Chelating agent for treating fly ash generated by waste incineration as well as preparation method and application of chelating agent

Abstract

The invention discloses a chelating agent for waste incineration treatment. The chelating agent comprises the following components in percentage by mass: 35-65% of a chitosan derivative, 20-40% of organic phosphate and 10-25% of metal chloride. The invention also discloses a preparation method of the chelating agent. The preparation method comprises the following steps: (1) a pretreatment stage: carrying out vacuum drying on the chitosan derivative at 40-60 DEG C for 2-4 hours; (2) mixing reaction stage: carrying out first stirring reaction on the pretreated chitosan derivative and organic phosphate under the condition that the pH is 5.8-6.5, controlling the reaction temperature to be 55-65 DEG C, and controlling the reaction time to be 1-2 hours; and (3) a post-treatment stage: adding a metal chloride solution at intervals for three times at an interval of 15-25 minutes, and finally carrying out ultrasonic treatment for 20-40 minutes at an ultrasonic frequency of 28-40 kHz. According to the chelating agent provided by the invention, chitosan-metal-phosphate-heavy metal three-dimensional mesh gel is formed through reaction of three components, namely the chitosan derivative, the organic phosphate and the metal chloride, and the obtained chelating agent has an extremely high metal leaching rate when being used for fly ash treatment.

Description

Technical Field

[0001] This invention relates to the field of environmental protection technology, and in particular to a chelating agent for the treatment of fly ash generated from waste incineration, its preparation method, and its application. Background Technology

[0002] Currently, waste incineration has become one of the important means of treating municipal solid waste. In the incineration process, chelating agents can be added for pretreatment, which can "lock" in heavy metals before the fly ash enters the final landfill or resource utilization, rendering them non-migratory and non-biotoxic. Specifically, adding chelating agents for pretreatment has the following advantages: First, it reduces the leaching toxicity of heavy metals: Fly ash particles are small and porous, and heavy metals mostly exist in soluble salt or adsorbed states; chelating agents (such as organosulfur compounds DTC, TMT, or phosphates) form insoluble, stable, and extremely low-migration complexes with heavy metal ions through coordination, reducing the leaching concentration to below the limits of the "Pollution Control Standard for Municipal Solid Waste Landfills" (GB 16889-2008), thus avoiding secondary pollution. Second, it reduces subsequent disposal capacity expansion and costs: Traditional cement solidification requires 15-30% cement content, resulting in significant capacity expansion and high transportation and landfill costs; while the dosage of chelating agents is usually only 1-3%, achieving the same or better stabilization effect, significantly reducing capacity expansion and overall costs. Third, it improves the feasibility of subsequent resource utilization: After chelation pretreatment, heavy metals in fly ash are stably encapsulated, allowing for safe use in roadbed materials, cement raw materials, or sintered ceramsite, expanding the utilization pathways of fly ash beyond safe landfill. Fourth, it offers flexibility to adapt to different incineration conditions: Different incinerator types and flue gas purification processes lead to significant differences in fly ash composition; chelating agent systems (organic / inorganic, functional group modified) can be flexibly compounded according to target heavy metal concentrations such as Pb, Cd, and Zn, achieving "one formula per plant" and ensuring long-term stability. Therefore, chelating agent pretreatment is a crucial link in the chain of "harmlessness → volume reduction → resource utilization" of waste incineration fly ash, satisfying environmental regulations and creating conditions for low-cost disposal or high-value utilization in the later stages. However, traditional chelating agents such as lime and diatomaceous earth have problems such as low chelation efficiency, high cost, and easy generation of secondary pollution. Therefore, it is necessary to develop a new type of chelating agent for waste incineration treatment. Summary of the Invention

[0003] The purpose of this invention is to provide a chelating agent for the treatment of fly ash generated from waste incineration, its preparation method, and its application.

[0004] To achieve the above objectives, the solution of the present invention is: A chelating agent for treating fly ash generated from waste incineration comprises the following components by weight percentage: Chitosan derivatives 35-65%, organophosphates 20-40%, metal chlorides 10-25%.

[0005] Preferably, the organophosphate is selected from a combination of at least two of aminotrimethylphosphonic acid (ATMP), hydroxyethylidene diphosphonic acid (HEDP), and sodium ethylenediaminetetramethylidenephosphonate (EDTMPS), and the mass ratio of the combination is 1:0.5-2.

[0006] Preferably, the metal chloride is a mixture of manganese chloride, aluminum chloride and ferric chloride.

