Method for removing nitrogen from aluminum ash by acid treatment in normal temperature environment

Abstract

This application discloses a method for denitrifying aluminum ash slag using acid treatment at room temperature, relating to the field of hazardous waste harmless treatment technology for aluminum ash slag. The method is as follows: Aluminum ash slag is placed in a ball mill with a grinding aid and ground into solid particles that pass through a 300-mesh sieve; the solid particles are placed in a reaction vessel, and carbon dioxide is introduced for denitrification; citric acid is then added to the reaction product for impurity removal; finally, the impurity-removed reaction product is placed in hydrochloric acid and stirred to obtain an aluminum chloride solution. This invention combines grinding and acidic solution treatment, achieving highly efficient denitrification of aluminum ash slag, reducing environmental pollution, and recovering aluminum, thus improving overall efficiency.

Description

Technical Field

[0001] This invention belongs to the field of hazardous waste harmless treatment technology of aluminum ash slag, specifically relating to a method for denitrification of aluminum ash slag by acid treatment at room temperature. Background Technology

[0002] Aluminum ash slag has a low aluminum content but contains many impurities, including harmful substances such as fluorides and aluminum nitride. Accumulation of aluminum ash can lead to soil pollution, affecting soil fertility and ecological balance. The infiltration and accumulation of harmful substances can negatively impact plant growth, affecting the health of agriculture and natural ecosystems. Furthermore, harmful substances in aluminum ash can spread through the air, water, or food chain, adversely affecting the health of surrounding residents, including respiratory problems, water pollution, and food safety issues. Therefore, comprehensive utilization and harmless treatment of aluminum ash slag are necessary. This can not only reduce pollution and resource waste but also promote economic growth and sustainable development.

[0003] In their article, "Research Progress on the Characteristics and Removal Process of Aluminum Nitride in Secondary Aluminum Ash," Zhang Yu and Li Yong pointed out that the presence of AlN not only causes aluminum ash to release ammonia gas with a pungent odor when damp, but also may lead to ammonia nitrogen (N-NH3) aggregation, posing a high toxicity risk to groundwater. Due to the lack of low-cost, large-scale, and relatively mature treatment processes, on-site landfill and stockpiling remain the main methods for disposing of SAD (aluminum nitride). Therefore, research on this topic, which involves low risk and low economic cost, is of great significance for reducing environmental pollution during aluminum industry production and achieving the effective recycling of aluminum resources.

[0004] Currently, high-temperature wet treatment is a widely studied method, but it is costly, inefficient, and can create new forms of pollution. Furthermore, the long hydrolysis time of AlN makes it difficult to effectively address some pollution issues associated with aluminum ash slag. Therefore, in practical applications, factors such as cost, aluminum ash quality, and resource and energy consumption must be considered when selecting a suitable treatment method. Summary of the Invention

[0005] Technical problems to be solved:

[0006] This application addresses the shortcomings of existing technologies by providing a method for denitrifying aluminum ash slag using acid treatment at room temperature. This method aims to achieve green treatment and high-value utilization of aluminum ash slag, thus responding to sustainable development.

[0007] Technical solution:

[0008] To achieve the above objectives, this application provides the following technical solution:

[0009] A method for denitrifying aluminum ash slag using acid treatment at room temperature includes the following steps:

[0010] S1: Mix aluminum ash slag and grinding aid in a mass ratio of 90-100:1-10. Put the aluminum ash slag and grinding aid into a ball mill and grind them until they pass through a 300-mesh sieve.

[0011] S2: Place the ground aluminum ash slag particles into a reaction vessel, soak them in tap water for 1-2 hours to obtain a reaction solution, then introduce carbon dioxide gas into the reaction vessel until the reaction solution becomes a saturated carbon dioxide solution, stir to carry out the reaction, the stirring time is 1-3 hours, and the stirring speed is 50-200 revolutions per minute.

[0012] S3: Mix the product obtained after stirring and reaction with citric acid solution at a mass ratio of 1:2-3 for 1-2 hours to remove impurities. Then add 1-2 times the mass of the product after impurity removal with hydrochloric acid solution to immerse it. Stir the reaction at a speed of 50-100 rpm for 3-4 hours to obtain the final denitrification product of aluminum ash slag.

[0013] As a preferred technical solution of this application: the ambient temperature is 20-25℃, and the particle size of the colloidal silica used in the grinding aid in step S1 is 10-50 nanometers.

[0014] As a preferred technical solution of this application: the rate at which carbon dioxide gas is introduced in step S2 is 30 or 50 mL / min.

