Method for processing cadmium telluride photovoltaic module scrap substrate

Abstract

The present application relates to the technical field of photovoltaic module waste treatment, and discloses a cadmium telluride photovoltaic module scrapped substrate treatment method, which comprises the following steps: crushing treatment, crushing the scrapped substrate to obtain substrate fragments; acid immersion treatment, mixing the substrate fragments with an acid immersion liquid, stirring and reacting for a set time, separating the substrate fragments from the acid immersion liquid to obtain acid-washed fragments, repeatedly using the acid immersion liquid until reaching a recycling standard, and collecting the acid immersion liquid; water washing treatment, water washing the acid-washed fragments to obtain quasi-clean fragments, and collecting and storing the washing water; fragment drying, drying the quasi-clean fragments; and fragment detection, detecting the heavy metal index of the dried quasi-clean fragments, and if the treatment standard is met, the treatment is completed, and if the treatment standard is not met, the quasi-clean fragments are mixed with the substrate fragments. The present application solves the problem of high treatment cost of scrapped substrates for cadmium telluride photovoltaic module production institutions.

Description

Technical Field

[0001] This invention relates to the technical field of photovoltaic module waste treatment, specifically to a method for treating scrap substrates of cadmium telluride photovoltaic modules. Background Technology

[0002] Cadmium telluride (CTD) photovoltaic modules are thin-film solar panels that convert light energy into electrical energy, and they are widely used in modern industry and construction. During the production of CTD photovoltaic modules, some waste glass substrates are inevitably generated. Storing these waste substrates requires a significant amount of space, and the cadmium telluride film on these substrates can easily cause heavy metal pollution and harm the environment if not handled properly.

[0003] In the existing technology, the purpose of processing the scrap substrates of cadmium telluride photovoltaic modules is to recover tellurium and cadmium from the substrates, so as to reuse tellurium and cadmium or sell them to obtain economic benefits.

[0004] However, with the aforementioned existing technologies, due to the limited amount of tellurium and cadmium on the scrapped substrates, it is difficult to obtain sufficient tellurium and cadmium during small-batch processing, often making it difficult to cover the processing costs. Therefore, the processing methods described in the existing technologies are only suitable for specialized hazardous materials handling facilities, and not for cadmium telluride photovoltaic module manufacturing facilities. For cadmium telluride photovoltaic module manufacturing facilities, the storage and transportation of scrapped substrates to hazardous materials handling facilities incurs high warehousing and transportation costs, and there is a risk of heavy metal pollution spreading. Summary of the Invention

[0005] In view of this, the present invention provides a method for processing waste substrates of cadmium telluride photovoltaic modules, in order to solve the problems of high processing costs and heavy metal pollution risks associated with the production of cadmium telluride photovoltaic modules.

[0006] This invention provides a method for processing scrapped substrates of cadmium telluride photovoltaic modules, comprising the following steps: crushing treatment, crushing the scrapped substrate to obtain substrate fragments; acid leaching treatment, mixing the substrate fragments with an acid leaching solution, stirring and reacting for a set time, separating the substrate fragments from the acid leaching solution to obtain acid-washed fragments, the acid leaching solution being reused until it reaches the recycling standard, and then collecting the acid leaching solution; water washing treatment, washing the acid-washed fragments with water to obtain semi-clean fragments, and collecting and storing the washing water; fragment drying, drying the semi-clean fragments; fragment detection, detecting heavy metal indicators in the dried semi-clean fragments, if they meet the processing standards, the processing is completed, if they do not meet the processing standards, the semi-clean fragments are mixed with the substrate fragments and awaited re-acid leaching treatment.

[0007] Beneficial Effects: Scrap substrates generated on the production line can be processed more efficiently after being crushed. Acid leaching of the substrate fragments separates the cadmium and tellurium films adhering to the substrate fragments. After washing, semi-clean fragments are obtained. These semi-clean fragments are then tested. If they meet the processing standards, the cadmium and tellurium residues on the semi-clean fragments no longer meet hazardous waste standards but are considered conventional waste. They can be collected, stored, and sold as ordinary glass fragments, resulting in low storage and processing costs and effectively saving enterprise costs. Since the main purpose of this method is to process scrap substrates into semi-clean fragments that meet conventional waste standards, rather than recycling cadmium or tellurium, it is suitable for small-batch scrap substrate processing. It allows for timely processing of scrap substrates, effectively controlling the storage and pollution control costs for cadmium telluride photovoltaic module production facilities. In addition, the repeated use of acid leaching solution can save material costs on the one hand, and enrich cadmium or tellurium on the substrate fragments in the collected acid leaching solution on the other hand. The collected acid leaching solution and cleaning water are then collected and stored in special containers, which is more convenient and less time- and economical than directly storing and controlling pollution of scrapped substrates.

