Modified sludge solidifying agent and preparation method thereof

Abstract

The application relates to the technical field of solid waste treatment and building materials, and discloses a modified sludge solidifying agent and a preparation method thereof, the solidifying agent contains modified aggregates 15-28 parts, a composite cementing agent 55-70 parts, an efficient water absorption modifier 6-12 parts, an organic polymer modifier 2-5 parts and early strength additives 1-3 parts in terms of weight fractions, and the components are mixed through proportioning and a segmented preparation process. The modified aggregates construct a framework support, the composite cementing agent provides hydration cementing action, the efficient water absorption modifier realizes rapid dehydration and heavy metal adsorption, the organic polymer modifier optimizes interface combination, and the early strength additives improve early strength. The application takes industrial solid waste as a main raw material, has high solid waste utilization rate, is low-carbon and environment-friendly, can quickly reduce the water content of sludge, significantly improves the mechanical properties and durability of a solidified body, effectively stabilizes heavy metals, and has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of solid waste treatment and building materials technology, specifically to a modified sludge solidification agent and its preparation method. Background Technology

[0002] With the advancement of water conservancy projects, municipal construction, and environmental governance, the amount of silt discharged from rivers, lakes, and sewage treatment plants is increasing year by year. Silt is characterized by high water content, high organic matter content, low strength, and high fluidity, and is often accompanied by pollutants such as heavy metals. If it is directly piled up or discharged, it will not only occupy a large amount of land resources, but also cause secondary environmental pollution and endanger ecological and environmental safety.

[0003] Currently, sludge solidification is the core technology for achieving sludge reduction, stabilization, harmlessness, and resource utilization. Commonly used solidifying agents mainly fall into three categories: inorganic, organic, and composite. Inorganic solidifying agents, such as cement, lime, and slag, are relatively inexpensive but suffer from problems such as high dosage, slow solidification speed, and poor solidification effect on sludge with high organic matter content. Furthermore, the production processes of cement and lime have high carbon emissions, which does not meet requirements. Organic solidifying agents, such as polymers, have fast solidification speed and high early strength, but are expensive and lack long-term durability, making large-scale application difficult. Existing composite solidifying agents attempt to combine the advantages of inorganic and organic materials, but there is still room for improvement in terms of solidification efficiency, strength enhancement, heavy metal stabilization effect, and solid waste utilization rate. Some formulations also suffer from complex composition and cumbersome preparation processes.

[0004] Therefore, developing a modified sludge solidifying agent that uses industrial solid waste as the main raw material, is environmentally friendly and low-carbon, has high solidification efficiency, excellent strength performance, and can effectively stabilize heavy metals is of great practical significance for promoting the resource utilization of sludge, reducing treatment costs, and protecting the ecological environment. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a modified sludge solidifying agent and its preparation method, which solves the problems of high dosage, poor solidification effect and high carbon emission of traditional solidifying agents, realizes waste treatment and low carbon environmental protection, improves the mechanical properties and environmental stability of sludge solidification, and broadens its resource utilization pathways.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a modified sludge solidifying agent, comprising the following components by weight: 15-28 parts of modified aggregate, 55-70 parts of composite binder, 6-12 parts of high-efficiency water-absorbing modifier, 2-5 parts of organic polymer modifier, and 1-3 parts of early strength additive. The modified aggregate composition consists of silica fume, steel slag particles, and lithium slag mixed in a specific mass ratio. The steel slag particles are strictly controlled to have a particle size of 2-8 mm. This particle size range allows for the formation of a continuously graded skeletal structure within the sludge, filling the gaps between sludge particles and improving the density of the solidified body. The silica fume is selected as a highly active micro-powder with a specific surface area of ​​15000 m² / kg. Its nano-sized particles can fill the micropores between the steel slag and sludge particles, while also participating in the hydration reaction to generate dense hydration products. The lithium slag is selected as a product activated by calcination at 900℃. Calcination treatment activates the active alumina and silica components in the lithium slag, enhancing its reactivity with the cementing system. Functional role: As a "rigid skeleton" of the solidified body, it bears the responsibility of transferring mechanical loads. Simultaneously, through optimized particle size distribution, it reduces internal porosity of the solidified body, improving impermeability and heavy metal encapsulation capacity.

[0007] The composite binder is composed of granulated blast furnace slag powder, fly ash, bentonite, and carbide steel slag powder mixed in a specific mass ratio. The granulated blast furnace slag powder has a specific surface area ≥450m² / kg, a glass content ≥90%, and a total content of calcium oxide, alumina, and silica ≥95% to ensure hydration reaction activity. The fly ash is grade II or above, and must meet the requirements of loss on ignition ≤8% and water demand ≤105%. Its spherical glass particles can improve the workability of the solidification system and participate in the secondary hydration reaction. The bentonite is calcium-based bentonite with a montmorillonite content ≥85% and an expansion ratio ≥20 times, which can enhance the water retention and colloidal stability of the system. The carbide steel slag powder has a specific surface area ≥400m² / kg and a free calcium oxide content ≤3%. The carbide-treated steel slag powder contains a large amount of calcium carbonate crystals, which can improve the early strength and corrosion resistance of the solidified body. Functions: Under the action of water, it undergoes a hydration reaction to generate cementitious products such as hydrated calcium silicate and hydrated calcium aluminate, which firmly bind the sludge particles and modified aggregates into a whole. At the same time, it initially fixes heavy metal ions through colloidal adsorption.

