Method for preparing concrete block from fly ash

Abstract

The invention relates to the technical field of fly ash treatment, in particular to a method for preparing a concrete block from fly ash. The method comprises the following steps: washing the fly ash with water to obtain chlorine-removed fly ash; mixing the chlorine-removed fly ash with an additive, and carrying out ball milling treatment to obtain detoxified fly ash; and mixing the detoxified fly ash, cement, bluestone and fine sand, and performing constant-temperature and constant-humidity maintenance to obtain the concrete block. According to the method, the fly ash is washed with water before ball milling treatment, chlorine salt in the fly ash can be effectively removed, the situation that the solidification effect of heavy metal is affected in the ball milling treatment is avoided, the water consumption of the ball milling treatment can be reduced, water is saved, and the quality of the fly ash is effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of fly ash treatment, and in particular to a method for preparing concrete blocks from fly ash. Background Art

[0002] Fly ash is captured by the flue gas purification system of municipal waste incineration. It is rich in a large number of harmful substances, such as highly toxic organic compounds and heavy metals (such as Pb, Hg, Cu, Zn and Cd, etc.). Therefore, it is classified as hazardous waste in my country (code: HW 18) and cannot be used directly as a secondary material. Special treatment is required before reuse or landfill to reduce its toxicity.

[0003] At present, the toxicity of fly ash can be reduced by thermal treatment and non-thermal treatment. Among them, non-thermal treatment includes cement solidification, biological / chemical reagent stabilization and mechanochemical treatment. The former two still have the risk of fly ash leaching, lack of long-term stability or single treatment effect, and high cost of reagents. The mechanochemical method is a green treatment method. It has attracted more and more attention and research due to its mild reaction conditions, simple operation, high efficiency, and no secondary pollution during the treatment process. In recent years, as the research on mechanochemical additives has continued to deepen into the field of industrial solid waste, the mechanochemical method has gradually achieved the coordinated treatment of hazardous solid waste and industrial solid waste while solidifying heavy metals and improving the quality of fly ash. Summary of the invention

[0004] The inventors of the present invention creatively disclose a method for preparing concrete blocks from fly ash.

[0005] To this end, the embodiments of the present invention disclose at least the following technical solutions: In a first aspect, an embodiment discloses a method for preparing a concrete block from fly ash. The method comprises: washing the fly ash with water to obtain chlorine-removed fly ash; The chlorine-removed fly ash is mixed with an additive and subjected to ball milling treatment to obtain detoxified fly ash; The detoxified fly ash, cement, bluestone and fine sand are mixed and maintained at a constant temperature and humidity to obtain the concrete building block.

[0006] In some embodiments, the water washing comprises: washing the fly ash with water; performing solid-liquid separation on a suspension containing fly ash; drying the fly ash slurry obtained through the solid-liquid separation; and crushing the dried fly ash.

[0007] In some embodiments, the water washing is performed at least twice.

[0008] In some embodiments, the amount of water added in the water washing is 3 times the weight of the fly ash.

[0009] In some embodiments, the additive is selected from at least one of aluminum nitrate or its nonahydrate, NaH2P4 and calcium oxide. Optionally, the additive is a mixture of aluminum nitrate and calcium oxide in a weight ratio of 7:3. Optionally, the additive is a mixture of aluminum nitrate, calcium oxide and NaH2P4 in a weight ratio of 7:1:2.

[0010] In some embodiments, during the ball milling process, the weight ratio of the additive to the chlorine-removed fly ash is (9:1) to (7:3).

[0011] In some embodiments, during the ball milling process, water is added at a weight ratio of 3 times the weight of the solid material, the weight of the ball milling beads used is 10 times the total weight of the material, the rotation speed is 300-600 rpm, and the ball milling time is 1-10 hours.

[0012] In some embodiments, the mixing ratio of the detoxified fly ash, cement, bluestone and fine sand is (10~25):(10~25):(30~50):(10~20).

[0013] In some embodiments, the curing temperature is 19-21°C, the curing humidity is not less than 90%, and the curing time is not less than 24 hours.

[0014] In some embodiments, the curing step includes: mixing the detoxified fly ash, cement, bluestone and fine sand in a ratio of 20:20:45:15, curing at a constant temperature and humidity of 20˚C and 95% humidity for 24 hours, and continuing to cure for up to 28 days after molding and demolding to obtain the concrete block.

[0015] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention washes the fly ash with water before ball milling, which can effectively remove the chloride salts in the fly ash, avoid affecting the solidification effect of heavy metals during ball milling, reduce the water consumption of ball milling, save water, and effectively improve the quality of fly ash.

