Fly ash heavy metal immobilization method based on flash Joule heating

Abstract

The invention relates to the technical field of waste treatment, in particular to a fly ash heavy metal immobilization method based on flash Joule heating, which comprises the following steps: placing fly ash on a conductive heater to form a conductive path; and pulse current is applied to the conductive heater to heat the fly ash, and fly ash residues are obtained. By applying the pulse current, the fly ash from various sources can be rapidly heated to high temperature within an extremely short time, efficient stabilization of heavy metal is achieved, the method has the advantages of being high in treatment speed, low in energy consumption, simple and convenient in process, high in universality and the like, and the problems that long-time high-temperature maintenance is needed for fixing the heavy metal in the fly ash through traditional heat treatment, and time and labor are wasted are solved. The technical problems of huge energy consumption, high operation cost, complex process, low universality and the like are solved. And the larger the scale of the method is, the lower the treatment energy consumption of each ton of fly ash is, so that the cost is greatly reduced, and large-scale application is facilitated.

Description

Technical Field

[0001] This invention relates to the field of waste treatment technology, specifically to a method for fixing heavy metals in fly ash based on flash Joule heating. Background Technology

[0002] Incineration of municipal solid waste (MSW) can achieve significant volume reduction and energy recovery, but the resulting fly ash (FA) accounts for only 3-5% of the total mass of the residue. However, it is rich in high concentrations of chlorides, dioxins, and carcinogenic heavy metals and is clearly listed as hazardous waste in the "List of Hazardous Wastes in China". It has become a prominent problem in urban environmental governance.

[0003] Currently, the harmless disposal of fly ash mainly relies on three technical routes: ① separation and extraction, which can only achieve the transfer and enrichment of heavy metals but cannot degrade dioxins; ② solidification / stabilization, which involves embedding heavy metals in cement, chelating agents, etc., but has a high volumetric efficiency and raises questions about long-term environmental safety; ③ heat treatment, which can dissolve heavy metals in the crystal lattice and completely decompose dioxins at high temperatures of 900-1400 ℃, and is recognized as the most thorough disposal method. Among them, the traditional sintering method usually requires processing in a high-temperature furnace at 900-1200 ℃ for several hours, relying on external radiation-conduction heating, which has high thermal inertia, long processing cycle, and high energy consumption; vitrification technology requires melting fly ash at temperatures above 1400 ℃ and then rapidly cooling it into a glassy body, which has the best harmless effect, but the cost of equipment materials and electricity consumption is extremely high; although microwave and other external field enhanced heating technologies can shorten the heating time to a certain extent, they still require long-term heat preservation, resulting in limited overall energy savings and difficulty in scaling up.

[0004] Therefore, traditional heat treatment requires maintaining high temperatures for extended periods, resulting in enormous energy consumption and high operating costs, which severely restricts its large-scale application and makes it difficult to meet the needs for efficient, harmless, and resource-based treatment of fly ash.

[0005] Existing technologies employ flash Joule heating to treat fly ash. For example, Chinese patent CN118417286A discloses a method for rapid detoxification and resource utilization of waste incineration fly ash based on Joule heating. This method removes soluble chloride and calcium components from fly ash by acid washing to reduce volume, then combines petroleum coke and sodium chloride to improve conductivity. A flash Joule heating device is used to achieve temperatures above 3000°C within 1-3 seconds, promoting the volatilization and condensation of heavy metals. Chinese patent CN120619034A discloses a method for removing heavy metals from waste incineration fly ash based on flash Joule heating technology. This method mixes waste incineration fly ash with conductive heat-generating materials such as carbon black and controls the resistance to ≤3Ω. Low-voltage pulse pretreatment is used to regulate electrical properties, followed by flash treatment with precise voltage (80–380V), time (0.1–1s), and frequency (1–5 times) to achieve rapid removal of heavy metals at second-level high temperatures (1000–3000°C).

