Method for recovering metal indium from waste liquid crystal screen

Abstract

The invention discloses a method for recycling metal indium from a waste liquid crystal screen, and belongs to the technical field of resource recycling of waste electronic products. The method comprises the following steps: stripping and crushing an indium tin oxide glass layer in the waste liquid crystal screen to obtain glass powder; and mixing the glass powder with a vulcanizing agent, roasting at the temperature of 655-750 DEG C in a reducing atmosphere, and collecting volatile matters generated in the roasting process to obtain the indium material. According to the method, high-selectivity volatilization and recovery of indium in the waste liquid crystal screen can be achieved through one-step low-temperature roasting, so that the indium is efficiently separated from impurity elements such as Si, Al and Mg, the indium smelting raw material which is high in quality and easy to use is obtained, and the method is simple in technical route, low in cost, safe and capable of meeting the industrialization requirement.

Description

Technical Field

[0001] The present invention relates to a method for treating waste liquid crystal displays, and particularly to a method for recovering indium metal from waste liquid crystal displays, belonging to the technical field of resource recovery of waste electronic products. Background Art

[0002] Waste liquid crystal displays are a typical type of solid waste generated after the scrapping of electronic and electrical products, which originate from the elimination and replacement of liquid crystal display modules in electronic devices such as televisions, computers, and mobile phones. Since waste liquid crystal displays contain heavy metal pollutants such as lead and mercury, alkyl cyclohexane compounds in the liquid crystal layer, and toxic and harmful substances such as halogen flame retardants in the backlight module, improper disposal will cause environmental risks such as soil heavy metal pollution and groundwater poisoning. At the same time, waste liquid crystal displays contain resources such as indium and high-purity silicon. Among them, indium, as the core material of transparent conductive films, has a grade far exceeding the industrial mining standard of primary ores and has significant economic value.

[0003] In liquid crystal displays, transparent conductive electrodes are usually formed by sputtering indium tin oxide (ITO) on the surface of a glass substrate. This structure has both excellent electrical conductivity and optical transparency characteristics, and its core components are composite oxides of indium oxide (In 2 O 3 ), and tin oxide (SnO 2 ). Among them, the indium-tin ratio is usually above 10. The In 2 O 3 content in ITO glass in waste liquid crystal displays generally reaches more than 300 ppm, and it can completely be used as a potential high-quality raw material for the indium industry.

[0004] Currently, some methods for recovering indium from waste liquid crystal displays have been disclosed in the prior art. For example, Chinese Patent (CN109112311B) discloses a method for recycling waste flat panel displays. The specific operation is to crush and acid-leach waste liquid crystal displays, and then perform extraction, zinc replacement, and electrolysis on the acid-leached solution to separate and recover indium metal. Chinese Patent (CN113234927B) discloses a device and method for recovering indium from waste liquid crystal displays. The specific operation is to spray-leach the glass substrate in waste liquid crystal displays, and use an indium resin adsorption device to adsorb and recover indium in the indium-containing leachate. The above two methods both recover indium from waste liquid crystal displays by wet methods. However, the existing wet recovery processes are lengthy, consume a large amount of acid, and the waste acid solution generated also needs to be disposed of additionally. Summary of the Invention

[0005] Aiming at the technical problems existing in the resource utilization methods of waste liquid crystal displays in the prior art, the purpose of the present invention is to provide a method for recovering indium metal from waste liquid crystal displays. This method can achieve the high-selectivity volatilization recovery of indium in waste liquid crystal displays through one-step low-temperature roasting, so as to efficiently separate it from impurity elements such as Si, Al, and Mg, in order to obtain high-quality and easily utilizable indium smelting raw materials. Moreover, this method has a simple technical route, low cost, and is safe, meeting the requirements of industrialization.

[0006] The present invention provides a method for recovering indium metal from waste liquid crystal displays. This method involves peeling and pulverizing the indium tin oxide glass layer in the waste liquid crystal displays to obtain glass powder; mixing the glass powder with a sulfurizing agent, placing it in a reducing atmosphere, roasting at a temperature of 655 - 750 °C, and collecting the volatiles generated during the roasting process to obtain indium materials; the sulfurizing agent is composed of iron sulfide and calcium sulfide according to a mass percentage of 10% - 35%: 65 - 90%; the ratio of the sulfurizing agent to the glass powder satisfies that the molar ratio of S / In elements is 1.55 - 2.55; the reducing atmosphere is an atmosphere containing H 2 atmosphere; the volume ratio of H 2 / H 2 O in the reducing atmosphere is 1.85 - 2.55.