[0008] In one alternative embodiment, during the crushing process, the scrapped substrate is crushed to a particle size of less than 2 cm.

[0009] Beneficial effects: By crushing scrap substrates to obtain substrate fragments and controlling the particle size of the substrate fragments to less than 2 cm, it is convenient for storage and transportation, and also improves the efficiency of subsequent acid leaching, water washing and drying processes.

[0010] In one optional embodiment, during the acid leaching process, the substrate fragments are placed into a drum reactor. When the drum of the drum reactor rotates in a first direction, the substrate fragments are stirred. When the drum of the drum reactor rotates in a second direction, the crushed substrate is discharged from the discharge port of the drum reactor. The acid-washed fragments are then separated from the acid leaching solution by a spiral separator.

[0011] Beneficial effects: Using a drum reactor instead of a reaction vessel for acid leaching of substrate fragments avoids the accumulation and blockage of the lower discharge port of the reaction vessel. Furthermore, the drum reactor allows for direct material addition via a feed hopper. The rotating drum reactor agitates the substrate fragments in two directions and discharges the acid-leached fragments from the drum, resulting in convenient operation, rapid feeding and discharging, and high efficiency. Additionally, a spiral separator separates the substrate fragments from the acid leaching solution. Within the spiral separator, the acid leaching solution continues to separate the thin film on the surface of the substrate fragments. Simultaneously, the spiral separator gradually lifts the substrate fragments above the liquid surface. As the substrate fragments rise, most of the acid leaching solution adhering to their surface flows back to the bottom of the spiral separator, which is convenient, quick, and reduces the difficulty of cleaning the acid-leached fragments. The spiral separator is less prone to blockage and jamming, and its separation efficiency for substrate fragments is stable and reliable, ensuring uniform output of the substrate fragments.

[0012] In one optional embodiment, when performing the acid leaching treatment, the acid leaching solution is sulfuric acid and hydrogen peroxide, wherein the concentration of sulfuric acid is 0.5 mol / L-8 mol / L and the concentration of hydrogen peroxide is 5%-15%; or, the acid leaching solution is nitric acid, wherein the concentration of nitric acid is 30%-65%, and during the acid leaching treatment, when the acid leaching solution is sulfuric acid and hydrogen peroxide, the acid leaching solution is heated to 40℃-85℃.

[0013] Beneficial effect: The cadmium telluride film attached to the substrate fragments is corroded and oxidized by acid leaching solution, thereby separating the cadmium telluride film from the substrate fragments.

[0014] In one optional embodiment, during the acid leaching treatment, the liquid-to-solid ratio of the acid leaching solution to the substrate fragment ranges from 3L:1kg to 10L:1kg, and the reaction time is 0.2 hours to 1 hour.

[0015] Beneficial effects: The liquid-to-solid ratio and reaction time can be flexibly adjusted according to the amount of cadmium telluride film adhering to the waste substrate during actual processing and the number of broken substrates to be processed, which further improves processing efficiency and saves reagent costs.

[0016] In one alternative embodiment, the collected acid leaching solution is diluted 5 to 10 times and then mixed with the cleaning water and stored together.

[0017] Beneficial effects: The collected acid leaching solution is mixed with the cleaning water and stored together, which reduces the corrosiveness of the collected acid leaching solution and makes it easier to store. The acid leaching solution is absorbed and then mixed with the cleaning water, which avoids too much residue during the neutralization process of concentrated acid recovery solution. In addition, the acid concentration in the reactor is too high, and the amount of reagent added is not easy to control, which affects the reaction effect.

[0018] In one alternative embodiment, the recycling standard is reached when the acid leaching solution is repeatedly used until the suspended solids in the acid leaching solution are greater than or equal to 30%.

[0019] Beneficial effects: During the repeated use of acid leaching solution, cadmium telluride film continuously accumulates in the acid leaching solution. At this time, the concentration of effective oxidant components in the acid leaching solution decreases, and the processing capacity weakens. Recycling the acid leaching solution can collect the accumulated cadmium and tellurium together, and it also helps to ensure the overall concentration of effective oxidant components in the acid leaching solution in the reaction vessel when adding new acid leaching solution, thereby ensuring the processing efficiency and quality of substrate fragments.

