Heavy metal stabilization and resourceful treatment method for household garbage incineration fly ash

Abstract

The invention belongs to the technical field of fly ash treatment, and discloses a heavy metal stabilization and resourceful treatment method for household garbage incineration fly ash, which comprises the following specific steps: step 1, fly ash pretreatment: collecting fly ash in a bag-type dust collector of a household garbage incineration plant; through gradient membrane separation desalination and targeted salt purification, the limitation of a traditional process is broken through, potassium chloride can be purified to the chemical fertilizer grade, sodium chloride can be purified to the industrial grade standard, the additional value of salt products is remarkably improved, efficient recovery of salt resources in fly ash is achieved, and more than 95% of soluble chlorine salt can be removed through gradient desalination; and an apatite-based composite stabilizer is matched to fix residual heavy metals, so that the binding material structure corrosion caused by chlorine salt residues is avoided, the risk of heavy metal dissolution is controlled, the compressive strength of the prepared chlorine salt-resistant special binding material reaches the standard, the chlorine salt resistance is excellent, the standard of building materials for ocean engineering is met, and meanwhile, a closed-loop process is integrated.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of fly ash treatment, and particularly relates to a heavy metal stabilization and resource treatment method for household garbage incineration fly ash. BACKGROUND

[0002] With the wide application of household garbage incineration treatment technology in China, the amount of fly ash generated in the incineration process increases year by year. The fly ash contains heavy metals such as lead, cadmium, zinc, copper and chromium, and a high content of soluble chlorides, and is listed as hazardous waste. If not properly treated, it can cause environmental pollution such as soil and water. At the same time, the salts and usable ingredients such as potassium and sodium contained in the fly ash have resource potential. Therefore, safe and stable treatment of household garbage incineration fly ash and resource recovery have become the focus of the industry.

[0003] At present, various technical means have been developed for the treatment of household garbage incineration fly ash in the industry, covering desalination, heavy metal stabilization and resource utilization in different aspects. However, the existing technology still has many shortcomings in practical application, and it is difficult to meet the needs of environmental protection requirements and efficient resource recovery. In the aspect of fly ash desalination, the existing technology often uses simple rinsing combined with evaporation crystallization. This method has limited separation and purification effect on salts, and the obtained salt product has low purity, which is mostly used as industrial grade waste, and the resource added value is not high, and the efficient recovery of salt resources has not been fully realized. In the aspect of fly ash-based cementitious material preparation, the existing technology often causes structure corrosion problems in the use process of the prepared cementitious material due to the high residual amount of chlorides in the fly ash. At the same time, if the heavy metals in the fly ash are not completely stabilized, there is a risk of leaching, which is difficult to meet the building material use standards in harsh environments. In the aspect of overall process integration, the existing technology often carries out fly ash desalination, heavy metal stabilization and resource utilization as independent processes, and there is a lack of effective integration between the aspects, which not only leads to low overall utilization rate of fly ash, but also easily produces secondary pollutants such as desalination wastewater or process residues, increases the subsequent disposal pressure and treatment cost, and restricts the large-scale popularization and application of fly ash treatment technology. Therefore, it needs to be improved. SUMMARY

[0004] The purpose of the present application is to provide a heavy metal stabilization and resource treatment method for household garbage incineration fly ash to solve the problems raised in the background art.

