A sludge synergistic stabilizer based on microbial mineralization and nanocomposite and a preparation method thereof

Abstract

The application discloses a kind of based on microbial mineralization and nanocomposite silt synergic curing agent and preparation method thereof.Silt synergic curing agent includes 20%~30% fly ash, 15%~20% sulphoaluminate cement, 10%~15% modified phosphogypsum powder, 15%~20% biochar load nano iron, 5%~10% attapulgite, 6%~10% polyaspartic acid-co-acrylamide, 4%~5% sodium carboxymethyl cellulose, 3%~5% silica fume, 1%~3% magnesium carbonate and 1%~2% tartaric acid by mass percentage.Silt synergic curing agent is used for river dredging silt, harmless treatment of industrial sludge, by the adsorption performance of biochar, the reduction stable effect of nano iron and the cementation effect of composite cementing system synergize, realize the rapid dewatering of silt, high-strength solidification and long-term stabilization of pollutants.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of solid waste treatment technology in environmental engineering, and particularly relates to a sludge synergistic solidifying agent based on microbial mineralization and nano-composite and a preparation method thereof. BACKGROUND

[0002] With the development of urbanization and industry, the discharge amount of sludge from municipal sewage treatment plants, dredging sludge from rivers and lakes, and industrial contaminated spoil is gradually increasing. If not properly treated, it will occupy land and pollute the environment through soil penetration and water diffusion, threatening the ecology and human health. At present, the industry commonly uses solidification and stabilization technology, that is, adding a solidifying agent to convert pollutants into stable, standard, and low secondary pollution risk solidified bodies, which are then landfilled or resourcefully utilized.

[0003] The existing solidification technology has the problems of long solidification period, low efficiency, and difficulty in emergency response. On the other hand, the stabilization effect is limited, and the solidified body may slowly release pollutants during long-term storage. In addition, the solidified body is prone to cracking due to water evaporation and temperature changes, forming pollution penetration channels. Furthermore, it is difficult to simultaneously stabilize both heavy metals and organic matter in complex sludge, and there is still a risk of exceeding the standard or release after treatment, which cannot meet the needs of complex scenarios.

[0004] In order to reduce costs, some solidification technologies introduce industrial waste residues such as steel slag and slag as auxiliary materials, which are widely available and low in price, can reduce the amount of high-priced inorganic cementing materials, and also meet the requirements of circular economy. In order to accelerate dewatering and shorten the period, some technologies use high molecular flocculants to allow colloidal particles and water to quickly aggregate and settle. At the same time, some technologies optimize the ratio of cement, lime, and other inorganic cementing materials to improve the strength and stability of the solidified body and reduce cracking.

[0005] However, free calcium in industrial waste residues can cause the solidified body to be alkaline, affecting the strength and destroying the acid-base balance of the soil. High molecular flocculants are easily biodegradable, which may destroy the stability of pollutants and lead to secondary release. Optimizing the ratio can only alleviate the problem, but cannot fundamentally solve it, and cannot break through the problem of simultaneous stabilization of heavy metals and organic matter in complex sludge. Therefore, it is an urgent need in the industry to develop a new composite solidifying agent that has efficient dewatering, rapid solidification, and multiple pollution control. SUMMARY

[0006] In order to solve the problems of insufficient stability and strength of the existing sludge solidifying agent, the present application aims to provide a sludge synergistic solidifying agent based on microbial mineralization and nano-composite and a preparation method thereof. Through the synergistic effect of the adsorption performance of biochar, the reduction and stabilization effect of nano-iron, and the cementation effect of the composite cementing system, rapid dewatering, high-strength solidification, and long-term stabilization of pollutants are achieved. The sludge synergistic solidifying agent is suitable for the harmless treatment and resource utilization of river dredging sludge, industrial sludge, and other high-water-content, high-organic-matter, and heavy-metal-polluted sludge.

[0007] To achieve the above object, the present application provides the following technical solutions:

[0008] The present application provides a kind of sludge synergistic stabilizer based on microbial mineralization and nanocomposite, including 20%~30% fly ash, 15%~20% sulphoaluminate cement, 10%~15% modified phosphogypsum powder, 15%~20% biochar load nano iron, 5%~10% attapulgite, 6%~10% polyaspartic acid-co-acrylamide, 4%~5% sodium carboxymethyl cellulose, 3%~5% silica ash, 1%~3% magnesium carbonate and 1%~2% tartaric acid by mass percentage.

[0009] The fly ash includes 45%~50% SiO2, 25%~30% Al2O3, 4%~6% Fe2O3 and 15%~20% CaO by mass percentage, and the rest is impurities.

[0010] The sulphoaluminate cement includes 40%~45% calcium sulphoaluminate, 25%~30% dicalcium silicate, 10%~15% tetracalcium aluminoferrite by mass percentage, and the rest is impurities.

[0011] The preparation method of the modified phosphogypsum powder comprises:

[0012] The citric acid solution and the phosphogypsum powder are mixed according to the liquid-solid mass ratio of 1: (2~3), and the reaction is carried out at 60~70°C until the pH is 6.5~7.5. The solid phase after the reaction is dried to obtain the modified phosphogypsum powder. The mass fraction of the citric acid solution is 3%~5%.

[0013] The preparation method of the biochar load nano iron comprises:

[0014] The biochar is added into the FeSO4 7H2O solution to obtain a first mixed solution. The concentration of the FeSO4 7H2O solution is 0.1~0.2 mol / L. The mass-volume ratio of the biochar and the FeSO4 7H2O solution is 1g: (10~15) mL.

[0015] In the inert gas, NaBH4 solution is added into the first mixed solution according to the molar ratio of Fe 2+ and BH4 - 1: (2~3) to obtain the biochar load nano iron. The concentration of the NaBH4 solution is 0.2~0.3 mol / L.

[0016] The preparation method of the attapulgite comprises:

[0017] According to a solid-liquid mass ratio of 1: (5-8), the attapulgite raw material is added into water and mixed uniformly, and after standing, the upper layer of the suspension is taken;

[0018] Hydrochloric acid solution is added into the upper layer of the suspension, and the reaction is carried out at 80-100 DEG C, and the solid phase after the reaction is washed, dried and ground to obtain attapulgite; the mass fraction of the hydrochloric acid solution is 3%-5%.

[0019] The preparation method of the polyaspartic acid-co-acrylamide comprises the following steps:

[0020] L-aspartic acid and acrylamide are dissolved in water to obtain a second mixed solution, and the molar ratio of L-aspartic acid and acrylamide is 1: (3-4) ;

[0021] Ammonium persulfate is added into the second mixed solution, and the reaction is carried out at 60-70 DEG C in an inert atmosphere to obtain a reaction product, and the reaction product is evaporated, precipitated and vacuum dried to obtain polyaspartic acid-co-acrylamide, and the mass of the added ammonium persulfate is 2%-3% of the total mass of L-aspartic acid and acrylamide.

[0022] The application also provides a preparation method of the sludge synergistic stabilizer based on microbial mineralization and nanocomposites, comprising the following steps:

[0023] Fly ash, sulphoaluminate cement and modified phosphogypsum powder are mixed to obtain a first stabilizer mixture;

[0024] Biochar loaded nano-iron and attapulgite are added into the first stabilizer mixture to obtain a second stabilizer mixture;

[0025] The polyaspartic acid-co-acrylamide is prepared into a polyaspartic acid-co-acrylamide solution, and the sodium carboxymethyl cellulose is prepared into a sodium carboxymethyl cellulose solution, and the polyaspartic acid-co-acrylamide solution and the sodium carboxymethyl cellulose solution are added into the second stabilizer mixture to obtain a third stabilizer mixture;

[0026] Silica ash, magnesium carbonate and tartaric acid are added into the third stabilizer mixture and mixed uniformly to obtain a sludge stabilizer.

[0027] The mass fraction of the polyaspartic acid-co-acrylamide solution is 10%-15%.

[0028] The mass fraction of the sodium carboxymethyl cellulose solution is 5%-10%.

