Method for hydrothermal chlorine reduction, heavy metal solidification and tobermorite synthesis of waste incineration fly ash

Abstract

The invention discloses a method for hydrothermally reducing chlorine, solidifying heavy metals and synthesizing tobermorite from waste incineration fly ash, which comprises the following steps: step 1, regulating the proportion of calcium, silicon and aluminum, stirring and mixing, and when a silicon source is added, the molar ratio of calcium to (silicon + aluminum) in the mixed ingredients is 0.80-0.85, and the molar ratio of aluminum to (silicon + aluminum) is 0.001-0.22; step 2, mixing and stirring a strong alkali solution: adding the strong alkali solution, mixing, transferring into a container, stirring and mixing, and sealing; step 3, hydrothermal reaction; and step 4, carrying out solid-liquid separation to obtain a hydrothermal solid product and a hydrothermal liquid product, wherein the hydrothermal solid product comprises tobermorite. According to the method, calcium, silicon and aluminum in the waste incineration fly ash are fully recycled by regulating and controlling the proportion of calcium, silicon and aluminum, and the performance of the synthesized tobermorite is also improved.

Description

Technical Field

[0001] The invention relates to the technical field of harmless treatment and resource utilization of waste incineration fly ash, and in particular to a method for hydrothermal chlorination reduction and solidification of heavy metals in waste incineration fly ash and synthesis of tobermorite. Background Art

[0002] Incineration technology is currently the mainstream means of treating urban domestic waste. Incineration will produce some by-products, including fly ash from incineration, which is difficult to treat. Fly ash from incineration accounts for about 3-5% of the total incineration volume. Fly ash from incineration is a hazardous waste with high environmental risks, posing a threat to natural water bodies and human bodies. Fly ash from incineration contains dioxins and heavy metals, and its chloride content can exceed 30% of the mass of the fly ash. However, the high content of calcium and chlorine in fly ash from incineration has potential utilization value. Therefore, it is of practical significance to reduce chlorine and solidify heavy metals in fly ash from incineration, and synthesize tobermorite for resource utilization.

[0003] Tobermorite has a zeolite-like structure with the structural formula of Ca5Si6O 16 (OH)2·4H2O, Ca2+ surrounded by silicate tetrahedrons 2+ Octahedral continuous chains. Tobermorite can be used as a bonding material, adsorbent and cation exchanger. Aluminum can participate in and promote the synthesis of aluminum-substituted tobermorite. Aluminum-substituted tobermorite can treat heavy metals in wastewater by ion exchange and adsorption.

[0004] The main components of waste incineration fly ash are CaO, KCl and NaCl, while the content of SiO2 and Al2O3 is relatively small. Silicon additives need to be added to synthesize tobermorite. The hydrothermal reaction conditions used in the conventional hydrothermal method are relatively extreme. Generally, a large amount of silicon additives, high-concentration alkaline solutions and high temperatures are used, which leads to problems such as high processing energy consumption and waste of alkaline solutions. Although the conventional hydrothermal method can synthesize tobermorite, it fails to make full use of elements such as calcium and chlorine in waste incineration fly ash. For example, CN114425549A discloses a method for microwave hydrothermal detoxification of waste incineration fly ash and simultaneous synthesis of tobermorite, wherein the waste incineration fly ash is subjected to stirring, water washing and wet ball milling dechlorination, and then mixed with a silicon source and a strong alkali solution and subjected to microwave hydrothermal reaction at 180-260°C, and the ingredients of the waste incineration fly ash, silicon source and strong alkali solution meet the following requirements: calcium-silicon molar ratio of 1.0-1.4:1, strong alkali solution concentration of 0.5-2 mol / L, and liquid-solid ratio of 5-10 ml / g. In summary, it is now urgent to find an efficient and convenient method for reducing chlorine, solidifying heavy metals and resource utilization of waste incineration fly ash. Summary of the invention

[0005] The purpose of the present invention is to provide a method for hydrothermal dechlorination and solidification of heavy metals in waste incineration fly ash and synthesis of tobermorite in view of the problems of high energy consumption and waste of alkaline solution in the prior art.

[0006] Another object of the present invention is to provide tobermorite prepared by the method.