[0005] In order to achieve the above-mentioned purpose, the present application provides the following technical scheme: a heavy metal stabilization and resource treatment method for household garbage incineration fly ash, the specific steps are as follows: Step 1: Fly ash pretreatment Fly ash from the bag filter of a municipal solid waste incineration plant is collected and conveyed to a screening device via a closed screw conveyor. A 1mm mesh screen is used to remove large particles of unburned residue. The sieved fly ash sample is then subjected to compositional analysis to determine the heavy metal content, total soluble chloride content, mass ratio of potassium chloride to sodium chloride, and pH value. Based on the test results, subsequent process parameters are determined. The qualified fly ash is then fed into a mixing tank, and water is added at a liquid-to-solid ratio of 10:1. The mixing device is started and stirred at 300 rpm for 30 minutes to form a uniform fly ash slurry. Step 2: Gradient membrane separation and desalination The fly ash slurry is fed into a microfiltration system using a hollow fiber microfiltration membrane with a rejection precision of 0.1 μm and an operating pressure of 0.1 MPa. The fly ash particles are retained to form filter residue, and the permeate is collected to obtain primary desalination liquid. The primary desalination liquid is introduced into a nanofiltration system using a nanofiltration membrane with a molecular weight cutoff of 500 Da and an operating pressure of 0.5 MPa. This process retains some large molecular impurities and multivalent ions. The nanofiltration permeate is collected and fed into a reverse osmosis system using an aromatic polyamide membrane element and an operating pressure of 1.5 MPa. This process retains more than 99% of soluble salts to form a concentrate. The reverse osmosis permeate is recycled back to the stirred tank from step one for reuse. This process removes more than 95% of soluble chloride salts from the fly ash. Step 3: Salt separation and purification The composition of the reverse osmosis concentrate was analyzed to determine the mass ratio of potassium chloride to sodium chloride. When the ratio was 1:2, a high sodium chloride and low potassium chloride system, the concentrate was sent to the first MVR evaporator crystallizer. The evaporation temperature was controlled at 100℃, and the solution density was monitored in real time by a mass flow meter. Evaporation was stopped when the density reached 1.2 g / cm3. At this time, pure sodium chloride crystals precipitated. The crystallized liquid was sent to a centrifuge for thermal centrifugation separation for 10 minutes to obtain wet sodium chloride crystals. These crystals were then sent to a dryer and dried at 105℃ for 2 hours to obtain industrial-grade sodium chloride with a purity of 99%. The first mother liquor after centrifugation is sent to a cooling crystallization tank and cooled to 25°C at a rate of 5°C per hour. After being kept at this temperature and allowed to stand for 2 hours, potassium chloride crystals are precipitated. The crystals are then separated by cold centrifugation for 10 minutes to obtain wet potassium chloride crystals. After drying at 105°C for 2 hours, fertilizer-grade potassium chloride with a purity of 98% is obtained. The composition of the second mother liquor after potassium chloride separation is tested. Potassium chloride is added in proportion to adjust the ratio to the 1:2 ratio required for sodium chloride evaporation and then returned to the first MVR evaporator crystallizer for recycling. Step 4: Stabilization of heavy metals in fly ash The desalinated fly ash filter residue retained by the microfiltration system in step two is fed into a twin-shaft mixer. Apatite-based composite stabilizer is added at a ratio of 2.5% of the desalinated fly ash mass, and water is added to adjust the moisture content of the mixture to 25%. The mixer is started and stirred for 15 minutes until the mixture is uniform. The mixture is then sent to a curing chamber and cured at 25°C and 90% relative humidity for 72 hours to allow the apatite-based composite stabilizer to form stable chelates with the lead, cadmium, zinc, copper, and chromium heavy metals in the fly ash. After curing, the leaching concentration of heavy metals in the material is tested to ensure that it meets the requirements. Step 5: Preparation of Chloride-Resistant Cementitious Materials Stabilized fly ash is fed into a batching tank, and 36% stabilized fly ash, 30% slag, 32% silicate cement, and 2% desulfurized gypsum are added according to the mass ratio. The mixing device is started and mixed for 10 minutes until uniform. 15% of the total mass of clean water is added to the mixture, and stirring is continued for 5 minutes to form a cementitious slurry. The slurry is poured into a mold and shaped. It is cured for 28 days at 20℃ and 85% relative humidity to obtain a special chloride-resistant cementitious material. The compressive strength of this material can reach more than 40MPa. After boiling in sodium chloride solution for 8 hours, the compressive strength decreases by no more than 4.3MPa, and the volume expansion rate is 0.48%, which meets the standards for building materials used in marine engineering.

[0006] Preferably, the screening equipment described in step one needs to be run unloaded for 30 minutes before use to check the screen fixation and operational stability. If the screen breakage rate exceeds 5%, it needs to be replaced in time to ensure the removal effect of large particles of residue.

[0007] Preferably, the fly ash component detection in step one should be completed within 2 hours after sampling. The detection process should be strictly carried out in accordance with the standard detection method. Inductively coupled plasma mass spectrometry is used for heavy metal detection, and silver nitrate titration is used for chloride content detection to ensure the accuracy of the detection results.