[0015] As a preferred technical solution of this application: the concentration of the saturated carbon dioxide solution in step S2 is 0.03 to 0.033 mol / L.

[0016] As a preferred technical solution of this application: the solid-liquid ratio of aluminum ash particles to saturated carbon dioxide solution in step S2 is 1:20-25.

[0017] As a preferred technical solution of this application: the stirring reaction time in step S2 is 2 hours.

[0018] As a preferred technical solution of this application: the citric acid solution in step S3 has a citric acid mass fraction of 25-35%.

[0019] As a preferred technical solution of this application: the molar concentration of hydrochloric acid solution in step S3 is 4.11-6.86 mol / L.

[0020] Explanation of the principle: First, the aluminum ash slag is soaked in tap water to pre-wet and disperse the aluminum ash slag particles, thus initiating a preliminary hydrolysis reaction. The chemical formula for the reaction is as follows:

[0021] AlN + 3H₂O → Al(OH)₃↓ + NH₃↑

[0022] Then, carbon dioxide gas is continuously passed through the tap water, gradually forming a saturated carbon dioxide solution. Because the hydrolysis of aluminum nitride produces a large amount of harmful ammonia gas, this ammonia gas is largely absorbed in the saturated carbon dioxide solution. The chemical formula for the reaction is as follows:

[0023]

[0024]

[0025] After removing impurities from the denitrified reaction product with citric acid, it is then reacted with hydrochloric acid to convert it into widely used solid aluminum chloride, which greatly improves the utilization rate of resources.

[0026] Beneficial effects:

[0027] This application provides a method for denitrification of aluminum ash slag using acid treatment at room temperature, which has the following advantages compared with the prior art:

[0028] 1. This invention utilizes a ball mill and uses colloidal silica as a grinding aid to fully grind aluminum ash slag into solid powder that passes through at least a 300-500 mesh sieve, reducing the particle size of the reactants and thus greatly increasing the contact area ratio between the reactants and the reaction solution, thereby improving the reaction rate and increasing the denitrification rate, while reducing the possibility of pollution.

[0029] 2. In the saturated carbon dioxide solution produced by this invention, the carbon dioxide is introduced at a rate of 50 mL / min, and the concentration of the saturated carbon dioxide solution is 0.03–0.033 mol / L. Extensive experiments have shown that an introduction rate of 50 mL / min can stabilize the pH of the reaction environment and create an acidic environment for ammonia absorption. Compared with ammonia absorption by tap water, the absorption capacity is significantly increased, and the nitrogen removal rate is higher, making it more environmentally friendly.

[0030] 3. This invention utilizes citric acid to remove impurities from the product after the first reaction, ensuring maximum stability of the reaction environment. The selected citric acid has a mass fraction of 25-35%, significantly reducing costs while also ensuring minimal resource utilization. After impurity removal, the purity of the reaction is guaranteed.

[0031] 4. This invention utilizes hydrochloric acid to perform secondary treatment on the mixture to obtain aluminum chloride, which greatly realizes the reuse of resources and renders harmful gases such as ammonia and harmful substances such as aluminum ash slag harmless. It well meets the needs of enterprises for the treatment of harmful aluminum ash slag. The treatment method can process aluminum ash slag on a large scale with high processing efficiency. Since it is carried out at normal temperature and pressure, the processing cost is relatively low.

[0032] 5. Compared with other existing inventions, this invention offers a better operating environment, operating at normal temperature and pressure, making it more operator-friendly and offering higher safety and feasibility. It requires simple facilities, has a simple processing procedure, and has broad application prospects. Attached Figure Description

[0033] Figure 1 This is a line graph showing the pH value of saturated carbon dioxide solutions at different carbon dioxide perfusion rates under normal temperature conditions as a function of time.

[0034] Figure 2 This is a line graph showing the nitrogen removal rate of aluminum nitride by saturated carbon dioxide solutions at different carbon dioxide passing rates under normal temperature conditions in this application.

[0035] Figure 3 This is a line graph showing the denitrification rate of aluminum ash treated with saturated carbon dioxide solution and alkali treated aluminum ash at different carbon dioxide rates under normal temperature conditions, as a function of time.