[0007] The technical solution adopted to achieve the purpose of the present invention is:

[0008] A method for hydrothermal dechlorination of waste incineration fly ash to solidify heavy metals and synthesize tobermorite, comprising the following steps:

[0009] Step 1, adjusting the ratio of calcium, silicon and aluminum and stirring and mixing: mixing untreated waste incineration fly ash with a silicon source to obtain a mixed batch, wherein the aluminum element in the waste incineration fly ash already meets the required ratio requirement and no additional addition is required, wherein when the silicon source is added, the molar ratio of calcium / (silicon+aluminum) of the mixed batch is 0.80-0.85, and the molar ratio of aluminum / (silicon+aluminum) is 0.001-0.22;

[0010] Step 2, mixing and stirring the strong alkali solution: adding the strong alkali solution to the mixed ingredients in step 1 to obtain a mixed reactant, transferring the mixed reactant to a container, stirring and mixing, and then sealing;

[0011] Step 3, hydrothermal reaction: heating the sealed container to a reaction temperature of 130-160°C, and the temperature deviation does not exceed ±5°C for hydrothermal reaction;

[0012] Step 4, solid-liquid separation: separating the product after the hydrothermal reaction in step 3 to obtain a hydrothermal solid product and a hydrothermal liquid product, wherein the hydrothermal solid product includes tobermorite.

[0013] In the above technical solution, the silicon source is amorphous silicon dioxide powder.

[0014] In the above technical solution, the liquid-to-solid ratio of the strong alkaline solution to the mixed ingredients is 8 to 15 mL / g.

[0015] In the above technical solution, the strong alkaline solution is a NaOH solution. Preferably, the concentration of the NaOH solution is 0.3-0.4 mol / L.

[0016] In the above technical solution, the mixing and stirring speed in step 2 is 500-700 r / min, and the mixing and stirring time is 8-10 h.

[0017] In the above technical solution, the heating rate in step 3 is 5 to 8°C / min;

[0018] The reaction time of the hydrothermal reaction is 12 to 24 hours.

[0019] In the above technical solution, part of the hydrothermal liquid product is used for hydrothermal reuse, and the remaining part is used for chloride salt recovery.

[0020] In the above technical solution, the total heavy metal solidification rate of the method is greater than 95%.

[0021] Another object of the present invention is to provide tobermorite prepared by the method described above.

[0022] In the above technical solution, the specific surface area of ​​the tobermorite is greater than 70m2 / g, and the pore volume is greater than 0.15cm 3 / g.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. In the hydrothermal reaction process of the method of the present invention, KCl and NaCl in the waste incineration fly ash will be dissolved in the strong alkaline solution, thereby achieving the effect of reducing chlorine. At the same time, calcium, silicon and aluminum in the waste incineration fly ash are fully utilized as resources, ensuring the purity and performance of tobermorite. The synthesized tobermorite can physically encapsulate, ion exchange and effectively adsorb heavy metals in the waste incineration fly ash.

[0025] 2. The present invention makes full use of calcium, silicon and aluminum in the fly ash of garbage incineration by regulating the ratio of calcium, silicon and aluminum, and also increases the performance of the synthesized tobermorite. The conventional hydrothermal method uses a calcium-silicon ratio of 1.0 to 1.4 to synthesize tobermorite, which is slightly different from the actual synthesis requirements of tobermorite, so the requirements for the hydrothermal temperature are high. The present invention uses the calcium-silicon-aluminum ratio to regulate the reaction temperature from 180°C in the conventional hydrothermal method to a mild condition of 130°C. At the same time, the solidification effect of tobermorite on heavy metals is guaranteed.

[0026] 3. The present invention does not have a pretreatment process, which shortens the treatment process of waste incineration fly ash and achieves the effects of reducing chlorine and solidifying heavy metals in an efficient and convenient manner.

[0027] 4. The hydrothermal fluid in the present invention can be used for hydrothermal reuse and chloride salt recovery, thereby further realizing the resource utilization of waste incineration fly ash.

[0028] 5. The present invention uses amorphous silicon dioxide powder as the silicon source, which increases the contact area between the silicon source and CaO and Al2O3 in the waste incineration fly ash and accelerates the reaction rate. At the same time, the silicon source does not need to undergo a crystal-amorphous phase transition, which reduces the requirement for a strong alkaline solution and reduces the concentration of the NaOH alkaline solution used in the hydrothermal method from 1.0 mol / L to 0.4 mol / L. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Shown is a process flow chart of the present invention.

[0030] Figure 2 Shown are XRD characterization patterns of the solid products obtained in Examples 1 and 2 of the present invention. DETAILED DESCRIPTION

[0031] The present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0032] The calculation formula for the heavy metal solidification rate in this application is:

[0033]

[0034] Among them, C f and C s Respectively represent the leaching concentration of heavy metals in untreated waste incineration fly ash and in the solid phase after hydrothermal reaction. l Represents the concentration of heavy metals in hydrothermal fluids. f and M s They represent the mass of untreated waste incineration fly ash and the solid phase after hydrothermal reaction, respectively.

