Detoxification method for simultaneously removing dioxin and heavy metal in waste incineration fly ash

Abstract

The invention relates to a detoxification method for simultaneously removing dioxin and heavy metal in waste incineration fly ash, which comprises the following steps of: pretreating fly ash and simultaneously removing dioxin and heavy metal in fly ash, namely, removing sodium salt and potassium salt in fly ash by adopting an immersion cleaning mode; the method comprises the following steps: pre-treating fly ash to avoid reducing the curing capacity of a sintering product formed by high-temperature sintering of the fly ash on heavy metals, separating the pre-treated fly ash to obtain a solid phase, mixing the solid phase with magnesium salt and / or calcium salt, and carrying out high-temperature roasting, so that chlorine decomposed by dioxin in the fly ash reacts with the heavy metals to form gaseous heavy metal chloride to remove the heavy metals in the fly ash; in the high-temperature roasting process, the magnesium salt and / or the calcium salt and ash in the fly ash form calcium silicate and / or magnesium silicate under high-temperature reaction, so that the curing capacity of crystal lattices in a fly ash sintering product is enhanced. After the waste incineration fly ash is subjected to detoxification treatment by adopting the method, heavy metals Hg, Pb, Cd, Cu and Ni are not detected in the fly ash leachate, so that the leaching risk of the heavy metals remained in the fly ash can be obviously reduced.

Description

Technical Field

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

[0002] The incineration of domestic waste complies with the principles of solid waste treatment of reduction, harmlessness and resource utilization, and is a waste disposal method encouraged by national policies. However, the fly ash generated during the incineration process is an industry problem. At present, the most common method of treating fly ash is to stabilize / solidify it and then landfill it. Landfilling only stabilizes the pollutants in the fly ash and preserves them, which poses a risk of long-term migration of pollutants. In addition, it wastes both land resources and heavy metals that can be utilized. Moreover, with the continuous reduction of landfill capacity and the rapid advancement of the construction of "zero-waste cities" across the country, the unsustainability of this treatment method has become increasingly prominent. Therefore, achieving harmless resource utilization of fly ash from waste incineration is an effective way to solve the drawbacks of existing fly ash landfill.

[0003] Fly ash contains heavy metals with complex components, and is also rich in various dioxins, chloride salts (such as sodium chloride, potassium chloride) and other substances. Among them, polychlorinated dibenzodioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are highly toxic chemicals. However, the existing harmless resource utilization of waste incineration fly ash mainly considers one of these aspects. For example, patent CN

[0004] 109437573B discloses a method for harmlessly treating dioxins in waste incineration fly ash, which takes into account the detoxification of dioxins in waste incineration fly ash. Specifically, waste incineration fly ash, waste glass powder, pickling sludge and dolomite powder are pressed into shape, and foam microcrystalline glass is prepared by high-temperature melting (1000-1250°C). During the high-temperature melting process for preparing the foam microcrystalline glass, the dioxins in the waste incineration fly ash are cracked at high temperature and the chlorine atoms react with alkaline earth metal oxides (CaO and MgO decomposed from dolomite at high temperature) to solidify in the foam microcrystalline glass. The generated flue gas is subjected to a rapid cooling treatment to cool the flue gas to below 200°C to avoid the residual chloride from synthesizing dioxins again.