[0036] Figure 4 This is a bar chart showing the nitrogen removal rate of aluminum ash slag by saturated carbon dioxide solution under different particle sizes in this application;

[0037] Figure 5 This is a bar chart showing the nitrogen removal rate of aluminum nitride by saturated carbon dioxide solution at different temperatures in this application. Detailed Implementation

[0038] The preferred embodiments of the present invention will now be described in detail so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0039] Example 1:

[0040] A method for denitrifying aluminum ash slag using acid treatment at room temperature includes the following steps:

[0041] S1: Put 10g of aluminum ash slag and 1g of colloidal silica into a ball mill and grind them until they pass through a 300-mesh sieve. The particle size of the colloidal silica is 30 nanometers.

[0042] S2: Place the ground aluminum ash slag particles into a reaction vessel, maintain the reaction environment temperature at 25℃, first add 250mL of tap water to the reaction vessel, and immerse all the aluminum ash slag particles in tap water for 1 hour to obtain a reaction solution, then introduce carbon dioxide gas into the reaction vessel at a rate of 50mL / min until the reaction solution becomes a saturated carbon dioxide solution with a concentration of 0.03mol / L, and stir the reaction at a speed of 150 rpm for 2 hours;

[0043] S3: The product obtained after stirring reaction is first purified by 248.85 mL of 30% citric acid solution for 1 h, then 207.75 mL of 6.86 mol / L hydrochloric acid solution is added to immerse it, and then the reaction is stirred at 100 rpm for 4 h to obtain the final denitrification product of aluminum ash slag.

[0044] Example 2:

[0045] A method for denitrifying aluminum ash slag using acid treatment at room temperature includes the following steps:

[0046] S1: Put 10g of aluminum ash slag and 1g of colloidal silica into a ball mill and grind them until they pass through a 300-mesh sieve. The particle size of the colloidal silica is 30 nanometers.

[0047] S2: Place the ground aluminum ash slag particles into a reaction vessel, maintain the reaction environment temperature at 25℃, first add 250mL of tap water to the reaction vessel, and immerse all the aluminum ash slag particles in tap water for 1 hour to obtain a reaction solution, then introduce carbon dioxide gas into the reaction vessel at a rate of 30mL / min until the reaction solution becomes a saturated carbon dioxide solution with a concentration of 0.03mol / L, and stir the reaction at a speed of 150 rpm for 2 hours;

[0048] S3: The product obtained after stirring reaction is first purified by 248.85 mL of 30% citric acid solution for 1 h, then 207.75 mL of 6.86 mol / L hydrochloric acid solution is added to immerse it, and then the reaction is stirred at 100 rpm for 4 h to obtain the final denitrification product of aluminum ash slag.

[0049] Comparative Example 1

[0050] Similar to Example 1, except that the rate at which carbon dioxide gas is continuously introduced into the tap water in step S2 is 40 mL / min.

[0051] Comparative Example 2

[0052] Similar to Example 1, except that the rate at which carbon dioxide gas is continuously introduced into the tap water in step S2 is 60 mL / min.

[0053] Comparative Example 3

[0054] Similar to Example 1, except that in step S1, 10g of aluminum ash slag is ground into solid powder that passes through a 100-mesh sieve.

[0055] Comparative Example 4

[0056] Similar to Example 1, except that in step S1, 10g of aluminum ash slag is ground into solid powder that passes through a 200-mesh sieve.

[0057] Comparative Example 5

[0058] Similar to Example 1, except that in step S1, 10g of aluminum ash slag is ground into solid powder that passes through a 400-mesh sieve.

[0059] Comparative Example 6

[0060] Similar to Example 1, except that in step S1, 10g of aluminum ash slag is ground into solid powder that passes through a 500-mesh sieve.

[0061] Comparative Example 7

[0062] Same as Example 1, except that the reaction environment temperature is kept at 0°C in step S2.

[0063] Comparative Example 8

[0064] Same as Example 1, except that the reaction environment temperature is maintained at 50°C in step S2.

[0065] Comparative Example 9

[0066] Same as Example 1, except that the reaction environment temperature is maintained at 75°C in step S2.

[0067] Comparative Example 10

[0068] Same as Example 1, except that the reaction environment temperature is maintained at 100°C in step S2.

[0069] Examples 1-2 and Comparative Examples 1-3 were compared to investigate the effect of different carbon dioxide flow rates on the pH value of the reaction environment during the reaction process. Using a pH sensor, the pH value of the reaction environment was measured every 20 minutes for each group of experiments, and the results are shown in Table 1.

[0070] Comparative Example 11:

[0071] A method for denitrifying aluminum ash slag using alkaline treatment at room temperature includes the following steps:

[0072] S1: Put 10g of aluminum ash slag and 1g of colloidal silica into a ball mill and grind them until they pass through a 300-mesh sieve. The particle size of the colloidal silica is 30 nanometers.

