A method for simultaneous removal and purification of multiple impurities in silicon cutting waste based on barium-based composite slag system

Abstract

This invention relates to a method for the simultaneous removal and purification of multiple impurities in silicon cutting waste based on a barium-based composite slag system, belonging to the field of photovoltaic silicon waste resource utilization and high-purity silicon preparation technology. Addressing the problem of existing technologies' difficulty in simultaneously and efficiently removing the complex array of metallic and non-metallic impurities in silicon cutting waste, this invention mixes pretreated silicon cutting waste with a barium-based slag refining agent (containing Ba and Cl) of a specific composition for high-temperature melt refining. The amount of Ba and Cl added is dynamically adjusted according to the oxygen content of the raw materials. Utilizing the strong slag-forming and impurity-solidifying ability of BaO and the chlorination and volatilization effect of BaCl2, the synergistic removal of multiple impurities such as Al, Fe, Ni, Ti, O, and B is achieved. After refining, slag-silicon separation and directional solidification purification yield high-purity silicon. This invention, through Ba-Cl synergy, enhances the enrichment and separation effect of impurities in the slag phase, achieving a simultaneous impurity removal rate of over 80% and a total impurity content in the product of less than 100 ppm.

Description

Technical Field

[0001] This invention relates to a method for simultaneous removal and purification of multiple impurities in silicon cutting waste based on a barium-based composite slag system, belonging to the technical field of photovoltaic silicon waste resource utilization and high-purity silicon preparation. Background Technology

[0002] In the process of photovoltaic monocrystalline silicon wafer slicing, approximately 30% of the 6N-grade high-purity silicon material is lost during cutting, resulting in silicon cutting waste (commonly known as silicon sludge), with an annual production volume reaching millions of tons. This waste has an extremely complex composition, enriched with various impurities such as Fe and Ni from the cutting line and Al, Ti, and B from auxiliary materials, in addition to the silicon particle matrix. Furthermore, the surface of the silicon particles is coated with a SiO2 oxide layer formed by environmental oxidation, resulting in a total impurity content of 1-5 wt.% for O, Al, Fe, Ni, Ti, and B. Efficiently purifying this waste to a level suitable for photovoltaic applications is crucial for achieving closed-loop utilization of silicon resources, but this presents a significant challenge: simultaneously and deeply removing multiple types of impurities.

[0003] Current high-temperature pyrometallurgical refining technologies are mainly developing along two routes, both of which have significant limitations. One is the oxidation slag refining route, typically using a CaO-SiO2-based slag system. This route is based on the principle of impurity distribution between slag and metal, and has a good removal effect on oxygen-loving impurities (such as Al and B) and the surface SiO2 layer. However, numerous studies have shown that binary and ternary slag systems based on CaO have extremely weak removal capabilities for transition metals such as Fe, Ni, and Ti. Therefore, the efficient removal of Fe, Ni, and Ti through high-temperature refining is a technical bottleneck in the fields of photovoltaic silicon waste resource utilization and high-purity silicon preparation. For example, in the refining experiment using CaO-based slag, the Al removal rate was approximately 85%, but the Fe removal rate was almost 0% (see: Study on recycling Si from silicon diamond-wire saw cutting waste by a slag refining process in industrial scale[J]. Journal of Cleaner Production, 2023, 398, 136557.). In the high-temperature refining of the CaO-Na2CO3 slag system, the Al removal rate was 54.69%, and in the high-temperature refining of the CaO-Na2CO3-Na3AlF6 and CaO-Na2CO3-NaCl slag systems, the Al removal rate was close to 99%. However, these three slag systems had almost no removal effect on Fe, Ni, and Ti (see: Novel reaction media of Na2CO3-CaO for silicon extraction and aluminum removal from diamond wire saw silicon powder by roasting-smelting process[J]. ACS Sustainable Chemistry & Engineering, 2020, 8, 10. 4146-4157; Investigation of Na2CO3-CaO-NaCl (or Na3AlF6) additives for the remanufacturing of silicon from diamond wire saw silicon powder waste[J]. Journal of Cleaner Production, 2021, 286, 125525.).In particular, for boron removal through slag refining, current slag systems rely on extremely high slag-to-silicon ratios. This means that slag agents with a mass far exceeding that of silicon cutting waste need to be added to remove boron. For example, in the Na2O-SiO2 slag refining process for boron removal, the slag-to-silicon ratio is 1 to 3:1 (Reference: Clean enhancing elimination of boron from silicon kerfusing Na2O-SiO2 slag treatment[J]. Journal of Cleaner Production, 2018, 186, 718-725).

[0004] The second approach is the vacuum / chlorine volatilization route, which utilizes the volatility of impurities under high vacuum or chlorine conditions for removal. This route is effective for easily volatile Al under vacuum conditions, but it is almost ineffective for non-volatile impurities (such as B) and oxides (SiO2), and it easily leads to severe silicon volatilization losses and low recovery rates. Studies have shown that the silicon recovery rate of the vacuum refining process is only 68.65%, and the removal rates of Fe, Ni, and B are only 9%, 17%, and 0%, respectively (see reference: Recycling high-puritysilicon from diamond-wire saw kerf slurry waste by vacuum refining process[J]. Journal of Cleaner Production, 2021, 286, 124979).

[0005] This reveals an inherent contradiction in existing technologies: the strong oxidizing slag-forming route struggles to remove transition metals (Fe, Ni, Ti), while the reducing volatilization route cannot effectively remove oxidizing or non-volatile impurities (O, B). Both current technologies are "single-mechanism" refining processes, unable to handle the complex system of multiple types of impurities coexisting in silicon cutting waste. This results in lengthy process flows, low silicon recovery rates, and significant product purity bottlenecks, hindering technological upgrades in the industry.

[0006] While using CaO smelting in conjunction with chlorination can enhance impurity migration, the removal rates of iron and nickel remain difficult to overcome (inventor's paper: Silicon recycling and iron, nickel removal from diamond wiresaw silicon powder waste: Synergistic chlorination with CaO smelting treatment [J]. Minerals Engineering, 2021, 169, 106966). Although the chlorinated molten salt formed by chlorides can improve the removal rate of Fe and remove some Ni, the high solubility of calcium in the silicon melt and the large segregation coefficient in the calcium-based slag system result in high calcium content and low overall purity in the product. Secondly, regarding the chlorination volatilization route, another work by the inventors systematically studied the chlorination refining of silicon cutting waste using BaCl2·2H2O (inventor's paper: Removal of SiO2, Al, and Ni from diamond wire saw silicon powder waste: An investigation of chlorination refining with BaCl2). 2H2O[J]. Journal of Environmental Chemical Engineering, 2024, 12, 114144), the results show that barium has the advantages of low solubility and low segregation coefficient in silicon melt, which can significantly improve the overall purity while efficiently removing Fe and Ni. However, although the single chlorination mechanism can effectively remove some metal impurities, it has low removal efficiency for high SiO2 content in raw materials and is difficult to suppress the simultaneous volatilization loss of silicon, resulting in the inability to achieve both recovery rate and purity.

