A method for deeply removing Fe and Ni impurities in silicon cutting waste based on chlorinated molten salt primary cell effect

Abstract

The present application relates to a kind of Fe, Ni impurity deep removal method in silicon cutting waste based on chlorinated molten salt primary cell effect, belong to silicon-based secondary resources high-value utilization technical field.The Fe, Ni metal particles dispersed in silicon cutting waste are contacted with chlorinated molten salt under high-temperature molten state, and micro area primary cell is spontaneously formed due to the difference of chloride ion concentration gradient;In anode area, Fe, Ni atom loses electron and is converted into ion, and Cl ‑ Low boiling point FeCl2, NiCl2 are formed by combination to be volatilized and removed in gaseous form, and the deep separation of Fe, Ni and silicon matrix is realized;In cathode area, dissolved oxygen atom and non-bridge oxygen dissociated from SiO2 in slag obtain electron and generate O 2‑ O 2‑ With Mg 2+ Or Ba 2+ MgO or BaO is deposited and precipitated by combination.This method utilizes the spontaneous electrochemical primary cell effect between impurity metal and molten salt in high-temperature chloride molten salt system, and the efficient separation and removal of Fe, Ni are realized by regulating temperature gradient, chloride salt component and atmosphere pressure, and the dependence on additional power supply and traditional oxidation slagging is got rid of.

Description

Technical Field

[0001] This invention relates to a method for deep removal of Fe and Ni impurities from silicon cutting waste based on the galvanic cell effect of molten salt chloride, belonging to the field of high-value utilization technology of silicon-based secondary resources. Background Technology

[0002] During the cutting process of photovoltaic monocrystalline silicon wafers, approximately 30-40% of the high-purity silicon enters the silicon cutting waste in the form of ultrafine silicon powder. Silicon cutting waste is an important secondary silicon resource, and metallic impurities such as Fe, Ni, and Al, as well as the surface SiO2 oxide layer, are the main targets for removal during its recycling and purification process.

[0003] Currently, the mainstream methods for recovering high-purity silicon from silicon cutting waste include wet acid leaching, vacuum melting, and slag refining. While wet acid leaching can effectively remove most metallic impurities, it is difficult to form silicon ingots. Vacuum melting can remove some volatile impurities, but its removal efficiency for Fe and Ni is extremely low. Slag refining is currently the pyrometallurgical route closest to industrialization. By adding slag-forming agents such as CaO and Na2CO3 to react with SiO2 to form a silicate slag phase, and simultaneously oxidizing oxygen-loving impurities such as Al into the slag, 3-4N grade industrial silicon can be obtained.

[0004] However, slag refining faces insurmountable technical bottlenecks in handling Fe and Ni impurities: the standard Gibbs free energy of Fe and Ni oxidation is much higher than that of Si, and their affinity for oxygen is much lower than that of Si and Al. In high-temperature melts, they preferentially dissolve in the silicon melt in a metallic state rather than entering the slag phase. Existing research confirms that CaO-SiO2 slag refining achieves a Fe removal rate of less than 30% and almost no removal effect on Ni. Even with laser-assisted vacuum melting or non-transfer arc-assisted vacuum melting, the Fe removal rate only reaches 35%–41%, and Ni removal remains very limited. This technical bottleneck of "difficulty in efficiently removing Fe and Ni" from silicon cutting waste severely restricts the industrialization process of recycling and purifying silicon cutting waste to produce high-purity silicon. Summary of the Invention

[0005] To address the technical shortcomings of existing refining processes due to the difficulty or low efficiency in removing Fe and Ni, this invention proposes a method for deep removal of Fe and Ni impurities from silicon cutting waste based on the galvanic cell effect of molten chloride salt. This method utilizes the self-generating chemical galvanic cell effect between the impurity metals and the molten salt in a high-temperature chloride molten salt system, eliminating reliance on external power sources and traditional oxidation slag formation. In a high-temperature molten state, Fe and Ni metal particles dispersed in the silicon cutting waste are brought into contact with molten chloride salt, spontaneously forming micro-cells due to the difference in chloride ion concentration gradient. In the anodic region, Fe and Ni atoms lose electrons and transform into ions, which then react with Cl... -The low-boiling-point FeCl2 and NiCl2 are combined and volatilized in gaseous form to remove them, thereby achieving deep separation of Fe and Ni from the silicon matrix; in the cathode region, dissolved oxygen atoms and non-bridged oxygen atoms dissociated from SiO2 in the slag gain electrons to generate O. 2- O 2- With Mg 2+ Or Ba 2+ Combined with the formation of MgO or BaO deposition. By controlling the temperature gradient, chloride salt composition and atmosphere pressure, efficient staged removal of Fe and Ni is achieved, with Fe removal rate ≥53%, and up to 90% or more, Ni removal rate ≥70%, and silicon recovery rate ≥70%.

