A solidified repair material for treating waste engineering slurry by using lithium residue, salt gypsum and chitosan composite and a preparation method thereof

Abstract

The application provides a kind of waste engineering slurry solidification repair material and preparation method using lithium residue, salt gypsum and chitosan complex compound, and relates to the technical field of environmental geotechnical materials.The waste engineering slurry solidification repair material comprises: a full solid waste cementing component a composed of 30-50 mass parts of salt gypsum, 30-50 mass parts of lithium residue and the rest of red mud, carbide slag and silica fume, and a functional polymer component composed of natural chitosan b and chitosan grafted with controllable degree of grafting p-nitrobenzaldehyde c.The application aims to construct a high-strength system of full solid waste by synergistically stimulating multiple sources of solid waste, and to achieve the essential transformation of waste engineering slurry from "high environmental load solid waste" to "high-performance low-carbon building resources" by supplementing the polymer component to deeply remove the shielding of reagents and the constraints of characteristic pollution.

Description

Technical Field

[0001] This invention relates to the field of environmental geotechnical materials technology, specifically to a solidification and remediation material and preparation method for treating waste engineering mud using lithium slag, salt gypsum, and chitosan composite. Background Technology

[0002] Waste construction mud includes slurries generated from bored pile foundation construction, diaphragm wall construction, slurry shield tunneling, horizontal directional drilling, and slurry pipe jacking. Among these, the resource utilization and disposal of shield tunneling mud is the most challenging. To ensure tunneling efficiency and reduce the risk of cutterhead "mud cake" and wear, large amounts of chemical additives such as surfactants (SLES, SDS, etc., mostly anionic) and dispersants (STPP, SHMP, etc., mostly phosphates) are added during construction to impart excellent plasticity and low adhesion strength to the excavated soil. However, the residue of these agents results in surfactant and phosphate concentrations in the mud leachate reaching as high as 10-20 mg / L and 2.0-5.0 mg / L, respectively, far exceeding environmental background values. Compared with the latest environmental protection standards, such as the Class IV standard in the "Groundwater Quality Standard" (GB / T 14848-2017) and the Class IV standard in the "Surface Water Environmental Quality Standard" (GB 3838-2002), there is a significant gap between the leaching level and the standard limits (anionic surfactants ≤ 0.3 mg / L; total phosphorus ≤ 0.3 mg / L). This severe environmental safety burden has become a core bottleneck restricting the compliant utilization of waste mud.

[0003] Traditional cement-based solidification systems can only enhance the engineering properties of slurry through limited physical coating, offering almost no adsorption or fixation capacity for highly soluble organic agents. This results in surfactant leaching concentrations exceeding standards by more than 30 times. Furthermore, when solidifying such slurries with traditional cement, surfactants adsorb onto the surface of cement particles, forming a molecular film that severely interferes with the formation of hydration products, leading to a loose solidified soil structure and delayed early strength development. Based on these shortcomings, there is an urgent need to develop a novel solidification material to achieve the goals of reducing pollutant leaching concentrations and improving soil strength.

[0004] Utilizing bulk solid waste to prepare engineering mud solidification materials (such as solidifying agents) through synergistic activation is currently a core approach to achieving "high-value utilization" and "carbon reduction and remediation" of engineering mud. The Sichuan-Chongqing region, as a national-level salt chemical industry base and an emerging semiconductor industry hub, has accumulated large amounts of salt gypsum associated with salt production in Zigong and lithium slag, a byproduct of chip manufacturing. Although using such solid waste to replace cement in the preparation of mud solidifying agents has significant carbon reduction advantages, its potential secondary environmental risks cannot be ignored: lithium slag carries characteristic pollutants such as Li. + The leaching concentration (5.0-10.0 mg / L) exceeds the EPA health reference standard by more than 500 times; SO4 in salt gypsum 2-(1000-2500 mg / L) and Cl - The leaching levels (500-1500 mg / L) far exceed the limits for Class IV water quality in the "Groundwater Quality Standard" (GB / T 14848-2017) (sulfate ≤350 mg / L; chloride ≤350 mg / L). High concentrations of sulfate and chloride ions not only lead to soil salinization in the service area but also pose a long-term threat to groundwater systems. Because existing solid waste-based engineering mud solidification and remediation materials generally lack targeted chemical remediation methods, this "waste-to-waste" process is highly susceptible to secondary migration of pollutants, constituting a core bottleneck for the high-value utilization of this type of solid waste. Summary of the Invention

[0005] This invention addresses the challenges of leaching and hydration inhibition caused by excessive anionic surfactants and phosphates in waste engineering slurries. Considering the secondary pollution risks associated with the resource utilization of salt gypsum and lithium slag in the Sichuan-Chongqing region, it proposes a synergistic remediation scheme using composite polymers. This scheme utilizes the charge neutralization effect of the active sites in the composite polymers (chitosan and grafted chitosan): the chitosan molecular chain contains a large number of amino groups (-NH2), which protonate in acidic or near-neutral aqueous solutions, transforming into positively charged ammonium groups (-NH3). + This mixture can adsorb anionic pollutants. Modified chitosan, through Schiff base grafting modification, consumes some amino groups and introduces strong electronic groups such as nitro (-NO2). Specific sites or residual groups on the molecular chain exhibit obvious anionic characteristics, enabling the adsorption of cationic pollutants. Combining these two materials effectively strips the organic molecular film from the surface of mud particles, eliminating the interference of surfactants on the hydration reaction of solid waste-based materials and ensuring the rapid construction of the mechanical framework of the solidified soil. Simultaneously, through the chemical chelation and ion exchange mechanism of the polymer long chains, a dual locking system of inorganic lattice trapping and organic network anchoring is formed at the microscopic level, achieving the adsorption of characteristic anionic pollutants (anionic surfactants, phosphates) and characteristic anionic / cationic composite pollutants (Li) from waste engineering mud. + SO4 2- Cl - The deep interception of waste engineering mud and regional solid waste in complex polluted environments has fundamentally solved the bottleneck of compliant utilization.