[0035] Example 1

[0036] A method for hydrothermal dechlorination of waste incineration fly ash to solidify heavy metals and synthesize tobermorite, such as Figure 1 As shown, the following steps are included:

[0037] Step 1, mixing waste incineration fly ash 1 and amorphous silicon dioxide according to a molar ratio of calcium / (silicon+aluminum) of 0.80 to obtain a mixed ingredient, and the corresponding molar ratio of aluminum / (silicon+aluminum) is 0.048;

[0038] Step 2: Add 0.4 mol / L NaOH solution to the mixed ingredients obtained in step 1 at a liquid-to-solid ratio of 10 mL / g, and transfer the mixture to the inner tank of the reactor and stir for 10 hours.

[0039] Step 3: After installing the stirred suspension on the reactor shell, transfer it to a heating oven and react at 130° C. for 24 hours.

[0040] Step 4: After the hydrothermal reaction is completed, wait for 6 hours, wait for the reactor to cool to room temperature, and dry the hydrothermal solid product at 105° C. overnight to obtain high-purity tobermorite. At the same time, the hydrothermal liquid is hydrothermally reused or the chloride salt is recovered.

[0041] The chlorine content of the treated waste incineration fly ash obtained in this embodiment is reduced by 91% compared with that before treatment. The heavy metal leaching concentration obtained by the acetic acid buffer solution method is shown in Table 1. It can be seen that the heavy metal leaching concentration of the treated waste incineration fly ash does not exceed the limit in GB 16889-2008 Municipal Waste Landfill Pollution Control Standard, and the total heavy metal solidification rate reaches 97.4%, that is, the heavy metals are effectively stabilized and will not cause pollution to the environment. The XRD spectrum of the hydrothermal product obtained is as follows: Figure 2 As shown in the figure, the hydrothermal products are three phases: tobermorite, calcite and sodium chloride. In summary, the treated waste incineration fly ash achieves the effect of reducing chlorine and solidifying heavy metals, and the obtained tobermorite can be used as a resource.

[0042] Example 2

[0043] A method for hydrothermal dechlorination of waste incineration fly ash to solidify heavy metals and synthesize tobermorite, comprising the following steps:

[0044] Step 1, mixing the waste incineration fly ash 2 and amorphous silicon dioxide according to a molar ratio of calcium / (silicon+aluminum) of 0.85 to obtain a mixed ingredient, and the corresponding molar ratio of aluminum / (silicon+aluminum) is 0.061;

[0045] Step 2: Add 0.4 mol / L NaOH solution to the mixed ingredients obtained in step 1 at a liquid-to-solid ratio of 10 mL / g, and transfer the mixture to the inner tank of the reactor and stir for 10 hours.

[0046] Step 3: After installing the stirred suspension on the reactor shell, transfer it to a heating oven and react at 160° C. for 24 hours.

[0047] Step 4: After the hydrothermal reaction is completed, wait for 6 hours, wait for the reactor to cool to room temperature, and dry the hydrothermal solid product at 105° C. overnight to obtain high-purity tobermorite. At the same time, the hydrothermal liquid is hydrothermally reused or the chloride salt is recovered.

[0048] The chlorine content of the treated waste incineration fly ash obtained in this embodiment is reduced by 90% compared with that before treatment. The heavy metal leaching concentration obtained by the acetic acid buffer solution method is shown in Table 1. It can be seen that the heavy metal leaching concentration of the treated waste incineration fly ash does not exceed the limit in GB 16889-2008 Municipal Waste Landfill Pollution Control Standard, and the total heavy metal solidification rate reaches 98.8%, that is, the heavy metals are effectively stabilized and will not cause pollution to the environment. The XRD spectrum of the hydrothermal product obtained is as follows: Figure 2 As shown, the hydrothermal products are two phases, tobermorite and calcite. In summary, the treated waste incineration fly ash achieves the effect of reducing chlorine and solidifying heavy metals, and the obtained tobermorite can be used as a resource.

[0049] Table 1 Heavy metal leaching concentration of waste incineration fly ash before and after treatment in Examples 1 and 2 of the present invention

[0050]

[0051] Example 3

[0052] A method for hydrothermal dechlorination of waste incineration fly ash to solidify heavy metals and synthesize tobermorite, comprising the following steps:

[0053] Step 1, mixing waste incineration fly ash 1 and amorphous silicon dioxide according to a molar ratio of calcium / (silicon+aluminum) of 0.83 to obtain a mixed ingredient, and the corresponding molar ratio of aluminum / (silicon+aluminum) is 0.05;

[0054] Step 2: Add 0.4 mol / L NaOH solution to the mixed ingredients obtained in step 1 at a liquid-to-solid ratio of 10 mL / g, and transfer the mixture to the inner tank of the reactor and stir for 10 hours.

[0055] Step 3: After installing the stirred suspension on the reactor shell, transfer it to a heating oven and react at 160° C. for 24 hours.

