Secondary aluminum ash denitrification pretreatment method
By combining dry ball milling and heat treatment, the Al2O3 layer in secondary aluminum ash is removed using transition metal salts and fluorinating agents to generate a loose AlF3 layer. This solves the problem of incomplete denitrification of secondary aluminum ash and achieves efficient hydrolysis reaction and low-cost treatment.
Patent Information
- Application Number
- CN202511598094.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-04
- Publication Date
- 2026-01-13
AI Technical Summary
Existing pretreatment methods cannot effectively destroy the chemical passivation layer on the AlN surface, resulting in incomplete denitrification of secondary aluminum ash, and the acid pickling pretreatment will corrode the aluminum and introduce acid radical ions.
Secondary aluminum ash, transition metal salts, and solid fluorinating agents were mixed by dry ball milling, followed by heat treatment under an inert atmosphere. The Al2O3 layer was removed by solid-state ion exchange between Fe3+ ions and the AlN surface and HF etching, generating a loose AlF3 layer, which promoted the hydrolysis reaction.
It significantly improves the hydrolysis reaction rate and denitrification rate, reduces the hydrolysis temperature and treatment cost, and avoids environmental pollution.
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Figure SMS_1
Abstract
Description
Technical Field
[0001] This invention relates to the field of secondary aluminum ash treatment technology, and in particular to a method for denitrification pretreatment of secondary aluminum ash. Background Technology
[0002] The main hazardous component in secondary aluminum ash is aluminum nitride (AlN), whose hydrolysis reaction (AlN + 3H₂O → Al(OH)₃ + NH₃) is the basis for denitrification and ammonia recovery. However, the surface of AlN particles is often coated with inert oxides (such as Al₂O₃) or salts, and its own hydrolysis product Al(OH)₃ will deposit on the surface to form a dense passivation layer, which severely hinders the internal diffusion of water molecules and the escape of ammonia, causing the hydrolysis reaction to terminate spontaneously and resulting in incomplete denitrification.
[0003] Existing pretreatment methods, such as simple ball milling, can only partially break the physical coating but cannot solve the problem of chemical passivation; while pickling pretreatment can destroy the oxide layer, it will also severely corrode elemental aluminum, generate a large amount of hydrogen gas, and introduce acid radical ions that affect subsequent processes.
[0004] Therefore, there is an urgent need for a pretreatment method that can effectively activate AlN. Summary of the Invention
[0005] To overcome the shortcomings of the prior art, the present invention discloses a secondary aluminum ash denitrification pretreatment method.
[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: A secondary aluminum ash denitrification pretreatment method includes the following steps: S1. The secondary aluminum ash is mixed with transition metal salts and / or solid fluorinating agents by dry ball milling; S2. The uniformly mixed powder is heat-treated under an inert atmosphere and then naturally cooled to obtain pretreated secondary aluminum ash.
[0007] Preferably, the transition metal salt is at least one of anhydrous ferric chloride or anhydrous ferric sulfate.
[0008] Preferably, the solid fluorinating agent is at least one of ammonium fluoride and ammonium bifluoride.
[0009] Preferably, when secondary aluminum ash is mixed with transition metal salt, the mass ratio is 100:3-10.
[0010] Preferably, when secondary aluminum ash is mixed with solid fluorinating agent, the mass ratio is 100:5-12.
[0011] Preferably, when secondary aluminum ash is mixed with transition metal salts and solid fluorinating agents, the mass ratio is 100:5-8:3-5.
[0012] Preferably, when using secondary aluminum ash mixed with transition metal salt, the S2 heat treatment temperature is increased to 300-500℃ at a rate of 5-10℃ / min, and the holding time is 0.5-2h.
[0013] Preferably, when secondary aluminum ash is mixed with solid fluorinating agent, the S2 heat treatment is to raise the temperature to 150-200℃ at a rate of 1-3℃ / min and hold it for 1-4 hours.
[0014] Preferably, when secondary aluminum ash is mixed with transition metal salts and solid fluorinating agents, the S2 heat treatment is to raise the temperature to 180-200℃ at 1-3℃ / min and hold for 30-60min, then raise the temperature to 280-350℃ at 3-5℃ / min and hold for 1-2h.
