Method for reducing coal ash stacking pollution of thermal power plant

Abstract

The invention discloses a method for reducing stacking pollution of coal ash of a thermal power plant, and belongs to the technical field of coal ash treatment of the thermal power plant, and the method comprises the following specific operation steps: (1) coal ash pretreatment: firstly, uniformly mixing the coal ash with a sodium dihydrogen phosphate solution to obtain pretreated coal ash; (2) fly ash stacking: laying a layer of adsorption matrix on the ground, and stacking the pretreated fly ash on the adsorption matrix to form a fly ash pile; and (3) innocent treatment: spraying the fly ash pile with a directional leaching acid solution, and spraying a sodium hydroxide solution on the surface of the fly ash pile to complete the treatment of the fly ash pile body of the thermal power plant. The problems of heavy metal migration pollution and flying dust pollution in the fly ash stacking process are solved.

Description

Technical Field

[0001] This invention relates to the field of reducing fly ash pollution from thermal power plants, and more particularly to a method for reducing pollution from fly ash stockpiling in thermal power plants. Background Technology

[0002] Fly ash is a major industrial solid waste generated during the coal combustion process in thermal power plants, and its annual emissions continue to rise with the expansion of industrial scale. Currently, the main method of disposing of fly ash before resource utilization is open-air stockpiling. However, fly ash particles are small and lightweight, and during open-air stockpiling, they are easily subjected to wind erosion, generating large amounts of dust. This not only wastes fly ash resources but also causes particulate pollution in the surrounding atmosphere. The main components of fly ash are silicon dioxide, alumina, and calcium oxide. In addition, it also contains trace amounts of heavy metals such as mercury, lead, and cadmium. Mercury, as a highly volatile and persistently toxic heavy metal, can easily seep into the soil and groundwater through rainwater leaching and surface runoff during stockpiling, or diffuse into the atmosphere through dust, posing a long-term threat to the surrounding ecosystem and human health. Therefore, it is necessary to treat fly ash stockpiles to reduce pollution during storage.

[0003] Current technologies for treating fly ash stockpiles include physical covering, wet spraying, and chemical consolidation. Physical covering methods include laying dust nets and covering with soil. Wet spraying increases the moisture content of fly ash by sprinkling water to suppress dust. Chemical consolidation involves spraying chemical agents to bind fly ash particles together and form a solidified layer. However, these methods can only control dust pollution from fly ash stockpiles and cannot solve the problem of heavy metal migration during the stockpiling process. Wet treatment may even exacerbate heavy metal migration. Therefore, there is an urgent need for a fly ash stockpiling treatment method that can suppress dust while reducing the migration of heavy metal mercury into the surrounding environment, thereby reducing fly ash stockpiling pollution. Summary of the Invention

[0004] Therefore, the purpose of this invention is to provide a method for reducing pollution from the stockpiling of fly ash from thermal power plants, and to solve the problem of heavy metal mercury migrating and polluting the surrounding environment during the stockpiling of fly ash from thermal power plants through dust and leaching.

[0005] The present invention solves the above-mentioned technical problems through the following technical means:

[0006] Fly ash treatment methods:

[0007] (1) Fly ash pretreatment: First, mix fly ash with sodium dihydrogen phosphate solution evenly to obtain pretreated fly ash;

[0008] (2) Fly ash stacking: Lay a layer of adsorption matrix on the ground, and then stack the pretreated fly ash on the adsorption matrix to form a fly ash stack;

[0009] (3) Harmless treatment: First, spray the fly ash pile with directional leaching acid solution. After the directional leaching acid solution is sprayed, spray 10wt% sodium hydroxide solution on the surface of the fly ash pile after an interval of 1 day to complete the treatment of the fly ash pile of the thermal power plant.

[0010] Furthermore, the concentration of sodium dihydrogen phosphate solution in (1) is 0.5 mol / L, and the mass ratio of fly ash to sodium dihydrogen phosphate solution is 20:1.

[0011] Furthermore, the raw materials of the adsorption matrix in (2) include polyvinyl alcohol, mercaptoacetic acid, glutaraldehyde, hydrochloric acid, and calcium sulfate.

[0012] Furthermore, the thickness of the adsorption matrix is ​​1-1.5 cm.

[0013] Furthermore, the directional leaching acid solution is an acetic acid solution of (0.1-0.15) mol / L.

[0014] Furthermore, the mass ratio of the directional leaching acid solution to the fly ash pile is 1:1, and it is sprayed uniformly at a rate of (2-3) L / (m²·min), preferably 3 L / (m²·min).

