A detoxification method for simultaneously removing dioxins and heavy metals from waste incineration fly ash.

Abstract

This invention relates to a detoxification method for simultaneously removing dioxins and heavy metals from waste incineration fly ash. The method includes fly ash pretreatment and simultaneous removal of dioxins and heavy metals. First, sodium and potassium salts are removed from the fly ash by immersion washing to avoid reducing the ability of the sintered products formed during high-temperature sintering to solidify heavy metals. Then, the pretreated fly ash is separated to obtain a solid phase, which is mixed with magnesium and / or calcium salts and subjected to high-temperature roasting. This allows the chlorine from the decomposition of dioxins in the fly ash to react with the heavy metals to form gaseous heavy metal chlorides, thus removing the heavy metals from the fly ash. During the high-temperature roasting process, the magnesium and / or calcium salts react with the ash in the fly ash to form calcium silicate and / or magnesium silicate, enhancing the solidification ability of the internal lattice of the fly ash sintered products. After detoxification treatment of waste incineration fly ash using this method, no heavy metals Hg, Pb, Cd, Cu, and Ni were detected in the fly ash leachate, significantly reducing the leaching risk of residual heavy metals in the fly ash.

Description

Technical Field

[0001] This invention relates to the field of solid waste treatment technology, and more specifically to a detoxification method for simultaneously removing dioxins and heavy metals from fly ash from waste incineration. Background Technology

[0002] Municipal solid waste incineration aligns with the principles of waste reduction, harmlessness, and resource recovery in solid waste treatment, and is a waste disposal method encouraged by national policies. However, the fly ash generated during incineration poses a significant challenge to the industry. Currently, the most common method for treating fly ash is stabilization / solidification followed by landfilling. Landfilling merely stabilizes and preserves the pollutants in the fly ash, posing a risk of long-term pollutant migration. Furthermore, it wastes both land resources and usable heavy metals. Moreover, with the continuous reduction of landfill capacity and the rapid advancement of "zero-waste city" construction nationwide, the unsustainability of this treatment method is becoming increasingly apparent. Therefore, achieving the harmless and resource-based utilization of waste incineration fly ash is an effective way to address the shortcomings of current fly ash landfilling practices.

[0003] Fly ash contains complex heavy metals and is also enriched with various dioxins and chloride salts (such as sodium chloride and potassium chloride). Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are highly toxic chemicals. However, existing methods for the harmless and resource-based utilization of fly ash from waste incineration mainly consider only one aspect. For example, patent CN...

[0004] 109437573B discloses a method for the harmless treatment of dioxins in waste incineration fly ash. This method focuses on the detoxification of dioxins in waste incineration fly ash. Specifically, it utilizes waste incineration fly ash, waste glass powder, pickling sludge, and dolomite powder to form a mold, which is then melted at high temperature (1000-1250℃) to prepare foam microcrystalline glass. During the high-temperature melting process of preparing foam microcrystalline glass, the dioxins in the waste incineration fly ash are decomposed at high temperature, and chlorine atoms react with alkaline earth metal oxides (CaO and MgO decomposed from dolomite at high temperature) and solidify them in the foam microcrystalline glass. The generated flue gas is rapidly cooled to below 200℃ to prevent residual chlorides from resynthesizing into dioxins.

[0005] Patent CN 108715519B discloses a method for the harmless and resource-based utilization of waste incineration fly ash, focusing on the removal of heavy metals from the fly ash. It first compresses calcium chloride and magnesium chloride with the fly ash into spherical particles, then calcines the granulated fly ash in a rotary kiln (temperature 900–1100℃) to react the non-volatile heavy metals in the fly ash with a chlorinating agent to generate volatile heavy metal chlorides. A kaolin adsorption layer is then used to adsorb the heavy metal chloride vapors at high temperature. The adsorbed kaolin is mixed with the harmless fly ash and used as building material. The removal rate of heavy metals (Pb, Cd, Cu, and Zn) from the treated fly ash can reach 90%. However, non-volatile heavy metal chlorides such as manganese chloride (MnCl2) and chromium chloride (CrCl3) have boiling points above 1100℃. At 900-1100℃, it is difficult to remove heavy metals such as manganese and chromium by forming heavy metal chloride vapors. They remain in the treated fly ash as heavy metals or heavy metal chlorides, and there is a risk of leaching or transfer in the later stage.

