JP2012184472A - Method for recovering silver from used display panel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for efficiently and safely separating and recovering silver from a used display panel containing the silver.SOLUTION: The used display panel is crushed and the silver contained in the used display panel is made to leach out by using mixed liquid of thiourea aqueous solution and acid to produce a leachate, and the effective separation and recovery of the silver can be achieved by applying a metal replacement method (for example, adding zinc powder) to the leachate or by using activated carbon.

Description

The present invention relates to a technique for separating and collecting silver with high purity from a used display panel (for example, a display panel containing silver such as a plasma display or a liquid crystal display).

Silver has traditionally been used as a photographic material and jewelry, but in recent years it has been used in many fields as an electrical / electronic material. Since silver is relatively expensive, it has been conventionally recovered from various wastes such as photographic waste liquids and X-ray photographic films of X-rays and waste liquids. However, the amount of silver contained in used plasma television display panels is very small, and it is not easy to selectively separate and recover silver from a large excess of glass or other metals. There has been no attempt.

In the recovery of silver contained in various solids including solid waste, a conventional method of elution using an alkaline cyanide solution has been adopted as in the case of gold. However, due to its strong toxicity, the method using cyan is expected to be difficult to implement in the future.
As a method for leaching gold or silver from ore, use of an aqueous thiocyanate solution or an aqueous thiourea solution has been studied other than using an alkali cyan solution. These techniques are reported in Non-Patent Documents 1 and 2, etc.

J.Ficeriova, P.Balaz, C.L.Villachica; “Thiosulphate leaching of silver, gold and bismuth from a complex sulfide concentrates”, Hydrometallurgy, 77, 35-39 (2005) P. Balaz, J. Ficeriova, V. Sepelak, R. Kammel; “Thiourea leaching of silver from mechanically activated tetrahedrite”, Hydrometallurgy, 43, 367-377 (1996)

However, there have been no reports of attempts to use these techniques to recover silver from used display panels, and it is unclear whether effective leaching of silver can be achieved with these leaching solutions (leaching stock solutions).

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a method for efficiently and safely separating and recovering silver from a used display panel containing silver.

The method for recovering silver from a used display panel according to the present invention in accordance with the above object is to smash or pulverize a used display panel (hereinafter sometimes simply referred to as “display panel”), The mixed liquid (“leaching stock solution”) is used to leach silver contained from the used display panel to produce a leachate, and the silver is recovered from the leachate. Here, the crushing includes not only crushing the used display panel so as to fit into the processing container but also crushing the used display panel. The display panel is preferably pulverized to a particle size of 1 mm or less (more preferably 300 μm or less) rather than simply crushing.

In the method for recovering silver from a used display panel according to the present invention, the silver is preferably dissolved as a cation complex of Ag [CS (NH ₂ ) ₂ ] _{3 in} the leachate.

Further, in the method for recovering silver from a used display panel according to the present invention, the crushed used display panel is immersed in the mixed solution and then left to stand for a certain period of time. It is preferred to perform leaching.

In the method for recovering silver from a used display panel according to the present invention, the mixed solution contains 0.05 to 1 mol of thiourea (preferably 0.1 to 0.25 mol, more preferably 0 to 0). .1 to 0.2 mol). The reason for this is that if the thiourea concentration is lower than this range, the reaction is slow, and even if the thiourea concentration is higher than this range, the amount of silver that can be extracted does not increase. A range is preferred.

In the method for recovering silver from a used display panel according to the present invention, it is preferable that an inorganic acid (for example, hydrochloric acid, sulfuric acid, nitric acid) having low toxicity is used as the acid.
In the method for recovering silver from a used display panel according to the present invention, the inorganic acid is sulfuric acid, preferably in the range of 0.05 mol to 0.25 mol.