[0006] The technical solution adopted in this invention is: A composite material for solidifying and repairing waste engineering mud using lithium slag, salt gypsum, and chitosan, comprising: The solid waste cementitious component a contains 30-50 parts by weight of salt gypsum, 30-50 parts by weight of lithium slag, and the remainder of red mud, carbide slag and silica fume. The polymer adsorption component comprises a functionalized polymer component composed of natural chitosan b and p-nitrobenzaldehyde grafted and modified chitosan c with controllable grafting degree.

[0007] Furthermore: The red mud comprises 5-15 parts by weight; The calcium carbide slag comprises 3-8 parts by weight; The silica fume accounts for 2-10 parts by weight.

[0008] Furthermore, the mass ratio of the natural chitosan b to the p-nitrobenzaldehyde-grafted modified chitosan c is 1:4-4:1.

[0009] Furthermore, the total mass ratio of the solid waste gelling component a to the polymer adsorption component is 100:0.05-100:0.5.

[0010] A method for preparing a solidification and remediation material for waste engineering mud using lithium slag, salt gypsum, and chitosan composite, comprising the following steps: Step S100: Prepare p-nitrobenzaldehyde-grafted modified chitosan c with controllable grafting degree by Schiff base grafting reaction of natural chitosan and p-nitrobenzaldehyde. In step S200, the raw materials of solid waste gelling component a, natural chitosan b, and p-nitrobenzaldehyde grafted modified chitosan c obtained in step S100 are dry-mixed to obtain waste engineering mud solidification and repair material.

[0011] Furthermore, the Schiff base grafting reaction in step S100 is carried out at a temperature of 50°C-70°C for 4-8 hours.

[0012] Furthermore, the Schiff base grafting reaction in step S100 is carried out in an acetic acid solution with a mass fraction of 1%-2%.

[0013] Furthermore, before the Schiff base grafting reaction in step S100, natural chitosan is dissolved in a 1%-2% acetic acid solution to prepare a chitosan-acetic acid solution with a mass concentration of 1%-3%, and stirred until completely transparent.

[0014] Further, after the stirring in step S100 is completely transparent, nitrobenzaldehyde is dissolved in anhydrous ethanol to prepare a solution with a mass fraction of 2%-10%.

[0015] Further, after the Schiff base grafting reaction in step S100 is completed, the precipitate is washed multiple times with anhydrous ethanol or isopropanol, and then vacuum dried and pulverized at 50℃-60℃ to obtain powdered p-nitrobenzaldehyde grafted modified chitosan c.

[0016] The beneficial effects of this invention are: 1. The solidification and repair material of this invention is composed entirely of five industrial solid wastes: salt gypsum, lithium slag, red mud, carbide slag, and silica fume. This completely eliminates the dependence on cement components in traditional engineering mud solidification and repair materials, reducing material costs and carbon emissions. Utilizing the strongly alkaline activation environment created by carbide slag and red mud, it synergistically induces a deep hydration reaction between the sulfur source in the salt gypsum and the active silicon and aluminum components in the lithium slag / silica fume. The system microscopically generates needle-like columnar ettringite (AFt) and hydrated calcium silicate (CSH) gel that interweave and fill each other, constructing a dense mechanical support framework.

[0017] 2. This invention introduces a composite system of natural chitosan b and p-nitrobenzaldehyde-grafted modified chitosan c into the curing and repair material. The imine groups introduced on the modified chitosan molecular chain form highly polar chelating centers with the nitro groups, which can bind with free cations (such as Li). + (etc.) form stable coordination bonds; at the same time, its protonated positive charge center forms stable coordination bonds with anions (such as anionic surfactants, PO4). 3- Cl - (e.g., [specific examples of this]) exhibit significant charge attraction and chemical precipitation effects, thereby inhibiting the migration of pollutants at the source. Furthermore, the controlled grafting method has the advantage of preventing material failure caused by charge neutralization with natural chitosan during subsequent compounding.

[0018] 3. The fluidized solidified soil prepared by this invention has good flow properties, supports pumping and in-situ filling construction, and exhibits extremely low leaching toxicity after solidification, while also possessing a certain strength, low pollution, and recyclability. This technology can transform high-risk shield tunneling slurry into mechanically stable and environmentally friendly engineering materials, effectively solving the problems of slag removal pressure and land resource occupation, and is particularly suitable for urban underground space filling and ecological restoration barriers. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a flowchart of the application method of the repair material of the present invention; Figure 2 This is a flowchart of the preparation method of the repair material of the present invention. Detailed Implementation

[0021] The following disclosure provides many different embodiments or examples for implementing different structures of the present invention. To simplify the disclosure of the present invention, the components and arrangements of specific examples are described below. Of course, these are merely examples and are not intended to limit the present invention.

[0022] The invention will now be described in detail with reference to the accompanying drawings.

[0023] Before providing a further detailed description of the embodiments of this application, some of the nouns and terms involved in the embodiments of this application will be explained. The nouns and terms involved in the embodiments of this application are subject to the following interpretations.

[0024] (1) Engineering mud: refers to waste mud generated during the construction of bored pile foundations, diaphragm walls, slurry shield tunnels, etc., which has high water content, strong fluidity, fine particles and may contain chemical additives. If this mud is discharged directly without treatment, it will not only occupy a large amount of land, but the pollutants contained in it may also cause long-term harm to the soil and groundwater.

