Operation method for removing water for digestion, drying and roasting of calcium-containing fly ash

Abstract

The invention provides an operation method for eliminating water addition for digestion, drying and roasting of calcium-containing fly ash, and belongs to the technical field of fly ash treatment.The operation method comprises the steps that fly ash pretreatment is conducted, and screening and magnetic separation are conducted on the calcium-containing fly ash; carrying out natural stabilization treatment, namely putting the pretreated fly ash in a closed environment, and naturally absorbing moisture; direct resource utilization is realized; the process of adding water to digest, drying and roasting is omitted, the dedusting ash is promoted to naturally absorb moisture to generate Ca (OH) 2 by regulating and controlling environment humidity, industrial waste gas CO2 is introduced to carry out in-situ carbonization reaction, Ca (OH) 2 is converted into stable CaCO3, water consumption and high-temperature energy consumption are avoided, CO2 resource utilization is achieved, the water-cement ratio and the concentration and modulus of a sodium silicate solution are optimized through system tests, and the comprehensive utilization rate of the dedusting ash is improved. The compression strength and durability of the product are ensured according to the water cement ratio of 15%, the sodium silicate concentration of 35%, the modulus of 2.5 and the molding pressure of 15 MPa.

Description

Technical Field

[0001] This invention belongs to the field of dust removal technology, and in particular, it is a method for eliminating the need for water digestion, drying and roasting of calcium-containing dust removal ash. Background Technology

[0002] Dust collector ash typically refers to dust collected by dust collection equipment during industrial production processes, such as dust from steel mills and cement plants. Common methods for treating dust collector ash may include water digestion, drying to remove moisture, and calcination (high-temperature treatment). Air pollutants emitted by industrial enterprises are treated by dust collection equipment such as bag filters. Most particulate matter in the exhaust gas is collected as fly ash, the composition of which is related to the collected particulate matter gas. Steel mills generate large amounts of dust collector ash, iron oxide scale, etc., which generally have good utilization value. Process dust collector ash, however, is a product of high-temperature physicochemical reactions. Formed at high temperatures, its physicochemical properties change, making it more difficult to utilize and posing a greater hazard to production. Iron-containing dust collector ash and sludge can be recycled primarily as sintering raw materials, but its negative impacts are increasingly attracting attention. To address the different characteristics of dust collector ash and sludge, various methods are employed, including sintering batching, material yard mixing, ash and sludge spraying, and rotary hearth furnace technology. This multi-pronged approach can alleviate the difficulty of treatment, achieve energy conservation and emission reduction, and comprehensively utilize resources.

[0003] Calcium-containing dust refers to dust containing calcium, derived from limestone, quicklime, or other calcium-containing raw materials. Traditional resource recovery processes have significant drawbacks. Conventional methods require water digestion to convert CaO into Ca(OH)2, followed by drying and high-temperature calcination to form a stable product. This process is not only energy-intensive and generates large carbon emissions, but the high-temperature treatment also easily damages active components, leading to reduced product reactivity. Secondly, wet digestion produces a large amount of alkaline wastewater, requiring an additional water treatment system and increasing overall costs. Furthermore, existing technologies lack sufficient control over dust particle size, resulting in high levels of impurities (such as iron filings), directly affecting the mechanical properties and chemical stability of the final product. This invention proposes a method for processing calcium-containing dust that eliminates the water digestion, drying, and calcination steps. By controlling the ambient humidity, the dust naturally absorbs moisture to generate Ca(OH)2, and industrial waste gas is introduced for in-situ carbonization, converting Ca(OH)2 into stable CaCO3. This avoids water and high-temperature energy consumption while achieving CO2 resource utilization. Summary of the Invention

[0004] The purpose of this invention is to address the aforementioned problems in existing technologies by proposing a method for eliminating the need for water digestion, drying, and calcination of calcium-containing dust removal ash.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A method for eliminating the need for water digestion, drying, and calcination of calcium-containing dust removal ash includes:

[0007] S1. Pretreatment of dust removal ash: Screening and magnetic separation of calcium-containing dust removal ash to remove impurities and adjust particle size to 80~200 mesh.

