JP6206382B2 - Method for producing indium hydroxide powder - Google Patents

Description

  The present invention relates to a method for producing indium hydroxide powder. In particular, the present invention relates to a method for producing indium hydroxide powder that suppresses the amount of NOx gas generated during electrolysis, has a uniform particle size, and a narrow particle size distribution.

  In recent years, the use of transparent conductive films has increased for solar cell applications and touch panel applications, and accordingly, the demand for materials for forming transparent conductive films in sputtering targets and the like has increased. As a material for forming the transparent conductive film, an indium oxide-based sintered material is mainly used, and indium oxide powder is used as the main raw material. The indium oxide powder used for the sputtering target desirably has a narrow particle size distribution as much as possible in order to obtain a high-density target.

  Therefore, in patent document 1, the manufacturing method of the indium hydroxide powder by an electrolytic method and the indium oxide powder using the same is described. This is because an electrolytic solution is stored in an electrolytic cell, and an anode (for example, metal indium) and a cathode (for example, insoluble titanium coated with platinum) are immersed in the electrolytic solution, and a voltage is applied between the electrodes. Indium hydroxide powder is deposited by applying electrolysis and applying electrolysis. And after collecting the collected indium hydroxide powder, firing the collected one to obtain indium oxide powder, mixing indium oxide powder with tin oxide powder at a predetermined ratio, pulverizing and granulating the mixed powder It has been proposed that an ITO target can be obtained by pressure molding and sintering the pressure molded material.

However, when an aqueous ammonium nitrate solution is used as the electrolytic solution, the standard electrode potential (+0.01 V) is the standard electrode potential (−0.83 V) of the water reduction reaction, as shown in the following reaction formula (1) showing the reduction reaction of nitrate ions. In the conventional cathode, the reduction reaction of nitrate ions (NO ₃ ⁻ ) is more likely to occur than the reduction reaction of water, and the concentration of nitrate ions decreases during electrolysis and nitrite ions (NO ₂ ⁻ ) Concentration increases.

The nitrite ions (NO ₂ ⁻ ) generated in the reaction formula (1) change into nitrous acid (HNO ₂ ) as shown in the following reaction formula (2) as the H ⁺ concentration in the electrolytic solution increases. The proportion of increases.

Specifically, as shown in FIG. 1, when the pH of the electrolytic solution is 5 or more, 98% or more of nitrite ions (NO ₂ ⁻ ) generated by electrolysis are retained in the form as they are. When it is less than 5, the rate of change to nitrous acid (HNO ₂ ) increases rapidly, and when the pH is 4, about 40% changes to nitrous acid (HNO ₂ ).

The produced nitrous acid (HNO ₂ ) becomes NOx gas (NO + NO ₂ ) by an equilibrium reaction as shown in the following reaction formula (3) and the following reaction formula (4).

Since NOx gas (NO + NO ₂ ) is a substance that can cause acid rain and photochemical smog and is restricted from being discharged by laws and regulations such as the Air Pollution Control Law, it suppresses the generation of NOx gas. desired.

As a conventional technique for suppressing NOx gas, in Patent Document 2 and Non-Patent Document 1, hydrogen peroxide is added to a mixed cleaning solution of nitric acid and hydrofluoric acid in order to suppress NOx gas generated during acid cleaning of the stainless steel surface. It is described to do. According to these, as shown in the following reaction formula (5), NOx gas (NO + NO ₂ ) is obtained by oxidizing nitrous acid (HNO ₂ ) generated by decomposition of nitric acid during acid cleaning into nitric acid (HNO ₃ ). It has been proposed to suppress the amount of generation.

Moreover, in patent document 3, as a part which suppresses generation | occurrence | production of NOx gas, the manufacturing method of the indium hydroxide powder by an electrolysis method is described. According to this, it has been proposed to suppress the generation of nitrite ions (NO ₂ ⁻ ) by supplying oxygen to the gas diffusion layer of the electrolytic layer partitioned by the cathode.

