A comprehensive recycling method for waste indium tin transparent electrodes on a glass substrate

Abstract

The present invention discloses a comprehensive recovery method for waste indium tin transparent electrodes on a glass substrate. The waste indium tin transparent electrodes on the glass substrate are immersed in a dilute solution of sulfuric acid or hydrochloric acid for reduction, obtaining a sulfuric acid or hydrochloric acid solution of trivalent indium ions and tin ions. Indium is first extracted with P204, the raffinate is oxidized and hydrolyzed, and a flocculant is added to precipitate the tin. The precipitate is filtered and dried, and then subjected to microwave vacuum carbon thermal reduction to obtain metallic tin. This method can comprehensively recover the entire glass substrate for reuse, recover the extracted indium and further obtain metallic indium, recover metallic tin and carbon monoxide for reuse, and reuse the soaking solution. Consequently, the recovery process is short, the recovery equipment is simple, investment is low, waste, waste, and pollution are minimized, and the overall recovery rate is high at low cost.

Description

Technical Field

[0001] The invention belongs to the field of hydrometallurgy, and in particular relates to a comprehensive method for recovering indium tin from waste transparent electrodes coated with an indium tin oxide film on a glass substrate. Background Art

[0002] The anti-fog and defrost glass of cars, trains, and airplanes, as well as the liquid crystal displays (LCDs) of televisions, computers, mobile phones, and other scientific instruments, flat-panel screens, and touchscreen substrates all use glass as a substrate, coated with an indium tin oxide film. This film, scientifically known as a transparent electrode, is commonly known as a liquid crystal display (LCD) or fluorescent screen. When televisions and computers are scrapped, the transparent electrodes are typically removed and disposed of separately. Currently, the main treatment methods are pulverization or pyrolysis of the entire glass transparent electrode, or acid-base washing. Pyrolysis not only produces a glass melt, but also recovers indium tin oxide as slag or dust. Pyrolysis is energy-intensive and polluting, resulting in a lengthy recovery process, low recovery rates, and high costs. Washing with a dilute acid solution, without a reducing agent, only leaches the indium, while the tin oxide remains attached to the glass substrate, remaining insoluble and unrecoverable. Furthermore, the entire glass substrate cannot be directly reused. When using sodium hydroxide for alkaline boiling, although indium tin is dissolved as sodium indiumate and sodium stannate, the glass matrix is also damaged, and sodium silicate enters the alkaline boiling solution, making it difficult to separate and recover indium and tin. Not only is the process complicated and costly, but the overall comprehensive recovery is also deteriorated.

[0003] Furthermore, since transparent electrode coatings are typically only a few microns to tens of microns thick, comprehensive recycling using the aforementioned methods is unlikely to yield economical recovery value, and wastes indium tin resources. Indium is a rare and dispersed metal. Currently, proven global reserves of indium are 12,000 tons, with approximately 10,000 tons in China. 70% of indium production is used to manufacture ITO targets, or transparent electrodes, making it a crucial strategic resource. Therefore, significant efforts must be made to recover indium from waste ITO targets and transparent electrodes. Summary of the Invention

[0004] In order to overcome the above-mentioned shortcomings of fire or wet recovery, such as difficulty, low recovery rate, high cost and high pollution, the present invention proposes a comprehensive recovery method for waste indium tin transparent electrodes on a glass substrate. The method can comprehensively recover the entire glass substrate for reuse, recover the extracted indium and further obtain metallic indium, recover metallic tin and carbon monoxide for reuse, and the soaking liquid can be reused. Therefore, the recovery process is short, the recovery equipment is simple, the investment is small, the three wastes and pollution are small, the comprehensive recovery rate is high and the cost is low.

