A method for washing and desalting of waste incineration fly ash

Abstract

The application relates to the solid waste treatment technical field and discloses a waste incineration fly ash water washing desalination method, which comprises the following steps: pretreating waste incineration fly ash to obtain fly ash suspension; adjusting the pH of the fly ash suspension to 11.5-12.5; adding a chelating agent in the fly ash suspension, and the adding amount of the chelating agent is 0.4%-0.9% of the weight of the waste incineration fly ash; stirring and washing the fly ash suspension for 2-3 hours under the condition that the pH is 11.5-12.5; continuing to stir for 40-50 minutes under the condition that the oxidation-reduction potential is-200 mV to-300 mV; performing solid-liquid separation on the fly ash suspension to obtain desalinated waste incineration fly ash solid and waste water; and treating the waste water by using a reverse osmosis membrane. The method can significantly improve the removal rate of heavy metals and salt.

Description

A method for desalination of fly ash from waste incineration by water washing Technical Field

[0001] This application relates to the field of solid waste treatment technology, and mainly to a method for water washing and desalination of fly ash from waste incineration. Background Technology

[0002] Waste incineration fly ash is a solid waste generated during the incineration of municipal solid waste. Its composition is complex, containing large amounts of salts (such as chlorides and sulfates), heavy metals (such as lead, cadmium, and chromium), and harmful substances such as dioxins. Direct disposal without treatment will cause serious environmental pollution. Currently, water washing and desalination is one of the commonly used methods for treating waste incineration fly ash.

[0003] However, traditional water washing desalination methods have many technical problems. First, water washing is often ineffective for heavy metals in incineration fly ash that exist in the form of sparingly soluble salts or oxides, resulting in low heavy metal removal rates. For example, chromium may exist as Cr2O3, which has extremely low solubility in water and is difficult to remove by simple water washing. Second, incineration fly ash particles are prone to agglomeration during water washing, forming large particle clumps. This reduces the contact area between the washing solution and the incineration fly ash particles, thus affecting the dissolution and diffusion of salts and heavy metals. The main reason for particle agglomeration is the electrostatic interaction and van der Waals forces on the surface of incineration fly ash particles.

[0004] Furthermore, pH control is crucial during the washing process. Improper pH control can cause dissolved heavy metal ions to redeprecipitate. For example, under alkaline conditions, lead ions readily form lead hydroxide precipitate, reducing desalination efficiency. In addition, traditional washing processes consume large amounts of water, resulting in high wastewater treatment costs. Pollutants such as salts, heavy metals, and organic matter in the wastewater require complex treatment processes to meet discharge standards, further increasing treatment costs.

[0005] Furthermore, existing technologies have limited capacity to handle the complex components of waste incineration fly ash. The composition of waste incineration fly ash varies depending on the source of the waste and the incineration process, resulting in a complex and variable composition. Existing water washing processes struggle to effectively treat fly ash with different compositions, leading to unstable desalination results. The efficiency of solid-liquid separation during water washing is also a significant issue. Waste incineration fly ash contains a large number of fine particles, which are easily lost with wastewater during washing, reducing desalination efficiency and increasing the difficulty of wastewater treatment. Additionally, secondary pollution may occur during washing, such as the release of harmful gases like ammonia, posing a threat to the environment and the health of operators. Ammonia primarily originates from the decomposition of nitrogen oxides in waste incineration fly ash. Finally, traditional water washing methods typically employ long washing times and large water volumes to ensure desalination effectiveness. However, this not only increases operating costs but may also lead to equipment corrosion and increased wastewater discharge.

[0006] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the purpose of this application is to provide a method for desalination of fly ash from waste incineration by water washing, which aims to improve the desalination effect.

[0008] The technical solution of this application is as follows:

[0009] A method for water washing and desalination of fly ash from waste incineration, comprising the following steps:

[0010] Step 1: Pre-treat the fly ash from waste incineration to obtain a fly ash suspension;

[0011] Step 2: Adjust the pH of the fly ash suspension to 11.5-12.5;

[0012] Step 3: Add a chelating agent to the fly ash suspension, wherein the amount of chelating agent added is 0.4%-0.9% of the weight of the waste incineration fly ash;

[0013] Step 4: Under conditions of pH 11.5-12.5, nitrogen gas is introduced for protection, and the fly ash suspension is stirred and washed with water for 2-3 hours.

