Method for efficiently preparing aluminum fluoride from aluminum ash

Abstract

This invention discloses a method for efficiently preparing aluminum fluoride from aluminum ash, comprising the following steps: Aluminum ash is ground, preheated, and then oxidized for denitrification. Silicon chloride is used to chlorinate the aluminum, iron, and magnesium in the oxidized aluminum ash into aluminum chloride, ferric chloride, and magnesium chloride. High-purity aluminum chloride is obtained through multi-stage condensation and purification. The aluminum chloride is then gasified, preheated, and reacted with silicon tetrafluoride to produce aluminum fluoride and silicon chloride. The silicon chloride is recycled for use in the chlorination process. This invention significantly improves the oxidative denitrification efficiency of aluminum ash through grinding and activation. The chlorination process uses silicon chloride as the chlorinating agent, eliminating the need for carbon addition. The chlorination products are easily separated, and the operation is simple. Silicon tetrafluoride is used to fluorinate aluminum chloride to prepare aluminum fluoride. The byproduct silicon chloride can be recycled within the system, effectively reducing production costs. Simultaneously, the system has high energy utilization, enabling the harmless treatment of aluminum ash and the large-scale, efficient 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 efficiently 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 efficiently preparing aluminum fluoride from aluminum ash.

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

[0007] A method for efficiently 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, Combustion Preheating I: High-temperature oxygen-enriched flue gas is obtained by burning excess oxygen with fuel, and the high-temperature oxygen-enriched flue gas is sent into the oxidation process in step S4.

[0011] S4. Oxidation: The hot fine ash obtained in step S2 is oxidized and denitrified using high-temperature oxygen-enriched flue gas to obtain high-temperature oxidized flue gas and oxides. The high-temperature oxidized flue gas is sent to the preheating process in step S2 to preheat the fine ash through heat exchange.

[0012] S5. Chlorination: High-temperature silicon chloride is used to react with the oxide obtained in step S4 to produce chlorinated flue gas and chlorinated slag. The chlorinated flue gas is sent to the multi-stage condensation process in step S9.

[0013] S6, Gasification I: Silicon chloride is vaporized to obtain gaseous silicon chloride, which is then sent to the heat exchange and cooling I process in step S6.

[0014] S7, Heat exchange cooling I: The chlorinated residue obtained in step S5 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 S8.

[0015] S8. Combustion Preheating II: The hot silicon chloride obtained in step S7 is preheated by the combustion of air and fuel to obtain high-temperature silicon chloride and combustion exhaust gas I. The high-temperature silicon chloride is sent to the chlorination process in step S5.

[0016] S9. Multi-stage condensation: The chlorinated flue gas obtained in step S5 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 I process in step S7 to cool the chlorinated slag through heat exchange.

[0017] S10, Gasification II: The solid aluminum chloride obtained in step S9 is gasified to obtain gaseous aluminum chloride;

[0018] S11. Heat exchange: The gaseous aluminum chloride obtained in step S10 is preheated to obtain hot aluminum chloride.

[0019] S12, Fluorination: High-temperature silicon tetrafluoride is used to react with the hot aluminum chloride obtained in step S11 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 S11 to preheat the gaseous aluminum chloride through heat exchange. The low-temperature fluorinated flue gas after heat exchange is sent to the separation process in step S15.

[0020] S13, Heat exchange cooling II: The hot aluminum fluoride obtained in step S12 is cooled by heat exchange using silicon tetrafluoride to obtain aluminum fluoride product and hot silicon tetrafluoride.

[0021] S14, Combustion Preheating III: The hot silicon tetrafluoride obtained in step S13 is preheated by the combustion of air and fuel to obtain high-temperature silicon tetrafluoride and combustion exhaust gas II. The high-temperature silicon tetrafluoride is then fed into the fluorination process in step S12.

[0022] S15. Separation: The low-temperature fluorinated flue gas is separated to obtain recycled silicon tetrafluoride and recycled silicon chloride II. The recycled silicon tetrafluoride is sent to the heat exchange cooling II process in step S13 to cool the hot aluminum fluoride through heat exchange. The recycled silicon chloride II is sent to the heat exchange cooling I process in step S7 to cool the chlorinated slag through heat exchange.

