Method for recycling silver in heterojunction battery piece

Abstract

The invention relates to the technical field of photovoltaic cells, in particular to a method for recycling silver in a heterojunction cell. The recycling method comprises the following steps: S1) acid pickling treatment: enabling acid liquor to react with a primary battery piece to obtain an intermediate battery piece, and separating the intermediate battery piece to obtain first silver-containing liquid; s2) ammonia water treatment: ammonia water reacts with the intermediate cell to obtain a silicon wafer to be recovered, and the silicon wafer to be recovered is separated to obtain a second silver-containing liquid; s3) mixing treatment: mixing the first silver-containing liquid and the second silver-containing liquid to obtain a silver-containing mixed solution, and controlling the pH value of the silver-containing mixed solution to be not less than 8, so that silver exists in the silver-containing mixed solution in the form of ions; and S4) reduction treatment: treating the silver-containing mixed solution through a reduction method to obtain the silver elementary substance. According to the recovery method, the silver in the heterojunction cell can be recovered, the recovery rate of the silver is very high, and meanwhile, the silicon wafer is prevented from being excessively corroded.

Description

Technical Field

[0001] The invention relates to the technical field of photovoltaic cells, and in particular to a method for recovering silver in a heterojunction cell sheet. Background Art

[0002] Currently, photovoltaic power generation is mainly achieved through solar cell modules, which means that while the installed capacity of photovoltaic power generation is increasing at a faster rate, the amount of photovoltaic material waste is also growing rapidly. Photovoltaic materials contain rare materials or precious metals. As a supporting industry, recycling photovoltaic materials is an important task.

[0003] For crystalline silicon cells in solar cell modules, silver recycling is a very important part. At present, the research on silver leaching in crystalline silicon cells is still at the stage of PERC cells (passivated emitter and rear local contact cells), which uses aqua regia combined with other high-concentration acids to corrode the silicon nitride layer and silver grid lines. However, with the continuous development of solar cells, the market position of PERC cells has gradually been occupied by heterojunction solar cells (HJT). Heterojunction solar cells are positively and negatively symmetrical, with N-type silicon wafers as substrates, and an ITO film (indium tin oxide) is formed on the surface of the substrate, and silver grid lines are formed on the ITO film. When processing heterojunction solar cells, if aqua regia combined with other high-concentration acids is used, the reaction is violent, and it is easy for the silicon wafers to be completely reacted, and the silicon wafers cannot be recycled. If only a single strong acid is used to treat heterojunction solar cells, the tin oxide in the ITO film is difficult to react, which will cause some silver grid lines to not fall off completely. In addition, it is difficult to avoid the presence of line marks on the surface of the silicon wafer. The silver grid lines at the line marks are located deep and have a small contact area with the outside world, so it is difficult to completely remove them through a single acid wash, and a large amount of strong acid needs to be used for multiple washes. The use of a large amount of acid will cause serious pollution to the environment, increase the recycling cost, and the concentration of the silver-containing mixture finally obtained is low, resulting in a low level of silver recovery efficiency in the later stage. Therefore, how to make the silver recovery rate higher while ensuring that the silicon wafers in the heterojunction solar cells are as intact as possible is a problem that needs to be solved urgently. Summary of the invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defect in the prior art that when processing heterojunction cells to recover silver, it is impossible to achieve a high silver recovery rate while keeping the silicon wafers in the heterojunction solar cells as intact as possible, thereby providing a method for recovering silver in heterojunction cells.

[0005] To this end, the present invention provides the following technical solutions:

[0006] The present invention provides a method for recovering silver in a heterojunction battery cell, comprising the following steps:

[0007] Step S1) acid pickling treatment: take the original battery cell, immerse the original battery cell in acid solution, the acid solution reacts with the original battery cell to make part of the silver grid lines on the original battery cell fall off, obtain an intermediate battery cell, separate the intermediate battery cell from the acid solution, and obtain a first silver-containing liquid; Step S2) ammonia water treatment: take the intermediate battery cell and immerse it in ammonia water, the ammonia water reacts with the intermediate battery cell to make the remaining silver grid lines on the intermediate battery cell fall off, obtain a silicon wafer to be recovered, separate the silicon wafer to be recovered from the ammonia water, and obtain a second silver-containing liquid; Step S3) mixing treatment: mix the first silver-containing liquid and the second silver-containing liquid to obtain a silver-containing mixed solution, and control the pH of the silver-containing mixed solution to be not less than 8, so that silver exists in the silver-containing mixed solution in the form of ions; Step S4) reduction treatment: treat the silver-containing mixed solution by a reduction method to obtain silver element.

[0008] Preferably, the mass of the primary battery sheet and the volume ratio of the acid solution is 1g:6.5-15mL. The amount of reagent used is relatively small, and it is environmentally friendly.

[0009] Preferably, the pH of the silver-containing mixed solution is controlled to be 8 to 10. To achieve a high pH, ​​a large amount of reagents are required, and a pH greater than 10 will not significantly improve the silver recovery rate, which will lead to a waste of reagents.

[0010] Preferably, the mass of the intermediate battery sheet and the volume ratio of the ammonia water are 1 g: 10-30 mL. The amount of reagent used is relatively small, and the process is environmentally friendly.

[0011] Preferably, the method for controlling the pH value of the silver-containing mixed solution to be not less than 8 includes controlling the ratio of the first silver-containing liquid to the second silver-containing liquid, or adding at least one of ammonia water. When there are sufficient amounts of the first silver-containing liquid and the second silver-containing liquid, the ratio of the addition amount of the first silver-containing liquid and the second silver-containing liquid can be directly adjusted according to the pH adaptability of the silver-containing mixed solution to control the pH value of the silver-containing mixed solution to be ≥ 8; when there is not enough amount of the second silver-containing liquid for use, ammonia water can be added to help control the pH value of the silver-containing mixed solution.