[0008] The high-efficiency water-absorbing modifier is composed of hemihydrate phosphogypsum, red mud, and modified bentonite mixed and ground in a certain mass ratio. The hemihydrate phosphogypsum needs to be dried at 180°C to ensure that the crystal water content is ≤5% to avoid cracking of the solidified body due to hydration expansion in the later stage. The red mud is Bayer process red mud with an iron oxide content of ≥30%. Its porous structure can enhance the adsorption performance. At the same time, the alkaline components in the red mud can adjust the pH value of the solidification system and promote the hydration reaction. The mixing and grinding process is as follows: hemihydrate phosphogypsum, red mud, and modified bentonite are put into a ball mill in a certain proportion and ground at a speed of 400-500 r / min for 12-15 min. The specific surface area of ​​the finished product is controlled at 420-480 m² / kg to ensure that the components are fully mixed and reach the optimal adsorption particle size. Functions: On the one hand, it rapidly removes free water and capillary water from sludge through capillary adsorption and crystal water absorption, reducing the water content of sludge; on the other hand, it physically adsorbs and fixes heavy metal ions through interlayer adsorption of modified bentonite and porous adsorption of red mud, forming a dual effect of "dehydration-adsorption".

[0009] The organic polymer modifier is composed of polyacrylamide (PAM), sodium carboxymethyl cellulose (CMC), and modified cashew nut shell powder mixed in a mass ratio of (2-3):1:1. The polyacrylamide used is non-ionic, with a molecular weight of 8-12 million and a degree of hydrolysis of 20%-30%. This parameter range ensures the formation of a highly efficient flocculation network in the sludge system, while maintaining good compatibility with inorganic cementitious products. The sodium carboxymethyl cellulose used has a degree of substitution ≥0.8 and a viscosity (2% aqueous solution, 25℃) ≥500 mPa·s, enhancing the adhesion and water retention of the solidified system. Functional effects: The flocculation network formed by polyacrylamide accelerates the aggregation of sludge particles; sodium carboxymethyl cellulose improves interfacial adhesion; and the active groups of modified cashew nut shell powder form chemical bonds with inorganic cementitious products. These three components synergistically construct an "organic-inorganic interpenetrating network structure," improving the flexibility, crack resistance, and long-term stability of the solidified body, while further locking in heavy metal ions.

[0010] Early-strength additive composition: It is composed of aluminum sulfate and lithium carbonate mixed in a specific mass ratio. The aluminum sulfate used is anhydrous aluminum sulfate with a purity ≥98% and a particle size ≤100μm. It can dissolve rapidly and react with hydration products to form hydrated calcium sulfoaluminate (ettringite), significantly improving early strength. The lithium carbonate has a purity ≥99% and a particle size ≤100μm. Its lithium ions can accelerate the formation and crystallization of CSH gel during cement hydration, while improving the microstructure of the cured body. Functional effect: The synergistic effect of aluminum sulfate and lithium carbonate, through a dual mechanism of "promoting setting and strengthening," solves the problem of low early strength in traditional curing agents, while optimizing the structure of hydration products and improving the overall mechanical properties and durability of the cured body.

[0011] The modified aggregate is composed of silica fume, steel slag particles and lithium slag mixed in a mass ratio of (0.2-0.6):(12-18):(3-6), and the steel slag particles have a particle size of 2-8 mm. The composite binder is made by mixing granulated blast furnace slag powder, fly ash, bentonite and carbide steel slag powder in a mass ratio of (5-6):(3-4):(1-2):(0.5-1).

[0012] Furthermore, in the composite binder, the granulated blast furnace slag powder has a specific surface area ≥ 450 m² / kg, the fly ash is grade II or above, and the carbide steel slag powder has a specific surface area ≥ 400 m² / kg.

[0013] Furthermore, the high-efficiency water-absorbing modifier is prepared by mixing and grinding hemihydrate phosphogypsum, red mud, and modified bentonite in a mass ratio of (6-7):(2-3):(1-2), with a grinding time of 12-15 minutes and a specific surface area controlled at 420-480 m² / kg; the modified bentonite is obtained by soaking in a 5%-8% hydrochloric acid solution for 2-3 hours, followed by filtration, drying, and grinding.

[0014] Furthermore, the organic polymer modifier is a mixture of polyacrylamide, sodium carboxymethyl cellulose, and modified cashew phenol in a mass ratio of (2-3):1:1. The polyacrylamide has a molecular weight of 8-12 million and a degree of hydrolysis of 20%-30%.

[0015] Further, the modified cashew nut phenol is prepared by adding 4.3-4.5g of cashew nut phenol and 3.0-3.2g of glycidol to a reaction flask, purging with nitrogen gas, stirring evenly for 15-20min, reacting at 76-80℃ for 1-2h, reacting at 95-100℃ for 3-4h, reacting at 110-120℃ for 1-2h, and then cooling to room temperature to modify the cashew nut phenol.

[0016] Furthermore, the early strength additive is a mixture of aluminum sulfate and lithium carbonate in a mass ratio of (3-4):1.

