Method for preparing underground cemented high-water-expansion filling material from negative carbon all-solid waste and application of underground cemented high-water-expansion filling material

Abstract

The invention discloses a method for preparing an underground cemented high-water-expansion filling material from negative carbon all-solid waste and application, the method comprises the following steps: raw material pretreatment: mixing magnesium slag, steel slag and a dispersion medium to prepare solid waste slurry, adding an inducer into the solid waste slurry, and carrying out wet ball milling treatment to obtain first slurry; wet grinding and carbonization: under the condition of continuously introducing CO2, carrying out wet ball-milling treatment on the first slurry to obtain second slurry; thickening and expansion regulation and control: adding a thickening agent and an expansion regulation and control agent into the second slurry, then carrying out wet ball milling treatment to obtain third slurry, mixing and molding, mixing the third slurry with a dispersion medium, gypsum and copper tailings, and carrying out vibration molding to obtain the underground cementing high-water-expansion filling material. The method takes industrial solid waste as a raw material, has double benefits of carbon sequestration and resource utilization, and is suitable for projects such as mine goaf filling and the like.

Description

Technical Field

[0001] This invention relates to the fields of industrial solid waste resource utilization, carbon sequestration, and underground backfill material preparation technology, and particularly to a method and application for preparing underground cemented high water expansion backfill material from negative carbon solid waste. Background Technology

[0002] Mine backfilling technology is a key means of stabilizing underground goaf areas and protecting the ecological environment. Traditional backfilling materials are mainly silicate cement, whose production process relies on high-temperature calcination of limestone, resulting in high energy consumption and high carbon emissions. Cement has insufficient binding performance for aggregates such as ultrafine tailings, making it difficult to meet the engineering requirements of high support strength. In recent years, industrial solid waste (such as steel slag, blast furnace slag, desulfurization gypsum, etc.) has become a research hotspot for replacing silicate cement due to its low-carbon and low-cost characteristics. China's annual tailings discharge exceeds 1 billion tons, with total discharges exceeding 10 billion tons. The surface disposal of large amounts of tailings has adversely affected the air, water, and soil environments. Cemented mine backfilling mainly involves mixing tailings or tailings slurry of a certain concentration generated during mining with cementing materials, transporting the mixture through backfilling pipelines to the underground mining area, filling it into the goaf area, and forming supporting pillars after hardening to control surrounding rock deformation, surface subsidence, protect the environment, and control ground pressure.

[0003] The development of cemented backfill mining methods can be roughly divided into three stages: low-concentration cemented backfill, high-concentration cemented backfill, and paste backfill. Achieving low-concentration backfill and ensuring the expansiveness of the backfill slurry are two key technical challenges in mine backfilling. Low-concentration slurries have good fluidity, enabling long-distance gravity-flow transport with high expansion rates, but they are prone to segregation, have high bleeding rates, and relatively low backfill strength. High-concentration slurries are less prone to segregation, have high solidification strength, and low bleeding rates, but their fluidity is poor, typically requiring pumping, leading to higher backfilling costs. However, achieving good roof contact, minimizing solidification shrinkage deformation, and minimizing roof subsidence remain the goals of mine backfilling, and the ideal backfill material to achieve these goals should possess expansiveness.

[0004] High water expansion backfill is an important development direction in the field of mine backfilling, and it is of even greater significance for mines that are severely lacking in backfill materials. CN115180913A discloses an expandable tailings backfill material for backfilling the roof of a mine goaf, which has low cost, good fluidity, and can achieve active roof connection of the backfill body; CN119707392A discloses a high-water backfill material, its preparation method and application, which has excellent compressive strength; CN119751004A discloses a coal-based solid waste-based ultra-high-water backfill material and its preparation method, which can improve the utilization rate of coal-based solid waste and significantly enhance the stability and environmental adaptability of the material; CN118005335A discloses a high-water backfill material for mine backfilling and its construction application method, which has the characteristics of high fluidity and long shelf life; CN117747027A discloses a design method for earthquake-resistant high-water backfill material in mines and the high-water backfill material, which has good earthquake resistance.

[0005] The aforementioned patents mainly focus on using a single type of solid waste to improve mine backfill performance and reduce costs. However, they have not yet proposed effective solutions to current problems such as meeting the needs of green transformation of mines while maximizing the utilization of solid waste resources to ensure the safety and stability of underground spaces.

[0006] Therefore, developing an environmentally friendly, cost-effective, and high-quality underground backfill material is of great significance for carbon utilization and storage, solid waste resource utilization, and the sustainable development and application of underground space. It is a technical problem that urgently needs to be solved. Summary of the Invention

[0007] To overcome the problems existing in the prior art, the present invention provides a method for preparing underground cemented high-water-swelling backfill material from negative carbon solid waste, comprising, Raw material pretreatment: Magnesium slag, steel slag and dispersion medium are mixed to prepare solid waste slurry. After adding an inducing agent to the solid waste slurry, wet ball milling is performed to obtain the first slurry. Wet milling carbonization: The first slurry is wet-milled under continuous CO2 supply to obtain the second slurry; Thickening and Expansion Control: Thickener and expansion control agent were added to the second slurry, followed by wet ball milling to obtain the third slurry. Mixing and molding: The third slurry is mixed with the dispersion medium, gypsum, and copper tailings, and then vibrated and molded to obtain underground cemented high water-swelling filling material.

