Method for synergistically refining industrial silicon based on sequential control gas-slag

Abstract

The invention discloses a method for synergistically refining industrial silicon based on sequential control gas-slag, and belongs to the technical field of industrial silicon purification. The method comprises the following steps: firstly, heating and melting an industrial silicon raw material under the protection of inert gas; then introducing a CO2-H2O mixed gas into the top of the silicon melt through a gas blowing pipe to carry out pre-impurity removal treatment; after the pre-impurity removal is finished, adding a composite slag agent into the silicon melt while keeping the introduction of the mixed gas, and carrying out two stages of slag spraying refining treatment; and after the refining is finished, stopping introducing gas, cooling, and separating slag and silicon to finally obtain a high-purity industrial silicon product. According to the method, through sequential optimization of gas-slag cooperation, the silicon loss rate in the industrial silicon refining process is remarkably reduced, impurities such as Al, Ca, B and Ti are efficiently and stably removed, the impurity removal dynamic conditions are enhanced, oxidation loss of silicon is effectively inhibited while deep purification is conducted, and the method has the advantages of being efficient, stable and low in consumption.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of industrial silicon purification, in particular to a method for refining industrial silicon based on time sequence control gas-slag cooperation. BACKGROUND

[0002] In the preparation process of solar-grade silicon, removing Al, Ca, Ti and other metal impurities in industrial silicon is a key step. The current main process is to directly blow O2 into the silicon melt, using the affinity of impurity elements for oxygen being stronger than that of silicon, so that it is preferentially oxidized into slag and removed. However, this traditional method has obvious drawbacks. This method can cause serious silicon loss. Due to the over-strong oxidation of pure oxygen, while oxidizing impurities, a large amount of silicon is oxidized into SiO2, resulting in a decrease in silicon recovery rate, usually more than 5% loss, and a large amount of waste silicon slag. The generated slag phase (mainly complex oxides composed of Al2O3, CaO, SiO2, etc.) has high viscosity, and the separation from the silicon melt is not complete, which can easily cause entrainment loss and separation difficulty. The viscous slag layer covering can hinder the continued diffusion and removal of subsequent impurities, resulting in economic losses. Secondly, this method has no obvious effect on the removal of B, Ti and other impurities: the physical and chemical behavior of Ti oxide in the slag system is complex, and the removal efficiency of Ti by single oxygen blowing is usually not ideal. The affinity of silicon for oxygen is greater than that of boron for oxygen, so boron cannot be oxidized and removed, and therefore the removal effect of boron is not obvious. The prior art such as patent CN101481112B (a method for directly oxidizing and refining purification of industrial silicon melt) uses compressed air, slag, water vapor and H2 to refine in stages, which can effectively reduce the content of B and P, but the SiO2-CaO slag agent is used fixedly, the slag phase has high viscosity and is difficult to separate. Although the improved technology uses O2-H2O mixed gas and optimizes the composition of the slag agent to reduce the content of impurity Fe (patent No. CN202311147500.3), it makes use of the hydrogenation effect of H2O to some extent, but it does not have obvious effect on Ti, and does not fundamentally solve the problem of silicon loss caused by strong oxidation environment, and does not pay enough attention to improving the fluidity of the slag system. In addition, different impurities require different refining strategies.

[0003] Currently, the industry relies on selecting and purchasing high-quality low-titanium quartz to control the content of B, Ti and other impurities. The traditional refining process cannot effectively remove B and Ti, so that the high-titanium quartz with abundant reserves cannot be utilized, which not only increases the production cost, but also seriously restricts the application of raw materials. Therefore, it is of great significance to develop a new refining method that can deeply remove impurities, minimize silicon loss and improve the process. SUMMARY

[0004] To solve the problems of removing impurities in silicon slag and reducing silicon loss, the application provides a method for gas-slag collaborative refining of industrial silicon based on time sequence control, which specifically comprises the following steps: (1) The industrial silicon raw material is heated and melted under the protection of inert gas to obtain a silicon melt.

[0005] (2) The CO2-H2O mixed gas is introduced into the silicon melt from the top through the gas blowing pipe to perform pre-impurity removal treatment, and a pre-impurity removal silicon melt is obtained.

[0006] (3) The CO2-H2O mixed gas is kept being introduced into the pre-impurity removal silicon melt, and a composite slag agent is added into the silicon melt with the CO2-H2O mixed gas as the carrier gas to perform two-stage slag refining treatment.

[0007] (4) After the slag refining treatment is completed, the aeration is stopped, and then the slag and silicon are separated to obtain an industrial silicon product.

[0008] Preferably, the inert gas in step (1) of the application is argon.