[0006] However, the above-mentioned methods for removing heavy metals based on flash Joule heating have two problems: First, they all require the addition of conductive additives such as sodium chloride, carbon black, and graphite, which results in high process costs and complex procedures. The dust from these conductive additives also poses an explosion risk. Furthermore, the related technologies can only target fly ash from a single source, making them less universally applicable. Second, the principle of these methods is the volatilization removal of heavy metals, which involves using high temperatures to volatilize and collect the heavy metals from the fly ash matrix. Summary of the Invention

[0007] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, this invention provides a method for fixing heavy metals in fly ash based on flash Joule heating. By applying a pulsed current, fly ash from various sources can be rapidly heated to a high temperature in a very short time, achieving efficient stabilization of heavy metals. This method features fast processing speed, low energy consumption, simple process, and strong versatility. The core features that distinguish this method from previously reported technologies are: first, this method does not require the addition of any additional conductive additives, thus having good applicability; second, this method involves the solidification of heavy metals, that is, stabilizing the heavy metals through vitrification and other methods to seal them within the fly ash matrix, thereby preventing leaching. Therefore, this technology is fundamentally different from previous fly ash heavy metal treatment methods based on flash Joule heating.

[0008] To achieve the above objectives, the present invention provides a method for fixing heavy metals in fly ash based on flash Joule heating, comprising the following steps: Fly ash is placed on a conductive heater to form a conductive path; A pulsed current is applied to the conductive heater to heat the fly ash, resulting in fly ash residue.

[0009] By employing the above technical solution, fly ash can be rapidly heated in a very short time by applying a pulsed current at the second level, achieving instantaneous sintering and heavy metal stabilization. Compared to the traditional heat treatment process that requires several hours, this method shortens the processing time to the second level, significantly improving processing efficiency. The flash Joule heating technology directly applies electrical energy to the sample, with an energy utilization rate close to 100%, effectively avoiding the heat loss of traditional indirect heating methods. The energy consumption is about 1 / 400 of that of traditional melting treatment methods, greatly reducing energy consumption and operating costs. Furthermore, it eliminates the need for additional conductive additives to adjust the resistance of the fly ash, further reducing costs, simplifying the process, and improving the applicability to fly ash from different sources.

[0010] According to an embodiment of the present invention, the conductive heater is a flat plate heater.

[0011] According to an embodiment of the present invention, the materials used in the flat plate heater include one or more of carbon paper, graphite felt, carbon fiber, or carbon-carbon composite materials.

[0012] According to an embodiment of the present invention, the source of the fly ash includes fly ash from solid waste incineration.

[0013] According to an embodiment of the present invention, the fly ash comprises one or more of the following: calcium compounds, chlorides, sulfides, iron compounds, aluminum compounds, and heavy metals.

[0014] According to an embodiment of the present invention, the heavy metal includes one or more of Zn, Cu, Pb, Cr, and Cd.

[0015] According to an embodiment of the present invention, the resistance of the conductive path is 0.5 to 5 Ω, preferably 1 Ω.

[0016] According to an embodiment of the present invention, the pulse satisfies at least one of the following conditions: The pulse current is 20–120A; The pulse voltage is 70–150V; The pulse duration is 1 to 20 seconds.

[0017] According to an embodiment of the present invention, the pulse satisfies any one of the following conditions: When M FA When the weight is less than 5g, the pulse current is 20-40A and the pulse voltage is 70-90V; When 5G <M FA When the weight is less than 15g, the pulse current is 100-120A and the pulse voltage is 130-150V; According to an embodiment of the present invention, the applied pulsed current is performed in a high-temperature resistant reaction chamber, which includes at least one of an electrode clamping structure and a vacuum interface.

[0018] According to an embodiment of the present invention, the application of the pulsed current is carried out in an inert gas environment.

[0019] According to an embodiment of the present invention, the inert gas includes one or more of nitrogen, argon, helium, and neon.

[0020] According to an embodiment of the present invention, the heated fly ash satisfies at least one of the following conditions: The heating temperature is 1000–1500℃; The fly ash is heated to 1100–1400°C; The heating rate of the fly ash is 700–900 °C / s.

