JP4895013B2 - Indium recovery method - Google Patents

Description

The present invention relates to a method for recovering indium that efficiently deposits spongy metallic indium from an indium chloride solution.

An indium-tin oxide (ITO) thin film is widely used as a semiconductor material, and this thin film is generally formed by a sputtering method. An ITO high-density sintered body is used as a sputtering target material, and a large amount of ITO scrap is generated as a used target material. Since high-purity materials are used for ITO sintering and the price is high, indium is recovered from such scrap materials. As this indium recovery method, a method of recovering indium after dissolving ITO scrap in hydrochloric acid, adding sodium hydroxide to the solution to separate and separate tin in the solution by tin hydroxide precipitation is known. (Patent Documents 1, 2, and 3).

As the conventional indium recovery method, there are known a method of recovering metal indium by electrowinning and a method of recovering sponge indium by displacement deposition. In the electrowinning method, the pH of the indium chloride solution separated from tin in the solution by precipitation with tin hydroxide is adjusted to precipitate indium hydroxide, which is recovered by filtration and dissolved in sulfuric acid. It is a method of collecting metal indium by electrolysis, a method of adjusting the pH of the indium chloride solution to neutral (pH 5-6) to precipitate indium hydroxide (Patent Document 1), and adjusting the pH of the indium chloride solution to alkaline ( A method (Patent Document 2) in which indium hydroxide is aggregated and precipitated by adjusting the pH to 7-9) is known.
A method for recovering sponge indium is a method in which zinc is added to an indium chloride solution from which tin hydroxide has been removed to displace and deposit sponge-like metal indium (Patent Document 3).

In the conventional method for recovering indium, the method of precipitating indium hydroxide and filtering it out is poor in filterability of the precipitate, and the process of dissolving the recovered indium hydroxide in sulfuric acid followed by electrolysis is complicated. It is.

On the other hand, in the conventional indium recovery method in which sponge indium is deposited by displacement precipitation, the concentration of indium in the solution is about 48.6 g / L, and the pH of the solution is adjusted to 1.5 to 2.5 to precipitate indium hydroxide. Indium is deposited so as not to occur, but if the concentration of indium ions is increased, a thin indium film is formed on the surface of the zinc plate, hindering the elution of zinc and inhibiting the substitution reaction between zinc and indium. There is a problem that cementation does not progress.
JP 2002-69684 A JP 2002-201025 A JP 2002-69544 A

The present invention solves the above-mentioned conventional problems in a method for recovering sponge indium, and unlike conventional methods, by actively allowing indium hydroxide to coexist with free indium ions in the liquid, Provided is a method for recovering indium that allows cementation to proceed smoothly and allows sponge indium to be deposited stably.

According to the present invention, a method for recovering indium that solves the above-described problems is provided by the following configuration.
(1) A method for recovering indium characterized in that in the step of depositing metal indium by adding zinc to an indium chloride solution, indium ions and indium hydroxide coexist in the solution to deposit metal indium.
(2) In the step of adding zinc to an indium chloride solution to deposit metallic indium, indium ions and indium hydroxide coexist in the liquid, and the concentration of indium ions in the liquid is set to 60 to 85 g / L. The method for recovering indium as described in (1) above.
(3) In the method of (1) or (2) above, the pH of the indium chloride solution is adjusted to 2.5 to 3.5 to produce indium hydroxide, and indium ions and indium hydroxide coexist. A method for recovering indium to deposit metal indium.
(4) Indium metal in an indium chloride solution in an initial concentration of 60 to 85 g / L and an initial indium hydroxide amount (in conversion) of 5 to 60 g / L (total indium concentration of 90 to 120 g / L). The method for recovering indium as described in any one of (1) to (3) above.

In the method of the present invention, in the step of adding zinc to an indium chloride solution to deposit metallic indium, metallic indium is deposited in the state where indium ions and indium hydroxide coexist in the liquid. While maintaining the concentration in a range suitable for cementation, the concentration of indium in the entire solution can be increased, and insolubilization of the zinc plate can be prevented and indium can be stably deposited.

Sponge-like metal indium recovered by the method of the present invention contains almost no indium hydroxide or zinc hydroxide, and metal indium with few impurities can be obtained.

Hereinafter, the present invention will be specifically described together with examples.
In the method of the present invention, in the step of depositing metal indium by adding zinc to an indium chloride solution, metal indium is deposited in a state where indium ions and indium hydroxide coexist in the liquid. It is a collection method.

The indium chloride solution of the present invention is, for example, a solution in which ITO scrap is dissolved in hydrochloric acid and the residue in the solution is filtered and separated by tin hydroxide precipitation or the like. Specifically, ITO scrap is dissolved in hydrochloric acid at a temperature of 60 to 90 ° C. An alkali (sodium hydroxide or the like) is added to the solution to adjust the pH to 1.5 to 2.5 to produce a tin hydroxide precipitate, and solid-liquid separation is performed to remove the tin hydroxide precipitate.

An alkali such as sodium hydroxide is further added to the indium chloride solution from which tin hydroxide has been removed to adjust the pH of the solution to 2.5 to 3.5 to produce indium hydroxide. If the pH is lower than 2.5, indium hydroxide precipitates are not sufficiently formed. If this pH is higher than 3.5, most of the indium ions are precipitated by indium hydroxide, and the concentration of indium ions in the liquid becomes too low. Cementation (substitution reaction between zinc and indium) is performed under liquidity in the above pH range.

