A method of processing polysilicon and single crystal silicon scrap

Abstract

This invention relates to a method for processing polycrystalline silicon and monocrystalline silicon waste, belonging to the field of waste material recycling and reuse. The method involves vacuum filtering monocrystalline silicon and polycrystalline silicon cutting waste slurry, mixing it with 40-50% TMn electrolytic manganese anode mud after pressure filtration, preheating and dehydrating, and then further heating to obtain heated material. The heated material is then placed in a reducing atmosphere for reduction roasting, and 1.5%-2% reducing agent is added. The mixture is heated to a molten state through electrodes, and the resulting slag is high-manganese slag. The silicon water discharged after heating is then cast into ingots to obtain crude silicon. This invention effectively recovers polycrystalline silicon and monocrystalline silicon waste while also processing electrolytic manganese anode mud, achieving comprehensive utilization of both types of waste. This method effectively solves the long-standing pollution problems caused by cutting waste and electrolytic manganese anode mud, improving the utilization rate of mineral resources.

Description

Technical Field

[0001] This invention belongs to the field of waste material recycling and reuse, specifically relating to a method for processing polycrystalline silicon and monocrystalline silicon waste. Background Technology

[0002] Silicon is mainly used to make high-purity semiconductors, high-temperature resistant materials, optical fiber communication materials, organosilicon compounds, alloys, etc.

[0003] With the rapid development of the semiconductor industry and photovoltaics, the demand for monocrystalline silicon and polycrystalline silicon is constantly increasing. Monocrystalline silicon wafers are square or octagonal wafers cut from monocrystalline silicon rods, collectively referred to in the industry as silicon wafers. Due to their advantages such as high precision and high surface quality, they are one of the basic functional materials for manufacturing integrated circuits, and are mainly used in the manufacture of solar cell modules, high-power rectifiers, high-power transistors, diodes, switching devices, etc.

[0004] Polycrystalline silicon can be used as a raw material for pulling monocrystalline silicon, and it is also used in semiconductors and solar cells. Depending on purity requirements, polycrystalline silicon is divided into electronic grade and solar grade. With the rapid development of the photovoltaic industry, the demand for polycrystalline silicon in solar cells is growing rapidly, and production capacity is also continuously increasing.

[0005] The manufacturing process of polycrystalline silicon and monocrystalline silicon generates a large amount of hazardous waste polycrystalline silicon and monocrystalline silicon. This is mainly due to the silicon wafer cutting process, which produces a large amount of silicon powder waste. In actual processing, up to 50% of the crystalline silicon is lost in the form of silicon powder. These wastes usually contain a variety of harmful substances, such as aluminum, copper, iron and other metallic impurities, and need to be properly treated.

[0006] Currently, there are various methods for treating waste slurry generated from cutting, both domestically and internationally. These include physical flotation methods and acid or alkali chemical treatment methods. However, these methods are generally complex, have high production costs, and are difficult to industrialize. Summary of the Invention

[0007] To address the aforementioned problems in existing technologies for recycling cutting waste slurry, this invention provides a method for processing polycrystalline and monocrystalline silicon waste. By using a suspension magnetization roasting-submerged arc furnace, silicon waste can be recycled and reused, achieving the effect of low-cost resource recycling.

[0008] A method for processing polycrystalline silicon and monocrystalline silicon waste comprises the following steps:

[0009] (1) Vacuum filter the waste slurry from monocrystalline silicon and polycrystalline silicon cutting and mix it with 40-50% TMn electrolytic manganese anode mud after pressure filtration to obtain a mixed raw material;

[0010] (2) After preheating and dehydrating the mixed raw materials, further heating is carried out to obtain the heated material;

[0011] (3) The heated material is placed in a reducing atmosphere and subjected to reduction roasting at a temperature of 700℃-780℃ for 1-1.5 hours to obtain the reduced material.

[0012] (4) Add 1.5%-2% of reducing agent to the reduced material and heat it to a melting state through electrodes. The temperature of the molten pool is 1700℃-1800℃. The slag obtained after heating is high manganese slag. Cast the silicon water discharged after heating into ingots to obtain crude silicon.

[0013] Further, the mixed raw material in step (1) contains 7-10% water, and the ratio of monocrystalline silicon and polycrystalline silicon cutting waste slurry to electrolytic manganese anode mud in the mixed raw material is 1:1.

[0014] Furthermore, the preheating temperature in step (2) is 300-350℃, and the heating temperature is 850-950℃.

[0015] Further, the reducing atmosphere in step (3) is CO, H2 or a mixture of both, and the reducing atmosphere accounts for 45-55%.