[0007] The key to the technical solution of the present invention lies in: on the one hand, taking advantage of the high saturated vapor pressure characteristics of low-valent indium sulfide at low temperatures, and the characteristics that impurity elements such as Si, Al, and Mg are difficult to volatilize at low temperatures, so that indium in waste liquid crystal displays can be converted into the form of low-valent indium sulfide and recovered by high-selectivity volatilization through sulfidation means; on the other hand, fully utilizing the reducing atmosphere to reduce the Gibbs free energy of the indium sulfidation reaction, so as to strengthen the selective sulfidation and volatilization of indium in waste liquid crystal displays at low temperatures, and the glass phase can be ensured not to be melted at low temperatures, improving the indium sulfidation and volatilization efficiency; in summary, the present invention realizes the high-selectivity sulfidation and volatilization of indium in waste liquid crystal displays at low temperatures by using a sulfurizing agent and a reducing atmosphere to obtain high-quality and easily utilizable indium smelting raw materials.

[0008] Another important innovation of the technical solution of the present invention is: adopting a sulfurizing agent mainly composed of iron sulfide and calcium sulfide, mainly because these two sulfides will not introduce impurity elements that are easily volatile at low temperatures, nor will they introduce substances that lower the melting point of the system, and the introduced iron and calcium are easy to form high-melting point phases, enabling the sulfurizing agent to provide a skeleton support effect for the system while playing a sulfidation role and not affecting the sulfidation reaction. If there are impurities in the sulfurizing agent that lower the melting point of the system, it will cause the system to melt and block the volatilization of indium sulfide. If volatile substances are introduced into the sulfurizing agent, it will affect the purity of the recovered indium materials.

[0009] As a preferred solution, the particle size of the glass powder satisfies that the mass ratio of the particle size less than 0.074 mm reaches 30% - 60%. When the particle size of the glass powder is too coarse, the contact between the glass powder and the sulfurizing agent is insufficient, and it is difficult to occur the sulfurization reaction of indium oxide, resulting in poor indium recovery rate. When the particle size of the glass powder is too fine, it is unstable in the air flow, and a large amount of energy is wasted in the fine grinding stage.

[0010] The method for peeling and crushing the indium tin oxide glass layer in the waste liquid crystal screen involved in the present invention adopts mature methods such as air low-temperature heating, mechanical peeling, centrifugal crushing, ball milling, etc. in the prior art. However, the required crushing particle size is that the particle size less than 0.074 mm should reach 30% - 60%.

[0011] The sulfurizing agent of the present invention is composed of iron sulfide and calcium sulfide according to the mass percentage of 10% - 35%: 65 - 90%. The combination of iron sulfide and calcium sulfide in an appropriate proportion is mainly based on the comprehensive consideration of the sulfur release efficiency, reaction controllability and cost of the two. When the two are combined in an appropriate proportion, the best sulfurization effect of indium oxide can be exerted. When the proportion of iron sulfide is too high or too low, it is not conducive to the formation of a high melting point skeleton with calcium, resulting in a decrease in the volatilization effect.

[0012] The ratio of the sulfurizing agent to the glass powder of the present invention satisfies that the molar ratio of S / In elements is 1.55 - 2.55. If the ratio of the sulfurizing agent is too low, the sulfurization reaction will be insufficient, and part of the indium will volatilize in the form of indium oxide. Its volatilization effect is not as good as indium sulfide, resulting in low indium recovery rate. If the ratio of the sulfurizing agent is too high, the introduction of excessive iron makes H 2 gas inevitably consumed additionally, which hinders the sulfurization and volatilization behavior of indium, resulting in a decrease in the sulfurization reaction rate and volatilization efficiency.

[0013] The reducing atmosphere of the present invention is an atmosphere containing H 2 and the volume ratio of H 2 / H 2 O in the reducing atmosphere is 1.85 - 2.55. If the partial pressure of H 2 is too low, the direct sulfurization reaction becomes the main reaction, and its Gibbs free energy is higher, resulting in a sharp drop in the indium volatilization rate. If the partial pressure of H 2 is too high, the system is prone to over-reduction, and indium oxide is directly reduced to metallic indium. Metallic indium volatilization requires a higher temperature, and it is easy to melt the glass phase at high temperature.