[0017] Furthermore, it includes the following steps: S1. Preparation of modified aggregate: Take steel slag particles, add silica fume and lithium slag in proportion, put them into a mixer and stir at a speed of 300-500 r / min until they are evenly mixed and ready for use. S2. Preparation of composite binder: Weigh out granulated blast furnace slag powder, fly ash, bentonite and carbide steel slag powder according to the proportion, put them into a planetary ball mill, mix and grind at 200-300 r / min for 4-6 min, and set aside after uniform mixing. S3. Preparation of high-efficiency water-absorbing modifier: Weigh hemihydrate phosphogypsum, red mud and modified bentonite according to the proportion, put them into a ball mill, grind at 400-500 r / min for 12-15 min, control the specific surface area at 420-480 m² / kg, and set aside. S4. Preparation of mixed additives: Weigh each component of the organic polymer modifier according to the proportion and mix them evenly; weigh each component of the early strength additive according to the proportion and mix them evenly, and set them aside separately. S5. Preparation of finished curing agent: Put the modified aggregate, composite binder and high-efficiency water-absorbing modifier into a mixer and stir at 350-450 r / min for 8-10 min. After adding the mixing aid, continue stirring for 5-6 min. After mixing evenly, the modified sludge curing agent is obtained.

[0018] Furthermore, the stirring time in S1 is 6-8 minutes.

[0019] Compared with the prior art, the present invention has the following beneficial technical effects: This invention employs a five-component synergistic design—modified aggregate, composite binder, high-efficiency water-absorbing modifier, organic polymer modifier, and early-strength additive—to form a functionally complementary curing system. The modified aggregate, acting as a rigid skeleton, fills the gaps between silt particles and transfers mechanical loads, laying the foundation for the solidified structure. The composite binder generates dense cementitious products through hydration reactions, firmly binding the silt particles to the aggregate to form an integral structure. The high-efficiency water-absorbing modifier utilizes both capillary adsorption and crystal water absorption to rapidly remove free water and capillary water from the silt, while simultaneously fixing heavy metals through porous adsorption and interlayer adsorption. The organic polymer modifier constructs an organic-inorganic interpenetrating network, improving interfacial adhesion and enhancing the flexibility and crack resistance of the solidified body. The early-strength additive accelerates the hydration process through coagulation and crystallization optimization, addressing the problem of insufficient early strength. The synergistic effect of each component achieves an integrated effect of "dehydration-binding-reinforcement-stabilization."

[0020] The curing agent uses industrial solid waste such as steel slag particles, lithium slag, granulated blast furnace slag powder, fly ash, and red mud as core raw materials. Through component optimization, it activates the active components in the solid waste, enabling them to participate in hydration reactions or perform skeletal and adsorption functions, significantly reducing reliance on traditional high-carbon emission raw materials such as cement and lime. On the one hand, it solves the problems of land occupation and environmental pollution caused by industrial solid waste dumping, achieving "waste treatment with waste"; on the other hand, it reduces carbon emissions during the curing agent production process, meeting requirements, while simultaneously reducing raw material costs and improving product economics.

[0021] The particle size distribution design of the modified aggregate and the micropore-filling effect of silica fume reduce the internal porosity of the solidified body and improve the structural density. The interpenetrating network structure formed by the organic polymer modifier and inorganic cementitious products retains the high strength characteristics of inorganic materials while also possessing the flexibility of organic materials, avoiding the defects of traditional solidified bodies that are prone to cracking and have poor damage resistance. The calcium carbonate crystals of carbide steel slag powder in the composite binder work synergistically with the hydration products to enhance the corrosion resistance and impermeability of the solidified body. The ettringite and other products generated by the early strength additive optimize the structure of the hydration products, further improving the overall mechanical properties and long-term stability of the solidified body and extending its service life.

[0022] Heavy metal stabilization is achieved through a dual mechanism of physical encapsulation and chemical adsorption. The dense microstructure of the solidified body forms a physical barrier, encapsulating heavy metal ions and preventing their leaching. The interlayer adsorption of modified bentonite in the high-efficiency water-absorbing modifier, the porous adsorption of red mud, and the complexation of functional groups in the organic polymer modifier form stable binding states with heavy metal ions. These multiple mechanisms work synergistically to reduce the migration of heavy metals, ensuring that the solidified product meets environmental protection requirements and providing a safe guarantee for resource utilization. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example

[0024] A modified sludge solidifying agent, by weight: 20 parts modified aggregate, 62 parts composite binder, 9 parts high-efficiency water-absorbing modifier, 3 parts organic polymer modifier, and 2 parts early-strength additive.

[0025] The modified aggregate contains silica fume, steel slag particles, and lithium slag in a mass ratio of 0.4:15:4.5, with steel slag particles having a diameter of 6mm. The composite binder contains granulated blast furnace slag powder, fly ash, bentonite, and carbide steel slag powder in a mass ratio of 5.5:3.5:1.5:0.8, with granulated blast furnace slag powder having a specific surface area of ​​480 m² / kg, fly ash being Class II fly ash, and carbide steel slag powder having a specific surface area of ​​420 m² / kg. The high-efficiency water-absorbing modifier contains hemihydrate phosphogypsum and red mud. The modified bentonite was prepared by soaking in a 6% hydrochloric acid solution for 2.5 hours and then grinding for 13 minutes, with a specific surface area of ​​450 m² / kg. The organic polymer modifier contained polyacrylamide, sodium carboxymethyl cellulose, and modified cashew nut shell powder in a mass ratio of 2.5:1:1. The polyacrylamide had a molecular weight of 10 million and a degree of hydrolysis of 25%. The early strength additive contained aluminum sulfate in a mass ratio of 3.5:1.