[0008] Furthermore, the amount of the inducing agent added is 1 wt.%-3 wt.% of the mass of the solid waste slurry; The inducing agent includes at least one of potassium citrate, sodium pyrophosphate, and sodium polyacrylate.

[0009] More preferably, the inducing agent is a mixture of potassium citrate and sodium polyacrylate in a mass ratio of 3:1. The inducing agent effectively disperses solid waste particles and stabilizes the carbonization reaction interface during wet milling through a combination of electrostatic repulsion and steric hindrance.

[0010] Furthermore, the amounts of the thickener and the swelling regulator added are 0.6wt.%-2.5wt.% and 0.5wt.%-2wt.% of the mass of the second slurry, respectively. The thickener is a warm-roll adhesive; The expansion regulator includes at least one of aluminum sulfate, ferrous sulfate, or boric acid.

[0011] More preferably, the amounts of the thickener and the swelling regulator added are 1.2 wt.%-2.0 wt.% and 0.8 wt.%-1.5 wt.% of the mass of the second slurry, respectively. The swelling regulator is selected as aluminum sulfate, which forms coordination bonds with the polysaccharide chains of the gelling agent during high-speed stirring, thereby regulating the growth rate of the gelling phase and achieving a dynamic balance between the swelling process and the strength development.

[0012] Furthermore, the median particle size of the second slurry is ≤15μm; The median particle size of the third slurry is ≤5μm.

[0013] Furthermore, the median particle size of the magnesium slag and steel slag is ≤100μm, the alkalinity coefficient of the steel slag is ≥2.5, and the solid content of the solid waste slurry is 35%-50%; The mass ratio of the three slurries to the dispersion medium, gypsum, and copper tailings is 1:1.2-1.5:0.3-0.5:5-7.

[0014] Furthermore, the magnesium slag has a magnesium oxide content of ≥20%, the steel slag has a calcium oxide content of ≥40%, and the particle size of both the magnesium slag and the steel slag is ≤100μm; The gypsum is desulfurized gypsum or phosphogypsum with a median particle size ≤40μm; the copper tailings have a particle size distribution of 0.2-1.2mm and a silicon content ≥40%.

[0015] Furthermore, CO2 originates from exhaust gases emitted from industrial or power plant flues, with an inlet flow rate of 1-4 L / min.

[0016] It should be noted that, unless otherwise specified, the dispersion medium used in this invention is water, which is the most conventionally selected medium in the art. Of course, it is not limited to water. Those skilled in the art can add some organic matter or inorganic salts to water to form a dispersion medium according to actual construction needs.

[0017] Compared with other alkaline solid wastes, steel slag and magnesium slag used in this invention have the following advantages: First, both steel slag and magnesium slag are large quantities of solid waste generated during industrial production, with huge output and low utilization rates. The synergistic carbonization and activation effect of steel slag and magnesium slag can improve the strength and performance of backfill materials, reduce the use of traditional cementitious materials such as cement, thereby reducing production costs and energy consumption. Second, magnesium oxide in magnesium slag and calcium oxide in steel slag will undergo an expansion reaction during wet grinding and carbonization. By reasonably controlling the ratio and reaction conditions of the two, the backfill material can be moderately expanded to fill the irregular spaces in underground mining areas and improve the density and stability of the backfill body. Third, the key reason why magnesium slag is difficult to utilize is its unstable physicochemical properties and high alkalinity. The key reason why steel slag is difficult to utilize is not only the presence of free calcium oxide and magnesium oxide, but also the presence of its RO glass phase, which has potential hydration activity but is difficult to activate. The carbonization and activation treatment of this invention can effectively solve this problem and achieve the overall goal of "treating waste with waste". Copper tailings are abundant and widely sourced, and exhibit excellent compatibility with the products from wet milling and carbonization. This specific particle size of copper tailings creates a complementary gradation effect with the carbonization products, and its siliceous components interact with the aragonite-type calcium carbonate generated during carbonization, constructing a three-dimensional network framework during vibration compaction. In particular, the high silicon content in copper tailings gradually releases active SiO2 under alkaline conditions, which interacts with the Ca in the carbonization products. 2+ The CSH gel, combined with aragonite-type calcium carbonate, forms a composite structure that combines rigidity and flexibility. This structure ensures early strength of the material through the rigid support of the aragonite-type calcium carbonate, while effectively buffering formation stress through the toughness of the CSH gel, giving the infill excellent resistance to deformation. The synergistic carbonation reaction between highly active calcium oxide in steel slag and magnesium oxide in magnesium slag generates carbonate minerals with a nanosheet structure, significantly improving the compressive strength of the material through the intercalation effect. In addition, gypsum injects new chemical activity into the system, activating inert silicates in copper tailings through the generation of sulfuric acid, increasing the silica dissolution rate, promoting the continuous growth of CSH gel, achieving material densification, and significantly improving the mechanical properties of the entire system.

