Method for controlling temperature and crystallization of heavy metals by fly ash and slag co-melting

Abstract

The present application relates to a kind of fly ash and slag synergistic melting temperature control crystallization solidification heavy metal method, comprising the following steps: garbage incineration fly ash is mixed with water stirring, solid-liquid separation and drying, obtain pretreatment fly ash;Pretreatment fly ash, bottom ash and waste glass are crushed dry, and according to the mass ratio of pretreatment fly ash, bottom ash and waste glass (1~5) :(1~5) :(3~6) dosing, so that mixed material system has the composition condition of forming glass phase and iron-containing crystal phase;Mixed material is ground and mixed;Mixed material is kept at 1200~1400 ℃ under the condition of melting;The molten body obtained in step S3 is kept at 850~1000 ℃ crystallization temperature zone and 600~750 ℃ annealing temperature zone and is segmented to stay, and glass-ceramic solidification product is obtained by cooling.Compared with prior art, the present application realizes the stable solidification of heavy metal, and the leaching concentration meets the limit value requirement of relevant standard.

Description

Technical Field

[0001] This invention belongs to the field of hazardous waste treatment technology, specifically relating to a method for co-melting and temperature-controlled crystallization and solidification of heavy metals from fly ash and slag. Background Technology

[0002] With the advancement of industrialization and urbanization in my country, the demand for urban solid waste and hazardous waste treatment is constantly increasing. Incineration, due to its advantages such as volume reduction, harmlessness, and energy recovery, has become an important method for treating municipal solid waste and some hazardous waste. However, incineration produces a large amount of fly ash. Fly ash is rich in heavy metals such as Zn, Cu, Pb, and Cr, as well as high concentrations of Cl and dioxins, and is listed as hazardous waste (No. HW18) in the National Hazardous Waste List. Improper disposal can lead to heavy metal leaching, causing serious harm to human health and the ecological environment.

[0003] Existing methods for treating hazardous fly ash include cement solidification, high-temperature sintering, and high-temperature melting. While co-processing in cement kilns can achieve resource utilization of fly ash, the high chloride ion content in the fly ash restricts the development of this technology, and the entry of heavy metals into cement products poses potential environmental risks. In contrast, fly ash treated by high-temperature melting can completely destroy toxic organic matter and utilize the Si-O network structure to achieve vitrification fixation of heavy metals, significantly reducing leaching toxicity. It has excellent stabilization effects and a high volume reduction rate, and the molten vitrified products can be used as building materials, thus realizing the resource utilization of fly ash.

[0004] However, vitrification of fly ash requires the addition of SiO2, resulting in high processing costs, and the melting temperature typically needs to be between 1350 and 1500°C, leading to significant energy consumption. Furthermore, the high chloride (Cl) content in fly ash promotes the volatilization of heavy metals at high temperatures, causing some heavy metals to enter the flue gas and form secondary pollution. In particular, chromium (Cr) readily forms CaCrO4 in a high-Cl environment, causing the leaching concentration to exceed the limit specified in GB5085.3, and resulting in unstable curing effects.

[0005] Bottom ash is the residue discharged from the bottom of the facility after waste incineration. Rich in components such as Fe2O3, SiO2, CaO, and Al2O3, it can provide a material source for ferrite / spinel crystalline phases and calcium silicate frameworks. Co-melting fly ash, bottom ash, and waste glass, with appropriate temperature control during the cooling stage, can promote crystalline phase precipitation while maintaining the glassy phase encapsulation effect, forming a more stable glass-ceramic solidified structure. Currently, bottom ash treatment mainly relies on simple landfill disposal, lacking resource utilization. Co-melting and vitrifying bottom ash and fly ash can transform these two solid wastes into a single high-value-added material, reducing the amount of additives needed and achieving resource utilization.

[0006] Chinese patent CN115532773A discloses a method for fixing heavy metals in incineration fly ash. The method involves mixing incineration fly ash with waste glass, boron-containing minerals, and aluminum ash as fixatives in a specific ratio, followed by high-temperature calcination and rapid cooling with liquid nitrogen to obtain vitrified products. This method achieves increased glass content and heavy metal fixation through optimized formulation, but it requires the addition of expensive fixatives such as boron-containing minerals and aluminum ash. Furthermore, the liquid nitrogen cooling method is costly and unsuitable for large-scale industrial applications. Additionally, it does not address the role of components such as Fe2O3 in the bottom ash in promoting heavy metal solidification.

