Multi-mechanism synergistic solidification characteristic multi-source solid waste heavy metal cementing material and preparation method thereof

Abstract

The application discloses a solidification system for heavy metal, which comprises 69-100 parts of a gelling matrix component, 5-10 parts of a wet carbonization component, 3.8-9.5 parts of a nano-solidification component, 0.5-1.5 parts of an iron-based stabilizing component, 0.6-1.0 parts of an enhanced control component and 28-35 parts of mixing water. The application constructs a multi-mechanism synergistic solidification system of 'gelling solidification-interlayer complexation-nano adsorption-iron-based reduction / precipitation-carbonate mineralization', wherein the gelling hydration product realizes structural wrapping and solidification of heavy metals, the nano LDO hydration bond breaking and recombination realizes interlayer complexation, the calcined nano C-S-H and nano MZT provide adsorption sites, the composite iron-based material promotes the reduction and precipitation of heavy metals, and the wet carbonized calcium-magnesium-based multi-alkali slag provides carbonate crystal nuclei and participates in the mineralization reaction, thereby significantly improving the solidification efficiency and long-term stability of heavy metals.

Description

Technical Field

[0001] This invention belongs to the field of industrial solid waste-based cementitious materials and heavy metal pollution control technology, specifically involving a multi-source solid waste heavy metal cementitious material with multi-mechanism synergistic solidification characteristics and its preparation method. Background Technology

[0002] With the rapid development of the alumina industry, the discharge of red mud, a major industrial solid waste generated during its production process, is increasing year by year. Red mud is characterized by its strong alkalinity, high water content, and rich content of various heavy metals. Long-term stockpiling not only occupies a large amount of land resources but also easily leads to the leakage of alkaline leachate and the migration of heavy metals, posing a potential threat to the surrounding soil and groundwater environment. Therefore, developing efficient and stable technologies for the resource utilization of red mud, especially its safe application in engineering materials, is of great significance for promoting the reduction, resource recovery, and harmless treatment of solid waste. Currently, red mud-based cementitious materials have become one of the important directions for the resource utilization of solid waste. By introducing a multi-component system including fly ash, slag, cement, and alkali activators, hydration products such as C-(A)-SH gel, NASH gel, and AFt can be formed under alkali activation conditions, thereby endowing the material with certain mechanical properties and physically encapsulating and chemically solidifying some heavy metals.

[0003] For example, patent CN 116903280 A discloses a clinker-free cement and a method for preparing clinker-free cement entirely from industrial solid waste. The clinker-free cement uses industrial solid waste as all raw materials, and the main components by mass percentage are: 8-20% desulfurized gypsum, 1-3% lime, 10-40% fly ash, 2-20% lithium slag, 0-20% slag, and 40-65% mineral powder. Triethanolamine, accounting for 2.0-2.5% of the total mass of raw materials, is added as a liquid grinding aid. The cement is prepared by microcomputer metering, belt conveying, and grinding to a specific surface area of ​​350-370 m² / kg. This invention uses industrial solid waste as raw material throughout the entire process, eliminating the need for clinker calcination, thus significantly reducing energy consumption and carbon emissions. The clinker-free slag cement and clinker-free fly ash cement produced meet the national standards for PSA32.5 and P.F32.5 grade cement, respectively. The 28-day compressive strength can reach 33~35MPa, and the stability is qualified. It features high strength, stable quality, low power consumption, and low operating costs, and can be used in construction projects such as walls and masonry, realizing the efficient resource utilization of industrial solid waste.

[0004] For example, patent CN 117819924 A discloses a nano-ultra-high performance concrete and its preparation method. The nano-ultra-high performance concrete includes the following components by weight: 150-400 parts of general silicate cement, 200-450 parts of slag powder, 100-150 parts of fly ash modified microspheres, 50-100 parts of metakaolin, 22-50 parts of composite alkali activator, 7-15 parts of nano calcium carbonate, 800-1200 parts of fine aggregate, 10-26 parts of water-reducing agent, and 40-90 parts of steel fiber, with a water-cement ratio of 0.15-0.27. The nano-ultra-high performance concrete described in this invention significantly reduces cement usage and carbon emissions through composite alkali activation and synergistic enhancement with nano-calcium carbonate. Compared with traditional ultra-high performance concrete, carbon emissions are reduced by more than 50%. It does not require high-temperature curing, the mixture has a spread of 500-750mm, a setting time of 2-6 hours, and a compressive strength of 130-200MPa after 28 days of curing at room temperature. It combines high toughness, low electrical flux, and excellent workability, and can meet both structural strength and green low-carbon requirements, making it suitable for the field of high-performance civil engineering.

[0005] For example, patent CN 121248164 A discloses a low-carbon composite cementitious material, a mortar preparation method, and its application. The low-carbon composite cementitious material comprises the following components by weight percentage: 50%–85% cement, 15%–50% Yellow River silt and sand powder, 0%–0.75% sodium hydroxide activator, and 0%–7.5% calcium hydroxide activator. This invention employs mechanical grinding and dual-alkali activation to synergistically activate the Yellow River silt and sand powder, fully stimulating its pozzolanic activity and promoting the generation of key hydration products such as C-(A)-SH, N-(A)-SH gel, and AFt. These products intertwine and fill pores, significantly improving the material's compressive and flexural strength, and imparting excellent mechanical properties. Simultaneously, the hydration products and dense structure can physically encapsulate and chemically solidify some heavy metals in the system, enhancing the material's environmental safety. This system can significantly reduce cement usage and carbon emissions. The prepared mortar is suitable for building structures, heavy masonry, and structural reinforcement and repair, providing a new low-carbon, high-value pathway for the large-scale resource utilization of Yellow River silt and sand.

