Method for degrading dioxin in fly ash and stabilizing heavy metals

Abstract

The invention discloses a method for degrading dioxin in fly ash and stabilizing heavy metals, which comprises the following steps: carrying out water washing treatment on the fly ash, and carrying out solid-liquid separation to obtain water washing slag; mixing the washed slag with water, adding zero-valent iron and sulfite, carrying out hydrothermal treatment, and carrying out solid-liquid separation to obtain hydrothermal slag and hydrothermal liquid; according to the method for degradation of dioxin in fly ash and stabilization of heavy metal in cooperation with degradation of dioxin in fly ash, under the combined action of zero-valent iron, chlorite and a hydrothermal environment, efficient degradation of dioxin in fly ash can be rapidly achieved under the lower reaction condition, stabilization of heavy metal in fly ash can be synchronously achieved, and the method is suitable for industrial production. The method has the advantages of being low in cost, mild in reaction condition, high in treatment efficiency, good in treatment effect, environmentally friendly and the like, can effectively solve the problems existing in the prior art, provides powerful support for harmless treatment and resource utilization of the waste incineration fly ash, and has wide engineering application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid waste treatment, and relates to a method for degrading dioxins in fly ash in coordination with heavy metal stabilization, and specifically to a method for jointly treating fly ash from the incineration of domestic waste by coupling zero-valent iron with a sulfite system using subcritical hydrothermal technology. Background Art

[0002] With the rapid development of industrialization and urbanization, waste incineration has become one of the main means of treating urban solid waste. Fly ash is produced during the incineration process, and these fly ashes contain toxic and harmful substances such as dioxins and heavy metals, which pose a serious threat to the environment and human health. Among them, dioxins, as a highly stable and bioaccumulative persistent organic pollutant, have potential hazards that cannot be ignored; and heavy metals such as lead and cadmium in fly ash also have potential ecological risks and human health risks. Therefore, the safe treatment and disposal of fly ash has become an environmental problem that needs to be solved urgently.

[0003] At present, the treatment and disposal technologies for fly ash are mainly divided into three categories: separation technology, solidification / stabilization technology and thermal treatment technology. Among them, separation technology is to recover useful resources in fly ash, such as soluble chloride salts and some heavy metals, through water washing and chemical leaching, but it has limitations in treating dioxins and is only applicable to the pretreatment stage. Solidification / stabilization technology refers to the use of cement or chemical reagents (phosphates, thiourea and chelating agents, etc.) to solidify / stabilize heavy metals in fly ash to prevent them from diffusing and migrating to the environment. Although this method performs well in stabilizing heavy metals, its degradation effect on dioxins is limited. Thermal treatment technology has attracted much attention for its ability to efficiently treat dioxins and heavy metals. According to the reaction temperature and operating conditions, thermal treatment methods can be divided into sintering, melting, vitrification and hydrothermal methods. Sintering and melting technology is that fly ash is bonded at a temperature of 900-1000°C to form a dense sintered body, and melted at 1400°C to generate a molten material; the vitrification process is to generate a glass phase at 1100-1500°C by adding auxiliary agents (such as silicon dioxide); the above heat treatment technologies can effectively stabilize heavy metals and decompose dioxins, but there are problems such as high energy consumption and flue gas treatment difficulties, which limit their wide application. In contrast, subcritical hydrothermal technology stands out with its mild reaction conditions (lower than the gas-liquid critical point of water 374.5°C) and significant detoxification effect. This technology uses the unique physical and chemical properties of subcritical water to accelerate the chemical reaction of pollutants in fly ash by adding aluminum sources, silicon sources, strong alkalis and other substances to fly ash, such as dechlorination of chlorinated plastics and degradation of dioxins, or stabilization of heavy metals. It can be seen that the subcritical hydrothermal method can achieve efficient treatment of fly ash at low energy consumption, showing broad application prospects.However, the existing methods for solidifying and stabilizing heavy metals or degrading dioxins in fly ash based on subcritical hydrothermal technology combined with chemical reagents still have the following defects: (1) The reaction conditions are relatively harsh. The solidification and stabilization of heavy metals are promoted by increasing the temperature and prolonging the reaction time, which requires higher temperature and reaction time, and is prone to high energy consumption and high processing costs. (2) A large amount of chemical reagents such as strong alkali or strong oxidants need to be added. For example, by adding auxiliary agents (alkaline activators, aluminum sources and silicon sources, etc.), the amount of fly ash added may be reduced, increasing the processing cost. In addition, the large amount of chemical reagents used is prone to corrode equipment and pose potential hazards to operators. It may also cause It can introduce new environmental risks and easily cause secondary pollution to the environment; (3) The use of microwave technology to improve the efficiency of hydrothermal reactions and shorten the reaction time has high requirements for equipment, further limiting its feasibility of large-scale industrial use; (4) Combining hydrothermal treatment with additives (such as strong alkali, hydrazine carbonate, methanol, etc.) to degrade dioxins requires a higher reaction temperature (greater than 200°C) and a long reaction time, resulting in high energy consumption and low efficiency. In addition, harmful byproducts may be produced during the treatment process, and secondary pollution problems are serious; (5) The dioxin degradation system constructed in the existing method has the problem of high selectivity and poor selectivity, making it difficult to completely remove all types of dioxins. In addition, the existing technology has not yet been able to simultaneously achieve the degradation of dioxins and the stabilization of heavy metals in fly ash under low temperature conditions, which limits the widespread use of subcritical hydrothermal technology in the field of fly ash treatment and disposal.