[0009] Preferably, the heating and melting conditions in step (1) of the application are heating to 1500-1650°C.

[0010] Preferably, the volume ratio of CO2 to H2O in the CO2-H2O mixed gas in steps (2) and (3) of the application is 1:1-4, and the mixed gas flow is 80-320 mL / min.

[0011] Preferably, the pre-impurity removal treatment conditions in step (2) of the application are pre-impurity removal treatment at 1500-1650°C for 30-60 minutes.

[0012] Preferably, the composite slag agent in step (3) of the application comprises two or more of CaF2, CaO, SiO2 and Na2CO3.

[0013] Preferably, the composite slag agent in step (3) of the application is one of the following composite slag agents, and the mass percentage of each component of the composite slag agent is specifically as follows: composite slag agent 1: CaO 40%-50%, SiO2 30%-40%, CaF2 10%-20%; composite slag agent 2: Na2CO3 30%-40%, SiO2 20%-30%, CaO 30%-40%; composite slag agent 3: SiO2 25%-35%, CaO 35%-45%, CaF2 20%-30%; composite slag agent 4: CaO 20%-40%, CaF2 60%-80%.

[0014] Preferably, the first stage of the two-stage slag injection refining process in step (3) of the present application is as follows: the composite slag agent is injected into the silicon melt in powder form, and then the refining process is maintained at 1500-1650 DEG C under the condition of ventilation for 10-30 minutes, and then the second stage of the slag injection refining process is carried out, that is, the composite slag agent powder is continuously injected into the silicon melt, and the refining process is maintained at 1500-1650 DEG C under the condition of ventilation for 30-90 minutes.

[0015] Preferably, in the first stage of the two-stage slag injection refining process in step (3) of the present application, the amount of the composite slag agent added is 1-2% of the mass of the silicon melt.

[0016] Preferably, in the second stage of the two-stage slag injection refining process in step (3) of the present application, the amount of the composite slag agent added is 1-2% of the mass of the silicon melt.

[0017] The entire process of refining industrial silicon in the present application is carried out under the condition of CO2-H2O mixed gas ventilation.

[0018] The mechanism of the present application is as follows: Based on the gas-slag synergistic refining mechanism of time sequence control, the mild oxidation characteristics of CO2 are utilized in the pre-impurity removal stage, and Al, Ca and other active impurity elements are selectively oxidized under the protection of high-temperature inert gas atmosphere, so that they are converted into oxides and enter the gas phase or the interface layer, effectively inhibiting the excessive oxidation of the silicon body and laying the foundation for reducing the silicon loss rate. At the same time, the water vapor destroys the surface structure of the impurity elements through high-temperature hydrolysis, promoting the preliminary conversion and removal of volatile species of B, Ti and other impurities. In the subsequent two-stage slag injection refining process, the gas-slag synergistic effect further strengthens the kinetic conditions for impurity removal: in the first stage, a proper amount of composite slag agent is injected to quickly capture the oxides and residual impurities precipitated in the pre-impurity removal process, forming a slag phase with low melting point and high fluidity, and promoting the mass transfer of impurities from the silicon melt to the slag phase; in the second stage, fresh slag agent is continuously supplied to maintain the high activity and unsaturated state of the reaction interface, especially for the slow-diffusion-rate titanium and other difficult-to-remove impurities, to provide a stable reaction interface, thereby achieving deep removal of Ti and other impurities and significantly improving the removal rate. In addition, the reactions of CO2 and H2O with B and other impurities are strong endothermic processes, and high-temperature conditions not only promote the forward progress of these reactions, but also significantly improve the overall impurity removal efficiency. Through the above functional sequential synergistic design, the silicon loss is effectively controlled, and the efficient removal of various impurities, especially the difficult-to-remove impurity titanium, is achieved, meeting the strict requirements of industrial silicon refining.

[0019] Compared with the prior art, the present application provides a method for refining industrial silicon based on time sequence control gas-slag synergistic refining, which has the following beneficial effects: (1) Silicon recovery rate is significantly improved: through the timing optimization of the process, the mild CO2-H2O mixed gas is passed for pre-decontamination, and the slag is sprayed in stages for collaborative refining, compared with the current production process of passing pure oxygen method, the silicon loss rate is significantly reduced.

[0020] (2) Impurity removal efficiency is improved: the removal rates of Al, Ca, B and Ti are significantly improved, especially the removal rate of Ti is improved to 55%.

[0021] (3) Process optimization: the slag agent is sprayed in stages to maintain the continuous purification ability, the excellent slag phase fluidity makes the slagging operation easy, and the refining process is stable.