[0006] However, this type of system still has the following shortcomings in engineering applications:

[0007] 1. The solidification mechanism is too simple, resulting in insufficient long-term stability of heavy metals;

[0008] Existing red mud-based cementitious materials primarily rely on gel structures formed from hydration products for the solidification of heavy metals, along with partial adsorption or simple precipitation. In the field of heavy metal solidification research, highly toxic heavy metals such as Cr and Pb exhibit strong migration capabilities, and their stability is easily affected by pH fluctuations, carbonization, and the external environment. Studies have found that solidification methods relying solely on gel encapsulation or physical adsorption are prone to structural degradation and heavy metal re-release during long-term service, making it difficult to achieve sustained and stable solidification.

[0009] 2. The synergistic effect of multi-source solid waste is insufficient, making it difficult to balance mechanical properties and environmental safety;

[0010] While existing technologies incorporate various industrial solid wastes such as red mud, fly ash, and slag to construct composite cementitious systems, the components are mostly simply superimposed, lacking an effective synergistic mechanism. In multi-source solid waste cementitious systems, the components differ in reactivity, ion release, and hydration pathways. Studies have found that without proper control, the system's reaction can easily become unbalanced or structurally unstable, making it difficult to simultaneously achieve synergistic optimization of mechanical property improvement and heavy metal solidification.

[0011] 3. The lack of a multi-mechanism coordinated regulation system means that the functional materials have not fully played their role;

[0012] Existing red mud-based cementitious material systems mostly focus on a single solidification mechanism, lacking a systematic approach that incorporates the synergistic effects of multiple mechanisms such as adsorption, ion exchange, structural embedding, and complex precipitation. Meanwhile, nanomaterials and iron-based materials show significant potential in promoting hydration reactions, optimizing microstructure, and enhancing heavy metal immobilization, but their synergistic mechanisms are either insufficiently introduced into existing systems or remain unclear. Research has revealed that the lack of multi-mechanism coupling regulation limits the stability and applicability of materials under complex environmental conditions.

[0013] Therefore, there is an urgent need to develop a multi-mechanism synergistic solidification system for heavy metals in multi-source solid waste. This system integrates structural solidification, adsorption-intercalation, ion exchange, and complexation precipitation to achieve efficient and stable solidification of heavy metals in red mud, thereby improving the material's overall performance and engineering applicability. By introducing multifunctional regulating components, a multi-mechanism synergistic solidification system integrating oxidation-reduction, adsorption-precipitation, and structural solidification can be constructed to achieve efficient and stable solidification of heavy metals in red mud and improve the material's overall performance and engineering applicability. Summary of the Invention

[0014] Addressing the core technical challenges of single solidification mechanisms, insufficient long-term stability, and low resource utilization rates of heavy metals in solid wastes such as red mud, this invention provides a multi-source solid waste heavy metal cementitious material with synergistic solidification mechanisms and its preparation method. This solves the problems of single solidification mechanisms, insufficient long-term stability, and difficulty in synergistically improving mechanical properties and environmental safety in existing solid waste-based cementitious materials during heavy metal solidification. By balancing material flow properties and structural construction capabilities, this invention achieves efficient and stable solidification of heavy metals and high-value utilization of multi-source solid waste.

[0015] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0016] This invention provides a multi-source solid waste heavy metal cementitious material with multi-mechanism synergistic solidification characteristics, comprising 69-100 parts of cementitious matrix component, 5-10 parts of wet carbonization component, 3.8-9.5 parts of nano-solidification component, 0.5-1.5 parts of iron-based stabilizing component, 0.6-1.0 parts of reinforcing and regulating component, and 28-35 parts of mixing water.

[0017] The cementitious matrix components of this invention include pretreated red mud, calcined shell powder, fly ash, slag, cement, and a composite alkali activator.

[0018] Further, the gel matrix components comprise, by weight parts:

[0019] The mixture consists of 35-45 parts pretreated red mud, 10-18 parts calcined shell powder, 8-14 parts fly ash, 6-10 parts S95 grade slag, 8-10 parts ordinary Portland cement, and 5.5-7.5 parts composite alkali activator.

[0020] The wet carbonization component of the present invention is wet carbonization calcium-magnesium-based multi-element alkali slag; the calcium-magnesium-based multi-element alkali slag comprises the following raw materials in parts by weight: 2-4 parts steel slag, 1-3 parts refining slag and 2-3 parts alkali slag.

[0021] Furthermore, the calcium-magnesium-based multi-element alkali slag is ball-milled and then passed through a 200-mesh sieve, with a particle size not exceeding 75 μm.

[0022] Furthermore, the wet-process carbonized calcium-magnesium-based multi-element alkaline slag is a carbonate composite product obtained by reacting carbon dioxide with calcium- and magnesium-containing alkaline composite solid waste in a liquid phase system.

[0023] Furthermore, the wet-process calcium-magnesium-based multi-element alkali slag mainly comprises calcium carbonate, hydrated calcium carbonate, and a carbonate gel phase.

[0024] The nano-cured components of this invention include nano-LDO, nano-CSH seed crystals, and nano-MZT functional materials; furthermore, the nano-LDO is prepared by calcining artificially synthesized nano-calcium-aluminum binary hydrotalcite, with a pore structure mainly composed of mesoporous structures; the calcination conditions are 300℃ for 2 hours, exhibiting a structural memory effect.

[0025] Furthermore, the nano-MZT is prepared by crushing and grinding natural zeolite, adding it to a 0.8 mol / L NaOH solution at a solid-liquid ratio of 1:10, stirring in a water bath at 80°C for 2 hours, and then centrifuging, washing, drying, and calcining at 300°C for 2 hours. It is a nano-functional material with ion exchange properties.