[0012] Optionally, the acid in the acid solution is selected from at least one of hydrochloric acid, nitric acid, sulfuric acid, and hydrofluoric acid; optionally, the acid in the acid solution is nitric acid.

[0013] Optionally, the mass percentage concentration of the acid in the acid solution is 40% to 48%; further optionally, it can be 45% to 48%.

[0014] Preferably, the mass percentage concentration of the ammonia water is 20% to 40%.

[0015] Optionally, before mixing the first silver-containing liquid and the second silver-containing liquid, the step of adjusting the pH of the second silver-containing liquid to be greater than 7 and less than or equal to 10 is also included, which can avoid violent reactions during mixing and make the entire operation safe and controllable; preferably, the pH of the second silver-containing liquid is adjusted by diluting with water to reduce costs.

[0016] Preferably, in the pickling treatment, the reaction between the acid solution and the original battery sheet is carried out under stirring.

[0017] Preferably, in the ammonia water treatment, the reaction between the ammonia water and the middle battery cell is carried out under stirring.

[0018] Preferably, the mixing treatment time is 25 to 35 minutes.

[0019] Preferably, the stirring includes magnetic stirring, the time of the magnetic stirring is 10 to 30 minutes, and the speed of the magnetic stirring is 200 to 400 rpm / min. Typically, but not limited to, the magnetic stirring is to add a magnetic stirring bar to the mixture, and through the effect of the magnetic field, the stirring bar is made to rotate in a circle to achieve the effect of stirring.

[0020] The method provided by the present invention is a method for recovering silver from heterojunction solar cells, typically and non-limitingly: when the reaction between the acid solution and the original solar cell reaches the end point, the blue ITO film on the original solar cell cannot be seen by the naked eye; and / or, the total content of In and Sn on the surface of the solar cell after the reaction is tested to be less than 100 ppb.

[0021] Preferably, the reduction method includes at least one of a reducing agent reduction method and an electrolysis method; optionally, the reducing agent used in the reducing agent reduction method includes at least one of a solid reducing agent, a liquid reducing agent, and a gas reducing agent.

[0022] Preferably, the reducing agent reduction method comprises the following steps: adding a chlorine-containing solution to the silver-containing mixed solution, performing a precipitation reaction, filtering to obtain silver chloride, adding a reducing agent to the silver chloride, performing a reduction reaction, and obtaining a silver-containing intermediate.

[0023] Optionally, the reducing agent includes at least one of glucose, hydrazine hydrate, ascorbic acid, sodium sulfite, and ferrous sulfate.

[0024] The method provided by the present invention is a method for recovering silver from heterojunction battery cells. When a silver-containing mixed solution is treated by a reducing agent reduction method, the amount of each reducing agent used is determined by the molar ratio of the reducing agent and silver chloride when reacting. At the same time, acid or alkali should be added according to the reaction conditions to assist the reduction reaction.

[0025] Preferably, the method further comprises the step of mixing the silver-containing intermediate with borax, heating to remove impurities, and obtaining silver. In the silver-containing mixed solution, other impurity ions are inevitably present, such as ammonium ions, metal cations (such as Na, K, Fe, etc.), and some impurity ions are converted into oxides and other impurities mixed in the silver-containing intermediate as silver is converted into silver chloride precipitation and silver chloride is reduced into elemental silver. Borax can melt and remove these impurities to achieve the purification of silver.

[0026] Preferably, the mass ratio of the silver-containing intermediate to the borax is 3.5 to 7.5:1.

[0027] Preferably, the heating temperature is 1000-1200° C., and the heating time is 0.5-2 h.

[0028] The method for recovering silver from a heterojunction cell provided by the present invention specifically comprises the following steps:

[0029] (1) Acid pickling treatment: taking the original battery cell, immersing the original battery cell in an acid solution with an acid mass percentage concentration of 40% to 48%, so that the mass ratio of the original battery cell to the acid solution is 1g:6.5 to 15mL, and magnetically stirring at a speed of 200 to 400 rpm / min for 10 to 30 minutes, so that the acid solution reacts with the original battery cell to cause part of the silver grid lines on the original battery cell to fall off, thereby obtaining an intermediate battery cell, and separating the intermediate battery cell from the acid solution to obtain a first silver-containing liquid;

[0030] (2) Ammonia treatment: the intermediate cell obtained in (1) is immersed in ammonia water with a mass percentage concentration of 20% to 40%, so that the mass ratio of the intermediate cell to the ammonia water is 1 g: 10 to 30 mL, and magnetic stirring is performed at a speed of 200 to 400 rpm / min for 10 to 30 min. The ammonia water reacts with the intermediate cell to cause the remaining silver grid lines on the intermediate cell to fall off, thereby obtaining a silicon wafer to be recovered, and the silicon wafer to be recovered is separated from the ammonia water to obtain a second silver-containing liquid;

[0031] (3) Mixing treatment: measuring the pH value of the second silver-containing liquid, if it is not within the range of greater than 7 and less than or equal to 10, diluting it with water to within the range, mixing the first silver-containing liquid obtained in (1) and the second silver-containing liquid obtained in (2) to obtain a silver-containing mixed solution, controlling the pH of the silver-containing mixed solution to be not less than 8, so that silver exists in the silver-containing mixed solution in the form of ions; the mixing treatment time is 25 to 35 minutes;

[0032] (4) Reduction treatment: treating the silver-containing mixed solution obtained in (3) by a reduction method to obtain silver element. The reduction method includes at least one of a reducing agent reduction method and an electrolytic method; the reducing agent reduction method specifically includes adding a chlorine-containing solution to the silver-containing mixed solution obtained in (3), performing a precipitation reaction, filtering to obtain silver chloride, adding a reducing agent to the silver chloride, performing a reduction reaction to obtain a silver-containing intermediate, mixing the silver-containing intermediate with borax at a mass ratio of 3.5 to 7.5:1, and heating at 1000 to 1200° C. for 0.5 to 2 h to obtain silver.