[0020] In one optional embodiment, the water washing process includes at least a first-stage water washing and a second-stage water washing performed sequentially. During both the first-stage and second-stage water washing processes, a spiral separator is used to clean the pickled fragments. Clean water is introduced into the spiral separator at a position 150mm-300mm above the liquid surface, allowing the clean water to flow from the end of the spiral separator to the front end. Compressed air is then delivered to the bottom of the feed trough of the spiral separator used in the first-stage water washing process.

[0021] Beneficial effects: By setting up a primary and secondary water wash, the pickled fragments are washed twice, thus cleaning the acid leaching solution adhering to the surface of the pickled fragments. Due to the use of a spiral separator to evenly lift the pickled fragments, compressed air is delivered to the bottom of the spiral separator's feed trough to agitate the pickled fragments, causing the pickled fragments to quickly separate from the acid leaching solution adhering to the surface. Then, clean water is introduced from near the end of the spiral separator to rinse the pickled fragments. The water flow carries the acid leaching solution washed off the pickled fragments back to the feed trough, allowing the pickled fragments to gradually clean themselves along the rising path. The secondary water wash of the spiral separator further rinses the pickled fragments, ensuring that most of the acid leaching solution is separated from the pickled fragments. This results in conventional glass shard waste that does not meet hazardous waste standards, which can be easily stored using simple methods or sold directly to ordinary waste recycling units.

[0022] In one optional embodiment, when performing the fragment detection, at least 2 kg of pre-clean fragment samples are taken and soaked in nitric acid with a pH less than 2 for 18-22 hours with shaking. The liquid-to-solid ratio of nitric acid to the pre-clean fragment samples is 10 L: 1 kg. After the treatment, the total cadmium is detected. If the total cadmium is less than 1 mg / L, the pre-clean fragments meet the treatment standard; otherwise, they do not meet the treatment standard.

[0023] Beneficial effects: The standard for hazardous waste is mainly the content of heavy metals in the waste. For scrapped substrates, the main standard is the cadmium content. Therefore, the total cadmium index in the pre-cleaning fragments is tested. If it meets the standard, the pre-cleaning fragments are not hazardous waste and can be sold directly. If it does not meet the standard, the pre-cleaning fragments have not been cleaned properly and need to be reprocessed and tested again.

[0024] In one optional embodiment, after collecting the acid leaching solution, the method further includes the following steps: tellurium separation, including pretreatment, where the collected acid leaching solution or the cleaning water is placed into a container, the pH value is adjusted to 2-3, and the voltage in the container is adjusted to 350MV-650MV. After reacting for 0.5-1.5 hours, a tellurium recovery solution is obtained; primary separation, where the pH value of the tellurium recovery solution is adjusted to 2.5-3.5, and the precipitate is filtered to obtain primary coarse tellurium and primary filtrate; secondary separation, where the pH value of the primary filtrate is adjusted to 3.5-4.5, and the precipitate is filtered to obtain secondary coarse tellurium and secondary filtrate; tertiary separation, where the pH value of the secondary filtrate is adjusted to 4.5-6.5, and the precipitate is filtered to obtain tertiary coarse tellurium and tertiary filtrate; and coarse tellurium collection, where the primary, secondary, and tertiary coarse tellurium are collected separately.

[0025] Beneficial effects: By separating crude tellurium at different pH values, the separation of tellurium from the solution can be more thorough, and the tellurium content of the first-grade crude tellurium can reach 40%-85%, the second-grade crude tellurium content can reach 20%-50%, and the third-grade crude tellurium content can reach 2%-30%. The first-grade, second-grade, and third-grade crude tellurium can be collected separately, and crude tellurium of different purity levels can be processed separately, resulting in good economic benefits.

[0026] In one optional embodiment, after obtaining the tertiary filtrate, the method further includes the following steps: cadmium separation, adjusting the pH value of the tertiary filtrate to 8.5-10.5, adding a chemical precipitant, reacting for 20-40 minutes, then adding polyaluminum chloride and polyacrylamide, reacting for 5 minutes, and separating the precipitate to obtain cadmium-containing precipitate and heavy metal-free wastewater.

