JP2012121750A - Powder containing indium oxide as major component, and method for producing the same - Google Patents

Abstract

Disclosed is a powder containing indium oxide having a low chlorine quality as a main component, which does not require waste liquid treatment and is provided efficiently and at low cost.
An indium chloride aqueous solution and an aqueous solution using an alkali metal hydroxide salt are mixed from the start to the end of mixing while maintaining a liquid temperature of less than 50 ° C. and a pH of 8 or more. An indium hydroxide is produced by using a carboxylic acid having a complex formation constant with indium ions of more than 2.37 and less than 19.43 and containing no amino group, and carboxylic acid concentration Was crystallized in the aqueous solution while maintaining the pH of the aqueous solution adjusted to 0.1 mol / L or more and 0.5 mol / L or less using an aqueous solution using an alkali metal hydroxide salt. Indium hydroxide is dispersed and held at a liquid temperature of 40 ° C. to 90 ° C. for 30 minutes or more, followed by filtration. The obtained powder is subjected to water washing and calcination treatment.
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Description

  The present invention relates to a powder containing indium oxide as a main component and a method for producing the same, and more particularly to the powder using indium chloride or a metal salt containing indium chloride as a main component as a starting material and a method for producing the same.

  A powder containing indium oxide as a main component (indium oxide powder or a powder containing indium oxide as a main component and containing other metal or metal oxide) is used as a conductive filler for resin kneading using its conductivity. In addition, it is widely used in applications of electronic materials as raw materials for transparent conductive film paints and target materials for producing transparent conductive thin films.

  The indium oxide powder is neutralized by adding a basic aqueous solution such as an aqueous ammonia solution or an aqueous sodium hydroxide solution to an indium salt aqueous solution to crystallize indium hydroxide, and the resulting indium hydroxide is washed with water. And dried and calcined.

  Since the conductive filler or the transparent conductive film paint is used for applications of electronic materials, it is problematic that impurities, particularly halogen elements, are contained. When a halogen element is present, there is a problem that corrosion or elution of a metal used in an electronic device tends to occur, and a resin mixed with indium oxide powder easily deteriorates with time.

  For such a problem, for example, Patent Document 1 (Japanese Patent Laid-Open No. 5-201731) describes the removal of chlorine as a halogen element in indium tin oxide (ITO) powder in which tin is doped into indium oxide. Has been. According to this, an ITO powder can be obtained by washing a coprecipitate precipitate obtained by neutralizing a mixed aqueous solution of indium chloride and tin chloride with an alkaline aqueous solution by decantation or centrifugal separation, and thermally decomposing the precipitate. Proposed.

  However, in order to make the chlorine quality of the ITO powder less than 100 ppm by mass, it is necessary to perform water washing by decantation or centrifugation until the electrical resistivity reaches 2000Ω · cm or more, preferably 5000Ω · cm or more. Yes, such water washing is expected to increase the cost of the process. Patent Document 1 describes that the amount of residual chlorine in the ITO powder is determined based on the eluted chlorine in distilled water, and the amount of chlorine in the obtained ITO powder is 6 to 390 mass ppm according to the eluted component analysis. Has been. However, normally, more chlorine than the eluate remains in the powder, so it is difficult to say that the residual chlorine in the powder is sufficiently removed.

  Patent Document 2 (Japanese Patent Application Laid-Open No. 2009-1114013) states that the liquid temperature at the time of mixing is less than 50 ° C., the pH is maintained at 8 or more, and the pH at the end of mixing is 11 to 14. In addition, a metal salt containing indium chloride as a main component is added to a basic aqueous solution such as an aqueous ammonia solution to crystallize indium hydroxide, and the obtained indium hydroxide is dispersed in an aqueous ammonia solution of 0.08 mol / L or more. Thus, it has been proposed to obtain indium oxide having a low residual chlorine concentration by filtering the suspension after maintaining the suspension at a liquid temperature of 60 ° C. to 100 ° C. However, since an aqueous ammonia solution is used in this technique, the waste liquid contains a nitrogen component, and a cost for keeping the emission standard is required.

