JP5217480B2 - Recovery method of crude indium - Google Patents

Description

  The present invention relates to a method for recovering crude indium, and more particularly, from indium tin oxide (ITO) target scrap, which has a purity suitable for electrolytic refining anode even when the content of impurity metal elements is high. The present invention relates to a method for recovering crude indium with high yield.

Indium has been conventionally used as dental alloys, solder, low melting point alloys, trace components for semiconductors, transparent conductive thin films for liquid crystal display devices, and ITO films for gas sensors. It is expanding.
In many cases, the ITO film is formed on the surface of a substrate or the like by using a sputtering method as a thin film forming means. In this sputtering method, a sputtering target (hereinafter referred to as an ITO target) formed by bonding ITO to a backing plate is used. At this time, the consumption due to sputtering of the ITO target proceeds locally rather than uniformly. When this exhaustion proceeds and the backing plate is exposed, the components of the backing plate are mixed into the thin film formed by sputtering, and the obtained thin film becomes a defective product. Therefore, the target is replaced with a new target before the backing plate is exposed. For this reason, about 60% of unused parts usually remain in the used target, and all of them become scrap. In addition, scrap is generated from polishing powder and cutting powder during the production of the ITO target.

Indium is an expensive rare metal and is also recovered from the viewpoint of resource reuse. By the way, as a method for recovering indium from a substance containing indium, for example, the following methods (1) and (2) have been proposed. However, each method has problems when applied to ITO target scrap.
(1) The indium-containing lump is pulverized, the pulverized product is leached in an acidic aqueous solution in the presence of hydrogen peroxide, and an aluminum plate is immersed in the leaching solution to deposit sponge indium on the aluminum plate by a substitution reaction. Then, the indium sponge is alkali-cast to obtain indium metal (see, for example, Patent Document 1).
However, this method is not suitable as a method for recovering indium from an ITO target scrap having an indium quality exceeding 60% by mass. According to the description in the publication, the indium content is usually relatively small. Usually, it is 60% by mass or less, and in many cases, 50% by mass or less.

(2) After cleaning and grinding the ITO target scrap, dissolve it in nitric acid, then pass hydrogen sulfide through the solution to precipitate and remove impurity elements such as tin, lead, copper, etc., and then add ammonia to this. It neutralizes and collect | recovers as indium hydroxide (for example, refer patent document 2).
However, in this method, the obtained indium hydroxide has poor filterability and takes a long time to operate, and contains a large amount of impurity elements such as silicon and aluminum, and the neutralization and aging conditions. Since the particle size and particle size distribution fluctuate, there is a problem in that the characteristics of the obtained ITO target cannot be stably maintained when an ITO target is produced using this as a raw material. In addition, this method cannot be applied to high-quality scrap having an indium content exceeding 60% by mass.

From the problems of the methods (1) and (2), an efficient dry method such as reduction and recovery is adopted as a method for recovering indium from an ITO target scrap having an indium quality exceeding 60% by mass. It is said that it is common. For example, as a dry method, the following method (3) has been proposed. (3) A substance containing indium oxide such as ITO target scrap is reduced in advance under a reducing gas at a temperature of 750 to 1200 ° C. After obtaining metallic indium, this is electrolytically purified (see, for example, Patent Document 3).

  However, according to the description of the publication, metal indium obtained by reducing a substance containing indium oxide such as ITO scrap under the above-mentioned conditions is, for example, a tin quality of 12 mass% and an iron content of 19 ppm as impurities. It has a high element content and is not sufficient as a raw material for obtaining high-purity indium by electrolytic purification. That is, as the indium oxide used for the ITO target production raw material, a high-purity one is used. For this reason, the indium used as the raw material for the indium oxide is also high-purity electrolytically purified. For example, crude indium used for electrolytic purification has a purity of about 95%.