JP 2014-74224 A Japanese Patent No. 3687314 International Publication No. 2013/179553

Shigeru Kitani and 4 others, “Development of new technology for NOx gas suppression in nitric hydrofluoric acid pickling of stainless steel and titanium”, Iron and Steel, Japan Iron and Steel Institute, 2002, Vol. 88, No. 4 No., p. 34-41

In Patent Document 1, in order to control the solubility of indium hydroxide powder in order to produce indium hydroxide powder having a uniform particle size and a narrow width of particle size distribution, the pH value of the electrolytic solution is set to 2.5 to 2.5. It is described that adjustment is made within a range of 5.0. When the pH value of the electrolytic solution is _2.5 to 5.0, NOx gas (NO + NO ₂ ) is likely to be generated, and thus processing of the generated NOx gas (for example, NOx gas processing equipment) is necessary. There is a problem of becoming.

  In a conventional method for producing indium hydroxide powder that produces indium hydroxide powder having a narrow particle size distribution by electrolysis, such indium hydroxide powder was produced without suppressing NOx gas generated during electrolysis. Later, NOx gas generated during electrolysis is treated in the post-treatment process. That is, Patent Document 1 does not mention suppression of NOx gas generated during electrolysis.

  Patent Document 2 and Non-Patent Document 1 refer to the suppression of NOx gas using hydrogen peroxide. However, no examination has been made as to whether or not the addition of hydrogen peroxide is effective in suppressing NOx gas in the method for producing indium hydroxide powder by the electrolytic method.

  Further, in Patent Document 3, there is a problem in terms of manufacturing cost because equipment for supplying oxygen to the cathode is required to oxidize nitrous acid with oxygen in order to efficiently suppress NOx gas. While mentioning the suppression of NOx gas when the pH of the electrolyte is around 5, in order to obtain indium hydroxide powder having a uniform particle size and a narrow particle size distribution, the electrolyte is controlled to a pH value lower than pH 5. The case is not mentioned.

  Therefore, the present invention has been proposed in view of such circumstances, and the amount of NOx gas discharged into the atmosphere when electrolyzed using an aqueous ammonium nitrate solution having a pH of 2.5 to 4.0 as an electrolytic solution. It aims at providing the manufacturing method of the indium hydroxide powder which produces | generates the indium hydroxide powder with a uniform particle size and the narrow width | variety of a particle size distribution, suppressing this.

That is, the manufacturing method of the indium hydroxide powder according to the present invention for achieving the above-described object is achieved by using an indium hydroxide aqueous solution having a pH of 2.5 to 4.0 as an electrolytic solution and indium hydroxide by an electrolytic method using indium as an anode. A method for producing an indium hydroxide powder for producing a powder, characterized in that hydrogen peroxide is supplied directly into an electrolyte solution within a supply rate range satisfying the following relational expression.
(Relational expression) 0.7 T mol / min ≦ Vadd. ≦ 1.5 T mol / min
[Where Vadd. Represents the supply rate of hydrogen peroxide, T represents {1 / (1 + 10 ^−3.3 × 10 ^P )} × 3A / 9650, and A represents the current supplied during electrolysis. An electric current value (A) is shown, P shows the pH value of the electrolyte solution during electrolysis. ]

In this way, in order to obtain a narrow indium hydroxide powder having a uniform particle size distribution is the particle size, even when the electrolytic solution is PH2.5～4.0, suppressing the amount of the NO _x gas generated can do. Further, by supplying hydrogen peroxide directly into the electrolytic solution, it becomes easy to suppress the amount of generated NO _x gas.

  In one embodiment of the present invention, it is particularly preferable to supply hydrogen peroxide near the cathode serving as the counter electrode of the anode.

In this way, hydrogen peroxide is supplied directly to the vicinity of the cathode where nitrite ions (NO ₂ ⁻ ) are generated, so that the amount of generated NOx gas can be efficiently suppressed.

  In the present invention, it is possible to produce indium hydroxide powder having a uniform particle size and a narrow particle size distribution while suppressing the discharge amount of NOx gas into the atmosphere.

In the electrolytic solution [HNO _2] concentration and [NO ₂ ^-] to the sum of the concentration [NO ₂ ^-] is an explanatory view showing a ratio of concentration.

