A fine aggregate concrete for iron tailings enhanced by magneto-thermal-chemical multi-field coupling and its preparation method

Abstract

This invention discloses a fine-aggregate concrete for iron tailings based on magneto-thermal-chemical multi-field coupling enhancement and its preparation method, belonging to the field of iron tailings fine-aggregate concrete preparation technology. This invention generates nano-Fe3O4 reinforcing particles in situ on the surface and inside the pores of iron tailings particles, which synergistically construct a magnetothermal response enhancement layer with the original iron-bearing minerals in the iron tailings, significantly amplifying the natural weak magnetic response and microwave thermal response capabilities of iron tailings. Under the action of an alternating magnetic field, stronger magnetic response disturbance behavior is generated, promoting microscale rearrangement of particles and optimization of slurry rheology. In a microwave field, the magnetothermal response enhancement layer preferentially absorbs electromagnetic energy and converts it into heat energy, achieving selective heating of the interface region, improving local hydration efficiency and interface density. In the concrete preparation process, this invention utilizes alternating magnetic field-mechanical vibration synergistic molding and microwave curing technology to achieve ultra-dense aggregate packing, improve the interface transition zone, and enhance the mechanical properties and durability of iron tailings concrete.

Description

Technical Field

[0001] This invention relates to the field of iron tailings fine aggregate concrete preparation technology, and particularly to a method for preparing iron tailings fine aggregate concrete based on magnetic-thermal-chemical multi-field coupling enhancement. Background Technology

[0002] With the rapid development of global industrialization, the demand for steel has continued to grow, leading to the accumulation of large amounts of solid waste—iron tailings—generated during iron ore beneficiation. Statistics show that by the end of 2025, China's accumulated tailings stockpile exceeded 20 billion tons, while its comprehensive utilization rate is generally less than 20%, and in some years even as low as 7%. Large-scale stockpiling has caused significant problems such as land occupation, ecological pollution, and safety risks to tailings ponds. The large-scale resource utilization of iron tailings has become an important research direction in the field of solid waste building materials.

[0003] Iron tailings typically contain residual magnetite, hematite, and other iron-bearing minerals, exhibiting certain natural weak magnetism and limited electromagnetic and thermal response characteristics. Currently, iron tailings are mainly used in concrete as inert fine aggregates to replace natural river sand, with their application primarily relying on simple physical substitution and failing to fully utilize their inherent magnetic and thermal response potential. Furthermore, due to the low surface activity, complex mineral composition, and poor interfacial affinity of iron tailings particles, the interfacial transition zone (ITZ) formed between them and cement paste often suffers from high porosity, low bond strength, and a loose interfacial structure, severely restricting the mechanical properties and durability of iron tailings concrete.

[0004] Current concrete forming processes primarily rely on mechanical vibration to achieve particle compaction, which cannot effectively stimulate the natural weak magnetic response behavior of iron tailings particles, making it difficult to achieve microscale directional rearrangement of particles. Traditional steam curing and external heating methods generally suffer from low heat transfer efficiency from the outside to the inside and large temperature gradients, easily inducing internal thermal stress concentration and microcracks. While conventional microwave curing has the advantage of internal heating, its precise temperature control mechanism for the selective response of functional iron tailings particles can easily lead to localized overheating, rapid moisture vaporization, and even specimen cracking.

[0005] Therefore, there is an urgent need to develop a new technology for preparing iron tailings concrete that can synergistically activate the natural weak magnetic-thermal response characteristics of iron tailings and simultaneously improve the particle compaction, interfacial structural stability, and internal temperature uniformity. Summary of the Invention

[0006] To address the problems in existing iron tailings concrete, such as the ineffective utilization of the natural weak magnetic properties and limited electromagnetic thermal response of fine aggregates, low particle surface activity, poor compatibility with cement paste, resulting in a loose and porous interfacial transition zone and low bond strength, this invention provides iron tailings fine aggregate concrete enhanced by magnetic-thermal-chemical multi-field coupling and its preparation method. Specifically, this is achieved through the following technologies.

[0007] This invention provides a fine aggregate concrete for iron tailings based on magnetic-thermal-chemical multi-field coupling enhancement. The raw materials include, by mass parts: 320-360 parts cement, 700-820 parts composite fine aggregate for iron tailings, 950-1050 parts coarse aggregate, 80-120 parts mineral admixture, 4-6 parts water-reducing agent, and 150-170 parts water.

[0008] The preparation method of the composite iron tailings fine aggregate is as follows:

[0009] The fine aggregate of iron tailings is mixed with alkaline solution and ball-milled to obtain a mixture.

[0010] The mixture is added to a mixing precursor solution and impregnated in a vacuum environment to obtain a synergistic mineralization precursor system; the mixing precursor solution includes Fe. 3+ and Fe 2+ ;

[0011] The synergistic mineralization precursor system is heated and stirred, a protective gas is introduced or an antioxidant is added, and the pH value is adjusted to be alkaline; microwave heating treatment and interfacial coupling treatment are performed sequentially, followed by filtration and drying to obtain the composite iron tailings fine aggregate.

[0012] The iron tailings fine aggregate concrete and its preparation method provided by the present invention utilize the natural weak magnetic response and microwave heat absorption characteristics of the residual iron-containing minerals in the iron tailings to construct a nano-Fe3O4 reinforcing layer in situ on its surface and inside the pores, and combine it with the interface coupling synergistic layer to form a magnetic-thermal synergistic response composite interface structure, thereby amplifying and strengthening the natural magnetic-thermal response capability of the iron tailings.

[0013] Furthermore, the mass ratio of the fine aggregate of the iron tailings to the pure solid alkali in the alkaline solution is 100:(1-2).

[0014] Furthermore, the mass ratio of the mixture to the mixing precursor liquid is 1:(1.5-3).

[0015] Furthermore, in the mixed precursor solution, Fe 3+ and Fe 2+ The molar ratio is 1:(0.5-1).

[0016] Furthermore, Fe 3+Provided by at least one of ferric chloride, ferric sulfate, and ferric nitrate solution, Fe 2+ It consists of at least one of ferrous chloride, ferrous sulfate, and ferrous nitrate solutions.

[0017] Furthermore, the conditions for heating and stirring the synergistic mineralization precursor system are 60-70℃ and 300-600r / min.

[0018] Furthermore, the microwave heating treatment method is as follows: microwave frequency 2.45GHz, microwave power 300-600 W, and reaction at 80-90℃ for 30-60 min.

[0019] Furthermore, the method for the interface coupling treatment is as follows: add 0.5-1% of the mass of the iron tailings fine aggregate as a silane coupling agent and stir for 15-20 minutes.