[0018] The overall concept of this invention is as follows: For underground backfilling projects, the performance of backfill materials must meet dual requirements: the backfilling performance (such as fluidity and cohesiveness) during the initial construction phase and the strength, shrinkage rate, and expansion rate after hardening are all key evaluation indicators. Simultaneously, gaps at the contact interface can easily lead to structural instability. Based on these considerations, this invention proposes introducing a high content of aragonite-type calcium carbonate precursor during the preparation of negative carbon underground cemented high-water-swelling backfill material. By synergistically regulating the cohesiveness and controllable expansion under high water content conditions, the comprehensive performance and service life of the backfill material are simultaneously improved. Research shows that aragonite-type calcium carbonate, with its fibrous crystal structure and high interfacial bonding force, can optimize the particle size distribution of the backfill system, significantly improving the fluidity and density of the backfill material. Simultaneously, the whisker reinforcement effect can improve the later-stage strength of the hardened body and reduce the settling rate. To achieve the directional generation of a high proportion of aragonite-type calcium carbonate precursor in the slurry and its synergistic regulation with backfilling performance, the technical solution of this invention mainly involves the following two improvements: First, the nucleation kinetics regulation of aragonite-type calcium carbonate. In the raw material pretreatment, solid waste slurry is treated using a synergistic wet milling carbonization activation technology, simultaneously introducing Mg from magnesium slag and steel slag. 2+ / Ca 2+ Ion competition system, utilizing Mg 2+ The specific adsorption of calcite crystal faces inhibits the preferential orientation growth of calcite crystals. Simultaneously, the addition of a composite inducer, through the interaction of β-diketone groups with Ca... 2+ The chelation effect of Ca in the liquid phase 2+ The concentration remained stable within the critical range for aragonite nucleation. In step S2, the wet grinding and carbonization stage, nanoscale active sites were generated on the surface of the solid waste particles through mechanochemical action, forming aragonite whisker templates in conjunction with the CO2 supersaturated solution. Simultaneously, the inducer formed a molecular barrier on the aragonite crystal face through electrostatic adsorption, inhibiting its transformation into calcite. This resulted in a high proportion of aragonite-type calcium carbonate.

[0019] Second, the synergistic enhancement of the filling material properties. In wet milling and carbonization, after wet milling and carbonization, the ultrafine particles of magnesium slag and steel slag form a three-dimensional network structure in the high water content system through van der Waals forces and hydrogen bonds, achieving a physical thickening effect and significantly improving the cohesiveness of the slurry. In thickening and expansion control, warm wheel gum and expansion regulator are added. Among them, the anionic polysaccharide chains of warm wheel gum interact with Ca in the system through carboxyl groups. 2+The complexation process forms a chemical cross-linked network, preventing segregation and bleeding of the backfill material under high water conditions. Simultaneously, the expansion regulator controls the expansion windows of calcium oxide and magnesium oxide in the steel slag and magnesium slag, achieving controllable expansion of the backfill material. This expansion control system matches the hydration reaction rates of f-CaO in the steel slag and MgO in the magnesium slag, generating controllable expansion stress in the backfill body during the initial hardening stage. This effectively closes the gap between the backfill body and the top plate interface and inhibits the formation of shrinkage cracks, thereby improving the performance and stability of the backfill material.

[0020] Furthermore, the raw materials used in the negative carbon underground cemented high water expansion backfill material provided by this invention, such as magnesium slag, steel slag, copper tailings and gypsum, are all industrial solid wastes. This invention utilizes alkaline industrial solid waste to treat CO2 emitted from industrial exhaust gas, achieving the environmental protection goal of "treating waste with waste".

[0021] More preferably, in wet milling carbonization, the inducer reacts with Mg in the magnesium slag. 2+ and Ca in steel slag 2+ The formation of stable chelate structures regulates the dissolution rate and distribution of alkaline ions, thereby controlling the nucleation and growth kinetics of calcium carbonate and magnesium hydroxide crystals. Studies have shown that when the inducer content is low, insufficient chelate sites lead to abnormally high local pH values, triggering uncontrolled rapid precipitation of calcium hydroxide and thus blocking subsequent carbonization reaction pathways. Conversely, when the inducer dosage is too high, excessive chelation will shield the active sites of solid waste particles, restricting the diffusion of carbonization precursors and reducing CO2 conversion efficiency. Considering these factors, this invention adds an inducer to solid waste slurry at a dosage of 1.5 wt.%-3.5 wt.%. Under these conditions, an appropriate amount of inducer can synergistically regulate the coordination environment of calcium and magnesium ions, achieving preferential directional growth of the CO2 mineralization reaction, promoting uniform nucleation of aragonite-type calcium carbonate and magnesium hydroxide micro / nano structures, while inhibiting heterogeneous growth of abnormal crystal forms, ensuring the consistency and stability of material properties.

[0022] More preferably, in this invention, in order to promote the formation and stability of aragonite-type calcium carbonate and ensure product performance, different ball milling speeds and times are set at different reaction stages: In the raw material pretreatment, after adding the inducing agent, wet milling at a ball milling speed of 15-35 rpm for 40-80 seconds allows the inducing agent to chemically react with the particle surface. This promotes the dissolution of alkaline ions and weakens the structural strength of the particles, making them easier to pulverize during wet milling. Low-speed wet milling ensures that the inducing agent reacts fully with the calcium and magnesium ions in the solid waste slurry, while avoiding excessive shear force or prolonged stirring time that could damage the structure of the inducing agent and thus affect the subsequent crystal form control effect.