[0023] Furthermore, in step S1, the particle size of the fine ash is <1μm.

[0024] Further, in step S4, the temperature for oxidative denitrification is 400-600℃, the time is 0.1-0.5h, and the reactor for oxidative 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, and the particle size of the inert oxides is 0.5-5mm.

[0025] Furthermore, in step S5, the chlorination reaction temperature is 700-900℃, the time is 0.5-1h, and the reactor for the chlorination reaction 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.

[0026] Further, in step S9, 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.

[0027] Furthermore, in step S12, the temperature of the fluorination reaction is 500-700℃, the 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.

[0028] Further, in step S15, the low-temperature fluorinated flue gas is separated at 20-50°C to obtain liquid-phase circulating silicon chloride II and gas-phase circulating silicon tetrafluoride.

[0029] The beneficial effects of this invention are as follows:

[0030] 1. This invention eliminates the need for pelletizing; by fine grinding and activation, it can significantly enhance the reactivity of aluminum ash oxidation and denitrification, resulting in high reaction efficiency.

[0031] 2. This invention uses a fluidized bed with inert large-particle oxides for oxidative denitrification and 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.

[0032] 3. This invention uses silicon chloride as the chlorinating agent, which eliminates the need for carbon preparation, simplifies operation, eliminates carbon emissions during the chlorination process, and makes the chlorination products easy to separate and purify;

[0033] 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 the chlorination process, effectively saving costs.

[0034] 5. This invention has a high waste heat recovery and utilization rate, which effectively improves the thermal efficiency of the overall process system;

[0035] 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

[0036] Figure 1 This is a flowchart illustrating the methods of various embodiments of the present invention. Detailed Implementation

[0037] 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.

[0038] Example 1

[0039] This embodiment provides a method for efficiently preparing aluminum fluoride from aluminum ash, such as... Figure 1 As shown, it includes the following steps:

[0040] S1. Grinding: Grind the aluminum ash to obtain fine ash with a particle size of less than 1μm.

[0041] S2. Preheating: Preheat the fine ash obtained in step S1 to obtain hot fine ash.

[0042] S3, Combustion Preheating I: High-temperature oxygen-enriched flue gas is obtained by burning excess oxygen with fuel, and the high-temperature oxygen-enriched flue gas is sent to the oxidation process in step S4.

[0043] S4. Oxidation: The hot fine ash obtained in step S2 is oxidized and denitrified using high-temperature oxygen-enriched flue gas to obtain high-temperature oxidized flue gas and oxides. The high-temperature oxidized flue gas is sent to the preheating process in step S2 to preheat the fine ash through heat exchange. The oxidation and denitrification temperature is 400℃ and the time is 0.5h. The reactor is a fluidized bed reactor. The fluidized bed reactor is equipped with inert oxides to assist fluidization and heat storage. The inert oxides are spherical alumina particles with a particle size of 0.5mm.

[0044] S5. Chlorination: The oxide obtained in step S4 is reacted with silicon chloride at high temperature to produce chlorinated flue gas and chlorinated slag. The chlorinated flue gas is sent to the multi-stage condensation process in step S9. The temperature of the chlorination reaction is 700℃ and the time is 1 hour. The 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 5 mm.

[0045] S6, Gasification I: Silicon chloride is vaporized to obtain gaseous silicon chloride, which is then sent to the heat exchange and cooling I process in step S6.

[0046] S7, Heat exchange cooling I: The chlorinated residue obtained in step S5 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 S8.

[0047] S8. Combustion Preheating II: The hot silicon chloride obtained in step S7 is preheated by the combustion of air and fuel to obtain high-temperature silicon chloride and combustion exhaust gas I. The high-temperature silicon chloride is sent to the chlorination process in step S5.

[0048] S9. Multi-stage condensation: The chlorinated flue gas obtained in step S5 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 I process in step S7 to cool the chlorinated slag through 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.

[0049] S10, Gasification II: The solid aluminum chloride obtained in step S9 is gasified to obtain gaseous aluminum chloride;

[0050] S11. Heat exchange: The gaseous aluminum chloride obtained in step S10 is preheated to obtain hot aluminum chloride.

