KR100370402B1 - Method for preparing indium tin oxide powder from indium tin oxide scrap - Google Patents

Abstract

The present invention provides a method for producing ITO powder and high density ITO sintered body from indium tin oxide (ITO) scrap. The method for producing ITO powder may include dissolving ITO scrap in a strong acid; Adding an alkali to the mixture to precipitate a mixed sludge of indium and tin; Filtering, washing and drying the sludge precipitated from the above step; Calcining the resultant formed from the step; And vacuuming the powder produced from the step. According to the present invention, ITO powder having excellent purity from ITO scrap can be produced through a relatively simple process, and the ITO waste target can be recycled through such a manufacturing process. In particular, it is possible to manufacture ITO powder with uniform particle size by reducing the variation between powders that can occur in the washing and calcination process through calcination after calcination, and excellent sinterability by lowering cohesion between particles through vacuum process ITO powder can be prepared. By pulverizing, molding and sintering the ITO powder, a high density ITO sintered body having a relative density of 98% or more can be obtained.

Description

Method for preparing indium tin oxide powder from indium tin oxide scrap

The present invention relates to a method for preparing ITO powder from ITO scrap that is a waste indium tin oxide (ITO) target, and more specifically, to indium oxide without undergoing a process of separating indium and tin from waste ITO scrap. And a method for recovering an ITO powder composed of a mixture of tin oxide and a predetermined ratio, and a method for producing a high density ITO sintered compact by pulverizing, molding and sintering the ITO powder.

ITO transparent conductive film, which is transparent and has high electric conductivity because of its high light transmittance in visible light, is widely used as a transparent electrode such as flat panel display devices such as liquid crystal display devices, plasma display panels, field emission display devices, and electroluminescent devices, solar cells, and transparent heating wires. It is used. Tin oxide (SnO ₂ ), zinc oxide (ZnO) and the like are also used as the transparent electrode material, but ITO having SnO ₂ added to In ₂ O ₃ is widely used as the most representative material.

ITO thin films are crystalline transparent films made by vapor deposition, sputtering, or the like, and are widely used as electrodes for liquid crystal display devices from high resistance regions (200 μs / square or more) to low resistance regions (10 μs / square or less). This ITO thin film is manufactured by various thin film deposition methods, but the sputtering method is most widely used because a large area uniform thin film is required when used in flat display devices. In order to use this sputtering method, the demand for ITO target, which is a high-density ITO sintered body, is increasing, but the utilization rate of the target is only about 30% due to process problems.

However, indium, which is a raw material of ITO target, is one of the expensive elements because it is obtained at the level of several hundred ppm from zinc ore, and there is no main source ore. Therefore, the process of recycling 70% of the remaining target after use is a very important technique.

In the conventional case, the method of recycling the ITO scrap is mainly a method of crushing the waste ITO target, forming and sintering it as shown in FIG. 1 (Japanese Patent Laid-Open No. 10-204673, Japanese Patent Laid-Open No. 8-91838, US Patent No. 5,660,599). ). However, the ITO target recovered by this method has a low sintered density, and there is a problem that a considerable amount of impurities may be mixed until the waste ITO target is pulverized to obtain tens of microns of ITO powder.

Another method for recycling ITO scrap is to obtain hydroxide of indium and tin in an electrolytic cell using ITO scrap as an anode using the conductivity of the target (US Pat. No. 5,543,031) or electrolytic reaction after reducing ITO scrap. For example, Japanese Patent Application Laid-Open No. 70145432. However, according to the methods disclosed in these patents, the composition of high purity ITO, which is a characteristic of ITO scrap, cannot be maintained as it is, and the energy consumption of the process is large, and the mass production of ITO powder is difficult, so that it is expensive to obtain a powder. There was a lifting issue.

In addition, another method of recycling ITO scrap is to separate indium and tin from the waste ITO target, and to prepare oxide powders of indium and tin, and to introduce the same into an existing ITO target molding process. However, this method adds the processing cost as much as the process of separating indium and tin and has a problem of being possible only in a company having a refinery of ore.

Unlike the ITO recycling method according to the prior art as described above, there is a need for a method for recycling ITO scrap, which is cost-saving through a relatively simple process, by preventing the mixing of impurities through proper handling of the already-purified ITO waste target. It is getting higher.

The technical problem to be achieved by the present invention is a method for recovering ITO powder composed of indium oxide and tin oxide in a predetermined ratio without separating indium and tin from waste ITO scrap and a method for producing an ITO sintered body from the ITO powder. To provide.