  In a target material for producing a transparent conductive thin film typified by ITO powder, the presence of a halogen element is said to inhibit the sinterability. For example, Patent Document 3 (Japanese Patent Laid-Open No. 10-182150) describes that when halogen elements such as chlorine remain, sintering is inhibited at a sintering temperature range, particularly at a temperature exceeding 800 ° C. Has been. For this reason, in Patent Document 3, by using indium nitrate that does not contain chlorine or sulfur and that leaves only nitrate ions that decompose at a relatively low temperature as a starting material, it is possible to eliminate a factor that inhibits sinterability. Proposed.

  However, indium nitrate as a starting material is more expensive than indium chloride, and the manufacturing cost is increased. Moreover, since nitric acid contains nitrogen, nitrate nitrogen is contained in a waste liquid, and the waste liquid processing cost will be expensive. Therefore, considering the entire production cost including waste liquid treatment, it can be said that a manufacturing process using indium chloride as a starting material is more desirable than a manufacturing process using indium nitrate as a starting material.

Thus, from the viewpoint of production cost, when indium oxide is synthesized using indium chloride as a starting material, chlorine remains in the obtained indium oxide, making it difficult to use it for electronic materials. On the other hand, when residual chlorine is removed, there is also a problem that the manufacturing cost increases due to the difficulty of removing chlorine. On the other hand, when indium nitrate is used as an alternative material that does not generate residual chlorine, a problem of waste liquid treatment occurs, and similarly, a problem arises in terms of manufacturing cost. Therefore, there is a demand for means capable of suppressing residual chlorine in indium oxide while eliminating the influence that leads to high costs such as waste liquid treatment.
Japanese Patent Laid-Open No. 5-201731 JP 2009-1114013 A JP-A-10-182150

  The object of the present invention has been made in view of such problems, and even when indium chloride or a metal salt containing indium chloride as a main component is used as a starting material, oxidation with low chlorine quality is achieved. An object of the present invention is to provide a production method in which powder containing indium as a main component can be obtained efficiently and at low cost without requiring waste liquid treatment.

  The present inventor established a method for producing a powder containing indium oxide having a low chlorine quality as a main component by using indium chloride or a metal salt containing indium chloride as a main component as a starting material. In order to reduce the nitrogen content, research and development was conducted intensively.

  As a result, an aqueous solution containing a metal salt mainly composed of indium chloride or indium chloride and an aqueous solution using an alkali metal hydroxide salt are controlled at a specific temperature and pH, and indium hydroxide is obtained. Alternatively, indium oxide with low chlorine quality is obtained by crystallization of indium composite hydroxide and washing the resulting indium hydroxide or indium composite hydroxide with an aqueous solution using a carboxylic acid not containing a specific amino group. As a result, the inventors have obtained the knowledge that the nitrogen content in the waste liquid in the crystallization step and the washing step can be reduced, and the present invention has been completed.

  In the method for producing a powder mainly composed of indium oxide according to the present invention, first, an aqueous solution containing indium chloride or an aqueous solution containing a metal salt mainly composed of indium chloride and an alkali metal hydroxide salt are used. Indium hydroxide or indium composite hydroxide by mixing the aqueous solution with the aqueous solution from the start of mixing to the end of mixing while maintaining the liquid temperature at less than 50 ° C. and maintaining the pH at 8 or more. Is generated.

  Next, a carboxylic acid having a complex formation constant with indium ions of more than 2.37 and less than 19.43 and containing no amino group is used, and the carboxylic acid concentration is 0.1 mol / L or more and 0.5 mol. The aqueous solution adjusted to / L or lower is dispersed in the aqueous solution containing the crystallized indium hydroxide or indium composite hydroxide while maintaining the pH at 8 or higher using an aqueous solution using an alkali metal hydroxide salt. And holding at a liquid temperature of 40 ° C. to 90 ° C. for 30 minutes or more, and then filtering to obtain a powder.

  And the powder which has indium oxide as a main component as a product is obtained by performing the process of water washing and calcination to this powder.