[0015] By employing the technical solution described above, the present invention has the following beneficial effects: The secondary aluminum ash denitrification pretreatment method disclosed in this invention significantly improves the denitrification effect during hydrolysis, greatly increases the hydrolysis reaction rate and improves the hydrolysis denitrification rate, and at the same time, hydrolysis can be carried out at a lower temperature, reducing the cost of hydrolysis treatment.
[0016] This invention utilizes transition metal salts, Fe 3+ Ions and Al on the surface of AlN lattice 3+ Solid-state ion exchange occurs. Some Fe... 3+ It will be doped into the lattice of the AlN surface. Due to Fe... 3+ With Al 3+ The difference in ionic radius and electronegativity introduces defects and stress into the AlN surface lattice, significantly reducing the stability of the Al-N bond and making it more susceptible to attack by water molecules during subsequent hydrolysis.
[0017] By heating with a fluorinating agent to generate HF, which reacts with Al₂O₃ on the AlN surface, the chemical barrier hindering hydrolysis is selectively dissolved and removed. While the HF etches away the Al₂O₃ layer, it reacts slightly with the exposed fresh AlN surface, forming a very thin aluminum fluoride (AlF₃) or oxyfluoride transition layer. This newly formed AlF₃ layer has a completely different crystal structure from the native Al₂O₃; it cannot form a dense passivation layer like Al₂O₃. Instead, the AlF₃ layer is porous and hydrophilic. This AlF₃ layer alters the electrical properties of the AlN surface, making it more susceptible to adsorbing water molecules (H₂O). In subsequent hydrolysis processes, water molecules can more quickly penetrate this porous AlF₃ layer into the AlN bulk, greatly accelerating the hydrolysis kinetics. The AlF₃ itself is stable during this process and ultimately enters the hydrolysis products.
[0018] By simultaneously using transition metal salts and fluorinating agents, Fe... 3+ Ions can directly contact and exchange solid-state ions with the newly exposed, more reactive AlN surface through the "channels" opened by HF. This avoids Fe 3+ The ions are blocked by the native thick Al2O3 layer. This direct contact greatly improves the efficiency of Fe³⁺ in lattice doping and defect creation in AlN, thereby weakening the Al-N bond from the root.
[0019] By adding quicklime after pretreatment, the hazards of introduced fluorinating agents and fluorides contained in the secondary aluminum ash are effectively eliminated, and environmental risks are completely resolved. Detailed Implementation Example 1
[0020] Secondary aluminum ash and anhydrous ferric chloride were dry-milled and mixed at a mass ratio of 100:3. The uniformly mixed powder was then heat-treated under an inert atmosphere by heating to 300℃ at a rate of 5℃ / min and holding for 2 hours. After natural cooling, the treated secondary aluminum ash was obtained. Example 2
[0021] Secondary aluminum ash and anhydrous ferric sulfate were dry-milled and mixed at a mass ratio of 100:10. The uniformly mixed powder was then heat-treated under an inert atmosphere by heating to 500℃ at a rate of 10℃ / min and holding for 0.5h. After natural cooling, the treated secondary aluminum ash was obtained. Example 3
[0022] Secondary aluminum ash and ammonium fluoride were dry-milled and mixed at a mass ratio of 100:5. The uniformly mixed powder was then heat-treated under an inert atmosphere by heating to 150℃ at a rate of 1℃ / min and holding for 1 hour. After natural cooling, the treated secondary aluminum ash was obtained. Example 4
[0023] Secondary aluminum ash and ammonium bifluoride were dry-milled and mixed at a mass ratio of 100:12. The uniformly mixed powder was then heat-treated under an inert atmosphere by heating to 200℃ at a rate of 3℃ / min and holding for 4 hours. After natural cooling, the treated secondary aluminum ash was obtained. Example 5
[0024] Secondary aluminum ash, ferric chloride, and ammonium fluoride were dry-milled and mixed at a mass ratio of 100:5:3. The uniformly mixed powder was then heat-treated under an inert atmosphere by heating to 180℃ at a rate of 1℃ / min and holding for 30 min, followed by heating to 280℃ at a rate of 3℃ / min and holding for 1 h. After natural cooling, the treated secondary aluminum ash was obtained. Example 6
[0025] Secondary aluminum ash, ferric chloride, and ammonium fluoride were dry-milled and mixed at a mass ratio of 100:8:5. The uniformly mixed powder was then heat-treated under an inert atmosphere by heating to 200℃ at 3℃ / min and holding for 60min, followed by heating to 350℃ at 5℃ / min and holding for 2h. After natural cooling, the treated secondary aluminum ash was obtained. Example 7
[0026] S1. The secondary aluminum ash is mixed with transition metal salts and / or solid fluorinating agents by dry ball milling; S2. The uniformly mixed powder is heat-treated under inert gas protection and then naturally cooled to obtain the treated secondary aluminum ash. S3. Add 12-20wt% quicklime to the treated secondary aluminum ash; S4. The mixture obtained in S3 is subjected to hydrolysis at 55-80℃ for 0.5-3 hours, and the waste gas generated by the reaction is purified and recovered. S5. Obtain harmless secondary aluminum ash. Comparative Example 1
[0027] Secondary aluminum ash that has not undergone pretreatment.