[0007] Preferably, it further comprises 0.1-1.5% of nano-titanium dioxide modified attapulgite clay, with a particle size of 50-200 nm and a specific surface area of ​​150-300 m². 2 / g.

[0008] The aforementioned method for preparing the chelating agent includes the following steps: (1) Pretreatment stage: The chitosan derivative is vacuum dried at 40-60℃ for 2-4 hours to obtain the pretreated chitosan derivative; (2) Mixing reaction stage: The pretreated chitosan derivative obtained in step (1) and the organophosphate are subjected to a first stirring reaction under pH 5.8-6.5 conditions, the reaction temperature is controlled at 55-65℃, and the time is 1-2 hours to obtain the chelating agent premix. (3) Post-processing stage: Add the metal chloride mixed solution to the chelating agent premix obtained in step (2) in three separate batches, with an interval of 15-25 minutes between each batch. Finally, perform ultrasonic treatment for 20-40 minutes at an ultrasonic frequency of 28-40 kHz to obtain the chelating agent.

[0009] Preferably, in step (2), the first stirring reaction is carried out using a double-helix counter-stirring stirrer with an inner helix speed of 80-120 rpm and an outer helix speed of 30-50 rpm.

[0010] Preferably, when adding the metal chloride solution in step (3), an inert gas is introduced simultaneously for protection, and the gas flow rate is controlled at 0.5-1.2 L / min.

[0011] Preferably, the ultrasonic treatment in step (3) adopts an intermittent ultrasonic mode with a working cycle of 5 seconds of ultrasound and 2 seconds of intermittent ultrasound.

[0012] The aforementioned chelating agent is used in the treatment of fly ash generated from waste incineration, specifically including the following steps: (1) The chelating agent is mixed with fly ash at a mass ratio of 1:15-25 to obtain a mixed system; (2) Adjust the pH value of the mixed system obtained in step (1) in three stages: the pH value of the first stage is 3.5-4.5 and is maintained for 10-15 minutes; the pH value of the second stage is 5.5-6.5 and is maintained for 20-30 minutes; the pH value of the third stage is 8.5-9.5 and is maintained for 30-45 minutes; a gradient heating process is carried out simultaneously in each pH adjustment stage, with a temperature change rate of 1-2℃ / min; a microwave treatment step is added after the third pH adjustment stage, with a microwave power of 300-500W, a frequency of 2.45GHz, and a treatment time of 5-8 minutes.

[0013] Preferably, the pH adjustment uses a citric acid-sodium hydroxide buffer system.

[0014] The principle of this invention is as follows: The chelating agent for treating fly ash generated from waste incineration provided by this invention is mainly composed of chitosan derivatives, organophosphates, and metal chlorides. In the prepared chelating agent, the chitosan derivative is the main functional component that plays a core chelation / adsorption synergistic role. The phosphate ions in the phosphate first form primary nuclei with the metal ions, and then are absorbed by the -NH groups on the chitosan chains. 3+ and -COO -By capturing these groups, a chitosan-phosphate-metal ternary network is formed, which effectively improves the mechanical strength and long-term stability of the chelating agent. Specifically, the chitosan derivative uses chitosan as its backbone, retaining a large number of -NH2 and -OH groups, and through chemical modification (carboxymethylation, hydroxyethylation, thiolation, etc.), additional active groups such as -COOH, -SH, and -POH2 are introduced. In the alkaline environment of fly ash, these groups can first capture, then chelate, and finally lock heavy metal ions such as Pb, Cd, Cu, and Zn in the three-dimensional gel, thereby achieving effective solidification of heavy metal ions. Phosphates play a dual role as "precipitant-coprecipitant + pH buffer": phosphonates coprecipitate with heavy metals to form insoluble phosphates, which have a tetrahedral structure, large specific surface area, and extremely low solubility; organophosphates can dissociate stepwise within a pH range of 4-12, neutralizing the high alkalinity in fly ash and preventing ammonia volatilization and hydroxide redissolution caused by pH greater than 11. Metal chlorides, on the other hand, act as "cross-linking-nucleation centers + auxiliary chelating agents." For example, aluminum chloride can generate polynuclear aluminum hydroxide complexes through in-situ hydrolysis-polymerization. These polynuclear complexes are positively charged, allowing them to electrostatically bind with the negatively charged regions of chitosan, forming "metal bridges" for cross-linking; they can also adsorb negatively charged phosphate or heavy metal complex anions, resulting in coprecipitation. The precipitates further form metal hydroxide microcrystals that interweave within the chitosan network, acting as "reinforcing steel and cement." Furthermore, the empty d orbitals of metal ions can interact with chitosan's -OH / -NH2 and phosphate's -PO4 groups. 3- The formation of octahedral or tetrahedral coordination significantly improves the stability of the complex.