1 is a process flow diagram for producing an ITO sintered body from ITO scrap according to the prior art,

2 is a process flow diagram for producing an ITO sintered body from ITO scrap according to the present invention,

3 is a view showing X-ray diffraction (XRD) experimental data of the ITO powder prepared according to Example 1 of the present invention,

4 is a view showing an electron scanning microscope (SEM) photograph of the ITO sintered body prepared according to Example 1 of the present invention,

5 is a view showing X-ray diffraction (XRD) experimental data of the ITO powder prepared according to Example 2 of the present invention,

6 is a view showing an electron scanning microscope (SEM) photograph of the ITO sintered body prepared according to Example 2 of the present invention,

7 is a view showing X-ray diffraction (XRD) experimental data of the ITO powder prepared according to Example 3 of the present invention,

8 is a view showing an electron scanning microscope (SEM) photograph of the ITO sintered body prepared according to Example 3 of the present invention,

9 is a view showing X-ray diffraction (XRD) experimental data of ITO powder prepared according to Comparative Example 1 of the present invention,

10 is a view showing an electron scanning micrograph of the ITO sintered body prepared according to Comparative Example 1 of the present invention,

FIG. 11 is a diagram showing X-ray diffraction (XRD) experimental data of ITO powder prepared according to Comparative Example 2 of the present invention.

12 is a view showing an electron scanning micrograph of the ITO sintered body prepared according to Comparative Example 2 of the present invention.

In the present invention to achieve the first technical problem, (a) dissolving ITO scrap in a strong acid;

(b) adding alkali to the mixture to precipitate mixed sludge of indium and tin;

(c) filtering, washing and drying the sludge precipitated from the step (b);

(d) calcining the resultant formed from (c); And

It provides a method for producing ITO powder from the ITO scrap comprising a; (e) vacuuming the powder produced from the step (d).

The method for producing ITO powder of the present invention may further include an aging step of crystallizing the sludge formed from the step (b) before the step (c).

The second technical problem of the present invention is to provide a method for producing an ITO sintered body from ITO scraps, which is obtained by pulverizing, molding and sintering the ITO powder prepared according to the above method.

Hereinafter, with reference to FIG. 2, a method for producing ITO powder from ITO scrap according to the present invention will be described in more detail.

First, the ITO scrap is finely pulverized to a size of less than 0.2 cm, and then a strong acid is added thereto to dissolve it. In this case, at least one selected from hydrochloric acid, nitric acid and sulfuric acid is used as the strong acid, and the content thereof is 1 to 5 equivalents, in particular 1.5 equivalents, based on 1 equivalent of indium in the ITO scrap. If the content of the strong acid is less than 1 equivalent, the complete dissolution of the waste target is impossible, and if more than 5 equivalents, there is a problem in that additional costs are generated due to the use of the strong acid more than necessary.

The reaction for dissolving the above-mentioned ITO scrap in a strong acid is preferably stirred at 40 to 100 ° C. for 6 to 48 hours. At this time, if the reaction temperature is less than 40 ℃, the reaction rate is too slow to completely dissolve the ITO scrap in a limited time, if it exceeds 100 ℃ the reaction is too violent to increase the additional cost for safety .

Thereafter, ultrapure water is added to the mixture in which the ITO scrap is dissolved to adjust the initial concentration of indium to be 0.01 to 4M. If the initial concentration of indium is less than 0.01M, the particle size of the precipitate is too small and the concentration is not easy to separate, and the apparatus cost increases because the reactor size must be increased to obtain the same amount of precipitate. If is larger than 4M, a uniform precipitate cannot be obtained because a gel is formed.

Then, by adjusting the pH to 8 to 10 by adding alkali to the mixture, indium and tin can be co-precipitated with hydroxides. The alkali used in this coprecipitation reaction is at least one selected from the group consisting of ammonium hydroxide, ammonium hydrogen carbonate and urea, and after completion of the precipitation reaction, the indium concentration in the mixture is adjusted to be 0.005 to 3M. If the initial concentration of indium is less than 0.005M, the particle size of the precipitate is too small and the concentration is not easy to separate, and the apparatus cost increases because the reactor size must be increased to obtain the same amount of precipitate. When is larger than 3M, a uniform precipitate cannot be obtained because a gel is formed.

