A pretreatment and temperature control method for efficient denitrification of aluminum ash

Abstract

The present invention provides a pretreatment and temperature control method for efficient denitrification of aluminum ash. In the method, aluminum ash and an ammonium salt of a strong acid and weak base are mixed in a reactor, nitrogen is introduced to replace the gas, and then warm water is added to perform a pretreatment reaction on the aluminum ash. The present invention uses secondary aluminum ash and an ammonium salt of a strong acid and weak base as raw materials, and has a simple process flow and low cost. It solves the problem of sudden temperature increases during the pretreatment process during the recycling of secondary aluminum ash, ensuring the safety of the efficient denitrification process of the aluminum ash and having good environmental benefits. The present invention can control and maintain the aluminum ash pretreatment temperature below 65°C, ensuring the hydrolysis of aluminum nitride while controlling the sudden temperature increase, thus greatly ensuring the safety of the aluminum ash treatment process.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid hazardous waste treatment, and in particular relates to a pretreatment and temperature control method for efficient denitrification of aluminum ash. Background Art

[0002] my country is the world's largest producer and consumer of aluminum, but the production process generates a significant amount of aluminum ash waste. Aluminum ash can be divided into primary and secondary aluminum ash. Primary aluminum ash has a high aluminum content and can be recycled into smelting. Secondary aluminum ash, however, has a low aluminum content and contains a large amount of AlN. AlN is a reaction product of molten aluminum and nitrogen during the smelting process. It readily hydrolyzes in water, generating the irritating and toxic gas NH3. Therefore, the harmless treatment of secondary aluminum ash is a current research hotspot and challenge in hazardous waste management.

[0003] Currently, there are two main treatment technologies for the harmless treatment of aluminum ash: wet and pyrolysis. Pyrolysis primarily utilizes rotary kilns and other processing facilities to recover aluminum metal. However, pyrolysis consumes significant energy and processing costs, and often the recovered value is lower than the cost of treatment. Therefore, pyrolysis has certain limitations. Wet treatment technologies primarily include acid leaching and alkaline leaching. Since aluminum is an amphoteric metal, the residual aluminum in the aluminum ash can be dissolved in both acid and alkaline solutions, enabling the recovery of aluminum metal. However, wet hydrolysis has low denitrification rates, high water consumption, and a long AlN hydrolysis induction period. A two-stage hydrolysis method can achieve higher denitrification rates, but the first pretreatment stage involves the rapid hydrolysis of aluminum nitride, aluminum carbide, and other substances in the aluminum ash, instantly releasing significant heat and producing large amounts of gas. This results in uncontrollable temperatures and pressure surges during the first hydrolysis stage, hindering safe production.

[0004] Uncontrolled temperature spikes are extremely dangerous for chemical reactions, potentially damaging the reaction vessel and even causing explosions and fires. Furthermore, extreme temperature fluctuations can cause thermal stress damage to equipment such as reactor heat exchangers. Large temperature fluctuations can also make continuous production difficult to control, impacting production stability and efficiency. In aluminum ash systems, the wet hydrolysis of aluminum ash solid waste produces large amounts of hydrogen, making uncontrolled temperature extremely hazardous to the system.

[0005] Several strategies are commonly used to address sudden temperature increases during chemical reactions, including increased cooling, catalyst control, slow feed, and emergency evacuation. However, in this system, which operates in a batch-type reactor, slow feed is not applicable. Furthermore, the generated gas is hydrogen-rich, which imposes stringent safety requirements, making emergency evacuation and other operations extremely dangerous. Therefore, physical cooling is not very effective in this system.

[0006] In summary, there is an urgent need for a method suitable for efficient denitrification pretreatment and temperature control of aluminum ash. Summary of the Invention

[0007] In order to solve the problem of uncontrolled temperature increase during the secondary aluminum ash efficient denitrification pretreatment, the technical solution of the present invention is as follows:

[0008] Step S1, crushing and screening the secondary aluminum ash;

[0009] Step S2, weighing the secondary aluminum ash and ammonium salts of strong acid and weak base treated in step S1 in sequence and putting them into a reactor, and replacing the air with an inert gas;

[0010] Step S3, adding water to the reactor of step S2 and performing a hydrolysis reaction under stirring;

[0011] Step S4, after the reaction is completed, the gas generated in step S3 is recovered through the absorption liquid in the absorption kettle.

[0012] Furthermore, in step S1, the particle size of the secondary aluminum ash after crushing and screening is 100-200 mesh.

