METHOD AND APPARATUS FOR RECOVERING INDIUM FROM WASTE LIQUID CRYSTAL DISPLAYS

Abstract

This invention provides a method and apparatus for recovering In in the form of an alloy or a metal simple substance as a valuable material from waste LCD. In the In recovery method and apparatus, there is no need to recover In as indium hydroxide, and In can be recovered as a valuable metal. Accordingly, unlike the case of indium hydroxide, the recovery does not suffer from poor handling, and In can easily be recovered through a filter or the like with significantly improved In recovery. The In recovery method is characterized by comprising crushing waste LCD containing indium tin oxide, dissolving indium tin oxide from the crushed waste LCD with an acid to give an indium compound-containing solution, allowing the solution to flow into a reactor for recovery and, further, adding particles of a metal having a larger ionization tendency than In into the reactor for recovery, fluidizing the metal particles, precipitating In or an In alloy contained in the indium compound-containing solution onto the surface of the metal particles, then separating the precipitated In or In alloy from the metal particles by separation means, and separating and recovering the separated solid In or In alloy from the liquid component.

Description

TECHNICAL FIELD

The present invention relates to a method and apparatus for recovering indium from waste liquid crystal displays, and more particularly a method and apparatus for recovering a valuable material, namely indium (In) in the form of an alloy or metal simple substance from waste liquid crystal televisions, cellular phones or portable game players, or liquid crystal displays (hereinafter also referred as waste LCD) discharged as rejected products during manufacturing processes.

BACKGROUND ART

For liquid crystal displays (hereinafter also referred as LCDs), indium tin oxide (ITO) films are used as transparent electrodes. ITO films are formed mainly by sputtering, in which In is used for its target. In is a rare metal produced during a zinc refining process and the fear of depletion has recently arose. About 300 mg/L of In is contained in a waste LCD, and due to the depleting In, demand exists for recovering In during recycling process.

In order to meet the above demand, an attempt has been made to recover In in waste LCDs. As a technique to do it, an invention is proposed in the following non-patent document 1. This invention relates to a fluidized bed treatment system for LCDs, and this fluidized bed treatment system for LCDs includes a fluidized bed treatment unit, a cyclone, a heat extractor, a high-temperature bag filter, a catalytic fluidized bed and a water washing tower, in which In mechanically separated by silicon sand as a bed material is accumulated in the bed material. However, according to a method using this treatment system, about 60% of In is accumulated in the bed material and the residual is caught by a bag filter, so that an overall indium recovery rate is about 60% and a low recovery rate of only about 60% was achieved.

Non-patent document 1: April 2002 Issue of Monthly Display, Pages 36-46.

In order to increase such a low recovery rate associated with a dry processing as described above, there has been developed a wet processing. For example, the following patent document 1 discloses a method that includes dissolving ITO in acid such as nitric acid or hydrochloric acid, then removing impurities such as Sn by sedimentation, and then adding ammonia thereto for neutralization, thus allowing indium to be recovered as indium hydroxide.

Patent document 1: Japanese Patent Application Laid-open No. 2000-128531

However, according to the method of the above wet processing, filterability of indium hydroxide produced by the treatment is poor and hence it takes a long time for operation, as well as there is a problem in that the characteristics of indium hydroxide produced by neutralization or the like are changed.

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

The present invention has been conceived to solve the above problems. It is an object of the present invention to provide an In recovering method and apparatus that is capable of recovering In as a valuable material without the necessity to recover it in the form of indium hydroxide unlike the conventional method, thereby being capable of preventing poor handling during recovering unlike indium hydroxide, easily recovering In by filter or the like and thus remarkably improving the In recovering rate.

Means to Solve the Problem

The present invention has been made in order to solve the above problems. A method of recovering indium from waste liquid crystal displays, of claim 1 is characterized in that it comprises: crushing waste liquid crystal displays that contain indium tin oxide; dissolving the indium tin oxide from the waste liquid crystal displays by using acid, thereby producing an indium composition-containing solution; flowing the same into a recovering reactor while adding metal particles of a metal having an ionization tendency larger than indium into the recovering reactor; fluidizing the metal particles; depositing indium or indium alloy contained in the indium composition-containing solution onto the surface of the metal particles; then separating the deposited indium or indium alloy from the metal particles by a separating means; and isolating and recovering the separated indium or indium alloy in a solidified form from the liquid component.

In claim 2, a method of recovering indium from waste liquid crystal displays according to claim 1 is characterized in that the metal particles of the metal having an ionization tendency larger than indium are any one of zinc particles and aluminium particles. In claim 3, a method of recovering indium from waste liquid crystal displays according to any one of claims 1 and 2 is characterized in that the separating means for separating the indium or indium alloy deposited onto the metal particles comprises any one of a vibrating means for vibrating the metal particles by ultrasonic waves and a stirring means for stirring the metal particles by electromagnet and thereby making the metal particles collide with one another.

In claim 4, a method of recovering indium from waste liquid crystal displays according to any one of claims 1 to 3 is characterized in that the indium composition-containing solution produced by dissolving the indium tin oxide from the waste liquid crystal displays is flown into an impurity removing reactor prior to the flowing of the indium composition-containing solution into the recovering reactor; metal particles of a metal having an ionization tendency larger than an impurity metal other than the indium in the indium composition-containing solution are added into the impurity removing reactor, thereby fluidizing the metal particles and depositing the impurity metal on the surface of the metal particles; and then the deposited impurity metal is separated and removed from the metal particles by the separating means.