[0004] Therefore, in view of the shortcomings and defects in the above-mentioned prior art, it is necessary to provide a subcritical hydrothermal treatment technology with milder reaction conditions, more efficient treatment and more environmentally friendly, aiming to simultaneously solve the problems of dioxin degradation and heavy metal stabilization. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a method for degrading dioxins and stabilizing heavy metals in fly ash which is low in cost, mild in reaction conditions, high in treatment efficiency, good in treatment effect and environmentally friendly.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions: A method for degrading dioxins in fly ash and stabilizing heavy metals, comprising the following steps: Step S1, washing the fly ash with water, separating the solid and the liquid, and obtaining washed slag and washed liquid; Step S2: mixing the washed slag with water, adding zero-valent iron and sulfite for hydrothermal treatment, and separating the solid and liquid to obtain hydrothermal slag and hydrothermal liquid.

[0007] The above method is further improved, in step S1, the fly ash is washed with circulating water; the process parameters of the washing treatment are: liquid-to-solid ratio of 2.5 to 5:1, circulation flux of 20 m 3 / h~50 m 3 / h, the time is 10 min to 60 min; the water washing process also includes stirring the water washing system at a rotation speed of 60 rpm to 200 rpm.

[0008] The above method is further improved, in step S1, the fly ash is at least one of fly ash from incineration of municipal solid waste and fly ash from incineration of industrial waste.

[0009] The above method is further improved, in step S1, the subsequent treatment method of the water washing liquid comprises the following steps: (1) treating the washing liquid; the water treatment includes hardness removal treatment and heavy metal removal treatment; (2) The water washing liquid after water treatment is evaporated and crystallized to obtain salt and condensed water; the condensed water is returned to step S1 for water washing treatment of fly ash.

[0010] The above method is further improved, in step S2, the amount of zero-valent iron added is 3% to 10% of the mass of the washed slag.

[0011] The above method is further improved in that in step S2, the amount of sulfite added is 0.7% to 4.2% of the mass of the water-washed slag.

[0012] The above method is further improved, in step S2, the sulfite is one of sodium sulfite and potassium sulfite.

[0013] The above method is further improved in that in step S2, the volume mass ratio of water to water-washed slag is 1 mL to 3 mL: 1 g.

[0014] The above method is further improved, in step S2, the temperature of the hydrothermal treatment is 120°C to 150°C; the time of the hydrothermal treatment is 30 min to 90 min; the hydrothermal process also includes stirring the hydrothermal system at a rotation speed of 50 rpm to 300 rpm.

[0015] The above method is further improved in that in step S2, the hydrothermal liquid is returned to the hydrothermal system of the hydrothermal treatment.

