Solidification treatment method for household garbage incineration fly ash

Abstract

The invention relates to the technical field of garbage treatment, and particularly discloses a household garbage incineration fly ash solidification treatment method which comprises the following steps: step 1, preparation of an arsenic sulfide slag leachate: mixing arsenic sulfide slag and water according to a solid-to-liquid ratio of 1: (2-7), stirring for 2 hours, and filtering to obtain the leachate; step 2, mixing and curing treatment: uniformly mixing the household garbage incineration fly ash with the leachate in the step 1, and molding by using a mold; 3, curing: curing the molded material in a mold for 2-3 days to obtain a cured product; the technical problem of secondary pollution caused by the fact that pollutants are released again due to the fact that the structure is easy to be interfered by the outside due to the fact that solidification is carried out by mainly utilizing an LDH interlayer anion point location adsorption technology in the solidification technology that fly ash and arsenic sulfide slag are mixed to form Friedel salt in the prior art is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of garbage treatment, and particularly to a method for solidifying municipal solid waste incineration fly ash. Background Art

[0002] With the acceleration of the urbanization process, the output of municipal solid waste incineration fly ash (hereinafter referred to as "fly ash") has been increasing year by year. Fly ash is enriched with various heavy metals (such as lead, arsenic, cadmium, chromium, etc.). If its leaching toxicity exceeds the limit value of the "Pollution Control Standard for Landfill of Municipal Solid Waste" (GB 16889-2008), it will seriously threaten the safety of soil and groundwater. For example, the leaching concentration of lead in a typical fly ash sample is as high as 3.171 mg / L (the standard limit value is 1.2 mg / L). There is an urgent need for an efficient and economical solidification technology to reduce its environmental risk.

[0003] At present, fly ash solidification technologies mostly use cement-based materials, chemical chelating agents or phosphates for solidification. For example, the patent document with the application number: CN202111229856.2 discloses a method for solidifying and treating garbage incineration fly ash using portland cement and a chelating agent. It uses the fly ash to be treated as the basic raw material, combines coal gangue powder, slaked lime and desulfurized gypsum to prepare pretreated fly ash, and then mixes the pretreated fly ash with the fly ash to be treated and solidifies it with portland cement to obtain a solidified landfill block for treating fly ash. Although this technology can solve the problem of fly ash solidification, there are technical problems such as high cost in the way of combining cement and chelating agent, and the curing agent (such as phosphate) may introduce phosphorus elements and cause the risk of secondary pollution.

[0004] At the same time, arsenic sulfide slag, as a by-product of non-ferrous metal smelting, contains arsenic (As) element, and the arsenic content in the slag is high. If it is in long-term contact with air, it will also be oxidized to arsenic oxide, causing serious secondary pollution to the environment. Therefore, arsenic sulfide slag is also a hazardous solid waste that needs to be treated. Existing research mostly focuses on the solidification treatment of arsenic sulfide slag; by adding additives, the additives react with arsenic sulfide slag to solidify arsenic elements chemically or physically, and at the same time use the solidification material to convert the waste residue into a solid substance that meets certain engineering properties, reducing the mobility of arsenic, and thus reducing the harm caused by the diffusion of arsenic elements. For example: CN102151690A discloses a method for treating arsenic sulfide slag. By adding an inorganic flocculant to arsenic sulfide slag, uniformly stirring and then adding a solid powder adsorbent, and finally adding asbestos wool, the leaching toxicity of arsenic in the treated arsenic sulfide slag is reduced to the entry requirements of a hazardous waste landfill. However, this method has a large consumption of chemicals and high treatment costs.

[0005] Based on the fact that both types of solid waste need to be treated, a technology of mixing arsenic sulfide slag and fly ash for solidification has emerged in the industry. For example, a patent document with the application number CN201911258864.2 discloses a treatment method for stabilizing / solidifying arsenic sulfide slag based on Friedel's salt. It uses waste incineration fly ash as the main matrix and replaces traditional cement with aluminate cement rich in active aluminum as a component regulator, so as to form a large amount of Friedel's salt in the solidification matrix to stabilize / solidify the arsenic sulfide slag and achieve the technical purpose of treating waste with waste.

