JP6040900B2 - Method for producing metal hydroxide - Google Patents

Description

  The present invention is a method for producing a metal hydroxide with less waste, for example, by extracting and reusing a cleaning solution such as an electrolyte component or pure water from a waste solution generated in the process of producing a metal hydroxide such as indium or tin. It is about.

  Metal hydroxides with high purity and fine particle size are used in various fields. In recent years, the use of transparent conductive films has increased for solar cell applications and touch panel applications. Accordingly, the demand for transparent conductive film forming materials such as sputtering targets is increasing. For these transparent conductive film forming materials, indium oxide-based sintered materials are mainly used, and indium oxide powder is used as the main raw material. In addition to being highly pure, the indium oxide powder used for the sputtering target desirably has as narrow a particle size distribution as possible in order to obtain a high-density target.

  As a method for producing indium oxide powder, mainly, a so-called medium-indium hydroxide precipitate formed by neutralizing an acidic aqueous solution such as an indium nitrate aqueous solution or an indium chloride aqueous solution with an alkaline aqueous solution such as ammonia water is dried and calcined. Manufactured by the sum method.

  In the neutralization method, in order to suppress aggregation of the obtained indium oxide powder, a method of obtaining acicular indium hydroxide by adding an alkali to a high-temperature indium nitrate aqueous solution of 70 to 95 ° C. has been proposed. (For example, refer to Patent Document 1). In this method, the obtained acicular indium hydroxide is dried at 90 to 260 ° C. and then calcined at 500 to 900 ° C. to obtain indium oxide powder with little aggregation.

  However, the indium oxide powder produced by the neutralization method tends to have non-uniform particle size and particle size distribution, and when the sputtering target is produced, the target density is difficult to increase, and uneven density tends to occur. This causes a problem that abnormal discharge is likely to occur. Further, the neutralization method has a problem that wastewater treatment costs increase because a large amount of nitrogen wastewater is generated after the production of indium oxide powder.

  As a method for solving such a problem, a method of producing indium oxide powder by precipitating indium hydroxide powder by electrolytic treatment of metal indium and so-called electrolytic method has been proposed. (For example, refer to Patent Document 2). Compared with the neutralization method, the electrolytic method can significantly reduce the amount of nitrogen drainage after the production of indium oxide powder, and can also make the particle size of the indium oxide powder obtained uniform.

  The electrolytic method is characterized in that the electrolyte used basically is not consumed. However, the nitric acid content and ammonium ions separated together with the generated metal hydroxide are decomposed and disappeared by drying and calcining. For this reason, since the part decomposed | disassembled and lose | disappeared from electrolyte solution is lost, the part must be replenished.

  In the method for producing a metal hydroxide by the electrolytic method, the electrolytic slurry containing the deposited metal hydroxide is subjected to solid-liquid separation to separate the metal hydroxide and the electrolytic solution. The filter cake obtained by solid-liquid separation contains an electrolyte component such as nitric acid and ammonium ions.

  Therefore, if the cake cake is washed thoroughly with pure water, the nitric acid and ammonium ions contained in the cake are extracted into pure water, and the pure water containing electrolytic components is included in the cake by treating it with waste liquid. The electrolyte component that has been discarded is discarded and lost.

  Therefore, if pure water containing an electrolytic solution component can be used as an electrolytic solution in an electrolysis process, loss of the electrolytic solution component can be suppressed. However, if the electrolytic solution component is washed away from the cake with pure water and filtered, the nitrate and ammonium ions can be removed from the cake and the filtrate can contain the electrolytic solution component. The filtrate containing the liquid component is diluted. Therefore, the filtrate cannot be returned as it is to the electrolyte of the original electrolysis process.

  Therefore, when it is unavoidable to treat wastewater, the environmental load must be considered. When draining nitrogen-containing wastewater into rivers and oceans, it is necessary to meet stringent environmental standards such as the Pollution Control Act Water Pollution Control Act.

  Therefore, as an essential measure, there is a demand for a production method in which the electrolytic solution is almost completely recycled and no waste is generated in the production method of metal hydroxide using the electrolytic method.

Japanese Patent No. 3314388 Japanese Patent No. 2829556 Japanese Patent No. 4396875

  Therefore, the present invention has been proposed in view of such circumstances, and in the production of a metal hydroxide by an electrolytic method, the electrolyte component contained in the cleaning solution when the metal hydroxide is cleaned is discarded. An object is to provide a method for producing a metal hydroxide which is not necessary.

