A method for preparing concrete blocks from fly ash

Abstract

The present application relates to the technical field of fly ash treatment, and particularly relates to a method for preparing concrete blocks from fly ash. The method comprises the following steps: washing the fly ash to obtain chlorine-removed fly ash; mixing the chlorine-removed fly ash with an additive and performing ball milling treatment to obtain detoxified fly ash; and mixing the detoxified fly ash, cement, green stone and fine sand, and curing under constant temperature and humidity to obtain the concrete blocks. The fly ash is washed before the ball milling treatment, so that the chlorine salt in the fly ash can be effectively removed, the solidification effect of heavy metals in the ball milling treatment is avoided, the water consumption in the ball milling treatment is reduced, water is saved, and the quality of the fly ash is effectively improved.

Description

Technical Field

[0001] This invention relates to the field of fly ash treatment technology, and specifically to a method for preparing concrete blocks from fly ash. Background Technology

[0002] Fly ash is a capture product of municipal solid waste incineration flue gas purification systems. It is rich in harmful substances, such as highly toxic organic compounds and heavy metals (e.g., Pb, Hg, Cu, Zn, and Cd). Therefore, it is classified as hazardous waste in my country (code: HW 18) and cannot be used directly as a secondary material. It requires special treatment to reduce its toxicity before reuse or landfill.

[0003] Currently, fly ash toxicity can be reduced through both thermal and non-thermal treatment. Non-thermal treatment includes cement solidification, biological / chemical reagent stabilization, and mechanochemical treatment. However, the former two still face challenges such as fly ash leaching risks, lack of long-term stability, limited treatment effectiveness, and high reagent costs. Mechanochemical treatment, on the other hand, is a greener approach due to its mild reaction conditions, simple operation, high efficiency, and lack of secondary pollution, attracting increasing attention and research. In recent years, with the deepening research into mechanochemical additives in the field of industrial solid waste, mechanochemical methods are gradually enabling the co-treatment of hazardous and industrial solid wastes while simultaneously solidifying heavy metals and improving fly ash quality. Summary of the Invention

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

[0005] Therefore, the embodiments of the present invention disclose at least the following technical solutions:

[0006] In a first aspect, embodiments disclose a method for preparing concrete blocks from fly ash. The method includes:

[0007] The fly ash is washed with water to obtain chlorine-removed fly ash;

[0008] The chlorine-removed fly ash is mixed with additives and ball-milled to obtain detoxified fly ash;

[0009] The detoxified fly ash, cement, bluestone and fine sand are mixed and cured under constant temperature and humidity to obtain the concrete blocks.

[0010] In some embodiments, the washing includes: washing the fly ash with water; performing solid-liquid separation on the suspension containing fly ash; drying the fly ash slurry after solid-liquid separation; and crushing the dried fly ash.

[0011] In some embodiments, the washing is performed at least twice.

[0012] In some embodiments, the amount of water added during the washing process is three times the weight of the fly ash.

[0013] 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.

[0014] 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).

[0015] 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 milling balls used is 10 times the total weight of the material, the rotation speed is 300~600 rpm, and the milling time is 1~10 hours.

[0016] 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).

[0017] 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.

[0018] 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% for 24 hours, and continuing to cure for 28 days after molding and demolding to obtain the concrete block.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) The present invention washes the fly ash with water before ball milling, which can effectively remove chloride salts in the fly ash, avoid affecting the solidification effect of heavy metals in ball milling, reduce the water consumption of ball milling, save water, and effectively improve the quality of fly ash.

[0021] (2) The appropriate ball milling conditions of the present invention can solidify the heavy metals in fly ash to the greatest extent, reduce reaction energy consumption, and save costs.