[0021] According to an embodiment of the present invention, the method further includes fly ash pretreatment, the pretreatment including one or more of grinding, sieving, and drying.

[0022] According to an embodiment of the present invention, before applying the pulse, the method further includes: connecting both ends of the conductive heater to electrodes and connecting it to a pulse current system.

[0023] According to an embodiment of the present invention, the fly ash residue can be used in at least one of building materials or roadbed materials.

[0024] According to an embodiment of the present invention, the heavy metal fixation method further includes performing heavy metal leaching toxicity testing on fly ash and fly ash residue to evaluate the stabilization effect.

[0025] According to an embodiment of the present invention, the heavy metal leaching concentration in the fly ash residue is lower than the pollution control standard limit for municipal solid waste landfills specified in GB 16889-2024.

[0026] Compared with the prior art, the present invention has at least the following beneficial effects: 1. This invention provides a method for fixing heavy metals in fly ash based on flash Joule heating. By applying a pulse current at the second level, the fly ash is rapidly heated in a very short time, realizing instantaneous sintering and heavy metal stabilization of the fly ash. Compared with the traditional heat treatment process that requires several hours, this method shortens the processing time to the second level, significantly improving the processing efficiency. 2. The flash Joule heating technology directly applies electrical energy to the sample, with an energy utilization rate of nearly 100%, effectively avoiding the heat loss of traditional indirect heating methods. The energy consumption is about 1 / 400 of that of traditional melting treatment methods, which greatly reduces energy consumption and operating costs. This method shows good applicability to incineration fly ash of urban solid waste from different regions and with different compositions. It can be effectively stabilized by adjusting process parameters, which is conducive to large-scale promotion and application. 3. The leaching concentrations of Zn, Cu, Cr and Cd in fly ash were reduced to below the instrument detection limit, and the leaching concentration of lead was reduced to 0.19 ppm, significantly reducing leaching toxicity and fully complying with the requirements of GB 16889-2024 pollution control standards for municipal solid waste landfills; the solidification process has no harmful gas emissions and does not generate secondary pollution, achieving harmless and volume reduction treatment of fly ash; 4. It can perform flash Joule heating on fly ash without adding additional conductive additives, achieving rapid heating and solidification of heavy metals. Compared with ordinary processes that remove heavy metals from fly ash based on flash Joule heating, this invention further simplifies the process, reduces costs, reduces environmental risks, improves energy utilization efficiency, increases equipment lifespan and product added value, while ensuring vitrification and heavy metal fixation effects. Attached Figure Description

[0027] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a schematic diagram of a method for fixing heavy metals in fly ash based on flash Joule heating; Figure 2 This is a SEM image of pretreated fly ash-I from Example 1; Figure 3 The image shows the XRD pattern of pretreated fly ash-I in Example 1. Figure 4 This is a comparison chart of the leaching concentrations of five heavy metals in the pretreated fly ash-I of Example 1 with the concentrations specified in GB 16889-2024; Figure 5 The temperature-time curve for fixing heavy metals in fly ash in Example 1; Figure 6 Here is a SEM image of fly ash residue-I from Example 1; Figure 7 The image shows the XRD pattern of fly ash residue-I in Example 1. Figure 8 This is a comparison chart of the leaching concentrations of five heavy metals in fly ash residue-I in Example 1 with the concentrations specified in GB 16889-2024; Figure 9 The image shows the XRD pattern of pretreated fly ash-II in Example 2. Figure 10 This is a comparison chart of the leaching concentrations of five heavy metals in pretreated fly ash-II in Example 2 with the concentrations specified in GB 16889-2024; Figure 11 The temperature-time curve for heavy metal fixation in fly ash in Example 2; Figure 12 This is a comparison chart of the leaching concentrations of five heavy metals in fly ash residue-II in Example 2 with the concentrations specified in GB 16889-2024; Figure 13 The image shows the XRD pattern of pretreated fly ash-III in Example 3; Figure 14 This is a comparison chart of the leaching concentrations of five heavy metals in the pretreated fly ash-III in Example 3 with the concentrations specified in GB 16889-2024; Figure 15 The temperature-time curve for heavy metal fixation in fly ash in Example 3; Figure 16 This is a comparison chart of the leaching concentrations of five heavy metals in fly ash residue-III in Example 3 with the concentrations specified in GB 16889-2024; Figure 17 This is a comparison chart of the leaching concentrations of five heavy metals in fly ash residue in Example 4 with the concentrations specified in GB 16889-2024; Figure 18This is an energy consumption diagram of the method of the present invention calculated based on the scale of Examples 1 and 4. Detailed Implementation