[0016] Compared with the prior art, the advantages of the present invention are: In view of the shortcomings of the method for treating fly ash based on subcritical hydrothermal technology combined with chemical reagents, such as high cost, harsh reaction conditions, low treatment efficiency, poor treatment effect, risk of secondary pollution, and difficulty in integrated realization of dioxin degradation and heavy metal stabilization in fly ash, the present invention creatively provides a method for degrading dioxins in fly ash and stabilizing heavy metals. The fly ash is first washed with water to remove soluble chloride salts in the wastewater, which is beneficial to improving the degradation effect of dioxins in fly ash, and the resource utilization of chloride salts (potassium chloride and sodium chloride) can be realized through evaporation and crystallization. On this basis, In the process of hydrothermal treatment, zero-valent iron (Fe) and sulfite (ZV) are added to the fly ash for hydrothermal treatment, thereby constructing a system of coupling zero-valent iron and sulfite with subcritical hydrothermal technology. This system has a series of physicochemical changes and chemical reactions, which can significantly promote the transformation and stabilization of pollutants (such as dioxins and heavy metals) in fly ash. Specifically, during the hydrothermal treatment process, the constructed subcritical hydrothermal system can cause changes in the physical and chemical properties of water, such as a decrease in the dielectric constant and an increase in the ion product, which helps to accelerate the chemical reaction rate and promote the chemical reaction of pollutants in fly ash. Furthermore, zero-valent iron (Fe 0 ) initiates a series of chemical reactions, such as Fe 0 First, it is oxidized to ferrous ions (Fe 2+ ), and further oxidized to iron ions (Fe 3+ ), these iron ions can react with sulfite (S(IV)) to activate sulfite to generate sulfate radicals (SO4 2- ) and other active oxygen species. These free radicals with high oxidation potential attack their carbon-carbon bonds and carbon-chlorine bonds, leading to the decomposition of dioxin molecules, thereby effectively oxidizing and degrading dioxin molecules. At the same time, during the hydrothermal treatment process, heavy metal ions can combine with mineral structures formed by elements such as silicon, aluminum, and iron to form stable heavy metal silicates or aluminates, thereby reducing their mobility and bioavailability in the environment. More importantly, sulfite can also generate SO3 through a single electron transfer reaction under hydrothermal conditions. - • It can react with oxygen to form peroxymonosulfate radicals (SO5 - •), which then reacts with S(Ⅳ) to generate more SO4 - • and sulfate (SO4 2- ), and SO4 - • Can also react with water or hydroxide (OH -) reacts to generate hydroxyl radicals (HO•), further enhancing the oxidative degradation capacity of the system, and plays a dual role in promoting the decomposition of organic pollutants such as dioxins and the stabilization of heavy metals. Compared with the conventional treatment method of combining subcritical hydrothermal technology with chemical reagents, the method of the present invention uses subcritical hydrothermal technology to couple zero-valent iron and sulfite systems to jointly treat fly ash from the incineration of domestic waste. In the synergistic mechanism of the physical and chemical reactions of water washing treatment and hydrothermal treatment, an efficient and environmentally friendly fly ash treatment system is jointly formed, which can achieve efficient degradation and stabilization of various pollutants (including dioxins and heavy metals) in fly ash. The advantages are: (a) It can be efficiently degraded and stabilized. In the subcritical hydrothermal system, a high temperature and high pressure environment can be provided to accelerate the chemical reaction rate. Then, combined with the effects of zero-valent iron and sulfite systems, dioxins in fly ash can be efficiently degraded, and the stable combination between heavy metal ions and solid matrix is ​​promoted through reduction to achieve the stabilization of heavy metals, which not only improves the treatment efficiency, but also simplifies the treatment process and reduces the complexity of operation. (b) Low energy consumption and cost. It can efficiently degrade dioxins in fly ash at a relatively low temperature range (120℃~150℃) and quickly stabilize heavy metals in fly ash, which can significantly reduce energy consumption. At the same time, since zero-valent iron and sulfite are relatively low in cost and easy to obtain, they help reduce the overall treatment cost. (c) Less secondary pollution and more environmentally friendly. Using zero-valent iron as a reducing agent, no toxic or harmful by-products will be produced during the reaction, and it is easy to recycle and reuse. The amount of sulfite used is small, which is environmentally friendly and can effectively reduce the risk of secondary pollution. At the same time, the entire treatment process follows the principles of green chemistry and is beneficial to environmental protection. (d) Wide applicability. It can be used to treat different types of fly ash, including fly ash from the incineration of municipal solid waste and fly ash from the incineration of industrial waste. At the same time, by adjusting the reaction conditions and the amount of additives, it can flexibly respond to the changes in the composition and concentration of pollutants in different fly ashes. (e) It can promote resource utilization. After the fly ash is treated by this method, heavy metals are effectively stabilized, and organic pollutants such as dioxins are greatly degraded, thereby improving the environmental safety and resource utilization potential of fly ash and broadening the disposal channels of fly ash. The method of degrading dioxins in fly ash and stabilizing heavy metals in the present invention can achieve efficient degradation of dioxins in fly ash more quickly under lower reaction conditions under the joint action of zero-valent iron, chlorite and hydrothermal environment, and can simultaneously achieve stabilization of heavy metals in fly ash. It has the advantages of low cost, mild reaction conditions, high treatment efficiency, good treatment effect, green environmental protection, etc. It can effectively solve the problems existing in the prior art, provide strong support for the harmless treatment and resource utilization of waste incineration fly ash, and has broad engineering application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention.