[0007] Chinese patent CN114455838B discloses a method for fixing volatile heavy metals in fly ash or secondary fly ash. The method involves ball milling the fly ash to nanoscale, mixing it with nano-silica, and then preparing a thermoplastic nanocomposite material with polyvinyl butyral and polyethylene glycol. The resulting composite material is then injection molded, degreased, and subjected to vitrification to achieve heavy metal fixation. This method is complex, requires the use of organic polymers and nanomaterials, and is costly. Furthermore, it primarily targets the fixation of volatile heavy metals and does not consider the co-processing of solid wastes such as incinerator bottom ash, which hinders its industrial-scale application.

[0008] In summary, the existing fly ash vitrification treatment technologies generally have the following common problems: (1) additional high-cost chemical reagents are required as fluxes or glass network forming agents; (2) there is a lack of targeted control measures for the volatilization of heavy metals caused by Cl in fly ash; (3) the potential of incinerator bottom ash in melting and solidification is not fully utilized; (4) cooling methods such as water quenching or liquid nitrogen are mostly used, which are high-cost methods and are not conducive to industrial promotion. Summary of the Invention

[0009] The purpose of this invention is to solve at least one of the above-mentioned problems by providing a simple, low-cost method for the co-melting and temperature-controlled crystallization solidification of heavy metals from fly ash and slag, which achieves stable heavy metal solidification. This method reduces the soluble chloride load in fly ash by water washing, adjusts the composition of the batching system, and combines it with stepped temperature-controlled cooling to form a glass-ceramic structure, thereby achieving stable solidification of heavy metals and improving process adaptability.

[0010] The objective of this invention can be achieved through the following technical solution: a method for co-melting and temperature-controlled crystallization and solidification of heavy metals from fly ash and slag, comprising the following steps: S0, Fly ash water washing and dechlorination pretreatment: The fly ash from waste incineration is mixed with water and stirred, then separated into solid and liquid and dried to obtain pretreated fly ash; S1. Raw material pretreatment and proportioning design: The pretreated fly ash, bottom ash and waste glass are crushed and dried, and proportioned according to the mass ratio of pretreated fly ash, bottom ash and waste glass (1~5): (1~5): (3~6) so that the mixture system has the composition conditions to form glass phase and iron-containing crystalline phase. S2. Homogenization mixing: Grinding and mixing the materials; S3. High-temperature melting: The mixture is melted at a temperature of 1200~1400℃. S4. Stepped temperature control cooling: The melt obtained in step S3 is kept in a crystallization temperature zone of 850~1000℃ and an annealing temperature zone of 600~750℃ in stages to cool and obtain a glass-ceramic solidified product.

[0011] Furthermore, in step S0, the fly ash from waste incineration is mixed with water at a liquid-to-solid ratio of 3-5:1, and the mixing time is 20-40 minutes.

[0012] Furthermore, in step S1, the mass ratio of pretreated fly ash, bottom ash and waste glass is (2~4):(2~4):(5~6).

[0013] Furthermore, in step S1, the mass ratio of pretreated fly ash, bottom ash, and waste glass is 4:2:6, 3:3:6, or 2:4:6.

[0014] Furthermore, the Fe2O3 content in the mixture system prepared in step S1 is 12~25wt%, and the Cl content is ≤2wt%.

[0015] Furthermore, the holding and melting time in step S3 is 30~90 min.

[0016] Furthermore, in step S3, the temperature for heat preservation and melting is 1300℃, and the time is 60 minutes.

[0017] Furthermore, in step S4, the crystallization temperature range is 900~950℃, the effective residence time is 0.5~2h, the annealing temperature range is 650~700℃, and the effective residence time is 0.5~1h.

[0018] A heavy metal-cured glass-ceramic product is prepared using the above method.

[0019] Furthermore, the product is a glass-ceramic structure comprising an amorphous glass phase, a calcium silicate or calcium aluminum silicate crystalline phase, and an iron-containing crystalline phase, and the heavy metal leaching concentration meets the leaching toxicity identification limit specified in GB 5085.3—2007 and the leaching hazardous substance limit for the corresponding use of vitrified products in GB / T 41015—2021.