  As an aqueous solution using the alkali metal hydroxide salt, an aqueous potassium hydroxide solution, an aqueous sodium hydroxide solution, or a mixed aqueous solution is preferably used.

  Examples of the carboxylic acid having a complex formation constant with the indium ion of more than 2.37 and less than 19.43 and not containing an amino group may include lactic acid, acetic acid, and malonic acid. It is preferable to use a mixture of two or more.

  By the production method of the present invention, it is possible to obtain a powder mainly composed of indium oxide having a residual chlorine quality of 50 mass ppm or less.

  According to the present invention, even when indium chloride or a metal salt containing indium chloride as a main component is used as a starting material, in any of the crystallization step and the washing step, a nitrogen component is contained in a waste solution such as an aqueous ammonia solution. Without using a material that brings about the above, a powder mainly composed of indium oxide having a low chlorine quality can be obtained efficiently and at low cost.

  A powder containing indium oxide as a main component and a method for producing the powder mainly include a crystallization step, a cleaning step, and a calcination step. Hereinafter, the manufacturing method of the powder which has indium oxide as a main component which concerns on this invention is demonstrated in detail.

(1) Crystallization process An indium chloride aqueous solution or an aqueous solution containing a metal salt containing indium chloride as a main component and an aqueous solution using an alkali metal hydroxide salt are kept at a liquid temperature of less than 50 ° C. and a pH of 8 or more. Mix while mixing. As the indium chloride aqueous solution, a commercially available product or a solution prepared by dissolving indium metal in a hydrochloric acid aqueous solution can be used.

  Liquid temperature when mixing an aqueous solution of indium chloride or an aqueous solution containing a metal salt containing indium chloride as a main component with an aqueous solution of an alkali metal hydroxide salt, that is, from the start of mixing to the end of mixing It is necessary to maintain the liquid temperature up to 50 ° C.

  When the liquid temperature is 50 ° C. or higher, the crystallized particles of indium hydroxide or indium composite hydroxide are aggregated. In this case, chlorine is present inside the particles of aggregated indium hydroxide and the like. However, since chlorine existing in the inside is difficult to be removed by subsequent water washing, indium hydroxide is present. More chlorine will remain in the powder. The liquid temperature at the time of mixing is not a problem as long as it is equal to or higher than the freezing point.

  Moreover, it is necessary to maintain the pH from the start of mixing to the end of mixing in the mixed solution of 8 or more, preferably in the range of 9-14. In general, the surface potential of crystallized indium hydroxide becomes 0 when the pH is 8 to 9, and becomes positive when the pH is lower than that, and becomes negative when the pH is higher than that. When the pH in the crystallization reaction is less than 8, the surface potential of the crystallized particles such as indium hydroxide is positively charged, and chloride ions having a negative charge are adsorbed on the particle surface.

Furthermore, when the pH is less than 8, the concentration of hydroxide ions contributing to the crystallization reaction decreases, so that the crystallization reaction does not proceed sufficiently. For this reason, some of the particles, such as indium hydroxide that crystallize, grow while taking in the adsorbed chloride ions, resulting in a structure in which chlorine is mixed like In (Cl _n (OH) _3-n ). It becomes. In this case, since it becomes difficult to remove chlorine by subsequent cleaning, a large amount of chlorine remains in the powder such as indium hydroxide.

  In the present invention, the pH of the mixed solution needs to be 8 or more from the start of mixing to the end of mixing. For example, when an indium chloride aqueous solution or an aqueous solution containing a metal salt containing indium chloride as a main component and an aqueous solution using an alkali metal hydroxide salt are directly put into a reaction vessel at the same time and mixed, There is a possibility that a region where the pH becomes less than 8 is partially generated due to uneven mixing. In this way, when the pH is partially less than 8, chlorine remains in the particles in the region, and the final chlorine residual amount may not be 50 ppm or less.

  In addition, when an aqueous solution containing an alkali metal hydroxide salt is added to an indium chloride aqueous solution or an aqueous solution containing a metal salt containing indium chloride as a main component, an indium chloride aqueous solution or a chloride Since the pH of the aqueous solution containing the metal salt containing indium as a main component is acidic, the pH may be less than 8 during the mixing process. Thus, in the mixing step, when the pH is partially or temporarily less than 8, the residual amount of chlorine increases.