  A specific embodiment to which the present invention is applied (hereinafter referred to as “the present embodiment”) will be described. Note that the present invention is not limited to the following embodiments, and various modifications can be made without departing from the scope of the present invention.

1. Method for Producing Indium Hydroxide Powder The method for producing indium hydroxide powder according to the present embodiment is a method of obtaining an electrolytic solution containing indium hydroxide powder that generates indium hydroxide powder (hereinafter referred to as “electrolytic slurry”). It has an electrolysis process of indium oxide powder, a recovery process of indium hydroxide powder for recovering the generated indium hydroxide powder, and a drying process of indium hydroxide powder for drying the recovered indium hydroxide powder.

(1-1) Electrolysis process of indium hydroxide powder In the electrolysis process of indium hydroxide powder, an anode, a cathode, and an aqueous ammonium nitrate solution are used as an electrolytic solution in an electrolytic bath, and the anode and the cathode are immersed in the electrolytic solution. By passing a current between the two electrodes, the anode metal is dissolved, and the indium hydroxide powder is crystallized to produce an electrolytic slurry. In addition, the pH and temperature of the electrolytic solution in the entire electrolytic cell are uniformly maintained by adjusting the pH and temperature of the electrolytic solution, and sending the adjusted electrolytic solution to the electrolytic cell by a circulating means such as a pump. Therefore, an adjustment tank may be provided separately. In this embodiment, the pH of the electrolytic solution is set to 2.5 to 4.0, and hydrogen peroxide is supplied into the electrolytic solution.

(anode)
Metal indium is used for the anode. The metal indium to be used is not particularly limited, but it is desirable that the metal indium has a high purity in order to suppress the mixing of impurities into the indium hydroxide powder and the indium oxide powder obtained by firing the indium hydroxide powder. As the metal indium, for example, a purity of 99.9999% (commonly called 6N product) can be cited as a suitable product. The size of the anode may be appropriately determined according to the production scale or in accordance with the target production amount.

(cathode)
For the cathode, a conductive metal, a carbon electrode, or the like is used. For example, stainless steel, insoluble titanium, or platinum can be used, and titanium can be coated with platinum. May be. The size of the cathode may be appropriately determined according to the production scale or in accordance with the target production amount.

  The distance between the anode and the cathode is not particularly specified, but is preferably 10 mm to 50 mm. When the distance between the electrodes exceeds 50 mm, a voltage drop due to the liquid resistance occurs, causing an increase in the liquid temperature, which is not preferable. On the other hand, when the distance between the electrodes is less than 10 mm, contact and short-circuiting between the electrodes is likely to occur, which is not preferable. The arrangement of the anode and the cathode is not particularly limited, and a general arrangement of electrodes can be adopted.

(Electrolyte)
As the electrolytic solution, an aqueous ammonium nitrate solution is used. In the case of using an aqueous ammonium nitrate solution, after the indium hydroxide powder is precipitated and dried and calcined, nitrate ions and ammonium ions are removed as nitrogen compounds and do not remain as impurities. The cost can be increased.

  The pH of the electrolytic solution is controlled to 2.5 to 4.0. When the pH of the electrolytic solution is less than 2.5, indium hydroxide powder does not precipitate. On the other hand, when the pH of the electrolytic solution exceeds 4.0, the indium hydroxide powder precipitates too quickly and precipitates are formed with non-uniform concentration of the electrolytic solution. The width of the particle size distribution cannot be controlled narrowly.

The electrolytic solution preferably has a solubility of the produced indium hydroxide powder in the range of 10 ⁻⁶ to 10 ⁻³ mol / L. As described above, since the growth of primary particles is moderately promoted, aggregation of primary particles is suppressed, the width of the particle size distribution is not widened, and an indium hydroxide powder having a uniform particle size and a narrow width of the particle size distribution is obtained. be able to.

When the solubility of the indium hydroxide powder is less than 10 ⁻⁶ mol / L, indium ions dissolved 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 recovery step of recovering the indium hydroxide powder. On the other hand, when the solubility of the indium hydroxide powder exceeds 10 ⁻³ mol / L, the particle growth is promoted, so that the primary particle diameter is increased. 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. If the difference in particle diameter is large, the degree of aggregation is affected, and as a result, the width of the particle size distribution of the indium hydroxide powder becomes wide.