[0015] Furthermore, the sodium hydroxide solution is sprayed evenly at a spraying rate of 1500-2000 g / m².

[0016] Mercury is a highly toxic heavy metal found in fly ash and easily migrates to surrounding areas through leaching by dust and rainwater. Therefore, this invention treats fly ash to remove and enrich mercury, preventing its migration and environmental pollution. Silica, alumina, calcium oxide, and magnesium oxide in fly ash are commonly used active substances for fly ash resource utilization. Silica and alumina are stable at low hydrogen ion concentrations, but calcium oxide and magnesium oxide readily react with acids and dissolve. To prevent the loss of calcium oxide and magnesium oxide during fly ash treatment, this invention first pre-treats the fly ash with sodium dihydrogen phosphate, reacting calcium oxide and magnesium oxide into insoluble phosphates. Then, an adsorption matrix is ​​placed at the bottom of the fly ash pile, followed by spraying the fly ash pile with a directional leaching acid solution. The directional leaching acid solution of this invention can… The invention dissolves mercury from fly ash without dissolving calcium, aluminum, magnesium, or other minerals. After dissolving in the directional leaching acid, the mercury permeates downwards into the adsorption matrix. The adsorption matrix complexes with the mercury in the acid, anchoring the mercury within the matrix and reducing its migration to surrounding areas, thus lowering fly ash pollution. Finally, the invention also sprays sodium hydroxide onto the surface of the fly ash pile. The highly alkaline sodium hydroxide activates the fly ash, causing the surface layer to hydrate and cement, forming a shell layer that reduces fly ash dust. This achieves simultaneous treatment of dust pollution and heavy metal mercury migration during the fly ash leaching process.

[0017] Furthermore, the method for preparing the adsorption substrate is as follows:

[0018] S1: Polyvinyl alcohol is added to water and heated to 95°C and stirred to dissolve to obtain a 6-8 wt% polyvinyl alcohol solution. After cooling to 70-80°C, mercaptoacetic acid is added and the mixture is stirred at a constant temperature for 8 hours. After cooling, a mercapto-modified polyvinyl alcohol solution is obtained.

[0019] S2: Add 0.1 mol / L hydrochloric acid and calcium sulfate powder to the mercapto-polyvinyl alcohol solution, stir evenly, then add glutaraldehyde, and stir at 30-40℃ for 1 h to obtain the adsorption matrix.

[0020] Furthermore, the polyvinyl alcohol has a degree of polymerization of 1700 and a degree of alcoholysis of 99%, and is typically designated as polyvinyl alcohol 1799.

[0021] Furthermore, the mass-to-volume ratio of polyvinyl alcohol and thioglycolic acid is 1:1.

[0022] Furthermore, the mass ratio of the mercapto-polyvinyl alcohol solution, hydrochloric acid, calcium sulfate, and glutaraldehyde is 100:0.1:(2-3):(6-8).

[0023] Immediately after the adsorption matrix is ​​laid, fly ash is piled on top of it. At this time, the adsorption matrix is ​​not completely solidified, and the fly ash at the bottom will mix deeply with the adsorption matrix. The calcium sulfate in the adsorption matrix can activate the fly ash. Under the action of hydrochloric acid in the adsorption matrix, the calcium sulfate reacts with the aluminum in the fly ash to form ettringite, which fills the adsorption matrix and increases its strength. This can prevent the adsorption matrix from collapsing during the fly ash stacking process and prevent the fly ash from directly contacting the ground, thus preventing mercury migration and environmental pollution that could affect the physical and chemical properties of the soil.

[0024] Thiol groups have a strong affinity for mercury metal and can rapidly complex mercury ions. In this invention, a mercury-grafted adsorption matrix is ​​laid at the bottom of a fly ash pile, and then a low-concentration acetic acid solution is sprayed onto the fly ash pile as a directional leaching acid to dissolve the mercury metal. The acetic acid solution is chosen for its low concentration and low hydrogen ion content, which prevents the dissolution of silica and alumina. Furthermore, acetic acid is weaker than phosphoric acid, thus preventing the dissolution of calcium phosphate and magnesium phosphate formed during pretreatment. As the directional leaching acid flows through the adsorption matrix, the mercury groups rapidly complex the mercury metal and anchor it in the gel-like adsorption matrix, reducing mercury migration into the soil. In addition, after the directional leaching acid flows through the adsorption matrix, the hydrogen ion content in the matrix increases, and calcium sulfate activates the fly ash, generating more ettringite to further enhance the strength of the adsorption matrix and improve its load-bearing capacity. Simultaneously, it tightly encapsulates the mercury fixed in the adsorption matrix, preventing leakage.