[0006] The above patent technology solidifies by mixing fly ash and arsenic sulfide slag to form Friedel's salt. Although it achieves the technical purpose of treating waste with waste, it mainly uses dry arsenic sulfide mixed with fly ash, and uses the adsorption and ion exchange of Friedel's salt in aluminate cement and fly ash to adsorb and solidify pollutants such as arsenic sulfide and arsenous sulfide in the arsenic sulfide slag into an arsenic-containing solidified body, thereby reducing the leaching toxicity concentration of the arsenic sulfide slag. This adsorption system mainly relies on the adsorption of anions by the interlayer structure of Friedel's salt and is easily interfered by the outside world and release pollutants again. For example, in an anion environment such as CO3 2- 、SO4 2- etc., ion exchange will occur to displace heavy metal pollution. Another example is that Friedel's salt is easily eroded by H + in a low pH environment (pH < 5), which can erode the LDH structure and cause the dissolution of the layer board. Therefore, the solidification method adsorbed by the Friedel's salt system has the technical problem of secondary pollution. Summary of the Invention

[0007] The purpose of the present invention is to provide a method for solidifying and treating waste incineration fly ash to solve the technical problem of secondary pollution in the existing technology of using fly ash and arsenic sulfide slag to form Friedel's salt for solidification, which mainly uses the technology of adsorbing anionic sites in the LDH interlayer for solidification and is prone to being interfered by the outside world and releasing pollutants again.

[0008] To solve the above problems, the technical solution adopted by the present invention is as follows: A method for solidifying and treating waste incineration fly ash, characterized by including the following steps:

[0009] Step 1, prepare an arsenic sulfide slag leaching solution: Mix arsenic sulfide slag and water at a solid-liquid ratio of 1:2 - 7, stir for 2 hours and then filter to obtain the leaching solution;

[0010] Step 2, mixing and solidifying treatment: Mix the waste incineration fly ash with the leaching solution in Step 1, after mixing evenly, use a mold to form;

[0011] Step 3: Curing: Curing the formed material in the mold for 2-3 days to obtain a cured product.

[0012] The beneficial effects of this embodiment are:

[0013] 1. Arsenic sulfide slag is arsenic-containing waste slag produced during the smelting and chemical treatment of arsenic-containing ores. The main substance containing heavy metal pollution elements is arsenic sulfide. Arsenic sulfide itself has stable chemical properties and is almost insoluble in water at room temperature. However, it is easily oxidized into soluble arsenic acid in a humid, aerobic environment. Its migration and diffusion into the soil and groundwater with rainwater infiltration, thereby causing serious environmental pollution. The chemical reaction equation is: As2S3+7O2+6H2O→2H3AsO4+3H2SO4. Therefore, in the traditional arsenic sulfide slag treatment process, the arsenic sulfide slag will be dried as much as possible to ensure that it is not oxidized into soluble arsenic acid by reducing the moisture content, so that it can be solidified in the material state of arsenic sulfide using additives or solidifying materials such as cement. In the prior art, the method of using arsenic sulfide slag and fly ash to treat waste with waste follows the traditional idea of ​​solidification and landfill of arsenic sulfide slag. Therefore, in the process, the arsenic sulfide slag is dried as much as possible before mixing with fly ash for solidification, and it is ensured that as little water as possible is introduced during the solidification process. Arsenic is mainly solidified in the form of layered adsorption of Friedel salt. Even in order to mix evenly and facilitate the solidification of the solidifying agent, only a small part of water is added to assist the mixing and solidification of the solidifying agent. However, the present application has found that after the leachate after the arsenic sulfide slag is soaked is mixed with fly ash, the experimental data show that its solidification effect is better. This phenomenon violates the idea of ​​traditional arsenic sulfide slag treatment, and it has achieved a good solidification effect. The present application speculates that its reaction mechanism is: speculation 1. During the soaking process, the arsenic sulfide slag gradually changes into the form of arsenite, or the complex form of arsenic sulfide; and it exists in the leachate during the soaking process. After mixing with fly ash, the two are combined, and the arsenite is in a stable state of scorodite with lead. It is speculated that fly ash contains a large amount of lead. The arsenic sulfide slag is fully soaked in water to oxidize it as much as possible into soluble arsenic acid and dissolve in water. Arsenic acid can form arsenate with heavy metals in the arsenic sulfide slag and exist in the leachate during the soaking process. When mixed with fly ash, since fly ash contains a large amount of lead, arsenic and lead are solidified simultaneously in the form of the reaction between lead and arsenic acid. The reaction formula is: 3PbO+2H3AsO4→Pb3(AsO4)2↓+3H2O; PbCl2+H3AsO4→PbHAsO4↓+2HCl; Pb(OH)2+H3AsO4→PbHAsO4↓+2H2O; it not only overcomes the technical prejudice that arsenic sulfide slag needs to be dried before solidification, but also the lead arsenate (Pb3(AsO4)2) generated by the reaction solidification is a stable inorganic compound. Compared with the Friedel salt adsorption system in the prior art, it is more stable and does not have the technical problem of secondary pollution.