In the method for recovering silver from a used display panel according to the present invention, the recovery of the silver is performed by a metal substitution method (for example, a method using a difference in ionization tendency), and the recovery of silver from the leachate is performed by activated carbon. Or by adding sodium sulfide or by adding a solution in which persimmon astringent is dissolved in water of pH 13-14.

In the method for recovering silver from a used display panel according to the present invention, one or more aqueous solutions of hydrochloric acid, sulfuric acid, nitric acid, and sodium thiosulfate are used instead of the mixed solution of the thiourea aqueous solution and the acid. Can also be used.

In the method for recovering silver from a used display panel according to the present invention, the silver contained in the used display panel can be efficiently separated and recovered by performing chemical treatment. In this case, since the liquid which has a direct toxicity with respect to a human body is not used for the process liquid conventionally, safety | security is high. Also, the liquid discharged from the entire system can be easily processed.

It is a graph which shows the particle size distribution of the grind | pulverized used display panel. It is a graph which shows the influence (Temperature: 30 degreeC, Shaking time: 4 hours) of the solid-liquid ratio to the leaching percentage of silver from the pulverized material of the used display panel. It is a graph which shows the influence (solid-liquid ratio: 250 mL / g, temperature: 30 degreeC, shaking time: 4 hours) of the concentration of thiourea and sulfuric acid concentration on the leaching of silver from the pulverized material of the used display panel. Effect of shaking time on the leaching of silver from pulverized spent display panels at various temperatures using a mixed aqueous solution of 0.05 M thiourea and 0.1 M sulfuric acid (solid liquid (Ratio: 250 mL / g, shaking speed: 200 rpm). Relationship between silver recovery percentage and solid-liquid ratio when recovering silver from leaching solution of mixed aqueous solution of 0.05M thiourea and 0.1M sulfuric acid by metal substitution method with zinc powder ( It is a graph which shows temperature: 30 degreeC. It is a graph which shows the relationship between the leaching percentage of silver at the time of using nitric acid with a density | concentration of 0.1-5M, and solid-liquid ratio. It is a graph which shows the relationship between the silver leaching percentage and solid-liquid ratio at the time of using 0.1-5M concentration hydrochloric acid. It is a graph which shows the relationship between the leaching amount percentage of silver at the time of using sodium thiosulfate aqueous solution of the density | concentration of 1.0, 0.5, and 0.25M, and pH (solid-liquid ratio = 150mL / g, shaking speed) = 150 rpm). It is a graph which shows the relationship between the leaching amount percentage of silver at the time of using the sodium thiosulfate aqueous solution of 1.0, 0.5, and 0.25M concentration, and a solid-liquid ratio (pH = 3, shaking speed = 150 rpm). ). It is a graph which shows the relationship between the addition amount at the time of adding sodium sulfide aqueous solution to the silver thiourea-dilute sulfuric acid liquid mixture, and the recovery percentage of silver by sulfide. The relationship between the solid-liquid ratio (mg of adsorbent added to 1 mL of liquid, horizontal axis) with respect to the percentage of silver adsorption (vertical axis) by activated charcoal from acidic thiourea aqueous solution and mandarin orange juice adsorbent (Bioadsorbent) This is a graph showing (shaking time = 12 hours, shaking speed = 150 rpm, temperature 30 ° C.). 6 is a graph showing the relationship between the percentage of silver recovered and the proportion of flocculant added when various flocculants / precipitants are used (temperature = 30 ° C., shaking time = 6-12 hours, shaking speed = 150 rpm, static (Set time = 24 hours).

Next, embodiments of the present invention will be described with reference to the accompanying drawings.
A used plasma television display panel (hereinafter sometimes simply referred to as a “display panel”), which is an example of a used display panel, was pulverized and the particle size distribution obtained by sieving a sample of the pulverized product was measured. The following results were obtained.
Since particles having a particle size of 53 to 75 μm and those having a particle size of 53 μm or less accounted for 74% of the total, a mixture of both was used as a sample in the subsequent implementation.

