Unfired sludge-based environment-friendly geopolymer brick as well as preparation method and application thereof

Abstract

The invention provides an unfired sludge-based environment-friendly geopolymer brick as well as a preparation method and application thereof, and relates to the technical field of resource recycling. The geopolymer brick comprises a mixture and an alkali activator, the mixture comprises sludge slurry, granulated blast furnace slag and secondary aluminum ash. The preparation method comprises the following steps: 1) mixing the sludge slurry, the secondary aluminum ash and the granulated blast furnace slag according to a set proportion to obtain a mixture; (2) adding an alkali activator into the mixture, controlling the liquid-solid ratio to be 0.3-0.4%, and stirring for 3-10 minutes at the rate of 300-600rpm at room temperature to form uniform polymer slurry; and (3) injecting the slurry into a mold for primary curing and hardening, demolding after reaching the set strength, and curing again to obtain the environment-friendly geopolymer brick. The alkali activator is causticized slurry obtained in the recovery process of waste alkali in the papermaking industry. The sludge is converted into the environment-friendly brick, resource utilization of the sludge is achieved, meanwhile, the novel environment-friendly brick is provided to replace a concrete material, and the environment-friendly brick has the advantages of being environmentally friendly and low in cost.

Description

Technical Field

[0001] This invention relates to the field of resource recycling technology, specifically to a non-fired sludge-based environmentally friendly polymer brick, its preparation method, and its application. Background Technology

[0002] As a viable alternative to key building materials such as concrete, the development and application value of environmentally friendly bricks is increasingly prominent. The large-scale mining of traditional natural aggregates in concrete not only exacerbates resource scarcity but also poses a significant threat to the ecological environment, potentially triggering landslides, disrupting water balance, and accelerating soil erosion. Therefore, promoting the performance optimization and large-scale replacement of concrete with environmentally friendly bricks has become an important development direction in the construction industry. Currently, the production process of environmentally friendly bricks still faces some common challenges, such as difficulty in meeting engineering construction requirements in terms of strength and durability; potential environmental impacts during production or use, such as the migration of harmful substances, making it difficult to fully comply with green building material standards.

[0003] On the other hand, the dredging of rivers and waterways generates a large amount of silt. If this silt is not properly treated and is indiscriminately dumped, it will occupy a significant amount of land resources. Furthermore, the harmful substances it contains may be washed into surrounding water bodies and soil by rainwater, causing secondary environmental pollution. Traditional silt treatment methods mainly include ocean discharge, landfill, or open-air dumping, but these methods all have many drawbacks and make it difficult to achieve efficient resource utilization of silt. Regarding the resource utilization of silt, existing technological approaches mainly include land reclamation, building material conversion, and engineering backfilling. However, these methods all have corresponding limitations: when used for land reclamation, a long stabilization process is required; when used to make building materials, it often relies on external materials and consumes a lot of energy; and as fill material, its performance is limited, and its application range is narrow.

[0004] Therefore, developing a technology that can efficiently dispose of sludge and produce lightweight, environmentally friendly bricks that meet performance standards is of urgent significance for alleviating the pressure on building material demand and promoting sludge treatment and resource recycling. Summary of the Invention

[0005] To overcome the shortcomings of the above-mentioned technologies, the purpose of this invention is to provide a non-fired sludge-based environmentally friendly geopolymer brick, its preparation method and application, to solve the environmental burden caused by the large-scale stockpiling of sludge and the environmental pollution caused by the mining of natural aggregates in building materials.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A non-fired sludge-based environmentally friendly geopolymer brick is characterized by its raw materials including a mixture and an alkali activator; the mixture includes sludge slurry, granulated blast furnace slag, and secondary alumina ash.

[0007] As a preferred embodiment, the mass percentages of each component in the mixture are as follows: 50-70% sludge slurry, 15-25% granulated blast furnace slag, and 15-25% secondary aluminum ash, with the total mass percentage of each component being 100%; wherein, the sludge slurry is calculated by dry weight.