[0029] Compared with the prior art, the application has the following beneficial effects:

[0030] The composite cementing phase composed of fly ash, sulphoaluminate cement and modified phosphogypsum powder generates cementitious products such as ettringite and C-S-H gel through hydration reaction to build a stable solidification body framework, and the cementitious products can effectively fill the pores inside the silt to realize silt dewatering and solidification. The component limitation of the composite cementing phase can ensure sufficient generation of hydration products, so that the unconfined compressive strength of the solidification body is stably up to ≥300kPa after 3 days; if the mass proportion of the composite cementing phase is too high, not only the cost will increase, but also the solidification body may crack due to excessive shrinkage during solidification. The functional adsorption phase composed of biochar loaded with nano-iron and attapulgite can efficiently remove pollutants in the silt; the biochar loaded with nano-iron has adsorption performance and reduction activity, which can not only adsorb heavy metal ions and organic pollutants in the silt, but also convert highly toxic heavy metals into low toxicity forms through the reduction of nano-iron, thereby greatly reducing the environmental risk of pollutants; the attapulgite can effectively improve the water absorption of the system, avoiding the problem of excessive water in the solidification body due to the excessive water absorption of the material, thereby causing strength reduction, and providing protection for the coordinated improvement of pollution stabilization and mechanical properties. The organic phase composed of poly-aspartic acid-co-acrylamide and sodium carboxymethyl cellulose tightly wraps the silt particles through the entanglement of the polymer chain and hydrogen bonding, thereby significantly enhancing the cohesiveness and toughness of the solidification body and effectively reducing the cracking risk caused by uneven structural stress during maintenance. Silica fume, magnesium carbonate and tartaric acid are used as functional regulators to fine-tune the hydration reaction rate, optimize the microstructure, and improve the early strength and late stability of the balanced solidification body. The silt synergistic solidification agent of the present application can realize efficient dewatering and solidification of the silt and improve the mechanical properties through synergistic effect and precise control of the amount of each component, and can also efficiently adsorb, reduce and stabilize heavy metals and organic pollutants, finally achieving the comprehensive effect of meeting the engineering application and environmental protection requirements, such as meeting the mechanical performance standard of the silt solidification body, long-term stability of pollutants, few structural defects and reasonable economic efficiency.

[0031] The preparation method of the silt synergistic solidification agent provided by the present application first uniformly disperses the composite cementing phase composed of fly ash, sulphoaluminate cement and modified phosphogypsum powder to ensure balanced strength during solidification of the cementing phase, then uniformly disperses the functional adsorption phase to avoid agglomeration, adds the organic phase through a solution to control the water content of the solidification agent system, and finally uniformly disperses the functional regulators such as silica fume, magnesium carbonate and tartaric acid to obtain a silt synergistic solidification agent with uniform composition and stable performance. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments will be briefly introduced as follows. It should be understood that the following drawings only show some of the embodiments of the present application, and therefore should not be considered as limiting the scope. For those skilled in the art, other related drawings can also be obtained without creative labor.

[0033] Figure 1 Micro-morphology diagram of biochar loaded with nano-iron;

[0034] Figure 2 ICP-MS (Inductively coupled plasma mass spectrometry, Inductively coupled plasma mass spectrometry) characterization of nano-iron loading in biochar loaded with nano-iron. Absorption peak spectrum. DETAILED DESCRIPTION

[0035] In order to make the technical problems, technical solutions and beneficial effects of the present application more clear, the present application will be further described in detail below in combination with embodiments. It should be understood that the specific embodiments described here are only used to explain the present application, and are not used to limit the present application.

[0036] In the present application, the term "and / or" describes the association relationship of the associated objects, which means that there can be three kinds of relationships, for example, A and / or B, which can represent the following cases: A exists alone, A and B exist together, and B exists alone. Wherein A and B can be singular or plural. The character " / " generally represents that the associated objects before and after it are in an "or" relationship.

[0037] In the present application, "at least one" means one or more, and "multiple" means two or more. "At least one of the following" or similar expressions means any combination of these items, including any combination of single item or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can represent a, b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, wherein a, b, and c can be single or multiple.

[0038] It should be understood that in various embodiments of the present application, the size of the serial number of each process does not mean the order of execution, and part or all of the steps can be executed in parallel or in sequence, and the execution order of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0039] The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in the description of the application and the appended claims, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0040] The weight of the related components mentioned in the specification of the embodiments of the application can not only refer to the specific content of each component, but also represent the proportional relationship between the weights of each component, therefore, as long as the content of the related components in the specification of the embodiments of the application is proportionally enlarged or reduced, it is within the scope disclosed in the specification of the embodiments of the application. Specifically, the mass mentioned in the specification of the embodiments of the application can be μg, mg, g, kg and other mass units commonly known in the chemical field.

[0041] Unless otherwise specified, the particle size of the particles in the application is determined by a laser particle size analyzer, the specific surface area is determined by the BET method (Brunauer, Emmett and Teller, gas adsorption method), the water content is determined by the drying method, the model of the jet mill in the embodiments is QLM-100, the model of the jaw crusher is PE-150x25, the model of the Raymond mill is 3R4119, the model of the tube furnace is GSL-1600X, the model of the double-screw metering scale is LXC-50, and the metering accuracy is ±1%. The pipe diameter of the pneumatic conveying pipeline is DN100, the air pressure is 0.2MPa, the model of the double-shaft paddle mixer is WZ-200, the effective volume is 0.5m 3 , and the paddles are arranged in a staggered manner with "left-handed + right-handed".

[0042] The application provides a sludge synergistic stabilizer based on microbial mineralization and nanocomposites, which comprises, in percentage by mass, 20-30% of fly ash, 15-20% of sulphoaluminate cement, 10-15% of modified phosphogypsum powder, 15-20% of biochar loaded with nano-iron, 5-10% of attapulgite, 6-10% of polyaspartic acid-co-acrylamide, 4-5% of sodium carboxymethyl cellulose, 3-5% of silica fume, 1-3% of magnesium carbonate and 1-2% of tartaric acid.

[0043] The limitation of the use amount of each component of the composite cementing phase composed of fly ash, sulphoaluminate cement and modified phosphogypsum powder in the sludge synergistic stabilizer provided by the application can ensure sufficient hydration products, and the 3-day unconfined compressive strength is ≥300kPa; the use amount ratio of the composite gel phase is too high, which can increase the cost and can cause cracking due to excessive shrinkage. The biochar loaded with nano-iron and the attapulgite form a functional adsorption phase, and the functional adsorption phase can adsorb Cr 6+ , Pb 2+Heavy metal ions and organic pollutants such as polycyclic aromatic hydrocarbons and phenols, nano-iron reduces highly toxic heavy metals, and realizes long-term stabilization of pollutants; the biochar loaded with nano-iron needs to reach 15% to 20% to ensure that the leaching rate of heavy metals is ≤0.1 mg / L; 5% to 10% of the attapulgite can avoid the decrease in strength caused by excessive water absorption; the organic phase composed of polyaspartic acid-co-acrylamide and sodium carboxymethyl cellulose can wrap the sludge particles through the entanglement of the polymer chain and the hydrogen bond, improve the cohesiveness and toughness of the solidified body, and reduce the cracking period, wherein, more than 10% of polyaspartic acid-co-acrylamide will increase the plasticity of the solidified body, and less than 6% will be insufficient in cohesiveness; 4% to 5% of sodium carboxymethyl cellulose can avoid the strength hysteresis caused by excessive water retention; silica fume, magnesium carbonate and tartaric acid are performance adjusters, which are used to fine-tune the hydration reaction rate, optimize the microstructure, and balance the early strength and late stability of the solidified body, wherein, more than 5% of silica fume will increase the water demand, more than 3% of magnesium carbonate will inhibit the strength growth, and more than 2% of tartaric acid will cause the final setting time to be too long, ensuring the long-term stabilization of heavy metals and organic pollutants.

[0044] In some embodiments, a method for preparing fly ash, comprising:

[0045] The fly ash raw material is selected from secondary fly ash of a thermal power plant, which meets the GB / T1596-2017 standard, and high-calcium fly ash generated by a circulating fluidized bed boiler is preferred, and the initial particle size is ≤150 μm.

[0046] The secondary fly ash of the thermal power plant is subjected to superfine treatment by an air flow mill to obtain fly ash, and the crushing pressure during the treatment process is 0.8 MPa, and the rotating speed of the grading wheel is 3000 r / min; the particle size distribution of the fly ash is D10=2 μm, D50=6 μm, and D90=12 μm, and the specific surface area is 450-550 m 2 / g;

[0047] The fly ash includes 45% to 50% of SiO2, 25% to 30% of Al2O3, 4% to 6% of Fe2O3, and 15% to 20% of CaO, and the rest is impurities, and the water demand ratio is ≤105%; the pozzolanic activity is sufficient to react with Ca(OH)2 to generate C-S-H gel.