  Furthermore, in order to effectively reuse the ITO target scrap, about 60% of unused portions of the used target are crushed and used as they are. As described above, as the indium recycling rate increases, the ITO target scrap may contain many kinds of impurity metals other than tin due to the mixing of the material components of the member and the targets for other transparent conductive films. It is becoming. Under such circumstances, the dry method such as the method (3) has a new problem that various impurity metals cannot be sufficiently removed.

JP-A-9-268334 (first and second pages) JP 2001-348632 A (first page, second page) JP-A-7-145432 (first page, second page)

  In view of the above-mentioned problems of the prior art, the object of the present invention is to obtain a high yield of crude indium having a purity suitable for electrolytic refining anode from ITO target scrap even when the content of impurity metal elements is high. It is to provide a method of collecting at a rate.

  In order to achieve the above-mentioned object, the present inventor conducted extensive research on a method for recovering crude indium used for electrolytic purification from ITO target scrap, and as a result, a step of leaching crushed ITO target scrap with hydrochloric acid was obtained. After adding zinc powder to the leachate under specific conditions and separating and recovering partially reduced precipitated sponge indium (1), the reduced precipitated metal in solids separated from the reduced indium in the suspension is separated. A step of bringing the obtained indium chloride aqueous solution into contact with aluminum to obtain a reduced-deposited sponge indium (2), and the sponge indium (1) and the sponge indium (2) are heated and melted to obtain crude indium. When the steps to obtain are sequentially performed, crude indium having a purity suitable for electrolytic purification is efficiently recovered with high yield. It found that it is theft, and have completed the present invention.

That is, according to the first invention of the present invention, there is provided a method for recovering crude indium characterized by including the following steps (A) to (D).
Step (a): The pulverized indium tin oxide target scrap is leached with hydrochloric acid, and then the insoluble residue is separated to obtain a leachate.
Step (b): Sponge indium composed of indium partially reduced and precipitated by adding zinc powder in an amount corresponding to 2 to 5 equivalents of the stoichiometric amount of substitution reduction reaction with respect to tin in the leachate. 1) and a reduced-precipitated solid suspension of impurity metal solids that is more precious than indium, and then separating and recovering sponge indium (1), the impurity metal solids in the suspension are removed. Separate to obtain an aqueous solution of indium chloride.
Step (c): Aluminum is brought into contact with the indium chloride aqueous solution to obtain sponge indium (2) composed of indium reduced and deposited.
Step (d): The sponge indium (1) and the sponge indium (2) are mixed individually or in combination with sodium hydroxide, and then heated and melted to remove the soda slag formed. Crude indium is obtained.

According to the second invention of the present invention, in the first invention, in the step (ii), the amount of hydrochloric acid is 1 in terms of the stoichiometric amount of the generation reaction of InCl ₃ with respect to the amount of indium in the scrap. Provided is a method for recovering crude indium, characterized in that it is 0.0 to 1.5 equivalents and the leaching temperature is from room temperature to 80 ° C. or less.

  According to the third invention of the present invention, in the first or second invention, in the step (b), the pH of the leachate is 1.0 to 2.0, and the temperature of the leachate is 10 to 30 ° C. There is provided a method for recovering crude indium characterized by adjusting.

  According to a fourth invention of the present invention, in any one of the first to third inventions, in the step (c), the pH of the indium chloride aqueous solution is 1.5 to 2.5, and the temperature of the indium chloride aqueous solution. There is provided a method for recovering crude indium characterized by adjusting the temperature to 30 to 60 ° C.

According to a fifth invention of the present invention, in any one of the first to fourth inventions, in the step (c), aluminum is an aluminum plate, and the aluminum plate is indium in an indium chloride aqueous solution. There is provided a method for recovering crude indium characterized by adding an amount having a surface area of 0.25 to 0.50 cm ² per gram.

  In the method for recovering crude indium according to the present invention, even when the content of the impurity metal element is high from the ITO target scrap, the crude indium having a purity of 95% by mass or more suitable for an electrolytic refinement anode is obtained, for example, %, The industrial value is extremely high as a means for improving the recycling rate of ITO target scrap.