[0013] Furthermore, in step S2, the ammonium salt of strong acid and weak base includes one or more of ammonium chloride, ammonium sulfate, ammonium bromide, ammonium iodide, ammonium nitrate, and ammonium dihydrogen phosphate, and the amount of the ammonium salt of strong acid and weak base is 1.75% to 15.0% of the weight of the secondary aluminum ash; and the inert gas is N2.

[0014] Furthermore, in step S3, the temperature of the water is 30-50° C., the weight ratio of the input water to the secondary aluminum ash is 0.3-0.6:1; the stirring rate is 200-350 r / min, and the hydrolysis reaction time is 1-3 h.

[0015] Furthermore, in step S4, the absorption liquid in the absorption kettle is one of 0.1-0.5 M sulfuric acid solution, 0.1-0.5 M nitric acid solution, 0.1-2 M sodium chloride solution, 0.1-0.5 M bromine aqueous solution, and 0.1-8 M phosphoric acid solution.

[0016] The mechanism of the present invention includes:

[0017] When ammonium salts of strong acid and weak base are dissolved in water, ammonium ions and chloride ions (or sulfate ions, bromide ions, iodide ions, nitrate ions, dihydrogen phosphate ions) interact with water molecules. As a result, after coupling ammonium salts of strong acid and weak base in the pretreatment stage (a hydrolysis process) of the secondary aluminum ash efficient denitrification, the maximum temperature of the system can be reduced, a sudden temperature increase can be avoided, and the temperature of the hydrolysis reaction can be controlled.

[0018] As a conjugate acid of a weak base, ammonium ion can be slightly hydrolyzed to produce hydrogen ions (H +) and ammonia (NH3·H2O), which is an endothermic process. Specifically, although ions usually release heat when forming hydrates with water molecules (i.e., ion hydration is exothermic), for salts such as ammonium salts with strong acids and weak bases, this exothermic process is not enough to compensate for the subsequent endothermic hydrolysis process. Moreover, the hydrolysis of ammonium ions is a typical endothermic reaction because it requires the breakage of NH4 + The hydrogen bonds between ammonium ions and water molecules, and the subsequent formation of new NH3·H2O molecular structures, all require energy absorption. The equation for the hydrolysis of ammonium ions can be expressed as: NH4 + + H2O ⇌NH3·H2O + H + . This equilibrium tends to shift to the right, which means that the hydrolysis process consumes heat in the environment. Although hydrolysis is endothermic, from the perspective of entropy, the dissolution process causes ions to disperse in water, increasing the disorder of the system. This is also an entropy-increasing process, which is usually associated with endothermicity. Therefore, although heat is released when ions combine with water molecules to form hydrates when the solute dissolves, the endothermic effect of the hydrolysis reaction when the ammonium ion strong acid and weak base salt dissolves exceeds this exothermic process, resulting in an overall endothermic reaction, which allows the reaction in the secondary aluminum ash pretreatment stage to proceed smoothly and safely.

[0019] Compared with the existing technology, the present invention has the following beneficial effects:

[0020] (1) The present invention does not require an external heat source and has low energy consumption;

[0021] (2) The present invention allows the secondary aluminum ash to spontaneously hydrolyze and release heat, and self-maintain the reaction temperature, so that the reaction proceeds smoothly and safely;

[0022] (3) The process of the present invention is simple, has a short processing cycle, and is temperature controllable, making it suitable for large-scale application. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Flow chart of the secondary aluminum ash pretreatment process DETAILED DESCRIPTION

[0024] In order to make researchers more clearly understand the technical solutions and technical advantages of the present invention, the present invention will be described in detail below with reference to the embodiments. It is particularly noted that the embodiments are only used to clearly and completely describe the present invention and should not be regarded as limiting the scope of the present invention.

[0025] Example 1

[0026] This embodiment provides a pretreatment and temperature control method for efficient denitrification of aluminum ash, and the specific implementation process is as follows:

[0027] (1) Crush and sieve the secondary aluminum ash, and collect the secondary aluminum ash between 100 and 200 mesh for the next experiment;

[0028] (2) Weigh 75 g of sieved secondary aluminum ash and place it in a reactor. Add 10 g of ammonium chloride and introduce nitrogen to replace the gas.

[0029] (3) Weigh 40 g of 50°C water and add it to the reactor. Stir and hydrolyze at 200 r / min for 3 h.