Method for producing a metal hydroxide according to the present invention for achieving the above object, in the method for producing a metal hydroxide to produce the indium hydroxide powder by electrolysis, indium and electrolysis in the electrolytic solution as the anode hydroxide a metal hydroxide generating step of generating indium powder, a solid-liquid separation step of solid-liquid separation of the obtained indium hydroxide powder and the electrolyte of a metal hydroxide producing step, is separated in solid-liquid separation step The electrolysis separated in the solid-liquid separation step has a washing step for washing the indium hydroxide powder with a washing solution, and a concentrate producing step for concentrating the washing solution containing the electrolyte component after the washing step to obtain a concentrated solution. The liquid and the concentrated liquid are used as an electrolytic solution in the metal hydroxide production step. Further, the metal hydroxide production method according to the present invention is a metal hydroxide production method for producing tin hydroxide powder by electrolysis. In the metal hydroxide production method, tin is used as an anode to produce tin hydroxide powder by electrolysis in an electrolytic solution. Metal hydroxide generation step, solid-liquid separation step for solid-liquid separation of the tin hydroxide powder obtained in the metal hydroxide generation step and the electrolyte, and tin hydroxide powder separated in the solid-liquid separation step And the concentrated solution producing step of obtaining the concentrated solution by concentrating the washed solution containing the electrolytic solution component after the washed step, and the separated electrolyte and concentrated solution in the solid-liquid separation step Is used for the electrolytic solution in the metal hydroxide production step.

  In the present invention, after the metal hydroxide is generated by the electrolytic method in the metal hydroxide generating step, the metal hydroxide is washed, and the washing solution containing the washed electrolyte component is concentrated. By using the concentrated solution again as the electrolytic solution in the metal hydroxide production step, it is not necessary to discard the washed cleaning solution, and the disappearance of the electrolytic solution component can be further suppressed.

It is a flowchart of the manufacturing method of the metal hydroxide which concerns on this invention. It is the schematic of the electrolysis apparatus used by the Example and the comparative example. It is the schematic which shows arrangement | positioning of the cathode and anode in the same electrolysis apparatus.

  Below, the manufacturing method of the metal hydroxide to which this invention is applied is demonstrated. Note that the present invention is not limited to the following detailed description unless otherwise specified. The method for producing a metal hydroxide to which the present invention is applied can produce, for example, indium hydroxide or tin hydroxide, and will be described in detail in the following order by taking indium hydroxide as an example.

1. 1. Metal hydroxide production process 2. Solid-liquid separation process 3. Washing process 4. Concentrate production process Drying process

1. Metal hydroxide generation process In the metal hydroxide generation process, as shown in FIG. 1, the metal hydroxide is produced using an electrolytic reaction using an electrolytic solution in which the concentration, pH, solubility of indium hydroxide powder, and the like are adjusted. Get. In this process, the metal used as a raw material is an anode (anode), a conductive metal or carbon electrode is used for the cathode (cathode) of the counter electrode, and both are immersed in an electrolytic solution to generate a potential difference between the two electrodes. As a result, dissolution of the metal proceeds at the anode. Further, the pH of the electrolytic solution is adjusted so that the solubility of the produced metal hydroxide is low, so that the metal hydroxide crystallizes and precipitates.

  The metal indium used for the anode is not particularly limited, but a high-purity metal is desirable in order to suppress contamination of impurities into the indium oxide powder. As metal indium, a purity of 99.9999% (commonly called 6N product) can be mentioned as a suitable product.

  As the cathode, a conductive metal, a carbon electrode, or the like is used. For example, insoluble titanium or the like can be used, and titanium may be coated with platinum.

  As the electrolytic solution, an aqueous solution of a general electrolyte salt such as a water-soluble nitrate, sulfate, or chloride salt can be used. Among these, an aqueous ammonium nitrate solution using ammonium nitrate in which nitrate ions and ammonium ions are removed as nitrogen compounds after drying and calcining after precipitation of indium hydroxide powder and does not remain as impurities is preferable.

The electrolytic solution preferably has a solubility of the produced indium hydroxide powder in the range of 10 ⁻⁶ to 10 ⁻³ mol / L. When the solubility of indium hydroxide powder is lower than 10 ⁻⁶ mol / L, indium ions released from the anode are likely to be nucleated, so that the primary particle diameter becomes too fine. When the primary particle diameter is too fine, it is not preferable because it becomes difficult to separate and recover the indium hydroxide powder in the subsequent step of recovering the indium hydroxide powder.

