Method for high-value utilization of secondary aluminum dross

Abstract

The application discloses a method for high-value utilization of secondary aluminum ash, and steps are as follows: after secondary aluminum ash is finely ground and preheated, the secondary aluminum ash is added into a fluidized bed and heated by microwaves under the assistance of high-temperature-resistant wave-absorbing materials to be chlorinated, aluminum and aluminum nitride in the secondary aluminum ash are converted into aluminum chloride, nitrogen and other hot flue gas, solid-phase aluminum chloride is obtained through heat exchange, cooling and condensation and dust collection, chlorination slag is obtained through heat exchange, cooling, water washing and drying, and soluble salts are removed from the water washing slag, after high-temperature-resistant wave-absorbing materials are recovered through screening, aluminum chloride solution is obtained through hydrochloric acid leaching, solid-phase aluminum chloride obtained through chlorination condensation is dissolved in the aluminum chloride solution, ammonia gas is introduced to adjust the pH to 2-5, and after aging and drying, polyaluminum chloride products can be obtained. The method can significantly reduce the chlorination temperature and improve the reaction efficiency by adopting fine grinding and activation and microwave heating, the carbon is not needed in the chlorination process, the operation is simple, the energy utilization rate of the system is high, the large-scale clean and efficient utilization of the secondary aluminum ash can be realized, and the method has good 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 the high-value utilization of secondary 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 over 3 million tons of aluminum ash annually. Because it contains hazardous substances such as aluminum nitride, soluble fluoride salts, and chloride salts, it is listed in the "National Hazardous Waste List." Secondary aluminum ash is the residue after primary aluminum ash has been processed using the ash-frying method to recover metallic aluminum. The hazardous substances in secondary aluminum ash are further enriched, increasing its reactivity and hazard. The harmless treatment and high-value utilization of secondary aluminum ash are of great significance to the green and high-quality development of the aluminum industry.

[0003] The harmless treatment of secondary aluminum ash mainly involves denitrification and desalination. The most common denitrification method is to calcine the secondary 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, a binder is used to form secondary aluminum ash and sodium alkali into pellets of 30-200mm. 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 technology in efficiently utilizing secondary aluminum ash, the key to achieving large-scale, efficient, and clean utilization of secondary aluminum ash lies in strengthening the denitrification, desalination, and high-value utilization of aluminum through process and technological innovation, thereby improving reaction efficiency and reducing process energy consumption. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention aims to provide a method for the high-value utilization of secondary aluminum ash.

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

[0007] A method for high-value utilization of secondary aluminum ash includes the following steps:

[0008] S1. Grinding process: Grind the secondary aluminum ash into fine powder to obtain fine ash;

[0009] S2. Preheating process: The fine ash obtained in step S1 is preheated to obtain hot fine ash;

[0010] S3, Microwave Chlorination Process: Using hot chlorine gas with the assistance of high-temperature resistant microwave absorbing material, the hot fine ash obtained in step S2 is microwave-heated and chlorinated to obtain chlorinated slag and a mixed gas phase of high-temperature nitrogen, chlorine and gaseous aluminum chloride; the mixed gas phase of high-temperature nitrogen, chlorine and gaseous aluminum chloride is sent to the preheating process of step S2 to preheat the fine ash through heat exchange; the mixed gas phase of low-temperature nitrogen, chlorine and gaseous aluminum chloride obtained after heat exchange is sent to the condensation and dust collection process of step S8.

[0011] S4. Heat exchange and cooling process: The chlorination residue obtained in step S3 is cooled by heat exchange using room temperature chlorine gas to obtain cooled residue and hot chlorine gas. The hot chlorine gas is then sent into the microwave chlorination process in step S3.

[0012] S5. Washing and drying process: The cooling residue obtained in step S4 is washed and dried with pure water to remove soluble fluorides and chlorides, resulting in washing liquid and washing residue.

[0013] S6. Screening process: The water washing residue obtained in step S5 is screened to obtain high temperature absorbing material and fine material. The high temperature absorbing material is sent to the microwave chlorination process in step S3.

[0014] S7. Hydrochloric acid leaching process: The fine material obtained in step S6 is leached with dilute hydrochloric acid to obtain aluminum chloride solution and tailings.

[0015] S8. Condensation and dust collection process: The mixed gas phase of low-temperature nitrogen, chlorine and gaseous aluminum chloride obtained in step S2 is condensed and dust collected to obtain nitrogen, chlorine and solid aluminum chloride. The nitrogen and chlorine are sent to the liquefaction and separation process in step S10.

[0016] S9. Aging and drying process: Dissolve the solid aluminum chloride obtained in step S8 into the aluminum chloride solution obtained in step S7, introduce ammonia gas to adjust the pH to 2-5, and then perform aging and drying to obtain polyaluminum chloride product.

[0017] S10, Liquefaction and Separation Process: The nitrogen and chlorine obtained in step S8 are liquefied and separated to obtain liquid chlorine and nitrogen;

[0018] S11. Gasification process: The liquid chlorine obtained in step S10 is vaporized to obtain chlorine gas, which is then sent to the heat exchange and cooling process in step S4.