[0014] Step 5: Add sodium sulfite solution to the fly ash suspension and adjust the redox potential to -200mV to -300mV;

[0015] Step 6: Continue stirring for 40-50 minutes at a redox potential of -200mV to -300mV;

[0016] Step 7: Perform solid-liquid separation on the fly ash suspension to obtain desalinated waste incineration fly ash solids and wastewater;

[0017] Step 8: Treat the wastewater using a reverse osmosis membrane;

[0018] The chelating agent comprises at least a sodium thioacetate-modified starch chelating agent;

[0019] The preparation method of the sodium thioacetate modified starch chelating agent includes the following steps:

[0020] a. Dissolve soluble starch in deionized water to prepare a starch solution with a mass-volume concentration of 5%;

[0021] b. Dissolve sodium thioacetate in deionized water to prepare a sodium thioacetate solution with a mass-volume concentration of 10%;

[0022] c. Add a catalyst to the starch solution; wherein the amount of the catalyst is 0.5% of the weight of the starch, and the catalyst is N,N-dimethyl-4-aminopyridine;

[0023] d. The sodium thioacetate solution is added dropwise to the starch solution, and the dropping rate is controlled to maintain the reaction temperature at 40-45℃;

[0024] e. Stir and react at room temperature for 8 hours;

[0025] f. Adjust the pH to 7.0 with hydrochloric acid solution to terminate the reaction;

[0026] g. The reaction product is precipitated with ethanol, washed, and dried to obtain the sodium thioacetate-modified starch chelating agent.

[0027] The waste incineration fly ash water washing desalination method of this application is divided into two stages: the first stage is carried out under alkaline conditions, using chelating agents to promote the dissolution of heavy metals; the second stage controls the valence state of heavy metals by adjusting the redox potential, thereby improving the binding capacity of the chelating agent.

[0028] The aforementioned method for water washing and desalination of waste incineration fly ash includes the following specific steps for pretreatment of the waste incineration fly ash:

[0029] Mix the fly ash from waste incineration with deionized water at a weight ratio of 1:6, stir at room temperature for 30-50 minutes, and let it stand to settle for 1.5-2.5 hours.

[0030] The method for desalinizing fly ash from waste incineration by washing, wherein the preparation method of the sodium thioacetate-modified starch chelating agent further includes the following steps:

[0031] Step A: Dissolve the sodium thioacetate modified starch chelating agent in deionized water to prepare a solution with a mass-volume concentration of 2%;

[0032] Step B: Add a crosslinking agent; wherein the crosslinking agent is epichlorohydrin or glutaraldehyde, and the amount of the crosslinking agent is 1% of the weight of the sodium thioacetate-modified starch chelating agent;

[0033] Step C: Adjust the pH to 8-9 using sodium hydroxide solution;

[0034] Step D: Stir the reaction at 35-45℃ for 3-5 hours at a stirring speed of 100-200 rpm;

[0035] Step E: Adjust the pH to 7.0 with hydrochloric acid solution to terminate the reaction;

[0036] Step F: The reaction product is precipitated with ethanol, washed, and dried to obtain the cross-linked sodium thioacetate modified starch chelating agent.

[0037] The waste incineration fly ash water washing desalination method, wherein the chelating agent is a combination of sodium thioacetate modified starch chelating agent and DTPA, and the amount of DTPA is 20% of the total weight of the chelating agent;

[0038] In step 4, before the stirring and washing, humic acid is added, and the amount of humic acid is 0.2% of the weight of the deionized water.

[0039] In the aforementioned waste incineration fly ash washing and desalination method, in step 2, sodium hydroxide solution is used to adjust the pH value of the fly ash suspension.

[0040] In the aforementioned waste incineration fly ash water washing and desalination method, in step 4, the stirring speed of the stirring water washing is 200-300 rpm.

[0041] In the aforementioned waste incineration fly ash water washing and desalination method, in step 6, the stirring speed of the continued stirring process is 200-300 rpm.

[0042] The waste incineration fly ash water washing and desalination method, wherein in step 7, the solid-liquid separation is performed using a ceramic membrane.

[0043] In the aforementioned waste incineration fly ash water washing and desalination method, in step 8, the molecular weight cutoff of the reverse osmosis membrane is 0.1 kDa.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] The waste incineration fly ash water washing and desalination method of this application consists of two stages: the first stage is carried out under alkaline conditions, utilizing a chelating agent to promote the dissolution of heavy metals; the second stage controls the valence state of heavy metals by adjusting the redox potential, thereby improving the binding capacity of the chelating agent. The waste incineration fly ash water washing and desalination method of this application has a simple process flow, is easy to operate, and is suitable for treating waste incineration fly ash containing high concentrations of heavy metals such as mercury and silver. Detailed Implementation

[0046] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0047] The waste incineration fly ash water washing and desalination method provided in this application specifically includes the following steps:

[0048] Step 1: Pre-treat the fly ash from waste incineration to obtain a fly ash suspension.

[0049] Specifically, in step 1, the fly ash from waste incineration is mixed with water at a weight ratio of 1:6, stirred at room temperature for 30-50 minutes, and allowed to settle for 1.5-2.5 hours.

[0050] Pre-treating fly ash from waste incineration removes large particulate impurities, which improves the efficiency of subsequent washing. It also removes soluble salts from the surface of the fly ash, reducing salt interference in the subsequent washing process and improving the removal efficiency of heavy metals.

[0051] Step 2: Adjust the pH of the fly ash suspension.

[0052] Specifically, in step 2, the pH of the pretreated fly ash suspension is adjusted to 11.5-12.5.

[0053] Adjusting the pH of the fly ash suspension to a strongly alkaline state (11.5-12.5) facilitates the release of chelating groups from the sodium thioacetate-modified starch chelating agent in subsequent steps, thereby promoting the dissolution of heavy metals.