[0048] The activity of the treated fly ash is detected: 50 g of fly ash is mixed with 200 mL of saturated Ca(OH)2 solution, and cured at 80°C for 7 days, and the Ca 2+ concentration reduction value is ≥30 mg / L, which proves that the pozzolanic activity meets the standard.

[0049] In some embodiments, a method for preparing sulphoaluminate cement, comprising:

[0050] The sulphoaluminate cement is a 42.5-grade fast-hardening sulphoaluminate cement, which meets the GB20472-2006 standard, has an initial setting time of 25-30 min, a final setting time of 90-120 min, and a 28d compressive strength of ≥42.5 MPa.

[0051] The sulphoaluminate cement includes 40%-45% calcium sulphoaluminate, 25%-30% dicalcium silicate, 10%-15% tetracalcium aluminoferrite, and the rest impurities in terms of mass percentage; these components can generate ettringite with needle-shaped crystals during hydration, thereby significantly improving early strength; the mass fraction of free CaO is ≤1.0%, which avoids expansion and cracking in the later hydration stage; and the mass fraction of SO3 is 8%-10%, which ensures the amount of ettringite generated.

[0052] In some embodiments, the method for preparing modified phosphogypsum powder includes:

[0053] The phosphogypsum powder raw material is phosphogypsum from phosphorus chemical industry waste residue, has an initial water content of ≤15%, and mainly includes dihydrate calcium sulfate (CaSO4 2H2O) with a mass fraction of ≥90%. The phosphogypsum from phosphorus chemical industry waste residue is first crushed to a particle size of ≤5 mm by a jaw crusher, and then quartz, feldspar and other impurities are removed through a 200-mesh vibrating screen to obtain phosphogypsum powder. The pH of the unmodified phosphogypsum powder is 10-12.

[0054] A citric acid solution with a mass fraction of 3%-5% is prepared, and analytical pure citric acid is used.

[0055] The citric acid solution and the phosphogypsum powder are mixed in a liquid-solid mass ratio of 1:(2-3), placed in a constant-temperature water bath at 60-70°C, mechanically stirred and soaked for 12 h, the stirring rate is 150 r / min, the pH value is detected every 2 h during the period, and the pH is stabilized at 6.5-7.5; vacuum filtration is performed under a vacuum degree of -0.08 MPa, and after filtration, air drying is performed at 80°C until the water content is below 5% to obtain modified phosphogypsum powder; the modified phosphogypsum powder is crushed to 300 mesh by a Raymond mill for use, the particle size of the modified phosphogypsum powder is ≤50 μm, and the dispersibility is ensured.

[0056] It should be noted that the free CaO in the phosphogypsum powder is neutralized by citric acid to reduce alkalinity, and part of the impurities such as phosphorus and fluorine are dissolved to avoid inhibiting the hydration reaction.

[0057] In some embodiments, the method for preparing biochar loaded with nano-iron includes:

[0058] The biomass raw material is ground until the particle size is 2-3 cm, washed with deionized water for 3 times, dried at 60°C until the water content is below 10%, and then ground until the particle size is 1-2 mm; the biomass raw material includes corn cobs, corn stalks, wheat stalks, branches, wood chips, etc.

[0059] The dried biomass material is placed in a tube furnace, nitrogen is introduced to drive oxygen for 30 min, the flow rate of nitrogen is 500 mL / min, and the temperature is raised to 500℃ at a rate of 10℃ / min, and the carbonization treatment is carried out for 3 h, and then the carbonization treatment is naturally cooled to room temperature, and then sieved through a 100 mesh sieve to obtain biochar, and the particle size of the biochar is less than 150 μm.

[0060] The specific surface area of the biochar is 350~400 m 2 / g; the total pore volume of the biochar is 0.25~0.3 cm 3 / g, and the pore size distribution is mainly micropores with a size of 2~5 nm, which is beneficial to the adsorption of small molecule organic matter, and the pH value of the biochar is 7.0~7.5, which avoids the influence of strong alkalinity on the activity of nano-iron.

[0061] FeSO4 7H2O is dissolved in deionized water to prepare a FeSO4 7H2O solution with a concentration of 0.1~0.2 mol / L.

[0062] The biochar is added to the FeSO4 7H2O solution and magnetically stirred at a speed of 300 r / min for 30 min to obtain a first mixture, and Fe 2+ is fully adsorbed on the surface of the biochar; the mass-volume ratio of the biochar to the FeSO4 7H2O solution is 1 g: (10~15) mL.

[0063] In an inert gas, the molar ratio of Fe 2+ to BH4 - is 1: (2~3), and NaBH4 solution is added dropwise to the first mixture for reaction, wherein the concentration of the NaBH4 solution is 0.2~0.3 mol / L, the dropwise addition rate of NaBH4 is 1 mL / min, and the flow rate of the inert gas is 200 mL / min; after 1 h of reaction, the reaction solution is vacuum filtered to obtain black nano-iron particles, the black nano-iron particles are washed with deionized water for 3 times to remove residual salt, and then washed with anhydrous ethanol for 1 time to reduce agglomeration, and then vacuum dried at 60℃ under a vacuum degree of -0.09 MPa for 8 h to obtain black powder, which is biochar loaded nano-iron.

[0064] The prepared biochar-supported iron nanoparticles were subjected to relevant performance tests. The particle size of the biochar-supported iron nanoparticles was characterized using TEM (Transmission Electron Microscopy). Before testing, the biochar-supported iron nanoparticles were uniformly dispersed in anhydrous acetone to ensure uniform distribution and facilitate clear observation of the microstructure. The microstructure of the prepared biochar-supported iron nanoparticles was observed using TEM, such as... Figure 1 As shown in the figure, the darker areas represent nano-iron. The smaller the nano-iron particles, the better the experimental results are achieved. The nano-iron in the biochar-supported platform is stably granular, and a small amount of even higher-quality nano-iron (reaching 30 nm) exists. Statistically, approximately 86% of the regions have nano-iron particles reaching 50-100 nm.

[0065] The loading of nano-iron was determined by ICP-MS, such as... Figure 2 As shown, four groups of solutions were set up: a blank group (Control), a standard solution group (Standard), an Agilent 7700 group, and a Thermo Fisher iCAPTQ group. The prepared solutions were introduced into an ICP-MS and monitored in real time. 56 The Fe signal ensures that the iron signal of each separated component can be accurately captured. An increase in the Fe signal in ICP-MS indicates a high content of nano-iron particles. Based on the absorption peaks at 11 min and 15 min, and in accordance with the instructions for use of the standard solutions, the loading of nano-iron in the test samples was statistically determined to be 8%–10%.

[0066] TEM characterization revealed that the iron nanoparticles supported on biochar had a particle size of 50–100 nm, and ICP-MS analysis showed that the iron loading was 8–10%. The iron nanoparticles were uniformly distributed on the biochar surface without significant agglomeration. Biochar-supported iron nanoparticles exhibit a dual "reduction-adsorption" mechanism; biochar possesses numerous porous structures and oxygen-containing functional groups, and zero-valent iron exhibits high surface activity and reducing power, enabling biochar-supported iron nanoparticles to effectively adsorb and immobilize heavy metal ions in sludge; Fe binds Cr... 6+ Reduced to Cr 3+ Carboxyl groups on the surface of biochar and Cr 3+ Forming stable chelates, Cr 3+ The leaching concentration is controlled below 0.02 mg / L.

[0067] In some embodiments, the method for preparing attapulgite includes:

[0068] The raw material for attapulgite clay is selected from attapulgite clay produced in Linze, Gansu Province, with a purity of over 85% and a mass fraction of attapulgite minerals of over 80%. The raw material for attapulgite clay is ground until the particle size is below 1mm.

[0069] The ground attapulgite raw material is added to deionized water in a solid-liquid mass ratio of 1: (5-8), stirred at a speed of 500 r / min for 30 min, uniformly stirred, and then left to stand for 2 h, and the upper layer of the suspension is taken.