This sample was dissolved using aqua regia, and the components in the solution were measured using an ICPS8100 atomic emission ICP spectrophotometer manufactured by Shimadzu and calculated as the concentration of each component in the solid sample. The following results were obtained. It was.
Sodium 2.96, potassium 6.12, calcium 6.63, iron 1.43, nickel 0.16, copper 0.37, zinc 7.14, silver 2.35, aluminum 0.27, silicon 3.21, It had 4.22 lead, 0.18 gold (unit: mg / g). It can be seen that zinc, lead, silicon and the like are contained at a relatively high concentration in addition to silver.

The leaching of silver from the pulverized product of the used display panel was performed using an aqueous solution of thiourea as the leaching solution (leaching stock solution). A predetermined concentration of leachate and a pulverized sample of a predetermined weight are placed in a 50 mL flask and shaken for a predetermined time using a THOMAS AT24R type constant temperature shaker maintained at a temperature of 30 ° C. (ie, a shaking treatment is performed). ) To leaching silver. The concentration of silver in the leachate after leaching was measured using an Shimadzu ICPS8100 atomic emission ICP spectrophotometer, and the amount of silver eluted in the liquor was calculated from this.

Also, calculate the amount of silver in the solid sample calculated from the weight of the solid sample (crushed sample) subjected to leaching and the silver concentration in the solid sample, and use these calculated values to calculate the silver elution ratio. Obtained as a percentage, and this was regarded as the leaching percentage. Various effects on the silver leaching percentage under various conditions were investigated.

Fig. 2 shows 1) a thiourea aqueous solution having a concentration of 0.05 M (mole), 2) a thiourea aqueous solution having a concentration of 0.1 M, 3) a thiourea having a concentration of 0.05 M, and a concentration of 0.05 M. The influence of the solid-liquid ratio on the leaching percentage of silver from the pulverized product of the display panel when a mixed aqueous solution (mixed solution) with sulfuric acid is used is shown. Here, the solid-liquid ratio means the ratio of the amount (mL) of the added leachate to 1 g of the pulverized product.
When only thiourea is used, silver leaching is hardly observed at any concentration. However, by mixing with sulfuric acid, it can be seen that near 100% leaching can be obtained under a solid-liquid ratio of 100 mL / g or more.

FIG. 3 shows the effects of the thiourea concentration and the sulfuric acid concentration on the leaching of silver from the pulverized material of the used display panel when the solid-liquid ratio is kept constant at 250 mL / g. Regarding the effect of sulfuric acid concentration, the percentage of leaching decreases slightly with increasing concentration, the degree of decrease being more pronounced as the thiourea concentration decreases. When the sulfuric acid concentration is lowered to 0.25M or 0.05M, the leaching percentage slightly decreases with the increase of the thiourea concentration, but the effect is small.

FIG. 4 shows the effect of shaking time on silver leaching from spent display panel grinds at various temperatures using a mixed aqueous solution of 0.05 M thiourea and 0.1 M sulfuric acid. Indicates. It can be seen that near 100% leaching can be achieved with a short shaking time, independent of temperature.

From the above results, it is effective to use a mixed aqueous solution of thiourea and sulfuric acid at a low concentration in the leaching of silver from the pulverized product of the used display panel. Specifically, the concentration of sulfuric acid is 0.25 M or less, preferably 0.1 to 0.05 M, and thiourea is 1 M or less, preferably 0.25 M or less, more preferably 0. When leaching is performed at a concentration of 1 to 0.05M, effective leaching can be achieved in a short time. Further, since the effect of temperature is small, leaching at room temperature is preferable.

Various methods can be considered for recovering silver leached in the leaching solution of a mixed aqueous solution of thiourea and sulfuric acid. To recover it as elemental solid silver, silver from the fixing waste solution of silver salt photography can be recovered. It is preferable to use a metal substitution method that has been practiced for recovery. By this method, metals such as iron, aluminum and zinc, which have a higher ionization tendency than silver, are added to the target liquid, and silver is converted into elemental high-purity silver by the oxidation-reduction reaction or the difference in ionization tendency between different metals. It can be recovered.

