Autoclaved aerated concrete blocks prepared using phosphogypsum and glass powder and their preparation method

Abstract

This invention provides an autoclaved aerated concrete (AAC) block and method for preparing it using phosphogypsum and glass powder. It belongs to the field of bulk solid waste resource utilization technology. It is an AAC block and method that enables large-scale, high-value synergistic utilization of phosphogypsum and glass powder, overcoming the problem of high dependence on natural resources in existing technologies. The product prepared by this method not only realizes the resource utilization of solid waste, but also achieves breakthroughs in key physical properties, with comprehensive advantages of being lightweight, high-strength, and having excellent thermal insulation properties.

Description

Technical Field

[0001] This invention belongs to the field of bulk solid waste resource utilization technology, specifically relating to an autoclaved aerated concrete block and method for preparing it using phosphogypsum and glass powder. Background Technology

[0002] Waste glass is a significant component of urban solid waste. my country generates a massive amount of waste glass annually, yet its recycling rate remains to be improved. Large quantities of discarded glass bottles, jars, and flat glass are chemically extremely stable and difficult to degrade in the natural environment. Traditional landfill disposal not only occupies valuable land resources for extended periods, but the sharp fragments formed after breakage can also damage soil structure, posing potential environmental and safety risks. Therefore, finding a large-scale, high-value resource-based solution for waste glass has become an urgent problem to be solved in urban solid waste management.

[0003] Dry desulfurization phosphogypsum is a large-scale industrial by-product gypsum generated during flue gas desulfurization processes in metallurgy, chemical industry, and other sectors. Unlike natural gypsum, its composition is complex and variable, often containing unreacted calcium-based desulfurizing agents (such as Ca(OH)2, CaCO3) and small amounts of impurities, resulting in unstable physical properties. For a long time, large stockpiles of phosphogypsum have not only encroached on land, but the leaching of its dust and soluble salts has also posed a pollution threat to surrounding soil and water bodies. Although its use in building material production is an ideal disposal method, its unique physicochemical properties (such as containing soluble phosphorus and fluorine, or exhibiting significant differences in reactivity as type II anhydrite) present technical bottlenecks when applied to precision building material systems such as autoclaved aerated concrete. These bottlenecks include inhibiting lime digestion, affecting slurry stability, and causing fluctuations in product performance, thus restricting its large-scale and safe application.

[0004] Against this backdrop, the co-processing and high-value utilization of dry desulfurized phosphogypsum, which is difficult to dispose of, and waste glass, which is difficult to dispose of, is of great significance. If both can be introduced into the production system of autoclaved aerated concrete (AAC), replacing part or even all of the natural gypsum and siliceous sand, it will not only solve the disposal problems of both types of solid waste and greatly reduce the environmental burden, but also create new green building materials with excellent performance, with broad market prospects and social benefits. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of the existing technologies mentioned above by providing a method for the large-scale, high-value synergistic utilization of phosphogypsum and glass powder to prepare autoclaved aerated concrete blocks. This overcomes the problem of high dependence on natural resources in existing technologies. The products prepared by this method not only realize the resource utilization of solid waste, but also achieve breakthroughs in key physical properties, possessing comprehensive advantages such as lightweight, high strength, and excellent thermal insulation performance.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: An autoclaved aerated concrete block prepared using phosphogypsum and glass powder is made from dry materials and auxiliary materials, wherein the dry materials consist of the following components by weight percentage: Ordinary cement: 10%–20%; Quicklime: 5%–15%; Phosphogypsum: 1%–10%; Composite silicon materials: 55%–70%; The remainder consists of waste generated during the production of autoclaved aerated concrete blocks; The composite siliceous material is composed of quartz tailings sand or natural sand and glass powder, wherein the glass powder accounts for 10% to 40% of the total weight of the composite siliceous material. The particle size distribution of the glass powder satisfies the following: 15%~30% of the particles are 120~170 mesh, 40%~55% are 170~250 mesh, and 15%~45% are 325~400 mesh. The auxiliary material is aluminum powder or aluminum powder paste.

[0008] Preferably, the ordinary cement is silicate cement with a C3A content greater than 5% and a CaO content greater than 50%.