[0022] (4) Cost-effective: while achieving higher purity, the loss of silicon is reduced; the reduction of B and Ti content has great practical significance and economic value for widening the selection range of raw material sources for industrial silicon production process and improving the quality of industrial silicon products. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 It is a process flow diagram of the present application. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0025] The initial impurities and mass percentage of industrial silicon used in the embodiments and comparative examples of the present application include: Al: 1.1110%, Ca: 2.2622%, B: 0.0090%, Ti: 0.0530%.

[0026] Example 1 A method for refining industrial silicon based on time control gas-slag collaboration, the components and mass percentage of the composite slag agent used in the present embodiment are as follows: SiO225%, CaO 45%, CaF230%, the specific steps are as follows: (1) The industrial silicon raw material is heated to 1550℃ under the protection of argon gas to obtain a silicon melt.

[0027] (2) The CO2-H2O mixed gas (the volume ratio of CO2 and H2O is 1:1, and the mixed gas flow is 80 mL / min) is passed from the top of the silicon melt through the gas blowing pipe for pre-decontamination treatment for 30 minutes to obtain a pre-decontaminated silicon melt.

[0028] (3) For the pre-decontamination silicon melt, keep the CO2-H2O mixed gas flowing, carry out the first stage of slag spraying decontamination treatment, spray the composite slag agent into the silicon melt in powder form with CO2-H2O mixed gas as the carrier gas (the addition amount of the composite slag agent is 1.5% of the mass of the silicon melt), and the slag spraying process lasts for about 1 minute, then keep the gas refining at 1550°C for 30 minutes, then carry out the second stage of slag spraying refining, continue to spray the composite slag agent powder into the silicon melt (the addition amount of the composite slag agent is 1.5% of the mass of the silicon melt), and the slag spraying process lasts for about 1 minute, and keep the gas refining at 1550°C for 60 minutes.

[0029] (4) After the slag spraying refining is completed, stop the gas flow, slowly cool, then separate the slag and silicon, and obtain the industrial silicon product.

[0030] In this embodiment, the Al removal rate is 96.26%, the Ca removal rate is 98.55%, the B removal rate is 91.23%, the Ti removal rate is 45.23%, and the silicon loss rate is calculated as 2.05%.

[0031] Example 2 A method for gas-slag collaborative refining of industrial silicon based on time sequence control, the composite slag agent used in this embodiment and the mass percentage of each component are as follows: SiO2 35%, CaO 45%, and CaF2 20%, and the specific steps are as follows: (1) The industrial silicon raw material is melted at 1500°C under the protection of argon gas to obtain a silicon melt.

[0032] (2) The CO2-H2O mixed gas (the volume ratio of CO2 to H2O is 1:4, and the flow rate of the mixed gas is 200 mL / min) is introduced into the silicon melt through the gas blowing pipe from the top to carry out the pre-decontamination treatment for 60 minutes, and a pre-decontamination silicon melt is obtained.

[0033] (3) For the pre-decontamination silicon melt, keep the CO2-H2O mixed gas flowing, carry out the first stage of slag spraying decontamination treatment, spray the composite slag agent into the silicon melt in powder form with CO2-H2O mixed gas as the carrier gas (the addition amount of the composite slag agent is 1% of the mass of the silicon melt), and the slag spraying process lasts for about 1 minute, then keep the gas refining at 1500°C for 10 minutes, then carry out the second stage of slag spraying refining, continue to spray the composite slag agent powder into the silicon melt (the addition amount of the composite slag agent is 1% of the mass of the silicon melt), and the slag spraying process lasts for about 1 minute, and keep the gas refining at 1500°C for 90 minutes.

[0034] (4) After the slag spraying refining is completed, stop the gas flow, slowly cool, then separate the slag and silicon, and obtain the industrial silicon product.

[0035] In this embodiment, the Al removal rate was 97.02%, the Ca removal rate was 98.78%, the B removal rate was 94.23%, the Ti removal rate was 55.25%, and the silicon loss rate was 2.0%.

[0036] Example 3 A method for co-refining industrial silicon based on time-controlled gas-slag synergistic process. In this embodiment, the composite slag agent used has the following components and their mass percentages: SiO2 30%, CaO 40%, CaF2 30%. The specific steps are as follows: (1) The industrial silicon raw material is heated to 1650°C under argon gas protection to melt it, and silicon melt is obtained.

[0037] (2) A CO2-H2O mixed gas (the volume ratio of CO2 and H2O is 1:2 and the flow rate of the mixed gas is 320 mL / min) is introduced into the silicon melt from the top through the gas blowing pipe for 30 minutes to perform pre-purification treatment and obtain pre-purified silicon melt.