The precipitate obtained according to the above process is filtered into a solid and a liquid using a filter press, a centrifugal dehydrator, or the like. After the filtration process, the solids are washed with ultrapure water and alcohols, where the alcohol washes have the effect of inhibiting aggregation between the particles during drying.

When hydrochloric acid is used as a strong acid for dissolving ITO scrap, washing is repeated until the amount of chlorine in the precipitate after washing is less than 100 ppm. If the amount of chlorine is more than 100ppm, the residual chlorine concentration increases, so the density of the final ITO sintered body is lowered.

After the cleaning process is completed, it is dried. At this time, the drying temperature is preferably 70 to 120 ℃, it is possible both under atmospheric pressure or vacuum atmosphere. If the drying temperature is less than 70 ° C, the drying time becomes too long, and if it exceeds 120 ° C, a solid dry product is obtained, which is not preferable.

The resultant dried according to the above procedure is then calcined in air. As for the temperature in this calcination step, 550-850 degreeC is preferable. If the calcination temperature is less than 550 ° C, volatile impurities are not completely removed, and if it exceeds 850 ° C, the sintering of the particles is not preferable.

Thereafter, the ITO powder produced in the calcination step is vacuumed at 80 to 300 ° C. for at least 6 hours. If the temperature during the vacuum treatment is less than 80 ℃ desorption rate is too slow, if it exceeds 300 ℃ indium oxide can be reduced in the vacuum atmosphere. As described above, the vacuum treatment process effectively removes the anion impurities released from the indium oxide lattice during calcination.

That is, during calcination, indium hydroxide forms stable indium oxide, and residual chlorine and sulfur are oxidized and removed. However, trace amounts of chlorine and sulfur are adsorbed on the surface of the powder, and these adsorbates can be removed by vacuum treatment.

The vacuum treated ITO powder is pulverized, molded and sintered according to a conventional method to obtain an ITO sintered body. Thus, the specific surface area of the ITO powder obtained by the manufacturing method of this invention is 50-80m <2> / g, and the ITO sintered compact has a relative density of 96% or more, and the ratio of indium and tin at this time is the same as that of ITO scrap. .

Hereinafter, the present invention will be described in detail with reference to the following examples, but the present invention is not limited only to the following examples.

<Example 1>

ITO scraps were ground and sieved to select only particles less than 2 mm in size. 60 g of the sieved particles were weighed and added to 200 ml of a stock solution of hydrochloric acid (36% HCl), and dissolved at 80 ° C. for 20 hours to obtain a solution in which indium and tin were dissolved. 2/5 of the solution was then poured into a beaker and deionized water was added to bring the total volume to 400 ml. At this time, the concentration of indium is 0.4M. The solution was stirred at 300 rpm while 28% ammonia water was added to the solution in which indium and tin were dissolved. The reaction was terminated when the pH of the mixture reached 8.5. At this time, the concentration of indium was 0.3M.

After the reaction was completed, the reaction mixture was aged at room temperature for 16 hours. The solution after aging was separated into a solid and a liquid using a centrifuge.

The water-soluble ions in the obtained solid were extracted into the liquid phase using ultrapure water, and the liquid phase was removed using a centrifuge. This washing process was repeated six times, and the washing process was further performed once with ethanol. The chlorine concentration in the precipitate after the above washing process was 75 ppm.

After that, the solid washed with ethanol was placed in a convection oven and dried overnight at 80 ℃. Subsequently, the obtained solid was ground to 100 micrometers or less, and the mixed powder of indium hydroxide and tin hydroxide was obtained. The powder was raised to 650 ° C. at an elevated rate of 3 ° C./min in an atmospheric atmosphere and then calcined at this temperature for 1 hour.

Subsequently, the oxidized powder after calcination was put in a vacuum oven and vacuum-treated at 180 ° C. for one day to obtain ITO powder.

The vacuumed ITO powder was ground in a ball mill for 12 hours and then dried to form a pressure of 3 tons under cold hydrostatic pressure. Subsequently, the molded body was raised to 1500 ° C. at an elevated temperature rate of 15 ° C./min in an air atmosphere and sintered for 1 hour to obtain an ITO sintered body.

The shape and size of the ITO powder and the crystal structure of the ITO powder obtained according to the above procedure were confirmed, and the results are shown in FIGS. 3 and 4.