[0009] Preferably, the quicklime has a slaking time of 5-10 minutes, a slaking temperature of 85-100℃, an effective CaO content of more than 70%, a fineness of more than 150 mesh, and a sieve residue of less than 15%.

[0010] Preferably, the phosphogypsum is a dry desulfurized phosphogypsum powder with a Ca(OH)2 content greater than 30%, a CaSO4 content greater than 40%, a CaCO3 content less than 15%, and a moisture content less than 1.5%.

[0011] Preferably, the quartz tailings sand or natural sand has a SiO2 content of more than 70%, an organic matter content of less than 2.5%, and a mud content of less than 5%.

[0012] Preferably, the glass powder is derived from waste glass that has been recycled, sorted, cleaned, and disinfected, including flat glass, bottle and jar glass, or everyday utensil glass.

[0013] The present invention also provides a method for preparing autoclaved aerated concrete blocks as described above, comprising the following steps: a. Wet-grind the quartz tailings sand until the fineness meets the requirement that the residue on a 0.08mm square hole sieve is less than 20%, and prepare a raw slurry with a moisture content of 30%~40%; b. Add graded glass powder to the slurry obtained in step a according to the proportion, and stir to form a composite silica suspension slurry; c. Mix the composite silica suspension slurry, cement, phosphogypsum and water for 60s~120s, controlling the water-to-material ratio to be 0.48~0.58; d. Add quicklime to the mixture obtained in step c and continue stirring, controlling the slurry diffusion to 20cm~26cm, and raise the temperature to 40℃~60℃; e. Add aluminum powder or aluminum powder paste and stir for 20-30 seconds before pouring; f. Allow the poured slurry to stand for 1.5 to 3 hours in an environment with a temperature of 20℃ to 60℃ and a humidity of 50% to 60%; g. Demold and cut the cured green body, and then send it into an autoclave for autoclaving. h. The autoclaving process includes: evacuating the vessel for 30-60 minutes to achieve a vacuum level of -0.04 MPa to -0.08 MPa; increasing the pressure and temperature to 0.70 MPa to 1.25 MPa and 183°C to 210°C within 1.5-3 hours, and maintaining this pressure and temperature for 5-10 hours; subsequently, venting the gas and reducing the temperature and pressure within 1.5-2 hours. i. After being removed from the pot, the product is naturally cured for 5 days to obtain the finished product.

[0014] Preferably, in step c, a step-by-step feeding process is adopted, in which the composite silica suspension slurry, cement, phosphogypsum and water are first pre-mixed and stirred, then quicklime is added in step d, and finally aluminum powder or aluminum powder paste is added in step e.

[0015] Preferably, during the batching process, sulfur-aluminum balance is achieved by controlling the molar ratio (S / A ratio) of sulfate to activated alumina between 2.6 and 3.2; wherein the molar amount of activated alumina is calculated based on the C3A content in the cement, and the molar amount of sulfate is calculated based on the SO3 content in the phosphogypsum.

[0016] The present invention also provides the application of the above-mentioned autoclaved aerated concrete blocks in building wall materials.

[0017] Compared to traditional autoclaved aerated concrete (AAC) systems, this invention completely replaces natural gypsum with dry-process desulfurized phosphogypsum and partially replaces quartz sand with specifically graded waste glass powder, achieving synergistic high-value utilization of these two bulk solid wastes in the building materials field. This significantly reduces the consumption of natural mineral resources and alleviates the environmental pressure caused by solid waste stockpiling. Its performance advantages include the following: Higher mechanical strength: Through the refined gradation design of glass powder, the finer particles can contribute certain activity under autoclaving, while the coarser particles serve as high-performance micro-aggregates. This, combined with the composite activation effect of dry desulfurized phosphogypsum, significantly optimizes the microstructure of the blocks, increasing their compressive strength by more than 10% compared to traditional similar products.

[0018] Superior thermal insulation performance: The glass material itself has a low thermal conductivity. Combined with the optimized porous structure, the thermal conductivity of the block of this invention is significantly reduced, and the thermal insulation performance is improved by more than 15%, which helps to reduce the energy consumption of building operation.