[0028] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0029] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0030] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0031] In this document, the terms “comprising” or “including” are open-ended expressions, meaning that they include the contents specified in this invention, but do not exclude other aspects.

[0032] In this document, the terms “optionally,” “optionally,” or “optionally” generally refer to an event or condition that may, but may not, occur, and the description includes both cases in which the event or condition occurs and cases in which the event or condition does not occur.

[0033] To address the technical problems of traditional heat treatment methods for fixing heavy metals in fly ash, which require prolonged high-temperature maintenance, resulting in high energy consumption, high operating costs, complex processes, and low applicability, this invention provides a method for fixing heavy metals in fly ash based on flash Joule heating. By applying pulsed current, fly ash from various sources can be rapidly heated to high temperatures in a very short time, achieving efficient stabilization of heavy metals. This method features fast processing speed, low energy consumption, simple process, and strong applicability.

[0034] To achieve the above objectives, the present invention provides a method for fixing heavy metals in fly ash based on flash Joule heating, comprising the following steps: Fly ash is placed on a conductive heater to form a conductive path; A pulsed current is applied to the conductive heater to heat the fly ash, resulting in fly ash residue.

[0035] By employing the above technical solution, fly ash can be rapidly heated in a very short time by applying a pulsed current at the second level, achieving instantaneous sintering and heavy metal stabilization. Compared to the traditional heat treatment process that requires several hours, this method shortens the processing time to the second level, significantly improving processing efficiency. The flash Joule heating technology directly applies electrical energy to the sample, with an energy utilization rate close to 100%, effectively avoiding the heat loss of traditional indirect heating methods. The energy consumption is about 1 / 400 of that of traditional melting treatment methods, greatly reducing energy consumption and operating costs. Furthermore, it eliminates the need for additional conductive additives to adjust the resistance of the fly ash, further reducing costs, simplifying the process, and improving the applicability to fly ash from different sources.

[0036] According to an embodiment of the present invention, the conductive heater includes a flat plate heater.

[0037] According to an embodiment of the present invention, the materials used in the flat plate heater include one or more of carbon paper, graphite felt, carbon fiber, or carbon-carbon composite materials.

[0038] By adopting the above technical solution, fly ash can be rapidly heated by flash Joule heating without the addition of additional conductive additives, thereby achieving rapid heating and solidification of heavy metals. This simplifies the process, reduces costs, reduces environmental risks, improves energy utilization efficiency, extends equipment life and increases product added value, while ensuring vitrification and heavy metal fixation effects. It also eliminates the need to adjust the type and amount of conductive additives for fly ash from different sources, making it highly versatile and easy to promote.

[0039] According to an embodiment of the present invention, the fly ash source includes fly ash from solid waste incineration obtained from mechanical grate incinerators or fluidized bed incinerators in different provinces and cities.

[0040] According to an embodiment of the present invention, the fly ash comprises one or more of the following: calcium compounds, chlorides, sulfides, iron compounds, aluminum compounds, and heavy metals.

[0041] By adopting the above technical solution, this invention can achieve instantaneous high-temperature homogenization of fly ash, whether it is high-chlorine and high-sodium "spicy fly ash" or high-calcium and high-sulfur "alkali fly ash". For fly ash of different sources and compositions, it can simultaneously vitrify and fix heavy metals without formula adjustment, and has strong universality.

[0042] According to an embodiment of the present invention, the heavy metal includes one or more of Zn, Cu, Pb, Cr, and Cd.