[0006] Patent CN 117066256B discloses a method for the harmless and resource-based utilization of fly ash from waste incineration. The method involves first pyrolyzing the fly ash at low temperature (400-500℃) to remove dioxins, then acid washing (acid washing solution pH < 2.64) to dissolve heavy metals from the fly ash. After solid-liquid separation, the solid phase is naturally air-dried and added to the bottom ash of waste incineration for use as building material, while the liquid phase is treated with sodium sulfate. After solid-liquid separation, 85-95% of the liquid phase is returned to the acid washing solution, and the remaining liquid phase is treated with a heavy metal chelating agent to remove heavy metals. Although this method can simultaneously remove dioxins and heavy metals from waste incineration fly ash, with the dioxin concentration reaching 17 ng-TEQ / kg after low-temperature pyrolysis treatment, further reduction is still needed. The removal rate of heavy metal ions using heavy metal chelating agents is 75%–87%, but the removal rate of heavy metals is relatively low, and there are many types of heavy metals in waste incineration fly ash. Some heavy metals (such as Pb, Hg, Cr, As, Sn) are difficult to dissolve in acid. For example, lead (Pb) exists in fly ash in different oxidation states, and some forms of lead are difficult to dissolve in acid. Mercury (Hg) mainly exists in fly ash in the form of mercuric sulfide (HgS), and mercuric sulfide is generally difficult to dissolve in acid. Chromium may exist in the form of trivalent chromium (Cr(III)) and hexavalent chromium (Cr(VI)), among which trivalent chromium is not easy to dissolve under certain conditions. Furthermore, existing technologies do not fully consider the interactions among dioxins, salts, and heavy metals in waste incineration fly ash, particularly the impact of sodium and potassium salts in the original fly ash on the leaching toxicity of residual heavy metals in the treated fly ash. Therefore, it is necessary to research a detoxification method that can synergistically and effectively remove heavy metals and dioxins from waste incineration fly ash, especially reducing the leaching toxicity of residual heavy metals in the treated fly ash, which will help promote the harmless and resource-based utilization of waste incineration fly ash. Summary of the Invention

[0007] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides a detoxification method for simultaneously removing dioxins and heavy metals from waste incineration fly ash. The purpose is to leverage the inherent characteristics of waste incineration fly ash, considering that sodium and potassium salts in the fly ash reduce the ability of the sintered products formed during high-temperature sintering to solidify residual heavy metals. This method employs a pre-washing process to remove sodium and potassium salts from the fly ash. After solid-liquid separation, the dried solid intermediate is mixed with magnesium and / or calcium salts. High-temperature sintering causes the chlorine from the decomposition of dioxins in the fly ash to react with heavy metals, forming gaseous heavy metal chlorides. Simultaneously, the magnesium and calcium salts added during high-temperature sintering react with the ash in the fly ash to form magnesium silicate and calcium silicate, enhancing the solidification ability of the internal crystal lattice of the sintered body and reducing the leaching toxicity of residual heavy metals in the fly ash. This solves the technical problems of existing technologies that use high-temperature roasting to remove limited types of heavy metals from waste incineration fly ash or have poor heavy metal removal efficiency, resulting in the risk of subsequent leaching of residual heavy metals.

[0008] To achieve the above objectives, according to one aspect of the present invention, a detoxification method is provided for simultaneously removing dioxins and heavy metals from waste incineration fly ash, comprising the following steps:

[0009] (1) Fly ash pretreatment: Sodium and potassium salts in waste incineration fly ash are removed by immersion washing, solid-liquid separation is performed to obtain solid intermediates and then dried.