[0026] Preparation method: Preparation of modified aggregate: Take steel slag particles, silica fume and lithium slag in proportion, put them into a twin-shaft paddle mixer and stir at 400 r / min for 7 min, mix evenly and set aside. Preparation of composite binder: Weigh each component according to the proportion, put them into a planetary ball mill and mix and grind them at 250 r / min for 5 min, then sieve and set aside. Preparation of high-efficiency water-absorbing modifier: Weigh each component according to the proportion, put them into a horizontal ball mill and grind them at 450 r / min for 13 min, control the specific surface area to 450 m² / kg, and set aside for later use; Preparation of mixed additives: Mix each component of the organic polymer modifier and each component of the early strength additive evenly and set aside for later use; Preparation of finished product: The modified aggregate, composite binder and high-efficiency water-absorbing modifier are put into a twin ribbon mixer and stirred at 400 r / min for 9 min. After adding the mixing aid, the mixture is stirred for another 5.5 min. After sieving, it is packaged.

[0027] Effects of use: When this solidifying agent is added at 15% of the silt mass, the initial moisture content of river silt with 100% initial moisture content (tested by drying method) is 85 mg / kg lead, 210 mg / kg zinc and 5.2 mg / kg cadmium.

[0028] Test results: Moisture content decreased to 15% after 3 days, and unconfined compressive strength was 3.8 MPa; After 14 days, the moisture content decreased to 8%, and the unconfined compressive strength was 7.5 MPa. The unconfined compressive strength at 28 days was 10.8 MPa, and the strength retention rate after 25 freeze-thaw cycles was 88%. The leaching concentrations of heavy metals lead, zinc, and cadmium were 0.32 mg / L, 1.25 mg / L, and 0.03 mg / L, respectively. Example

[0029] A modified sludge solidifying agent, by weight: 15 parts modified aggregate, 55 parts composite binder, 6 parts high-efficiency water-absorbing modifier, 2 parts organic polymer modifier, and 1 part early-strength additive.

[0030] The modified aggregate contains silica fume, steel slag particles, and lithium slag in a mass ratio of 0.2:12:3, with steel slag particles having a diameter of 2-4 mm. The composite binder contains granulated blast furnace slag powder, fly ash, bentonite, and carbide steel slag powder in a mass ratio of 5:3:1:0.5, with granulated blast furnace slag powder having a specific surface area of ​​450 m² / kg, fly ash being Class II fly ash, and carbide steel slag powder having a specific surface area of ​​400 m² / kg. The high-efficiency water-absorbing modifier contains hemihydrate phosphogypsum. The mass ratio of red mud and modified bentonite is 6:2:1. The modified bentonite is prepared by soaking in a 5% hydrochloric acid solution for 2 hours and then grinding for 12 minutes, with a specific surface area of ​​420 m² / kg. The mass ratio of polyacrylamide, sodium carboxymethyl cellulose, and modified cashew nut shell powder in the organic polymer modifier is 2:1:1. The molecular weight of polyacrylamide is 8 million and the degree of hydrolysis is 20%. The mass ratio of aluminum sulfate to lithium carbonate in the early strength additive is 3:1.

[0031] Preparation method: Preparation of modified aggregate: Take steel slag particles with a particle size of 2 mm, add silica fume and lithium slag at a mass ratio of 0.2:12:3, put them into a mixer and stir at 300 r / min for 6 min. After mixing evenly, set aside. Preparation of composite binder: Weigh granulated blast furnace slag powder, grade II or above fly ash, bentonite and carbide steel slag powder in a mass ratio of 5:3:1:0.5, put them into a planetary ball mill, mix and grind at 200 r / min for 4 min, and set aside after uniform mixing. Preparation of high-efficiency water-absorbing modifier: weigh hemihydrate phosphogypsum, red mud, and modified bentonite treated by soaking in 5% hydrochloric acid solution for 2 hours according to the mass ratio of 6:2:1, put them into a ball mill and grind them at 400 r / min for 12 min, controlling the specific surface area of ​​the product to be 420 m² / kg, and set aside for later use; Preparation of mixed additives: Weigh polyacrylamide, sodium carboxymethyl cellulose, and modified cashew nut shell powder in a mass ratio of 2:1:1, mix them evenly to obtain an organic polymer modifier; weigh aluminum sulfate and lithium carbonate in a mass ratio of 3:1, mix them evenly to obtain an early strength additive, and set them aside separately. Preparation of finished curing agent: The modified aggregate prepared in step 1, the composite binder prepared in step 2, and the high-efficiency water-absorbing modifier prepared in step 3 are put into a mixer and stirred at 350 r / min for 8 min. After adding the mixing aid prepared in step 4, stirring is continued for 5 min. After mixing evenly, the modified sludge curing agent is obtained.

[0032] Results: When this solidifying agent is added at 14% of the sludge mass, it is used to treat sludge from a wastewater treatment plant with an initial moisture content of 90% (tested by drying method). The initial heavy metal content of the sludge (dry basis) is: lead 72mg / kg, zinc 185mg / kg, cadmium 4.8mg / kg.