[0033] The technical solution provided by the present invention has the following advantages:

[0034] 1. The method for recovering silver from heterojunction cells provided by the present invention first performs pickling treatment, uses acid solution to react with the original cell to obtain an intermediate cell and a first silver-containing liquid, specifically, the acid will react with the resin glue and part of the ITO film (i.e., indium tin oxide) attached to the silver grid lines of the original cell to remove them, thereby causing part of the silver grid lines to fall off; at the same time, part of the silicon wafer under the ITO film is exposed, which is convenient for the subsequent reaction between the reagent and the silicon wafer, and the acid solution will not corrode the silicon wafer, thereby ensuring the integrity of the silicon wafer. Then, the intermediate cell is treated with ammonia water to obtain a second silver-containing liquid, and the remaining ITO film and silver at the line marks on the intermediate cell will also fall off, and the ammonia water treatment combined with the pickling treatment realizes the complete shedding of the silver grid lines on the original cell, thereby improving the recovery rate of silver; in addition, since the ammonia water ionization equilibrium constant is small, the hydroxide content is low, the reaction is stable and not violent, and only the silicon on the surface of the silicon wafer is reacted, so that the silicon wafer after the reaction is relatively complete, which is conducive to the recycling of the silicon wafer. Then, a mixing treatment is performed to mix the first silver-containing liquid and the second silver-containing liquid to obtain a silver-containing mixed solution, and the pH value of the silver-containing mixed solution is controlled to be not less than 8. By controlling the pH value of the silver-containing mixed solution, it is ensured that solid silver is converted into silver ions, so as to facilitate the subsequent reduction and recovery of the silver ions.

[0035] In short, the method can make silver fall off fully and improve the conversion rate of silver ions, thereby improving the recovery rate of silver, while avoiding excessive corrosion of the silicon wafer after treatment, improving its integrity, and facilitating the recycling of silicon wafers. Overall, the silver and silicon wafers in the heterojunction cell are fully recovered, reducing waste; moreover, there is no need for multiple flushing with a large amount of strong acid, and the overall recovery process is environmentally friendly and low-cost. DETAILED DESCRIPTION

[0036] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0037] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0038] Experimental Materials:

[0039] Heterojunction solar cell.

[0040] The present invention provides a method for recovering silver in a heterojunction battery cell, which specifically comprises the following steps:

[0041] (1) Acid pickling: taking a primary cell and immersing the primary cell in an acid solution, wherein the acid solution reacts with the primary cell to cause a portion of the silver grid lines on the primary cell to fall off, thereby obtaining an intermediate cell; and separating the intermediate cell from the acid solution to obtain a first silver-containing liquid.

[0042] (2) Ammonia treatment: The intermediate cell obtained in (1) is immersed in ammonia, and the ammonia reacts with the intermediate cell to cause the remaining silver grid lines on the intermediate cell to fall off, thereby obtaining a silicon wafer to be recycled. The silicon wafer to be recycled is separated from the ammonia to obtain a second silver-containing liquid.

[0043] (3) Mixing treatment: mixing the first silver-containing liquid obtained in (1) and the second silver-containing liquid obtained in (2) to obtain a silver-containing mixed solution, and controlling the pH of the silver-containing mixed solution to be not less than 8 so that silver exists in the silver-containing mixed solution in the form of ions.

[0044] (4) Reduction treatment: The silver-containing mixed solution obtained in (3) is treated by a reduction method to obtain silver element.

[0045] The method for recovering silver in heterojunction cell provided by the present invention first performs pickling treatment, uses acid solution to react with the original cell, specifically, the acid reacts with the resin glue and part of the indium tin oxide (i.e., ITO film) attached to the silver grid line during screen printing, removes them, and makes part of the silver grid line attached thereto fall off, so that the silicon slice under the ITO film is exposed. In addition, during the screen printing process, line marks will be generated on the silicon slice, and the coated silver paste will partially penetrate into the line marks. The silver remaining at the line marks is deep and has a small contact area with the outside world, and cannot fall off from the original cell during the pickling treatment. Then, weak alkaline ammonia water is used for treatment, and the hydroxide in the ammonia water reacts with the silicon on the middle cell to generate silicate and hydrogen. Since the ammonia water ionization equilibrium constant is small, the hydroxide content is low, the reaction is stable and not violent, and it is convenient to control that only the silicon on the surface of the silicon slice is reacted, which can ensure the integrity of the silicon slice after the reaction, and is conducive to the recycling of the silicon slice. At the same time, the ammonia reacts with the silicon on the surface of the silicon wafer to generate silicate and dissolve it, and the remaining indium tin oxide attached to the surface of the silicon wafer and the silver at the line marks will also fall off. At this point, the remaining silver grid lines on the middle battery sheet are all fallen off, that is, the silver grid lines on the original battery sheet are all fallen off, which improves the recovery rate of silver, and there is no use of other impurity metal reagents in the step, which will not affect the purity of the recovered silver. The first silver-containing liquid and the second silver-containing liquid are then mixed, and the acid in the first silver-containing liquid and the ammonia in the second silver-containing liquid undergo acid-base neutralization reaction to obtain a silver-containing mixed solution; secondly, the pH of the silver-containing mixed solution is controlled to be not less than 8, so that the solid silver is converted into silver ions, that is, all the silver exists in the silver-containing mixed solution in the form of ions, so as to facilitate the subsequent recovery of silver. The first silver-containing liquid and the second silver-containing liquid are mixed, and the alkaline second silver-containing liquid is used as an alkali liquid to neutralize the acid in the first silver-containing liquid, and even the pH of the silver-containing mixed solution can be directly made ≥8, which realizes the full use of materials in the treatment process, reduces the amount of external agents, and reduces costs. The method can make silver fully fall off and improve the conversion rate of silver ions, thereby improving the recovery rate of silver, and at the same time improve the integrity of the silicon wafer after treatment, which is conducive to the recycling of the silicon wafer, and generally realizes the full recovery of the secondary recyclable components in the heterojunction battery sheet, reducing waste; moreover, the method does not use other impurity metal reagents, and is easy to obtain high-purity silver, which can be directly supplied to the silver paste factory for use, and the overall recovery process is environmentally friendly