[0006] A method for deep removal of Fe and Ni impurities from silicon cutting waste based on the galvanic cell effect of molten salt chloride, the specific steps of which are as follows: (1) Silicon cutting waste containing Fe and Ni impurities is mixed evenly with chloride to obtain a mixture, wherein the chloride is composed of one or two of NaCl and BaCl2 and MgCl2; (2) The mixture is placed in a vacuum or inert atmosphere and heated to 700-900℃ at a heating rate of 5-10℃ / min and held for 30-60min. Then, it is heated to 1200-1400℃ at a heating rate of 3-8℃ / min and held for 30-60min. Finally, it is heated to 1450-1700℃ at a heating rate of 2-5℃ / min to form a two-phase system of molten chloride salt and silicon melt. The Fe and Ni metal particles dispersed in the system spontaneously form a micro-cell with the molten chloride salt having a chloride ion concentration gradient. In the micro-cell, the oxidation reaction of Fe and Ni occurs in the anode region to generate Fe. 2+ and Ni 2+ It then reacts with Cl in the molten salt of chloride. - The combination forms low-boiling-point FeCl2 and NiCl2, which escape from the molten chloride system in gaseous form; in the cathode region, a reduction reaction occurs between dissolved oxygen and non-bridging oxygen dissociated from SiO2 in the slag to generate O. 2- O 2- With Mg in molten salt of chloride 2+ Or Ba 2+ The combination forms MgO or BaO deposits; the molten chloride salt acts as an electrolyte to conduct ions, providing the Cl required for chlorination volatilization. - And maintain the charge balance throughout the electrochemical process; (3) Under vacuum or inert atmosphere, the molten chloride salt-silicon melt two-phase system is kept at 1450~1700℃ for 1~3h to promote the agglomeration and sedimentation separation of molten silicon liquid droplets, and the low boiling point FeCl2 and NiCl2 are fully released. After cooling to room temperature, high-purity silicon ingots are obtained.

[0007] The Fe content in the silicon cutting waste in step (1) is 200~2000ppmw, the Ni content is 30~200ppmw, and the SiO2 content is 2~6wt%.

[0008] Preferably, in step (1), the amount of NaCl added to the chloride is 20~60wt%, and the mass ratio of silicon cutting waste to chloride is 1:0.1~0.5.

[0009] One or both of the BaCl2 and MgCl2 may be directly added BaCl2 or MgCl2 chlorides, or anions of Cl- in a high-temperature molten salt system. - With cation Ba 2+ Mg 2+ The secondary combination of BaCl2 and MgCl2 chlorides.

[0010] This invention relates to the mechanism of deep removal of Fe and Ni impurities from silicon cutting waste based on the galvanic cell effect of molten chloride salt: Based on the micro-cell effect of chloride ion concentration gradient, in a high-temperature molten chloride system, Fe and Ni metal particles dispersed in silicon waste come into contact with molten salt. Due to the concentration difference of chloride ions at the metal / molten salt interface, numerous micro-cells are spontaneously formed. Anodic reaction: Metal atoms on the surface of Fe and Ni particles lose electrons and are oxidized into ions, such as Fe → Fe 2+ +2e - Ni→Ni 2+ +2e - The generated metal ions Fe 2+ Ni 2+ Then react with Cl in the molten salt - They combine to form low-boiling-point chlorides FeCl2 and NiCl2, which then escape from the molten salt chloride system in gaseous form. Cathode reaction: Oxygen atoms dissolved in the molten salt and non-bridging oxygen atoms dissociated from SiO2 in the slag gain electrons in the cathode region and are reduced: O + 2e → O 2- O 2- With Mg in molten salt of chloride 2+ Or Ba 2+ The silicon reacts to form MgO or BaO deposits. BaO can also act as an absorbent for the SiO2 shell, promoting the dissociation of the Si-SiO2 core-shell structure and the release of silicon droplets. An appropriate amount of BaO added is beneficial for obtaining a high silicon recovery rate.

[0011] In the chloride molten salt system, the electrochemical-chlorination volatilization of Fe and Ni converts them into low-boiling-point chlorides and removes them in the gaseous state through the micro-cell effect; the aggregation and recovery of silicon melt, after the removal of metal impurities, the silicon droplets aggregate and settle under gravity to form high-purity silicon ingots; the chemical dissociation of the SiO2 shell, the oxides generated by BaO, etc. can react with SiO2 to form silicates, eliminate the oxide barrier on the surface of silicon particles, expose the internal silicon matrix and Fe and Ni impurities, and allow the Fe and Ni impurities wrapped by SiO2 to be released and participate in the galvanic cell reaction.