[0026] Furthermore, the nano-cured components include, by weight, 2-5 parts of nano-LDO, 1-2.5 parts of calcined nano-CSH seed crystals, and 0.8-2 parts of nano-MZT.

[0027] The iron-based stabilizing component includes ZVI and iron salt modified materials; further, the mass ratio of ZVI to iron salt modified materials is (1-2):(2-5).

[0028] The reinforcing and regulating components include fiber reinforcing agents and water-reducing agents; further, the reinforcing and regulating components include, by weight, 0.4 to 0.6 parts of fiber reinforcing agents and 0.2 to 0.4 parts of polycarboxylate water-reducing agents.

[0029] Furthermore, the composite alkaline activator includes one or more of water glass, sodium hydroxide, and alkaline activating salts.

[0030] This invention also provides a method for preparing a multi-source solid waste heavy metal cementitious material with the above-mentioned multi-mechanism synergistic solidification characteristics, comprising the following steps:

[0031] (1) The pretreated red mud, calcined shell powder, fly ash, slag, cement, wet carbonized calcium magnesium-based multi-element alkali slag, nano LDO, calcined nano CSH seed crystals, nano MZT and iron-based stabilizing components are put into a mixing device and mixed to obtain a dry mixture.

[0032] (2) The composite alkali activator, polycarboxylate superplasticizer and mixing water are mixed to obtain a liquid phase system;

[0033] (3) The liquid phase system is added to the dry mixture and mixed under stirring conditions to form a uniform slurry;

[0034] (4) Add the liquid phase system to the dry mixture and mix under stirring conditions to form a uniform slurry.

[0035] Furthermore, the mixing time in step (1) is 2 to 5 minutes.

[0036] Furthermore, in step (1), the pretreated red mud is ball-milled and then passed through a 200-mesh sieve, with a particle size not exceeding 75 μm; the particle size of the fly ash, slag, and cement is 0–250 μm, excluding 0 μm.

[0037] Furthermore, in step (2), the premixing time of the liquid phase system is 1 to 3 minutes to ensure that the activator is fully dissolved and uniformly dispersed.

[0038] Furthermore, in step (3), the stirring speed is 80-180 r / min and the stirring time is 2-5 min.

[0039] Further, during the stirring process in step (3), fiber reinforcing agent is added and stirring continues to ensure that it is evenly dispersed in the system.

[0040] Furthermore, the curing conditions in step (4) are a temperature of 20±2℃ and a relative humidity of ≥95%.

[0041] This invention also provides a method for preparing wet-process calcium-magnesium-based multi-element alkali slag, comprising the following steps:

[0042] (1) Pre-treat the calcium-magnesium-based multi-element alkali slag, which includes steel slag, refining slag and alkali slag, and mix them after crushing, grinding, removing impurities and drying.

[0043] (2) By weight, add 2-4 parts of pretreated steel slag, 1-3 parts of refining slag, and 2-3 parts of alkali slag to the liquid medium to form a suspension system;

[0044] (3) Sodium gluconate is added to the suspension system as a structure regulator, and the amount added is 0.05% to 0.30% of the mass of the calcium-magnesium-based multi-element alkali slag; the sodium gluconate complexes with Ca 2+ and Mg 2+ It regulates the nucleation and growth process of carbonate minerals, thereby promoting the dissolution and structural reconstruction of silicon components and improving the uniformity of the system reaction;

[0045] (4) Carbon dioxide gas is introduced into the suspension system and carbonization reaction is carried out under stirring conditions to obtain wet carbonized calcium-magnesium-based multi-element alkali slag slurry;

[0046] (5) The slurry after carbonization reaction is subjected to solid-liquid separation, and the resulting solid product is dried to obtain wet carbonized calcium-magnesium-based multi-element alkali slag.

[0047] Furthermore, the calcium-magnesium-based multi-element alkali slag, after being crushed and ground, has a particle size of no more than 150 μm.

[0048] Furthermore, the liquid medium is water or a weakly alkaline solution, and the solid-liquid mass ratio is 1:(5-15).

[0049] Further, the amount of sodium gluconate added is 0.08% to 0.15% of the mass of the calcium-magnesium-based multi-element alkali slag; more preferably, it is 0.1%.

[0050] Furthermore, the carbonization reaction temperature is 20–60°C, and the reaction time is 20–120 min.

[0051] Furthermore, the carbon dioxide is introduced via continuous bubbling or intermittent bubbling, with a gas flow rate of 0.1–1.0 L / min.

[0052] Furthermore, the pH value of the system during carbonization is 7–10.

[0053] Furthermore, the drying temperature is 60–105°C.

[0054] The present invention also provides the application of the multi-source solid waste heavy metal cementitious material with the above-mentioned multi-mechanism synergistic solidification characteristics, and uses the cementitious material as a structural material or functional filler material in road engineering, underground engineering and municipal engineering.

[0055] Furthermore, the cementitious material is used as a base or surface layer material in road engineering, an initial support material in underground engineering, a foundation pouring material for buildings, a slope protection material in municipal engineering, and a material for precast concrete components. It is suitable for engineering environments with high requirements for controlling heavy metal leaching, including ecological restoration projects, municipal infrastructure projects, and projects in environmentally sensitive areas.

[0056] The beneficial technical effects of this invention are as follows:

[0057] (1) Achieving multi-mechanism synergistic solidification and improving material mechanical properties, and achieving synergistic optimization of structural and environmental performance: This invention constructs a multi-mechanism synergistic solidification system of "gelation solidification-interlayer complexation-nano adsorption-iron-based reduction / precipitation-carbonate mineralization". In this system, gelation hydration products achieve structural encapsulation and solidification of heavy metals, nano-LDO hydration bond breaking and repolymerization achieve interlayer complexation, calcined nano-CSH and nano-MZT provide adsorption sites, composite iron-based materials promote the reduction and precipitation fixation of heavy metals, and wet carbonization calcium magnesium-based multi-element alkaline slag provides carbonate crystal nuclei and participates in mineralization reaction, thereby significantly improving the solidification efficiency and long-term stability of heavy metals.

