A method for recovering metallic silver from waste photovoltaic cells by combining pyrometallurgy and hydrometallurgy

Abstract

The present invention relates to a method for recovering metallic silver from waste photovoltaic cells by a pyrometallurgical combined with a hydrometallurgical method, and belongs to the technical field of secondary silver resource recycling. The present invention adds waste photovoltaic silicon cells into concentrated nitric acid for acid leaching, and solid-liquid separation obtains solid-phase aluminum-containing silicon sheets and silver nitrate solution; sodium chloride is added into the silver nitrate solution to precipitate silver ions to obtain silver chloride precipitate; the silver chloride precipitate is mixed with sodium carbonate powder and then reduced and smelted to obtain a solid-phase and gaseous mixed gas, wherein the solid phase is metallic silver and reduction residue, and the gaseous mixed gas is carbon dioxide and oxygen; the reduction residue is added into hydrochloric acid for acid leaching, and solid-liquid separation obtains sodium chloride solution, which is returned for recycling after evaporation and crystallization; the gaseous mixed gas is passed into a sodium hydroxide solution to react and fix carbon to obtain a NaHCO3 solution, which is evaporated and crystallized to obtain sodium carbonate, and the sodium carbonate is returned for recycling. The present invention can realize the separation of silver from aluminum-containing silicon sheets, and efficiently recover metallic silver element.

Description

Technical Field

[0001] The present invention relates to a method for recovering metallic silver from waste photovoltaic cells by combining pyrometallurgy and hydrometallurgy, and belongs to the technical field of secondary silver resource recycling and utilization. Background Art

[0002] Secondary resources of silver mainly come from industrial wastewater, waste electronic products, waste photovoltaic cells, etc. Through efficient recovery technologies, silver in these waste materials can be extracted and reused in production to achieve the maximum utilization of resources.

[0003] With the rapid development of the photovoltaic industry, the production of photovoltaic installations has increased sharply. Over time, these photovoltaic cells will be phased out due to reasons such as reduced efficiency and physical damage, resulting in an explosive growth in the number of waste photovoltaic cells. This not only brings environmental problems but also wastes the precious metal silver contained in the cells. Silver is mainly used as a conductive paste in photovoltaic cells and is one of the key materials for the efficient operation of the cells. Currently, the recovery technologies for silver in waste photovoltaic cells mainly include two categories: physical methods and chemical methods. Physical methods usually involve advanced sorting and purification technologies, including mechanical crushing, electrostatic separation, etc. However, the separation efficiency of physical methods is low, and the separated product is a mixture of multiple metals containing silver. Chemical methods are mainly hydrometallurgical technologies, such as a series of complex and delicate processes including acid / cyanide leaching, precipitation, oxidation, reduction, electrolysis, etc. This method can effectively extract silver from complex waste materials, but it faces problems of cost and environmental impact during the recovery process. The research and development of new, efficient, environmentally friendly, and low-cost silver recovery technologies are the key to the future development of the industry. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technologies in silver recovery from waste photovoltaic cells, such as low efficiency, high cost, and environmental pollution, the present invention proposes a method for recovering metallic silver from waste photovoltaic cells by combining pyrometallurgy and hydrometallurgy. Concentrated nitric acid is used to dissolve the silver in the waste photovoltaic silicon cells into the solution to obtain a silver nitrate solution, and sodium chloride is used to precipitate silver ions to obtain silver chloride precipitate. After the silver chloride precipitate is mixed with sodium carbonate, reduction smelting is carried out to obtain metallic silver, reduction residue, carbon dioxide, and oxygen; the reduction residue mainly contains sodium carbonate and sodium chloride, and hydrochloric acid is used to leach the reduction residue to convert the sodium carbonate in the residue into sodium chloride; the reduction product carbon dioxide is introduced into a sodium hydroxide solution for fixation to produce sodium carbonate. The present invention adopts a fire-wet combined process, reduces the discharge of waste liquid, the reduction residue generated during the recovery process is converted into sodium chloride, and the discharged carbon dioxide is converted into sodium carbonate, and both are returned to the invention process for recycling.