[0070] A hydrochloric acid solution with a mass fraction of 3-5% is added to the upper layer of the suspension, and the reaction is carried out at 80-100°C for 2 h to remove carbonate impurities. After the reaction, the reaction liquid is filtered, the solid phase after filtration is washed with deionized water until neutral, and then dried at 100-120°C. The attapulgite is obtained by ultrafine grinding, the particle size D50 of the attapulgite is 2-3 μm, the specific surface area is more than 200 m 2 / g, the Cation Exchange Capacity (CEC) is more than 20 meq / 100 g, as determined by the ammonium acetate method.

[0071] It should be noted that the attapulgite has a layered structure, the layered structure adsorbs heavy metals through ion exchange, and the fibrous crystals are inserted into the solidified body to enhance the crack resistance. The adsorption capacity of the interlayer pores of the attapulgite for benzene series is more than 30 mg / g, the aromatic structure of the biochar adsorbs polycyclic aromatic hydrocarbons through π-π interaction, and the removal rate of organic pollutants is more than 90% under the combined action, and the desorption rate is less than 5% after 60 days of oscillation.

[0072] In some embodiments, the method for preparing polyaspartic acid-co-acrylamide comprises:

[0073] L-aspartic acid and acrylamide are dissolved in water to obtain a second mixture, the mass fraction of the second mixture is 30%, and the molar ratio of L-aspartic acid to acrylamide is 1: (3-4) ;

[0074] Ammonium persulfate is added to the second mixture and mixed uniformly, and a polymerization reaction is initiated in an inert gas at a constant temperature of 60-70°C for 4 h to obtain a reaction product, which is a light yellow viscous liquid. The reaction product is concentrated to a solid content of ≥30% by rotary evaporation at 60°C and a vacuum degree of -0.08 MPa, and then purified by ethanol precipitation. After drying at 80-100°C and a vacuum degree of -0.08 MPa, the product is ground through an 80-mesh sieve to obtain polyaspartic acid-co-acrylamide. The mass of ammonium persulfate added is 2-3% of the total mass of L-aspartic acid and acrylamide.

[0075] The prepared polyaspartic acid-co-acrylamide has a number average molecular weight of 5000-8000 determined by gel permeation chromatography (GPC), a Ca 2+ chelation value of 100 mg / g or more determined by ethylene diamine tetraacetic acid (EDTA) titration, and a viscosity of a 2% polyaspartic acid-co-acrylamide aqueous solution of 300 mPa s or more at 25°C determined by a rotational viscometer.

[0076] The polyaspartic acid-co-acrylamide is added to deionized water and stirred at a speed of 500 r / min until completely dissolved to obtain a polyaspartic acid-co-acrylamide solution for standby, and the mass fraction of the polyaspartic acid-co-acrylamide solution is 10%-15%.

[0077] It should be noted that the carboxyl groups of the aspartic acid units chelate metal ions, and the amide groups of the acrylamide units form hydrogen bonds with soil particles to construct a three-dimensional network structure.

[0078] In some embodiments, the degree of substitution of carboxymethyl cellulose sodium (CMC-Na) is 0.8-1.0, the degree of substitution is 80-100 carboxymethyl groups introduced per 100 glucose units, and the purity is more than 99%.

[0079] The viscosity of a 2% carboxymethyl cellulose sodium aqueous solution is 500-800 mPa s at 25°C and a speed of 60 r / min determined by an NDJ-1 viscometer, the pH value is 6.5-7.5, and the water-insoluble substance is less than 0.5%, so as to ensure that the CMC-Na is uniformly dispersed in the silt.

[0080] The CMC-Na is removed from agglomeration by an 80-mesh sieve, the CMC-Na is added to deionized water at 60°C and stirred at a speed of 500 r / min until completely dissolved to obtain a carboxymethyl cellulose sodium solution for standby, and the mass fraction of the carboxymethyl cellulose sodium solution is 5%-10%.

[0081] It should be noted that the carboxymethyl cellulose sodium can improve the workability of the solidifying agent and the silt, reduce dust in the stirring process, and maintain water during the curing period to prevent surface cracking.

[0082] In some embodiments, the silica ash is selected from a ferrosilicon smelting byproduct of a ferroalloy factory, the mass fraction of SiO2 in the silica ash is ≥90%, and the specific surface area is 15000-20000 m 2 / g, the particle size is 0.1-0.5 μm, and the density is 2.2-2.3 g / cm 3 .

[0083] It should be noted that the silica ash is a superfine particle, which can fill the pores of the C-S-H cementitious system and improve the density; and reacts with Ca(OH)2 to generate additional C-S-H gel, thereby enhancing the strength of the interface transition zone.

[0084] In some embodiments, the magnesium carbonate is selected as light magnesium carbonate, wherein the purity of the light magnesium carbonate is above 95%, the particle size is below 10 μm, the whiteness is above 90%, and the moisture is below 2%.

[0085] It should be noted that the Mg(OH)2 generated by the slow hydration reaction of magnesium carbonate reduces the alkalinity of the liquid phase, delays the generation rate of ettringite, and avoids cracks caused by concentrated early heat release.

[0086] In some embodiments, the tartaric acid is selected as analytical pure tartaric acid, wherein the content of C4H6O6 is above 99.5%, the particle size is 50-100 μm, and the tartaric acid is easily soluble in water.

[0087] It should be noted that the tartaric acid has a retarding effect, which inhibits the nucleation of hydrated calcium silicate by adsorbing on the surface of cement particles, controls the initial setting time of the silt synergistic solidification agent to be 4-6 h, meets the construction operation window, and the final setting time is below 12 h.

[0088] The preparation method of the above-mentioned silt synergistic solidification agent based on microbial mineralization and nanocomposites comprises:

[0089] S1, mixing fly ash, sulphoaluminate cement, and modified phosphogypsum powder to obtain a first solidification agent mixture;

[0090] S2, adding biochar loaded nano-iron and attapulgite to the first solidification agent mixture to obtain a second solidification agent mixture;

[0091] S3, adding polyaspartic acid-co-acrylamide to water to obtain a polyaspartic acid-co-acrylamide solution, adding sodium carboxymethyl cellulose to water to obtain a sodium carboxymethyl cellulose solution, and uniformly mixing the polyaspartic acid-co-acrylamide solution and the sodium carboxymethyl cellulose solution into the second solidification agent mixture to obtain a third solidification agent mixture;

[0092] S4, uniformly mixing silica ash, magnesium carbonate, and tartaric acid into the third solidification agent mixture to obtain the silt synergistic solidification agent.

[0093] In some embodiments, the sludge synergistic solidifying agent is prepared by a double-shaft mixer; in S1, stirring at 200 r / min for 8 min, sampling at 3, component deviation ≤2%, ensuring uniformity of the powder; in S2, stirring at 300 r / min for 5 min, dispersing nanoparticles by shear force; in S3, stirring at 250 r / min for 10 min, slowly adding polyaspartic acid-co-acrylamide solution and sodium carboxymethyl cellulose solution during the stirring process; controlling the water content of the composite system ≤10%; in S4, stirring at 200 r / min for 5 min, detecting by sieving method, the particle size of the sludge synergistic solidifying agent ≤1 mm. During the mixing process, the stirring speed is dynamically adjusted according to the material state to prevent dust, and the final mixing uniformity is ≥95% verified by fluorescence labeling method.

[0094] During the preparation process of the sludge synergistic solidifying agent, the temperature is controlled at 20-30°C, and when the environmental temperature is too low, the jacket is turned on for heating, and at the same time, the organic phase is prevented from degrading due to high temperature.

[0095] The prepared sludge synergistic solidifying agent is stored in a double-layer polyethylene bag, the inner layer of the double-layer polyethylene bag is vacuum packaged, the outer layer is moisture-proof, each bag contains 25 kg, and is stored in a dry environment ≤30°C, with a shelf life of 6 months, regular sampling inspection, and ensuring that the activity reduction rate ≤5%.

[0096] The quality detection index of the sludge synergistic solidifying agent needs to meet the following requirements:

[0097] (1) Component uniformity, randomly sampling 3 parts, measuring the mass fraction of SiO2 and Al2O3, and the relative deviation ≤3%.

[0098] (2) Particle size distribution, wet sieving, 300 mesh residue ≤5%.