[0016] (2) The appropriate ball milling conditions of the present invention can solidify the heavy metals in the fly ash to the greatest extent, reduce reaction energy consumption, and save costs.

[0017] (3) The present invention uses additives during the ball milling process to effectively reduce the leaching concentration of heavy metals. During the ball milling process, fly ash is broken into small particles and then agglomerated into large particles to achieve the sealing of heavy metals. Secondly, the high content of silicon, calcium, iron, etc. in the additives is conducive to the formation of hydration products including hydrocalumite, calcium iron aluminum and aluminosilicate minerals, further promoting the solidification of heavy metals, providing a new idea for the coordinated treatment of industrial solid waste and hazardous waste, and further providing the ratio of fly ash as an auxiliary gel material for preparing concrete blocks, providing a practical solution for the resource utilization of fly ash as a building material, and forming a relatively complete fly ash detoxification and building material utilization path. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. The reagents not described separately in detail in the present invention are all conventional reagents and can be obtained from commercial channels; the methods not described in detail are all conventional experimental methods and can be obtained from the prior art.

[0019] Example 1 This embodiment provides a method for preparing concrete blocks from fly ash. The method comprises: 1) washing the fly ash to be treated in three stages with a water-ash ratio of 3:1 by weight, and drying the washed fly ash to obtain chlorine-free fly ash; 2) mixing the chlorine-removed fly ash and aluminum nitrate in a weight ratio of 9:1, and performing ball milling treatment with a planetary ball mill, and obtaining detoxified fly ash after intermittent ball milling; 3) The detoxified fly ash, cement, bluestone and fine sand are mixed in a ratio of 20:20:45:15, placed in a constant temperature and humidity chamber at a temperature of 20°C and a humidity of 95% for curing for 24 hours, and continued to be cured for 28 days after molding and demolding to prepare a concrete block.

[0020] Among them, the three-stage water washing step includes: using a water washing tank to receive fly ash and water for water washing; using a plate and frame filter press to filter the washed fly ash to obtain fly ash slurry and primary water washing liquid; and using a diaphragm pump to transport the fly ash slurry to the water washing tank for water washing again to obtain fly ash that has undergone secondary water washing; washing and filtering the fly ash that has undergone secondary water washing again to obtain fly ash slurry that has undergone tertiary water washing; using a single-drum dryer to dry the fly ash slurry that has undergone tertiary water washing; and using a stirred reactor to crush the dried fly ash.

[0021] The ball milling treatment is wet milling treatment, with a liquid-solid ratio of 3:1, a ball-to-material ratio of 10:1, a rotation speed of 300 rpm, and a ball milling time of 6 hours.

[0022] Example 2 The sampling process and processing conditions are substantially the same as those in Example 1, except that the additive in step 2) is a mixture of aluminum nitrate and calcium oxide in a weight ratio of 7:3.

[0023] Example 3 The sampling process and processing conditions are substantially the same as those in Example 1, except that the additive in step 2) is a mixture of aluminum nitrate, calcium oxide, and NaH2P4 in a weight ratio of 7:1:2.

[0024] Example 4 The sampling process and processing conditions are substantially the same as those in Example 1, except that the detoxified fly ash, cement, bluestone and fine sand are mixed in a ratio of 25:15:45:15.

[0025] Example 5 The sampling process and processing conditions are substantially the same as those in Example 1, except that the detoxified fly ash, cement, bluestone and fine sand are mixed in a ratio of 20:25:40:15.

[0026] Comparative Example 1 The sampling process and processing conditions are substantially the same as those in Example 1, except that the additive in step 2) is steel slag.

[0027] Comparative Example 2 The sampling process and processing conditions are substantially the same as those in Example 1, except that the detoxified fly ash, cement, bluestone and fine sand are mixed in a ratio of 5:25:45:15.

[0028] In the present invention, the fly ash to be treated contains 413.5 mg / kg Cr, 329.7 mg / kg Cd, 909.7 mg / kg Cu, 122.5 mg / kg Ni, 3102.2 mg / kg Pb, 6739 mg / kg Zn, 325.9 mg / kg Se, 288.4 mg / kg Mn, and 196.2 mg / kg As.

[0029] In the above-mentioned Examples 1-5 and Comparative Examples 1-2, the weight of the processed fly ash is 18 g, the weight of the additives in the ball milling process is 2 g, and the weight of the ball milling beads is 200 g.