[0038] (3) For the pre-depurified silicon melt, CO2-H2O mixed gas is introduced to carry out the first stage of slag spraying and depurification treatment. The composite slag agent is sprayed into the silicon melt in powder form using CO2-H2O mixed gas as carrier gas (the amount of composite slag agent added is 1.5% of the mass of silicon melt). The slag spraying process lasts for about 1 minute. Then, the gas is maintained at 1650℃ for 30 minutes for refining. Then, the second stage of slag spraying and refining is carried out. The composite slag agent powder is sprayed into the silicon melt again (the amount of composite slag agent added is 1.5% of the mass of silicon melt). The slag spraying process lasts for about 1 minute. The gas is maintained at 1650℃ for 30 minutes for refining.

[0039] (4) After the slag spraying refining is completed, the gas supply is stopped, the temperature is slowly lowered and cooled, and then the slag silicon is separated to obtain industrial silicon products.

[0040] In this embodiment, the Al removal rate is 95.86%, the Ca removal rate is 96.15%, the B removal rate is 89.96%, the Ti removal rate is 28.16%, and the silicon loss rate is 1.92%.

[0041] Example 4 A method for co-refining industrial silicon based on time-controlled gas-slag synergistic process, wherein the composite slag agent used in this embodiment comprises the following components and their mass percentages: CaO 40%, SiO2 40%, CaF2 20%. The specific steps are as follows: (1) The industrial silicon raw material is heated to 1550°C under argon gas protection to obtain silicon melt.

[0042] (2) A CO2-H2O mixed gas (the volume ratio of CO2 and H2O is 1:3 and the flow rate of the mixed gas is 80 mL / min) is introduced into the silicon melt from the top through the blowing pipe for 30 minutes to perform pre-purification treatment and obtain pre-purified silicon melt.

[0043] (3) For the pre-de-impure silicon melt, CO2-H2O mixed gas is introduced to carry out the first stage of slag spraying and impurity removal treatment. The composite slag agent is sprayed into the silicon melt in powder form using CO2-H2O mixed gas as carrier gas (the amount of composite slag agent added is 1.5% of the mass of silicon melt). The slag spraying process lasts for about 1 minute. Then, the gas is maintained at 1550℃ for 30 minutes for refining. Then, the second stage of slag spraying and refining is carried out. The composite slag agent powder is sprayed into the silicon melt again (the amount of composite slag agent added is 1.5% of the mass of silicon melt). The slag spraying process lasts for about 1 minute. The gas is maintained at 1550℃ for 60 minutes for refining.

[0044] (4) After the slag spraying refining is completed, the gas supply is stopped, the temperature is slowly lowered and cooled, and then the slag silicon is separated to obtain industrial silicon products.

[0045] In this embodiment, the Al removal rate was 97.40%, the Ca removal rate was 95.10%, the B removal rate was 96.55%, the Ti removal rate was 43.58%, and the silicon loss rate was 3.56%. Example 5 A method for co-refining industrial silicon based on time-controlled gas-slag synergistic process, wherein the composite slag agent used in this embodiment comprises the following components and their mass percentages: CaO 30%, SiO2 50%, CaF2 20%, and the specific steps are as follows: (1) The industrial silicon raw material is heated to 1500℃ under argon gas protection to melt it, and silicon melt is obtained.

[0046] (2) A CO2-H2O mixed gas (the volume ratio of CO2 and H2O is 1:2 and the flow rate of the mixed gas is 200 mL / min) is introduced into the silicon melt from the top through the gas blowing pipe for 60 minutes to pre-depurify the silicon melt and obtain the pre-depurified silicon melt.

[0047] (3) For the pre-de-impure silicon melt, CO2-H2O mixed gas is introduced to carry out the first stage of slag spraying and impurity removal treatment. The composite slag agent is sprayed into the silicon melt in powder form using CO2-H2O mixed gas as carrier gas (the amount of composite slag agent added is 1% of the mass of silicon melt). The slag spraying process lasts for about 1 minute. Then, the gas is maintained at 1500℃ for 10 minutes for refining. Then, the second stage of slag spraying and refining is carried out. The composite slag agent powder is sprayed into the silicon melt (the amount of composite slag agent added is 1% of the mass of silicon melt). The slag spraying process lasts for about 1 minute. The gas is maintained at 1500℃ for 90 minutes for refining.

[0048] (4) After the slag spraying refining is completed, the gas supply is stopped, the temperature is slowly lowered and cooled, and then the slag silicon is separated to obtain industrial silicon products.