[0099] (3) Activity index, mixed with reference cement at a mass ratio of 1:3, 28d compressive strength ratio ≥95% (GB / T12957-2005 method).

[0100] (4) Heavy metal adsorption performance, static adsorption capacity of Cr 6+ ≥20 mg / g, the initial concentration of the test object Cr 6+ is 100 mg / L.

[0101] Through the above fine process control, the sludge synergistic solidifying agent realizes the synergistic effect of "gelling skeleton construction-pollutant adsorption and solidification-toughness network reinforcement" in sludge treatment, 3-day unconfined compressive strength ≥300 kPa, and heavy metal leaching concentration ≤0.05 mg / L (GB 5085.3-2007 standard).

[0102] The application also provides a method for applying the sludge synergistic curing agent, comprising:

[0103] The sludge is treated by adopting a two-stage screening process, the first stage adopts a grating screen, the grating has a pore size of 10 mm, and large impurities such as branches and plastics are removed; the second stage adopts a vibrating screen, the vibrating screen is 20 mesh, the amplitude is 3-5 mm, the frequency is 50 Hz, and the sand and stone particles with a particle size greater than 0.85 mm are separated, so that the uniformity of the particle size of the sludge entering the subsequent process is ensured; the screened sludge is sent to a horizontal homogenizing tank for conditioning and homogenization, the effective volume of the horizontal homogenizing tank is 10 m 3 , double-layer stirring paddles are arranged in the tank, the upper paddle has a diameter of 1.2 m, the lower paddle has a diameter of 0.8 m, the rotating speed of the two paddles is 60 r / min, the stirring is continuously performed for 30 min, and an infrared moisture meter is used for online monitoring, so that the fluctuation of the moisture content of the sludge is controlled within ±2%. If the initial moisture content of the sludge is greater than 85%, the pretreated dried sludge is added to the homogenizing tank through a screw conveyor, the moisture content of the dried sludge is less than or equal to 30%, the dried sludge is added until the moisture content is reduced to 75%-80%, and a stirrable state is reached; if the moisture content is less than 70%, deionized water is added for adjustment, so that the sludge is in a flowable state, and the consistency index is 1.2-1.5. The sludge is pretreated, the initial moisture content of the sludge is reduced, the large impurities are removed, and conditions for uniform mixing of the curing agent are created.

[0104] The sludge synergistic curing agent is accurately proportioned and mixed with the sludge by a double-screw metering scale, wherein the main material screw conveys the sludge synergistic curing agent, the rotating speed is 50-100 r / min, and the rotating speed is adjusted according to actual needs; the auxiliary material screw conveys the sludge, the rotating speed is automatically matched according to the sludge synergistic curing agent addition amount, the two are linked and controlled through a PLC system, the mass ratio of the sludge synergistic curing agent to the sludge is 1: (5-7), and the uniformity of the curing reaction is ensured.

[0105] The sludge synergistic curing agent is sent into a double-shaft paddle mixer through a pneumatic conveying pipeline, a Venturi nozzle is arranged at the end of the pipeline, the sludge synergistic curing agent is dispersed into a mist state with a particle size of less than 0.5 mm, and the sludge synergistic curing agent is uniformly sprayed into the sludge flow at a flow speed of 1.5-2 m / s to avoid local agglomeration. The sludge synergistic curing agent and the sludge are mixed in the double-shaft paddle mixer at a rotating speed of 150 r / min for 15 min, three-point sampling is performed through sampling detection, and the mixing uniformity is ensured to be more than 90%.

[0106] The mixed material is uniformly laid on a construction area, a film is covered on the surface, the air permeability of the film is 500 g / m 2 24h, and primary curing is performed for 24-48h in an environment with a humidity of 80-90%; the primary curing is mainly to promote the rapid generation of ettringite.

[0107] The film is removed and natural curing is carried out in a natural environment for 48h to 7d, an automatic spraying system is used during the natural curing process, water is sprayed once every 6h, the spraying amount is 1% of the mass of the solidified body, the water content of the surface is kept above 80% to keep the surface wet, and meanwhile, the environmental temperature is controlled to be 15-25 DEG C through a sunshade to avoid surface dry shrinkage caused by direct sunlight.

[0108] The hydration reaction is promoted to proceed in an orderly manner through gradient humidity control, and solidified body cracking is avoided.

[0109] The sludge synergistic curing agent provided by the application can inhibit the generation of microcracks during the curing period by adding 0.5% of polypropylene fibers, the length of the polypropylene fibers is 12mm, the tensile strength is above 600MPa, the mass loss rate of the polypropylene fibers is below 3% after 25 freeze-thaw cycle tests of freezing for 4h at-20 DEG C and thawing for 4h at 20 DEG C, and the strength retention rate is above 85%.

[0110] In the following examples, unless otherwise specified, each material used can be obtained through an ordinary channel; and the test method used is a conventional method in the field.

[0111] Example 1

[0112] Preparation of the base material:

[0113] The secondary fly ash of a thermal power plant is subjected to superfine treatment through an air flow mill, the crushing pressure is 0.8MPa during the treatment process, and the rotating speed of the grading wheel is 3000r / min; the particle size distribution of the fly ash is D10=2.1um, D50=5.8um, and D90=11.7um, and the specific surface area is 486m 2 / g; in terms of mass percentage, the fly ash comprises 45% of SiO2, 28.6% of Al2O3, 6% of Fe2O3, 16.5% of CaO, and the rest is impurities.

[0114] In terms of mass percentage, the sulphoaluminate cement comprises 40% of calcium sulphoaluminate, 25.7% of dicalcium silicate, 12.6% of tetracalcium aluminoferrite, and the rest is impurities.

[0115] The citric acid solution and the phosphogypsum powder are mixed in a liquid-solid mass ratio of 1:3, placed in a constant temperature water bath at 60 DEG C, mechanically stirred and soaked for 12h, the stirring rate is 150r / min, the pH value is detected every 2h during the period, and the pH value is stabilized at 6.8; vacuum filtration is carried out under a vacuum degree of-0.08MPa, the modified phosphogypsum powder is obtained after air drying at 80 DEG C until the water content is 4.7% after the vacuum filtration; the modified phosphogypsum powder is crushed to 300 mesh through a Raymond mill for use, and the mass fraction of the citric acid solution is 3%.

[0116] adding biochar into FeSO4 7H2O solution, and stirring for 30 min at a rotating speed of 300 r / min to obtain a first mixed solution; under nitrogen, adding NaBH4 solution into the first mixed solution at a molar ratio of 1:2 of Fe 2+ and BH4 - , and stirring for 1 h to obtain black nano-iron particles; washing the black nano-iron particles with deionized water for 3 times, and then washing with anhydrous ethanol for 1 time; vacuum drying at 60℃ and a vacuum degree of-0.09 MPa for 8 h to obtain black powder, which is biochar loaded nano-iron, wherein the mass-volume ratio of biochar to FeSO4 7H2O solution is 1g:10mL, and the concentration of FeSO4 7H2O solution is 0.1 mol / L; the concentration of NaBH4 solution is 0.2 mol / L; through detection, the particle size of nano-iron in the biochar loaded nano-iron is 72 nm, and the loading amount of nano-iron is 8.6%.

[0117] adding the ground attapulgite into deionized water at a solid-liquid mass ratio of 1:5, and stirring for 30 min at a rotating speed of 500 r / min; after uniform stirring, standing for 2 h to obtain upper suspension; adding hydrochloric acid solution with a mass fraction of 5% into the upper suspension, and stirring for 2 h at 80℃ to react; after reaction, performing suction filtration on the reaction liquid; washing the solid phase after suction filtration with deionized water until neutral; drying at 100℃; and then ultrafine grinding to obtain attapulgite; through purification, the CEC of the attapulgite is 22.3 meq / 100g.

[0118] dissolving L-aspartic acid and acrylamide in water to obtain a second mixed solution, wherein the molar ratio of L-aspartic acid to acrylamide is 1:3; adding ammonium persulfate into the second mixed solution and uniformly mixing; under nitrogen, initiating polymerization reaction in a constant temperature water bath at 60℃ for 4 h to obtain a reaction product; performing rotary evaporation on the reaction product in an environment with a vacuum degree of-0.08 MPa at 60℃, and concentrating to a solid content of 30%; purifying by ethanol precipitation, and drying in an environment with a vacuum degree of-0.08 MPa at 80℃, and then grinding through an 80-mesh sieve to obtain polyaspartic acid-co-acrylamide; the mass of ammonium persulfate added is 3% of the total mass of L-aspartic acid and acrylamide.