[0020] Furthermore, the particle size composition of the composite iron tailings fine aggregate is as follows: 0-0.075 mm: 150-180 parts; 0.075-0.15 mm: 45-55 parts; 0.15-0.30 mm: 55-70 parts; 0.30-0.60 mm: 75-90 parts; 0.60-1.18 mm: 95-105 parts; 1.18-2.36 mm: 120-140 parts; 2.36-4.75 mm: 160-180 parts.

[0021] Furthermore, the mineral admixture is slag powder and / or fly ash; the coarse aggregate is limestone crushed stone, granite crushed stone, basalt crushed stone, diabase crushed stone, quartzite crushed stone, or gravel.

[0022] This invention also provides a method for preparing the above-mentioned iron tailings fine aggregate concrete, comprising the following steps:

[0023] The raw materials for the iron tailings fine aggregate concrete are mixed to form a mixture; the mixture is then molded under alternating magnetic field and mechanical vibration conditions.

[0024] Pre-curing to the initial setting stage, microwave heating curing, cooling and demolding followed by standard curing, yields the iron tailings fine aggregate concrete.

[0025] In the above-mentioned method for preparing iron tailings fine aggregate concrete provided by the present invention, the super-dense packing of aggregates is achieved by using alternating magnetic field-mechanical vibration synergistic molding and internal feedback microwave curing technology, which improves the interface transition zone and significantly enhances the mechanical properties and durability of iron tailings concrete.

[0026] Compared with the prior art, the advantages of the present invention are:

[0027] 1. This invention fully activates and enhances the natural magnetic-thermal response potential of iron tailings, realizing the transformation of iron tailings fine aggregates from inert filler materials to functional responsive materials.

[0028] Iron tailings contain residual weakly magnetic iron-bearing minerals, exhibiting a naturally low-level magnetic response and limited microwave thermal absorption capacity. This invention significantly amplifies the natural weak magnetic and microwave thermal response capabilities of iron tailings by in-situ generating nano-Fe3O4 reinforcing particles on the surface and within the pores of the iron tailings particles. These particles synergistically form a magnetocaloric response enhancement layer with the original iron-bearing minerals in the iron tailings.

[0029] Under the influence of an alternating magnetic field, the reinforced iron tailings fine aggregate exhibits stronger magnetic response disturbance behavior, promoting microscale particle rearrangement and slurry rheological optimization. In a microwave field, the reinforcing layer preferentially absorbs electromagnetic energy and converts it into heat energy, achieving selective heating of the interface region and improving local hydration efficiency and interface density.

[0030] 2. This invention abandons simple physical filling and constructs an active modified layer on the surface of iron tailings fine aggregates through in-situ mineralization and coupling agent modification technology, which greatly improves the interfacial stability and synergistic enhancement effect of iron tailings fine aggregates.

[0031] One end of the silane coupling agent dehydrates and condenses with the hydroxyl groups on the surface of the aggregate, while the other end's organic functional group extends into the cement paste. Through physical anchoring and improved interfacial wettability, a stable organic-inorganic transition layer is established between the inorganic aggregate and the cement paste, significantly improving the interfacial bond strength.

[0032] The surface-loaded nano-Fe3O4 reinforcing particles have excellent microwave absorption characteristics, and become a high-density "micro heat source" during microwave curing. They preferentially heat the aggregate interface, promote the rapid generation and densification of cement hydration products (CSH gel) at the interface, and eliminate the defect that the interface is often a weak area in traditional processes.

[0033] 3. The alternating magnetic-vibration co-forming method provided by this invention utilizes the alternating magnetic field torque generated by industrial frequency alternating current to induce "in-situ high-frequency micro-shearing" motion in weakly magnetic iron tailings particles in a suspended state. Compared to simple mechanical vibration, this motion can more effectively break the water film covering the aggregate surface, expel micro-bubbles, and achieve ultra-dense packing of iron tailings aggregate.

[0034] 4. The internal feedback temperature control microwave curing process adopted in this invention achieves precise monitoring of the core temperature through pre-embedded fiber optic probes. Combined with an intermittent heating strategy, it effectively balances the contradiction between the rapid heating of iron tailings and the lag in heat conduction of cement paste. This not only eliminates cracks caused by temperature gradients but also avoids the risk of explosion caused by thermal runaway, providing a safe and feasible technical path for the rapid high-strength concrete of iron tailings. Detailed Implementation

[0035] The technical solution of the present invention will be clearly and completely described below. 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] In some embodiments of the present invention, the raw materials of the iron tailings fine aggregate concrete based on magnetic-thermal-chemical multi-field coupling enhancement include, by mass parts: 320-360 parts of cement, 700-820 parts of composite iron tailings fine aggregate, 950-1050 parts of coarse aggregate, 80-120 parts of mineral admixture, 4-6 parts of water-reducing agent, and 150-170 parts of water.

[0037] Optionally, the preparation method of composite iron tailings fine aggregate is as follows:

[0038] (1) Pre-activation of particle surface: Mix the fine aggregate of iron tailings with alkaline solution (e.g., NaOH solution with a mass concentration of 2%-5%), put it into a ball mill for low-speed (150-250 r / min) wet ball milling treatment for 20-30 min to obtain the mixture.

[0039] Through the aforementioned synergistic effect of mechanochemical processes, the inert layer on the particle surface is removed, the particle surface structure is roughened, the active sites of natural iron-bearing minerals in the iron tailings particles are exposed, and active hydroxyl sites are introduced on the surface, providing a nucleation basis for subsequent magnetic mineralization.

[0040] Optionally, the mass ratio of iron tailings fine aggregate to alkali solution on a dry basis is 100:(1-2).

[0041] (2) Magnetic precursor infiltration and impregnation: The mixture is added to the mixed precursor solution and impregnated in a vacuum environment for 30-40 min to obtain a synergistic mineralization precursor system; the mixed precursor solution includes Fe 3+ and Fe 2+ .

[0042] Optionally, the mass ratio of the mixture to the precursor liquid is 1:(1.5-3).

[0043] Optionally, Fe 3+ and Fe 2+ The molar ratio is 1:(0.5-1).

[0044] Optionally, Fe 3+ Provided by at least one of ferric chloride, ferric sulfate, and ferric nitrate solution, Fe 2+ It consists of at least one of ferrous chloride, ferrous sulfate, and ferrous nitrate solutions.

[0045] Specifically, the preparation method of the mixed precursor solution is as follows:

[0046] (1) Solvent deoxygenation and acid pretreatment: Take an appropriate amount of deionized water and continuously pass high-purity nitrogen gas into it for 10-15 minutes to deoxygenate the liquid.

