CN112456499B - Method for preparing high-purity silicon by using silicon cutting waste - Google Patents
Method for preparing high-purity silicon by using silicon cutting waste Download PDFInfo
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- CN112456499B CN112456499B CN202011458320.3A CN202011458320A CN112456499B CN 112456499 B CN112456499 B CN 112456499B CN 202011458320 A CN202011458320 A CN 202011458320A CN 112456499 B CN112456499 B CN 112456499B
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- Y02E10/546—Polycrystalline silicon PV cells
Abstract
The invention relates to a method for preparing high-purity silicon by using silicon cutting waste, belonging to the technical field of solid waste resource utilization and material preparation. Mixing silicon cutting waste, a slagging agent and fluorine-free chlorine-free slag, carrying out slagging refining in an inert atmosphere, and separating slag from silicon to obtain massive silicon and fluorine-free chlorine-free slag; taking eutectic Al-Si, Ca-Si or Mg-Si alloy as a refining agent, mixing massive silicon with the refining agent, melting to form hypereutectic Al-Si, Ca-Si or Mg-Si melt, and separating and purifying silicon in the hypereutectic Al-Si, Ca-Si or Mg-Si melt by directional solidification, zone melting or crystal growth method to obtain hypermetallurgical grade silicon and eutectic Al-Si, Ca-Si or Mg-Si alloy containing a small amount of impurities; and (3) performing vacuum directional solidification on the super metallurgical grade silicon to remove impurities such as Al, Mg or Ca and the like to obtain high-purity silicon with the purity of more than 99.999 percent. The invention prepares high-purity silicon by recycling silicon cutting waste, and simultaneously, the generated fluorine-free and chlorine-free residue and eutectic Al-Si, Ca-Si or Mg-Si alloy containing a small amount of impurities can be recycled.
Description
Technical Field
The invention relates to a method for preparing high-purity silicon by using silicon cutting waste, belonging to the technical field of solid waste resource utilization and material preparation.
Background
Due to the large exploitation and consumption of traditional energy sources (such as oil, natural gas, coal and the like), the reserves of the traditional energy sources are nearly exhausted, and the energy shortage becomes a main problem which currently restricts the development of economic society of various countries in the world. At present, China has continuously become the largest energy consumption country in the world for many years, and the annual energy consumption accounts for 1/5 of the global total. Therefore, the energy problem faced by China in the future is particularly serious, and the search for new alternative energy is urgent. Solar energy is a clean and good new energy source, is widely distributed and has huge reserves, and is generally considered to have bright prospect in future energy source use. Solar cells are devices that convert solar energy into electrical energy based on the photovoltaic effect.
The installed capacity of the solar cell in the photovoltaic industry of China continuously occupies the first place of the world, and high-purity silicon (99.999%) is a raw material for manufacturing the solar cell and is the basis of the whole photovoltaic industry. The preparation of the high-purity silicon solar cell firstly needs to cut a polycrystalline silicon ingot or a monocrystalline silicon rod into silicon wafers with the thickness of 0.18-0.19mm, the existing crystalline silicon cutting method mainly adopts a linear cutting technology and a mortar cutting technology, and because the thickness of the silicon wafers is approximately equal to the cutting clearance in the silicon ingot, 35% -40% of crystalline silicon enters cutting waste slurry in the cutting process in the form of silicon powder and is lost, so that the great resource waste and the serious environmental pollution are caused, and only 24 million tons of silicon cutting waste materials are generated every year. As a large amount of impurities such as carbon and oxygen elements brought in by cooling liquid are brought in the silicon crystal during cutting, aluminum elements and the like are brought in the silicon ingot when the fixing base is cut, the content of silicon in the silicon cutting waste is 60-90%, and the total amount of the mixed impurities reaches more than 10% and is difficult to remove.