In claim 5, a method of recovering indium from waste liquid crystal displays according to claim 4 is characterized in that the separating means for separating the impurity metal deposited onto the metal particles comprises any one of a vibrating means for vibrating the metal particles by ultrasonic waves and a stirring means for stirring the metal particles by electromagnet and thereby making the metal particles collide with one another. In claim 6, a method of recovering indium from waste liquid crystal displays according to any one of claims 4 and 5 is characterized in that the impurity metal is tin. In claim 7, a method of recovering indium from waste liquid crystal displays according to any one of claims 4 to 6 is characterized in that the metal particles of the metal having an ionization tendency larger than the impurity metal are iron particles. In claim 8, a method of recovering indium from waste liquid crystal displays according to claim 7 is characterized in that alkali is added into the indium composition-containing solution with the impurity metal removed therefrom, and iron is removed in the form of hydroxide by sedimentation. A method of recovering indium from waste liquid crystal displays of claim 9 is characterized in that it comprises: crushing waste liquid crystal liquid displays that contain indium tin oxide; dissolving the indium tin oxide from the waste liquid crystal displays by using acid, while the crushed waste liquid crystal displays are kept placed in a bag, thereby producing an indium composition-containing solution; and washing and neutralizing the waste liquid crystal displays placed in the bag and then drying the same.

An apparatus for recovering indium from waste liquid crystal displays of claim 10 is characterized in that it comprises: crusher for crushing waste liquid crystal displays that contain indium tin oxide; an indium dissolution device for dissolving the indium tin oxide from the waste liquid crystal displays, thereby producing an indium composition-containing solution; a recovering reactor for allowing the indium composition-containing solution produced by the indium dissolution device to flow into the recovering reactor while allowing metal particles of a metal having an ionization tendency larger than indium to be added into the recovering reactor, thereby carrying out a metal deposition reaction that deposits indium or indium alloy onto the metal particles; a separating means for separating the deposited indium or indium alloy from the metal particles to recover the same; and an isolating means for isolating the separated indium or indium alloy in a solidified form from the liquid component.

In claim 11, an apparatus for recovering indium from waste liquid crystal displays according to claim 10 is characterized in that the metal particles of the metal having an ionization tendency larger than indium are any one of zinc particles and aluminium particles. In claim 12, an apparatus for recovering indium from waste liquid crystal displays according to any one of claims 10 and 11 is characterized in that the separating means for separating the indium or indium alloy deposited onto the metal particles comprises any one of a vibrating means for vibrating the metal particles by ultrasonic waves and a stirring means for stirring the metal particles by electromagnet and thereby making the metal particles collide with one another.

In claim 13, an apparatus for recovering indium from waste liquid crystal displays according to any one of claims 10 to 12 is characterized in that an impurity removing reactor is disposed on the upstream side of the recovering reactor, said impurity removing reactor being arranged to flow the indium composition-containing solution produced by the indium dissolution device into the impurity removing reactor; add metal particles of a metal having an ionization tendency larger than an impurity metal other than the indium in the indium composition-containing solution into the impurity removing reactor, thereby fluidizing the metal particles and depositing the impurity metal onto the surface of the metal particles; and have a means of separating and removing the deposited impurity metal from the metal particles.

In claim 14, an apparatus for recovering indium from waste liquid crystal displays according to claim 13, is characterized in that the separating means for separating the impurity metal deposited onto the metal particles comprises any one of a vibrating means for vibrating the metal particles by ultrasonic waves and a stirring means for stirring the metal particles by electromagnet and thereby making the metal particles collide with one another. In claim 15, an apparatus for recovering indium from waste liquid crystal displays according to any one of claims 13 and 14 is characterized in that the impurity metal is tin.

In claim 16, an apparatus for recovering indium from waste liquid crystal displays according to any one of claims 13 to 15 is characterized in that the metal particles of the metal having an ionization tendency larger than the impurity metal are iron particles. In claim 17, an apparatus for recovering indium from waste liquid crystal displays according to claim 16 is characterized in that alkali is added into the indium composition-containing solution with the impurity metal removed therefrom, and iron is removed in the form of hydroxide by sedimentation.

ADVANTAGES OF THE INVENTION

As mentioned above, according to the present invention, there is provided a method of recovering indium from waste liquid crystal displays, which comprises crushing waste liquid crystal displays (LCDs) that contain indium tin oxide; dissolving the indium tin oxide from the waste LCDs, thereby producing an indium composition-containing solution; flowing the same into a recovering reactor while adding metal particles of a metal having an ionization tendency larger than indium (In) into the recovering reactor; fluidizing the metal particles; depositing In or In alloy contained in the indium composition-containing solution onto the surface of the metal particles; then separating the deposited In or In alloy from the metal particles by a separating means; and isolating and recovering the separated In or In alloy in a solidified form from the liquid component. With this method, ITO can be easily and efficiently dissolve from waste LCDs. By combining a cementation reaction utilizing the ionization tendency with the separating technique, and specifically, using metal particles in recovering In from a solution with In dissolved therein, the overall surface area of a metal for metal deposition reaction is increased, thereby improving the deposition reaction rate, and furthermore, by separating a deposited metal, which has been grown to some extent, by the separating means, a fresh surface of the metal is constantly exposed so that the reaction rate can be kept constant. Whereby, there is an advantage in that the In recovering rate from waste LCDs can be remarkably improved, even compared with any of the conventional drying type and the wet type. In the present invention, with respect to the In recovering rate from wastewater, a high recovering rate, namely 80% or higher was achieved.

Unlike the conventional wet processing, In is not necessarily recovered in the form of indium hydroxide, while In can be recovered as a valuable metal. Therefore, unlike the case of indium hydroxide, there are advantages in that the recovery does not suffer from poor handling and In can be easily recovered by filter or the like.

Furthermore, when the impurity removing reactor that causes a metal deposition reaction in the same manner as the recovering reactor is disposed on the upstream side of the recovering reactor, it is possible to appropriately remove Sn or the like as an impurity metal by adding metal particles such as iron (Fe) having an ionization tendency larger than that of the impurity metal other than In contained in an indium composition-containing solution with indium tin oxide dissolved from waste LCDs, such as tin (Sn), thereby fluidizing the indium composition-containing solution, hence depositing the impurity metal such as Sn contained in the wastewater onto the metal particles, and then separating the deposited impurity metal from the metal particles by the separating means.