[0030] (4) After the reaction is completed, use 1M sodium chloride solution to collect the gas and remove the secondary aluminum ash after pretreatment.

[0031] Example 2

[0032] This embodiment provides a pretreatment and temperature control method for efficient denitrification of aluminum ash, and the specific implementation process is as follows:

[0033] (1) Grind and sieve the secondary aluminum ash to 100-200 mesh;

[0034] (2) Weigh 85 g of sieved secondary aluminum ash and place it in a reactor. Add 10 g of ammonium sulfate and introduce nitrogen to replace the gas.

[0035] (3) Add 40 g of 50 °C aqueous solution to the reactor and stir at 350 r / min for 2 h for hydrolysis.

[0036] (4) After the reaction is completed, the gas is collected with 0.4M sulfuric acid solution and the secondary aluminum ash after pretreatment is removed.

[0037] Example 3

[0038] This embodiment provides a pretreatment and temperature control method for efficient denitrification of aluminum ash, and the specific implementation process is as follows:

[0039] (1) Grind and sieve the secondary aluminum ash to 100-200 mesh;

[0040] (2) Weigh 70 g of sieved secondary aluminum ash and place it in a reactor. Add 4 g of ammonium nitrate and 2 g of ammonium bromide, and introduce nitrogen to replace the gas.

[0041] (3) Add 40 g of 40°C aqueous solution to the reactor and stir at 200 r / min for hydrolysis for 1 h;

[0042] (4) After the reaction is completed, the gas is collected with a 0.3 M bromine aqueous solution and the secondary aluminum ash after pretreatment is removed.

[0043] Example 4

[0044] This embodiment provides a pretreatment and temperature control method for efficient denitrification of aluminum ash, and the specific implementation process is as follows:

[0045] (1) Grind and sieve the secondary aluminum ash to 100-200 mesh;

[0046] (2) Weigh 70 g of sieved secondary aluminum ash and place it in a reactor. Add 2 g of ammonium dihydrogen phosphate and introduce nitrogen to replace the gas.

[0047] (3) Add 40 g of 40°C aqueous solution to the reactor and stir at 350 r / min for 2 h for hydrolysis.

[0048] (4) After the reaction is completed, use 2M phosphoric acid solution to collect the gas and remove the secondary aluminum ash after pretreatment.

[0049] Example 5

[0050] This embodiment provides a pretreatment and temperature control method for efficient denitrification of aluminum ash, and the specific implementation process is as follows:

[0051] (1) Grind and sieve the secondary aluminum ash to 100-200 mesh;

[0052] (2) Weigh 70 g of sieved secondary aluminum ash and place it in a reactor, add 5 g of ammonium chloride, and introduce nitrogen to replace the gas;

[0053] (3) Add 28 g of 50 °C aqueous solution to the reactor and stir at 200 r / min for 2 h;

[0054] (4) After the reaction is completed, the gas is collected with 0.1M sulfuric acid solution and the secondary aluminum ash after pretreatment is removed.

[0055] Comparative Example 1

[0056] (1) Crush and sieve the secondary aluminum ash, and collect the secondary aluminum ash between 100 and 200 mesh for the next experiment;

[0057] (2) Weigh 75 g of the sieved secondary aluminum ash and place it in a reactor, introducing nitrogen to replace the gas;

[0058] (3) Weigh 40 g of 50°C water and add it to the reactor. Stir and hydrolyze at 200 r / min for 3 h.

[0059] (4) After the reaction is completed, use 1M sodium chloride solution to collect the gas and remove the secondary aluminum ash after pretreatment.

[0060] Comparative Example 2

[0061] (1) Crush and sieve the secondary aluminum ash, and collect the secondary aluminum ash between 100 and 200 mesh for the next experiment;

[0062] (2) Weigh 75 g of sieved secondary aluminum ash and place it in a reactor. Add 10 g of ammonium chloride and introduce nitrogen to replace the gas.

[0063] (3) Weigh 40 g of 60°C water and add it to the reactor. Stir and hydrolyze at 200 r / min for 3 h.

[0064] (4) After the reaction is completed, use 1M sodium chloride solution to collect the gas and remove the secondary aluminum ash after pretreatment.