[0025] (2) All-solid-waste cementitious component: refers to a cement-free solid waste mixture in a specific ratio, used to provide the main cementitious material required for the solidification reaction. This component is designed to synergistically utilize various industrial solid wastes to generate products with cementing ability through chemically activated reactions, thereby replacing traditional cement and achieving the goal of green and low-carbon solidification.

[0026] (3) Schiff base grafting reaction with controllable grafting degree: This refers to a chemical modification method used to attach the functional groups of p-nitrobenzaldehyde to the molecular chains of natural chitosan. In this invention, by controlling the reaction to proceed under mild conditions, Schiff base groups and nitro groups are introduced into part of the molecular chains of natural chitosan, achieving partial amino selective grafting of chitosan and endowing the modified chitosan with the ability to target and adsorb specific types of pollutants (such as cationic pollutants). At the same time, some unreacted amino groups are retained, making the modified chitosan exhibit amphoteric properties, avoiding charge neutralization with natural chitosan in subsequent reactions, ensuring the stable coexistence and synergistic effect of the two components, and achieving efficient capture of multiple types of pollutants.

[0027] (4) Dry mixing treatment: This refers to the process of thoroughly mixing all powdered raw materials, including the all-solid waste gelling component a, natural chitosan b, and p-nitrobenzaldehyde-grafted modified chitosan c, in a dry state before adding the engineering mud solidification and repair material to the engineering mud. This step ensures that the functional components are evenly distributed in the final product and is a key step in ensuring the performance stability and uniformity of the engineering mud solidification and repair material.

[0028] Existing solid waste-based engineering mud solidification and remediation materials, such as those using slag and fly ash, while capable of disposing of industrial waste and reducing some costs and carbon emissions, still have many shortcomings. These mainly stem from the inherent environmental pollution effects of existing solid waste-based engineering mud solidification and remediation materials, and the difficulty in activating their activity, hindering their full and effective utilization.

[0029] To address the aforementioned problems in the prior art, this invention first provides an engineering slurry solidification and remediation material. This material is added to engineering slurry to solidify it and remediates contamination through polymer adsorption, thereby recovering waste engineering slurry to produce fluidized solidified soil. This engineering slurry solidification and remediation material can utilize the synergistic effect of multiple solid wastes to completely detach from cement, forming a high-strength activated cementitious system based entirely on solid waste. The engineering slurry solidification and remediation material mainly comprises: a solid waste cementitious component, etc.

[0030] The solid waste gelling component a mainly consists of various industrial solid wastes, including salt gypsum, lithium slag, red mud carbide slag, and silica fume. Based on this, the present invention specifically introduces chitosan and p-nitrobenzaldehyde-modified chitosan, which performs environmental remediation functions through anionic and cationic adsorption treatment.

[0031] The engineering mud solidification and remediation material of this invention is composed entirely of five industrial solid wastes: gypsum, lithium slag, red mud, carbide slag, and silica fume. This completely eliminates the dependence on cement components in traditional engineering mud solidification and remediation materials, reducing material costs and carbon emissions. Furthermore, by utilizing the alkaline activation environment created by carbide slag and red mud, a synergistic hydration reaction is induced in the active components of gypsum and lithium slag, generating a large amount of ettringite (AFt) and hydrated calcium silicate (CSH) gel, constructing a high-strength mechanical framework. This not only solves the problem of poor performance of existing solid waste-based materials but also endows the solidified body with excellent environmental barrier functions. Especially effective against certain cations (Li... + (etc.), anionic pollutants (such as anionic surfactants, PO4, etc.) 3- Cl - It has a significant stabilizing effect on highly mobile pollutants (such as...).

[0032] Meanwhile, the solution of this invention not only significantly reduces material costs and carbon emissions, but also opens up a scientific path for the large-scale and high-value utilization of bulk solid waste (such as salt gypsum and lithium slag) in Sichuan and other regions.

[0033] Preferably, in an optional embodiment, in the solid waste gelling component a, gypsum salt accounts for 30-50 parts by mass and lithium slag accounts for 30-50 parts by mass. In some regions, such as Sichuan, factories have a large demand for processing, and it is suitable to add them in a high proportion to achieve a synergistic effect.

[0034] Preferably, in an optional embodiment, in the solid waste cementitious component a, red mud accounts for 5-15 parts by mass, calcium carbide slag accounts for 3-8 parts by mass, and silica fume accounts for 2-10 parts by mass.

[0035] On the other hand, the aforementioned solid waste-based engineering mud solidification and remediation materials mainly focus on mechanical solidification, neglecting the environmental hazards of residual chemical additives in the mud. These organic pollutants cannot be effectively adsorbed by inorganic cementitious materials, and under long-term hydrological action, there is a risk of migration and diffusion with the leachate, causing secondary pollution and limiting the application of solidified soil in scenarios with high environmental protection requirements. Therefore, in an optional embodiment, natural chitosan b and p-nitrobenzaldehyde-grafted modified chitosan c with controllable grafting degree are also added to the engineering mud solidification and remediation material of this embodiment. Among them, natural chitosan b and p-nitrobenzaldehyde-grafted modified chitosan c together constitute a dual adsorption system. The molecular chain of natural chitosan b is rich in amino groups, which can be protonated and become positively charged in the mud environment, capturing anionic pollutants in the mud through electrostatic adsorption, such as chloride ions that may remain in salt gypsum or phosphate ions in engineering additives. Meanwhile, nitrobenzaldehyde-grafted chitosan C utilizes the coordination center provided by the lone pair electrons of the imine bond, the negative anionic potential induced by the nitro group, and the chelation space formed by the hydroxyl and imine groups to collectively capture cationic pollutants (such as lithium ions that may leach from lithium slag). This two-pronged approach further addresses the shortcomings of the aforementioned engineering mud solidification and remediation materials, which only focus on mechanical properties and lack environmental remediation capabilities, leading to the risk of long-term pollutant leaching.