[0051] S12, Fluorination: High-temperature silicon tetrafluoride is reacted with the hot aluminum chloride obtained in step S11 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 S11 to preheat the gaseous aluminum chloride. The low-temperature fluorinated flue gas after heat exchange is sent to the separation process in step S15. The temperature of the fluorination reaction is 500℃ and the time is 1h. The reactor is a fluidized bed reactor. Seed powder is provided in the fluidized bed reactor 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.

[0052] S13, Heat exchange cooling II: The hot aluminum fluoride obtained in step S12 is cooled by heat exchange using silicon tetrafluoride to obtain aluminum fluoride product and hot silicon tetrafluoride.

[0053] S14, Combustion Preheating III: The hot silicon tetrafluoride obtained in step S13 is preheated by the combustion of air and fuel to obtain high-temperature silicon tetrafluoride and combustion exhaust gas II. The high-temperature silicon tetrafluoride is then fed into the fluorination process in step S12.

[0054] S15. Separation: The low-temperature fluorinated flue gas is separated at 20°C to obtain liquid-phase circulating silicon chloride II and gas-phase circulating silicon tetrafluoride. The circulating silicon tetrafluoride is sent to the heat exchange cooling II process in step S13 to cool the hot aluminum fluoride through heat exchange. The circulating silicon chloride II is sent to the heat exchange cooling I process in step S7 to cool the chlorinated slag through heat exchange.

[0055] Example 2

[0056] The method flow of this embodiment is basically the same as that of Embodiment 1, except that: in step S4, the temperature of oxidation denitrification is 600℃ and the time is 0.1h, and the particle size of spherical alumina particles in the fluidized bed reactor is 5mm; in step S5, the temperature of chlorination reaction is 900℃ and the time is 0.5h, and the particle size of spherical silica particles in the fluidized bed reactor is 0.5mm; in step S9, solid-phase ferric chloride is first obtained by condensation at 290℃, and then solid-phase aluminum chloride is obtained by condensation at 170℃; in step S12, the temperature of fluorination reaction is 700℃ and the fluorination time is 0.5h, and the seed powder in the fluidized bed reactor is 0.5mm aluminum fluoride particles; in step S15, the low-temperature fluorination flue gas is separated at 50℃ to obtain liquid-phase circulating silicon chloride II and gas-phase circulating silicon tetrafluoride.

[0057] Example 3

[0058] The method flow of this embodiment is basically the same as that of Embodiment 1, except that: in step S4, the temperature of oxidation denitrification is 500℃ and the time is 0.3h, and the particle size of the spherical zirconium oxide particles in the fluidized bed reactor is 0.5mm; in step S5, the temperature of the chlorination reaction is 800℃ and the time is 0.6h, and the particle size of the spherical silica particles in the fluidized bed reactor is 3mm; in step S9, solid-phase ferric chloride is first obtained by condensation at 250℃, and then solid-phase aluminum chloride is obtained by condensation at 100℃; in step S12, the temperature of the fluorination reaction is 600℃ and the fluorination time is 0.8h, and the seed powder in the fluidized bed reactor is 0.3mm aluminum fluoride particles; in step S15, the low-temperature fluorination flue gas is separated at 30℃ to obtain liquid-phase circulating silicon chloride II and gas-phase circulating silicon tetrafluoride.

[0059] Example 4

[0060] The method flow of this embodiment is basically the same as that of Embodiment 1, except that: in step S4, the temperature of oxidation denitrification is 530℃ and the time is 0.2h, and the particle size of the spherical zirconium oxide particles in the fluidized bed reactor is 5mm; in step S5, the temperature of the chlorination reaction is 780℃ and the time is 0.7h, and the particle size of the spherical silica particles in the fluidized bed reactor is 1mm; in step S9, solid-phase ferric chloride is first obtained by condensation at 220℃, and then solid-phase aluminum chloride is obtained by condensation at 120℃; in step S12, the temperature of the fluorination reaction is 620℃ and the fluorination time is 0.7h, and the seed powder in the fluidized bed reactor is 0.2mm aluminum fluoride particles; in step S15, the low-temperature fluorination flue gas is separated at 40℃ to obtain liquid-phase circulating silicon chloride II and gas-phase circulating silicon tetrafluoride.