[0047] Subsequently, a non-oxidizing homologous dilute acid with a concentration of 1 mol / L (if using a ferric chloride / ferrous chloride system, add dilute hydrochloric acid; if using a ferric sulfate / ferrous sulfate system, add dilute sulfuric acid) was added dropwise to the deoxygenated deionized water to adjust the pH of the solvent to 1.0-2.0, thus obtaining a strongly acidic deoxygenating solvent.

[0048] The strongly acidic environment constructed here serves a dual purpose: firstly, to completely inhibit the hydrolysis of Fe³⁺ during the subsequent solution preparation process; and secondly, to neutralize any residual strong alkali that may be carried on the surface of the fine aggregate from the iron tailings in the preceding pre-activation step, thus preventing premature precipitation of iron ions on the surface before they penetrate into the aggregate pores.

[0049] (2) Weighing and dissolving: Pre-set the target preparation volume of the precursor solution and control the total iron ion concentration within the range of 0.1-0.5 mol / L.

[0050] Based on the above parameters, combined with Fe 3+ and Fe 2+ The molar ratio is 1:(0.5-1). Accurately calculate and weigh the corresponding ferric and ferrous salt crystals. Quickly add the weighed crystals to the prepared strong acid deoxygenating solvent.

[0051] (3) Sealed mixing: Under normal temperature and with nitrogen continuously introduced to form a sealed protective gas mass, turn on the non-metallic mechanical stirrer or magnetic stirrer and stir continuously at a speed of 300-500 r / min for 10-20 min until the metal salt solid is completely dissolved to obtain a uniform and clear mixed precursor liquid, which is then sealed for later use.

[0052] The above treatment enables iron ions to fully penetrate into the microcracks and pores on the particle surface, and form a synergistic mineralization precursor system with the residual iron-bearing minerals in the iron tailings.

[0053] (3) In-situ magnetic mineralization to construct an enhanced response layer: The synergistic mineralization precursor system (solid-liquid mixture after impregnation with mixed precursor liquid) is heated to 60-70℃, and a protective gas (e.g., inert gas or nitrogen) is introduced under mechanical stirring (stirring speed 300-600 r / min) or an antioxidant (e.g., at least one of ascorbic acid, sodium sulfite or hydrazine hydrate) is added. NaOH solution (concentration 1.0-3.0 mol / L) is slowly added to adjust the pH value to alkaline (e.g., pH value = 10-11).

[0054] Then, stirring was stopped, and microwave heating and interfacial coupling treatments were performed sequentially.

[0055] Optionally, the microwave heating treatment conditions are: microwave frequency 2.45 GHz, microwave power 300-600 W, and reaction at 80-90℃ for 30-60 min.

[0056] Optionally, the interface coupling treatment method is as follows: keep the slurry stirring, add 0.5-1% of the mass of ordinary iron tailings fine aggregate as silane coupling agent, and stir for 15-20 min.

[0057] Nano-Fe3O4 particles, generated in situ on the surface and within the pores of fine aggregates in iron tailings, synergistically construct a continuous magneto-thermal response enhancement layer with the original weakly magnetic iron-bearing minerals in the iron tailings. This amplifies and strengthens the natural weak magnetic response and microwave heat absorption capacity of the iron tailings. Microwave-assisted heating is used to promote uniform nucleation and growth of crystal nuclei and dense deposition at the interface, improving the uniformity and bonding stability of the mineralization layer.

[0058] After interfacial coupling treatment, the coupling agent undergoes a condensation reaction with the hydroxyl groups on the surface of the mineralized layer, and a stable organic-inorganic coupling synergistic layer is constructed outside the magneto-thermal response enhancement layer. The synergistic layer is used to enhance the bonding stability between nano Fe3O4 particles and iron tailings substrate, while improving its interfacial wettability with cement slurry and the continuity of interfacial heat transfer.

[0059] (4) Solidification and shaping to form magnetic-thermal synergistic response composite iron tailings fine aggregate: The product after interface coupling treatment is filtered, and the resulting filter cake is not washed with water. It is directly placed in an oven at 105-110℃ to dry and solidify for 2-3 hours to obtain the composite iron tailings fine aggregate.

[0060] Optionally, the raw material used in this invention is composite iron tailings fine aggregate, and its gradation adopts artificial full gradation. Based on previous experiments, the preferred particle size composition is as follows: 0-0.075 mm: 150-180 parts; 0.075-0.15 mm: 45-55 parts; 0.15-0.30 mm: 55-70 parts; 0.30-0.60 mm: 75-90 parts; 0.60-1.18 mm: 95-105 parts; 1.18-2.36 mm: 120-140 parts; 2.36-4.75 mm: 160-180 parts.

[0061] Optionally, the mineral admixture is slag powder and / or fly ash.

[0062] Optionally, the coarse aggregate may be limestone crushed stone, granite crushed stone, basalt crushed stone, diabase crushed stone, quartzite crushed stone, or gravel. Among them, 570-630 parts are of particle size of 5-10 mm, and 380-420 parts are of particle size of 10-15 mm.

[0063] The method for preparing iron tailings fine aggregate concrete provided by the present invention includes the following steps:

[0064] The raw materials for the iron tailings fine aggregate concrete are mixed to form a mixture; the mixture is then molded under alternating magnetic field and mechanical vibration conditions.

[0065] Pre-curing to the initial setting stage, microwave heating curing, cooling and demolding followed by standard curing, yields the iron tailings fine aggregate concrete.

[0066] Under the action of an alternating magnetic field, the magnetic-thermal response enhancement layer on the surface of the composite iron tailings fine aggregate undergoes magnetic response micro-perturbation behavior, which promotes the micro-scale directional rearrangement of particles and the local redistribution of slurry. At the same time, mechanical vibration destroys macro-agglomeration, achieving multi-scale synergistic dense packing of particles.

[0067] In the above concrete preparation method, the molding device selected is a molding device based on alternating magnetic-vibration synergistic enhancement. This device includes a non-magnetic molding mold, an electromagnetic excitation subsystem, and a mechanical vibration subsystem.

[0068] Optionally, the non-magnetic molding die is made of polypropylene (PP) or polyvinyl chloride (PVC) or other low-permeability non-magnetic materials with a relative permeability μ. r ≈ 1, to avoid electromagnetic shielding effect and eddy current loss.

[0069] Optionally, the electromagnetic excitation subsystem includes a hollow solenoid frame surrounding the mold, an excitation coil wound around the frame, and an adjustable AC excitation power supply. The AC excitation power supply outputs a low-frequency alternating current with a frequency control range of 50-100 Hz, generating a vertically oriented alternating magnetic field inside the mold. The magnetic induction intensity is controlled within a range sufficient to drive the iron tailings functional fine aggregate to produce a slight magnetic response disturbance, specifically selectable as 60-120 mT.