On the other hand, when the solubility is higher than 10 ⁻³ mol / L, the grain growth is promoted, so that the primary particle diameter becomes large. For this reason, the larger the particle is grown, the larger the difference in particle size between the growing particle and the non-growing particle. Since the difference in particle diameter affects the degree of aggregation, as a result, the width of the particle size distribution becomes wide. If the width of the particle size distribution of the indium hydroxide powder becomes wider, the width of the particle size distribution of the indium oxide powder obtained by calcining the indium hydroxide powder also becomes wider, and the density of the sputtering target obtained by sintering this becomes higher. This is not preferable because it is difficult to achieve density.

Therefore, in the electrolyte, since the growth of primary particles is moderately promoted by setting the solubility of indium hydroxide to be in the range of 10 ⁻⁶ to 10 ⁻³ mol / L, aggregation is suppressed and the width of the particle size distribution is increased. Indium hydroxide powder that is not wide, has a narrow particle size distribution, and a uniform particle size can be obtained.

The electrolyte solution may have a solubility of indium hydroxide powder in the range of 10 ⁻⁶ to 10 ⁻³ mol / L, and the solubility can be controlled by the concentration, pH, liquid temperature, and the like of ammonium nitrate. The electrolyte solution has a solubility of 10 ⁻⁶ by adjusting the concentration of ammonium nitrate to 0.1 to 2.0 mol / L, the pH to 2.5 to 4.0, and the liquid temperature to 20 to 60 ° C., for example. It can control to the range of -10 < ^-3 > mol / L. The pH can be adjusted by the amount of ammonium nitrate added.

  Regarding the concentration of the electrolyte, the lower the concentration, the lower the cost. However, if the concentration is lower than 0.1 mol / L, the electrical conductivity of the electrolyte is too low and no current is generated, or the necessary voltage exceeds the practical range. It is not preferable. On the other hand, if the concentration is 2.0 mol / L, sufficient electric conductivity is ensured. Therefore, it is uneconomical and unnecessary to make the concentration higher than 2.0 mol / L.

  If the pH of the electrolyte is less than 2.5, no hydroxide precipitation occurs, and if it is greater than 4.0, the precipitation rate of the hydroxide is too high and the concentration is not uniform. Is not preferable because the particle size distribution width is widened.

  When the electrolyte temperature is lower than 20 ° C., the precipitation rate is too slow, and when it is higher than 60 ° C., the precipitation rate is too high and precipitates are formed with non-uniform concentration. Is unfavorable.

The electrolysis conditions are not particularly limited, but the current density is preferably 3 A / dm ^{2 to} 15 A / dm ² . When the current density is lower than 3 A / dm ² , the production efficiency of indium hydroxide powder is lowered. When the current density is higher than 15 A / dm ² , problems such as an increase in the electrolysis voltage, an increase in the liquid temperature, and a passivation of the surface of the metal indium make it difficult to perform electrolysis. Therefore, the current density is preferably 3 A / dm ^{2 to} 15 A / dm ² .

  In order to improve the dissolution stability of the metal hydroxide, an oxygen-containing chelate compound such as citric acid, tartaric acid or glycolic acid or a nitrogen-containing chelate such as EDTA may be added as necessary.

  Indium hydroxide powder produced by electrolysis under the above conditions is collected in an electrolytic cell. The obtained indium hydroxide powder has a columnar shape with a particle size of submicron or several microns, a narrow particle size distribution, and a uniform particle size. Aggregation can be further suppressed by the columnar shape of the indium hydroxide powder.

(2. Solid-liquid separation process)
Next, as shown in FIG. 1, a solid-liquid separation step is performed in which the indium hydroxide powder produced in the metal hydroxide production step and the electrolytic solution are subjected to solid-liquid separation. In the solid-liquid separation step, the indium hydroxide powder is separated by a method such as filtration or centrifugation.

As a filtration method, cake filtration such as a filter press or centrifugal filtration, cross flow filtration, or the like can be used. Moreover, decanter separation without using filtration with a filter cloth is also possible. A cross-flow type rotary filter is preferable because it is difficult to cause clogging even if it is a fine powder and the collection efficiency is high. The filter cloth used in the rotary filter is preferably as low in air permeability as possible in order to further improve the recovery efficiency of indium hydroxide powder. The air permeability is preferably 0.3 cm ³ / sec / cm ² or less.

