Method for separating Si, Al and Ag in waste photovoltaic cell by high gravity and cupellation

Abstract

This invention relates to a method for separating Si, Al, and Ag from waste photovoltaic cells using a high-gravity melting-precipitation technique, belonging to the field of photovoltaic solid waste recycling technology. The invention involves placing waste photovoltaic cells in a high-gravity separation device and heating them under an inert atmosphere to completely melt the Ag and Al on the surface, while the internal Si remains solid. High-gravity melting separation yields solid elemental Si and an Al-Ag-Si melt. The Al-Ag-Si melt is then cooled at a uniform rate and melted to obtain a mixture of Al-Ag melt and solid elemental Si. High-gravity melting separation yields Al-Ag melt and solid elemental Si. Metallic Mg is added to the Al-Ag melt and completely dissolved. Stirring and melting separation yields a mixture of Al melt and solid Ag-Mg compound. High-gravity melting separation yields Al melt and solid Ag-Mg compound. The solid Ag-Mg compound is then separated by vacuum distillation at 900–1000°C to obtain metallic Ag and metallic Mg, with the metallic Mg being recycled. This invention enables the efficient separation of valuable metals Si, Al, and Ag from waste photovoltaic cells.

Description

Technical Field

[0001] This invention relates to a method for separating Si, Al, and Ag from waste photovoltaic cells using supergravity-melting separation, belonging to the field of photovoltaic solid waste recycling technology. Background Technology

[0002] Photovoltaic cells in discarded photovoltaic modules contain valuable metals such as Si, Al, and Ag. Recycling these metals not only helps reduce ore mining but also reduces energy consumption. Compared to extraction from ores, recycling valuable metals from discarded photovoltaic cells can reduce energy consumption by approximately 35% and carbon dioxide emissions by 14%. Therefore, the recycling of valuable metals from discarded photovoltaic cells is crucial for the green and sustainable development of photovoltaic energy.

[0003] Currently, the extraction of valuable metals from waste photovoltaic cells mainly employs hydrometallurgical processes. This process first dissolves Ag in a solution through acid leaching, followed by filtration to obtain aluminum-containing Si wafers and an Ag-containing solution. Then, the aluminum-containing Si wafers are subjected to alkaline leaching to convert Al to Al(OH)3 and recover the solid Si wafers. For the Ag-containing solution, multiple steps are required, such as precipitation, oxidation, reduction, and electrolysis, to separate and prepare high-purity Ag. However, these extraction processes are complex, using large amounts of acids, alkalis, hydrazine, organic solutions, and electrolytes, resulting in the generation of large quantities of harmful waste liquid and increasing the risk of environmental pollution. Therefore, there is an urgent need to develop a green and environmentally friendly new technology for the separation and recovery of valuable metals such as Si, Al, and Ag from waste photovoltaic cells. Summary of the Invention

[0004] To address the potential environmental pollution issues encountered in the extraction of valuable metals from waste photovoltaic cells using existing technologies, this invention provides a method for separating Si, Al, and Ag from waste photovoltaic cells using a supergravity-melting-precipitation technique. Utilizing the difference in melting points (Si: 1414℃, Ag: 962℃, Al: 660℃), the waste photovoltaic cells are heated, causing the surface Al and Ag to melt while the internal Si remains solid. Supergravity technology (achieved through centrifugation) is then used for melting separation, yielding an Al-Ag-Si melt and solid Si. Subsequently, taking advantage of the low solubility of Si in the Al-Ag-Si melt, the melt is cooled to allow Si to precipitate (melting-precipitation), and supergravity separation is used again to obtain solid Si. The process involves separating Si and Al-Ag melts. Since Al and Ag have similar vapor pressures (difference of only one order of magnitude in the 600–1000℃ range), they are difficult to separate by vacuum distillation. Therefore, Mg (with a strong affinity for Ag) is added to the Al-Ag melt, and the mixture is held at 790–810℃ to allow Ag in the Al melt to precipitate as Ag-Mg compounds (melting precipitation). A third centrifugal separation is then performed to obtain the Al melt and the Ag-Mg compounds. Because the vapor pressures of Mg and Ag in the Ag-Mg compounds differ significantly (difference of 5–6 orders of magnitude in the 700–1000℃ range), vacuum distillation is used to separate metallic Ag and metallic Mg, which can then be recycled.