[0025] In addition, this invention selects polyvinyl alcohol with high degree of polymerization and high degree of alcoholysis as the gel material of the adsorption matrix. The prepared adsorption matrix has strong acid and alkali resistance and can maintain structural stability when dissolved in acid, preventing the adsorption matrix from degrading and failing in acid leaching, which would cause secondary release of mercury metal and aggravate pollution.

[0026] Beneficial effects:

[0027] This invention provides a method for treating fly ash. An adsorption matrix is ​​laid at the bottom of the fly ash pile. A directional leaching acid solution is used to selectively dissolve mercury from the fly ash. Mercury is complexed and fixed by the adsorption matrix, reducing mercury migration into the soil and lowering the pollution from the fly ash pile. Finally, an alkaline activator is used to treat the fly ash pile, forming a solidified shell on the surface to reduce dust emissions and further reduce pollution. Furthermore, after treatment by this invention, mercury is concentrated in the fly ash, facilitating centralized processing. The reduced mercury content in the fly ash promotes its subsequent resource utilization. Detailed Implementation

[0028] The present invention will be described in detail below with reference to specific embodiments:

[0029] Example 1:

[0030] Preparation of the adsorption matrix:

[0031] S1: Add 100g of polyvinyl alcohol 1799 to water, heat to 95℃ and stir to dissolve to obtain an 8wt% polyvinyl alcohol solution. Cool the polyvinyl alcohol solution to 70℃ and add 100ml of mercaptoacetic acid. Stir at a constant temperature for 8h to obtain a mercapto-modified polyvinyl alcohol solution.

[0032] S2: Add 0.1g of 0.1mol / L hydrochloric acid solution and 2g of calcium sulfate powder to 100g of mercaptopolyvinyl alcohol solution, stir evenly, then add 8g of glutaraldehyde, and stir at 40℃ for 1h to obtain the adsorption matrix.

[0033] Example 2:

[0034] Preparation of the adsorption matrix:

[0035] S1: Add 80g of polyvinyl alcohol 1799 to water and heat to 95℃ and stir to dissolve to obtain a 6wt% polyvinyl alcohol solution. Cool the polyvinyl alcohol solution to 80℃ and add 80ml of mercaptoacetic acid. Stir and react at a constant temperature for 8h. Cool to obtain a mercapto-modified polyvinyl alcohol solution.

[0036] S2: Add 0.1g of 0.1mol / L hydrochloric acid solution and 3g of calcium sulfate powder to 100g of mercaptopolyvinyl alcohol solution, stir evenly, then add 6g of glutaraldehyde, and stir at 30℃ for 1h to obtain the adsorption matrix.

[0037] Comparative Example 1:

[0038] Compared with Example 1, the only difference is the preparation of the adsorption matrix in Comparative Example 1. Specifically, the polyvinyl alcohol is not subjected to thiolation treatment. The specific preparation method is as follows:

[0039] Add 0.1g of 0.1mol / L hydrochloric acid solution and 2g of calcium sulfate powder to 100g of 8wt% polyvinyl alcohol 1799 solution, stir well, then add 8g of glutaraldehyde, and stir at 40℃ for 1h to obtain the adsorption matrix.

[0040] Comparative Example 2:

[0041] Compared with Example 1, the only difference is the polyvinyl alcohol used in Comparative Example 2. Specifically, this comparative example uses polyvinyl alcohol 1588 with a degree of polymerization of 1500 and a degree of alcoholysis of 88%. The specific preparation method is as follows:

[0042] S1: Add 100g of polyvinyl alcohol 1588 to water and heat to 95℃ and stir to dissolve to obtain an 8wt% polyvinyl alcohol solution. Cool the polyvinyl alcohol solution to 70℃ and add 100ml of mercaptoacetic acid. Stir and react at a constant temperature for 8h to obtain a mercapto-modified polyvinyl alcohol solution.

[0043] S2: Add 0.1g of 0.1mol / L hydrochloric acid solution and 2g of calcium sulfate powder to 100g of mercaptopolyvinyl alcohol solution, stir evenly, then add 8g of glutaraldehyde, and stir at 40℃ for 1h to obtain the adsorption matrix.

