Process for the production of aluminum fluoride from aluminum dross

Abstract

This invention discloses a method for preparing aluminum fluoride from aluminum ash, comprising the following steps: First, chlorination and denitrification of finely ground and preheated aluminum ash is performed using chlorine gas, converting aluminum and aluminum nitride in the ash into aluminum chloride and nitrogen. Second, a secondary chlorination of aluminum, iron, and magnesium in the primary chlorination product is performed using silicon chloride, converting them into aluminum chloride, ferric chloride, and magnesium chloride. High-purity aluminum chloride is obtained through multi-stage condensation and separation. The aluminum chloride obtained from the two chlorinations is then gasified, preheated, and reacted with silicon tetrafluoride to produce aluminum fluoride and silicon chloride. The silicon chloride is recycled for secondary chlorination. This invention uses chlorine and silicon chloride sequentially to chlorinate aluminum ash twice, eliminating the need for carbon addition. The chlorination products are easily separated, and the operation is simple. The use of silicon tetrafluoride to fluorinate aluminum chloride to prepare aluminum fluoride, along with the recycling of the byproduct silicon chloride within the system, effectively reduces production costs. Simultaneously, the system has high energy utilization, enabling the harmless treatment of aluminum ash and the large-scale clean preparation of aluminum fluoride, resulting in significant economic and social benefits.

Description

Technical Field

[0001] This invention relates to the fields of chemical industry, non-ferrous metallurgy, and environmental protection, specifically to a method for preparing aluminum fluoride from aluminum ash. Background Technology

[0002] Aluminum ash is an industrial byproduct generated during the production of electrolytic aluminum, cast aluminum, and waste aluminum recycling. my country's aluminum industry produces more than 3 million tons of aluminum ash annually. Because aluminum ash contains harmful substances such as aluminum nitride, soluble fluoride salts, and chloride salts, it is listed in the "National Hazardous Waste List". The harmless treatment and high-value utilization of aluminum ash are of great significance to the green and high-quality development of the aluminum industry.

[0003] The harmless treatment of aluminum ash mainly involves denitrification and desalination. The most common denitrification method is to calcine the aluminum ash at high temperature in air to convert aluminum nitride into nitrogen and alumina. However, during the oxidative calcination process, a dense alumina film easily forms on the surface of the aluminum nitride particles, hindering the further denitrification reaction and resulting in low denitrification efficiency. Chinese patent application CN112744850A discloses a method for the comprehensive utilization of secondary aluminum ash resources. First, secondary aluminum ash and sodium alkali are used to form pellets of 30-200mm using a binder. Then, these pellets are placed in a high-temperature kiln for calcination. The sodium alkali is used to oxidize aluminum nitride to convert the resulting alumina into sodium aluminate, thereby alleviating the barrier effect of the formed alumina film and enhancing the denitrification reaction. Although this method uses alkali sintering to improve denitrification efficiency, the amount of alkali added is large, resulting in high production costs. Furthermore, the large pellet diameter leads to uneven heating, high solid-phase reaction temperature, long reaction time, and high energy consumption. Chinese patent application CN110902706A discloses a method for preparing polyaluminum chloride from aluminum ash. First, aluminum ash and coke are formed into 5-20 mm pellets using a binder. Then, these pellets are calcined in chlorine gas at 700-1100℃ in a moving bed, converting aluminum nitride into nitrogen and aluminum chloride. While this method can denitrify aluminum nitride and obtain high-value-added aluminum chloride, the use of large-particle pellets in the chlorination calcination process leads to uneven heating and high diffusion resistance for the generated aluminum chloride and nitrogen, resulting in a slow reaction rate, low efficiency, and high energy consumption. Chinese patent application CN112850762A discloses a method for preparing aluminum chloride from aluminum ash pellets via chlorination-oxygen pressure conversion and utilizing all components. First, aluminum ash and coke are mixed uniformly in a certain proportion to form pellets. Then, these pellets are calcined in chlorine gas at 1000℃ in a moving bed, yielding nitrogen and high-value-added products such as aluminum chloride, silicon chloride, and magnesium chloride. Although this scheme can harmlessly treat aluminum ash and realize the high-value utilization of elements such as aluminum, silicon, and magnesium, it also suffers from problems such as slow reaction rate, low efficiency, and high energy consumption due to the use of pellet chlorination, which results in large gas phase diffusion resistance.