[0119] The silica ash is a by-product of ferrosilicon smelting in an alloy factory, with a SiO2 content of 90%, a particle size of 0.1-0.5μm, and a density of 2.2g / cm 3 .

[0120] The magnesium carbonate is light magnesium carbonate; and the tartaric acid is analytical pure tartaric acid.

[0121] The sludge synergic curing agent is prepared based on the above-mentioned base material, and the preparation method comprises the following steps:

[0122] The fly ash, the sulphoaluminate cement and the modified phosphogypsum powder are mixed to obtain a first curing agent mixture.

[0123] The biochar loaded nano-iron and the attapulgite are added to the first curing agent mixture to obtain a second curing agent mixture.

[0124] The polyaspartic acid-co-acrylamide solution and the carboxymethyl cellulose sodium solution are added to the second curing agent mixture to obtain a third curing agent mixture.

[0125] The silica fume, the magnesium carbonate and the tartaric acid are added to the third curing agent mixture to obtain the sludge synergic curing agent.

[0126] The sludge synergic curing agent prepared in the embodiment is mixed with the sludge, the initial water content of the sludge is 82.5%, the dried sludge is added until the water content is reduced to 77.3%, and the mass ratio of the sludge synergic curing agent to the sludge is 1:5.8. After mixing, the primary curing is performed in an environment with a humidity of 86% for 48 hours, and then the natural curing is performed for 7 days; the cured body is tested, the 3-day unconfined compressive strength is 326 kPa, the Cr 6+ The leaching concentration is 0.042 mg / L, and the benzene series removal rate is 91.7%.

[0127] Example 2

[0128] The base material is prepared as follows:

[0129] The fly ash of a thermal power plant is superfined by using an air flow mill to obtain the fly ash, the crushing pressure in the process is 0.8 MPa, and the rotating speed of the grading wheel is 3000 r / min; the particle size distribution of the fly ash is as follows: D10=1.9 μm, D50=6.2 μm, D90=12.3 μm, and the specific surface area is 462 m 2 / g; in terms of mass percentage, the fly ash comprises 50% of SiO2, 26.5% of Al2O3, 4.2% of Fe2O3, 15% of CaO, and the rest is impurities.

[0130] In terms of mass percentage, the sulphoaluminate cement comprises 42.5% of calcium sulphoaluminate, 25% of dicalcium silicate, 10% of tetracalcium aluminoferrite, and the rest is impurities.

[0131] The citric acid solution and the phosphogypsum powder are mixed according to a liquid-solid mass ratio of 1:2.5, and are placed in a constant-temperature water bath at 65 DEG C, and are mechanically stirred and soaked for 12 hours, the stirring rate is 150 r / min, and during the period, the pH value is detected every 2 hours until the pH value is stabilized at 7.5; vacuum filtration is carried out under a vacuum degree of -0.08 MPa, and after the filtration, air drying is carried out at 80 DEG C until the water content is 4.3%, and the modified phosphogypsum powder is obtained; the modified phosphogypsum powder is crushed to 300 meshes by using a Raymond mill for later use, and the mass fraction of the citric acid solution is 5%.

[0132] The biochar is added into a FeSO4 7H2O solution, and is magnetically stirred at a rotating speed of 300 r / min for 30 min to obtain a first mixed solution; under nitrogen, a NaBH4 solution is added dropwise into the first mixed solution according to a molar ratio of Fe 2+ and BH4 - of 1:3 to carry out a reaction, and after the reaction for 1 hour, the reaction liquid is vacuum filtered to obtain black nano-iron particles; the black nano-iron particles are washed with deionized water for 3 times, and are washed with anhydrous ethanol for 1 time, and are vacuum dried at 60 DEG C under a vacuum degree of -0.09 MPa for 8 hours to obtain a black powder, which is the biochar-loaded nano-iron, wherein, the mass-volume ratio of the biochar and the FeSO4 7H2O solution is 1 g:12 mL, the concentration of the FeSO4 7H2O solution is 0.2 mol / L, and the concentration of the NaBH4 solution is 0.2 mol / L; through detection, the particle size of the nano-iron in the biochar-loaded nano-iron is 65 nm, and the loading amount of the nano-iron is 9.3%.

[0133] The ground attapulgite raw material is added into deionized water according to a solid-liquid mass ratio of 1:8, and is stirred at a rotating speed of 500 r / min for 30 min, and after being uniformly stirred, is placed for 2 hours, and the upper layer of the suspension is taken; a hydrochloric acid solution with a mass fraction of 5% is added into the upper layer of the suspension, and is stirred at 100 DEG C for 2 hours to carry out a reaction, and after the reaction, the reaction liquid is filtered, and the solid phase after the filtration is washed with deionized water until neutral, and is dried at 100 DEG C, and is further micronized to obtain attapulgite; the CEC of the attapulgite after the purification is 21.7 meq / 100 g.

[0134] A second mixture solution was prepared by dissolving L-aspartic acid and acrylamide in water, the molar ratio of L-aspartic acid to acrylamide being 1:3.5; ammonium persulfate was added into the second mixture solution and mixed uniformly, and a polymerization reaction was initiated in a constant temperature water bath at 60°C under nitrogen for 4 hours to obtain a reaction product; the reaction product was concentrated to a solid content of 30% by rotary evaporation under the condition of 65°C and a vacuum degree of-0.08 MPa, and then purified by ethanol precipitation; after drying at 80°C under a vacuum degree of-0.08 MPa, the product was ground through an 80-mesh sieve to obtain poly-aspartic acid-co-acrylamide; the mass of ammonium persulfate was 2% of the total mass of L-aspartic acid and acrylamide.

[0135] The silica ash was a by-product of ferrosilicon smelting in an alloy factory, the SiO2 content was 90%, the particle size was 0.1-0.5 μm, and the density was 2.2 g / cm 3 .

[0136] The magnesium carbonate was light magnesium carbonate, and the tartaric acid was analytical pure tartaric acid.

[0137] The sludge synergistic curing agent was prepared based on the above-mentioned base material, and the preparation method included the following steps:

[0138] 20% of fly ash, 17% of sulphoaluminate cement, and 15% of modified phosphogypsum powder were mixed to obtain a first curing agent mixture.

[0139] 18.2% of biochar loaded nano-iron and 10% of attapulgite were added into the first curing agent mixture to obtain a second curing agent mixture.

[0140] 6% of poly-aspartic acid-co-acrylamide was added into water to prepare a poly-aspartic acid-co-acrylamide solution with a mass fraction of 10%, and 5% of carboxymethyl cellulose sodium was added into water to prepare a carboxymethyl cellulose sodium solution with a mass fraction of 10%; the poly-aspartic acid-co-acrylamide solution and the carboxymethyl cellulose sodium solution were added into the second curing agent mixture and mixed uniformly to obtain a third curing agent mixture.

[0141] 3.8% of silica ash, 3% of magnesium carbonate, and 2% of tartaric acid were added into the third curing agent mixture and mixed uniformly to obtain the sludge synergistic curing agent.

[0142] The sludge synergistic curing agent prepared in the example was mixed with sludge, the initial moisture content of the sludge was 84.2%, dry sludge was added until the moisture content was reduced to 78.5%, and the mass ratio of the sludge synergistic curing agent to the sludge was 1:6.3; after mixing, the sludge was cured for 48 hours in an environment with a humidity of 83% for primary curing, and then cured naturally for 7 days; the cured body was tested, the 3-day unconfined compressive strength was 312 kPa, the Cr 6+ The leaching concentration was 0.038 mg / L, and the removal rate of polycyclic aromatic hydrocarbons was 92.3%.