[0005] Patent CN 108715519B discloses a method for harmless resource utilization of waste incineration fly ash, which considers the removal of heavy metals in waste incineration fly ash. First, calcium chloride and magnesium chloride are pressed into spherical particles with the incineration fly ash, and then the granulated fly ash is calcined in a rotary kiln (temperature 900-1100°C) to make the non-volatile heavy metals in the fly ash react with the chlorinating agent to form volatile heavy metal chlorides, and the kaolin adsorption layer is used to adsorb the heavy metal chloride vapor at high temperature. The adsorbed kaolin is mixed with the harmless fly ash and used as a building material. The removal rate of heavy metals (Pb, Cd, Cu and Zn) in the incineration fly ash after treatment can reach 90%. However, non-volatile heavy metal chlorides such as manganese chloride (MnCl 2 ), chromium chloride (CrCl 3 ) has a boiling point above 1100°C. It is difficult to remove heavy metals such as manganese and chromium by forming heavy metal chloride vapor at 900-1100°C. Heavy metals such as manganese and chromium still remain in the treated fly ash in the form of 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 harmless resource utilization of fly ash from waste incineration, which firstly performs low-temperature pyrolysis (400-500°C) of the fly ash to remove dioxins, and then performs acid washing (pH of the acid washing liquid is less than 2.64) to dissolve the heavy metals in the fly ash. After solid-liquid separation, the solid phase is naturally air-dried and added to the bottom ash of the waste incineration for use as a 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 liquid, and the remaining liquid phase is subjected to heavy metal chelating agents to remove heavy metals. Although this method can achieve the simultaneous removal of dioxins and heavy metals in waste incineration fly ash, the dioxin concentration of the fly ash after low-temperature pyrolysis treatment can reach 17ng-TEQ / kg, but it still needs to be further reduced; the removal rate of heavy metal ions using heavy metal chelating agents is 75% to 87%, but the removal rate of heavy metals is low, and there are many types of heavy metals in waste incineration fly ash, some of which (such as Pb, Hg, Cr, As, Sn) are difficult to dissolve in acid, such as lead (Pb) exists in fly ash in different oxidation states, and some forms of lead are difficult to dissolve in acid; mercury (Hg) exists in fly ash mainly 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. In addition, the existing technology does not fully consider the mutual influence between dioxins, salts and heavy metals in waste incineration fly ash, especially the influence of sodium salts and potassium salts in the original fly ash on the leaching toxicity of heavy metals remaining in the fly ash after high temperature treatment. Therefore, a detoxification method that can synergistically remove heavy metals and dioxins in waste incineration fly ash for a long time, especially reducing the leaching toxicity of heavy metals remaining in the fly ash after treatment, is studied to promote the utilization of waste incineration fly ash harmless resource. Summary of the invention

[0007] In view of the above defects or improvement needs of the prior art, the present invention provides a detoxification method for simultaneously removing dioxins and heavy metals in waste incineration fly ash. The purpose is to remove the sodium salt and potassium salt in the fly ash by leaching first, after solid-liquid separation, mix the dried solid intermediate with magnesium salt and / or calcium salt, and react the chlorine decomposed by dioxins in the fly ash with heavy metals to form gaseous heavy metal chlorides through high-temperature sintering. At the same time, the magnesium salt and calcium salt added during the high-temperature sintering process react with the ash in the fly ash to form magnesium silicate and calcium silicate, which can enhance the solidification ability of the internal lattice of the sintered body and reduce the leaching toxicity of the residual heavy metals in the fly ash, thereby solving the technical problems that the types of heavy metals in the waste incineration fly ash removed by high-temperature roasting are limited or the heavy metal removal effect is poor, and the residual heavy metals have the risk of leaching in the later stage.

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

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

[0010] (2) Simultaneous removal of dioxins and heavy metals from fly ash: adding magnesium salt and / or calcium salt according to 5% to 25% of the mass of the solid intermediate after drying in (1), mixing and then calcining at high temperature so that the chlorine decomposed from dioxins in the fly ash reacts with the heavy metals to form gaseous heavy metal chlorides to remove the heavy metals in the fly ash; during the high-temperature calcination process, the magnesium salt and / or calcium salt reacts with the ash in the fly ash at high temperature to form calcium silicate and / or magnesium silicate, so as to enhance the solidification ability of the internal lattice of the fly ash sintering product and reduce the leaching toxicity of the residual heavy metals in the fly ash.

[0011] Preferably, in the method, during the formation of magnesium silicate and / or calcium silicate, 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, the high-temperature roasting temperature is 1000-1200°C, 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 low-volatile heavy metals include Cu and Ni.

[0013] Preferably, in the method, the magnesium salt that reacts with ash in fly ash at high temperature to form magnesium silicate comprises magnesium chloride, and the calcium salt comprises 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 the magnesium chloride reacts with the ash in the 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 three-stage countercurrent water washing or acid washing, and after multiple washings, solid-liquid separation is performed to obtain a solid intermediate.

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

[0018] Preferably, in the method, the fly ash pretreatment adopts three-stage countercurrent pickling, and the volume ratio of fly ash mass to leaching liquid is 1:1 to 3, and the pickling is performed 2 to 4 times.