[0016] Furthermore, the reducing agent in step (4) is low-sulfur coal, wherein the fixed carbon content of the low-sulfur coal is ≥85% and the particle size is 10-25mm.

[0017] Furthermore, the flue gas generated in step (4) is returned to the suspension roasting furnace for waste heat recovery, and the flue gas from the suspension magnetization roasting furnace is discharged after denitrification and desulfurization.

[0018] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention can effectively recover polycrystalline silicon and monocrystalline silicon waste while also treating electrolytic manganese anode sludge, achieving comprehensive utilization of both types of waste; secondly, the process of this invention is simple and easy to implement, the equipment is mature, and it is easy to industrialize. This method can effectively solve the long-standing pollution problems caused by cutting waste and electrolytic manganese anode sludge, improving the utilization rate of mineral resources. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0020] In the description of this invention, it should be noted that unless specific conditions are specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0021] Example 1

[0022] The raw material is a mixture of TMn50% manganese anode mud and polycrystalline silicon and monocrystalline silicon cutting waste slurry containing 25% silicon carbide, 50% metallic silicon, and 8% iron by weight, with the remainder being other impurities.

[0023] (1) Since both materials have relatively fine particle size, there is no need to crush them in the early stage. The two materials are filtered to a water content of about 10%, and then the filtered materials are mixed in a ratio of 1:1.

[0024] (2) The mixed material is conveyed to the pipeline of the suspension magnetization roasting furnace by belt conveyor. After weighing and metering, it is fed into the system pipeline by feeding screw. It is mixed with the hot flue gas generated by the burner in the main furnace and preheated and dehydrated in the pipeline. At the same time, the flue gas temperature is reduced. The preheating temperature is 300℃. The preheated powdery material is then put into the main furnace for further heating.

[0025] (3) Heating is carried out from the main furnace at a temperature of 850°C. The heated powdered material enters the reduction chamber. The reducing agent is a mixture of CO and H2, with the mixture accounting for 55%. The reduction is carried out at a temperature of 700°C for 1 hour. During this period, the tetravalent manganese in the electrolytic manganese anode mud will be reduced to divalent manganese, and impurities such as iron in monocrystalline silicon and polycrystalline silicon will also be reduced, but the silicon will not be affected.

[0026] (4) The feeding pipe of the suspension roasting furnace is installed in the central material tank of the electric arc furnace. A set feeding device is added to the feeding pipe. 1.5% of reducing agent is added to the feeding pipe. The mixed material is put into the storage tank of the electric arc furnace. The roasted material is added to the electrode root through the feeding pipe. The material is then heated to the melting state through the electrode. The melting pool temperature is 1800℃. Under the conditions of under-reduction, relatively low furnace temperature and acidic slag, manganese is retained in the slag to the maximum extent. At the same time, impurities such as iron in the silicon waste are also enriched in the slag. While the silicon in the silicon waste is melting, some of the impurities such as iron in the silicon waste are also enriched in the slag.

[0027] (5) The slag discharged from the electric arc furnace is high manganese slag, which can be further applied. The discharged molten silicon is used to cast ingots to obtain crude silicon.

[0028] (6) The flue gas generated by the electric arc furnace is returned to the suspension roasting furnace for waste heat recovery. The flue gas from the suspension magnetization roasting furnace is discharged after denitrification and desulfurization.

[0029] The final product is a manganese-rich slag containing 46% manganese and crude silicon containing 83% silicon.

[0030] Example 2

[0031] The mixture of the above two types of waste materials is used as raw material, which contains 47% TMn manganese anode mud and solids from polycrystalline silicon and monocrystalline silicon cutting waste slurry, with a weight percentage of 25% silicon carbide, 50% metallic silicon, 8% iron, and the remainder being other impurities.

[0032] (1) Since both materials have relatively fine particle size, there is no need to crush them in the early stage. The two materials are filtered to a water content of about 10%, and then the filtered materials are mixed in a ratio of 1:1.

[0033] (2) The mixed material is conveyed to the pipeline of the suspension magnetization roasting furnace by belt conveyor. After weighing and metering, it is fed into the system pipeline by feeding screw. It is mixed with the hot flue gas generated by the burner in the main furnace and preheated and dehydrated in the pipeline. At the same time, the flue gas temperature is reduced. The preheating temperature is 310℃. The preheated powdery material is then put into the main furnace for further heating.