[0008] As a preferred embodiment, the alkali activator is causticized pulp obtained from the waste alkali recovery process in the papermaking industry. The causticized pulp is obtained by treating papermaking black liquor. The treatment process includes: firstly, concentrating the black liquor produced during pulping in the papermaking process to a solid mass concentration >60% through a multi-effect evaporation system; then, sending the concentrated black liquor into an alkali recovery furnace and burning it at a high temperature of 500±50℃ for 10-30 minutes, where the organic matter decomposes to provide energy, and the inorganic sodium salt melts to generate a molten material; the main components of the molten material are sodium carbonate and sodium sulfide; finally, dissolving the molten material in water or dilute white liquor to form green liquor, and then causticizing it with lime to obtain a viscous liquid, which is the causticized pulp. The amount of lime added is 5-10% of the mass of the green liquor. The water content of the causticizing slurry is 45-55 wt%. In addition to water, the causticizing slurry also contains Na2SO4, Na2SiO3, NaOH and other components. Taking the total of Na2SO4, Na2SiO3, NaOH and other components as 100%, the mass percentages of each component are 5-15%, 15-25%, 60-70%, and 4-6%, respectively.

[0009] As a preferred embodiment, the unconfined compressive strength of the environmentally friendly brick is not less than 30 MPa. The finished product has excellent performance, with an unconfined compressive strength of over 30 MPa, meeting the technical requirements of the national standard "Permeable Pavement Bricks and Permeable Pavement Panels" (GB / T25993-2023).

[0010] This invention also provides a method for preparing the above-mentioned non-fired sludge-based environmentally friendly geopolymer bricks, which is characterized by including the following steps: 1) Mix the sludge slurry, secondary aluminum ash and granulated blast furnace slag in a set ratio to obtain a mixture; 2) Add alkali activator to the mixture, control the liquid-to-solid ratio to 0.3-0.4wt%, and stir at 300-600 rpm for 3-10 minutes at room temperature to form a uniform polymer slurry; 3) The slurry is injected into the mold for initial curing and hardening. After the compressive strength reaches 1-2 MPa, it is demolded and further cured to obtain environmentally friendly polymer bricks.

[0011] As a preferred embodiment, the sludge slurry is obtained by removing impurities from dredged sludge; the impurities include large-volume biomass such as branches and dead leaves; the moisture content of the sludge slurry is measured before use in order to calculate the amount to be added.

[0012] As a preferred embodiment, in step 2), the stirring rate is 450-550 rpm, and the stirring time is 4-7 minutes. Stirring uses its mechanical energy to thoroughly mix the materials, and a preliminary chemical reaction occurs during this process, thereby promoting the final gelation reaction. If the stirring speed is too low or the stirring time is too short, it will be difficult to achieve the effect of activating the reaction. However, if the stirring speed reaches a certain level or the stirring time is excessively extended, further increasing the stirring speed will have little effect on improving product performance, and may even wear down the mechanical equipment and increase energy consumption. Therefore, the stirring rate is further preferably 450-550 rpm, and the stirring time is preferably 4-7 minutes.

[0013] As a preferred option, in step 3), the maintenance is natural maintenance at room temperature.

[0014] This invention also provides the application of the above-mentioned non-fired sludge-based environmentally friendly geopolymer bricks in the preparation of permeable pavement bricks.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention relates to a non-fired sludge-based environmentally friendly geopolymer brick, its preparation method, and its application. It transforms sludge into environmentally friendly bricks, realizing the resource utilization of sludge while providing a new type of environmentally friendly brick to replace concrete materials. It has the advantages of being environmentally friendly and low-cost.

[0016] The raw materials used in this invention are widely available and low in cost. Furthermore, the non-firing process results in low energy consumption and a simple and easy-to-implement preparation process, which is conducive to large-scale promotion and use.

[0017] The method of this invention uses simple equipment, avoids the use of high temperature, high alkalinity solution and cement, and is highly feasible, energy-efficient and has good social benefits.

[0018] This invention utilizes an alkali activator to activate the gelling activity of sludge and adds other industrial solid waste to achieve the compressive strength of the final product. The alkali activator is prepared from waste alkali from the papermaking industry. Applying industrial waste such as secondary aluminum ash and granulated blast furnace slag to the preparation of environmentally friendly bricks not only solves the problems of waste disposal and treatment, reducing environmental pollution, but also achieves resource recycling, aligning with the concept of sustainable development. The alkali activator reacts with the active components in the sludge to generate a geopolymer network gel with low permeability and high stability. This gel fills the pores inside the brick, reducing the entry channels for harmful substances, thereby improving the brick's corrosion resistance and extending the service life of the concrete structure.