[0073] S2: Place the ground aluminum ash slag particles into the reaction vessel, maintain the reaction environment temperature at 25℃, and pour 156.8mL of 5% sodium hydroxide solution into the reaction vessel;

[0074] S3: Pour 50 mL of 1.5 mg / L sodium alkyl sulfonate solution into the reaction vessel, and react for 2 hours to obtain the final denitrification product of aluminum ash slag.

[0075] Table 1. Comparison of the effect of different carbon dioxide passage rates on the pH value of the reaction environment.

[0076]

[0077]

[0078] Examples 1-2 and Comparative Examples 1-3 were compared to conduct comparative experiments on the denitrification rate of saturated carbon dioxide solutions with different carbon dioxide flow rates on aluminum ash slag. During the experiments, reaction cycles were set, and the mass was measured at regular intervals after each reaction cycle. By comparing the difference between the mass of the aluminum ash slag and the mass before the experiment, the denitrification rate at each time point can be indirectly calculated. The results are shown in Table 2 below.

[0079] Table 2 Comparison of nitrogen removal rate of aluminum ash slag at different carbon dioxide passage rates

[0080] Example 2 Comparative Example 1 Example 1 Comparative Example 2 Comparative Example 3 20min 15.7 16.4 19.3 18.7 19.5 40min 32.1 32.9 35.8 34.2 35.1 60min 43.8 46.9 49.2 49.8 48.7 80min 55.2 56.3 60.7 58.4 59.6 100min 71.5 73.6 76.1 75.2 76.8 120min 85.7 87.4 90.3 90.8 90.5

[0081] Example 1 was compared with Comparative Example 11, and a comparative experiment was conducted under the same ambient temperature environment but with different treatment methods, namely acid treatment and alkali treatment, to compare the denitrification rate. Similar to the previous experiment, a reaction cycle was set during the experiment, and the mass was measured at regular intervals after each reaction cycle. By comparing the difference with the mass of the aluminum ash slag before the experiment, the denitrification rate at each time point can be indirectly calculated. The results are shown in Table 3 below:

[0082] Table 3 Comparison of nitrogen removal rates under different pH conditions

[0083]

[0084]

[0085] Example 1 was compared with Comparative Examples 3-6, where the aluminum ash slag was ground to different particle sizes, and the denitrification rate of the saturated carbon dioxide solution was compared. After the reaction time was completed, the mass of ammonia produced was measured to obtain the denitrification rate for each experimental group. The results are shown in Table 4 below:

[0086] Table 4 Comparison of denitrification rates of aluminum ash slag with different particle sizes

[0087] Comparative Example 3 Comparative Example 4 Example 1 Comparative Example 5 Comparative Example 6 nitrogen removal rate 85.5 88.2 90.3 90.8 91.1

[0088] Example 1 was compared with Comparative Examples 7-10. The denitrification rate of saturated carbon dioxide solution on aluminum ash powder varied under different reaction temperatures. After the reaction time was completed, the mass of ammonia produced was measured to obtain the denitrification rate for each experimental group. The results are shown in Table 5 below:

[0089] Table 5 Comparison of nitrogen and aluminum removal results in aluminum ash slag under different reaction ambient temperatures

[0090] Comparative Example 7 Example 1 Comparative Example 8 Comparative Example 9 Comparative Example 10 nitrogen removal rate 89.2 90.3 88.4 85.3 80.9

[0091] AlN + 3H₂O → Al(OH)₃↓ + NH₃↑

[0092] Based on the above expression, the mass of nitrogen lost from aluminum nitride can be indirectly calculated by calculating the mass of ammonia. Then, by dividing the mass of lost nitrogen by the original mass of nitrogen in the aluminum ash slag, the required nitrogen removal rate can be obtained.

[0093]

[0094]

[0095] According to the above expression, not only can ammonia gas be dissolved in water to form ammonia water, but ammonium ions and carbonate ions will also combine, which can absorb ammonia gas to a greater extent compared with alkaline treatment of aluminum ash slag.

[0096] Tables 1 and 2 show that the nitrogen removal rate of saturated carbon dioxide solution on aluminum ash slag varies with the pH value of the reaction environment. However, once the pH value drops to around 5.5, further decreases in pH do not significantly improve the nitrogen removal efficiency of the solution on the aluminum ash slag. Based on the principle of minimizing resources, a carbon dioxide flow rate of 50 mL / min yields the highest efficiency. This achieves the minimum chemical dosage and minimizes costs.