[0020] Compared with the prior art, the present invention has the following beneficial effects: (1) In view of the problem that heavy metals such as Zn, Cu, Cr and Pb are easily leached from waste incineration fly ash and that soluble chloride salts may affect the high-temperature stabilization process, this invention uses waste incineration fly ash (HFA), waste incineration bottom ash (HBA) and waste glass (WG) as raw materials, and prepares a solidified product with a glass ceramic structure by water washing dechlorination pretreatment, fly ash / slag / waste glass ratio control, high-temperature co-melting and step-by-step temperature control cooling.

[0021] (2) This invention removes soluble chloride salts from fly ash by washing with water, thereby reducing the risk of heavy metal chlorination volatilization during high-temperature processes; it provides components such as Fe2O3 through bottom slag, and utilizes the synergistic effect of bottom slag and waste glass to provide iron-containing components and glass network structure respectively, thereby reducing the need for external raw materials; (3) Through stepped temperature control cooling, the ferrite spinel structure related crystal phase formed can fix heavy metals through solid solution or lattice substitution, so as to achieve stable solidification of heavy metals and the leaching concentration meets the relevant standard limit requirements. (4) Use waste glass as a glass network forming agent and combine it with the fluxing components in the bottom slag to reduce melting temperature and energy consumption; (5) Using air as the cooling medium to replace the traditional water quenching method saves water resources and reduces the risk of secondary pollution and treatment costs.

[0022] (6) It enables the co-processing of fly ash, bottom slag and waste glass, and has good resource utilization value. Attached Figure Description

[0023] Figure 1 This is a flowchart of the method of the present invention; Figure 2 The XRD patterns of the products obtained in Examples 1-2 are shown below. Figure 3 The image shows the XRD patterns of the products obtained in Comparative Examples 1-3. Detailed Implementation

[0024] The present invention will now be described in detail with reference to specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0025] Waste incineration fly ash contains large amounts of heavy metals such as Zn, Cu, Pb, and Cr, as well as high concentrations of Cl, classifying it as hazardous waste. High-temperature vitrification is an effective method for treating fly ash, but current technologies still have the following shortcomings: 1) When fly ash is vitrified alone, additional components such as SiO2 need to be added, which increases the cost and the melting temperature is higher; 2) Fly ash has a high Cl content, which easily generates volatile metal chlorides at high temperatures, causing heavy metal loss. At the same time, it may form CaCrO4, increasing the risk of Cr leaching. 3) Bottom ash is mostly disposed of by landfill, failing to fully utilize its rich composition of Fe2O3, SiO2, CaO and other components; 4) Traditional processes use water quenching for cooling, which consumes a lot of water and is prone to secondary pollution.

[0026] This invention achieves heavy metal solidification by co-melting fly ash and slag through the following technical solution, such as... Figure 1 As shown, it includes the following steps: S0. Fly ash water washing dechlorination pretreatment: Mix fly ash and water at a liquid-solid ratio of 3~5:1 and stir for 20~40 minutes. Separate the solid and liquid and dry to remove soluble chloride salts such as NaCl / KCl and reduce chlorine interference; S1. Raw material pretreatment and proportioning: The pretreated fly ash (HFA), bottom ash (HBA) and waste glass (WG) are crushed and dried, and proportioned in a mass ratio of (1~5):(1~5):(3~6), preferably 4:2:6, 3:3:6 or 2:4:6; so that the mixture system has the composition conditions for forming glass phase and iron-containing crystalline phase: the Fe2O3 content in the mixture system is 12~25wt%, and the Cl content is ≤2wt%.

[0027] S2. Homogenization mixing: Grinding or ball milling the mixture; S3. High-temperature melting: Melt at 1200~1400℃ for 30~90min; preferably, the melting temperature is 1300℃ and the time is 60min.

[0028] S4. Stepped temperature control cooling: The product is effectively held in the crystallization temperature range of 850~1000℃ for 0.5~2h, and in the annealing temperature range of 600~750℃ for 0.5~1h, and then cooled to room temperature to obtain the glass-ceramic cured product.

[0029] This invention reduces interference from soluble chloride salts through water washing, provides components such as Fe2O3 through bottom slag, and promotes the formation of spinel-type ferrite-like crystalline phases and a stable silicate framework through temperature-controlled cooling. This allows heavy metals to be stabilized through the synergistic effect of glassy phase encapsulation, silicate framework consolidation, and spinel lattice fixation. It is suitable for the synergistic harmless and resource-based disposal of fly ash, bottom slag, and waste glass. Specific embodiments are described below.