[0033] Test results: Moisture content decreased to 14% after 3 days, and unconfined compressive strength was 3.6 MPa; After 14 days, the moisture content decreased to 7%, and the unconfined compressive strength was 7.2 MPa. The unconfined compressive strength at 28 days was 10.2 MPa, and the strength retention rate after 25 freeze-thaw cycles was 86%. The leaching concentrations of heavy metals lead, zinc, and cadmium were 0.35 mg / L, 1.32 mg / L, and 0.04 mg / L, respectively. Example

[0034] A modified sludge solidifying agent, by weight: 28 parts modified aggregate, 70 parts composite binder, 12 parts high-efficiency water-absorbing modifier, 5 parts organic polymer modifier, and 3 parts early-strength additive.

[0035] The modified aggregate contains silica fume, steel slag particles, and lithium slag in a mass ratio of 0.6:18:6, with steel slag particles having a diameter of 5-8 mm. The composite binder contains granulated blast furnace slag powder, fly ash, bentonite, and carbide steel slag powder in a mass ratio of 6:4:2:1, with granulated blast furnace slag powder having a specific surface area of ​​500 m² / kg, fly ash being Class I fly ash, and carbide steel slag powder having a specific surface area of ​​450 m² / kg. The high-efficiency water-absorbing modifier contains hemihydrate phosphogypsum, ... The red mud and modified bentonite were in a mass ratio of 7:3:2. The modified bentonite was prepared by soaking in an 8% hydrochloric acid solution for 3 hours and then grinding for 15 minutes. The specific surface area was 480 m² / kg. The organic polymer modifier contained polyacrylamide, sodium carboxymethyl cellulose, and modified cashew nut shell powder in a mass ratio of 3:1:1. The polyacrylamide had a molecular weight of 12 million and a degree of hydrolysis of 30%. The early strength additive contained aluminum sulfate and lithium carbonate in a mass ratio of 4:1.

[0036] Preparation method: Preparation of modified aggregate: Take steel slag particles with a particle size of 5 mm, add silica fume and lithium slag at a mass ratio of 0.6:18:6, put them into a mixer and stir at 500 r / min for 8 min. After mixing evenly, set aside. Preparation of composite binder: Weigh granulated blast furnace slag powder, grade II or above fly ash, bentonite and carbide steel slag powder according to the mass ratio of 6:4:2:1, put them into a planetary ball mill, mix and grind at 300 r / min for 6 min, and set aside after uniform mixing. Preparation of high-efficiency water-absorbing modifier: weigh hemihydrate phosphogypsum, red mud, and modified bentonite treated by soaking in 8% hydrochloric acid solution for 3 hours according to the mass ratio of 7:3:2, put them into a ball mill and grind them at 500 r / min for 15 min, controlling the specific surface area of ​​the product to be 480 m² / kg, and set aside for later use; Preparation of mixed additives: Weigh polyacrylamide, sodium carboxymethyl cellulose, and modified cashew nut shell powder in a mass ratio of 3:1:1, mix them evenly to obtain an organic polymer modifier; weigh aluminum sulfate and lithium carbonate in a mass ratio of 4:1, mix them evenly to obtain an early strength additive, and set them aside separately. Preparation of finished curing agent: The modified aggregate prepared in step 1, the composite binder prepared in step 2, and the high-efficiency water-absorbing modifier prepared in step 3 are put into a mixer and stirred at 450 r / min for 10 min. After adding the mixing aid prepared in step 4, stirring is continued for 6 min. After mixing evenly, the modified sludge curing agent is obtained.

[0037] Effects of use: When this solidifying agent is added at 17% of the silt mass, it is used to treat soft soil foundation silt with an initial moisture content of 110% (tested by drying method). The initial heavy metal content of the silt (dry basis) is: lead 90mg / kg, zinc 220mg / kg, cadmium 5.5mg / kg.

[0038] Test results: Moisture content decreased to 16% after 3 days, and unconfined compressive strength was 3.7 MPa; After 14 days, the moisture content decreased to 9%, and the unconfined compressive strength was 7.3 MPa. The unconfined compressive strength at 28 days was 10.5 MPa, and the strength retention rate after 25 freeze-thaw cycles was 87%. The leaching concentrations of heavy metals lead, zinc, and cadmium were 0.38 mg / L, 1.40 mg / L, and 0.05 mg / L, respectively.

[0039] Comparative Example 1 (insufficient silica fume content in modified aggregate) Formula composition (by weight) 28 parts modified aggregate, 70 parts composite binder, 12 parts high-efficiency water-absorbing modifier, 5 parts organic polymer modifier, and 3 parts early strength additive.

[0040] Modified aggregate: the mass ratio of silica fume, steel slag particles, and lithium slag is 0.1:18:6 (the original Example 3 was 0.6:18:6, and the proportion of silica fume is lower than the specified range of 0.2-0.6). Preparation method Except for adjusting the proportion of silica fume added to the modified aggregate, the other steps are completely the same as in Example 3.