[0005] A method for recovering metallic silver from waste photovoltaic cells by combining pyrometallurgy and hydrometallurgy, the specific steps are as follows:

[0006] (1) Add waste photovoltaic silicon cells to excessive concentrated nitric acid for acid leaching, and perform solid-liquid separation to obtain a solid phase containing aluminum-silicon wafers and a silver nitrate solution; add excessive sodium chloride to the silver nitrate solution to precipitate silver ions to obtain silver chloride precipitate;

[0007] (2) Mix the silver chloride precipitate and sodium carbonate powder and perform reduction smelting to obtain a mixed gas of solid and gas phases. The solid phase is metallic silver and reduction residue, and the gaseous mixed gas is carbon dioxide and oxygen;

[0008] (3) Add the reduction residue to hydrochloric acid for acid leaching, and perform solid-liquid separation to obtain a sodium chloride solution. After the sodium chloride solution is evaporated and crystallized, it is returned to step (1) for recycling;

[0009] (4) The gaseous mixed gas is successively passed into a sodium hydroxide solution for multi-stage reaction to fix carbon to obtain a NaHCO3 solution. The NaHCO3 solution is evaporated and crystallized to obtain sodium carbonate, and the sodium carbonate is returned to step (2) for recycling.

[0010] The concentration of the concentrated nitric acid in step (1) is 8-12 mol / L.

[0011] The mass ratio of the silver chloride precipitate to the sodium carbonate powder in step (2) is 3:2-4.

[0012] The temperature of the reduction smelting in step (2) is 1100-1300 °C, and the time is 2-3 h.

[0013] The concentration of the hydrochloric acid in step (3) is 2-5 mol / L, the acid leaching temperature is 25-60 °C, and the time is 20-60 min.

[0014] The concentration of the sodium hydroxide solution in step (4) is 6-10 mol / L; preferably, the number of stages of the reaction for carbon fixation is 2-3 stages.

[0015] The beneficial effects of the present invention are:

[0016] (1) The present invention adopts a method combining fire and wet to recover silver in waste photovoltaic cells (chemical precipitation-reduction furnace), which not only reduces the discharge of waste liquid (the cost of waste liquid treatment is reduced), but also simplifies the recovery process, thereby effectively reducing the overall recovery cost;

[0017] (2) During the silver recovery process of the present invention, the generated waste carbon dioxide is converted into a useful chemical, sodium carbonate, and at the same time, the by-products sodium chloride and sodium carbonate are recycled, significantly reducing the discharge of waste. Brief Description of the Drawings

[0018] Figure 1 It is a process flow chart of the present invention;

[0019] Figure 2Variation of silver content in the reduction residue with smelting time in Example 1;

[0020] Figure 3 Variation of the CO2 collection rate after carbon fixation in the first, second, and third times in Example 4. Detailed implementation manners

[0021] The present invention will be further described in detail below in conjunction with the specific implementation manners, but the protection scope of the present invention is not limited to the content described.

[0022] Example 1: A method for recovering metallic silver from waste photovoltaic cell chips by combining pyrometallurgy and hydrometallurgy (see Figure 1 ), and the specific steps are as follows:

[0023] (1) Add waste photovoltaic silicon cell chips into concentrated nitric acid with a concentration of 12 mol / L in excess for acid leaching, and perform solid-liquid separation to obtain a solid phase containing aluminum-silicon chips and a silver nitrate solution; add an excess of sodium chloride to the silver nitrate solution to precipitate silver ions, and perform solid-liquid separation to obtain silver chloride precipitate;

[0024] (2) Mix the silver chloride precipitate and sodium carbonate powder evenly, heat up to a temperature of 1300 °C and perform reduction smelting for 0.5 - 4 h to obtain a mixed gas of a solid phase and a gas phase. The solid phase is metallic silver and reduction residue, and the gas phase mixed gas is carbon dioxide and oxygen; the mass ratio of the silver chloride precipitate to the sodium carbonate powder is 3:4;