[0019] Lower dry density: While ensuring that the strength is not reduced or even increased, the present invention can effectively reduce the dry density of the product, which is conducive to the lightweighting of building structures and saves transportation and construction costs. Detailed Implementation

[0020] To enable those skilled in the art to better understand and implement the present invention, the technical means and effects of achieving the intended purpose of the invention are described in detail below with reference to specific embodiments. These embodiments are for illustrative purposes only.

[0021] 1. Preparation of Composite Silica Suspension Slurry: First, quartz or quartz tailings sand is ground to a sieve thickness of less than 20% (0.08 square mesh) and a moisture content ≤40% to form a tailings sand slurry. Simultaneously, prepared graded glass powder (120-170 mesh 15%-30%, 170-250 mesh 40%-55%, 325-400 mesh 15%-45%) is accurately weighed according to the designed proportions (10%-40% of the total weight of the silica material). Then, under stirring conditions, the weighed graded glass powder is gradually added to the tailings sand slurry, and stirring is continued until the mixture is homogeneous, forming a 'quartz tailings sand-graded glass powder' composite suspension slurry. This composite slurry serves as the silica material component of this invention for subsequent batching.

[0022] 2. Reaction mechanism of sulfur-aluminum equilibrium In autoclaved aerated concrete (AAC) systems employing dry-process desulfurized phosphogypsum, the reaction between sulfates and active aluminates is the core chemical process for achieving early structural stability and final performance optimization. Its mechanism can be divided into two distinct stages: Phase 1: Static Curing Period – Formation of the Etuff Structural Framework This stage occurs in the static environment (40~60℃) after slurry pouring. The sulfate ions (SO₄²⁻) provided by the dissolution of dry desulfurized phosphogypsum... 2- The precipitate reacts rapidly with tricalcium aluminate (3CaO·Al2O3, abbreviated as C3A) in silicate cement to form needle-like ettringite crystals. This reaction is the fundamental source of the green body's early cutting strength.

[0023] The main chemical reaction formulas are as follows: C3A+3CaSO4+32H2O→3CaO·Al2O3·3CaSO4·32H2O Key point: The Ca(OH)2 component in the dry desulfurized phosphogypsum increases the alkalinity of the slurry, further promoting the dissolution of C3A and the above-mentioned reactions, enabling the ettringite network to form more quickly and fully.

[0024] Phase Two: Autoclaving Period – Transformation of Eundum and Formation of Tobermorite In a high-temperature, high-pressure autoclave (183℃~210℃, 0.70MPa-1.25 MPa), ettringite is a thermodynamically unstable phase. It will decompose, and its decomposition products (such as Al) 3+ SO4 2- It reacts with a large amount of siliceous materials (SiO2) and calcareous materials (Ca(OH)2) in the system to generate the main crystalline phase that ultimately gives the product its strength—tobermorite.

[0025] 3. Calculation method for sulfur-aluminum balance The core objective of sulfur-aluminum balance is to ensure the formation of an appropriate amount of ettringite during the static resting period to stabilize the green body by precisely controlling the initial ratio of sulfate to aluminum phase, while ensuring that it can be completely and smoothly transformed into stable tobermorite during the autoclaving period, thus avoiding the formation of harmful phases such as residual gypsum (CaSO4) or monosulfate calcium sulfoaluminate (AFm) due to excessive sulfate or aluminum phase.

[0026] To achieve optimized control of the above mechanism, this invention proposes the following quantitative calculation method, the core of which is to control the molar ratio (S / A ratio) of sulfate (calculated as SO3) to activated alumina (Al2O3).

[0027] Step 1: Determine the total molar amount of the active aluminum phase (based on Al2O3). The active aluminum phase mainly originates from C3A in cement, while the aluminum phase in other raw materials is considered inactive during the static resting period.

[0028] Let M be the amount of cement used. C (kg), the mass percentage of C3A in the cement used is W C3A (%).