[0034] (3) Heating is carried out from the main furnace at a temperature of 870°C. The heated powdered material enters the reduction chamber. The reducing agent is a mixture of CO and H2, with the mixture accounting for 53%. Reduction roasting is carried out at a temperature of 730°C for 1.2 hours. During this period, the tetravalent manganese in the electrolytic manganese anode mud will be reduced to divalent manganese, and impurities such as iron in monocrystalline silicon and polycrystalline silicon will also be reduced, but the silicon will not be affected.

[0035] (4) The feeding pipe of the suspension roasting furnace is installed in the central material tank of the electric arc furnace. A set feeding device is added to the feeding pipe. 1.6% of reducing agent is added to the feeding pipe. The mixed material is put into the storage tank of the electric arc furnace. The roasted material is added to the electrode root through the feeding pipe. The material is then heated to the melting state through the electrode. The melting pool temperature is 1800℃. Under the conditions of under-reduction, relatively low furnace temperature and acidic slag, manganese is retained in the slag to the maximum extent. At the same time, impurities such as iron in the silicon waste are also enriched in the slag. The silicon in the silicon waste melts and some of the impurities such as iron in the silicon waste are also enriched in the slag.

[0036] (5) The slag discharged from the electric arc furnace is high manganese slag, which can be further applied. The discharged molten silicon is used to cast ingots to obtain crude silicon.

[0037] (6) The flue gas generated by the electric arc furnace is returned to the suspension roasting furnace for waste heat recovery. The flue gas from the suspension magnetization roasting furnace is discharged after denitrification and desulfurization.

[0038] The final product is a manganese-rich slag containing 44% manganese and crude silicon containing 84% silicon.

[0039] Example 3

[0040] The mixture of the above two types of waste materials is used as raw material, which contains 45% TMn manganese anode mud and solids from polycrystalline silicon and monocrystalline silicon cutting waste slurry, with a weight percentage of 25% silicon carbide, 50% metallic silicon, 8% iron, and the remainder being other impurities.

[0041] (1) Since both materials have relatively fine particle size, there is no need to crush them in the early stage. The two materials are filtered to a water content of about 10%, and then the filtered materials are mixed in a ratio of 1:1.

[0042] (2) The mixed material is conveyed to the pipeline of the suspension magnetization roasting furnace by belt conveyor. After weighing and metering, it is fed into the system pipeline by feeding screw. It is mixed with the hot flue gas generated by the burner in the main furnace and preheated and dehydrated in the pipeline. At the same time, the flue gas temperature is reduced. The preheating temperature is 320℃. The preheated powdery material is then put into the main furnace for further heating.

[0043] (3) Heating is carried out from the main furnace at a temperature of 890°C. The heated powdered material enters the reduction chamber. The reducing agent is a mixture of CO and H2, with the mixture accounting for 50%. Reduction roasting is carried out at a temperature of 750°C for 1.2 hours. During this period, the tetravalent manganese in the electrolytic manganese anode mud will be reduced to divalent manganese, and impurities such as iron in monocrystalline silicon and polycrystalline silicon will also be reduced, but the silicon will not be affected.

[0044] (4) The feeding pipe of the suspension roasting furnace is installed in the central material tank of the electric arc furnace. A set feeding device is added to the feeding pipe. 1.6% of reducing agent is added to the feeding pipe. The mixed material is put into the storage tank of the electric arc furnace. The roasted material is added to the electrode root through the feeding pipe. The material is then heated to the melting state through the electrode. The melting pool temperature is 1800℃. Under the conditions of under-reduction, relatively low furnace temperature and acidic slag, manganese is retained in the slag to the maximum extent. At the same time, impurities such as iron in the silicon waste are also enriched in the slag. The silicon in the silicon waste melts and some of the impurities such as iron in the silicon waste are also enriched in the slag.

[0045] (5) The slag discharged from the electric arc furnace is high manganese slag, which can be further applied. The discharged molten silicon is used to cast ingots to obtain crude silicon.

[0046] (6) The flue gas generated by the electric arc furnace is returned to the suspension roasting furnace for waste heat recovery. The flue gas from the suspension magnetization roasting furnace is discharged after denitrification and desulfurization.

[0047] The final product is a manganese-rich slag containing 45% manganese and crude silicon containing 83% silicon.

[0048] Example 4

[0049] The mixture of the above two types of waste materials is used as raw material, which contains 43% TMn manganese anode mud and solids from polycrystalline silicon and monocrystalline silicon cutting waste slurry, with a weight percentage of 25% silicon carbide, 50% metallic silicon, 8% iron, and the remainder being other impurities.

[0050] (1) Since both materials have relatively fine particle size, there is no need to crush them in the early stage. The two materials are filtered to a water content of about 10%, and then the filtered materials are mixed in a ratio of 1:1.