[0025] When performing reduction smelting at a temperature of 1300 °C for 2 h, the purity of metallic silver in this example is 99.2%, and the main impurity components are: Sn 0.25 wt%, Pb 0.07 wt%, Si 0.03 wt%, Al 0.02 wt%, Na 0.05 wt%, Fe 0.01%; the variation of the silver content in the reduction residue with smelting time at a temperature of 1300 °C is as Figure 2 shown. The silver contents in the residue after reduction smelting for 0.5 h, 1 h, 2 h, 3 h, and 4 h are 21.8 wt.%, 8.7 wt.%, 4.6 wt.%, 1.5 wt.%, and 0.008 w.t% respectively;

[0026] (3) Add the reduction residue into hydrochloric acid with a concentration of 5 mol / L, perform acid leaching at a temperature of 60 °C for 20 min, perform solid-liquid separation to obtain a sodium chloride solution, evaporate and crystallize the sodium chloride solution to obtain NaCl crystals, and return the NaCl crystals to step (1) for recycling; the purity of the NaCl crystals in this example is 99.5 wt.%;

[0027] (4) The gaseous mixture (a mixture of CO2 and O2) is introduced into a sodium hydroxide solution with a concentration of 10 mol / L for the first carbon fixation reaction to obtain a NaHCO3 solution. The un-fixed CO2 is continuously introduced into a NaOH solution with a concentration of 8 mol / L for the second carbon fixation reaction (two-stage carbon fixation, CO2 collection rate 86.9%), obtaining a NaHCO3 solution. The NaHCO3 solution is evaporated and crystallized to obtain Na2CO3 powder, and the Na2CO3 powder is returned to step (2) for recycling; the purity of the Na2CO3 powder obtained by evaporation and crystallization in this example is 99.5 wt.%.

[0028] Example 2: A method for recovering metallic silver from waste photovoltaic cell chips by combining pyrometallurgy and hydrometallurgy (see Figure 1 ), and the specific steps are as follows:

[0029] (1) The waste photovoltaic silicon cell chips are added to concentrated nitric acid with a concentration of 8 mol / L in excess for acid leaching, and solid-liquid separation is performed to obtain a solid phase containing aluminum-silicon chips and a silver nitrate solution; an excessive amount of sodium chloride is added to the silver nitrate solution to precipitate silver ions, and solid-liquid separation is performed to obtain silver chloride precipitate;

[0030] (2) The silver chloride precipitate and sodium carbonate powder are mixed evenly, heated to a temperature of 1100 °C and subjected to reduction smelting for 4 h to obtain a solid phase and a gaseous mixture. The solid phase is metallic silver and reduction residue, and the gaseous mixture is carbon dioxide and oxygen; the mass ratio of the silver chloride precipitate to the sodium carbonate powder is 3:2; the purity of metallic silver in this example is 99.3%, and the main impurity components are: Sn 0.23 wt%, Pb 0.06 wt%, Si 0.03 wt%, Al 0.05 wt%, Na 0.03 wt%, Fe 0.01%;

[0031] (3) The reduction residue is added to hydrochloric acid with a concentration of 2 mol / L, and acid leaching is performed at a temperature of 25 °C for 60 min. Solid-liquid separation is performed to obtain a sodium chloride solution. The sodium chloride solution is evaporated and crystallized to obtain NaCl crystals, and the NaCl crystals are returned to step (1) for recycling; the purity of the NaCl crystals in this example is 99.0 wt.%;

[0032] (4) The gaseous mixed gas (a mixed gas of CO2 and O2) is introduced into a sodium hydroxide solution with a concentration of 8 mol / L for the first carbon fixation reaction to obtain a NaHCO3 solution. The un-fixed CO2 is continuously introduced into a NaOH solution with a concentration of 6 mol / L for the second carbon fixation reaction to obtain a NaHCO3 solution. The un-fixed CO2 is continuously introduced into a NaOH solution with a concentration of 6 mol / L for the third carbon fixation reaction (tertiary carbon fixation, CO2 collection rate 92.3%) to obtain a NaHCO3 solution. The NaHCO3 solution is evaporated and crystallized to obtain Na2CO3 powder, and the Na2CO3 powder is returned to step (2) for recycling; the purity of the Na2CO3 powder obtained by evaporation and crystallization in this example is 99.7 wt.%.