Thus, since the wastewater having the impurity metals other than In, such as Sn previously removed therefrom can be supplied into the recovering reactor, there is an advantage in that the purity of In recovered by the recovering reactor can be further improved. Specifically, In could be recovered at a purity of 95% or higher by disposing the impurity removing reactor on the upstream side of the recovering reactor.

When impurity metals have been removed by using such impurity removing reactor, ions of the added metals, such as the aforesaid iron, are eluted. However, by providing the sedimentation removing device disposed on the downstream side, which allows metals such as iron to be precipitated in the form of hydroxide by adding alkali, the hydroxide of iron and the like can be previously removed before the wastewater is supplied into the recovering reactor. In this case, when pH is increased, a precipitation of indium hydroxide may be generated. However, the precipitation generation rate of iron hydroxide is much higher than that of indium hydroxide. Therefore, the retention time control in the sedimentation removing device can prevent generation of indium hydroxide and hence supply In to the next recovering reactor almost without the loss of In. In addition, even if a part of In exists in the form of indium hydroxide in a solution, the In recovering rate is not deteriorated since the indium hydroxide is again dissolved by adjusting pH in the next recovering reactor.

When an In elution treatment by acid, a washing and neutralization treatment, and a drying treatment are carried out while waste LCDs are kept placed in a bag, there is an advantage in that a simplified process can be achieved by continuously placing waste LCDs finely crushed in the waste LCD crushing step in the bag throughout the process. In addition, since there is no need to handle powdery waste LCDs received from the waste LCD crushing step, in which they are finely crushed, it is not difficult to handle them.

As mentioned above, the present invention can provide an In recovering method with a high recovering rate. Therefore, even when the recovering recycle of LCDs becomes required by a home appliance recycling law, there is an actual advantage in that the present invention can be applied as an In recovering method in a recycling process in a recycle plant of liquid crystal displays.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of an apparatus for recovering In from waste LCDs according to one embodiment.

FIG. 2 is a schematic front view of an impurity removing reactor or recovering reactor in the In recovering apparatus.

FIG. 3 is a schematic front view of an impurity removing reactor or recovering reactor of another embodiment.

FIG. 4 is a schematic front view of an impurity removing reactor or recovering reactor of still another embodiment.

FIG. 5 is a schematic plan view of a slide board equipped with electromagnets for use in the embodiment of FIG. 4.

FIG. 6 is a schematic block diagram illustrating an In recovering apparatus of yet another embodiment.

FIG. 7 is a schematic cross sectional view of an elution treatment device in the In recovering apparatus.

FIG. 8 is a schematic explanatory view of an apparatus used in Examples.

DESCRIPTION OF THE REFERENCE NUMERALS

2: impurity removing reactor, 3: sedimentation removing device, 4: recovering reactor

Best Mode for Carrying Out the Invention

Now, the description will be hereinafter made for embodiments of the present invention with reference to the drawings attached hereto.

Embodiment 1

An apparatus for recovering indium from waste LCDs, of this embodiment includes, as illustrated in FIG. 1, an indium dissolution device (hereinafter referred also as an In dissolution device) 1 for dissolving ITO from waste LCDs by using hydrochloric acid; an impurity removing reactor 2 for removing impurity metals other than In by adding iron particles (Fe particles) into an indium compound-containing solution that contains In dissolved at the In dissolution device 1; a deposit removing device 3 for removing the Fe particles in the form of hydroxide of iron (Fe) by sedimentation from wastewater with impurity metals removed therefrom at the impurity removing reactor 2; and a recovering reactor 4 for recovering In from the wastewater with the Fe hydroxide removed therefrom at the deposit removing device 3. Although no illustration is made, a crusher for crushing waste LCDs is disposed on the upstream side of the In dissolution device 1. By the crushing is meant in the present invention crushing waste LCDs, and accordingly, the size of crushed pieces is not the matter. For example, the crushing is meant to also contain pulverizing which is generally recognized as reduction to very small pieces by crushing, grinding or the like.

The In dissolution device 1 is to produce an indium composition-containing solution by dissolving In from crushed waste LCDs by hydrochloric acid (aqueous hydrochloric acid solution). An indium composition-containing solution is prepared to contain 100-300 mg/L of In. Furthermore, this indium composition-containing solution is prepared to have a hydrochloric acid concentration of 20% and allow the hydrochloric acid to have a pH of 1.5.

The impurity removing reactor 2 is to remove Sn as an impurity from the indium composition-containing solution, and arranged with a vertically long reactor body 5, as illustrated in FIG. 2. This reactor body 5 is, as illustrated in this Figure, made up of a reactor upper portion 6, a reactor intermediate portion 7 and a reactor lower portion 8, in which these portions are interconnected to each other with interconnection portions 9, 10. The reactor upper portion 6, the reactor intermediate portion 7 and the reactor lower portion 8 each have a uniform width, while the reactor upper section 6 is larger in cross sectional area than the reactor intermediate section 7 and the reactor intermediate section 7 is larger in cross sectional area than the reactor lower section 8. Thus, the cross sectional area of the reactor body 5 as a whole discontinuously increases towards the upper side. The interconnection portions 9, 10 each have a tapered shape with the width increasing towards the upper side.