[0018] Figure 1 This is a schematic diagram of the process flow of the method for resource utilization of municipal sludge filtrate in Example 1 of the present invention. DETAILED DESCRIPTION

[0019] The present invention is further described below in conjunction with the accompanying drawings and specific preferred embodiments, but the protection scope of the present invention is not limited thereby.

[0020] In the following examples of the present invention, unless otherwise specified, the materials and instruments used are commercially available, the equipment used is conventional equipment, and the data obtained are the average values ​​of more than three repeated experiments.

[0021] In view of the shortcomings of the method for treating fly ash based on subcritical hydrothermal technology combined with chemical reagents, such as high cost, harsh reaction conditions, low treatment efficiency, poor treatment effect, risk of secondary pollution, and difficulty in integrated realization of dioxin degradation and heavy metal stabilization in fly ash, the present invention creatively provides a method for degrading dioxins in fly ash and stabilizing heavy metals. The fly ash is first washed with water to remove soluble chloride salts in the wastewater, which is beneficial to improving the degradation effect of dioxins in fly ash, and the resource utilization of chloride salts (potassium chloride and sodium chloride) can be realized through evaporation and crystallization. On this basis, In the process of hydrothermal treatment, zero-valent iron (Fe) and sulfite (ZV) are added to the fly ash for hydrothermal treatment, thereby constructing a system of coupling zero-valent iron and sulfite with subcritical hydrothermal technology. This system has a series of physicochemical changes and chemical reactions, which can significantly promote the transformation and stabilization of pollutants (such as dioxins and heavy metals) in fly ash. Specifically, during the hydrothermal treatment process, the constructed subcritical hydrothermal system can cause changes in the physical and chemical properties of water, such as a decrease in the dielectric constant and an increase in the ion product, which helps to accelerate the chemical reaction rate and promote the chemical reaction of pollutants in fly ash. Furthermore, zero-valent iron (Fe 0 ) initiates a series of chemical reactions, such as Fe 0 First, it is oxidized to ferrous ions (Fe 2+ ), and further oxidized to iron ions (Fe 3+ ), these iron ions can react with sulfite (S(IV)) to activate sulfite to generate sulfate radicals (SO4 2-) and other active oxygen species. These free radicals with high oxidation potential attack their carbon-carbon bonds and carbon-chlorine bonds, leading to the decomposition of dioxin molecules, thereby effectively oxidizing and degrading dioxin molecules. At the same time, during the hydrothermal treatment process, heavy metal ions can combine with mineral structures formed by elements such as silicon, aluminum, and iron to form stable heavy metal silicates or aluminates, thereby reducing their mobility and bioavailability in the environment. More importantly, sulfite can also generate SO3 through a single electron transfer reaction under hydrothermal conditions. - • It can react with oxygen to form peroxymonosulfate radicals (SO5 - •), which then reacts with S(Ⅳ) to generate more SO4 - • and sulfate (SO4 2- ), and SO4 - • Can also react with water or hydroxide (OH - ) reacts to generate hydroxyl radicals (HO•), which further enhance the oxidative degradation capacity of the system and play a dual role in promoting the decomposition of organic pollutants such as dioxins and the stabilization of heavy metals.