FIG. 3 is a diagram showing X-ray diffraction (XRD) experimental data of ITO powder prepared according to Example 1. FIG. Referring to this, it was found that SnO ₂ was completely substituted at the In ₂ O ₃ site with the same ratio of the original target, indium and tin.

In addition, Figure 4 is a SEM photograph of the ITO powder prepared according to Example 1. Referring to this, it was found that the ITO powder is a powder having a particle size of nanosize having a primary particle size of about 20 nm or less.

On the other hand, the sintering characteristics of the ITO sintered compact obtained in Example 1 were observed. As a result, the density of the ITO sintered compact was 7.08 g / cm <3>, and the relative density was 99%.

<Example 2>

ITO scraps were ground and sieved to select only particles less than 2 mm in size. 60 g of the sieved particles were weighed and placed in 200 ml of a stock solution where nitric acid and sulfuric acid were mixed in a 1: 1 ratio, and dissolved at 80 ° C. for 48 hours to obtain a solution in which indium and tin were dissolved. 4/5 of the solution was taken and poured into a beaker and deionized water was added to bring the total volume to 400 ml. At this time, the concentration of indium is about 0.8M.

Subsequently, the reaction mixture was stirred at 300 rpm while adding 28% ammonia water to the solution in which indium and tin were dissolved. The reaction was terminated when the pH of the mixture reached 8.5. At this time, the concentration of indium was 0.6M.

After the reaction was completed, the mixture was aged at room temperature for 16 hours. The solution after aging was separated into a solid and a liquid using a centrifuge.

The water-soluble ions in the obtained solid were extracted into the liquid phase using deionized water, and the liquid phase was removed using a centrifuge. This washing process was repeated eight times, and the washing process was further performed twice using ethanol.

After the ethanol wash was completed, the solid was placed in a convection oven and dried at 80 ° C. overnight. The dried solid was pulverized to 100 μm or less to obtain a mixed powder of indium hydroxide and tin hydroxide. The powder was calcined at this temperature for 1 hour after the temperature was raised to 700 ° C. per minute at 3 ° C. per minute.

The oxidized powder after calcination was put in a vacuum oven and vacuum-treated at 180 ° C. for one day to obtain ITO powder.

The vacuumed ITO powder was ground in a ball mill for 12 hours, then dried and molded at a pressure of 3 tons under cold hydrostatic pressure. Subsequently, the molded body was raised to 1500 ° C. at an elevated temperature rate of 15 ° C./min under an air atmosphere, and then sintered at this temperature for 1 hour to obtain an ITO sintered body.

The shape, particle size and crystal structure of the ITO powder prepared according to Example 2 were examined.

5 is a diagram showing X-ray diffraction (XRD) experimental data of ITO powder prepared according to Example 2 of the present invention. Referring to this, it was found that the ratio of the original target and tin was the same, and that SnO ₂ was completely substituted at In ₂ O ₃ sites.

6 is an electron scanning microscope (SEM) photograph of the ITO sintered body manufactured according to Example 2 of the present invention. Referring to this, it can be seen that the ITO powder has a particle size of nanosize having a primary particle diameter of about 40 nm or less.

The sintering characteristics of the ITO sintered body prepared according to Example 2 were investigated.

As a result, the density of the ITO sintered compact was 7.01 g / cm <3>, and the relative density was 98%.

<Example 3>

The ITO scraps were ground and sieved to select particles less than 2 mm in size. 60 g of the sieved particles were weighed and placed in 200 ml of a stock solution in which nitric acid and hydrochloric acid were mixed in a 1: 1 ratio, and dissolved at 80 ° C. for 48 hours to obtain a solution of indium and tin. 2/5 of the solution was taken and poured into a beaker and deionized water was added to bring the total volume to 400 ml. At this time, the concentration of indium is about 0.4M.

The reaction mixture was stirred at 300 rpm while adding 28% ammonia water to the solution in which indium and tin were dissolved. The reaction was terminated when the pH of the reaction mixture reached 8.5, at which time the concentration of indium was 0.35M.

At the end of the reaction, the reaction mixture was stored at room temperature for 16 hours. This solution was separated into solid and liquid using a centrifuge. The water-soluble ions in the obtained solid were extracted into the liquid phase using deionized water, and the liquid phase was removed using a centrifuge. This washing process was repeated six times.