[0008] Preferably, the microfiltration membrane, nanofiltration membrane and reverse osmosis membrane mentioned in step two need to be rinsed with deionized water for 30 minutes before use to remove the protective agent remaining on the membrane surface. During use, backwashing should be performed for 10 minutes every 2 hours of operation, and the backwashing pressure should be 0.8 times the working pressure to extend the service life of the membrane elements.

[0009] Preferably, the MVR evaporator crystallizer described in step three needs to be preheated to 50°C before starting. Nitrogen gas is introduced during the preheating process to prevent the concentrate from oxidizing when it comes into contact with air. The steam pressure is kept stable at 0.3 MPa during the evaporation process to ensure a uniform evaporation rate.

[0010] Preferably, the centrifuge speed in step three should be controlled at 3000 rpm. The clarity of the centrifuged liquid should be monitored in real time during the separation process. When the clarity is lower than 95%, the separation time should be extended by 5 minutes to ensure that the salt crystals are fully separated from the mother liquor.

[0011] Preferably, the apatite-based composite stabilizer described in step four needs to be sealed and stored in a dry environment, with the storage temperature controlled between 15°C and 30°C. Before use, it needs to be passed through a 0.075mm sieve to ensure that the stabilizer is evenly dispersed.

[0012] Preferably, the curing room in step four needs to be equipped with an automatic temperature and humidity control system, and the temperature and humidity fluctuation range should be controlled within ±1℃ and ±3%, respectively. During the curing period, the curing room door should not be opened frequently to prevent drastic changes in temperature and humidity from affecting the stabilization effect.

[0013] Preferably, the raw materials added to the mixing tank in step five should be in the order of solid to solid. First, add stabilized fly ash and slag and mix for 5 minutes, then add silicate cement and desulfurized gypsum and continue mixing for 5 minutes to ensure that all raw materials are mixed evenly and there is no local clumping.

[0014] The beneficial effects of this invention are as follows: By employing gradient membrane separation desalination and targeted salt purification, this method overcomes the limitations of traditional processes, purifying potassium chloride to fertilizer grade and sodium chloride to industrial grade standards. This significantly increases the added value of salt products and enables efficient recovery of salt resources from fly ash. Gradient desalination removes over 95% of soluble chlorides, and combined with apatite-based composite stabilizers to fix residual heavy metals, it avoids corrosion of cementitious materials caused by chloride residues and controls the risk of heavy metal leaching. The resulting chloride-resistant special cementitious material meets compressive strength standards and exhibits excellent chloride resistance, conforming to marine engineering building material standards. Furthermore, the integrated closed-loop process achieves 100% fly ash utilization, with reverse osmosis permeate recycled and reused, reducing water consumption and secondary treatment pressure, lowering treatment costs, and balancing environmental safety with the economic viability of resource recovery, thus facilitating large-scale promotion. Attached Figure Description