Therefore, the electrolyte solution preferably has a solubility of indium hydroxide powder in the range of 10 ⁻⁶ mol / L to 10 ⁻³ mol / L, and controls the solubility of indium hydroxide powder by the concentration, pH, liquid temperature, etc. of the aqueous ammonium nitrate solution. can do. Thus, since it can control to the suitable solubility of an indium hydroxide powder, the indium hydroxide powder with a uniform particle size and a narrow width | variety of a particle size distribution can be obtained.

  It is preferable that the electrolyte solution adjusts the concentration of the aqueous ammonium nitrate solution to 0.1 mol / L to 2.0 mol / L. When the concentration of the aqueous ammonium nitrate solution is less than 0.1 mol / L, the voltage rise during electrolysis is increased, and problems such as heating of the energizing part and increased power cost are not preferable. On the other hand, when the concentration of the ammonium nitrate aqueous solution exceeds 2.0 mol / L, the solubility of the indium hydroxide powder in the electrolytic solution increases, so that the indium hydroxide particles become coarse and the variation in particle size increases, This is not preferable because the width of the distribution increases.

  The liquid temperature of the electrolytic solution is preferably adjusted to 20 ° C to 60 ° C. When the temperature of the electrolytic solution is less than 20 ° C., the indium hydroxide powder is deposited too slowly. On the other hand, when the liquid temperature of the electrolytic solution exceeds 60 ° C., indium hydroxide powder is deposited too quickly and precipitates are formed while the concentration of the electrolytic solution is not uniform, thereby widening the range of particle size distribution. .

Current density during electrolysis ^is preferably controlled to ^{4A / dm 2 ~20A / dm 2} . As a result, a wide range of current densities can be obtained. When the current density during electrolysis is less than 4 A / dm ² , the production efficiency of indium hydroxide powder is reduced. On the other hand, when the current density during electrolysis exceeds 20 A / dm ² , the electrolysis voltage increases, the liquid temperature is likely to increase, or the surface of the anode (indium metal) is passivated and is difficult to electrolyze. The problem of becoming. The current density indicates a current flowing per unit area of the electrode.

For example, in the electrolysis process, by applying a voltage between the anode and cathode electrodes made of indium disposed in the electrolyte, electrons are generated, and nitrate ions (NO ₃ ⁻ ) generated at the cathode are The electrons are received, a reduction reaction as shown in the following reaction formula (1) occurs, and nitrite ions (NO ₂ ⁻ ) are generated.

Here, in order to produce indium hydroxide powder having a uniform particle size and a narrow particle size distribution, it is necessary to control the pH in the electrolytic solution to 2.5 to 4.0. Therefore, as shown in FIG. 1, the generated nitrite ions generate HNO ₂ if the pH of the electrolyte is low. This is because since the pH is low, the hydrogen ion concentration is high, and nitrite (HNO ₂ ) is generated from nitrite ions (NO ₂ ⁻ ) according to the low pH value as shown in the following reaction formula (2). is there.

The generated nitrite (HNO ₂₎ is lower and pH2.5~4.0 of the electrolytic solution, the equilibrium reaction of the following reaction formula (3) and the following reaction formula (4), NOx (NO + NO 2) Gas is generated.

  Thus, the present inventors have found that the amount of NOx gas generated by electrolysis is determined by the current value and the pH value of the electrolytic solution in the method for producing indium hydroxide powder by the electrolysis method.