The method for recovering crude indium according to the present invention includes the following steps (a) to (d).
Step (a): The pulverized indium tin oxide target scrap is leached with hydrochloric acid, and then the insoluble residue is separated to obtain a leachate.
Step (b): Sponge indium composed of indium partially reduced and precipitated by adding zinc powder in an amount corresponding to 2 to 5 equivalents of the stoichiometric amount of substitution reduction reaction with respect to tin in the leachate. 1) and a reduced-precipitated solid suspension of impurity metal solids that is more precious than indium, and then separating and recovering sponge indium (1), the impurity metal solids in the suspension are removed. Separate to obtain an aqueous solution of indium chloride.
Step (c): Aluminum is brought into contact with the indium chloride aqueous solution to obtain sponge indium (2) composed of indium reduced and deposited.
Step (d): The sponge indium (1) and the sponge indium (2) are mixed individually or in combination with sodium hydroxide, and then heated and melted to remove the soda slag formed. Crude indium is obtained.

Hereinafter, the method for recovering crude indium according to the present invention will be described with reference to the drawings. Here, in the description of each step, the action and its technical significance will also be described.
FIG. 1 is a process diagram showing an example of a method for recovering crude indium according to the present invention. The method for recovering crude indium according to the present invention is not limited to this.
In FIG. 1, first, in the leaching process 1 corresponding to the process (A), hydrochloric acid 6 is added to dissolve the indium tin oxide (ITO) target scrap 5 to obtain a leaching solution 7.
Next, substitution reduction corresponding to step (b) (1) In step 2, sodium hydroxide aqueous solution 8 is added to leachate 7 to adjust the pH of leachate 7 to a desired value, and then a predetermined amount of zinc powder 9 is added. The indium chloride aqueous solution 10 is separated by separating the sponge indium (1) 11 made of indium partially reduced and precipitated and the impurity metal solid content 12 that is reduced and deposited more precious than indium by a substitution reduction reaction. obtain.
Next, substitution reduction corresponding to step (c) (2) In step 3, sodium hydroxide aqueous solution 8 is added to indium chloride aqueous solution 10 to adjust the pH of indium chloride aqueous solution 10 to a desired value, and then a desired amount of aluminum 13 is added, and the reduction-deposited sponge indium (2) 15 and the substitution final solution 14 are obtained by substitution reduction reaction.
Thereafter, in the melting step 4 corresponding to the step (d), the solid sodium hydroxide 16 is mixed with the sponge indium (1) 11 and the sponge indium (2) 15 individually or combined, and heated and melted. , Soda slag 17 and crude indium 18 are obtained.

The ITO target scrap used in the method of the present invention is not particularly limited, and scraps generated by pulverizing used scrap in sputtering of a normal ITO target to a desired size, or cutting waste generated in the target manufacturing process or Polishing scraps are used. These usually contain about 90% by mass of indium oxide (In ₂ O ₃ ) and about 10% by mass of stannic oxide (SnO ₂ ), and contain copper, lead, nickel, zinc and the like as other components. The pulverized size of the scrap is not particularly limited as long as it can be leached with hydrochloric acid.

The step (a) is a step of leaching the crushed indium tin oxide target scrap with hydrochloric acid and then separating the insoluble residue to obtain a leachate.
Here, the powder obtained by pulverizing the ITO target scrap is reacted with hydrochloric acid, and indium is leached into the solution, while tin is left in an insoluble residue mainly composed of metastannic acid. Specifically, water may be added to the powder to form a slurry, and concentrated hydrochloric acid (concentration: 12N) may be added thereto. Alternatively, the powder may be added to a hydrochloric acid solution.

In the step (a), although not particularly limited, the amount of hydrochloric acid is 1.0 to 1.5 equivalents in terms of the stoichiometric amount of the generation reaction of InCl ₃ with respect to the amount of indium in the scrap, The leaching temperature is preferably from room temperature to 80 ° C. or less. The InCl ₃ production reaction is represented by the following formula (1). That is, when the amount of hydrochloric acid is less than 1.0 equivalent, the leaching rate becomes slow and the amount of undissolved component increases. On the other hand, if the amount of hydrochloric acid exceeds 1.5 equivalents, the leaching itself is not hindered, but the pH adjustment in the next step increases the amount of alkali required and impairs economy.