[0015] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] like Figure 1 As shown in the figure, this invention provides a method for stabilizing and recycling heavy metals in fly ash from municipal solid waste incineration. The specific steps are as follows: Step 1: Fly Ash Pretreatment Fly ash from the bag filter of a municipal solid waste incineration plant is collected and conveyed to a screening device via a closed screw conveyor. A 1mm mesh screen is used to remove large particles of unburned residue. The sieved fly ash sample is then subjected to compositional analysis to determine the heavy metal content, total soluble chloride content, mass ratio of potassium chloride to sodium chloride, and pH value. Based on the test results, subsequent process parameters are determined. The qualified fly ash is then fed into a mixing tank, and water is added at a liquid-to-solid ratio of 10:1. The mixing device is started and stirred at 300 rpm for 30 minutes to form a uniform fly ash slurry. Step 2: Gradient membrane separation and desalination The fly ash slurry is fed into a microfiltration system using a hollow fiber microfiltration membrane with a rejection precision of 0.1 μm and an operating pressure of 0.1 MPa. The fly ash particles are retained to form filter residue, and the permeate is collected to obtain primary desalination liquid. The primary desalination liquid is introduced into a nanofiltration system using a nanofiltration membrane with a molecular weight cutoff of 500 Da and an operating pressure of 0.5 MPa. This process retains some large molecular impurities and multivalent ions. The nanofiltration permeate is collected and fed into a reverse osmosis system using an aromatic polyamide membrane element and an operating pressure of 1.5 MPa. This process retains more than 99% of soluble salts to form a concentrate. The reverse osmosis permeate is recycled back to the stirred tank from step one for reuse. This process removes more than 95% of soluble chloride salts from the fly ash. Step 3: Salt separation and purification The composition of the reverse osmosis concentrate was analyzed to determine the mass ratio of potassium chloride to sodium chloride. When the ratio was 1:2, a high sodium chloride and low potassium chloride system, the concentrate was sent to the first MVR evaporator crystallizer. The evaporation temperature was controlled at 100℃, and the solution density was monitored in real time by a mass flow meter. Evaporation was stopped when the density reached 1.2 g / cm3. At this time, pure sodium chloride crystals precipitated. The crystallized liquid was sent to a centrifuge for thermal centrifugation separation for 10 minutes to obtain wet sodium chloride crystals. These crystals were then sent to a dryer and dried at 105℃ for 2 hours to obtain industrial-grade sodium chloride with a purity of 99%. The first mother liquor after centrifugation is sent to a cooling crystallization tank and cooled to 25°C at a rate of 5°C per hour. After being kept at this temperature and allowed to stand for 2 hours, potassium chloride crystals are precipitated. The crystals are then separated by cold centrifugation for 10 minutes to obtain wet potassium chloride crystals. After drying at 105°C for 2 hours, fertilizer-grade potassium chloride with a purity of 98% is obtained. The composition of the second mother liquor after potassium chloride separation is tested. Potassium chloride is added in proportion to adjust the ratio to the 1:2 ratio required for sodium chloride evaporation and then returned to the first MVR evaporator crystallizer for recycling. Step 4: Stabilization of heavy metals in fly ash The desalinated fly ash filter residue retained by the microfiltration system in step two is fed into a twin-shaft mixer. Apatite-based composite stabilizer is added at a ratio of 2.5% of the desalinated fly ash mass, and water is added to adjust the moisture content of the mixture to 25%. The mixer is started and stirred for 15 minutes until the mixture is uniform. The mixture is then sent to a curing chamber and cured at 25°C and 90% relative humidity for 72 hours to allow the apatite-based composite stabilizer to form stable chelates with the lead, cadmium, zinc, copper, and chromium heavy metals in the fly ash. After curing, the leaching concentration of heavy metals in the material is tested to ensure that it meets the requirements. Step 5: Preparation of Chloride-Resistant Cementitious Materials Stabilized fly ash is fed into a batching tank, and 36% stabilized fly ash, 30% slag, 32% silicate cement, and 2% desulfurized gypsum are added according to the mass ratio. The mixing device is started and mixed for 10 minutes until uniform. 15% of the total mass of clean water is added to the mixture, and stirring is continued for 5 minutes to form a cementitious slurry. The slurry is poured into a mold and shaped. It is cured for 28 days at 20℃ and 85% relative humidity to obtain a special chloride-resistant cementitious material. The compressive strength of this material can reach more than 40MPa. After boiling in sodium chloride solution for 8 hours, the compressive strength decreases by no more than 4.3MPa, and the volume expansion rate is 0.48%, which meets the standards for building materials used in marine engineering.

[0018] Pretreatment removes large particles of fly ash residue and accurately detects its composition, providing pure raw materials and scientific parameters for subsequent processes; gradient membrane desalination removes soluble chloride salts and saves water through permeate circulation; salt purification yields fertilizer-grade potassium chloride and industrial-grade sodium chloride, increasing the added value of salt products; heavy metal stabilization ensures leaching concentration meets standards, eliminating environmental risks; finally, chloride-resistant cementitious materials are produced that meet marine engineering standards, achieving 100% resource recovery of fly ash, forming a closed loop without secondary disposal pressure, and balancing environmental protection and resource recycling.

[0019] In step one, the screening equipment needs to be run unloaded for 30 minutes before use to check the screen fixation and operational stability. If the screen breakage rate exceeds 5%, it needs to be replaced in time to ensure the removal effect of large particles of residue.