[0046] In some embodiments, the mass of the primary battery sheet and the volume ratio of the acid solution are 1 g: 6.5-15 mL. The amount of reagent used is relatively small, and the process is environmentally friendly.

[0047] In some embodiments, the mass of the intermediate battery sheet and the volume ratio of the ammonia water are 1 g: 10-30 mL. The amount of reagent used is relatively small, and the process is environmentally friendly.

[0048] In some embodiments, the pH of the silver-containing mixed solution is controlled to be 8-10, because a pH greater than 10 will not significantly improve the silver recovery rate, but will require a larger amount of reagents, thereby causing unnecessary waste.

[0049] In some embodiments, the method for controlling the pH of the silver-containing mixed solution to be not less than 8 includes controlling the ratio of the first silver-containing liquid to the second silver-containing liquid, or adding at least one of ammonia water. When there are sufficient amounts of the first silver-containing liquid and the second silver-containing liquid, the ratio of the addition of the first silver-containing liquid and the second silver-containing liquid can be directly adjusted according to the pH adaptability of the silver-containing mixed solution to control the pH of the silver-containing mixed solution to be ≥ 8, so as to fully utilize the material; when there is not enough second silver-containing liquid for use, ammonia water can be added to help control the pH of the silver-containing mixed solution.

[0050] In some embodiments, the acid in the acid solution is selected from at least one of hydrochloric acid, nitric acid, sulfuric acid, and hydrofluoric acid; preferably, the acid in the acid solution is nitric acid.

[0051] In some embodiments, the mass percentage concentration of the acid in the acid solution is 40% to 48%, preferably 45% to 48%.

[0052] In some embodiments, the mass percentage concentration of the ammonia water is 20% to 40%.

[0053] In some embodiments, before mixing the first silver-containing liquid and the second silver-containing liquid, a step of adjusting the pH of the second silver-containing liquid to be greater than 7 and less than or equal to 10 is included, which can avoid violent reactions during mixing and make the entire operation safe and controllable. Preferably, the pH of the second silver-containing liquid is adjusted by diluting with water to reduce costs.

[0054] In some embodiments, the mixing treatment time is 25 to 35 minutes.

[0055] In some embodiments, in the acid pickling treatment, the reaction between the acid solution and the original battery cell is carried out under stirring; in the ammonia water treatment, the reaction between the ammonia water and the intermediate battery cell is carried out under stirring, and the stirring includes magnetic stirring, the time is 200 to 400 rpm / min, and the speed is 10 to 30 min; this can help the acid solution and the original battery cell, and the ammonia water and the intermediate battery cell to fully react.

[0056] In some embodiments, the reduction method includes at least one of a reducing agent reduction method and an electrolysis method; optionally, the reducing agent used in the reducing agent reduction method includes at least one of a solid reducing agent, a liquid reducing agent, and a gas reducing agent.

[0057] In some embodiments, the reducing agent reduction method comprises the following steps: adding a chlorine-containing solution to the silver-containing mixed solution, performing a precipitation reaction, filtering to obtain silver chloride, adding a reducing agent to the silver chloride, performing a reduction reaction, and obtaining a silver-containing intermediate.

[0058] In some embodiments, the reducing agent includes at least one of glucose, hydrazine hydrate, ascorbic acid, sodium sulfite, and ferrous sulfate.

[0059] In some embodiments, the method further comprises mixing the silver-containing intermediate with borax and heating to remove impurities to obtain silver.

[0060] In some embodiments, the mass ratio of the silver-containing intermediate to the borax is 3.5-7.5:1.

[0061] In some embodiments, the heating temperature is 1000-1200° C., and the heating time is 0.5-2 h.