Disposed on the lower side of the reactor lower section 8 is an inflow chamber 11 of a substantially conical shape for allowing inflow of an indium composition-containing solution to be treated, and disposed on the lower side of the inflow chamber 11 is an inflow pipe 12. Although not illustrated, a check valve is disposed in the inflow pipe 12. Disposed on the upper side of the reactor upper section 6 is an upper chamber 13 with an outflow pipe 14 attached to a lateral side thereof for allowing Sn as an impurity metal to be deposited onto metal particles (Fe particles) and discharged therethrough. The upper chamber 13 is a section for discharging Sn together with Fe particles by such outflow pipe 14, as well as is a section for allowing Fe particles to be thrown therein, in which Fe particles cause a so-called cementation reaction (metal deposition reaction) based on the difference in ionization tendency between Fe and Sn as an impurity to be removed. In practice, the cementation reaction of Fe and Sn takes place in the entire reactor body 1.

It is so structured that the indium composition-containing solution flown in through the inflow pipe 12 allows its wastewater to form a fluidized bed of Fe particles while moving up vertically, until it reaches the outflow pipe 14. Ultrasonic oscillation members 15a, 15b, 15c as a means of removing Sn, which is an impurity metal contained in the indium composition-containing solution and deposited onto the Fe particles by the cementation reaction, are provided respectively in the reactor upper section 6, the reactor intermediate section 7 and the reactor lower section 8.

In this embodiment, Fe particles are used as metal particles to be thrown in. Metal particles such as Fe particles having an average particle diameter of 0.1 to 8 mm are preferably used. In this embodiment, particles having an average particle diameter of about 3 mm are used. The average particle diameter is measured by an image analysis method or a screening test according to JIS Z 8801.

The sedimentation removing device 3 is to remove the Fe particles as hydroxide by sedimentation. The precipitate removal of hydroxide is achieved by adding alkali (alkali solution) such as sodium hydrate. The pH of wastewater within the sedimentation removing device 3 is adjusted to 8 to 9.

The recovering reactor 4 is to remove Sn as an impurity as described above, and recover In from an indium composition-containing solution with Fe removed in the form of hydroxide by sedimentation, and has the same structure as that of the impurity removing reactor 2. That is, as illustrated in FIG. 2, the recovering reactor 4 includes the reactor body 5 made up of the reactor upper section 6, the reactor intermediate section 7 and the reactor lower section 8 interconnected via the interconnection portions 9, 10. The pH within the recovering reactor 4 is adjusted to 1.5 or lower.

The recovering reactor 4 is the same as the impurity removing reactor 2 in structure in that the inflow chamber 11, the inflow pipe 12, the upper chamber 13 and the outflow pipe 14 are disposed, and the ultrasonic oscillation members 15a, 15b, 15c are disposed respectively in the reactor upper section 6, the reactor intermediate section 7 and the reactor lower section 8.

Now, the description will be made for a method of recovering In from waste LCDs by an apparatus having the above structure for recovering In from waste LCDs. First, waste LCDs are crushed by a crusher (not illustrated) and crushed waste LCDs are supplied into the In dissolution device 1. Then, hydrochloric acid (aqueous hydrochloric acid solution) is added into this In dissolution device 1 to elute In from the waste LCDs by the hydrochloric acid, and thus an indium composition-containing solution, which contains 100 to 300 mg/L of In is produced within the In dissolution device 1.

Then, this indium composition-containing solution is supplied into the impurity removing reactor 2. The indium composition-containing solution supplied into the impurity removing reactor 2 flows through the inflow pipe 12 of the impurity removing reactor 2 into the reactor body 5 via the inflow chamber 11. On the other hand, metal particles (Fe particles) for causing a cementation reaction are thrown into the reactor body 5 through the upper chamber 13. In the reactor body 5, the indium composition-containing solution flown in moves up in a vertical direction, while this indium composition-containing solution and the Fe particles thrown in through the upper chamber 13 are brought into fluidized state to form a fluidized bed.

Then, based on the difference in ionization tendency between impurity metals other than In contained in the indium composition-containing solution, more specifically Sn, and Fe as metal particles thrown in, a so-called cementation reaction is caused. Giving a detailed explanation of this, the reduction reactions of the respective metal ions are represented in the following expressions, in which the standard electrode potentials (E°) of the respective metal ions are indicated.

$\begin{array}{cc}{\mathrm{Fe}}^{2+}+2e->\mathrm{Fe}-0.44V& \left(1\right)\\ {\mathrm{Sn}}^{2+}+2e->\mathrm{Sn}-0.14V& \left(2\right)\end{array}$

As being apparent from the above (1) and (2), the standard electrode potential of Fe²⁺ is smaller than that of Sn²⁺. In other words, Fe is larger than Sn in ionization tendency. Therefore, under the above fluidized state, Fe having a large ionization tendency turns to be Fe²⁺ (a reversed reaction of the above (1) expression) and is eluted into the indium composition-containing solution, while Sn²⁺ contained in the indium composition-containing solution turns to be Sn and is deposited onto the surface of Fe particles.

Then, after Sn has been deposited onto the surface of Fe particles by such cementation reaction, the ultrasonic oscillation members 15a, 15b, 15c are actuated. By the actuation of the ultrasonic oscillation members 15a, 15b, 15c, ultrasonic waves emitted therefrom apply vibration force and stirring force to Fe particles with the Sn deposited thereon so that deposited Sn is forcibly separated from the Fe particles.

The thus separated Sn is discharged to the outside of the reactor body 5 from the upper chamber 13 through the outflow pipe 14, and hence removed from the indium composition-containing solution. In this case, in this embodiment, metal (Fe) thrown in for removing impurity metals is in a particulate form, and therefore the surface area of the metal (Fe) for causing the cementation reaction is increased as compared with a case, in which, for example, iron pieces are thrown in. Hence, the rate of the deposition reaction of Sn is improved. Then, after it has been confirmed that the deposited metal was grown to some extent, a fresh surface of the metal (surface of Fe particles) is constantly exposed by the forced separation by the above ultrasonic vibration, thereby enabling the reaction rate to be kept constant.