[0029] The formula for calculating the total molar amount of active Al2O3 is: M Al (mol)=M C ×(W C3A / 100)×P Where P is a conversion factor. Given that the mass percentage of Al₂O₃ (molecular weight approximately 10⁻²) in C₃A (molecular weight approximately 270) is approximately 0.377, therefore P≈1000 / 10²×0.377≈3.70. That is: M Al ≈Mc×W C3A ×0.037 (W in the formula) C3A Substitute the percentage value, for example, substitute 7% into 7). Step 2: Set the target sulfur-aluminum molar ratio (S / A) Based on extensive experimental verification, controlling the S / A molar ratio (n(SO3) / n(Al2O3)) between 2.6 and 3.2, preferably between 2.8 and 3.0, achieves the best balance between processability and final performance. This ratio is denoted as R.

[0030] Step 3: Calculate the total molar amount M of sulfate (as SO3) required. S M S (mol) = M Al ×R Step 4: Calculate the precise dosage m of dry desulfurization phosphogypsum. g Let the mass percentage of SO3 in the target dry desulfurization phosphogypsum be W. SO3 (%) (obtained from the test report). The molar mass of SO3 is approximately 80 g / mol.

[0031] The theoretically required mass of dry desulfurized phosphogypsum is: m g (kg) = (M S ×0.080) / (W SO3 / 100) Considering the reaction efficiency of raw materials and process fluctuations, an empirical correction coefficient K (0.9-1.1) is introduced, and the final calculation formula is: m g (kg) = (M S ×0.080) / (W SO3 / 100)×K 4. Key processes for achieving sulfur-aluminum balance: To ensure that the above theoretical calculations can be accurately realized in industrial production, a matching "stepwise feeding and stirring" process must be adopted to control the reaction sequence.

[0032] Premixing and preferential reaction stage: The raw slurry, cement, dry desulfurized phosphogypsum, and water (water-to-material ratio 0.54~0.64) are mixed and stirred for 60~120 seconds. The core purpose of this stage is to force the release of SO4 in an environment free from quicklime interference. 2- It preferentially and fully reacts with C3A to generate ettringite crystal nuclei, pre-constructs an early strength framework, and "consumes" most of the sulfate ions.

[0033] In the lime addition and final activation stage, all quicklime is added to the premixed slurry and stirring continues. At this point, because a large amount of sulfate ions have been coordinated and consumed, their inhibitory effect on quicklime is greatly weakened, allowing the quicklime to digest rapidly, release heat intensely, and efficiently drive slurry thickening and aluminum powder gas generation.

[0034] Process synergy: This step-by-step process is closely integrated with the sulfur-aluminum balance calculation model, achieving a unity of "precise stoichiometric design" and "precise control of the reaction process." It ensures that the calculated sulfate is used to the maximum extent to form a beneficial structural framework (ettringite), while freeing up the heat source function of quicklime, thereby simultaneously optimizing the performance of the green body and the final product.

[0035] 5. A preferred embodiment of the present invention is provided below: In this embodiment, A3.5B06 grade autoclaved aerated concrete blocks were designed and prepared according to the method described in this invention.

[0036] (1) Formula (based on the percentage of dry material weight in the design) Composite suspension slurry: 72.0% (graded glass powder accounts for 38.96%), PO 42.5 cement: 14.0%, quicklime: 6.0%, dry desulfurized phosphogypsum: 3.0%, recycled waste slurry (dry basis): 5%, aluminum powder paste: 0.066% (approximately 0.40 kg / m³ of product). During production, the water-to-material ratio is controlled at 0.52. Following the aforementioned preparation steps, the slurry is poured, cured statically, cut, and autoclaved. After autoclaving at 187℃ and 0.80 MPa for 7 hours, it undergoes inspection upon exiting the autoclave, is packaged and stored, and then naturally cured for 5 days to obtain the finished product.

[0037] (2) Product performance test results According to GB / T11969-2008 "Test Methods for Performance of Autoclaved Aerated Concrete", the dry density of autoclaved aerated concrete blocks in Example 1 was 639 kg / m3, and the cubic compressive strength was 5.3 MPa.