[0054] In this step, the concentration of sodium hydroxide solution used to adjust the pH can be 1-3 mol / L.

[0055] Step 3: Add a chelating agent to the fly ash suspension.

[0056] Specifically, in step 3, a chelating agent is added to the fly ash suspension at a concentration of 0.4%-0.9% of the weight of the waste incineration fly ash. Insufficient chelating agent will result in poor chelation; excessive chelating agent will increase costs.

[0057] In this step, the chelating agent can be one or a combination of sodium thioacetate-modified starch chelating agent and DTPA. Sodium thioacetate-modified starch chelating agent can form stable complexes with heavy metal ions, thereby increasing the solubility of heavy metals.

[0058] Furthermore, the sodium thioacetate-modified starch chelating agent is prepared by modifying soluble starch with sodium thioacetate through an esterification reaction. Specifically, the preparation method of the sodium thioacetate-modified starch chelating agent includes the following steps:

[0059] a. Dissolve soluble starch in deionized water to prepare a starch solution with a concentration of 5% (w / v);

[0060] b. Dissolve sodium thioacetate in deionized water to prepare a 10% (w / v) sodium thioacetate solution;

[0061] c. Add an appropriate amount of catalyst to the starch solution, the amount of catalyst being 0.5% of the starch weight. The catalyst can be N,N-dimethyl-4-aminopyridine.

[0062] d. Slowly add sodium thioacetate solution dropwise to starch solution, controlling the dropping rate to maintain the reaction temperature at 40-45℃;

[0063] e. Stir and react at room temperature for 8 hours;

[0064] f. Adjust the pH to 7.0 with hydrochloric acid solution to terminate the reaction;

[0065] g. The reaction product was precipitated with ethanol, washed, and dried to obtain sodium thioacetate-modified starch chelating agent;

[0066] The prepared sodium thioacetate-modified starch chelating agent is a pH / redox dual-responsive chelating agent. Under strongly alkaline conditions, the hydroxyl groups on starch are deprotonated, and the sulfide ions on sodium thioacetate exhibit strong chelating ability, forming stable complexes with heavy metal ions. By adjusting the redox potential and controlling the valence state of heavy metals, the binding capacity of the chelating agent can be improved.

[0067] In practical applications, although the chelating agent can be recycled and reused, the removal efficiency of sodium thioacetate-modified starch chelating agents for heavy metals decreases, requiring frequent replacement to maintain the removal effect and increasing operating costs. Research has found that the prepared sodium thioacetate-modified starch chelating agent is prone to hydrolysis or oxidation under strongly alkaline conditions, especially at high temperatures or during long-term storage, leading to a decrease in chelating capacity. Therefore, the preparation method of sodium thioacetate-modified starch chelating agents has been optimized, and the preparation method further includes the following steps:

[0068] Step A: Dissolve the prepared sodium thioacetate modified starch chelating agent in deionized water to prepare a 2% (w / v) solution.

[0069] Step B: Add the crosslinking agent epichlorohydrin. The amount of epichlorohydrin is 1% of the weight of the sodium thioacetate-modified starch chelating agent.

[0070] Step C: Adjust the pH to 8-9 using sodium hydroxide solution.

[0071] Step D: Stir the reaction at 35-45℃ for 3-5 hours at a stirring speed of 100-200 rpm.

[0072] Step E: Adjust the pH to 7.0 with hydrochloric acid solution to terminate the reaction.

[0073] Step F: The reaction product is precipitated with ethanol, washed, and dried to obtain the cross-linked sodium thioacetate modified starch chelating agent.

[0074] In the preparation of sodium thioacetate-modified starch chelating agent, a crosslinking agent is introduced to crosslink the starch, forming a three-dimensional network structure, thereby improving its mechanical strength and chemical stability. The crosslinking agent can be epichlorohydrin or glutaraldehyde, etc.; epichlorohydrin is used in the embodiments of this application. Furthermore, by optimizing storage conditions, lowering the storage temperature, and avoiding direct sunlight, the decomposition of the sodium thioacetate-modified starch chelating agent can be reduced. By improving the stability of the sodium thioacetate-modified starch chelating agent, its service life is extended, and the replacement frequency of the chelating agent is reduced, thereby lowering operating costs and ensuring the removal effect of heavy metals.

[0075] Step 4: Wash with alkaline water.

[0076] Specifically, in step 4, under the condition of pH value of 11.5-12.5, nitrogen gas is introduced for protection, and the fly ash suspension is stirred and washed with water for 2-3 hours at a stirring speed of 200-300 rpm.

[0077] In this step, the fly ash suspension is stirred and washed with water for 2-3 hours under strongly alkaline conditions to promote the dissolution and chelation of heavy metals. Simultaneously, nitrogen gas is introduced for protection to prevent oxidation. Too high or too low a pH range will affect the dissolution and complexation of heavy metals; therefore, the pH value is limited to 11.5-12.5 in this step.