[0036] Preferably, in an optional embodiment, the mass ratio of natural chitosan b to p-nitrobenzaldehyde-grafted modified chitosan c is 1:4 to 4:1. This range of ratios provides the engineering mud solidification and remediation material with great flexibility. When the mud to be treated is mainly composed of anionic pollutants, the proportion of natural chitosan b can be increased; conversely, when cationic pollutants are the main risk, the amount of modified chitosan can be increased. This adjustable design allows the engineering mud solidification and remediation material to precisely match the pollution characteristics under different working conditions, achieving targeted remediation, thereby maximizing the efficiency and economy of pollutant fixation while ensuring the solidification effect.

[0037] Preferably, in an optional embodiment, the total mass ratio of the solid waste gelling component a to natural chitosan b and p-nitrobenzaldehyde-grafted modified chitosan c is 100:0.05 to 100:0.5. This ratio range is the result of extensive experimental optimization, aiming to balance the economic cost and environmental remediation performance of engineering mud solidification and remediation materials. Solid waste gelling component a, as the main material, is inexpensive, while the two types of chitosan, as functional additives, are relatively expensive. By controlling the total amount of chitosan added within the extremely low range of 0.05% to 0.5%, its key role in effectively adsorbing pollutants can be ensured without significantly increasing the overall cost of the engineering mud solidification and remediation material. This approach effectively controls material costs while guaranteeing technical effectiveness, demonstrating promising application prospects.

[0038] Based on the above embodiments, the present invention also provides a method for preparing engineering mud solidification and repair materials. For example... Figure 1 As shown, the method mainly includes the following steps: Step S100 involves preparing p-nitrobenzaldehyde-grafted modified chitosan c with controllable grafting degree through a Schiff base grafting reaction between natural chitosan b and p-nitrobenzaldehyde. This step is crucial for obtaining the adsorption capacity for cationic pollutants.

[0039] In step S200, the raw materials of the solid waste gelling component a, natural chitosan b, and the grafted p-nitrobenzaldehyde grafted modified chitosan c obtained in step S100 are dry-mixed to obtain the final engineering mud solidification and repair material.

[0040] Preferably, in an optional embodiment, the Schiff base grafting reaction in step S100 is carried out at a temperature of 50°C-70°C for 4-8 hours. This range of process parameters is crucial for achieving efficient grafting. Too low a temperature results in a slow reaction rate, leading to incomplete reaction and low yield; too high a temperature may cause chitosan degradation or side reactions, affecting product performance. Similarly, too short a reaction time results in insufficient grafting; too long a time increases energy consumption with limited yield improvement. Therefore, controlling the temperature and time within this preferred range is the optimal solution that balances reaction efficiency, product quality, and production cost. Furthermore, controlling the grafting degree under these mild conditions avoids excessive modification leading to the loss of active amino groups.

[0041] Preferably, in an optional embodiment, the Schiff base grafting reaction in step S100 is carried out in an acetic acid solution with a mass fraction of 1%-2%. Chitosan itself is insoluble in water but soluble in dilute acid solutions. Using a 1%-2% acetic acid solution as a solvent can effectively dissolve natural chitosan b, allowing its molecular chains to fully unfold and exposing more reactive sites (amino groups), thereby greatly promoting the subsequent grafting reaction with p-nitrobenzaldehyde. This solvent concentration ensures sufficient dissolution while avoiding excessive acidity that could damage the chitosan molecular chains, which is an important condition for successful modification.

[0042] Preferably, in an optional embodiment, before the Schiff base grafting reaction in step S100, natural chitosan is first dissolved in a 1%-2% acetic acid solution to prepare a chitosan-acetic acid solution with a mass concentration of 1%-3%, and stirred until completely transparent; after stirring until completely transparent, nitrobenzaldehyde is dissolved in anhydrous ethanol to prepare a solution with a mass fraction of 2%-10%; after the Schiff base grafting reaction is completed, the precipitate is washed multiple times with anhydrous ethanol or isopropanol to remove unreacted aldehydes, and then vacuum dried and pulverized at 50℃-60℃ to obtain powdered p-nitrobenzaldehyde grafted modified chitosan c.

[0043] When the engineering mud solidification and remediation material of this invention is added to engineering mud and stirred, its working process exhibits distinct temporality and synergy. First, the natural chitosan b and modified chitosan dispersed in the system, due to their large specific surface area and abundant active sites, preferentially undergo rapid adsorption reactions with various dissolved pollutants in the mud. This step is crucial because it can quickly neutralize or fix chemical additives (such as surfactants) that interfere with subsequent gelation reactions, effectively suppressing their air-entraining effect and preventing the formation of numerous harmful pores in the solidified body, thus ensuring the compactness of the final solidified soil. Following this, after the pollutant activity is effectively suppressed, the hydration reaction of the solid waste gelling component a proceeds on a large scale. The resulting gel and crystal network structure grows healthily in an undisturbed environment, ultimately forming a high-strength mechanical framework. Simultaneously, pollutants already adsorbed onto the chitosan chains are encapsulated and fixed within the continuously generated inorganic gelling network along with the chitosan molecules, achieving dual locking through physical coating and chemical adsorption. Through the above structural design and working principle, the engineering mud solidification and repair material of the present invention achieves the combination of two major functions: mechanical solidification and environmental remediation.