[0070] Optionally, the mechanical vibration subsystem is a concrete magnetic vibration table with a vibration frequency controlled at 30-50 Hz and an amplitude controlled at 0.5-1.5 mm. The vibration frequency and amplitude are matched with the alternating magnetic field to eliminate macroscopic particle agglomeration and improve the efficiency of slurry flow rearrangement.

[0071] Optionally, the synergistic effect time of the alternating magnetic field and mechanical vibration is 30-60 s.

[0072] Optionally, in the following specific implementation examples, the method of constructing the molding device and the mode of operation and control are as follows:

[0073] (1) Assembly of the forming device: First, the relative permeability μ rA non-magnetic forming mold of approximately 1 is fixed in the center of the vibration table. Then, a hollow solenoid frame is suspended and fixed using an independent support frame, allowing it to surround the mold from the outside, ensuring the coil's central axis is perpendicular to the mold. The excitation coil is then wound around the frame. During assembly, ensure that there is no physical contact between the control coil and the outer wall of the mold or the vibration table surface, leaving a safety gap to prevent damage to the coil during vibration and to ensure that the alternating magnetic field can completely penetrate the mold without shielding.

[0074] (2) No-load calibration and operation of magnetic field parameters: Power the coil with an adjustable AC excitation power supply. Before pouring the mixture, perform a no-load calibration: turn on the excitation power supply and adjust it to the preset working frequency (50-100 Hz), then vertically lower the probe of the high-precision teslameter to the center of the empty mold. Then adjust the output voltage or current of the AC power supply and observe the real-time reading of the teslameter until the vertical magnetic induction intensity at the center of the mold stabilizes at the target value (60-120 mT). After locking the power parameters and removing the probe, pour in the mixture and start the magnetic-vibration co-molding process.

[0075] In the following specific implementation cases, the fine aggregate of iron tailings comes from the Benxi mining area in Liaoning Province, and the specifications of each raw material used are shown in Tables 1 and 2 below.

[0076] Table 1 Specifications of each raw material

[0077]

[0078] Table 2 Main chemical components of iron tailings

[0079]

[0080] Example 1

[0081] The raw materials for the iron tailings fine aggregate concrete based on magnetic-thermal-chemical multi-field coupling enhancement provided in this embodiment include, by mass parts: 320 parts cement, 700 parts composite iron tailings fine aggregate, 950 parts coarse aggregate, 80 parts mineral admixture, 4 parts water-reducing agent, and 150 parts water.

[0082] The gradation of the composite iron tailings fine aggregate used in this embodiment is as follows: 0-0.075 mm: 150 parts; 0.075-0.15 mm: 45 parts; 0.15-0.30 mm: 55 parts; 0.30-0.60 mm: 75 parts; 0.60-1.18 mm: 95 parts; 1.18-2.36 mm: 120 parts; 2.36-4.75 mm: 160 parts.

[0083] In this embodiment, the coarse aggregate used has 570 parts with a particle size of 5-10 mm and 380 parts with a particle size of 10-15 mm.

[0084] The composite iron tailings fine aggregate selected in this embodiment was prepared using the following method:

[0085] (1) Pre-activation of particle surface: Mix the fine aggregate of iron tailings with alkaline solution (e.g., 3% NaOH solution by mass concentration), put it into a ball mill for low-speed (200 r / min) wet ball milling treatment for 30 min to obtain the mixture.

[0086] The mass ratio of fine aggregate from iron tailings to pure solid alkali in the alkali solution is 100:1.

[0087] (2) Magnetic precursor infiltration impregnation: The mixture is added to the mixed precursor solution and impregnated in a vacuum environment for 30 min to obtain a synergistic mineralization precursor system; the mixed precursor solution includes Fe 3+ and Fe 2+ .

[0088] The mass ratio of the mixture to the precursor liquid is 1:3.

[0089] The mixed precursor solution consisted of aqueous solutions of ferric chloride and ferrous chloride, with concentrations of 0.2 mol / L and 0.1 mol / L, respectively. That is, Fe... 3+ and Fe 2+ The molar ratio is 1:0.5.

[0090] (3) In-situ magnetic mineralization to construct an enhanced response layer: The synergistic mineralization precursor system (solid-liquid mixture after impregnation with mixed precursor liquid) is heated to 65°C, and a protective gas (e.g., inert gas or nitrogen) is introduced under mechanical stirring (stirring speed 500 r / min). NaOH solution (concentration 2.0 mol / L) is slowly added to adjust the pH value to alkaline (e.g., pH value = 10-11).

[0091] Subsequently, microwave heating treatment was performed, specifically using a microwave frequency of 2.45 GHz, a microwave power of 500 W, and a reaction temperature of 90°C for 30 minutes.

[0092] Next, perform interface coupling treatment. The specific method is as follows: keep the slurry stirring, add 1% of the silane coupling agent by mass of the iron tailings fine aggregate, and stir for 15 minutes.

[0093] (4) Solidification and shaping to form composite iron tailings fine aggregate: The product after interfacial coupling treatment is filtered, and the resulting filter cake is dried and solidified in an oven at 110°C for 2 hours without being washed with water, to obtain the composite iron tailings fine aggregate.

[0094] The method for preparing iron tailings fine aggregate concrete provided in this embodiment is as follows:

[0095] S1. Weighing and mixing raw materials to prepare iron tailings concrete mixture.

[0096] Dry mixing: Weigh cement, composite iron tailings fine aggregate and ordinary coarse aggregate according to the mix proportion, put them into a forced mixer and dry mix for 90 seconds to fully mix the cementitious materials with fine aggregate and coarse aggregate of different particle sizes, eliminate the agglomeration of iron tailings powder, and obtain the mixture.

[0097] Slurry preparation: Add the water-reducing agent and water together to the mixer and wet mix for 150 seconds. At this point, it is observed that the mixture has formed a homogeneous slurry with good flowability and no dry powder residue.

[0098] Discharge: Obtain a uniformly dispersed iron tailings concrete mixture and immediately proceed with subsequent molding operations.

[0099] S2. After the mixture is placed into a non-magnetic mold, it is placed on a vibration table. An electromagnetic excitation coil is fitted around the outside of the mold. Molding is achieved through the combined action of an alternating magnetic field and mechanical vibration.

[0100] Alternating magnetic fields are used to stimulate the magnetic response behavior of the enhanced response layer in composite reinforced iron tailings fine aggregates, promoting microscale directional rearrangement of particles and local slurry redistribution.

[0101] In the molding apparatus, the non-magnetic molding die is made of polyvinyl chloride (PVC) material, with a die size of 100×100×100mm and a relative magnetic permeability μ. r ≈ 1. The AC excitation power supply outputs a low-frequency alternating current with a frequency of 75 Hz, and the magnetic induction intensity of the alternating magnetic field is 100 mT.

