Pretreatment and temperature control method for efficient denitrification of aluminum ash

Abstract

The invention provides a pretreatment and temperature control method for efficient denitrification of aluminum ash, which comprises the following steps: mixing aluminum ash with ammonium strong acid and weak base salt in a reaction kettle, introducing nitrogen to replace gas, and adding warm water to carry out pretreatment reaction on the aluminum ash. According to the method, the secondary aluminum ash and the ammonium strong acid and weak base salt are used as raw materials, the technological process is simple, the cost is low, the problem that the temperature is suddenly increased in the pretreatment process in the process of recycling the secondary aluminum ash is solved, the safety of the efficient nitrogen removal process of the aluminum ash is guaranteed, and good environmental benefits are achieved; by means of the method, the aluminum ash pretreatment temperature can be controlled and maintained below 65 DEG C, aluminum nitride hydrolysis is guaranteed while temperature sudden increase is controlled, and great safety guarantee is achieved in the aluminum ash treatment process.

Description

Technical Field

[0001] The 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 aluminum producer and consumer, but a large amount of aluminum ash waste is generated during the production process. Aluminum ash can be divided into primary aluminum ash and secondary aluminum ash. Primary aluminum ash has a high aluminum content and can be recycled into smelting. Secondary aluminum ash has a low aluminum content and contains a large amount of AlN. AlN is the reaction product of aluminum liquid and nitrogen during the smelting process. It is easily hydrolyzed in water and generates irritating and toxic gas NH3. Therefore, how to harmlessly treat secondary aluminum ash is a research hotspot and difficult problem in the current treatment of hazardous waste.

[0003] There are two main treatment technologies for harmless treatment of aluminum ash: wet treatment and pyrolysis. Pyrolysis mainly uses treatment facilities such as rotary kilns to recycle metal aluminum, but pyrolysis consumes a lot of energy and has high treatment costs. In many cases, the value of recovery is lower than the treatment cost, so pyrolysis has certain limitations. Wet treatment technologies mainly include acid leaching and alkaline leaching. Since aluminum is an amphoteric metal, the residual aluminum element in aluminum ash can be dissolved in acid and alkaline solutions to achieve the recovery of metal aluminum, but the wet hydrolysis denitrification rate is low, the water consumption is large, and the AlN hydrolysis induction period is long. For wet treatment, a two-stage hydrolysis method can achieve a higher denitrification rate, but due to the first pretreatment process, aluminum nitride, aluminum carbide and other substances in aluminum ash are violently hydrolyzed, instantly releasing a large amount of heat and producing a large amount of gas, resulting in uncontrollable temperature during the first hydrolysis process and a surge in pressure, which is not conducive to safe production.

[0004] Uncontrolled temperature surges are extremely dangerous for chemical reactions. Uncontrolled temperature may damage the reaction vessel and even cause explosions and fires. In addition, extreme temperature changes may also cause thermal stress damage to equipment such as reactor heat exchangers. Large temperature fluctuations make continuous production processes difficult to control, affecting production stability and efficiency. In the aluminum ash system, a large amount of hydrogen will be produced due to the wet hydrolysis of aluminum ash solid waste. Uncontrolled temperature is extremely dangerous to the system.

[0005] In response to the sudden increase in temperature during chemical reactions, there are usually several coping strategies, namely, increasing cooling measures, slow feeding of catalysts, emergency emptying, etc. However, in this system, intermittent kettle operation is adopted, and the slow feeding measures are not applicable. In addition, the generated gas is hydrogen-rich gas, which has high safety requirements, and emergency emptying and other operations are extremely dangerous. Therefore, the use of physical cooling control has little effect on this system.

[0006] In summary, a method suitable for efficient denitrification pretreatment and temperature control of aluminum ash is urgently needed. Summary of the invention

[0007] In order to solve the problem of sudden temperature increase and loss of control in 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 strong acid and weak base salts processed in step S1 in sequence and putting them into a reactor, and replacing the air with an inert gas;

[0010] Step S3, adding water into 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 meshes.

[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 diammonium 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 secondary aluminum ash efficient denitrification, the maximum temperature of the system can be reduced, sudden temperature increases can be avoided, and the temperature of the hydrolysis reaction can be controlled.

[0018] As a conjugate acid of a weak base, ammonium ions 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 they form hydrates with water molecules (i.e., ion hydration is exothermic), for salts such as ammonium salts of strong acids and weak bases, this exothermic process is not enough to compensate for the subsequent hydrolysis endothermic process. Moreover, the hydrolysis of ammonium ions is a typical endothermic reaction because it requires the breaking of NH4 + The hydrogen bonds between the ammonium ion and the water molecules and the subsequent formation of the new NH3·H2O molecular structure all require the absorption of energy. 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, and is 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 in conjunction with 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) The secondary aluminum ash was crushed and sieved, and the secondary aluminum ash between 100 and 200 meshes was collected for the next experiment;

[0028] (2) Weigh 75 g of the 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 the 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 into the reactor and stir at 350 r / min for 2 h.

[0036] (4) After the reaction is completed, the gas is collected with 0.4 M 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 the 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 into 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 the 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 into the reactor and stir at 350 r / min for 2 h.

[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 the screened 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 into the reactor and stir at 200 r / min for 2 h for hydrolysis;

[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) The secondary aluminum ash was crushed and sieved, and the secondary aluminum ash between 100 and 200 meshes was collected for the next experiment;

[0057] (2) Weigh 75 g of the screened secondary aluminum ash and place it in a reactor, and introduce 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) The secondary aluminum ash was crushed and sieved, and the secondary aluminum ash between 100 and 200 meshes was collected for the next experiment;

[0062] (2) Weigh 75 g of the 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 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 above table reflects the different effects of different initial reaction temperatures and different amounts of ammonium strong acid weak base salt addition on the first stage hydrolysis (pretreatment) temperature of secondary aluminum ash. The results show that after adding ammonium strong acid weak base salt in Examples 1 to 5, the water temperature can be controlled and maintained at below 65°C at 30 to 50°C, and the maximum pressure is controlled below 0.65MPa. At this temperature and pressure, the hydrolysis of nitrides and carbides in the secondary aluminum ash is guaranteed, while the temperature of the entire hydrolysis reaction is reduced and kept stable.

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

[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 to facilitate the understanding and use of the present invention by those skilled in the art. Those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative labor. Therefore, the above description is only the embodiments and comparative examples of the present invention, and cannot limit the scope of the implementation of the present invention, that is, simple equivalent changes and modifications made according to the present invention are still within the scope of patent protection of the present invention.

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 root strong acid and weak base salts processed in step S1 in sequence and putting them into a reactor, and replacing the air with an inert gas; the ammonium root strong acid and weak base salts include one or more of ammonium chloride, ammonium sulfate, ammonium bromide, ammonium iodide, ammonium nitrate, and diammonium phosphate; Step S3, adding water into the reactor of step S2, and performing a hydrolysis reaction under stirring; 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 particle size of the secondary aluminum ash after crushing and screening is 100-200 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 dosage of the ammonium salt of strong acid and weak base is 1.75% to 15.0% of the weight of the secondary aluminum ash.

4. 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.

5. The pretreatment and temperature control method for efficient denitrification of aluminum ash according to claim 1, characterized in that: In step S3, the temperature of the water is 30-50°C, and the weight ratio of the input water to the secondary aluminum ash is 0.3-0.6:

1.

6. 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.

7. 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 0.1-0.5 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.

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