Therefore, how to efficiently recycle the silicon waste from the cutting of crystalline silicon is a problem faced at present. At present, the following main methods for recycling silicon waste comprise phase transfer, electrophoresis and gravity settling, wet acid washing and vacuum carbothermic reduction; the method for preparing high-purity silicon carbide, silicon carbide ceramic, silicon carbide-based composite materials and other silicon-containing materials has great significance in developing more feasible silicon waste recycling treatment schemes.
Disclosure of Invention
The invention provides a method for preparing high-purity silicon by using silicon cutting waste materials, aiming at the problem of battery recovery in the prior art, eutectic Al-Si, Ca-Si or Mg-Si alloy is used as a refining agent to carry out silicon refining to obtain super metallurgical grade silicon, and impurities such as Al, Mg or Ca and the like are removed from the obtained super metallurgical silicon by a vacuum directional solidification method to obtain high-purity silicon (99.999%); not only can recycle industrial solid waste such as silicon cutting waste, but also can obtain high-purity silicon material according with solar grade. Has obvious economic benefit and industrialization prospect.
A method for preparing high-purity silicon by using silicon cutting waste comprises the following specific steps:
(1) mixing silicon cutting waste, a slagging agent and fluorine-free chlorine-free slag, carrying out slagging refining in an inert atmosphere, and separating slag from silicon to obtain massive silicon and fluorine-free chlorine-free slag; the fluorine-free and chlorine-free residue can be used as the fluorine-free and chlorine-free residue in the raw materials for recycling after the components of the fluorine-free and chlorine-free residue are readjusted by adding a slagging agent;
(2) taking eutectic Al-Si, Ca-Si or Mg-Si alloy as a refining agent, mixing the massive silicon in the step (1) with the refining agent, melting to form hypereutectic Al-Si, Ca-Si or Mg-Si melt, and separating and purifying silicon in the hypereutectic Al-Si, Ca-Si or Mg-Si melt by directional solidification, zone melting or crystal growth method to obtain hypermetallurgical silicon and eutectic Al-Si, Ca-Si or Mg-Si alloy containing trace impurities; eutectic Al-Si, Ca-Si or Mg-Si alloy containing trace impurities can be recycled as a refining agent;
(3) performing vacuum directional solidification on the super metallurgical grade silicon obtained in the step (2) to remove impurities such as Al, Mg or Ca and the like to obtain high-purity silicon with the purity of more than 99.999%;
the silicon cutting waste in the step (1) is one or more of diamond wire cutting silicon waste, silicon carbide wire cutting silicon waste and mortar cutting silicon waste; preferably, the silicon cutting waste is diamond wire cutting silicon waste;
the temperature of slagging and refining in the step (1) is not lower than 1773K, and the time is 0.5-10 h;
the slag former in the step (1) is CaO and SiO 2 、MgO、Al 2 O 3 The fluoride-free and chlorine-free slag is oxide slag without chloride, fluoride and sodium elements; preferably, the fluorine-free and chlorine-free slag is CaO-SiO 2 Oxide slag as a main component;
the heating temperature of the directional solidification, zone melting or crystal growth method in the step (2) is not lower than the melting point of the corresponding hypereutectic Al-Si, Ca-Si or Mg-Si alloy; the moving speed of a heater or a sample in the directional solidification or zone melting is 1-10 mu m/s, the crystal face orientation of the seed crystal of the crystal growth method is not limited, and the moving speed of the seed crystal rod of the crystal growth method is 1-5 mm/min;
the vacuum directional solidification temperature in the step (3) is not lower than 1723K, the moving speed is 1-10 mu m/s, and the vacuum degree is less than 10 -3 Pa。
The invention has the beneficial effects that:
(1) the method has obvious removal effect on C, O, Al and other impurities in the silicon cutting waste, and the blocky silicon with high purity is obtained after slagging and refining;
(2) the method can recycle the fluorine-free and chlorine-free residues generated after slagging and refining, and the slagging and refining are continuously carried out on the silicon cutting waste after a proper amount of slagging agent is added into the fluorine-free and chlorine-free residues to readjust the components; the fluoride-free and chlorine-free slag does not contain fluoride, chloride and sodium elements which have influence on the environment, and has good environmental protection effect;
(3) the invention refines the massive silicon by adopting the method of directional solidification, zone melting or crystal growth to obtain the super metallurgical grade silicon, wherein, the refining agent (eutectic Al-Si, Ca-Si or Mg-Si alloy) can be recycled, although the impurities in the silicon enter the refining agent after the silicon is refined, the impurities content in the refining agent is very low, so the eutectic Al-Si, Ca-Si or Mg-Si alloy containing a small amount of impurities can be recycled as the refining agent;
(4) the invention has no waste gas generation, no carbon emission, low cost, environmental protection and high efficiency.