[0143] Example 3

[0144] Preparation of substrate:

[0145] The fly ash of a thermal power plant was superfined by a jet mill to obtain fly ash, and the crushing pressure was 0.8 MPa and the rotating speed of the grading wheel was 3000 r / min during the superfine treatment. The particle size distribution of the fly ash was D10 = 2.2 μm, D50 = 5.9 μm and D90 = 11.5 μm, and the specific surface area was 512 m2 / g. The fly ash contained 46.2% of SiO2, 30% of Al2O3, 4% of Fe2O3 and 17.5% of CaO, and the rest was impurities. 2

[0146] The sulphoaluminate cement contained 44.6% of calcium sulphoaluminate, 30% of dicalcium silicate, 13.8% of tetracalcium aluminoferrite and the rest was impurities.

[0147] The citric acid solution and the phosphogypsum powder were mixed in a liquid-solid mass ratio of 1:3, and were placed in a constant temperature water bath at 70°C, and were mechanically stirred and soaked for 12 h, and the stirring rate was 150 r / min. The pH value was detected every 2 h during the period until the pH value was stable at 6.5. Vacuum filtration was carried out under a vacuum degree of -0.08 MPa, and the modified phosphogypsum powder was obtained after air drying at 80°C until the water content was 5.1%. The modified phosphogypsum powder was crushed to 300 mesh by a Raymond mill for use. The mass fraction of the citric acid solution was 4%.

[0148] The biochar was added into a FeSO4 2+ 7H2O solution, and was magnetically stirred at a rotating speed of 300 r / min for 30 min to obtain a first mixture. In a nitrogen atmosphere, NaBH4 solution was added dropwise into the first mixture at a molar ratio of Fe - and BH4 3 was 1:2.5, and the reaction was carried out for 1 h. The reaction liquid was vacuum filtered to obtain black nano iron particles. The black nano iron particles were washed with deionized water for 3 times and with anhydrous ethanol for 1 time. The black nano iron particles were vacuum dried at 60°C and a vacuum degree of -0.09 MPa for 8 h to obtain a black powder, which was the biochar loaded nano iron. The mass-volume ratio of the biochar and the FeSO4 7H2O solution was 1 g:15 mL, and the concentration of the FeSO4 7H2O solution was 0.15 mol / L. The concentration of the NaBH4 solution was 0.3 mol / L. Through detection, the particle size of the nano iron in the biochar loaded nano iron was 83 nm, and the loading amount of the nano iron was 8.9%.

[0149] ​The ground attapulgite raw material is added to deionized water in a solid-liquid mass ratio of 1:7, stirred at a speed of 500 r / min for 30 min, uniformly stirred for 2 h, and the upper layer of the suspension is taken; 3% hydrochloric acid solution is added to the upper layer of the suspension, stirred at 90°C for 2 h for reaction, and after reaction, the reaction liquid is filtered, the solid phase after filtration is washed to neutral with deionized water, and is dried at 100°C, and is then ultra-finely pulverized to obtain attapulgite; the CEC of the attapulgite after purification is 23.1 meq / 100g.

[0150] L-aspartic acid and acrylamide are dissolved in water to obtain a second mixed solution, and the molar ratio of L-aspartic acid to acrylamide is 1:4; ammonium persulfate is added to the second mixed solution and mixed uniformly, and a polymerization reaction is initiated in a nitrogen atmosphere in a constant temperature water bath at 60°C for 4 h to obtain a reaction product; the reaction product is concentrated to a solid content of 30% by rotary evaporation in a vacuum environment at 60°C and a vacuum degree of-0.08 MPa, and then purified by ethanol precipitation, dried at 80°C and a vacuum degree of-0.08 MPa, and then ground through an 80-mesh sieve to obtain polyaspartic acid-co-acrylamide; the mass of ammonium persulfate is 2.2% of the total mass of L-aspartic acid and acrylamide.

[0151] The silica ash is selected from a by-product of ferrosilicon smelting in a ferroalloy plant, has a SiO2 content of 90%, a particle size of 0.1-0.5 μm, and a density of 2.2 g / cm 3 .

[0152] The magnesium carbonate is selected from light magnesium carbonate; and the tartaric acid is selected from analytical pure tartaric acid.

[0153] The sludge synergistic solidification agent is prepared based on the above-mentioned substrate, and includes:

[0154] 30% fly ash, 18.7% sulfoaluminate cement, and 10% modified phosphogypsum powder are mixed to obtain a first solidification agent mixture.

[0155] 15% biochar-loaded nano-iron and 5% attapulgite are added to the first solidification agent mixture to obtain a second solidification agent mixture.

[0156] 8.7% polyaspartic acid-co-acrylamide is added to water to prepare a polyaspartic acid-co-acrylamide solution with a mass fraction of 12%; 4.8% carboxymethyl cellulose sodium is added to water to prepare a carboxymethyl cellulose sodium solution with a mass fraction of 8%; and the polyaspartic acid-co-acrylamide solution and the carboxymethyl cellulose sodium solution are added to the second solidification agent mixture and mixed uniformly to obtain a third solidification agent mixture.

[0157] Add 5% silica fume, 1.6% magnesium carbonate and 1.2% tartaric acid to the third curing agent mixture and mix evenly to obtain a sludge synergistic curing agent.

[0158] The sludge synergistic curing agent prepared in this embodiment was mixed with sludge. The initial moisture content of the sludge was 79.6%. Dried sludge was added until the moisture content dropped to 75.8%. The mass ratio of the sludge synergistic curing agent to the sludge was 1:5.5. After mixing, the mixture was initially cured in an environment with 87% humidity for 48 hours, followed by natural curing for 6.5 days. The cured body was tested, and the unconfined compressive strength after 3 days was 341 kPa, and the Pb content was [not specified]. 2+ The leaching concentration was 0.035 mg / L, and the phenol removal rate was 90.8%.

[0159] Example 4

[0160] Substrate preparation:

[0161] Secondary fly ash from thermal power plants was ultra-finely processed using an air jet mill to obtain fly ash. The milling pressure during the process was 0.8 MPa, and the classifying wheel speed was 3000 r / min. The particle size distribution of the fly ash was: D10 = 2.0 μm, D50 = 6.1 μm, D90 = 12.1 μm, with a specific surface area of ​​475 m². 2 / g; by mass percentage, fly ash comprises 48.3% SiO2, 25% Al2O3, 5.2% Fe2O3, 20% CaO, with the remainder being impurities.

[0162] By mass percentage, sulfoaluminate cement comprises 45% calcium sulfoaluminate, 28.2% dicalcium silicate, 15% tetracalcium aluminoferrite, and the remainder being impurities.

[0163] Citric acid solution and phosphogypsum powder were mixed at a liquid-to-solid mass ratio of 1:2 and placed in a constant temperature water bath at 70°C. The mixture was mechanically stirred and soaked for 12 hours at a stirring rate of 150 r / min. During this period, the pH value was measured every 2 hours until the pH value stabilized at 7.0. Vacuum filtration was performed under a vacuum of -0.08 MPa. After filtration, the powder was dried at 80°C with forced air until the moisture content reached 4.5%, thus obtaining modified phosphogypsum powder. The modified phosphogypsum powder was then pulverized to 300 mesh using a Raymond mill for later use. The mass fraction of the citric acid solution was 4%.

[0164] Adding biochar to FeSO4 The solution was magnetically stirred at 300 rpm for 30 minutes in 7H2O to obtain the first mixture; then, under nitrogen atmosphere, Fe was added... 2+ and BH4 -The molar ratio of FeSO4·7H2O and NaBH4 is 1:2, and the NaBH4 solution is added dropwise into the first mixed solution for reaction. After 1h of reaction, the reaction solution is vacuum filtered to obtain black nano-iron particles. The black nano-iron particles are washed with deionized water for 3 times and then washed with anhydrous ethanol for 1 time. The black nano-iron particles are vacuum dried at 60℃ and a vacuum degree of-0.09MPa for 8h to obtain black powder, which is the biochar loaded nano-iron. The mass-volume ratio of the FeSO4·7H2O solution is 1g:15mL. The concentration of the FeSO4·7H2O solution is 0.1mol / L, and the concentration of the NaBH4 solution is 0.25mol / L. Through detection, the particle size of the nano-iron in the biochar loaded nano-iron is 58nm, and the loading amount of the nano-iron is 9.1%.