[0058] (2) Introducing wet carbonization calcium-magnesium-based multi-element alkali slag to achieve synergistic effect of carbonization, mineralization and solidification: This invention uses wet carbonization calcium-magnesium-based multi-element alkali slag as a functional component, which contains calcium carbonate and related carbonate phases, and can participate in the reaction process as mineralization nuclei to promote the transformation of heavy metal ions into stable carbonate forms; at the same time, it realizes the resource utilization of carbon dioxide, and to a certain extent has the effect of carbon fixation, enhancing the green and low-carbon properties of the material.

[0059] (3) High-efficiency synergistic utilization of multi-source solid waste, reducing costs and improving resource utilization level: This invention uses red mud as the main raw material and synergistically utilizes industrial solid wastes such as fly ash and slag, as well as biomass wastes such as shell powder, to realize the high-value utilization of multi-source solid waste, significantly reduce the amount of cement used in cementitious materials, thereby reducing material costs and carbon emissions, and has good economic and environmental benefits. Attached Figure Description

[0060] Figure 1 is a process flow diagram for preparing multi-source solid waste heavy metal solidification cementitious materials. Detailed Implementation

[0061] To make the objectives and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0062] This invention provides a multi-source solid waste heavy metal cementitious material with multi-mechanism synergistic solidification characteristics, comprising 69-100 parts of cementitious matrix component, 5-10 parts of wet carbonization component, 3.8-9.5 parts of nano-solidification component, 0.5-1.5 parts of iron-based stabilizing component, 0.6-1.0 parts of reinforcing and regulating component, and 28-35 parts of mixing water.

[0063] In some embodiments of the present invention, the cementitious matrix component includes pretreated red mud, calcined shell powder, fly ash, slag, cement, and a composite alkali activator. By weight, it comprises: 35-45 parts pretreated red mud, 10-18 parts calcined shell powder, 8-14 parts fly ash, 6-10 parts S95 grade slag, 8-10 parts ordinary silicate cement, and 5.5-7.5 parts composite alkali activator.

[0064] In some embodiments of the present invention, the wet carbonization component includes wet carbonization calcium-magnesium-based multi-element alkaline slag. This is a carbonate composite product obtained by reacting carbon dioxide with calcium-magnesium-containing alkaline solid waste in a liquid phase system, mainly comprising calcium carbonate, hydrated calcium carbonate, and a carbonate gel phase.

[0065] In some embodiments of the present invention, the nano-cured component includes nano-LDO, nano-CSH seed crystals, and nano-MZT functional material. By weight, it comprises: 2-5 parts nano-LDO, 1-2.5 parts calcined nano-CSH seed crystals, and 0.8-2 parts nano-MZT.

[0066] In some embodiments of the present invention, the iron-based stabilizing component comprises zero-valent iron (ZVI) and iron salt modified materials. The mass ratio is (1-2):(2-5).

[0067] In some embodiments of the present invention, the reinforcing and regulating components include a fiber reinforcing agent and a water-reducing agent. By weight, it comprises: 0.4 to 0.6 parts of fiber reinforcing agent and 0.2 to 0.4 parts of polycarboxylate water-reducing agent.

[0068] In some embodiments of the present invention, the pretreated red mud is ball-milled and then passed through a 200-mesh sieve, with a particle size not exceeding 75 μm.

[0069] In some embodiments of the present invention, the composite alkaline activator includes one or more of water glass, sodium hydroxide, and alkaline activating salt.

[0070] This invention also provides a method for preparing multi-source solid waste heavy metal cementitious materials with the above-mentioned multi-mechanism synergistic solidification characteristics, comprising the following steps:

[0071] (1) Add pretreated red mud, calcined shell powder, fly ash, slag, cement, wet carbonized calcium magnesium-based multi-element alkali slag, nano LDO, calcined nano CSH seed crystals, nano MZT and iron-based stabilizing components into a mixer and mix for 2-5 minutes to obtain a uniform dry mixture;

[0072] (2) Mix the composite alkali activator, polycarboxylate superplasticizer and mixing water, and stir at room temperature for 1 to 3 minutes to obtain a liquid phase system;

[0073] (3) Add the liquid system obtained in step (2) to the dry mixture obtained in step (1), and mix and stir in a stirring device at a stirring rate of 80-180 r / min for 2-5 min;

[0074] (4) Add fiber reinforcing agent during the stirring process and continue stirring to disperse it evenly in the system and form a uniform slurry;

[0075] (5) The obtained slurry is cast into a mold and cured to obtain a multi-source solid waste heavy metal cementitious material.

[0076] In some embodiments of the present invention, the pretreated red mud is ball-milled and then passed through a 200-mesh sieve, with a particle size not greater than 75 μm; the particle sizes of the fly ash, slag and cement are each independently 0 to 250 μm, excluding 0 μm.

[0077] In some embodiments of the present invention, the composite alkali activator is prepared by mixing water glass and sodium hydroxide according to a set modulus and concentration, and then subjected to thorough stirring and aging.

[0078] In some embodiments of the present invention, the stirring in step (3) is carried out in a staged stirring method, first stirring at 80-120 r / min for 2-3 min, and then stirring at 120-180 r / min for 2-3 min.

[0079] In some embodiments of the present invention, the curing conditions in step (5) are a temperature of 20±2℃ and a relative humidity of ≥95%.