When cementation is performed by immersing a zinc plate in an indium chloride solution, the initial concentration of indium ions is preferably in the range of about 70 g / L. If the initial concentration of indium ions is higher than this, for example, about 150 g / L, a thin indium film is formed on the surface of the zinc plate, hindering zinc elution and inhibiting the substitution reaction between zinc and indium. The stationation will not progress. On the other hand, if the indium ion concentration in the liquid is significantly lower than the initial concentration, it takes time to deposit metal indium, and the efficiency is lowered.

In addition, since the indium ion concentration in the liquid gradually decreases as the deposition of metal indium proceeds, when cementation is performed in the range where the initial concentration of indium ions is around 70 g / L, a sufficient amount without replenishing indium ions. In order to obtain this metal indium, a large amount of initial liquid is required, and indium loss in the final process increases.

The recovery method of the present invention adjusts the pH of the indium chloride solution to 2.5 to 3.5 to produce indium hydroxide, and deposits metal indium in the state where indium ions and indium hydroxide coexist in the liquid. Therefore, it is possible to perform cementation while increasing the indium concentration of the entire solution including indium hydroxide while maintaining the concentration of indium ions in the solution within a concentration range suitable for cementation, so that the zinc plate is insolubilized. Indium can be stably deposited.

Specifically, the initial concentration of indium chloride in the indium chloride solution used for cementation is in the range of indium ion concentration of 60 to 100 g / L, preferably 60 to 85 g / L, the amount of indium hydroxide in the liquid (In conversion) 5 A range of 60 g / L and therefore a total indium concentration of 90 to 120 g / L is preferred. A zinc plate is immersed in an indium chloride solution in this concentration range to perform a substitution reaction between indium and zinc. When the substitution reaction proceeds and the indium ion concentration in the liquid decreases, indium hydroxide in the liquid dissolves and indium ions are supplied into the liquid, and the equilibrium of the indium ion concentration is maintained.

Note that, in the pH range where the cementation is performed (pH 2.5 to 3.5), the reaction of zinc ions eluted in the liquid to combine with hydroxyl groups to generate zinc hydroxide does not proceed. Does not contain zinc hydroxide.

By adding sodium hydroxide or the like to the indium chloride solution and adjusting the pH to the above range, indium hydroxide is generated and the liquid becomes cloudy. When a zinc plate is immersed in this, the substitution reaction proceeds, and sponge-like metal indium is deposited and collected at the bottom of the container. On the other hand, the indium hydroxide in the liquid is consumed in the substitution reaction, and the solution gradually becomes transparent. After the reaction, dehydration is performed to recover sponge-like metal indium. Indium hydroxide is consumed in its entirety, and zinc ions do not produce zinc hydroxide. The recovered metal indium does not contain indium hydroxide and zinc hydroxide, and metal indium with less impurities can be recovered. .

Examples of the present invention are shown below together with comparative examples.

[Example 1]
Sodium hydroxide is added to 6500 liters of indium chloride solution to adjust the pH to 2.8 to produce indium hydroxide. The amount of indium hydroxide in the solution (In conversion) is 25 g / L, the amount of free indium ions is 69 g / L (total) A cloudy solution having an indium concentration of 94 g / L was obtained. A plurality of zinc plates (area: 1200 cm ² ) were immersed in this solution under the above pH and left for 72 hours to become a transparent solution, and a precipitate was deposited on the bottom of the container. The precipitate was collected by filtration, dehydrated and dried to obtain 604.5 kg of spongy metallic indium. Indium hydroxide and zinc hydroxide contained in the metal indium were below the detection limit. The results are shown in Table 1.

[Examples 2 to 3, Comparative Examples 1 and 2]
Sponge-like metal indium was obtained in the same manner as in Example 1 except that the pH of the indium chloride solution was adjusted to the value shown in Table 1. The results are shown in Table 1.

As shown in Table 1, Examples 1 to 3 of the present invention have a large amount of recovered metal indium and a small amount of impurities contained in the recovered metal indium. On the other hand, in Comparative Example 1 in which indium hydroxide does not coexist, the amount of recovered metal indium is much smaller than that in Example, and in Comparative Example 2 in which most of indium is indium hydroxide, cementation hardly proceeds. The amount of recovered metal indium is extremely small.

Claims (4)

A method for recovering indium, characterized in that, in a step of depositing metal indium by adding zinc to an indium chloride solution, indium ions and indium hydroxide coexist in the solution to deposit metal indium.
In the step of depositing metal indium by adding zinc to an indium chloride solution, indium ions and indium hydroxide coexist in the liquid, and the concentration of indium ions in the liquid is set to 60 to 85 g / L. Item 2. The method for recovering indium according to Item 1.
3. The method of claim 1, wherein the indium chloride solution is adjusted to a pH of 2.5 to 3.5 to produce indium hydroxide, and indium ions and indium hydroxide coexist to deposit metal indium. Collection method.
Claims for depositing metal indium in an indium chloride solution in an indium ion initial concentration of 60 to 85 g / L and an initial indium hydroxide amount (in conversion) of 5 to 60 g / L (total indium concentration of 90 to 120 g / L). Item 4. The method for recovering indium according to any one of Items 1 to 3.