[0049] In this embodiment, the Al removal rate is 97.0%, the Ca removal rate is 97.52%, the B removal rate is 94.65%, the Ti removal rate is 53.65%, and the silicon loss rate is 3.95%.

[0050] Example 6 A method for co-refining industrial silicon based on time-controlled gas-slag synergistic process, wherein the composite slag agent used in this embodiment comprises the following components and their mass percentages: CaO 50%, SiO2 40%, CaF2 10%, and the specific steps are as follows: (1) The industrial silicon raw material is heated to 1650°C under argon gas protection to melt it, and silicon melt is obtained.

[0051] (2) A CO2-H2O mixed gas (the volume ratio of CO2 and H2O is 1:4 and the flow rate of the mixed gas is 320 mL / min) is introduced into the silicon melt from the top through the gas blowing pipe for 50 minutes to pre-depurify the silicon melt and obtain the pre-depurified silicon melt.

[0052] (3) For the pre-de-impure silicon melt, CO2-H2O mixed gas is introduced to carry out the first stage of slag spraying and impurity removal treatment. The composite slag agent is sprayed into the silicon melt in powder form using CO2-H2O mixed gas as carrier gas (the amount of composite slag agent added is 2% of the mass of silicon melt). The slag spraying process lasts for about 1 minute. Then, the gas is maintained at 1650℃ for 20 minutes for refining. Then, the second stage of slag spraying and refining is carried out. The composite slag agent powder is sprayed into the silicon melt (the amount of composite slag agent added is 2% of the mass of silicon melt). The slag spraying process lasts for about 1 minute. The gas is maintained at 1650℃ for 80 minutes for refining.

[0053] (4) After the slag spraying refining is completed, the gas supply is stopped, the temperature is slowly lowered and cooled, and then the slag silicon is separated to obtain industrial silicon products.

[0054] In this embodiment, the Al removal rate was 97.32%, the Ca removal rate was 97.88%, the B removal rate was 95.53%, the Ti removal rate was 52.18%, and the silicon loss rate was 3.48%.

[0055] Example 7 A method for co-refining industrial silicon based on time-controlled gas-slag refining, wherein the composite slag agent used in this embodiment comprises the following components and their mass percentages: Na₂CO₃ 30%, SiO₂ 30%, CaO 40%. The specific steps are as follows: (1) The industrial silicon raw material is heated to 1550°C under argon gas protection to obtain silicon melt.

[0056] (2) A CO2-H2O mixed gas (the volume ratio of CO2 and H2O is 1:1 and the flow rate of the mixed gas is 80 mL / min) is introduced into the silicon melt from the top through the gas blowing pipe for 30 minutes to perform pre-purification treatment and obtain pre-purified silicon melt.

[0057] (3) For the pre-de-impure silicon melt, CO2-H2O mixed gas is introduced to carry out the first stage of slag spraying and impurity removal treatment. The composite slag agent is sprayed into the silicon melt in powder form using CO2-H2O mixed gas as carrier gas (the amount of composite slag agent added is 1.5% of the mass of silicon melt). The slag spraying process lasts for about 1 minute. Then, the gas is maintained at 1550℃ for 30 minutes for refining. Then, the second stage of slag spraying and refining is carried out. The composite slag agent powder is sprayed into the silicon melt again (the amount of composite slag agent added is 1.5% of the mass of silicon melt). The slag spraying process lasts for about 1 minute. The gas is maintained at 1550℃ for 60 minutes for refining.

[0058] (4) After the slag spraying refining is completed, the gas supply is stopped, the temperature is slowly lowered and cooled, and then the slag silicon is separated to obtain industrial silicon products.

[0059] In this embodiment, the Al removal rate was 95.98%, the Ca removal rate was 96.56%, the B removal rate was 90.24%, the Ti removal rate was 42.13%, and the silicon loss rate was 2.65%.

[0060] Example 8 A method for co-refining industrial silicon based on time-controlled gas-slag synergistic process. In this embodiment, the composite slag agent used has the following components and their mass percentages: Na₂CO₃ 40%, SiO₂ 20%, CaO 40%. The specific steps are as follows: (1) The industrial silicon raw material is heated to 1500℃ under argon gas protection to melt it, and silicon melt is obtained.

[0061] (2) A CO2-H2O mixed gas (the volume ratio of CO2 and H2O is 1:2 and the flow rate of the mixed gas is 200 mL / min) is introduced into the silicon melt from the top through the gas blowing pipe for 60 minutes to pre-depurify the silicon melt and obtain the pre-depurified silicon melt.