[0043] According to an embodiment of the present invention, the resistance of the conductive path is 0.5 to 5 Ω, preferably 1 Ω.

[0044] By adopting the above technical solution, it is beneficial to output a suitable current instantaneously at a lower voltage, without the need for an additional arc-starting device, with a fast heating rate, improved energy utilization, heat concentration inside the sample, less electrode heating, low cooling load, and avoidance of the possibility of capacitor overcurrent explosion, which helps to extend the equipment life.

[0045] According to an embodiment of the present invention, the pulse satisfies at least one of the following conditions: The pulse current is 20–120A; The pulse voltage is 70–150V; The pulse duration is 1 to 20 seconds.

[0046] By employing the above technical solution, multiple cycles of "thermal shock-quenching" can be achieved within seconds, completing lattice reconstruction, heavy metal solidification, and the formation of a silicate glass phase. Simultaneously, the instantaneous high temperature promotes complete dioxin decomposition, while rapid cooling and quenching "freezes" heavy metals within a dense glass network, significantly reducing leaching toxicity and making it suitable for large-scale continuous feeding. Therefore, the combination of "high voltage-short pulse-rapid quenching" can complete the vitrification and heavy metal fixation of fly ash within seconds, significantly reducing energy consumption and operating costs, improving processing efficiency, and offering advantages such as high efficiency, low carbon footprint, and easy scalability.

[0047] According to an embodiment of the present invention, the pulse satisfies any one of the following conditions: When M FA When the weight is less than 5g, the pulse current is 20-40A and the pulse voltage is 70-90V; thus, it helps to avoid unnecessary power loss. When 5G <M FA When the fly ash is less than 15g, the pulse current is 100-120A and the pulse voltage is 130-150V; thus, it is beneficial to ensure that all fly ash is completely sintered.

[0048] According to an embodiment of the present invention, the applied pulsed current is performed in a high-temperature resistant reaction chamber, which includes at least one of an electrode clamping structure and a vacuum interface.

[0049] According to an embodiment of the present invention, the application of the pulsed current is carried out in an inert gas environment.

[0050] By adopting the above technical solution, the formation of low-boiling-point oxides of heavy metals such as Pb, Zn, and Cd can be suppressed, the volatilization rate can be reduced, and the amount of heavy metals fixed can be increased; the formation of carcinogenic CrO4² by high-temperature oxidation can be avoided. - This reduces leaching concentration; prevents dioxin resynthesis; and ensures the melt does not come into contact with air during cooling, thus stabilizing Fe²⁺. + / Fe³ +The proportions improve the transparency and added value of the vitreous.

[0051] According to an embodiment of the present invention, the inert gas includes one or more of nitrogen, argon, helium, and neon.

[0052] According to an embodiment of the present invention, the heated fly ash satisfies at least one of the following conditions: The heating temperature is 1000–1500℃; The fly ash is heated to 1100–1400°C; The heating rate of the fly ash is 700–900 °C / s.

[0053] By adopting the above technical solution, it is possible to instantly break through 1100-1400 ℃ at a rapid heating rate, achieving "millisecond superheat + instantaneous quenching", which is conducive to promoting complete lattice disintegration, improving the degree of glassization, significantly reducing leaching toxicity; significantly improving energy utilization rate and saving energy; improving the recovery rate of heavy metals; inhibiting dioxin resynthesis and grain growth, and preventing the precipitation of harmful phases.

[0054] According to an embodiment of the present invention, the method further includes fly ash pretreatment, the pretreatment including one or more of grinding, sieving, and drying.

[0055] In one embodiment, the drying temperature is 100–120°C.

[0056] According to an embodiment of the present invention, before applying the pulse, the method further includes: connecting both ends of the conductive heater to electrodes and connecting it to a pulse current system.

[0057] According to an embodiment of the present invention, the fly ash residue can be used in at least one of building materials or roadbed materials.