[0004] Therefore, given the current limitations of efficient aluminum ash utilization in process technology, the key to achieving large-scale, efficient, clean, and high-value utilization of aluminum ash lies in strengthening the denitrification and desalination process, improving reaction efficiency, reducing process energy consumption, and utilizing the aluminum resources in aluminum ash to prepare high-value-added products through process and technological innovation. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention aims to provide a method for preparing aluminum fluoride from aluminum ash.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing aluminum fluoride from aluminum ash includes the following steps:

[0008] S1. Grinding: Grinding aluminum ash to obtain fine ash;

[0009] S2. Preheating: Preheat the fine ash obtained in step S1 to obtain hot fine ash;

[0010] S3, Chlorination I: High-temperature chlorine gas is used to chlorinate and denitrify the hot fine ash obtained in step S2, resulting in high-temperature chlorinated flue gas and chlorinated slag I; the high-temperature chlorinated flue gas is sent to the preheating process of step S2 to preheat the hot fine ash through heat exchange, and the low-temperature chlorinated flue gas obtained after heat exchange is sent to the condensation and dust collection process of step S7.

[0011] S4, Heat exchange cooling I: The chlorinated slag I obtained in step S3 is cooled by heat exchange using room temperature chlorine gas to obtain hot chlorine gas and cooled slag. The hot chlorine gas is sent to the combustion preheating I process in step S6.

[0012] S5. Washing and drying: The cooling residue obtained in step S4 is washed and dried with deionized water to obtain washing liquid and washing residue. The washing residue is sent to the chlorination II process in step S10.

[0013] S6. Combustion Preheating I: The hot chlorine gas obtained in step S4 is preheated by the combustion of air and fuel to obtain high-temperature chlorine gas and combustion tail gas I. The high-temperature chlorine gas is sent into the chlorination I process in step S3.

[0014] S7. Condensation and dust collection: The low-temperature chlorinated flue gas is condensed to obtain nitrogen, chlorine and solid aluminum chloride. The solid aluminum chloride is sent to the gasification III process in step S15.

[0015] S8. Liquefaction and separation: Separate the nitrogen and chlorine obtained in step S7 to obtain nitrogen and liquid chlorine;

[0016] S9. Gasification I: The liquid chlorine obtained in step S8 is gasified to obtain circulating chlorine gas. The circulating chlorine gas is sent to the heat exchange and cooling I process in step S4 to cool the chlorinated slag I obtained in step S3 by heat exchange.

[0017] S10, Chlorination II: Chlorinate the water-washed residue obtained in step S5 using high-temperature silicon chloride to obtain chlorinated flue gas and chlorinated residue II. The chlorinated flue gas is sent to the multi-stage condensation process in step S14.

[0018] S11, Gasification II: Silicon chloride is vaporized to obtain gaseous silicon chloride, which is then fed into the heat exchange and cooling II process in step S12.

[0019] S12, Heat exchange cooling II: The chlorinated residue II obtained in step S10 is cooled by heat exchange using gaseous silicon chloride to obtain hot silicon chloride and tailings. The hot silicon chloride is sent to the combustion preheating II process in step S13.

[0020] S13, Combustion Preheating II: The hot silicon chloride obtained in step S12 is preheated by the combustion of air and fuel to obtain high-temperature silicon chloride and combustion exhaust gas II. The high-temperature silicon chloride is sent to the chlorination II process in step S10.

[0021] S14. Multi-stage condensation: The chlorinated flue gas obtained in step S10 is subjected to multi-stage condensation separation and purification to obtain solid aluminum chloride, solid ferric chloride and circulating silicon chloride I respectively. Circulating silicon chloride I is sent to the heat exchange cooling II process in step S12 to cool the chlorinated slag II obtained in step S10 by heat exchange.

[0022] S15, Gasification III: The solid aluminum chloride obtained in steps S7 and S14 is gasified to obtain gaseous aluminum chloride;

[0023] S16. Heat exchange: Preheat the gaseous aluminum chloride obtained in step S15 to obtain hot aluminum chloride.