[0019] The environmentally friendly bricks prepared by this invention have an unconfined compressive strength of over 30 MPa, which meets the national standard "Permeable Pavement Bricks and Permeable Pavement Panels" (GB / T25993-2023). Attached Figure Description

[0020] Figure 1 This is an X-CT scan of the non-fired sludge-based environmentally friendly polymer brick in Example 3; Figure 2 This is a microscopic scanning image of the non-fired sludge-based environmentally friendly polymer bricks in Example 3; Figure 3 The image shows the XPS analysis spectrum of Si element in the environmentally friendly brick in Example 3. Detailed Implementation

[0021] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1 A non-fired sludge-based environmentally friendly geopolymer brick, the raw materials of which include a mixture and an alkali activator; the mixture includes 50wt% sludge slurry (dry weight), 25wt% granulated blast furnace slag, and 25wt% secondary alumina ash.

[0023] Alkali activator is a causticized pulp obtained during the recovery of waste alkali in the papermaking industry. The alkali activator is obtained by recovering and treating waste alkali liquor from the papermaking industry. The main process is as follows: First, the dilute black liquor produced during pulping is concentrated to a solid mass concentration >60% using a multi-effect evaporation system. Then, the concentrated black liquor is sent to an alkali recovery furnace and burned at 500±50℃ for 20 minutes. The organic matter decomposes to provide energy, and the inorganic sodium salts melt to form a molten substance, the main components of which are sodium carbonate and sodium sulfide. Finally, these molten substances are dissolved in water to form a green liquor, which is then subjected to lime causticization treatment. The lime dosage is 8% of the green liquor mass. The final viscous liquid obtained is the alkali activator, with a water content of 50wt%. Besides water, it also contains Na2SO4, Na2SiO3, NaOH, and other components. Assuming the total content of Na2SO4, Na2SiO3, NaOH, and other components is 100%, the mass percentages of each component are 10%, 20%, 65%, and 5%, respectively.

[0024] The preparation method of the above-mentioned non-fired sludge-based environmentally friendly polymer bricks includes the following steps: 1) Mix the sludge slurry, granulated blast furnace slag and secondary aluminum ash in a set ratio to obtain a mixture.

[0025] 2) Preparation of geopolymer slurry: Add alkali activator to the mixture, control the liquid-solid ratio to 0.35wt%, and stir at 300rpm for 3min at room temperature to form a uniform geopolymer slurry; the room temperature is 25±2℃.

[0026] 3) The slurry is poured into a mold for initial curing and hardening. After demolding, it is cured again to obtain environmentally friendly polymer bricks. The specific operation is as follows: The slurry is poured into a 700mm×700mm×700mm cubic mold with an internal release agent. After compaction on a vibrating table for 1 minute, it is allowed to stand at room temperature for initial curing for 24 hours. After reaching 2MPa, it is demolded and then cured at room temperature for another 14 days to obtain the geopolymer brick.

[0027] The obtained environmentally friendly geopolymer bricks were subjected to heavy metal leaching tests according to the "Identification Standard for Hazardous Waste - Leaching Toxicity Identification Method" (HJ / T 300-2007). The results showed that the concentrations of heavy metals such as Pb, Cd, and Cr were 0.08 mg / L, 0.005 g / L, and 0.11 g / L, respectively, all far below the leaching limits for hazardous waste in my country, indicating that the geopolymer bricks have a good curing and sealing effect on heavy metals.

[0028] The apparent density of the obtained environmentally friendly geopolymer bricks is 1700 kg / m³. 3 The water absorption rate is 4.5%. According to the national standard "Permeable Pavement Bricks and Permeable Pavement Panels" (GB / T25993-2023), the obtained environmentally friendly polymer bricks were tested after 28 days of curing and found to have a compressive strength of 32.5MPa, an elastic modulus of 28GPa, and a slump of 105mm, which meet the general structural and road use requirements.