[0058] It should be noted that the fly ash residue forms a stable sintered body with significantly reduced interparticle gaps and a smooth surface, which is beneficial for providing high compressive strength, low water absorption, and potential cementitious activity. Replacing sand and gravel with it or using it as a cement admixture in building materials and roadbed materials facilitates the realization of zero-cost building materials.

[0059] According to an embodiment of the present invention, the heavy metal fixation method further includes performing heavy metal leaching toxicity testing on fly ash and fly ash residue to evaluate the stabilization effect.

[0060] According to an embodiment of the present invention, the heavy metal leaching concentration in the fly ash residue is lower than the pollution control standard limit for municipal solid waste landfills specified in GB 16889-2024.

[0061] The present invention will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0062] Example 1 The method for fixing heavy metals in fly ash based on flash Joule heating includes the following steps: Fly ash-I was ground and passed through a 100-mesh standard sieve, then placed in a forced ventilation drying oven and dried at 100℃ for 24 hours to obtain pretreated fly ash-I. Connect both ends of the flat plate heater to electrodes and connect it to a pulsed current system. The flat plate heater uses 4cm × 4cm carbon paper as a carrier, and the carbon paper is fixed by graphite plates on both sides. Weigh 0.5g of the pretreated fly ash-I and spread it evenly on the flat plate heater (e.g., Figure 1 (as shown), while monitoring the circuit resistance value, the fly ash contact state is adjusted to stabilize the resistance value at around 1Ω; Under a nitrogen atmosphere, a pulsed current of 30 V and a maximum current of 39 A was applied to the flat plate heater for 10 seconds. Simultaneously, the sample temperature was monitored in real-time using a high-precision infrared temperature probe to obtain a temperature-time curve (e.g., ...). Figure 5 (As shown), after cooling, fly ash residue-Ⅰ is obtained.

[0063] Example 2 The method for fixing heavy metals in fly ash based on flash Joule heating includes the following steps: The fly ash-II was ground and passed through a 100-mesh standard sieve, then placed in a forced ventilation drying oven and dried at 100℃ for 24 hours to obtain pretreated fly ash-II. Connect the two ends of the flat plate heater to the electrodes and connect it to the pulse current system. The flat plate heater uses 4cm×4cm carbon paper as a carrier, and the carbon paper is fixed by graphite plates on both sides. Weigh 0.5g of the pretreated fly ash-II and spread it on the flat plate heater. At the same time, monitor the circuit resistance value and adjust the fly ash contact state to stabilize the resistance value at about 1Ω. Under a nitrogen atmosphere, a pulsed current of 30 V and a maximum current of 35 A was applied to the plate heater for 10 seconds. Simultaneously, the sample temperature was monitored in real-time using a high-precision infrared temperature probe to obtain a temperature-time curve (e.g., ...). Figure 11 (As shown), after cooling, fly ash residue-II is obtained.

[0064] Example 3 The method for fixing heavy metals in fly ash based on flash Joule heating includes the following steps: Fly ash-III was ground and passed through a 100-mesh standard sieve, then placed in a forced ventilation drying oven and dried at 100℃ for 24 hours to obtain pretreated fly ash-III. Connect the two ends of the flat plate heater to the electrodes and connect it to the pulse current system. The flat plate heater uses 4cm×4cm carbon paper as a carrier, and the carbon paper is fixed by graphite plates on both sides. Weigh 0.5g of the pretreated fly ash-III and spread it on the flat plate heater. At the same time, monitor the circuit resistance value and adjust the fly ash contact state to stabilize the resistance value at about 1Ω. Under a nitrogen atmosphere, a pulsed current of 30 V and a maximum current of 37 A was applied to the flat plate heater for 10 seconds. Simultaneously, the sample temperature was monitored in real-time using a high-precision infrared temperature probe to obtain a temperature-time curve (e.g., ...). Figure 15 (As shown), after cooling, fly ash residue-III is obtained.