[0097] Al(OH)3 + 3HCl → AlCl3 + 3H2O

[0098] Based on the above expression, the denitrified aluminum hydroxide product can be purified by citric acid before reacting with hydrochloric acid to obtain aluminum chloride. This method converts unused aluminum hydroxide precipitate into widely used solid aluminum chloride, significantly improving resource utilization.

[0099] As shown in Table 3, under the same ambient temperature conditions, acid-treated aluminum ash achieves a better denitrification rate than alkali-treated aluminum ash. Furthermore, the time required to reach the optimal denitrification rate is also shorter.

[0100] Table 4 shows that, under the same ambient temperature conditions, the particle size of different aluminum ash slag particles affects the denitrification rate. Smaller particle sizes result in a larger contact area, leading to higher reaction efficiency and a more complete reaction. However, it can be observed that increasing the mesh size to over 200 mesh does not significantly improve the denitrification rate. This is because ball milling causes powder to fly, polluting the air and the operating environment, with smaller particles resulting in higher levels of pollution. Therefore, setting the particle size to at least 200 mesh significantly reduces environmental damage while maintaining the denitrification rate.

[0101] As shown in Table 5, the nitrogen removal rate of saturated carbon dioxide solution on aluminum ash powder did not continuously increase with increasing temperature under different reaction ambient temperatures. This is because the carbon dioxide content in the saturated carbon dioxide solution is affected by the ambient temperature. The higher the temperature, the lower the carbon dioxide content in the solution. Consequently, its ability to absorb ammonia is lower, and the solution quickly becomes saturated with ammonia, inhibiting the hydrolysis reaction of aluminum nitride. Therefore, a room temperature of 20-25℃ is the optimal choice.

[0102] As shown in Table 2, the mass of nitrogen remaining in the solution is obtained by subtracting the mass of nitrogen removed from the total mass of nitrogen calculated in Example 1. When the reaction time reaches 2 hours, the nitrogen removal rate reaches 90.3%, and the ammonia nitrogen concentration in the solution is 120 mg / L. According to the Integrated Wastewater Discharge Standard (GB8978-1996) and relevant industry-specific water pollutant discharge standards, the ammonia nitrogen standard limit range is 0.02 mg / L to 150 mg / L, which meets the discharge requirements.

[0103] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for denitrifying aluminum ash slag using acid treatment at room temperature, characterized in that, Specifically, the steps include the following: S1: Mix aluminum ash slag and grinding aid in a mass ratio of 90-100:1-10. Put the aluminum ash slag and grinding aid into a ball mill and grind them until they pass through a 300-mesh sieve. The ambient temperature is 20-25℃. The particle size of the colloidal silica used in the grinding aid in step S1 is 10-50 nanometers. S2: Place the ground aluminum ash slag particles into a reaction vessel and soak them in tap water for 1-2 hours to obtain a reaction solution. Then, introduce carbon dioxide gas into the reaction vessel until the reaction solution becomes a saturated carbon dioxide solution. Stir the reaction for 1-3 hours at a speed of 50-200 revolutions per minute. The rate at which carbon dioxide gas is introduced in step S2 is 30 or 50 mL / min. S3: Mix the product obtained after stirring and reaction with citric acid solution at a mass ratio of 1:2-3 for 1-2 hours to remove impurities. Then add 1-2 times the mass of the product after impurity removal with hydrochloric acid solution to immerse it. Stir the reaction at 50-100 rpm for 3-4 hours to obtain the final denitrification product of aluminum ash slag. The mass fraction of citric acid in the citric acid solution in step S3 is 25-35%.

2. The method for denitrification of aluminum ash slag by acid treatment in a normal temperature environment according to claim 1, characterized in that: In step S2, the concentration of the saturated carbon dioxide solution is 0.03~0.033 mol / L.

3. The method for denitrification of aluminum ash slag by acid treatment in a normal temperature environment according to claim 1, characterized in that: In step S2, the solid-liquid ratio of aluminum ash particles to saturated carbon dioxide solution is 1:20~25.

4. The method for denitrification of aluminum ash slag by acid treatment in a normal temperature environment according to claim 1, characterized in that: The stirring reaction time in step S2 is 2 hours.

5. The method for denitrification of aluminum ash slag by acid treatment in a normal temperature environment according to claim 1, characterized in that: In step S3, the molar concentration of the hydrochloric acid solution is 4.11-6.86 mol / L.

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