Burning-free steam-curing-free all-solid waste type iron tailing artificial fine aggregate and preparation method thereof

Abstract

The invention relates to the technical field of building materials, and discloses a burning-free steam-curing-free all-solid waste type iron tailing artificial fine aggregate and a preparation method thereof.The preparation method comprises the following steps that iron tailings are dried and screened, and iron tailing powder with the particle size smaller than 0.3 mm is obtained; mixing the pozzolanic material, the exciting agent, the expanding agent and the reinforcing agent, and uniformly stirring to obtain an all-solid waste cementing material; the iron tailing powder and part of the all-solid waste cementing material are mixed, ground and stirred evenly, and a mixture is obtained; carrying out rolling and watering treatment on the mixture to obtain iron tailing microspheres with the diameter of 1-4mm; adding the residual all-solid waste cementing material into the iron tailing microspheres for rolling treatment, so that the surfaces of the iron tailing microspheres are wrapped with the all-solid waste cementing material, and composite particles with core-shell structures are obtained; the composite particles of the core-shell structure are subjected to curing treatment, and the iron tailing artificial fine aggregate is obtained. Energy consumption, carbon emission and production cost can be reduced, high-value utilization of multi-element solid waste is realized, and shortage of natural gravel aggregate is relieved.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, and relates to a non-fired, non-steam-cured, solid waste-type artificial fine aggregate for iron tailings and its preparation method. Background Technology

[0002] Converting industrial solid waste such as iron tailings into sand and gravel aggregates can not only effectively solve the problem of solid waste disposal, but also alleviate the shortage of natural building materials resources. With both environmental and economic benefits, it has become a research hotspot and an important development direction in the field of building materials.

[0003] To achieve the resource utilization of industrial solid waste, those skilled in the art have conducted numerous explorations. CN111116070A proposes a method for preparing non-fired aggregate using iron tailings. This method mainly involves mixing and granulating iron tailings with a particle size less than 150 μm, cement, and silica fume, followed by curing at room temperature, and finally sieving to obtain non-fired aggregate. The innovation of this scheme lies in avoiding high-temperature sintering and steam curing treatment, thereby reducing production energy consumption.

[0004] While the aforementioned existing technologies have promoted the resource utilization of industrial solid waste to some extent, their inherent technical principles and material selection strategies have gradually revealed deep-seated limitations in achieving large-scale, economical, and sustainable applications, leading to more complex systemic contradictions. Although the sintering and hydrothermal synthesis methods mentioned above can effectively impart the required mechanical properties to artificial aggregates, their core processes—high-temperature sintering and steam curing—are inherently high-energy-consuming processes.

[0005] High-temperature sintering requires heating materials to thousands of degrees Celsius, and steam curing also consumes a lot of heat energy to maintain a high-temperature and high-humidity environment. This undoubtedly increases production costs and, to some extent, offsets the environmental protection intention of utilizing solid waste.

[0006] A deeper contradiction lies in the fact that even in attempts at non-sintering processes, as described in CN111116070A, high-temperature treatment is avoided by introducing cement as the main cementing material. While this avoids the energy consumption of direct sintering or steam curing, it introduces new environmental and economic challenges. Cement production itself is an energy-intensive industry, accompanied by significant carbon dioxide emissions, resulting in high manufacturing costs and a high carbon footprint.

[0007] Although the aggregate production process can be made fire-free, its overall energy consumption and carbon emissions throughout its life cycle have not been fundamentally optimized. Instead, it may shift the environmental burden to the cement production process. Furthermore, over-reliance on commercial cement as a binder limits the possibility of using other potentially reactive industrial solid wastes, such as iron tailings, alkali slag, and red mud, as core binder components to replace cement. This not only reduces the comprehensive utilization rate of various bulk industrial solid wastes, preventing them from fully realizing their potential binder or activator activity, but also forces the products to still bear the high material costs associated with traditional cement. This hinders the widespread adoption and market competitiveness of artificial aggregates in engineering applications, and the mining of natural sand and gravel aggregates also leads to ecological damage and resource shortages.

[0008] In other words, when existing technologies attempt to solve a problem (solid waste disposal) by converting industrial solid waste into sand and gravel aggregates, another problem often arises: production models that rely on high-temperature sintering, steam curing, or excessive reliance on cement fail to achieve synergistic optimization of low energy consumption, low cost, low carbon emissions, and high-value utilization of diverse solid wastes at the system level. This is especially true in how to get rid of the high-energy-consuming model of high-temperature sintering and steam curing, while avoiding excessive reliance on traditional high-carbon-footprint cementitious materials (such as cement), and maximizing the use of diverse low-value-added industrial solid wastes as active components to build a truly environmentally friendly, economically sustainable, and reliable artificial fine aggregate production system.

[0009] Therefore, how to fully utilize diverse industrial solid wastes as core cementing and functional components to construct an environmentally friendly, economically feasible, and comprehensive solid waste-based technical solution that ensures the excellent comprehensive performance of artificial fine aggregates, while achieving a low-energy-consumption and low-cost preparation process without burning or steam curing, has become a key challenge and an urgent technical problem for those skilled in the art. Summary of the Invention

[0010] In view of this, the present invention provides a non-fired, non-steam-cured, solid waste-type artificial fine aggregate for iron tailings and its preparation method. The main purpose is to solve the deep-seated contradictions in existing industrial solid waste resource utilization technologies, such as high energy consumption, large carbon emissions, and excessive reliance on traditional high-carbon footprint cementing materials.