[0022] (3) The present invention uses additives during the ball milling process, which can effectively reduce the leaching concentration of heavy metals. During the ball milling process, fly ash is broken into small particles and then agglomerates into large particles, thereby achieving the sealing of heavy metals. Secondly, the high content of silicon, calcium, iron and other elements in the additives is conducive to the formation of hydration products including hydrated calcium aluminate, calcium iron aluminate and aluminosilicate minerals, which further promotes the solidification of heavy metals, providing a new idea for the co-treatment of industrial solid waste and hazardous waste. Furthermore, it provides the proportion of fly ash as an auxiliary gelling material for the preparation of concrete blocks, providing a practical solution for the building material and resource utilization of fly ash, and forming a relatively complete path for the detoxification and building material utilization of fly ash. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Reagents not specifically described in detail in this invention are all conventional reagents and are commercially available; methods not specifically described in detail are all conventional experimental methods and can be obtained from the prior art.

[0024] Example 1

[0025] This embodiment provides a method for preparing concrete blocks from fly ash. The method includes:

[0026] 1) The fly ash to be treated is subjected to three-stage water washing and dried to obtain chlorine-removed fly ash with a water-ash ratio of 3:1 by weight.

[0027] 2) The chlorine-removed fly ash is mixed with aluminum nitrate at a weight ratio of 9:1 and ball-milled using a planetary ball mill. After intermittent ball milling, detoxified fly ash is obtained.

[0028] 3) Mix the detoxified fly ash, cement, bluestone and fine sand in a ratio of 20:20:45:15, place in a constant temperature and humidity chamber at 20˚C and 95% humidity for 24 hours, and continue curing for 28 days after molding and demolding to prepare concrete blocks.

[0029] The three-stage washing process includes: receiving fly ash and water in a washing tank for washing; using a plate and frame filter press to filter the washed fly ash to obtain fly ash slurry and primary washing liquid; pumping the fly ash slurry back to the washing tank for secondary washing to obtain secondary washed fly ash; washing and filtering the secondary washed fly ash again to obtain tertiary washed fly ash slurry; drying the tertiary washed fly ash slurry using a single-drum dryer; and crushing the dried fly ash using a stirred reactor.

[0030] The ball milling process is a wet milling process with a liquid-to-solid ratio of 3:1, a ball-to-material ratio of 10:1, a rotation speed of 300 rpm, and a milling time of 6 hours.

[0031] Example 2

[0032] The sampling process followed roughly the same steps and conditions as in Example 1, except that the additive in step 2) was a mixture of aluminum nitrate and calcium oxide in a weight ratio of 7:3.

[0033] Example 3

[0034] The sampling process followed roughly the same steps and conditions as in Example 1, except that the additive in step 2) was a mixture of aluminum nitrate, calcium oxide, and NaH2P4 in a weight ratio of 7:1:2.

[0035] Example 4

[0036] The sampling process follows roughly the same steps and conditions as in Example 1, except that the detoxified fly ash, cement, bluestone, and fine sand are mixed in a ratio of 25:15:45:15.

[0037] Example 5

[0038] The sampling process follows roughly the same steps and conditions as in Example 1, except that the detoxified fly ash, cement, bluestone, and fine sand are mixed in a ratio of 20:25:40:15.

[0039] Comparative Example 1

[0040] The sampling process follows roughly the same steps and conditions as in Example 1, except that the additive in step 2) is steel slag.

[0041] Comparative Example 2

[0042] The sampling process follows roughly the same steps and conditions as in Example 1, except that the detoxified fly ash, cement, bluestone, and fine sand are mixed in a ratio of 5:25:45:15.

[0043] In this invention, the fly ash to be treated contains 413.5 mg / kg of Cr, 329.7 mg / kg of Cd, 909.7 mg / kg of Cu, 122.5 mg / kg of Ni, 3102.2 mg / kg of Pb, 6739 mg / kg of Zn, 325.9 mg / kg of Se, 288.4 mg / kg of Mn, and 196.2 mg / kg of As.

[0044] In the above Examples 1-5 and Comparative Examples 1-2, the weight of the fly ash processed was 18g, the weight of the additives in the ball milling process was 2g, and the weight of the ball milling beads was 200g.