[0005] A method for separating Si, Al, and Ag from waste photovoltaic cells using supergravity-melting separation, with the following specific steps:

[0006] (1) The crushed waste photovoltaic cells are placed in a super gravity separation device, heated to 980-1080℃ in an inert atmosphere and kept at that temperature so that the Ag and Al on the surface of the waste photovoltaic cells are completely melted and the Si cells inside remain solid. The solid elemental Si and Al-Ag-Si melt are obtained by super gravity melting separation through a centrifugal device.

[0007] (2) The Al-Ag-Si melt is cooled at a constant rate to the preset melt precipitation temperature under stirring conditions, so that the Al-Ag-Si melt is melted to obtain a mixture of Al-Ag melt and solid elemental Si. The mixture is then separated by centrifugation under high gravity to obtain Al-Ag melt and solid elemental Si.

[0008] (3) Add metallic Mg to Al-Ag melt and dissolve it completely. Stir and melt at a preset melt melting temperature to obtain a mixture of Al melt and solid Ag-Mg compound. Separate Al melt and solid Ag-Mg compound by centrifugation.

[0009] (4) The solid Ag-Mg compound is heated to 900-1000℃ under vacuum conditions and separated by vacuum distillation to obtain metallic Ag and metallic Mg. Metallic Mg is returned to step (3) for recycling.

[0010] Preferably, the hypergravity coefficient in step (1) is 600–900G.

[0011] Preferably, the cooling rate in step (2) is 1-3℃ / min, the preset melt melting temperature is 670-800℃, and the hypergravity coefficient is 400-600G.

[0012] Preferably, the amount of Mg added in step (3) is 5-7 wt% of the Al-Ag melt.

[0013] Preferably, the melt melting temperature in step (3) is preset to be 790-810℃ and the hypergravity coefficient is 500-700G.

[0014] The beneficial effects of this invention are:

[0015] (1) This invention utilizes the principle of difference in melting point and difference in solubility to selectively separate valuable metals such as Si, Al, and Ag in waste photovoltaic cells, and applies supergravity to enhance the separation process and improve the metal separation efficiency.

[0016] (2) The methods of supergravity and melting separation used in this invention are both physical processes and will not produce three wastes (waste acid, waste gas and waste residue) that are harmful to the environment.

[0017] (3) The present invention achieves the separation of metals Si, Al and Ag through a multi-step separation process, thereby achieving secondary resource recycling, and the additional metal Mg introduced can also be recycled in the recycling process. Attached Figure Description

[0018] Figure 1 This is a process flow diagram of the present invention;

[0019] Figure 2 The graph shows the variation of the residual Al and Ag content in solid-phase Si with the gravity coefficient.

[0020] Figure 3 The graph shows the variation of residual Ag content in Al melt with melting temperature and gravity coefficient.

[0021] Figure 4 The graph shows the variation of residual Ag content in Al melt with the amount of Mg added. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0023] Example 1: A method for separating Si, Al, and Ag from waste photovoltaic cells using supergravity-melting separation (see...) Figure 1 The specific steps are as follows:

[0024] (1) The crushed waste photovoltaic cells are placed in the heating zone of a high-gravity separation device and heated to 1080°C under an inert atmosphere (argon) for 30 minutes to completely melt the Ag and Al on the surface of the waste photovoltaic cells, while the Si wafers inside remain in a solid phase. The cells are then centrifuged for 10 minutes under high-gravity melting separation (high-gravity coefficient 900G) to obtain solid elemental Si and Al-Ag-Si melt. In this embodiment, the residual Al and Ag contents in the solid elemental Si are 0.11wt% and 0.023wt% respectively (high-gravity coefficient 900G). The residual Al and Ag contents in the solid Si vary with the gravity coefficient (500~800G) as follows: Figure 2 As shown, under conditions of supergravity coefficients of 500G, 600G, 700G, and 800G, the residual Al content in solid-phase Si is 0.29wt%, 0.23wt%, 0.18wt%, and 0.13wt%, respectively, and the Ag content is 0.055wt%, 0.048wt%, 0.037wt%, and 0.031wt%, respectively.