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

[0020] In general, compared with the prior art, the above technical solution conceived by the present invention can achieve the following beneficial effects because the present invention takes into account the mutual influence between dioxins, sodium salts, potassium salts and heavy metals in waste incineration fly ash:

[0021] The present invention provides a detoxification method for simultaneously removing dioxins and heavy metals from fly ash from garbage incineration. The method first removes sodium salts and potassium salts from fly ash to avoid reducing the solidification ability of sintered products formed by high-temperature sintering of fly ash for heavy metals; then the pretreated fly ash solid phase intermediate is mixed with magnesium salts and / or calcium salts, and high-temperature sintering is used to make the chlorine decomposed from dioxins in the fly ash react with heavy metals to form gaseous heavy metal chlorides for removal; during the high-temperature roasting process, the magnesium salts and / or calcium salts react with the ash in the fly ash to form calcium silicate and / or magnesium silicate under high-temperature reaction to enhance the solidification ability of the internal lattice of the fly ash sintered product. The method is used to detoxify fly ash from garbage incineration, and the fly ash after detoxification is tested for heavy metal leaching toxicity. As a result, no heavy metals Hg, Pb, Cd, Cu and Ni are detected in the leaching solution, indicating that the method can significantly reduce the leaching risk of residual heavy metals in the fly ash. DETAILED DESCRIPTION

[0022] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation method, structure, characteristics and effects of the present invention are described in detail below in combination with the preferred embodiments.

[0023] The existing waste incineration fly ash harmless treatment technology mainly removes heavy metals from fly ash by acid leaching to dissolve the heavy metals in the waste incineration fly ash, or reduces the toxicity of heavy metals by mixing and diluting with other substances (dilution method), which has legal loopholes; or based on the principle of high-temperature chlorination and adsorption of heavy metals, the non-volatile heavy metals in the fly ash are reacted with the chlorinating agent to generate volatile heavy metal chloride vapor by high-temperature melting, but there is a problem of limited types of heavy metals removed. The effect of the existing waste incineration fly ash harmless treatment technology on removing dioxins from fly ash needs to be further improved. Although the existing waste incineration fly ash harmless treatment technology can achieve the removal of dioxins and / or heavy metals in waste incineration fly ash to a certain extent, it does not fully consider the mutual influence between dioxins, salts and heavy metals in waste incineration fly ash, especially the influence of sodium salts and potassium salts in the original fly ash on the solidification effect of residual heavy metals in the fly ash after treatment.

[0024] The present invention uses high-temperature roasting to decompose dioxins in the fly ash from garbage incineration to form chlorine and heavy metals in the fly ash to form volatile heavy metal chlorides, while the difficult-to-volatilize heavy metal chlorides remain in the sintered body after high-temperature roasting. However, it is considered that the sodium salt and potassium salt in the original fly ash will affect the strength of the roasted product (sintered body), resulting in a weakened solidification effect on the residual heavy metals. The inventor first removes the sodium salt and potassium salt in the fly ash from the garbage incineration by washing, and after solid-liquid separation, the solid phase is dried, and exogenous magnesium salts and / or calcium salts are added. High-temperature roasting is used to react the exogenous magnesium salt and / or calcium salt with the ash in the incineration fly ash at high temperature to form a sintered body containing calcium silicate and magnesium silicate, wherein 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 sintering product to the residual difficult-to-volatilize heavy metals, thereby reducing the leaching toxicity of the heavy metals in the fly ash after treatment.

[0025] In addition, during the high-temperature roasting process, the chlorine generated by the decomposition of dioxins in the fly ash reacts with the heavy metals in the fly ash to form volatile heavy metal chloride vapor to remove part of the heavy metals, while the unreacted or difficult-to-volatize heavy metal chlorides are solidified by the fly ash sintering product. Since the calcium silicate and magnesium silicate formed during the high-temperature roasting process can enhance the solidification ability of the lattice inside the sintered body, the leaching toxicity of the residual heavy metals in the fly ash after treatment is reduced. In particular, for the high content of heavy metals in the original fly ash, the chlorine generated by the high-temperature decomposition of dioxins in the fly ash is not enough to react with the heavy metals to form heavy metal chlorides for removal. Preferably, the magnesium salt is magnesium chloride and the calcium salt is calcium chloride, which can further promote the formation of volatile heavy metal chloride vapor from the heavy metals in the fly ash during the high-temperature sintering process, thereby reducing the total amount of residual heavy metals in the fly ash after treatment.