[0007] Therefore, the development of novel composite refining methods that achieve simultaneous, efficient, and short-process removal of multiple types of impurities has become a pressing technical bottleneck that needs to be overcome in this field. Summary of the Invention

[0008] To address the industry bottlenecks of existing pyrometallurgical purification technologies, such as the disconnect between the "slag-forming" and "volatilization" mechanisms, the limited impurity removal capabilities of conventional slag systems, the tendency to introduce slag-forming elements that reduce product purity, and the inability to simultaneously and efficiently remove multiple impurities from silicon cutting waste, this invention proposes a method for the simultaneous removal and purification of multiple impurities from silicon cutting waste based on a barium-based composite slag system. The method involves mixing pretreated silicon cutting waste with a specific composition of barium-based slag refining agent (containing Ba and Cl) for high-temperature melt refining. The addition amounts of Ba and Cl are dynamically adjusted according to the oxygen content of the raw materials. Utilizing the strong slag-forming and impurity-solidifying capabilities of BaO and the chlorination and volatilization effects of BaCl2, the method achieves the synergistic removal of multiple impurities such as Al, Fe, Ni, Ti, O, and B. Furthermore, this composite slag system reduces the residue of slag-forming elements and enables near-clean slag-forming refining without secondary pollution. After refining, the silicon is separated from the slag and purified by directional solidification to obtain high-purity silicon. By precisely designing composite slag components and optimizing and integrating process parameters, and coupling the dual mechanisms of "enhanced slag formation" and "activated chlorination volatilization", the synergistic deep removal of key impurities such as O (mainly SiO2), Al, Fe, Ni, Ti, and B is achieved within one refining cycle, and the silicon recovery rate is significantly improved.

[0009] A method for simultaneous removal and purification of multiple impurities in silicon cutting waste based on barium-based composite slag system, the specific steps of which are as follows: (1) The silicon cutting waste is crushed, dried and screened to obtain pretreated silicon cutting waste particles; (2) The silicon cutting waste particles pretreated in step (1) are mixed evenly with the barium-based slag refining agent, and then heated to a preset first temperature under a protective gas atmosphere or vacuum environment for roasting treatment. Then, the mixture is heated to a preset second temperature to form a molten system and is melted and refined to obtain a refined melt. The barium-based slag refining agent contains Ba and Cl. The preset first temperature is lower than the melting point temperature of silicon, and the preset second temperature is higher than the melting point temperature of silicon. (3) Let the refined melt from step (2) stand and separate into layers. The refined slag enriched with impurity elements floats to the surface of the silicon melt. Separate the refined slag to obtain high-purity silicon melt. (4) The high-purity silicon melt from step (3) is subjected to directional solidification and purification to obtain a high-purity silicon ingot.

[0010] Preferably, the silicon cutting waste in step (1) contains metallic and non-metallic impurities. The metallic impurities include Al, Fe, Ni and Ti, and the non-metallic impurities include O and B.

[0011] Preferably, the median particle size D of the silicon cutting waste particles pretreated in step (1) is... 50 Less than 1μm.

[0012] Preferably, the barium-based slag refining agent can be a BaO-BaCl2 binary slag refining agent, a BaO-NaCl binary slag refining agent, a BaO-MgCl2 binary slag refining agent, a BaCO3-MgCl2 binary slag refining agent, a BaCO3-NaCl binary slag refining agent, a BaCO3-BaCl2 binary slag refining agent, or a BaCl2·2H2O slag refining agent.

[0013] Preferably, the barium-based slag refining agent forms a chloride molten salt in a high-temperature molten system; based on elemental content, the added mass of Ba is 1.2 to 3.6 times the total oxygen content in the silicon cutting waste, and the added mass of Cl is 3 to 12% of the silicon cutting waste mass; ensuring that sufficient BaO can effectively react with the oxygen in the SiO2 oxide layer on the particle surface to generate a low-melting-point, highly fluid barium silicate (BaO·SiO2) slag system, which not only destroys the impurity diffusion barrier but also provides an ideal reaction medium for subsequent chlorination reactions; at the same time, BaO has a strong ability to fix oxygen-loving impurities such as Al and B; the added or generated molten BaCl2, as a highly efficient chlorination medium, can fully penetrate into the porous or molten slag structure formed by the reaction of BaO, directly contact the trapped metal impurities such as Fe, Ni, and Ti, and undergo chlorination reactions to generate chlorides (such as FeCl2 and NiCl2). The chlorides have high vapor pressure at high temperatures, allowing them to be efficiently volatilized and removed from the silicon melt.

[0014] Preferably, the total mass ratio of the added barium-based slag refining agent to the mass ratio of silicon cutting waste is 0.15~0.36:1.

[0015] Preferably, the protective gas atmosphere is nitrogen or an inert atmosphere, and the vacuum degree of the vacuum environment is not higher than 100 Pa.

[0016] Preferably, the roasting treatment temperature is 873~1687K and the time is 30~60min. Here, the roasting effect during the heating stage ensures that the barium-based slag refining agent fully forms molten salt and fully wets and contacts the metal impurities in the silicon cutting waste, and ionizes the metal impurities through a chlorination reaction.

[0017] Preferably, the melting and refining temperature is 1687~1973K and the time is 0.5~3h.

[0018] Preferably, the alkalinity of the refining slag in step (4) is 1.3 to 3.75. Within this alkalinity range, the refining slag and the melt can be guaranteed to have a good slag-gold interface separation effect, which is conducive to obtaining a higher silicon recovery rate.

[0019] The beneficial effects of this invention are: (1) In view of the problem of low Fe and Ni removal rate in calcium-based slag refining, the present invention utilizes the activating chlorination effect of BaCl2 to significantly improve the removal rate of Fe and Ni; at the same time, BaO has stronger alkalinity than CaO and a stronger affinity for SiO2, ensuring efficient removal of O, Al and B; the comprehensive removal rate of key impurities such as Al, Fe, Ni, Ti and B can reach more than 80%, realizing the simultaneous and efficient removal of multiple impurities. (2) By controlling the alkalinity of refining slag, the present invention optimizes the physicochemical properties of the slag system, reduces the mechanical inclusion and chemical dissolution loss of silicon in the slag; it can be combined with vacuum conditions to promote chloride volatilization, avoid silicon oxidation disproportionation loss, so that the total silicon recovery rate is stable at more than 90%, and greatly improves the silicon recovery rate. (3) The barium-based composite slag system proposed in this invention has low solubility and low segregation coefficient in silicon melt. After high-temperature refining, the residual slag agent elements in silicon are extremely low, there is no secondary pollution, and it can be cleaned and refined, which significantly improves the overall purity of high-purity silicon products.

[0020] (4) For the removal of B by high-temperature pyrometallurgical slag refining of silicon cutting waste, the barium-based composite slag system proposed in this invention has the advantages of low slag-to-silicon ratio and low slag addition. In terms of industrial application, it has the advantages of low production cost and easy promotion.