[0045] Table 1 shows the percentage decrease in heavy metal leaching concentration in fly ash after ball milling in each of Examples 1-5 and Comparative Examples 1-2. It is the percentage of the difference between the heavy metal leaching concentration of the fly ash after ball milling and the heavy metal leaching concentration of the fly ash to be treated relative to the heavy metal leaching concentration of the fly ash to be treated.

[0046] Table 1 (%)

[0047]

[0048] As shown in Table 1, the fly ash from Examples 1-5, after water washing and ball milling, showed significantly higher reduction rates in the leaching concentrations of heavy metals Cd, Cr, Cu, Ni, Pb, and Zn compared to Comparative Example 1. This indicates that the ball milling process using special components as additives in this invention can reduce the leaching rates of heavy metals Cd, Cr, Cu, Ni, Pb, and Zn in fly ash, inhibiting the leaching of these heavy metals and improving their solidification effect. Furthermore, the fly ash from Examples 1-5, after water washing and ball milling, showed significantly higher reduction rates in the leaching concentrations of heavy metals Se, Mn, and As compared to Comparative Example 1. This indicates that this invention can also solidify these special heavy metals, improving the solidification effect of heavy metals in fly ash.

[0049] Table 2

[0050]

[0051] Determination of carbon fixation content:

[0052] The mass gain method was selected, which measures the change in mass of the blocks before and after mineralization as the carbon fixation amount. To reduce the error in carbon fixation measurement caused by moisture evaporation during mineralization, the blocks to be mineralized were placed in a 40×40×40 mm plastic mold with holes on each side to ensure full contact with CO2 on all four sides. The top was sealed with plastic wrap and perforated to allow CO2 circulation, thus ensuring that most of the evaporated moisture was retained in the plastic mold. The specific carbon fixation rate was calculated as 100%×(M1-M0) / Mb, where M1 is the total weight after mineralization (g), M0 is the total weight before mineralization (g), and Mb is the weight of the dry block material before mineralization (g).

[0053] Table 2 shows the 28-day compressive strength of the concrete blocks provided in Examples 1-5 and Comparative Examples 1-2. All of them meet the 15MPa requirement of the national standard GB / T 13544-2019. The 28-day compressive strength of the concrete blocks provided in Examples 1-5 is higher than that of Comparative Examples 1-2, indicating that the concrete blocks prepared by the method provided by the present invention have better mechanical strength.

[0054] As can be seen from Table 2, the carbon dioxide curing rate of the concrete blocks provided in Examples 1-5 is significantly higher than that in Comparative Examples 1-2, indicating that the water washing and ball milling treatment provided by the present invention can improve the carbon fixation capacity of concrete blocks.

[0055] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing concrete blocks from fly ash, comprising: The fly ash is washed with water to obtain chlorine-removed fly ash. The washing is performed at least twice, and the amount of water added during the washing is three times the weight of the fly ash. The chlorine-removed fly ash is mixed with an additive and ball-milled to obtain detoxified fly ash. The additive is a mixture of aluminum nitrate and calcium oxide in a weight ratio of 7:

3. The detoxified fly ash, cement, bluestone and fine sand are mixed and cured under constant temperature and humidity to obtain the concrete blocks; The water washing includes: The fly ash was washed with water; Solid-liquid separation of suspensions containing fly ash; The fly ash slurry obtained after solid-liquid separation is dried and the dried fly ash is crushed. In the ball milling process, the weight ratio of the additive to the chlorinated fly ash is 1:

9. Water is added in a weight ratio of 3 times the weight of the solid material. The weight of the milling balls used is 10 times the total weight of the material. The rotation speed is 300~600 rpm. The milling time is 1~10 hours.

2. According to the method of claim 1, the mixing ratio of the detoxified fly ash, cement, bluestone and fine sand is (10~25):(10~25):(30~50):(10~20).

3. 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 24h.

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