[0080] This invention also provides a method for preparing wet-process calcium-magnesium-based multi-element alkali slag, comprising the following steps:

[0081] 1) Steel slag, refining slag and alkali slag are crushed, ground, dried and mixed to obtain pretreated calcium-magnesium based multi-element alkali slag;

[0082] 2) By weight, add 2-4 parts of pretreated steel slag, 1-3 parts of refining slag, and 2-3 parts of alkali slag to the liquid medium to form a suspension system;

[0083] 3) Sodium gluconate is added to the suspension system as a structure regulator, and the amount added is 0.05% to 0.30% of the mass of the pretreated calcium-magnesium-based multi-element alkali slag;

[0084] 4) Carbon dioxide gas is introduced into the suspension system, and carbonization reaction is carried out under stirring conditions to obtain wet carbonized calcium-magnesium-based multi-element alkali slag slurry;

[0085] 5) The slurry after carbonization reaction is subjected to solid-liquid separation, and the resulting solid product is dried to obtain wet carbonized calcium-magnesium-based multi-element alkali slag.

[0086] In some embodiments of the present invention, the particle size of the calcium-magnesium based multi-element alkali slag in step 1) is not greater than 150 μm.

[0087] In some embodiments of the present invention, the liquid medium in step 2) is water or a weakly alkaline solution, and the solid-liquid mass ratio is 1:(5-15).

[0088] In some embodiments of the present invention, the amount of sodium gluconate added in step 3) is 0.08% to 0.15% of the mass of the calcium-magnesium-based polyalkali slag; more preferably, it is 0.1%.

[0089] In some embodiments of the present invention, the carbonization reaction temperature in step 4) is 20–60°C and the reaction time is 20–120 min.

[0090] In some embodiments of the present invention, the carbon dioxide is introduced by continuous bubbling or intermittent bubbling, the gas flow rate is 0.1 to 1.0 L / min, and the pH value of the system during carbonization is 7 to 10.

[0091] In some embodiments of the present invention, the drying temperature in step 5) is 60–105°C.

[0092] In some embodiments of the present invention, the wet-process calcium-magnesium-based multi-element alkali slag mainly comprises calcium carbonate, hydrated calcium carbonate and carbonate gel phase.

[0093] To better illustrate the technical solution of the present invention, further comparisons are made below with comparative examples and embodiments of the present invention. The experimental design is as follows:

[0094] Table 1 Mix proportions for Experiment 1

[0095]

[0096] in:

[0097] 1. The amount of mixing water used in each group can be slightly adjusted according to the actual fluidity, with a fluctuation range of ±1 part;

[0098] 2. All variable groups adopt the "single variable principle", only changing the amount of the target raw material, while the amounts of other raw materials remain the same as the base group;

[0099] 3. The experiment focuses on the synergistic effect among the four core raw materials on key properties of cementitious materials, such as strength and heavy metal stabilization effect;

[0100] Example 1-1

[0101] To further illustrate the effect of the multi-mechanism synergistic curing system in this invention, the components were weighed according to the mixing ratio shown in Table 1, Experiment 1-1, including 40 parts of pretreated red mud, 15 parts of calcined shell powder, 10 parts of fly ash, 8 parts of S95 slag, 9 parts of ordinary silicate cement, 6.5 parts of composite alkali activator, 7.5 parts of wet-process calcium-magnesium carbide-based multi-element alkali slag, 3.5 parts of nano-LDO, 1.5 parts of calcined nano-CSH seed crystals, 1.4 parts of nano-MZT, 1 part of composite iron-based material, 0.5 parts of fiber reinforcing agent, 0.3 parts of polycarboxylate superplasticizer, and 32 parts of water.

[0102] Its preparation method is as follows:

[0103] (1) Add pretreated red mud, calcined shell powder, fly ash, slag, cement, wet-process calcium magnesium-based multi-element alkali slag, nano LDO, calcined nano CSH seed crystals, nano MZT and composite iron-based materials into a mixer and dry mix for 2 to 5 minutes to obtain a uniform dry mix.

[0104] (2) Add the composite alkali activator and polycarboxylate superplasticizer to the mixing water and stir at room temperature for 1 to 3 minutes to obtain a liquid phase system;

[0105] (3) Add the liquid phase system to the dry mixture and stir for 2 to 5 minutes at 80 to 180 r / min. Add the fiber reinforcing agent during the stirring process and continue stirring to disperse it evenly and form a uniform slurry.

[0106] (4) The obtained slurry is cast into a mold and cured at a temperature of 20±2℃ and a relative humidity of ≥95% to obtain a multi-source solid waste heavy metal cementitious material;

[0107] The preparation method of the wet-process calcium-magnesium-based multi-element alkali slag in step (1) is as follows:

[0108] 1) Steel slag, refining slag and alkali slag are pretreated to remove impurities and then crushed, ground and dried in sequence. They are then mixed in a set ratio to obtain pretreated calcium-magnesium-based multi-element alkali slag.

[0109] Preferably, the particle size after crushing is no greater than 5 mm, and the particle size after ball milling is no greater than 150 μm, in order to improve the reactivity; the drying temperature is 60–105 °C.

[0110] 2) The pretreated calcium-magnesium-based multi-element alkali slag is added to a liquid medium to form a uniform suspension system;

[0111] Preferably, the liquid medium is water or a weakly alkaline solution, the solid-liquid mass ratio is 1:(5-15), and the mixture is stirred at room temperature for 5-15 minutes to fully disperse the solid particles.