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

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

[0028] (2) Simultaneous removal of dioxins and heavy metals from fly ash: Add magnesium salt and / or calcium salt according to 5% to 25% of the mass of the solid intermediate after drying in (1), mix and then calcine at high temperature in a protective gas atmosphere so that the chlorine decomposed from dioxins in the fly ash reacts with heavy metals to form gaseous heavy metal chlorides which are discharged with the flue gas; during the high-temperature calcination process, the magnesium salt and / or calcium salt reacts with the ash in the fly ash to form calcium silicate and / or magnesium silicate at high temperature to enhance the solidification ability of the internal lattice of the fly ash sintering product, improve the solidification effect of the sintered body on the residual heavy metals, and reduce the leaching toxicity of the residual heavy metals in the fly ash after treatment. The ash in the fly ash includes metal oxides and inorganic salts, among which the metal oxides are silicon dioxide (SiO 2 ) and aluminum oxide (Al 2 O 3 ) is the main component, usually accounting for about 50%-70%. The added magnesium salt or calcium salt can react with the ash in the 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°C, and the roasting time is 3-5h, so that the volatile heavy metals, semi-volatile heavy metals and a small amount of non-volatile heavy metals in the fly ash can form corresponding gaseous heavy metal chlorides in the process of forming magnesium silicate and / or calcium silicate. The high temperature roasting temperature of 1000-1200°C, preferably 1100-1200°C, is conducive to the reaction of magnesium salts, calcium salts and ash in the fly ash to form magnesium silicate and calcium silicate, so as to enhance the strength of the sintered body and reduce the leaching of residual heavy metals; the roasting time of 3-5h can make the volatile heavy metals (such as Hg, etc.), semi-volatile heavy metals (such as Pb, Zn, Cd, etc.) and a small amount of non-volatile heavy metals (such as Cu, Ni, etc.) in the fly ash form corresponding gaseous heavy metal chlorides, and the high temperature gas is discharged after being concentrated and enriched to remove or recover heavy metals.

[0030] In some embodiments, after the waste incineration fly ash is detoxified by the present 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, and the leaching toxicity of Hg, Pb, Zn, Cd, Cu and Ni are reduced by 99.92%, 99.71%, 97.33%, 99.93%, 99.90% and 96.37%, respectively, wherein the detection limits of 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 adopts countercurrent water washing or acid washing, and the sodium salt and potassium salt in the fly ash are removed by multiple leaching, and the solid-liquid separation is performed to obtain a solid phase intermediate. In some embodiments, the fly ash pretreatment adopts three-stage countercurrent water washing, and the volume ratio of the fly ash mass to the leaching liquid is 1:1-3, and the water washing is 3-6 times; or three-stage countercurrent acid washing is adopted, and the volume ratio of the fly ash mass to the leaching liquid is 1:1-3, and the acid washing is 2-4 times, and the concentration of the acid in the leaching liquid is preferably 20%-40%. Acid washing can not only remove the sodium salt and potassium salt in the fly ash, but also dissolve part of the heavy metals in the fly ash, and remove the acid-soluble heavy metals by solid-liquid separation, wherein the separated liquid phase can also recover the dissolved heavy metals, sodium salts and potassium salts, which are used to refine heavy metals or prepare industrial salts, which is conducive to improving the resource utilization of waste incineration fly ash.

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

[0033] The following are examples

[0034] Example 1

[0035] S1: The waste incineration fly ash is washed by three-stage countercurrent water washing to remove most of the soluble sodium and potassium salts in the fly ash, wherein the ratio of fly ash mass (g) to water washing liquid volume (mL) is 1:3, and the number of water washings is 3 times. After water 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 the water of the solid intermediate is dried, the dried solid intermediate is mixed with a magnesium salt such as MgCl 2 Physical mixing was performed by mechanical stirring, wherein MgCl 2 The amount of addition is 15% of the fly ash mass, and it is calcined in a tube furnace under air atmosphere at a high temperature of 1150°C for 3 hours. After calcination, the molten residue is obtained, and after cooling, the fly ash after detoxification treatment is obtained, which can be used as building materials such as roadbed and filler. The high-temperature gas containing heavy metal chlorides can also be discharged after concentration and enrichment to remove or recover heavy metals.