[0015] Compared to existing methods, the gains of this invention are as follows: 1. The chelating agent for treating fly ash generated from waste incineration provided by this invention forms a three-dimensional network gel of "chitosan-metal-phosphate-heavy metal" through the reaction of chitosan derivatives, organophosphates and metal chlorides. The resulting chelating agent has an extremely high metal leaching rate when used for treating fly ash generated from waste incineration.

[0016] 2. The chelating agent preparation method provided by the present invention uses relatively inexpensive raw materials and has a simple preparation process, which effectively reduces the treatment cost of fly ash generated by waste incineration.

[0017] 3. The chelating agent provided by this invention can be successfully used to treat fly ash produced by waste incineration. It does not produce new harmful substances during use, successfully reducing secondary pollution and is environmentally friendly. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to embodiments. It should also be understood that the following embodiments are only for further illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. The specific mass, reaction time, temperature, process parameters, etc., in the examples are merely examples within a suitable range. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention.

[0019] Unless otherwise specified, all reagents used were commercially available and were not further purified before use; unless otherwise specified, all operations were performed under a nitrogen atmosphere.

[0020] The titanium dioxide-modified attapulgite clay used in some embodiments of the present invention is a non-commercial reagent. The specific preparation conditions are as follows: (1) Grind the attapulgite clay and sieve it to 200 mesh for later use. (2) Under ice bath conditions, 10 mL of TiCl4 was slowly added dropwise to 100 mL of dry anhydrous ethanol over 25 min; immediately after the addition was completed, 3 mL of glacial acetic acid was added, and the resulting mixture was stirred under ice bath conditions for 40 min until a pale yellow transparent titanium dioxide sol solution was obtained. (3) Add 7.5g of the attapulgite clay prepared in step (1) to the light yellow transparent titanium dioxide sol solution obtained in step (2), sonicate the mixture for 45 min, and dry it at 80℃ for 24 hours. After the mixture gels, titanium dioxide attapulgite clay gel mixture is prepared. (4) Add the titanium dioxide attapulgite clay gel mixture prepared in step (3) into a stainless steel high-pressure reactor, and then add 80 mL of deionized water for hydrothermal reaction; set the reaction temperature to 200℃, the reaction time to 12 hours, and the pressure to 2MPa; after the reaction is completed, cool naturally to room temperature; after filtration, wash the obtained solid with 15 mL of anhydrous ethanol and 15 mL of deionized water in sequence, and dry the washed solid in a vacuum drying oven at 110℃ for 6 hours to obtain the titanium dioxide modified attapulgite clay product, totaling 11.7 g.

[0021] The fly ash used in some embodiments of this invention was taken from a bag filter dust collector at a municipal solid waste incineration plant in Nanning. The test results of heavy metal content in the fly ash are as follows: Zn: 3859 ug / g, Cu: 583 ug / g, Cr: 195 ug / g, Pb: 1174 ug / g, Cd: 301 ug / g, As: 223 ug / g, Hg: 176 ug / g.

[0022] Example 1 The preparation steps for the chelating agent used in the treatment of fly ash generated from waste incineration are as follows: (1) Pretreatment stage: 1000g of carboxymethyl chitosan was vacuum dried at 60℃ for 2 hours to obtain pretreated chitosan derivatives; (2) Mixing reaction stage: 400g of the pretreated chitosan derivative carboxymethyl chitosan obtained in step (1) was added to a double helix counter-stirring device with 100g of aminotrimethylphosphonic acid and 150g of hydroxyethylidene diphosphonic acid. The pH of the system was adjusted to 6.0 using a 10% sodium carbonate solution. Then the first stirring reaction was carried out. The inner helix speed was set to 90 rpm and the outer helix speed was set to 40 rpm. The reaction temperature was controlled at 60℃. After stirring for 1.5h, the chelating agent premix was obtained. (3) Post-processing stage: Add 100 ml of a mixed solution consisting of manganese chloride (mass concentration of 5%), aluminum chloride (mass concentration of 10%) and ferric chloride (mass concentration of 5%) to the chelating agent premix obtained in step (2) in three separate additions at intervals of about 20 min each time. When adding the metal chloride mixed solution, high-purity nitrogen gas needs to be introduced simultaneously for protection, and the nitrogen gas flow rate is controlled at 1.0 L / min. Finally, the obtained mixture is ultrasonically treated for 30 min at a frequency of 30 kHz. The ultrasonic treatment adopts an intermittent ultrasonic mode with a working cycle of 5 s / interval. After filtration, the obtained solid is dried overnight at 80 °C in a vacuum drying oven to obtain the chelating agent, totaling 857 g. The obtained chelating agent is named CMC-ATMP-HEDP-M-1.