[0023] In wet milling carbonization, a ball milling speed of 250-450 rpm is maintained for 25-35 minutes. This moderate milling speed and continuous carbon dioxide introduction are designed to efficiently convert CO2 into carbonate ions under alkaline conditions, which then react with calcium ions to form calcium carbonate. A moderate milling speed helps maintain the homogeneity of the reaction system and effective collisions between reactants, promoting the nucleation and growth of aragonite-type calcium carbonate. If the milling speed is set too high during this stage, it may lead to excessive particle breakage in the reaction system, affecting the crystal form and stability of the aragonite-type calcium carbonate.

[0024] In the wet milling carbonization and thickening and expansion control of this invention, a highly efficient wet activation carbonization synergistic mechanical force process is adopted: in the wet mechanical force-carbonization synergistic activation system, the composite treatment of steel slag and magnesium slag exhibits a significant synergistic effect. In an aquatic environment, through the mechanochemical coupling effect of high-energy ball milling, the RO phase glass in the steel slag and the glassy components in the magnesium slag undergo simultaneous depolymerization reactions. The high-speed collision of the grinding media not only significantly increases the surface energy of the particles, but also induces alkali metal ions (Ca) on the particle surface. 2+ Mg 2+ The selective activation of alkali metal ions (CSH) is achieved through a mechanochemical activation process that breaks weakly bonded ionic bonds on the surface, promoting the rapid dissolution of active ions. As mechanoactivation continues, the inert layer on the particle surface is effectively stripped away, exposing highly active internal regions and significantly increasing the dissolution rate of alkali metal ions. In the subsequent carbonation stage, continuous CO2 injection triggers a multiphase interfacial reaction: firstly, calcium ions in the CSH gel layer are selectively carbonized, forming a high-specific-surface-area amorphous silica gel network structure; secondly, the rapid enrichment of carbonate ions leads to a supersaturated solution, providing a thermodynamic driving force for the heterogeneous nucleation of aragonite-type calcium carbonate. Furthermore, the in-situ generated nanoscale calcium carbonate particles have a dual function: on the one hand, they act as heterogeneous nucleation sites for C3S hydration products, inducing the oriented growth of these products; on the other hand, they fill the gel pores, reducing the porosity of the composite system. This structural densification effect, combined with the unique needle-like morphology of the aragonite phase, ultimately significantly improves the compressive strength of the composite material.

[0025] In some preferred embodiments, the median particle size of the third slurry obtained after wet milling and carbonization is ≤5μm. In this invention, further reducing the median particle size of the third slurry offers the following advantages: First, it improves the carbonization effect: a median particle size ≤5μm increases the specific surface area of ​​the particles, allowing the solid waste particles in the slurry to have more contact area with the introduced carbon dioxide, thereby improving the efficiency of the reaction with CO2, accelerating the nucleation and growth process of calcium carbonate, promoting the carbonization reaction, and better achieving the goal of negative carbon. Second, it optimizes material properties: in the subsequent preparation of negative carbon underground cemented high-water-swelling backfill material, a second slurry with a median particle size ≤5μm helps improve the uniformity and density of the material. A uniform particle distribution makes the internal structure of the material more stable after molding, thereby improving its mechanical properties and durability, enabling the backfill material to better withstand the effects of external pressure and environmental factors. Third, it ensures construction performance: during backfilling operations, a slurry with a median particle size ≤5μm helps maintain the cohesiveness and fluidity of the material. Suitable cohesiveness and flowability facilitate the transport and filling of materials in underground engineering, reducing resistance and clogging problems during construction and improving construction efficiency and quality. Fourth, stable material structure: a median particle size ≤5μm helps to form a more uniform and dense pore structure. A uniform and dense pore structure can reduce weak areas inside the material, improve the strength and stability of the material, and make the filling material more reliable in long-term use.

[0026] Furthermore, the ball milling speeds for raw material pretreatment, wet milling carbonization, and thickening and expansion control are 15-35 rpm, 250-450 rpm, and 500-700 rpm, respectively; the grinding ball gradation is 6mm:4mm:2mm = 2:3:1, and the ball-to-material mass ratio is 0.4-0.6:1. This specific gradation design ratio is based on the coupled analysis of the energy gradient distribution characteristics and particle size crushing efficiency of the wet milling process, which is beneficial for improving the specific surface area and particle uniformity of the material, thereby improving the final performance of the product. The ball-to-material ratio is controlled at 0.4-0.6:1. This ratio is designed based on a balance between wet milling efficiency and cost control. Too low a ratio will limit the collision frequency of the grinding media, leading to low grinding efficiency and potentially causing excessive water absorption, resulting in an abnormal increase in slurry viscosity, thus reducing grinding efficiency. More preferably, the ball-to-material ratio is controlled at 0.4:1. The addition of grinding media significantly enhances the activation energy of the steel slag-magnesium slag system through mechanochemical effects. On the one hand, it promotes the depolymerization of the RO phase in the steel slag and the calcium silicate glass in the magnesium slag under the action of grinding shear force, breaking the Si-O-Al bonds and releasing active SiO4. 4- and AlO 2- At the same time, the Ca encapsulated in the RO phase is exposed. 2+ / Mg 2+ This process forms a high-density Ca-Mg-O active site. 2+The release rate and the CO2 introduction rate form a kinetic match, providing ion concentration gradient conditions for the directional growth of aragonite-type calcium carbonate. On the other hand, the cavitation effect generated by medium collisions strips away the CaCO3 / MgCO3 passivation layer, dynamically stripping away the reaction stagnation caused by the surface coating, thereby improving carbonation efficiency and refining the calcium carbonate particle size.