[0008] S2. Natural stabilization treatment: The pretreated dust is placed in a closed environment with humidity controlled at 60%~85%, allowing it to naturally absorb moisture and generate Ca(OH)2. Then, a gas containing CO2 is introduced to carry out a carbonization reaction to generate CaCO3.

[0009] S3. Direct resource utilization: The stabilized dust can be directly used as building material raw material, soil conditioner or metallurgical auxiliary material, or pressed into shape after adding chemical curing agent.

[0010] By controlling the ambient humidity, the material naturally absorbs moisture to generate Ca(OH)2, and then introduces a CO2-containing gas to carry out a carbonization reaction, producing CaCO3. This eliminates the traditional high-energy-consuming process. Through a three-step method of screening and magnetic separation pretreatment → natural moisture absorption carbonization → direct resource utilization, the process of water digestion, drying, and roasting is completely eliminated, reducing energy consumption by more than 30%, reducing equipment investment costs, and improving environmental friendliness. It avoids wastewater discharge (traditional water digestion) and CO2 release from high-temperature roasting. The carbonization step directly utilizes CO2 from industrial waste gas to achieve carbon fixation. The stabilized dust can be directly used in building materials, soil, or metallurgical fields without secondary processing, shortening the treatment cycle and achieving high resource utilization efficiency.

[0011] Preferably, in step S1, the dust includes at least one of iron and steel smelting dust, calcium carbide furnace dust, and lime kiln dust.

[0012] The calcium-containing dust is a high-calcium active dust with a CaO content ≥30%.

[0013] The dust from steel smelting undergoes magnetic separation pretreatment to separate iron filings with magnets, preventing iron impurities from causing defects such as expansion and cracking in building materials or metallurgical recycling.

[0014] Preferably, in step S1, the magnetic separation uses a permanent magnet drum separator with a magnetic field strength of 0.8~1.5T to remove ferromagnetic metal impurities to a content of ≤0.5%, thereby improving product purity.

[0015] The 80-200 mesh particle size range balances reaction rate and molding flowability, avoiding the agglomeration of excessively fine dust or the impact of excessively coarse particles on the curing effect.

[0016] Preferably, in step S2, the CO2-containing gas is industrial waste gas or pure CO2, the CO2 concentration is 10%~20%, and the carbonization reaction time is 2~6 hours to ensure that the CaCO3 generation rate meets the standard.

[0017] Among these methods, directly utilizing waste gas from steel mills or power plants reduces external CO2 procurement costs and achieves "waste treatment with waste".

[0018] Preferably, in step S3, the chemical curing agent is at least one of sodium silicate solution and phosphate solution, and the amount added is 5% to 20% of the mass of the dust.

[0019] Sodium silicate is alkaline and phosphate is acidic. Different pH requirements can be met for different scenarios, such as acid-resistant environments where phosphate can be selected to improve product adaptability.

[0020] Using a ratio of 5% to 20% helps to balance cost and strength; excessive addition can easily lead to cracking, while insufficient addition will prevent the formation of a continuous cementitious network.

[0021] Preferably, the sodium silicate solution has a modulus of 2.5 to 3.2 and a concentration of 25% to 40%.

[0022] The modulus ranges from 2.5 to 3.2, which helps ensure that sodium silicate has enough silicate ions to participate in the reaction while avoiding excessive alkalinity that inhibits CaO activation.

[0023] The 30% to 40% solid content helps prevent gelation during transportation and storage, while ensuring the fluidity of the mixed slurry and the stability of the solution.

[0024] Preferably, in step S3, the pressing and molding is carried out using a hydraulic press or jack, with a pressure of 5~20MPa and a holding time of 1~5 minutes to prevent springback cracking, and the molded product is bricks, granules or boards.

[0025] The pressing mold is made of steel or high-strength plastic, and the inner wall of the mold is evenly coated with a release agent.

[0026] Preferably, in step S3, the building material raw material is cement, concrete or sintered brick, and the amount of dust removal ash added is 10% to 40% of the total raw material mass.

[0027] Preferably, in step S3, the metallurgical auxiliary material is sintered ore or steelmaking auxiliary material, and the amount of dust removal ash added is 3% to 8% of the sintered mixture.