[0041] Test results: (Same test conditions as in Example 3) Add a solidifying agent at 17% of the silt mass to treat soft soil foundation silt with an initial moisture content of 110% (initial heavy metal content is the same as in Example 3): With a 3-day moisture content reduced to 20%, the unconfined compressive strength is 2.0 MPa. After 14 days, the moisture content decreased to 13%, and the unconfined compressive strength was 5.1 MPa. The unconfined compressive strength at 28 days was 7.9 MPa, and the strength retention rate after 25 freeze-thaw cycles was 73%. The leaching concentrations of heavy metals lead, zinc, and cadmium were 0.85 mg / L, 2.32 mg / L, and 0.13 mg / L, respectively.

[0042] Comparative Example 2 (Cashewol instead of modified cashewol) The difference between this comparative example and Example 3 is that cashew phenol is used instead of modified cashew phenol.

[0043] Test results: (Same test conditions as in Example 3) Add a solidifying agent at 17% of the silt mass to treat soft soil foundation silt with an initial moisture content of 110% (initial heavy metal content is the same as in Example 3): The moisture content dropped to 17% after 3 days, and the unconfined compressive strength was 2.4 MPa. After 14 days, the moisture content decreased to 11%, and the unconfined compressive strength was 5.6 MPa. The unconfined compressive strength at 28 days was 8.8 MPa, and the strength retention rate after 25 freeze-thaw cycles was 71%. The leaching concentrations of heavy metals lead, zinc, and cadmium were 0.98 mg / L, 2.65 mg / L, and 0.16 mg / L, respectively.

[0044] Comparative Example 3 (Reduced proportion of aluminum sulfate in early-strength additive) Formula composition (by weight) 28 parts modified aggregate, 70 parts composite binder, 12 parts high-efficiency water-absorbing modifier, 5 parts organic polymer modifier, and 3 parts early strength additive.

[0045] The components, proportions, and parameters of the modified aggregate, composite binder, high-efficiency water-absorbing modifier, and organic polymer modifier are the same as in Example 3; Early strength additive: aluminum sulfate to lithium carbonate mass ratio 2:1 (original Example 3 was 4:1, which is lower than the specified range of 3-4:1).

[0046] Preparation method Except for the adjustment of the early strength additive ratio, the other steps are completely the same as in Example 3.

[0047] Test results: (Same test conditions as in Example 3) Add a solidifying agent at 17% of the silt mass to treat soft soil foundation silt with an initial moisture content of 110% (initial heavy metal content is the same as in Example 3): The moisture content dropped to 18% after 3 days, and the unconfined compressive strength was 1.3 MPa. After 14 days, the moisture content dropped to 10%, and the unconfined compressive strength was 4.9 MPa. The unconfined compressive strength at 28 days was 9.2 MPa, and the strength retention rate after 25 freeze-thaw cycles was 78%. The leaching concentrations of heavy metals lead, zinc, and cadmium were 0.62 mg / L, 1.98 mg / L, and 0.09 mg / L, respectively.

[0048] I. Dewatering Efficiency: Examples 1-3 all achieved highly efficient dewatering for different types of sludge (river sludge, sewage treatment plant sludge, and soft soil foundation sludge), with the 3-day moisture content controlled at 14%-16%, and further reduced to 7%-9% after 14 days. Among them, Example 2 treated sewage treatment plant sludge with an initial moisture content of 90%, achieving a moisture content of only 7% after 14 days, demonstrating the best dewatering effect. Example 3 treated soft soil foundation sludge with an initial moisture content of 110%, achieving a moisture content of 16% after 3 days and 9% after 14 days, while still maintaining stable and efficient dewatering capacity. This is attributed to the dense structure formed by the synergistic action of the five components, which can quickly discharge free water and capillary water.

[0049] Comparative Example 1, due to the low silica fume content (only 0.1%, below the 0.2-0.6 range specified in the invention), lacked nanoscale micropore filling, resulting in insufficient hydration reaction and delayed densification of the solidified structure. The moisture content at 3 days increased to 20%, a 25% increase compared to Example 3, and at 14 days it reached 13%, a 44.4% increase compared to Example 3, indicating significant obstruction to moisture drainage. Comparative Example 2 used ordinary cashew nut shell powder instead of modified cashew nut shell powder. Ordinary cashew nut shell powder lacks many active groups and cannot form chemical bonds with inorganic cementitious products, thus failing to construct an organic-inorganic interpenetrating network. This resulted in poor interfacial adhesion and difficulty in rapid moisture penetration and drainage. The moisture content at 3 days was 17%, and at 14 days it was 11%, increases of 6.2% and 22.2% respectively compared to Example 3. In Comparative Example 3, the mass ratio of aluminum sulfate to lithium carbonate in the early strength additive was 2:1 (lower than the limit of 3-4:1). The formation of ettringite was insufficient, the coagulation effect was weakened, and the hydration process was slow. The water content was 18% at 3 days and 10% at 14 days, which were 12.5% ​​and 11.1% higher than those in Example 3, respectively, and the dehydration rate was significantly slowed down.

[0050] II. Mechanical Properties: (I) Early Strength (3d, 14d) Examples 1-3 exhibited excellent early strength performance, with 3-day unconfined compressive strengths all exceeding 3.6 MPa (Example 1: 3.8 MPa, Example 2: 3.6 MPa, Example 3: 3.7 MPa), and 14-day strengths all surpassing 7.2 MPa (Example 1: 7.5 MPa, Example 2: 7.2 MPa, Example 3: 7.3 MPa), meeting the load-bearing requirements of rapid construction. This is because the early-strength additive, when mixed in a defined ratio, exerts a "setting-strengthening" effect; silica fume participates in hydration to generate dense products; modified cashew phenol optimizes interfacial bonding; and multiple components synergistically promote rapid strength improvement.