Various weights of zinc powder were added to the leachate of a mixed aqueous solution of 0.05 M thiourea and 0.1 M sulfuric acid containing silver to precipitate silver. After collecting the precipitated silver by filtration, the concentration of silver in the filtrate is measured using an ICPS8100 atomic emission ICP spectrophotometer manufactured by Shimadzu, and compared with the silver concentration before addition of zinc powder. Percentage was determined. FIG. 5 shows the relationship between the silver recovery percentage and the solid-liquid ratio when silver is recovered at 30 ° C. In this case, the solid-liquid ratio indicates the ratio between the volume of the leachate and the weight of the added zinc powder. From the figure, it can be seen that 100% of silver can be recovered by adding 6 mg or more of zinc powder to 1 mL of leachate.

In the above embodiment, when only an aqueous solution of thiourea is used, there is almost no silver leaching effect, and the leaching effect is remarkably enhanced by mixing sulfuric acid. Here, although sulfuric acid was used as an acid for forming an acidic thiourea aqueous solution, other inorganic acids (for example, hydrochloric acid, nitric acid, etc.) can be mixed into thiourea and used.

Next, FIG. 6 and FIG. 7 show the leaching percentage of silver when a nitric acid aqueous solution having a concentration of 0.1 to 5M and a hydrochloric acid aqueous solution having a concentration of 0.1 to 5M are used in place of the acidic thiourea aqueous solution. . Here, 100% is a case where 0.5 M thiourea and 0.1 M sulfuric acid are mixed and an aqueous solution of acidic thiourea is used.
6 and 7, it can be seen that silver can be extracted although the leaching rate is lower compared to the aqueous solution of acidic thiourea in the case of nitric acid or hydrochloric acid.

Further, FIG. 8 shows the influence of pH on the percentage of silver leaching when an aqueous sodium thiosulfate solution is used, and it can be seen that pH is not particularly related to the leaching rate.
FIG. 9 is a graph showing the influence of the solid-liquid ratio on the silver leaching percentage in the case of using an aqueous sodium thiosulfate solution.

Since silver is a soft Lewis acid, it is expected to react selectively with a sulfur compound that is a soft Lewis base. Then, it tried to collect | recover silver as a silver sulfide precipitation by adding sodium sulfide to a test liquid. FIG. 10 shows the influence of the added liquid-liquid ratio (added sodium sulfide aqueous solution / test solution) on the silver precipitation recovery percentage when 20 mL and 50 mL sodium sulfide aqueous solutions were added. It can be seen that quantitative recovery can be achieved by adding 0.05 mL of an aqueous sodium sulfide solution to 1 mL of the test solution.

Since the silver monothiourea complex (Ag [CS (NH ₂ ) ₂ ] ₃ ⁺ ) is a cation, it is acidic using an adsorbent for citrus juice that is a cation exchange zone and activated carbon that is a typical adsorbent. Silver was collected and adsorbed from the aqueous thiourea solution. FIG. 11 shows the relationship between the adsorbent and the acidic thiourea aqueous solution with respect to the silver adsorption percentage. In activated carbon, silver is recovered quantitatively regardless of the solid-liquid ratio, but adsorption by citrus juice is small. However, since it is necessary to take out the silver as a solid after the adsorption, the silver adsorbed by the activated carbon is subsequently recovered by a method such as incineration.

In the adsorption method, the adsorbed silver needs to be further converted into a solid silver compound by incineration or the like. Then, in order to collect | recover as a solid silver compound, it tried to isolate | separate the silver compound by the coagulation precipitation method using astringent astringent or cationic cellulose. For the persimmon astringent, a persimmon powder containing 18% persimmon tannin was used. As cationic cellulose, Kathional HC / LC manufactured by Toho Chemical was used.