[0102] During the pouring process, at least one test block is selected as a temperature test sample. The fiber optic temperature probe is suspended at the geometric center of the mold using a fixed bracket, ensuring that the concrete mixture completely covers the temperature-sensing end of the probe; ensuring that the probe does not contact the inner wall of the mold. The probe is covered with a microwave-transparent and smooth protective sleeve for easy removal and reuse later.

[0103] Simultaneously, the mechanical vibration table and excitation power supply are activated. Under the action of an alternating magnetic field, the magneto-thermal response enhancement layer on the surface of the composite reinforced iron tailings fine aggregate undergoes magnetic response micro-perturbation behavior, promoting micro-scale directional rearrangement of particles and local slurry redistribution. At the same time, mechanical vibration disrupts macroscopic agglomeration, achieving multi-scale synergistic dense packing of particles. The synergistic effect time of the alternating magnetic field and mechanical vibration is 60 s.

[0104] After molding is completed, the mechanical vibration table is turned off first, and the excitation system is turned off after a delay of 3-5 seconds, so as to stabilize the microstructure by utilizing the residual magnetism effect.

[0105] S3. Static curing until the concrete initially sets.

[0106] S4. Move the test block into the microwave heating cavity and perform intermittent microwave heating curing with internal feedback temperature control.

[0107] Intermittent pulse heating stage: Connect the fiber optic temperature probe to the signal monitoring system and use the intermittent pulse microwave heating mode. Each heating cycle lasts for 120 seconds and the shutdown time is 240 seconds, until the center temperature monitored by the fiber optic temperature probe reaches 85℃ for the first time.

[0108] Closed-loop isothermal enhancement stage: After the center temperature reaches the target temperature, the microwave start and stop are dynamically adjusted according to the real-time feedback signal of the fiber optic probe to achieve closed-loop temperature control and maintain the center temperature of the test block in the range of 85-95℃ for 3 hours.

[0109] Slow cooling stage: After microwave input is stopped, the test block is kept in the sealed cavity and allowed to cool naturally until the center temperature is below 40°C.

[0110] S5. After cooling in the furnace to a center temperature below 40°C, demold and transfer to a standard curing room for curing.

[0111] Example 2

[0112] The raw materials for the iron tailings fine aggregate concrete based on magnetic-thermal-chemical multi-field coupling enhancement provided in this embodiment include, by mass parts: 360 parts cement, 820 parts composite iron tailings fine aggregate, 1050 parts coarse aggregate, 120 parts mineral admixture, 6 parts water-reducing agent, and 170 parts water.

[0113] The gradation of the composite iron tailings fine aggregate used in this embodiment is as follows: 0-0.075 mm: 180 parts; 0.075-0.15 mm: 55 parts; 0.15-0.30 mm: 70 parts; 0.30-0.60 mm: 90 parts; 0.60-1.18 mm: 105 parts; 1.18-2.36 mm: 140 parts; 2.36-4.75 mm: 180 parts.

[0114] In this embodiment, the coarse aggregate used has 630 parts with a particle size of 5-10 mm and 420 parts with a particle size of 10-15 mm.

[0115] The preparation method of composite iron tailings fine aggregate and the preparation method of iron tailings fine aggregate concrete are the same as in Example 1.

[0116] Example 3

[0117] The raw materials for the iron tailings fine aggregate concrete based on magnetic-thermal-chemical multi-field coupling enhancement provided in this embodiment include, by mass parts: 340 parts cement, 780 parts composite iron tailings fine aggregate, 1000 parts coarse aggregate, 100 parts mineral admixture, 5 parts water-reducing agent, and 160 parts water.

[0118] The gradation of the composite iron tailings fine aggregate used in this embodiment is as follows: 0-0.075 mm: 170 parts; 0.075-0.15 mm: 50 parts; 0.15-0.30 mm: 65 parts; 0.30-0.60 mm: 85 parts; 0.60-1.18 mm: 100 parts; 1.18-2.36 mm: 135 parts; 2.36-4.75 mm: 175 parts.

[0119] In this embodiment, the coarse aggregate has 600 parts with a particle size of 5-10 mm and 400 parts with a particle size of 10-15 mm.

[0120] The preparation method of composite iron tailings fine aggregate and the preparation method of iron tailings fine aggregate concrete are the same as in Example 1.

[0121] Comparative Example 1

[0122] The iron tailings fine aggregate concrete provided in this comparative example has the same raw material composition and proportions as Example 1. The difference lies in the fact that the preparation method of the composite iron tailings fine aggregate did not involve microwave heating treatment, but only interfacial coupling treatment.

[0123] The preparation method of composite iron tailings fine aggregate is as follows:

[0124] (1) Pre-activation of particle surface: Iron tailings fine aggregate is mixed with alkaline solution (e.g., 3% NaOH solution can be used) and put into a ball mill for low-speed (200 r / min) wet ball milling treatment for 30 min to obtain the mixture.

[0125] The mass ratio of fine aggregate from iron tailings to pure solid alkali in the alkali solution is 100:1.

[0126] (2) Magnetic precursor infiltration impregnation: The mixture is added to the mixed precursor solution and impregnated in a vacuum environment for 30 min to obtain a synergistic mineralization precursor system; the mixed precursor solution includes Fe 3+ and Fe 2+ .

[0127] The mass ratio of the mixture to the precursor liquid is 1:3.

[0128] The mixed precursor solution consisted of aqueous solutions of ferric chloride and ferrous chloride, with concentrations of 0.2 mol / L and 0.1 mol / L, respectively. That is, Fe... 3+ and Fe 2+ The molar ratio is 1:0.5.

[0129] (3) In-situ magnetic mineralization to construct an enhanced response layer: The synergistic mineralization precursor system (solid-liquid mixture after impregnation with mixed precursor liquid) is heated to 65°C, and a protective gas (e.g., inert gas or nitrogen) is introduced under mechanical stirring (stirring speed 500 r / min). NaOH solution (concentration 2 mol / L) is slowly added to adjust the pH value to alkaline (e.g., pH value = 10-11).

[0130] After standing for 30 minutes, perform interface coupling treatment. The specific method is as follows: keep stirring the slurry, add 1% of the silane coupling agent by mass of the iron tailings fine aggregate, and stir for 15 minutes.

[0131] (4) Solidification and shaping to form composite iron tailings fine aggregate: The product after interfacial coupling treatment is filtered, and the resulting filter cake is dried and solidified in an oven at 110°C for 2 hours without being washed with water, to obtain the composite iron tailings fine aggregate.

[0132] The preparation method of iron tailings fine aggregate concrete is the same as in Example 1.