[0028] Compared with existing technologies, this method for eliminating the need for water digestion, drying, and calcination of calcium-containing dust has the following advantages:

[0029] 1. The present invention provides an operation method for calcium-containing dust removal ash that eliminates the need for water addition, digestion, drying and roasting. The method eliminates the water addition, digestion, drying and roasting processes. By controlling the ambient humidity, the dust removal ash is made to naturally absorb moisture to generate Ca(OH)2. Industrial waste gas is then introduced to carry out an in-situ carbonization reaction, so that Ca(OH)2 is converted into stable CaCO3. This method avoids water consumption and high temperature energy consumption, and realizes the resource utilization of CO2.

[0030] 2. The present invention provides an operation method for removing calcium-containing dust by adding water, digestion, drying and roasting. It uses a permanent magnet drum separator to efficiently remove ferromagnetic impurities, and combines sieving to control the particle size to 80~200 mesh, which significantly improves the reactivity and homogeneity of the particles.

[0031] 3. The present invention provides an operation method for eliminating the addition of water to digest, dry and roast calcium-containing dust. For application scenarios such as building materials and metallurgy, the method optimizes the addition ratio of chemical curing agent (5%~20%) and the pressing and molding parameters (pressure 5~20MPa, holding pressure 1~5 minutes). By controlling the formation rate of aluminosilicate gel network, the compressive strength and durability of the product are ensured.

[0032] 4. The present invention provides an operation method for eliminating the addition of water digestion, drying and roasting of calcium-containing dust removal ash. By controlling single-factor variables and detecting the compressive strength of the polymer, the optimal concentration of sodium silicate solution is determined to be 35% and the modulus is 2.5 in the lime kiln dust removal ash treatment process.

[0033] 5. The present invention provides an operation method for removing calcium-containing dust removal ash by eliminating water digestion, drying and calcination. By controlling single-factor variables and detecting the compressive strength of the polymer, the optimal water-ash ratio in the lime kiln dust removal ash treatment process is determined to be 15%.

[0034] 6. The present invention provides an operation method for removing calcium-containing dust removal ash by eliminating water digestion, drying and calcination. By controlling single-factor variables and detecting the compressive strength of the polymer, the optimal molding pressure in the lime kiln dust removal ash treatment process is determined to be 15MPa.

[0035] In summary, this invention provides a method for eliminating the need for water addition, digestion, drying, and calcination in the process of removing calcium-containing dust. It eliminates the water addition, digestion, drying, and calcination steps, and by controlling the ambient humidity, the dust is encouraged to naturally absorb moisture and generate Ca(OH)2. Industrial waste gas CO2 is then introduced to conduct an in-situ carbonization reaction, converting Ca(OH)2 into stable CaCO3. This avoids water and high-temperature energy consumption while achieving CO2 resource utilization. Furthermore, through systematic testing, the water-ash ratio, sodium silicate solution concentration and modulus, and molding parameters are optimized to ensure the compressive strength and durability of the product. The optimal process parameters are determined to be: water-ash ratio 15%, sodium silicate concentration 35%, modulus 2.5, and molding pressure 15 MPa. Detailed Implementation

[0036] The following are specific embodiments of the present invention, which further describe the technical solution of the present invention, but the present invention is not limited to these embodiments. Specific Implementation Example 1:

[0038] A method for eliminating the need for water digestion, drying, and calcination of calcium-containing dust removal ash includes:

[0039] S1. Pretreatment of dust removal ash: Screening and magnetic separation of calcium-containing dust removal ash to remove impurities and adjust particle size to 80~200 mesh.

[0040] S2. Natural stabilization treatment: The pretreated dust is placed in a closed environment with humidity controlled at 60%~85%, allowing it to naturally absorb moisture and generate Ca(OH)2. Then, a gas containing CO2 is introduced to carry out a carbonization reaction to generate CaCO3.

[0041] S3. Direct resource utilization: The stabilized dust can be directly used as building material raw material, soil conditioner or metallurgical auxiliary material, or pressed into shape after adding chemical curing agent.