[0021] (5) The high-purity silicon obtained by the method of the present invention has a total content of metal and non-metal impurities of less than 100 ppm, and can be directly used as photovoltaic silicon raw material to realize high-value recycling of silicon cutting waste. Attached Figure Description

[0022] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0023] 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.

[0024] The silicon cutting waste of this invention is the cutting slurry filter cake (silicon mud) generated during the photovoltaic monocrystalline silicon slicing process. It contains metallic impurities and non-metallic impurities. The metallic impurities include Al, Fe, Ni and Ti, and the non-metallic impurities include O and B.

[0025] Example 1: The impurity content of the silicon cutting waste in this example is 4.81% O, 1200ppmw Al, 480ppmw Ni, and the total silicon content is 93.49%. A method for simultaneous removal and purification of multiple impurities in silicon cutting waste based on barium-based composite slag system, the specific steps of which are as follows: (1) The silicon cutting waste is crushed, dried and screened to obtain a particle size D. 50 Pretreated silicon cutting waste particles with a diameter of 0.88 μm; (2) The pretreated silicon cutting waste particles from step (1) are mixed evenly with the barium-based slag refining agent (BaCl2·2H2O refining agent). The mixture is heated to a preset first temperature of 1173K under a protective gas atmosphere for calcination treatment and held for 30 minutes. Then, the mixture is heated to a preset second temperature of 1923K to form a molten system and is molten and refined to obtain a refined melt. The refining holding time is 3 hours. The barium-based slag refining agent is BaCl2·2H2O. Based on elemental content, the added mass of Ba is 1.86 times the total oxygen content in the silicon cutting waste, and the added mass of Cl is 3.9% of the mass of the silicon cutting waste. The amount of barium-based slag refining agent (BaCl2·2H2O refining agent) added is 16% of the mass of the pretreated silicon cutting waste particles. (3) The refined melt from step (2) is allowed to stand and separate into layers. The refined slag enriched with impurity elements floats to the surface of the silicon melt. The refined slag is separated to obtain high-purity silicon melt. The theoretical binary basicity of BaO and SiO2 in the refined slag is 1.5. The impurity content in the high-purity silicon is Al 32ppmw, Ni 6.2ppmw, and the recovery rate is 34.7%. (4) The high-purity silicon melt in step (3) is purified by vacuum directional solidification. The pull-down rate during the directional solidification process is 10 μm / s, and the vacuum degree is 10~100Pa. After purification is completed and the head and tail parts are cut off, the central casting obtained is the high-purity silicon ingot. In this embodiment, the impurity content of high-purity silicon is 6 ppmw Al and 1.2 ppmw Ni, and the impurity removal rates are 99.5% Al and 98.71% Ni, respectively.

[0026] Example 2: The impurity content of the silicon cutting waste in this example is 4.81% O, 1200 ppmw Al, 480 ppmw Ni, and the total silicon content is 93.49%. A method for simultaneous removal and purification of multiple impurities in silicon cutting waste based on barium-based composite slag system, the specific steps of which are as follows: (1) The silicon cutting waste is crushed, dried and screened to obtain a particle size of D. 50 Pretreated silicon cutting waste particles with a diameter of 0.88 μm; (2) The pretreated silicon cutting waste particles from step (1) are mixed evenly with the barium-based slag refining agent (BaCl2·2H2O refining agent). The mixture is heated to a preset first temperature of 1273K under a protective gas atmosphere for vacuum roasting. The vacuum degree is 10~100Pa and the holding time is 60min. Then, the mixture is heated to a preset second temperature of 1773K to form a molten system and is melted and refined to obtain a refined melt. The refining holding time is 2h. The barium-based slag refining agent is BaCl2·2H2O. Based on elemental content, the added mass of Ba is 2.2 times the total oxygen content in the silicon cutting waste, and the added mass of Cl is 4.6% of the mass of the silicon cutting waste. The added amount of barium-based slag refining agent (BaCl2·2H2O refining agent) is 19% of the mass of the pretreated silicon cutting waste particles. (3) The refined melt from step (2) is allowed to stand and separate into layers. The refined slag enriched with impurity elements floats to the surface of the silicon melt. The refined slag is separated to obtain high-purity silicon melt. The theoretical binary basicity of BaO and SiO2 in the refined slag is 1.7. The impurity content of high-purity silicon is Al 67ppmw and Ni 54ppmw, with a recovery rate of 55.8%. (4) The high-purity silicon melt from step (3) is purified by vacuum directional solidification. The pull-down rate during the directional solidification process is 5 μm / s, and the vacuum degree is 0.1~10 Pa. The center casting obtained after purification and cutting off the head and tail is the high-purity silicon ingot. In this embodiment, the impurity content of high-purity silicon is 14 ppmw Al and 16 ppmw Ni, and the impurity removal rates are 98.83% Al and 96.67% Ni, respectively.

[0027] Example 3: The impurity content of the silicon cutting waste in this example is 4.81% O, 1200 ppmw Al, 480 ppmw Ni, and the total silicon content is 93.49%. A method for simultaneous removal and purification of multiple impurities in silicon cutting waste based on barium-based composite slag system, the specific steps of which are as follows: (1) The silicon cutting waste was crushed, dried and screened to obtain pretreated silicon cutting waste particles with a particle size of D50=0.88 μm; (2) The pretreated silicon cutting waste particles from step (1) are mixed evenly with the barium-based slag refining agent (BaCl2·2H2O refining agent). The mixture is heated to a preset first temperature of 1687K under a protective gas atmosphere for calcination treatment and held for 30 minutes. Then, the mixture is heated to a preset second temperature of 1737K to form a molten system and is molten and refined to obtain a refined melt. The refining holding time is 0.5 hours. The barium-based slag refining agent is BaCl2·2H2O. Based on elemental content, the added mass of Ba is 2.53 times the total oxygen content in the silicon cutting waste, and the added mass of Cl is 5.3% of the mass of the silicon cutting waste. The amount of barium-based slag refining agent (BaCl2·2H2O refining agent) added is 22% of the mass of the pretreated silicon cutting waste particles. (3) The refined melt from step (2) is allowed to stand and separate into layers. The refined slag enriched with impurity elements floats to the surface of the silicon melt. The refined slag is separated to obtain high-purity silicon melt. The theoretical binary basicity of BaO and SiO2 in the refined slag is 2.0. The impurity content of high-purity silicon is Al 29ppmw and Ni 39ppmw, with a recovery rate of 21.50%. (4) The high-purity silicon melt in step (3) is purified by vacuum directional solidification. The pull-down rate during the directional solidification process is 10 μm / s, and the vacuum degree is 50~100Pa. After purification is completed and the head and tail parts are cut off, the central casting obtained is the high-purity silicon ingot. In this embodiment, the impurity content of high-purity silicon is 7.6 ppmw Al and 9.7 ppmw Ni, and the impurity removal rates are 99.37% Al and 97.98% Ni, respectively.