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FIG. 1 is a schematic flow chart of the present invention.
Detailed Description
The present invention will be described in further detail with reference to specific embodiments, but the scope of the present invention is not limited to the description.
Example 1: a method for preparing high purity silicon using silicon cutting scraps (see fig. 1), comprising the steps of:
(1) cutting silicon scraps (the content of Si is 86.9 wt%, wherein the content of C, O, Al impurity is 0.83 wt%, 3.85 wt% and 0.87 wt%, respectively) with diamond wire, slagging agent (CaO) and fluorine-free and chlorine-free slag (34 wt% CaO and 65 wt% SiO) 2 ) Mixing, carrying out slagging refining for 1h in an inert atmosphere at 1773K to remove C, O and Al impurities, and separating slag silicon to obtain bulk silicon with the purity of 99.8 percent and fluorine-free and chlorine-free residues; the fluorine-free and chlorine-free residue can be used as the fluorine-free and chlorine-free residue in the raw materials for recycling after the components of the fluorine-free and chlorine-free residue are readjusted by adding a slagging agent; wherein the usage amount of the slag former CaO accounts for 8.3 wt% of the mass of the fluorine-free and chlorine-free slag, and the proportion of the total slag amount of the slag former and the fluorine-free and chlorine-free slag to the usage amount of the diamond wire-electrode cutting silicon waste material is 1.67: 1; the fluorine-free and chlorine-free residue contained 27.5 wt% CaO and 67.3 wt% SiO 2 And 0.68 wt% Al 2 O 3 ；
(2) Taking eutectic Al-12.6 wt% Si alloy as a refining agent, mixing the massive silicon in the step (1) with the refining agent eutectic Al-12.6 wt% Si alloy, heating and melting to form hypereutectic Al-Si melt, preserving heat for 0.5h under the condition that the melting temperature is 1273K, and separating and purifying silicon in the hypereutectic Al-Si melt by adopting an electromagnetic induction heating directional solidification method to obtain super metallurgical grade silicon with the purity of 99.98% and eutectic Al-Si alloy containing trace (0.2 wt%) impurities; the eutectic Al-Si alloy containing trace (0.2 wt%) impurities can be recycled as a refining agent; wherein the moving speed of the sample in the directional solidification process is 10 mu m/s;
(3) carrying out vacuum directional solidification on the super metallurgical grade silicon (wherein the Al impurity is 150ppmw) with the purity of 99.98% in the step (2) to remove impurities such as Al and the like so as to obtain high-purity silicon with the purity of 99.999%; wherein the temperature of vacuum directional solidification is 1773K, and the vacuum degree is 10 -3 Pa, smelting time is 1h, and the directional moving speed of the sample is 1 mu m/s;
the content of Al, Fe, Ti, Ca and Mg impurities in the high-purity silicon of the embodiment is respectively 8ppmw, 0.3ppmw, 0.1ppmw, 1ppmw and 0.02ppmw through detection.