Formula (1): In ₂ O ₃ + 6HCl = 2InCl ₃ + 3H ₂ O

  The leaching temperature is preferably from room temperature to 80 ° C. That is, since the leaching reaction with hydrochloric acid such as indium oxide in the powder is an exothermic reaction, the temperature of the liquid may exceed 80 ° C. and boil if left at room temperature for leaching. Therefore, it is preferable to keep the leaching temperature at 80 ° C. or lower in consideration of safety in handling and work environment. Here, in order to control the leaching temperature, the reaction vessel may have a structure that can be cooled, but simply, hydrochloric acid or the powder is added in several portions while observing the state of the temperature of the liquid. It is desirable.

  In the step (b), a sponge composed of indium partially reduced and precipitated by adding zinc powder in an amount corresponding to 2 to 5 equivalents of the stoichiometric amount of the substitution reduction reaction with respect to tin in the leachate. After forming indium (1) and a reduced suspension of impurity metal solids that are noble than indium, and then separating and recovering sponge indium (1), the impurity metal solids in the suspension This is a step of separating the components to obtain an indium chloride aqueous solution.

  Here, when zinc powder is added to the leaching solution, first, a part of indium ions in the solution and zinc undergo a substitution reduction reaction represented by the following formula (2) to form sponge-like indium, ie, sponge indium ( 1) is reduced and deposited. Next, the sponge indium (1) and a metal ion that is electrochemically more noble than the indium present in the solution undergo a substitution reduction reaction, and impurity metal solids are reduced and deposited. A part of this reduced and precipitated impurity metal solid is adsorbed as an impurity on the surface of sponge indium (1), but most of it forms a fine cementitious suspension. It does not significantly affect the quality of the crude indium produced.

Formula (2): In ³⁺ + 3 / 2Zn = In + 3 / 2Zn ²⁺

  The amount of zinc powder used in the step (b) is an amount corresponding to 2 to 5 equivalents of the stoichiometric amount of the substitution reduction reaction represented by the following formula (3) with respect to tin in the leachate. . That is, if only the reductive precipitation of tin, which is the main component of the impurity element dissolved in the liquid, it is sufficient to add 2 equivalents of zinc, but to improve the condensability of sponge indium (1), And, in order to increase the reaction rate, it is desirable to use 5 equivalents.

Formula (3): Sn ⁴⁺ + 2Zn = Sn + 2Zn ²⁺

  Although it does not specifically limit in the said process (b), It is preferable to adjust the pH of a leaching solution to 1.0-2.0, and the temperature of a leaching solution to 10-30 degreeC. By the way, the condensability of the sponge indium (1) produced by the substitution reduction reaction by adding zinc powder is better as the pH is lower and the reaction temperature is lower, and the produced sponge indium (1) is scraped out from the reaction vessel. easy. However, the degree of substitution inhibition due to the formation of a local battery with an impurity metal element also increases as the pH decreases.

That is, when the pH of the leachate is less than 1.0, the substitution efficiency is lowered because the zinc powder of the substitution agent is dissolved in free hydrochloric acid. On the other hand, if the pH of the leaching solution exceeds 2.0, the condensability of sponge indium (1) is deteriorated, which hinders the substitution reduction reaction. Here, the pH can be adjusted by adding, for example, an aqueous sodium hydroxide solution as a pH adjuster.
In addition, when the temperature of the leachate is less than 10 ° C., the deposition rate is slow, whereas when the temperature of the leachate exceeds 30 ° C., the condensability of sponge indium (1) is deteriorated.

