to obtain a better chlorine removal effect. When the suspension is stirred during this holding, a higher dechlorination effect is obtained as compared with the case where the suspension is left standing. When the suspension is stirred by rotation, the rotation speed is preferably 200 rpm or more, more preferably 300 rpm or more, and further preferably 400 rpm or more.
The suspension thus obtained was filtered, and the resulting indium hydroxide cake was redispersed in water to form a suspension, which was then stirred and washed, and filtered to obtain indium hydroxide. It can be further reduced. And if the obtained indium hydroxide is further washed with water, the chlorine quality can be further reduced.
In order to further lower the chlorine quality in indium hydroxide obtained by washing with an aqueous ammonia solution, the following washing is more efficient than washing with indium hydroxide. That is, it is effective to dry the obtained indium hydroxide cake, then mix the dried product and water, create a suspension again, and filter. It seems that chlorine can be effectively removed by adding dry enough to re-wash water into the indium hydroxide powder.

  At this time, it is preferable to prepare a suspension again using an ammonium nitrate solution rather than water. In particular, it is more preferable to form a suspension again using an aqueous ammonium nitrate solution and control the pH to 8.0 to 10.0, followed by filtration. preferable. The concentration of the ammonium nitrate aqueous solution may be 0.0001 to 0.01 mol / L.

  The amount of liquid used for water washing or suspension is not particularly limited, and may be a liquid amount that is normally used. However, a liquid amount that can sufficiently absorb chlorine and can be sufficiently stirred is required. Decide it in consideration of the amount.

  The amount of residual chlorine in the indium hydroxide obtained as described above is as low as 40 ppm by mass or less, and the indium oxide powder obtained by calcining this is suitable for electronic materials.

[Example 1]
Neutralization was carried out by adding 0.9 times the equivalent amount using 50 ml of 0.88 mol / l (about 100 g / l) indium chloride aqueous solution as a raw material and an aqueous ammonium solution as a base. While stirring an indium chloride aqueous solution as a raw material at 300 rpm, a 25% ammonium aqueous solution was added thereto at a rate of 2.5 ml / min to obtain an indium hydroxide suspension.
When the pH of this indium hydroxide suspension was measured, it was 9.21 when the liquid temperature was 25 ° C., and it was usually 9.3 to 9. pH when neutralization was performed with an equivalent of 1.0 times the base. The pH was slightly lower than about 4. When nitric acid was added to this indium hydroxide suspension and the pH was adjusted to 8.8, which is the isoelectric point of indium hydroxide, the amount of nitric acid used was 2.7 ml. After adjusting the pH, the suspension was filtered to obtain indium hydroxide, but the filterability was good.

  When the concentration of indium in the filtrate was measured, it was less than 0.01 g / L, and the yield of indium was 99.9% or more. Despite the added base equivalent of 0.9 times, almost all of the indium content in the aqueous solution could be recovered as indium hydroxide.

The total amount of indium hydroxide obtained by filtration was dispersed in 112 ml of pure water, washed with water for 60 minutes while stirring, and the total amount of indium hydroxide obtained by filtration was dispersed in 112 ml of aqueous ammonia solution having a concentration of 0.2 M / L. The suspension was made into a suspension, and allowed to stand for 120 minutes in an air dryer heated to 80 ° C. The suspended suspension was filtered to obtain indium hydroxide. This indium hydroxide was dispersed again in 112 ml of pure water, washed with water for 60 minutes with stirring, filtered again to obtain indium hydroxide, and this was heated to 80 ° C. Drying was performed using an air dryer.
Next, the entire amount of dried indium hydroxide was dispersed in 112 ml of 0.001 M / L ammonium nitrate aqueous solution, pH was adjusted to 8, washed with ammonium nitrate aqueous solution for 60 minutes with stirring, and filtered. The obtained indium hydroxide was dispersed in 112 ml of pure water, washed with water for 60 minutes while stirring, filtered again, and dried in a drier heated to 80 ° C. When the chlorine quality in the obtained indium hydroxide was measured, it was 22 mass ppm.
The amount of residual chlorine in indium hydroxide is obtained by dissolving the obtained indium hydroxide with nitric acid, adding silver nitrate to precipitate silver chloride, and measuring the chlorine in the precipitate by fluorescent X-ray quantitative analysis (PnNalytical). The amount of residual chlorine was determined by measurement with Magix).
[Example 2]
An indium hydroxide suspension was obtained in the same manner as in Example 1 except that the equivalent amount of added ammonia was 0.85 times. When the pH of this indium hydroxide suspension was measured, it was 9.04 at a liquid temperature of 25 ° C., which was a pH lower than that of Example 1. When nitric acid was added to this indium hydroxide suspension and the pH was adjusted to 8.8, which is the isoelectric point of indium hydroxide, the amount of nitric acid used was 1.3 ml, which is smaller than in Example 1, and the suspension was adjusted after pH adjustment. Was filtered to obtain indium hydroxide, but the filterability was also good.