[0022] In order to better understand the innovation of the technical solution of the present invention, the following embodiments and comparative examples are provided.

[0023] Example 1 A method for resource utilization of municipal sludge filtrate, the process flow chart of which is as follows Figure 1 As shown, the following steps are included: Step S1: Take 200 kg of fly ash from a domestic waste incineration project in Changsha, add 600 L of water (control the liquid-to-solid ratio to be 3:1), and enter the external forced circulation water washing device for water washing (single water washing). The water washing parameters are: stirring speed 100 rpm, circulation flux 32 m 3 / h, the washing time is 30 min, and after the washing is completed, solid-liquid separation is carried out to obtain washing residue and washing liquid.

[0024] Step S2: According to the liquid-solid ratio of 1:1, the washed slag is mixed with water and added into the hydrothermal device. At the same time, the amount of zero-valent iron added is 5% of the mass of the washed slag, and the amount of sulfite added is 1.4% of the mass of the washed slag. Zero-valent iron (commercially available) and sulfite (sodium sulfite) are added into the hydrothermal device, mixed evenly, and the hydrothermal system is hydrothermally treated. The reaction parameters of the hydrothermal treatment are: stirring speed of 180 rpm, hydrothermal temperature of 150°C, reaction time of 60 min, solid-liquid separation, and hydrothermal slag and hydrothermal liquid are obtained. The hydrothermal slag meets the national standard after testing and is recycled.

[0025] In this embodiment, if zero-valent iron is not added, the heavy metal stabilization and dioxin degradation effects are poor, and the treated product exceeds the national standard limit.

[0026] In this embodiment, the zero-valent iron used cannot be replaced by other iron salts for the following reasons: first, zero-valent iron undergoes an oxidation reaction on its surface in the reaction system, has a slow-release property, and forms soluble iron ions, while other iron salts form insoluble hydroxide precipitates in this system; second, zero-valent iron has extremely strong reducing properties, and this reducing property is further enhanced under high temperature and strong alkaline conditions, which enables zero-valent iron to react more effectively with a variety of environmental pollutants. At the same time, it can also undergo redox reactions with organic pollutants, decomposing them into low-toxic or non-toxic substances. This strong reducing property is unmatched by other iron salts; third, zero-valent iron has a high reactivity, and it can react with environmental pollutants in a relatively short time.

[0027] In this embodiment, if sulfite is not added, highly oxidizing active free radicals cannot be generated. At the same time, the stabilization of heavy metals in the reaction system is also affected, resulting in the treatment product being difficult to achieve the ideal treatment effect and causing the product indicators to exceed the standard.

[0028] In this embodiment, persulfate cannot be used in the present invention for the following reasons: first, the reagent is expensive and toxic, and the system will produce residual peroxide ions, which are very stable and can produce chronic physiological toxicity; second, it cannot play a synergistic role with zero-valent iron.

[0029] In step S1 of this embodiment, the subsequent treatment method of the obtained water washing liquid includes the following steps: (1) Treat the water washing liquid, specifically: remove hardness and heavy metals from the water washing liquid.

[0030] (2) The water washing liquid after water treatment is evaporated and crystallized to obtain salt and condensed water, wherein the condensed water is returned to step S1 for water washing of fly ash; the main components of the salt are sodium chloride and potassium chloride, which can be recycled.

[0031] In step S2 of this embodiment, the obtained hydrothermal liquid is returned to the hydrothermal system of the hydrothermal treatment, which is beneficial to reduce the treatment cost.