[0065] Example 4 The method for fixing heavy metals in fly ash based on flash Joule heating includes the following steps: Connect the two ends of the flat plate heater to the electrodes and connect it to the pulse current system. The flat plate heater uses 13cm×16cm carbon paper as a carrier. The carbon paper is fixed by graphite plates on both sides. Weigh 10g of the pretreated fly ash-I described in Example 1 and spread it on the flat plate heater. At the same time, monitor the circuit resistance value and adjust the fly ash contact state to stabilize the resistance value at about 1Ω. Under a nitrogen atmosphere, a pulsed current of 80 V and 140 A was applied to the flat plate heater for 10 seconds. At the same time, the sample temperature was monitored in real time by a high-precision infrared temperature probe until it reached 1400°C. After cooling, fly ash residue-Ⅳ was obtained.

[0066] Effect test 1. Characterization of pretreated fly ash Scanning electron microscopy (SEM) was performed on the pretreated fly ash-I, and the results are as follows: Figure 2 As shown; X-ray diffraction (XRD) tests were performed on pretreated fly ash-I, pretreated fly ash-II, and pretreated fly ash-III, respectively, and the results are shown below. Figure 3 , Figure 9 and Figure 13 As shown; according to standard HJ / T 300-2007, heavy metal leaching tests were conducted on pretreated fly ash-I, pretreated fly ash-II, and pretreated fly ash-III, respectively, and the results are as follows. Figure 4 , Figure 10 and Figure 14 As shown.

[0067] from Figure 2It can be seen that the surface of the pretreated fly ash-I particles is rough and has a large number of debris particles attached, with obvious gaps between the particles; from Figure 3 , Figure 9 It can be seen that the crystalline minerals of pretreated fly ash-I, pretreated fly ash-II, and pretreated fly ash-III are mainly calcium-based crystals (such as CaCO3 and CaSO4) and chloride-based crystals (such as NaCl and KCl); from Figure 4 , Figure 10 and Figure 14 It can be seen that the leaching concentrations of Zn, Cu, Pb, and Cd in pretreated fly ash-I and pretreated fly ash-III are all higher than those specified in standard GB 16889-2024, and the heavy metal leaching concentration of pretreated fly ash-III is significantly higher than that of pretreated fly ash-I; the heavy metal leaching concentration of pretreated fly ash-II is significantly lower than that of pretreated fly ash-I, but the leaching concentrations of Pb and Cd are still higher than those specified in standard GB16889-2024.

[0068] 2. Characterization of fly ash residue SEM and XRD tests were performed on fly ash residue I, and the results are as follows: Figures 5-6 As shown. By Figures 5-6 It can be seen that the fly ash residue-I particles exhibit significant agglomeration, with smaller pore sizes and smoother particle surfaces due to melting. The fly ash produces two stable mineral phases, Larnite and Gehlenite, proving that after treatment with the fly ash heavy metal fixation method described in this invention, the fly ash was successfully heated to a molten state and then cooled.

[0069] Heavy metal leaching tests were conducted on fly ash residue-I, fly ash residue-II, fly ash residue-III, and fly ash residue-IV using the above method, and the results are as follows. Figure 7 , Figure 12 , Figure 16 and Figure 17 As shown.

[0070] from Figure 7 , Figure 12 , Figure 16 It can be seen that the leaching concentration of heavy metals in fly ash residue is significantly lower than that of the corresponding pretreated fly ash. For example, the leaching concentrations of Zn, Cu, Cr and Cd in fly ash residue-I are reduced to below the instrument detection limit, and the leaching concentration of lead is reduced to 0.19 ppm. Moreover, the leaching toxicity of the five heavy metals in fly ash residue-I, fly ash residue-II and fly ash residue-III fully comply with the provisions of standard GB 16889-2024.

[0071] As can be seen, after treatment by the method described in this invention, the leaching toxicity of the five heavy metals in the fly ash residue from the three different sources and combinations mentioned above was reduced from exceeding the requirements of standard GB 16889-2024 in all or part to fully complying with the requirements of GB 16889-2024. This proves that the method described in this invention can effectively immobilize heavy metals in fly ash from different sources and compositions within seconds, significantly reducing their leaching toxicity, while achieving efficient control of pollutants. This provides a rapid, efficient, and energy-saving new approach for the safe disposal of fly ash from municipal solid waste incineration.