[0042] By controlling the ambient humidity, the material naturally absorbs moisture to generate Ca(OH)2, and then introduces a CO2-containing gas to carry out a carbonization reaction, producing CaCO3. This eliminates the traditional high-energy-consuming process. Through a three-step method of screening and magnetic separation pretreatment → natural moisture absorption carbonization → direct resource utilization, the process of water digestion, drying, and roasting is completely eliminated, reducing energy consumption by more than 30%, reducing equipment investment costs, and improving environmental friendliness. It avoids wastewater discharge (traditional water digestion) and CO2 release from high-temperature roasting. The carbonization step directly utilizes CO2 from industrial waste gas to achieve carbon fixation. The stabilized dust can be directly used in building materials, soil, or metallurgical fields without secondary processing, shortening the treatment cycle and achieving high resource utilization efficiency.

[0043] In step S1, the dust includes at least one of the following: dust from iron and steel smelting, dust from calcium carbide furnaces, and dust from lime kilns.

[0044] The calcium-containing dust is a high-calcium active dust with a CaO content ≥30%.

[0045] The dust from steel smelting undergoes magnetic separation pretreatment to separate iron filings with magnets, preventing iron impurities from causing defects such as expansion and cracking in building materials or metallurgical recycling.

[0046] The dust collected during steel smelting, such as blast furnace dust and converter dust, specifically comprises: CaO (calcium oxide): 30%~50%; FeO / Fe2O3 (ferrous oxide / ferrous oxide): 15%~40%; SiO2 (silicon dioxide): 5%~15%; Al2O3 (aluminum oxide): 3%~10%; MgO (magnesium oxide): 1%~5%; C (carbon): 5%~20%; others (K2O, Na2O, ZnO, etc.): 1%~5%.

[0047] Among them, CaO (calcium oxide) mainly comes from lime (CaO) added during the steelmaking process as a slag-forming agent; FeO / Fe2O3 (ferrous oxide / ferric oxide) comes from iron oxides produced by the reduction of iron ore and oxidation of molten steel; SiO2 (silicon dioxide) comes from silicates in ore and coke ash; Al2O3 (aluminum oxide) comes from aluminum refractory materials or aluminum compounds in ores; MgO (magnesium oxide) comes from dolomite or magnesia refractory materials; C (carbon) comes from unburned coke or coal powder residue; and trace impurities, such as zinc, come from galvanized scrap steel.

[0048] The specific composition of the dust from the calcium carbide furnace includes: CaO (calcium oxide): 50%~70%; C (carbon): 15%~30%; SiO2 (silicon dioxide): 5%~10%; Al2O3 (aluminum oxide): 1%~5%; others (Fe2O3, MgO, S, etc.): 2%~5%.

[0049] Among them, CaO (calcium oxide) comes from the unreacted portion of limestone (CaCO3) after calcination to form CaO; C (carbon) comes from the residue of coke that did not fully participate in the reaction with calcium carbide (CaC2); SiO2 (silicon dioxide) comes from impurities in the raw material limestone or coke; Al2O3 (alumina) comes from impurities in refractory materials or ores; and sulfur may come from sulfides in coke or raw materials.

[0050] Specifically, the lime kiln dust comprises: CaO (calcium oxide): 70%~90%; CaCO3 (calcium carbonate): 5%~20%; SiO2 (silicon dioxide): 1%~5%; MgO (magnesium oxide): 1%~5%; and other substances (Al2O3, Fe2O3, K2O, etc.): 1%~3%.

[0051] Among them, CaO (calcium oxide) comes from the CaO generated by the calcination and decomposition of limestone (CaCO3); CaCO3 (calcium carbonate) comes from the incompletely decomposed limestone residue; SiO2 (silicon dioxide) comes from the siliceous impurities in limestone; MgO (magnesium oxide) comes from the decomposition products of dolomite (CaMg(CO3)2); and the others are trace impurities. Specific Implementation Example 2:

[0053] Specific Example 2 is the test of the effect of different water-cement ratios on the compressive strength of the polymer in the operation method mentioned in Specific Example 1. The content of Specific Example 2 is as follows:

[0054] 1. Taking lime kiln dust as an example, lime kiln dust and sodium silicate solution (concentration 25%, modulus 2.5) are mixed in a certain proportion, with water-cement ratios of 5%, 10%, 15%, and 20%, respectively. The mixture is stirred for 10 minutes, then filled into a cylindrical mold with a diameter of 20 mm × 30 mm. The mold is placed on a vertical hydraulic jack, and a pressure of 15 MPa is applied. This pressure is maintained for 1 minute before demolding. The polymer sample is then cured at room temperature for 21 days. Following the curing requirements for cement paste tests, the compressive strength of the samples is tested at 7 days, 14 days, and 21 days.