[0014] As a preferred embodiment, the roasting time is 2 to 3 hours. Based on the effect of the reducing gas, the Gibbs free energy of the sulfidation reaction of indium oxide is reduced, so that the formation and volatilization of indium sulfide can occur at a relatively low temperature of 655 to 750 °C. Therefore, the reaction can be carried out by controlling the temperature below the melting temperature of the glass. However, too low a temperature makes the sulfidation reaction difficult to occur, and too high a temperature will cause the glass phase to melt, deteriorating the recovery of indium by volatilization. A roasting time of more than 2 hours can achieve a good indium recovery effect, and too long a time has no positive impact on the result.

[0015] Compared with the prior art, the beneficial technical effects brought by the technical solution of the present invention are:

[0016] The present invention can realize the selective sulfidation volatilization recovery of indium in waste liquid crystal displays through one-step low-temperature roasting, and the separation from other impurity elements, and can obtain high-quality and easy-to-use indium smelting raw materials, providing a new way for the large-scale disposal and utilization of waste liquid crystal displays, and solving the problems of long process flow and high acid consumption in traditional wet leaching processes, and the easy melting of glass in traditional pyrometallurgical processes affecting the recovery effect.

[0017] The present invention makes full use of the characteristics of the high saturated vapor pressure of low-valent indium sulfide at relatively low temperatures, adds an appropriate amount of sulfiding agent to selectively convert indium in waste liquid crystal displays into low-valent indium sulfide for volatilization, and at the same time reduces the Gibbs free energy of indium sulfidation reaction with the help of a reducing atmosphere to strengthen the low-temperature and high-efficiency sulfidation of indium, and ensure that the glass phase is not melted, improving the volatilization efficiency of low-valent indium sulfide. Impurity elements such as Si, Al, and Mg in the system are difficult to react and volatilize at low temperatures, thus realizing the selective recovery of metallic indium and obtaining high-quality and easy-to-use indium smelting raw materials at the same time.

[0018] The present invention can be implemented by using mature large-scale industrial equipment such as rotary kilns and reduction shaft furnaces. The technical route is simple and the cost is low, greatly improving the recovery efficiency and resource recycling rate of waste liquid crystal displays. Specific Embodiments

[0019] The following examples are intended to further illustrate the content of the present invention rather than limit the protection scope of the claims of the present invention.

[0020] Comparative Example 1

[0021] This comparative example is mainly used to illustrate that if the sulfiding agent ratio is improper, it is not conducive to the volatilization and separation of indium in waste liquid crystal displays.

[0022] Compared with Example 1, the only difference is that the proportion of iron sulfide in the sulfiding agent is 60%.

[0023] The collected products were tested and analyzed: the indium content was 48.4%, and the indium recovery rate was only 46.8%.

[0024] Comparative Example 2

[0025] This comparative example is mainly used to illustrate that if the molar ratio of S / In elements is too low, it is not conducive to the selective volatilization of indium.

[0026] Compared with Example 1, the only difference is that the molar ratio of S / In elements is controlled to be 1.20.

[0027] The collected products were tested and analyzed: the indium content was 38.3%, and the indium recovery rate was only 36.8%.

[0028] Comparative Example 3

[0029] This comparative example is mainly used to illustrate that if the volume ratio of H 2 / H 2 O is too low, it is not conducive to reduction sulfidation and volatilization.

[0030] Compared with Example 1, the only difference is that the volume ratio of H 2 / H 2 O is 1.55.

[0031] The collected products were tested and analyzed: the indium content was 48.7%, and the indium recovery rate was only 46.1%.

[0032] Comparative Example 4

[0033] This comparative example is mainly used to illustrate that if the roasting temperature is too high, it will cause the glass phase to melt, which is not conducive to volatilization and separation.

[0034] Compared with Example 1, the only difference is that the roasting temperature is 950 °C.

[0035] The collected products were tested and analyzed: the indium content was 47.1%, and the indium recovery rate was only 32.9%.