[0024] S17, Fluorination: High-temperature silicon tetrafluoride is used to react with the hot aluminum chloride obtained in step S16 to produce hot aluminum fluoride and high-temperature fluorinated flue gas. The high-temperature fluorinated flue gas is sent to the heat exchange process in step S16 to preheat the gaseous aluminum chloride through heat exchange. The low-temperature fluorinated flue gas obtained after heat exchange is sent to the separation process in step S20.

[0025] S18, Heat exchange cooling III: The hot aluminum fluoride obtained in step S17 is cooled by heat exchange using silicon tetrafluoride to obtain aluminum fluoride product and hot silicon tetrafluoride.

[0026] S19, Combustion Preheating III: The hot silicon tetrafluoride obtained in step S18 is preheated by the combustion of air and fuel to obtain high-temperature silicon tetrafluoride and combustion exhaust gas III. The high-temperature silicon tetrafluoride is sent to the fluorination process in step S17.

[0027] S20. Separation: The low-temperature fluorinated flue gas is separated to obtain circulating silicon tetrafluoride and circulating silicon chloride II. The circulating silicon tetrafluoride is sent to the heat exchange and cooling III process in step S18 to cool the hot aluminum fluoride obtained in step S17 by heat exchange. The circulating silicon chloride II is sent to the gasification II process in step S11 for gasification.

[0028] Furthermore, in step S1, the particle size of the fine ash is <1μm.

[0029] Furthermore, in step S3, the temperature for chlorination denitrification is 400-600℃, the chlorination denitrification time is 0.1-0.5h, and the reactor for chlorination denitrification is a fluidized bed reactor. The fluidized bed reactor is equipped with inert oxides for auxiliary fluidization and heat storage. The inert oxides are one or a combination of spherical alumina particles and spherical zirconium oxide particles, with a particle size of 0.5-5mm.

[0030] Furthermore, in step S7, the condensation temperature is 25-170℃.

[0031] Furthermore, in step S8, the liquefaction separation temperature is -40 to -190°C.

[0032] Further, in step S10, the chlorination temperature is 700-900℃, the chlorination time is 0.5-1h, and the chlorination reactor is a fluidized bed reactor. The fluidized bed reactor is equipped with inert oxides for auxiliary fluidization and heat storage. The inert oxides are spherical silica particles with a particle size of 0.5-5mm.

[0033] Further, in step S14, solid ferric chloride is first obtained by condensation at 200-290°C, and then solid aluminum chloride is obtained by condensation at 70-170°C.

[0034] Furthermore, in step S17, the temperature of the fluorination reaction is 500-700℃, the fluorination reaction time is 0.5-1h, and the reactor for the fluorination reaction is a fluidized bed reactor, wherein the fluidized bed reactor contains seed powder, which is aluminum fluoride particles of 0.1-0.5mm.

[0035] Further, in step S20, recycled silicon tetrafluoride in the gas phase and recycled silicon chloride II in the liquid phase are separated at 20-50°C.

[0036] The beneficial effects of this invention are as follows:

[0037] 1. This invention eliminates the need for pelletizing. Through fine grinding and activation, it can significantly enhance the reactivity of primary chlorination and denitrification and secondary chlorination of aluminum ash, resulting in high reaction efficiency, low temperature, and effective reduction of energy consumption.

[0038] 2. This invention uses a fluidized bed with inert large-particle oxides for primary chlorination denitrification and secondary chlorination reactions. The inert large-particle oxides can inhibit the agglomeration of fine particles, break up bubbles, enhance mass and heat transfer between the gas and solid phases, and also play a role in heat storage, effectively improving the reaction efficiency and the stability of system operation.

[0039] 3. Based on the phase characteristics of the raw materials, this invention uses chlorine and silicon chloride as chlorinating agents to carry out primary chlorination denitrification and secondary chlorination reactions, respectively. No carbon is required, the operation is simple, there is no carbon emission during the chlorination process, and the chlorination products are easy to separate and purify.