[0062] Example 1

[0063] This embodiment provides a method for recovering silver from a battery cell, comprising the following steps:

[0064] (1) Acid pickling treatment: at room temperature, heterojunction solar cell waste sheets (original cells) and hydrochloric acid with a mass percentage concentration of 45% were mixed in a mass volume ratio of 10 g:100 mL, and magnetic stirring was performed at a speed of 200 rpm / min for 10 min to react until the blue ITO film could not be seen by the naked eye. At this time, the total content of In and Sn on the surface of the waste cell sheets was measured to be less than 100 ppb (tested by ICPMS, the same below), and the waste cell sheets and the filtration residue were obtained by filtering with a sieve. The waste cell sheets were washed three times with deionized water in a mass volume ratio of 10 g:100 mL to the initial heterojunction solar cell waste sheets to obtain an intermediate cell sheet, and the water used to wash the waste cell sheets and the filtration residue were combined as the first silver-containing liquid;

[0065] (2) Ammonia treatment: at room temperature, add ammonia with a mass percentage concentration of 20% to the intermediate battery sheet obtained in (1), the mass volume ratio of the intermediate battery sheet to the ammonia with a mass percentage concentration of 20% is 9.8 g:100 mL, and magnetic stirring is performed at a speed of 200 rpm / min for 10 min. After the reaction, the battery waste sheet and the filtration residue are obtained by filtration with a mesh, and the battery waste sheet is washed three times with deionized water with a mass volume ratio of 10 g:100 mL to the intermediate battery sheet to obtain a silicon wafer to be recycled, and the water used to wash the battery waste sheet and the filtration residue are combined as the second silver-containing liquid;

[0066] (3) Mixing treatment: The pH value of the second silver-containing liquid is measured to be 9.5, and the first silver-containing liquid obtained in (1) is mixed with the second silver-containing liquid obtained in (2), and the mixture is reacted for 30 minutes to obtain a silver-containing mixed solution. During the reaction, no external adjustment is performed, and the pH value is maintained at ≥ 8. After the reaction, the pH value of the silver-containing mixed solution is 8.3;

[0067] (4) Reduction treatment: Use a reducing agent reduction method to treat the silver-containing mixed solution: add a sodium chloride solution with a mass percentage concentration of 30% to the silver-containing mixed solution until no white solid is generated, filter to obtain white silver chloride solid, and dry. Based on the amount of white silver chloride obtained, add materials according to the chemical equation of silver ammonia reaction, that is, the molar ratio of silver ion to ammonia is 1:3, and the molar ratio of silver ion to glucose is 2:1, add ammonia water with a mass percentage concentration of 20%, and glucose solution with a mass percentage concentration of 2%, and obtain a silver-containing intermediate through silver ammonia reaction at 50°C. The chemical equation of silver ammonia reaction is:

[0068] 2AgCl+6NH HO=2[Ag(NH) OH]+4H O+2NH4Cl

[0069] CH2OH(CHOH)4CHO+2Ag(NH3)2OH→CH2OH(CHOH)4COONH4+

[0070] 2Ag↓+3NH3+H2O

[0071] The mass of the silver-containing intermediate was weighed, borax was added at a mass ratio of 4.2:1 between the silver-containing intermediate and borax, and the temperature was raised to 1000° C. and heated for 0.5 h to obtain silver.

[0072] Example 2

[0073] This embodiment provides a method for recovering silver from a battery cell, comprising the following steps:

[0074] (1) Acid pickling treatment: at room temperature, heterojunction solar cell waste sheets (original cells) and hydrofluoric acid with a mass percentage concentration of 48% were mixed in a mass volume ratio of 10 g:100 mL, and magnetic stirring was performed at a speed of 400 rpm / min for 30 min to react until a blue ITO film could not be seen by naked eyes. At this time, the total content of In and Sn on the surface of the waste cell sheets was measured to be less than 100 ppb. The waste cell sheets and the filtration residue were obtained by filtering with a sieve. The waste cell sheets were washed three times with deionized water in a mass volume ratio of 10 g:100 mL to the initial heterojunction solar cell waste sheets to obtain an intermediate cell sheet. The water used to wash the waste cell sheets and the filtration residue were combined as the first silver-containing liquid;

[0075] (2) Ammonia treatment: at room temperature, add ammonia with a mass percentage concentration of 20% to the intermediate battery sheet obtained in (1), the mass volume ratio of the intermediate battery sheet to the ammonia with a mass percentage concentration of 20% is 9.8 g:100 mL, and magnetic stirring is performed at a speed of 200 rpm / min for 10 min. After the reaction, the battery waste sheet and the filtration residue are obtained by filtration with a mesh, and the battery waste sheet is washed three times with deionized water with a mass volume ratio of 10 g:100 mL to the intermediate battery sheet to obtain a silicon wafer to be recycled, and the water used to wash the battery waste sheet and the filtration residue are combined as the second silver-containing liquid;

[0076] (3) Mixing treatment: The pH value of the second silver-containing liquid is measured to be 8, and the first silver-containing liquid obtained in (1) is mixed with the second silver-containing liquid obtained in (2), and the mixture is reacted for 30 minutes to obtain a silver-containing mixed solution. No external adjustment is performed during the reaction, and the pH value is maintained at ≥ 8. After the reaction, the pH value of the silver-containing mixed solution is 9;

[0077] (4) Reduction treatment: Use a reducing agent reduction method to treat the silver-containing mixed solution: add a sodium chloride solution with a mass percentage concentration of 30% to the silver-containing mixed solution until no white solid is generated, filter to obtain white silver chloride solid, and dry. Based on the amount of white silver chloride obtained, add other materials according to the chemical reaction equation, that is, the molar ratio of silver ion to hydrazine hydrate is 4:5, mix silver chloride and hydrazine hydrate, add deionized water with a volume of 10 times that of silver chloride and hydrazine hydrate, add sodium hydroxide at 80°C until the silver chloride is completely dissolved, and reduce the reaction to obtain a silver-containing intermediate, the chemical equation is:

[0078] 4AgCl+5N2H4·H2O=4Ag↓+4N2H5Cl+N2↑+5H2O

[0079] The mass of the silver-containing intermediate was weighed, borax was added at a mass ratio of 3.8:1 between the silver-containing intermediate and borax, and the temperature was raised to 1100° C. and heated for 0.5 h to obtain silver.