[0044] Preferably, in an optional embodiment, the amount of engineering mud solidification and repair material used is 4%-20% of the dry mass of the solid phase contained in the engineering mud to be solidified. This dosage range gives the invention broad engineering adaptability. For non-load-bearing backfill scenarios with low contamination levels and low strength requirements, a low dosage of around 4% can be used to effectively save costs. However, for critical engineering parts with high contaminant concentrations or requiring high bearing capacity of the solidified soil, a dosage as high as 20% can be used to ensure reliable solidification and repair effects. This broad and effective dosage range allows construction parties to flexibly adjust according to specific needs, achieving a dynamic balance between technical performance and economic benefits.

[0045] The present invention will now be described in detail through specific embodiments.

[0046] Example 1

[0047] The waste drilling mud used in the experiment was taken from a tunnel boring machine project in Chongqing. The initial water content of the waste mud was 62.7%, and its natural density was 1.21 g / cm³. 3 Compaction tests showed that its optimum moisture content was 13.09%, corresponding to a maximum dry density of 1.78 g / cm³. 3 The dry components were analyzed by X-ray fluorescence spectroscopy, and the main chemical components are as follows: Table 1. Main chemical components of engineering mud (unit: w t / %)

[0048] Based on the chemical agents added during the tunnel boring machine (TBM) project, the potential pollutants were determined as shown in Table 2 below: Table 2. Main chemical components in waste engineering mud

[0049] The salt gypsum was extracted from a salt chemical plant in Zigong. Due to the influence of the salt mining and refining processes, this material exhibits typical characteristics of high salt leaching. The characteristic pollutant Cl in this salt gypsum in the aqueous system is... - The leaching concentration reached as high as 865.2 mg / L, far exceeding the environmental limit of 350 mg / L in GB / T 14848-2017; at the same time, its SO4 content was also high. 2- The leaching concentration reached 2243 mg / L. X-ray fluorescence spectrometry analysis revealed its main chemical components as follows: Table 3. Main chemical components of salt gypsum materials (unit: w t / %)

[0050] The lithium slag, sourced from a lithium battery material processing plant in the Sichuan-Chongqing region, is an industrial byproduct of lithium extraction from lepidolite. Its dry composition primarily consists of silicon dioxide and aluminum oxide, exhibiting high pozzolanic activity. However, due to residual effects from the lithium extraction process, this material carries a significant risk of contamination leaching. Experimental results show that the lithium slag releases high concentrations of the characteristic pollutant Li in an aqueous system. + (5.84 mg / L, leaching concentration exceeding the EPA health reference standard by more than 500 times), its main chemical components were analyzed by X-ray fluorescence spectroscopy as follows: Table 4 Main chemical components of lithium slag materials (unit: w t / %)

[0051] The red mud was taken from an alumina plant in Southwest China and is a highly alkaline solid waste generated during the Bayer process for aluminum production. Its main chemical components were analyzed using X-ray fluorescence spectroscopy as follows: Table 5. Main chemical components of red mud materials (unit: w t / %)

[0052] The calcium carbide slag was taken from the acetylene production workshop of a chemical company in Chongqing. Its main phase is calcium oxide. The main chemical components were analyzed by X-ray fluorescence spectrometry as follows: Table 6 Main Chemical Components of Calcium Carbide Slag Materials (Unit: w t / %)

[0053] The silica fume was collected from a ferroalloy processing enterprise. It is an ultrafine dust collected during the smelting of industrial silicon. The main chemical components of the silica fume were analyzed by X-ray fluorescence spectroscopy as follows: Table 7 Main Chemical Components of Silica Fume (Unit: w t / %)

[0054] This embodiment provides a solid waste-based fluidized solidified soil material with pollutant adsorption function. The preparation process is as follows: First, take 30 parts by weight of salt gypsum, 50 parts by weight of lithium slag, 10 parts by weight of red mud, 5 parts by weight of carbide slag and 5 parts by weight of silica fume to form solid waste cementitious component a. Next, p-nitrobenzaldehyde-grafted modified chitosan c was prepared by Schiff base grafting reaction of natural chitosan b with p-nitrobenzaldehyde. The reaction temperature was 50℃, the reaction time was 8 hours, and the reaction was carried out in a 2% acetic acid solution. Then, the raw materials of 1.5 kg of solid waste gelling component a, 1.5 g of natural chitosan b, and 1.5 g of p-nitrobenzaldehyde grafted modified chitosan c were dry-mixed to obtain waste engineering mud solidification and repair material. The obtained 1.5 kg of waste engineering mud solidification and repair material was mixed with 10 kg of waste shield tunneling mud from a certain rail transit project with an absolute dry matter content to obtain a fluidized solidified soil material. The waste shield tunneling mud from the rail transit project contained anionic dispersants (containing PO4). 3- The moisture content is 62.7%.

[0055] Example 2 This embodiment provides a solid waste-based fluidized solidified soil material with pollutant adsorption function. The raw materials and experimental subjects used are the same as in Example 1, and the preparation process is as follows: First, take 40 parts by weight of salt gypsum, 40 parts by weight of lithium slag, 15 parts by weight of red mud, 3 parts by weight of carbide slag and 2 parts by weight of silica fume to form solid waste cementitious component a. Next, p-nitrobenzaldehyde-grafted modified chitosan c was prepared by Schiff base grafting reaction of natural chitosan b with p-nitrobenzaldehyde. The reaction temperature was 60℃ and the reaction time was 6 hours, carried out in a 1.5% acetic acid solution. Then, the raw materials of 1.5 kg of solid waste gelling component a, 1.5 g of natural chitosan b, and 1.5 g of p-nitrobenzaldehyde grafted modified chitosan c were dry-mixed to obtain waste engineering mud solidification and repair material. The obtained 1.5 kg of waste engineering mud solidification and repair material was mixed with 10 kg of waste shield tunneling mud from a certain rail transit project with an absolute dry matter content to obtain a fluidized solidified soil material. The waste shield tunneling mud from the rail transit project contained anionic dispersant (containing PO4). 3- The moisture content is 62.7%.