[0012] The beneficial effects of this invention are: (1) This invention breaks through the thermodynamic limitations of traditional oxidation slag making and achieves efficient simultaneous removal of Fe and Ni: Existing slag refining methods face insurmountable technical bottlenecks. The standard Gibbs free energy of Fe and Ni oxidation is higher than that of Si, and their affinity for oxygen is much lower than that of Si and Al. In high-temperature melts, they preferentially dissolve in the silicon melt in a metallic state rather than enter the slag phase. The removal rate of Fe by CaO-SiO2 slag refining is less than 30%, and it has almost no removal effect on Ni. This invention utilizes the self-generating chemical galvanic cell effect between Fe and Ni metal particles and chlorinated molten salt to get rid of the thermodynamic limitations of oxidation slag making. It does not need to rely on oxidation to enter the slag. After one treatment, the Fe removal rate is ≥53%, and can reach more than 90%, and the Ni removal rate is ≥70%. (2) The present invention simultaneously removes the SiO2 shell and metal impurities, and simultaneously improves the silicon recovery rate and impurity removal rate: Since the silicon cutting waste particles have a core-shell structure of Si core-SiO2 shell, the SiO2 shell covers the surface of the silicon particles, which not only directly causes the loss of silicon resources, but also constitutes a physical barrier, hindering the exposure and removal of metal impurities. In existing methods, although carbothermal reduction can remove the SiO2 layer, some C reacts with the reduction product Si to generate new SiC impurities, introducing new pollution. In this invention, the MgCl2 and BaCl2 components generate MgO and BaO deposits in the cathode region. MgO and BaO can also act as highly efficient absorbents for the SiO2 shell, reacting with SiO2 to generate silicate slag phase, eliminating the oxide barrier on the surface of silicon particles, and exposing the internal silicon matrix and Fe and Ni impurities. This achieves a self-sustaining cycle of "SiO2 chemical dissociation → oxygen supply → cathode reaction → generation of MgO and BaO → continued dissociation of SiO2". The removal of the SiO2 shell not only directly promotes silicon recovery, achieving a silicon recovery rate of ≥70%, but also allows the Fe and Ni impurities encased in SiO2 to be released and participate in the galvanic cell reaction, achieving a synergistic effect of silicon recovery and impurity removal. (3) This invention does not require an external power source or strong acid medium, achieving low energy consumption and low emission recovery: Although acid leaching can remove metal impurities, the strong acids used (HCl, H2SO4, HF, etc.) severely corrode the equipment and generate a large amount of strong acid waste liquid. Existing electrolytic refining methods require an external power source to drive the electrolytic reaction, resulting in high energy consumption; This invention achieves impurity removal driven by spontaneous galvanic cell effect in the molten salt system, without the need for an external power source. It relies on the spontaneous formation of micro-region galvanic cells between Fe and Ni impurities and molten chloride salt due to the difference in chloride ion concentration gradient, and the reaction is driven by the chemical energy of the impurity metal itself, which is a thermodynamic spontaneous process; (4) This invention is applicable to silicon cutting waste from different sources and with different impurities: Due to the differences in cutting fluids, diamond wires and process parameters used by different photovoltaic monocrystalline silicon cutting and processing enterprises, the types and contents of impurities in the silicon cutting waste generated vary significantly. Existing refining processes or refining slag-forming agents are usually designed for specific impurity types and are difficult to adapt to the fluctuations in impurity composition of waste from different sources. The chlorinated molten salt of this invention has both chemical slag-forming function and the galvanic cell-chlorination function of chloride salt, and shows a stable treatment effect on raw materials with different impurity compositions. It has good industrial promotion value and avoids the cumbersome process of redesigning processes for raw materials from different sources. Attached Figure Description

[0013] Figure 1 This is a cross-sectional macroscopic morphology diagram of the high-purity silicon ingot from Example 1; Figure 2 This is a cross-sectional macroscopic morphology diagram of a high-purity silicon ingot from Example 2; Figure 3 This is a cross-sectional macroscopic morphology diagram of the high-purity silicon ingot in Example 3; Figure 4 This is a cross-sectional macroscopic morphology diagram of the high-purity silicon ingot in Example 4; Figure 5 This is a cross-sectional macroscopic morphology diagram of the high-purity silicon ingot in Example 5; Figure 6 This is a cross-sectional macroscopic morphology diagram of the high-purity silicon ingot in Example 6; Figure 7 This is a cross-sectional macroscopic morphology diagram of the high-purity silicon ingot in Example 7; Figure 8 This is a cross-sectional macroscopic morphology diagram of the high-purity silicon ingot in Example 7. Detailed Implementation

[0014] 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.