[0011] On the one hand, the present invention provides a method for preparing artificial fine aggregate from iron tailings that is non-fired and non-steam-cured and is entirely solid waste, comprising the following steps: S1. The iron tailings are dried and screened to obtain iron tailings powder with a particle size of less than 0.3 mm. S2. Mix the pozzolanic material, activator, expanding agent and reinforcing agent, and stir evenly to obtain a solid waste cementitious material; wherein, the pozzolanic material is S95 grade mineral powder and II grade fly ash, the activator is alkaline slag, carbide slag and red mud, the expanding agent is steel slag, and the reinforcing agent is desulfurized gypsum. S3. Mix the iron tailings powder and part of the solid waste cementitious material, crush and stir evenly to obtain a mixture; S4. The mixture is rolled and sprayed with water to obtain iron tailings microspheres with a diameter of 1-4 mm; S5. Add the remaining solid waste cementitious material to the iron tailings microspheres for rolling treatment, so that the solid waste cementitious material coats the surface of the iron tailings microspheres to obtain core-shell structured composite particles. S6. The core-shell structured composite particles are cured to obtain artificial fine aggregate of iron tailings.

[0012] Preferably, the weight ratio of the iron tailings powder to the solid waste cementitious material is 1:0.2-0.5.

[0013] Preferably, in step S1: The iron tailings are composed of silicon dioxide, ferric oxide, and aluminum oxide; and / or When drying the iron tailings, the moisture content of the iron tailings is less than 0.5 wt%, the drying temperature is 80-120℃, and the drying time is 1-2 hours.

[0014] Preferably, in step S2: The weight ratio of the volcanic ash material, the activator, the expanding agent, and the reinforcing agent is 1:0.5-1.0:0.1-0.2:0.05-0.1; and / or The S95 grade mineral powder is an amorphous or microcrystalline silicate and aluminate; and / or The Class II fly ash is composed of amorphous silica and aluminum oxide; and / or The weight ratio of the S95 grade mineral powder to the II grade fly ash is 1:0.2-0.4; and / or The alkaline residue is composed of calcium oxide, sodium oxide, and potassium oxide; and / or The carbide slag is calcium hydroxide; and / or The red mud is composed of ferric oxide, aluminum oxide, silicon dioxide, and sodium oxide; and / or The weight ratio of the alkaline residue, the carbide slag, and the red mud is 1:0.8-1.2:0.1-0.5; and / or The steel slag is composed of free calcium oxide and free magnesium oxide; and / or The specific surface area of ​​the steel slag is greater than or equal to 400 m².2 / kg.

[0015] Preferably, in step S2: The volcanic ash material, the activator, the expansion agent, and the reinforcing agent are placed in a planetary mixing vessel for mixing. The planetary mixing vessel uses the rotation and revolution of the agitator to perform multi-dimensional and all-round shearing, mixing, and diffusion of the material. The mixing time is 2-4 minutes.

[0016] Preferably, in step S3: The amount of the solid waste cementitious material added is 70-85 wt% of the total weight of the solid waste cementitious material; and / or The iron tailings powder and 70-85 wt% of the total solid waste cementitious material are placed in a roller mill for compaction and mixing, and the compaction and mixing time is 4-6 minutes.

[0017] Preferably, in step S4: The mixture is poured into a disc pelletizer, and the tilt angle and speed of the disc pelletizer are adjusted for rolling. At the same time, water accounting for 2-6% of the total mass of the mixture is sprayed evenly through a precision spraying system for 3-6 minutes to obtain iron tailings microspheres with a diameter of 1-4 mm. Preferably, in step S5: The remaining solid waste cementitious material is added to the disc pelletizer for rolling treatment. The rolling continues for 2-5 minutes, so that the solid waste cementitious material coats the surface of the iron tailings microspheres, thus obtaining the core-shell structured composite particles.

[0018] Preferably, in step S6: The core-shell structured composite particles were placed in an environment with a temperature of 15-30℃ and a relative humidity of over 90% for 28 days to cure them, thus obtaining the artificial fine aggregate of iron tailings.

[0019] Another aspect of the present invention provides a non-fired, non-steam-cured, solid waste-type artificial fine aggregate for iron tailings, wherein the artificial fine aggregate for iron tailings is prepared by the above-mentioned preparation method of the non-fired, non-steam-cured, solid waste-type artificial fine aggregate for iron tailings.

[0020] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a method for preparing artificial fine aggregate from iron tailings using a non-fired, non-steam-cured, all-solid-waste process. It establishes a novel artificial fine aggregate production system that relies entirely on diverse industrial solid wastes as raw materials and achieves performance development through ambient temperature and humidity curing. This system eliminates the energy-intensive processes of high-temperature sintering and steam curing, significantly reducing production costs and carbon emissions. Simultaneously, by precisely controlling the proportions of various solid waste materials and their synergistic effects during preparation, the pozzolanic materials are fully activated, compensating for shrinkage and enhancing strength, ensuring the artificial fine aggregate possesses excellent mechanical properties and durability. This invention offers environmental, economic, and social benefits in addressing the challenges of large-scale industrial solid waste disposal, alleviating the shortage of natural sand and gravel aggregate resources, and promoting the green and sustainable development of the building materials industry. Attached Figure Description

[0021] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a flowchart illustrating the preparation method of non-fired, non-steam-cured, solid waste-type artificial fine aggregate from iron tailings, as described in an embodiment of the present invention.

[0023] Figure 2 This is a diagram of the raw materials for the artificial fine aggregate made from iron tailings of the present invention.

[0024] Figure 3 This is a diagram of the first stage of the artificial fine aggregate for iron tailings prepared in this invention.