[0023] Example 2 The steps for using chelating agents to treat fly ash generated from waste incineration are as follows: (1) A mixed system was obtained by mixing 100g of chelating agent CMC-ATMP-HEDP-M-1 with 2000g of fly ash; (2) The pH value of the mixed system obtained in step (1) was adjusted in three stages using a citric acid-sodium hydroxide buffer system: the pH value of the first stage was 3.5-4.5 and held for 15 min; the pH value of the second stage was 5.5-6.5 and held for 30 min; the pH value of the third stage was 8.5-9.5 and held for 45 min; a gradient heating process was carried out simultaneously in each pH adjustment stage, with a temperature change rate of 0.5℃ / min; a microwave treatment step was added after the third pH adjustment stage, with a microwave power of 400W, a frequency of 2.45GHz, and a treatment time of 6 min; after the treatment, samples were taken and the heavy metal content was analyzed by inductively coupled plasma mass spectrometry (ICP-MS), and the metal leaching rate is shown in Table 1.

[0024] Example 3 The preparation of the chelating agent for the treatment of fly ash generated from waste incineration is based on Example 1, except that the carboxymethyl chitosan in step (1) is replaced with quaternary ammonium salt chitosan, and the other steps are the same as in Example 1; the resulting chelating agent is denoted as CQAS-ATMP-HEDP-M-2.

[0025] The steps for using chelating agents to treat fly ash generated from waste incineration are the same as in Example 2, except that the chelating agent CMC-ATMP-HEDP-M1 is replaced with CQAS-ATMP-HEDP-M-2; the remaining steps are the same as in Example 2; the metal leaching rate is shown in Table 1.

[0026] Example 4 The preparation of the chelating agent for the treatment of fly ash generated from waste incineration is described in Example 1, except that the hydroxyethylidene diphosphonic acid in step (2) is replaced with sodium ethylenediaminetetramethylidene phosphonate, and the remaining steps are the same as in Example 1; the resulting chelating agent is denoted as CMC-ATMP-EDTMPS-M-3.

[0027] The steps for using chelating agents to treat fly ash generated from waste incineration are the same as in Example 2, except that the chelating agent CMC-ATMP-HEDP-M-1 is replaced with CMC-ATMP-EDTMPS-M-3; the remaining steps are the same as in Example 2; the metal leaching rate is shown in Table 1.

[0028] Example 5 The preparation of the chelating agent for the treatment of fly ash generated from waste incineration is described in Example 1, except that aminotrimethylphosphonic acid in step (2) is replaced with sodium ethylenediaminetetramethylphosphonate, and the remaining steps are the same as in Example 1; the resulting chelating agent is denoted as CMC-HEDP-EDTMPS-M-4.

[0029] The steps for using chelating agents to treat fly ash generated from waste incineration are the same as in Example 2, except that the chelating agent CMC-ATMP-HEDP-M-1 is replaced with CMC-HEDP-EDTMPS-M-4; the remaining steps are the same as in Example 2; the metal leaching rate is shown in Table 1.

[0030] Example 6 The preparation of the chelating agent for the treatment of fly ash generated from waste incineration is based on Example 1, except that the carboxymethyl chitosan in step (1) is replaced with a homogeneous mixture of carboxymethyl chitosan and quaternary ammonium salt chitosan in a mass ratio of 2:1. The remaining steps are the same as in Example 1. The resulting chelating agent is denoted as CMC-CQAS-ATMP-HEDP-M-5.

[0031] The steps for using chelating agents to treat fly ash generated from waste incineration are the same as in Example 2, except that the chelating agent CMC-ATMP-HEDP-M1 is replaced with CMC-CQAS-ATMP-HEDP-M-5; the remaining steps are the same as in Example 2; the metal leaching rate is shown in Table 1.