[0030] The main chemical compositions of waste incineration fly ash (HFA), waste incineration bottom ash (HBA), and waste glass (WG) used in the embodiments of this invention are shown in Table 1: Table 1. Main chemical composition of raw materials (wt%) .

[0031] Example 1 Waste incineration fly ash was mixed with water at a liquid-to-solid ratio of 4:1, stirred for 30 minutes, and then separated into solid and liquid components and dried. Water extraction and chloride ion determination showed that the soluble chloride content of the fly ash before washing was 5 wt%, and after washing, the soluble chloride content decreased to 1 wt%, with a dechlorination rate of approximately 80%.

[0032] The pretreated fly ash, bottom ash, and waste glass were pulverized separately, with fly ash particle size ≤75μm and bottom ash and waste glass particle size ≤150μm, and dried at 105℃ for 24h. The mixture was then batched according to HFA:HBA:WG = 4:2:6, specifically weighing 8g of pretreated fly ash, 4g of bottom ash, and 12g of waste glass. Calculations or testing showed that the Fe2O3 content in this mixture was approximately 13.73wt%, and the Cl content was approximately 0.53wt%.

[0033] The weighed raw materials were ground and mixed for 30 minutes to obtain a homogenized batch. The batch was placed in a crucible and sent into a box-type muffle furnace. The temperature was raised to 1300℃ and held for 60 minutes to allow the system to melt completely.

[0034] After melting, a stepped temperature-controlled cooling process is adopted: the temperature is lowered to the crystallization temperature zone of 850~1000℃ and held for 0.5h; the temperature is further lowered to the annealing temperature zone of 600~750℃ and held for 0.5~1h; after the process is completed, the furnace is cooled to below 200℃ and taken out, and then air-cooled to room temperature to obtain the glass-ceramic cured product.

[0035] Example 2 The difference from Example 1 is that in step S1, the ingredients are prepared according to the ratio of HFA:HBA:WG = 2:4:6, specifically weighing 4g of pretreated fly ash, 8g of bottom slag, and 12g of waste glass. Calculations or tests show that the Fe2O3 content in the mixture system under this ratio is approximately 17.54wt%, and the Cl content is approximately 0.49wt%. The remaining steps are the same as in Example 1.

[0036] Comparative Example 1 Fly ash, bottom ash, and waste glass were crushed separately and dried at 105℃ for 24 hours without water washing or dechlorination pretreatment. The mixture was prepared according to an HFA:HBA:WG ratio of 4:2:6, specifically weighing 8g of fly ash, 4g of bottom ash, and 12g of waste glass. The melting conditions were 1300℃ for 60 minutes, followed by direct air cooling to room temperature without stepped temperature control.

[0037] Comparative Example 2 The difference from Comparative Example 1 is that the ingredients are prepared according to the ratio of HFA:HBA:WG = 2:4:6, specifically weighing out 4g of fly ash, 8g of bottom slag, and 12g of waste glass. The remaining steps are the same as Comparative Example 1.

[0038] Comparative Example 3 The difference from Comparative Example 1 is that no bottom ash is added in step S1. The materials are mixed according to HFA:HBA:WG = 6:0:6, specifically 12g of fly ash, 0g of bottom ash, and 12g of waste glass. Calculations show that the Fe2O3 content in the mixture system under this ratio is approximately 9.92wt%, and the Cl content is approximately 2.63wt%.

[0039] Performance testing (1) Dechlorination effect test by water washing: Fly ash before and after water washing was collected, and deionized water was added at a solid-liquid ratio of 1:500. The mixture was stirred at 1000 r / min for 30 min. After centrifugation, the supernatant was collected, and the Cl was determined by ion chromatography. - The concentration was calculated and converted into the soluble Cl content in fly ash.

[0040] (2) Phase detection: The phase of the molten product was characterized by X-ray diffraction (XRD) and phase search was performed using software such as Jade. The amorphous glass phase was determined by the broad diffuse peaks in the range of 20° to 35° in the XRD pattern, the calcium silicate / calcium aluminum silicate crystal phase was determined by the characteristic peaks around 30°, and the spinel ferrite crystal phase was determined by the characteristic peaks around 35°, 57°, and 62°.