Metal particles of Fe are fluidized in the reactor body 5 and Fe²⁺ is eluted by the above cementation reaction, and therefore the particle size in the initial stage of the throwing-in of metal particles, which have been thrown into the upper chamber 13, necessarily decreases as the time elapses. As a result, since wastewater moves upward within the reactor body 5 at substantially the same upflow rate under ordinal circumstances, metal particles having the particle size decreasing as they advance towards the upper side may unintentionally overflow from the reactor body 5.

However, in this embodiment, since the cross sectional area of the reactor body 5 is discontinuously increased towards the upper side, the upflow rate of the wastewater within the reactor body 5 is gradually decreased and hence metal particles with the particle size having been decreased by the above cementation reaction become more likely to be retained within the reactor body 5 without unintentional overflow, in an upper portion of the reactor body 5, which portion having an increasing cross sectional area.

Since an indium composition-containing solution, which flows in through the lower side of the reactor body 5, allows a subject metal such as Sn to be deposited onto metal particles of Fe by the cementation reaction when it passes the inside of the reactor body 5, the concentration of metal impurity in the indium composition-containing solution decreases as the indium composition-containing solution moves towards the upper side of the reactor body 5.

However, in this embodiment, it is confirmed that the metal particles become finer as they are closer to the upper side of the reactor body 5, and the number of metal particles is increased as the upflow rate of the indium composition-containing solution is gradually decreased. Thus, the overall surface area of the metal particles is increased as they are closer to the upper side of the reactor body 5. As a result, the rate of the cementation reaction (efficiency of the impurity metal deposition) is improved. Thus, Ni and Sn as impurity metals can be efficiently removed even in an upper portion of the reactor body 5, in which the concentration of impurity metals is lowered.

Then, the indium composition-containing solution with Sn removed therefrom is supplied into the deposit removing device 3. Alkali (alkaline solution), such as sodium hydrate, is added into the deposit removing device 3. Whereby, hydroxides of Fe and solid products of indium hydroxide are generated. Specifically, in the impurity removing reactor 2, Sn is deposited onto the Fe particles and removed by the cementation reaction, while Fe ions (Fe²⁺) are eluted into the indium composition-containing solution. Accordingly, it is necessary to remove the Fe²⁺ as well before the indium composition-containing solution is supplied into the recovering reactor 4 disposed on the downstream side. In this regard, although hydroxides of Fe and solid products of indium hydroxide are generated by the addition of alkali, the hydroxides of Fe are easily removed in the sedimentation removing device 3, which is similar to a coagulation sedimentation tank, by controlling the time for which the subject water is retained in the sedimentation removing device 3, since the hydroxides of Fe generate a deposit at a much greater rate than indium hydroxide.

Then, the indium composition-containing solution with the hydroxides of Fe removed is adjusted to a pH of 1.5 or lower, thereby causing the indium hydroxide to be again dissolved therein, and then is supplied into the recovering reactor 4. The indium composition-containing solution supplied into the recovering reactor 4 is flown into the reactor body 5 from the inflow pipe 12 via the inflow chamber 11, in the same manner as in the case of the impurity removing reactor 2. On the other hand, metal particles (Zn particles or Al particles) for causing the cementation reaction are thrown into the reactor body 5 from the upper chamber 13. In the same manner as in the case of the impurity removing reactor 2, an indium composition-containing solution flown in the reactor body 5 moves upward so that metal particles thrown in from the upper chamber 13 are brought into fluidized state.

Then, a so-called cementation reaction is caused based on the difference in ionization tendency between In in the indium composition-containing solution to be recovered and Zn or Al as metal particles thrown in. The reduction reactions of the respective metal ions are represented in the following expressions, in which the standard electrode potentials (E°) of the respective metal ions are indicated.

$\begin{array}{cc}{\mathrm{In}}^{3+}3e->\mathrm{In}-0.34V& \left(3\right)\\ {\mathrm{Zn}}^{2+}+2e->\mathrm{Zn}-0.76V& \left(4\right)\\ {\mathrm{Al}}^3+3e->\mathrm{Al}-1.66V& \left(5\right)\end{array}$

As being apparent from the above (3) to (5), the standard electrode potential of Zn²⁺ or Al³⁺ is smaller than that of In³⁺. In other words, Zn or Al is larger than In in ionization tendency. Therefore, under the above fluidized state, Zn or Al having a large ionization tendency turns to be Zn²⁺ or Al³⁺ (a reversed reaction of the above (4) and (5) expressions) and is eluted into the indium composition-containing solution, while In³⁺ contained in the indium composition-containing solution turns to be In and is deposited onto the surface of Zn or Al particles.

Then, after In has been deposited onto the surface of Zn or Al particles by such a cementation reaction, the ultrasonic oscillation members 15a, 15b, 15c are actuated. By the actuation of the ultrasonic oscillation members 15a, 15b, 15c, ultrasonic waves emitted therefrom apply vibration force and stirring force to Zn or Al particles with the In separated therefrom, and thereby precipitated In is forcibly separated from the Zn or Al particles.

The thus separated In is discharged to the outside of the reactor body 5 from the upper chamber 13 through the outflow pipe 14, and thereby In is recovered as a valuable metal. In this case, in this embodiment, since Zn or Al to be thrown in is in a particulate form in the same manner as in the case of iron of the impurity removing reactor 2, and therefore the surface area of the metal for causing the cementation reaction is increased and hence the rate of the precipitation reaction of In is improved.

Then, after it has been confirmed that the precipitated metal was grown to some extent, a fresh surface of the Zn or Al particles is constantly exposed by the forced separation by the above supersonic vibration, thereby enabling the reaction rate to be kept constant.