Thereafter, the washing process was further performed once using ethanol. At this time, the chlorine concentration of the precipitate was 60 ppm. The solid after washing with ethanol was placed in a convection oven and dried overnight at 80 ° C. The dried solid was pulverized to 100 μm or less to obtain a mixed powder of indium hydroxide and tin hydroxide. The powder was raised to 650 ° C. at 3 ° C. per minute in an atmospheric atmosphere and then calcined at this temperature for 1 hour. The oxidized powder after calcination was put in a vacuum oven and vacuum-treated at 180 degrees for one day to obtain ITO powder.

The vacuumed ITO powder was ground in a ball mill for 12 hours, then dried and molded at a pressure of 3 tons under cold hydrostatic pressure. Subsequently, the molded body was raised to 1500 ° C. at an elevated temperature rate of 15 ° C./min in an air atmosphere, and then sintered at this temperature for 1 hour to obtain an ITO sintered body.

The shape, particle size and crystal structure of the ITO powder prepared according to Example 3 were examined.

7 is a diagram showing X-ray diffraction (XRD) experimental data of ITO powder prepared according to Example 3 of the present invention. Referring to this, it was found that the ratio of the original target and tin was the same, and that SnO ₂ was completely substituted at In ₂ O ₃ sites.

8 is a view showing an electron scanning microscope (SEM) photograph of the ITO sintered body prepared according to Example 3 of the present invention. Referring to this, it can be seen that the ITO powder has a particle size of nanosize having a primary particle size of about 20 nm or less.

The sintering characteristics of the ITO sintered body prepared according to Example 3 were investigated.

As a result, the density of the ITO sintered compact was 7.08 g / cm <3>, and the relative density was 99%.

Comparative Example 1

ITO scraps were ground and sieved to select only particles less than 2 mm in size. 60 g of the particles were weighed into 200 ml of stock solution of hydrochloric acid (36% HCl) and dissolved at 80 ° C. for 20 hours to obtain a solution in which indium and tin were dissolved. 2/5 of the solution was taken and poured into a beaker and deionized water was added to bring the total volume to 400 ml. At this time, the concentration of indium is about 0.2M.

The reaction mixture was stirred at 300 rpm while adding 28% aqueous ammonia at a rate of 0.3 ml / sec to the solution containing tin and indium. The reaction was terminated when the pH of the reaction mixture reached 8.5.

At the end of the reaction, the reaction mixture was aged at room temperature for 16 hours. Thereafter, a solid and a liquid were separated from the solution after aging using a centrifuge. The water-soluble ions in the obtained solid were extracted into the liquid phase using deionized water, and the liquid phase was removed using a centrifuge. This washing process was repeated three times, and the washing process was further performed once with ethanol. At this time, the chlorine concentration of the precipitate was 500 ppm.

The solid after washing with ethanol was placed in a convection oven and dried overnight at 80 ° C. The dried solid was pulverized to 100 μm or less to obtain a mixed powder of indium hydroxide and tin hydroxide. The powder was raised to 600 ° C. at 3 ° C. per minute in an atmospheric atmosphere and then calcined at this temperature for 1 hour to obtain ITO powder.

Thereafter, the ITO powder was molded at a pressure of 3 tons under cold hydrostatic pressure. The molded body was raised to 600 ° C. at an elevated temperature rate of 15 ° C./min in an air atmosphere, and maintained at this temperature for 1 hour to obtain an ITO sintered body.

The shape and particle size and crystal structure of the ITO powder prepared according to Comparative Example 1 were examined.

9 is a view showing X-ray diffraction (XRD) experimental data of ITO powder prepared according to Comparative Example 1 of the present invention. Referring to this, it was found that the ratio of the original target and tin was the same, and that SnO ₂ was completely substituted at In ₂ O ₃ sites.

10 is a view showing an electron scanning microscope (SEM) photograph of the ITO sintered body prepared according to Comparative Example 1 of the present invention. Referring to this, it can be seen that the ITO powder has a particle size of nanosize having a primary particle diameter of about 40 nm or less.

The sintering characteristics of the ITO sintered body prepared according to Comparative Example 1 were investigated.

As a result, the density of the ITO sintered compact was 4.25 g / cm <3>, and the relative density was 60%.

Comparative Example 2

ITO scraps were ground and sieved to select only particles less than 2 mm in size. 60 g of the particles were weighed into 200 ml of stock solution of hydrochloric acid (36% HCl) and dissolved at 80 ° C. for 20 hours to obtain a solution in which indium and tin were dissolved. 2/5 of the solution was taken and poured into a beaker and deionized water was added to bring the total volume to 400 ml. At this time, the concentration of indium is about 0.2M.