[0015] Example 1: A method for deep removal of Fe and Ni impurities from silicon cutting waste based on the galvanic cell effect of molten salt chloride, the specific steps of which are as follows: (1) Silicon cutting waste containing Fe and Ni impurities is mixed evenly with chlorides (NaCl and BaCl2) to obtain a mixture; the Fe content in the silicon cutting waste is 600 ppmw, the Ni content is 65 ppmw, and the SiO2 content is 3 wt%; the NaCl content in the chloride is 30 wt%, and the BaCl2 content is 70 wt%; the mass ratio of silicon cutting waste to chlorides (NaCl and BaCl2) is 1:0.5; (2) The mixture was placed in a vacuum (vacuum degree 200 Pa), heated to 750°C at a heating rate of 6°C / min and held for 40 min, then heated to 1250°C at a heating rate of 4°C / min and held for 40 min, and then heated to 1550°C at a heating rate of 3°C / min to form a two-phase system of molten chloride salt-silicon melt. The Fe and Ni metal particles dispersed in the system spontaneously formed a micro-cell with the molten chloride salt having a chloride ion concentration gradient. In the micro-cell, the oxidation reaction of Fe and Ni occurred in the anode region to generate Fe. 2+ and Ni 2+ It then reacts with Cl in the molten salt of chloride. - The combination forms low-boiling-point FeCl2 and NiCl2, which escape from the molten chloride system in gaseous form; in the cathode region, a reduction reaction occurs between dissolved oxygen and non-bridging oxygen dissociated from SiO2 in the slag to generate O. 2- O 2- With Ba in molten salt of chloride 2+ The combination forms BaO deposits; the molten chloride salt acts as an electrolyte to conduct ions, providing the Cl required for chloride volatilization. - And maintain the charge balance throughout the electrochemical process; (3) Under vacuum atmosphere, the molten chloride salt-silicon melt two-phase system is heated to 1550℃ and kept at that temperature for 1.5h to promote the droplet aggregation and sedimentation separation of molten silicon liquid, and the low boiling point FeCl2 and NiCl2 are fully released. After cooling to room temperature, high-purity silicon ingots are obtained. The cross-sectional macroscopic morphology of the high-purity silicon ingot in this embodiment is shown in the figure below. Figure 1 ,from Figure 1 As can be seen, the silicon phase has formed several large aggregated regions, but there are still some independent small pieces and dispersed silicon phase. The overall boundary between the silicon phase and the slag phase is relatively clear, indicating that the silicon droplets have undergone significant agglomeration and sedimentation. In this embodiment, the purity of the high-purity silicon ingot is 99.952 wt%, the Fe content is 47.4 ppmw, the Ni content is 12.9 ppmw, the SiO2 content is 0.021 wt%, the silicon recovery rate is 70.4%, and the Fe and Ni removal rates are 92.1% and 80.2%, respectively.

[0016] Example 2: A method for deep removal of Fe and Ni impurities from silicon cutting waste based on the galvanic cell effect of molten salt chloride, the specific steps of which are as follows: (1) Silicon cutting waste containing Fe and Ni impurities is mixed evenly with chlorides (NaCl and MgCl2) to obtain a mixture; the Fe content in the silicon cutting waste is 1400 ppmw, the Ni content is 140 ppmw, and the SiO2 content is 4.8 wt%; the NaCl content in the chloride is 45 wt%, and the MgCl2 content is 55 wt%; the mass ratio of silicon cutting waste to chlorides (NaCl and MgCl2) is 1:0.1; (2) The mixture was placed in a flowing argon protective atmosphere with an absolute pressure of 1 atm, heated to 850°C at a heating rate of 8°C / min and held for 50 min, then heated to 1350°C at a heating rate of 6°C / min and held for 50 min, and then heated to 1600°C at a heating rate of 4°C / min to form a two-phase system of molten chloride salt and silicon melt. The Fe and Ni metal particles dispersed in the system spontaneously formed a micro-cell with the molten chloride salt having a chloride ion concentration gradient. In the micro-cell, the oxidation reaction of Fe and Ni occurred in the anode region to generate Fe. 2+ and Ni 2+ It then reacts with Cl in the molten salt of chloride. - The combination forms low-boiling-point FeCl2 and NiCl2, which escape from the molten chloride system in gaseous form; in the cathode region, a reduction reaction occurs between dissolved oxygen and non-bridging oxygen dissociated from SiO2 in the slag to generate O. 2- O 2- With Mg in molten salt of chloride 2+ The MgO deposits are formed by the combination of molten chloride and chloride; the molten chloride salt acts as an electrolyte to conduct ions, providing the Cl required for chloride volatilization. - And maintain the charge balance throughout the electrochemical process; (3) Under a vacuum atmosphere, the molten chloride salt-silicon melt two-phase system is heated to 1600℃ and kept at that temperature for 2 hours to promote the agglomeration and sedimentation separation of molten silicon liquid, and the low-boiling-point FeCl2 and NiCl2 are fully released. After cooling to room temperature, high-purity silicon ingots are obtained. The cross-sectional macroscopic morphology of the high-purity silicon ingot in this embodiment is shown in the figure below. Figure 2 ,from Figure 2 As can be seen, the silicon phase has aggregated and formed three large and dense regions, and the boundary between the silicon phase and the surrounding slag phase is clear, indicating that the molten silicon droplets have achieved effective aggregation and sedimentation separation. The purity of the high-purity silicon ingot in this embodiment is 99.916 wt%, the Fe content is 646 ppmw, the Ni content is 38.3 ppmw, the SiO2 content is 0.018 wt%, the silicon recovery rate is 93.4%, and the Fe and Ni removal rates are 53.9% and 72.6%, respectively.