  In the solid-liquid separation step, the solid content (cake portion) generated by the solid-liquid separation contains indium hydroxide powder and an electrolytic solution, and the electrolytic solution is separated as a filtrate. Here, in the method for producing a metal hydroxide according to the present embodiment, as shown in FIG. 1, the electrolytic solution separated as a filtrate is not treated as a wastewater, and is electrolyzed in the metal hydroxide production process. Reuse as liquid. Since the electrolytic solution separated in the solid-liquid separation step has the same concentration as the electrolytic solution in the metal hydroxide production step, it can be reused as it is in the metal hydroxide production step. Note that in the case where impurities or the like are contained in the separated electrolytic solution, a treatment for removing the impurities may be performed.

(3. Cleaning process)
Next, as shown in FIG. 1, the washing | cleaning process which repulp-washes the solid content (cake part) of the indium hydroxide powder isolate | separated by the solid-liquid separation process with a washing | cleaning liquid is performed. In the washing step, the electrolytic solution contained in the solid content (cake portion) of the indium hydroxide powder separated in the solid-liquid separation step is extracted into the washing solution, and the electrolytic solution is removed from the indium hydroxide powder.

  Specifically, in the cleaning step, for example, pure water is added as a cleaning liquid to the solid content (cake portion) of the indium hydroxide powder and stirred to redisperse, and the electrolyte contained in the solid content (cake portion) is purified. Extract into water and perform solid-liquid separation. For this solid-liquid separation, cake filtration, crossflow filtration, decanter separation, or the like can be used as in the above-described solid-liquid separation step.

  It is desirable that the pure water to be used has less impurities, and it is particularly desirable that the pure water is A2 grade or higher as defined in JIS K0557. If the grade is lower than this, impurities such as silica are mixed, which is not preferable.

  The amount of pure water added is determined by selecting an appropriate minimum amount that can sufficiently reduce the concentration of the electrolytic solution in the solid content (cake portion) of the indium hydroxide powder. For example, it is appropriate to determine by measuring the amount of electrolyte remaining in the solid content after washing. For example, it is desirable to wash with 5 to 20 L of pure water per 1 kg of indium hydroxide. If the amount of pure water added is too small, for example less than 5 L, a large amount of electrolyte component such as ammonium nitrate remains in the indium hydroxide powder, and when the indium hydroxide powder is dried, the indium hydroxide powder The risk of fire increases when calcining and obtaining indium oxide powder. When the amount added is too large, for example, more than 20 L, pure water is wasted because it is more than necessary, and the concentration process in the concentration step described later increases and costs increase.

  In the washing step, a washing solution such as pure water is added to the solid content (cake portion) of the indium hydroxide powder containing the electrolytic solution component, and stirring is performed as necessary. In the washing step, the electrolytic solution can be removed from the solid content of the indium hydroxide powder by performing repulp washing at least once by adding a washing liquid such as pure water to the indium hydroxide powder and stirring and then filtering.

  Here, in the cleaning process, the cleaning liquid mixed with the electrolytic solution is not treated as waste, and the concentrated liquid obtained by concentrating the cleaning liquid in the subsequent concentrated liquid generation process is used as the electrolytic solution in the metal hydroxide generation process. Reuse.

(4. Concentrate production process)
In the concentrated liquid production step, as shown in FIG. 1, the concentrated liquid is obtained by concentrating the cleaning liquid mixed with the electrolytic solution obtained in the cleaning process. In the concentrated solution generation step, the cleaning solution is concentrated to obtain a concentrated solution concentrated to the concentration of the electrolytic solution used in the above-described metal hydroxide generation step. The obtained concentrated liquid is again used as the electrolytic solution in the above-described metal hydroxide production step.

  As a concentration method, there is a distillation method in which the cleaning liquid mixed with the electrolytic solution component is heated to evaporate the cleaning liquid other than the electrolytic solution component, that is, the cleaning liquid, and then cooled again to obtain the cleaning liquid. In this distillation method, the electrolyte component is concentrated in the remaining concentrated solution.

  Among the distillation methods, vacuum distillation is preferable because of its high thermal efficiency. In addition to simple distillation, a multistage distillation method in which a large number of vacuum chambers are combined can also be employed. The conditions of the distillation method, the cooling method, and the like are not particularly limited as long as the cleaning liquid mixed with the electrolytic solution component is concentrated to obtain a concentrated liquid composed of the electrolytic solution component.

