JPH0382720A - Method for recovering indium - Google Patents

Abstract

PURPOSE:To recover In having high purity by subjecting the water soln. of hydrochloric acid or nitric acid including In to reducing treatment and thereafter regulating its pH to specified value. CONSTITUTION:The pH of the water soln. of hydrochloric acid or nitric acid including In obtd. from the by-products of zinc refining or lead smelting or from indium oxide scraps doped with tin is regulated to 2 to 5 in the presence of a reducing agent. In the above manner, the ions of impurity metals such as iron, zinc, tin, copper and Ta are reduced and the pH is regulated to the one at which these components are hard to settle, by which In components can selectively be formed. At this time, as the reducing agent to be used, hydrazine, ascorbic acid, sodium sulfite or the like are given, and above all, the former two components including no Na and S are preferably used. The obtd. hydroxide of In has excellent filtrability, and by an ion exchange method, an electrolytic precipitating method or the like, high purity In metal or In compounds can easily be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for recovering indium, which is a valuable material, from an aqueous solution of hydrochloric acid or nitric acid containing indium.

[Prior Art and Problems to be Solved by the Invention] Aqueous solutions containing indium as a main component include, for example, an indium solution obtained as a by-product of a zinc smelting process and a smelting intermediate, and tin-doped indium oxide. (Hereinafter referred to as ITO) Examples include sputtering target scraps dissolved in acid.

Currently, indium is used in intermetallic compounds such as s I nP and 1nAs, and transparent conductive thin films such as ITO, and the demand for indium is expected to increase further in the future.

Originally, there was no regular ore of indium, and industrial production was carried out by recovering indium concentrated in the byproducts of zinc smelting and lead smelting.

However, the indium obtained in this way contains many metal impurities such as iron, zinc, aluminum, cadmium, copper, and thallium, and it takes a complicated process to remove these metal impurities and recover high-purity indium. Is required.

Generally, the above-described indium recovery process is carried out by a combination of several types of chemical refining and an electrolytic refining method, a combination with a solvent extraction method, a combination with an ion exchange method, and the like.

Among these, a method of chemical purification has been proposed in which the pt+ of a hydrochloric acid or nitric acid aqueous solution containing indium is adjusted, indium is precipitated as a hydroxide, and at the same time is separated from other metals. This method takes advantage of the difference in the hydroxide generation region of metal ions. For example, to separate zinc, aluminum and indium, by raising the pH to 12 or higher, zinc and aluminum are dissolved and precipitated. This is a method for recovering indium hydroxide.

In this method, the indium hydroxide produced has extremely poor filterability and requires a long filtration operation. Furthermore, metals such as iron, cadmium, copper, and thallium cannot be separated from indium using this method. In addition, a method has been proposed in which impurity metals are precipitated as sulfides and separated from indium, but in this method, hydrogen sulfide remains in the hydrochloric acid or nitric acid solution of indium, and sulfur remains in the recovered indium component.

On the other hand, as mentioned above, industrial production of indium uses by-products such as zinc smelting as an indium source, but there are also expectations for a method of recovering indium from scraps from electronic materials such as ITO as another indium source. . For example, ITO thin films have a poor yield during the manufacturing process, and most of the indium used becomes scrap. However, when recovering indium, which is a valuable resource, from these scraps, impurities such as iron, calcium, sodium, and zirconium are mixed in in addition to tin, and there is a method to remove these and effectively recover high-purity indium. has not yet been proposed.

[Object of the Invention] The present invention was made to solve the above-mentioned problems of the prior art, and its purpose is to recover highly pure indium from an aqueous solution of hydrochloric acid or nitric acid containing indium.

[Means for Solving the Problems] As a result of intensive study on a method for recovering indium that does not contain other metal impurities from an aqueous solution of hydrochloric acid or nitric acid containing indium, the present inventors found that iron and thallium contained in the solution The present invention was completed by discovering a method for recovering indium as hydroxide by reducing metal ions such as Pe2+ to low-valence metal ions with low solubility, and adjusting the pH of this solution.