[0028] Example 4: The impurity content of the silicon cutting waste in this example is 3.24% O, 40 ppmw Al, 50 ppmw Ni, and 560 ppmw Fe, with a total silicon content of 95.47%. A method for simultaneous removal and purification of multiple impurities in silicon cutting waste based on barium-based composite slag system, the specific steps of which are as follows: (1) The silicon cutting waste is crushed, dried and screened to obtain a particle size of D. 50 Pretreated silicon cutting waste particles with a diameter of 1.0 μm; (2) The silicon cutting waste particles pretreated in step (1) are mixed evenly with a barium-based slag refining agent (BaCO3-NaCl mixed refining agent). The mixing ratio of silicon cutting waste to refining agent (BaCO3-NaCl mixed refining agent, the mass ratio of BaCO3 to NaCl is 0.56:1) is 1:0.16. The mixture is heated to a preset first temperature of 873K under a protective gas atmosphere for calcination treatment and held for 30 minutes. Then, it is heated to a preset second temperature of 1973K to form a molten system and is molten and refined to obtain a refined melt. The refining holding time is 3 hours. The barium-based slag refining agent is a BaCO3-NaCl mixed refining agent. The mass of Ba added is 1.2 times the total oxygen content in the silicon cutting waste, and the mass of Cl added is 6.1% of the mass of the silicon cutting waste. (3) The refined melt from step (2) is allowed to stand and separate into layers. The refined slag enriched with impurity elements floats to the surface of the silicon melt. The refined slag is separated to obtain high-purity silicon melt. The theoretical binary basicity of BaO and SiO2 in the refined slag is 1.3. The impurity content in the high-purity silicon is Al 29ppmw, Ni 7ppmw, and Fe 27ppmw, with a recovery rate of 76.88%. (4) The high-purity silicon melt in step (3) is purified by vacuum directional solidification. The pull-down rate during the directional solidification process is 5 μm / s, and the vacuum degree is 100~500 Pa. The center casting obtained after purification and cutting off the head and tail is the high-purity silicon ingot. In this embodiment, the purity of the high-purity silicon is 99.998%, and the impurity content is Al 2.6 ppmw, Ni 3.1 ppmw, Fe 9.7 ppmw, and the total content is 15.4 ppmw. The impurity removal rates are Al 93.5%, Ni 93.8%, Fe 98.23%, and the total removal rate is 97.63%.

[0029] Example 5: The impurity content of the silicon cutting waste in this example is O 3.24%, Al 40ppmw, Ni 50ppmw, Fe 560ppmw, and the total silicon content is 95.47%. A method for simultaneous removal and purification of multiple impurities in silicon cutting waste based on barium-based composite slag system, the specific steps of which are as follows: (1) The silicon cutting waste is crushed, dried and screened to obtain a particle size of D. 50 Pretreated silicon cutting waste particles with a diameter of 1.0 μm; (2) The silicon cutting waste particles pretreated in step (1) are mixed evenly with a barium-based slag refining agent (BaCO3-NaCl mixed refining agent). The mixing ratio of silicon cutting waste to refining agent (BaCO3-NaCl mixed refining agent, the mass ratio of BaCO3 to NaCl is 0.625:1) is 1:0.16. The mixture is heated to a preset first temperature of 1273K under a protective gas atmosphere for vacuum roasting. The vacuum degree is 10~100Pa and the holding time is 60min. Then, the mixture is heated to a preset second temperature of 1073K to form a molten system and is melted and refined to obtain a refined melt. The refining holding time is 2h. The barium-based slag refining agent is a BaCO3-NaCl mixed refining agent. The mass of Ba added is 1.3 times the total oxygen content in the silicon cutting waste, and the mass of Cl added is 6.1% of the mass of the silicon cutting waste. (3) The refined melt from step (2) is allowed to stand and separate into layers. The refined slag enriched with impurity elements floats to the surface of the silicon melt. The refined slag is separated to obtain high-purity silicon melt. The theoretical binary basicity of BaO and SiO2 in the refined slag is 1.4. The impurity content in the high-purity silicon is Al 8ppmw, Ni 16ppmw, and Fe 95ppmw, with a recovery rate of 86.63%. (4) The high-purity silicon melt in step (3) is purified by vacuum directional solidification. The pull-down rate during the directional solidification process is 20 μm / s, the vacuum degree is 10~100Pa, and the center casting obtained after purification and cutting off the head and tail is the high-purity silicon ingot. In this embodiment, the purity of the high-purity silicon is 99.997%, and the impurity content is Al 1.1 ppmw, Ni 3.4 ppmw, Fe 16 ppmw, and the total content is 20.5 ppmw. The impurity removal rates are Al 97.25%, Ni 93.2%, Fe 97.12%, and the total removal rate is 96.85%.

[0030] Example 6: The impurity content of the silicon cutting waste in this example is 3.24% O, 40 ppmw Al, 50 ppmw Ni, and 560 ppmw Fe, with a total silicon content of 95.47%. A method for simultaneous removal and purification of multiple impurities in silicon cutting waste based on barium-based composite slag system, the specific steps of which are as follows: (1) The silicon cutting waste is crushed, dried and screened to obtain a particle size of D. 50 Pretreated silicon cutting waste particles with a diameter of 1.0 μm; (2) The silicon cutting waste particles pretreated in step (1) are mixed evenly with a barium-based slag refining agent (BaCO3-NaCl mixed refining agent). The mixing ratio of silicon cutting waste to refining agent (BaCO3-NaCl mixed refining agent, BaCO3 to NaCl mass ratio is 0.738:1) is 1:0.17. The mixture is heated to a preset first temperature of 873K under a protective gas atmosphere for calcination treatment and held for 60 minutes. Then, it is heated to a preset second temperature of 1973K to form a molten system and is molten and refined to obtain a refined melt. The refining holding time is 0.5 hours. The barium-based slag refining agent is a BaCO3-NaCl mixed refining agent. The mass of Ba added is 1.6 times the total oxygen content in the silicon cutting waste, and the mass of Cl added is 6.1% of the mass of the silicon cutting waste. (3) The refined melt from step (2) is allowed to stand and separate into layers. The refined slag enriched with impurity elements floats to the surface of the silicon melt. The refined slag is separated to obtain high-purity silicon melt. The theoretical binary basicity of BaO and SiO2 in the refined slag is 1.7. The impurity content in the high-purity silicon is Al 7 ppmw, Ni 22 ppmw, and Fe 106 ppmw, with a recovery rate of 94.84%. (4) The high-purity silicon melt in step (3) is purified by vacuum directional solidification. The pull-down rate during the directional solidification process is 5 μm / s, and the vacuum degree is 100~500 Pa. The center casting obtained after purification and cutting off the head and tail is the high-purity silicon ingot. In this embodiment, the purity of the high-purity silicon is 99.996%, and the impurity content is Al 1.3 ppmw, Ni 3.7 ppmw, Fe 27 ppmw, and the total content is 32 ppmw. The impurity removal rates are Al 96.75%, Ni 92.6%, Fe 95.18%, and the total removal rate is 95.08%.