The amount of change from nitrate ion (NO ₃ ⁻ ) to nitrite ion (NO ₂ ⁻ ) according to the above reaction formula (1) is the amount of nitrite ion (NO ₂ ⁻ ) per minute according to Faraday's second law. The amount of substance can be derived as in the following formula (i).

n = (At / zF) × 1 / E (i)
[In the formula, n represents the amount (mol) of nitrite ions, A represents the current value (A) supplied during electrolysis, t represents time (seconds), and z represents the ionic valence. , F represents a Faraday constant of 9.65 × 10 ⁴ (C / mol), and E represents a physical quantity (mol) of electrons necessary to generate 1 mol of nitrite ion. ]

In the above formula (i), the current value (A) to be supplied during electrolysis, the time (60 seconds), the ionic valence (1) of the electron in the above reaction formula (1), the Faraday constant (9.65 × 10 ⁴ ) Substituting the physical quantity (2) of electrons necessary for generating 1 mol of nitrite ions, the following formula (ii) is derived.

n = (A × 60) / (2 × 9.65 × 10 ⁴ ) = 3A / 9650 (ii)

Further, in the reaction from nitrite ion (NO ₂ ⁻ ) to nitrous acid (HNO ₂ ) according to the above reaction formula (2), it depends on the pH of the electrolytic solution during electrolysis. iii) is derived.

[HNO ₂ ] / ([HNO ₂ ] + [NO ₂ ⁻ ]) = 1 / (1 + 10 ^−3.3 × 10 ^P )
... (iii)
[In formula, P shows the pH value of the electrolyte solution during electrolysis. ]

From the above formula (ii) and the above formula (iii), the amount of hydrogen peroxide with respect to the reaction amount from nitrate ion (NO ₃ ⁻ ) through nitrite ion (NO ₂ ⁻ ) to nitrous acid (HNO ₂ ) Is reacted at a ratio of 1: 1 to produce nitric acid (HNO ₃ ). In this case, the supply amount T per minute of hydrogen peroxide is represented by the following formula (iv) according to the current value and the pH of the electrolytic solution.

T = (1 / (1 + 10 ^−3.3 × 10 ^P )) × 3A / 9650 (iv)

Therefore, the present inventors derive a reference equation T = (1 / (1 + 10 ^−3.3 × 10 ^P )) × 3A / 9650 for defining the hydrogen peroxide supply rate Vadd. (Mol / min). We were able to.

In the present embodiment, the supply rate Vadd. Of hydrogen peroxide is such that hydrogen peroxide is supplied so as to satisfy the following relational expression based on the reference expression for defining the above.
(Relational expression) 0.7 T mol / min ≦ Vadd. ≦ 1.5 T mol / min
[Where Vadd. Represents the supply rate of hydrogen peroxide, T represents {1 / (1 + 10 ^−3.3 × 10 ^P )} × 3A / 9650, and A represents the current supplied during electrolysis. An electric current value (A) is shown, P shows the pH value of the electrolyte solution during electrolysis. ]

Thus, in order to obtain indium hydroxide powder having a uniform particle size and a narrow particle size distribution, even when the electrolyte is adjusted to pH 2.5 to 4.0, by supplying hydrogen peroxide, As shown in (5), nitrous acid (HNO ₂ ) generated during electrolysis can be decomposed into nitric acid (HNO ₃ ) and water (H ₂ O), and the reaction described above involving nitrous acid (HNO ₂ ). Since the equilibrium reaction as in the equations (3) and (4) does not occur, the amount of NOx gas generated can be suppressed.

When the supply rate Vadd. Of hydrogen peroxide is less than 0.7 T, as shown in FIG. 1, when the electrolyte solution has a pH of 2.5 to 4.0, a large amount of HNO ₂ is generated during electrolysis. Insufficient hydrogen peroxide is supplied to oxidize HNO ₂ . Therefore, since HNO ₂ produced is NOx gas (NO + NO ₂₎ by the equilibrium reaction, the lower the effect of suppressing the NOx gas emissions. On the other hand, when the supply rate Vadd. Of hydrogen peroxide exceeds 1.5T, excess hydrogen peroxide is self-decomposed and does not contribute to the suppression of NOx gas, so the supplied hydrogen peroxide is wasted. It is not preferable.

The concentration of hydrogen peroxide is not particularly limited as long as hydrogen peroxide necessary for decomposing nitrous acid (HNO ₂ ) into nitric acid (HNO ₃ ) and water (H ₂ O) can be supplied. However, supply of hydrogen peroxide having a low concentration causes a wasteful increase in the total amount of the electrolyte solution. Therefore, the concentration of hydrogen peroxide is preferably as high as possible, for example, 35% which is generally available. It is desirable to be at least hydrogen oxide.

