Solidification and stabilizing agents and treatment methods for screening humus in landfills

Abstract

This invention discloses a solidification and stabilization agent and treatment method for sieved humic soil in landfills. The agent comprises: a cementing component, a heavy metal stabilizing component, an organic matter passivating component, a pore-regulating component, and a process conditioning component. The cementing component includes steel slag, fly ash, and sulfoaluminate cement; the heavy metal stabilizing component includes calcium dihydrogen phosphate and sodium sulfide; the organic matter passivating component includes potassium permanganate; the pore-regulating component includes desulfurized gypsum and an air-entraining agent; and the process conditioning component includes a polycarboxylate superplasticizer and a triethanolamine early-strength agent. This invention provides core strength through a synergistic cementing system of steel slag-fly ash-sulfoaluminate cement, combines a phosphate-sodium sulfide dual stabilization mechanism to fix heavy metals, uses potassium permanganate to oxidize and passivate humic acids, and introduces desulfurized gypsum and an air-entraining agent to regulate the pore structure. The agent of this invention can significantly improve the mechanical properties of the solidified body, reduce permeability, and effectively inhibit the leaching of heavy metals and organic pollutants.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization technology, specifically to a multi-component composite solidification and stabilization agent and treatment method for humus soil screened in landfills, applicable to the solidification treatment and resource utilization of humus soil screened from aged waste. Background Technology

[0002] After excavation and screening, the humus soil in municipal solid waste landfills can account for 40%-70% of the total volume. Its composition is complex, containing a large amount of organic matter, heavy metals, and potential pollutants. Direct utilization of this soil poses environmental risks, and its high organic matter content (usually 7%-25%) can inhibit the solidification effect of traditional cement, leading to problems such as low strength and poor durability.

[0003] Existing curing technologies mostly use ordinary Portland cement (OPC) or a single curing agent, which has the following limitations:

[0004] 1. Organic matter interference: Humic acid and cement hydration products Ca 2+ Al 3+ Combined, it inhibits the hydration reaction and reduces the intensity development;

[0005] 2. Risk of heavy metal leaching: Traditional cement has low efficiency in fixing heavy metals such as As and Pb, and its long-term stability is insufficient;

[0006] 3. High cost and large carbon footprint: High cement content (often more than 20%) leads to increased costs and does not conform to the green concept of "treating waste with waste". Summary of the Invention

[0007] To address the problems of low strength, high risk of heavy metal leaching, and organic matter interference in the treatment of humus from landfill screening using traditional solidification technologies, this invention provides a highly efficient, economical, and environmentally friendly multi-component composite solidification and stabilization agent and treatment method for humus from landfill screening, so as to achieve efficient solidification and safe utilization of humus.

[0008] This invention discloses a solidification and stabilization agent for screening humus in landfills, comprising: a cementing component, a heavy metal stabilizing component, an organic matter passivation component, a pore-regulating component, and a process conditioning component; wherein,

[0009] The cementitious components include steel slag, fly ash, and sulfoaluminate cement;

[0010] The heavy metal stabilizing components include calcium dihydrogen phosphate and sodium sulfide;

[0011] The organic passivating component includes potassium permanganate;

[0012] The pore-regulating components include desulfurized gypsum and an air-entraining agent;

[0013] The process control components include polycarboxylate superplasticizer and triethanolamine early strength agent.

[0014] As a further improvement of the present invention, it comprises, by weight percentage:

[0015] The composition includes 30%-45% steel slag, 15%-28% fly ash, 12%-25% sulfoaluminate cement, 3%-8% calcium dihydrogen phosphate, 1%-3% sodium sulfide, 0.5%-2% potassium permanganate, 4%-6% desulfurized gypsum, 0.5%-1.5% air-entraining agent, 0.5%-1% polycarboxylate superplasticizer, and 1%-2% triethanolamine early strength agent.