[0032] The washed slag and hydrothermal slag were analyzed and tested, and the dioxin content was measured according to the "Determination of Dioxins in Solid Waste by Isotope Dilution High Resolution Gas Chromatography-High Resolution Mass Spectrometry" (HJ 77.3-2008), the soluble chlorine content and heavy metal leaching concentration were measured according to the "Solid Waste Leaching Toxicity Leaching Method Horizontal Oscillation Method" (HJ 557-2010), and the heavy metal leaching concentration was measured according to the "Hazardous Waste Identification Standard-Leaching Toxicity Identification" (GB5805.3-2007). The results are shown in Tables 1 and 2 below: Table 1 Soluble chlorine content and dioxin content in water-washed slag and hydrothermal slag (wt%)

[0033] As can be seen from Table 1, the soluble chlorine content in the washed slag obtained after one water washing meets the national standard limit, and the soluble chlorine content is further reduced during the subsequent hydrothermal treatment. At the same time, after the water washing treatment, the fly ash is reduced, but dioxins are insoluble in water, so the dioxins in the fly ash after water washing increase, and dioxin degradation is achieved after hydrothermal treatment. The dioxin concentration and soluble chlorine content in the hydrothermal slag meet the requirements of the "Technical Specifications for Pollution Control of Fly Ash from the Incineration of Municipal Waste (Trial)" (HJ1134-2020). Table 2 Heavy metal leaching concentrations and national standard limits in water-washed slag and hydrothermal slag (mg / L)

[0034] The hydrothermal slag is taken according to the "Horizontal Oscillation Method for Leaching Toxicity of Solid Waste" HJ557-2010 to determine the leaching concentration of the water-washed residue and the "Determination of Dioxins in Solid Waste by Isotope Dilution High Resolution Gas Chromatography-High Resolution Mass Spectrometry" (HJ 77.3-2008) to measure the dioxin content. It should meet the limit values ​​in the "Technical Specifications for Pollution Control of Fly Ash from Incineration of Municipal Waste (Trial)" (HJ1134-2020). The heavy metal leaching concentration is measured according to the "Hazardous Waste Identification Standard-Leaching Toxicity Identification" (GB5805.3-2007). The results are shown in Table 2. The heavy metal leaching concentration meets the national standard limit, and the heavy metal leaching meets the general solid waste requirements.

[0035] Comparative Example 1 A method for degrading dioxins in fly ash and stabilizing heavy metals is basically the same as Example 1, except that zero-valent iron and sodium sulfite are not added. The results are shown below: Table 3 Soluble chlorine content and dioxin content in hydrothermal slag (wt%)

[0036] Table 4 Heavy metal leaching concentrations in hydrothermal slag and national standard limits (mg / L)

[0037] The hydrothermal slag is taken according to the "Horizontal Oscillation Method for Leaching Toxicity of Solid Waste" HJ557-2010 to determine the leaching concentration of the water-washed residue and the "Determination of Dioxins in Solid Waste by Isotope Dilution High Resolution Gas Chromatography-High Resolution Mass Spectrometry" (HJ 77.3-2008) to measure the dioxin content. It should meet the limit values ​​in the "Technical Specifications for Pollution Control of Fly Ash from Incineration of Municipal Waste (Trial)" (HJ1134-2020) and the heavy metal leaching concentration is measured according to the "Hazardous Waste Identification Standard-Leaching Toxicity Identification" (GB5805.3-2007). The results are shown in Tables 3 and 4. The soluble chlorine content meets the national standard limit, the dioxin content meets the national standard, but the heavy metal Pb leaching concentration exceeds the national standard limit. At the same time, the heavy metal leaching meets the general solid waste requirements.