The reaction mixture was stirred at 300 rpm while adding 28% aqueous ammonia at a rate of 0.3 ml / sec to the solution in which indium and tin were dissolved. The reaction was terminated when the pH of the reaction mixture reached 8.5.

After the reaction was completed, the reaction mixture was aged at room temperature for 16 hours. A centrifuge was used to separate the solid and liquid from the solution after aging. The water-soluble ions in the obtained solid were extracted into the liquid phase using deionized water, and the liquid phase was removed using a centrifuge. This washing process was repeated three times, and the washing process was further performed once with ethanol. At this time, the concentration of chlorine was 500 ppm.

The solid after washing with ethanol was placed in a convection oven and dried overnight at 80 ° C. The dried solid was pulverized to 100 μm or less to obtain a mixed powder of indium hydroxide and tin hydroxide. The powder was raised to 600 ° C. at a temperature of 3 ° C. per minute in an air atmosphere, and then calcined at this temperature for 1 hour to obtain ITO powder.

The ITO powder after the calcining was molded at a pressure of 3 tons under cold hydrostatic pressure. Subsequently, the molded body was raised to 600 ° C. at an elevated temperature rate of 15 ° C./min in an air atmosphere, and maintained at this temperature for 1 hour to obtain an ITO sintered body.

The shape, particle size, and crystal structure of the ITO powder prepared according to Comparative Example 2 were examined.

FIG. 11 shows X-ray diffraction (XRD) experimental data of ITO powder prepared according to Comparative Example 2 of the present invention. FIG. Referring to this, it was found that the ratio of the original target and tin was the same, and that SnO ₂ was completely substituted at In ₂ O ₃ sites.

12 is an electron scanning microscope (SEM) photograph of the ITO sintered body manufactured according to Example 2 of the present invention. Referring to this, it can be seen that the ITO powder has a particle size of nanosize having a primary particle diameter of about 40 nm or less.

The sintering characteristics of the ITO sintered body prepared according to Comparative Example 2 were investigated.

As a result, the density of the ITO sintered compact after sintering was 4.25 g / cm <3>, and the relative density was 60%.

As described above, the density and relative density characteristics of the ITO sintered body prepared according to Example 1-3 were superior to those of Comparative Examples 1-2 after vacuum treatment.

According to the present invention, ITO powder having excellent purity from ITO scrap can be produced through a relatively simple process, and the ITO waste target can be recycled through such a manufacturing process. In particular, it is possible to manufacture ITO powder with uniform particle size by reducing the variation between powders that can occur in the washing and calcination process through calcination after calcination, and excellent sinterability by lowering cohesion between particles through vacuum process ITO powder can be prepared. By pulverizing, molding and sintering the ITO powder, a high density ITO sintered body having a relative density of 98% or more can be obtained.

Claims (11)

(a) dissolving ITO scrap in one or more strong acids selected from the group consisting of hydrochloric acid, nitric acid and sulfuric acid; (b) adding alkali to the mixture to adjust the pH to 8 to 10 to precipitate a mixed sludge of indium and tin; (c) filtering, washing and drying the sludge precipitated from step (b) at 70 to 120 ° C; (d) calcining the resultant formed from (c) at 550 to 850 ° C .; And (e) vacuuming the powder produced in step (d) at 80 to 300 ° C .; a method for producing ITO powder from ITO scraps, comprising: a. The method according to claim 1, further comprising an aging step of crystallizing by aging the sludge precipitated from step (b) before performing step (c). The method of claim 1, wherein the content of the strong acid added in step (a) is 1 to 5 equivalents based on 1 equivalent of indium. The method for producing ITO powder from ITO scrap according to claim 1, wherein step (a) is performed at 40 to 100 ° C. The method for preparing ITO powder from ITO scrap according to claim 1, wherein the initial concentration of indium before adding alkali in step (b) is 0.01 to 4M. The method for producing ITO powder from ITO scrap according to claim 1, wherein the concentration of indium after addition of alkali in step (b) is 0.005 to 3M. delete The method of claim 1, wherein in step (b), the alkali is at least one selected from the group consisting of ammonium hydroxide, ammonium bicarbonate and urea. The method according to claim 1, wherein when hydrochloric acid is used as the strong acid in step (a), the amount of chlorine in the precipitate after washing in step (c) is less than 100 ppm each. delete delete