[0010] (2) Simultaneous removal of dioxins and heavy metals from fly ash: Add magnesium salts and / or calcium salts at 5% to 25% of the mass of the dried solid intermediate in (1), mix and then calcine at high temperature so that the chlorine from the decomposition of dioxins in fly ash reacts with the heavy metals to form gaseous heavy metal chlorides, thereby removing the heavy metals from the fly ash; during the high-temperature calcination process, magnesium salts and / or calcium salts react with the ash in fly ash at high temperature to form calcium silicate and / or magnesium silicate, thereby enhancing the solidification ability of the internal lattice of the fly ash sintering product and reducing the leaching toxicity of residual heavy metals in fly ash.

[0011] Preferably, in the process of forming magnesium silicate and / or calcium silicate, the volatile heavy metals, semi-volatile heavy metals and a small amount of non-volatile heavy metals in fly ash are converted into corresponding gaseous heavy metal chlorides, and the high-temperature roasting temperature is 1000-1200℃ and the roasting time is 3-5h.

[0012] Preferably, in the method, the volatile heavy metals include Hg, the semi-volatile heavy metals include Pb, Zn and Cd, and the non-volatile heavy metals include Cu and Ni.

[0013] Preferably, in the method, the magnesium salt formed by the high-temperature reaction with ash in fly ash to form magnesium silicate includes magnesium chloride, and the calcium salt includes calcium chloride.

[0014] Preferably, in the method, the magnesium salt is magnesium chloride, and the high-temperature roasting temperature in step (2) is 1100-1200°C so that magnesium chloride reacts with the ash in fly ash to form magnesium silicate.

[0015] Preferably, in the method, the amount of magnesium chloride added is 15% to 25% of the mass of the solid intermediate.

[0016] Preferably, in the method, the fly ash pretreatment adopts a three-stage countercurrent water washing or acid washing, and after multiple immersion washing, solid-liquid separation is obtained to obtain a solid intermediate.

[0017] Preferably, in the method, the fly ash pretreatment adopts a three-stage countercurrent water washing, with the fly ash mass to washing liquid volume ratio being 1:1 to 3, and the washing is performed 3 to 6 times.

[0018] Preferably, in the method, the fly ash pretreatment adopts a three-stage countercurrent acid washing, with the fly ash mass to washing liquid volume ratio being 1:1 to 3, and the acid washing is performed 2 to 4 times.

[0019] Preferably, in the method, the concentration of acid in the immersion solution is 20% to 40%.

[0020] In summary, compared with the prior art, the technical solutions conceived in this invention, taking into account the interactions between dioxins, sodium and potassium salts, and heavy metals in waste incineration fly ash, can achieve the following beneficial effects:

[0021] This invention provides a detoxification method for simultaneously removing dioxins and heavy metals from waste incineration fly ash. First, sodium and potassium salts are removed from the fly ash to prevent reducing the solidification ability of the sintering products formed during high-temperature sintering of the fly ash for heavy metals. Then, the pretreated fly ash solid intermediate is mixed with magnesium and / or calcium salts, and high-temperature sintering is used to react the chlorine from the decomposition of dioxins with the heavy metals to form gaseous heavy metal chlorides, which are then removed. During high-temperature roasting, the magnesium and / or calcium salts react with the ash in the fly ash to form calcium silicate and / or magnesium silicate, thereby enhancing the solidification ability of the internal lattice of the fly ash sintering products. Using this method to detoxify waste incineration fly ash, heavy metal leaching toxicity testing was performed on the detoxified fly ash. The results showed that no heavy metals Hg, Pb, Cd, Cu, and Ni were detected in the leachate, indicating that this method can significantly reduce the leaching risk of residual heavy metals in fly ash. Detailed Implementation

[0022] To further illustrate the technical means and effects of the present invention in achieving the intended purpose, the following detailed description of the specific implementation methods, structures, features and effects of the present invention, in conjunction with preferred embodiments, is provided below.