  In the concentrate production step, the residual solution is sampled during distillation to analyze the density, and it is confirmed whether or not the electrolyte solution concentration in the metal hydroxide production step has been restored. When it has returned to the electrolyte solution concentration used in the metal hydroxide production step, the concentrated solution can be reused as the electrolyte solution in the metal hydroxide production step.

  In addition, when pure water is used as the cleaning liquid in the above-described cleaning process, the water distilled in the concentrate generation process is pure water, and therefore can be used again as pure water used in the cleaning process.

  Further, as a concentration method, a reverse osmosis method, or a kind of filtration membrane called a reverse osmosis membrane by applying pressure to washing water can be used. This reverse osmosis method is a method of concentrating an electrolyte solution by passing a cleaning solution in which an electrolyte component is mixed into a filtration membrane and allowing only water to pass through the reverse osmosis membrane. Although the water which permeate | transmitted the reverse osmosis membrane by this method contains comparatively much electrolyte component rather than the distillation method, it can fully be used as washing water in a washing | cleaning process.

  In the reverse osmosis method, it is necessary to permeate water by applying a high pressure to the reverse osmosis membrane. Examples of the reverse osmosis membrane include a hollow fiber membrane that is formed into a pasta-like thickness and hollow inside and is filtered from the outside to the inside. Alternatively, it is also possible to use a spiral membrane in which one filtration membrane is overlapped with a strong mesh-like support in order to maintain strength and closed in a bag shape, wound in a roll cake shape and pressurized from the cross-sectional direction. For pressurization, a high-pressure pump such as a turbine pump or a plunger pump can be used.

  In this way, in the concentrated liquid production step, the obtained concentrated liquid can be reused as the electrolytic solution, and the obtained cleaning liquid can be reused as the cleaning liquid in the cleaning step. It is not necessary to process as. In addition, when the concentration of the concentrated solution becomes too higher than the concentration of the electrolytic solution, the concentration may be adjusted by adding pure water.

(5. Drying process)
In the drying step, as shown in FIG. 1, the indium hydroxide powder after the cleaning step is dried. As a drying method, there is a method using a dryer such as a spray dryer, an air convection type drying furnace, an infrared drying furnace or the like.

  The drying conditions are not particularly limited as long as the moisture of the indium hydroxide powder can be removed. For example, the drying temperature is preferably in the range of 80 ° C to 150 ° C. When the drying temperature is lower than 80 ° C., the drying is insufficient. When the drying temperature is higher than 150 ° C., the indium hydroxide changes to indium oxide. The drying time varies depending on the temperature, but is about 10 hours to 24 hours.

  As described above, in the method for producing indium hydroxide, indium hydroxide powder is obtained through a drying process from a metal hydroxide production process using an electrolytic reaction. In this indium hydroxide powder production method, after the indium hydroxide powder is produced, the concentrated solution that concentrates the electrolyte solution obtained in the solid-liquid separation step of separating the indium hydroxide powder from the electrolyte solution or the cleaning solution mixed with the electrolyte solution. By reusing the electrolyte obtained in the production process as the electrolyte in the metal hydroxide production process, wastewater treatment is not performed as in the conventional case, so that loss of the electrolyte component can be suppressed and the load on the environment is suppressed. be able to.

  In the above description, the method for producing indium hydroxide has been described as an example. However, the present invention is not limited to this, and the present invention can be similarly applied to a method for producing tin hydroxide. In the case of producing tin hydroxide, although there is a difference from the method for producing indium hydroxide powder in that the pH during electrolysis is about 8, the other requirements are the same. Also in the manufacturing method of tin hydroxide, since the wastewater treatment is not performed as in the conventional case by reusing the electrolytic solution and the cleaning solution, the loss of the electrolytic solution can be suppressed and the load on the environment can be suppressed.

  Specific examples to which the present invention is applied will be described below, but the present invention is not limited to these examples.

<Example>
In the examples, the metal hydroxide production step to the drying step were performed as follows.

(1) Metal hydroxide production | generation process In the metal hydroxide production | generation process, indium hydroxide was produced | generated using the electrolyzer 1 shown in FIG. The electrolysis apparatus 1 shown in FIG. 2 includes a 36 L electrolytic cell 2 having a length of 30 cm, a width of 40 cm, and a depth of 30 cm, and an 80 L adjustment tank 3 having a length of 40 cm, a width of 40 cm, and a depth of 50 cm. Are adjacent. The electrolytic bath 2 and the adjustment bath 3 are connected by a circulation pump 4.