[0056] Example 3 This embodiment provides a solid waste-based fluidized solidified soil material with pollutant adsorption function. The raw materials and experimental subjects used are the same as in Example 1, and the preparation process is as follows: First, take 50 parts by weight of salt gypsum, 30 parts by weight of lithium slag, 5 parts by weight of red mud, 5 parts by weight of carbide slag and 10 parts by weight of silica fume to form solid waste cementitious component a. Next, p-nitrobenzaldehyde-grafted modified chitosan c was prepared by Schiff base grafting reaction of natural chitosan b with p-nitrobenzaldehyde. The reaction temperature was 70℃ and the reaction time was 4 hours, carried out in a 1% acetic acid solution. Then, the raw materials of 1.5 kg of solid waste gelling component a, 1.5 g of natural chitosan b, and 1.5 g of p-nitrobenzaldehyde grafted modified chitosan c were dry-mixed to obtain waste engineering mud solidification and repair material. The obtained 1.5 kg of waste engineering mud solidification and repair material was mixed with 10 kg of waste shield tunneling mud from a certain rail transit project with an absolute dry matter content to obtain a fluidized solidified soil material. The waste shield tunneling mud from the rail transit project contained anionic dispersant (containing PO4). 3- The moisture content is 62.7%.

[0057] Example 4 This embodiment provides a solid waste-based fluidized solidified soil material with pollutant adsorption function. The raw materials and experimental subjects used are the same as in Example 1, and the preparation process is as follows: First, take 40 parts by weight of salt gypsum, 40 parts by weight of lithium slag, 10 parts by weight of red mud, 5 parts by weight of carbide slag and 5 parts by weight of silica fume to form solid waste cementitious component a. Next, p-nitrobenzaldehyde-grafted modified chitosan c was prepared by Schiff base grafting reaction of natural chitosan b with p-nitrobenzaldehyde. The reaction temperature was 50℃, the reaction time was 8 hours, and the reaction was carried out in a 2% acetic acid solution. Then, the raw materials of 1.5 kg of solid waste gelling component a, 0.6 g of natural chitosan b, and 2.4 g of p-nitrobenzaldehyde grafted modified chitosan c were dry-mixed to obtain waste engineering mud solidification and repair material. The obtained 1.5 kg of waste engineering mud solidification and repair material was mixed with 10 kg of waste shield tunneling mud from a certain rail transit project with an absolute dry matter content to obtain a fluidized solidified soil material. The waste shield tunneling mud from the rail transit project contained anionic dispersant (containing PO4). 3- The moisture content is 62.7%.

[0058] Example 5 This embodiment provides a solid waste-based fluidized solidified soil material with pollutant adsorption function. The raw materials and experimental subjects used are the same as in Example 1, and the preparation process is as follows: First, take 40 parts by weight of salt gypsum, 40 parts by weight of lithium slag, 10 parts by weight of red mud, 5 parts by weight of carbide slag and 5 parts by weight of silica fume to form solid waste cementitious component a. Next, p-nitrobenzaldehyde-grafted modified chitosan c was prepared by Schiff base grafting reaction of natural chitosan b with p-nitrobenzaldehyde. The reaction temperature was 50℃, the reaction time was 8 hours, and the reaction was carried out in a 2% acetic acid solution. Then, the raw materials of 1.5 kg of solid waste gelling component a, 1.5 g of natural chitosan b, and 1.5 g of p-nitrobenzaldehyde grafted modified chitosan c were dry-mixed to obtain waste engineering mud solidification and repair material. The obtained 1.5 kg of waste engineering mud solidification and repair material was mixed with 10 kg of waste shield tunneling mud from a certain rail transit project with an absolute dry matter content to obtain a fluidized solidified soil material. The waste shield tunneling mud from the rail transit project contained anionic dispersant (containing PO4). 3- The moisture content is 62.7%.

[0059] Example 6 This embodiment provides a solid waste-based fluidized solidified soil material with pollutant adsorption function. The raw materials and experimental subjects used are the same as in Example 1, and the preparation process is as follows: First, take 40 parts by weight of salt gypsum, 40 parts by weight of lithium slag, 10 parts by weight of red mud, 5 parts by weight of carbide slag and 5 parts by weight of silica fume to form solid waste cementitious component a. Next, p-nitrobenzaldehyde-grafted modified chitosan c was prepared by Schiff base grafting reaction of natural chitosan b with p-nitrobenzaldehyde. The reaction temperature was 50℃, the reaction time was 8 hours, and the reaction was carried out in a 2% acetic acid solution. Then, the raw materials of 1.5 kg of solid waste gelling component a, 2.4 g of natural chitosan b, and 0.6 g of p-nitrobenzaldehyde grafted modified chitosan c were dry-mixed to obtain waste engineering mud solidification and repair material. The obtained 1.5 kg of waste engineering mud solidification and repair material was mixed with 10 kg of waste shield tunneling mud from a certain rail transit project with an absolute dry matter content to obtain a fluidized solidified soil material. The waste shield tunneling mud from the rail transit project contained anionic dispersant (containing PO4). 3- The moisture content is 62.7%.