[0029] Example 2 The difference between this embodiment and Embodiment 1 is that: In this embodiment, the raw materials for the non-fired sludge-based environmentally friendly geopolymer bricks include: 60wt% sludge slurry (dry weight), 20wt% granulated blast furnace slag, and 20wt% secondary alumina ash; In step 2) of the preparation method of non-fired sludge-based environmentally friendly polymer bricks in this embodiment, the liquid-solid ratio is controlled at 0.37wt%, the stirring rate is 500rpm, and the stirring time is 5min.

[0030] The apparent density of the environmentally friendly geopolymer bricks obtained in this embodiment is 1735 kg / m³. 3 The water absorption rate was 4.2%. After 28 days of curing, the compressive strength was 35.5 MPa, the elastic modulus was 29 GPa, and the slump was 102 mm. The heavy metal leaching test results showed that the concentrations of heavy metals such as Pb, Cd, and Cr were 0.07 mg / L, 0.003 mg / L, and 0.12 mg / L, respectively.

[0031] Example 3 The difference between this embodiment and Embodiment 1 is that: In this embodiment, the raw materials for the non-fired sludge-based environmentally friendly geopolymer bricks include: 70wt% sludge slurry (dry weight), 15wt% granulated blast furnace slag, and 15wt% secondary alumina ash; In step 2) of the preparation method of non-fired sludge-based environmentally friendly polymer bricks in this embodiment, the liquid-solid ratio is controlled at 0.4wt%, the stirring rate is 600rpm, and the stirring time is 10min.

[0032] X-CT scans were performed on the environmentally friendly polymer bricks obtained in this embodiment, and the results are as follows: Figure 1 As shown, the prepared environmentally friendly bricks have a uniform and dense internal structure, without obvious defects such as pores, cracks, or voids. This indicates that during the molding and curing process, the components are evenly distributed and tightly bonded, forming a highly dense microstructure. This non-porous characteristic usually means that the environmentally friendly bricks have high mechanical strength and durability, effectively resisting erosion from external environments such as moisture and corrosion, while also improving their functional properties such as thermal insulation and sound insulation. From a process perspective, this result reflects that the proportioning, mixing, compaction, and curing conditions during the preparation process were properly controlled, thus ensuring the integrity and reliability of the finished product at the microscale, meeting the structural requirements of high-quality building materials.

[0033] Microscopic scanning was performed on the environmentally friendly geopolymer bricks obtained in this embodiment, and the results are as follows: Figure 2 As shown in the SEM images, the microstructure of the environmentally friendly bricks is mainly composed of highly reactive amorphous substances. These substances tightly bind different particles together, forming dense and uniform aggregates. This microscopic feature is the reason for its macroscopically dense and defect-free structure, giving the bricks high strength and high durability.

[0034] XPS analysis was performed on the Si element in the environmentally friendly polymer bricks obtained in this embodiment, and the results are as follows: Figure 3 As shown, XPS analysis reveals that approximately 50% of the area in the brick contains characteristic peaks with binding energies below 102 eV for Si. This binding energy range corresponds to a low-polymerization degree silicon-oxygen tetrahedral structure, characteristic of amorphous cementitious products such as calcium silicate hydrate (CSH) gel. This data confirms from a chemical state perspective that a large amount of amorphous silicate gel phase was generated in the system. This result is consistent with the amorphous dense structure observed by SEM, jointly explaining the origin of the material's macroscopic density and mechanical properties.

[0035] The environmentally friendly geopolymer bricks obtained in this embodiment, after 28 days of curing, showed a compressive strength of 31.5 MPa, an elastic modulus of 28 GPa, a slump of 106 mm, and an apparent density of 1739 kg / m³. 3The water absorption rate is 4.2%. Heavy metal leaching tests showed that the concentrations of heavy metals such as Pb, Cd, and Cr were 0.08 mg / L, 0.002 mg / L, and 0.13 mg / L, respectively.

[0036] After immersing specimens cured for 28 days in water for 30 days, the mass change rate was found to be less than 0.5%, the compressive strength retention rate was over 95%, and the specimens remained intact without cracking, crumbling, or disintegration. These results demonstrate that the material's dense microstructure (confirmed by SEM and XPS results) effectively resists the physical erosion and softening effects of water, and the cementitious phase remains stable in the aqueous environment without significant hydrolysis or structural degradation. Combined with the aforementioned low water absorption and low heavy metal leaching characteristics, the water immersion test data systematically proves that this brick exhibits excellent volume stability, strength retention, and durability under actual humid service conditions.