[0027] In some preferred embodiments, the negative carbon underground cemented high water-swelling backfill material meets the requirements of C3 strength grade, F3 expansion and S1 shrinkage rate in tailings concrete used for backfilling mining goaf areas; furthermore, the negative carbon underground cemented high water-swelling backfill material has a carbon sequestration capacity of 205-253 kg per ton of carbon, realizing the sequestration and utilization of carbon dioxide, and providing a new way for the high-value-added utilization of carbonization products.

[0028] This invention also provides an underground cemented high water-swelling filling material, which is prepared by the above method.

[0029] The present invention also provides the application of the above-mentioned underground cemented high water-swellable filling material in mine goaf filling, foundation reinforcement projects or underground engineering backfilling.

[0030] Compared with the prior art, the present invention has the following beneficial effects: (1) The efficient induction and stable existence of aragonite-type calcium carbonate were achieved. Through the mechanical-chemical coupling activation effect, the active components in magnesium slag and steel slag were rapidly dissolved, and the CO2 flow rate and ball milling speed were synergistically controlled to maintain a high CO3 content in the system. 2- / Ca 2+ The ratio is adjusted to induce the formation of high-content aragonite-type calcium carbonate. The inducer plays a key regulatory role in crystal nucleation and growth, effectively stabilizing the aragonite precursor and inhibiting its transformation into the more thermodynamically stable calcite. The generated aragonite-type calcium carbonate possesses a needle-like porous structure, significantly increasing the specific surface area of ​​the slurry, providing a highly active interface for subsequent cementation reactions, and simultaneously enhancing the early hydration rate of the material, laying the structural foundation for the excellent mechanical properties of the filling material.

[0031] (2) It possesses coordinated workability, expansibility, and mechanical properties. By introducing thickeners and expansion regulators, and combining the inherent expansion characteristics of steel slag and magnesium slag, precise control of the material's expansion behavior is achieved. Thickeners effectively enhance the adhesion and fluidity of the slurry, promote the formation of a continuous skeleton structure during the curing process, thereby improving the material's cohesion and overall mechanical properties. Expansibility regulators endow the material with appropriate expansion capacity, enabling it to better adapt to irregular spaces during filling, improve filling density and top-joining effect, and significantly improve the integrity and long-term stability of the filling body. In addition, components such as gypsum and copper tailings are highly compatible with the system. The calcium sulfate component in gypsum enhances the system's strength through chemical reactions, while copper tailings not only provide abundant crystal nucleation sites but also synergistically promote the growth of hydrated calcium silicate gel with carbonization products, jointly enhancing the material's density and durability.

[0032] (3) Meets engineering standards and has active roof support capability. The prepared negative carbon underground cemented high water expansion backfill material meets the requirements of C2 strength grade, F3 expansion and S1 shrinkage rate in JC / T 2478-2018 "Tail Sand Concrete for Backfilling Goaf in Mines". The material has adjustable expansion performance, which can achieve active and tight contact with the roof, effectively improving the problem of poor roof support effect of traditional backfill materials, and has wide application value in mine and underground engineering backfilling.

[0033] (4) It has significant environmental and resource benefits. The material uses industrial solid waste as the main raw material and achieves CO2 sequestration and utilization during the preparation process. Each ton of material can sequester up to 253 kg of carbon dioxide, achieving a negative carbon effect and helping to reduce greenhouse gas emissions. At the same time, this technology provides a high-value-added resource utilization pathway for solid wastes such as steel slag, magnesium slag, and copper tailings. While solving the problem of solid waste disposal, it provides high-performance materials for the treatment of mining subsidence areas, foundation reinforcement, and backfilling of underground projects, thus having environmental, economic, and social benefits. Detailed Implementation

[0034] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0035] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] The chemical composition and particle size distribution of the main raw materials used in Examples 1-4 and Comparative Examples 1-6 of this invention are shown in Tables 1 and 2, where the copper tailings were taken from a copper mine.

[0037] Table 1

[0038] Table 2

[0039] The weight proportions of raw materials and specific process parameters in Examples 1-4 and Comparative Examples 1-6 of this invention are shown in Table 3.

[0040] Table 3

[0041] In the table above, the inducing agent is a mixture of potassium citrate and sodium polyacrylate in a mass ratio of 3:1. Potassium citrate is a white powder with a purity ≥99%, and potassium citrate is a pale yellow viscous liquid with a solid content of 90%. Warm wheel glue is a yellow powder with a purity ≥99%. The expansion regulator is aluminum sulfate, which is a white powder with a purity ≥99%. The solid waste slurry is a mixture of steel slag and magnesium slag (median particle size ≤100μm) obtained by crushing and screening, and water in a mass ratio of 1:1:3-5. The carbon dioxide used in Examples 1-4 and Comparative Examples 1-3 is industrial by-product gas collected from industrial emissions.

