Method for hydrothermally synthesizing goethite from waste incineration fly ash and application of goethite

Abstract

The invention relates to the field of garbage treatment, in particular to a method for hydrothermally synthesizing goethite from garbage incineration fly ash and application of the method. The synthesis method comprises the following steps: step 1, preparing a strong alkali solution, and transferring the strong alkali solution into a polytetrafluoroethylene reaction lining; step 2, weighing an iron source and the waste incineration fly ash, adding the iron source and the waste incineration fly ash into a strong alkali solution, and uniformly stirring; step 3, transferring the lining into a hydrothermal reaction kettle, transferring the reaction kettle into a drying oven, and carrying out hydrothermal reaction; and step 4, performing centrifugal treatment on a product after the hydrothermal reaction, separating out a solid-phase product, and drying to obtain goethite. According to the method, resource utilization of the iron-containing raw materials and the heavy metal waste can be achieved. According to the method, iron-containing waste or minerals can be directly used as an iron source and converted into goethite products with high additional value in the hydrothermal reaction, meanwhile, heavy metal is stabilized in a mineral phase, waste is turned into wealth, consumption of iron resources is reduced, and a new material and a new way are provided for heavy metal pollution treatment.

Description

Technical Field

[0001] This invention relates to the field of waste treatment, specifically to a method for hydrothermal synthesis of goethite from waste incineration fly ash and its application. Background Technology

[0002] Waste incineration technology is widely used in developed countries due to its advantages such as high volume reduction (90% reduction in volume), small footprint, and energy recovery. However, fly ash (MSWI FA) generated during incineration accounts for approximately 3%–5% of the total waste volume. Because it contains heavy metals and various toxic and hazardous substances, it is classified as hazardous waste, and improper disposal can easily cause secondary pollution to soil and groundwater. Therefore, improving the stability of its heavy metal content is a key issue for the safe disposal of waste incineration fly ash.

[0003] Hydrothermal treatment, as a solid waste treatment technology with broad application prospects, has gradually attracted widespread attention from researchers and has been used to treat various wastes such as electrolytic iron slag, incineration sludge ash, and red mud. Waste incineration fly ash (MSWI FA) is mainly generated in the highly oxidizing environment of the incinerator, and its chemical composition is mainly oxides, commonly including CaO and SiO2. This type of fly ash is usually rich in elements such as calcium, silicon, and aluminum.

[0004] The prerequisite for the resource utilization of waste incineration fly ash is the stabilization of its heavy metals to prevent them from entering the natural environment. Existing research indicates that adding a silica-alumina source through a hydrothermal process can convert it into aluminosilicate minerals such as zeolite and sodalite. However, during the hydrothermal reaction of waste incineration fly ash (MSWI FA), alkaline reagents can promote the formation of complex anions of amphoteric metals (such as Pb and Zn). Zeolite minerals typically have negatively charged framework structures, making it difficult to effectively adsorb or fix these equally negatively charged metal hydroxyl complexes. Therefore, the residual concentration of amphoteric metals in the solution after the hydrothermal reaction is often high. In summary, there is an urgent need to find a method that can simultaneously stabilize multiple heavy metals for the resource utilization of waste incineration fly ash. Summary of the Invention

[0005] To address the aforementioned problems and existing issues in the prior art, the present invention aims to provide a method for hydrothermal synthesis of goethite from waste incineration fly ash and simultaneous stabilization of multiple heavy metals. This method uses a one-step hydrothermal process to stabilize multiple heavy metals while synthesizing goethite, achieving harmless treatment and resource utilization of waste incineration fly ash.

[0006] This invention employs a one-step hydrothermal method to treat waste incineration fly ash, achieving efficient synthesis of goethite and simultaneous stabilization of multiple heavy metals. The process uses raw fly ash directly as raw material, completing mineral phase transformation and heavy metal stabilization in a single step within a high-temperature, high-pressure hydrothermal reaction environment. Through the uniform temperature field and continuous thermal action of the hydrothermal system, the active components in the waste incineration fly ash are effectively activated and transformed into well-crystallized goethite. Simultaneously, various heavy metal ions such as lead, cadmium, zinc, and copper in the fly ash are stably fixed in the goethite phase through mechanisms such as adsorption, lattice solid solution, and surface complexation. Conventional one-step hydrothermal methods typically cause heavy metals in waste incineration fly ash to migrate to the liquid phase. The method used in this invention stabilizes most heavy metals in the hydrothermal products rather than allowing them to migrate to the liquid phase, significantly reducing their leaching toxicity and bioavailability, and providing a reliable pathway for the harmless and resource-based utilization of fly ash.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] In a first aspect, the present invention provides a method for hydrothermal synthesis of goethite using fly ash from waste incineration and its application, comprising the following steps:

[0009] Step 1: Prepare a strong alkaline solution and transfer it to a polytetrafluoroethylene reaction liner;

[0010] Step 2: Weigh the iron source and the fly ash from the waste incineration and add them to the strong alkaline solution, stirring until well mixed;

[0011] Step 3: Transfer the polytetrafluoroethylene reaction liner to the hydrothermal reactor, and then transfer the reactor to an oven for hydrothermal reaction.

[0012] Step 4: After the hydrothermal reaction, the product is centrifuged to separate the solid product, which is then dried to obtain goethite.

[0013] Preferably, in step 1, the concentration of the strong alkali solution is 0.1-2 mol / L.

[0014] Preferably, in step 1, the strong alkaline solution is a sodium hydroxide solution and / or a potassium hydroxide solution. The strong alkaline solution mainly acts as a catalyst for the synthesis of goethite.

[0015] In the reaction between waste incineration fly ash and silicon sources, the strong alkaline solution mainly acts as a catalyst, while the fly ash provides an alkaline environment and structure-inducing components, promoting the formation of Fe. 3 The oxidation and hydrothermal crystallization of ⁺ mainly occur in the following reactions in the microwave hydrothermal reaction system:

[0016] Fe2(SO4)3 + 3Ca(OH)2 (from fly ash) → 2FeOOH + 2H2O + 3CaSO4

[0017] Preferably, in step 2, the iron source is at least one of ferric chloride and ferric sulfate.

[0018] Preferably, in step 2, the molar concentration of the iron source is 0.1-2 mol / L.

[0019] Preferably, in step 2, the liquid-to-solid ratio of the strong alkaline solution and the fly ash from waste incineration is 2-10 mL / g.

[0020] Preferably, in step 3, the hydrothermal reaction temperature is 90-200℃ and the time is 0.5-24h.

[0021] During the hydrothermal reaction, the heating rate is controlled at 6-10℃ / min. After the reaction temperature is raised to 90-200℃, the temperature is kept constant by adjusting the oven power, and the temperature deviation does not exceed ±2℃.

[0022] Preferably, in step 4, the drying is carried out at 60-120°C for 8-24 hours.

[0023] Secondly, the present invention provides a goethite, which is prepared by the above-described preparation method.

[0024] Secondly, the present invention provides a goethite synthesized by hydrothermal synthesis of fly ash from waste incineration for the adsorption and fixation of heavy metal ions.

[0025] Preferably, the heavy metal ion is at least one of Pb, Cd, Cu, and Zn.

[0026] The beneficial effects of this invention are as follows:

[0027] 1. This invention proposes a one-step hydrothermal synthesis method for goethite and simultaneous stabilization of multiple heavy metals. This method optimizes reaction conditions to directly promote the formation of goethite crystal phases during the hydrothermal process. Simultaneously, it utilizes goethite's unique layered structure and surface active sites to achieve efficient adsorption and fixation of various heavy metal ions (such as Pb, Cd, Cu, Zn, etc.). The one-step process simplifies the complexity of traditional multi-step treatments, significantly shortens reaction time, reduces energy consumption and operating costs, and the high specific surface area and strong ion exchange capacity of goethite enhance the stabilization effect on heavy metals, resulting in leaching concentrations far below national standard limits.

[0028] 2. This invention can achieve simultaneous, efficient, and stable treatment of multiple heavy metals. During the nucleation and growth process of goethite, heavy metal ions can be firmly fixed in its tunnel structure or interlayer domain through various mechanisms such as adsorption, coating, and isomorphous substitution, significantly reducing the mobility and bioavailability of heavy metals. The final product toxicity leaching concentration meets the requirements of the "Standard for Pollution Control of Hazardous Waste Landfill" (GB 18598-2019), truly achieving the harmless treatment of heavy metal pollutants.

[0029] 3. This invention enables the resource utilization of iron-containing raw materials and heavy metal waste. This method directly uses iron-containing waste or minerals as an iron source, converting them into high-value-added goethite products through a hydrothermal reaction. Simultaneously, it stabilizes heavy metals within the mineral phase, turning waste into treasure. This reduces iron resource consumption and provides new materials and approaches for heavy metal pollution control.