[0020] By conducting no-load test runs and replacing damaged screens before using the screening equipment, the problem of incomplete removal of large particles of residue caused by unstable screen fixing, abnormal operation, or damage can be effectively avoided, ensuring the purity of fly ash raw materials entering subsequent processes.

[0021] In step one, the fly ash composition detection must be completed within 2 hours after sampling. The detection process must be strictly carried out in accordance with the standard detection methods. Inductively coupled plasma mass spectrometry is used for heavy metal detection, and silver nitrate titration is used for chloride content detection to ensure the accuracy of the test results.

[0022] The fly ash composition analysis is completed within 2 hours of sampling using standard testing methods to avoid changes in composition due to prolonged sample storage.

[0023] In step two, the microfiltration membrane, nanofiltration membrane, and reverse osmosis membrane need to be rinsed with deionized water for 30 minutes before use to remove the residual protective agent on the membrane surface. During use, backwashing should be performed for 10 minutes every 2 hours of operation, with the backwashing pressure being 0.8 times the working pressure, to extend the service life of the membrane elements.

[0024] Rinsing the membrane elements with deionized water before use and backwashing them regularly during operation can thoroughly remove residual protective agents on the membrane surface and impurities adsorbed during operation, prevent membrane pore blockage, extend the service life of the membrane elements, maintain stable operating pressure and processing efficiency of the membrane separation system, and ensure the removal effect of soluble chloride salts.

[0025] In step three, the MVR evaporator crystallizer needs to be preheated to 50°C before starting. Nitrogen gas is introduced during the preheating process to prevent the concentrate from oxidizing when it comes into contact with air. The steam pressure is kept stable at 0.3 MPa during the evaporation process to ensure a uniform evaporation rate.

[0026] MVR evaporator crystallizers feature preheating before startup, nitrogen protection, and stable steam pressure control during evaporation. This prevents oxidation reactions caused by contact between the concentrate and air, while ensuring a uniform evaporation rate. It also prevents purity decreases due to rate fluctuations during salt crystallization, ensuring that industrial-grade sodium chloride and fertilizer-grade potassium chloride meet product quality standards.

[0027] In step three, the centrifuge speed should be controlled at 3000 rpm. During the separation process, the clarity of the centrifuged liquid should be monitored in real time. If the clarity is lower than 95%, the separation time should be extended by 5 minutes to ensure that the salt crystals are fully separated from the mother liquor.

[0028] Real-time monitoring of the clarity of the centrifuged liquid ensures that salt crystals are fully separated from the mother liquor, reduces mother liquor residue in the crystal particles, lowers impurity content, further improves the purity of salt products, and avoids product grade reduction due to incomplete separation.

[0029] In step four, the apatite-based composite stabilizer must be sealed and stored in a dry environment with the storage temperature controlled between 15°C and 30°C. Before use, it must be passed through a 0.075mm sieve to ensure that the stabilizer is evenly dispersed.

[0030] Apatite-based composite stabilizers should be sealed and stored as required and sieved before use to effectively prevent them from getting damp and clumping, ensuring that the stabilizer particles are uniform. After being added to fly ash, they can be fully dispersed, increasing the contact area with heavy metals such as lead, cadmium, and zinc, improving the chelation reaction efficiency, and ensuring that the leaching concentration of heavy metals after stabilization treatment meets the standards.

[0031] In step four, the curing room must be equipped with an automatic temperature and humidity control system. The temperature and humidity fluctuation ranges should be controlled within ±1℃ and ±3%, respectively. During the curing period, the curing room door should not be opened frequently to prevent drastic changes in temperature and humidity from affecting the stabilization effect.

[0032] The curing room is equipped with an automatic temperature and humidity control system and operates in a standardized manner. It can maintain a stable curing environment of 25°C and 90% relative humidity, avoiding drastic fluctuations in temperature and humidity that could affect the chelation reaction process between the stabilizer and heavy metals, ensuring a full and thorough reaction, and guaranteeing that the heavy metal stabilization treatment of fly ash meets the standards.