Example 2: a method for preparing high purity silicon using silicon cutting scraps (see fig. 1), comprising the steps of:
(1) cutting silicon scraps (the content of Si is 86.9 wt%, wherein the content of C, O, Al impurity is 0.83 wt%, 3.85 wt% and 0.87 wt%, respectively) with diamond wire, slagging agent (CaO and Al) 2 O 3 ) And fluorine-free and chlorine-free slag (38 wt% CaO and 61 wt% SiO) 2 ) Mixing, carrying out slagging refining for 1.5h in inert atmosphere at 1873K to remove C, O and Al impurities, and separating slag silicon to obtain bulk silicon with purity of 99.7% and fluorine-free and chlorine-free residue; the fluorine-free and chlorine-free residue can be used as the fluorine-free and chlorine-free residue in the raw materials for recycling after the components of the fluorine-free and chlorine-free residue are readjusted by adding a slagging agent; wherein the slag former CaO and Al 2 O 3 The dosage of the slag forming agent is respectively 3.3 wt% and 1 wt% of the mass of the fluorine-free and chlorine-free slag, and the ratio of the total slag amount of the slag forming agent and the fluorine-free and chlorine-free slag to the dosage of the diamond wire cutting silicon waste material is 1.8: 1; the fluorine-free and chlorine-free residue contained 26.5 wt% CaO and 68.2 wt% SiO 2 And 1.64 wt% Al 2 O 3 ；
(2) Taking eutectic Ca-61.4 wt% Si alloy as a refining agent, mixing the massive silicon in the step (1) with the refining agent eutectic Ca-61.4 wt% Si alloy, heating and melting to form hypereutectic Ca-Si melt, preserving heat for 0.5h under the condition that the melting temperature is 1573K, and separating and purifying silicon in the hypereutectic Ca-Si melt by adopting a zone melting method to obtain the hypermetallurgical-grade silicon with the purity of 99.98% and the eutectic Ca-Si alloy containing trace (0.6 wt%) impurities; the eutectic Ca-Si alloy containing trace (0.6 wt%) impurities can be recycled as a refining agent; wherein the moving speed of the sample in the directional solidification process is 1 mu m/s;
(3) performing vacuum directional solidification on the super metallurgical grade silicon with the purity of 99.99 percent in the step (2) (wherein the Ca impurity is 180ppmw) to remove impurities such as Ca and the like so as to obtain high-purity silicon with the purity of 99.9991 percent; wherein the temperature of vacuum directional solidification is 1873K, and the vacuum degree is 10 -4 Pa, the smelting time is 1.5h, and the directional moving speed of the sample is 10 mu m/s;
the content of Al, Fe, Ti, Ca and Mg impurities in the high-purity silicon of the embodiment is detected to be 0.3ppmw, 0.4ppmw, 0.06ppmw, 8ppmw and 0.05ppmw respectively.
Example 3: a method for preparing high purity silicon using silicon cutting scraps (see fig. 1), comprising the steps of:
(1) cutting silicon scrap (Si content 86.9 wt%, C, O, Al impurity content 0.83 wt%, 3.85 wt% and 0.87 wt%), slagging agent (CaO and MgO) and fluorine-free and chlorine-free slag (34 wt% CaO and 65 wt% SiO) with diamond wire 2 ) Mixing, carrying out slagging refining for 2h in inert atmosphere at 1873K to remove C, O and Al impurities, and separating slag silicon to obtain bulk silicon with purity of 99.6% and fluorine-free and chlorine-free residue; the fluorine-free and chlorine-free residue can be used as the fluorine-free and chlorine-free residue in the raw materials for recycling after the components of the fluorine-free and chlorine-free residue are readjusted by adding a slagging agent; wherein the usage amounts of CaO and MgO of the slagging agent respectively account for 8.3 wt% and 1.2 wt% of the mass of the fluorine-free and chlorine-free slag, and the proportion of the total slag amount of the slagging agent and the fluorine-free and chlorine-free slag to the usage amount of the silicon waste material for diamond wire cutting is 2: 1; the fluorine-free and chlorine-free residue contained 28.4 wt% CaO and 67.3 wt% SiO 2 、0.63wt％Al 2 O 3 And 1.1 wt% MgO;