[0051] (2) The mixed material is conveyed to the pipeline of the suspension magnetization roasting furnace by belt conveyor. After weighing and metering, it is fed into the system pipeline by feeding screw. It is mixed with the hot flue gas generated by the burner in the main furnace and preheated and dehydrated in the pipeline. At the same time, the flue gas temperature is reduced. The preheating temperature is 330℃. The preheated powdery material is then put into the main furnace for further heating.

[0052] (3) Heating is carried out from the main furnace at a temperature of 900°C. The heated powdered material enters the reduction chamber. The reducing agent is a mixture of CO and H2, with the mixture accounting for 47%. The reduction is carried out at a temperature of 750°C for 1.3 hours. During this period, the tetravalent manganese in the electrolytic manganese anode mud will be reduced to divalent manganese, and impurities such as iron in monocrystalline silicon and polycrystalline silicon will also be reduced, but the silicon will not be affected.

[0053] (4) The feeding pipe of the suspension roasting furnace is installed in the central material tank of the electric arc furnace. A set feeding device is added to the feeding pipe. 1.7% of reducing agent is added to the feeding pipe. The mixed material is put into the storage tank of the electric arc furnace. The roasted material is added to the electrode root through the feeding pipe. The material is then heated to the melting state through the electrode. The melting pool temperature is 1800℃. Under the conditions of under-reduction, relatively low furnace temperature and acidic slag, manganese is retained in the slag to the maximum extent. At the same time, impurities such as iron in the silicon waste are also enriched in the slag. While the silicon in the silicon waste is melting, some of the impurities such as iron in the silicon waste are also enriched in the slag.

[0054] (5) The slag discharged from the electric arc furnace is high manganese slag, which can be further applied. The discharged molten silicon is used to cast ingots to obtain crude silicon.

[0055] (6) The flue gas generated by the electric arc furnace is returned to the suspension roasting furnace for waste heat recovery. The flue gas from the suspension magnetization roasting furnace is discharged after denitrification and desulfurization.

[0056] The final product is a manganese-rich slag containing 44% manganese and crude silicon containing 82% silicon.

[0057] Example 5

[0058] The raw material is a mixture of TMn50% manganese anode mud and polycrystalline silicon and monocrystalline silicon cutting waste slurry containing 25% silicon carbide, 50% metallic silicon, and 8% iron by weight, with the remainder being other impurities.

[0059] (1) Since both materials have relatively fine particle size, there is no need to crush them in the early stage. The two materials are filtered to a water content of about 10%, and then the filtered materials are mixed in a ratio of 1:1.

[0060] (2) The mixed material is conveyed to the pipeline of the suspension magnetization roasting furnace by belt conveyor. After weighing and metering, it is fed into the system pipeline by feeding screw. It is mixed with the hot flue gas generated by the burner in the main furnace and preheated and dehydrated in the pipeline. At the same time, the flue gas temperature is reduced. The preheating temperature is 350℃. The preheated powdery material is then put into the main furnace for further heating.

[0061] (3) Heating is carried out from the main furnace at a temperature of 950°C. The heated powdered material enters the reduction chamber. The reducing agent is a mixture of CO and H2, with the mixture accounting for 55%. The reduction is carried out at a temperature of 780°C for 1.5 hours. During this period, the tetravalent manganese in the electrolytic manganese anode mud will be reduced to divalent manganese, and impurities such as iron in monocrystalline silicon and polycrystalline silicon will also be reduced, but the silicon will not be affected.

[0062] (4) The feeding pipe of the suspension roasting furnace is installed in the central material tank of the electric arc furnace. A set feeding device is added to the feeding pipe. 2% of reducing agent is added to the feeding pipe. The mixed material is put into the storage tank of the electric arc furnace. The roasted material is added to the electrode root through the feeding pipe. The material is then heated to the melting state through the electrode. The melting pool temperature is 1800℃. Under the conditions of under-reduction, relatively low furnace temperature and acidic slag, manganese is retained in the slag to the maximum extent. At the same time, impurities such as iron in the silicon waste are also enriched in the slag. While the silicon in the silicon waste is melting, some of the impurities such as iron in the silicon waste are also enriched in the slag.

[0063] (5) The slag discharged from the electric arc furnace is high manganese slag, which can be further applied. The discharged molten silicon is used to cast ingots to obtain crude silicon.

[0064] (6) The flue gas generated by the electric arc furnace is returned to the suspension roasting furnace for waste heat recovery. The flue gas from the suspension magnetization roasting furnace is discharged after denitrification and desulfurization.