[0027] Beneficial effects: After the tellurium is recovered, cadmium is separated from the solution to obtain cadmium-containing precipitate, which is then sold to cadmium recycling units. Meanwhile, the heavy metal-free wastewater, having eliminated the two main pollutants, tellurium and cadmium, is no different from ordinary chemical wastewater and can be directly fed into a wastewater treatment pond for unified treatment.

[0028] In one optional embodiment, the chemical precipitant is sodium sulfide or a 5%-15% sodium phosphate solution, the polyaluminum chloride has a concentration of 5%-15%, and the polyacrylamide has a concentration of 0.1%.

[0029] Beneficial effects: By adding chemical precipitants, the precipitation of cadmium is promoted, making the separation of cadmium from the solution more thorough. Attached Figure Description

[0030] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0031] Fig. 1 This is a schematic diagram of the waste substrate processing and recycling process of a method for processing waste substrates of cadmium telluride photovoltaic modules according to an embodiment of the present invention.

[0032] Fig. 2 This is a schematic diagram of the overall process of a method for processing scrap substrates of cadmium telluride photovoltaic modules according to an embodiment of the present invention.

[0033] Fig. 3 This is a schematic diagram illustrating the process of transferring substrate fragments between various devices in a method for processing scrap substrates of cadmium telluride photovoltaic modules according to an embodiment of the present invention.

[0034] Fig. 4 This is a schematic diagram of the tellurium separation and cadmium separation process in a method for treating scrap substrates of cadmium telluride photovoltaic modules according to an embodiment of the present invention. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] The following is combined with Figs. 1 to 4 The following describes embodiments of the present invention.

[0037] According to an embodiment of the present invention, a method for processing scrap substrates of cadmium telluride photovoltaic modules is provided, comprising the following steps: crushing treatment, crushing the scrap substrates to obtain substrate fragments; acid leaching treatment, mixing the substrate fragments with an acid leaching solution, stirring and reacting for a set time, separating the substrate fragments from the acid leaching solution to obtain acid-washed fragments, repeatedly using the acid leaching solution until it reaches the recycling standard, and collecting the collected acid leaching solution; water washing treatment, washing the acid-washed fragments with water to obtain semi-clean fragments, and collecting and storing the washing water; fragment drying, drying the semi-clean fragments; fragment detection, detecting heavy metal indicators on the dried semi-clean fragments, and if they meet the processing standards, the processing is completed; if they do not meet the processing standards, the semi-clean fragments are mixed with the substrate fragments and awaited re-acid leaching treatment.

[0038] In this embodiment, the scrap substrates generated on the production line are more easily and efficiently processed after being crushed. The substrate fragments are acid-leached to separate the cadmium and tellurium films adhering to the substrate fragments from the substrate. After washing, semi-clean fragments are obtained. These semi-clean fragments are tested. If they meet the processing standards, meaning the cadmium and tellurium residues on the semi-clean fragments no longer meet the hazardous waste standards but are considered conventional waste, they can be collected, stored, and sold as ordinary glass fragments. The storage and processing costs are low, effectively saving enterprise costs. Since the main purpose of this method is to process scrap substrates into semi-clean fragments that meet the conventional waste standards, rather than recycling cadmium or tellurium, it is suitable for small-batch processing of scrap substrates. It can process scrap substrates in a timely manner, thereby effectively controlling the storage and pollution control costs of cadmium telluride photovoltaic module production institutions for storing scrap substrates. In addition, the repeated use of acid leaching solution can save material costs. On the other hand, it can enrich cadmium or tellurium on the substrate fragments in the collected acid leaching solution. The collected acid leaching solution and cleaning water can then be collected and stored in a special container. This method is more convenient and has lower time and economic costs than directly storing and controlling pollution of scrapped substrates.

[0039] Specifically, the set time for the stirring reaction depends on the type and ratio of the acid leaching solution and the actual total amount of cadmium telluride film on the substrate fragments. In actual operation, the set time can be determined through sample experiments. During the fragment drying process, the quasi-clean fragments are separated from moisture by drying or draining.

[0040] It should be noted that during the production of cadmium telluride photovoltaic modules, scrap substrates are collected in collection boxes and then transported to crushers and other equipment via belt conveyors for crushing.

[0041] In one embodiment, during the crushing process, the scrapped substrate is crushed to a particle size of less than 2 cm.

[0042] Specifically, the scrapped substrate may be a whole substrate or a broken substrate. The scrapped substrate is first crushed by a shredder and then put into a crusher for secondary crushing to obtain substrate fragments with smaller particle size.