[0040] 4. This invention prepares aluminum fluoride by reacting silicon tetrafluoride with aluminum chloride in a fluidized bed. By setting seed powder, nucleation sites and matrix are provided for the newly generated aluminum fluoride, promoting the fluorination reaction. The product has high purity and is easy to collect. At the same time, the by-product silicon chloride can be recycled for secondary chlorination process, effectively saving costs.

[0041] 5. This invention has a high waste heat recovery and utilization rate, which effectively improves the overall thermal efficiency of the process;

[0042] 6. This invention can not only achieve the harmless treatment of aluminum ash, but also efficiently convert the aluminum resources therein into high-value-added aluminum fluoride, resulting in significant economic and social benefits. Attached Figure Description

[0043] Figure 1 This is a flowchart illustrating the methods of various embodiments of the present invention. Detailed Implementation

[0044] The present invention will be further described below with reference to the accompanying drawings. It should be noted that this embodiment is based on the present technical solution and provides detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to this embodiment.

[0045] Example 1

[0046] This embodiment provides a method for preparing aluminum fluoride from aluminum ash, such as... Figure 1 As shown, it includes the following steps:

[0047] S1. Grinding: Grind the aluminum ash to obtain fine ash with a particle size of less than 1μm;

[0048] S2. Preheating: Preheat the fine ash obtained in step S1 to obtain hot fine ash;

[0049] S3, Chlorination I: High-temperature chlorine gas is used to chlorinate and denitrify the hot fine ash obtained in step S2, resulting in high-temperature chlorinated flue gas and chlorinated slag I. The high-temperature chlorinated flue gas is sent to the preheating process of step S2 to preheat the hot fine ash through heat exchange. The low-temperature chlorinated flue gas obtained after heat exchange is sent to the condensation and dust collection process of step S7. The chlorination and denitrification temperature is 400℃, the chlorination and denitrification time is 0.5h, and the chlorination and denitrification reactor is a fluidized bed reactor. The fluidized bed reactor is equipped with inert oxides for auxiliary fluidization and heat storage. The inert oxides are spherical alumina particles with a particle size of 0.5mm.

[0050] S4, Heat exchange cooling I: The chlorinated slag I obtained in step S3 is cooled by heat exchange using room temperature chlorine gas to obtain hot chlorine gas and cooled slag. The hot chlorine gas is sent to the combustion preheating I process in step S6.

[0051] S5. Washing and drying: The cooling residue obtained in step S4 is washed and dried with deionized water to obtain washing liquid and washing residue. The washing residue is sent to the chlorination II process in step S10.

[0052] S6. Combustion Preheating I: The hot chlorine gas obtained in step S4 is preheated by the combustion of air and fuel to obtain high-temperature chlorine gas and combustion tail gas I. The high-temperature chlorine gas is sent into the chlorination I process in step S3.

[0053] S7. Condensation and dust collection: The low-temperature chlorinated flue gas is condensed at 25°C to obtain nitrogen, chlorine and solid aluminum chloride. The solid aluminum chloride is sent to the gasification III process in step S15.

[0054] S8. Liquefaction and separation: The nitrogen and chlorine obtained in step S7 are separated at -40°C to obtain nitrogen and liquid chlorine.

[0055] S9. Gasification I: The liquid chlorine obtained in step S8 is gasified to obtain circulating chlorine gas. The circulating chlorine gas is sent to the heat exchange and cooling I process in step S4 to cool the chlorinated slag I obtained in step S3 by heat exchange.

[0056] S10, Chlorination II: The water-washed slag obtained in step S5 is chlorinated using high-temperature silicon chloride to obtain chlorinated flue gas and chlorinated slag II. The chlorinated flue gas is sent to the multi-stage condensation process in step S14. The chlorination temperature is 700℃ and the chlorination time is 1h. The chlorination reactor is a fluidized bed reactor. The fluidized bed reactor is equipped with inert oxides for auxiliary fluidization and heat storage. The inert oxides are spherical silica particles with a particle size of 5mm.

[0057] S11, Gasification II: Silicon chloride is vaporized to obtain gaseous silicon chloride, which is then fed into the heat exchange and cooling II process in step S12.