  As a method for supplying hydrogen peroxide, it can be quantitatively supplied by a metering pump or other chemical-resistant pump, and may be a known method. For example, as a method of supplying hydrogen peroxide, hydrogen peroxide is directly supplied to the electrolytic cell by a metering pump, or a pump is supplied together with an electrolytic solution whose pH and liquid temperature are adjusted by supplying hydrogen peroxide to a regulating tank. For example, an adjusted electrolytic solution containing hydrogen peroxide is fed into the electrolytic cell through a circulation means such as the above.

  As a method for supplying hydrogen peroxide, it is preferable to supply hydrogen peroxide directly into the electrolyte solution through a tube or the like in order to efficiently supply the hydrogen peroxide. This is because when hydrogen peroxide is dropped on the surface of the electrolytic solution, hydrogen peroxide is easily decomposed in the air, so that the function of the hydrogen peroxide as an oxidizing agent is prevented from being impaired. Thus, by supplying hydrogen peroxide directly into the electrolytic solution, the amount of generated NOx gas can be easily suppressed.

In particular, since nitrite ions (NO ₂ ⁻ ) are generated at the cathode during electrolysis, nitrite ions (NO ₂ ) are used as a method of supplying hydrogen peroxide directly into the electrolyte solution in order to efficiently suppress NOx gas. ₂ ^- the cathode nearby the source of), it is more preferable to supply hydrogen peroxide. Thus, since hydrogen peroxide can be supplied directly to the vicinity of the cathode, the generated NOx gas can be more efficiently suppressed. Specifically, the NOx gas generation amount can be suppressed to 6.0 × 10 ⁻⁶ m ³ / A · hr or less.

(1-2) Recovery process of indium hydroxide powder In the recovery process of indium hydroxide powder, the electrolytic slurry produced in the electrolysis process of indium hydroxide powder is solid-liquid separated from the electrolytic solution, and separated indium hydroxide powder. The product is washed with pure water or the like, and separated and recovered again.

  Examples of the solid-liquid separation method include filtration by a rotary filter, centrifugal separation, filter press, pressure filtration, vacuum filtration, etc., but use of a rotary filter with high recovery efficiency is preferable. In addition, the frequency | count of washing | cleaning is not specifically limited, It performs several times as needed.

(1-3) Indium hydroxide powder drying step In the indium hydroxide powder drying step, the recovered indium hydroxide powder is dried. The drying method is performed by 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 not preferable. On the other hand, when the drying temperature exceeds 150 ° C., it changes from indium hydroxide powder to indium oxide powder, which is inconvenient in adjusting the particle size distribution of indium oxide powder in the method for producing indium oxide powder. The drying time varies depending on the temperature, but is preferably about 10 to 24 hours.

  As described above, in the method for producing indium hydroxide powder according to the present embodiment, hydrogen peroxide is electrolyzed even in an environment where the pH of the electrolytic solution is likely to generate NOx gas such as 2.5 to 4.0. By supplying the liquid, NOx gas generated during electrolysis can be suppressed, and the load on the environment can be reduced. Further, in this manufacturing method, since nitrous acid generated during electrolysis is oxidized to nitric acid by hydrogen peroxide, it is not necessary to separately provide a processing facility for treating NOx gas generated during electrolysis. Furthermore, in this production method, indium hydroxide powder having a uniform particle size and a narrow particle size distribution can be obtained.

2. Indium oxide powder manufacturing method In the indium oxide powder manufacturing method, the indium hydroxide powder after drying is calcined to produce indium oxide powder. The calcination conditions are preferably, for example, a calcination temperature of 600 ° C. to 800 ° C. and a calcination time of 1 hour to 10 hours.

  The indium oxide powder has inherited the characteristic that the width of the particle size distribution of the indium hydroxide powder obtained by the method for producing indium hydroxide powder as described above is narrow. For this reason, in the manufacturing method of indium oxide powder, indium oxide powder with a narrow particle size distribution width is obtained by using indium hydroxide powder with a narrow particle size distribution width.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited by these.