[0042] Example 1 A type of underground cemented high-water-swellable backfill material comprises, by weight, 240 parts solid waste slurry, 40 parts gypsum, 2.4 parts inducing agent, 1.4 parts thermal slurry, 1.2 parts aluminum sulfate, 500 parts copper tailings, and 288 parts water. The preparation method of the underground cemented high-water-swellable backfill material includes the following steps: Step 1: Mix steel slag, magnesium slag and water (the mass ratio of steel slag: magnesium slag: water is 1:1:3) to obtain solid waste slurry. Place 2.4 parts of inducing agent and 240 parts of solid waste slurry in a wet mill and stir at 15 rpm for 60 seconds to obtain the first slurry. Step 2: Continuously introduce CO2 into the wet mill at a flow rate of 1L / min, and add grinding balls (grind ball gradation is 6mm:4mm:2mm=2:3:1, ball-to-material ratio is 0.4:1). Stir the first slurry at 250rpm for 25min to obtain the second slurry; the wet milling environment is at room temperature and pressure. Step 3: Add 1.4 parts of warm wheel colloid and 1.2 parts of aluminum sulfate to the second slurry, and stir at 500 rpm for 5 minutes to obtain a third slurry with a median particle size ≤40μm; wherein, the wet grinding environment is at room temperature and pressure; Step 4: Place 245 parts of the third slurry, 40 parts of gypsum, 500 parts of copper tailings and 288 parts of water prepared in Step 3 into a mixer and mix them. Mix and stir evenly at 30 rpm and vibrate for 60-70 times to obtain underground cemented high water expansion filling material.

[0043] Example 2 A type of underground cemented high-water-swellable backfill material comprises, by weight, 300 parts solid waste slurry, 50 parts gypsum, 4.8 parts inducing agent, 3 parts thermal slurry, 3 parts aluminum sulfate, 600 parts copper tailings, and 390 parts water. The preparation method of the underground cemented high-water-swellable backfill material includes the following steps: Step 1: Mix steel slag, magnesium slag and water (the mass ratio of steel slag: magnesium slag: water is 1:1:4) to obtain solid waste slurry. Place 4.8 parts of inducing agent and 300 parts of solid waste slurry in a wet mill and stir at 20 rpm for 60 seconds to obtain the first slurry. Step 2: Continuously introduce CO2 into the wet mill at a flow rate of 2L / min, and add grinding balls (grind ball gradation is 6mm:4mm:2mm=2:3:1, ball-to-material ratio is 0.4:1). Stir the first slurry at 300rpm for 30min to obtain the second slurry; the wet milling environment is at room temperature and pressure. Step 3: Add 4.8 parts of warm wheel gum and 3 parts of aluminum sulfate to the second slurry, and stir at 600 rpm for 8 minutes to obtain a third slurry with a median particle size ≤20μm; wherein, the wet grinding environment is at room temperature and pressure; Step 4: Place 310.8 parts of the third slurry, 50 parts of gypsum, 600 parts of copper tailings and 390 parts of water prepared in Step 3 into a mixer and mix them. Mix and stir evenly at 30 rpm and vibrate for 60-70 times to obtain underground cemented high water expansion filling material.

[0044] Example 3 A type of underground cemented high-water-swellable backfill material comprises, by weight, 320 parts solid waste slurry, 55 parts gypsum, 6.4 parts inducing agent, 6.4 parts thermal slurry, 4.8 parts aluminum sulfate, 650 parts copper tailings, and 448 parts water. The preparation method of the underground cemented high-water-swellable backfill material includes the following steps: Step 1: Mix steel slag, magnesium slag and water (the mass ratio of steel slag: magnesium slag: water is 1:1:4) to obtain solid waste slurry. Place 6.4 parts of inducing agent and 320 parts of solid waste slurry in a wet mill and stir at 25 rpm for 60 seconds to obtain the first slurry. Step 2: Continuously introduce CO2 into the wet mill at a flow rate of 3L / min, and add grinding balls (grind ball gradation is 6mm:4mm:2mm=2:3:1, ball-to-material ratio is 0.4:1). Stir the first slurry at 350rpm for 30min to obtain the second slurry; the wet milling environment is at room temperature and pressure. Step 3: Add 6.4 parts of warm wheel adhesive and 4.8 parts of aluminum sulfate to the second slurry, and stir at 600 rpm for 10 min to obtain a third slurry with a median particle size ≤10 μm; wherein, the wet grinding environment is at room temperature and pressure; Step 4: Place 337.6 parts of the third slurry, 55 parts of gypsum, 650 parts of copper tailings and 448 parts of water prepared in Step 3 into a mixer and mix them. Mix and stir evenly at 30 rpm and vibrate for 60-70 times to obtain underground cemented high water expansion filling material.

[0045] Example 4 A type of underground cemented high-water-swellable backfill material comprises, by weight, 360 parts solid waste slurry, 60 parts gypsum, 10.8 parts inducing agent, 9 parts thermal slurry, 7.5 parts aluminum sulfate, 700 parts copper tailings, and 540 parts water. The preparation method of the underground cemented high-water-swellable backfill material includes the following steps: Step 1: Mix steel slag, magnesium slag and water (the mass ratio of steel slag: magnesium slag: water is 1:1:5) to obtain solid waste slurry. Place 10.8 parts of inducing agent and 360 parts of solid waste slurry in a wet mill and stir at 35 rpm for 60 seconds to obtain the first slurry. Step 2: Continuously introduce CO2 into the wet mill at a flow rate of 4L / min, and add grinding balls (grind ball gradation is 6mm:4mm:2mm=2:3:1, ball-to-material ratio is 0.4:1). Stir the first slurry at 450rpm for 30min to obtain the second slurry; the wet milling environment is at room temperature and pressure. Step 3: Add 9 parts of warm wheel colloid and 7.5 parts of aluminum sulfate to the second slurry, and stir at 700 rpm for 12 min to obtain a third slurry with a median particle size ≤10 μm; wherein, the wet grinding environment is at room temperature and pressure; Step 4: Place 387 parts of the third slurry, 60 parts of gypsum, 700 parts of copper tailings and 540 parts of water prepared in Step 3 into a mixer and mix them. Mix and stir evenly at 30 rpm and vibrate 60-70 times to obtain underground cemented high water expansion filling material.