[0019] Furthermore, in step S1, the particle size of the fine ash is <1μm.

[0020] Furthermore, in step S3, the chlorination temperature is 350-550℃, the chlorination time is 0.5-1h, and the reactor used for chlorination is a fluidized bed reactor, which is equipped with high-temperature resistant microwave absorbing material.

[0021] Furthermore, the high-temperature resistant microwave absorbing material is spherical iron oxide particles, and the particle size of the spherical iron oxide particles is 0.5-3mm.

[0022] Furthermore, in step S8, the condensation temperature is 25-170℃.

[0023] Furthermore, in step S9, the concentration of the aluminum chloride solution obtained after dissolving the solid aluminum chloride obtained in step S8 into the aluminum chloride solution obtained in step S7 is 2-5 mol / L.

[0024] Furthermore, in step S10, the liquefaction temperature is -40 to -190°C.

[0025] The beneficial effects of this invention are as follows:

[0026] 1. This invention does not require carbon addition. It enhances the reactivity of secondary aluminum ash through fine grinding and uses chlorine to convert aluminum and aluminum nitride in the finely ground secondary aluminum ash into aluminum chloride and nitrogen. The reaction temperature is low, which effectively reduces energy consumption.

[0027] 2. This invention does not require pelletizing. It uses microwave heating of high-temperature resistant microwave absorbing material to provide the heat required for the chlorination reaction. The heating rate is fast and the heating is uniform. At the same time, the high-temperature resistant microwave absorbing material can significantly improve the fluidization quality of the secondary aluminum ash fine powder, strengthen the gas-solid contact, improve the mass and heat transfer rate between the gas and solid phases, and result in a fast reaction rate and high reaction efficiency.

[0028] 3. The high-temperature absorbing material used in this invention has good thermal stability and excellent wave absorption performance, and can be recycled in the system, effectively saving costs;

[0029] 4. The present invention has a high waste heat recovery and utilization rate, which effectively improves the thermal efficiency of the overall process system.

[0030] 5. This invention is easy to operate, has a simple process, strong applicability of raw materials, and produces high-quality products with high added value, enabling the clean and efficient utilization of secondary aluminum ash. Attached Figure Description

[0031] Figure 1 This is a flowchart illustrating the methods of various embodiments of the present invention. Detailed Implementation

[0032] 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.

[0033] Example 1

[0034] This embodiment provides a method for the high-value utilization of secondary aluminum ash, such as... Figure 1 As shown, it includes the following steps:

[0035] S1. Grinding process: Grind the secondary aluminum ash into fine powder to obtain fine ash with a particle size of less than 1μm;

[0036] S2. Preheating process: The fine ash obtained in step S1 is preheated to obtain hot fine ash;

[0037] S3, Microwave Chlorination Process: Using hot chlorine gas with the assistance of a high-temperature resistant microwave absorbing material, the hot fine ash obtained in step S2 is microwave-heated and chlorinated to obtain chlorinated slag and a mixed gas phase of high-temperature nitrogen, chlorine gas and gaseous aluminum chloride; the chlorination temperature is 350℃, the chlorination time is 1h, the reactor is a fluidized bed reactor, and the high-temperature resistant microwave absorbing material is spherical iron oxide particles with a particle size of 0.5mm;

[0038] The high-temperature nitrogen, chlorine and gaseous aluminum chloride mixture is fed into the preheating process of step S2 to preheat the fine ash through heat exchange. The low-temperature nitrogen, chlorine and gaseous aluminum chloride mixture obtained after heat exchange is fed into the condensation and dust collection process of step S8.

[0039] S4. Heat exchange and cooling process: The chlorination residue obtained in step S3 is cooled by heat exchange using room temperature chlorine gas to obtain cooled residue and hot chlorine gas. The hot chlorine gas is then sent into the microwave chlorination process in step S3.

[0040] S5. Washing and drying process: The cooling residue obtained in step S4 is washed and dried with pure water to remove soluble fluorides and chlorides, resulting in washing liquid and washing residue.

[0041] S6. Screening process: The water washing residue obtained in step S5 is screened to obtain high temperature absorbing material and fine material. The high temperature absorbing material is sent to the microwave chlorination process in step S3.

[0042] S7. Hydrochloric acid leaching process: The fine material obtained in step S6 is leached with dilute hydrochloric acid to obtain aluminum chloride solution and tailings.

[0043] S8. Condensation and dust collection process: The mixed gas phase of low-temperature nitrogen, chlorine and gaseous aluminum chloride obtained in step S2 is condensed and dust collected to obtain nitrogen, chlorine and solid aluminum chloride. The nitrogen and chlorine are sent to the liquefaction and separation process in step S10; the condensation temperature is 25℃.

[0044] S9. Aging and drying process: The solid aluminum chloride obtained in step S8 is dissolved in the aluminum chloride solution obtained in step S7 to obtain an aluminum chloride solution with a concentration of 5 mol / L. Ammonia gas is introduced to adjust the pH to 4, and then aging and drying are carried out to obtain polyaluminum chloride product.