[0030] 4. The wastewater from the process of this invention can be recycled. After simple adjustment, the liquid after hydrothermal reaction can be reused in the preparation of the upstream slurry, achieving zero discharge of the liquid phase. This not only avoids secondary pollution but also reduces the consumption of treatment agents and operating costs, thus having good environmental benefits and economic efficiency. Attached Figure Description

[0031] The present invention will be further described with reference to the accompanying drawings, but the embodiments in the drawings do not constitute any limitation on the present invention. For those skilled in the art, other drawings can be obtained based on the following drawings without creative effort.

[0032] Figure 1 This is a schematic diagram of the process for hydrothermal synthesis of goethite from waste incineration fly ash according to the present invention.

[0033] Figure 2 These are the XRD patterns of the hydrothermal products prepared in Example 1 and Comparative Example 1. Detailed Implementation

[0034] The technical solution of the present invention is illustrated below through specific examples. It should be understood that the one or more method steps mentioned in the present invention do not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps; it should also be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention. Furthermore, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or defining the scope of the present invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the present invention.

[0035] To better understand the above technical solutions, exemplary embodiments of the present invention are described in more detail below. While exemplary embodiments of the present invention are shown, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the invention to those skilled in the art.

[0036] The present invention will be further described below with reference to the following embodiments.

[0037] Example 1

[0038] A method for hydrothermal synthesis of goethite from waste incineration fly ash and simultaneous stabilization of multiple heavy metals includes the following steps:

[0039] (1) Prepare a 0.5 mol / L KOH solution and transfer it to the reactor. Then add waste incineration fly ash at a liquid-to-solid ratio of 0.1 g / ml. The waste incineration fly ash is calculated by mass percentage and includes: 31.59% O, 5.72% F, 10.11% Na, 0.77% Al, 2.38% Si, 4.54% S, 14.06% Cl and 24.63% Ca. At the same time, add ferric sulfate and control the concentration of ferric sulfate at 0.5 mol / L.

[0040] (2) Place the reactor containing the above suspension on a stirrer and stir at a speed of 500 rpm for 20 minutes to make it fully mixed.

[0041] (3) Transfer the sealed reactor containing the above suspension to the oven, control the heating rate to 10℃ / min, and after raising the temperature to 160℃, adjust the oven power to keep the temperature constant, with the temperature deviation not exceeding ±2℃, and the constant temperature reaction time is 12h.

[0042] (4) After the reaction is completed, the reactor is cooled to room temperature, and the hydrothermal reaction liquid and hydrothermal solid product are separated by centrifugation. The hydrothermal solid product is dried at 80°C for 12 hours to obtain goethite.

[0043] The heavy metal leaching concentrations obtained from the treated waste incineration fly ash in this embodiment using the horizontal oscillation method are shown in Table 1. As can be seen from the table, the leaching concentrations of heavy metals did not exceed the limits set by the "Pollution Control Standard for Municipal Solid Waste Landfills" (GB 16889-2008), indicating that the heavy metals were effectively stabilized and would not cause environmental pollution. Furthermore, the residual heavy metal concentrations in the hydrothermal fluid after hydrothermal treatment all met the Class I standard of the "Integrated Wastewater Discharge Standard" (GB 8978-1996), meaning that the generated hydrothermal fluid would not cause secondary pollution.

[0044] Example 2

[0045] A method for hydrothermal synthesis of goethite from waste incineration fly ash and simultaneous stabilization of multiple heavy metals includes the following steps:

[0046] (1) Prepare a 1 mol / L KOH solution and transfer it into the reactor. Then add waste incineration fly ash and ferric sulfate at a liquid-to-solid ratio of 0.5 g / ml, and control the concentration of ferric sulfate at 1 mol / L.

[0047] (2) Place the reactor containing the above suspension on a stirrer and stir at a speed of 500 rpm for 20 minutes to ensure thorough mixing.

[0048] (3) Transfer the sealed reactor containing the above suspension to an oven, control the heating rate at 10℃ / min, and raise the temperature to 160℃. After raising the temperature, adjust the oven power to keep the temperature constant, with a temperature deviation not exceeding ±2℃. The constant temperature reaction time is 16h.

[0049] (4) After the reaction is completed, the reactor is cooled to room temperature, and the hydrothermal reaction liquid and hydrothermal solid product are separated by centrifugation. The hydrothermal solid product is dried at 80°C for 12 hours to obtain goethite.