[0043] In this embodiment, substrate fragments are obtained by crushing scrap substrates. The particle size of the substrate fragments is controlled within 2 cm by passing them through a sieve, which facilitates storage and transportation and also improves the efficiency of subsequent acid leaching, water washing and drying processes.

[0044] In one embodiment, during the acid leaching process, substrate fragments are placed into a drum reactor. When the drum of the drum reactor rotates in a first direction, the substrate fragments are stirred. When the drum of the drum reactor rotates in a second direction, the substrate fragments are crushed and discharged from the discharge port of the drum reactor. The acid-washed fragments are then separated from the acid leaching solution by a spiral separator.

[0045] Specifically, the drum reactor has helical blades inside the drum, and the drum's axis is horizontally oriented. When the drum rotates in a first direction, the blades agitate the substrate fragments. When the drum rotates in a second direction opposite to the first direction, the substrate fragments move towards the discharge port of the drum reactor under the influence of the blades. Upon discharge, substrate fragments and a small amount of acid leaching solution are discharged. The feed trough of the spiral separator is located at the discharge port of the drum reactor to receive the acid leaching solution and substrate fragments.

[0046] In addition, specifically, the feed tank of the spiral separator used for acid leaching also contains acid leaching solution, and the thin film on the surface of the substrate fragment continues to react with the oxidant in the acid leaching solution after entering the spiral separator.

[0047] In this embodiment, a drum reactor is used instead of a reaction vessel for acid leaching of substrate fragments. This avoids the accumulation of substrate fragments in the reaction vessel, which can clog the lower outlet of the reaction vessel. Furthermore, the drum reactor allows for direct material addition via a feed hopper. The drum reactor rotates in two directions to agitate the substrate fragments and discharge the acid-leached fragments from the drum. This method is convenient, fast, and efficient. Additionally, a spiral separator separates the substrate fragments from the acid leaching solution. Inside the spiral separator, the acid leaching solution continues to separate the thin film on the surface of the substrate fragments. Simultaneously, the spiral separator gradually lifts the substrate fragments above the liquid surface. As the substrate fragments rise, most of the acid leaching solution adhering to their surface flows back to the bottom of the spiral separator, which is convenient and quick, reduces the difficulty of cleaning the acid-leached fragments, and prevents the spiral separator from becoming clogged or jammed. The separation efficiency for the substrate fragments is stable and reliable, ensuring uniform output of the substrate fragments.

[0048] In one embodiment, during acid leaching, the leaching solution is sulfuric acid and hydrogen peroxide, wherein the concentration of sulfuric acid is 0.5 mol / L-8 mol / L and the concentration of hydrogen peroxide is 5%-15%, or the leaching solution is nitric acid, wherein the concentration of nitric acid is 30%-65%. During the acid leaching process, when the leaching solution is sulfuric acid and hydrogen peroxide, the leaching solution is heated to 40°C-85°C.

[0049] In this embodiment, the cadmium telluride film attached to the substrate fragment is etched and oxidized by an acid leaching solution, thereby separating the cadmium telluride film from the substrate fragment.

[0050] In one embodiment, during the acid leaching process, the liquid-to-solid ratio of the acid leaching solution to the substrate fragments ranges from 3L:1kg to 10L:1kg, and the reaction time is 0.2 hours to 1 hour.

[0051] In this embodiment, the liquid-to-solid ratio and reaction time are flexibly adjusted according to the amount of cadmium telluride film adhering to the waste substrate during actual processing and the number of broken substrates to be processed, which further improves processing efficiency and saves reagent costs.

[0052] In one embodiment, the collected acid leaching solution is diluted 5 to 10 times and then mixed with cleaning water and stored together.

[0053] In this embodiment, the collected acid leaching solution is mixed with the cleaning water and stored together, which reduces the corrosiveness of the collected acid leaching solution and facilitates storage. The acid leaching solution is absorbed and then mixed with the cleaning water to avoid the situation where there is a lot of solid residue during the neutralization process of concentrated acid recovery solution, and the acid concentration in the reactor is high, making it difficult to control the amount of reagents added, which affects the reaction effect.

[0054] In one embodiment, the recycling standard is reached when the acid leaching solution is repeatedly used until the suspended solids in the acid leaching solution are greater than or equal to 30%.