[0133] Comparative Example 2

[0134] The iron tailings fine aggregate concrete provided in this comparative example has the same raw material composition and proportions as Example 1. The difference lies in the fact that the preparation method of the composite iron tailings fine aggregate did not involve interfacial coupling treatment, but only microwave heating treatment.

[0135] (1) Pre-activation of particle surface: Mix the fine aggregate of iron tailings with alkaline solution (e.g., 3% NaOH solution by mass concentration), put it into a ball mill for low-speed (200 r / min) wet ball milling treatment for 30 min to obtain the mixture.

[0136] The mass ratio of fine aggregate from iron tailings to alkali solution, on a dry basis, is 100:1.

[0137] (2) Magnetic precursor infiltration impregnation: The mixture is added to the mixed precursor solution and impregnated in a vacuum environment for 30 min to obtain a synergistic mineralization precursor system; the mixed precursor solution includes Fe 3+ and Fe 2+ .

[0138] The mass ratio of the mixture to the precursor liquid is 1:3.

[0139] The mixed precursor solution consisted of aqueous solutions of ferric chloride and ferrous chloride, with concentrations of 0.2 mol / L and 0.1 mol / L, respectively. That is, Fe... 3+ and Fe 2+ The molar ratio is 1:0.5.

[0140] (3) In-situ magnetic mineralization to construct an enhanced response layer: The synergistic mineralization precursor system (solid-liquid mixture after impregnation with mixed precursor liquid) is heated to 65°C, and a protective gas (e.g., inert gas or nitrogen) is introduced under mechanical stirring (stirring speed 500 r / min). NaOH solution (concentration 2 mol / L) is slowly added to adjust the pH value to alkaline (e.g., pH value = 10-11).

[0141] Subsequently, microwave heating treatment was performed, specifically using a microwave frequency of 2.45 GHz, a microwave power of 500 W, and a reaction temperature of 90°C for 30 minutes.

[0142] (4) Solidification and shaping to form composite iron tailings fine aggregate: The product after interfacial coupling treatment is filtered, and the resulting filter cake is dried and solidified in an oven at 110°C for 2 hours without being washed with water, to obtain the composite iron tailings fine aggregate.

[0143] Comparative Example 3

[0144] The iron tailings fine aggregate concrete provided in this comparative example has the same raw material composition and proportions as in Example 1, and the preparation method of the composite iron tailings fine aggregate is the same as in Example 1.

[0145] The difference lies in the fact that iron tailings fine aggregate concrete is not treated with an alternating magnetic field during preparation. The specific preparation method is as follows:

[0146] S1. Weighing and mixing raw materials to prepare iron tailings concrete mixture.

[0147] Dry mixing: Weigh cement, composite iron tailings fine aggregate and ordinary coarse aggregate according to the mix proportion, put them into a forced mixer and dry mix for 90 seconds to fully mix the cementitious materials with fine aggregate and coarse aggregate of different particle sizes, eliminate the agglomeration of iron tailings powder, and obtain the mixture.

[0148] Pulping: Add the water-reducing agent and water together to the mixer and wet mix for 150 seconds.

[0149] Discharge: Obtain a uniformly dispersed iron tailings concrete mixture and immediately proceed with subsequent molding operations.

[0150] S2. After loading the mixture into a non-magnetic mold, place it on a vibration table.

[0151] During the pouring process, at least one test block is selected as a temperature test sample. The fiber optic temperature probe is suspended at the geometric center of the mold using a fixed bracket, ensuring that the concrete mixture completely covers the temperature-sensing end of the probe; ensuring that the probe does not contact the inner wall of the mold. The probe is covered with a microwave-transparent and smooth protective sleeve for easy removal and reuse later.

[0152] The alternating magnetic field is not activated throughout the process; instead, the mechanical vibration table is turned on for 60 seconds. After molding is complete, the mechanical vibration table is turned off.

[0153] S3. Static curing until the concrete initially sets.

[0154] S4. Move the test block into the microwave heating cavity and perform intermittent microwave heating curing with internal feedback temperature control.

[0155] Intermittent pulse heating stage: Connect the fiber optic temperature probe to the signal monitoring system and use the intermittent pulse microwave heating mode. Each heating cycle lasts for 120 seconds and the shutdown time is 240 seconds, until the center temperature monitored by the fiber optic temperature probe reaches 85℃ for the first time.

[0156] Closed-loop isothermal enhancement stage: After the center temperature reaches the target temperature, the microwave start and stop are dynamically adjusted according to the real-time feedback signal of the fiber optic probe to achieve closed-loop temperature control and maintain the center temperature of the test block in the range of 85-95℃ for 3 hours.

[0157] Slow cooling stage: After microwave input is stopped, the test block is kept in the sealed cavity and allowed to cool naturally until the center temperature is below 40°C.

[0158] S5. After cooling in the furnace to a center temperature below 40°C, demold and transfer to a standard curing room for curing.

[0159] Comparative Example 4

[0160] The iron tailings fine aggregate concrete provided in this comparative example has the same raw material composition and proportions as in Example 1, and the preparation method of the composite iron tailings fine aggregate is the same as in Example 1.

[0161] The difference lies in the fact that the iron tailings fine aggregate concrete was not subjected to mechanical vibration treatment during preparation. The specific preparation method is as follows:

[0162] The method for preparing iron tailings fine aggregate concrete provided in this embodiment is as follows:

[0163] S1. Weighing and mixing raw materials to prepare iron tailings concrete mixture.

[0164] Dry mixing: Weigh cement, composite iron tailings fine aggregate and ordinary coarse aggregate according to the mix proportion, put them into a forced mixer and dry mix for 90 seconds to fully mix the cementitious materials with fine aggregate and coarse aggregate of different particle sizes, eliminate the agglomeration of iron tailings powder, and obtain the mixture.

[0165] Pulping: Add the water-reducing agent and water together to the mixer and wet mix for 150 seconds.

[0166] Discharge: Obtain a uniformly dispersed iron tailings concrete mixture and immediately proceed with subsequent molding operations.

[0167] S2. After the mixture is placed into a non-magnetic mold, it is placed on a vibration table. An electromagnetic excitation coil is fitted around the outside of the mold. Molding is achieved through the combined action of an alternating magnetic field and mechanical vibration.

[0168] Alternating magnetic fields are used to stimulate the magnetic response behavior of the enhanced response layer in composite reinforced iron tailings fine aggregates, promoting microscale directional rearrangement of particles and local slurry redistribution.

[0169] In the molding apparatus, the non-magnetic molding die is made of polyvinyl chloride (PVC) material, with a die size of 100×100×100mm and a relative magnetic permeability μ. r ≈ 1. The AC excitation power supply outputs a low-frequency alternating current with a frequency of 75 Hz, and the magnetic induction intensity of the alternating magnetic field is 100 mT.