  From the indium sponge (1) made of partially reduced precipitated indium formed in this way and the suspension of impurity metal solids nobler than indium, which is reduced and precipitated, first, the sponge indium (1) is added. After removing from the reaction vessel, the impurity metal solids are separated from the suspension by solid-liquid separation to recover the indium chloride aqueous solution.

  In the step (c), aluminum is brought into contact with the indium chloride aqueous solution to obtain sponge indium (2) composed of indium reduced and deposited. Here, the total amount of indium contained in the indium chloride aqueous solution is recovered by a substitution reduction reaction represented by the following formula (4).

Formula (4): In ³⁺ + Al = In + Al ³⁺

In the step (c), although not particularly limited, it is preferable to adjust the pH of the indium chloride aqueous solution to 1.5 to 2.5 and the temperature of the indium chloride aqueous solution to 30 to 60 ° C.
That is, when the pH of the indium chloride aqueous solution is less than 1.5, aluminum is dissolved in free hydrochloric acid, so that the substitution efficiency is reduced. On the other hand, when the pH of the indium chloride aqueous solution exceeds 2.5, generation of a precipitate of indium hydroxide starts. Here, the pH can be adjusted by adding, for example, an aqueous sodium hydroxide solution as a pH adjuster.
Further, when the temperature of the indium chloride aqueous solution is less than 30 ° C., the reaction rate is slow. On the other hand, when the temperature of the indium chloride aqueous solution exceeds 60 ° C., the chemical dissolution of aluminum proceeds and the substitution efficiency of indium is reduced. In addition, in order to collect | recover sponge indium (2) rapidly and efficiently, it is more preferable to set it as 45-50 degreeC.

In the above step (c), the shape of aluminum is not particularly limited, and may be powdery, granular, massive, or plate-like, and is not particularly limited. Is preferred. That is, when using an aluminum plate, heat generation is moderate, temperature control is easy, and productivity is good. The aluminum plate is preferably added in an amount having a surface area of 0.25 to 0.50 cm ² per gram of indium in the indium chloride aqueous solution.

In the above step (d), the sodium hydroxide is mixed with the sponge indium (1) and the sponge indium (2) individually or in combination, and then heated and melted to remove the generated soda slag. In this step, crude indium is obtained. For example, specifically, sponge indium is washed with water, and after dehydration, sodium hydroxide is added to melt at a temperature equal to or higher than the melting point of indium, and then the generated soda slag is separated. As a result, while effectively separating impurity metals such as aluminum contained in sponge indium, 95% by mass or more of crude indium suitable for electrolytic purification can be obtained in high yield, and indium recovery rate can be improved. A decrease can be prevented.
In addition, the indium yield can be further improved by effectively using the obtained soda slag as a pH adjuster in the reduction substitution (1) and (2) steps.

  The amount of sodium hydroxide added in the step (d) is not particularly limited, but is preferably 3 to 10% by mass with respect to the amount of indium contained in the sponge indium. That is, when the amount of sodium hydroxide added is less than 3% by mass, impurities such as oxide and aluminum adhering to the surface of sponge indium cannot be sufficiently removed, and sometimes oxidative combustion may occur. On the other hand, if the amount of sodium hydroxide added exceeds 10% by mass, no further effect is obtained and the economy is impaired.

  Hereinafter, the present invention will be described in more detail by way of examples and comparative examples of the present invention, but the present invention is not limited to these examples. In addition, the analysis of the metal used by the Example and the comparative example was performed by the ICP emission analysis method.

Example 1
ITO target scrap with high content of pulverized impurity metal as raw material powder (however, composition is indium quality: 68.7 mass%, tin quality: 6.9 mass%, copper quality: 0.26 mass%, lead Grade: 0.11% by mass, nickel grade: 0.17% by mass, tungsten grade: 0.09% by mass, chromium grade: 0.26% by mass, and titanium grade: 0.8% by mass). Then, according to the process diagram shown in FIG. 1, the following steps were sequentially performed to obtain crude indium.