Zn²⁺ or Al³⁺ is eluted from Zn or Al particles by the cementation reaction, and therefore the particle size of Zn or Al thrown into the upper chamber 13 in the initial stage of the throwing-in necessarily decreases as the time elapses. As a result, since the indium composition-containing solution moves upward within the reactor body 5 at substantially the same upflow rate under ordinal circumstances, Zn or Al particles having the particle size decreasing as they advance towards the upper side may unintentionally overflow from the reactor body 5.

However, in this embodiment, since the cross sectional area of the reactor body 5 is discontinuously increased towards the upper side, the upflow rate of the indium composition-containing solution within the reactor body 5 is gradually decreased and hence metal particles with the particle size having been decreased by the above cementation reaction become more likely to be retained within the reactor body 5 without unintentional overflow, in an upper portion of the reactor body 5, which portion having an increasing cross sectional area.

Since an indium composition-containing solution, which flows in through the lower side of the reactor body 5, allows In as a subject to be deposited onto Zn or Al particles by the cementation reaction when it passes the inside of the reactor body 5, the concentration of In in the indium composition-containing solution decreases as the indium composition-containing solution moves towards the upper side of the reactor body 5.

However, in this embodiment, it is confirmed that the Zn or Al particles become finer as they are closer to the upper side of the reactor body 5, and the number of Zn or Al particles is increased as the upflow rate of the indium composition-containing solution is gradually decreased. Thus, the overall surface area of the Zn or Al particles is increased as they are closer to the upper side of the reactor body 5. As a result, the rate of the cementation reaction (efficiency of the In deposition) is improved. Thus, In as a subject to be recovered can be more efficiently removed from the indium composition-containing solution even in an upper portion of the reactor body 5, in which portion the concentration of In is lowered.

Embodiment 2

This embodiment is different from Embodiment 1 in structure of the impurity removing reactor 2 and the recovering reactor 4. Specifically, in this embodiment, as illustrated in FIG. 3, the entire circumferential wall of the reactor body 5 is tapered upward, and the cross sectional area of the reactor body 5 is continuously increased. This embodiment is different in this respect from Embodiment 1, in which the cross sectional area of the reactor body 5 is discontinuously increased towards the upper side.

Since the cross sectional area is increased towards the upper side not discontinuously but continuously, the reactor body 5 is not arranged with separate sections, such as the reactor upper section 6, the reactor intermediate section 7 and the reactor lower section 8.

However, this embodiment is the same as Embodiment 2 in that the ultrasonic oscillation members 15a, 15b, 15c are provided at three points on the way from the upper portion to the lower portion, of the reactor body 5. Therefore, in this embodiment, there is provided an advantage in that Sn as an impurity metal, which is deposited onto metal particles and must be removed, or In as a metal to be recovered, can be forcibly separated by ultrasonic waves emitted from the ultrasonic oscillation members 15a, 15b, 15c, in the same manner as in Embodiment 1.

Although there is a difference between the discontinuous formation and continuous formation, of the cross sectional area, this embodiment is the same as Embodiment 2 in that the cross sectional area is increased towards the upper side. Therefore, in this embodiment, there are provided an advantage in that metal fine particles having a reduced particle size are retained in the upper portion of the reactor body 5, thereby preventing unintentional overflow, and an advantage in that a subject metal can be efficiently removed or recovered in an upper portion of the reactor body 5, in which portion the concentration of the subject metal is low.

Embodiment 3

In this embodiment, as a means for separating a deposited metal from metal particles, a stirring means by using electromagnet is employed in place of a vibrating means by ultrasonic waves emitted by the ultrasonic oscillation members of Embodiments 1 and 2. Specifically, in this embodiment, a slide board 17 equipped with electromagnets 16 as illustrated in FIG. 5 is mounted on guide rails 18 so as to be able to be moved upward and downward, which guide rails being disposed on the lateral sides of the reactor body 5 having a rectangular horizontal cross section, as illustrated in FIG. 4. The slide board 17 has a space 19 at a center portion, as illustrated in FIG. 5, and the reactor body 5 is placed in the space 19 so that the reactor body 5 is surrounded by the slide board 17. Metal particles used in this embodiment are a magnetic substance such as iron or the like.

As illustrated by the arrow 20 of FIG. 4, the slide board 17 is moved alternatively upward and downward to stir metal particles within the reactor body 5, while making a number of the metal particles collide with one another, thereby forcibly separating the deposited metal from the metal particles. Although there is a difference in means for separating a deposited metal from metal particles, in this embodiment as well, the deposited metal is appropriately separated from the metal particles so that an impurity metal can be appropriately removed or In as a valuable metal can be appropriately recovered.

Embodiment 4

The description will be made for this embodiment by taking a case in which an In elution treatment by acid, a washing and neutralization treatment, and a drying treatment are carried out while waste LCDs are kept placed in a bag. An apparatus for recovering indium from waste LCDs in this embodiment includes an elution treatment device 25, a washing and neutralizing device 26 and a drying device 27, as illustrated in FIG. 6. The elution treatment device 25 includes an elution treatment container 22, such as a tank made of FRP, as illustrated in FIG. 7. This elution treatment container 22 is sized to accommodate waste LCDs placed in a bag 21 such as a flexible container bag, made of resin or cloth. A porous plate 23 and a porous-plate supporting member 24 are disposed on a lower portion of the elution treatment container 22. The bag 21 is structured to be supported on this porous plate 23.

While waste LCDs crushed by a crusher or the like are kept placed in the bag 21, a hydrochloric acid solution for In dissolution and extraction is circulated so that In is eluted from the waste LCDs when the hydrochloric acid solution passes through a waste LCD layer 28. That is, indium tin oxide is dissolved from waste LCDs by using hydrochloric acid to produce an indium composition-containing solution.