[0055] Specifically, during the acid leaching process, the leaching solution in both the drum reactor and the spiral separator is consumed over time. Normally, once the leaching solution is consumed to a certain extent, operators only need to replenish it with new solution. This is not only simple to operate but also allows tellurium and cadmium components from the substrate fragments to continuously accumulate in the leaching solution. However, as some of the leaching solution is reused more frequently, the overall proportion of oxidant in the solution decreases, and suspended solids increase, necessitating replacement of the leaching solution.

[0056] In this embodiment, during the repeated use of the acid leaching solution, the cadmium telluride film continuously accumulates in the acid leaching solution. At this time, the concentration of the effective oxidant component in the acid leaching solution decreases, and the processing capacity weakens. Recycling the acid leaching solution can collect the accumulated cadmium and tellurium together, and it also helps to ensure the overall concentration of the effective oxidant component in the acid leaching solution in the reaction vessel when adding new acid leaching solution, thereby ensuring the processing efficiency and quality of the substrate fragments.

[0057] It should be noted that after the collected acid leaching solution is recovered, the suspended solids in the acid leaching solution can be filtered by pressure, and the waste residue from the pressure filter can be tested. If the tellurium content is greater than 1%, the waste residue is stored. After accumulating a certain amount, it is acid washed and the tellurium is precipitated and collected. If the content is less than or equal to 1%, the waste residue is directly sold to a hazardous waste treatment facility.

[0058] In one embodiment, the water washing process includes at least a first-stage water washing and a second-stage water washing performed sequentially. During both the first-stage and second-stage water washing processes, a spiral separator is used to clean the pickled fragments. Clean water is introduced into the spiral separator at a position 150mm-300mm above the liquid surface, allowing the clean water to flow from the end of the spiral separator to the front end. Compressed air is delivered to the bottom of the feed trough of the spiral separator used in the first-stage water washing process.

[0059] Specifically, in order to ensure that the pickled fragments are more thoroughly cleaned as they rise in the water-washing spiral separator, the height of the input clean water position can be controlled between 200mm and 300mm.

[0060] In this embodiment, the pickled fragments are washed twice by setting up a primary water wash and a secondary water wash, thereby cleaning the acid leaching solution adhering to the surface of the pickled fragments. Due to the use of a spiral separator to evenly lift the pickled fragments, compressed air is delivered to the bottom of the feed trough of the spiral separator to stir the pickled fragments, so that the pickled fragments are quickly separated from the acid leaching solution adhering to the surface. Then, clean water is introduced from near the end of the spiral separator to rinse the pickled fragments. The water flow carries the acid leaching solution washed off the pickled fragments back to the feed trough, so that the pickled fragments are gradually cleaned along the rising path. The pickled fragments are then further rinsed by the secondary water wash spiral separator, which can ensure that most of the acid leaching solution is separated from the pickled fragments, thereby obtaining conventional glass fragment waste that does not meet the hazardous waste standards. It is easy to stack and store using simple methods, or directly sell it to ordinary waste recycling units.

[0061] In one embodiment, when performing fragment testing, at least 2 kg of pre-clean fragment samples are taken and soaked in nitric acid with a pH less than 2 for 18-22 hours with shaking. The liquid-solid ratio of nitric acid to pre-clean fragment samples is 10 L: 1 kg. After treatment, the total cadmium is tested. If the total cadmium is less than 1 mg / L, the pre-clean fragments meet the treatment standard; otherwise, they do not meet the treatment standard.

[0062] In this embodiment, the standard for hazardous waste is mainly the content of heavy metals in the waste. For scrapped substrates, the main standard is the cadmium content. Therefore, the total cadmium index in the pre-cleaning fragments is tested. If it meets the standard, the pre-cleaning fragments are not hazardous waste and can be sold directly. If it does not meet the standard, the pre-cleaning fragments are not cleaned properly and need to be reprocessed and tested again.

[0063] In one embodiment, after collecting the acid leaching solution, the method further includes the following steps: tellurium separation, including pretreatment, where the collected acid leaching solution or washing water is placed into a container, the pH value is adjusted to 2-3, the voltage inside the container is adjusted to 350MV-650MV, and after reacting for 0.5-1.5 hours, a tellurium recovery solution is obtained; primary separation, where the pH value of the tellurium recovery solution is adjusted to 2.5-3.5, and the precipitate is filtered to obtain primary coarse tellurium and primary filtrate; secondary separation, where the pH value of the primary filtrate is adjusted to 3.5-4.5, and the precipitate is filtered to obtain secondary coarse tellurium and secondary filtrate; tertiary separation, where the pH value of the secondary filtrate is adjusted to 4.5-6.5, and the precipitate is filtered to obtain tertiary coarse tellurium and tertiary filtrate; and coarse tellurium collection, where the primary, secondary, and tertiary coarse tellurium are collected separately.