[0032] Example 7 The preparation of the chelating agent for the treatment of fly ash generated from waste incineration is based on Example 1, except that the carboxymethyl chitosan in step (1) is replaced with a homogeneous mixture of carboxymethyl chitosan and quaternary ammonium chitosan in a mass ratio of 2:1; 15g of titanium dioxide modified attapulgite clay is added in step (2) and then stirred; the remaining steps are the same as in Example 1; the resulting chelating agent is denoted as CMC-CQAS-ATMP-HEDP-Ti-M-6.

[0033] The steps for using chelating agents to treat fly ash generated from waste incineration are the same as in Example 2, except that the chelating agent CMC-ATMP-HEDP-M1 is replaced with CMC-CQAS-ATMP-HEDP-Ti-M-6; the remaining steps are the same as in Example 2; the metal leaching rate is shown in Table 1.

[0034] Example 8 The preparation of the chelating agent for the treatment of fly ash generated from waste incineration is based on Example 1, except that the carboxymethyl chitosan in step (1) is replaced with a homogeneous mixture of carboxymethyl chitosan and quaternary ammonium chitosan in a mass ratio of 2:1; 10g of titanium dioxide modified attapulgite clay is added in step (2) and then stirred; the remaining steps are the same as in Example 1; the resulting chelating agent is denoted as CMC-CQAS-ATMP-HEDP-Ti-M-7.

[0035] The steps for using chelating agents to treat fly ash generated from waste incineration are the same as in Example 2, except that the chelating agent CMC-ATMP-HEDP-M1 is replaced with CMC-CQAS-ATMP-HEDP-Ti-M-7; the remaining steps are the same as in Example 2; the metal leaching rate is shown in Table 1.

[0036] Example 9 The preparation of the chelating agent for the treatment of fly ash generated from waste incineration is based on Example 1, except that the carboxymethyl chitosan in step (1) is replaced with a homogeneous mixture of carboxymethyl chitosan and quaternary ammonium chitosan in a mass ratio of 2:1; 5g of titanium dioxide modified attapulgite clay is added in step (2) and then stirred; the remaining steps are the same as in Example 1; the resulting chelating agent is denoted as CMC-CQAS-ATMP-HEDP-Ti-M-8.

[0037] The steps for using chelating agents to treat fly ash generated from waste incineration are the same as in Example 2, except that the chelating agent CMC-ATMP-HEDP-M1 is replaced with CMC-CQAS-ATMP-HEDP-Ti-M-8; the remaining steps are the same as in Example 2; the metal leaching rate is shown in Table 1.

[0038] Table 1. Metal leaching rates of chelating agents used in the treatment of fly ash from waste incineration.

[0039] Example 10 The preparation of the chelating agent for the treatment of fly ash generated from waste incineration is based on Example 1, except that the carboxymethyl chitosan in step (1) is replaced with a homogeneous mixture of carboxymethyl chitosan and quaternary ammonium chitosan in a mass ratio of 2:1; 1g of titanium dioxide modified attapulgite clay is added in step (2) and then stirred; the remaining steps are the same as in Example 1; the resulting chelating agent is denoted as CMC-CQAS-ATMP-HEDP-Ti-M-9.

[0040] The steps for using chelating agents to treat fly ash generated from waste incineration are the same as in Example 2, except that the chelating agent CMC-ATMP-HEDP-M1 is replaced with CMC-CQAS-ATMP-HEDP-Ti-M-9; the remaining steps are the same as in Example 2; the metal leaching rate is shown in Table 1.

[0041] Comparative Example 1 The preparation of the chelating agent for the treatment of fly ash generated from waste incineration is described in Example 1, except that the carboxymethyl chitosan in step (1) is replaced with ordinary commercially available unmodified chitosan; the remaining steps are the same as in Example 1; the resulting chelating agent is denoted as CS-ATMP-HEDP-M-10.

[0042] The steps for using chelating agents to treat fly ash generated from waste incineration are the same as in Example 2, except that the chelating agent compound CMC-ATMP-HEDP-M1 is replaced with CS-ATMP-HEDP-M-10; the remaining steps are the same as in Example 2; the metal leaching rate is shown in Table 1.

[0043] Comparative Example 2 The preparation of the chelating agent for the treatment of fly ash generated from waste incineration is described in Example 9, except that the titanium dioxide modified attapulgite clay is replaced with ordinary commercially available unmodified attapulgite clay; the remaining steps are the same as in Example 1; the resulting chelating agent is denoted as CMC-CQAS-ATMP-HEDP-Ti-M-11.