[0017] Example 3: A method for deep removal of Fe and Ni impurities from silicon cutting waste based on the galvanic cell effect of molten salt chloride, the specific steps of which are as follows: (1) Silicon cutting waste containing Fe and Ni impurities is mixed evenly with chlorides (NaCl and MgCl2) to obtain a mixture; the Fe content in the silicon cutting waste is 2000 ppmw, the Ni content is 200 ppmw, and the SiO2 content is 6 wt%; the NaCl content in the chloride is 60 wt%, and the MgCl2 content is 40 wt%; the mass ratio of silicon cutting waste to chlorides (NaCl and MgCl2) is 1:0.5; (2) The mixture is placed in a vacuum (vacuum degree 200 Pa), heated to 900℃ at a heating rate of 10℃ / min and held for 60 min, then heated to 1400℃ at a heating rate of 8℃ / min and held for 60 min, and then heated to 1700℃ at a heating rate of 5℃ / min to form a two-phase system of molten chloride salt-silicon melt. The Fe and Ni metal particles dispersed in the system spontaneously form a micro-cell with the molten chloride salt having a chloride ion concentration gradient. In the micro-cell, the oxidation reaction of Fe and Ni occurs in the anode region to generate Fe. 2+ and Ni 2+ It then reacts with Cl in the molten salt of chloride. - The combination forms low-boiling-point FeCl2 and NiCl2, which escape from the molten chloride system in gaseous form; in the cathode region, a reduction reaction occurs between dissolved oxygen and non-bridging oxygen dissociated from SiO2 in the slag to generate O. 2- O 2- With Mg in molten salt of chloride 2+ The MgO deposits are formed by the combination of molten chloride and chloride; the molten chloride salt acts as an electrolyte to conduct ions, providing the Cl required for chloride volatilization. - And maintain the charge balance throughout the electrochemical process; (3) Under an inert atmosphere, the molten chloride salt-silicon melt two-phase system was heated to 1700℃ and kept at that temperature for 3h to promote the droplet aggregation and sedimentation separation of molten silicon liquid, and the low-boiling-point FeCl2 and NiCl2 were fully released. After cooling to room temperature, high-purity silicon ingots were obtained. The cross-sectional macroscopic morphology of the high-purity silicon ingot in this embodiment is shown in the figure below. Figure 3 ,from Figure 3 As can be seen from the data, the silicon phase aggregates into several large blocky regions with complete outlines and relatively clear interfaces with the slag phase, with only a few local separations, indicating that high-temperature long-term heat preservation is conducive to the aggregation of silicon droplets. In this embodiment, the high-purity silicon ingot has a purity of 99.925 wt%, an Fe content of 726 ppmw, a Ni content of 43 ppmw, a SiO2 content of 0.016 wt%, a silicon recovery rate of 93.8%, and Fe and Ni removal rates of 63.7% and 78.5%, respectively.

[0018] Example 4: A method for deep removal of Fe and Ni impurities from silicon cutting waste based on the galvanic cell effect of molten salt chloride, the specific steps of which are as follows: (1) A mixture is obtained by uniformly mixing silicon cutting waste containing Fe and Ni impurities with chlorides (NaCl, BaCl2 and MgCl2); the silicon cutting waste contains 1100 ppmw of Fe, 115 ppmw of Ni, and 4 wt% of SiO2; the chlorides contain 40 wt% of NaCl, 20 wt% of BaCl2, and 40 wt% of MgCl2; the mass ratio of silicon cutting waste to chlorides (NaCl, BaCl2 and MgCl2) is 1:0.2. (2) The mixture is placed in a vacuum (vacuum degree 120 Pa), heated to 750°C at a heating rate of 7°C / min and held for 45 min, then heated to 1300°C at a heating rate of 5°C / min and held for 45 min, and then heated to 1575°C at a heating rate of 3°C / min to form a two-phase system of molten chloride salt-silicon melt. The dispersed Fe and Ni metal particles in the system spontaneously form a micro-cell with the molten chloride salt having a chloride ion concentration gradient. In the micro-cell, Fe and Ni oxidation reaction occurs in the anode region to generate Fe. 2+ and Ni 2+ It then reacts with Cl in the molten salt of chloride. - The combination forms low-boiling-point FeCl2 and NiCl2, which escape from the molten chloride system in gaseous form; in the cathode region, a reduction reaction occurs between dissolved oxygen and non-bridging oxygen dissociated from SiO2 in the slag to generate O. 2- O 2- With Mg in molten salt of chloride 2+ and Ba 2+ The combination produces MgO and BaO deposits; the molten chloride salt acts as an electrolyte to conduct ions, providing the Cl required for chloride volatilization. - And maintain the charge balance throughout the electrochemical process; (3) Under a vacuum atmosphere, the molten chloride salt-silicon melt two-phase system is heated to 1575℃ and kept at that temperature for 2 hours to promote the agglomeration and sedimentation separation of molten silicon liquid droplets, and the low-boiling-point FeCl2 and NiCl2 are fully released. After cooling to room temperature, high-purity silicon ingots are obtained. The cross-sectional macroscopic morphology of the high-purity silicon ingot in this embodiment is shown in the figure below. Figure 4 ,from Figure 4 As can be seen from the data, the silicon phase exhibits a large, continuous aggregated morphology, with a dense main area, a clear silicon slag interface, and only a few pores or inclusions in some areas, indicating that the silicon droplets have good aggregation and settling effects. The high-purity silicon ingot in this embodiment has a purity of 99.967 wt%, an Fe content of 77 ppmw, a Ni content of 20.7 ppmw, a SiO2 content of 0.012 wt%, a silicon recovery rate of 94.4%, and Fe and Ni removal rates of 93.0% and 82.0%, respectively.