[0033] In step five, the raw materials in the batching tank must be added in the order of solid to solid. First, add stabilized fly ash and slag and mix for 5 minutes, then add silicate cement and desulfurized gypsum and continue mixing for 5 minutes to ensure that all raw materials are mixed evenly and there is no local clumping.

[0034] Adding raw materials to the batching tank in a specified order and controlling the mixing time can prevent local agglomeration and clumping when different raw materials are mixed, ensure that the stabilized fly ash, slag, silicate cement and other components are evenly distributed, ensure the consistency of the internal structure of the cementitious material, and improve the compressive strength and chloride salt erosion resistance of the product.

[0035] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0036] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for stabilizing and recycling heavy metals in fly ash from municipal solid waste incineration, characterized in that, The specific steps are as follows: Step 1: Fly Ash Pretreatment Fly ash from the bag filter of a municipal solid waste incineration plant is collected and conveyed to a screening device via a closed screw conveyor. A 1mm mesh screen is used to remove large particles of unburned residue. The sieved fly ash sample is then subjected to compositional analysis to determine the heavy metal content, total soluble chloride content, mass ratio of potassium chloride to sodium chloride, and pH value. Based on the test results, subsequent process parameters are determined. The qualified fly ash is then fed into a mixing tank, and water is added at a liquid-to-solid ratio of 10:

1. The mixing device is started and stirred at 300 rpm for 30 minutes to form a uniform fly ash slurry. Step 2: Gradient membrane separation and desalination The fly ash slurry is fed into a microfiltration system using a hollow fiber microfiltration membrane with a rejection precision of 0.1 μm and an operating pressure of 0.1 MPa. The fly ash particles are retained to form filter residue, and the permeate is collected to obtain primary desalination liquid. The primary desalination liquid is introduced into a nanofiltration system using a nanofiltration membrane with a molecular weight cutoff of 500 Da and an operating pressure of 0.5 MPa. This process retains some large molecular impurities and multivalent ions. The nanofiltration permeate is collected and fed into a reverse osmosis system using an aromatic polyamide membrane element and an operating pressure of 1.5 MPa. This process retains more than 99% of soluble salts to form a concentrate. The reverse osmosis permeate is recycled back to the stirred tank from step one for reuse. This process removes more than 95% of soluble chloride salts from the fly ash. Step 3: Salt separation and purification The composition of the reverse osmosis concentrate was analyzed to determine the mass ratio of potassium chloride to sodium chloride. When the ratio was 1:2, a high sodium chloride and low potassium chloride system, the concentrate was sent to the first MVR evaporator crystallizer. The evaporation temperature was controlled at 100℃, and the solution density was monitored in real time by a mass flow meter. Evaporation was stopped when the density reached 1.2 g / cm3. At this time, pure sodium chloride crystals precipitated. The crystallized liquid was sent to a centrifuge for thermal centrifugation separation for 10 minutes to obtain wet sodium chloride crystals. These crystals were then sent to a dryer and dried at 105℃ for 2 hours to obtain industrial-grade sodium chloride with a purity of 99%. The first mother liquor after centrifugation is sent to a cooling crystallization tank and cooled to 25°C at a rate of 5°C per hour. After being kept at this temperature and allowed to stand for 2 hours, potassium chloride crystals are precipitated. The crystals are then separated by cold centrifugation for 10 minutes to obtain wet potassium chloride crystals. After drying at 105°C for 2 hours, fertilizer-grade potassium chloride with a purity of 98% is obtained. The composition of the second mother liquor after potassium chloride separation is tested. Potassium chloride is added in proportion to adjust the ratio to the 1:2 ratio required for sodium chloride evaporation and then returned to the first MVR evaporator crystallizer for recycling. Step 4: Stabilization of heavy metals in fly ash The desalinated fly ash filter residue retained by the microfiltration system in step two is fed into a twin-shaft mixer. Apatite-based composite stabilizer is added at a ratio of 2.5% of the desalinated fly ash mass, and water is added to adjust the moisture content of the mixture to 25%. The mixer is started and stirred for 15 minutes until the mixture is uniform. The mixture is then sent to a curing chamber and cured at 25°C and 90% relative humidity for 72 hours to allow the apatite-based composite stabilizer to form stable chelates with the lead, cadmium, zinc, copper, and chromium heavy metals in the fly ash. After curing, the leaching concentration of heavy metals in the material is tested to ensure that it meets the requirements. Step 5: Preparation of Chloride-Resistant Cementitious Materials Stabilized fly ash is fed into a batching tank, and 36% stabilized fly ash, 30% slag, 32% silicate cement, and 2% desulfurized gypsum are added according to the mass ratio. The mixing device is started and mixed for 10 minutes until uniform. 15% of the total mass of clean water is added to the mixture, and stirring is continued for 5 minutes to form a cementitious slurry. The slurry is poured into a mold and shaped. It is cured for 28 days at 20℃ and 85% relative humidity to obtain a special chloride-resistant cementitious material. The compressive strength of this material can reach more than 40MPa. After boiling in sodium chloride solution for 8 hours, the compressive strength decreases by no more than 4.3MPa, and the volume expansion rate is 0.48%, which meets the standards for building materials used in marine engineering.