[0025] Figure 4 This is a diagram of the second stage of the artificial fine aggregate for iron tailings prepared in this invention.

[0026] Figure 5 This is a finished product image of the artificial fine aggregate for iron tailings prepared in this invention. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0028] Please see, Figures 1 to 5 , Figure 2This invention provides a non-fired, non-steam-cured, all-solid-waste type artificial fine aggregate made from iron tailings, along with its preparation method. The resulting artificial fine aggregate comprises five core components: iron tailings powder, pozzolanic material, activator, expansion agent, and reinforcing agent. These components are all derived from industrial solid waste and, through precise mass ratio configuration and synergistic effects, jointly construct the structural and functional system of the artificial fine aggregate. This method aims to change the traditional production paradigm of sand and gravel aggregates through the integrated application of systematic engineering design and materials science principles, particularly focusing on the high-value and low-carbon utilization of large-scale industrial solid waste. The unique feature of this artificial fine aggregate lies in its main framework, composed of precisely size-controlled iron tailings powder particles. These particles are uniformly coated with a layer of all-solid-waste cementitious material generated by the synergistic reaction of multiple industrial solid wastes, thus forming composite particles with a typical core-shell structure. The generation and strength development of this all-solid-waste cementitious material rely entirely on ambient temperature and humidity curing conditions, eliminating the enormous energy consumption and carbon emissions associated with traditional high-temperature sintering or steam curing processes.

[0029] The specific solution of this invention is as follows: Figure 1 This is a flowchart of the preparation method of non-fired and non-steam-cured solid waste-type artificial fine aggregate in an embodiment of the present invention. Through a series of precisely controlled physical and chemical process steps, multi-element solid waste is transformed into high-value-added artificial fine aggregate.

[0030] This invention provides a method for preparing artificial fine aggregate from iron tailings that is non-fired, non-steam-cured, and entirely solid waste, such as... Figure 1 As shown, it includes the following steps: S1. The iron tailings are dried and screened to obtain iron tailings powder with a particle size of less than 0.3 mm.

[0031] In this step, the main chemical components of iron tailings are typically including, but not limited to, oxides such as silica, ferric oxide, and aluminum oxide. Their particle morphology and specific surface area are optimized through pretreatment to ensure that their physical properties meet the requirements of subsequent refined production, thereby further enhancing their ability to form a stable and dense interface structure with subsequent cementing components.

[0032] Preferably, when drying iron tailings, the free water in the iron tailings is removed, and the moisture content of the iron tailings is controlled to be less than 0.5 wt%. The drying operation is usually carried out in a dedicated rotary dryer or fluidized bed dryer, with a drying temperature of 80-120℃. The specific drying time is set according to the initial moisture content and the efficiency of the selected equipment, usually 1-2 hours.

[0033] The dried iron tailings are then precisely screened to ensure that all particles are less than 0.3 mm in diameter. The particle size range is determined by several factors: First, the relatively fine particle size provides the iron tailings powder with a larger specific surface area, offering a broad reaction interface for sufficient contact and interfacial bonding with the solid waste cementitious material, thus improving its interfacial bonding ability. Second, appropriate fineness ensures the density of particle packing during subsequent pelleting. This particle size range facilitates tight packing and filling of particles during pelleting, forming a dense spherical core structure, laying a solid foundation for the mechanical strength and durability of the final artificial aggregate. Third, it avoids the agglomeration effect that may occur with excessively fine particles during mixing and pelleting, as well as the uneven coating or insufficient interfacial bonding that may result from excessively coarse particles.

[0034] S2. Mix the volcanic ash material, activator, expansion agent and reinforcing agent, and stir evenly to obtain the solid waste cementitious material.

[0035] In this step, the key active components of the cementing system in this embodiment of the invention are S95 grade mineral powder and II grade fly ash, the activator is alkaline slag, carbide slag and red mud, the expansion agent is steel slag, and the reinforcing agent is desulfurized gypsum.

[0036] Preferably, the weight ratio of the volcanic ash material, activator, expansion agent and reinforcing agent is 1:0.5-1.0:0.1-0.2:0.05-0.1.

[0037] Preferably, in the pozzolanic material, S95 grade mineral powder has excellent potential hydraulic properties and is rich in amorphous or microcrystalline silicates and aluminates, while Grade II fly ash has good pozzolanic activity and is composed of amorphous silica and aluminum oxide; the weight ratio of S95 grade mineral powder to Grade II fly ash is 1:0.2-0.4.

[0038] Specifically, S95 grade mineral powder and II grade fly ash are the main contributors to the strength and density of the cementitious system.

[0039] S95 grade blast furnace slag powder, also known as blast furnace slag powder, is characterized by its excellent potential hydraulic properties. Its key performance indicators, such as fineness, activity index, and fluidity, all meet or exceed the high-activity requirements of national standards. S95 grade blast furnace slag powder is rich in amorphous or microcrystalline silicates and aluminates. Under suitable alkaline activation conditions, these active components can undergo hydration reactions with water to generate calcium silicate hydrates, calcium aluminum hydrates, and other compounds with cementing properties.

[0040] Grade II fly ash, in which the Grade II quality indicates that its loss on ignition, water demand ratio, and fineness all meet national standards, and it possesses good pozzolanic activity. The main chemical components of fly ash are amorphous silica and alumina, and its particles are usually spherical. This unique morphology is beneficial for improving the rheological properties of the mixture and the density of the final aggregate.