[0033] Example 3: A method for recovering metallic silver from waste photovoltaic cell chips by combining pyrometallurgy and hydrometallurgy (see Figure 1 ), and the specific steps are as follows:

[0034] (1) The waste photovoltaic silicon cell chips are added to concentrated nitric acid with a concentration of 10 mol / L in excess for acid leaching, and solid-liquid separation is carried out to obtain a solid phase containing aluminum-silicon chips and a silver nitrate solution; an excessive amount of sodium chloride is added to the silver nitrate solution to precipitate silver ions, and solid-liquid separation is carried out to obtain silver chloride precipitate;

[0035] (2) The silver chloride precipitate and sodium carbonate powder are mixed evenly, heated to a temperature of 1200 °C and subjected to reduction smelting for 3 h to obtain a solid phase and a gaseous mixed gas. The solid phase is metallic silver and reduction residue, and the gaseous mixed gas is carbon dioxide and oxygen; the mass ratio of the silver chloride precipitate to the sodium carbonate powder is 3:3; the purity of metallic silver in this example is 99.4%, and the main impurity components are: Sn 0.2 wt%, Pb 0.05 wt%, Si 0.03 wt%, Al 0.03 wt%, Na 0.01 wt%, Fe 0.01%;

[0036] (3) The reduction residue is added to hydrochloric acid with a concentration of 3 mol / L, and acid leaching is carried out at a temperature of 40 °C for 40 min. Solid-liquid separation is carried out to obtain a sodium chloride solution. After evaporation and crystallization of the sodium chloride solution, NaCl crystals are obtained, and the NaCl crystals are returned to step (1) for recycling; the purity of the NaCl crystals in this example is 99.3 wt.%;

[0037] (4) The gaseous mixed gas (a mixed gas of CO2 and O2) is introduced into a sodium hydroxide solution with a concentration of 10 mol / L for the first carbon fixation reaction to obtain a NaHCO3 solution. The un-fixed CO2 is continuously introduced into a NaOH solution with a concentration of 6 mol / L for the second carbon fixation reaction to obtain a NaHCO3 solution. The un-fixed CO2 is continuously introduced into a NaOH solution with a concentration of 6 mol / L for the third carbon fixation reaction (tertiary carbon fixation, CO2 collection rate 96.2%) to obtain a NaHCO3 solution. The NaHCO3 solution is evaporated and crystallized to obtain Na2CO3 powder, and the Na2CO3 powder is returned to step (2) for recycling; the purity of the Na2CO3 powder obtained by evaporation and crystallization in this example is 99.5 wt.%.

[0038] Example 4: A method for recovering metallic silver from waste photovoltaic cell chips by combining pyrometallurgy and hydrometallurgy (see Figure 1 ), and the specific steps are as follows:

[0039] (1) The waste photovoltaic silicon cell chips are added to concentrated nitric acid with a concentration of 8 mol / L in excess for acid leaching, and solid-liquid separation is carried out to obtain a solid phase containing aluminum-silicon chips and a silver nitrate solution; an excessive amount of sodium chloride is added to the silver nitrate solution to precipitate silver ions, and solid-liquid separation is carried out to obtain silver chloride precipitate;

[0040] (2) The silver chloride precipitate and sodium carbonate powder are mixed evenly, heated to a temperature of 1300 °C and subjected to reduction smelting for 2 h to obtain a solid phase and a gaseous mixed gas. The solid phase is metallic silver and reduction residue, and the gaseous mixed gas is carbon dioxide and oxygen; the mass ratio of the silver chloride precipitate to the sodium carbonate powder is 3:2; the purity of metallic silver in this example is 99.3%, and the main impurity components are: Sn 0.26 wt%, Pb 0.08 wt%, Si 0.03 wt%, Al 0.04 wt%, Na 0.03 wt%, Fe 0.01%;

[0041] (3) The reduction residue is added to hydrochloric acid with a concentration of 3 mol / L, and acid leaching is carried out at a temperature of 50 °C for 30 min. Solid-liquid separation is carried out to obtain a sodium chloride solution. The sodium chloride solution is evaporated and crystallized to obtain NaCl crystals, and the NaCl crystals are returned to step (1) for recycling; the purity of the NaCl crystals in this example is 99.4 wt.%.