[0064] Specifically, the voltage in the liquid within the container is controlled by an oxidation-reduction potentiometer. The pH value is adjusted by adding caustic soda through an online pH controller. In the primary separation process, after adjusting the pH value, the solution is filtered three times to obtain primary crude tellurium, and the primary filtrate is transferred to the secondary separation reaction tank. In the secondary separation process, after adjusting the pH value, the solution is filtered three times to obtain secondary crude tellurium, and the secondary filtrate is transferred to the tertiary separation reaction tank. In the tertiary separation process, after adjusting the pH value, the solution is filtered three more times to obtain tertiary crude tellurium.

[0065] In this embodiment, by separating crude tellurium at different pH values, the separation of tellurium from the solution can be more thorough, and the tellurium content of the first-grade crude tellurium can reach 40%-85%, the second-grade crude tellurium content can reach 20%-50%, and the third-grade crude tellurium content can reach 2%-30%. The first-grade, second-grade, and third-grade crude tellurium are then collected separately, allowing for the separate processing of crude tellurium of different purity levels, thus achieving good economic benefits.

[0066] In one embodiment, after obtaining the tertiary filtrate, the following steps are further included: cadmium separation, adjusting the pH value of the tertiary filtrate to 8.5-10.5, adding a chemical precipitant, reacting for 20-40 minutes, then adding polyaluminum chloride and polyacrylamide, reacting for 5 minutes, and separating the precipitate to obtain cadmium-containing precipitate and heavy metal-free wastewater.

[0067] In this embodiment, after the tellurium is recovered, cadmium is separated from the solution to obtain cadmium-containing precipitate, which is then sold to a cadmium recycling unit. The heavy metal-free wastewater, having eliminated the two main polluting elements, tellurium and cadmium, is no different from ordinary chemical wastewater and can be directly fed into a wastewater treatment pond for unified treatment.

[0068] In one embodiment, the chemical precipitant is sodium sulfide or a 5%-15% sodium phosphate solution, the concentration of polyaluminum chloride is 5%-15%, and the concentration of polyacrylamide is 0.1%.

[0069] In this embodiment, the addition of a chemical precipitant promotes the precipitation of cadmium, making the separation of cadmium from the solution more thorough.

[0070] It should be noted that in some of the above embodiments, if nitric acid is used as the leaching solution in the acid leaching process, after the cadmium separation is completed, the heavy metal-free wastewater is treated to remove nitrates. Ferrate or other oxidants are added to the heavy metal wastewater to convert the nitrites in the heavy metal-free wastewater into nitrates. Then, the nitrates in the heavy metal-free wastewater are separated by a nitrate adsorption resin (A-62MP). Finally, the heavy metal-free wastewater is discharged into the wastewater treatment pond.

[0071] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A method for processing scrap substrates of cadmium telluride photovoltaic modules, characterized in that, Includes the following steps: Crushing process: The scrapped substrate is crushed to obtain substrate fragments; Acid leaching treatment involves mixing the substrate fragments with an acid leaching solution, stirring and reacting for a set time, separating the substrate fragments from the acid leaching solution to obtain acid-washed fragments, and repeatedly using the acid leaching solution until it reaches the recycling standard, after which the acid leaching solution is collected and stored. The acid-washed fragments are washed with water to obtain semi-clean fragments, and the washing water is collected and stored. Fragment drying: The semi-clean fragments are dried. Fragment detection: The dried semi-clean fragments are tested for heavy metal content. If they meet the processing standards, the processing is completed. If they do not meet the processing standards, the semi-clean fragments are mixed with the substrate fragments and awaited re-acid leaching treatment. After collecting the acid leaching solution, the following steps are also included: Tellurium separation, including pretreatment, involves putting the collected acid leaching solution or the cleaning water into a container, adjusting the pH value to 2-3, adjusting the voltage in the container to 350MV-650MV, reacting for 0.5 hours to 1.5 hours, and then obtaining tellurium recovery solution. In the first stage of separation, the pH value of the tellurium recovery solution is adjusted to 2.5-3.5, and the precipitate is filtered to obtain primary coarse tellurium and primary filtrate. Secondary separation: the pH value of the primary filtrate is adjusted to 3.5-4.5, and the precipitate is filtered to obtain secondary coarse tellurium and secondary filtrate; The process involves three stages of separation: adjusting the pH of the secondary filtrate to 4.5-6.5, filtering the precipitate to obtain tertiary coarse tellurium and tertiary filtrate. Coarse tellurium is collected, and the primary, secondary, and tertiary coarse tellurium are collected separately.