On the other hand, the waste LCDs, which have been subjected to the dissolution and extraction treatment, are moved to the next washing and neutralizing device 26 while being still kept placed in the bag 21, and are placed in the washing and neutralizing device 26, at which they are subjected to the washing and neutralization treatment. The movement from the elution treatment device 25 to the washing and neutralizing device 26 is achieved by utilizing a hoist or the like. In the same manner as the In dissolution treatment, the washing is made by circulating water and the neutralization is made by circulating an alkaline solution. The circulation treatment may be made by either downward flow or upward flow of these circulating fluids. The waste LCDs, which have been subjected to the washing and neutralization treatment, are moved to the drying device 27 while being still kept placed in the bag. The drying device 27 is to carry out a drying treatment by, for example, flash drying, but it is possible to carry out a drying treatment by, for example, a drying method such as solar drying without using this drying device 27. The waste LCDs, which have been subjected to the drying treatment, are shipped to tile-making plants, glass-making plates or the like as recycled materials, while being still kept placed in the bag 21.

In this embodiment, a simplified process can be achieved by continuously placing waste LCDs finely crushed in the waste LCD crushing step in the bag 21 throughout the process. In addition, since there is no need to handle powdery waste LCDs received from the waste LCD crushing step, in which they are finely crushed, it is not difficult to handle them.

The bag 21 may be mesh (porous) with such a size of openings not to allow waste LCDs to fall therethrough, and therefore a cloth bag or the like is satisfactorily used for it. The bag may be entirely porous to such an extent as to allow a hydrochloric acid solution to pass therethrough, or may be porous only for a bottom surface. In any arrangement, tight contact between the bag 21 and the elution treatment container 22 can be achieved by the weight of the waste LCDs in the bag 21 upon placing the bag 21 on the porous plate 23 within the elution treatment container 22, so that a hydrochloric acid passes through a waste LCD layer and moves to a bottom portion of the elution treatment container 22 from the bottom surface of the bag 21 via the porous plate 23, thereby enabling In to be dissolved and extracted from the waste LCDs by the circulation treatment.

Other Embodiments

The description was made for the above embodiments by taking the case in which Sn is removed as an impurity metal other than In contained in an indium composition-containing solution produced from waste LCDs by dissolving ITO by using a hydrochloric acid, while it is possible to remove a metal other than Sn. In such a case, it is possible to add metal particles other than Fe.

Also, the description was made for the above embodiments by taking the case in which In is precipitated onto metal particles and the precipitated In is separated from the metal particles, while it is not necessarily limit to a metal simple substance such as In. The present invention is applicable to the case in which an alloy of In and other metals, or an In alloy is precipitated onto metal particles and the precipitated In alloy is separated from the metal particles.

In the above embodiments, as acid for dissolving ITO from waste LCDs, hydrochloric acid is used, while it is not necessary to limit the type of the acid to hydrochloric acid. For example, it is possible to use sulfuric acid, nitric acid or the like, or possible to use a mixed acid.

In the above embodiments, it is possible to provide a preferable effect as mentioned above by providing the impurity removing reactor 2 of the above type, while it is not essential for the present invention to provide the impurity removing reactor 2. Furthermore, although the above embodiments were described by taking the case in which Zn or Al particles are added to recover In, the metal particles to be added to a recovering reactor are not necessarily limited to Zn or Al particles of the above embodiments, and it is essential to use a metal having an ionization tendency larger than In.

In the above embodiments, the particle diameter of the metal particles is about 3 mm. This particle size of metal particles is not necessarily limited to that of the above embodiments, and is preferably 0.1 to 8 mm. When it is smaller than 0.1 mm, an appropriate cementation reaction is not necessarily caused, and the deposited metal separated from the metal particles may not be easily recovered. When it exceeds 8 mm, the number of metal particles that can be retained in the reactor body may be lowered, with the result that the overall surface area of the metal particles is reduced, hence the efficiency of the deposition reaction may be deteriorated, and, in addition, metals other than valuable metals or impurity metals to be recovered may be deposited on the metal particles.

Furthermore, in Embodiments 1 and 2, the cross sectional area of the reactor body 5 is increased as it advances towards the upper side to produce the above preferable effect, while it is not essential for the present invention to form the reactor body 5 into such a shape. Still furthermore, a means for separating a deposited metal from metal particles is not necessarily achieved by a means by ultrasonic waves of Embodiments 1 and 2 or a means by the electromagnet of Embodiment 3, while it may be achieved by any other means.

Example

In dissolution and extraction treatments for In recovering were carried out by an apparatus as illustrated in FIG. 8, using 1%, 3% and 10% hydrochloric acid solutions. In FIG. 8, reference numerals 28 represents a waste LCD layer described in FIG. 7 as well; 29 represents a tube pump; 30 represents hydrochloric acid; 31 represents a resin container; and 32 represents a mesh basket, respectively. According to the analysis, the waste LCDs contained 400 mg/kg of In. The elution treatment was made by retaining 24 kg of waste LCDs in a cotton bag; placing the bag in the resin container 31 that is placed on the mesh basket installed within a 100-L resin container, as illustrated in FIG. 8, and that has a number of openings in a bottom surface; throwing 14 L of hydrochloric acid thereinto; and circulating it at room temperature by using the tube pump 29. In order to prevent change in concentration and amount of hydrochloric acid due to evaporation of water during the elution treatment, a gasket is disposed in a lid of the 100-L resin container, and an insertion/taking-out portion of the tube pump 29 of the lid for use, which enables sealing between the 100-L resin container and the lid, is sealed with a caulking agent.

The test result is shown in Table 1.

	TABLE 1
	1% Hydrochloric Acid	3% Hydrochloric Acid	10% Hydrochloric Acid
	Solution	Solution	Solution
Elution Time of 24 Hrs	In Conc.: 670 ppm	In Conc.: 680 ppm	In Conc.: 680 ppm
Elution Time of 48 Hrs	In Conc.: 680 ppm	In Conc.: 685 ppm	In Conc.: 685 ppm
In Recovering Rate	99% or higher	99% or higher	99% or higher

As being apparent from Table 1, a satisfactory In recovering rate, namely 98% or higher, was achieved by the elution treatment for 24 hours in all the treatments. The recovering rate was determined based on the weight of the waste LCDs and the In-containing rate, and the In concentration in hydrochloric acid and amount of hydrochloric acid after the treatment.