  Therefore, in the step of crystallizing indium hydroxide or indium composite hydroxide, it is necessary to control the pH to 8 or more from the start of mixing to the end of mixing. As a method for maintaining the pH of the mixed solution at 8 or more from the start to the end of the mixing, an indium chloride aqueous solution, an aqueous solution containing a metal salt containing indium chloride as a main component, and an alkali metal hydroxide salt are used. An aqueous solution containing a relatively large amount of an alkali metal hydroxide salt and an aqueous solution containing an indium chloride aqueous solution or a metal salt containing indium chloride as a main component when mixing with an aqueous solution using Is added little by little. Thereby, pH can be stably controlled to 8 or more. However, when there is a means that can prevent the pH from becoming less than 8 during the mixing process, the present invention is not limited to this.

  There is no problem as long as the pH is 8 or more, but the pH is preferably 14 or less. Even if the pH exceeds 14, the effect of removing chlorine is not increased, and not only the indium yield deteriorates due to re-dissolution of indium hydroxide, but also the amount of aqueous solution using a necessary alkali metal hydroxide salt. However, since it increases further, it becomes disadvantageous also in cost.

  In order to maintain pH at 8 or more, when adding an aqueous solution containing an indium chloride aqueous solution or a metal salt containing indium chloride as a main component to an aqueous solution using an alkali metal hydroxide salt, At the same time, an aqueous solution of a basic substance that is not a salt containing nitrogen such as ammonia or an amine compound may be added. Thereby, the fall of pH by addition of the aqueous solution containing indium chloride aqueous solution or the metal salt which has indium chloride as a main component can be suppressed, and it can be ensured that pH is maintained at 8 or more.

  The aqueous solution using the alkali metal hydroxide salt is preferably added in an equivalent amount or more. By adding an indium chloride aqueous solution or an aqueous solution containing a metal salt containing indium chloride as a main component to an aqueous solution using an alkali metal hydroxide salt of an equivalent amount or more, the pH is adjusted in a region where mixing occurs. It can be ensured that the value is maintained at 8 or more.

  The aqueous solution using an alkali metal hydroxide salt is not particularly limited as long as it can crystallize indium hydroxide or indium composite hydroxide, but from the viewpoint of cost, sodium hydroxide aqueous solution, potassium hydroxide aqueous solution. , And a mixed aqueous solution thereof are preferably used. Similarly, as the basic substance applicable to the present invention, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, and a mixture thereof can be used.

  By using an aqueous solution using an alkali metal hydroxide salt instead of a basic solution containing a nitrogen source such as ammonia water, the possibility that a nitrogen component is contained in the waste liquid can be eliminated. Alkali metal hydroxide salts are strongly alkaline substances, and dissociate completely in aqueous solution to produce hydroxide ions. Therefore, the minimum amount of addition produces sufficient and sufficient hydroxide ions. Therefore, an aqueous solution with a high pH can be obtained at a low cost, and the pH during crystallization can be easily maintained at 8 or more.

(2) Cleaning process
The indium hydroxide or indium composite oxide powder obtained in the crystallization step is dispersed in an aqueous carboxylic acid solution containing no amino group and having a pH of 8 or higher. The carboxylic acid to be used needs to contain no amino group in the composition and have a complex formation constant with indium ions of more than 2.37 and less than 19.43.

  The reason why the complex formation constant with indium ions needs to exceed 2.37 is that the complex formation constant between indium ions and chloride ions is 2.37, whereas the complex formation constant with indium ions. Is less than 19.43 because the complex formation constant between indium ions and hydroxide ions is 19.43.

  Chlorine remaining in particles such as indium hydroxide remains in a form partially incorporated into the composition as described above. By washing this with an aqueous carboxylic acid solution having a complex formation constant with indium ions of more than 2.37, chloride ions bonded to indium are replaced with carboxylate ions having a larger complex formation constant, As a result, indium-carboxylic acid complex ion formation and chloride ion separation occur. Furthermore, the carboxylate ions bonded to indium are replaced by hydroxide ions having a larger complex formation constant, resulting in indium-hydroxide complex ion formation and separation of the carboxylate ions.