[0041] (3) Heavy metal leaching toxicity test: Leaching toxicity test was conducted according to HJ / T 299—2007 "Leaching Toxicity of Solid Waste - Leaching Method - Sulfuric Acid and Nitric Acid Method". The content of As, Cd, Cr, Cu, Mn, Ni, Pb and Zn in the leachate was detected by inductively coupled plasma atomic emission spectrometry in accordance with the leaching limits for the corresponding uses in GB 5085.3—2007 "Identification Standard for Hazardous Waste - Leaching Toxicity Identification" and GB / T 41015—2021 "Technical Requirements for Vitrification Products of Solid Waste".

[0042] Test results Table 2. Results of water washing for dechlorination and XRD phase composition. .

[0043] Table 3. Heavy metal leaching concentrations and relevant standard limits (mg / L) for each example and comparative example. "-" indicates not detected in the examples and comparative examples, i.e., below the detection limit of the detection method; in the standard limit row, it indicates that the standard does not specify a corresponding limit. All heavy metal leaching concentrations are expressed as elemental, in mg / L.

[0044] As can be seen from the table above: (1) Analysis of the dechlorination effect of water washing: After the water washing pretreatment in step S0, the soluble Cl content in fly ash decreased from 5wt% to 1wt%, and the dechlorination rate was about 80%. This result shows that the water washing step can effectively remove soluble chloride salts in fly ash and reduce the chloride salt load entering the molten system.

[0045] (2) XRD phase analysis: The XRD results of Examples 1 and 2 are as follows Figure 2 As shown, the product exhibits a broad, diffuse peak in the 20°–35° range, indicating the formation of an amorphous glass phase. A strong diffraction peak appears near 2θ around 30°, which, according to Jade indexing, can be classified as a calcium silicate / calcium aluminum silicate phase such as CaSiO3. Furthermore, distinct spinel-type ferrite-like phase characteristic peaks appear near 35°, 57°, and 62°, corresponding to iron-based spinel structures such as ZnFe2O4, CuFe2O4, Fe3O4, and FeCr2O4. The results indicate that stepped temperature-controlled cooling effectively promotes the formation of both calcium silicate / calcium aluminum silicate and spinel-type ferrite-like phases.

[0046] In contrast, the XRD patterns of Comparative Examples 1, 2, and 3 mainly show broad, diffuse peaks in the 20°–35° range, with weaker characteristic peaks of the crystalline phase. This indicates that without step-controlled temperature cooling, the products mainly exhibit a glassy phase or a low-crystallinity glass-ceramic structure, with limited precipitation of stable calcium silicate and spinel-type ferrite phases. Compared to the comparative examples, the characteristic peaks of the crystalline phases in Examples 1 and 2 are clearer after step-controlled temperature cooling, indicating that this temperature-controlled cooling process can provide a suitable temperature range and residence time for crystalline phase nucleation and growth, thereby promoting the formation of glass-ceramic structures and reducing the risk of migration and release of heavy metals in the leaching environment.

[0047] (3) Leaching Results Analysis: ICP leaching results showed that the leaching concentrations of heavy metals such as As, Cd, Cr, Cu, Mn, Ni, Pb, and Zn in the cured products obtained in Examples 1 and 2 were all at low levels. All detected items were lower than the leaching toxicity identification limits specified in GB 5085.3—2007 and the leaching hazardous substance limits for the corresponding uses of vitrified products in GB / T 41015—2021. In contrast, the leaching concentrations of heavy metals in Comparative Examples 1-3 were higher. Compared with Comparative Examples 1 and 2, the examples maintained the heavy metal leaching at a low level through water washing dechlorination and temperature-controlled crystallization, indicating that this process can further improve the stabilization reliability based on the already superior formulation. Specifically: Example 1 (Formulation HFA:HBA:WG = 4:2:6, water washing and controlled temperature cooling): Only As was detected, with a leaching concentration of 0.02 mg / L. Other heavy metals (Cd, Cr, Cu, Mn, Ni, Pb, Zn) were not detected. All detected items were far below the corresponding limits in GB / T 41015—2021 (As: 0.1 mg / L, etc.).

[0048] Example 2 (formulation HFA:HBA:WG=2:4:6, water washing and controlled temperature cooling): As, Cu, Ni and Zn were detected, with leaching concentrations of 0.01 mg / L, 0.004 mg / L, 0.0023 mg / L and 0.02 mg / L, respectively, all below the standard limits listed in Table 3; Cd, Cr, Mn and Pb were not detected.