[0031] Example 7: The impurity content of the silicon cutting waste in this example is O 3.24%, Al 40ppmw, Ni 50ppmw, Fe 560ppmw, and the total silicon content is 95.47%. A method for simultaneous removal and purification of multiple impurities in silicon cutting waste based on barium-based composite slag system, the specific steps of which are as follows: (1) The silicon cutting waste is crushed, dried and screened to obtain a particle size of D. 50 Pretreated silicon cutting waste particles with a diameter of 1.0 μm; (2) The silicon cutting waste particles pretreated in step (1) are mixed evenly with a barium-based slag refining agent (BaCO3-NaCl mixed refining agent). The mixing ratio of silicon cutting waste to refining agent (BaCO3-NaCl mixed refining agent, BaCO3 to NaCl mass ratio is 0.825:1) is 1:0.19. The mixture is heated to a preset first temperature of 1687K under a protective gas atmosphere for calcination treatment and held for 30 minutes. Then, it is heated to a preset second temperature of 1923K to form a molten system and is molten and refined to obtain a refined melt. The refining holding time is 3 hours. The barium-based slag refining agent is a BaCO3-NaCl mixed refining agent. The mass of Ba added is 1.8 times the total oxygen content in the silicon cutting waste, and the mass of Cl added is 6.1% of the mass of the silicon cutting waste. (3) The refined melt from step (2) is allowed to stand and separate into layers. The refined slag enriched with impurity elements floats to the surface of the silicon melt. The refined slag is separated to obtain high-purity silicon melt. The theoretical binary basicity of BaO and SiO2 in the refined slag is 1.9. The impurity content in the high-purity silicon is Al 9 ppmw, Ni 20 ppmw, and Fe 224 ppmw, with a recovery rate of 65.32%. (4) The high-purity silicon melt from step (3) is purified by vacuum directional solidification. The pull-down rate during the directional solidification process is 5 μm / s, and the vacuum degree is 0.1~10Pa. The center casting obtained after purification and cutting off the head and tail is the high-purity silicon ingot. In this embodiment, the purity of the high-purity silicon is 99.997%, and the impurity content is Al 0.9 ppmw, Ni 3.6 ppmw, Fe 18 ppmw, and the total content is 22.5 ppmw. The impurity removal rates are Al 97.75%, Ni 92.8%, Fe 96.79%, and the total removal rate is 96.54%.

[0032] Example 8: The impurity content of the silicon cutting waste in this example is 3.24% O, 40 ppmw Al, 50 ppmw Ni, and 560 ppmw Fe, with a total silicon content of 95.47%. A method for simultaneous removal and purification of multiple impurities in silicon cutting waste based on barium-based composite slag system, the specific steps of which are as follows: (1) The silicon cutting waste is crushed, dried and screened to obtain a particle size D. 50 Pretreated silicon cutting waste particles with a diameter of 1.0 μm; (2) The silicon cutting waste particles pretreated in step (1) are mixed evenly with a barium-based slag refining agent (BaCO3-NaCl mixed refining agent). The mixing ratio of silicon cutting waste to refining agent (BaCO3-NaCl mixed refining agent, the mass ratio of BaCO3 to NaCl is 1.48:1) is 1:0.12. The mixture is heated to a preset first temperature of 1473K under a protective gas atmosphere for vacuum roasting. The vacuum degree is 10~100Pa and the holding time is 60min. Then, the mixture is heated to a preset second temperature of 1787K to form a molten system and is melted and refined to obtain a refined melt. The refining holding time is 3h. The barium-based slag refining agent is a BaCO3-NaCl mixed refining agent. The mass of Ba added is 1.6 times the total oxygen content in the silicon cutting waste, and the mass of Cl added is 3% of the mass of the silicon cutting waste. (3) The refined melt from step (2) is allowed to stand and separate into layers. The refined slag enriched with impurity elements floats to the surface of the silicon melt. The refined slag is separated to obtain high-purity silicon melt. The theoretical binary basicity of BaO and SiO2 in the refined slag is 1.7. The impurity content in the high-purity silicon is Al 11 ppmw, Ni 67 ppmw, and Fe 288 ppmw, with a recovery rate of 51.62%. (4) The high-purity silicon melt in step (3) is purified by vacuum directional solidification. The pull-down rate during the directional solidification process is 5 μm / s, and the vacuum degree is 100~500Pa. After purification is completed and the head and tail parts are cut off, the central casting obtained is the high-purity silicon ingot. In this embodiment, the purity of the high-purity silicon is 99.997%, and the impurity content is Al 2.9 ppmw, Ni 8 ppmw, Fe 11 ppmw, and the total content is 21.9 ppmw. The impurity removal rates are Al 92.75%, Ni 84%, Fe 98.01%, and the total removal rate is 96.63%.

[0033] Example 9: The impurity content of the silicon cutting waste in this example is O 3.24%, Al 40ppmw, Ni 50ppmw, Fe 560ppmw, and the total silicon content is 95.47%. A method for simultaneous removal and purification of multiple impurities in silicon cutting waste based on barium-based composite slag system, the specific steps of which are as follows: (1) The silicon cutting waste is crushed, dried and screened to obtain a particle size D. 50 Pretreated silicon cutting waste particles with a diameter of 1.0 μm; (2) The silicon cutting waste particles pretreated in step (1) are mixed evenly with a barium-based slag refining agent (BaCO3-NaCl mixed refining agent), wherein the mixing ratio of silicon cutting waste and refining agent (BaCO3-NaCl mixed refining agent, the mass ratio of BaCO3 to NaCl is 0.49:1) is 1:0.22. The mixture is heated to a preset first temperature of 1023K under a protective gas atmosphere for calcination treatment and held for 60 minutes. Then, the mixture is heated to a preset second temperature of 1973K to form a molten system and is molten and refined to obtain a refined melt. The refining holding time is 0.5 hours. The barium-based slag refining agent is a BaCO3-NaCl mixed refining agent. In terms of elemental content, the added mass of Ba is 1.6 times the total oxygen content in the silicon cutting waste, and the added mass of Cl is 9% of the mass of the silicon cutting waste. (3) The refined melt from step (2) is allowed to stand and separate into layers. The refined slag enriched with impurity elements floats to the surface of the silicon melt. The refined slag is separated to obtain high-purity silicon melt. The theoretical binary basicity of BaO and SiO2 in the refined slag is 1.7. The impurity content in the high-purity silicon is Al 6 ppmw, Ni 34 ppmw, and Fe 181 ppmw, with a recovery rate of 54.57%. (4) The high-purity silicon melt from step (3) is purified by vacuum directional solidification. The pull-down rate during the directional solidification process is 5 μm / s, and the vacuum degree is 0.1~10 Pa. The center casting obtained after purification and cutting off the head and tail is the high-purity silicon ingot. In this embodiment, the purity of the high-purity silicon is 99.997%, with impurity contents of 0.8 Al ppmw, 8 Ni ppmw, 14 Fe ppmw, and a total content of 22.8 ppmw. The impurity removal rates are 98% for Al, 84% for Ni, 97.5% for Fe, and a total removal rate of 96.49%.