  When a carboxylic acid having a complex formation constant with indium ions of 2.37 or less is used, the above-described substitution between chlorine and carboxylic acid is difficult to occur, and the residual amount of chlorine is not reduced. On the other hand, when a carboxylic acid having a complex formation constant with indium ions of 19.43 or more is used, the generated indium-carboxylic acid complex ions are in a stable state. As a result, the crystallized particles such as indium hydroxide are re-dissolved, and the yield of particles such as indium hydroxide is reduced. From the viewpoint of reaction stability, the complex formation constant with indium ions is preferably 3.0 or more and less than 15.0.

  Examples of such carboxylic acids include lactic acid, acetic acid, malonic acid (complex formation constants with indium ions are 5.74, 3.18, and 10.13, respectively). Since the carboxylic acid aqueous solution containing no amino group does not contain a nitrogen component, the waste liquid treatment after use becomes easy. On the other hand, carboxylic acids such as citric acid and succinic acid are unsuitable for use in the present invention because their complex formation constants with indium ions exceed 21.02, 26.00 and 19.43.

  At the same time, the pH of the aqueous carboxylic acid solution containing no amino group must be 8 or higher. When the pH is 8 or more, the carboxylate ions in the indium-carboxylic acid complex ions described above can be replaced with hydroxide ions. In addition, resorption of chloride ions can be suppressed by negatively charging the surface potential of particles such as indium hydroxide. For this reason, indium hydroxide or indium composite hydroxide with a small amount of residual chlorine can be produced. If the pH is below 8, the concentration of hydroxide ions in the aqueous solution is not sufficient to produce indium hydroxide and the like, reducing the yield of particles such as indium hydroxide. In addition, since the surface potential of particles such as indium hydroxide is positively charged, re-adsorption of separated chloride ions occurs. If the pH is 8 or more, there is no problem, but from the viewpoint of the stability of the reaction, the pH is preferably in the range of 9-14.

  The concentration of the carboxylic acid containing no amino group needs to be 0.1 mol / L or more and 0.5 mol / L or less. If the concentration is less than 0.1 mol / L, the cleaning effect is insufficient because the concentration is low. If it exceeds 0.5 mol / L, the cleaning effect is not affected, but the cost increases. In addition, from the viewpoint of cleaning efficiency, it is preferably 0.2 mol / L or more and 0.5 mol / L or less.

  In addition, a suspension obtained by dispersing a powder of indium hydroxide or the like in a carboxylic acid aqueous solution not containing an amino group needs to be maintained at a liquid temperature of 40 to 90 ° C. When the liquid temperature is lower than 40 ° C., the substitution reaction between chlorine and carboxylic acid does not proceed sufficiently, and chlorine remaining in the powder such as indium hydroxide cannot be sufficiently reduced. On the other hand, if the liquid temperature exceeds 90 ° C., the energy cost for maintaining the temperature increases, which is not appropriate. The suspension holding time is 30 minutes or more. When the retention time is less than 30 minutes, the substitution of chlorine and carboxylic acid does not proceed sufficiently, and it may not be sufficient to reduce chlorine. More preferably, it is held for 1 hour or longer in order to stably reduce chlorine. Similarly, from the viewpoint of reaction efficiency, it is preferable that the liquid temperature is maintained in the range of 60 ° C. to 80 ° C. and the retention time is 3 hours or less.

  Thereafter, the suspension is filtered, washed with pure water at room temperature for 15 minutes or more, and the washed indium hydroxide and the like are filtered to remove excess impurities, followed by drying and calcination. Despite this cleaning, even if the carboxylic acid used for the cleaning in the previous step remains in indium hydroxide or the like, there is no problem because it is decomposed and removed as carbon dioxide during drying and calcining.