[0005] The technical solution of the present invention:

[0006] A comprehensive recycling method for waste indium tin transparent electrodes on a glass substrate is characterized by comprising the following steps:

[0007] (1) Degrease and clean the waste glass indium tin transparent electrode and defrost anti-fog glass as a whole, place them in a container, and add dilute sulfuric acid or hydrochloric acid to soak them;

[0008] (2) slowly introducing reducing gas into the soaking liquid of step (1) to heat and soak; when the indium tin film on the glass substrate is completely dissolved, remove the glass body and then place the glass electrode without removing the indium tin film;

[0009] (3) When the sulfuric acid or hydrochloric acid soaking solution in step (2) contains trivalent indium ions of more than 100 mg / L, remove the solution and replace it with a new one;

[0010] (4) extracting trivalent indium ions with P204, and returning the raffinate to step (1);

[0011] (5) When the raffinate of step (4) contains tin ≥ 5 g / L, it is not returned to the soaking process, but is subjected to oxidative hydrolysis, and a flocculant is added to precipitate and filter to obtain a Sn(OH)4(SnO2*2H2O) product;

[0012] (6) drying the Sn(OH)4 (SnO2*2H2O) obtained in step (5) and then subjecting it to microwave carbon thermal reduction to obtain metallic tin and carbon monoxide gas; the carbon monoxide gas is used as a reducing gas in step 2;

[0013] By implementing the above steps, the glass matrix, metallic indium, metallic tin and carbon monoxide gas are comprehensively recovered.

[0014] Furthermore, the waste indium tin transparent electrode on the glass substrate refers to the indium tin transparent electrode coating on the defrosting and anti-fog glass of waste televisions, computers, mobile phones, airplanes, and cars, or on the display screens of other scientific instruments.

[0015] Furthermore, the dilute sulfuric acid in step (1) is a solution containing 100-150 g / L of sulfuric acid, and the dilute hydrochloric acid is a solution containing 2-3 N hydrochloric acid.

[0016] Furthermore, the reducing gas in step (2) is hydrogen, sulfur dioxide, or carbon monoxide gas; the sulfur dioxide gas is directly sulfur dioxide or sulfur dioxide gas generated by adding sodium sulfite solution to react with sulfuric acid or hydrochloric acid in the soaking liquid; the reducing gas or liquid is introduced from the bottom of the soaking liquid and slowly passes through the gas distribution plate to ensure that the soaking liquid can be fully stirred; the soaking temperature is 20-50°C.

[0017] Furthermore, the oxidative hydrolysis in step 5 is carried out by adding hydrogen peroxide or potassium permanganate, or introducing ozone, to the indium extraction residual solution containing tin ions ≥5g / L at 50-80°C; using air or oxygen-enriched air as the oxidant, neutralizing to a pH of 2 or above, and simultaneously adding divalent copper ions or carrying out the process under pressurized conditions, and adding 0.2-0.5g / L of animal glue, polyacrylamide or polyether as a flocculant.

[0018] Furthermore, the microwave vacuum carbon thermal reduction in step (6) is carried out in a vacuum furnace equipped with a microwave radiation element; the amount of reducing carbon is 1.2-1.5 times that calculated according to the reaction equation 2C+SnO2→Sn+2CO, and is mixed with the dried Sn(OH)4 hydrolysis product with a particle size of more than 60 mesh, and the reducing carbon is coke powder, activated carbon powder or carbon black powder; the reduction temperature is 500-1000°C.

[0019] The working principle and main features of the present invention are:

[0020] 1. A transparent electrode based on a glass substrate is produced by depositing an ITO target (tin-doped indium oxide) via DC magnetron sputtering, chemical vapor deposition, sol-gel deposition, or pulsed microwave deposition. The film thickness ranges from several microns to tens of microns. The indium tin in the film is crystalline indium trioxide and tin dioxide, making it resistant to direct leaching by acids or alkalis. The present invention employs the introduction of reducing gases such as hydrogen, sulfur dioxide, and carbon monoxide during dilute sulfuric acid or hydrochloric acid soaking. This not only disrupts the crystal structure of indium trioxide and tin dioxide, but also reduces the high-valent oxides of indium tin to low-valent oxides, facilitating their leaching into the solution by sulfuric acid or hydrochloric acid. Long-term, heated, reducing soaking allows for slow leaching of the film from the glass substrate. By continuously replacing used transparent electrodes and returning the indium extraction residue, the indium tin concentration in the soaking solution can be increased, facilitating recovery. This is because tin dioxide is insoluble in acids and alkalis, and crystalline tin dioxide is even more resistant to acid or alkali dissolution. Tin oxide, on the other hand, readily reacts with acids to form divalent tin ions and water. When tin dioxide is reduced to tin oxide and dissolved, the indium tin oxide crystalline film is destroyed and easily separated from the glass substrate.