[0044] Comparative Example 3:

[0045] Compared with Example 1, the only difference in Comparative Example 3 is the crosslinking agent used; specifically, boric acid is used as the crosslinking agent. The specific preparation method is as follows:

[0046] S1: Add 100g of polyvinyl alcohol 1799 to water, heat to 95℃ and stir to dissolve to obtain an 8wt% polyvinyl alcohol solution. Cool the polyvinyl alcohol solution to 70℃ and add 100ml of mercaptoacetic acid. Stir at a constant temperature for 8h to obtain a mercapto-modified polyvinyl alcohol solution.

[0047] S2: Add 0.1g of 0.1mol / L hydrochloric acid solution and 2g of calcium sulfate powder to 100g of mercaptopolyvinyl alcohol solution, stir evenly, then add 8g of boric acid, and stir at 40℃ for 1h to obtain the adsorption matrix.

[0048] Comparative Example 4:

[0049] Compared with Example 1, the only difference is that calcium sulfate was not added in Comparative Example 4. The specific preparation method is as follows:

[0050] S1: Add 100g of polyvinyl alcohol 1799 to water, heat to 95℃ and stir to dissolve to obtain an 8wt% polyvinyl alcohol solution. Cool the polyvinyl alcohol solution to 70℃ and add 100ml of mercaptoacetic acid. Stir at a constant temperature for 8h to obtain a mercapto-modified polyvinyl alcohol solution.

[0051] S2: Add 0.1g of 0.1mol / L hydrochloric acid solution to 100g of mercaptopolyvinyl alcohol solution, stir evenly, then add 8g of glutaraldehyde, and stir at 40℃ for 1h to obtain the adsorption matrix.

[0052] Comparative Example 5:

[0053] In contrast to Example 1, specifically in Comparative Example 5, mercaptoacetic acid was simply mixed into the adsorption matrix. The specific preparation method is as follows:

[0054] Add 50 ml of mercaptoacetic acid and 0.1 g of 0.1 mol / L hydrochloric acid solution to 50 g of 8 wt% polyvinyl alcohol solution, stir well, then add 8 g of glutaraldehyde, and stir at 40 °C for 1 h to obtain the adsorption matrix.

[0055] Example 3:

[0056] Fly ash treatment methods:

[0057] (1) Pretreatment of fly ash: First, fly ash and 0.5 mol / L sodium dihydrogen phosphate solution are mixed evenly at a solid-liquid mass ratio of 20:1 to obtain pretreated fly ash;

[0058] (2) Fly ash stacking: The adsorption matrix prepared in Example 1 is laid on the ground with a thickness of 1.5 cm, and then the pretreated fly ash is stacked on the adsorption matrix to form a fly ash stack;

[0059] (3) Harmless treatment: Spray 0.1 mol / L acetic acid solution with fly ash at a mass ratio of 1:1 at a spraying rate of 3 L / (m²·min). After the acid solution is sprayed in a directional manner, wait 1 day, then spray 10 wt% sodium hydroxide solution on the surface of the fly ash pile at a rate of 2000 g / m² to complete the treatment of the fly ash pile of the thermal power plant.

[0060] Example 4:

[0061] Fly ash treatment methods:

[0062] (1) Pretreatment of fly ash: First, fly ash and 0.5 mol / L sodium dihydrogen phosphate solution are mixed evenly at a solid-liquid mass ratio of 20:1 to obtain pretreated fly ash;

[0063] (2) Fly ash stacking: The adsorption matrix prepared in Example 1 is laid on the ground with a thickness of 1 cm, and then the pretreated fly ash is stacked on the adsorption matrix to form a fly ash stack;

[0064] (3) Harmless treatment: Spray 0.15 mol / L acetic acid solution with fly ash at a mass ratio of 1:1 at a spraying rate of 2 L / (m²·min). After the acid solution is sprayed in a directional manner, wait 1 day, and then spray 10 wt% sodium hydroxide solution on the surface of the fly ash pile at a rate of 1500 g / m² to complete the treatment of the fly ash pile of the thermal power plant.

[0065] Comparative Example 6:

[0066] Compared with Example 3, the only difference is that the fly ash in Comparative Example 6 was not pretreated with sodium dihydrogen phosphate. The specific treatment method is as follows:

[0067] (1) Fly ash stacking: The adsorption matrix prepared in Example 1 is laid on the ground with a thickness of 1.5 cm, and then fly ash is stacked on the adsorption matrix to form a fly ash stack;

[0068] (2) Harmless treatment: Spray 0.1 mol / L acetic acid solution with fly ash at a mass ratio of 1:1 at a spraying rate of 3 L / (m²·min). After the acid solution is sprayed in a directional manner, wait 1 day, and then spray 10 wt% sodium hydroxide solution on the surface of the fly ash pile at a rate of 2000 g / m² to complete the treatment of the fly ash pile of the thermal power plant.