[Leaching process]
First, 500 ml of water and 2000 ml of hydrochloric acid (concentration: 12N) were charged into a reaction vessel equipped with a stirrer, and then 700 g of the raw material powder was slowly added while stirring. Six hours later, 300 g of raw material powder was added again, and a total of 1000 g of raw material powder was used. Thereafter, stirring was continued for 16 hours from the initial addition of the raw material powder, and the raw material powder and hydrochloric acid were reacted to be leached. The maximum temperature reached during this period was 60 ° C. The amount of hydrochloric acid with respect to the raw material powder is 2.0 ml per 1 g of the raw material powder, and corresponds to 1.16 equivalent in terms of the stoichiometric amount of the generation reaction of InCl ₃ with respect to indium in the raw material powder.
After completion of leaching, the insoluble residue was separated to obtain a leaching solution. Here, the obtained insoluble residue has a wet weight of 122 g and a dry weight of 83 g, an indium quality of 11.2% by mass, and an indium leaching rate in the leaching step is 98. It was 6%.

[Substitutional reduction (1) step]
First, using a reaction vessel equipped with a stirrer, 550 ml of an aqueous sodium hydroxide solution having a concentration of 25% by mass was added to the leachate obtained in the leaching step, and the pH was adjusted to 1.5. The amount of the leachate after pH adjustment was 3100 ml, the indium concentration was 219 g / l, and the tin concentration was 3.8 g / l.
Next, while maintaining the temperature of the leachate after pH adjustment at 21 ° C. while stirring at a rotating speed of the stirrer of 200 rpm, zinc equivalent to 5 equivalents of the stoichiometric amount of the substitution reduction reaction with respect to tin in the leachate The powder 65g was added and it stirred for 48 hours. During this time, a suspension of massive sponge indium (1) and a blackened impurity metal solid was formed.
Thereafter, the produced bulk sponge indium (1) was taken out from the reaction vessel. The obtained sponge indium (1) had a wet weight of 117 g, a dry weight of 71 g, and an indium quality of 70.1% by mass. Next, the impurity metal solids remaining in the suspension were subjected to solid-liquid separation to obtain 3090 ml of an indium chloride aqueous solution.
During this time, in order to observe the progress of the reaction depending on the contact time between the leachate after adjustment of the pH and the zinc powder, the concentration of each metal component (soluble component) dissolved in the solution was analyzed by sampling the solution at an appropriate time. The results are shown in Table 1.

  From Table 1, it can be seen that tin, copper, lead, and nickel, which are elements nobler than indium, show a decrease in concentration in time series and have a remarkable smoky action. On the other hand, with tungsten, chromium and titanium, no significant concentration reduction is observed over time.

[Substitution reduction (2) step]
First, using a reaction vessel equipped with a stirrer, the indium chloride aqueous solution obtained in the substitution reduction (1) step was heated to 45 ° C., and the shape was 8 cm long × 10 cm wide × 3 cm thick, An aluminum plate having a weight of 648 g and a surface area of 268 cm ² was immersed and left for 48 hours. The pH of the indium chloride aqueous solution was maintained at 1.5 as in the previous step.
Thereafter, sponge indium (2) deposited by the substitution reduction reaction was scraped out from the reaction vessel. The obtained sponge indium (2) had a wet weight of 204 g. Further, the substitution final solution after completion of the substitution reaction had an indium concentration of 0.08 g / l. Moreover, the weight loss of the aluminum plate was 57.7 g. Here, 81.0% was obtained as the substitution efficiency in the substitution reduction (2) step.