[0080] Example 3

[0081] This embodiment provides a method for recovering silver from a battery cell, comprising the following steps:

[0082] (1) Acid washing treatment: at room temperature, heterojunction solar cell waste sheets (original cells) and sulfuric acid with a mass percentage concentration of 45% were mixed in a mass volume ratio of 10 g:150 mL, and magnetic stirring was performed at a speed of 300 rpm / min for 20 min to react until a blue ITO film could not be seen by the naked eye. At this time, the total content of In and Sn on the surface of the waste cell sheets was measured to be less than 100 ppb. The waste cell sheets and the filtration residue were obtained by filtering with a sieve, and the waste cell sheets were washed three times with deionized water in a mass volume ratio of 10 g:100 mL to the initial heterojunction solar cell waste sheets to obtain an intermediate cell sheet, and the water used to wash the waste cell sheets and the filtration residue were combined as the first silver-containing liquid;

[0083] (2) Ammonia treatment: at room temperature, add ammonia with a mass percentage concentration of 30% to the intermediate battery sheet obtained in (1), wherein the mass volume ratio of the intermediate battery sheet to the ammonia with a mass percentage concentration of 30% is 5 g:150 mL, and magnetic stirring is performed at a speed of 300 rpm / min for 20 min. After the reaction, the battery waste sheet and the filtration residue are obtained by filtering with a mesh. The battery waste sheet is washed three times with deionized water with a mass volume ratio of 10 g:100 mL to the intermediate battery sheet to obtain a silicon wafer to be recycled. The water used to wash the battery waste sheet and the filtration residue are combined as the second silver-containing liquid;

[0084] (3) Mixing treatment: the pH value of the second silver-containing liquid is measured to be 11, water is added to dilute it to a pH value of 10, the first silver-containing liquid obtained in (1) is mixed with the second silver-containing liquid obtained in (2), and the mixture is reacted for 35 minutes to obtain a silver-containing mixed solution. During the reaction, ammonia water with a mass percentage concentration of 30% is used to adjust the pH value of the mixed solution to 8;

[0085] (4) Reduction treatment: Use a reducing agent reduction method to treat the silver-containing mixed solution: add a sodium chloride solution with a mass percentage concentration of 30% to the silver-containing mixed solution until no white solid is generated, filter to obtain white silver chloride solid, and dry. Based on the amount of white silver chloride obtained, add other materials according to the chemical reaction equation, that is, the molar ratio of silver ion to ascorbic acid is 2:1, add silver chloride to a sodium hydroxide solution with a mass percentage concentration of 30%, add a 20% ascorbic acid solution with a mass percentage concentration, and finally make the pH of the mixed solution 10. At 50°C, a reduction reaction is performed to obtain a silver-containing intermediate; each material is added according to the chemical equation, and the chemical equation is:

[0086] 2AgCl + ascorbic acid → 2Ag↓ + dehydroascorbic acid

[0087] The mass of the silver-containing intermediate was weighed, borax was added at a mass ratio of the silver-containing intermediate to borax of 4.9:1, the temperature was raised to 1000° C. and heated for 0.5 h to obtain silver.

[0088] Example 4

[0089] This embodiment provides a method for recovering silver from a battery cell, comprising the following steps:

[0090] (1) Acid pickling treatment: at room temperature, heterojunction solar cell waste sheets (original cells) and nitric acid with a mass percentage concentration of 48% were mixed in a mass volume ratio of 15 g:100 mL, and magnetic stirring was performed at a speed of 400 rpm / min for 30 min to react until a blue ITO film could not be seen by naked eyes. At this time, the total content of In and Sn on the surface of the waste cell sheets was measured to be less than 100 ppb. The waste cell sheets and the filtration residue were obtained by filtering with a sieve, and the waste cell sheets were washed three times with deionized water in a mass volume ratio of 10 g:100 mL to the initial heterojunction solar cell waste sheets to obtain an intermediate cell sheet, and the water used to wash the waste cell sheets and the filtration residue were combined as the first silver-containing liquid;

[0091] (2) Ammonia treatment: at room temperature, adding ammonia with a mass percentage concentration of 40% to the intermediate battery sheet obtained in (1), wherein the mass volume ratio of the intermediate battery sheet to the ammonia with a mass percentage concentration of 40% is 10 g:100 mL, and magnetic stirring is performed at a speed of 400 rpm / min for 30 min. After the reaction, filtering is performed with a mesh to obtain waste battery sheets and filtration residues, and the waste battery sheets are washed three times with deionized water with a mass volume ratio of 10 g:100 mL to the intermediate battery sheet to obtain silicon sheets to be recycled, and the water used to wash the waste battery sheets and the filtration residues are combined as the second silver-containing liquid;

[0092] (3) Mixing treatment: the pH value of the second silver-containing liquid is measured to be 11, water is added to dilute it to a pH value of 8, the first silver-containing liquid obtained in (1) is mixed with the second silver-containing liquid obtained in (2), and the mixture is reacted for 25 minutes to obtain a silver-containing mixed solution. During the reaction, ammonia water with a mass percentage concentration of 40% is used to adjust the pH value of the mixed solution to 12;

[0093] (4) Reduction treatment: Use a reducing agent to treat the silver-containing mixed solution: add a sodium chloride solution with a mass percentage concentration of 30% to the silver-containing mixed solution until no white solid is generated, filter to obtain white silver chloride solid, and dry. Based on the amount of white silver chloride obtained, add other materials according to the chemical reaction equation, that is, the molar ratio of silver ions to sulfite is 1:1, add a sodium sulfite solution with a mass percentage concentration of 40%, adjust the solution pH to 5, and perform a reduction reaction at 50°C to obtain a silver-containing intermediate. The chemical equation is:

[0094] 2H + +SO3 2- →SO2+H2O

[0095] AgCl + SO2 + H2O → Ag↓ + H + +HSO4- +Cl -

[0096] The mass of the silver-containing intermediate was weighed, borax was added at a mass ratio of the silver-containing intermediate to borax of 7.1:1, the temperature was raised to 1200° C. and heated for 2 h to obtain silver.