[0028] Table 1. Effects of secondary aluminum ash hydrolysis reaction after treatment in Examples 1-6
[0029] As can be seen from Table 1, compared with untreated secondary aluminum ash, the hydrolysis reaction time of the secondary aluminum ash treated by the present invention is shortened, the required temperature is reduced, and the denitrification effect is also greatly improved.
[0030] The parts of this invention not described in detail are prior art. It will be apparent to those skilled in the art that this invention is not limited to the details of the above exemplary embodiments, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be regarded as exemplary and non-limiting in all respects. The scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all changes falling within the meaning and scope of the equivalents of the claims be included within the invention.
Claims
1. A method for secondary denitrification pretreatment of aluminum ash, characterized in that: Includes the following steps: S1. The secondary aluminum ash is mixed with transition metal salts and / or solid fluorinating agents by dry ball milling; S2. The uniformly mixed powder is heat-treated under inert gas protection and then naturally cooled to obtain the treated secondary aluminum ash.
2. The secondary aluminum ash denitrification pretreatment method as described in claim 1, characterized in that: The transition metal salt is at least one of anhydrous ferric chloride or anhydrous ferric sulfate.
3. The secondary aluminum ash denitrification pretreatment method as described in claim 1, characterized in that: The solid fluorinating agent is at least one of ammonium fluoride and ammonium bifluoride.
4. The secondary aluminum ash denitrification pretreatment method as described in claim 1, characterized in that: When using secondary aluminum ash mixed with transition metal salts, the mass ratio is 100:3-10.
5. The secondary aluminum ash denitrification pretreatment method as described in claim 1, characterized in that: When using secondary aluminum ash mixed with solid fluorinating agent, the mass ratio is 100:5-15.
6. The secondary aluminum ash denitrification pretreatment method as described in claim 1, characterized in that: When using secondary aluminum ash mixed with transition metal salts and solid fluorinating agents, the mass ratio is 100:5-8:3-5.
7. The secondary aluminum ash denitrification pretreatment method as described in claim 1, characterized in that: When using secondary aluminum ash mixed with transition metal salts, the S2 heat treatment temperature is 300-500℃ and the treatment time is 0.5-2h.
8. The secondary aluminum ash denitrification pretreatment method as described in claim 1, characterized in that: When using secondary aluminum ash mixed with solid fluorinating agent, the S2 heat treatment temperature is 150-300℃ and the treatment time is 1-4h.
9. The secondary aluminum ash denitrification pretreatment method as described in claim 1, characterized in that: When using secondary aluminum ash mixed with transition metal salts and solid fluorinating agents, the S2 heat treatment involves heating at 1-3℃ / min to 180-220℃ and holding for 30-60 min, then heating at 3-5℃ / min to 280-350℃ and holding for 1-2 h.
10. The secondary aluminum ash denitrification pretreatment method as described in claim 1, characterized in that: The pretreated secondary aluminum ash can be hydrolyzed at 55-80℃ for 0.5-3 hours after adding 12-20wt% quicklime. The waste gas generated by the reaction is then purified and recovered to finally obtain harmless secondary aluminum ash.