[0078] Step 5: Adjust the redox potential.

[0079] Specifically, in step 5, sodium sulfite solution is added to the fly ash suspension to adjust the redox potential to -200mV to -300mV. Adjusting the redox potential too high or too low will affect the valence state of heavy metals and the binding capacity of the chelating agent. Therefore, in this step, the redox potential adjustment range is limited to -200mV to -300mV.

[0080] In the embodiments of this application, the concentration of sodium sulfite solution used to adjust the redox potential can be 0.1 mol / L.

[0081] Step 6: Stable in acidic conditions.

[0082] Specifically, in step 6, under the condition of redox potential of -200mV to -300mV, stirring is continued for 40-50 minutes at a stirring speed of 200-300rpm to ensure the stable existence of the heavy metal-chelating agent complex.

[0083] Step 7: Solid-liquid separation.

[0084] Specifically, in step 7, the fly ash suspension is subjected to solid-liquid separation to obtain desalinated waste incineration fly ash solids and wastewater.

[0085] Solid-liquid separation can be achieved using a filter press, a centrifuge, or a ceramic membrane, among other methods.

[0086] In the embodiments of this application, a ceramic membrane is used to perform solid-liquid separation on fly ash suspension, and the pore size of the ceramic membrane is 0.1 μm.

[0087] Step 8: Reverse osmosis membrane separation.

[0088] Specifically, in step 7, the wastewater is treated using a reverse osmosis membrane with a molecular weight cutoff of 0.1 kDa. The reverse osmosis membrane can effectively retain chelating agents and heavy metal complexes, enabling recycling. The recovered chelating agents and heavy metal complexes can be desorbed under acidic conditions, allowing for the recovery of both and achieving resource utilization.

[0089] Preferably, the wastewater can be pre-concentrated before being treated with a reverse osmosis membrane. This can remove some water, reduce the feed rate to the reverse osmosis membrane, and improve treatment efficiency.

[0090] Compared with existing technologies, this process has the following advantages:

[0091] 1. Sodium thioacetate-modified starch chelating agent is used as a pH / redox dual-responsive chelating agent to improve the chelation efficiency and selectivity of heavy metals, especially mercury and silver.

[0092] 2. By adjusting the redox potential, the valence state of heavy metals can be controlled, thereby improving the binding capacity of the chelating agent.

[0093] 3. Wastewater is treated using reverse osmosis membranes to achieve the recovery and reuse of chelating agents and heavy metals, thereby reducing wastewater treatment costs and minimizing secondary pollution.

[0094] 4. The process is simple and easy to operate, and it is suitable for treating fly ash from waste incineration containing high concentrations of heavy metals such as mercury and silver.

[0095] In practical applications, the composition of waste incineration fly ash is complex, containing various heavy metal ions such as lead, cadmium, chromium, mercury, and silver. While sodium thioacetate-modified starch chelating agents have good chelating effects on mercury and silver, their chelating ability for other heavy metals may be weak, leading to incomplete heavy metal removal. Furthermore, waste incineration fly ash also contains a large amount of salt and organic matter, which may interfere with the binding of the chelating agent to heavy metal ions, reducing chelation efficiency.

[0096] To improve the chelating ability and selectivity of chelating agents for various heavy metals, effectively remove multiple heavy metals from waste incineration fly ash, enhance desalination efficiency, and reduce the difficulty of wastewater treatment, this application further optimizes the process:

[0097] Specifically, in step 3, sodium thioacetate modified starch chelating agent and diethylenetriaminepentaacetic acid (DTPA) are added simultaneously to the fly ash suspension, with the amount of DTPA accounting for 20% of the total weight of the chelating agent;

[0098] In step 4, before stirring and washing, humic acid is added, and the amount of humic acid is 0.2% of the weight of deionized water.

[0099] DTPA is a multidentate ligand with multiple chelating sites, capable of forming stable complexes with various heavy metal ions. Humic acid is a natural organic compound containing various functional groups, such as carboxyl and phenolic hydroxyl groups, which can undergo complexation reactions with various heavy metal ions. The synergistic effect of sodium thioacetate-modified starch chelating agent, DTPA, and humic acid can enhance the chelating capacity and selectivity for multiple heavy metals in waste incineration fly ash, achieving effective removal of various heavy metals from waste incineration fly ash. This also reduces the difficulty and cost of wastewater treatment.

[0100] The present application will be further illustrated below through specific embodiments. Embodiment 1

[0101] 1. Source of fly ash from waste incineration: a waste incineration plant in a certain city.

[0102] 2. Experimental steps:

[0103] (1) Preparation of sodium thioacetate modified starch chelating agent:

[0104] a. Dissolve soluble starch (Shanghai Aladdin Biochemical Technology Co., Ltd., S104452) in deionized water to prepare a starch solution with a concentration of 5% (w / v);

[0105] b. Dissolve sodium thioacetate in deionized water to prepare a 10% (w / v) sodium thioacetate solution;

[0106] c. Add N,N-dimethyl-4-aminopyridine catalyst to the starch solution, the amount of catalyst being 0.5% of the starch weight;

[0107] d. Slowly add sodium thioacetate solution dropwise to starch solution, controlling the dropping rate to maintain the reaction temperature at 40-45℃;

[0108] e. Stir and react at room temperature for 8 hours;

[0109] f. Adjust the pH to 7.0 with hydrochloric acid solution to terminate the reaction;

[0110] g. The reaction product was precipitated with ethanol, washed, and dried to obtain sodium thioacetate-modified starch chelating agent.