[0097] Example 5

[0098] This embodiment provides a method for recovering silver in batteries. The recovery method is basically the same as that in Embodiment 1, except that in step (1), the mass percentage concentration of hydrochloric acid is 40%.

[0099] Example 6

[0100] This embodiment provides a method for recovering silver in a battery. The recovery method is basically the same as that in Embodiment 3, except that in step (3), the step of diluting the second silver-containing liquid with water to a pH value of 10 is not included, and the first silver-containing liquid obtained in (1) and the second silver-containing liquid obtained in (2) are directly mixed.

[0101] Comparative Example 1

[0102] This comparative example provides a method for recovering silver from batteries. The recovery method is basically the same as that in Example 1, except that the treatment process in step (2) is different. The specific process of step (2) in this comparative example is as follows:

[0103] (2) At room temperature, a nitric acid solution with a mass percentage concentration of 50% is added to the intermediate battery sheet obtained in (1), wherein the mass volume ratio of the intermediate battery sheet to the nitric acid solution with a mass percentage concentration of 50% is 9.8 g:100 mL, and magnetic stirring is performed at a speed of 200 rpm / min for 10 minutes. After the reaction, the battery waste sheet and the filtration residue are obtained by filtering with a mesh, and the battery waste sheet is washed three times with deionized water with a mass volume ratio of 10 g:100 mL to the intermediate battery sheet to obtain the battery waste sheet treated with nitric acid, and the water used to wash the battery waste sheet and the filtration residue are combined as the second silver-containing liquid.

[0104] Comparative Example 2

[0105] This comparative example provides a method for recovering silver from batteries. The recovery method is basically the same as that of Example 1, except that the steps of using ammonia water treatment and then using hydrochloric acid treatment are as follows: Steps (1) and (2) are as follows:

[0106] (1) at room temperature, mixing heterojunction solar cell waste sheets and ammonia water with a mass percentage concentration of 20% in a mass volume ratio of 10 g:100 mL, and magnetically stirring at a speed of 200 rpm / min for 10 min. After the reaction, filtering with a mesh to obtain battery waste sheets and filtration residues, washing the battery waste sheets with deionized water in a mass volume ratio of 10 g:100 mL to the initial heterojunction solar cell waste sheets for three times to obtain battery waste sheets treated with ammonia water, and combining the water for washing the battery waste sheets with the filtration residues as the second silver-containing liquid;

[0107] (2) At room temperature, adding hydrochloric acid with a mass percentage concentration of 45% to the battery waste sheets treated with ammonia water obtained in (1), wherein the mass volume ratio of the battery waste sheets treated with ammonia water to the hydrochloric acid with a mass percentage concentration of 45% is 9.8 g:100 mL, magnetic stirring is performed at a speed of 200 rpm / min for 10 minutes, and the reaction is performed, and the battery waste sheets and filtration residues are obtained by filtering with a sieve, and the battery waste sheets are washed three times with deionized water with a mass volume ratio of 10 g:100 mL to the battery waste sheets treated with ammonia water to obtain acid-treated battery waste sheets, and the water used to wash the battery waste sheets and the filtration residue are combined as the first silver-containing liquid.

[0108] Comparative Example 3

[0109] This comparative example provides a method for recovering silver from a battery. The recovery method is substantially the same as that of Example 3, except that in step (3), after mixing the first silver-containing liquid obtained in (1) and the second silver-containing liquid obtained in (2), the pH value is not adjusted, and subsequent treatment steps are performed at a pH value of <8 (about 7.5).

[0110] Experimental Example 1

[0111] The recovery rate of silver in the above embodiments and comparative examples is calculated by the formula: S=M2 / (N×M1), where S is the recovery rate (%), N is the silver content in the battery waste (g / kg), M1 is the mass of the battery waste (kg), and M2 is the mass of silver (g). The mass of silver is obtained by weighing, and the silver content in the battery waste is obtained by sodium chloride potentiometric titration (see national standard GB / T 18996-2021 for details).

[0112] The purity of the recovered silver was determined by sodium chloride potentiometric titration (see national standard GB / T 18996-2021 for details).

[0113] The results are shown in Table 1.

[0114] Table 1

[0115]

[0116]

[0117] In the embodiment, the method for recovering silver from a battery cell provided by the present invention can achieve a silver recovery rate of 99.99%, and the purity of the obtained silver is above 79.9%, which is relatively high. When carrying out Example 6, compared with Example 3, the step of diluting the second silver-containing liquid with water to a pH value of 10 is not included, and the first silver-containing liquid obtained in (1) and the second silver-containing liquid obtained in (2) are directly mixed, which makes the reaction violent when the two are mixed, and the safety is low.

[0118] In Comparative Example 1, compared with Example 1, the treatment with ammonia water (alkali) in step (2) was changed to treatment with nitric acid, and the final silver recovery rate was 89.94%, which was lower than the silver obtained in the Example. Because the amount of nitric acid required to achieve the same removal effect of the remaining silver grid line as ammonia water would be very large, nitric acid was added in a ratio equal to that of ammonia water in Example 1 in Comparative Example 1, which ultimately resulted in a low silver recovery rate.