[0050] The heavy metal leaching concentrations obtained from the treated waste incineration fly ash in this embodiment using the horizontal oscillation method are shown in Table 1. As can be seen from the table, the leaching concentrations of heavy metals did not exceed the limits set by the "Pollution Control Standard for Municipal Solid Waste Landfills" (GB 16889-2008), indicating that the heavy metals were effectively stabilized and would not cause environmental pollution. Furthermore, the residual heavy metal concentrations in the hydrothermal fluid after hydrothermal treatment all met the Class I standard of the "Integrated Wastewater Discharge Standard" (GB 8978-1996), meaning that the generated hydrothermal fluid would not cause secondary pollution.

[0051] Example 3

[0052] A method for hydrothermal synthesis of goethite from waste incineration fly ash and simultaneous stabilization of multiple heavy metals includes the following steps:

[0053] (1) Prepare a 0.1 mol / L KOH solution and transfer it into the reactor. Then add waste incineration fly ash and ferric sulfate at a liquid-to-solid ratio of 0.3 g / ml, and control the concentration of ferric sulfate at 0.444 mol / L.

[0054] (2) Place the reactor containing the above suspension on a stirrer and stir at a speed of 500 rpm for 20 minutes to ensure thorough mixing.

[0055] (3) Transfer the sealed reactor containing the above suspension to an oven, control the heating rate at 10℃ / min, and raise the temperature to 180℃. After raising the temperature, adjust the oven power to keep the temperature constant, with a temperature deviation not exceeding ±2℃. The constant temperature reaction time is 24h.

[0056] (4) After the reaction is completed, the reactor is cooled to room temperature, and the hydrothermal reaction liquid and hydrothermal solid product are separated by centrifugation. The hydrothermal solid product is dried at 80°C for 12 hours to obtain goethite.

[0057] Comparative Example 1

[0058] The traditional hydrothermal method of pretreatment by water washing is used to hydrothermally synthesize zeolite-like minerals from waste incineration fly ash, including the following steps:

[0059] Water washing pretreatment: (1): Water was added to the waste incineration fly ash at a liquid-to-solid ratio of 2 ml / g, and mechanically stirred at 300 r / min for 20 min. After the reaction, the waste incineration fly ash was obtained by centrifugation or filtration. Then, water was added to the waste incineration fly ash at a liquid-to-solid ratio of 2 ml / g for a second water washing. The waste incineration fly ash was mechanically stirred at 300 r / min for 20 min. After the reaction, the waste incineration fly ash was obtained by centrifugation or filtration. The soluble chloride salts in the first water washing solution were then separated and recycled to the second water washing stage, while the second water washing solution was recycled to the first water washing stage.

[0060] Hydrothermal steps: (1) Add silicon dioxide and aluminum oxide to the water-washed waste incineration fly ash according to the silicon-aluminum ratio of 1.0, and add 0.5 mol / L NaOH solution to it. The liquid-solid ratio is 5 ml / g, and transfer this mixture to the reactor.

[0061] (2) Transfer the sealed reactor containing the above suspension to a conventional hydrothermal reaction equipment and react at 180°C for 48 hours.

[0062] (3) After the reaction is completed, the reactor is cooled to room temperature, and the hydrothermal product is dried at 100°C for 6 hours to obtain zeolite-like mineral powder. At the same time, the hydrothermal reaction solution is circulated for hydrothermal reaction.

[0063] The XRD patterns of the hydrothermal products obtained in Example 1 and Comparative Example 1 are as follows: Figure 2 As shown, it can be seen that the hydrothermal product obtained by adding a silicon-aluminum source in Comparative Example 1 is a zeolite-like mineral phase, while the hydrothermal product obtained by adding an iron source in Example 1 is goethite.

[0064] Comparative Example 1 involved leaching heavy metals using a horizontal oscillation method. The leaching concentrations of Cr and Cd exceeded the limits set by the "Pollution Control Standard for Municipal Solid Waste Landfills" (GB 16889-2008). Meanwhile, the residual concentrations of Pb and Zn in the hydrothermal solution after hydrothermal treatment, as shown in Table 2, exceeded the Class I standard of the "Integrated Wastewater Discharge Standard" (GB 8978-1996).