That is, the present invention relates to a method for recovering indium, which is characterized by subjecting a hydrochloric acid or nitric acid aqueous solution containing indium to a reduction treatment, and then adjusting the pH of this aqueous solution to 2 to 5 to separate the indium component in the aqueous solution. be.

The present invention will be explained in more detail below.

As mentioned above, zinc smelting, lead smelting by-products, or ITO
Metal ions other than indium in a hydrochloric acid or nitric acid aqueous solution containing indium obtained from scrap etc. include iron, zinc, tin, copper, aluminum, cadmium, thallium, calcium, magnesium, sodium, etc. Although the content of impurities depends on the type of indium source used, for example, a hydrochloric acid solution of ITO scrap contains a large amount of tin.

When using a hydrochloric acid solution of ITO scrap as a raw material for indium recovery, the tin mentioned above is separated in the pretreatment of the indium recovery process and the tin content is reduced.
A highly pure indium component can be obtained, and the amount of reducing agent used can also be reduced. Examples of a method for separating tin using this pretreatment include a method for separating tin as a halogenostannate.

That is, it is a method in which a halogenostannate is produced from an aqueous solution containing tin under strong acidity and in the presence of halogen ions, and tin is selectively separated. When producing this halogenostannate, the tin-containing solution needs to be strongly acidic, and the hydrochloric acid concentration of the strongly acidic aqueous solution corresponds to the proton concentration in the solution, which is 0.5 mmoJ/1 or more. is preferable, and further 3rAo! /J or more is particularly preferred. When the proton concentration is low, the amount of halogenostannate precipitate is reduced. Further, when precipitating a halogen stannate, the presence of halogen ions is required in the aqueous solution containing indium and tin. The halogen ion concentration of the strongly acidic aqueous solution containing indium and tin is preferably at least 50 times the molar content of tin, particularly preferably at least 80 times the molar content, although it depends on the type of halogen ions.

At this time, the halogen ions may be adjusted by adding an acid containing halogen ions, such as hydrochloric acid, or by adding a salt containing halogen ions such as sodium chloride or ammonium chloride. good.

A counter ion of a halide stannate ion is supplied to an aqueous solution containing indium and tin in which such a strong acid and a halogen ion coexist to generate a halide stannate. The amount of cation to be added as a counter ion to the halogen stannate depends on the halogen ion concentration and acid concentration in the solution, but it should be added so that the counter ion of the halogen stannate is at least equimolar to tin. is preferred. The type of cation used here may be one that acts as an electrolyte in an aqueous solution, and may be inorganic or organic. Examples of inorganic substances include bases such as aqueous ammonia, sodium hydroxide, and potassium hydroxide, and their hydrochlorides, nitrates, and sulfates. Examples of organic substances include bases such as methylamine and dimethylamine, and their hydrochlorides. It is preferable to produce the halogenostannate as an ammonium salt and/or a salt of amines, and at this time, it is preferable to avoid mixing inorganic metal ions such as sodium ions and calcium ions into the solution.

In this way, the generated halogenostannate can be separated and removed, and an indium solution with a low tin content can be obtained.

The obtained solution is an aqueous hydrochloric acid solution containing indium with a low tin content, and the hydrochloric acid solution contains metal impurities such as iron and is a target of the treatment of the present invention.

On the other hand, the dissolution rate of ITO target scrap in an aqueous nitric acid solution is slower than that of an aqueous hydrochloric acid solution, but an aqueous solution of indium in nitric acid has an extremely low tin content, so it is not necessarily necessary to separate tin using a halogenostannate. , this solution is an extremely good solution to be treated according to the present invention.

In addition, hydrochloric acid or nitric acid aqueous solutions containing a large amount of indium and metal impurities, which are obtained in the zinc scouring process, etc., are solutions to be treated in the present invention.