[0036] Example 1

[0037] Using a certain waste liquid crystal screen (the In 2 O 3 content in ITO glass is 530 ppm), iron sulfide, calcium sulfide and hydrogen as raw materials. First, the indium tin oxide glass layer in the waste liquid crystal screen is peeled off by heating with hot air and crushed to a proportion of less than 0.074 mm accounting for 30%. Then, a sulfurizing agent is added, with iron sulfide accounting for 10%. The molar ratio of S / In elements is controlled to be 2.55 and mixed evenly. The mixed raw materials are subjected to hydrogen reduction roasting, with the H 2 / H 2 O volume ratio being 2.55, the roasting temperature being 750 °C, and holding for 2 hours. After the roasting is completed, the volatiles obtained are the indium raw materials.

[0038] The collected products were tested and analyzed. The indium content was 49.8%, and the indium recovery rate was 96.4%.

[0039] Example 2

[0040] Using a certain kind of waste liquid crystal screen (the In content in the ITO glass is 2 O 3 530 ppm), iron sulfide, calcium sulfide and hydrogen as raw materials. First, the indium tin oxide glass layer in the waste liquid crystal screen was peeled off by heating with hot air and crushed to a proportion of less than 0.074 mm accounting for 60%. Then, a sulfurizing agent was added, with iron sulfide accounting for 30%. The molar ratio of S / In elements was controlled at 1.55, and they were mixed evenly. The mixed raw materials were subjected to hydrogen reduction roasting, with the H 2 / H 2 O volume ratio of 2.55, the roasting temperature of 675 °C, and holding for 2 hours. After the roasting was completed, the volatiles obtained were the indium raw materials.

[0041] The collected products were tested and analyzed. The indium content was 49.6%, and the indium recovery rate was 97.7%.

[0042] Example 3

[0043] Using a certain kind of waste liquid crystal screen (the In content in the ITO glass is 2 O 3 530 ppm), iron sulfide, calcium sulfide and hydrogen as raw materials. First, the indium tin oxide glass layer in the waste liquid crystal screen was peeled off by heating with hot air and crushed to a proportion of less than 0.074 mm accounting for 50%. Then, a sulfurizing agent was added, with iron sulfide accounting for 35%. The molar ratio of S / In elements was controlled at 1.95, and they were mixed evenly. The mixed raw materials were subjected to hydrogen reduction roasting, with the H 2 / H 2 O volume ratio of 1.85, the roasting temperature of 750 °C, and holding for 2 hours. After the roasting was completed, the volatiles obtained were the indium raw materials.

[0044] The collected products were tested and analyzed. The indium content was 49.4%, and the indium recovery rate was 96.9%.

[0045] Example 4

[0046] Using a certain kind of waste liquid crystal screen (the In content in the ITO glass is 2 O 3 530 ppm), iron sulfide, calcium sulfide and hydrogen as raw materials. First, the indium tin oxide glass layer in the waste liquid crystal screen was peeled off by heating with hot air and crushed to a proportion of less than 0.074 mm accounting for 30%. Then, a sulfurizing agent was added, with iron sulfide accounting for 20%. The molar ratio of S / In elements was controlled at 1.95, and they were mixed evenly. The mixed raw materials were subjected to hydrogen reduction roasting, with the H2 / H 2 The volume ratio of O is 1.85, the roasting temperature is 655 °C, and it is kept warm for 3 hours. After the roasting is completed, the volatiles collected are the indium raw materials.

[0047] The collected products are tested and analyzed. The indium content is 49.4%, and the indium recovery rate is 96.5%.

Claims

1. A method for recovering metallic indium from waste liquid crystal screens, characterized in that: The indium tin oxide glass layer in the waste liquid crystal screen is peeled off and crushed to obtain glass powder; the glass powder is mixed with a vulcanizing agent, placed in a reducing atmosphere and roasted at a temperature of 655-750°C, and volatiles generated during the roasting process are collected to obtain indium material; the vulcanizing agent is composed of iron sulfide and calcium sulfide in a mass percentage of 10%-35%: 65-90%; the ratio of the vulcanizing agent to the glass powder satisfies: the S / In element molar ratio is 1.55-2.55; the reducing atmosphere is an atmosphere containing H2; the volume ratio of H2 / H2O in the reducing atmosphere is 1.85-2.

55.

2. The method for recovering metallic indium from waste liquid crystal screens according to claim 1, characterized in that: The particle size of the glass powder meets the requirement that the mass proportion of the particle size less than 0.074 mm is 30% to 60%.

3. The method for recovering metallic indium from waste liquid crystal screens according to claim 1, characterized in that: The calcination time is 2 to 3 hours.