[Melting process]
Here, in order to clarify the behavior of the respective impurity metals of sponge indium (1) and sponge indium (2) obtained in the above step, they were individually subjected to a melting step.
Sponge indium (1) and 5 g of sodium hydroxide were placed in a crucible, heated and melted at 350 ° C., and the generated soda slag was separated to obtain 61 g of crude indium (1). The composition of the crude indium (1) obtained was as follows: tin 18.1% by mass, copper 0.44% by mass, lead 0.77% by mass, nickel 0.02% by mass, zinc 0.39% by mass, and the balance indium And its purity was 79.8% by mass. Similarly, sponge indium (2) and 35 g of sodium hydroxide were placed in a crucible, heated and melted at 350 ° C., and the generated soda slag was separated to obtain 602 g of crude indium (2). The composition of the obtained crude indium (2) is 0.01% by mass of tin, 0.02% by mass of nickel, 0.01% by mass or less of aluminum, and the balance of indium, and its purity is 99.9% by mass. there were.
Here, the crude indium obtained when the crude indium (1) and the crude indium (2) are combined and averaged has a purity of 98.1% by mass, which is sufficient as crude indium for electrolytic purification. It was purity. Moreover, the indium yield from the raw material powder when the crude indium (1) and the crude indium (2) were united was 95%.
In addition, when combined with sponge indium (1) and sponge indium (2), the same sodium hydroxide was used for the indium in the sponge indium and heated and melted under the same conditions. In the purity and the indium yield from the raw material powder, the same results as those obtained when individually heated and melted were obtained.

(Example 2)
[Leaching process]
First, in a reaction vessel equipped with a stirrer, 500 ml of water and 1000 g of the raw material powder similar to that of Example 1 were introduced, and while stirring, hydrochloric acid (concentration: 12 N) was intermittently kept so that the temperature of the liquid did not exceed 80 ° C. ) 2000 ml was added and stirring was continued for 16 hours from the start of charging, and the raw material powder and hydrochloric acid were reacted to leach out. The amount of hydrochloric acid relative to the raw material powder was the same as in Example 1.
After completion of leaching, the insoluble residue was separated to obtain a leaching solution. The amount of the obtained leachate, the indium concentration and the tin concentration were the same as those in Example 1.
[Substitution reduction (1) step], [Substitution reduction (2) step] and [Melting step]
In the same manner as in Example 1, sponge indium (1) and sponge indium (2) were obtained, and crude indium (1) and crude indium (2) were obtained using them.
The crude indium obtained when both were united and averaged had a purity of 98.0% by mass, and was sufficiently pure as crude indium for electrolytic purification. Moreover, the indium yield from the raw material powder when the crude indium (1) and the crude indium (2) were united was 95%.

(Examples 3 and 4)
The amount of hydrochloric acid with respect to the raw material powder used in the [leaching step] is 1.0 equivalent (Example 3) or 1.5 equivalent (Example) in terms of the stoichiometric amount of the formation reaction of InCl ₃ with respect to indium in the raw material powder. Except that it was set as 4), a leachate was obtained in the same manner as in Example 1, and further crude indium (1) and crude indium (2) were obtained.
The crude indium obtained when both were united and averaged had a purity of 98.0% by mass, and was sufficiently pure as crude indium for electrolytic purification. Further, the indium yield from the raw material powder when the crude indium (1) and the crude indium (2) were combined was about 93% in Example 3 and about 95% in Example 4. .

(Example 5)
In the [Substitutional reduction (1) step], crude indium (1 ) And crude indium (2).
The crude indium obtained when both were combined and averaged had a purity of 97.0% by mass, and was sufficiently pure as crude indium for electrolytic purification. Moreover, the indium yield from the raw material powder when the crude indium (1) and the crude indium (2) were combined was about 95%.

(Comparative Example 1)
The leaching solution was the same as in Example 1 except that the amount of hydrochloric acid relative to the raw material powder used in the [leaching step] was 0.9 equivalent in terms of the stoichiometric amount of the InCl ₃ generation reaction with respect to indium in the raw material powder Further, crude indium (1) and crude indium (2) were obtained.
The crude indium obtained when both were united and averaged had a purity of 98.0% by mass, and was sufficiently pure as crude indium for electrolytic purification. However, the indium yield from the raw material powder when the crude indium (1) and the crude indium (2) were combined was about 80%. This can be considered to be due to the fact that indium is not sufficiently leached during the leaching process.