When removing metal impurities from such an aqueous hydrochloric acid or nitric acid solution containing indium and recovering the indium component, in the present invention, the aqueous hydrochloric acid or nitric acid solution containing indium is adjusted to pH 2 to 5 in the presence of a reducing agent. In this way, the presence of a reducing agent reduces impurity metal ions such as iron, zinc, copper, thallium, etc., and by adjusting the pH to a level at which these components are difficult to precipitate, it is possible to selectively generate indium components. can. At this time, the pH is adjusted using a common alkali such as alkali metal hydroxide, alkaline earth metal hydroxide, ammonia, etc., and the indium hydroxide is recovered. If ammonia is used here, metal ions such as sodium ions and potassium ions will not be mixed into the hydrochloric acid or nitric acid aqueous solution containing indium, so it is particularly preferable when recovering high-purity indium. When producing indium as a hydroxide from an aqueous solution of hydrochloric acid or nitric acid containing indium, this is done in the presence of a reducing agent.
Sulfur dioxide, etc. can be used, and hydrazine and ascorbic acid, which do not contain sodium or sulfur, are preferred. The amount of the reducing agent added varies depending on the type of reducing agent, but for example, if the impurity is iron and the reducing agent is ascorbic acid, it is sufficient to add twice the amount of iron. In this way, iron is F
By changing e3+ to Pe2+, ferrous hydroxide, which has a relatively high solubility, can be prevented from coprecipitating with indium hydroxide.

The neutralization method for adjusting the pH of a hydrochloric acid or nitric acid aqueous solution containing indium is not particularly limited, but it is preferable to carry out the neutralization separately for hydrochloric acid or nitric acid and neutralization for precipitation of indium hydroxide. . Although the concentration of the alkali used for neutralizing hydrochloric acid or nitric acid is not limited, a high concentration of alkali is preferable in order to prevent an increase in the amount of treated liquid and improve production efficiency. The high-concentration alkali mentioned here is, for example, one with a concentration of 5 normal or higher. Neutralization of hydrochloric acid or nitric acid is performed using pHO
It will end in the range of ~3. However, when treating a nitric acid solution, it is preferable to finish the treatment at a pH of 1.5 to 1.5.

The process of adding alkali to further raise the pH from the pH at the end of neutralization with hydrochloric acid or nitric acid is called neutralization for precipitation of indium hydroxide.

During neutralization with hydrochloric acid or nitric acid, the temperature of the solution increases due to the heat of neutralization, so it is preferable to lower the temperature of the solution before proceeding to neutralization for precipitation of indium hydroxide. If neutralization is carried out to precipitate indium hydroxide at a high temperature, the produced indium hydroxide will become gel-like, resulting in extremely poor filterability. Therefore, neutralization for precipitation of indium hydroxide is preferably carried out at 5 to BO°C, particularly at 5°C to BO°C.
~85°C is preferred.

In addition, the addition of the reducing agent is carried out after the neutralization of hydrochloric acid or nitric acid is completed.
It is preferable to perform the neutralization for precipitation of indium hydroxide. If a long time elapses after adding the reducing agent, the reduced metal ions will be oxidized by dissolved oxygen in the aqueous solution, and the effect of adding the reducing agent will decrease.

After adding the reducing agent, alkali is added again to generate indium hydroxide. When the aqueous solution containing indium that has been neutralized to a predetermined pH is a hydrochloric acid aqueous solution, it is preferable to add the alkali until the pH reaches a range of 8 to 5, particularly 3.5 to 4.5. It is preferable to set it as the range of. Similarly, in the case of a nitric acid aqueous solution, it is preferable to carry out the reaction until the pH is in the range of 1.5 to 3.5, particularly preferably in the range of 2 to 3. This pH
If is too high, impurities such as iron will co-precipitate with indium, and p
If H is too low, the indium hydroxide production efficiency will be low.