[0060] Comparative Example 1 Sodium carboxymethyl cellulose is a common anionic organic polymer adsorbent that can be used for the adsorption of cationic pollutants. This embodiment provides a solid waste-based fluidized bed material with pollutant adsorption function. The raw materials and experimental subjects used are the same as in Example 1, and the preparation process is as follows: First, take 40 parts by weight of salt gypsum, 40 parts by weight of lithium slag, 10 parts by weight of red mud, 5 parts by weight of carbide slag and 5 parts by weight of silica fume to form solid waste cementitious component a. Then, the raw materials of 1.5 kg of solid waste gelling component a and 3 g of sodium carboxymethyl cellulose were dry-mixed to obtain waste engineering mud solidification and repair material. The obtained 1.5 kg of waste engineering mud solidification and repair material was mixed with 10 kg of waste shield tunneling mud from a certain rail transit project with an absolute dry matter content to obtain a fluidized solidified soil material. The waste shield tunneling mud from the rail transit project contained anionic dispersant (containing PO4). 3- The moisture content is 62.7%.

[0061] Comparative Example 2 Polyacrylamide is a common cationic organic polymer adsorbent that can be used for the adsorption of anionic pollutants. This embodiment provides a solid waste-based fluidized bed material with pollutant adsorption function. The raw materials and experimental subjects used are the same as in Example 1, and the preparation process is as follows: First, take 40 parts by weight of salt gypsum, 40 parts by weight of lithium slag, 10 parts by weight of red mud, 5 parts by weight of carbide slag and 5 parts by weight of silica fume to form solid waste cementitious component a. Then, the raw materials of 1.5 kg of solid waste gelling component a and 3 g of polyacrylamide were dry-mixed to obtain waste engineering mud solidification and repair material. The obtained 1.5 kg of waste engineering mud solidification and repair material was mixed with 10 kg of waste shield tunneling mud from a certain rail transit project with an absolute dry matter content to obtain a fluidized solidified soil material. The waste shield tunneling mud from the rail transit project contained anionic dispersant (containing PO4). 3- The moisture content is 62.7%.

[0062] Comparative Example 3 This embodiment provides a solid waste-based fluidized solidified soil material with pollutant adsorption function. The raw materials and experimental subjects used are the same as in Example 1, and the preparation process is as follows: First, take 40 parts by weight of salt gypsum, 40 parts by weight of lithium slag, 10 parts by weight of red mud, 5 parts by weight of carbide slag and 5 parts by weight of silica fume to form solid waste cementitious component a. The obtained 1.5 kg of solid waste cementitious component a was mixed with 10 kg of waste shield tunneling slurry from a certain rail transit project (with an absolute dry content) as a solidification and remediation material for waste engineering slurry, to obtain a fluidized solidified soil material. The waste shield tunneling slurry from the rail transit project contained anionic dispersants (containing PO4). 3-The moisture content is 62.7%.

[0063] Comparative Example 4 The materials used in this comparative example were common Portland cement, specifically grade 42.5, purchased from a cement plant in Nanjing, Jiangsu Province. The experimental materials used in this comparative example were from the same source as in Example 1. 1.5 kg of this cement material was mixed with 10 kg of waste shield tunneling slurry from a certain rail transit project, which had an absolute dry matter content, to obtain a fluidized solidified soil material. The waste shield tunneling slurry from the rail transit project contained anionic dispersants (containing PO4). 3- The moisture content is 62.7%.

[0064] The experimental design scheme is shown in Table 8 below.

[0065] Table 8 Specific Material Dosage Design Scheme (Dry Mass Ratio, Dimensionless)

[0066] Note: The curing agent dosage refers to the ratio of the total mass of the engineering mud curing and repair material to the dry mass of the mud (sodium carboxymethyl cellulose and polyacrylamide are the most common anion / cation adsorbents, respectively).

[0067] The basic physical and chemical properties of the cement in the above embodiments and comparative examples are shown in Table 9 below.

[0068] Table 9. Basic physicochemical properties of waste engineering mud solidified soil after adding engineering mud solidification and repair materials

[0069] The pH values ​​of Examples 1-6 were generally maintained between 10.1 and 10.4, far lower than that of the cement-based Comparative Example 4 (pH > 12.4). This not only reduces the risk of alkaline contamination of surrounding groundwater by the material, but also promotes the chemical stability of the solidified soil during long-term service. Since the hydration products generated by the all-solid-waste system increase the tortuosity of the seepage channels, and the grafted chitosan has a certain degree of hydrophilic swelling property that can further fill micropores, it is expected that the permeability coefficient of the material of this invention under the action of contaminated liquid will be significantly better than that of traditional cement-based materials.

[0070] The mechanical property test results of the cement in the above embodiments and comparative examples are shown in Table 10 below.

[0071] Table 10. Performance Comparison of Waste Engineering Slurry Fluidized Solidified Soil After Adding Engineering Slurry Solidification and Repair Materials

[0072] For pumping and backfilling waste engineering slurry, fluidity is the core metric for workability. While Comparative Example 3 (without adsorption modifier) ​​exhibited high initial fluidity, its density was significantly lower due to numerous air bubbles caused by residual foaming agents and surfactants. Examples 1-6 introduced a compounded grafted chitosan, utilizing its abundant positive charge centers on the molecular chain to neutralize and chemically adsorb the anionic surfactants in the slurry. This process effectively suppressed the development of pores caused by air bubbles, increasing the density of Examples 1-6 by approximately 15% compared to Comparative Examples 1-3 and Comparative Example 4. This ensured both good pumpability and a dense structure after solidification.