[0112] More preferably, sodium gluconate is added to the suspension system as a structure modifier, and the amount added is 0.10% of the mass of the pretreated calcium-magnesium-based multi-element alkali slag. The sodium gluconate complexes with Ca... 2+ and Mg 2+ It regulates the nucleation and growth process of carbonate minerals, thereby promoting the dissolution and structural reconstruction of silicon components and improving the uniformity of the system reaction.

[0113] 3) Carbon dioxide gas is introduced into the suspension system, and carbonization reaction is carried out under continuous stirring to obtain wet carbonized calcium-magnesium-based multi-element alkali slag slurry.

[0114] Preferably:

[0115] The carbonization reaction temperature is 20–60℃;

[0116] The stirring speed is 200–500 r / min;

[0117] Carbon dioxide can be introduced via continuous bubbling or intermittent bubbling.

[0118] The gas flow rate is 0.1–1.0 L / min;

[0119] The reaction time is 20–120 min;

[0120] The pH of the system is controlled at 7–10 during the reaction to promote the formation of carbonate minerals and inhibit excessive acidification.

[0121] More preferably, the reaction progress can be judged by online monitoring of pH or conductivity changes during carbonization, and the aeration can be stopped when the pH tends to stabilize.

[0122] 4) The slurry after carbonization reaction is subjected to solid-liquid separation, and the resulting solid product is dried to obtain wet carbonization calcium-magnesium-based multi-element alkali slag.

[0123] Preferably, the solid-liquid separation method is filtration or centrifugation; the drying temperature is 60–105°C, and the drying time is 6–24 h.

[0124] Furthermore, the resulting wet-process calcium-magnesium-based multi-element alkali slag is mainly composed of calcium carbonate, hydrated calcium carbonate and carbonate gel phase, which can serve as carbonate crystal nuclei to participate in subsequent gelation reactions and heavy metal mineralization and fixation processes.

[0125] Examples 1-2 to 1-15

[0126] Based on Example 1-1, a multi-factor combination control method was adopted to investigate the synergistic effect among four core raw materials: wet carbonization component, nano LDO, calcined nano CSH seed crystals and nano MZT. Combination design was carried out for these materials. The types, ratios and preparation methods of the remaining raw materials were the same as those in Example 1-1. The specific ratios are shown in Table 1.

[0127] Each embodiment constructs the following typical systems through combinations of different functional components:

[0128] Single-mechanism missing system (e.g., 1-2, 1-3, 1-4, 1-5): removal of a certain nano or carbonized component;

[0129] Dual-mechanism coupling systems (such as 1-6, 1-7, 1-8, 1-9, 1-10, 1-11): retain two functional components;

[0130] Single-mechanism systems (such as 1-12, 1-13, 1-14, 1-15): retain only one functional component.

[0131] The samples obtained in Examples 1-1 to 1-15 were subjected to compressive strength and heavy metal leaching tests in accordance with the "Specifications for Design of Asphalt Pavement of Highway" (JTG D50-2017) and the "Standard for Identification of Hazardous Waste" (GB 5085.3-2007). The results are shown in Table 2.

[0132] Table 2 Mechanical properties and heavy metal leaching results of different Examples 1

[0133]

[0134] As shown in Table 2, Examples 1-1 simultaneously contain four key functional components: wet carbonization components, nano-LDO, calcined nano-CSH seeds, and nano-MZT. These components work together to construct a complete multi-mechanism synergistic curing system. Its 28-day compressive strength reaches 26.8 MPa, and the Pb and Cr leaching concentrations are 0.12 mg / L and 0.08 mg / L, respectively, exhibiting optimal mechanical properties and heavy metal curing effect. This indicates that the multi-mechanism synergistic effect can significantly promote the densification of the material's internal structure and improve the stabilization ability of heavy metals.

[0135] Secondly, Examples 1-2 to 1-5 each lacked a key functional component (nano-MZT, nano-CSH seed crystals, nano-LDO, or wet carbonization component), meaning that while one functional component was removed from the complete system, all three functional components still participated in the process. The 28-day compressive strength of this type of system was 24.7–25.1 MPa, with overall performance only slightly lower than the complete synergistic system; simultaneously, its heavy metal leaching concentration was slightly increased, but still significantly better than the subsequent systems. This indicates that even with most key components remaining, the system can still form a relatively complete structural network and a multi-path curing mechanism.

[0136] Next, Examples 1-6 to 1-11 retained two functional components, forming a dual-mechanism synergistic system. The 28-day compressive strength of this type of system decreased to 22.9–23.4 MPa, significantly lower than the first two systems in Examples 1-1 to 1-5; simultaneously, the leaching concentrations of heavy metals such as Pb and Cr further increased. This indicates that although a certain synergistic effect still exists in this system, the reduced number of functional components involved in the reaction results in a significant deficiency in the effective curing pathway and structural building capacity, leading to a decline in overall performance.

[0137] Finally, Examples 1-12 to 1-15 retained only one functional component, and the system mainly relied on the basic gelation reaction or a single curing mechanism. The 28-day compressive strength of these systems further decreased to 20.3–22.6 MPa, and the leaching concentration of heavy metals increased significantly. In Examples 1-15, Pb and Cr reached 0.30 mg / L and 0.24 mg / L, respectively, exhibiting the worst overall performance. This indicates that a single curing mechanism is difficult to form a stable and dense structure, has limited ability to fix heavy metals, and is prone to migration and release.

[0138] Comprehensive analysis revealed some fluctuations in the experimental results, which may be related to differences in the microstructure of the raw materials and uneven reaction, but the overall trend remained consistent. As the number of functional components decreased, the mechanical properties and heavy metal curing ability of the material generally declined.