[0041] In an alkaline environment, the active silica and alumina in fly ash can react with the calcium ions provided in the system to generate gels and calcium aluminum silicate hydrates. These gels interpenetrate and intertwine with the mineral powder hydration products, further enhancing the strength and long-term stability of the cementing system.

[0042] The weight ratio of S95 grade mineral powder to Class II fly ash is controlled within the range of 1:0.2-0.4. Through their unique potential hydraulic properties and pozzolanic effect, they form a highly efficient synergistic cementing mechanism, which together form the basis of the cement-free cementing system in the embodiments of this invention. This optimizes the pozzolanic activity and particle size distribution of the two materials, achieving the best cementing effect, pore structure filling, and overall density improvement.

[0043] Preferably, the activator contains a high proportion of calcium oxide, sodium oxide, and potassium oxide in the alkaline slag, calcium hydroxide in the carbide slag, and oxides such as ferric oxide, aluminum oxide, silicon dioxide, and sodium oxide in the red mud. The activator is used to activate the potential activity of pozzolanic materials, promoting their efficient hydration reaction under normal temperature and humidity conditions. The activator is a compound of alkaline slag, carbide slag, and red mud in a specific ratio, controlled within the range of 1:0.8-1.2:0.1-0.5, to provide sufficient alkalinity and calcium source, ensuring that the pozzolanic materials can be fully activated. At the same time, it balances the cost, performance contribution, and potential negative effects of different activators, achieving a synergistic activation effect of multiple industrial solid wastes.

[0044] Specifically, the alkali residue mainly contains a high proportion of calcium oxide, sodium oxide and potassium oxide. These strongly alkaline oxides hydrate in water to form strongly alkaline hydroxides, providing a strongly alkaline environment for the system. This can effectively promote the depolymerization and dissolution of the aluminosilicate network in S95 grade mineral powder and II grade fly ash, thereby accelerating the hydration reaction.

[0045] Calcium carbide slag, whose main chemical component is calcium hydroxide, is a highly alkaline material and an important source of calcium. Its hydration products not only provide a continuous supply of calcium ions for pozzolanic materials but also further enhance the alkalinity of the system, thereby promoting the rapid formation and accumulation of gel.

[0046] Red mud, a complex industrial solid waste, contains various oxides in its chemical composition, such as ferric oxide, aluminum oxide, silicon dioxide, and sodium oxide. The high alkalinity of the sodium oxide component in red mud makes it an effective alkaline activator, while its inherent potential aluminate activity allows it to participate in the reaction as an auxiliary cementing material, providing additional active components for the formation of hydration products. The introduction of red mud not only further enhances the alkaline activation strength of the system but also improves the component diversity and reaction product structure of the cementing system to a certain extent.

[0047] Preferably, the addition of an expansive agent effectively compensates for the autogenous shrinkage and drying shrinkage that may occur in the artificial fine aggregate during the hydration and hardening process, thereby improving the volume stability and crack resistance of the aggregate. The expansive agent selected has a specific surface area of ​​400 m² or more. 2 Steel slag with a surface area of ​​ / kg has high chemical activity, and its main chemical components usually include calcium oxide, magnesium oxide, silicon dioxide, aluminum oxide, iron oxide, etc.

[0048] Specifically, free calcium oxide (f-calcium oxide) and free magnesium oxide (f-MgO) are the main sources of expansion. During hydration, f-calcium oxide reacts rapidly with water to form calcium hydroxide, while f-MgO hydrates relatively slowly to form magnesium hydroxide. These hydration reactions are accompanied by crystal growth and volume expansion. This expansion effect can effectively offset early drying shrinkage and later self-shrinkage, thereby reducing the generation of microcracks caused by shrinkage stress concentration inside the aggregate, and thus improving its overall durability and long-term stability.

[0049] The amount of steel slag used needs to be precisely controlled to achieve an appropriate expansion compensation effect. Too little slag may not be enough to offset shrinkage, while too much slag may lead to excessive expansion, which may cause cracking and affect the structural integrity and mechanical properties of the aggregate.

[0050] Preferably, the introduction of the reinforcing agent optimizes the structure of hydration products in the cementitious system, increases the amount of hydration products generated, thereby improving the density of the artificial fine aggregate, reducing porosity, and ultimately enhancing its mechanical strength. The reinforcing agent is desulfurized gypsum, whose main chemical component is calcium sulfate dihydrate. In the alkaline activation system constructed by the alkaline activator, desulfurized gypsum, as an activator of sulfoaluminate, can react with the active aluminum phase in the pozzolanic material to generate hydrated calcium sulfoaluminate with a unique crystal morphology, namely ettringite or monosulfide-type hydrated calcium sulfoaluminate.

[0051] Specifically, ettringite is a needle-like or rod-shaped crystal whose unique crystal morphology allows it to form an interlocking, overlapping network structure in cementing systems. This network structure not only effectively fills the micropores in the cementing system and improves the density of the cement layer, but also contributes to the strength development of cementitious materials through the mechanical interlocking and physical overlapping of its crystals, similar to the fiber reinforcement effect.

[0052] In addition, the addition of desulfurized gypsum can also regulate the hydration reaction rate to a certain extent, promote the dissolution and polymerization of active silicon and aluminum components, optimize the gel structure, and make it more dense and uniform.

[0053] The amount of desulfurized gypsum used is precisely formulated to ensure that ettringite can be generated in the system in an appropriate amount. Too little desulfurized gypsum will not be able to fully exert its reinforcing effect, while too much desulfurized gypsum may cause unnecessary volume expansion or durability problems.