[0019] Example 5: A method for deep removal of Fe and Ni impurities from silicon cutting waste based on the galvanic cell effect of molten salt chloride, the specific steps of which are as follows: (1) Silicon cutting waste containing Fe and Ni impurities is mixed evenly with chlorides (NaCl, BaCl2 and MgCl2) to obtain a mixture; the silicon cutting waste contains 650 ppmw of Fe, 70 ppmw of Ni and 3 wt% of SiO2; the chlorides contain 30 wt% of NaCl, 25 wt% of BaCl2 and 45 wt% of MgCl2; the mass ratio of silicon cutting waste to chlorides is 1:0.3. (2) The mixture was placed in a flowing argon protective atmosphere with an absolute pressure of 1 atm, heated to 800℃ at a heating rate of 6℃ / min and held for 35 min, then heated to 1250℃ at a heating rate of 4℃ / min and held for 40 min, and then heated to 1500℃ at a heating rate of 3℃ / min to form a two-phase system of molten chloride salt-silicon melt. The Fe and Ni metal particles dispersed in the system and the molten chloride salt with a chloride ion concentration gradient spontaneously formed a micro-cell. In the micro-cell, the oxidation reaction of Fe and Ni occurred in the anode region to generate Fe. 2+ and Ni 2+ It then reacts with Cl in the molten salt of chloride. - The combination forms low-boiling-point FeCl2 and NiCl2, which escape from the molten chloride system in gaseous form; in the cathode region, a reduction reaction occurs between dissolved oxygen and non-bridging oxygen dissociated from SiO2 in the slag to generate O. 2- O 2- With Mg in molten salt of chloride 2+ and Ba 2+ The combination produces MgO and BaO deposits; the molten chloride salt acts as an electrolyte to conduct ions, providing the Cl required for chloride volatilization. - And maintain the charge balance throughout the electrochemical process; (3) Under vacuum atmosphere, the molten chloride salt-silicon melt two-phase system is heated to 1500℃ and kept at 1.5h to promote the droplet aggregation and sedimentation separation of molten silicon liquid, and the low boiling point FeCl2 and NiCl2 are fully released. After cooling to room temperature, high-purity silicon ingots are obtained. The cross-sectional macroscopic morphology of the high-purity silicon ingot in this embodiment is shown in the figure below. Figure 5 ,from Figure 5As can be seen from the data, the silicon phase forms a continuous block with a relatively large area and a relatively complete overall outline. The silicon phase is relatively dense inside and has a clear boundary with the surrounding slag phase, indicating that stable silicon slag separation can be achieved under this salt ratio. In this embodiment, the purity of the high-purity silicon ingot is 99.960 wt%, the Fe content is 52.0 ppmw, the Ni content is 14.0 ppmw, the SiO2 content is 0.018 wt%, the silicon recovery rate is 95.0%, and the Fe and Ni removal rates are 92.0% and 80.0%, respectively.