[0062] (3) For the pre-de-impure silicon melt, CO2-H2O mixed gas is introduced to carry out the first stage of slag spraying and impurity removal treatment. The composite slag agent is sprayed into the silicon melt in powder form using CO2-H2O mixed gas as carrier gas (the amount of composite slag agent added is 1% of the mass of silicon melt). The slag spraying process lasts for about 1 minute. Then, the gas is maintained at 1500℃ for 10 minutes for refining. Then, the second stage of slag spraying and refining is carried out. The composite slag agent powder is sprayed into the silicon melt (the amount of composite slag agent added is 1% of the mass of silicon melt). The slag spraying process lasts for about 1 minute. The gas is maintained at 1500℃ for 90 minutes for refining.

[0063] (4) After the slag spraying refining is completed, the gas supply is stopped, the temperature is slowly lowered and cooled, and then the slag silicon is separated to obtain industrial silicon products.

[0064] In this embodiment, the Al removal rate was 97.99%, the Ca removal rate was 98.63%, the B removal rate was 88.65%, the Ti removal rate was 51.11%, and the silicon loss rate was 3.12%.

[0065] Example 9 A method for co-refining industrial silicon based on time-controlled gas-slag synergistic process. In this embodiment, the composite slag agent used has the following components and their mass percentages: Na2CO3 40%, SiO2 30%, CaO 30%. The specific steps are as follows: (1) The industrial silicon raw material is heated to 1650°C under argon gas protection to melt it, and silicon melt is obtained.

[0066] (2) A CO2-H2O mixed gas (the volume ratio of CO2 and H2O is 1:4 and the flow rate of the mixed gas is 320 mL / min) is introduced into the silicon melt from the top through the gas blowing pipe for 50 minutes to pre-depurify the silicon melt and obtain the pre-depurified silicon melt.

[0067] (3) For the pre-de-impure silicon melt, CO2-H2O mixed gas is introduced to carry out the first stage of slag spraying and impurity removal treatment. The composite slag agent is sprayed into the silicon melt in powder form using CO2-H2O mixed gas as carrier gas (the amount of composite slag agent added is 2% of the mass of silicon melt). The slag spraying process lasts for about 1 minute. Then, the gas is maintained at 1650℃ for 20 minutes for refining. Then, the second stage of slag spraying and refining is carried out. The composite slag agent powder is sprayed into the silicon melt (the amount of composite slag agent added is 2% of the mass of silicon melt). The slag spraying process lasts for about 1 minute. The gas is maintained at 1650℃ for 80 minutes for refining.

[0068] (4) After the slag spraying refining is completed, the gas supply is stopped, the temperature is slowly lowered and cooled, and then the slag silicon is separated to obtain industrial silicon products.

[0069] In this embodiment, the Al removal rate was 98.69%, the Ca removal rate was 99.02%, the B removal rate was 90.25%, the Ti removal rate was 50.36%, and the silicon loss rate was 2.69%.

[0070] Example 10 A method for co-refining industrial silicon based on time-controlled gas-slag refining, wherein the composite slag agent used in this embodiment has the following components and their mass percentages: CaO 20%, CaF 280%, and the specific steps are as follows: (1) The industrial silicon raw material is heated to 1550°C under argon gas protection to obtain silicon melt.

[0071] (2) A CO2-H2O mixed gas (the volume ratio of CO2 and H2O is 1:1 and the flow rate of the mixed gas is 80 mL / min) is introduced into the silicon melt from the top through the gas blowing pipe for 30 minutes to perform pre-purification treatment and obtain pre-purified silicon melt.

[0072] (3) For the pre-de-impure silicon melt, CO2-H2O mixed gas is introduced to carry out the first stage of slag spraying and impurity removal treatment. The composite slag agent is sprayed into the silicon melt in powder form using CO2-H2O mixed gas as carrier gas (the amount of composite slag agent added is 1.5% of the mass of silicon melt). The slag spraying process lasts for about 1 minute. Then, the gas is maintained at 1550℃ for 30 minutes for refining. Then, the second stage of slag spraying and refining is carried out. The composite slag agent powder is sprayed into the silicon melt again (the amount of composite slag agent added is 1.5% of the mass of silicon melt). The slag spraying process lasts for about 1 minute. The gas is maintained at 1550℃ for 60 minutes for refining.

[0073] (4) After the slag spraying refining is completed, the gas supply is stopped, the temperature is slowly lowered and cooled, and then the slag silicon is separated to obtain industrial silicon products.

[0074] In this embodiment, the Al removal rate was 89.39%, the Ca removal rate was 92.56%, the B removal rate was 88.42%, the Ti removal rate was 36.45%, and the silicon loss rate was 4.36%.