[0111] (2) Washing and desalting fly ash from waste incineration:

[0112] Step 1: Mix 100g (octane dry weight) of waste incineration fly ash with 600g of deionized water (weight ratio 1:6), stir at 25℃ for 40 minutes at a stirring speed of 300rpm. Let stand and settle for 2 hours.

[0113] Step 2: Adjust the pH of the pretreated fly ash suspension to 12 using a 2 mol / L sodium hydroxide solution.

[0114] Step 3: Add 0.4g of sodium thioacetate modified starch chelating agent (0.4% of the weight of waste incineration fly ash) to the fly ash suspension.

[0115] Step 4: Wash with water for 2.5 hours at pH 12 with stirring at a speed of 250 rpm, while simultaneously introducing nitrogen gas for protection to prevent oxidation.

[0116] Step 5: Add sodium sulfite solution (0.1 mol / L) to the washed fly ash suspension and adjust the redox potential to -250 mV.

[0117] Step 6: Continue stirring for 45 minutes at a stirring speed of 250 rpm under a redox potential of -250 mV.

[0118] Step 7: Solid-liquid separation is performed using a ceramic membrane to obtain desalinated waste incineration fly ash solids and wastewater. The ceramic membrane has a pore size of 0.1 μm.

[0119] Step 8: Reverse osmosis membrane separation. Wastewater is treated using a reverse osmosis membrane to recover sodium thioacetate-modified starch and heavy metals. The reverse osmosis membrane has a molecular weight cutoff of 0.1 kDa.

[0120] 3. Performance Testing:

[0121] (1) Heavy metal removal rate: The content of heavy metals in the fly ash from waste incineration before and after water washing was determined by inductively coupled plasma mass spectrometry (ICP-MS, Thermo Fisher iCAPRQ). Test standard: HJ 766-2015 Determination of gaseous pollutants (mercury, cadmium, lead) in exhaust gas from stationary sources by inductively coupled plasma mass spectrometry.

[0122] (2) Salt removal rate: The contents of chloride and sulfate ions in the fly ash from waste incineration before and after water washing were determined by ion chromatography (Dionex ICS-600). Test standard: HJ 84-2017 Determination of anions in water quality by ion chromatography.

[0123] (3) Recovery rate of sodium thioacetate-modified starch chelating agent: The content of sodium thioacetate-modified starch chelating agent in the wastewater after reverse osmosis membrane separation was determined by ultraviolet-visible spectrophotometry (UV-Vis, Thermo Fisher Evolution 220). Test standard: HJ / T 192-2005 Determination of sulfides in water quality by methylene blue spectrophotometry.

[0124] (4) Stability test of chelating agent: The prepared sodium thioacetate modified starch chelating agent was stored at 25°C for 7 days under the condition of pH=12, and the change of its chelating ability before and after storage was measured. The chelating ability was characterized by its ability to chelate mercury ions. The chelating ability test method was as follows: the chelating agent was mixed with 0.1 mol / L Hg2+ solution, and the remaining concentration of Hg2+ was measured after the reaction, and the chelating ability of the chelating agent was calculated.

[0125] 4. Performance data results:

[0126] (1) Heavy metal removal rate: Mercury removal rate 95.2%, silver removal rate 93.8%, lead removal rate 82.5%, cadmium removal rate 78.9%, chromium removal rate 75.6%.

[0127] (2) Salt removal rate: chloride ion removal rate 90.5%, sulfate ion removal rate 88.7%.

[0128] (3) Recovery rate of sodium thioacetate modified starch chelating agent: 92.3%.

[0129] (4) Stability of sodium thioacetate-modified starch chelating agent: 85%. Example 2

[0130] 1. Source of fly ash from waste incineration: Another municipal waste incineration plant.

[0131] 2. Experimental steps:

[0132] (1) The sodium thioacetate modified starch chelating agent of Example 1 was used.

[0133] (2) Washing and desalting fly ash from waste incineration:

[0134] Step 1: Mix 100g (octane dry weight) of waste incineration fly ash with 600g of deionized water (weight ratio 1:6), stir at 25℃ for 40 minutes at a stirring speed of 300rpm. Let stand and settle for 2 hours.

[0135] Step 2: Adjust the pH of the pretreated fly ash suspension to 11.5 using a 2 mol / L sodium hydroxide solution.

[0136] Step 3: Add chelating agent. Add 0.9g of sodium thioacetate modified starch chelating agent (0.9% of the weight of waste incineration fly ash) to the fly ash suspension.