[0020] Example 6: A method for deep removal of Fe and Ni impurities from silicon cutting waste based on the galvanic cell effect of molten salt chloride, the specific steps of which are as follows: (1) Silicon cutting waste containing Fe and Ni impurities is mixed evenly with chlorides (NaCl, BaCl2 and MgCl2) to obtain a mixture; the silicon cutting waste contains 1550 ppmw of Fe, 160 ppmw of Ni and 5 wt% of SiO2; the chlorides contain 50 wt% of NaCl, 30 wt% of BaCl2 and 20 wt% of MgCl2, and the mass ratio of silicon cutting waste to chlorides is 1:0.4; (2) The mixture is placed in a vacuum (vacuum degree 150 Pa), heated to 850°C at a heating rate of 10°C / min and held for 55 min, then heated to 1350°C at a heating rate of 7°C / min and held for 50 min, and then heated to 1550°C at a heating rate of 5°C / min to form a two-phase system of molten chloride salt-silicon melt. The dispersed Fe and Ni metal particles in the system spontaneously form a micro-cell with the molten chloride salt having a chloride ion concentration gradient. In the micro-cell, the oxidation reaction of Fe and Ni occurs in the anode region to generate Fe. 2+ and Ni 2+ It then reacts with Cl in the molten salt of chloride. - The combination forms low-boiling-point FeCl2 and NiCl2, which escape from the molten chloride system in gaseous form; in the cathode region, a reduction reaction occurs between dissolved oxygen and non-bridging oxygen dissociated from SiO2 in the slag to generate O. 2- O 2- With Mg in molten salt of chloride 2+ and Ba 2+ The combination produces MgO and BaO deposits; the molten chloride salt acts as an electrolyte to conduct ions, providing the Cl required for chloride volatilization. - And maintain the charge balance throughout the electrochemical process; (3) Under vacuum atmosphere, the molten chloride salt-silicon melt two-phase system is heated to 1550℃ and kept at the temperature for 2.5h to promote the droplet aggregation and sedimentation separation of molten silicon liquid, and the low boiling point FeCl2 and NiCl2 are fully released. After cooling to room temperature, high-purity silicon ingots are obtained. The cross-sectional macroscopic morphology of the high-purity silicon ingot in this embodiment is shown in the figure below. Figure 6 ,from Figure 6 As can be seen from the data, the silicon phase is mainly composed of large-area continuous dense blocks, with only a few independent small blocks in the upper part. The boundary between the main silicon phase and the slag phase is clear, showing a high degree of droplet aggregation and silicon slag separation effect. In this embodiment, the high-purity silicon ingot has a purity of 99.967 wt%, an Fe content of 89.9 ppmw, a Ni content of 24.8 ppmw, a SiO2 content of 0.014 wt%, a silicon recovery rate of 95.6%, and Fe and Ni removal rates of 94.2% and 84.5%, respectively.

[0021] Example 7: A method for deep removal of Fe and Ni impurities from silicon cutting waste based on the galvanic cell effect of molten salt chloride, the specific steps of which are as follows: (1) A mixture is obtained by uniformly mixing silicon cutting waste containing Fe and Ni impurities with chlorides (NaCl, BaCl2 and MgCl2); the silicon cutting waste contains 850 ppmw of Fe, 95 ppmw of Ni and 3.5 wt% of SiO2; the chlorides contain 35 wt% of NaCl, 40 wt% of BaCl2 and 25 wt% of MgCl2, and the mass ratio of silicon cutting waste to chlorides is 1:0.25; (2) The mixture is placed in a vacuum (vacuum degree 100 Pa), heated to 700℃ at a heating rate of 8℃ / min and held for 40 min, then heated to 1300℃ at a heating rate of 6℃ / min and held for 45 min, and then heated to 1600℃ at a heating rate of 4℃ / min to form a two-phase system of molten chloride salt-silicon melt. The Fe and Ni metal particles dispersed in the system spontaneously form a micro-cell with the molten chloride salt having a chloride ion concentration gradient. In the micro-cell, the oxidation reaction of Fe and Ni occurs in the anode region to generate Fe. 2+ and Ni 2+ It then reacts with Cl in the molten salt of chloride. - The combination forms low-boiling-point FeCl2 and NiCl2, which escape from the molten chloride system in gaseous form; in the cathode region, a reduction reaction occurs between dissolved oxygen and non-bridging oxygen dissociated from SiO2 in the slag to generate O. 2- O 2- With Mg in molten salt of chloride 2+ and Ba 2+ The combination produces MgO and BaO deposits; the molten chloride salt acts as an electrolyte to conduct ions, providing the Cl required for chloride volatilization. - And maintain the charge balance throughout the electrochemical process; (3) Under a vacuum atmosphere, the molten chloride salt-silicon melt two-phase system is heated to 1600℃ and kept at that temperature for 2 hours to promote the agglomeration and sedimentation separation of molten silicon liquid, and the low-boiling-point FeCl2 and NiCl2 are fully released. After cooling to room temperature, high-purity silicon ingots are obtained. The cross-sectional macroscopic morphology of the high-purity silicon ingot in this embodiment is shown in the figure below. Figure 7 ,from Figure 7 As can be seen, the silicon phase forms a large continuous block with a relatively dense main area and a relatively complete overall outline. However, there are still a small number of irregular slag phases and inclusion areas at the local edges, and pores are visible in some parts of the interior. The boundary between the silicon phase and the slag phase is generally clear, indicating that the silicon droplets have achieved relatively sufficient aggregation and sedimentation separation. In this embodiment, the high-purity silicon ingot has a purity of 99.965 wt%, an Fe content of 55.3 ppmw, a Ni content of 16.6 ppmw, a SiO2 content of 0.012 wt%, a silicon recovery rate of 96.0%, and Fe and Ni removal rates of 93.5% and 82.5%, respectively.