[0046] Comparative Example 1 The difference between this comparative example and Example 3 is that no inducing agent was added. All other operations remained unchanged, resulting in a negative carbon underground cemented high water-swelling backfill material.

[0047] Comparative Example 2 The difference between this comparative example and Example 3 is that no warm wheel adhesive was added, while the rest of the operation remained the same, resulting in a negative carbon underground cemented high water expansion filling material.

[0048] Comparative Example 3 The difference between this comparative example and Example 3 is that no expansion regulator was added, but the rest of the operations remained the same, resulting in a negative carbon underground cemented high water expansion filling material.

[0049] Comparative Example 4 The difference between this comparative example and Example 3 is that ball milling is not performed in the thickening and expansion control stage, while the other operations remain unchanged, resulting in a negative carbon underground cemented high water expansion filling material.

[0050] Comparative Example 5 The difference between this comparative example and Example 3 is that the ball milling speed was adjusted to 250 rpm during the wet milling carbonization stage, while the other operations remained unchanged, resulting in a negative carbon underground cemented high water expansion backfill material.

[0051] Comparative Example 6 The difference between this comparative example and Example 3 is that, in the wet grinding and carbonization stage, the CO2 injection rate was adjusted to 1L / min, while the other operations remained unchanged, resulting in a negative carbon underground cemented high water expansion backfill material.

[0052] Application performance testing The application performance of the negative carbon underground cemented high water-swelling backfill materials prepared in Examples 1-4 and Comparative Examples 1-6 was tested. The carbon fixation content was determined using the TG test method (GB / T 27761-2011 "Thermogravimetric Analysis - Loss of Weight"). Compressive strength was tested for 28 days using the 28-day compressive strength test method (JGJ / T 70-2009 "Basic Performance Test Methods for Building Mortar"). The 28-day shrinkage rate and expansion were tested using the tailings concrete method (JC / T 2478-2018 "Tailings Concrete for Backfilling Mining Goaf"). The expansion rate of the material was tested using the GB / T 50082-2009 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete". The relevant test results are shown in Table 4.

[0053] Table 4

[0054] As shown in Table 4 above, the carbon sequestration of the negative carbon underground cemented high water-swelling backfill materials prepared in Examples 1-4 of this invention is greater than 200 kg / t, which meets the requirements for negative carbon materials; the 28-day expansion rate is greater than 5% and less than 10%, which meets the requirements for active backfilling and ensures the stability of the backfill material; the 28-day compressive strength exceeds 2.0 MPa, which meets the requirements of C2 strength grade tailings concrete in JC / T2478-2018 "Tailings Concrete for Backfilling Goaf in Mines" standard; the spread of the negative carbon underground cemented high water-swelling backfill materials prepared in Examples 1-4 is greater than 350 mm, which meets the F3 spread grade requirement in this standard; the 28-day shrinkage rate of Examples 1-4 is also less than 3%, which meets the S1 shrinkage rate requirement in this standard. By comparing the preferred embodiment 3 with the comparative examples, the specific contributions of each key component and process parameter to the material properties can be clearly revealed. Compared with Comparative Example 1 without the inducer, Example 3 showed a significant 92.1% increase in 28-day compressive strength, a 56.1% decrease in shrinkage, and an 83.3% increase in carbon fixation. This significant difference demonstrates the core role of the inducer in promoting the formation of aragonite-type calcium carbonate and optimizing the carbonation reaction pathway. Compared with Comparative Example 2 without the use of acetone, Example 3 achieved a 94.4% increase in compressive strength, a significant 70.8% improvement in shrinkage, and a 27.8% increase in carbon fixation, highlighting the key value of the thickener in maintaining system stability and improving final performance. Compared with Comparative Example 3 lacking the expansion regulator, Example 3 showed a 148.0% increase in compressive strength, a 6.27% increase in expansion, and a 35.3% increase in carbon fixation, fully demonstrating the important function of the expansion regulator in coordinating the material's expansion behavior and mechanical properties.

[0055] Of particular note is the decisive impact of process parameter optimization on material properties. Compared to Comparative Example 4, which did not undergo ball milling during the thickening and expansion control stages, Example 3 showed a 57.5% increase in compressive strength, a 39.3% decrease in shrinkage, and a 26.5% increase in carbon fixation. This comparison strongly demonstrates the necessity of ball milling at this stage for achieving excellent material properties. Under fixed formulation conditions, in-depth analysis of the key wet milling carbonization process further revealed the optimization potential of process parameters: compared to Comparative Example 5, which reduced the ball milling speed, Example 3, with its superior mechanical activation strength, achieved increases in carbon fixation and compressive strength of 17.7% and 28.6%, respectively; compared to Comparative Example 6, which reduced the CO2 inlet rate, Example 3, through optimized carbonization mass transfer efficiency, increased carbon fixation and compressive strength by 29.7% and 34.0%, respectively. These systematic single-factor comparative experiments collectively confirm that the ball milling speed (350 rpm) and CO2 inlet flow rate (3 L / min) used in Example 3 indeed constitute the process parameter window for achieving optimal performance.