<Example 1>
In Example 1, in an electrolytic cell (length 40 cm × width 40 cm × height 50 cm), four cathodes made of a titanium metal plate having a width of 26 cm, a height of 40 cm, and a thickness of 4 mm, and indium metal having a purity of 99.9999% were placed. Three anodes molded into a plate shape having a width of 26 cm, a height of 40 cm, and a thickness of 8 mm were alternately arranged, and the distance between the cathode and the anode was adjusted to 2.0 cm. Next, 75 L of an ammonium nitrate aqueous solution used as an electrolytic solution was accommodated in the electrolytic cell, and the concentration of this aqueous solution was 1.0 mol / L, the pH was 3.5, and the liquid temperature was 40 ° C.

In the electrolysis process of the indium hydroxide powder, the anode current density was adjusted to 15 A / dm ² (battery current 936 A), and was carried out for 6 hours. As shown in Table 1, hydrogen peroxide supplied during electrolysis was 11.6 mol / L of 35% hydrogen peroxide (manufactured by Mitsubishi Gas Chemical Co., Ltd.), and was supplied at a rate of 10 mL / min. In this electrolysis step, an indium hydroxide slurry was obtained 6 hours after the start of electrolysis.

The amount of NOx gas generated during electrolysis is exhausted every minute using a NOx meter for exhaust gas (42CHL manufactured by Nippon Thermo Co., Ltd.) while exhausting 1.5m ³ / min in the electrolytic cell. The NOx gas concentration was measured and obtained from the sum of all NOx gas concentrations after electrolysis. In Example 1, this NOx gas generation amount is shown in Table 1.

  The obtained indium hydroxide slurry was filtered and washed with pure water twice, and then dried at 110 ° C. for 15 hours to produce indium hydroxide powder. Then, the produced indium hydroxide powder was calcined at 750 ° C. for 4 hours to produce indium oxide powder.

  In Example 1, the particle size distribution of the produced indium hydroxide powder and indium oxide powder was measured by a laser diffraction / scattering method (SALD-2200, manufactured by Shimadzu Corporation) and is shown in Table 2.

<Example 2>
In Example 2, as shown in Table 1, the indium hydroxide powder was obtained in the same manner as in Example 1 except that the magnification was 0.8 T with respect to the reference formula T for defining the hydrogen peroxide supply rate Vadd. Indium oxide powder was prepared. In Example 2, the amount of NOx gas generated during electrolysis is shown in Table 1. Furthermore, in Example 2, the particle size distribution of the produced indium hydroxide powder and indium oxide powder is shown in Table 2, respectively.

<Example 3>
In Example 3, as shown in Table 1, the indium hydroxide powder was obtained in the same manner as in Example 1 except that the magnification was 0.7 T with respect to the reference formula T for defining the hydrogen peroxide supply rate Vadd. Indium oxide powder was prepared. In Example 3, the amount of NOx gas generated during electrolysis is shown in Table 1. Furthermore, in Example 3, the particle size distribution of the produced indium hydroxide powder and indium oxide powder is shown in Table 2, respectively.

<Example 4>
In Example 4, as shown in Table 1, the indium hydroxide powder was changed in the same manner as in Example 1 except that the magnification was 1.5 T with respect to the reference formula T for defining the hydrogen peroxide supply rate Vadd. Indium oxide powder was prepared. In Example 4, the amount of NOx gas generated during electrolysis is shown in Table 1. Furthermore, in Example 4, the particle size distribution of the produced indium hydroxide powder and indium oxide powder is shown in Table 2, respectively.

<Comparative Example 1>
In Comparative Example 1, indium hydroxide powder and indium oxide powder were prepared in the same manner as in Example 1 except that hydrogen peroxide was not supplied as shown in Table 1. In Comparative Example 1, the amount of NOx gas generated during electrolysis is shown in Table 1. Furthermore, in Comparative Example 1, the particle size distributions of the produced indium hydroxide powder and indium oxide powder are shown in Table 2, respectively.