[0023] Current technologies for the harmless treatment of waste incineration fly ash primarily remove heavy metals by acid leaching to dissolve some of the heavy metals, or by diluting with other substances (dilution method) to reduce heavy metal toxicity, which has legal loopholes. Alternatively, they rely on the principle of high-temperature chlorination and adsorption of heavy metals, using high-temperature melting to react non-volatile heavy metals with chlorinating agents to generate volatile heavy metal chloride vapors, but both methods have limitations in removing a limited range of heavy metals. Furthermore, the effectiveness of existing technologies in removing dioxins from fly ash needs further improvement. While existing technologies can remove dioxins and / or heavy metals to some extent, they do not fully consider the interactions between dioxins, salts, and heavy metals in the fly ash, especially the impact of sodium and potassium salts in the original fly ash on the solidification of residual heavy metals in the treated fly ash.

[0024] This invention employs high-temperature roasting to cause the chlorine formed from the decomposition of dioxins in waste incineration fly ash to react with heavy metals in the fly ash to form volatile heavy metal chlorides, while the non-volatile heavy metal chlorides remain in the sintered body after high-temperature roasting. However, considering that sodium and potassium salts in the original fly ash can affect the strength of the roasted product (sintered body), thus weakening its solidification effect on residual heavy metals, the inventors first remove sodium and potassium salts from the waste incineration fly ash by washing. After solid-liquid separation, the solid phase is dried, and exogenous magnesium and / or calcium salts are added. High-temperature roasting is then used to allow the exogenous magnesium and / or calcium salts to react with the ash in the incineration fly ash at high temperatures to form a sintered body containing calcium silicate and magnesium silicate. The formed calcium silicate and magnesium silicate can enhance the solidification ability of the internal lattice of the sintered body, thereby improving the solidification ability of the fly ash sintered product on residual non-volatile heavy metals, and thus reducing the leaching toxicity of heavy metals in the treated fly ash.

[0025] Furthermore, during the high-temperature roasting process, the chlorine produced by the decomposition of dioxins in the fly ash reacts with the heavy metals in the fly ash to form volatile heavy metal chloride vapors, thus removing some of the heavy metals. Unreacted or non-volatile heavy metal chlorides are solidified by the fly ash sintering products. Since the calcium silicate and magnesium silicate formed during the high-temperature roasting process can enhance the solidification ability of the internal crystal lattice of the sintered body, the leaching toxicity of residual heavy metals in the treated fly ash is reduced. Especially when the original fly ash has a high heavy metal content, and the chlorine produced by the high-temperature decomposition of dioxins in the fly ash is insufficient to react with the heavy metals to form heavy metal chlorides for removal, it is preferable that the magnesium salt is magnesium chloride and the calcium salt is calcium chloride. This can further promote the formation of volatile heavy metal chloride vapors from the heavy metals in the fly ash during the high-temperature sintering process, reducing the total amount of residual heavy metals in the treated fly ash.

[0026] Based on this, the present invention provides a detoxification method for simultaneously removing dioxins and heavy metals from waste incineration fly ash, comprising the following steps:

[0027] (1) Fly ash pretreatment: Sodium and potassium salts in waste incineration fly ash are removed by immersion washing, solid-liquid separation is performed, solid intermediate is obtained and dried;

[0028] (2) Simultaneous removal of dioxins and heavy metals from fly ash: Add magnesium salts and / or calcium salts at 5% to 25% of the mass of the dried solid intermediate in (1), mix and then roast at high temperature under a protective gas atmosphere so that the chlorine from the decomposition of dioxins in fly ash reacts with the heavy metals to form gaseous heavy metal chlorides which are discharged with the flue gas; during the high-temperature roasting process, magnesium salts and / or calcium salts react with the ash in fly ash to form calcium silicate and / or magnesium silicate, thereby enhancing the solidification ability of the internal lattice of the fly ash sintering product, improving the solidification effect of the sintered body on residual heavy metals, and reducing the leaching toxicity of residual heavy metals in the treated fly ash. The ash in fly ash includes metal oxides and inorganic salts. The metal oxides are mainly composed of silicon dioxide (SiO2) and aluminum oxide (Al2O3), which usually account for about 50%-70%. The added magnesium salts or calcium salts can react with the ash in fly ash under high temperature conditions to form magnesium silicate or calcium silicate, which can enhance the solidification ability of the internal lattice of the sintered body for heavy metals.