[0075] Example 11 A method for co-refining industrial silicon based on time-controlled gas-slag refining, wherein the composite slag agent used in this embodiment has the following components and their mass percentages: CaO 40%, CaF 260%, and the specific steps are as follows: (1) The industrial silicon raw material is heated to 1500℃ under argon gas protection to melt it, and silicon melt is obtained.

[0076] (2) A CO2-H2O mixed gas (the volume ratio of CO2 and H2O is 1:2 and the flow rate of the mixed gas is 200 mL / min) is introduced into the silicon melt from the top through the gas blowing pipe for 60 minutes to pre-depurify the silicon melt and obtain the pre-depurified silicon melt.

[0077] (3) For the pre-de-impure silicon melt, CO2-H2O mixed gas is introduced to carry out the first stage of slag spraying and impurity removal treatment. The composite slag agent is sprayed into the silicon melt in powder form using CO2-H2O mixed gas as carrier gas (the amount of composite slag agent added is 1% of the mass of silicon melt). The slag spraying process lasts for about 1 minute. Then, the gas is maintained at 1500℃ for 10 minutes for refining. Then, the second stage of slag spraying and refining is carried out. The composite slag agent powder is sprayed into the silicon melt (the amount of composite slag agent added is 1% of the mass of silicon melt). The slag spraying process lasts for about 1 minute. The gas is maintained at 1500℃ for 90 minutes for refining.

[0078] (4) After the slag spraying refining is completed, the gas supply is stopped, the temperature is slowly lowered and cooled, and then the slag silicon is separated to obtain industrial silicon products.

[0079] In this embodiment, the Al removal rate was 94.21%, the Ca removal rate was 95.22%, the B removal rate was 90.12%, the Ti removal rate was 45.22%, and the silicon loss rate was 3.54%.

[0080] Example 12 A method for co-refining industrial silicon based on time-controlled gas-slag refining, wherein the composite slag agent used in this embodiment has the following components and their mass percentages: CaO 30%, CaF 270%, and the specific steps are as follows: (1) The industrial silicon raw material is heated to 1650°C under argon gas protection to melt it, and silicon melt is obtained.

[0081] (2) A CO2-H2O mixed gas (the volume ratio of CO2 and H2O is 1:4 and the flow rate of the mixed gas is 320 mL / min) is introduced into the silicon melt from the top through the gas blowing pipe for 50 minutes to pre-depurify the silicon melt and obtain the pre-depurified silicon melt.

[0082] (3) For the pre-de-impure silicon melt, CO2-H2O mixed gas is introduced to carry out the first stage of slag spraying and impurity removal treatment. The composite slag agent is sprayed into the silicon melt in powder form using CO2-H2O mixed gas as carrier gas (the amount of composite slag agent added is 2% of the mass of silicon melt). The slag spraying process lasts for about 1 minute. Then, the gas is maintained at 1650℃ for 20 minutes for refining. Then, the second stage of slag spraying and refining is carried out. The composite slag agent powder is sprayed into the silicon melt (the amount of composite slag agent added is 2% of the mass of silicon melt). The slag spraying process lasts for about 1 minute. The gas is maintained at 1650℃ for 80 minutes for refining.

[0083] (4) After the slag spraying refining is completed, the gas supply is stopped, the temperature is slowly lowered and cooled, and then the slag silicon is separated to obtain industrial silicon products.

[0084] In this embodiment, the Al removal rate was 96.36%, the Ca removal rate was 95.25%, the B removal rate was 95.36%, the Ti removal rate was 50.23%, and the silicon loss rate was 3.01%.

[0085] Comparative Example 1 The difference between this comparative example and Example 1 is that pure oxygen was introduced for refining, and no composite slag agent was added; the other conditions are the same as in Example 1.

[0086] In this comparative example, the Al removal rate was 95.32%, the Ca removal rate was 96.21%, the B removal rate was -0.12%, the Ti removal rate was 0.0%, and the silicon loss rate was 6.52%.

[0087] Comparative Example 2 The difference between this comparative example and Example 1 is that pure oxygen is introduced and the composite slag agent is added at once; the other conditions are the same as in Example 1.

[0088] In this comparative example, the Al removal rate was 95.98%, the Ca removal rate was 97.56%, the B removal rate was 1.56%, the Ti removal rate was 1.12%, and the silicon loss rate was 5.22%.

[0089] Comparative Example 3 The difference between this comparative example and Example 1 is that CO2 is introduced for refining, while the other conditions are the same as in Example 1.

[0090] In this embodiment, the Al removal rate was 85.51%, the Ca removal rate was 87.23%, the B removal rate was 0.0%, the Ti removal rate was 2.56%, and the silicon loss rate was 2.14%.