[0058] S12, Heat exchange cooling II: The chlorinated residue II obtained in step S10 is cooled by heat exchange using gaseous silicon chloride to obtain hot silicon chloride and tailings. The hot silicon chloride is sent to the combustion preheating II process in step S13.

[0059] S13, Combustion Preheating II: The hot silicon chloride obtained in step S12 is preheated by the combustion of air and fuel to obtain high-temperature silicon chloride and combustion exhaust gas II. The high-temperature silicon chloride is sent to the chlorination II process in step S10.

[0060] S14. Multi-stage condensation: The chlorinated flue gas obtained in step S10 is subjected to multi-stage condensation separation and purification to obtain solid aluminum chloride, solid ferric chloride and circulating silicon chloride I. Circulating silicon chloride I is sent to the heat exchange cooling II process in step S12 to cool the chlorinated slag II obtained in step S10 by heat exchange. Specifically, solid ferric chloride is first condensed at 200°C to obtain solid ferric chloride, and then solid aluminum chloride is condensed at 70°C.

[0061] S15, Gasification III: The solid aluminum chloride obtained in steps S7 and S14 is gasified to obtain gaseous aluminum chloride;

[0062] S16. Heat exchange: Preheat the gaseous aluminum chloride obtained in step S15 to obtain hot aluminum chloride.

[0063] S17, Fluorination: High-temperature silicon tetrafluoride is reacted with the hot aluminum chloride obtained in step S16 to produce hot aluminum fluoride and high-temperature fluorinated flue gas. The high-temperature fluorinated flue gas is sent to the heat exchange process in step S16 to preheat the gaseous aluminum chloride. The low-temperature fluorinated flue gas obtained after heat exchange is sent to the separation process in step S20. The temperature of the fluorination reaction is 500℃, the reaction time is 1h, and the reactor for the fluorination reaction is a fluidized bed reactor. The fluidized bed reactor is equipped with seed powder to provide nucleation sites and matrix for the newly generated aluminum fluoride and promote the fluorination reaction. The seed powder is 0.1mm aluminum fluoride particles.

[0064] S18, Heat exchange cooling III: The hot aluminum fluoride obtained in step S17 is cooled by heat exchange using silicon tetrafluoride to obtain aluminum fluoride product and hot silicon tetrafluoride.

[0065] S19, Combustion Preheating III: The hot silicon tetrafluoride obtained in step S18 is preheated by the combustion of air and fuel to obtain high-temperature silicon tetrafluoride and combustion exhaust gas III. The high-temperature silicon tetrafluoride is sent to the fluorination process in step S17.

[0066] S20. Separation: The low-temperature fluorinated flue gas is separated at 20°C to obtain gaseous circulating silicon tetrafluoride and liquid circulating silicon chloride II. The circulating silicon tetrafluoride is sent to the heat exchange cooling III process in step S18 to cool the hot aluminum fluoride obtained in step S17 by heat exchange. The circulating silicon chloride II is sent to the gasification II process in step S11 for gasification.

[0067] Example 2

[0068] The method flow of this embodiment is basically the same as that of Embodiment 1, except that: in step S3, the chlorination denitrification temperature is 600℃ and the time is 0.1h, and the fluidized bed reactor contains 0.5mm spherical zirconium oxide particles; in step S7, the condensation temperature is 170℃; in step S8, the liquefaction separation temperature is -190℃; in step S10, the chlorination temperature is 900℃ and the chlorination time is 0.5h, and the particle size of the spherical silica particles in the fluidized bed reactor is 0.5mm; in step S14, solid-phase ferric chloride is first condensed at 290℃, and then solid-phase aluminum chloride is condensed at 170℃; in step S17, the fluorination temperature is 700℃ and the fluorination time is 0.5h, and the seed powder in the fluidized bed reactor consists of 0.5mm aluminum fluoride particles; in step S20, gaseous circulating silicon tetrafluoride and liquid-phase circulating silicon chloride II are separated at 50℃.