FIG. 12 shows the supply of 1 mL of silver with the percentage of silver recovered by aggregation precipitation (= (initial silver concentration−silver concentration after precipitation) / initial silver concentration × 100) using various coagulant liquids. The relationship with the ratio of the liquid volume (mL) of the flocculant added to the test liquid is shown. It can be seen that when a flocculant (PTS-C) prepared by dissolving 60 mg of persimmon astringent powder in 30 mL of pH = 13.85 water is used, silver can be recovered almost quantitatively by the addition of 0.3 mL / mL. On the other hand, other flocculants cannot be sufficiently recovered even when the same volume of flocculant as the test solution is added. In FIG. 12, PTS-A is a solution obtained by dissolving 2.5 g of persimmon astringent powder in 50 mL of pH 7 water, PTS-B is a solution obtained by dissolving 2.5 g of persimmon astringent powder in 50 mL of pH 12 water, PTS- C represents a solution obtained by dissolving 60 mg of persimmon astringent powder in 30 mL of pH 13.85 water, and National HC / LC represents a solution obtained by dissolving 0.25 g of National HC / LC in 100 mL of pH 7 water.

Therefore, the following can be understood from the above.
1) Silver in the powder of plasma TV panel waste can be efficiently leached in a short time with a mixed aqueous solution of dilute sulfuric acid and thiourea. Silver can also be leached with hydrochloric acid, nitric acid, sulfuric acid, sodium thiosulfate, or the like.
2) The leached silver is adsorbed quantitatively by the activated carbon, but solid silver by incineration or the like thereafter needs to be recovered.
3) When a solution obtained by dissolving strawberry astringent powder in water of pH = 13 to 14 is added to the above leachate, silver is quantitatively recovered as a precipitate.
4) Silver is also recovered as a silver sulfide precipitate by the addition of sodium sulfide.

In the above embodiment, the case where silver is leached from a used plasma television display panel has been described, but the same processing can be applied to other used display panels (for example, liquid crystal panels).

Claims (9)

Crushing a used display panel, leaching silver contained in the used display panel using a mixed solution of a thiourea aqueous solution and an acid to make a leachate, and collecting the silver from the leachate How to recover silver from used display panels. 2. The method for recovering silver from a used display panel according to claim 1, wherein the silver is dissolved as a cation complex of Ag [CS (NH ₂ ) ₂ ] _{3 in} the leachate. For collecting silver from used display panels. 3. The method for recovering silver from a used display panel according to claim 1 or 2, wherein the crushed used display panel is immersed in the mixed solution, and then subjected to a shaking treatment for a predetermined time, thereby leaching the silver. A method for recovering silver from a used display panel. The method for recovering silver from a used display panel according to claim 1, wherein the mixed solution contains thiourea in a range of 0.05 mol to 1 mol. How to recover silver from used display panels. The method for recovering silver from a used display panel according to claim 1, wherein an inorganic acid is used as the acid. 6. The method for recovering silver from a used display panel according to claim 5, wherein the inorganic acid is sulfuric acid and is in the range of 0.05 mol to 0.25 mol. Silver recovery method. The method for recovering silver from a used display panel according to claim 1, wherein the silver is recovered from the leachate by a metal substitution method. The method for recovering silver from a used display panel according to claim 1, wherein the recovery of silver from the leachate is performed by using activated carbon, adding sodium sulfide, or dissolving a persimmon astringent in water having a pH of 13-14. A method for recovering silver from a used display panel, which is characterized by being added. The method for recovering silver from a used display panel according to claim 1, wherein any one of hydrochloric acid, sulfuric acid, nitric acid, and sodium thiosulfate is used instead of the mixed solution of the thiourea aqueous solution and the acid. A method for recovering silver from a used display panel, wherein the aqueous solution 1 or 2 is used.

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