[0069] Comparative Example 7:

[0070] Compared with Example 3, the only difference in Comparative Example 7 is that after laying the adsorption matrix, a small amount of fly ash was added, cured for 2 days, and then the fly ash was piled up. The specific treatment method is as follows:

[0071] (1) Pretreatment of fly ash: First, fly ash and 0.5 mol / L sodium dihydrogen phosphate solution are mixed evenly at a solid-liquid mass ratio of 20:1 to obtain pretreated fly ash;

[0072] (2) Fly ash stacking: The adsorption matrix prepared in Example 1 is laid on the ground with a thickness of 1.5cm. Then, a layer of 1mm fly ash is laid on the surface of the adsorption matrix, and 0.1mol / L hydrochloric acid solution is sprayed at a rate of 1000g / m². After solidification for 2 days, the pretreated fly ash is stacked on the adsorption matrix to form a fly ash stack.

[0073] (3) Harmless treatment: Spray 0.1 mol / L acetic acid solution with fly ash at a mass ratio of 1:1 at a spraying rate of 3 L / (m²·min). After the acid solution is sprayed in a directional manner, wait 1 day, then spray 10 wt% sodium hydroxide solution on the surface of the fly ash pile at a rate of 2000 g / m² to complete the treatment of the fly ash pile of the thermal power plant.

[0074] Comparative Example 8:

[0075] Compared with Example 3, the only difference is the concentration of the directional leaching acid solution used in Comparative Example 8. Specifically, a 0.05 mol / L acetic acid solution was used as the directional leaching acid solution, and the specific treatment method is as follows:

[0076] Step (1) fly ash pretreatment and step (2) fly ash stockpiling are the same as in Example 3;

[0077] (3) Harmless treatment: Spray 0.05 mol / L acetic acid solution with fly ash at a mass ratio of 1:1 at a spraying rate of 3 L / (m²·min). After the acid solution is sprayed in a directional manner, wait 1 day, and then spray 10 wt% sodium hydroxide solution on the surface of the fly ash pile at a rate of 2000 g / m² to complete the treatment of the fly ash pile of the thermal power plant.

[0078] Comparative Example 9:

[0079] Compared with Example 3, the only difference is the concentration of the directional leaching acid solution used in Comparative Example 9. Specifically, a 0.2 mol / L acetic acid solution was used as the directional leaching acid solution, and the specific treatment method is as follows:

[0080] Step (1) fly ash pretreatment and step (2) fly ash stockpiling are the same as in Example 3;

[0081] (3) Harmless treatment: Spray 0.2 mol / L acetic acid solution with fly ash at a mass ratio of 1:1 at a spraying rate of 3 L / (m²·min). After the acid solution is sprayed in a directional manner, wait 1 day, and then spray 10 wt% sodium hydroxide solution on the surface of the fly ash pile at a rate of 2000 g / m² to complete the treatment of the fly ash pile of the thermal power plant.

[0082] Comparative Example 10:

[0083] Compared with Example 3, the only difference is that the directional leaching acid solution used in Comparative Example 10 is different. Specifically, a 0.1 mol / L hydrochloric acid solution is used as the directional leaching acid solution, and the specific treatment method is as follows:

[0084] Step (1) fly ash pretreatment and step (2) fly ash stockpiling are the same as in Example 3;

[0085] (3) Harmless treatment: Spray 0.1 mol / L hydrochloric acid solution with fly ash at a mass ratio of 1:1 at a spraying rate of 3 L / (m²·min). After the acid solution is sprayed in a directional manner, wait 1 day, and then spray 10 wt% sodium hydroxide solution on the surface of the fly ash pile at a rate of 2000 g / m² to complete the treatment of the fly ash pile of the thermal power plant.

[0086] Comparative Example 11:

[0087] Compared with Example 3, the only difference in Comparative Example 11 is that the directional leaching acid solution was not sprayed, but water was used instead. The specific treatment method is as follows:

[0088] Step (1) fly ash pretreatment and step (2) fly ash stockpiling are the same as in Example 3;

[0089] (3) Harmless treatment: Spray clean water and fly ash at a mass ratio of 1:1 at a spraying rate of 3L / (m²·min). After the clean water spraying is completed, spray 10wt% sodium hydroxide solution at a rate of 2000g / m² onto the surface of the fly ash pile to complete the treatment of the fly ash pile of the thermal power plant.