[0056] Example 3 achieves optimal overall performance, particularly the highest carbon fixation rate (253 kg / t), due to its comprehensive parameter synergy: suitable ball milling speed and CO2 inlet flow rate ensure efficient mechanochemical activation and gas mass transfer processes; optimized inducer dosage effectively regulates crystal nucleation and growth kinetics, promoting the stable formation of high-content aragonite-type calcium carbonate; and the scientific combination of thickener and expansion regulator constructs a stable three-dimensional network structure, achieving a perfect balance between material workability, strength development, and expansion behavior. This multi-level synergistic effect makes the material more dense and uniform in microstructure and exhibits excellent comprehensive properties in macroscopic performance.

[0057] In summary, the negative carbon underground cemented high water-swelling backfill material of this invention achieves negative carbon emissions because it uses only low-carbon, all-solid waste raw materials and has the capacity to sequester 253 kg of carbon per ton. Simultaneously, this material can actively connect with the roof slab, maintain excellent cohesiveness under high water content conditions, and meet the requirements of C2 strength grade, F3 spread, and S1 shrinkage rate tailings concrete. It provides an innovative technical solution for achieving the triple goals of "solid waste resource utilization," "negative carbon emissions," and "safe backfilling of underground spaces," and has broad prospects for widespread application.

[0058] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included in the present invention.

Claims

1. A method for preparing underground cemented high-water-swelling backfill material from carbon-negative solid waste, characterized in that, include, Raw material pretreatment: Magnesium slag, steel slag and dispersion medium are mixed to prepare solid waste slurry. After adding an inducing agent to the solid waste slurry, wet ball milling is performed to obtain the first slurry. Wet milling carbonization: The first slurry is wet-milled under continuous CO2 supply to obtain the second slurry; Thickening and Expansion Control: Thickener and expansion control agent were added to the second slurry, followed by wet ball milling to obtain the third slurry. Mixing and molding: The third slurry is mixed with the dispersion medium, gypsum, and copper tailings, and then vibrated and molded to obtain underground cemented high water expansion filling material.

2. The method for preparing underground cemented high-water-swelling backfill material from negative carbon solid waste according to claim 1, characterized in that, The amount of the inducing agent added is 1 wt.%-3 wt.% of the mass of the solid waste slurry; The inducing agent includes at least one of potassium citrate, sodium pyrophosphate, and sodium polyacrylate.

3. The method for preparing underground cemented high-water-swelling backfill material from negative carbon solid waste according to claim 1, characterized in that, The amounts of the thickener and the swelling regulator added are 0.6wt.%-2.5wt.% and 0.5wt.%-2wt.% of the mass of the second slurry, respectively. The thickener is a warm-roll adhesive; The expansion regulator includes at least one of aluminum sulfate, ferrous sulfate, or boric acid.

4. The method for preparing underground cemented high-water-swelling backfill material from carbon-negative solid waste according to claim 1, characterized in that, The median particle size of the second slurry is ≤15μm; The median particle size of the third slurry is ≤5μm.

5. The method for preparing underground cemented high-water-swelling backfill material from negative carbon solid waste according to claim 1, characterized in that, The median particle size of the magnesium slag and steel slag is ≤100μm, the alkalinity coefficient of the steel slag is ≥2.5, and the solid content of the solid waste slurry is 25%-50%. The mass ratio of the third slurry to the dispersion medium, gypsum, and copper tailings is 1:1.15-1.45:0.15-0.17:1.80-2.

10.

6. The method for preparing underground cemented high-water-swelling backfill material from negative carbon solid waste according to claim 5, characterized in that, The magnesium slag has a magnesium oxide content of ≥20%, the steel slag has a calcium oxide content of ≥40%, and the particle size of both the magnesium slag and the steel slag is ≤100μm. The gypsum is desulfurized gypsum or phosphogypsum with a median particle size ≤40μm; the copper tailings have a particle size distribution of 0.2-1.2mm and a silicon content ≥40%.

7. The method for preparing underground cemented high-water-swelling backfill material from negative carbon solid waste according to claim 1, characterized in that, The ball milling speeds for raw material pretreatment, wet milling carbonization, and thickening and expansion control are 15-35 rpm, 250-450 rpm, and 500-700 rpm, respectively; the grinding ball gradation is 6mm:4mm:2mm=2:3:1, and the ball-to-material mass ratio is 0.4-0.6:

1.

8. The method for preparing underground cemented high-water-swelling backfill material from carbon-negative solid waste according to claim 1, characterized in that, CO2 originates from exhaust gases emitted from industrial or power plant flues, with an inlet flow rate of 1-4 L / min.

9. A type of underground cemented high-water-swelling infill material, characterized in that, The underground cemented high water-swelling backfill material prepared by the method according to any one of claims 1-8 comprises, by weight, the following raw materials: Magnesium slag 120-180 parts, steel slag 120-180 parts, gypsum 40-60 parts, copper tailings 500-700 parts, water 288-540 parts, inducing agent 2.4-10.8 parts, thickener 1.4-9 parts, expansion regulator 1.2-7.2 parts.

10. The application of the underground cemented high water-swelling filling material as described in claim 9 in filling goaf areas, foundation reinforcement projects, or backfilling of underground projects.

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