[0016] As a further improvement of the present invention, the properties of the cementitious component are 20-30% higher than those of conventional components; wherein, the steel slag contains ≥18% Fe2O3, ≥35% CaO, ≤2.5% f-CaO, and has a specific surface area ≥380-430 m². 2 / kg; the fly ash contains SiO2+Al2O3 content ≥80%, activity index ≥80% after 28 days, loss on ignition ≤3.5%, and residue on 45μm sieve ≤5%; the sulfoaluminate cement is rapid-hardening sulfoaluminate cement with a 3-day compressive strength ≥42.5Mpa, a 3-day flexural strength ≥6.5Mpa, and an initial setting time no earlier than 25min.

[0017] As a further improvement of the present invention, the calcium dihydrogen phosphate is a white crystalline powder or flaky crystal with a Ca(H2PO4)2·H2O content ≥92.0%; the sodium sulfide is a reddish-brown or yellowish-brown blocky solid with a Na2S content ≥70.0%; and the mass ratio of sodium sulfide to calcium dihydrogen phosphate is 1:2-1:3.

[0018] As a further improvement of the present invention, the potassium permanganate has a purity of ≥99.0% and is used under acidic conditions (pH < 7) and a temperature of 20℃-60℃.

[0019] As a further improvement of the present invention, the content of calcium sulfate dihydrate (CaSO4·2H2O) in the desulfurized gypsum is ≥95.0%, and the typical particle size range is 30-60μm; the air-entraining agent includes at least one of sodium dodecyl sulfate, sodium dodecyl sulfonate and triterpenoid saponins, and the average pore size of the air-entraining agent is <200μm and the porosity coefficient is <200μm.

[0020] As a further improvement of the present invention, the mother liquor of the polycarboxylate superplasticizer is a mixture of methyl allyl polyoxyethylene ether, hydroxyethyl acrylate and maleic anhydride as monomers, wherein the molar ratio of methyl allyl polyoxyethylene ether, hydroxyethyl acrylate and maleic anhydride is 5:20:3, the pH value of the mother liquor is 10.0~13.0, the water reduction rate is 45.8~51.3%, and the setting time is 82~104 min; the triethanolamine early strength agent has a triethanolamine main content (TEOA) ≥99.0%, and the compressive strength of the sample after adding triethanolamine is increased by 20%~30% at the same time.

[0021] This invention also discloses a method for treating humus soil screened from landfills based on solidification and stabilization agents, comprising:

[0022] Step 1: Crush the humus soil from the landfill to a particle size ≤2mm and adjust the moisture content to 15%-25%;

[0023] Step 2: Prepare the solidification and stabilization agent, and weigh the solidification and stabilization agent according to the mass ratio of agent to dry soil of 10%-25%;

[0024] Step 3: Use dry mixing to mix the solidification and stabilizing agent weighed in Step 2 with the humus soil that has been crushed and had its moisture content adjusted in Step 1. Control the mixing speed to be 100-150 rpm and the time to be 5-10 min to obtain a mixture.

[0025] Step 4: Compact the mixture from Step 3 to a compaction degree ≥95% for curing; the curing temperature is 20±2℃, the humidity is ≥90%, and the curing time is 7-28 days.

[0026] As a further improvement of the present invention, in step 2, the method for preparing the curing and stabilizing agent includes:

[0027] Steel slag and fly ash were ground separately to a specific surface area ≥ 400 m². 2 / kg, and mix the ground steel slag, fly ash, sulfoaluminate cement, desulfurized gypsum and other dry powder components evenly in a mixer according to the design ratio (mixer speed is 100-120rpm, mixing time is 10-15min); then add functional components such as calcium dihydrogen phosphate, sodium sulfide, potassium permanganate, water-absorbing agent and continue mixing for 5min; finally add polycarboxylate superplasticizer and triethanolamine early strength agent, mix evenly and seal packaging.