(Comparative Example 2)
In [Substitutional reduction (1) step], crude indium was prepared in the same manner as in Example 1 except that the amount of zinc powder added was 1.5 equivalents of the stoichiometric amount of the substitution reduction reaction with respect to tin in the leachate. (1) and crude indium (2) were obtained.
The purity of the crude indium obtained by combining and averaging both is 94.0% by mass, and although it can be used as the crude indium for electrolytic purification, it is not necessarily a sufficiently satisfactory purity.

From the above, in Examples 1 to 5, the leaching step (step (a)), the substitution reduction (1) step (step (b)), the substitution reduction (2) step (step (c)), and melting Since the steps (step (d)) were sequentially carried out according to the method of the present invention, even when the content of the impurity metal element is high from the ITO target scrap, the crude having a purity suitable for electrolytic refining anode. It can be seen that indium can be recovered in high yield.
On the other hand, in Comparative Example 1 or 2, the leaching step or the substitution reduction (1) step does not meet the above-mentioned conditions, so that satisfactory results cannot be obtained in the purity or yield of the obtained crude indium. I understand.

  As is clear from the above, the method for recovering crude indium can efficiently recover crude indium having a purity of 95% by mass or more suitable for electrolytic purification from ITO target scrap with high yield. In addition, high-purity indium obtained by electrolytic purification using this is particularly suitable as a high-purity indium raw material used in the field of sputtering targets for forming transparent conductive films such as liquid crystal display devices.

It is process drawing showing an example of the collection | recovery method of the crude indium of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Leaching process 2 Substitution reduction (1) process 3 Substitution reduction (2) process 4 Melting process 5 Indium tin oxide (ITO) target scrap 6 Hydrochloric acid 7 Leaching liquid 8 Sodium hydroxide aqueous solution 9 Zinc powder 10 Indium chloride (In) aqueous solution 11 Sponge indium (In) (1)
12 Impurity metal solid content 13 Aluminum 14 Replacement final solution 15 Sponge indium (In) (2)
16 Sodium hydroxide 17 Soda slag 18 Crude indium

Claims (5)

A method for recovering crude indium, comprising the following steps (a) to (d).
Step (a): The pulverized indium tin oxide target scrap is leached with hydrochloric acid, and then the insoluble residue is separated to obtain a leachate.
Step (b): Sponge indium composed of indium partially reduced and precipitated by adding zinc powder in an amount corresponding to 2 to 5 equivalents of the stoichiometric amount of substitution reduction reaction with respect to tin in the leachate. 1) and a reduced-precipitated solid suspension of impurity metal solids that is more precious than indium, and then separating and recovering sponge indium (1), the impurity metal solids in the suspension are removed. Separate to obtain an aqueous solution of indium chloride.
Step (c): Aluminum is brought into contact with the indium chloride aqueous solution to obtain sponge indium (2) composed of indium reduced and deposited.
Step (d): The sponge indium (1) and the sponge indium (2) are mixed individually or in combination with sodium hydroxide, and then heated and melted to remove the soda slag formed. Crude indium is obtained. In the step (ii), the amount of hydrochloric acid is 1.0 to 1.5 equivalent in terms of the stoichiometric amount of the generation reaction of InCl ₃ with respect to the amount of indium in the scrap, and the leaching temperature is from room temperature to 80 ° C. The method for recovering crude indium according to claim 1, wherein:   The method for recovering crude indium according to claim 1 or 2, wherein, in the step (b), the pH of the leachate is adjusted to 1.0 to 2.0, and the temperature of the leachate is adjusted to 10 to 30 ° C.   In the step (c), the pH of the indium chloride aqueous solution is adjusted to 1.5 to 2.5, and the temperature of the indium chloride aqueous solution is adjusted to 30 to 60 ° C. Of recovering crude indium. In the step (c), the aluminum is an aluminum plate, and the aluminum plate is added in an amount having a surface area of 0.25 to 0.50 cm ² per 1 g of indium in the indium chloride aqueous solution. The method for recovering crude indium according to claim 1.

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