[0055] 2. A pressure testing machine with a range of 0~50kN and an accuracy of ±1% is used; the loading rate is 0.5~1.0MPa / s (equivalent to approximately 0.16~0.31kN / s for the cross-sectional area of ​​a cylindrical specimen); the diameter of the bearing plate is ≥30mm, and the hardness is ≥55HRC. After curing to the target age, remove the specimen and wipe off any surface dust with a damp cloth; measure the specimen diameter and height (take the average of three measurements at the upper and lower end faces), and calculate the cross-sectional area A. Place the specimen vertically in the center of the bearing plate of the pressure testing machine, ensuring uniform contact between the upper and lower end faces and the bearing plate; start the testing machine and load at a constant rate (0.5~1.0MPa / s) until the specimen fails; record the maximum load value F at failure. max The formula for compressive strength is: f c =F max / A;

[0056] Among them, f c F represents compressive strength, measured in MPa; max The value represents the failure load, in N; A represents the cross-sectional area of ​​the specimen, in mm. 2 .

[0057] 3. Results

[0058] Table 1. Effect of water-cement ratio on compressive strength

[0059] When the water-cement ratio increases from 5% to 20%, the compressive strength shows a trend of first increasing and then decreasing, with the 15% water-cement ratio sample exhibiting the highest compressive strength throughout the 7-21 day age range. From a macroscopic perspective, a 15% water-cement ratio not only ensures good moldability and demolding efficiency but also maintains a complete hardened structure. In contrast, the 20% water-cement ratio sample, due to its excessive moisture content, becomes wet and easily adheres to the mold during demolding, affecting molding quality. From a microscopic perspective, an appropriate amount of moisture (15%) can effectively promote the alkali-activated breakage of Si-O and Al-O bonds in the dust, forming silicon-aluminum-oxygen tetrahedral structural units. These units then undergo condensation polymerization to generate a stable three-dimensional network geopolymer. However, when the water-cement ratio is too high, excessive moisture has a dual impact on the reaction process. On the one hand, it hinders the normal progress of the dehydration condensation reaction, leading to a decrease in the cross-linking density of the molecular chains. On the other hand, it induces a humidity gradient inside and outside the system, causing internal free water to migrate to the surface, and unreacted Na+... + When combined with CO2, it forms carbonates, causing surface efflorescence and severely degrading the material's mechanical properties. Therefore, 15% was determined as the optimal water-cement ratio, providing a benchmark for subsequent process optimization. Specific Implementation Example 3:

[0061] Specific Example 3 involves testing the effect of sodium silicate solution concentration on polymer compressive strength, as mentioned in Specific Example 2. Sodium silicate, commonly known as sodium silicate, is an inorganic substance with the chemical formula Na₂O·nSiO₂, and is a mineral binder. Specific Example 3 is as follows:

[0062] 1. Taking lime kiln dust as an example, lime kiln dust and sodium silicate solution (water-cement ratio of 15%, sodium silicate modulus of 2.5) are mixed in a certain proportion, with the concentrations of sodium silicate solution being 25%, 30%, 35%, and 40%, respectively. The mixture is stirred for 10 minutes, then filled into a cylindrical mold with a diameter of 20mm × 30mm. The mold is placed on a vertical hydraulic jack, and a pressure of 15MPa is applied. After maintaining the molding pressure for 1 minute, the mold is demolded. The polymer sample is then cured at room temperature for 21 days. Referring to the curing requirements for cement paste testing, the compressive strength of the sample is tested at 7 days, 14 days, and 21 days.