[0165] The ground attapulgite raw material is added into deionized water at a solid-liquid mass ratio of 1:6, and stirred at a speed of 500r / min for 30min. After uniform stirring, the upper layer of the suspension is taken after standing for 2h. A hydrochloric acid solution with a mass fraction of 4% is added into the upper layer of the suspension, and the reaction is carried out under stirring at 80℃ for 2h. After the reaction, the reaction solution is filtered. The solid phase after filtration is washed with deionized water until neutral. The solid phase is dried at 100℃, and then ultra-finely pulverized to obtain attapulgite. The CEC of the attapulgite after purification is 20.8meq / 100g.

[0166] L-aspartic acid and acrylamide are dissolved in water to obtain a second mixed solution, and the molar ratio of L-aspartic acid and acrylamide is 1:3. Ammonium persulfate is added into the second mixed solution and uniformly mixed. Under nitrogen, a polymerization reaction is initiated in a constant temperature water bath at 60℃ for 4h to obtain a reaction product. The reaction product is concentrated to a solid content of 30% by rotary evaporation in an environment with a vacuum degree of-0.08MPa at 70℃. The reaction product is purified by ethanol precipitation, and then dried in an environment with a vacuum degree of-0.08MPa at 80℃. The dried product is ground through an 80-mesh sieve to obtain polyaspartic acid-co-acrylamide. The mass of ammonium persulfate added is 2.8% of the total mass of L-aspartic acid and acrylamide.

[0167] The silica ash is a by-product of ferrosilicon smelting in a ferroalloy plant, and has a SiO2 content of 90%, a particle size of 0.1-0.5μm, and a density of 2.2g / cm 3 .

[0168] The magnesium carbonate is light magnesium carbonate, and the tartaric acid is analytical pure tartaric acid.

[0169] The sludge synergistic solidification agent is prepared based on the above-mentioned substrate, and includes:

[0170] In mass percentage, 24.3% of fly ash, 20% of sulfoaluminate cement, and 12.3% of modified phosphogypsum powder are mixed to obtain a first solidification agent mixture. ​

[0171] 17.3% of the biochar-loaded nano-iron and 8.5% of the attapulgite are added into the first solidification agent mixture to obtain a second solidification agent mixture.

[0172] 7.8% of the polyaspartic acid-co-acrylamide is added into water to prepare a polyaspartic acid-co-acrylamide solution with a mass fraction of 12%, and 4.3% of the sodium carboxymethyl cellulose is added into water to prepare a sodium carboxymethyl cellulose solution with a mass fraction of 8%. The polyaspartic acid-co-acrylamide solution and the sodium carboxymethyl cellulose solution are added into the second solidification agent mixture and uniformly mixed to obtain a third solidification agent mixture.

[0173] 3% of the silica fume, 1% of the magnesium carbonate and 1.5% of the tartaric acid are added into the third solidification agent mixture and uniformly mixed to obtain the silt cooperative solidification agent.

[0174] The silt cooperative solidification agent prepared in the embodiment is mixed with the silt, the initial water content of the silt is 83.7%, dry silt is added until the water content is reduced to 76.9%, and the mass ratio of the silt cooperative solidification agent to the silt is 1:6.1. After the mixing, primary curing is performed in an environment with a humidity of 84% for 48 hours, and then natural curing is performed for 7 days. The cured body is tested, and the 3-day unconfined compressive strength is 332 kPa, the Cr 6+ The leaching concentration is 0.045 mg / L, and the comprehensive removal rate of the organic pollutants is 91.2%.

[0175] The endpoints of the ranges and any values disclosed in the present application are not limited to the precise values stated. The ranges or values should be interpreted as being approximate to the exact values. For ranges of values, the endpoints of the ranges are included as well as the individual points within the ranges, and the individual points are included in the ranges. Any combination of the individual points or the endpoints of the ranges are included in the present application. In the following, the technical solutions can be combined with each other to obtain new technical solutions.

[0176] The above embodiments are only used to illustrate the technical solutions of the present application but not to limit the present application. Although the present application has been described in detail with reference to the above embodiments, the specific implementation manners of the present application can be modified or replaced by equivalents by those skilled in the art. Any modification or replacement without departing from the spirit and scope of the present application is included in the protection scope of the claims of the present application.

Claims

1. A microbial mineralization and nanocomposite-based sludge synergistic stabilizer, characterized in that, The fly ash includes 45% to 50% of SiO2, 25% to 30% of Al2O3, 4% to 6% of Fe2O3, and 15% to 20% of CaO, and the rest is impurities. The modified phosphogypsum powder is prepared by the following method: The citric acid solution and the phosphogypsum powder are mixed in a liquid-solid mass ratio of 1: (2-3), and reacted at 60-70 DEG C until the pH is 6.5-7.5, and the solid phase after reaction is dried to obtain the modified phosphogypsum powder; the mass fraction of the citric acid solution is 3%-5%. The poly-aspartic acid-co-acrylamide is prepared by the following method: L-aspartic acid and acrylamide are dissolved in water to obtain a second mixed solution, and the molar ratio of L-aspartic acid to acrylamide is 1: (3-4). Ammonium persulfate is added to the second mixed solution, and the reaction product is obtained by reacting at 60-70 DEG C in an inert atmosphere, and the poly-aspartic acid-co-acrylamide is obtained by evaporation, precipitation and vacuum drying of the reaction product; the mass of ammonium persulfate added is 2%-3% of the total mass of L-aspartic acid and acrylamide.

2. The microbial-mineralization and nanocomposite-based silt synergic stabilizer according to claim 1, characterized in that, The fly ash includes 45% to 50% of SiO2, 25% to 30% of Al2O3, 4% to 6% of Fe2O3, and 15% to 20% of CaO, and the rest is impurities.

3. The microbial-mineralization and nanocomposite-based sludge synergic stabilizer according to claim 1, characterized in that, The sulphoaluminate cement includes 40%-45% of calcium sulphoaluminate, 25%-30% of dicalcium silicate, 10%-15% of tetracalcium aluminoferrite, and the rest is impurities.

4. The microbial-mineralization and nanocomposite-based sludge synergic stabilizer according to claim 1, characterized in that, The biochar loaded nano-iron is prepared by the following method: adding biochar into FeSO4 7H2O solution to obtain a first mixture, FeSO4 7H2O solution has a concentration of 0.1-0.2 mol / L; the biochar and FeSO4 7H2O solution has a mass-volume ratio of 1 g:(10-15) mL; Inert gas, according to the molar ratio of Fe 2+ And BH4 - 1﹕ (2~3) to the first mixed solution, NaBH4 solution is added to obtain biochar loaded nano iron, and the concentration of NaBH4 solution is 0.2~0.3mol / L.

5. The microbial-mineralization and nanocomposite-based sludge synergic stabilizer according to claim 1, characterized in that, The attapulgite is prepared by the following method: The attapulgite raw material is added to water in a solid-liquid mass ratio of 1: (5-8), and mixed uniformly, and the upper layer of the suspension is taken after standing; Hydrochloric acid solution is added to the upper layer of the suspension, and the reaction is carried out at 80-100 DEG C, and the solid phase after reaction is washed, dried and ground to obtain attapulgite; The mass fraction of the hydrochloric acid solution is 3%-5%.

6. A method for preparing the microbial-mineralization and nanocomposite-based sludge synergic stabilizer according to any one of claims 1-5, characterized in that, The fly ash, the sulphoaluminate cement and the modified phosphogypsum powder are mixed to obtain a first solidifying agent mixture; The biochar loaded nano-iron and the attapulgite are added to the first solidifying agent mixture to obtain a second solidifying agent mixture; The poly-aspartic acid-co-acrylamide is prepared into a poly-aspartic acid-co-acrylamide solution, and the carboxymethyl cellulose sodium is prepared into a carboxymethyl cellulose sodium solution, and the poly-aspartic acid-co-acrylamide solution and the carboxymethyl cellulose sodium solution are added to the second solidifying agent mixture to obtain a third solidifying agent mixture; The silica ash, the magnesium carbonate and the tartaric acid are added to the third solidifying agent mixture and mixed uniformly to obtain a sludge solidifying agent. The mass fraction of the poly-aspartic acid-co-acrylamide solution is 10%-15%.

7. The method for preparing the microbial mineralization and nanocomposite-based sludge synergistic stabilizer according to claim 6, characterized in that, The mass fraction of the carboxymethyl cellulose sodium solution is 5%-10%.

8. The method for preparing the microbial mineralization and nanocomposite based sludge synergistic stabilizer according to claim 6, characterized in that, ​

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