[0139] This invention introduces multiple functional components, including wet carbonization components, nano-LDO, calcined nano-CSH seeds, and nano-MZT, to play roles in structure building, ion immobilization, and mineralization precipitation within the system. Research indicates that material properties depend not only on the type of curing mechanism but also on the number of functional components participating in the reaction.

[0140] When the number of functional components involved in the process decreases, the effective reaction pathways in the system decrease accordingly, thereby weakening the structural building capacity and the ability to fix heavy metals. By constructing a multi-mechanism synergistic curing system, the functional components promote and synergistically interact with each other, thereby achieving a simultaneous improvement in the material's mechanical properties and the heavy metal stabilization effect.

[0141] Table 3 Mix proportions for Experiment 2

[0142]

[0143] in:

[0144] 1. The amount of mixing water used in each group can be slightly adjusted according to the actual fluidity, with a fluctuation range of ±1 part;

[0145] 2. All variable groups adopt the "single variable principle", only changing the amount of the target raw material, while the amounts of other raw materials remain the same as the base group;

[0146] 3. The experiment focuses on the effects of different dosages of four core raw materials on key properties of cementitious materials, such as strength and heavy metal stabilization effect;

[0147] Example 2-1

[0148] To further illustrate the technical solution of this invention, the components were weighed according to the basic mix proportions shown in Table 3, including 40 parts of pretreated red mud, 15 parts of calcined shell powder, 10 parts of fly ash, 8 parts of S95 slag, 9 parts of ordinary silicate cement, 6.5 parts of composite alkali activator, 7.5 parts of wet-process calcium-magnesium-based multi-element alkali slag, 3.5 parts of nano-LDO, 1.5 parts of calcined nano-CSH seed crystals, 1.4 parts of nano-MZT, 1 part of composite iron-based material, 0.5 parts of fiber reinforcing agent, 0.3 parts of polycarboxylate superplasticizer, and 32 parts of water. The specific method is as follows:

[0149] (1) Add pretreated red mud, calcined shell powder, fly ash, slag, cement, wet-process calcium magnesium-based multi-element alkali slag, nano LDO, calcined nano CSH seed crystals, nano MZT and composite iron-based materials into a mixer and dry mix for 2 to 5 minutes to obtain a uniform dry mix.

[0150] (2) Add the composite alkali activator and polycarboxylate superplasticizer to the mixing water and stir at room temperature for 1 to 3 minutes to obtain a liquid phase system;

[0151] (3) Add the liquid phase system to the dry mixture and stir for 2 to 5 minutes at 80 to 180 r / min. Add the fiber reinforcing agent during the stirring process and continue stirring to disperse it evenly and form a uniform slurry.

[0152] (4) The obtained slurry is cast into a mold and cured at a temperature of 20±2℃ and a relative humidity of ≥95% to obtain a multi-source solid waste heavy metal cementitious material.

[0153] Examples 2-2 to 2-10

[0154] Based on Example 2-1, the dosage of the key component was adjusted using the single variable principle. The types, ratios, and preparation methods of the remaining raw materials were the same as in Example 2-1, as detailed below:

[0155] Example 2-2: The amount of wet carbonization calcium-magnesium-based multi-element alkali slag used is 5 parts;

[0156] Examples 2-3: The amount of wet carbonization calcium-magnesium-based multi-element alkali slag used is 10 parts;

[0157] Examples 2-4: The amount of nano-LDO used was 2 parts;

[0158] Examples 2-5: The amount of nano-LDO used is 5 parts;

[0159] Examples 2-6: The amount of calcined nano-CSH seed crystals used was 1 part;

[0160] Examples 2-7: The amount of calcined nano-CSH seed crystals used was 2.5 parts;

[0161] Examples 2-8: The amount of nano-MZT used was 0.8 parts;

[0162] Examples 2-9: The amount of nano-MZT used was 2 parts;

[0163] Examples 2-10: No wet carbonization components or nano-curing components were added.

[0164] The samples obtained in Examples 2-1 to 2-10 were subjected to compressive strength and heavy metal leaching tests in accordance with the "Specifications for Design of Asphalt Pavement of Highway" (JTG D50-2017) and the "Standard for Identification of Hazardous Waste" (GB 5085.3-2007). The results are shown in Table 4.

[0165] Table 4 Mechanical properties and heavy metal leaching results of different embodiments

[0166]

[0167] As shown in Table 4, in the basic system constructed in Example 2-1, the mechanical properties and heavy metal curing effect of the material can be significantly affected by controlling the key functional components such as wet carbonization components, nano-LDO, nano-CSH seeds, and nano-MZT. Overall, Example 2-1 exhibits good comprehensive performance, while Examples 2-2 to 2-10 further verify the role of each functional component in the multi-mechanism synergistic curing system.

[0168] Among them, Examples 2-5 and 2-7 showed the highest 28-day compressive strength, reaching 30.5 MPa and 31.2 MPa respectively. This indicates that appropriately increasing the content of nano-LDO and nano-CSH seed crystals helps to promote the hydration reaction and optimize the microstructure, thereby significantly improving the mechanical properties of the material.

[0169] Regarding heavy metal solidification, compared with the blank control group (Examples 2-10), the leaching concentrations of heavy metals such as Pb, Cr, and Cd in each example were significantly reduced. Among them, Examples 2-7 showed the lowest heavy metal leaching concentrations, with Pb and Cr decreasing to 0.08 mg / L and 0.04 mg / L, respectively, indicating that nanocrystals and the synergistic effect of multiple mechanisms have a significant promoting effect on heavy metal solidification.