[0073] In engineering application evaluation, unconfined compressive strength is a key indicator for determining whether solidified shield tunneling slurry can be used as backfill material or engineering soil. Table 3 shows the strength performance of each embodiment at different ages. The results show that the strength of Examples 1-6 is significantly better than that of Comparative Example 4, which is solidified with traditional cement, and Comparative Examples 1-3 are also better. Example 5 shows the best strengthening effect, with a 28-day compressive strength as high as 1.96 MPa, which is about 115% higher than that of traditional cement components. Analysis of the reasons: The salt gypsum selected in this invention, in the strongly alkaline environment constructed by carbide slag and red mud, stimulates the active silicon and aluminum elements in lithium slag and silica fume, causing a pozzolanic reaction and generating hydrated calcium silicate (CSH) gel. At the same time, salt gypsum provides sufficient sulfate ions, promoting the formation of ettringite (AFt) with high early strength. Through the penetration and filling of pores by needle-like crystals, it significantly improves the mechanical support capacity of the solidified soil. Furthermore, the addition of natural chitosan (b) and p-nitrobenzaldehyde-grafted modified chitosan (c) to the solid waste gelling component (a) further enhanced the overall strength. In Example 5 (salt gypsum:lithium slag = 1:1), the strength reached its peak at 28 days. This indicates that an equal proportion of sulfate activator and active aluminosilicate precursor can achieve optimal chemical reaction equilibrium, constructing the densest framework structure.

[0074] The ion leaching test results of the cement in the above embodiments and comparative examples are shown in Table 4 below.

[0075] Table 4. Leaching concentration of waste engineering mud solidified soil after adding engineering mud solidification and repair materials (unit: mg / L)

[0076] Note: The maintenance period is 28 days.

[0077] Environmental remediation performance is a significant feature that distinguishes this invention from traditional solidification technologies, primarily evaluated by measuring the leaching concentration of characteristic pollutants. Lithium slag, as an industrial solid waste, carries trace amounts of lithium ions with extremely high mobility. Table 3 shows that Example 6 (pseudocation adsorption type) for Li... + The locking effect is superior, which is attributed to the fact that the modified chitosan, through the introduction of functional groups via grafting, forms a stable chelate structure with heavy metal ions, firmly binding them within the solidified framework. This results in a leaching concentration far below the groundwater quality standard. The residual Cl in the salt gypsum... - and the PO4 contained in the dispersant 3- It is a major source of environmental risk. Example 4, by increasing the proportion of natural chitosan b and utilizing the positive charge advantage of protonated amino groups, achieved the control of Cl... - and PO4 3- The system exhibits high efficiency in trapping anions and cations. Example 5 (1:1 compound group) demonstrates the best balance in locking anions and cations, proving that the compound system can cope with multi-component pollution stress under complex operating conditions.

[0078] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A material for solidifying and repairing waste engineering mud using lithium slag, salt gypsum, and chitosan composite, characterized in that... Include: The solid waste cementitious component a contains 30-50 parts by weight of salt gypsum, 30-50 parts by weight of lithium slag, and the remainder of red mud, carbide slag and silica fume. The polymer adsorption component comprises a functionalized polymer component composed of natural chitosan b and p-nitrobenzaldehyde grafted and modified chitosan c with controllable grafting degree.

2. The material for solidifying and repairing waste engineering mud using lithium slag, salt gypsum, and chitosan as described in claim 1, characterized in that... : The red mud comprises 5-15 parts by weight; The calcium carbide slag comprises 3-8 parts by weight; The silica fume accounts for 2-10 parts by weight.

3. The material for solidifying and repairing waste engineering mud using lithium slag, salt gypsum, and chitosan as described in claim 1, characterized in that... The mass ratio of the natural chitosan b to the p-nitrobenzaldehyde-grafted modified chitosan c is 1:4-4:

1.

4. The material for solidifying and repairing waste engineering mud using lithium slag, salt gypsum, and chitosan as described in claim 1, characterized in that... The total mass ratio of the solid waste gelling component a to the polymer adsorption component is 100:0.05-100:0.

5.

5. A method for preparing a solidification and remediation material for waste engineering mud using lithium slag, salt gypsum, and chitosan, for use in preparing the solidification and remediation material for waste engineering mud as described in any one of claims 1-4, characterized in that... Includes the following steps: Step S100: Prepare p-nitrobenzaldehyde-grafted modified chitosan c with controllable grafting degree by Schiff base grafting reaction of natural chitosan and p-nitrobenzaldehyde. In step S200, the raw materials of solid waste gelling component a, natural chitosan b, and p-nitrobenzaldehyde grafted modified chitosan c obtained in step S100 are dry-mixed to obtain waste engineering mud solidification and repair material.

6. The preparation method of the waste engineering mud solidification and remediation material using lithium slag, salt gypsum, and chitosan composite as described in claim 5, characterized in that... The Schiff base grafting reaction in step S100 is carried out at a temperature of 50°C-70°C for 4-8 hours.

7. The preparation method of the waste engineering mud solidification and remediation material using lithium slag, salt gypsum, and chitosan composite as described in claim 5, characterized in that... The Schiff base grafting reaction in step S100 is carried out in an acetic acid solution with a mass fraction of 1%-2%.

8. The preparation method of the waste engineering mud solidification and remediation material using lithium slag, salt gypsum, and chitosan composite as described in claim 7, characterized in that... Before the Schiff base grafting reaction in step S100, natural chitosan is dissolved in a 1%-2% acetic acid solution to prepare a chitosan-acetic acid solution with a mass concentration of 1%-3%, and stirred until completely transparent.

9. The preparation method of the waste engineering mud solidification and remediation material using lithium slag, salt gypsum, and chitosan composite as described in claim 8, characterized in that... After the stirring in step S100 is completely transparent, nitrobenzaldehyde is dissolved in anhydrous ethanol to prepare a solution with a mass fraction of 2%-10%.

10. The preparation method of the waste engineering mud solidification and remediation material using lithium slag, salt gypsum, and chitosan composite as described in claim 5, characterized in that... After the Schiff base grafting reaction in step S100 is completed, the precipitate is washed multiple times with anhydrous ethanol or isopropanol, and then vacuum dried and pulverized at 50℃-60℃ to obtain powdered p-nitrobenzaldehyde grafted modified chitosan c.

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