[0137] Step 4: Wash with water for 2.5 hours at pH 11.5 with stirring at 250 rpm, while simultaneously introducing nitrogen gas for protection to prevent oxidation.

[0138] Step 5: Add sodium sulfite solution (0.1 mol / L) to the washed fly ash suspension and adjust the redox potential to -300 mV.

[0139] Step 6: Continue stirring for 45 minutes at a stirring speed of 250 rpm under a redox potential of -300 mV.

[0140] Step 7: Solid-liquid separation is performed using a ceramic membrane to obtain desalinated waste incineration fly ash solids and wastewater. The ceramic membrane has a pore size of 0.1 μm.

[0141] Step 8: Wastewater is treated using a reverse osmosis membrane to recover sodium thioacetate-modified starch and heavy metals. The reverse osmosis membrane has a molecular weight cutoff of 0.1 kDa.

[0142] 3. Performance Testing:

[0143] The testing method is the same as in Example 1.

[0144] 4. Performance data results:

[0145] (1) Heavy metal removal rate: Mercury removal rate 96.5%, silver removal rate 95.1%, lead removal rate 84.2%, cadmium removal rate 80.5%, chromium removal rate 77.1%.

[0146] (2) Salt removal rate: chloride ion removal rate 92.1%, sulfate ion removal rate 90.3%.

[0147] (3) Recovery rate of sodium thioacetate-modified starch chelating agent: 91.5%. Example 3

[0148] 1. Source of fly ash from waste incineration: Same as in Example 1.

[0149] 2. Experimental steps:

[0150] (1) The sodium thioacetate modified starch chelating agent of Example 1 was optimized as follows:

[0151] Step A: Dissolve 10g of the prepared sodium thioacetate modified starch chelating agent in deionized water to prepare a 2% (w / v) solution.

[0152] Step B: Add the crosslinking agent epichlorohydrin. The amount of epichlorohydrin used is 0.1g of the weight of the sodium thioacetate-modified starch chelating agent.

[0153] Step C: Adjust the pH to 8-9 using sodium hydroxide solution.

[0154] Step D: Stir the reaction at 35-45℃ for 3-5 hours at a stirring speed of 100-200 rpm.

[0155] Step E: Adjust the pH to 7.0 with hydrochloric acid solution to terminate the reaction.

[0156] Step F: The reaction product is precipitated with ethanol, washed, and dried to obtain the cross-linked sodium thioacetate modified starch chelating agent.

[0157] (2) Washing and desalting fly ash from waste incineration:

[0158] Step 1: Mix 100g (octane dry weight) of waste incineration fly ash with 600g of deionized water (weight ratio 1:6), stir at 25℃ for 40 minutes at a stirring speed of 300rpm. Let stand and settle for 2 hours.

[0159] Step 2: Adjust the pH of the pretreated fly ash suspension to 12 using a 2 mol / L sodium hydroxide solution.

[0160] Step 3: Add 0.32g of sodium thioacetate modified starch chelating agent (0.32% of the weight of waste incineration fly ash) and 0.08g of diethylenetriaminepentaacetic acid (DTPA, Shanghai Aladdin Biochemical Technology Co., Ltd.) (20% of the total weight of chelating agent) to the fly ash suspension.

[0161] Step 4: Add 1.2g of humic acid (Shanghai Maclean Biochemical Technology Co., Ltd.) (0.2% of the weight of deionized water), and wash with water for 2.5 hours at pH 12 with stirring speed of 250rpm. At the same time, nitrogen gas is introduced for protection to prevent oxidation.

[0162] Step 5: Add sodium sulfite solution (0.1 mol / L) to the washed fly ash suspension and adjust the redox potential to -250 mV.

[0163] Step 6: Continue stirring for 45 minutes at a stirring speed of 250 rpm under a redox potential of -250 mV.

[0164] Step 7: Solid-liquid separation is performed using a ceramic membrane to obtain desalinated waste incineration fly ash solids and wastewater. The ceramic membrane has a pore size of 0.1 μm.

[0165] Step 8: Wastewater is treated using a reverse osmosis membrane to recover sodium thioacetate-modified starch and heavy metals. The reverse osmosis membrane has a molecular weight cutoff of 0.1 kDa.

[0166] 3. Performance Testing:

[0167] The testing method is the same as in Example 1.

[0168] 4. Performance data results:

[0169] (1) Heavy metal removal rate: Mercury removal rate 96.8%, silver removal rate 95.5%, lead removal rate 92.1%, cadmium removal rate 88.5%, chromium removal rate 85.2%.

[0170] (2) Salt removal rate: chloride ion removal rate 91.8%, sulfate ion removal rate 89.9%.

[0171] (3) Recovery rate of sodium thioacetate modified starch chelating agent: 91.9%.

[0172] (4) Stability of sodium thioacetate-modified starch chelating agent: 90%. Example 4

[0173] 1. Source of fly ash from waste incineration: Same as in Example 2.

[0174] 2. Experimental steps:

[0175] (1) The sodium thioacetate modified starch chelating agent of Example 3 was used.