(2) taking eutectic Mg-60.7 wt% Si alloy as a refining agent, mixing the massive silicon in the step (1) with the refining agent eutectic Mg-60.7 wt% Si alloy, heating and melting to form hypereutectic Mg-Si melt, preserving heat for 1h under the condition that the melting temperature is 1373K, and separating and purifying silicon in the hypereutectic Mg-Si melt by adopting a method of growing monocrystalline silicon by a pulling method to obtain the hypermetallurgical-grade silicon with the purity of 99.99% and the eutectic Mg-Si alloy containing trace (0.4 wt%) impurities; eutectic Mg-Si alloy containing trace (0.4 wt%) impurities can be recycled as a refining agent; wherein the pulling speed of the seed rod is 1 mm/min;
(3) performing vacuum directional solidification on the super metallurgical grade silicon with the purity of 99.99 percent in the step (2) (wherein the Mg impurity is 60ppmw) to remove Mg and other impurities to obtain high-purity silicon with the purity of 99.9993 percent; wherein the temperature of vacuum directional solidification is 1773K, and the vacuum degree is 10 -4 Pa, the smelting time is 1h, and the directional moving speed of the sample is 2 mu m/s;
the content of Al, Fe, Ti, Ca and Mg impurities in the high-purity silicon of the embodiment is detected to be 0.1ppmw, 0.05ppmw, 0.02ppmw, 1.2ppmw and 5ppmw respectively.
While the present invention has been described in detail with reference to the specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.
Claims (5)
1. A method for preparing high-purity silicon by using silicon cutting waste is characterized by comprising the following specific steps:
(1) mixing silicon cutting waste, a slagging agent and fluorine-free chlorine-free slag, carrying out slagging refining in an inert atmosphere, and separating slag from silicon to obtain massive silicon and fluorine-free chlorine-free slag; the slagging agent is CaO or SiO 2 、MgO、Al 2 O 3 One or more of the fluorine-free and chlorine-free slag is oxide slag without chloride, fluoride and sodium elements, and the fluorine-free and chlorine-free slag is CaO-SiO 2 Oxide slag as a main component;
(2) taking eutectic Al-Si, Ca-Si or Mg-Si alloy as a refining agent, mixing the massive silicon in the step (1) with the refining agent, melting to form hypereutectic Al-Si, Ca-Si or Mg-Si melt, and separating and purifying silicon in the hypereutectic Al-Si, Ca-Si or Mg-Si melt by directional solidification, zone melting or crystal growth method to obtain super metallurgical grade silicon and the eutectic Al-Si, Ca-Si or Mg-Si alloy;
(3) and (3) performing vacuum directional solidification on the super metallurgical grade silicon obtained in the step (2) to remove impurities to obtain high-purity silicon.
2. The method for preparing high purity silicon using silicon cutting scraps as set forth in claim 1, wherein: the silicon cutting waste in the step (1) is one or more of diamond wire cutting silicon waste, silicon carbide wire cutting silicon waste and mortar cutting silicon waste.
3. The method for preparing high purity silicon using silicon cutting scraps as set forth in claim 1, wherein: the temperature of slagging and refining in the step (1) is not lower than 1773K, and the time is 0.5-10 h.
4. The method for preparing high purity silicon using silicon cutting scraps as set forth in claim 1, wherein: the moving speed of a heater or a sample in the step (2) of directional solidification or zone melting is 1-10 mu m/s, and the moving speed of a seed rod of a crystal growth method is 1-5 mm/min.
5. The method for preparing high purity silicon using silicon cutting scraps as set forth in claim 1, wherein: the vacuum directional solidification temperature of the step (3) is not lower than 1723K, the moving speed is 1-10 mu m/s, and the vacuum degree< 10 -3 Pa。
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