[0025] (2) The Al-Ag-Si melt was heated to 1100℃ and cooled to the preset melt precipitation temperature (670℃) at a rate of 3℃ / min under stirring conditions and held for 2h to allow the Al-Ag-Si melt to precipitate and obtain a mixture of Al-Ag melt and solid elemental Si. The mixture was then subjected to centrifugal melting separation for 10min (with a centrifugal coefficient of 700G) to obtain Al-Ag melt and solid elemental Si. The residual Al and Ag contents in the solid elemental Si were 0.05wt% and 0.02wt%, respectively.

[0026] (3) The Al-Ag melt is heated to 1000℃, and metallic Mg (7wt% of the Al-Ag melt) is added to the Al-Ag melt and completely dissolved. The mixture is then cooled at a constant rate to the preset melt precipitation temperature (810℃) and stirred for 4 hours to obtain a mixture of Al melt and solid Ag-Mg compound. The mixture is then centrifuged for 15 minutes under high gravity (high gravity coefficient is 500G) to obtain Al melt and solid Ag-Mg compound (AgMg). The residual Ag content in the Al melt is 0.30%.

[0027] (4) The solid Ag-Mg compound was heated to 1000℃ under vacuum (vacuum degree 50Pa) and vacuum distilled for 40min to obtain metallic Ag (distillation residue) and metallic Mg (distillation condensate). The metallic Mg was returned to step (3) for recycling.

[0028] In this embodiment, the purity of metallic Ag is 98.3% (the main impurities are: 0.7wt% Mg, 0.8wt% Al, and 0.05wt% Si).

[0029] Example 2: A method for separating Si, Al, and Ag from waste photovoltaic cells using supergravity-melting separation (see Example 2). Figure 1 The specific steps are as follows:

[0030] (1) The crushed waste photovoltaic cells are placed in the heating zone of the supergravity separation device and heated to 980°C under an inert atmosphere (argon) and held for 40 min to completely melt the Ag and Al on the surface of the waste photovoltaic cells, while the Si cells inside remain solid. The cells are then centrifuged and subjected to supergravity melting separation for 15 min (supergravity coefficient is 600G) to obtain solid elemental Si and Al-Ag-Si melt. In this embodiment, the residual Al and Ag contents in the solid elemental Si are 0.19wt% and 0.037wt%, respectively.

[0031] (2) The Al-Ag-Si melt was heated to 1150℃ and cooled to the preset melt precipitation temperature (800℃) at a rate of 1℃ / min under stirring conditions and held for 1h to allow the Al-Ag-Si melt to precipitate and obtain a mixture of Al-Ag melt and solid elemental Si. The mixture was then subjected to centrifugal melting separation for 15min (with a centrifugal coefficient of 400G) to obtain Al-Ag melt and solid elemental Si. The residual Al and Ag contents in the solid elemental Si were 0.09wt% and 0.04wt%, respectively.

[0032] (3) The Al-Ag melt was heated to 1050℃, and metallic Mg (5wt% of the Al-Ag melt) was added to the Al-Ag melt and completely dissolved. The mixture was then cooled at a constant rate to the preset melt precipitation temperature (790℃) and stirred for 4 hours to obtain a mixture of Al melt and solid Ag-Mg compound. The mixture was then centrifuged for 10 minutes under high gravity (high gravity coefficient of 700G) to obtain Al melt and solid Ag-Mg compound (AgMg). The residual Ag content in the Al melt was 0.13%.

[0033] During the melting-gravity process (5wt% Mg addition), the variation of residual Ag content in the Al melt with melting temperature and gravity coefficient is as follows: Figure 3As shown: After melting at 790℃, 800℃, and 810℃ for 4 hours and separation under a gravity coefficient of 500G, the residual Ag content in the Al melt was 0.18wt%, 0.24wt%, and 0.26wt%, respectively; after melting at 790℃, 800℃, and 810℃ for 4 hours and separation under a gravity coefficient of 700G, the residual Ag content in the Al melt was 0.13wt%, 0.19wt%, and 0.22wt%, respectively.