[0044] The steps for using chelating agents to treat fly ash generated from waste incineration are the same as in Example 2, except that the chelating agent compound CMC-ATMP-HEDP-M1 is replaced with CMC-CQAS-ATMP-HEDP-Ti-M-11; the remaining steps are the same as in Example 2; the metal leaching rate is shown in Table 1.

[0045] Comparative Example 3 The preparation of the chelating agent for the treatment of fly ash generated from waste incineration is the same as in Example 1.

[0046] The steps for treating fly ash generated from waste incineration with chelating agents are the same as in Example 2, except that the condition in step (2) "after the third pH adjustment stage, a microwave treatment step is added, with a microwave power of 400W, a frequency of 2.45GHz, and a treatment time of 6min" is changed to: after the third pH adjustment stage, constant temperature heating is added for 4h; the rest of the steps are the same as in Example 2; the metal leaching rate is shown in Table 1.

[0047] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention.

Claims

1. A chelating agent for treating fly ash produced by waste incineration, characterized in that, Includes the following components by mass percentage: Chitosan derivatives 35-65%, organophosphates 20-40%, metal chlorides 10-25%.

2. The chelating agent according to claim 1, characterized in that, The organophosphate is selected from at least two of aminotrimethylphosphonic acid (ATMP), hydroxyethylidene diphosphonic acid (HEDP), and sodium ethylenediaminetetramethylidenephosphonate (EDTMPS), and the mass ratio of the combination is 1:0.5-2.

3. The chelating agent according to claim 1, characterized in that, The metal chloride is a mixture of manganese chloride, aluminum chloride and ferric chloride.

4. The chelating agent according to claim 1, characterized in that, It also contains 0.1-1.5% of nano-titanium dioxide modified attapulgite clay, with a particle size of 50-200 nm and a specific surface area of ​​150-300 m². 2 / g.

5. A method for preparing the chelating agent according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Pretreatment stage: The chitosan derivative is vacuum dried at 40-60℃ for 2-4 hours to obtain the pretreated chitosan derivative; (2) Mixing reaction stage: The pretreated chitosan derivative obtained in step (1) and organophosphate are subjected to a first stirring reaction under pH 5.8-6.5 conditions, the reaction temperature is controlled at 55-65℃, and the time is 1-2 hours to obtain the chelating agent premix. (3) Post-processing stage: Add the metal chloride mixed solution to the chelating agent premix obtained in step (2) in three separate batches, with an interval of 15-25 minutes between each batch. Finally, perform ultrasonic treatment for 20-40 minutes at an ultrasonic frequency of 28-40 kHz to obtain the chelating agent.

6. The preparation method according to claim 5, characterized in that, In step (2), the first stirring reaction is carried out using a double-helix counter-stirring stirrer with an inner helix speed of 80-120 rpm and an outer helix speed of 30-50 rpm.

7. The preparation method according to claim 5, characterized in that, When adding the metal chloride solution in step (3), an inert gas is introduced simultaneously for protection, and the gas flow rate is controlled at 0.5-1.2 L / min.

8. The preparation method according to claim 5, characterized in that, The ultrasonic treatment in step (3) adopts an intermittent ultrasonic mode with a working cycle of 5 seconds of ultrasound and 2 seconds of intermittent ultrasound.

9. The application of the chelating agent according to any one of claims 1-4 in the treatment of fly ash generated from waste incineration, characterized in that, Specifically, the steps include the following: (1) The chelating agent is mixed with fly ash at a mass ratio of 1:15-25 to obtain a mixed system; (2) Adjust the pH value of the mixed system obtained in step (1) in three stages: the pH value of the first stage is 3.5-4.5 and is maintained for 10-15 minutes; the pH value of the second stage is 5.5-6.5 and is maintained for 20-30 minutes; the pH value of the third stage is 8.5-9.5 and is maintained for 30-45 minutes; a gradient heating process is carried out simultaneously in each pH adjustment stage, with a temperature change rate of 0.5-2℃ / min; a microwave treatment step is added after the third pH adjustment stage, with a microwave power of 300-500W, a frequency of 2.45GHz, and a treatment time of 5-8 minutes.

10. The processing method according to claim 9, characterized in that, The pH adjustment uses a citric acid-sodium hydroxide buffer system.

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