[0037] After the cooled molten residue was crushed, the dioxin and soluble chlorine content, as well as the heavy metal concentration and leaching toxicity in the leaching solution were tested. HJ 77.3-2008 "Determination of dioxins in solid waste by isotope dilution high-resolution gas chromatography-high-resolution mass spectrometry" was used to test the dioxin content; HJ 557-2010 "Solid waste leaching toxicity leaching method horizontal oscillation method" was used to prepare the leaching solution and test its heavy metal leaching toxicity; HJ 781-2016 "Determination of 22 metal elements in solid waste by inductively coupled plasma emission spectrometry" was used to test the total amount of heavy metals. The test results of each index are shown in Tables 1 and 2.

[0038] Example 2

[0039] S1: The fly ash is subjected to a three-stage countercurrent acid leaching method to remove sodium salts, potassium salts and some acid-soluble heavy metals in the fly ash, wherein the acid used is HCl, and the HCl concentration in the leaching liquid is about 30% by volume. The fly ash mass (g) and the acid washing liquid volume (mL) are 1:2, and the acid washing is performed twice, and solid-liquid separation is performed after the acid washing to obtain a solid intermediate.

[0040] S2: After the water of the solid intermediate is dried, the dried solid intermediate is mixed with a magnesium salt such as MgCl 2 Physical mixing was performed by mechanical stirring, wherein MgCl 2 The addition amount is 15% of the fly ash mass, and high-temperature calcination is carried out in a tubular furnace under an air atmosphere. The calcination temperature is 1150°C and the calcination time is 3 hours. After calcination, a molten residue is obtained, which is the detoxified fly ash after cooling.

[0041] After the cooled molten residue was crushed, the dioxin and soluble chlorine contents in the treated fly ash, as well as the heavy metal concentration and heavy metal leaching toxicity in the leaching solution were detected 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 garbage incineration was dried and crushed without any treatment, and the soluble chlorine content and dioxin content in the fly ash were tested. The total amount of heavy metals and leaching toxicity in the leaching solution were also tested. The results are shown in Tables 1 and 2.

[0044] Comparative Example 2

[0045] S1: After the waste incineration fly ash is dried, it is directly calcined at high temperature in a tubular furnace in an air atmosphere without any pretreatment. The calcination temperature is 1150°C and the calcination time is 3 hours. After calcination, a molten residue is obtained, which is the detoxified fly ash after cooling.

[0046] S2: After the cooled molten residue is crushed, its soluble chlorine and dioxin contents are tested, and its leachate is tested for the total amount of heavy metals and leaching toxicity. The results are shown in Tables 1 and 2.

[0047] Taking the original fly ash from waste incineration in Comparative Example 1 as a control, the total amount of heavy metals, leaching toxicity, soluble chlorine and dioxin content in the fly ash after treatment in Example 1, Example 2 and Comparative Example 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 carried out by preparing the leaching solution according to the HJ 557 method and determining it by ion chromatography or silver nitrate volumetric method.

[0051] It can be seen from the results in Table 1 that compared with the fly ash from incineration of garbage that was not detoxified in Comparative Example 1, the detoxification methods of Example 1 and Example 2 were used to detoxify the fly ash from incineration of garbage. The dioxin and soluble chlorine contents in the fly ash after detoxification were significantly reduced. The dioxin removal rate of the fly ash in Example 1 after detoxification was 97.74%, and the dioxin concentration in the fly ash after treatment was as low as 6.8 ng / kg; the dioxin removal rate of the fly ash in Example 2 after detoxification was 97.58%, and the dioxin concentration in the fly ash after treatment was as low as 7.3 ng / kg.