(3) Calcination process The calcination temperature is preferably a temperature usually used, and preferably 700 to 1200 ° C. If it is less than 700 degreeC, the conversion from a hydroxide to an oxide may not be enough, and if it exceeds 1200 degreeC, an indium oxide may sinter. The atmosphere at the time of calcination is not particularly limited, but is preferably an oxidizing atmosphere, and more preferably an air atmosphere from the viewpoint of cost. The feature of the present invention lies in the crystallization process and the cleaning process, and is not limited by the calcination process. Indium oxide or indium composite oxide is appropriately converted from indium hydroxide or indium composite hydroxide. Any method can be used without being limited to the above conditions.

  The powder mainly composed of indium oxide obtained as described above has little residual chlorine and is 50 mass ppm or less, which is suitable for use as an electronic material. Residual chlorine is measured by a turbidimetric method after dissolving the calcined indium oxide powder or indium composite oxide with nitric acid and adding silver nitrate. Thereby, the chlorine quality can be measured in a form including not only chlorine existing on the surface but also chlorine existing inside the powder.

  Furthermore, in the present invention, there is no chemical solution containing nitrogen components such as nitric acid, aqueous ammonia, ammonium salts such as ammonium nitrate, amines, etc. in the aqueous solution used, and nitrogen components are contained in the effluent of the crystallization process and cleaning process. In principle, the environmental standard for the nitrogen content of the waste liquid (nitrogen content: 0.12 g / L or less) can be easily achieved.

Example 1
A 25% aqueous sodium hydroxide solution (pH 13.6) prepared by dissolving 32 g of sodium hydroxide (manufactured by Kanto Chemical Co., Ltd., reagent grade) in 100 ml of pure water was maintained at a liquid temperature of 35 ° C. and a stirring speed of 400 rpm. In this state, 0.6 mol / in prepared by dissolving indium metal (manufactured by Kojundo Chemical Laboratory Co., Ltd.) in 36% hydrochloric acid (manufactured by Kanto Chemical Co., Ltd., reagent grade) and diluting with pure water. 100 ml of L indium chloride aqueous solution (pH-0.2) was added at a rate of 5 ml / min to crystallize indium hydroxide. The pH of the solution in the vicinity of the crystallization reaction was maintained at 12 or more, and the pH of the solution at the end of crystallization was 13.1.

  After filtering the solution and washing the resulting indium hydroxide powder with pure water, lactic acid (manufactured by Kanto Chemical Co., Inc., reagent grade, complex formation constant with indium ions: 5.74) was diluted in pure water. Then, this powder was dispersed in 500 ml of 0.5 mol / L lactic acid aqueous solution adjusted to pH 13.0 using sodium hydroxide to obtain a suspension. Thereafter, the obtained suspension was held at 80 ° C. for 2 hours with stirring, then filtered, washed with pure water, and dried to obtain indium hydroxide powder.

  Furthermore, indium oxide powder was obtained by calcining the obtained indium hydroxide powder at 800 ° C. for 5 hours in an air atmosphere.

  The indium recovery rate with respect to the obtained indium oxide powder was 99%, and the residual chlorine concentration in the powder was 40 mass ppm as measured using a turbidimetric method. In addition, the nitrogen content in the waste liquid generated in the crystallization process and the washing process was measured using a pack test (manufactured by Kyoritsu Riken Laboratories Co., Ltd.). No nitrogen component was detected, and no nitrogen treatment was required. It was.

(Example 2)
Indium hydroxide was crystallized in the same manner as in Example 1. After washing the obtained indium hydroxide powder with pure water, acetic acid (manufactured by Kanto Chemical Co., Inc., reagent grade, complex formation constant with indium ions: 3.18) is diluted in pure water, and sodium hydroxide is used. A suspension was obtained by dispersing this powder in 500 ml of a 0.3 mol / L acetic acid aqueous solution adjusted to pH 12.5. Thereafter, the obtained suspension was kept at 70 ° C. for 2 hours with stirring, then filtered, washed with pure water, and dried to obtain indium hydroxide powder.

  Furthermore, indium oxide powder was obtained by calcining the obtained indium hydroxide powder at 800 ° C. for 5 hours in an air atmosphere.