[0090] Comparative Example 12:

[0091] Compared with Example 3, the only difference is that Comparative Example 12 does not use an adsorption matrix. The specific treatment method is as follows:

[0092] (1) Pretreatment of fly ash: First, fly ash and 0.5 mol / L sodium dihydrogen phosphate solution are mixed evenly at a solid-liquid mass ratio of 20:1 to obtain pretreated fly ash;

[0093] (2) Fly ash stockpiling: Pretreated fly ash is stockpiled on the ground to form fly ash stockpiles;

[0094] (3) Harmless treatment: Spray 0.1 mol / L acetic acid solution with fly ash at a mass ratio of 1:1 at a spraying rate of 3 L / (m²·min). After the acid solution is sprayed in a directional manner, wait 1 day, then spray 10 wt% sodium hydroxide solution on the surface of the fly ash pile at a rate of 2000 g / m² to complete the treatment of the fly ash pile of the thermal power plant.

[0095] Comparative Example 13:

[0096] Compared with Example 3, the only difference is that Comparative Example 13 did not involve spraying sodium hydroxide solution. The specific treatment method is as follows:

[0097] (1) Pretreatment of fly ash: First, fly ash and 0.5 mol / L sodium dihydrogen phosphate solution are mixed evenly at a solid-liquid mass ratio of 20:1 to obtain pretreated fly ash;

[0098] (2) Fly ash stacking: The adsorption matrix is ​​laid on the ground with a thickness of 1.5cm, and then the pretreated fly ash is stacked on the adsorption matrix to form a fly ash stack;

[0099] (2) Harmless treatment: Spray 0.1 mol / L acetic acid solution with fly ash at a mass ratio of 1:1 at a spraying rate of 3 L / (m²·min) to complete the treatment of fly ash pile in thermal power plant.

[0100] Experiment 1: Mercury Adsorption Test on Adsorption Matrix

[0101] Mercuric chloride was added to 0.1 mol / L hydrochloric acid solution to prepare a mercury solution of 1000 μg / L. The adsorption matrix prepared in Example 1 and Comparative Groups 1-5 was solidified and prepared into samples of 2 cm × 2 cm × 1.5 cm. Each sample was placed in 250 mL of mercury solution and soaked for 4 h. The mercury concentration of the mercury solution was then measured. The experiment was repeated three times, and the mercury adsorption rate of the adsorption matrix was calculated. The average value of the results is shown in Table 1.

[0102] Table 1

[0103]

[0104] Experiment 2: Fly Ash Pile Treatment Experiment

[0105] The same batch of fly ash from a thermal power plant was tested, and its initial mercury content was 465.2 ng / g. 2 kg of fly ash was taken from each group for fly ash stockpiling treatment experiments. Experimental group 1, control groups 1-13 and blank group were set up, and the experiment was repeated three times.

[0106] Fly ash disposal:

[0107] (1) Fly ash pretreatment: First, mix 2 kg of fly ash with 100 g of 0.5 mol / L sodium dihydrogen phosphate solution to obtain pretreated fly ash;

[0108] (2) Fly ash stacking: The adsorption matrix is ​​laid on the ground with an area of ​​30cm×30cm and a thickness of 1.5cm. Then the pretreated fly ash is stacked on the adsorption matrix to form a fly ash stack.

[0109] (3) Harmless treatment: Spray 0.1 mol / L hydrochloric acid and fly ash at a mass ratio of 1:1 at a spraying rate of 3 L / (m²·min). After the acid solution is sprayed in a directional manner, wait 1 day, and then spray 10 wt% sodium hydroxide solution on the surface of the fly ash pile at a rate of 2000 g / m² to complete the treatment of the fly ash pile.

[0110] Experimental group 1 and control groups 6-13 used the adsorption matrix prepared in Example 1, control groups 1-5 used the adsorption matrix prepared in Comparative Examples 1-5 respectively, and the blank group did not use an adsorption matrix. Experimental group 1 and control groups 1-5 were treated with the treatment method of Example 3, and control groups 6-13 were treated with the method of control group 6-13 respectively. In the blank group, the fly ash was directly piled up after being treated with clean water for both pretreatment and harmless treatment, without the use of an adsorption matrix.

[0111] 1. Mercury removal and adsorption tests: Two days after the fly ash pile treatment was completed, the remaining mercury content in the fly ash was tested, and the mercury removal rate and mercury removal amount were calculated; the mercury content in the matrix was tested, and the mercury adsorption rate was calculated; the mercury content in the leachate was tested, and the mercury migration amount was obtained.