[0021] 2. The second feature of the present invention is that due to the charge difference between the trivalent indium ions and divalent tin ions entering the soaking liquid, at higher acidity, the trivalent indium ions are preferentially extracted by the cationic extractant P204 and separated from the divalent tin ions. The higher the acidity, the better the extraction and separation effect. Therefore, the present invention requires that the sulfuric acid concentration of the soaking liquid be 100-150g / L and the hydrochloric acid concentration be 2-3N. The acidity of P204 for extracting divalent tin ions is preferably between 20-50g / L. As the acidity decreases, divalent tin ions are easily oxidized to tetravalent tin ions and hydrolyzed. Sn(OH)4 is a colloid and will seriously affect the normal extraction process. At high acidity, divalent tin ions are relatively stable, which is conducive to the extraction and separation of indium and tin.

[0022] 3. The third feature of the present invention is that when the residual indium extract contains tin ions ≥5g / L, it is not returned for soaking, but removed for oxidative hydrolysis, and a flocculant is added to precipitate Sn(OH)4. This is because the hydrolysis pH of tetravalent tin ions is very low, about pH = 0.254, while the hydrolysis pH of divalent tin ions is 0.753. The divalent tin ions in the residual extract are mainly oxidized to tetravalent tin ions, which can hydrolyze and precipitate the tetravalent tin ions without the need for neutralization and acid adjustment. After filtering Sn(OH)4, the filtrate can still be returned for soaking. The oxidant is hydrogen peroxide, ozone or potassium permanganate. This type of oxidant can oxidize divalent tin ions to tetravalent tin ions under high acid conditions, that is, or or S can also be achieved by using air or oxygen-enriched air under pressurized conditions, lowering the acidity, and adding divalent copper ions. n 2+ →S n 4+ However, the oxidative hydrolysis reaction under high acidity can make the filtrate more easily returnable for use. Since Sn(OH)4 is a colloidal substance, a flocculant must be added to flocculate into large micelles. Polyether is better than animal glue and polyacrylamide.

[0023] 4. A fourth feature of the present invention is that the Sn(OH)4 hydrolysis precipitate is washed with water, dried, and then mixed with reducing carbon powder at 1.2-1.5 times the theoretical calculated amount of 2C + SnO2 → Sn + 2CO. The mixture is granulated or agglomerated, and then carbon-thermal reduction is performed in a microwave vacuum furnace. The excess reducing carbon ensures that the gas produced by the reduction reaction is entirely carbon monoxide, which is then returned to the reduction soaking step. The use of microwave vacuum carbon-thermal reduction not only enables efficient and pollution-free SnO2 carbon-thermal reduction, but also facilitates the recovery of carbon monoxide gas and simultaneously obtains relatively pure metallic tin. DETAILED DESCRIPTION

[0024] The present invention will be further described below by way of examples.

[0025] A comprehensive recycling method for waste indium tin transparent electrodes on a glass substrate, the specific implementation steps are as follows:

[0026] (1) Degrease the waste glass transparent electrode and the anti-fog and defrosting glass as a whole (no need to break them), place them in a container after decontamination, and soak them in dilute sulfuric acid or dilute hydrochloric acid. The concentration of dilute sulfuric acid is 100-150g / L, and the concentration of dilute hydrochloric acid is 2-3N. The bottom of the container is designed as two layers, and the upper layer is a porous gas distribution and dispersion disk.

[0027] (2) slowly introducing a reducing gas into the soaking liquid of step (1) from the bottom, and heating the soaking liquid through a gas dispersion plate at a soaking temperature of 20-50° C. After the indium tin film on the glass substrate is completely dissolved, the glass body is removed, and a transparent glass electrode or anti-fog and defrosting glass without removing the indium tin film is placed therein; the reducing gas is hydrogen, sulfur dioxide, or carbon monoxide; the sulfur dioxide gas is obtained by introducing a sodium sulfite solution from the bottom of the container for acid decomposition;

[0028] (3) When the indium content of the soaking solution in step (2) reaches 100 mg / L or more, remove it, filter it, and replace it with a new soaking solution;

[0029] (4) extracting indium with a volume concentration of 30-40% P204 kerosene extractant at the natural temperature of the solution, and preparing metallic indium according to a conventional method; the raffinate is returned to step (1) for use;