  The indium recovery rate with respect to the obtained indium oxide powder was 98%, and the residual chlorine concentration in the powder was 45 ppm by mass. Moreover, when the nitrogen content in the waste liquid produced in the crystallization step and the washing step was measured, no nitrogen component was detected and no nitrogen treatment was necessary.

(Example 3)
Indium hydroxide was crystallized in the same manner as in Example 1. The obtained indium hydroxide powder was washed with pure water, and then malonic acid (manufactured by Kanto Chemical Co., Ltd., reagent grade 1, complex formation constant with indium ions: 10.13) was diluted in pure water, and hydroxylated. A suspension was obtained by dispersing this powder in 500 ml of a 0.4 mol / L malonic acid aqueous solution adjusted to pH 11.0 using sodium. Thereafter, the obtained suspension was kept at 70 ° C. for 2 hours with stirring, then filtered, washed with pure water, and dried to obtain indium hydroxide powder.

  Furthermore, indium oxide powder was obtained by calcining the obtained indium hydroxide powder at 800 ° C. for 5 hours in an air atmosphere.

  The indium recovery rate with respect to the obtained indium oxide powder was 98%, and the residual chlorine concentration in the powder was 40 mass ppm. Moreover, when the nitrogen content in the waste liquid produced in the crystallization step and the washing step was measured, no nitrogen component was detected and no nitrogen treatment was necessary.

(Comparative Example 1)
Indium hydroxide was crystallized in the same manner as in Example 1. The obtained indium hydroxide powder was washed with pure water, and then a 0.2 mol / L aqueous ammonia solution (pH 12.2) prepared by diluting 28% ammonia water (manufactured by Kanto Chemical Co., Ltd., reagent special grade) with pure water. 8) A suspension was obtained by dispersing in 500 ml. Thereafter, the obtained suspension was kept at 80 ° C. for 2 hours with stirring, then filtered, washed with water, and dried to obtain indium hydroxide powder.

  The obtained indium hydroxide powder was calcined at 800 ° C. for 5 hours in an air atmosphere to obtain indium oxide. The indium recovery rate with respect to this indium oxide powder was 97%, and the residual chlorine concentration in the powder was 40 ppm by mass, which was the same as in the examples. However, the nitrogen content in the waste liquid generated in the crystallization step and the washing step was 1. It was 2 g / L, exceeding 0.12 g / L regulated by the Water Pollution Control Law, and nitrogen treatment in the waste liquid was necessary.

(Comparative Example 2)
Indium hydroxide was crystallized in the same manner as in Example 1 except that the aqueous sodium hydroxide solution in the crystallization step was changed to 28% aqueous ammonia (manufactured by Kanto Chemical Co., Inc., reagent grade, pH 13.3). The pH of the liquid after crystallization was 10.5, which was somewhat lower than when sodium hydroxide aqueous solution was used.

  After washing the obtained indium hydroxide powder with water, a 0.2 mol / L aqueous ammonia solution (pH 12.8) prepared by diluting 28% ammonia water (manufactured by Kanto Chemical Co., Ltd., reagent special grade) with pure water. A suspension was obtained by dispersing in 500 ml. Thereafter, the obtained suspension was kept at 80 ° C. for 2 hours with stirring, then filtered, washed with water, and dried to obtain indium hydroxide powder.

  The indium recovery rate for the indium oxide powder obtained by calcining the obtained indium hydroxide powder at 800 ° C. for 5 hours in the air atmosphere was 99%, and the residual chlorine concentration in the powder was 50 ppm by mass. Although it was equivalent, the nitrogen content in the waste liquid generated in the crystallization process and the washing process was 20.3 g / L, exceeding 0.12 g / L regulated by the Water Pollution Control Law, and in the waste liquid. Nitrogen treatment was required.