[0049] The above results indicate that the sample prepared by water washing dechlorination and step-controlled temperature cooling can simultaneously inhibit the leaching of multiple typical heavy metals such as As, Cr, Cu, Ni, Pb, and Zn, with good heavy metal solidification effect, low leaching toxicity risk, and provide a good structural basis for reducing long-term leaching risk.

[0050] Comparative Example 1 (formulation same as Example 1, without water washing and dechlorination pretreatment, and without temperature control and cooling): Cr and Ni were detected, with leaching concentrations of 0.01 mg / L for both. Although this value is still lower than the standard limits listed in Table 3, compared to Example 1 where Cr and Ni were not detected, Comparative Example 1 showed detectable leaching of some heavy metals.

[0051] Comparative Example 2 (formula same as Example 2, but without water washing and dechlorination pretreatment, and without temperature-controlled cooling): Cu, Mn, Ni, and Zn were detected, with leaching concentrations of 0.08 mg / L, 0.02 mg / L, 0.05 mg / L, and 0.28 mg / L, respectively. Compared with Example 2, the Cu leaching concentration was approximately 20 times that of Example 2 (0.08 vs 0.004), the Zn leaching concentration was approximately 14 times that of Example 2 (0.28 vs 0.02), and the Ni leaching concentration was approximately 21.7 times that of Example 2 (0.05 vs 0.0023). The detection of Mn indicates that the lack of temperature-controlled cooling significantly reduced the heavy metal curing effect.

[0052] Comparative Example 3 (formulation HFA:HBA:WG=6:0:6, without water washing and dechlorination pretreatment, and without temperature control cooling): As 0.07 mg / L, Cr 1.37 mg / L, and Ni 0.03 mg / L were detected. The Cr leaching concentration (1.37 mg / L) far exceeded the limit of GB / T41015—2021 (0.2 mg / L), exceeding the limit by approximately 6.85 times. This comparative example not only lacked the HBA component but also lacked temperature control cooling, resulting in a significant increase in the Cr leaching concentration, making it difficult to meet the relevant limit requirements for resource utilization of vitrification products in GB / T 41015—2021.

[0053] Comparing Example 1 with Comparative Example 1, and Example 2 with Comparative Example 2, it can be seen that, under the same formulation, water washing dechlorination and stepped temperature-controlled cooling can reduce the leaching concentration of various heavy metals (Cr, Cu, Mn, Ni, Zn) to undetectable levels or by more than one order of magnitude. This result demonstrates that the synergistic process of water washing dechlorination and stepped temperature-controlled cooling can effectively inhibit the migration of heavy metals within the material and promote the formation of stable phases such as spinel-type ferrites (combined with XRD results), thereby firmly solidifying the heavy metal lattice.

[0054] (4) Analysis of the slag-free comparative example: Comparative example 3 did not add bottom slag. The Fe2O3 and calcium silicate / calcium aluminum silicate formation capacity in the system was insufficient. At the same time, no water washing dechlorination pretreatment and step-by-step temperature control cooling were performed. The Cr leaching concentration in the obtained product reached 1.37 mg / L, which is higher than the Cr limit in GB / T 41015—2021. Based on the formulation characteristics of comparative example 3, it can be seen that bottom slag not only participates in co-processing as a solid waste raw material, but also promotes the formation of glass ceramic framework and spinel-type ferrite crystalline phase by providing components such as Fe2O3, SiO2, CaO, and Al2O3.

[0055] (5) Stabilization Mechanism Analysis: This invention achieves heavy metal stabilization through water washing dechlorination, synergistic batching, and stepped temperature-controlled cooling. First, water washing dechlorination pretreatment removes soluble chloride salts such as NaCl and KCl from fly ash, reducing the Cl content in the molten system and minimizing the risk of heavy metal chlorination volatilization and the formation of unstable chromium-containing phases during high-temperature processes, thus providing a raw material system with lower chloride salt interference for subsequent melting and solidification. Second, the bottom slag and waste glass provide components such as Fe2O3, CaO, Al2O3, and SiO2, respectively, providing a material basis for the formation of glass networks, calcium silicate / calcium aluminum silicate crystalline phases, and spinel-type ferrite crystalline phases. Finally, stepped temperature-controlled cooling enables the solidified product to form a glass-ceramic structure in which amorphous glass phases, calcium silicate / calcium aluminum silicate crystalline phases, and spinel-type ferrite crystalline phases coexist. In this invention, the amorphous glass phase physically encapsulates and chemically binds heavy metals through a Si-O network, while the calcium silicate / calcium aluminum silicate crystalline phase forms a stable inorganic framework, reducing the migration pathways of heavy metals in the leaching medium. The spinel-type ferrite crystalline phase can fix metal elements such as Cr, Cu, Ni, and Zn into a stable lattice through solid solution or lattice substitution. The synergistic effect of low-chlorine interference, glass phase encapsulation, silicate framework consolidation, and spinel lattice fixation results in a low heavy metal release level in the cured product under leaching conditions. This demonstrates that the present invention can achieve efficient and stable curing of various heavy metals and provides a structural basis for their long-term environmental stability.