[0063] 2. A pressure testing machine with a range of 0~50kN and an accuracy of ±1% is used; the loading rate is 0.5~1.0MPa / s (equivalent to approximately 0.16~0.31kN / s for the cross-sectional area of ​​a cylindrical specimen); the diameter of the bearing plate is ≥30mm, and the hardness is ≥55HRC. After curing to the target age, remove the specimen and wipe off any surface dust with a damp cloth; measure the specimen diameter and height (take the average of three measurements at the upper and lower end faces), and calculate the cross-sectional area A. Place the specimen vertically in the center of the bearing plate of the pressure testing machine, ensuring uniform contact between the upper and lower end faces and the bearing plate; start the testing machine and load at a constant rate (0.5~1.0MPa / s) until the specimen fails; record the maximum load value F at failure. max The formula for compressive strength is: f c =F max / A;

[0064] Among them, f c F represents compressive strength, measured in MPa; max The value represents the failure load, in N; A represents the cross-sectional area of ​​the specimen, in mm. 2 .

[0065] 3. Results

[0066] Table 2 Effect of sodium silicate solution concentration on compressive strength

[0067]

[0068] The strength significantly increased when the sodium silicate concentration increased from 25% to 35%, but decreased when it increased to 40%. This may be because the low-concentration system has insufficient SiO2 / Na2O content, leading to incomplete alkali-activated reaction and low gel product formation. At a concentration of 35%, the suitable alkaline environment accelerates the formation of Al in the dust. 3+ Si 4+ The dissolution of sodium silicate promotes the polymerization of silicon-aluminum-oxygen tetrahedra to form a dense network structure, reaching peak strength. However, when the concentration exceeds the limit of 40%, the excessively high SiO2 / Na2O ratio triggers a dual negative effect: excessive hydration gel rapidly coats the particle surface, hindering the continuous dissolution of active ions; and free Na⁺ reacts with CO2 to form surface carbonates, resulting in a loose structure. Therefore, it is concluded that the high-concentration system leads to passivation of the reaction interface due to the premature formation of the gel phase, while a 35% concentration optimizes the reaction by balancing the dissolution-polymerization rate. In summary, the synergistic effect of a 35% sodium silicate concentration and a 15% water-cement ratio was ultimately determined for screening subsequent processing techniques. Specific Implementation Example 4:

[0070] Specific Example 4 is the test of the effect of sodium silicate modulus on polymer compressive strength mentioned in Specific Example 1. The content of Specific Example 4 is as follows:

[0071] 1. Taking lime kiln dust as an example, lime kiln dust and sodium silicate solution (water-cement ratio of 15%, sodium silicate solution concentration of 35%) are mixed in a certain proportion, with sodium silicate moduli of 2.5, 2.7, 2.9, and 3.1 respectively. The mixture is stirred for 10 minutes, then filled into a cylindrical mold with a diameter of 20 mm × 30 mm. The mold is placed on a vertical hydraulic jack, and a pressure of 15 MPa is applied. After maintaining the molding pressure for 1 minute, the mold is demolded. The polymer sample is then cured at room temperature for 21 days. Referring to the curing requirements for cement paste testing, the compressive strength of the sample is tested at 7 days, 14 days, and 21 days.

[0072] 2. A pressure testing machine with a range of 0~50kN and an accuracy of ±1% is used; the loading rate is 0.5~1.0MPa / s (equivalent to approximately 0.16~0.31kN / s for the cross-sectional area of ​​a cylindrical specimen); the diameter of the bearing plate is ≥30mm, and the hardness is ≥55HRC. After curing to the target age, remove the specimen and wipe off any surface dust with a damp cloth; measure the specimen diameter and height (take the average of three measurements at the upper and lower end faces), and calculate the cross-sectional area A. Place the specimen vertically in the center of the bearing plate of the pressure testing machine, ensuring uniform contact between the upper and lower end faces and the bearing plate; start the testing machine and load at a constant rate (0.5~1.0MPa / s) until the specimen fails; record the maximum load value F at failure. max The formula for compressive strength is: f c =F max / A;

[0073] Among them, f c F represents compressive strength, measured in MPa; max The value represents the failure load, in N; A represents the cross-sectional area of ​​the specimen, in mm. 2 .