[0028] As a further improvement of the present invention, in step 4, aerobic biological pretreatment is adopted during the maintenance process: the spacing between gas injection wells is 1.0-2.5m, and the aeration rate is 0.5-1.0L / min·m. 3Oxygen concentration ≥5%, temperature 40-60℃, aeration operation for 20-60 days; reduces organic matter activity and improves the long-term stability of the solidified body.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] This invention provides core strength through a synergistic cementitious system of steel slag-fly ash-sulfoaluminate cement, combines a phosphate-sodium sulfide dual stabilization mechanism to fix heavy metals, uses potassium permanganate to passivate humic acids, and introduces desulfurized gypsum-air-entraining agent to regulate pore structure. The agents of this invention can significantly improve the mechanical properties of the solidified body (28-day unconfined compressive strength ≥1.5 MPa) and reduce permeability (permeability coefficient ≤10). -7 The method effectively inhibits the leaching of heavy metals (such as Pb, Cd, and As) and organic pollutants (meeting the Class IV standard of the Groundwater Quality Standard), enabling the safe resource utilization of screened humus. Attached Figure Description

[0031] Figure 1 This is a flowchart of the landfill humus treatment method disclosed in this invention.

[0032] Figure 2 This is a comparison chart of the curves showing the change of unconfined compressive strength of the cured body as a function of curing time, as disclosed in this invention.

[0033] Figure 3 This is a comparison chart of the leaching concentrations of heavy metals (Pb, Cd, As) disclosed in this invention. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0035] The present invention will now be described in further detail with reference to the accompanying drawings:

[0036] This invention provides a solidification and stabilization agent for screening humus in landfills, comprising, by weight percentage:

[0037] (1) Cementitious components: 30%-45% steel slag, 15%-28% fly ash, 12%-25% sulfoaluminate cement; among which, steel slag is used to provide alkali-activated cementitious properties and hydrate to generate CSH gel; fly ash enhances later strength based on the pozzolanic effect; sulfoaluminate cement has rapid hardening and early strength, compensating for the inhibition of strength by organic matter;

[0038] (2) Heavy metal stabilizing components: 3%-8% calcium dihydrogen phosphate, 1%-3% sodium sulfide; among which, calcium dihydrogen phosphate can react with heavy metal Pb 2+ Cd 2+ Phosphate precipitates form and remain stable over a long period; sodium sulfide can reduce and fix Cr. 6+ As 5+ Heavy metals with variable valence form sulfide precipitates;

[0039] (3) Organic matter passivation component: potassium permanganate 0.5%-2%; among which, potassium permanganate is used to oxidize and degrade humic acid, destroy its complex structure, and reduce the inhibition of hydration;

[0040] (4) Pore control components: 4%-6% desulfurized gypsum, 0.5%-1.5% air-entraining agent; wherein, the desulfurized gypsum is used to provide SO4 2- It can activate fly ash and regulate pore structure; air-entraining agents are used to introduce microbubbles, improve brittleness, and enhance freeze-thaw resistance.

[0041] (5) Process adjustment components: 0.5%-1% polycarboxylate superplasticizer and 1%-2% triethanolamine early strength agent; among which, polycarboxylate superplasticizer is used to reduce water consumption and improve density; triethanolamine early strength agent is used to accelerate early strength development and shorten the curing cycle.

[0042] Specifically:

[0043] The properties of the cementitious component of this invention are 20-30% higher than those of conventional components; specifically, the steel slag contains ≥18% Fe2O3, ≥35% CaO, ≤2.5% f-CaO, and has a specific surface area ≥380-430 m². 2 / kg; the SiO2+Al2O3 content in fly ash is ≥80%, the activity index after 28 days is ≥80%, the loss on ignition is ≤3.5%, and the residue on a 45μm sieve is ≤5%; the sulfoaluminate cement is a rapid-hardening sulfoaluminate cement with a 3-day compressive strength ≥42.5Mpa, a 3-day flexural strength ≥6.5Mpa, and an initial setting time no earlier than 25min.