[0061] 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 efficiently 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, Combustion Preheating I: High-temperature oxygen-enriched flue gas is obtained by burning excess oxygen with fuel, and the high-temperature oxygen-enriched flue gas is sent into the oxidation process in step S4. S4. Oxidation: The hot fine ash obtained in step S2 is oxidized and denitrified using high-temperature oxygen-enriched flue gas to obtain high-temperature oxidized flue gas and oxides. The high-temperature oxidized flue gas is sent to the preheating process in step S2 to preheat the fine ash through heat exchange. The temperature of oxidation and denitrification is 400-600℃, and the time is 0.1-0.5h. The reactor for oxidation and denitrification is a fluidized bed reactor, which is equipped with inert oxides to assist fluidization and heat storage. S5. Chlorination: High-temperature silicon chloride is reacted with the oxide obtained in step S4 to produce chlorinated flue gas and chlorinated slag. The chlorinated flue gas is sent to the multi-stage condensation process in step S9. The temperature of the chlorination reaction is 700-900℃ and the time is 0.5-1h. The reactor for the chlorination reaction is a fluidized bed reactor, which is equipped with inert oxides to assist fluidization and heat storage. S6, Gasification I: Silicon chloride is vaporized to obtain gaseous silicon chloride, which is then fed into the heat exchange and cooling I process in step S7. S7, Heat exchange cooling I: The chlorinated residue obtained in step S5 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 S8. S8. Combustion Preheating II: The hot silicon chloride obtained in step S7 is preheated by the combustion of air and fuel to obtain high-temperature silicon chloride and combustion exhaust gas I. The high-temperature silicon chloride is sent to the chlorination process in step S5. S9. Multi-stage condensation: The chlorinated flue gas obtained in step S5 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 I process in step S7 to cool the chlorinated slag through heat exchange. First, solid ferric chloride is obtained by condensation at 200-290℃, and then solid aluminum chloride is obtained by condensation at 70-170℃. S10, Gasification II: The solid aluminum chloride obtained in step S9 is gasified to obtain gaseous aluminum chloride; S11. Heat exchange: The gaseous aluminum chloride obtained in step S10 is preheated to obtain hot aluminum chloride. S12, Fluorination: High-temperature silicon tetrafluoride is used to react with the hot aluminum chloride obtained in step S11 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 S11 to preheat the gaseous aluminum chloride through heat exchange. The low-temperature fluorinated flue gas after heat exchange is sent to the separation process in step S15. S13, Heat exchange cooling II: The hot aluminum fluoride obtained in step S12 is cooled by heat exchange using silicon tetrafluoride to obtain aluminum fluoride product and hot silicon tetrafluoride. S14, Combustion Preheating III: The hot silicon tetrafluoride obtained in step S13 is preheated by the combustion of air and fuel to obtain high-temperature silicon tetrafluoride and combustion exhaust gas II. The high-temperature silicon tetrafluoride is then fed into the fluorination process in step S12. S15. Separation: The low-temperature fluorinated flue gas is separated to obtain recycled silicon tetrafluoride and recycled silicon chloride II. The recycled silicon tetrafluoride is sent to the heat exchange cooling II process in step S13 to cool the hot aluminum fluoride through heat exchange. The recycled silicon chloride II is sent to the heat exchange cooling I process in step S7 to cool the chlorinated slag through heat exchange.

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 S4, the inert oxide is one or a combination of two of spherical alumina particles and spherical zirconium oxide particles, and the particle size of the inert oxide is 0.5-5 mm.

4. The method according to claim 1, characterized in that, In step S5, the inert oxide is spherical silica particles with a particle size of 0.5-5 mm.

5. The method according to claim 1, characterized in that, In step S12, the temperature of the fluorination reaction is 500-700℃ and the time is 0.5-1h. The reactor for the fluorination reaction is a fluidized bed reactor, and the fluidized bed reactor contains seed powder, which is aluminum fluoride particles of 0.1-0.5mm.

6. The method according to claim 1, characterized in that, In step S15, the low-temperature fluorinated flue gas is separated at 20-50°C to obtain liquid-phase circulating silicon chloride II and gas-phase circulating silicon tetrafluoride.

Images