[0014] 2. In the prior art's technical solution of treating fly ash and arsenic sulfide slag with waste, since the Friedel salt adsorption method is adopted, additional materials such as aluminate cement, alkali activator, and water glass need to be added, resulting in high costs. In this application, the lead element in the fly ash reacts with arsenic acid to form lead arsenate, an invaluable compound. After 7 - 28 days of curing, the compressive strength is 10 - 20 MPa, and the flexural strength requirement reaches 2 - 5 MPa. Therefore, no additional solidifying materials need to be added, and the cost is lower.

[0015] 3. As a layered double metal hydroxide, Friedel salt (Ca2Al(OH)6Cl·2H2O)'s adsorption of heavy metals is restricted by the interlayer anion exchange sites. Therefore, once the adsorption capacity is reached, it cannot adsorb again, and the heavy metals adsorbed under specific conditions (acidic conditions or other anion environments) may be re - released. In this application, the solidification method is to generate inorganic compounds, which does not have the problem of limited adsorption sites, significantly reducing the leaching concentration of heavy metals such as lead and arsenic (for example, lead is reduced to below 0.24 mg / L), providing an innovative solution for the safe disposal of fly ash.

[0016] 4. This application takes out the arsenic element pollutants in the arsenic sulfide slag in the form of leachate, mixes it with fly ash and then solidifies it, also solving the pollution problem of the arsenic sulfide slag.

[0017] Furthermore, in step 1, the solid - liquid ratio of arsenic sulfide slag to water is 1:5. Experimental data shows that for the lead (Pb) leaching concentration, the solid - liquid ratio of 1:2 is 0.21 mg / L (optimal); 1:5 is 0.24 mg / L; 1:7 is 0.36 mg / L. For the arsenic (As) leaching concentration, the solid - liquid ratio of 1:5 is 0.096 mg / L; 1:7 is 0.066 mg / L (optimal). Therefore, overall, when the solid - liquid ratio is 1:5, the comprehensive effect is the best, the leaching concentrations of lead and arsenic are significantly lower than the landfill standard, and the stability of the solidified body is high.

[0018] Furthermore, in step 1, after stirring for 2 hours, the pH value of the stirred solution needs to be measured and filtered only when it is lower than 3.5. When it is higher than 3.5, the stirring time is extended until the pH value of the stirred solution is lower than 3.5 and then filtered to obtain the leachate, ensuring that the arsenic sulfide in the arsenic sulfide slag is fully oxidized to arsenic acid and dissolved in the leachate.

[0019] Furthermore, when stirring in step 1, air can be introduced into the stirred solution. After introducing air, the oxidation process of arsenic sulfide in the leachate can be enhanced, making it easier for arsenic sulfide to be oxidized to arsenic acid and reducing the stirring time of the leachate.

[0020] Further, in the step 2, the mixing mass ratio of the municipal solid waste incineration fly ash to the leachate is 5:2, and the mixture is stirred until it presents a homogeneous paste. It is easy to form and convenient to prepare the solidified block.