[0044] The calcium dihydrogen phosphate of this invention is a white crystalline powder or flaky crystal with a Ca(H2PO4)2·H2O content ≥92.0%; sodium sulfide is a reddish-brown or yellowish-brown blocky solid with a Na2S content ≥70.0%; the mass ratio of sodium sulfide to calcium dihydrogen phosphate is 1:2-1:3.

[0045] The potassium permanganate of this invention has a purity of ≥99.0% and is used under acidic conditions (pH < 7) and a temperature of 20℃-60℃.

[0046] The desulfurized gypsum of the present invention contains ≥95.0% calcium sulfate dihydrate (CaSO4·2H2O) and has a typical particle size range of 30-60 μm; the air-entraining agent includes at least one of sodium dodecyl sulfate, sodium dodecyl sulfonate and triterpenoid saponins, and the average pore size of the air-entraining agent is <200 μm and the porosity coefficient is <200 μm.

[0047] The mother liquor of the polycarboxylate superplasticizer of the present invention is a mixture of methyl allyl polyoxyethylene ether, hydroxyethyl acrylate and maleic anhydride as monomers, wherein the molar ratio of methyl allyl polyoxyethylene ether, hydroxyethyl acrylate and maleic anhydride is 5:20:3, the pH value of the mother liquor is 10.0~13.0, the water reduction rate is 45.8~51.3%, and the setting time is 82~104 min; the triethanolamine early strength agent has a triethanolamine main content (TEOA) ≥99.0%, and the compressive strength of the sample after adding triethanolamine is increased by 20%~30% at the same time.

[0048] like Figure 1 As shown, this invention provides a method for treating sieving humus soil from landfills based on solidification and stabilization agents, comprising:

[0049] Step 1, reagent preparation: Grind steel slag and fly ash separately to a specific surface area ≥400m² / kg, and mix them evenly with dry powder components such as sulfoaluminate cement and desulfurized gypsum in a mixer according to the design ratio (speed 100-120rpm, time 10-15min). Then add functional components such as calcium dihydrogen phosphate, sodium sulfide, potassium permanganate, and water-absorbing agent and continue mixing for 5min. Finally, add polycarboxylate superplasticizer and triethanolamine early strength agent, mix evenly, and seal and package.

[0050] Step 2, Humus Pretreatment: Air dry the sieved humus naturally or dry it at a low temperature of 60°C until the moisture content is ≤15%, crush it and pass it through a 2mm sieve to remove large-sized impurities.

[0051] Step 3, Mixing and Molding: Weigh the agent according to the mass ratio of agent to dry humus soil = 10%-25%, and dry mix it with the pretreated humus soil using a mechanical mixer for 2 minutes. Then, add water according to the optimal moisture content (usually 16%-26%) and wet mix for 5 minutes until uniform. The mixture is shaped by static pressing, and the compaction degree is controlled at ≥95%.

[0052] Step 4, Curing and Strengthening: The molded body is cured under standard conditions of (20±2)℃ and ≥90% humidity for 7-28 days. To improve long-term stability, it can be cured under aerobic biological pretreatment conditions (aeration through injection wells at a rate of 0.5-1.0L / min·m³ for 20-60 days to reduce the activity of organic matter).

[0053] This invention combines an industrial solid waste-based gelling system, a phosphate-sulfide heavy metal stabilization system, potassium permanganate organic matter oxidation passivation, and aerobic biological pretreatment to form a multi-barrier, synergistic solidification and stabilization technology system. This system effectively solves the problem of solidification of high-organic-matter humus soil and provides key technical support for its resource utilization in fields such as roadbed fill and landscaping soil.

[0054] Example 1: Solidification treatment of humus soil screened from a landfill in Guangdong Province

[0055] Humus properties: moisture content 22.5%, organic matter content 18.3%, pH=7.6; main heavy metals: Pb 86.5mg / kg, Cd 1.2mg / kg, As 15.8mg / kg.