[0112] 2. Dust control experiment: After drying the fly ash of each group after treatment to a moisture content of 5%, the mass was weighed and recorded as M1. Then, a blowing experiment was carried out at a wind speed of 15 m / s. After blowing for 5 minutes, the mass of the remaining fly ash was weighed and recorded as M2. The dust control rate was calculated, and the results are shown in Table 2.

[0113] Mercury removal rate = (initial mercury content - residual mercury content) / initial mercury content × 100%;

[0114] Mercury removal amount = initial mercury content × mercury removal rate × fly ash mass;

[0115] Mercury adsorption = Mercury content in the matrix / Mercury removal amount × 100%;

[0116] Dust emission rate = (M1-M2) / M1×100%.

[0117] Table 2

[0118] Analysis of the data in Tables 1 and 2 shows that:

[0119] 1. Experimental group 1 adopted the fly ash stockpile treatment method of the present invention. The directional leaching acid solution can remove a large amount of mercury metal from the fly ash. The adsorption matrix can efficiently adsorb and fix the mercury metal dissolved by the acid solution, effectively reducing the migration of mercury metal and meeting the discharge standard of mercury in industrial wastewater ≤50ng / g. Sodium hydroxide treatment on the surface of the fly ash pile activates and hydrates the pretreated fly ash to form a gel material, forming a solidified shell layer on the surface of the fly ash pile, effectively reducing dust and further reducing the pollution generated by fly ash stockpiling.

[0120] 2. Compared with experimental group 1, the preparation of the adsorption matrix in control groups 1-5 differed. In control group 1, the polyvinyl alcohol in the adsorption matrix was not grafted with thiol groups, resulting in a significantly lower mercury adsorption rate. This led to a greater amount of mercury migrating to the outside environment with the leaching of water, easily causing pollution. In control group 2, the polyvinyl alcohol 1588 used in the preparation of the adsorption matrix had a lower degree of polymerization and alcoholysis, resulting in decreased acid and alkali resistance. After directional leaching with acidic solution, the matrix's strength decreased, reducing its mercury fixation effect and increasing mercury migration. In control group 3, the adsorption matrix was cross-linked with boric acid. Boric acid and polyvinyl alcohol are cross-linked by ester bonds, which are easily broken in acidic solutions. This made the adsorption matrix prone to degradation after directional leaching with acidic solution. In contrast, the adsorption and fixation of mercury in the control group 4 was reduced, leading to increased mercury migration and environmental pollution. In control group 5, the adsorption matrix was prepared without calcium sulfate, resulting in a slight decrease in matrix strength. This could cause localized collapse when pulverized coal was piled up, allowing fly ash to directly contact the ground. Some of the directional leaching acid would then migrate directly to the ground without passing through the adsorption matrix, increasing mercury migration. In control group 5, the adsorption matrix was prepared by simply mixing mercaptoacetic acid with polyvinyl alcohol. The mercaptoacetic acid in the adsorption matrix, after complexing with mercury, could not be anchored in the gel-like adsorption matrix. The free thiol groups were easily oxidized and deactivated, leading to a decrease in mercury adsorption rate and an increase in migration.

[0121] 3. Compared with experimental group 1, control group 6 did not pretreat the fly ash. During directional acid leaching, the calcium oxide and magnesium oxide in the fly ash easily reacted with the acid. The consumption of the directional leaching acid led to a decrease in the removal rate of mercury. At the same time, the amount of calcium and aluminum participating in the hydration and cementation of fly ash decreased, the strength of the solidified shell layer formed on the surface of the fly ash pile decreased, and the dust rate increased. In control group 7, the adsorption matrix was first reacted with a small amount of fly ash to solidify into a higher strength material before the fly ash was piled up. The pores of the adsorption matrix after reacting and solidifying with the fly ash were filled, making it difficult for the directional leaching acid to penetrate from the adsorption matrix. As a result, the adsorption effect of the adsorption matrix on mercury was significantly reduced, and a large amount of mercury migrated, which did not meet the emission standards.

[0122] 4. Compared with experimental group 1, the concentrations of the directional leaching acid used in control groups 8 and 9 were different. Control group 8 used a lower acid concentration, resulting in a lower mercury removal rate. The residual mercury in the fly ash affected the resource utilization of fly ash. Control group 9 used a higher acid concentration, and the mercury removal rate was similar to that of experimental group 1. However, the increased acid concentration led to an increase in hydrogen ion content, causing the alumina in the fly ash to dissolve slowly, resulting in a decrease in the hydration gel strength of the fly ash pile surface and a slight increase in dust emission. Control group 10 used hydrochloric acid as the directional leaching acid. Hydrochloric acid is a strong acid and reacts with calcium phosphate and magnesium phosphate in the pretreated fly ash. The consumption of acid led to a decrease in the mercury removal rate. At the same time, the reduction in calcium and magnesium ions in the fly ash decreased the strength of the surface hydration gel shell and increased the dust emission. Control group 11 did not spray directional leaching acid and used water instead. The mercury removal rate was low, and a large amount of mercury remained in the fly ash, which affected the resource utilization of fly ash.