[0029] Preferably, the high-temperature roasting temperature is 1000–1200℃, and the roasting time is 3–5 hours. This allows volatile heavy metals, semi-volatile heavy metals, and a small amount of non-volatile heavy metals in fly ash to form corresponding gaseous heavy metal chlorides during the formation of magnesium silicate and / or calcium silicate. The high-temperature roasting temperature of 1000–1200℃, preferably 1100–1200℃, facilitates the reaction of magnesium salts and calcium salts with the ash in fly ash to form magnesium silicate and calcium silicate, thereby enhancing the strength of the sintered body and reducing the leaching of residual heavy metals. The roasting time of 3–5 hours allows volatile heavy metals (such as Hg), semi-volatile heavy metals (such as Pb, Zn, Cd), and a small amount of non-volatile heavy metals (such as Cu, Ni) in fly ash to form corresponding gaseous heavy metal chlorides. The high-temperature gas is then concentrated and enriched to remove or recover heavy metals before being discharged.

[0030] In some embodiments, after detoxification treatment of waste incineration fly ash using this method, the total amounts of Hg, Pb, Zn, Cd, Cu, and Ni in the molten residue after fly ash treatment are reduced by 96.63%, 98.3%, 82.63%, 96%, 53.3%, and 43%, respectively. The leaching toxicity of Hg, Pb, Zn, Cd, Cu, and Ni is reduced by 99.92%, 99.71%, 97.33%, 99.93%, 99.90%, and 96.37%, respectively. The detection limits for Hg, Pb, Cd, and Ni are 0.00002 mg / L, 0.022 mg / L, 0.002 mg / L, and 0.009 mg / L, respectively.

[0031] The fly ash pretreatment employs countercurrent water washing or acid washing, with multiple immersions to remove sodium and potassium salts from the fly ash, followed by solid-liquid separation to obtain a solid intermediate. In some embodiments, the fly ash pretreatment uses a three-stage countercurrent water washing process, with a fly ash mass to immersion liquid volume ratio of 1:1 to 3, and 3 to 6 washes; or a three-stage countercurrent acid washing process, with a fly ash mass to immersion liquid volume ratio of 1:1 to 3, and 2 to 4 acid washes. Preferably, the acid concentration in the immersion liquid is 20% to 40%. Acid washing removes sodium and potassium salts from the fly ash while also dissolving some of the heavy metals. The acid-soluble heavy metals are removed through solid-liquid separation. The separated liquid phase can also be used to recover dissolved heavy metals, sodium and potassium salts for heavy metal refining or industrial salt preparation, thus improving the resource utilization of waste incineration fly ash.

[0032] In some embodiments, the magnesium salt is magnesium chloride. After fly ash pretreatment, it is added at 15% of the mass of the solid intermediate. The solid intermediate and magnesium chloride are uniformly mixed by mechanical stirring or ball milling. The mixture is then calcined at 1150°C for 3 hours and cooled to obtain the calcined product, which can be used as a building material such as roadbed and filler.

[0033] The following are examples.

[0034] Example 1

[0035] S1: Most of the soluble sodium and potassium salts in the fly ash from waste incineration are removed by a three-stage countercurrent water washing process. The ratio of fly ash mass (g) to washing liquid volume (mL) is 1:3, and the washing is performed three times. After washing, solid-liquid separation is performed to obtain a solid intermediate. The separated liquid phase can also be used to recover sodium and potassium salts.

[0036] S2: After drying the moisture in the solid intermediate, the dried solid intermediate is physically mixed with magnesium salts such as MgCl2 by mechanical stirring. The amount of MgCl2 added is 15% of the fly ash mass. The mixture is then calcined at high temperature in a tube furnace under an air atmosphere at 1150℃ for 3 hours. The resulting molten residue, after cooling, is the detoxified fly ash, which can be used as a building material such as roadbed or filler. The high-temperature gases containing heavy metal chlorides can be further concentrated and enriched to remove or recover the heavy metals before being discharged.