[0054] Preferably, the volcanic ash material, activator, expanding agent and reinforcing agent are placed in a planetary mixing vessel for mixing. The planetary mixing vessel achieves multi-dimensional and all-round shearing, mixing and diffusion of the material through the rotation and revolution of the agitator. The mixing process lasts for 2-4 minutes to ensure that the volcanic ash material, activator, expanding agent and reinforcing agent form a uniformly dispersed solid waste cementitious material.

[0055] Specifically, the stirring time is set to 2-4 minutes. The purpose is to fully premix all industrial solid waste materials, which serve as both cementing and functional components, to form a highly uniform composite powder of all-solid waste cementitious materials. This time range is sufficient to ensure that the various fine powders are fully and evenly mixed, guaranteeing that the subsequent hydration reaction can proceed synchronously and efficiently. Too short a time may lead to uneven mixing, while too long a time will increase unnecessary energy consumption without any significant benefit. During this stage, sufficient physical contact and dispersion are achieved between the particles of each solid waste material, creating ideal initial conditions for the subsequent chemical reaction in the presence of water.

[0056] S3. Mix the iron tailings powder and a portion of the solid waste cementitious material, then crush and stir until homogeneous to obtain a mixture. Please refer to [reference needed]. Figure 3 , Figure 3 This is a diagram of the first stage of the artificial fine aggregate for iron tailings prepared in this invention.

[0057] The weight ratio of iron tailings powder to solid waste cementitious materials (i.e., the sum of pozzolanic materials, activators, expansion agents and reinforcing agents) is controlled within the range of 1:0.2-0.5, ensuring that the iron tailings powder can be fully coated and cemented by sufficient cementitious components to form artificial aggregates with final strength and durability that meet the requirements of engineering applications.

[0058] In this step, the iron tailings powder obtained in step S1 and 70-85 wt% of the total solid waste cementitious material prepared in step S2 are added to a roller mill mixer according to a preset ratio for rolling and mixing to obtain a uniform mixture. The rolling and mixing process lasts for 4-6 minutes. This step is a key preliminary mixing step before pelletizing, and its core lies in achieving material homogenization and pre-compaction through mechanical action.

[0059] Preferably, the pretreated iron tailings powder and most of the cementing materials are accurately weighed and then fed into a roller mill mixer for mixing. The roller mill mixer combines the actions of rolling, shearing, and mixing, and is particularly suitable for mixing semi-dry materials. The enormous pressure applied to the material by its heavy rollers can effectively break up agglomerates and promote close contact between particles of different sizes and properties, forming a high-density mixture. This strong mechanical action is important for the subsequent pelletizing process, as it can improve the strength and density of green pellets and reduce the dependence on moisture during pelletizing.

[0060] Specifically, the rolling and mixing time is controlled at 4-6 minutes to ensure that the materials are fully and evenly mixed to obtain a uniform mixture with high density and stable quality, and to achieve the required initial moisture and compaction, so as to provide stable and uniform raw materials for the next stage of pelletizing.

[0061] S4. The mixture is rolled and sprayed with water to obtain iron tailings microspheres with a diameter of 1-4 mm. Please refer to [reference needed]. Figure 4 , Figure 4 This is a diagram of the second stage of the artificial fine aggregate for iron tailings prepared in this invention.

[0062] In this step, the uniform mixture is poured into the disc pelletizer. Under the combined effect of the equipment's tilt angle and rotation speed, the material begins to form a tumbling bed in the disc, and the particles roll, collide, and aggregate under the action of gravity and centrifugal force.

[0063] Preferably, water, accounting for 2-6% of the total mass of the mixture, is evenly sprayed using a high-precision spraying system for 3-6 minutes until iron tailings microspheres with a diameter of 1-4 mm are formed. The sprayed water is a key medium in the pelleting process, acting as a carrier for the formation of liquid bridging forces, binding fine powder particles into larger spheres.

[0064] Specifically, the amount of water should be controlled at 2-6% of the total mass of the mixture: too little water will result in insufficient liquid bridging force, making it difficult to form effective pellets; while too much water will cause the pellets to be too wet, resulting in insufficient strength and easy adhesion between them. The rolling time should last for 3-6 minutes to ensure that the pellet cores can grow uniformly to the target diameter range of 1-4 mm. This size range is highly matched with the particle size distribution of natural fine aggregates, thus ensuring its good applicability in applications such as concrete or mortar.

[0065] S5. Add the remaining solid waste cementitious material to the iron tailings microspheres for rolling treatment, so that the solid waste cementitious material coats the surface of the iron tailings microspheres to obtain core-shell structured composite particles.

[0066] In this step, after the iron tailings microspheres are formed, the pelletizing process does not need to be interrupted. The remaining 15-30 wt% of cementitious material is directly added to the disc pelletizer, and rolling continues for 2-5 minutes. The purpose is to perform a secondary coating on the formed iron tailings microspheres to enhance their surface properties and density. The remaining cementitious material adheres to the moist surface of the iron tailings microspheres and is rolled and compacted to form a dense, smooth, and uniform outer shell. This coating layer not only further improves the compressive strength and abrasion resistance of the artificial fine aggregate but also effectively prevents the aggregate particles from sticking together due to mutual friction or humid environments during subsequent storage and transportation, ensuring good dispersibility and flowability of the final product. The 2-5 minute rolling time ensures that the coating layer forms uniformly and completely, achieving the ideal state of a smooth, non-adhesive outer shell. This is of great significance for improving product appearance quality, reducing construction difficulty, and ensuring engineering performance.