<Comparative example 2>
In Comparative Example 2, as shown in Table 1, indium hydroxide powder was used in the same manner as in Example 1 except that the magnification was 0.5 T with respect to the reference formula T for defining the hydrogen peroxide supply rate Vadd. Indium oxide powder was prepared. In Comparative Example 2, the amount of NOx gas generated during electrolysis is shown in Table 1. Further, in Comparative Example 2, Table 2 shows the particle size distributions of the produced indium hydroxide powder and indium oxide powder.

<Comparative Example 3>
In Comparative Example 3, as shown in Table 1, indium hydroxide powder was used in the same manner as in Example 1 except that the magnification was 1.6 T with respect to the reference formula T for defining the hydrogen peroxide supply rate Vadd. Indium oxide powder was prepared. In Comparative Example 3, the amount of NOx gas generated during electrolysis is shown in Table 1. Furthermore, in Comparative Example 3, Table 2 shows the particle size distributions of the produced indium hydroxide powder and indium oxide powder.

※Ｔ＝{１／（１＋１０^−３．３×１０^Ｐ）}×３Ａ／９６５０

* T = {1 / (1 + 10 ^−3.3 × 10 ^P )} × 3A / 9650

In Examples 1 to 4, as shown in Table 1, it was confirmed that the NOx gas generation amount was suppressed as the hydrogen peroxide supply rate Vadd. Was increased. On the other hand, in Comparative Example 1 and Comparative Example 2, as shown in Table 1, it was confirmed that the NOx gas generation amount exceeded 6.0 × 10 ⁻⁶ m ³ / A · hr, and NOx gas could not be suppressed. . Further, in Comparative Example 3, it was confirmed that even when the hydrogen peroxide supply rate Vadd. Was increased, there was no difference in the amount of NOx gas generated from that in Example 4. That is, it was confirmed that hydrogen peroxide hardly contributes to the suppression of NOx gas generation when the magnification with respect to the reference formula T for defining the hydrogen peroxide supply rate Vadd. Exceeds 1.5 T mol / min. .

  In Example 1 and Comparative Example 1, as shown in Table 1, it was confirmed that the generation amount of NOx gas was reduced to 1/56 when compared with the case where a predetermined amount of hydrogen peroxide was supplied.

  In Examples 1 to 4, as shown in Table 2, even when hydrogen peroxide was supplied during electrolysis, it was confirmed that the width of the particle size distribution of the indium hydroxide powder and the particle size distribution of the indium oxide powder was narrow. Moreover, in Comparative Example 1 thru | or Comparative Example 3, as shown in Table 2, it confirmed that the width | variety of the particle size distribution of indium hydroxide powder and the particle size distribution of indium oxide powder was narrow.

  Therefore, when the relational expression 0.7T to 1.5T indicating the hydrogen peroxide supply rate Vadd., Indium hydroxide powder that suppresses NOx gas generated during electrolysis, has a uniform particle size, and a narrow particle size distribution range. It was confirmed that it was useful for producing Further, it was confirmed that supplying hydrogen peroxide during electrolysis does not affect the particle size distribution of the indium hydroxide powder and the particle size distribution of the indium oxide powder using the indium hydroxide powder.

Claims (2)

A method for producing indium hydroxide powder, which produces indium hydroxide powder by an electrolytic method using indium as an anode in an ammonium nitrate aqueous solution having a pH of 2.5 to 4.0 as an electrolytic solution,
A method for producing indium hydroxide powder, characterized in that hydrogen peroxide is supplied directly into the electrolyte within a range of a supply rate satisfying the following relational expression.
(Relational expression) 0.7 T mol / min ≦ Vadd. ≦ 1.5 T mol / min
[Where Vadd. Represents the supply rate of hydrogen peroxide, T represents {1 / (1 + 10 ^−3.3 × 10 ^P )} × 3A / 9650, and A represents the current supplied during electrolysis. An electric current value (A) is shown, P shows the pH value of the electrolyte solution during electrolysis. ] The method for producing indium hydroxide powder according to claim 1 , wherein the hydrogen peroxide is supplied into the electrolyte near a cathode that is a counter electrode of the anode.

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