[0037] After the cooled molten residue was crushed, its dioxin and soluble chlorine content, as well as the heavy metal concentration and leaching toxicity in its leachate, were tested. The dioxin content was tested using HJ 77.3-2008 "Determination of Dioxins in Solid Waste - Isotope Dilution High-Resolution Gas Chromatography-High-Resolution Mass Spectrometry". The leachate was prepared using HJ 557-2010 "Leaching Toxicity of Solid Waste - Horizontal Oscillation Method" to test its heavy metal leaching toxicity. The total heavy metal content was tested using HJ 781-2016 "Determination of 22 Metallic Elements in Solid Waste - Inductively Coupled Plasma Atomic Emission Spectrometry". The test results for each indicator are shown in Tables 1 and 2.

[0038] Example 2

[0039] S1: The fly ash is subjected to a three-stage countercurrent acid leaching process to remove sodium and potassium salts, as well as some acid-soluble heavy metals. The acid used is HCl, and the HCl concentration in the leaching solution is approximately 30% by volume. The fly ash mass (g) to acid leaching solution volume (mL) ratio is 1:2, and the leaching is performed twice. After acid leaching, solid-liquid separation is carried out to obtain a solid intermediate.

[0040] S2: After drying the moisture in the solid intermediate, the dried solid intermediate is physically mixed with magnesium salts such as MgCl2 by mechanical stirring. The amount of MgCl2 added is 15% of the fly ash mass. The mixture is then calcined at high temperature in a tube furnace under an air atmosphere at 1150℃ for 3 hours. After calcination, a molten residue is obtained, which, after cooling, becomes the detoxified fly ash.

[0041] After the cooled molten residue was crushed, the dioxin and soluble chlorine content in the treated fly ash, as well as the heavy metal concentration and heavy metal leaching toxicity in its leachate, were tested using the same method as in Example 1. The results are shown in Tables 1 and 2.

[0042] Comparative Example 1

[0043] The fly ash from waste incineration was dried and crushed without any treatment to detect the soluble chlorine and dioxin content in the fly ash, as well as the total heavy metal content and leaching toxicity in its leachate. The results are shown in Tables 1 and 2.

[0044] Comparative Example 2

[0045] S1: After drying the fly ash from waste incineration, it is directly roasted at high temperature in a tubular furnace in an air atmosphere without any pretreatment. The roasting temperature is 1150℃ and the roasting time is 3h. After roasting, molten residue is obtained, which is then cooled to obtain detoxified fly ash.

[0046] S2: After the cooled molten residue was crushed, its soluble chlorine and dioxin content were tested, and the total heavy metal content and leaching toxicity of its leachate were tested. The results are shown in Table 1 and Table 2.

[0047] Using the original fly ash from waste incineration in Comparative Example 1 as a control, the total heavy metal content, leaching toxicity, soluble chlorine, and dioxin content in the fly ash after treatment in Examples 1, 2, and 2 were tested. The test results are shown in Tables 1 and 2.

[0048] Table 1. Dioxin and soluble chloride content in fly ash before and after treatment.

[0049]

[0050] The detection of dioxins in fly ash before and after treatment in Table 1 was carried out according to the method specified in HJ 77.3. The determination of soluble chlorine content before and after fly ash treatment was performed by preparing leachate using the method of HJ 557 and determining it using ion chromatography or silver nitrate titration.

[0051] As shown in Table 1, compared with the untreated incinerated fly ash in Comparative Example 1, the dioxin and soluble chlorine content in the fly ash was significantly reduced after detoxification treatment using the methods in Examples 1 and 2. In Example 1, the dioxin removal rate after detoxification treatment was 97.74%, and the dioxin concentration in the fly ash was as low as 6.8 ng / kg. In Example 2, the dioxin removal rate after detoxification treatment was 97.58%, and the dioxin concentration in the fly ash was as low as 7.3 ng / kg.

[0052] Compared to Examples 1 and 2, the fly ash in Comparative Example 2 had relatively lower dioxin and soluble chlorine content after direct high-temperature calcination, but the reason is unknown. It is speculated that the added magnesium salt is magnesium chloride, whose chlorine competes with the chlorine decomposing from dioxins, which may inhibit the decomposition of dioxins to some extent.