[0022] Example 8: A method for deep removal of Fe and Ni impurities from silicon cutting waste based on the galvanic cell effect of molten salt chloride, the specific steps of which are as follows: (1) A mixture is obtained by uniformly mixing silicon cutting waste containing Fe and Ni impurities with chlorides (NaCl, BaCl2 and MgCl2); the silicon cutting waste contains 1800 ppmw of Fe, 180 ppmw of Ni and 5.5 wt% of SiO2; the chlorides contain 55 wt% of NaCl, 20 wt% of BaCl2 and 25 wt% of MgCl2, and the mass ratio of silicon cutting waste to chlorides is 1:0.35; (2) The mixture is placed in a vacuum (vacuum degree 150 Pa), heated to 875°C at a heating rate of 10°C / min and held for 55 min, then heated to 1375°C at a heating rate of 7°C / min and held for 55 min, and then heated to 1675°C at a heating rate of 5°C / min to form a two-phase system of molten chloride salt-silicon melt. The Fe and Ni metal particles dispersed in the system spontaneously form a micro-cell with the molten chloride salt having a chloride ion concentration gradient. In the micro-cell, the oxidation reaction of Fe and Ni occurs in the anode region to generate Fe. 2+ and Ni 2+ It then reacts with Cl in the molten salt of chloride. - The combination forms low-boiling-point FeCl2 and NiCl2, which escape from the molten chloride system in gaseous form; in the cathode region, a reduction reaction occurs between dissolved oxygen and non-bridging oxygen dissociated from SiO2 in the slag to generate O. 2- O 2- With Mg in molten salt of chloride 2+ and Ba 2+The combination produces MgO and BaO deposits; the molten chloride salt acts as an electrolyte to conduct ions, providing the Cl required for chloride volatilization. - And maintain the charge balance throughout the electrochemical process; (3) Under a vacuum atmosphere, the molten chloride salt-silicon melt two-phase system was heated to 1675℃ and kept at that temperature for 2.5h to promote the droplet aggregation and sedimentation separation of molten silicon liquid, and the low-boiling-point FeCl2 and NiCl2 were fully released. After cooling to room temperature, high-purity silicon ingots were obtained. The cross-sectional macroscopic morphology of the high-purity silicon ingot in this embodiment is shown in the figure below. Figure 8 ,from Figure 8 As can be seen from the data, the silicon phase is mainly composed of large-area continuous dense blocks, with only a few independent small blocks in the upper part. The boundary between the main silicon phase and the surrounding slag phase is clear. The silicon phase has good continuity and the slag phase has little residue, indicating that the degree of silicon droplet aggregation and the silicon slag separation effect are good. In this embodiment, the purity of the high-purity silicon ingot is 99.972 wt%, the Fe content is 99.0 ppmw, the Ni content is 24.3 ppmw, the SiO2 content is 0.010 wt%, the silicon recovery rate is 96.4%, and the Fe and Ni removal rates are 94.5% and 86.5%, respectively.

[0023] 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 deep removal of Fe and Ni impurities from silicon cutting waste based on the galvanic cell effect of molten salt chloride, characterized in that, The specific steps are as follows: (1) Silicon cutting waste containing Fe and Ni impurities is mixed evenly with chloride to obtain a mixture, wherein the chloride is composed of one or two of NaCl and BaCl2 and MgCl2; (2) The mixture is placed in a vacuum or inert atmosphere and heated to 700-900℃ at a heating rate of 5-10℃ / min and held for 30-60min. Then, it is heated to 1200-1400℃ at a heating rate of 3-8℃ / min and held for 30-60min. Finally, it is heated to 1450-1700℃ at a heating rate of 2-5℃ / min to form a two-phase system of molten chloride salt and silicon melt. The Fe and Ni metal particles dispersed in the system spontaneously form a micro-cell with the molten chloride salt having a chloride ion concentration gradient. In the micro-cell, the oxidation reaction of Fe and Ni occurs in the anode region to generate Fe. 2+ and Ni 2+ It then reacts with Cl in the molten salt of chloride. - The combination forms low-boiling-point FeCl2 and NiCl2, which escape in gaseous form from the molten chloride system; in the cathode region, a reduction reaction occurs between dissolved oxygen and non-bridging oxygen dissociated from SiO2 in the slag to generate O. 2- O 2- With Mg in molten salt of chloride 2+ Or Ba 2+ The combination forms MgO or BaO deposits; the molten chloride salt acts as an electrolyte to conduct ions, providing the Cl required for chlorination volatilization. - And maintain the charge balance throughout the electrochemical process; (3) Under vacuum or inert atmosphere, the molten chloride salt-silicon melt two-phase system is kept at 1450~1700℃ for 1~3h to promote the agglomeration and sedimentation separation of molten silicon liquid droplets, and the low boiling point FeCl2 and NiCl2 are fully released. After cooling to room temperature, high-purity silicon ingots are obtained.

2. The method for deep removal of Fe and Ni impurities from silicon cutting waste based on the galvanic cell effect of molten salt chloride according to claim 1, characterized in that: Step (1) The Fe content in the silicon cutting waste is 200~2000ppmw, the Ni content is 30~200ppmw, and the SiO2 content is 2~6wt%.

3. The method for deep removal of Fe and Ni impurities from silicon cutting waste based on the galvanic cell effect of molten salt chloride according to claim 1, characterized in that: In step (1), the amount of NaCl added to the chloride is 20~60wt%, and the mass ratio of silicon cutting waste to chloride is 1:0.1~0.5.

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