[0021] Further, the temperature of the curing environment in the step 3 is 25°C, and the relative humidity is 65%. The solidified block formed under this curing environment has high strength. Brief Description of the Drawings

[0022] Figure 1 It is the process flow chart of the present invention. Detailed Embodiments

[0023] The following is further detailed through specific embodiments:

[0024] Example 1 is as Figure 1 shown:

[0025] A method for solidifying and treating municipal solid waste incineration fly ash

[0026] Step 1: Preparation of the leachate of arsenic sulfide residue

[0027] Take arsenic sulfide residue, add deionized water according to the solid-liquid ratio of 1:2, and stir and mix in a stirring tank. During the stirring process, air can be introduced into the stirred liquid. A Rushton turbine stirrer can be installed in the stirring tank, and a titanium alloy sintered porous plate (pore diameter 10 - 50 μm) can be set at the bottom of the tank for aeration. Combining the stirring shear force and prolonging the bubble residence time, so that the arsenic sulfide residue is fully mixed with the water body and air in the stirring tank. After stirring for 2 hours, when the pH value of the stirred liquid is measured to be lower than 3.5, stop stirring. When the pH is higher than 3.5, prolong the stirring time until the pH value of the stirred liquid is lower than 3.5. After the stirred liquid meets the requirements, filter the stirred liquid to obtain the leachate. During the reaction process, slight heat release is observed and accompanied by the generation of white foam and white smoke. Remove two samples, and the detection data of their leachate are shown in Table 1:

[0028]

[0029] Step 2: Solidification treatment of fly ash

[0030] Take the municipal solid waste incineration fly ash, add the leachate prepared in Step 1, and the addition amount is 40% of the mass of the fly ash. Continuously stir with a stirring rod until the mixture presents a homogeneous paste. Among them, the municipal solid waste incineration fly ash with excessive heavy metals is selected. In this application, all the fly ash comes from Fuquan Haichuang, and the detection data of the fly ash are shown in Table 2:

[0031] Table 2 Heavy metal content of fly ash samples

[0032]

[0033] As can be seen from the data in Table 2, among the heavy metal indicators of the municipal solid waste incineration fly ash used in this application, the lead exceeds the standard quite significantly, reaching about 3.17.

[0034] Step 3: Curing and forming

[0035] Load the mixed materials into a cylindrical mold (diameter 5 cm, height 10 cm) and place it in a constant temperature and humidity chamber for curing. Curing conditions: temperature 25°C ± 2°C, relative humidity 65% ± 5%, curing time 3 days.

[0036] Step 4: Detect the curing effect

[0037] After curing, crush the solidified body and determine the heavy metal leaching concentration by inductively coupled plasma emission spectrometer.

[0038] Example 2

[0039] The difference between Example 2 and Example 1 is that in Step 1, the leaching solution is prepared at a solid-liquid ratio of 1:3, and the rest of the operations are the same as in Example 1.

[0040] Example 3

[0041] The difference between Example 3 and Example 1 is that in Step 1, the leaching solution is prepared at a solid-liquid ratio of 1:4, and the rest of the operations are the same as in Example 1.

[0042] Example 4

[0043] The difference between Example 4 and Example 1 is that in Step 1, the leaching solution is prepared at a solid-liquid ratio of 1:5, and the rest of the operations are the same as in Example 1.

[0044] Example 5

[0045] The difference between Example 4 and Example 1 is that in Step 1, the leaching solution is prepared at a solid-liquid ratio of 1:7, and the rest of the operations are the same as in Example 1

[0046] Comparative Example 1

[0047] The difference between Comparative Example 1 and the Example is that:

[0048] Experimental data: After crushing the solidified samples of Examples 1-5, the leaching toxicity of heavy metals was measured. When testing the elements of arsenic (As) and mercury (Hg), the detection was carried out strictly in accordance with the "Determination of Mercury, Arsenic, Selenium, Bismuth and Antimony in Solid Waste - Microwave Digestion / Atomic Fluorescence Spectrometry" (HJ 702-2014), and for other heavy metals, it was strictly detected in accordance with the "Determination of 22 Metal Elements in Solid Waste - Inductively Coupled Plasma Optical Emission Spectrometry" (HJ 781-2016). The detected data was compared with the landfill standards of some heavy metals in the "Pollution Control Standard for Hazardous Waste Landfill" (GB18598-2019). The summarized data is shown in Table 3 as follows:

[0049]

[0050] The experimental data of Examples 1, 2, 3, 4, and 5 show that for the leaching concentration of lead (Pb), the solid-liquid ratio of 1:2 is 0.21 mg / L (optimal); the solid-liquid ratio of 1:5 is 0.24 mg / L; the solid-liquid ratio of 1:7 is 0.36 mg / L. For the leaching concentration of arsenic (As), the solid-liquid ratio of 1:5 is 0.096 mg / L; the solid-liquid ratio of 1:7 is 0.066 mg / L (optimal). Therefore, overall, when the solid-liquid ratio is 1:5, the comprehensive effect is the best, the leaching concentrations of lead and arsenic are significantly lower than the landfill standards, and the stability of the solidified body is high.

[0051] Example 6

[0052] The difference between Example 6 and Example 1 is that in step 2, the stirring time of fly ash and leaching solution is 20 minutes.

[0053] Example 7

[0054] The difference between Example 7 and Example 1 is that in step 2, the stirring time of fly ash and leaching solution is 60 minutes.

[0055] Compared with Examples 6 and 7, Example 1 has a uniform mixture without caking, is easy to form, and the heavy metal solidification efficiency is increased by 15%-20%.

[0056] Example 8

[0057] The difference between Example 8 and Example 1 is that in step 3, the curing conditions are set at different temperature and humidity conditions, with the temperature set at 20°C ± 2°C and the relative humidity at 55% ± 5%, and the rest of the operations are the same.

[0058] Example 9

[0059] The difference between Example 9 and Example 1 is that in step 3, the curing conditions are set with the temperature at 30°C ± 2°C and the relative humidity at 75% ± 5%, and the rest of the operations are the same.

[0060] Compared with Example 8 and Example 9, the cured body in Example 1 has the highest compressive strength when cured at 25°C and 65% humidity. The compressive strength is generally required to reach 10 - 20 MPa after 7 - 28 days of curing, the flexural strength is required to reach 2 - 5 MPa, and the heavy metal leaching rate is the lowest.

[0061] The above are only examples of the present invention. Common knowledge such as specific structures and characteristics known in the art are not described in detail herein. It should be noted that for those skilled in the art, without departing from the structure of the present invention, several modifications and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the implementation effect of the present invention and the practicability of the patent. The protection scope required by this application shall be subject to the content of its claims, and the specific implementation manners described in the specification can be used to interpret the content of the claims.

Claims

1. A method for solidifying municipal solid waste incineration fly ash, characterized in that, It includes the following steps: Step 1, preparing an arsenic sulfide residue leaching solution: mixing arsenic sulfide residue and water at a solid-liquid ratio of 1:2 - 7, stirring for 2 hours and then filtering to obtain the leaching solution; Step 2, mixing and solidifying treatment: mixing municipal solid waste incineration fly ash with the leaching solution in Step 1, and after mixing evenly, forming it using a mold; Step 3, curing: curing the formed material in the mold for 2 - 3 days to obtain the solidified product.

2. The method according to claim 1, wherein: In Step 1, the solid-liquid ratio of arsenic sulfide residue to water is 1:

5.

3. The method according to claim 2, characterized in that: In Step 1, after stirring for 2 hours, it is necessary to measure that the pH value of the stirred solution is lower than 3.5 before filtering. When it is higher than 3.5, extend the stirring time until the pH value of the stirred solution is lower than 3.5 and then filter to obtain the leaching solution.

4. The method according to claim 3, characterized in that: When stirring in Step 1, air can be introduced into the stirred solution.

5. The method according to claim 4, characterized in that: In Step 2, the mixing mass ratio of municipal solid waste incineration fly ash to the leaching solution is 5:2, and stir until the mixture presents a homogeneous paste.

6. The method according to claim 5, wherein: In Step 3, the curing environment temperature is 25°C and the relative humidity is 65%.

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