[0034] Example 10: The impurity content of the silicon cutting waste in this example is O 3.24%, Al 40ppmw, Ni 50ppmw, Fe 560ppmw, and the total silicon content is 95.47%. A method for simultaneous removal and purification of multiple impurities in silicon cutting waste based on barium-based composite slag system, the specific steps of which are as follows: (1) The silicon cutting waste is crushed, dried and screened to obtain pretreated silicon cutting waste particles with a particle size of D50=1.0 μm; (2) The silicon cutting waste particles pretreated in step (1) are mixed evenly with a barium-based slag refining agent (BaCO3-NaCl mixed refining agent). The mixing ratio of silicon cutting waste to refining agent (BaCO3-NaCl mixed refining agent, the mass ratio of BaCO3 to NaCl is 0.37:1) is 1:0.27. The mixture is heated to a preset first temperature of 1587K under a protective gas atmosphere for calcination treatment and held for 60 minutes. Then, it is heated to a preset second temperature of 1787K to form a molten system and is molten and refined to obtain a refined melt. The refining holding time is 3 hours. The barium-based slag refining agent is a BaCO3-NaCl mixed refining agent. The mass of Ba added is 1.6 times the total oxygen content in the silicon cutting waste, and the mass of Cl added is 12% of the mass of the silicon cutting waste. (3) The refined melt from step (2) is allowed to stand and separate into layers. The refined slag enriched with impurity elements floats to the surface of the silicon melt. The refined slag is separated to obtain high-purity silicon melt. The theoretical binary basicity of BaO and SiO2 in the refined slag is 1.7. The impurity content in the high-purity silicon is Al 5 ppmw, Ni 29 ppmw, and Fe 145 ppmw, with a recovery rate of 67.57%. (4) The high-purity silicon melt in step (3) is purified by vacuum directional solidification. The pull-down rate during the directional solidification process is 15 μm / s, and the vacuum degree is 10~100Pa. The center casting obtained after purification and cutting off the head and tail is the high-purity silicon ingot. In this embodiment, the purity of the high-purity silicon is 99.998%, and the impurity content is Al 0.9 ppmw, Ni 7.4 ppmw, Fe 9.6 ppmw, and the total content is 17.9 ppmw. The impurity removal rates are Al 97.75%, Ni 85.20%, Fe 98.23%, and the total removal rate is 97.25%.

[0035] Example 11: The impurity content of the silicon cutting waste in this example is O 3.24%, Fe 560 ppmw, Ti 72 ppmw, Ni 50 ppmw, Al 40 ppmw, B 30 ppmw, and the total silicon content is 95.47%. A method for simultaneous removal and purification of multiple impurities in silicon cutting waste based on barium-based composite slag system, the specific steps of which are as follows: (1) The silicon cutting waste is crushed, dried and screened to obtain a particle size D. 50 Pretreated silicon cutting waste particles with a diameter of 1.0 μm; (2) The silicon cutting waste particles pretreated in step (1) are mixed evenly with a barium-based slag refining agent (BaO-BaCl2 mixed refining agent). The mixing ratio of silicon cutting waste to refining agent (BaO-BaCl2 mixed refining agent, with a mass ratio of BaO to BaCl2 of 0.65:1) is 1:0.33. The mixture is heated to a preset first temperature of 1587K under a protective gas atmosphere for vacuum roasting. The vacuum degree is 50~100Pa and the holding time is 60min. Then, the mixture is heated to a preset second temperature of 1923K to form a molten system and is melt-refined to obtain a refined melt. The refining holding time is 3h. The barium-based slag refining agent is a BaO-BaCl2 mixed refining agent. The mass of Ba added is 3.6 times the total oxygen content in the silicon cutting waste, and the mass of Cl added is 6.8% of the mass of the silicon cutting waste. (3) The refined melt from step (2) is allowed to stand and separate into layers. The refined slag enriched with impurity elements floats to the surface of the silicon melt. The refined slag is separated to obtain high-purity silicon melt. The theoretical binary basicity of BaO and SiO2 in the refined slag is 3.75. The impurity content in the high-purity silicon is Al 14 ppmw, Ti 10 ppmw, Ni 5 ppmw, Fe 23 ppmw, and B 5 ppmw, with a recovery rate of 95.25%. (4) The high-purity silicon melt from step (3) is purified by vacuum directional solidification. The pull-down rate during the directional solidification process is 5 μm / s, and the vacuum degree is 0.1~10 Pa. The center casting obtained after purification and cutting off the head and tail is the high-purity silicon ingot. In this embodiment, the high-purity silicon has a purity of 99.998%, with impurity contents of Al 0.7 ppmw, Ni 2.1 ppmw, Fe 3.8 ppmw, Ti 3.2 ppmw, B 3.4 ppmw, and a total content of 13.2 ppmw. The impurity removal rates are Al 98.25%, Ni 95.8%, Fe 99.32%, Ti 95.56%, B 88.67%, and the total removal rate is 98.24%.

[0036] Example 12: The impurity content of the silicon cutting waste in this example is O 3.24%, Fe 560 ppmw, Ti 72 ppmw, Ni 50 ppmw, Al 40 ppmw, B 30 ppmw, and the total silicon content is 95.47%. A method for simultaneous removal and purification of multiple impurities in silicon cutting waste based on barium-based composite slag system, the specific steps of which are as follows: (1) The silicon cutting waste is crushed, dried and screened to obtain a particle size D. 50 Pretreated silicon cutting waste particles with a diameter of 1.0 μm; (2) The silicon cutting waste particles pretreated in step (1) are mixed evenly with a barium-based slag refining agent (BaO-BaCl2 mixed refining agent), wherein the mixing ratio of silicon cutting waste to refining agent (BaO-BaCl2 mixed refining agent, the mass ratio of BaO to BaCl2 is 0.17:1) is 1:0.29. The mixture is heated to a preset first temperature of 1473K under a protective gas atmosphere for calcination treatment and held for 30 minutes. Then, it is heated to a preset second temperature of 1973K to form a molten system and is molten and refined to obtain a refined melt. The refining holding time is 0.5 hours. The barium-based slag refining agent is a BaO-BaCl2 mixed refining agent. In terms of elemental content, the added mass of Ba is 1.2 times the total oxygen content in the silicon cutting waste, and the added mass of Cl is 8.5% of the mass of the silicon cutting waste. (3) The refined melt from step (2) is allowed to stand and separate into layers. The refined slag enriched with impurity elements floats to the surface of the silicon melt. The refined slag is separated to obtain high-purity silicon melt. The theoretical binary basicity of BaO and SiO2 in the refined slag is 1.3. The impurity content in the high-purity silicon is Al 27 ppmw, Ti 8 ppmw, Ni 13 ppmw, Fe 46 ppmw, and B 2 ppmw, with a recovery rate of 87.43%. (4) The high-purity silicon melt from step (3) is purified by vacuum directional solidification. The pull-down rate during the directional solidification process is 10 μm / s, and the vacuum degree is 0.1~10 Pa. The center casting obtained after purification and cutting off the head and tail is the high-purity silicon ingot. In this embodiment, the purity of the high-purity silicon is 99.997%, and the impurity content is Al 3.4 ppmw, Ni 1.7 ppmw, Fe 14 ppmw, Ti 2.7 ppmw, B 0.8 ppmw, with a total content of 22.6 ppmw. The impurity removal rates are Al 91.5%, Ni 96.6%, Fe 97.5%, Ti 96.25%, B 97.3%, and the total removal rate is 96.99%.