[0091] Comparative Example 4 The difference between this comparative example and Example 1 is that H2O is introduced for refining, while the other conditions are the same as in Example 1.

[0092] In this embodiment, the Al removal rate was 84.21%, the Ca removal rate was 82.14%, the B removal rate was 0.11%, the Ti removal rate was 1.58%, and the silicon loss rate was 4.26%.

[0093] Table 1 shows the removal rate of impurities and silicon loss rate in silicon slag for Examples 1-12 and Comparative Examples 1-4 of the present invention.

[0094] Table 1 The CO2-H2O pre-purification and staged injection composite slag agent technology used in this invention (specific process flow as follows) Figure 1 As shown in Examples 1-12, the process exhibits excellent silicon recovery and impurity removal. Through time-series optimization and staged slag spraying, this process achieves efficient and synergistic refining under a mild atmosphere. It not only significantly improves silicon recovery but also greatly reduces the content of impurities such as Al, Ca, B, and Ti. The present invention has good slag flowability and stable operation during the refining process. It effectively controls silicon loss while achieving high purity, and has excellent overall cost-effectiveness. It provides a reliable path for broadening raw material sources and improving product quality.

[0095] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for co-refining industrial silicon based on time-controlled gas-slag refining, characterized in that, Specifically, the following steps are included: (1) Industrial silicon raw materials are heated and melted under inert gas protection to obtain silicon melt; (2) A CO2-H2O mixed gas is introduced into the silicon melt from the top through a blowing pipe to perform pre-purification treatment and obtain a pre-purified silicon melt; (3) For the pre-depurified silicon melt, CO2-H2O mixed gas is kept in the pipeline, and composite slag agent is added to the silicon melt using CO2-H2O mixed gas as carrier gas for two-stage slag spraying refining treatment. (4) After the slag spraying refining process is completed, the gas supply is stopped, the mixture is cooled, and then the slag silicon is separated to obtain industrial silicon products.

2. The method for co-refining industrial silicon based on time-controlled gas-slag co-refining according to claim 1, characterized in that, The inert gas mentioned in step (1) is argon.

3. The method for co-refining industrial silicon based on time-controlled gas-slag co-refining according to claim 1, characterized in that, The heating and melting conditions described in step (1) are heating to 1500~1650℃.

4. The method for co-refining industrial silicon based on time-controlled gas-slag co-refining according to claim 1, characterized in that, In steps (2) and (3), the volume ratio of CO2 to H2O in the CO2-H2O mixed gas is 1:1~4, and the flow rate of the mixed gas is 80~320mL / min.

5. The method for co-refining industrial silicon based on time-controlled gas-slag co-refining according to claim 1, characterized in that, The pre-purification treatment conditions in step (2) are: pre-purification treatment at 1500~1650℃ for 30~60 minutes.

6. The method for co-refining industrial silicon based on time-controlled gas-slag co-refining according to claim 1, characterized in that, The composite slag agent mentioned in step (3) contains two or more of CaF2, CaO, SiO2 and Na2CO3.

7. The method for co-refining industrial silicon based on time-controlled gas-slag co-refining according to claim 6, characterized in that, The composite slag agent is one of the following composite slag agents, and the specific components and their mass percentages of the composite slag agent are as follows: Composite slag agent 1: CaO 40%~50%, SiO2 30%~40%, CaF2 10%~20%; Composite slag agent 2: Na2CO3 30%~40%, SiO2 20%~30%, CaO 30%~40%; Composite slag agent 3: SiO2 25%~35%, CaO 35%~45%, CaF2 20%~30%; Composite slag agent 4: CaO 20%~40%, CaF2 60%~80%.

8. The method for co-refining industrial silicon based on time-controlled gas-slag co-refining according to claim 1, characterized in that, In step (3), the first stage of the two-stage slag spraying refining process is as follows: the composite slag agent is sprayed into the silicon melt in powder form, and then the refining is carried out under the condition of 1500~1650℃ for 10~30 minutes. Then the second stage of slag spraying refining is carried out. The second stage of slag spraying and impurity removal process is as follows: the composite slag agent powder is sprayed into the silicon melt, and the refining is carried out under the condition of 1500~1650℃ for 30~90 minutes.

9. The method for co-refining industrial silicon based on time-controlled gas-slag co-refining according to claim 8, characterized in that, In the first stage of slag spraying refining treatment in step (3), the amount of composite slag agent added is 1~2% of the mass of silicon melt; in the second stage of slag spraying refining treatment, the amount of composite slag agent added is 1~2% of the mass of silicon melt.

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