[0034] (4) The solid Ag-Mg compound obtained by melting 5wt% Mg at 790℃ under 700G hypergravity conditions was heated to 900℃ under vacuum (vacuum degree 30Pa) and separated by vacuum distillation for 40min to obtain metallic Ag (distillation residue) and metallic Mg (distillation condensate). The metallic Mg was returned to step (3) for recycling.

[0035] In this embodiment, the purity of metallic Ag is 98.6% (the main impurities are: 0.6wt% Mg, 0.7wt% Al, and 0.06wt% Si).

[0036] Example 3: A method for separating Si, Al, and Ag from waste photovoltaic cells using supergravity-melting separation (see Example 3). Figure 1 The specific steps are as follows:

[0037] (1) The crushed waste photovoltaic cells are placed in the heating zone of the supergravity separation device and heated to 1050°C under an inert atmosphere (argon) and held for 35 min to completely melt the Ag and Al on the surface of the waste photovoltaic cells, while the Si cells inside remain solid. The cells are then centrifuged and subjected to supergravity melting separation for 10 min (supergravity coefficient is 800G) to obtain solid elemental Si and Al-Ag-Si melt. In this embodiment, the residual Al and Ag contents in the solid elemental Si are 0.14wt% and 0.029wt%, respectively.

[0038] (2) The Al-Ag-Si melt was heated to 1100℃ and cooled to the preset melt precipitation temperature (750℃) at a rate of 2℃ / min under stirring conditions and held for 2h to allow the Al-Ag-Si melt to precipitate and obtain a mixture of Al-Ag melt and solid elemental Si. The mixture was then subjected to centrifugal melting separation for 10min (with a centrifugal coefficient of 500G) to obtain Al-Ag melt and solid elemental Si. The residual Al and Ag contents in the solid elemental Si were 0.07wt% and 0.03wt%, respectively.

[0039] (3) The Al-Ag melt was heated to 1020℃, and metallic Mg (6wt% of the Al-Ag melt) was added to the Al-Ag melt and completely dissolved. The mixture was then cooled at a constant rate to the preset melt precipitation temperature (800℃) and stirred for 4 hours to obtain a mixture of Al melt and solid Ag-Mg compound. The mixture was then centrifuged for 15 minutes under high gravity (high gravity coefficient of 600G) to obtain Al melt and solid Ag-Mg compound (AgMg). The residual Ag content in the Al melt was 0.19%.

[0040] (4) The solid Ag-Mg compound was heated to 950°C under vacuum (vacuum degree 40Pa) and separated by vacuum distillation for 40min to obtain metallic Ag (distillation residue) and metallic Mg (distillation condensate). The metallic Mg was returned to step (3) for recycling.

[0041] In this embodiment, the purity of metallic Ag is 98.5% (the main impurities are: 0.5wt% Mg, 0.8wt% Al, and 0.07wt% Si).

[0042] Example 4: A method for separating Si, Al, and Ag from waste photovoltaic cells using supergravity-melting separation (see Example 4). Figure 1 The specific steps are as follows:

[0043] (1) The crushed waste photovoltaic cells are placed in the heating zone of the supergravity separation device and heated to 1020°C under an inert atmosphere (argon) and held for 35 min to completely melt the Ag and Al on the surface of the waste photovoltaic cells, while the Si cells inside remain solid. The cells are then centrifuged and subjected to supergravity melting separation for 25 min (supergravity coefficient is 700G) to obtain solid elemental Si and Al-Ag-Si melt. In this embodiment, the residual Al and Ag contents in the solid elemental Si are 0.15wt% and 0.031wt%, respectively.

[0044] (2) The Al-Ag-Si melt was heated to 1180℃ and cooled to the preset melt precipitation temperature (700℃) at a rate of 2℃ / min under stirring conditions and held for 0.5h to allow the Al-Ag-Si melt to precipitate and obtain a mixture of Al-Ag melt and solid elemental Si. The mixture was then subjected to centrifugal melting separation for 10min (with a centrifugal coefficient of 600G) to obtain Al-Ag melt and solid elemental Si. The residual Al and Ag contents in the solid elemental Si were 0.04wt% and 0.02wt%, respectively.