[0037] Example 13: The impurity content of the silicon cutting waste in this example is O 3.24%, Fe 560 ppmw, Ti 72 ppmw, Ni 50 ppmw, Al 40 ppmw, B 30 ppmw, and the total silicon content is 95.47%. A method for simultaneous removal and purification of multiple impurities in silicon cutting waste based on barium-based composite slag system, the specific steps of which are as follows: (1) The silicon cutting waste is crushed, dried and screened to obtain a particle size of D. 50 Pretreated silicon cutting waste particles with a diameter of 1.0 μm; (2) The silicon cutting waste particles pretreated in step (1) are mixed evenly with a barium-based slag refining agent (BaO-BaCl2 mixed refining agent). The mixing ratio of silicon cutting waste to refining agent (BaO-BaCl2 mixed refining agent, with a mass ratio of BaO to BaCl2 of 0.48:1) is 1:0.26. The mixture is heated to a preset first temperature of 973K under a protective gas atmosphere for calcination treatment and held for 60 minutes. Then, it is heated to a preset second temperature of 1973K to form a molten system and is molten and refined to obtain a refined melt. The refining holding time is 3 hours. The barium-based slag refining agent is a BaO-BaCl2 mixed refining agent. The mass of Ba added is 2.4 times the total oxygen content in the silicon cutting waste, and the mass of Cl added is 6.1% of the mass of the silicon cutting waste. (3) The refined melt from step (2) is allowed to stand and separate into layers. The refined slag enriched with impurity elements floats to the surface of the silicon melt. The refined slag is separated to obtain high-purity silicon melt. The theoretical binary basicity of BaO and SiO2 in the refined slag is 2.5. The impurity content in the high-purity silicon is Al 8 ppmw, Ti 14 ppmw, Ni 7 ppmw, Fe 81 ppmw, and B 3 ppmw, with a recovery rate of 91.23%. (4) The high-purity silicon melt from step (3) is purified by vacuum directional solidification. The pull-down rate during the directional solidification process is 20 μm / s, and the vacuum degree is 10~100 Pa. The center casting obtained after purification and cutting off the head and tail is the high-purity silicon ingot. In this embodiment, the high-purity silicon has a purity of 99.997%, with impurity contents of Al 1.9 ppmw, Ni 2.1 ppmw, Fe 17 ppmw, Ti 4.4 ppmw, B 1.3 ppmw, and a total content of 26.7 ppmw. The impurity removal rates are Al 95.25%, Ni 95.8%, Fe 96.97%, Ti 93.89%, B 95.67%, and the total removal rate is 96.45%.

[0038] Example 14: The impurity content of the silicon cutting waste in this example is O 3.35%, Fe 450 ppmw, Ti 77 ppmw, Ni 35 ppmw, Al 560 ppmw, B 17 ppmw, and the total silicon content is 96.23%. A method for simultaneous removal and purification of multiple impurities in silicon cutting waste based on barium-based composite slag system, the specific steps of which are as follows: (1) The silicon cutting waste is crushed, dried and screened to obtain a particle size of D. 50 Pretreated silicon cutting waste particles with a diameter of 0.72 μm; (2) The silicon cutting waste particles pretreated in step (1) are mixed evenly with a barium-based slag refining agent (BaO-BaCl2 mixed refining agent). The mixing ratio of silicon cutting waste to refining agent (BaO-BaCl2 mixed refining agent, with a mass ratio of BaO to BaCl2 of 0.67:1) is 1:0.33. The mixture is heated to a preset first temperature of 1273K under a protective gas atmosphere for calcination treatment and held for 60 minutes. Then, it is heated to a preset second temperature of 1923K to form a molten system and is molten and refined to obtain a refined melt. The refining holding time is 3 hours. The barium-based slag refining agent is a BaO-BaCl2 mixed refining agent. The mass of Ba added is 3.6 times the total oxygen content in the silicon cutting waste, and the mass of Cl added is 6.8% of the mass of the silicon cutting waste. (3) The refined melt from step (2) is allowed to stand and separate into layers. The refined slag enriched with impurity elements floats to the surface of the silicon melt. The refined slag is separated to obtain high-purity silicon melt. The theoretical binary basicity of BaO and SiO2 in the refined slag is 2.4. The impurity content in the high-purity silicon is Al 10 ppmw, Ti 14 ppmw, Ni 5 ppmw, Fe 71 ppmw, and B 4 ppmw, with a recovery rate of 93.26%. (4) The high-purity silicon melt from step (3) is purified by vacuum directional solidification. The pull-down rate during the directional solidification process is 10 μm / s, and the vacuum degree is 0.1~10Pa. The center casting obtained after purification and cutting off the head and tail is the high-purity silicon ingot. In this embodiment, the purity of the high-purity silicon is 99.998%, and the impurity content is Al 1.4 ppmw, Ni 2.8 ppmw, Fe 9 ppmw, Ti 2.7 ppmw, B 1.8 ppmw, with a total content of 17.6 ppmw. The impurity removal rates are Al 96.5%, Ni 94.4%, Fe 98.39%, Ti 96.25%, B 94%, and the total removal rate is 97.66%.

[0039] Example 15: The impurity content of the silicon cutting waste in this example is O 3.90%, Fe 1211 ppmw, Ti 210 ppmw, Ni 35 ppmw, Al 97 ppmw, B 35 ppmw, and the total silicon content is 95.57%. A method for simultaneous removal and purification of multiple impurities in silicon cutting waste based on barium-based composite slag system, the specific steps of which are as follows: (1) The silicon cutting waste is crushed, dried and screened to obtain a particle size of D. 50 Pretreated silicon cutting waste particles with a diameter of 0.78 μm; (2) The silicon cutting waste particles pretreated in step (1) are mixed evenly with a barium-based slag refining agent (BaO-BaCl2 mixed refining agent). The mixing ratio of silicon cutting waste to refining agent (BaO-BaCl2 mixed refining agent, with a mass ratio of BaO to BaCl2 of 0.78:1) is 1:0.36. The mixture is heated to a preset first temperature of 1273K under a protective gas atmosphere for vacuum roasting. The vacuum degree is 10~100Pa and the holding time is 60min. Then, the mixture is heated to a preset second temperature of 1923K to form a molten system and is melt-refined to obtain a refined melt. The refining holding time is 3h. The barium-based slag refining agent is a BaO-BaCl2 mixed refining agent. The mass of Ba added is 3.6 times the total oxygen content in the silicon cutting waste, and the mass of Cl added is 6.8% of the mass of the silicon cutting waste. (3) The refined melt from step (2) is allowed to stand and separate into layers. The refined slag enriched with impurity elements floats to the surface of the silicon melt. The refined slag is separated to obtain high-purity silicon melt. The theoretical binary basicity of BaO and SiO2 in the refined slag is 2.1. The impurity content in the high-purity silicon is Al 10 ppmw, Ti 12 ppmw, Ni 5 ppmw, Fe 64 ppmw, and B 3 ppmw, with a recovery rate of 92.18%. (4) The high-purity silicon melt from step (3) is purified by vacuum directional solidification. The pull-down rate during the directional solidification process is 5 μm / s, and the vacuum degree is 0.1~10Pa. The center casting obtained after purification and cutting off the head and tail is the high-purity silicon ingot. In this embodiment, the high-purity silicon has a purity of 99.998%, with impurity contents of 1.4 Al ppmw, Ni 0.9 ppmw, Fe 11 ppmw, Ti 3.8 ppmw, B 1.1 ppmw, and a total content of 18.2 ppmw. The impurity removal rates are 96.5% for Al, 98.2% for Ni, 98% for Fe, 94.72% for Ti, 96.33% for B, and a total removal rate of 97.58%.