[0030] Table 1 shows the percentage decrease in heavy metal leaching concentration in the fly ash after ball milling treatment in each of Examples 1 to 5 and Comparative Examples 1 to 2, which is the percentage of the difference between the heavy metal leaching concentration of the fly ash after ball milling treatment and the heavy metal leaching concentration of the fly ash to be treated to the heavy metal leaching concentration of the fly ash to be treated.

[0031] Table 1 (%)

[0032] As shown in Table 1, the heavy metal leaching concentration reduction rates of Cd, Cr, Cu, Ni, Pb and Zn in the fly ashes of Examples 1 to 5 after water washing and ball milling are significantly higher than those in Comparative Example 1, indicating that the present invention uses special components as additives for ball milling, which can reduce the heavy metal leaching rates of Cd, Cr, Cu, Ni, Pb and Zn in the fly ashes, inhibit the leaching of these heavy metals, and improve their solidification effect. In addition, the heavy metal leaching concentration reduction rates of Se, Mn and As in the fly ashes provided by Examples 1 to 5 after water washing and ball milling are significantly higher than those in Comparative Example 1, indicating that the present invention can also solidify these special heavy metals and improve the solidification effect of heavy metals in fly ashes.

[0033] Table 2

[0034] Determination of carbon fixation: The mass gain method is used, that is, the mass change of the block before and after mineralization is the carbon fixation amount. In order to reduce the error in the determination of carbon fixation caused by water evaporation during the mineralization process. In this paper, the blocks that need mineralization and maintenance are placed in a 40×40×40 mm plastic mold with hollowed-out sides to ensure that the four sides of the blocks are fully in contact with CO2. The top is sealed with plastic wrap and punctured to ensure the circulation of CO2, thereby ensuring that most of the evaporated water will be retained in the plastic mold. The specific carbon fixation rate = 100% × (M1-M0) / Mb, where M1 is the overall weight after mineralization, in g; M0 is the overall weight before mineralization, in g; Mb is the weight of the dry material of the block before mineralization, in g.

[0035] Table 2 shows the 28-day compressive strength of the concrete blocks provided by Examples 1 to 5 and Comparative Examples 1 to 2, all of which meet the 15 MPa required by the national standard GB / T 13544-2019, and the 28-day compressive strength of the concrete blocks provided by Examples 1 to 5 is higher than that of Comparative Examples 1 to 2, indicating that the concrete blocks prepared by the method provided by the present invention have better mechanical strength.

[0036] It can also be seen from Table 2 that the carbon dioxide solidification rate of the concrete blocks provided by Examples 1 to 5 is significantly higher than that of Comparative Examples 1 to 2, indicating that the water washing and ball milling treatment provided by the present invention can improve the carbon fixation capacity of the concrete blocks.

[0037] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing concrete blocks from fly ash, comprising: washing the fly ash with water to obtain chlorine-removed fly ash; The chlorine-removed fly ash is mixed with an additive and subjected to ball milling treatment to obtain detoxified fly ash; The detoxified fly ash, cement, bluestone and fine sand are mixed and maintained at a constant temperature and humidity to obtain the concrete building block.

2. The method according to claim 1, wherein the washing comprises: Washing the fly ash with water; Solid-liquid separation of the suspension containing fly ash; The fly ash slurry obtained through the solid-liquid separation is dried and the dried fly ash is crushed.

3. The method according to claim 1, wherein the number of times of washing is at least two times.

4. The method according to claim 1, wherein the amount of water added in the water washing is 3 times the weight of the fly ash.

5. The method according to claim 1, wherein the additive is selected from at least one of aluminum nitrate or its nonahydrate, NaH2P4 and calcium oxide; optionally, the additive is a mixture of aluminum nitrate and calcium oxide in a weight ratio of 7:3; optionally, the additive is a mixture of aluminum nitrate, calcium oxide and NaH2P4 in a weight ratio of 7:1:

2.

6. The method according to claim 1, wherein during the ball milling process, the weight ratio of the additive to the chlorine-removed fly ash is (9:1) to (7:3).

7. The method according to claim 1, wherein during the ball milling process, water is added in an amount three times the weight of the solid material, the weight of the ball milling beads used is 10 times the total weight of the material, the rotation speed is 300-600 rpm, and the ball milling time is 1-10 hours.

8. The method according to claim 1, wherein the mixing ratio of the detoxified fly ash, cement, bluestone and fine sand is (10-25):(10-25):(30-50):(10-20).

9. The method according to claim 1, wherein the curing temperature is 19-21°C, the curing humidity is not less than 90%, and the curing time is not less than 24 hours.

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