The concentration of the alkali added is preferably low, and preferably 5N or less. If the concentration of this alkali is too high, impurities will be mixed into the indium hydroxide produced, resulting in a decrease in the purity of the indium obtained.

Next, indium hydroxide is separated and recovered from the obtained slurry containing indium hydroxide.

For this separation, conventional equipment such as centrifuges, belt filters, drum filters, etc. can be used. Indium hydroxide has extremely good filterability and can be easily separated into solid and liquid in a short time.

The obtained indium hydroxide is preferably washed using pure water, an aqueous solution of a dilute acid, or an aqueous solution containing a reducing agent such as ascorbic acid. When cleaning with a dilute acid aqueous solution or an aqueous solution containing a reducing agent, metal salts other than indium attached to indium hydroxide can be easily removed.
Furthermore, oxidation reactions caused by dissolved oxygen in pure water can be prevented.

The indium hydroxide thus obtained can be dried and fired to form indium oxide. Further, in order to recover indium of higher purity, the obtained hydroxide may be dissolved in an acid and recovered as indium metal by electrolytic deposition, or ion exchange or solvent extraction may be used.

For example, when using an ion exchange method, the obtained indium hydroxide cake is dissolved in an acid and used as an adsorption liquid for an ion exchange column. The types of acids used here include hydrochloric acid, sulfuric acid, nitric acid, etc. The indium-containing adsorbent thus obtained is supplied to an ion exchange column. The ion exchange resin used here may be one having a sulfonic acid group,
For example, the commercially available product name “Amberlight 252Jr Amberlight Il?-120BJ r Diamond Ion 5K
Examples include resins such as IBJ, but macroporous type "Amberlite 252" and the like are preferred. The counter ion of the sulfonic acid group of these ion exchange resins is proton,
Ammonium ions and the like are preferred, and protons are particularly preferred. When these counterions are used, the amount of impurities mixed in is small, and when protons are used, the separation of indium and other metal ions is extremely good.

The counter ion of the sulfonic acid group can be easily converted into a proton type by supplying and adjusting an acid such as hydrochloric acid to an ion exchange column.

The operating procedure for the ion exchange method at this time is to first conduct adjustment by passing an acid such as hydrochloric acid through the ion exchange column, then pass an adsorption solution containing indium through the ion exchange column to deposit indium onto the top of the ion exchange column. An adsorption zone is formed, washed with water, and then an aqueous solution of a complex forming agent is passed through the top of the ion exchange column for elution. The complex forming agents used here are ethylenediaminetetraacetic acid (EDTA), N-hydroxyethylethylenediaminetriacetic acid (HEDT), and nitriloacetic acid (NTA).
), but EDTA is preferred because of its good separability.

By passing these complexing agent aqueous solutions from the upper part of the ion exchange tower, a purified indium complexing agent aqueous solution is obtained from the lower part of the ion exchange tower.

High-purity indium oxide can be obtained by recovering indium as hydroxide, oxalate, etc. from the obtained solution and firing the recovered indium.

The reason why indium can be purified so easily is that indium is sufficiently purified according to the present invention.

Next, when recovering indium metal, indium hydroxide is dissolved in acid. The acid used here may be an inorganic acid such as hydrochloric acid, nitric acid, or sulfuric acid, or an organic acid such as formic acid, citric acid, or tartaric acid. Indium is electrolytically extracted using such an acid aqueous solution containing indium as an electrolyte. The higher the pH of the electrolyte at this time, the more hydrogen generation can be suppressed during operation, and the current efficiency can be improved.
If the pH is too high than necessary, hydrolysis of indium will occur, so the pH of the electrolytic solution is preferably 0 to 3.5, although it depends on the concentration of metal ions other than indium. In addition, electrolysis can be carried out at a temperature ranging from room temperature to below the boiling point of the electrolyte used, but generally the higher the temperature, the faster the dissolution rate of metals in acids, so it is more efficient to carry out electrolysis at a lower temperature. . Preferably, electrolysis is carried out at a temperature ranging from room temperature to 60°C.