[0065] The final product is a manganese-rich slag containing 40% manganese and crude silicon containing 80% silicon.

[0066] Example 6

[0067] The raw material is a mixture of TMn50% manganese anode mud and polycrystalline silicon and monocrystalline silicon cutting waste slurry containing 25% silicon carbide, 50% metallic silicon, and 8% iron by weight, with the remainder being other impurities.

[0068] (1) Since both materials have relatively fine particle size, there is no need to crush them in the early stage. The two materials are filtered to a water content of about 10%, and then the filtered materials are mixed in a ratio of 1:1.

[0069] (2) The mixed material is conveyed to the pipeline of the suspension magnetization roasting furnace by belt conveyor. After weighing and metering, it is fed into the system pipeline by feeding screw. It is mixed with the hot flue gas generated by the burner in the main furnace and preheated and dehydrated in the pipeline. At the same time, the flue gas temperature is reduced. The preheating temperature is 320℃. The preheated powdery material is then put into the main furnace for further heating.

[0070] (3) Heating is carried out from the main furnace at a temperature of 900°C. The heated powdered material enters the reduction chamber. The reducing agent is a mixture of CO and H2, with the mixture accounting for 50%. The reduction is carried out at a temperature of 750°C for 1.2 hours. During this period, the tetravalent manganese in the electrolytic manganese anode mud will be reduced to divalent manganese, and impurities such as iron in monocrystalline silicon and polycrystalline silicon will also be reduced, but the silicon will not be affected.

[0071] (4) The feeding pipe of the suspension roasting furnace is installed in the central material tank of the electric arc furnace. A set feeding device is added to the feeding pipe. 1.7% of reducing agent is added to the feeding pipe. The mixed material is put into the storage tank of the electric arc furnace. The roasted material is added to the electrode root through the feeding pipe. The material is then heated to the melting state through the electrode. The melting pool temperature is 1800℃. Under the conditions of under-reduction, relatively low furnace temperature and acidic slag, manganese is retained in the slag to the maximum extent. At the same time, impurities such as iron in the silicon waste are also enriched in the slag. While the silicon in the silicon waste is melting, some of the impurities such as iron in the silicon waste are also enriched in the slag.

[0072] (5) The slag discharged from the electric arc furnace is high manganese slag, which can be further applied. The discharged molten silicon is used to cast ingots to obtain crude silicon.

[0073] (6) The flue gas generated by the electric arc furnace is returned to the suspension roasting furnace for waste heat recovery. The flue gas from the suspension magnetization roasting furnace is discharged after denitrification and desulfurization.

[0074] The final product is a manganese-rich slag containing 45% manganese and crude silicon containing 83% silicon.

Claims

1. A method for processing polycrystalline silicon and monocrystalline silicon waste, characterized in that: Follow these steps: (1) Vacuum filter the waste slurry of monocrystalline silicon and polycrystalline silicon cutting and mix it with 40%-50% of the electrolytic manganese anode mud TMn after pressure filtration to obtain a mixed raw material; the mixed raw material contains 7%-10% water and the ratio of monocrystalline silicon and polycrystalline silicon cutting waste slurry to electrolytic manganese anode mud in the mixed raw material is 1:1; (2) After preheating and dehydrating the mixed raw materials, further heating is carried out to obtain the heated material; the preheating temperature is 300-350℃ and the heating temperature is 850-950℃. (3) The heated material is placed in a reducing atmosphere and subjected to reduction roasting at a temperature of 700℃-780℃ for 1-1.5 hours to obtain the reduced material; (4) Add 1.5%-2% of reducing agent to the reduced material and heat it to a melting state through electrodes. The temperature of the molten pool is 1700℃-1800℃. The slag obtained after heating is high manganese slag. Cast the silicon water discharged after heating into ingots to obtain crude silicon.

2. The method for processing polycrystalline silicon and monocrystalline silicon waste according to claim 1, characterized in that: The reducing atmosphere described in step (3) is CO, H2, or a mixture of both.

3. The method for processing polycrystalline silicon and monocrystalline silicon waste according to claim 1, characterized in that: The reducing agent in step (4) is low-sulfur coal with a fixed carbon content of ≥85% and a particle size of 10-25 mm.

4. The method for processing polycrystalline silicon and monocrystalline silicon waste according to claim 1, characterized in that: The flue gas generated in step (4) is returned to the suspension roasting furnace for waste heat recovery. The flue gas from the suspension magnetization roasting furnace is discharged after denitrification and desulfurization.