[0052] Compared with Example 1 and Example 2, the dioxin and soluble chlorine contents of the fly ash in Comparative Example 2 after direct high-temperature calcination are relatively lower, but the reason is unknown. It is speculated that the reason may be that the added magnesium salt is magnesium chloride, and its chlorine competes with the chlorine decomposed by dioxins, which may have a certain inhibitory effect on the decomposition of dioxins.

[0053] Table 2 Detoxification effect of heavy metals in fly ash before and after treatment

[0054]

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

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

[0057] It can be seen from the results in Table 2 that after the fly ash is detoxified by the method, the total amount of Hg, Pb, Zn, Cd, Cu and Ni in the molten residue in the fly ash is reduced by 96.63%, 98.3%, 82.63%, 96%, 53.3% and 43% respectively, wherein no heavy metals Hg, Pb, Cd and Ni are detected in the leaching solution in Example 1, and no heavy metals Hg, Pb, Cd, Cu and Ni are detected in the leaching solution in Example 2. The detection limits of Hg, Pb, Cd and Ni are 0.00002 mg / L, 0.022 mg / L, 0.002 mg / L and 0.009 mg / L respectively, that is, after the waste incineration fly ash is detoxified by the method, the leaching risk of residual heavy metals such as Hg, Pb, Cd, Cu and Ni can be significantly reduced. In addition, after the waste incineration fly ash is detoxified by the method, the leaching toxicity of the heavy metal Zn is reduced by 97.33%, and the leaching toxicity concentration can be as low as 0.6 mg / L.

[0058] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A detoxification method for simultaneously removing dioxins and heavy metals from waste incineration fly ash, characterized in that: The steps include: (1) Fly ash pretreatment: Sodium and potassium salts in waste incineration fly ash are removed by leaching, solid-liquid separation is performed to obtain a solid intermediate and then dried; (2) Simultaneous removal of dioxins and heavy metals from fly ash: adding magnesium salt and / or calcium salt according to 5% to 25% of the mass of the solid intermediate after drying in (1), mixing and then calcining at high temperature so that the chlorine decomposed from dioxins in the fly ash reacts with the heavy metals to form gaseous heavy metal chlorides to remove the heavy metals in the fly ash; during the high-temperature calcination process, the magnesium salt and / or calcium salt reacts with the ash in the fly ash to form calcium silicate and / or magnesium silicate at high temperature, so as to enhance the solidification ability of the internal lattice of the fly ash sintering product and reduce the leaching toxicity of the residual heavy metals in the fly ash.

2. The method according to claim 1, characterized in that In the process of forming magnesium silicate and / or calcium silicate, volatile heavy metals, semi-volatile heavy metals and a small amount of non-volatile heavy metals in the fly ash are transformed into corresponding gaseous heavy metal chlorides. The high-temperature roasting temperature is 1000-1200°C and the roasting time is 3-5h.

3. The method according to claim 2, characterized in that The volatile heavy metals include Hg, the semi-volatile heavy metals include Pb, Zn and Cd, and the less volatile heavy metals include Cu and Ni.

4. The method according to claim 3, characterized in that The magnesium salt that reacts with the ash in the fly ash at high temperature to form magnesium silicate includes magnesium chloride, and the calcium salt includes calcium chloride.

5. The method according to claim 4, characterized in that The magnesium salt is magnesium chloride, and the high temperature roasting temperature in step (2) is 1100-1200° C. so that the magnesium chloride reacts with the ash in the fly ash to form magnesium silicate.

6. The method according to claim 5, characterized in that The amount of magnesium chloride added is 15% to 25% of the mass of the solid intermediate.

7. The method according to any one of claims 1 to 6, characterized in that: The fly ash pretreatment adopts three-stage countercurrent water washing or acid washing, and after multiple washings, solid-liquid separation is performed to obtain a solid intermediate.

8. The method according to claim 7, characterized in that The fly ash pretreatment adopts three-stage countercurrent water washing, and the volume ratio of fly ash mass to leaching liquid is 1:1-3, and the water washing is 3-6 times.

9. The method according to claim 7, characterized in that The fly ash pretreatment adopts three-stage countercurrent pickling, and the volume ratio of fly ash mass to leaching liquid is 1:1-3, and the pickling is performed 2-4 times.

10. The method according to claim 9, characterized in that The acid concentration in the leaching solution is 20% to 40%.

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