The cathode for recovering indium by electrodeposition is preferably indium metal, and the electrodeposited cathode can be made into an ingot as it is. Further, as the anode, any material can be used as long as it is not corroded by the electrolytic solution, but from the viewpoint of durability, it is preferable to use platinum or graphite.

However, if the electrolytic cell is partitioned with an anion exchange membrane, it will not be affected by the metal ions dissolved from the anode.
The anode may be soluble.

[Effects of the Invention] According to the present invention, indium can be purified to a high degree of purity, and the resulting indium hydroxide has excellent filterability and is easy to filter. In addition, the indium hydroxide obtained in the present invention can be easily purified to high purity (
99.9% or more) indium metal and/or indium compounds can be obtained.

[Examples] Examples, comparative examples, and reference examples of the present invention are shown below, but the present invention is not limited thereto.

Example 1 A 36X hydrochloric acid aqueous solution II, 200 g of a scrap ITO target, and 107 g of ammonium chloride were placed in an 11 separable flask equipped with a stirrer, and the mixture was stirred at 80° C. for 3 hours to dissolve the target. The obtained solution was filtered to remove the residue and the composition was analyzed. Hydrochloric acid concentration: 8.5o+oj/jIn:
1.14 Ioi/ISn: lo,
1m IIoi/J! (:a: 1.1tx mo
l/JZr: 1.9m IOJ/
jPe: 0.8i mo1/INa
: 8 mmoj/J! Met.

This target solution solution 100-500 was heated using a stirrer.
d was placed in a separable flask, and 28% ammonia water was added thereto to adjust the pH to 2.5. Thereafter, it was allowed to cool to a liquid temperature of 25°C. Next, 0.41 g of ascorbic acid was added to this solution while stirring, and then 1.4% ammonia water was added to adjust the pH of the solution to 4.2 to produce indium hydroxide. The temperature at this time was 30°C. Next, after suction filtration with No. 5C filter paper and washing with water, indium hydroxide was obtained. The filtration performance was very good, and the indium recovery rate was estimated to be 97% based on the amount of indium in the filtrate.

The obtained cake was redissolved in hydrochloric acid and analyzed for metal elements other than indium using an inductively coupled plasma emission spectrometer, and it was found that Sn was 3500 ppm relative to indium oxide.
, 10 ppm of Ca, 90 ppm of Fe, 300 ppm of ISzr, and 10 ppm of ISNa. However, Na was measured using an atomic absorption spectrometer.

Example 2 60% in a lj separable flask equipped with a stirrer
1j of nitric acid aqueous solution and 200g of scrap ITO target
was added and stirred at 80°C for 10 hours to dissolve the target. The obtained solution was filtered to remove the residue, and the composition was analyzed. As a result, In: 1.114 5 oil
/ jSn : 0.3m vIol /
iCa: lml1oJ! /jZr
: 1.7IlioJ/iFe
: 0.8i moj/INa:
2. It was liIImol/1.

100 ij of this target solution was added to a 50 liter tube equipped with a stirrer.
The mixture was placed in a 0 mA separable flask, and 28% aqueous ammonia was added to adjust the pH to 1. Thereafter, it was allowed to cool to a liquid temperature of 25°C. Next, 0.1 g of ascorbic acid was added to this solution while stirring, and then 1.4% ammonia water was added to adjust the pH of the solution to 3.2 to produce indium hydroxide. The temperature at this time was 30°C. Next, suction filtration was performed using No. 5G filter paper, and after washing with water, indium hydroxide was obtained. The filterability was very good, and the indium recovery rate was estimated to be 97% based on the amount of indium in the filtrate. The obtained cake was redissolved in hydrochloric acid and analyzed for metal elements other than indium in the same manner as in Example 1. Sn was 30 ppm % and Ca was 1 Op with respect to indium oxide.
pa+, re is 95 ppm.