[0030] (5) When the raffinate of step (4) contains tin ≥ 5 g / L, it is not returned to step (1) for use, but is subjected to oxidative hydrolysis, and a flocculant is added for precipitation and filtration to obtain a Sn(OH)4(SnO2*2H2O) product; the oxidative hydrolysis conditions are as follows: the oxidant is hydrogen peroxide or potassium permanganate solution, ozone, or oxygen-enriched air; the hydrolysis pH is 2-5, and the product is neutralized with sodium alkali or ammonium alkali solution; the oxidative hydrolysis temperature is 50-80°C, and the flocculant is 0.2-0.5 g / L of animal glue or polyacrylamide solution or polyether solution;

[0031] (6) drying the Sn(OH)4(SnO2*2H2O) in step 5 and subjecting it to microwave vacuum carbon thermal reduction to obtain metallic tin and carbon monoxide gas; the carbon monoxide gas is returned to be used as reducing gas in step (2); the microwave vacuum furnace carbon thermal reduction is carried out in a vacuum furnace equipped with a microwave radiation element; the dried Sn(OH)4 is mixed with carbon powder according to 1.2-1.5 times the amount calculated by the reaction equation 2C+SnO2→Sn+2CO and reduced at 500-1000°C to obtain a metallic tin liquid ingot and obtain carbon monoxide gas, which is discharged and recovered in a sealed manner through a vacuum pump.

[0032] Example 1: Recycled used mobile phones were disassembled to extract over 20 pieces of display glass, which were then washed, degreased, and cleaned. The glass was then soaked in 150g / L dilute sulfuric acid. The soaking solution was maintained at 50°C, and hydrogen was slowly introduced to disperse and stir the solution. The soaking container was covered and the hydrogen released through an exhaust pipe. After soaking for 24 hours, the soaking solution was tested and found to contain 2.5mg / L indium and 0.8mg / L tin. After soaking for 48 hours, the soaking solution was tested again and found to contain 4.2mg / L indium and 1.3mg / L tin. The glass substrate was removed and inspected to determine that approximately 80% of the indium-tin coating had been removed. After soaking for 60 hours, the indium-tin coating had been substantially removed. Replace the display glass and continue soaking, controlling the volume and acidity of the soaking solution until the soaking solution contains more than 100 mg / L of indium. Remove the soaking solution and extract it with P204. The residual solution contains 25.2 mg / L of tin. Return it and continue soaking until the residual solution contains 1.5 g / L of tin. Then remove it and add 10 mL of concentrated hydrogen peroxide per liter. The hydrolysis precipitation rate of Sn(OH)4 is 98.3%. The hydrolysis residual solution is returned for use. The oxidation and hydrolysis equation of tin sulfate is:

[0033] SnSO4+H2O2+2H2O→H2SO4+Sn(OH)4.

[0034] Example 2: Degrease and clean several old LCD screens of televisions and place them in a 2m 3 In a container, add 130g / L of dilute sulfuric acid solution and heat it to 40-50℃. Then slowly and continuously introduce 10% sodium sulfite solution from the bottom and soak for 24 hours. The soaking liquid is tested to contain 53.2mg / L of indium and 10.5mg / L of tin. After the display screen is demoulded, take it out and add the undemolded display screen until the indium content of the soaking liquid reaches 150mg / L. Take it out, clarify and filter it, and then use a 30% P204 kerosene extractant to extract indium in two stages. The residual liquid is returned to the acid preparation and continued to be used for soaking. After more than 10 cycles, the tin content of the indium extraction residual liquid can reach 2.1g / L. Take it out and introduce ozone oxidation and hydrolysis, add polyether flocculation and precipitation of Sn(OH)4, and the oxidation and hydrolysis precipitation rate is 99.2%. After filtration, the filtrate is returned to the acid preparation and used for soaking.

[0035] Example 3: Take 100g of Sn(OH)4 precipitate, dry it and add charcoal powder at a ratio of carbon / tin = 1.5, grind and mix evenly, and granulate it with 5% paper pulp as a binder to a particle size of 1-5mm. After drying, place it in a graphite crucible and a ceramic crucible, respectively. Then, place it in a microwave vacuum furnace modified from a household microwave oven for microwave vacuum carbon thermal reduction. Carbothermal reduction is carried out at 800°C for 1.5 hours. The discharged gas can be ignited, which proves to be carbon monoxide. Metallic tin is obtained in both crucibles, with a reduction rate of 95.8% for the graphite crucible and 93.2% for the ceramic crucible.