  The electrolytic cell 2 is provided with a punch plate 6 for dispersing the liquid flow of the electrolytic solution 5 in parallel with the bottom at a height of 2 cm from the bottom. That is, the punch plate 6 has a total of 25 holes of 3 mm in diameter, 5 rows in a row and 5 rows in a 10 cm square. As a result, in the electrolytic cell 2, the electrolytic solution 5 injected into the lower part of the electrolytic cell 2 by the circulation pump 4 passes through the punch plate 6, and each liquid flow can ensure a substantially uniform liquid flow with no drift.

  In addition, a cathode 7 and an anode 8 were disposed in the electrolytic cell 2 as shown in FIG. For the cathode (cathode) 7, five titanium metal plates having a width of 30 cm, a height of 25 cm, and a thickness of 1 mm were prepared. Four anode (anode) electrodes 8 were prepared by molding indium metal having a purity of 99.9999% into a plate shape having a width of 30 cm, a height of 25 cm, and a thickness of 5 mm. As shown in FIG. 3, these five cathodes 7 and four anodes 8 were arranged alternately on the punch plate 6 in the electrolytic cell 2 so that both electrodes were parallel to each other. The distance between the cathode 7 and the anode 8 was adjusted to 3.0 cm. The four cathodes 7 are electrically connected by a conducting wire 9.

  The adjustment tank 3 includes a temperature control heater 11 and a cooler 12 for controlling and maintaining the temperature of the electrolytic solution 5. Moreover, the adjustment tank 3 is equipped with the stirring rod 13 which stirs the electrolyte solution 5 in a tank.

In the electrolysis apparatus 1, 100 L of 1.0 mol / L ammonium nitrate aqueous solution is contained in the adjustment tank 3. In the adjustment tank 3, 1N nitric acid was added to the ammonium nitrate aqueous solution of the electrolytic solution 5 to adjust the hydrogen ion concentration index pH to 4.0. The pH was measured using the pH electrode 10 attached to the adjustment tank 3. While maintaining this state, the temperature of the electrolytic solution 5 was maintained at 40 ° C. using the temperature control heater 11 and the cooler 12. In the adjustment tank 3, the electrolytic solution 5 was adjusted by stirring the electrolytic solution 5 in the tank with the stirring rod 13. The solubility of indium hydroxide at this time is 10 ⁻⁵ mol / L.

  During the electrolysis, the electrolytic solution 4 in the adjusting tank 3 was sent to the electrolytic tank 2 by the circulation pump 4 at a speed of 20 L / min. The electrolytic solution 5 in the electrolytic tank 2 is returned to the adjustment tank 3 due to overflow.

The electrode current density was adjusted to 15 A / dm ² and electrolysis was continued for 6 hours. An indium hydroxide slurry having a concentration of 4% was obtained. The concentration of the indium hydroxide slurry can be obtained by [mass of indium hydroxide powder / (mass of indium hydroxide powder + mass of electrolytic solution)].

(2) Solid-liquid separation process Next, solid-liquid separation of the indium hydroxide slurry was performed. The solid-liquid separation was performed using a rotary filter (RFU-02B manufactured by Kotobuki Industries Co., Ltd.) and a filter cloth (KE-022, air permeability 0.1 cm ³ / sec / cm ² ). As a result of solid-liquid separation, an indium hydroxide cake having a water content of 55% and a separated electrolyte solution were obtained.

(3) Washing step Next, the indium hydroxide powder is washed. In the washing step, 80 L of pure water was added to the indium hydroxide cake and stirred and redispersed in a stainless bucket container. This was subjected to a solid / liquid separation operation in the same manner as in the solid / liquid separation step to obtain an indium hydroxide cake having a water content of 55% again.

(4) Concentrated liquid production | generation process Next, the concentrated liquid production | generation process was performed. In the concentrated liquid production process, using a vacuum distillation apparatus (Eco Prima) manufactured by Nippon Steel Environmental Engineering Co., Ltd., 100 liters of the cleaning liquid obtained in the cleaning process was charged into a heater for concentration heating (capacity 1 m ³ ), and an electric heater 100 kW Distillation under reduced pressure was performed at / hr for 4 hours.