[0040] Example 16: The impurity content of the silicon cutting waste in this example is O 3.90%, Fe 1211 ppmw, Ti 210 ppmw, Ni 35 ppmw, Al 97 ppmw, B 35 ppmw, and the total silicon content is 95.57%. A method for simultaneous removal and purification of multiple impurities in silicon cutting waste based on barium-based composite slag system, the specific steps of which are as follows: (1) The silicon cutting waste is crushed, dried and screened to obtain a particle size D. 50 Pretreated silicon cutting waste particles with a diameter of 0.78 μm; (2) The silicon cutting waste particles pretreated in step (1) are mixed evenly with a barium-based slag refining agent (BaO-MgCl2 mixed refining agent). The mixing ratio of silicon cutting waste to refining agent (BaO-MgCl2 mixed refining agent, with a mass ratio of BaO to MgCl2 of 1.3:1) is 1:0.36. The mixture is heated to a preset first temperature of 1273K under a protective gas atmosphere for vacuum roasting. The vacuum degree is 10~100Pa and the holding time is 60min. Then, the mixture is heated to a preset second temperature of 1923K to form a molten system and is melt-refined to obtain a refined melt. The refining holding time is 3h. The barium-based slag refining agent is a BaO-MgCl2 mixed refining agent. The mass of Ba added is 2.98 times the total oxygen content in the silicon cutting waste, and the mass of Cl added is 7.5% of the mass of the silicon cutting waste. (3) The refined melt from step (2) is allowed to stand and separate into layers. The refined slag enriched with impurity elements floats to the surface of the silicon melt. The refined slag is separated to obtain high-purity silicon melt. The theoretical binary basicity of BaO and SiO2 in the refined slag is 3.2. The impurity content in the high-purity silicon is Al 17 ppmw, Ti 24 ppmw, Ni 7.8 ppmw, Fe 71 ppmw, and B 4 ppmw, with a recovery rate of 87.46%. (4) The high-purity silicon melt from step (3) is purified by vacuum directional solidification. The pull-down rate during the directional solidification process is 10 μm / s, and the vacuum degree is 0.1~10Pa. The center casting obtained after purification and cutting off the head and tail is the high-purity silicon ingot. In this embodiment, the high-purity silicon has a purity of 99.996%, with impurity contents of 3.2 Al ppmw, Ni 2.6 ppmw, Fe 23 ppmw, Ti 7.6 ppmw, B 2.3 ppmw, and a total content of 38.7 ppmw. The impurity removal rates are 92% for Al, 94.8% for Ni, 95.6% for Fe, 89.44% for Ti, 92.33% for B, and a total removal rate of 94.85%.

[0041] 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 simultaneous removal and purification of multiple impurities in silicon cutting waste based on a barium-based composite slag system, characterized in that, The specific steps are as follows: (1) The silicon cutting waste is crushed, dried and screened to obtain pretreated silicon cutting waste particles; (2) The silicon cutting waste particles pretreated in step (1) are mixed evenly with the barium-based slag refining agent, and then heated to a preset first temperature under a protective gas atmosphere or vacuum environment for roasting treatment. Then, the mixture is heated to a preset second temperature to form a molten system and is melted and refined to obtain a refined melt. The barium-based slag refining agent contains Ba and Cl. The preset first temperature is lower than the melting point temperature of silicon, and the preset second temperature is higher than the melting point temperature of silicon. (3) Let the refined melt from step (2) stand and separate into layers. The refined slag enriched with impurity elements floats to the surface of the silicon melt. Separate the refined slag to obtain high-purity silicon melt. (4) The high-purity silicon melt from step (3) is subjected to directional solidification and purification to obtain a high-purity silicon ingot.

2. The method for simultaneous removal and purification of multiple impurities in silicon cutting waste based on barium-based composite slag system according to claim 1, characterized in that: Step (1) Silicon cutting waste contains metallic and non-metallic impurities. The metallic impurities include Al, Fe, Ni and Ti, and the non-metallic impurities include O and B.

3. The method for simultaneous removal and purification of multiple impurities in silicon cutting waste based on barium-based composite slag system according to claim 1, characterized in that: Step (1) The median particle size D of the pretreated silicon cuttings waste particles 50 less than 1 pm.

4. The method for simultaneous removal and purification of multiple impurities in silicon cutting waste based on barium-based composite slag system according to claim 1, characterized in that: Step (2) Barium-based slag refining agent forms chloride molten salt in high-temperature molten system; in terms of elemental content, the added mass of Ba is 1.2 to 3.6 times the total oxygen content in silicon cutting waste, and the added mass of Cl is 3 to 12% of the mass of silicon cutting waste.

5. The method for simultaneous removal and purification of multiple impurities in silicon cutting waste based on barium-based composite slag system according to claim 1, characterized in that: In step (2), the total mass of the added barium-based slag refining agent is 0.15~0.36:1 in mass ratio to the silicon cutting waste.

6. The method for simultaneous removal and purification of multiple impurities in silicon cutting waste based on barium-based composite slag system according to claim 1, characterized in that: The protective gas atmosphere is nitrogen or an inert atmosphere, and the vacuum level of the vacuum environment is not higher than 100 Pa.

7. The method for simultaneous removal and purification of multiple impurities in silicon cutting waste based on barium-based composite slag system according to claim 1, characterized in that: Step (2) The roasting temperature is 873~1687K and the time is 30~60min.

8. The method for simultaneous removal and purification of multiple impurities in silicon cutting waste based on barium-based composite slag system according to claim 1, characterized in that: Step (2) The melting and refining temperature is 1687~1973K and the time is 0.5~3h.

9. The method for simultaneous removal and purification of multiple impurities in silicon cutting waste based on barium-based composite slag system according to claim 1, characterized in that: Step (2) The basicity of the refining residue is 1.3~3.75.

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