[0065] Table 1 shows the heavy metal leaching concentrations obtained by the horizontal oscillation method from the treated waste incineration fly ash obtained in Examples 1-3. As can be seen from Table 1, the leaching concentrations of heavy metals did not exceed the limits set by the "Pollution Control Standard for Municipal Solid Waste Landfills" (GB 16889-2008), indicating that the heavy metals were effectively stabilized and would not cause environmental pollution. Meanwhile, the residual heavy metal concentrations in the hydrothermal fluid after hydrothermal treatment, as shown in Table 2, all met the Class I standard of the "Integrated Wastewater Discharge Standard" (GB 8978-1996), meaning that the generated hydrothermal fluid would not cause secondary pollution.

[0066] Table 1. Heavy metal leaching concentrations of fly ash from waste incineration after different treatment methods.

[0067] heavy metal Cr (mg / L) Ni (mg / L) Cu (mg / L) Zn (mg / L) Cd (mg / L) Pb (mg / L) Comparative Example 1 5.23 0.35 13.15 40.13 0.59 0.13 Example 1 0.01 0.32 2.59 38.83 0.09 0.03 Example 2 0.03 0.42 3.69 30.07 0.11 0.09 Example 3 0.05 0.36 7.25 25.74 0.14 0.14 Limit 4.5 0.5 40 100 0.15 0.25

[0068] Table 2. Residual concentrations of heavy metals in hydrothermal fluids after different treatment methods.

[0069] heavy metal Cr (mg / L) Ni (mg / L) Cd (mg / L) Cu (mg / L) Comparative Example 1 2.23 0.83 0.37 0.92 Example 1 0.23 0.01 0.06 0.01 Example 2 0.31 0.03 0.03 0.02 Example 3 0.59 0.01 0.07 0.05 Limit 1.5 1 0.1 1

[0070] This invention achieves simultaneous synthesis of goethite and stabilization of multiple heavy metals through a one-step hydrothermal method. It has advantages such as simple process, high reaction efficiency, good stability, low cost, and environmental friendliness, providing a reliable technical path for the synergistic treatment and resource recovery of heavy metal pollutants.

[0071] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. The illustrative expressions of the above terms in this specification should not be construed as necessarily referring 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. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0072] 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 hydrothermal synthesis of goethite using fly ash from waste incineration, characterized in that, Includes the following steps: Step 1: Prepare a strong alkaline solution and transfer it to a polytetrafluoroethylene reaction liner; Step 2: Weigh the iron source and the fly ash from the waste incineration and add them to the strong alkaline solution, stirring until well mixed; Step 3: Transfer the polytetrafluoroethylene reaction liner to the hydrothermal reactor, and then transfer the reactor to an oven for hydrothermal reaction. Step 4: After the hydrothermal reaction, the product is centrifuged to separate the solid product, and after drying, goethite is obtained.

2. The method for hydrothermal synthesis of goethite using fly ash from waste incineration according to claim 1, characterized in that, In step 1, the concentration of the strong alkali solution is 0.1-2 mol / L; the strong alkali solution is sodium hydroxide solution and / or potassium hydroxide solution.

3. The method for hydrothermal synthesis of goethite using fly ash from waste incineration according to claim 1, characterized in that, In step 2, the iron source is at least one of ferric chloride and ferric sulfate; the molar concentration of the iron source is 0.1-2 mol / L.

4. The method for hydrothermal synthesis of goethite using fly ash from waste incineration according to claim 1, characterized in that, In step 2, the liquid-to-solid ratio of the strong alkaline solution and the fly ash from waste incineration is 2-10 mL / g.

5. The method for hydrothermal synthesis of goethite using fly ash from waste incineration according to claim 1, characterized in that, In step 3, the hydrothermal reaction temperature is 90-200℃ and the time is 0.5-24h.

6. The method for hydrothermal synthesis of goethite using fly ash from waste incineration according to claim 1, characterized in that, In step 3, during the hydrothermal reaction, the heating rate is controlled at 6-10℃ / min. After the reaction temperature is raised to 90-200℃, the oven power is adjusted to keep the temperature constant, with a temperature deviation not exceeding ±2℃.

7. The method for hydrothermal synthesis of goethite using fly ash from waste incineration according to claim 1, characterized in that, In step 4, drying is carried out at 60-120℃ for 8-24 hours.

8. A goethite synthesized hydrothermally from waste incineration fly ash, prepared by the method described in claim 1.

9. An application of goethite synthesized hydrothermally from waste incineration fly ash as described in claim 8, characterized in that, The goethite is used for the adsorption and fixation of heavy metal ions.

10. The application of hydrothermal synthesis of goethite from waste incineration fly ash according to claim 9, characterized in that, The heavy metal ion is at least one of Pb, Cd, Cu, and Zn.

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