[0042] (4) The gaseous mixed gas (a mixed gas of CO2 and O2) is introduced into a sodium hydroxide solution with a concentration of 10 mol / L for the first reaction of carbon fixation to obtain a NaHCO3 solution. The un-fixed CO2 is continuously introduced into a NaOH solution with a concentration of 10 mol / L for the second reaction of carbon fixation to obtain a NaHCO3 solution. The un-fixed CO2 is continuously introduced into a NaOH solution with a concentration of 10 mol / L for the third reaction of carbon fixation (tertiary carbon fixation) to obtain a NaHCO3 solution; the CO2 collection rate for each carbon fixation is as Figure 3 shown. In a 10 mol / L NaOH solution, after the first, second, and third carbon fixations, the CO2 collection rates are 83.5%, 93.1%, and 98.9% respectively; the NaHCO3 solution is evaporated and crystallized to obtain Na2CO3 powder, and the Na2CO3 powder is returned to step (2) for recycling; the purity of the Na2CO3 powder obtained by evaporation and crystallization in this example is 99.7 wt.%.

[0043] The specific embodiments of the present invention have been described in detail above, but the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art, various changes can be made without departing from the gist of the present invention.

Claims

1. A method for recovering metallic silver from waste photovoltaic cells by combining pyrometallurgy with hydrometallurgy, characterized in that: The specific steps are as follows: (1) adding waste photovoltaic silicon cells into excess concentrated nitric acid for acid leaching, and performing solid-liquid separation to obtain solid-phase aluminum-containing silicon cells and silver nitrate solution; adding excess sodium chloride to the silver nitrate solution to precipitate silver ions to obtain silver chloride precipitate; (2) mixing the silver chloride precipitate and the sodium carbonate powder and performing reduction smelting to obtain a solid phase and a gaseous phase mixed gas, wherein the solid phase is metallic silver and a reduction residue, and the gaseous phase mixed gas is carbon dioxide and oxygen; the reduction smelting temperature is 1100-1300° C., and the time is 2-3 hours; (3) adding the reduced residue into hydrochloric acid for acid leaching, separating the solid and liquid to obtain a sodium chloride solution, and then evaporating and crystallizing the sodium chloride solution and returning it to step (1) for recycling; (4) The gas phase mixed gas is sequentially introduced into the sodium hydroxide solution to carry out multi-stage reaction to fix carbon to obtain NaHCO3 solution, and the NaHCO3 solution is evaporated and crystallized to obtain sodium carbonate, which is returned to step (2) for recycling.

2. The method for recovering metallic silver from waste photovoltaic cells by combining pyrometallurgy and hydrometallurgy according to claim 1, characterized in that: The concentration of concentrated nitric acid in step (1) is 8-12 mol / L.

3. The method for recovering metallic silver from waste photovoltaic cells by combining pyrometallurgy and hydrometallurgy according to claim 1, characterized in that: The mass ratio of the silver chloride precipitate to the sodium carbonate powder in step (2) is 3:2-4.

4. The method for recovering metallic silver from waste photovoltaic cells by combining pyrometallurgy and hydrometallurgy according to claim 1, characterized in that: In step (3), the hydrochloric acid concentration is 2-5 mol / L, the acid leaching temperature is 25-60°C, and the time is 20-60 min.

5. The method for recovering metallic silver from waste photovoltaic cells by combining pyrometallurgy and hydrometallurgy according to claim 1, characterized in that: The concentration of the sodium hydroxide solution in step (4) is 6-10 mol / L.

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