[0045] (3) The Al-Ag melt is heated to 1000℃, and metallic Mg (7wt% of the Al-Ag melt) is added to the Al-Ag melt and completely dissolved. The mixture is then cooled at a constant rate to the preset melt precipitation temperature (790℃) and stirred for 4 hours to obtain a mixture of Al melt and solid Ag-Mg compound. The mixture is then centrifuged for 10 minutes under high gravity melting separation (high gravity coefficient is 700G) to obtain Al melt and solid Ag-Mg compound (AgMg). The residual Ag content in the Al melt is 0.11%.

[0046] During the melting-high gravity (700G) process, the variation of residual Ag content in the Al melt with the amount of Mg added and the melting temperature is as follows: Figure 4 As shown: with the addition of 7wt% metallic Mg, after melting and centrifugation at 790℃, 800℃, and 810℃, the residual Ag content in the Al melt was 0.14wt%, 0.12wt%, and 0.11wt%, respectively; with the addition of 6wt% metallic Mg, after melting and centrifugation at 790℃, 800℃, and 810℃, the residual Ag content in the Al melt was 0.19wt%, 0.17wt%, and 0.14wt%, respectively; with the addition of 5wt% metallic Mg, after melting and centrifugation at 790℃, 800℃, and 810℃, the residual Ag content in the Al melt was 0.24wt%, 0.22wt%, and 0.18wt%, respectively.

[0047] (4) The solid Ag-Mg compound obtained under the conditions of melting at 7wt% Mg at 790℃ and 700G gravity was heated to 1000℃ under vacuum (vacuum degree 30Pa) and separated by vacuum distillation for 40min to obtain metallic Ag (distillation residue) and metallic Mg (distillation condensate). The metallic Mg was returned to step (3) for recycling.

[0048] In this embodiment, the purity of metallic Ag is 98.7% (the main impurities are: 0.5wt% Mg, 0.6wt% Al, and 0.08wt% Si).

[0049] The specific embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for separating Si, Al, and Ag from waste photovoltaic cells using supergravity-melting separation, characterized in that, The specific steps are as follows: (1) The crushed waste photovoltaic cells are placed in a super gravity separation device, heated to 980-1080℃ in an inert atmosphere and kept at that temperature so that the Ag and Al on the surface of the waste photovoltaic cells are completely melted and the Si cells inside remain solid. The solid elemental Si and Al-Ag-Si melt are obtained by super gravity melting separation through a centrifugal device. (2) The Al-Ag-Si melt is cooled at a constant rate to the preset melt precipitation temperature under stirring conditions, so that the Al-Ag-Si melt is melted to obtain a mixture of Al-Ag melt and solid elemental Si. The mixture is then separated by centrifugation under high gravity to obtain Al-Ag melt and solid elemental Si. (3) Add metallic Mg to Al-Ag melt and dissolve it completely. Stir and melt at a preset melt melting temperature to obtain a mixture of Al melt and solid Ag-Mg compound. Separate Al melt and solid Ag-Mg compound by centrifugation. (4) The solid Ag-Mg compound is heated to 900-1000℃ under vacuum conditions and separated by vacuum distillation to obtain metallic Ag and metallic Mg. Metallic Mg is returned to step (3) for recycling.

2. The method for separating Si, Al, and Ag from waste photovoltaic cells using supergravity-melting separation according to claim 1, characterized in that: Step (1) The hypergravity coefficient is 600-900G.

3. The method for separating Si, Al, and Ag from waste photovoltaic cells using supergravity-melting separation according to claim 1, characterized in that: Step (2) The cooling rate is 1-3℃ / min, the preset melt melting temperature is 670-800℃, and the hypergravity coefficient is 400-600G.

4. The method for separating Si, Al, and Ag from waste photovoltaic cells using supergravity-melting separation according to claim 1, characterized in that: In step (3), the amount of Mg metal added is 5-7 wt% of the Al-Ag melt.

5. The method for separating Si, Al, and Ag from waste photovoltaic cells using supergravity-melting separation according to claim 1, characterized in that: Step (3) The preset melt melting temperature is 790~810℃ and the hypergravity coefficient is 500~700G.

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