(Comparative Example 3)
Indium hydroxide was crystallized in the same manner as in Example 1. After washing the obtained indium hydroxide powder with pure water, oxalic acid (manufactured by Kanto Chemical Co., Inc., reagent grade, complex formation constant with indium ions: 26.00) is diluted in pure water, and sodium hydroxide is used. The suspension was prepared by dispersing this powder in 500 ml of 0.5 mol / L oxalic acid aqueous solution adjusted to pH 12.0. Thereafter, the obtained suspension was held at 80 ° C. for 2 hours with stirring, then filtered, washed with pure water, and dried to obtain indium hydroxide powder.

  The obtained indium hydroxide powder was calcined at 800 ° C. for 5 hours in an air atmosphere to obtain indium oxide. Although the residual chlorine concentration in the indium oxide powder was 40 mass ppm, which was the same as that in the example, the indium recovery rate was as low as 86%. Nitrogen components were not detected in the waste liquid generated in the crystallization process and the washing process, and there was no need for nitrogen treatment.

(Comparative Example 4)
Indium hydroxide was crystallized in the same manner as in Example 1. After washing the obtained indium hydroxide powder with pure water, lactic acid (manufactured by Kanto Chemical Co., Inc., reagent special grade, complex formation constant with indium ions: 5.74) is diluted in pure water, and sodium hydroxide is used. A suspension was obtained by dispersing this powder in 500 ml of a 0.5 mol / L lactic acid aqueous solution adjusted to pH 7.0. Thereafter, the obtained suspension was held at 80 ° C. for 2 hours with stirring, then filtered, washed with pure water, and dried to obtain indium hydroxide powder.

  The obtained indium hydroxide powder was calcined at 800 ° C. for 5 hours in an air atmosphere to obtain indium oxide. The residual chlorine concentration in the indium oxide powder was 70 mass ppm, which was higher than that of the example, and the indium recovery rate was as low as 88%. Nitrogen components were not detected in the waste liquid generated in the crystallization process and the washing process, and there was no need for nitrogen treatment.

As is clear from the above, in the production method of the present invention, indium chloride or a metal salt mainly composed of indium chloride is used as a starting material, both in the crystallization step and the washing step. In addition, a powder mainly composed of indium oxide having a low chlorine quality can be obtained efficiently and at a low cost without using a waste liquid such as an aqueous ammonia solution that causes a nitrogen component. In addition, the obtained powder containing indium oxide as a main component is suitable for use in electronic materials, and is not only used in the field of high-density indium-containing oxide targets for forming transparent conductive thin films, but also for resin kneading. It is also used in the field of conductive fillers and transparent conductive film coatings, and is extremely useful industrially.

Claims (4)

An indium chloride aqueous solution, or an aqueous solution containing a metal salt containing indium chloride as a main component and an aqueous solution using an alkali metal hydroxide salt, the liquid temperature is less than 50 ° C. from the start of mixing to the end of mixing, and , By mixing while maintaining the pH at 8 or more to cause a crystallization reaction, indium hydroxide or indium composite hydroxide is produced,
A complex formation constant with indium ions is more than 2.37 and less than 19.43, and a carboxylic acid containing no amino group is used, and the carboxylic acid concentration is 0.1 mol / L or more and 0.5 mol / L or less. While maintaining the pH of the aqueous solution adjusted to 1 to 8 or higher using an aqueous solution using an alkali metal hydroxide salt, the crystallized indium hydroxide or indium composite hydroxide is dispersed in the aqueous solution, and 40 After maintaining at a liquid temperature of ℃ ~ 90 ℃ for 30 minutes or more, by obtaining a powder by filtration,
The powder is subjected to water washing and calcination treatment,
A method for producing a powder mainly composed of indium oxide.   The method for producing a powder containing indium oxide as a main component according to claim 1, wherein the aqueous solution using the alkali metal hydroxide salt is an aqueous potassium hydroxide solution, an aqueous sodium hydroxide solution, or a mixed aqueous solution.   The method for producing a powder containing indium oxide as a main component according to claim 1 or 2, wherein the carboxylic acid comprises at least one of lactic acid, acetic acid, and malonic acid.   A powder comprising indium oxide as a main component, which is produced by the production method according to any one of claims 1 to 3 and has a chlorine quality of 50 mass ppm or less.