Claims

1. A method of recovering indium from waste liquid crystal displays, comprising:

crushing waste liquid crystal displays that contain indium tin oxide; dissolving the indium tin oxide from the waste liquid crystal displays by using acid, thereby producing an indium composition containing solution; flowing the same into a recovering reactor while adding metal particles of a metal having an ionization tendency larger than indium into the recovering reactor; fluidizing the

metal particles; precipitating indium or indium alloy contained in the indium composition containing solution onto the surface of the metal particles; then separating the deposited indium or indium alloy from the metal particles by a separating means; and isolating and recovering the separated indium or indium alloy in a solidified form from the liquid component.

2. A method of recovering indium from waste liquid crystal displays according to claim 1, wherein the metal particles of the metal having an ionization tendency larger than indium are any one of zinc particles and aluminium particles.

3. A method of recovering indium from waste liquid crystal displays according to claim 1, wherein the separating means for separating the indium or indium alloy deposited onto the metal particles comprises any one of a vibrating means for vibrating the metal particles by ultrasonic waves and a stirring means for stirring the metal particles by electromagnet and thereby making the metal particles collide with one another.

4. A method of recovering indium from waste liquid crystal displays according to claim 1, wherein the indium composition-containing solution produced by dissolving the indium tin oxide from the waste liquid crystal displays is flown into an impurity removing reactor prior to the flowing of the indium composition-containing solution into the recovering reactor; metal particles of a metal having an ionization tendency larger than an impurity metal other than the indium in the indium composition-containing solution are added into the impurity removing reactor, thereby fluidizing the metal particles and depositing the impurity metal on the surface of the metal particles; and then the deposited impurity metal is separated and removed from the metal particles by the separating means.

5. A method of recovering indium from waste liquid crystal displays according to claim 4, wherein the separating means for separating the impurity metal deposited onto the metal particles comprises any one of a vibrating means for vibrating the metal particles by ultrasonic waves and a stirring means for stirring the metal particles by electromagnet and thereby making the metal particles collide with one another.

6. A method of recovering indium from waste liquid crystal displays according to claim 4, wherein the impurity metal is tin.

7. A method of recovering indium from waste liquid crystal displays according to claim 4, wherein the metal particles of the metal having an ionization tendency larger than the impurity metal are iron particles.

8. A method of recovering indium from waste liquid crystal displays according to claim 7, wherein alkali is added into the indium composition-containing solution with the impurity metal removed therefrom, and iron is removed in the form of hydroxide by sedimentation.

9. A method of recovering indium from waste liquid crystal displays, comprising:

crushing waste liquid crystal liquid displays that contain indium tin oxide; dissolving the indium tin oxide from the waste liquid crystal displays by using acid, while the crushed waste liquid crystal displays are kept placed in a bag, thereby producing an indium composition-containing solution; and washing and neutralizing the waste liquid crystal displays placed in the-bag and then drying the same.

10. An apparatus for recovering indium from waste liquid crystal displays, comprising:

a crusher for crushing waste liquid crystal liquid displays that contain indium tin oxide; an indium dissolution device for dissolving the indium tin oxide from the waste liquid crystal displays by using acid, thereby producing an indium composition-containing solution; a recovering reactor for allowing the indium composition-containing solution produced by the indium dissolution device to flow into the recovering reactor while allowing metal particles of a metal having an ionization tendency larger than indium to be added into the recovering reactor, thereby carrying out a metal deposition reaction that deposits indium or indium alloy onto the metal particles; a separating means for separating the deposited indium or indium alloy from the metal particles to recover the same; and an isolating means for isolating the separated indium or indium alloy in a solidified form from the liquid component.

11. An apparatus for recovering indium from waste liquid crystal displays according to claim 10, wherein the metal particles of the metal having an ionization tendency larger than indium are any one of zinc particles and aluminium particles.

12. An apparatus for recovering indium from waste liquid crystal displays according to claim 10, wherein the separating means for separating the indium or indium alloy deposited onto the metal particles comprises any one of a vibrating means for vibrating the metal particles by ultrasonic waves and a stirring means for stirring the metal particles by electromagnet and thereby making the metal particles collide with one another.

13. An apparatus for recovering indium from waste liquid crystal displays according to claim 10, wherein an impurity removing reactor is disposed on the upstream side of the recovering reactor, said impurity removing reactor being arranged to flow the indium composition-containing solution produced by the indium dissolution device into the impurity removing reactor; add metal particles of a metal having an ionization tendency larger than an impurity metal other than the indium in the indium composition-containing solution into the impurity removing reactor, thereby fluidizing the metal particles and depositing the impurity metal onto the surface of the metal particles; and have a means of separating and removing the deposited impurity metal from the metal particles.

14. An apparatus for recovering indium from waste liquid crystal displays according to claim 13, wherein the separating means for separating the impurity metal deposited onto the metal particles comprises any one of a vibrating means for vibrating the metal particles by ultrasonic waves and a stirring means for stirring the metal particles by electromagnet, thereby making the metal particles collide with one another.

15. An apparatus for recovering indium from waste liquid crystal displays according to claim 13, wherein the impurity metal is tin.

16. An apparatus for recovering indium from waste liquid crystal displays according to claim 13, wherein the metal particles of the metal having an ionization tendency larger than the impurity metal are iron particles.

17. An apparatus for recovering indium from waste liquid crystal displays according to claim 16, wherein alkali is added into the indium composition-containing solution with the impurity metal removed therefrom, and iron is removed in the form of hydroxide by sedimentation.