[0056] Step 4: After the hydrothermal reaction is completed, wait for 6 hours, wait for the reactor to cool to room temperature, and dry the hydrothermal solid product at 105° C. overnight to obtain high-purity tobermorite. At the same time, the hydrothermal liquid is hydrothermally reused or the chloride salt is recovered.

[0057] The properties of the high-purity tobermorite of this embodiment are shown in Table 2. It can be seen from Table 2 that the specific surface areas of the products obtained by treating with a calcium / (silicon+aluminum) molar ratio of less than 0.80 and greater than 0.85 are 6.5 m 2 / g and 17.1m 2 / g, while the specific surface area of ​​the product obtained by using the optimal calcium / (silicon + aluminum) molar ratio is 80.7m 2 / g. It can be seen that the product obtained by treating with a calcium / (silicon+aluminum) molar ratio of 0.80 to 0.85 has the largest specific surface area, strong adsorption capacity, and optimal performance.

[0058] Comparative Example 1

[0059] The difference between this comparative example and Example 3 is that the waste incineration fly ash 1 and silicon dioxide are mixed according to a molar ratio of calcium / (silicon+aluminum) of 0.66.

[0060] Comparative Example 2

[0061] The difference between this comparative example and Example 3 is that the waste incineration fly ash 2 and silicon dioxide are mixed according to a molar ratio of calcium / (silicon+aluminum) of 1.14.

[0062] Table 2 Performance of the waste incineration fly ash treated product of the present invention

[0063]

[0064] The above is only a preferred embodiment of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for hydrothermal dechlorination of waste incineration fly ash to solidify heavy metals and synthesize tobermorite, characterized in that: The following steps are involved: Step 1, adjusting the ratio of calcium, silicon and aluminum and stirring and mixing: mixing untreated waste incineration fly ash with a silicon source to obtain a mixed batch, wherein the aluminum element in the waste incineration fly ash already meets the required ratio requirement and no additional addition is required, wherein when the silicon source is added, the molar ratio of calcium / (silicon+aluminum) of the mixed batch is 0.80-0.85, and the molar ratio of aluminum / (silicon+aluminum) is 0.001-0.22; Step 2, mixing and stirring the strong alkali solution: adding the strong alkali solution to the mixed ingredients in step 1 to obtain a mixed reactant, transferring the mixed reactant to a container, stirring and mixing, and then sealing; Step 3, hydrothermal reaction: heating the sealed container to a reaction temperature of 130-160°C with a temperature deviation of no more than ±5°C for hydrothermal reaction; Step 4, solid-liquid separation: separating the product after the hydrothermal reaction in step 3 to obtain a hydrothermal solid product and a hydrothermal liquid product, wherein the hydrothermal solid product includes tobermorite.

2. The method for hydrothermal dechlorination of waste incineration fly ash and solidification of heavy metals and synthesis of tobermorite as claimed in claim 1, characterized in that: The silicon source is amorphous silicon dioxide powder.

3. The method for hydrothermal dechlorination and solidification of heavy metals and synthesis of tobermorite from waste incineration fly ash as claimed in claim 1, characterized in that: The liquid-to-solid ratio of the strong alkali solution to the mixed ingredients is 8-15 mL / g.

4. The method for hydrothermal dechlorination of waste incineration fly ash and solidification of heavy metals and synthesis of tobermorite as claimed in claim 1, characterized in that: The strong alkaline solution is a NaOH solution. Preferably, the concentration of the NaOH solution is 0.3-0.4 mol / L.

5. The method for hydrothermal dechlorination of waste incineration fly ash and solidification of heavy metals and synthesis of tobermorite as claimed in claim 1, characterized in that: The mixing and stirring speed in step 2 is 500-700 r / min, and the mixing and stirring time is 8-10 h.

6. The method for hydrothermal dechlorination and solidification of heavy metals and synthesis of tobermorite from waste incineration fly ash as claimed in claim 1, characterized in that: The heating rate in step 3 is 5-8°C / min; The reaction time of the hydrothermal reaction is 12 to 24 hours.

7. The method for hydrothermal dechlorination and solidification of heavy metals and synthesis of tobermorite from waste incineration fly ash as claimed in claim 1, characterized in that: Part of the hydrothermal liquid product is used for hydrothermal reuse, and the remaining part is used for chloride salt recovery.

8. The method for hydrothermal dechlorination of waste incineration fly ash to solidify heavy metals and synthesize tobermorite as claimed in claim 1, characterized in that: The total heavy metal curing rate of the method is greater than 95%.

9. A tobermorite, characterized in that: It is prepared by the method according to any one of claims 1 to 8.

10. The tobermorite according to claim 9, characterized in that The specific surface area of ​​the tobermorite is greater than 70 m 2 / g, pore volume greater than 0.15cm 3 / g.

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