[0056] The reagent formulation is as follows: steel slag 40%, fly ash 25%, sulfoaluminate cement 18%, calcium dihydrogen phosphate 5.5%, sodium sulfide 2%, potassium permanganate 1.2%, desulfurized gypsum 5%, air-entraining agent 1%, polycarboxylate superplasticizer 0.8%, and triethanolamine 1.5%. The reagent dosage is 18% of the dry humus soil mass.

[0057] This invention provides a method for treating the above-mentioned humus soil screened from landfills, comprising:

[0058] S1. Air-dry the humus to a moisture content of 15% and pass it through a 2mm sieve.

[0059] S2. All components of the reagent are mixed evenly in proportion.

[0060] S3. Dry mix the agent with dry soil mechanically for 2 minutes, then add water at a moisture content of 22% and wet mix for 5 minutes.

[0061] S4. The mixture is statically pressed into a mold (compaction degree 96%).

[0062] S5. The specimens were cured at 20℃ and 95% humidity for 28 days.

[0063] Effect: such as Figure 2 , 3 As shown, the 28-day unconfined compressive strength reaches 2.1 MPa, and the permeability coefficient is 3.2 × 10⁻⁶. -8cm / s. The leaching concentrations of Pb, Cd, and As were 0.08 mg / L, 0.003 mg / L, and 0.02 mg / L, respectively, which are far below the Class IV standard limits of GB / T 14848 (Pb≤0.1 mg / L, Cd≤0.01 mg / L, As≤0.05 mg / L).

[0064] Example 2: Aerobic biological pretreatment enhances curing effect

[0065] Pretreatment parameters: Air injection wells (spaced 1.5m apart) are set up around the solidified body, and air is injected at a rate of 0.8L / min·m³ for 30 days. The temperature of the pile body (maintained at 40-60℃) and the oxygen concentration (≥5%) are monitored.

[0066] Results: After pretreatment, the organic matter content of the cured body was reduced to 15.5%, the 28-day strength was further increased to 2.4 MPa, and the heavy metal leaching concentration was further reduced.

[0067] The advantages of this invention are:

[0068] 1. Significantly improved strength: The synergistic effect of the multi-component cementitious system results in an unconfined compressive strength of 1.5-3.0 MPa at 28 days (more than 50% higher than that of traditional OPC cured bodies).

[0069] 2. High efficiency and stability of heavy metals: The dual mechanism of phosphate and sulfide ensures that the leaching concentration of heavy metals such as Pb, Cd, and As is lower than the Class IV limit of the "Groundwater Quality Standard" (GB / T 14848).

[0070] 3. Inhibition of organic matter interference: Potassium permanganate effectively oxidizes and degrades humic acid (degradation rate ≥30%), reducing its inhibition of hydration.

[0071] 4. Resource utilization and low carbon: mainly industrial solid waste such as steel slag and fly ash (accounting for ≥60%), reducing costs by about 30% and carbon footprint by 40%.

[0072] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A solidification and stabilization agent for screening humus in landfills, characterized in that, include: The components include gelling components, heavy metal stabilizing components, organic matter passivation components, pore-regulating components, and process conditioning components; among which, The cementitious components include steel slag, fly ash, and sulfoaluminate cement; The heavy metal stabilizing components include calcium dihydrogen phosphate and sodium sulfide; The organic passivating component includes potassium permanganate; The pore-regulating components include desulfurized gypsum and an air-entraining agent; The process control components include polycarboxylate superplasticizer and triethanolamine early strength agent; By weight percentage, including: The composition includes 30%-45% steel slag, 15%-28% fly ash, 12%-25% sulfoaluminate cement, 3%-8% calcium dihydrogen phosphate, 1%-3% sodium sulfide, 0.5%-2% potassium permanganate, 4%-6% desulfurized gypsum, 0.5%-1.5% air-entraining agent, 0.5%-1% polycarboxylate superplasticizer, and 1%-2% triethanolamine early-strength agent; the mass ratio of sodium sulfide to calcium dihydrogen phosphate is 1:2-1:

3.