  When the concentration of indium in the filtrate was measured, it was less than 0.01 g / L, and even when the equivalent of the base was 0.85 times, almost the entire amount of indium in the aqueous solution could be recovered as indium hydroxide.

When the above indium hydroxide was dechlorinated in the same manner as in Example 1, the chlorine quality in the obtained indium hydroxide was 13 mass ppm.

Although almost all of the indium content in the aqueous solution could be recovered as indium hydroxide, the amount of nitric acid used was 3.2 ml, and it was necessary to use more nitric acid than in Example 1.
[Comparative Example 2]
An indium hydroxide suspension was obtained in the same manner as in Example 1 except that the equivalent amount of added ammonia was 0.8 times. When the pH of this indium hydroxide suspension was measured, it was 8.44 at a liquid temperature of 25 ° C. In order to adjust the pH of this indium hydroxide suspension to 8.8, which is the isoelectric point of indium hydroxide, a small amount of sodium hydroxide solution was added, and nitric acid was not used. When the suspension was filtered after pH adjustment to obtain indium hydroxide, the filterability was good.

  When the indium concentration in the filtrate was measured, it was less than 0.01 g / L, and the yield of indium was 99.9% or more. Even when the base equivalent was 0.8 times, almost all of the indium content in the aqueous solution could be recovered as indium hydroxide.

When the indium hydroxide was washed in the same manner as in Example 1, the chlorine quality in the obtained indium hydroxide was 63 ppm by mass , which was significantly higher than that of the example and was not preferable for electronic materials. became.
It can be seen that indium hydroxide can be recovered even if the base equivalent during neutralization is reduced to 0.8 times, but low chlorine grade indium hydroxide cannot be obtained.

Claims (4)

In the method of adding an alkaline solution to a solution containing indium chloride and neutralizing to obtain an indium hydroxide suspension, and then filtering and washing the indium hydroxide to obtain a low chlorine grade indium hydroxide, the alkaline solution Using an aqueous ammonia solution, the amount of ammonia to be added is more than 0.8 times and less than 1.0 times in terms of the amount of indium ions in the solution, and then the pH of the resulting indium hydroxide suspension is adjusted. filtered after controlling the 8.5-9.5, the resulting indium hydroxide concentration 0.08~1.0mol / L basic aqueous solution is dispersed in as a suspension, of the suspension 60 to 100 [° C. A method for producing indium hydroxide, characterized by holding at a liquid temperature for at least 0.25 hours, followed by filtration and washing. After controlling the pH of the indium hydroxide suspension obtained by adding an aqueous ammonia solution to the indium solution to 6 or more at one end, the pH is controlled to 8.5 to 9.5 , and then filtered, washed, and washed with low chlorine quality. The method for producing indium hydroxide according to claim 1, wherein indium hydroxide is obtained. 3. The method for producing indium hydroxide according to claim 1 , wherein the indium hydroxide obtained is dried and then washed with water. In the invention according to claim 1 or 2 , the cleaning method comprises drying the obtained indium hydroxide and mixing it with an ammonium nitrate solution to obtain a suspension, and adjusting the pH of the suspension to 8.0 to 10.0 prior to filtration. And then filtering off to obtain indium hydroxide, and further washing the obtained indium hydroxide with water.