[0065] Table 1 Maximum temperature and maximum pressure of secondary aluminum ash reaction under different conditions

[0066] condition Maximum temperature / ℃ Maximum pressure / MPa Example 1 75g secondary aluminum ash, 40g 50℃ water, 200r / min, 3h, 10g ammonium chloride 56.62 0.56 Example 2 85g secondary aluminum ash, 40g 50℃ water, 350r / min, 2h, 10g ammonium sulfate 55.87 0.55 Example 3 70g secondary aluminum ash, 40g 40℃ water, 200r / min, 1h, 4g ammonium nitrate, 2g ammonium bromide 46.71 0.13 Example 4 70g secondary aluminum ash, 40g 40℃ water, 350r / min, 2h, 2g diammonium hydrogen phosphate 50.48 0.28 Example 5 70g secondary aluminum ash, 28g 50℃ water, 200r / min, 2h, 5g ammonium chloride 64.76 0.63 Comparative Example 1 75g secondary aluminum ash, 40g 50℃ water, 200r / min, 3h 138.16 1.06 Comparative Example 2 75g secondary aluminum ash, 40g 60℃ water, 200r / min, 3h, 10g ammonium chloride 110.65 0.65

[0067] The table above demonstrates the effects of varying initial reaction temperatures and the addition amounts of ammonium salts of strong acid and weak base on the temperature of the first-stage hydrolysis (pretreatment) of secondary aluminum ash. The results show that, in Examples 1-5, after the addition of ammonium salts of strong acid and weak base, the temperature of the secondary aluminum ash pretreatment (first-stage hydrolysis) can be controlled and maintained below 65°C at a water temperature of 30-50°C, and the maximum pressure below 0.65 MPa. At these temperatures and pressures, the hydrolysis of nitrides and carbides in the secondary aluminum ash is ensured while simultaneously lowering and maintaining the overall hydrolysis reaction temperature.

[0068] Compared with Example 1, in Comparative Example 1, no ammonium salt of strong acid and weak base was added, and the temperature value rose rapidly and eventually exceeded 100°C, reaching a maximum of 138.76°C, and the maximum pressure reached 1.06 MPa, with obvious temperature and pressure surges.

[0069] Compared with Example 1, when the initial temperature of Comparative Example 2 is 60°C, its temperature rises to 110.65°C, which is higher than the boiling point of water, causing a large amount of water to evaporate and turn into water vapor, resulting in incomplete contact between water and aluminum ash, affecting the final hydrolysis efficiency.

[0070] The above description of the embodiments is intended to facilitate understanding and application of the present invention by those skilled in the art. Those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the above descriptions are merely examples and comparative examples of the present invention and are not intended to limit the scope of the present invention. In other words, simple equivalent variations and modifications based on the present invention are still within the scope of patent protection.

Claims

1. A pretreatment and temperature control method for efficient denitrification of aluminum ash, characterized in that: The following steps are involved: Step S1, crushing and screening the secondary aluminum ash; Step S2, weighing the secondary aluminum ash and ammonium salts of strong acid and weak base after the treatment in step S1 in sequence and putting them into a reactor, replacing the air with an inert gas; the ammonium salts of strong acid and weak base include one or more of ammonium chloride, ammonium sulfate, ammonium bromide, ammonium iodide, ammonium nitrate, and ammonium dihydrogen phosphate; the amount of the ammonium salts of strong acid and weak base is 1.75% to 15.0% by weight of the secondary aluminum ash; Step S3, adding water to the reactor of step S2 and performing a hydrolysis reaction under stirring; the temperature of the water is 30-50° C., and the weight ratio of the added water to the secondary aluminum ash is 0.3-0.6:1; Step S4, after the reaction is completed, the gas generated in step S3 is recovered through the absorption liquid in the absorption kettle.

2. The pretreatment and temperature control method for efficient denitrification of aluminum ash according to claim 1, characterized in that: In step S1, the secondary aluminum ash is crushed and sieved to a particle size of 100 to 200 meshes.

3. The pretreatment and temperature control method for efficient denitrification of aluminum ash according to claim 1, characterized in that: In step S2, the inert gas is N2.

4. The pretreatment and temperature control method for efficient denitrification of aluminum ash according to claim 1, characterized in that: In step S3, the stirring rate is 200-350 r / min, and the hydrolysis reaction time is 1-3 h.

5. The pretreatment and temperature control method for efficient denitrification of aluminum ash according to claim 1, characterized in that: In step S4, the absorption liquid in the absorption kettle is one of 0.1-0.5M sulfuric acid solution, 0.1-0.5M nitric acid solution, 0.1-2M sodium chloride solution, 0.1-0.5M bromine aqueous solution, and 0.1-8M phosphoric acid solution.

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