[0067] S6. The core-shell structured composite particles are cured to obtain artificial fine aggregate of iron tailings. Please refer to [reference needed]. Figure 5 , Figure 5 This is a finished product image of the artificial fine aggregate for iron tailings prepared in this invention.

[0068] In this step, the obtained core-shell structured composite particles are removed from the disc pelletizer and cured for 28 days in an environment with a temperature of 15-30℃ and a relative humidity maintained above 90%, thus obtaining artificial fine aggregate from iron tailings. This step is the final embodiment of the core technology route of this invention: no-firing and no-steam curing. Curing in a normal temperature and high humidity environment avoids the high temperature and high energy consumption required by traditional sintering processes, as well as the expensive equipment investment and high operating costs required by steam curing. Under these specific curing conditions, the multi-component solid waste cementing system composed of pozzolanic materials and activators will continuously undergo complex hydration and pozzolanic reactions.

[0069] Ideally, a high-humidity environment ensures a continuous supply of moisture required for the reaction, effectively preventing self-drying and reaction interruption caused by excessively rapid internal moisture evaporation, thus guaranteeing the full progress of the hydration reaction. Temperature control within the range of 15-30℃ provides suitable kinetic conditions for the gelation reaction, preventing both excessively rapid initiation of early cracks and excessively slow development that could affect strength.

[0070] Ideally, during a 28-day curing period, a large number of hydration products such as calcium silicate hydrates, calcium aluminum silicate hydrates, sodium aluminum silicate hydrate gels, and ettringite will be continuously generated within the system. These nano- and micron-sized products intertwine and fill the pores, gradually improving the density, hardness, and compressive strength of the artificial fine aggregate, ultimately forming a high-quality artificial fine aggregate with stable performance that meets the requirements of various engineering applications.

[0071] To more fully reveal the advantages and feasibility of the non-fired, non-steam-cured, solid waste-type artificial fine aggregate for iron tailings and its preparation method, the following detailed description will be provided through specific examples and comparative proportions, along with quantitative experimental data.

[0072] Example 1 This embodiment provides a method for preparing non-fired, non-steam-cured, solid waste-type artificial fine aggregate from iron tailings, comprising the following steps: 1) Prepare raw materials: The weight ratio of iron tailings powder and solid waste cementitious material is 1:0.3.

[0073] In the all-solid-waste cementitious material, the weight ratio of pozzolanic material, activator, expanding agent, and reinforcing agent is 1:0.7:0.15:0.08. Specifically, the weight ratio of S95 grade mineral powder to Grade II fly ash in the pozzolanic material is 1:0.3; the weight ratio of alkaline slag, carbide slag, and red mud in the activator is 1:1.0:0.3; and the specific surface area of ​​steel slag in the expanding agent is 420 m². 2 / kg.

[0074] 2) Preparation of all-solid-waste cementitious material: Put the volcanic ash material, activator, expansion agent and reinforcing agent into a planetary mixer and stir for 3 minutes until uniform to obtain the all-solid-waste cementitious material.

[0075] 3) Preparation of mixture: Put 80wt% of the total amount of iron tailings powder and solid waste cementitious materials into a roller mill and grind and mix for 5 minutes to obtain the mixture.

[0076] 4) Preparation of iron tailings microspheres: Pour the mixture into a disc pelletizer and spray water while rolling. The amount of water sprayed should be 4% of the total mass of the mixture. Stir for 4.5 minutes until iron tailings microspheres with a diameter of 1-4 mm are formed.

[0077] 5) Preparation of core-shell composite particles: Add the remaining solid waste cementitious material to the disc pelletizer and continue rolling for 3.5 minutes until the surface of the iron tailings microspheres is completely covered by the solid waste cementitious material, forming core-shell composite particles with smooth outer shells and no adhesion.

[0078] 6) Obtaining artificial fine aggregate of iron tailings: The core-shell structured composite particles are placed in an environment with a temperature of 20℃ and a relative humidity of 95% for 28 days to obtain artificial fine aggregate of iron tailings.

[0079] The artificial fine aggregate of iron tailings prepared in this embodiment was tested, and the test results are shown in Table 1. The 28-day compressive strength was 6.2 MPa, and the bulk density was 1450 kg / m³. 3 It has a water absorption rate of 6.8% and a volume shrinkage rate of 0.32%.

[0080] Example 2 The only difference between this embodiment and Embodiment 1 is that: In step 1), the weight ratio of iron tailings powder to solid waste cementitious material is 1:0.2.

[0081] In the solid waste cementitious material, the weight ratio of pozzolanic material, activator, expanding agent, and reinforcing agent is 1:0.5:0.1:0.05. Among them, the weight ratio of S95 grade mineral powder and Class II fly ash in the pozzolanic material is 1:0.2; the weight ratio of alkaline slag, carbide slag, and red mud in the activator is 1:0.8:0.1.

[0082] In step 2), the volcanic ash material, activator, expansion agent and reinforcing agent are placed in a planetary mixing pot and stirred for 2 minutes.

[0083] In step 3), 75 wt% of the total amount of iron tailings powder and solid waste cementitious materials are put into a roller mill and crushed for 4 minutes.

[0084] In step 4), the amount of water sprayed accounts for 2% of the total mass of the mixture, and the mixture is stirred for 3.5 minutes.

[0085] In step 5), continue scrolling for 2.5 minutes.

[0086] In step 6), the core-shell composite particles are placed in an environment with a temperature of 15°C and a relative humidity of 90% for 28 days for curing.