[0119] In Comparative Example 2, compared with Example 1, the order of step (1) acid treatment of the cell and step (2) ammonia (alkali) treatment of the cell is reversed, and the cell is first treated with alkali and then with acid. The final silver recovery rate is 89.91%, which is lower than the silver obtained in the example. After the acid treatment, the acid will react with the indium tin oxide in the cell and the resin glue attached to the silver grid line, causing the silver grid line to fall off, but some silver will still remain at the screen printing line mark. Then, the surface of the silicon wafer is corroded by alkali treatment, so that the remaining residual silver can be basically removed; while the alkali treatment is used first, since there are a large number of screen-printed silver grid lines remaining on the surface of the ITO film, the alkali treatment cannot remove the organic glue contained in the grid line, and the silver remaining in the line mark cannot be completely reacted during the subsequent acid treatment. Therefore, the acid-first-then-alkali treatment method is adopted.

[0120] In Comparative Example 3, compared with Example 3, after mixing the first silver-containing liquid obtained in (1) and the second silver-containing liquid obtained in (2), the pH value was not adjusted, and the pH value was maintained at about 7.5 for subsequent treatment steps. However, at a pH of 7.5, the reaction of dissolving solid silver could not proceed, and silver could not be recovered.

[0121] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A method for recovering silver from heterojunction solar cells, characterized in that: The steps include: Step S1) acid pickling treatment: taking a primary cell, immersing the primary cell in an acid solution, wherein the acid solution reacts with the primary cell to cause a portion of the silver grid lines on the primary cell to fall off, thereby obtaining an intermediate cell, and separating the intermediate cell from the acid solution to obtain a first silver-containing liquid; Step S2) ammonia water treatment: immersing the intermediate cell into ammonia water, the ammonia water reacts with the intermediate cell to cause the remaining silver grid lines on the intermediate cell to fall off, thereby obtaining a silicon wafer to be recycled, and separating the silicon wafer to be recycled from the ammonia water to obtain a second silver-containing liquid; Step S3) mixing treatment: mixing the first silver-containing liquid and the second silver-containing liquid to obtain a silver-containing mixed solution, and controlling the pH value of the silver-containing mixed solution to be not less than 8 so that silver exists in the silver-containing mixed solution in the form of ions; Step S4) Reduction treatment: treating the silver-containing mixed solution by a reduction method to obtain silver element.

2. The method for recovering silver from heterojunction solar cells according to claim 1, characterized in that: The mass of the original battery sheet and the volume ratio of the acid solution are 1g:6.5-15mL; and / or, controlling the pH value of the silver-containing mixed solution to be 8 to 10; and / or, the mass of the intermediate battery sheet to the volume ratio of the ammonia water is 1 g: 10 to 30 mL; And / or, the method of controlling the pH value of the silver-containing mixed solution to be not less than 8 includes controlling the ratio of the first silver-containing liquid to the second silver-containing liquid, or adding at least one of ammonia water.

3. The method for recovering silver from heterojunction solar cells according to claim 1 or 2, characterized in that: The acid in the acid solution is selected from at least one of hydrochloric acid, nitric acid, sulfuric acid, and hydrofluoric acid; and / or the mass percentage concentration of the acid in the acid solution is 40% to 48%; and / or the mass percentage concentration of the ammonia water is 20% to 40%.

4. The method for recovering silver from heterojunction solar cells according to claim 3, characterized in that: The acid in the acid solution is nitric acid; and / or the mass percentage concentration of the acid in the acid solution is 45% to 48%.

5. The method for recovering silver from heterojunction solar cells according to claim 1, characterized in that: Before mixing the first silver-containing liquid and the second silver-containing liquid, the method further includes adjusting the pH value of the second silver-containing liquid to be greater than 7 and less than or equal to 10; optionally, the pH value of the second silver-containing liquid is adjusted by diluting with water.

6. The method for recovering silver from heterojunction solar cells according to claim 1, characterized in that: During the pickling treatment, the reaction between the acid solution and the original battery sheet is carried out under stirring; and / or, in the ammonia water treatment, the reaction between the ammonia water and the intermediate battery sheet is carried out under stirring; And / or, the mixing treatment time is 25 to 35 minutes.

7. The method for recovering silver from heterojunction solar cells according to claim 6, characterized in that: The stirring includes magnetic stirring, the time of the magnetic stirring is 10 to 30 minutes, and the rotation speed of the magnetic stirring is 200 to 400 rpm / min.

8. The method for recovering silver from heterojunction solar cells according to claim 1, characterized in that: The reduction method includes at least one of a reducing agent reduction method and an electrolysis method; wherein the reducing agent used in the reducing agent reduction method includes at least one of a solid reducing agent, a liquid reducing agent, and a gas reducing agent.

9. The method for recovering silver from heterojunction solar cells according to claim 8, characterized in that: The reducing agent reduction method comprises the following steps: adding a chlorine-containing solution to the silver-containing mixed solution to perform a precipitation reaction, filtering to obtain silver chloride, adding a reducing agent to the silver chloride to perform a reduction reaction to obtain a silver-containing intermediate; Wherein, the reducing agent includes at least one of glucose, hydrazine hydrate, ascorbic acid, sodium sulfite and ferrous sulfate.

10. The method for recovering silver from heterojunction solar cells according to claim 9, characterized in that: The step also includes mixing the silver-containing intermediate with borax and heating to remove impurities to obtain silver; Optionally, the mass ratio of the silver-containing intermediate to the borax is 3.5 to 7.5:1; Optionally, the heating temperature is 1000-1200° C., and the heating time is 0.5-2 h.

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