  This concentrated liquid is mixed with the electrolytic solution separated in the solid-liquid separation step, and adjusted by adding pure water so as to be the same as the electrolytic solution 5 used in the metal hydroxide generation step, and then again in the adjustment tank 3. Then, it was put into the electrolytic cell 2 through the pump 4 to perform new electrolysis. In the steps so far, the electrolytic solution has not been discarded as a waste solution.

  This operation was repeated three times, and the resulting indium hydroxide slurry was sampled and the particle size distribution was measured by the laser light Doppler method. As a result, the minimum diameter was 0.3 μm and the maximum diameter was 1.2 μm. It had a similar good distribution with a narrow distribution width.

(5) Drying step and firing step The indium hydroxide powder obtained by this method was spray-dried with a spray dryer and fired at 700 ° C in the air. The particle size distribution of the obtained indium oxide powder had a minimum diameter of 0.3 μm and a maximum diameter of 1.2 μm in all three times, and similarly had a good distribution with a narrow particle size distribution.

<Comparative example>
In the comparative example, the metal hydroxide production | generation process, the solid-liquid separation process, and the washing | cleaning process were performed similarly to the Example, and the concentrate production | generation process was not performed. In the comparative example, since the nitrogen concentration of the cleaning liquid after cleaning in the cleaning process was 10,000 ppm, in order to dilute to 80 ppm which is 120 ppm or less, which is the drainage nitrogen standard of the Pollution Control Law Water Pollution Control Law, 13 m ³ Needed water. In the comparative example, the electrolytic solution separated in the solid-liquid separation step was returned to the metal hydroxide production step.

  In the above embodiment, not only the electrolytic solution separated in the solid-liquid separation step but also the concentrated solution containing the electrolytic solution component obtained by concentrating the cleaning solution mixed with the electrolytic solution is used for the electrolysis in the metal hydroxide production step. By reusing the solution, the loss of the electrolyte component can be suppressed, and dilution for wastewater treatment is not necessary. On the other hand, in the comparative example, since the waste water treatment cannot be performed as it is in the waste water treatment in which the electrolyte solution is mixed, it takes time and effort to dilute with a large amount of water, and the electrolyte component is lost. I understand that.

  DESCRIPTION OF SYMBOLS 1 Electrolysis apparatus, 2 Electrolysis tank, 3 Adjustment tank, 4 Circulation pump, 5 Electrolyte, 6 Punch plate, 7 Cathode, 8 Anode, 9 Conductor, 10 pH electrode, 11 Heater apparatus, 12 Cooling apparatus, 13 Stirring rod

Claims (3)

In the method for producing a metal hydroxide for producing indium hydroxide powder by electrolysis,
A metal hydroxide generating step of generating indium hydroxide powder by electrolysis in an electrolytic solution using indium as an anode;
A solid-liquid separation step for solid-liquid separation of the indium hydroxide powder obtained in the metal hydroxide generation step and the electrolytic solution;
A washing step of washing the indium hydroxide powder separated in the solid-liquid separation step with a washing liquid;
A concentrated solution generating step of concentrating the cleaning solution containing the electrolyte component after the cleaning step to obtain a concentrated solution,
A method for producing a metal hydroxide, comprising using the electrolytic solution and the concentrated solution separated in the solid-liquid separation step as the electrolytic solution in the metal hydroxide production step. In the method for producing a metal hydroxide for producing tin hydroxide powder by electrolysis,
A metal hydroxide generating step of generating tin hydroxide powder by electrolysis in an electrolytic solution using tin as an anode;
A solid-liquid separation step for solid-liquid separation of the tin hydroxide powder obtained in the metal hydroxide production step and the electrolytic solution;
A washing step of washing the tin hydroxide powder separated in the solid-liquid separation step with a washing solution;
A concentrated solution generating step of concentrating the cleaning solution containing the electrolyte component after the cleaning step to obtain a concentrated solution,
A method for producing a metal hydroxide, comprising using the electrolytic solution and the concentrated solution separated in the solid-liquid separation step as the electrolytic solution in the metal hydroxide production step. In the cleaning step, pure water is used for the cleaning liquid,
In the concentrated liquid generation step, a concentrated liquid is generated by removing the pure water from the cleaning liquid,
The method for producing a metal hydroxide according to claim 1 or 2, wherein the pure water removed in the concentrated liquid producing step is used as the pure water in the washing step.

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