2" contained 310ppiSNa at 8ppm.

Comparative Example 1 An experiment was conducted in the same manner as in Example 1 using 10hj of the target solution of Example 1, except that ascorbic acid was not added. Sn is 3500ppm, C
a is 10ppm% Fe is 700ppm, Zr is 3
00ppa+.

It contained loppm of Na.

Comparative Example 2 Target solution 100a+J of Example 1! into a 5001Ii separable flask equipped with a stirrer, and add 28
% ammonia water was added to adjust the pH to 2.5. Thereafter, it was allowed to cool to a liquid temperature of 25°C. Next, while stirring this solution, 0.41 g of ascorbic acid was added, followed by 1.4 g of ascorbic acid.
% ammonia water was added to adjust the pH of the solution to 2.9, but no indium hydroxide was produced.

Comparative Example 3 Same as Example 1 except that 1.4% ammonia water was added until the pH of the indium solution reached 6.5 when indium hydroxide was generated using the target solution 100111 of Example 1. When an experiment was conducted, it was found that Sn was 4% relative to indium oxide in the obtained indium hydroxide.
000ppm, Ca 50ppIISFe 700p
It contained 700 ppm of Zr, and lippm of Na.

Comparative Example 4 An experiment similar to Example 1 was conducted using 100sj of the target solution of Example 2, except that ascorbic acid was not added. Sn is 35ppm, Ca is lOppw, SPe is 720pHSZr is 310ppI
l.

It contained lOppm of Na.

Comparative Example 5 100d of the target solution of Example 2 was added to 5001J equipped with a stirrer! Transfer to a separable flask and add 28%
Aqueous ammonia was added to adjust the pH to 1. Thereafter, it was allowed to cool to a liquid temperature of 25°C. Next, 0.41 g of ascorbic acid was added to this solution while stirring, and then 1.4% ammonia water was added to adjust the pi of the solution to 14, but no indium hydroxide was produced.

Comparative Example 6 Same as Example 2 except that 1000 of the target solution of Example 2 was used and 1.4% ammonia water was added until the pH of the indium solution reached 6.5 when indium hydroxide was generated. When an experiment was conducted, it was found that the obtained indium hydroxide contained 40p of Sn relative to the indium oxide.
pm, Ca is 55ppIl, Pa is 7LOppm
.

It contained 7301)I)II for Zr and 10pp11 for Ha.

Reference Example 1 In an electrolytic cell with metal indium as electrodes for both the anode and cathode and a fluorine-based anion exchange membrane 5P-34 manufactured by Tosoh Corporation as a diaphragm, the electrolyte on the anode side was a 20% formic acid aqueous solution and the electrolyte on the cathode side was was carried out in the same manner as in Example 1 to produce an indium hydroxide cake, and the cake was converted into 2
Electrolysis was performed using the product obtained by dissolving in 0X formic acid aqueous solution.

Electrolysis temperature was 25℃, current density was 20ffiA/cI1
It was set to 12. During electrolysis, the voltage between the electrodes was stable, the current efficiency on the anode side was 105%, and the current efficiency on the cathode side was 98%. The reason why the current efficiency on the anode side is 100% or more is due to the natural dissolution of metallic indium.

Next, the metallic indium deposited on the cathode is dissolved in hydrochloric acid,
- When the content of impurities was examined by ICP, the pH of tin was 340 ppm relative to indium, and the pH of each of calcium, iron, and zirconia was 10 or less, and it was possible to recover 3N indium metal. On the other hand, the electrolyte in the anode chamber was heated and concentrated to produce indium formate, and the obtained indium formate was then calcined at 700°C for 5 hours to obtain indium oxide with an average particle size of 0.2 μm. .

Claims (1)

[Claims] A method for recovering indium, which comprises reducing an aqueous solution of hydrochloric acid or nitric acid containing indium, adjusting the pH of the aqueous solution to 2 to 5, and separating the indium component in the aqueous solution.