[0176] (2) Washing and desalting fly ash from waste incineration:

[0177] Step 1: Mix 100g (octane dry weight) of waste incineration fly ash with 600g of deionized water (weight ratio 1:6), stir at 25℃ for 40 minutes at a stirring speed of 300rpm. Let stand and settle for 2 hours.

[0178] Step 2: Adjust the pH of the pretreated fly ash suspension to 11.5 using a 2 mol / L sodium hydroxide solution.

[0179] Step 3: Addition of chelating agent. Add 0.72g of sodium thioacetate modified starch chelating agent (0.72% of the weight of waste incineration fly ash) and 0.18g of diethylenetriaminepentaacetic acid (DTPA, Shanghai Aladdin Biochemical Technology Co., Ltd.) (20% of the total weight of chelating agent) to the fly ash suspension.

[0180] Step 4: Add 1.2g of humic acid (Shanghai Maclean Biochemical Technology Co., Ltd.) (0.2% of the weight of deionized water), and stir and wash with water for 2.5 hours at pH 11.5 with a stirring speed of 250rpm. At the same time, nitrogen gas is introduced for protection to prevent oxidation.

[0181] Step 5: Add sodium sulfite solution (0.1 mol / L) to the washed fly ash suspension and adjust the redox potential to -300 mV.

[0182] Step 6: Continue stirring for 45 minutes at a stirring speed of 250 rpm under a redox potential of -300 mV.

[0183] Step 7: Solid-liquid separation is performed using a ceramic membrane to obtain desalinated waste incineration fly ash solids and wastewater. The ceramic membrane has a pore size of 0.1 μm.

[0184] Step 8: Wastewater is treated using a reverse osmosis membrane to recover sodium thioacetate-modified starch and heavy metals. The reverse osmosis membrane has a molecular weight cutoff of 0.1 kDa.

[0185] 3. Performance Testing:

[0186] The testing method is the same as in Example 1.

[0187] 4. Performance data results:

[0188] (1) Heavy metal removal rate: Mercury removal rate 97.5%, silver removal rate 96.2%, lead removal rate 93.5%, cadmium removal rate 89.8%, chromium removal rate 86.5%.

[0189] (2) Salt removal rate: chloride ion removal rate 93.2%, sulfate ion removal rate 91.5%.

[0190] (3) Recovery rate of sodium thioacetate modified starch chelating agent: 91.1%.

[0191] Compare with Example 1

[0192] 1. Source of fly ash from waste incineration: Same as in Example 1.

[0193] 2. Experimental steps:

[0194] Step 1: Mix the fly ash from waste incineration with deionized water at a weight ratio of 1:6, stir for 40 minutes, and let it stand for 2 hours to settle.

[0195] Step 2: Adjust the pH of the pretreated fly ash suspension to 12 using a 2 mol / L sodium hydroxide solution.

[0196] Step 3: Add disodium EDTA to the fly ash suspension at a rate of 0.6% of the fly ash weight.

[0197] Step 4: Stabilize at pH 12 for 2.5 hours with stirring at a speed of 250 rpm.

[0198] Step 5: Solid-liquid separation is performed using a ceramic membrane to obtain desalinated waste incineration fly ash solids and wastewater. The ceramic membrane has a pore size of 0.1 μm.

[0199] 3. Performance Testing:

[0200] The testing method is the same as in Example 1.

[0201] 4. Performance data results:

[0202] (1) Heavy metal removal rate: Mercury removal rate 66.5%, silver removal rate 62.1%, lead removal rate 54.2%, cadmium removal rate 50.5%, chromium removal rate 47.1%.

[0203] (2) Salt removal rate: chloride ion removal rate 72.1%, sulfate ion removal rate 70.3%.

[0204] Compare with Example 2

[0205] 1. Source of fly ash from waste incineration: Same as in Example 1.

[0206] 2. Experimental steps:

[0207] Step 1: Mix the fly ash from waste incineration with deionized water at a weight ratio of 1:6, stir for 40 minutes, and let it stand for 2 hours to settle.

[0208] Step 2: Adjust the pH of the pretreated fly ash suspension to 12 using a 2 mol / L sodium hydroxide solution.

[0209] Step 3: Add DTPA to the fly ash suspension at a rate of 0.6% of the fly ash weight.

[0210] Step 4: Stabilize at pH 12 for 2.5 hours with stirring at a speed of 250 rpm.

[0211] Step 5: Solid-liquid separation is performed using a ceramic membrane to obtain desalinated waste incineration fly ash solids and wastewater. The ceramic membrane has a pore size of 0.1 μm.

[0212] 3. Performance Testing:

[0213] The testing method is the same as in Example 1.

[0214] 4. Performance data results:

[0215] (1) Heavy metal removal rate: Mercury removal rate 53.6%, silver removal rate 59.3%, lead removal rate 85.3%, cadmium removal rate 80.2%, chromium removal rate 60.5%.

[0216] (2) Salt removal rate: chloride ion removal rate 70%, sulfate ion removal rate 75.5%.