[0036] The present invention proposes soaking in sulfuric acid or hydrochloric acid under a reducing atmosphere, so that indium and tin can be leached into the soaking liquid at the same time, and the glass substrate is not damaged and can be placed in its entirety. When the coating on the glass substrate is completely leached, it is taken out and washed with water for recovery. A new transparent electrode is then placed in. When the indium content of the soaking liquid reaches 100 mg / L or more, the soaking liquid is replaced, and the indium is recovered by extraction, and the residual liquid is returned to the soaking tank for continued use. As long as the soaking container is large enough, large-scale production can be achieved. The beneficial effects obtained are good comprehensive recovery, high recovery rate of each component, low pollution and low cost.

[0037] The above embodiments are only intended to further illustrate the present invention, and the present invention is not limited thereto.

Claims

1. A comprehensive recycling method for waste indium tin transparent electrodes on a glass substrate, characterized by: The following steps are involved: (1) Degrease and clean the waste glass indium tin transparent electrode and defrost anti-fog glass as a whole and place them in a container, and add dilute sulfuric acid or hydrochloric acid to soak them; The dilute sulfuric acid in step (1) is a solution containing 100-150 g / L of sulfuric acid, and the dilute hydrochloric acid is a solution containing 2-3 N hydrochloric acid; (2) Slowly introducing reducing gas into the soaking liquid of step (1) for heating and soaking; when the indium tin film on the glass substrate is completely dissolved, remove the glass body and then place the glass electrode without removing the indium tin film; (3) When the sulfuric acid or hydrochloric acid soaking solution in step (2) contains trivalent indium ions exceeding 100 mg / L, remove the soaking solution and replace it with a new one; (4) Extracting trivalent indium ions with P204, and returning the raffinate to step (1) for use; (5) When the raffinate in step (4) contains tin ≥ 5 g / L, it is not returned to the soaking process, but is subjected to oxidative hydrolysis, and a flocculant is added to precipitate and filter to obtain the Sn(OH)4 product; (6) drying the Sn(OH)4 obtained in step (5) and then subjecting it to microwave carbon thermal reduction to obtain metallic tin and carbon monoxide gas; the carbon monoxide gas is used as a reducing gas in step 2; Through the above steps, the glass matrix, metallic indium, metallic tin and carbon monoxide gas are comprehensively recovered respectively; The reducing gas in step (2) is hydrogen, sulfur dioxide, or carbon monoxide gas; the sulfur dioxide gas is directly sulfur dioxide or sulfur dioxide gas generated by the reaction of sulfuric acid or hydrochloric acid in the soaking liquid with a sodium sulfite solution; the reducing gas or liquid is introduced from the bottom of the soaking liquid and slowly passed through the gas distribution plate to ensure that the soaking liquid can be fully stirred; the soaking temperature is 20-50°C; The oxidative hydrolysis in step (5) is carried out by adding hydrogen peroxide or potassium permanganate, or introducing ozone, to the indium extraction residual solution containing tin ions ≥ 5 g / L at 50-80°C; using air or oxygen-enriched air as the oxidant, neutralizing to a pH of 2 or above, and simultaneously adding divalent copper ions or performing the process under pressurized conditions, and adding 0.2-0.5 g / L of animal glue, polyacrylamide, or polyether as a flocculant; The microwave vacuum carbon thermal reduction in step (6) is carried out in a vacuum furnace equipped with a microwave radiation element; the amount of reducing carbon used is 1.2-1.5 times that calculated according to the reaction equation 2C+SnO2→Sn+2CO, and is mixed with the dried Sn(OH)4 hydrolysis product with a particle size of more than 60 mesh, and the reducing carbon is coke powder, activated carbon powder or carbon black powder; the reduction temperature is 500-1000°C.

2. The comprehensive recycling method for waste indium tin transparent electrodes on a glass substrate according to claim 1, characterized in that: Waste indium tin transparent electrodes on glass substrates refer to the defrosting and anti-fog glass of waste televisions, computers, mobile phones, airplanes, and cars, or the indium tin transparent electrode coatings on the display screens of various scientific instruments.