[0038] It can be seen from the above results that, compared with the conventional treatment method of combining subcritical hydrothermal technology with chemical reagents, the method of the present invention uses subcritical hydrothermal technology to couple zero-valent iron and sulfite system to jointly treat fly ash from the incineration of domestic waste. In the synergistic mechanism of the physical and chemical reactions of water washing treatment and hydrothermal treatment, an efficient and environmentally friendly fly ash treatment system is jointly formed, which can achieve efficient degradation and stabilization of various pollutants (including dioxins and heavy metals) in fly ash. The advantages are: (a) It can be efficiently degraded and stabilized. In the subcritical hydrothermal system, a high temperature and high pressure environment can be provided to accelerate the chemical reaction rate. Combined with the effects of zero-valent iron and sulfite system, dioxins in fly ash can be efficiently degraded, and the stable combination between heavy metal ions and solid matrix is ​​promoted through reduction to achieve stabilization of heavy metals. This not only improves the treatment efficiency, but also simplifies the treatment process and reduces the complexity of operation. (b) Low energy consumption and cost. It can efficiently degrade dioxins in fly ash at a relatively low temperature range (120℃~150℃) and quickly stabilize heavy metals in fly ash, which can significantly reduce energy consumption. At the same time, since zero-valent iron and sulfite are relatively low in cost and easy to obtain, they help reduce the overall treatment cost. (c) Less secondary pollution and more environmentally friendly. Using zero-valent iron as a reducing agent, no toxic or harmful by-products will be produced during the reaction, and it is easy to recycle and reuse. The amount of sulfite used is small, which is environmentally friendly and can effectively reduce the risk of secondary pollution. At the same time, the entire treatment process follows the principles of green chemistry and is beneficial to environmental protection. (d) Wide applicability. It can be used to treat different types of fly ash, including fly ash from the incineration of municipal solid waste and fly ash from the incineration of industrial waste. At the same time, by adjusting the reaction conditions and the amount of additives, it can flexibly respond to the changes in the composition and concentration of pollutants in different fly ashes. (e) It can promote resource utilization. After the fly ash is treated by this method, heavy metals are effectively stabilized, and organic pollutants such as dioxins are greatly degraded, thereby improving the environmental safety and resource utilization potential of fly ash and broadening the disposal channels of fly ash. The method of degrading dioxins in fly ash and stabilizing heavy metals in the present invention can achieve efficient degradation of dioxins in fly ash more quickly under lower reaction conditions under the joint action of zero-valent iron, chlorite and hydrothermal environment, and can simultaneously achieve stabilization of heavy metals in fly ash. It has the advantages of low cost, mild reaction conditions, high treatment efficiency, good treatment effect, green environmental protection, etc. It can effectively solve the problems existing in the prior art, provide strong support for the harmless treatment and resource utilization of waste incineration fly ash, and has broad engineering application prospects.

[0039] The above embodiments are only preferred implementations of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A method for degrading dioxins in fly ash and stabilizing heavy metals, characterized in that: The following steps are involved: Step S1, washing the fly ash with water, separating the solid and the liquid, and obtaining washed slag and washed liquid; Step S2: mixing the washed slag with water, adding zero-valent iron and sulfite for hydrothermal treatment, and separating the solid and liquid to obtain hydrothermal slag and hydrothermal liquid.

2. The method according to claim 1, characterized in that In step S1, the fly ash is washed with circulating water; the process parameters of the washing treatment are: liquid-to-solid ratio of 2.5 to 5:1, circulation flux of 20 m 3 / h~50 m 3 / h, the time is 10 min to 60 min; the water washing process also includes stirring the water washing system at a rotation speed of 60 rpm to 200 rpm.

3. The method according to claim 2, characterized in that In step S1, the fly ash is at least one of fly ash from incineration of municipal solid waste and fly ash from incineration of industrial waste.

4. The method according to claim 2, characterized in that: In step S1, the subsequent treatment method of the water washing liquid comprises the following steps: (1) Treat the washing liquid; (2) The water washing liquid after water treatment is evaporated and crystallized to obtain salt and condensed water; the condensed water is returned to step S1 for water washing treatment of fly ash.

5. The method according to any one of claims 1 to 4, characterized in that: In step S2, the amount of zero-valent iron added is 3% to 10% of the mass of the washed slag.

6. The method according to claim 5, characterized in that In step S2, the amount of sulfite added is 0.7% to 4.2% by mass of the washed slag.

7. The method according to claim 6, characterized in that In step S2, the sulfite is one of sodium sulfite and potassium sulfite.

8. The method according to any one of claims 1 to 4, characterized in that In step S2, the volume mass ratio of the water to the water-washed slag is 1 mL to 3 mL: 1 g.

9. The method according to any one of claims 1 to 4, characterized in that In step S2, the temperature of the hydrothermal treatment is 120°C to 150°C; the time of the hydrothermal treatment is 30 min to 90 min; and the hydrothermal process also includes stirring the hydrothermal system at a rotation speed of 50 rpm to 300 rpm.

10. The method according to any one of claims 1 to 4, characterized in that: In step S2, the hydrothermal liquid is returned to the hydrothermal system of the hydrothermal treatment.

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