[0069] Example 3

[0070] The method flow of this embodiment is basically the same as that of Embodiment 1, except that: in step S3, the chlorination denitrification temperature is 450℃ and the time is 0.4h, and 5mm spherical zirconium oxide particles are provided in the fluidized bed reactor; in step S7, the condensation temperature is 100℃; in step S8, the liquefaction separation temperature is -100℃; in step S10, the chlorination temperature is 750℃ and the chlorination time is 0.7h, and the particle size of the spherical silica particles in the fluidized bed reactor is 2mm; in step S14, solid-phase ferric chloride is first condensed at 220℃, and then solid-phase aluminum chloride is condensed at 100℃; in step S17, the fluorination temperature is 550℃ and the fluorination time is 0.8h, and the seed powder in the fluidized bed reactor is 0.3mm aluminum fluoride particles; in step S20, gaseous circulating silicon tetrafluoride and liquid-phase circulating silicon chloride II are separated at 30℃.

[0071] Example 4

[0072] The method flow of this embodiment is basically the same as that of Embodiment 1, except that: in step S3, the chlorination denitrification temperature is 570℃ and the time is 0.2h, and the fluidized bed reactor contains 5mm spherical alumina particles; in step S7, the condensation temperature is 50℃; in step S8, the condensation temperature is 100℃; in step S8, the liquefaction separation temperature is -50℃; in step S10, the chlorination temperature is 840℃ and the chlorination time is 0.6h, and the particle size of the spherical silica particles in the fluidized bed reactor is 3mm; in step S14, solid-phase ferric chloride is first condensed at 250℃, and then solid-phase aluminum chloride is condensed at 150℃; in step S17, the fluorination temperature is 660℃ and the fluorination time is 0.6h, and the seed powder in the fluidized bed reactor consists of 0.2mm aluminum fluoride particles; in step S20, gaseous circulating silicon tetrafluoride and liquid circulating silicon chloride II are separated at 25℃.

[0073] For those skilled in the art, various corresponding changes and modifications can be made based on the above technical solutions and concepts, and all such changes and modifications should be included within the protection scope of the claims of this invention.