2. The curing and stabilizing agent as described in claim 1, characterized in that, The steel slag contains ≥18% Fe2O3, ≥35% CaO, ≤2.5% f-CaO, and has a specific surface area ≥380-430 m². 2 / kg; the fly ash contains SiO2+Al2O3 content ≥80%, activity index ≥80% after 28 days, loss on ignition ≤3.5%, and residue on 45μm sieve ≤5%; the sulfoaluminate cement is rapid-hardening sulfoaluminate cement with a 3-day compressive strength ≥42.5Mpa, a 3-day flexural strength ≥6.5Mpa, and an initial setting time no earlier than 25min.

3. The curing and stabilizing agent as described in claim 1, characterized in that, The calcium dihydrogen phosphate is a white crystalline powder or flaky crystal, with a Ca(H2PO4)2·H2O content ≥92.0%; the sodium sulfide is a reddish-brown or yellowish-brown blocky solid, with a Na2S content ≥70.0%.

4. The curing and stabilizing agent as described in claim 1, characterized in that, The potassium permanganate has a purity of ≥99.0% and is used under acidic conditions at a temperature of 20℃-60℃.

5. The curing and stabilizing agent as described in claim 1, characterized in that, The desulfurized gypsum has a calcium sulfate dihydrate content ≥95.0% and a particle size range of 30-60 μm; the air-entraining agent includes at least one of sodium dodecyl sulfate, sodium dodecyl sulfonate and triterpenoid saponins, and the average pore size of the air-entraining agent is <200 μm and the porosity coefficient is <200 μm.

6. The curing and stabilizing agent as described in claim 1, characterized in that, The mother liquor of the polycarboxylate superplasticizer is a mixture of methyl allyl polyoxyethylene ether, hydroxyethyl acrylate, and maleic anhydride as monomers, wherein the molar ratio of methyl allyl polyoxyethylene ether, hydroxyethyl acrylate, and maleic anhydride is 5:20:3, the pH value of the mother liquor is 10.0~13.0, the water reduction rate is 45.8~51.3%, and the setting time is 82~104 min; the triethanolamine early strength agent has a triethanolamine content ≥99.0%.

7. A method for treating sieving humus soil from landfills based on the solidification and stabilization agent according to any one of claims 1 to 6, characterized in that, include: Step 1: Crush the humus soil from the landfill to a particle size ≤2mm and adjust the moisture content to 15%-25%; Step 2: Prepare the solidification and stabilization agent, and weigh the solidification and stabilization agent according to the mass ratio of agent to dry soil of 10%-25%; Step 3: Use dry mixing to mix the solidification and stabilizing agent weighed in Step 2 with the humus soil that has been crushed and had its moisture content adjusted in Step 1. Control the mixing speed to be 100-150 rpm and the time to be 5-10 min to obtain a mixture. Step 4: Compact the mixture from Step 3 to a compaction degree ≥95% for curing; the curing temperature is 20±2℃, the humidity is ≥90%, and the curing time is 7-28 days.

8. The method for treating humus soil screened from landfills as described in claim 7, characterized in that, In step 2, the method for preparing the curing and stabilizing agent includes: Steel slag and fly ash were ground separately to a specific surface area ≥ 400 m². 2 / kg, and mix the ground steel slag, fly ash, sulfoaluminate cement, and desulfurized gypsum evenly in a mixer according to the design ratio; then add calcium dihydrogen phosphate, sodium sulfide, potassium permanganate, and water-absorbing agent and continue mixing; finally add polycarboxylate superplasticizer and triethanolamine early strength agent, mix evenly, and seal and package.

9. The method for treating humus soil screened from landfills as described in claim 7, characterized in that, In step 4, aerobic biological pretreatment is used during the curing process: the spacing between injection wells is 1.0-2.5m, and the aeration rate is 0.5-1.0L / min·m. 3 Oxygen concentration ≥5%, temperature 40-60℃, aeration operation for 20-60 days.

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