[0056] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention. Equivalent substitutions, conventional adjustments, or combinations made by those skilled in the art without departing from the spirit and substance of the present invention should all fall within the scope of protection of the present invention.

Claims

1. A method for co-melting and temperature-controlled crystallization and solidification of heavy metals in fly ash and slag, characterized in that, Includes the following steps: S0, Fly ash water washing and dechlorination pretreatment: The fly ash from waste incineration is mixed with water and stirred, then separated into solid and liquid and dried to obtain pretreated fly ash; S1. Raw material pretreatment and proportioning design: The pretreated fly ash, bottom ash and waste glass are crushed and dried, and proportioned according to the mass ratio of pretreated fly ash, bottom ash and waste glass (1~5): (1~5): (3~6) so that the mixture system has the composition conditions to form glass phase and iron-containing crystalline phase. S2. Homogenization mixing: Grinding and mixing the materials; S3. High-temperature melting: The mixture is melted at a temperature of 1200~1400℃. S4. Stepped temperature control cooling: The melt obtained in step S3 is kept in a crystallization temperature zone of 850~1000℃ and an annealing temperature zone of 600~750℃ in stages to cool and obtain a glass-ceramic solidified product.

2. The method for co-melting and temperature-controlled crystallization and solidification of heavy metals in fly ash and slag according to claim 1, characterized in that, In step S0, the fly ash from waste incineration is mixed with water at a liquid-to-solid ratio of 3-5:1, and the stirring time is 20-40 minutes.

3. The method for co-melting and temperature-controlled crystallization and solidification of heavy metals in fly ash and slag according to claim 1, characterized in that, In step S1, the mass ratio of pretreated fly ash, bottom ash and waste glass is (2~4):(2~4):(5~6).

4. The method for co-melting and temperature-controlled crystallization and solidification of heavy metals in fly ash and slag according to claim 1, characterized in that, In step S1, the mass ratio of pretreated fly ash, bottom ash and waste glass is 4:2:6, 3:3:6 or 2:4:

6.

5. The method for co-melting and temperature-controlled crystallization and solidification of heavy metals in fly ash and slag according to claim 1, characterized in that, The Fe2O3 content in the mixture system prepared in step S1 is 12~25wt%, and the Cl content is ≤2wt%.

6. The method for co-melting and temperature-controlled crystallization and solidification of heavy metals in fly ash and slag according to claim 1, characterized in that, The time for heat preservation and melting in step S3 is 30~90 minutes.

7. The method for co-melting and temperature-controlled crystallization and solidification of heavy metals in fly ash and slag according to claim 1, characterized in that, In step S3, the temperature for heat preservation and melting is 1300℃, and the time is 60 minutes.

8. The method for co-melting and temperature-controlled crystallization and solidification of heavy metals in fly ash and slag according to claim 1, characterized in that, In step S4, the crystallization temperature range is 900~950℃, and the effective residence time is 0.5~2h. The annealing temperature range is 650~700℃, and the effective residence time is 0.5~1h.

9. A heavy metal-cured glass-ceramic product, characterized in that, Prepared using the method described in any one of claims 1 to 8.

10. A heavy metal-cured glass-ceramic product according to claim 9, characterized in that, The product is a glass-ceramic structure containing an amorphous glass phase, a calcium silicate or calcium aluminum silicate crystalline phase, and an iron-containing spinel crystalline phase. The heavy metal leaching concentration meets the leaching toxicity identification limit specified in GB 5085.3—2007 and the leaching hazardous substance limit for the corresponding use of vitrified products in GB / T 41015—2021.

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