[0072] from Figure 17 It can be seen that the leaching toxicity of the five heavy metals in fly ash residue-IV fully complies with the provisions of standard GB 16889-2024, proving that for large-scale fly ash scaled up by linear methods, the fly ash heavy metal fixation method based on flash Joule heating described in this invention can still effectively fix heavy metals within seconds, significantly reduce their leaching toxicity, achieve efficient control of pollutants, and can be applied to large-scale production.

[0073] 3. Energy consumption calculation The real-time current and voltage recorded in the methods described in Examples 1 and 4 were derived, and the energy consumption Q of the method for processing one ton of fly ash was calculated by integral according to the following formula. The results were recorded in [the relevant database]. Figure 18 .

[0074]

[0075] Where Q is the energy consumption (kWh / t) for processing one ton of fly ash. P is the power (W), which can be calculated using the formula P=U×I (where U is the discharge voltage and I is the discharge current). t is the pulse discharge time; M represents the scale and mass of each batch of fly ash; Coefficient 2.78 × 10 -7 Representative: 1 J = 2.78 × 10 -7 kWh conversion; Coefficient 10 6 Representative: 1 ton = 1 × 10 6 The conversion.

[0076] according to Figure 18It can be seen that the fly ash heavy metal fixation method based on flash Joule heating described in this invention consumes less than 7000 kWh / t based on the data of 0.5g fly ash in Example 1. When the fly ash scale increases, the energy consumption is further reduced. Based on the data of 10g fly ash in Example 4, the energy consumption is even as low as below 2000 kWh / t. This indicates that the fly ash heavy metal fixation method based on flash Joule heating described in this invention significantly reduces the energy consumption of fly ash treatment, and the energy consumption per ton of fly ash is further reduced after the scale is expanded, resulting in a significant reduction in cost, which is conducive to large-scale application.

[0077] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," "one implementation," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0078] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for fixing heavy metals in fly ash based on flash Joule heating, comprising the following steps: Fly ash is placed on a conductive heater to form a conductive path; A pulsed current is applied to the conductive heater to heat the fly ash, resulting in fly ash residue.

2. The method according to claim 1, characterized in that, The conductive heater includes a flat plate heater, and the materials used in the flat plate heater include one or more of carbon paper, graphite felt, carbon fiber, or carbon-carbon composite materials.

3. The method according to claim 1, characterized in that, The resistance of the conductive path is 0.5 to 5 Ω.

4. The method according to any one of claims 1 to 3, characterized in that, The pulse satisfies at least one of the following conditions: The pulse current is 20–120A; The pulse voltage is 70–150V; The pulse duration is 1 to 20 seconds.

5. The method according to claim 4, characterized in that, The pulse satisfies any one of the following conditions: When M FA When the weight is less than 5g, the pulse current is 20-40A and the pulse voltage is 70-90V; When 5G <M FA When the weight is less than 15g, the pulse current is 100-120A and the pulse voltage is 130-150V.

6. The method according to any one of claims 1 to 3, characterized in that, The fly ash comprises one or more of the following: calcium compounds, chlorides, sulfides, iron compounds, aluminum compounds, and heavy metals.

7. The method according to any one of claims 1 to 3, characterized in that, The heated fly ash satisfies at least one of the following conditions: The heating temperature is 1000–1500℃; The fly ash is heated to 1100–1400°C; The heating rate of the fly ash is 700–900 °C / s.

8. The method according to any one of claims 1 to 3, characterized in that, The application of the pulsed current is carried out in an inert gas environment, the inert gas including one or more of nitrogen, argon, helium, and neon.

9. The method according to any one of claims 1 to 3, characterized in that, The method further includes fly ash pretreatment, which includes one or more of grinding, sieving, and drying.

10. The method according to any one of claims 1 to 3, characterized in that, The leaching concentration of heavy metals in the fly ash residue is lower than the pollution control standard limit for municipal solid waste landfills specified in GB 16889-2024.

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