[0123] 5. Compared with experimental group 1, control group 12 did not use an adsorption matrix, so the mercury was not adsorbed after removal, and a large amount of the removed mercury migrated, causing serious pollution; control group 13 did not treat the surface of the fly ash pile with sodium hydroxide, and the fly ash was light in weight after natural drying, making it very easy to generate dust and cause pollution.

[0124] 6. The blank group did not use an adsorption matrix and was only treated with water. Water can dissolve a small amount of mercury in fly ash. Long-term storage can cause mercury in fly ash to leach into the soil with rainwater and pollute the environment. At the same time, the dust rate is high and it is easy to cause dust pollution.

[0125] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for reducing pollution from fly ash stockpiling in thermal power plants, characterized in that, The method is as follows: (1) Fly ash pretreatment: First, mix fly ash with sodium dihydrogen phosphate solution evenly to obtain pretreated fly ash; (2) Fly ash stacking: A layer of adsorption matrix is ​​laid on the ground, and then the pretreated fly ash is stacked on the adsorption matrix to form a fly ash stack; (3) Harmless treatment: First, spray the fly ash pile with directional leaching acid solution. After the directional leaching acid solution is sprayed, spray 10wt% sodium hydroxide solution on the surface of the fly ash pile after an interval of 1 day to complete the treatment of the fly ash pile of the thermal power plant.

2. The method for reducing pollution from fly ash stockpiling in thermal power plants as described in claim 1, characterized in that, The concentration of sodium dihydrogen phosphate solution in (1) is 0.5 mol / L, and the mass ratio of fly ash to sodium dihydrogen phosphate solution is 20:

1.

3. The method for reducing pollution from fly ash stockpiling in thermal power plants as described in claim 2, characterized in that, The raw materials of the adsorption matrix in (2) include polyvinyl alcohol, mercaptoacetic acid, glutaraldehyde, hydrochloric acid, and calcium sulfate.

4. The method for reducing pollution from fly ash stockpiling in thermal power plants as described in claim 3, characterized in that, The thickness of the adsorption matrix in (2) is 1-1.5cm.

5. A method for reducing pollution from fly ash stockpiling in thermal power plants as described in claim 4, characterized in that, The directional leaching acid solution in (3) is an acetic acid solution of (0.1-0.15) mol / L, and the mass ratio of the directional leaching acid solution to the fly ash pile is 1:1, and it is sprayed at a rate of (2-3) L / (m²·min).

6. A method for reducing pollution from fly ash stockpiling in thermal power plants as described in claim 5, characterized in that, The sodium hydroxide solution (3) is sprayed at a rate of 1500-2000 g / m².

7. A method for reducing pollution from fly ash stockpiling in thermal power plants as described in any one of claims 1-6, characterized in that, The adsorption substrate is prepared as follows: S1: Polyvinyl alcohol is added to water and heated to 95°C and stirred to dissolve to obtain a 6-8 wt% polyvinyl alcohol solution. After cooling to 70-80°C, mercaptoacetic acid is added and the mixture is stirred at a constant temperature for 8 hours. After cooling, a mercapto-modified polyvinyl alcohol solution is obtained. S2: Add 0.1 mol / L hydrochloric acid and calcium sulfate powder to the mercapto-polyvinyl alcohol solution, stir evenly, then add glutaraldehyde, and stir at 30-40℃ for 1 h to obtain the adsorption matrix.

8. A method for reducing pollution from fly ash stockpiling in thermal power plants as described in claim 7, characterized in that, In step S1, the degree of polymerization of polyvinyl alcohol is 1700, the degree of alcoholysis is 99%, and the mass-to-volume ratio of polyvinyl alcohol to mercaptoacetic acid is 1g:1ml.

9. A method for reducing pollution from fly ash stockpiling in thermal power plants as described in claim 8, characterized in that, In step S2, the mass ratio of mercapto-polyvinyl alcohol solution, hydrochloric acid, calcium sulfate, and glutaraldehyde is 100:0.1:(2-3):(6-8).

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