Claims

1. A method for preparing aluminum fluoride from aluminum ash, characterized in that: Includes the following steps: S1. Grinding: Grinding aluminum ash to obtain fine ash; S2. Preheating: Preheat the fine ash obtained in step S1 to obtain hot fine ash; S3, Chlorination I: High-temperature chlorine gas is used to chlorinate and denitrify the hot fine ash obtained in step S2, resulting in high-temperature chlorinated flue gas and chlorinated slag I. The high-temperature chlorinated flue gas is fed into the preheating process of step S2 to preheat the hot fine ash through heat exchange. The low-temperature chlorinated flue gas obtained after heat exchange is fed into the condensation and dust collection process of step S7. The chlorination and denitrification temperature is 400-600℃, the chlorination and denitrification time is 0.1-0.5h, and the chlorination and denitrification reactor is a fluidized bed reactor. The fluidized bed reactor is equipped with inert oxides for auxiliary fluidization and heat storage. S4, Heat exchange cooling I: The chlorinated slag I obtained in step S3 is cooled by heat exchange using room temperature chlorine gas to obtain hot chlorine gas and cooled slag. The hot chlorine gas is sent to the combustion preheating I process in step S6. S5. Washing and drying: The cooling residue obtained in step S4 is washed and dried with deionized water to obtain washing liquid and washing residue. The washing residue is sent to the chlorination II process in step S10. S6. Combustion Preheating I: The hot chlorine gas obtained in step S4 is preheated by the combustion of air and fuel to obtain high-temperature chlorine gas and combustion tail gas I. The high-temperature chlorine gas is sent into the chlorination I process in step S3. S7. Condensation and dust collection: The low-temperature chlorinated flue gas is condensed to obtain nitrogen, chlorine and solid aluminum chloride. The solid aluminum chloride is sent to the gasification III process in step S15. S8. Liquefaction and separation: Separate the nitrogen and chlorine obtained in step S7 to obtain nitrogen and liquid chlorine; S9. Gasification I: The liquid chlorine obtained in step S8 is gasified to obtain circulating chlorine gas. The circulating chlorine gas is sent to the heat exchange and cooling I process in step S4 to cool the chlorinated slag I obtained in step S3 by heat exchange. S10, Chlorination II: The water-washed residue obtained in step S5 is chlorinated using high-temperature silicon chloride to obtain chlorinated flue gas and chlorinated residue II. The chlorinated flue gas is sent to the multi-stage condensation process in step S14. The chlorination temperature is 700-900℃, the chlorination time is 0.5-1h, and the chlorination reactor is a fluidized bed reactor. The fluidized bed reactor is equipped with inert oxides for auxiliary fluidization and heat storage. S11, Gasification II: Silicon chloride is vaporized to obtain gaseous silicon chloride, which is then fed into the heat exchange and cooling II process in step S12. S12, Heat exchange cooling II: The chlorinated residue II obtained in step S10 is cooled by heat exchange using gaseous silicon chloride to obtain hot silicon chloride and tailings. The hot silicon chloride is sent to the combustion preheating II process in step S13. S13, Combustion Preheating II: The hot silicon chloride obtained in step S12 is preheated by the combustion of air and fuel to obtain high-temperature silicon chloride and combustion exhaust gas II. The high-temperature silicon chloride is sent to the chlorination II process in step S10. S14. Multi-stage condensation: The chlorinated flue gas obtained in step S10 is subjected to multi-stage condensation separation and purification to obtain solid aluminum chloride, solid ferric chloride and circulating silicon chloride I respectively. Circulating silicon chloride I is sent to the heat exchange cooling II process in step S12 to cool the chlorinated slag II obtained in step S10 by heat exchange. S15, Gasification III: The solid aluminum chloride obtained in steps S7 and S14 is gasified to obtain gaseous aluminum chloride; S16. Heat exchange: Preheat the gaseous aluminum chloride obtained in step S15 to obtain hot aluminum chloride. S17, Fluorination: High-temperature silicon tetrafluoride is reacted with the hot aluminum chloride obtained in step S16 to produce hot aluminum fluoride and high-temperature fluorinated flue gas. The high-temperature fluorinated flue gas is sent to the heat exchange process in step S16 to preheat the gaseous aluminum chloride. The low-temperature fluorinated flue gas obtained after heat exchange is sent to the separation process in step S20. The temperature of the fluorination reaction is 500-700℃, the reaction time is 0.5-1h, and the reactor for the fluorination reaction is a fluidized bed reactor. The fluidized bed reactor contains seed powder, which is aluminum fluoride particles of 0.1-0.5mm. S18, Heat exchange cooling III: The hot aluminum fluoride obtained in step S17 is cooled by heat exchange using silicon tetrafluoride to obtain aluminum fluoride product and hot silicon tetrafluoride. S19, Combustion Preheating III: The hot silicon tetrafluoride obtained in step S18 is preheated by the combustion of air and fuel to obtain high-temperature silicon tetrafluoride and combustion exhaust gas III. The high-temperature silicon tetrafluoride is sent to the fluorination process in step S17. S20. Separation: The low-temperature fluorinated flue gas is separated to obtain circulating silicon tetrafluoride and circulating silicon chloride II. The circulating silicon tetrafluoride is sent to the heat exchange and cooling III process in step S18 to cool the hot aluminum fluoride obtained in step S17 by heat exchange. The circulating silicon chloride II is sent to the gasification II process in step S11 for gasification.

2. The method according to claim 1, characterized in that, In step S1, the particle size of the fine ash is <1μm.

3. The method according to claim 1, characterized in that, In step S3, the inert oxide is one or a combination of two of spherical alumina particles and spherical zirconium oxide particles, with a particle size of 0.5-5 mm.

4. The method according to claim 1, characterized in that, In step S7, the condensation temperature is 25-170℃.

5. The method according to claim 1, characterized in that, In step S8, the liquefaction separation temperature is -40 to -190℃.

6. The method according to claim 1, characterized in that, In step S10, the inert oxide is spherical silicon dioxide particles with a particle size of 0.5-5 mm.

7. The method according to claim 1, characterized in that, In step S14, solid ferric chloride is first obtained by condensation at 200-290℃, and then solid aluminum chloride is obtained by condensation at 70-170℃.

8. The method according to claim 1, characterized in that, In step S20, recycled silicon tetrafluoride in the gas phase and recycled silicon chloride II in the liquid phase are separated at 20-50°C.

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