[0051] Comparative Example 1, due to insufficient silica fume, experienced increased porosity within the cured body, reduced hydration product formation, and decreased structural load-bearing capacity. Its 3-day strength was only 2.0 MPa, a 45.9% decrease compared to Example 3, and its 14-day strength was 5.1 MPa, a 29.9% decrease compared to Example 3. Comparative Example 2, using ordinary cashew phenol, could not form chemical bonds with inorganic cementitious products, resulting in poor flexibility and insufficient crack resistance in the cured system. Its 3-day strength was 2.4 MPa, a 35.1% decrease compared to Example 3, and its 14-day strength was 5.6 MPa, a 23.3% decrease compared to Example 3. Comparative Example 3 was most significantly affected by deviations in the early-strength additive ratio. Insufficient aluminum sulfate led to a substantial reduction in the formation of ettringite (a core product for early strength), resulting in a 3-day strength of only 1.3 MPa, a sharp drop of 64.9% compared to Example 3, and a 14-day strength of 4.9 MPa, a 32.9% decrease compared to Example 3, failing to meet early-stage construction load-bearing requirements.

[0052] (ii) Later strength (28d) and durability (freeze-thaw cycle strength retention rate) The 28-day unconfined compressive strength of Examples 1-3 remained consistently above 10.2 MPa (Example 1: 10.8 MPa, Example 2: 10.2 MPa, Example 3: 10.5 MPa), and the strength retention rate after 25 freeze-thaw cycles reached 86%-88%, demonstrating a balance of strength and toughness. This is because the optimized particle size distribution of the modified aggregate and the micropore filling of silica fume resulted in high structural density; the organic-inorganic interpenetrating network constructed by the organic polymer modifier improved crack resistance and damage resistance; and the calcium carbonate crystals and hydration products of the carbide steel slag powder in the composite binder synergistically enhanced corrosion resistance. These multiple effects ensured long-term strength and durability.

[0053] Comparative Example 1 showed a 28-day strength of only 7.9 MPa, a decrease of 24.8% compared to Example 3. Its freeze-thaw strength retention rate was 73%, a decrease of 14 percentage points compared to Example 3. High porosity caused pore water to freeze and expand during freeze-thaw cycles, damaging the solidified structure and resulting in significant strength loss. Comparative Example 2 showed a 28-day strength of 8.8 MPa, a decrease of 16.2% compared to Example 3. Its freeze-thaw strength retention rate was 71%, a decrease of 16 percentage points compared to Example 3. Ordinary cashew phenol lacks active groups and cannot improve the system's flexibility, easily causing and propagating cracks during freeze-thaw cycles, leading to a significant decline in strength. Comparative Example 3 showed a 28-day strength of 9.2 MPa, a decrease of 12.4% compared to Example 3. Its freeze-thaw strength retention rate was 78%, a decrease of 9 percentage points compared to Example 3. Although the subsequent hydration reaction continued, somewhat compensating for the strength loss, improper early-strength additive formulation resulted in an unoptimized structure of the hydration products, and the durability remained significantly insufficient.

[0054] III. Heavy Metal Stabilization Effect: Examples 1-3 achieve efficient stabilization of heavy metals through a dual mechanism of "physical encapsulation + chemical adsorption," maintaining the leaching concentrations of lead, zinc, and cadmium at low levels: lead 0.32-0.38 mg / L, zinc 1.25-1.40 mg / L, and cadmium 0.03-0.05 mg / L, meeting environmental protection and resource recovery requirements. The dense solidified structure forms a physical barrier, preventing heavy metal leaching; the interlayer adsorption of modified bentonite in the high-efficiency water-absorbing modifier, the porous adsorption of red mud, and the complexation of functional groups in the organic polymer modifier form stable binding states with heavy metal ions, with multiple mechanisms working synergistically to ensure the stabilization effect.

[0055] Comparative Example 1, due to insufficient silica fume content, experienced a decrease in the density of the solidified structure, resulting in the failure of the physical encapsulation barrier. Heavy metals easily penetrated the pores and leached out, with lead leaching concentrations reaching 0.85 mg / L (123.7% higher than Example 3), zinc 2.32 mg / L (65.7% higher than Example 3), and cadmium 0.13 mg / L (160% higher than Example 3). Comparative Example 2, using ordinary cashew phenol instead of modified cashew phenol, lacked the chemical adsorption effect of functional group complexation. Physical encapsulation alone was insufficient to stabilize heavy metals, resulting in lead leaching concentrations of 0.98 mg / L (157.9% higher than Example 3), zinc 2.65 mg / L (89.3% higher than Example 3), and cadmium 0.16 mg / L (220% higher than Example 3), making it the worst performing group in terms of heavy metal stabilization. In Comparative Example 3, due to improper formulation of early strength additives, the hydration products had a loose structure and weakened physical encapsulation ability. The lead leaching concentration was 0.62 mg / L (63.2% higher than in Example 3), zinc was 1.98 mg / L (41.4% higher than in Example 3), and cadmium was 0.09 mg / L (80% higher than in Example 3). The stabilizing effect was significantly reduced compared to the examples.