2. The method for heavy metal stabilization and resource recovery of fly ash from municipal solid waste incineration according to claim 1, characterized in that: Before using the screening equipment described in step one, a no-load test run of 30 minutes is required to check the screen fixation and operational stability. If the screen breakage rate exceeds 5%, it must be replaced in time to ensure the removal effect of large particle residues.

3. The method for heavy metal stabilization and resource recovery of fly ash from municipal solid waste incineration according to claim 1, characterized in that: The fly ash composition detection described in step one must be completed within 2 hours after sampling. The detection process must be strictly carried out in accordance with the standard detection methods. Inductively coupled plasma mass spectrometry is used for heavy metal detection, and silver nitrate titration is used for chloride content detection to ensure the accuracy of the detection results.

4. The method for heavy metal stabilization and resource recovery of fly ash from municipal solid waste incineration according to claim 1, characterized in that: Before using the microfiltration membrane, nanofiltration membrane, and reverse osmosis membrane mentioned in step two, they need to be rinsed with deionized water for 30 minutes to remove the residual protective agent on the membrane surface. During use, backwash for 10 minutes every 2 hours of operation, with the backwash pressure being 0.8 times the working pressure, to extend the service life of the membrane elements.

5. The method for heavy metal stabilization and resource recovery of fly ash from municipal solid waste incineration according to claim 1, characterized in that: Before starting the MVR evaporator crystallizer described in step three, it needs to be preheated to 50°C. During the preheating process, nitrogen gas is introduced for protection to prevent the concentrate from oxidizing when it comes into contact with air. During the evaporation process, the steam pressure is kept stable at 0.3 MPa to ensure a uniform evaporation rate.

6. The method for heavy metal stabilization and resource recovery of fly ash from municipal solid waste incineration according to claim 1, characterized in that: In step three, the centrifuge speed should be controlled at 3000 rpm. During the separation process, the clarity of the centrifuged liquid should be monitored in real time. If the clarity is lower than 95%, the separation time should be extended by 5 minutes to ensure that the salt crystals are fully separated from the mother liquor.

7. The method for heavy metal stabilization and resource recovery of fly ash from municipal solid waste incineration according to claim 1, characterized in that: The apatite-based composite stabilizer described in step four needs to be sealed and stored in a dry environment with the storage temperature controlled between 15°C and 30°C. Before use, it needs to be passed through a 0.075mm sieve to ensure that the stabilizer is evenly dispersed.

8. The method for heavy metal stabilization and resource recovery of fly ash from municipal solid waste incineration according to claim 1, characterized in that: The curing room described in step four needs to be equipped with an automatic temperature and humidity control system. The temperature and humidity fluctuation range should be controlled within ±1℃ and ±3%, respectively. During the curing period, the curing room door should not be opened frequently to prevent drastic changes in temperature and humidity from affecting the stabilization effect.

9. The method for heavy metal stabilization and resource recovery of fly ash from municipal solid waste incineration according to claim 1, characterized in that: In step five, the raw materials in the mixing tank should be added in the order of solid to solid. First, add stabilized fly ash and slag and mix for 5 minutes. Then add silicate cement and desulfurized gypsum and continue mixing for 5 minutes to ensure that all raw materials are mixed evenly and there is no local clumping.

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