[0038] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A steam pressure aerated concrete block prepared by using phosphogypsum and glass powder, which is made of a dry material and an auxiliary material, characterized in that, The dry material is composed of the following components by weight percentage: Ordinary cement: 10%~20%; Quicklime: 5%~15%; Phosphogypsum: 1%~10%; Composite siliceous material: 55%~70%; The balance is waste generated during the production of autoclaved aerated concrete blocks; The composite siliceous material is composed of quartz tailings sand or natural sand and glass powder, and the glass powder accounts for 10%~40% of the total weight of the composite siliceous material; The particle size distribution of the glass powder satisfies: 120~170 mesh particles account for 15%~30%, 170~250 mesh particles account for 40%~55%, and 325~400 mesh particles account for 15%~45%; The auxiliary material is aluminum powder or aluminum paste.

2. The autoclaved aerated concrete block according to claim 1, characterized in that, The ordinary cement is Portland cement with C3A content greater than 5% and CaO content greater than 50%.

3. The autoclaved aerated concrete block according to claim 1, characterized in that, The digestion time of the quicklime is 5~10 minutes, the digestion temperature is 85~100℃, the effective CaO content is greater than 70%, the fineness is greater than 150 mesh, and the sieve residue is less than 15%.

4. The autoclaved aerated concrete block according to claim 1, characterized in that, The phosphogypsum is a dry desulfurization phosphogypsum powder, with Ca(OH)2 content greater than 30%, CaSO4 content greater than 40%, CaCO3 content less than 15%, and water content less than 1.5%.

5. The autoclaved aerated concrete block according to claim 1, characterized in that, The SiO2 content of the quartz tailings sand or natural sand is greater than 70%, the organic matter content is less than 2.5%, and the clay content is less than 5%.

6. The autoclaved aerated concrete block of claim 1, wherein, The glass powder is derived from waste glass after recycling, sorting, cleaning, and sterilization treatment, including flat glass, bottle glass, or daily utensil glass.

7. A method of manufacturing the autoclaved aerated concrete block according to any one of claims 1 to 6, characterized in that, The method comprises the following steps: a. Wet grinding quartz tailings sand to a fineness that satisfies a 0.08mm square hole sieve residue of less than 20%, to produce a raw slurry with a water content of 30%~40%; b. Incorporating graded glass powder into the raw slurry obtained in step a. in proportion, stirring and mixing to form a composite siliceous suspension raw slurry; c. Mixing and stirring the composite siliceous suspension raw slurry, cement, phosphogypsum, and water for 60s~120s, controlling the water material ratio to be 0.48~0.58; d. Adding quicklime to the mixture obtained in step c. and continuing to stir, controlling the slurry spread degree to be 20cm~26cm, and heating to 40℃~60℃; e. Adding aluminum powder or aluminum paste and stirring for 20s~30s, then pouring; f. Pouring the slurry after pouring in an environment with a temperature of 20℃~60℃ and a humidity of 50%~60% for 1.5h~3h; g. Demolding and cutting the green body after static curing, and then sending it to an autoclave for autoclaving; h. The autoclaving process includes: vacuumizing for 30min~60min to make the vacuum degree in the autoclave reach -0.04MPa ~ -0.08MPa; Rising pressure and temperature to 0.70MPa~1.25MPa, 183℃~210℃ within 1.5h~3h, and keeping constant pressure and temperature for 5h~10h; then degassing and cooling within 1.5h~2h; i. After coming out of the autoclave, natural curing for 5 days to obtain the finished product.

8. The method of claim 7, wherein, In step c, a step feeding process is adopted, first, the composite siliceous suspension raw slurry, cement, phosphogypsum and water are pre-mixed and stirred in the first stage, then step d is performed to add quicklime, and finally step e is performed to add aluminum powder or aluminum paste.

9. The method of claim 5 or 6, wherein, When batching, the sulfur-aluminum balance is achieved by controlling the molar ratio of sulfate to active alumina (S / A ratio) between 2.6 and 3.2; wherein the molar amount of active alumina is calculated by the C3A content in cement, and the molar amount of sulfate is calculated by the SO3 content in phosphogypsum.

10. Use of autoclaved aerated concrete blocks according to any one of claims 1 to 6 in building wall materials.