[0170] During the pouring process, at least one test block is selected as a temperature test sample. The fiber optic temperature probe is suspended at the geometric center of the mold using a fixed bracket, ensuring that the concrete mixture completely covers the temperature-sensing end of the probe; ensuring that the probe does not contact the inner wall of the mold. The probe is covered with a microwave-transparent and smooth protective sleeve for easy removal and reuse later.

[0171] Turn on the excitation power supply. Under the action of the alternating magnetic field, the magnetic-thermal response enhancement layer on the surface of the composite reinforced iron tailings fine aggregate undergoes magnetic response micro-perturbation behavior, promoting micro-scale directional rearrangement of particles and local slurry redistribution. The alternating magnetic field is applied for 60 s.

[0172] After molding is completed, the excitation system is turned off after a delay of 3-5 seconds to utilize the residual magnetism effect to stabilize the microstructure.

[0173] S3. Static curing until the concrete initially sets.

[0174] S4. Move the test block into the microwave heating cavity and perform intermittent microwave heating curing with internal feedback temperature control.

[0175] Intermittent pulse heating stage: Connect the fiber optic temperature probe to the signal monitoring system and use the intermittent pulse microwave heating mode. Each heating cycle lasts for 120 seconds and the shutdown time is 240 seconds, until the center temperature monitored by the fiber optic temperature probe reaches 85℃ for the first time.

[0176] Closed-loop isothermal enhancement stage: After the center temperature reaches the target temperature, the microwave start and stop are dynamically adjusted according to the real-time feedback signal of the fiber optic probe to achieve closed-loop temperature control and maintain the center temperature of the test block in the range of 85-95℃ for 3 hours.

[0177] Slow cooling stage: After microwave input is stopped, the test block is kept in the sealed cavity and allowed to cool naturally until the center temperature is below 40°C.

[0178] S5. After cooling in the furnace to a center temperature below 40°C, demold and transfer to a standard curing room for curing.

[0179] Comparative Example 5

[0180] The iron tailings fine aggregate concrete provided in this comparative example has the same raw material composition and proportions as in Example 1, and the preparation method of the composite iron tailings fine aggregate is the same as in Example 1.

[0181] The difference lies in the fact that the iron tailings fine aggregate concrete was not subjected to intermittent microwave heating curing during preparation. The specific preparation method is as follows:

[0182] The method for preparing iron tailings fine aggregate concrete provided in this embodiment is as follows:

[0183] S1. Weighing and mixing raw materials to prepare iron tailings concrete mixture.

[0184] Dry mixing: Weigh cement, composite iron tailings fine aggregate and ordinary coarse aggregate according to the mix proportion, put them into a forced mixer and dry mix for 90 seconds to fully mix the cementitious materials with fine aggregate and coarse aggregate of different particle sizes, eliminate the agglomeration of iron tailings powder, and obtain the mixture.

[0185] Slurry preparation: Add the water-reducing agent and water together to the mixer and wet mix for 150 seconds. At this point, it is observed that the mixture has formed a homogeneous slurry with good flowability and no dry powder residue.

[0186] Discharge: Obtain a uniformly dispersed iron tailings concrete mixture and immediately proceed with subsequent molding operations.

[0187] S2. After the mixture is placed into a non-magnetic mold, it is placed on a vibration table. An electromagnetic excitation coil is fitted around the outside of the mold. Molding is achieved through the combined action of an alternating magnetic field and mechanical vibration.

[0188] Alternating magnetic fields are used to stimulate the magnetic response behavior of the enhanced response layer in composite reinforced iron tailings fine aggregates, promoting microscale directional rearrangement of particles and local slurry redistribution.

[0189] In the molding apparatus, the non-magnetic molding die is made of polyvinyl chloride (PVC) material, with a die size of 100×100×100mm and a relative magnetic permeability μ. r ≈ 1. The AC excitation power supply outputs a low-frequency alternating current with a frequency of 75 Hz, and the magnetic induction intensity of the alternating magnetic field is 100 mT.

[0190] During the pouring process, at least one test block is selected as a temperature test sample. The fiber optic temperature probe is suspended at the geometric center of the mold using a fixed bracket, ensuring that the concrete mixture completely covers the temperature-sensing end of the probe; ensuring that the probe does not contact the inner wall of the mold. The probe is covered with a microwave-transparent and smooth protective sleeve for easy removal and reuse later.

[0191] Simultaneously, the mechanical vibration table and excitation power supply are activated. Under the action of an alternating magnetic field, the magneto-thermal response enhancement layer on the surface of the composite reinforced iron tailings fine aggregate undergoes magnetic response micro-perturbation behavior, promoting micro-scale directional rearrangement of particles and local slurry redistribution. At the same time, mechanical vibration disrupts macroscopic agglomeration, achieving multi-scale synergistic dense packing of particles. The synergistic effect time of the alternating magnetic field and mechanical vibration is 60 s.

[0192] After molding is completed, the mechanical vibration table is turned off first, and the excitation system is turned off after a delay of 3-5 seconds, so as to stabilize the microstructure by utilizing the residual magnetism effect.

[0193] S3. Static curing until the concrete initially sets.

[0194] S4. After pre-curing is completed, demold and transfer to a standard curing room for curing.

[0195] Test Example: Performance Testing of Iron Tailings Fine Aggregate Concrete

[0196] The compressive and flexural strengths of the iron tailings fine aggregate concrete prepared in Examples 1-3 and Comparative Examples 1-5 were tested according to the "Standard for Test Methods of Physical and Mechanical Properties of Concrete" (GB / T 50081-2019). The durability of the iron tailings fine aggregate concrete prepared in Examples 1-3 and Comparative Examples 1-5 was tested according to the "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete" (GB / T 50082-2024). The test results are shown in Table 3 below.

[0197] Table 3 Performance tests of iron tailings fine aggregate concrete in Examples 1-3 and Comparative Examples 1-5

[0198]

[0199] As can be seen from the test results in Table 3, the iron tailings fine aggregate concrete prepared in Examples 1-3 of this invention exhibits excellent mechanical and durability properties. The highest 28-day compressive strength reaches 63.5 MPa, the flexural strength reaches 7.4 MPa, the mass loss rate after 150 freeze-thaw cycles is controlled at an extremely low level, and the chloride ion migration coefficient is below 2.0 × 10⁻⁶. -12 m 2 / s. Comparative Example 1 did not undergo microwave mineralization treatment, resulting in uneven growth of the generated nano-Fe3O4 crystal nuclei, loose interface deposition, and poor bonding stability of the mineralization layer. This not only weakened the magneto-thermal response capability of the aggregate in subsequent molding and curing, but also caused its 28-day compressive and flexural strengths to decrease significantly by 10.3 MPa and 1.4 MPa, respectively, compared to Example 1.