[0037] The comprehensive performance test results of the non-fired silt-based environmentally friendly bricks prepared in this embodiment fully demonstrate the core advantages of the product in terms of lightweight, high strength, and durability: First, the material exhibits significant lightweight characteristics, with an apparent density of only 1700-1739 kg / m³. 3 The strength of this material is significantly lower than that of traditional clay bricks and ordinary concrete, mainly due to the utilization of porous sludge and the low-density cementitious structure formed by geopolymerization. Secondly, the material possesses excellent high-strength properties, with a 28-day compressive strength of 31.5-35.5 MPa and an elastic modulus of 28-29 GPa. This is directly attributed to the dense, defect-free microstructure revealed by X-CT and SEM, and the strong bonding effect of a large number of amorphous gel phases such as low-polymerization-degree CSH confirmed by XPS. Furthermore, the material exhibits outstanding durability and environmental safety, with a water absorption rate as low as 4.2-4.5% and heavy metal leaching concentrations far below standard limits, proving that its structure can effectively block moisture and corrosive media and can stably solidify heavy metal ions. In summary, this product, through reasonable formulation and processing, successfully achieves a balance between lightweight, high strength, and durability, providing a reliable path for the preparation of high-performance environmentally friendly building materials using sludge and industrial solid waste.

[0038] This invention utilizes alkaline substances from industrial waste as a chemical activator to promote a cementation reaction in silt and other aluminosilicate materials at room temperature, solidifying them to form bricks. This method avoids the high energy consumption of traditional sintering, significantly reducing carbon emissions, while simultaneously achieving the dual resource utilization of waste alkali and silt. Furthermore, this reaction process helps to encapsulate and stabilize harmful components in the silt, reducing leaching risks and enhancing the environmental compatibility of the product. Through scientific formulation and process optimization, the waste alkali-activated non-fired technology holds promise for producing lightweight, high-strength, and durable environmentally friendly bricks, providing the construction industry with a low-carbon, economical, and sustainable material solution.

[0039] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A non-fired sludge-based environmentally friendly polymer brick, characterized in that, Its raw materials include a mixture and an alkali activator; the mixture includes sludge slurry, granulated blast furnace slag and secondary aluminum ash.

2. The non-fired sludge-based environmentally friendly geopolymer brick according to claim 1, characterized in that, The mass percentages of each component in the mixture are as follows: sludge slurry 50-70%, granulated blast furnace slag 15-25%, and secondary aluminum ash 15-25%; wherein, the sludge slurry is calculated by dry weight.

3. The non-fired sludge-based environmentally friendly geopolymer brick according to claim 1, characterized in that, The alkali activator is a causticized pulp obtained from the waste alkali recovery process in the papermaking industry.

4. The non-fired sludge-based environmentally friendly geopolymer brick according to any one of claims 1-3, characterized in that, The unconfined compressive strength of the environmentally friendly brick is not less than 30 MPa.

5. The method for preparing the non-fired sludge-based environmentally friendly geopolymer brick according to any one of claims 1-4, characterized in that, Includes the following steps: 1) Mix the sludge slurry, secondary aluminum ash and granulated blast furnace slag in a set ratio to obtain a mixture; 2) Add alkali activator to the mixture, control the liquid-to-solid ratio to 0.3-0.4%, and stir at 300-600 rpm for 3-10 minutes at room temperature to form a uniform polymer slurry; 3) The slurry is injected into a mold for initial curing and hardening, then demolded and further cured to obtain environmentally friendly polymer bricks.

6. The preparation method according to claim 5, characterized in that, The sludge slurry is obtained by removing impurities from dredged sludge; the impurities include tree branches and dead leaves.

7. The preparation method according to claim 5, characterized in that, In step 2), the stirring rate of the stirring process is 450-550 rpm and the stirring time is 4-7 min.

8. The preparation method according to any one of claims 5-7, characterized in that, In step 3), the maintenance is natural maintenance at room temperature.

9. The application of the non-fired sludge-based environmentally friendly geopolymer brick according to any one of claims 1-4, characterized in that, Used to prepare permeable paving bricks.

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