[0217] The comparison between the examples and control cases shows that the proposed solution significantly improves the removal rate of heavy metals and salts in the treatment of waste incineration fly ash. Compared with existing chelating agents, this solution is particularly effective in removing heavy metals such as mercury and silver, and it also enables the recycling of the chelating agent, reducing wastewater treatment costs. The optimized solutions (Examples 3 and 4) further improve the removal efficiency of heavy metals, indicating that the addition of DTPA and humic acid effectively enhances the chelating ability and selectivity of the chelating agent for various heavy metals.

Claims

1. A method for water washing and desalination of fly ash from waste incineration, characterized in that, The process includes the following steps: Step 1: Pre-treating the fly ash from waste incineration to obtain a fly ash suspension; Step 2: Adjusting the pH of the fly ash suspension to 11.5-12.5; Step 3: Adding a chelating agent to the fly ash suspension, wherein the amount of chelating agent added is 0.4%-0.9% of the weight of the waste incineration fly ash; Step 4: Under a pH of 11.5-12.5, purging with nitrogen for protection, and stirring and washing the fly ash suspension with water for 2-3 hours; Step 5: Add sodium sulfite solution to the fly ash suspension to adjust the redox potential to -200mV to -300mV; Step 6: Continue stirring for 40-50 minutes under the condition of redox potential of -200mV to -300mV; Step 7: Perform solid-liquid separation on the fly ash suspension to obtain desalinated waste incineration fly ash solids and wastewater; Step 8: Treat the wastewater using a reverse osmosis membrane; The chelating agent includes at least sodium thioacetate-modified starch chelating agent; The preparation method of the sodium thioacetate modified starch chelating agent includes the following steps: a. Dissolving soluble starch in deionized water to prepare a starch solution with a mass-volume concentration of 5%; b. Dissolving sodium thioacetate in deionized water to prepare a sodium thioacetate solution with a mass-volume concentration of 10%; c. Adding N,N-dimethyl-4-aminopyridine to the starch solution; wherein the amount of N,N-dimethyl-4-aminopyridine is 0.5% of the weight of the soluble starch; d. Adding the sodium thioacetate solution dropwise to the starch solution, controlling the dropping rate to maintain the reaction temperature at 40-45℃; e. Stirring the reaction at room temperature for 8 hours; f. Adjusting the pH to 7.0 with hydrochloric acid solution to terminate the reaction; g. Precipitating the reaction product with ethanol, washing, and drying to obtain the sodium thioacetate modified starch chelating agent.

2. The method for water washing and desalination of waste incineration fly ash according to claim 1, characterized in that, The pretreatment process for waste incineration fly ash is as follows: the waste incineration fly ash and deionized water are mixed at a weight ratio of 1:6, stirred at room temperature for 30-50 minutes, and allowed to settle for 1.5-2.5 hours.

3. The method for water washing and desalination of waste incineration fly ash according to claim 2, characterized in that, The preparation method of the sodium thioacetate modified starch chelating agent also includes The reaction includes the following steps: Step A: Dissolving the sodium thioacetate-modified starch chelating agent in deionized water to prepare a 2% (w / v) solution; Step B: Adding a crosslinking agent; wherein the crosslinking agent is epichlorohydrin or glutaraldehyde, and the amount of the crosslinking agent is 1% of the weight of the sodium thioacetate-modified starch chelating agent; Step C: Adjusting the pH to 8-9 using sodium hydroxide solution; Step D: Stirring the reaction at 35-45℃ for 3-5 hours at a stirring speed of 100-200 rpm; Step E: Adjusting the pH to 7.0 using hydrochloric acid solution to terminate the reaction; Step F: Precipitating the reaction product with ethanol, washing, and drying to obtain the crosslinked sodium thioacetate-modified starch chelating agent.

4. The method for water washing and desalination of waste incineration fly ash according to claim 3, characterized in that, The chelating agent is a combination of the sodium thioacetate modified starch chelating agent and DTPA, and the amount of DTPA is 20% of the total weight of the chelating agent.

5. The method for water washing and desalination of waste incineration fly ash according to claim 4, characterized in that, In step 4, before the stirring and washing, humic acid is added, and the amount of humic acid is 0.2% of the weight of the deionized water.

6. The method for water washing and desalination of waste incineration fly ash according to claim 1, characterized in that, In step 2, the pH value of the fly ash suspension is adjusted using sodium hydroxide solution.

7. The method for water washing and desalination of waste incineration fly ash according to claim 1, characterized in that, In step 4, the stirring speed of the stirring water washing is 200-300 rpm.

8. The method for water washing and desalination of waste incineration fly ash according to claim 1, characterized in that, In step 6, the stirring speed during the continued stirring process is 200-300 rpm.

9. The method for water washing and desalination of waste incineration fly ash according to claim 1, characterized in that, In step 7, the solid-liquid separation method is to use a ceramic membrane for solid-liquid separation.

10. The method for water washing and desalination of waste incineration fly ash according to claim 1, characterized in that, In step 8, the molecular weight cutoff of the reverse osmosis membrane is 0.1 kDa.