[0170] Further analysis revealed that the wet carbonization component promoted heavy metal mineralization and precipitation by providing carbonate nuclei; nano-LDO achieved interlayer complexation and ion fixation through structural memory effect; nano-CSH seeds accelerated hydration and formed a dense structure; nano-MZT enhanced the adsorption capacity for heavy metals through ion exchange; and iron-based materials further stabilized the heavy metal speciation through reduction and precipitation. The synergistic effect of these components constructed a multi-mechanism solidification system encompassing "gelation solidification—carbonate mineralization—nano-adsorption—interlayer complexation—iron-based reduction."

[0171] In summary, this invention achieves efficient and stable solidification of heavy metals by improving the mechanical properties of materials through multi-mechanism synergistic regulation, and has good prospects for engineering applications.

[0172] The foregoing has shown and described the basic principles and main features of the present invention, as well as its advantages. 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 illustrative of the principles of 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 this invention is defined by the appended claims and their equivalents.

Claims

1. A multi-source solid waste heavy metal cementitious material with multi-mechanism synergistic solidification characteristics, characterized in that, The multi-source solid waste heavy metal cementitious material comprises, by weight, 69-100 parts of cementitious matrix component, 5-10 parts of wet carbonization component, 3.8-9.5 parts of nano-curing component, 0.5-1.5 parts of iron-based stabilizing component, 0.6-1.0 parts of reinforcing and regulating component, and 28-35 parts of mixing water.

2. The multi-source solid waste heavy metal cementitious material with multi-mechanism synergistic solidification characteristics according to claim 1, characterized in that, The cementitious matrix components, by weight, include: 35-45 parts of pretreated red mud, 10-18 parts of calcined shell powder, 8-14 parts of fly ash, 6-10 parts of S95 grade slag, 8-10 parts of ordinary Portland cement, and 5.5-7.5 parts of composite alkali activator.

3. The multi-source solid waste heavy metal cementitious material with multi-mechanism synergistic solidification characteristics according to claim 1, characterized in that, The wet carbonization component is a wet carbonized calcium-magnesium-based multi-element alkali slag, and its preparation method is as follows: The calcium-magnesium-based multi-element alkali slag is pretreated by crushing, grinding, removing impurities, and drying, and then mixed for later use; the calcium-magnesium-based multi-element alkali slag includes steel slag, refining slag, and alkali slag. By weight, 2-4 parts of the pretreated steel slag, 1-3 parts of the refining slag, and 2-3 parts of the alkali slag are added to a liquid medium to form a suspension system; sodium gluconate is added to the suspension system as a structure regulator, and its addition amount is 0.05%-0.30% of the total mass of the calcium-magnesium-based multi-element alkali slag; carbon dioxide gas is introduced into the suspension system, and a carbonization reaction is carried out under stirring conditions to obtain a wet carbonized calcium-magnesium-based multi-element alkali slurry; then the slurry is subjected to solid-liquid separation, and the obtained solid product is dried to obtain the wet carbonized calcium-magnesium-based multi-element alkali slag.

4. The multi-source solid waste heavy metal cementitious material with multi-mechanism synergistic solidification characteristics according to claim 3, characterized in that: The calcium-magnesium based multi-element alkaline slag is crushed and ground to a particle size of no more than 150 μm; the liquid medium is water or a weakly alkaline solution with a solid-liquid mass ratio of 1:(5-15); the carbonization reaction temperature is 20-60℃ and the reaction time is 20-120 min; the carbon dioxide is introduced by continuous or intermittent bubbling with a gas flow rate of 0.1-1.0 L / min; the pH value of the system is controlled at 7-10 during the carbonization process.

5. The multi-source solid waste heavy metal cementitious material with multi-mechanism synergistic solidification characteristics according to claim 1, characterized in that, The nano-cured components, by weight, include: 2-5 parts of nano-LDO, 1-2.5 parts of calcined nano-CSH seed crystals, and 0.8-2 parts of nano-MZT functional materials.

6. The multi-source solid waste heavy metal cementitious material with multi-mechanism synergistic solidification characteristics according to claim 1, characterized in that, The iron-based stabilizing component includes ZVI and iron salt modified materials; the mass ratio of ZVI to iron salt modified materials is (1-2):(2-5).

7. The multi-source solid waste heavy metal cementitious material with multi-mechanism synergistic solidification characteristics according to claim 1, characterized in that, The reinforcing and regulating components include, by weight, 0.4 to 0.6 parts of fiber reinforcing agent and 0.2 to 0.4 parts of polycarboxylate superplasticizer.

8. The multi-source solid waste heavy metal cementitious material with multi-mechanism synergistic solidification characteristics according to claim 1, characterized in that, The composite alkaline activator includes one or more of water glass, sodium hydroxide, and alkaline activating salts.

9. The preparation method of the multi-source solid waste heavy metal cementitious material with multi-mechanism synergistic solidification characteristics according to any one of claims 1-8, characterized in that... Includes the following steps: (1) The pretreated red mud, calcined shell powder, fly ash, slag, cement, wet carbonized calcium magnesium-based multi-element alkali slag, nano LDO, calcined nano CSH seed crystals, nano MZT and iron-based stabilizing components are put into a mixing device and mixed to obtain a dry mixture. (2) The composite alkali activator, polycarboxylate superplasticizer and mixing water are mixed to obtain a liquid phase system; (3) Add the liquid phase system to the dry mixture, add the fiber reinforcing agent under stirring conditions, and continue stirring and mixing to form a uniform slurry; (4) The obtained slurry is cast into a mold and cured to obtain a multi-source solid waste heavy metal cementitious material.

10. The method for preparing multi-source solid waste heavy metal cementitious material with multi-mechanism synergistic solidification characteristics according to claim 9, characterized in that, In step (1), the pretreated red mud is ball-milled and then passed through a 200-mesh sieve with a particle size not greater than 75 μm; the particle size of the fly ash, slag and cement is 0 to 250 μm, excluding 0 μm.

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