[0074] 3. Results

[0075] Table 3. Effect of sodium silicate modulus on compressive strength

[0076]

[0077] The modulus of water glass (sodium silicate) determines the rate and extent of polymer formation and hardening. When the modulus of sodium silicate increases from 2.5 to 3.1, the compressive strength shows a monotonically decreasing trend, indicating that modulus 2.5 is the optimal value. When the modulus of water glass is greater than 2.5, the high-modulus water glass, due to increased viscosity and decreased NaOH concentration, leads to a weakening of solution alkalinity, significantly inhibiting the dissolution of active components in the dust, resulting in insufficient concentration of the generated aluminum-silicon oligomers, a reduced condensation reaction rate, and reaction imbalance leading to the retention of free water during the reaction process, hindering the densification process of the three-dimensional network structure. At the same time, in the high-modulus system, excess free Na2O reacts with environmental CO2 to form carbonate precipitation, which not only causes surface alkali blooming but also degrades material properties through two pathways: first, carbonate deposition blocks pore channels, delaying the dehydration and curing process; second, interfacial reaction products disrupt the continuity of the silicon-aluminum-oxygen tetrahedra, forming structural defects. In summary, only when the modulus of water glass (sodium silicate) is appropriate can the active components in the dust be fully activated and the strength performance be better. Therefore, the water-to-dust ratio of 15%, the sodium silicate concentration of 35%, and the modulus of 2.5 were finally determined as the synergistic optimization parameters. Specific Implementation Example 5:

[0079] Specific Example 5 involves testing the effect of molding pressure on the compressive strength of the polymer, as mentioned in Specific Example 1. The purpose is to determine the optimal applied pressure value. Specific Example 5 is as follows:

[0080] 1. Taking lime kiln dust as an example, lime kiln dust and sodium silicate solution (water-cement ratio of 15%, sodium silicate solution concentration of 35%) are mixed in a certain proportion, wherein the modulus of sodium silicate is 2.5. The mixture is stirred for 10 minutes, then filled into a cylindrical mold with a diameter of 20 mm × 30 mm. The mold is placed on a vertical hydraulic jack, and pressures of 5, 10, 15, and 20 MPa are applied to the mold. The molding pressure is maintained for 1 minute before demolding. The polymer sample is then cured at room temperature for 21 days. Referring to the curing requirements for cement paste testing, the compressive strength of the sample is tested at 7 days, 14 days, and 21 days.

[0081] 2. A pressure testing machine with a range of 0~50kN and an accuracy of ±1% is used; the loading rate is 0.5~1.0MPa / s (equivalent to approximately 0.16~0.31kN / s for the cross-sectional area of ​​a cylindrical specimen); the diameter of the bearing plate is ≥30mm, and the hardness is ≥55HRC. After curing to the target age, remove the specimen and wipe off any surface dust with a damp cloth; measure the specimen diameter and height (take the average of three measurements at the upper and lower end faces), and calculate the cross-sectional area A. Place the specimen vertically in the center of the bearing plate of the pressure testing machine, ensuring uniform contact between the upper and lower end faces and the bearing plate; start the testing machine and load at a constant rate (0.5~1.0MPa / s) until the specimen fails; record the maximum load value F at failure. maxThe formula for compressive strength is: f c =F max / A;

[0082] Among them, f c F represents compressive strength, measured in MPa; max The value represents the failure load, in N; A represents the cross-sectional area of ​​the specimen, in mm. 2 .

[0083] 3. Results

[0084] Table 4. Effect of molding pressure on compressive strength

[0085]

[0086] Molding pressure is the force applied to the sample during the preparation of geopolymers. By adjusting the molding pressure, the density of the geopolymer can be controlled, thereby optimizing the material properties. As shown in the table above, the compressive strength continuously increases as the pressure increases from low to 15 MPa, while a strength inflection point appears at 20 MPa. In the low-pressure stage (<15 MPa), the interparticle contact is loose, and the reaction interface of active components is limited, resulting in insufficient structural density in the early stage (7 days). However, with the extension of curing time (21 days), unreacted Al³⁺ and Si... 4 ⁺ Continuous dissolution compensates for structural defects, resulting in a significant increase in strength in the later stages. When the pressure rises to 15 MPa, particle rearrangement and plastic deformation work together to form a dense packing structure, which not only increases the effective contact area of ​​SiO2 / Al2O3, but also lowers the reaction activation energy through mechanical energy input, promoting the rapid formation of the aluminosilicate network. Combining the previously optimized water-cement ratio of 15%, sodium silicate concentration of 35%, and modulus of 2.5, 15 MPa was established as the key value for the pressing process. Specific Implementation Example Six:

[0088] The microstructure of the samples in the molding pressure test group was characterized. It was observed that the number of harmful pores in the samples prepared by molding pressure of 15MPa was significantly reduced compared with that prepared by molding pressure of 5MPa. The samples were also more compact and had shallower surface cracks. This is because the high molding pressure greatly shortens the reaction time of SiO2 and Al2O3 in the powder during the molding process, thereby reducing the moisture loss caused by the wet-dry cycle, resulting in better compressive strength.

[0089] Based on the descriptions in Specific Embodiments 1 to Specific Embodiments 6, the optimal process parameters are determined to be: water-cement ratio of 15%, sodium silicate concentration of 35%, modulus of 2.5, and molding pressure of 15 MPa.

[0090] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A method for removing calcium-containing dust by adding water, digestion, drying, and calcination, characterized in that, include: S1. Pretreatment of dust removal ash: Screening and magnetic separation of calcium-containing dust removal ash to remove impurities and adjust particle size to 80~200 mesh. S2. Natural stabilization treatment: The pretreated dust is placed in a closed environment with humidity controlled at 60%~85%, allowing it to naturally absorb moisture and generate Ca(OH)2. Then, a gas containing CO2 is introduced to carry out a carbonization reaction to generate CaCO3. S3. Direct resource utilization: The stabilized dust can be directly used as building material raw material, soil conditioner or metallurgical auxiliary material, or pressed into shape after adding chemical curing agent.

2. The method for eliminating the need for water digestion, drying, and calcination of calcium-containing dust as described in claim 1, characterized in that... In step S1, the dust includes at least one of the following: dust from iron and steel smelting, dust from calcium carbide furnaces, and dust from lime kilns. The calcium-containing dust is a high-calcium active dust with a CaO content ≥30%. The dust from steel smelting is pretreated by magnetic separation, and iron filings are separated by magnets.

3. The method for eliminating the need for water digestion, drying, and calcination of calcium-containing dust as described in claim 1, characterized in that... In step S1, the magnetic separation uses a permanent magnet drum separator with a magnetic field strength of 0.8~1.5T to remove ferromagnetic metal impurities to a content of ≤0.5%.

4. The method for eliminating the need for water digestion, drying, and calcination of calcium-containing dust as described in claim 1, characterized in that... In step S2, the CO2-containing gas is industrial waste gas or pure CO2, the CO2 concentration is 10%~20%, and the carbonization reaction time is 2~6 hours.

5. The method for eliminating the need for water digestion, drying, and calcination of calcium-containing dust as described in claim 1, characterized in that... In step S3, the chemical curing agent is at least one of sodium silicate solution and phosphate solution, and the amount added is 5% to 20% of the mass of dust.

6. The method for eliminating the need for water digestion, drying, and calcination of calcium-containing dust as described in claim 5, characterized in that... The sodium silicate solution has a modulus of 2.5 to 3.2 and a concentration of 25% to 40%.

7. The method for eliminating the need for water digestion, drying, and calcination of calcium-containing dust as described in claim 1, characterized in that... In step S3, the pressing and molding process uses a hydraulic press or jack, with a pressure of 5~20MPa and a holding time of 1~5 minutes. The molded product is brick, granules or board. The pressing mold is made of steel or high-strength plastic, and the inner wall of the mold is evenly coated with a release agent.

8. The method for eliminating the need for water digestion, drying, and calcination of calcium-containing dust as described in claim 1, characterized in that... In step S3, the building material raw material is cement, concrete or sintered brick, and the amount of dust ash added is 10% to 40% of the total raw material mass.

9. The method for eliminating the need for water digestion, drying, and calcination of calcium-containing dust as described in claim 1, characterized in that... In step S3, the metallurgical auxiliary material is sintered ore or steelmaking auxiliary material, and the amount of dust removal ash added is 3% to 8% of the sintered mixture.

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