[0087] The artificial fine aggregate of iron tailings prepared in this embodiment was tested, and the test results are shown in Table 1. The 28-day compressive strength was 5.5 MPa, and the bulk density was 1380 kg / m³. 3 It has a water absorption rate of 8.2% and a volume shrinkage rate of 0.45%.

[0088] Example 3 The only difference between this embodiment and Embodiment 1 is that: In step 1), the weight ratio of iron tailings powder to solid waste cementitious material is 1:0.5.

[0089] In the solid waste cementitious material, the weight ratio of pozzolanic material, activator, expanding agent, and reinforcing agent is 1:1.0:0.2:0.1. Among them, the weight ratio of S95 grade mineral powder and Class II fly ash in the pozzolanic material is 1:0.4; the weight ratio of alkaline slag, carbide slag, and red mud in the activator is 1:1.2:0.5.

[0090] In step 2), the volcanic ash material, activator, expansion agent and reinforcing agent are placed in a planetary mixing pot and stirred for 4 minutes.

[0091] In step 3), 85 wt% of the total amount of iron tailings powder and solid waste cementitious materials are put into a roller mill and crushed for 6 minutes.

[0092] In step 4), the amount of water sprayed accounts for 6% of the total mass of the mixture, and the mixture is stirred for 6 minutes.

[0093] In step 5), continue scrolling for 5 minutes.

[0094] In step 6), the core-shell composite particles are placed in an environment with a temperature of 30°C and a relative humidity of 98% for 28 days for curing.

[0095] The artificial fine aggregate of iron tailings prepared in this embodiment was tested, and the test results are shown in Table 1. The 28-day compressive strength was 7.1 MPa, and the bulk density was 1520 kg / m³. 3 It has a water absorption rate of 5.3% and a volume shrinkage rate of 0.25%.

[0096] Example 4 The only difference between this embodiment and Embodiment 1 is that: In step 1), the weight ratio of iron tailings powder to solid waste cementitious material is 1:0.4.

[0097] In the solid waste cementitious material, the weight ratio of pozzolanic material, activator, expanding agent, and reinforcing agent is 1:0.8:0.18:0.09. Among them, the weight ratio of alkaline slag, carbide slag, and red mud in the activator is 1:1.1:0.4.

[0098] In step 3), 82 wt% of the total amount of iron tailings powder and solid waste cementitious materials are put into a roller mill and crushed for 5.5 minutes.

[0099] In step 4), the amount of water sprayed accounts for 5% of the total mass of the mixture, and the mixture is stirred for 5 minutes.

[0100] In step 5), continue scrolling for 4 minutes.

[0101] In step 6), the core-shell composite particles are placed in an environment with a temperature of 25°C and a relative humidity of 96% for 28 days for curing.

[0102] The artificial fine aggregate of iron tailings prepared in this embodiment was tested, and the test results are shown in Table 1. The 28-day compressive strength was 6.8 MPa, and the bulk density was 1480 kg / m³. 3 It has a water absorption rate of 5.9% and a volume shrinkage rate of 0.28%.

[0103] Example 5 The only difference between this embodiment and Embodiment 1 is that: In step 1), the weight ratio of iron tailings powder to solid waste cementitious material is 1:0.35.

[0104] In the solid waste cementitious material, the weight ratio of pozzolanic material, activator, expanding agent, and reinforcing agent is 1:0.6:0.12:0.06. Among them, the weight ratio of S95 grade mineral powder and Class II fly ash in the pozzolanic material is 1:0.25; the weight ratio of alkaline slag, carbide slag, and red mud in the activator is 1:0.9:0.2.

[0105] In step 2), the volcanic ash material, activator, expansion agent and reinforcing agent are placed in a planetary mixing pot and stirred for 2.5 minutes.

[0106] In step 3), 70 wt% of the total amount of iron tailings powder and solid waste cementitious materials are put into a roller mill and crushed for 4.5 minutes.

[0107] In step 4), the amount of water sprayed accounts for 3% of the total mass of the mixture, and the mixture is stirred for 4 minutes.

[0108] In step 5), continue scrolling for 3 minutes.

[0109] In step 6), the core-shell composite particles are placed in an environment with a temperature of 22°C and a relative humidity of 94% for 28 days for curing.

[0110] The artificial fine aggregate of iron tailings prepared in this embodiment was tested, and the test results are shown in Table 1. The 28-day compressive strength was 6.0 MPa, and the bulk density was 1420 kg / m³. 3 It has a water absorption rate of 7.1% and a volume shrinkage rate of 0.35%.

[0111] Example 6 The only difference between this embodiment and Embodiment 1 is that: In step 1), the weight ratio of iron tailings powder to solid waste cementitious material is 1:0.45.

[0112] In the solid waste cementitious material, the weight ratio of pozzolanic material, activator, expanding agent, and reinforcing agent is 1:0.9:0.16:0.07. Among them, the weight ratio of S95 grade mineral powder and Class II fly ash in the pozzolanic material is 1:0.35; the weight ratio of alkaline slag, carbide slag, and red mud in the activator is 1:1.0:0.4.

[0113] In step 2), the volcanic ash material, activator, expansion agent and reinforcing agent are placed in a planetary mixing pot and stirred for 3.5 minutes.

[0114] In step 3), 83 wt% of the total amount of iron tailings powder and solid waste cementitious materials are put into a roller mill and crushed for 5.5 minutes.

[0115] In step 4), the amount of water sprayed accounts for 4.5% of the total mass of the mixture, and the mixture is stirred for 5.5 minutes.

[0116] In step 5), continue scrolling for 4.5 minutes.