2. The method for treating scrapped substrates of cadmium telluride photovoltaic modules according to claim 1, characterized in that, During the crushing process, the scrapped substrate is crushed to a particle size of less than 2 cm.

3. The method for treating scrapped substrates of cadmium telluride photovoltaic modules according to claim 1, characterized in that, During the acid leaching process, the substrate fragments are placed into a drum reactor. When the drum of the drum reactor rotates in a first direction, the substrate fragments are stirred. When the drum of the drum reactor rotates in a second direction, the substrate fragments are discharged from the discharge port of the drum reactor. Then, the acid-leached fragments are separated from the acid leaching solution by a spiral separator.

4. The method for treating scrapped substrates of cadmium telluride photovoltaic modules according to claim 1, characterized in that, During the acid leaching treatment, the acid leaching solution is sulfuric acid and hydrogen peroxide, wherein the concentration of sulfuric acid is 0.5 mol / L-8 mol / L and the concentration of hydrogen peroxide is 5%-15%. Alternatively, the leaching solution is nitric acid, and the concentration of the nitric acid is 30%-65%. During the leaching process, when the leaching solution is sulfuric acid hydrogen peroxide, the leaching solution is heated to 40℃-85℃.

5. The method for treating scrapped substrates of cadmium telluride photovoltaic modules according to claim 4, characterized in that, During the acid leaching process, the liquid-to-solid ratio of the acid leaching solution to the substrate fragment ranges from 3L:1kg to 10L:1kg, and the reaction time is 0.2 hours to 1 hour.

6. The method for treating scrapped substrates of cadmium telluride photovoltaic modules according to claim 1, characterized in that, The collected acid leaching solution is diluted 5 to 10 times and then mixed with the cleaning water and stored together.

7. The method for treating scrapped substrates of cadmium telluride photovoltaic modules according to claim 6, characterized in that, The recovery standard is achieved when the acid leaching solution is repeatedly used until the suspended solids in the acid leaching solution are greater than or equal to 30%.

8. The method for treating scrapped substrates of cadmium telluride photovoltaic modules according to claim 1, characterized in that, The water washing process includes at least a first-stage water washing and a second-stage water washing performed sequentially. During both the first-stage and second-stage water washing processes, a spiral separator is used to clean the pickled fragments. Clean water is introduced into the spiral separator at a position 150mm-300mm above the liquid surface, allowing the clean water to flow from the end of the spiral separator to the front end. Compressed air is then delivered to the bottom of the feed trough of the spiral separator used in the first-stage water washing process.

9. The method for treating scrapped substrates of cadmium telluride photovoltaic modules according to claim 1, characterized in that, When performing the fragment testing, take no less than 2 kg of pre-clean fragment samples and soak them in nitric acid with a pH less than 2 for 18-22 hours with shaking. The liquid-solid ratio of nitric acid to the pre-clean fragment samples is 10 L: 1 kg. After the treatment, the total cadmium is tested. If the total cadmium is less than 1 mg / L, the pre-clean fragments meet the treatment standard; otherwise, they do not meet the treatment standard.

10. The method for treating scrapped substrates of cadmium telluride photovoltaic modules according to claim 1, characterized in that, After obtaining the tertiary filtrate, the following steps are also included: For cadmium separation, the pH value of the three-stage filtrate is adjusted to 8.5-10.5, then a chemical precipitant is added, and the reaction time is 20-40 minutes. Subsequently, polyaluminum chloride and polyacrylamide are added, the reaction is carried out for 5 minutes, and the precipitate is separated to obtain cadmium-containing precipitate and heavy metal-free wastewater.

11. The method for treating scrapped substrates of cadmium telluride photovoltaic modules according to claim 10, characterized in that, The chemical precipitant is sodium sulfide or a 5%-15% sodium phosphate solution, the polyaluminum chloride has a concentration of 5%-15%, and the polyacrylamide has a concentration of 0.1%.

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