[0045] S10, Liquefaction and Separation Process: The nitrogen and chlorine obtained in step S8 are liquefied and separated to obtain liquid chlorine and nitrogen; the liquefaction temperature is -40℃.

[0046] S11. Gasification process: The liquid chlorine obtained in step S10 is vaporized to obtain chlorine gas, which is then sent to the heat exchange and cooling process in step S4.

[0047] Example 2

[0048] The method flow of this embodiment is basically the same as that of Embodiment 1, except that: in step S3, the chlorination temperature is 550℃, the chlorination time is 0.5h, and the particle size of the spherical iron oxide particles is 3mm; in step S8, the condensation temperature is 170℃; in step S9, the concentration of the aluminum chloride solution obtained after dissolving the solid aluminum chloride obtained in step S8 into the aluminum chloride solution obtained in step S7 is 3mol / L, and ammonia gas is introduced to adjust the pH to 2; in step S10, the liquefaction temperature is -190℃.

[0049] Example 3

[0050] The method flow of this embodiment is basically the same as that of Embodiment 1, except that: in step S3, the chlorination temperature is 400℃, the chlorination time is 0.7h, and the particle size of the spherical iron oxide particles is 1mm; in step S8, the condensation temperature is 150℃; in step S9, the concentration of the aluminum chloride solution obtained after dissolving the solid aluminum chloride obtained in step S8 into the aluminum chloride solution obtained in step S7 is 2mol / L, and ammonia gas is introduced to adjust the pH to 5; in step S10, the liquefaction temperature is -100℃.

[0051] 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 high-value utilization of secondary aluminum dross, characterized by: Includes the following steps: S1. Grinding process: Grind the secondary aluminum ash into fine powder to obtain fine ash; the particle size of the fine ash is <1μm; S2, Preheating process: The fine ash obtained in step S1 is preheated to obtain hot fine ash; S3, Microwave Chlorination Process: Using hot chlorine gas with the assistance of a high-temperature resistant microwave absorbing material, the hot fine ash obtained in step S2 is microwave-heated and chlorinated to obtain chlorinated slag and a mixed gaseous phase of high-temperature nitrogen, chlorine, and gaseous aluminum chloride. The high-temperature mixed gaseous phase of nitrogen, chlorine, and gaseous aluminum chloride is fed into the preheating process of step S2 for preheating the fine ash through heat exchange. The resulting low-temperature mixed gaseous phase of nitrogen, chlorine, and gaseous aluminum chloride is then fed into the condensation and dust collection process of step S8. The high-temperature resistant microwave absorbing material is spherical iron oxide particles with a particle size of 0.5-3 mm. S4. Heat exchange and cooling process: The chlorination residue obtained in step S3 is cooled by heat exchange using room temperature chlorine gas to obtain cooled residue and hot chlorine gas. The hot chlorine gas is then sent into the microwave chlorination process in step S3. S5. Washing and drying process: The cooling residue obtained in step S4 is washed and dried with pure water to remove soluble fluorides and chlorides, resulting in washing liquid and washing residue. S6. Screening process: The water washing residue obtained in step S5 is screened to obtain high temperature resistant microwave absorbing material and fine material. The high temperature resistant microwave absorbing material is sent to the microwave chlorination process in step S3. S7. Hydrochloric acid leaching process: The fine material obtained in step S6 is leached with dilute hydrochloric acid to obtain aluminum chloride solution and tailings. S8. Condensation and dust collection process: The mixed gas phase of low-temperature nitrogen, chlorine and gaseous aluminum chloride obtained in step S2 is condensed and dust collected to obtain nitrogen, chlorine and solid aluminum chloride. The nitrogen and chlorine are sent to the liquefaction and separation process in step S10. S9. Aging and drying process: Dissolve the solid aluminum chloride obtained in step S8 into the aluminum chloride solution obtained in step S7, introduce ammonia gas to adjust the pH to 2-5, and then perform aging and drying to obtain polyaluminum chloride product. S10, Liquefaction and Separation Process: The nitrogen and chlorine obtained in step S8 are liquefied and separated to obtain liquid chlorine and nitrogen; S11. Gasification process: The liquid chlorine obtained in step S10 is vaporized to obtain chlorine gas, which is then sent to the heat exchange and cooling process in step S4.

2. The method of claim 1, wherein, In step S3, the chlorination temperature is 350-550℃, the chlorination time is 0.5-1h, and the chlorination reactor is a fluidized bed reactor with high-temperature resistant microwave absorbing material installed inside.

3. The method of claim 1, wherein, In step S8, the condensation temperature is 25-170℃.

4. The method of claim 1, wherein, In step S9, the aluminum chloride solution obtained by dissolving the solid aluminum chloride obtained in step S8 into the aluminum chloride solution obtained in step S7 has a concentration of 2-5 mol / L.

5. The method of claim 1, wherein, In step S10, the liquefaction temperature is -40 to -190°C.

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