[0053] Table 2. Heavy metal detoxification effect of fly ash before and after treatment.

[0054]

[0055] In Table 2, “ND” means “not detected”. The total heavy metals in Table 2 refer to the total amount of heavy metals remaining in fly ash.

[0056] The fly ash treatment products were used to prepare leachate according to the HJ 557 method (the method specified in HJ1134), and the total amount of heavy metals and leaching toxicity were tested.

[0057] As shown in Table 2, after detoxification treatment of fly ash using this method, the total amounts of Hg, Pb, Zn, Cd, Cu, and Ni in the molten residue of the fly ash were reduced by more than 96.63%, 98.3%, 82.63%, 96%, 53.3%, and 43%, respectively. Specifically, no heavy metals Hg, Pb, Cd, or Ni were detected in the leachate of Example 1 and Example 2. The detection limits for Hg, Pb, Cd, and Ni were 0.00002 mg / L, 0.022 mg / L, 0.002 mg / L, and 0.009 mg / L, respectively. This indicates that detoxification treatment of waste incineration fly ash using this method can significantly reduce the leaching risk of residual heavy metals such as Hg, Pb, Cd, Cu, and Ni. Furthermore, after using this method to detoxify fly ash from waste incineration, the leaching toxicity of the heavy metal Zn was reduced by 97.33%, and its leaching toxicity concentration could be as low as 0.6 mg / L.

[0058] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A detoxification method for simultaneously removing dioxins and heavy metals from waste incineration fly ash, characterized by, It comprises the following steps: (1) fly ash pretreatment: sodium salt and potassium salt in the waste incineration fly ash are removed by immersion washing, and a solid-phase intermediate is obtained by solid-liquid separation and drying; the fly ash pretreatment adopts three-stage countercurrent water washing or acid washing, and the solid-phase intermediate is obtained by solid-liquid separation after multiple immersion washing; (2) simultaneous removal of dioxins and heavy metals in fly ash: according to 5%~25% of the mass of the solid-phase intermediate after drying in step (1), magnesium salt and / or calcium salt is added, mixed and then high-temperature calcined to make the chlorine decomposed from dioxins in fly ash react with heavy metals to form gaseous heavy metal chlorides and remove heavy metals in fly ash; during high-temperature calcination, magnesium salt and / or calcium salt reacts with ash in fly ash at high temperature to form magnesium silicate and / or calcium silicate, so as to enhance the solidification capacity of the internal crystal lattice of the fly ash sintering product and reduce the leaching toxicity of residual heavy metals in fly ash; The magnesium salt that reacts with ash in fly ash at high temperature to form magnesium silicate includes magnesium chloride, and the calcium salt that reacts with ash to form calcium silicate includes calcium chloride; during the formation of magnesium silicate and / or calcium silicate, volatile heavy metals, semi-volatile heavy metals and a small amount of difficult-to-volatile heavy metals in fly ash form corresponding gaseous heavy metal chlorides, the high-temperature calcination temperature is 1000~1200℃, and the calcination time is 3-5h; the volatile heavy metal includes Hg, the semi-volatile heavy metal includes Pb, Zn and Cd, and the difficult-to-volatile heavy metal includes Cu and Ni.

2. The method of claim 1, wherein, The magnesium salt is magnesium chloride, and the high-temperature calcination temperature in step (2) is 1100~1200℃ to make magnesium chloride react with ash in fly ash to form magnesium silicate.

3. The method of claim 2, wherein, The addition amount of magnesium chloride is 15%~25% of the mass of the solid-phase intermediate.

4. The method of claim 3, wherein, The fly ash pretreatment adopts three-stage countercurrent water washing, and the volume ratio of fly ash mass to immersion washing liquid is 1:1~3, and water washing is 3~6 times.

5. The method of claim 4, wherein, The fly ash pretreatment adopts three-stage countercurrent acid washing, and the volume ratio of fly ash mass to immersion washing liquid is 1:1~3, and acid washing is 2~4 times.

6. The method of claim 5, wherein, The concentration of acid in the immersion washing liquid is 20%~40%.

Images