[0056] Moisture content test: According to the "Standard for Geotechnical Test Methods" (GB / T50123-2019), the drying method is adopted. Take 50g of solidified silt sample, place it in an oven at 105±5℃ and dry it to constant weight, and calculate the moisture content. Compressive strength test: In accordance with the "Test Procedure for Inorganic Binder Stabilized Materials for Highway Engineering" (JTGE51-2009), cylindrical specimens with a diameter of 50mm and a diameter of 50mm were prepared and cured under standard conditions (temperature 20±2℃, humidity ≥95%) until the specified age. The unconfined compressive strength was tested using a pressure testing machine at a loading rate of 1mm / min. Heavy metal leaching concentration test: According to the "Leaching Toxicity of Solid Waste - Horizontal Oscillation Method" (HJ557-2010), the solid-liquid ratio was 1:10, the oscillation frequency was 110±10 times / min, the oscillation time was 18±2h, and the leaching solution was filtered through a 0.45μm filter membrane. The contents of lead, zinc and cadmium were determined by inductively coupled plasma mass spectrometry (ICP-MS). Durability test: The freeze-thaw cycle test (freezing at -20℃ for 24 hours and thawing in water at 20℃ for 24 hours constitutes one cycle, for a total of 25 cycles) was used to test the retention rate of compressive strength after freeze-thaw. It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0057] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

[0058] Those skilled in the art should understand that the above descriptions are merely several specific embodiments of the present invention, and not all embodiments.

Claims

1. A modified sludge solidifying agent, characterized in that, By weight, it includes the following components: 15-28 parts modified aggregate, 55-70 parts composite binder, 6-12 parts high-efficiency water-absorbing modifier, 2-5 parts organic polymer modifier, and 1-3 parts early strength additive. The modified aggregate is a mixture of silica fume, steel slag particles and lithium slag in a mass ratio of (0.2-0.6):(12-18):(3-6), the steel slag particles have a particle size of 2-8 mm, and the lithium slag is the product of calcination and activation at 900℃. The composite binder is made by mixing granulated blast furnace slag powder, fly ash, bentonite and carbide steel slag powder in a mass ratio of (5-6):(3-4):(1-2):(0.5-1); The high-efficiency water-absorbing modifier is prepared by mixing and grinding hemihydrate phosphogypsum, red mud, and modified bentonite in a mass ratio of (6-7):(2-3):(1-2) for 12-15 minutes, with a specific surface area controlled at 420-480 m² / kg; the modified bentonite is obtained by soaking in a 5%-8% hydrochloric acid solution for 2-3 hours, followed by filtration, drying, and grinding. The organic polymer modifier is a mixture of polyacrylamide, sodium carboxymethyl cellulose, and modified cashew nut shell powder in a mass ratio of (2-3):1:

1. The polyacrylamide has a molecular weight of 8-12 million and a degree of hydrolysis of 20%-30%. The modified cashew nut phenol is prepared by adding 4.3-4.5g of cashew nut phenol and 3.0-3.2g of glycidol to a reaction flask, introducing nitrogen gas, and stirring evenly for 15-20 minutes. The reaction is carried out at 76-80℃ for 1-2 hours, at 95-100℃ for 3-4 hours, at 110-120℃ for 1-2 hours, and then cooled to room temperature to prepare the modified cashew nut phenol.

2. The modified sludge solidifying agent according to claim 1, characterized in that, In the composite binder, the granulated blast furnace slag powder has a specific surface area ≥ 450 m² / kg; the fly ash is grade II or above; the carbide steel slag powder has a specific surface area ≥ 400 m² / kg and a free calcium oxide content ≤ 3%.

3. The modified sludge solidifying agent according to claim 1, characterized in that, The early strength additive is a mixture of aluminum sulfate and lithium carbonate in a mass ratio of (3-4):

1.

4. The method for preparing the modified sludge solidifying agent according to any one of claims 1-3, characterized in that, Includes the following steps: S1. Preparation of modified aggregate: Take steel slag particles, add silica fume and lithium slag in proportion, put them into a mixer and stir at a speed of 300-500 r / min until they are evenly mixed and ready for use. S2. Preparation of composite binder: Weigh out granulated blast furnace slag powder, fly ash, bentonite and carbide steel slag powder according to the proportion, put them into a planetary ball mill, mix and grind at 200-300 r / min for 4-6 min, and set aside after uniform mixing. S3. Preparation of high-efficiency water-absorbing modifier: Weigh hemihydrate phosphogypsum, red mud and modified bentonite according to the proportion, put them into a ball mill, grind at 400-500 r / min for 12-15 min, control the specific surface area at 420-480 m² / kg, and set aside. S4. Preparation of mixed additives: Weigh each component of the organic polymer modifier according to the proportion and mix them evenly; weigh each component of the early strength additive according to the proportion and mix them evenly, and set them aside separately. S5. Preparation of finished curing agent: Put the modified aggregate, composite binder and high-efficiency water-absorbing modifier into a mixer and stir at 350-450 r / min for 8-10 min. After adding the mixing aid, continue stirring for 5-6 min. After mixing evenly, the modified sludge curing agent is obtained.

5. A method for preparing the modified sludge solidifying agent as described in claim 4, characterized in that, The stirring time in S1 is 6-8 minutes.