[0200] Comparative Example 2, lacking the silane coupling agent modification step, showed a significant decrease in flexural strength of 1.7 MPa compared to Example 1. This indicates that the organic-inorganic chemical bond (synergistic layer) constructed by the coupling agent between the inorganic nanomineralized layer and the cement hydration products plays a decisive role in resisting flexural stress. The absence of this chemical anchoring leads to the easy initiation of microcracks in the interfacial transition zone (ITZ).

[0201] In Comparative Example 3, no alternating magnetic field was applied during molding. Mechanical vibration alone could not completely overcome the internal friction caused by the extremely high angularity of the iron tailings, resulting in loose particle packing and a significant decrease in all properties.

[0202] Comparative Example 4, without mechanical vibration and relying solely on an alternating magnetic field, exhibited a drop in compressive strength to 42.5 MPa, a surge in mass loss rate to 4.50%, and a chloride ion migration coefficient as high as 5.5 × 10⁻⁶. -12 m 2 / s. This proves that a single microscopic magnetic response perturbation is insufficient to eliminate macroscopic slurry agglomeration and large bubbles; only by deeply coordinating macroscopic mechanical vibration with microscopic alternating magnetic field in the embodiments can a dense multi-scale arrangement of iron tailings concrete skeleton be truly achieved.

[0203] Comparative Example 5 omitted the microwave curing step and adopted conventional standard curing. Its 28-day compressive and flexural strengths decreased by 9.2 MPa and 1.3 MPa, respectively, compared to Example 1. This fully confirms the "endogenous micro-heat source" mechanism designed in this invention: through pre-embedded fiber optic probes and closed-loop microwave heating, the nano-Fe3O4 adhering to the surface of iron tailings preferentially absorbs microwave heat, prompting the surrounding moisture to preferentially participate in hydration, thereby targeting and generating an extremely high-density CSH gel shell at the originally weakest aggregate interface.

[0204] The above detailed embodiments describe the implementation of the present invention; however, the present invention is not limited to the specific details described in the above embodiments. Within the scope of the claims and technical concept of the present invention, various simple modifications and changes can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

Claims

1. A fine aggregate concrete for iron tailings enhanced by magnetic-thermal-chemical multi-field coupling, characterized in that, Its raw materials, by mass parts, include: 320-360 parts cement, 700-820 parts composite iron tailings fine aggregate, 950-1050 parts coarse aggregate, 80-120 parts mineral admixture, 4-6 parts water-reducing agent, and 150-170 parts water. The preparation method of the composite iron tailings fine aggregate is as follows: The fine aggregate of iron tailings is mixed with alkaline solution and ball-milled to obtain a mixture. The mixture is added to a mixing precursor solution and impregnated in a vacuum environment to obtain a synergistic mineralization precursor system; the mixing precursor solution includes Fe. 3+ and Fe 2+ ; The synergistic mineralization precursor system is heated and stirred, a protective gas is introduced or an antioxidant is added, and the pH value is adjusted to be alkaline; microwave heating treatment and interfacial coupling treatment are performed sequentially, followed by filtration and drying to obtain the composite iron tailings fine aggregate.

2. The iron tailings fine aggregate concrete based on magneto-thermal-chemical multi-field coupling enhancement according to claim 1, characterized in that, The mass ratio of the fine aggregate of the iron tailings to the pure solid alkali in the alkali solution is 100:(1-2).

3. The iron tailings fine aggregate concrete based on magneto-thermal-chemical multi-field coupling enhancement according to claim 1, characterized in that, The mass ratio of the mixture to the precursor liquid is 1:(1.5-3).

4. The iron tailings fine aggregate concrete based on magneto-thermal-chemical multi-field coupling enhancement according to claim 1, characterized in that, In the mixed precursor solution, Fe 3+ and Fe 2+ The molar ratio is 1:(0.5-1); Furthermore, Fe 3+ Provided by at least one of ferric chloride, ferric sulfate, and ferric nitrate solution, Fe 2+ It consists of at least one of ferrous chloride, ferrous sulfate, and ferrous nitrate solutions.

5. The iron tailings fine aggregate concrete based on magneto-thermal-chemical multi-field coupling enhancement according to claim 1, characterized in that, The conditions for heating and stirring the synergistic mineralization precursor system are 60-70℃ and 300-600 r / min.

6. The iron tailings fine aggregate concrete based on magneto-thermal-chemical multi-field coupling enhancement according to claim 1, characterized in that, The microwave heating treatment method is as follows: microwave frequency 2.45GHz, microwave power 300-600W, and reaction at 80-90℃ for 30-60 minutes.

7. The iron tailings fine aggregate concrete based on magneto-thermal-chemical multi-field coupling enhancement according to claim 1, characterized in that, The method for interfacial coupling treatment is as follows: add 0.5-1% of the mass of the iron tailings fine aggregate as a silane coupling agent and stir for 15-20 minutes.

8. The iron tailings fine aggregate concrete based on magneto-thermal-chemical multi-field coupling enhancement according to claim 1, characterized in that, The particle size distribution of the composite iron tailings fine aggregate is as follows: 0-0.075 mm: 150-180 parts; 0.075-0.15 mm: 45-55 parts. 0.15-0.30mm: 55-70 parts; 0.30-0.60mm: 75-90 parts; 0.60-1.18mm: 95-105 parts; 1.18-2.36mm: 120-140 parts; 2.36-4.75mm: 160-180 parts.

9. The iron tailings fine aggregate concrete based on magneto-thermal-chemical multi-field coupling enhancement according to claim 1, characterized in that, The mineral admixture is slag powder and / or fly ash; the coarse aggregate is limestone crushed stone, granite crushed stone, basalt crushed stone, diabase crushed stone, quartzite crushed stone or gravel.

10. The method for preparing iron tailings fine aggregate concrete based on magneto-thermal-chemical multi-field coupling enhancement as described in any one of claims 1-9, characterized in that, Includes the following steps: The raw materials for the iron tailings fine aggregate concrete are mixed to form a mixture; the mixture is then molded under alternating magnetic field and mechanical vibration conditions. Pre-curing to the initial setting stage, microwave heating curing, cooling and demolding followed by standard curing, to obtain the iron tailings fine aggregate concrete; Furthermore, the alternating magnetic field is generated by an alternating current with a frequency of 50-100 Hz output from an AC excitation power supply, and the magnetic induction intensity is 60-120 mT. Furthermore, the mechanical vibration mode is a vibration frequency of 30-50 Hz and an amplitude of 0.5-1.5 mm.

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