[0117] In step 6), the core-shell composite particles are placed in an environment with a temperature of 28°C and a relative humidity of 97% for 28 days for curing.

[0118] The artificial fine aggregate of iron tailings prepared in this embodiment was tested, and the test results are shown in Table 1. The 28-day compressive strength was 6.9 MPa, and the bulk density was 1500 kg / m³. 3 It has a water absorption rate of 6.2% and a volume shrinkage rate of 0.30%.

[0119] Comparative Example 1 The only difference between this comparative example and Example 1 is that: In step 1), the weight ratio of iron tailings powder to (all solid waste cementitious material + P.O42.5 cement) is 1:0.3, wherein P.O42.5 cement is introduced into the all solid waste cementitious material.

[0120] In the all-solid-waste cementitious material, the weight ratio of pozzolanic material, activator + P.O42.5 cement, expanding agent, and reinforcing agent is 1:0.5:0.1:0.05. Among them, the weight ratio of S95 grade mineral powder and Class II fly ash in the pozzolanic material is 1:0.2; the weight ratio of alkaline slag, carbide slag, and red mud in the activator is 1:0.8:0.1.

[0121] The artificial fine aggregate of iron tailings prepared in this comparative example was tested, and the test results are shown in Table 1. The 28-day compressive strength was 5.0 MPa, and the bulk density was 1400 kg / m³. 3 It has a water absorption rate of 9.5% and a volume shrinkage rate of 0.55%.

[0122] Comparative Example 2 The only difference between this comparative example and Example 1 is that: In step 1), the weight ratio of iron tailings powder to solid waste cementitious material is 1:0.5, and no expansion agent is added to the solid waste cementitious material.

[0123] In the solid waste cementitious material, the weight ratio of pozzolanic material, activator, and reinforcing agent is 1:1.0:0.1. Among them, the weight ratio of S95 grade mineral powder and Class II fly ash in the pozzolanic material is 1:0.4; the weight ratio of alkaline slag, carbide slag, and red mud in the activator is 1:1.2:0.5.

[0124] In step 2), the volcanic ash material, activator and reinforcing agent are placed in a planetary mixing pot and stirred for 4 minutes.

[0125] In step 3), 85 wt% of the total amount of iron tailings powder and solid waste cementitious materials are put into a roller mill and crushed for 6 minutes.

[0126] In step 4), the amount of water sprayed accounts for 6% of the total mass of the mixture, and the mixture is stirred for 6 minutes.

[0127] In step 5), continue scrolling for 5 minutes.

[0128] In step 6), the core-shell composite particles are placed in an environment with a temperature of 30°C and a relative humidity of 98% for 28 days for curing.

[0129] The preparation parameters for steps 2) to 6) in this comparative example are the same as those in Example 3.

[0130] The artificial fine aggregate of iron tailings prepared in this comparative example was tested, and the test results are shown in Table 1. The 28-day compressive strength was 5.2 MPa, and the bulk density was 1480 kg / m³. 3 It has a water absorption rate of 7.8% and a volume shrinkage rate of 0.85%.

[0131] Table 1 Mechanical properties of artificial fine aggregates from iron tailings

[0132] The artificial fine aggregates of iron tailings prepared in Examples 1-6 all exhibited a 28-day compressive strength between 5.5 and 7.1 MPa, meeting the engineering requirement of ≥5 MPa compressive strength for artificial fine aggregates used in construction; their bulk density was 1380-1520 kg / m³. 3 It is in the range of natural fine aggregates (1400-1600 kg / m³). 3 Within a reasonable range, it can directly replace natural sand; its water absorption rate is 5.3-8.2%, lower than the durability threshold of ≤10% for artificial fine aggregates; its volume shrinkage rate is 0.25-0.45%, demonstrating excellent volume stability and preventing later cracking. This indicates that the patented technical route of all-solid waste proportioning + normal temperature and humidity curing can stably prepare high-performance artificial fine aggregates.

[0133] Comparative Example 1, due to the introduction of cement to replace part of the solid waste, showed a 19.4% decrease in 28-day compressive strength (6.2→5.0 MPa), a 39.7% increase in water absorption (6.8→9.5%), and a 71.9% increase in volume shrinkage (0.32→0.55%) compared to Example 1. This is because the introduction of cement disrupted the synergistic activation mechanism of the various solid wastes, and cement itself has significant shrinkage and poor interfacial bonding with solid waste, while also increasing carbon emissions (cement production emits approximately 800 kg CO2 / ton), thus demonstrating the rationale for the patent's decision to abandon reliance on cement.

[0134] Comparative Example 2, lacking an expanding agent, exhibited a 240% increase in volume shrinkage compared to Example 3 (0.25→0.85%), far exceeding the allowable range for engineering applications (≤0.5%), and a 26.8% decrease in compressive strength (7.1→5.2MPa). This demonstrates that the addition of the steel slag expanding agent in the embodiments of the present invention can effectively compensate for hydration shrinkage, which is crucial for ensuring the volume stability and mechanical properties of the aggregate.

[0135] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the term "include" or any other variation thereof is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus.

[0136] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their likenesses.

Claims

1. A method for preparing non-fired, non-steam-cured, solid waste-type artificial fine aggregate from iron tailings, characterized in that, Includes the following steps: S1. The iron tailings are dried and screened to obtain iron tailings powder with a particle size of less than 0.3 mm. S2. Mix the pozzolanic material, activator, expanding agent and reinforcing agent, and stir evenly to obtain a solid waste cementitious material; wherein, the pozzolanic material is S95 grade mineral powder and II grade fly ash, the activator is alkaline slag, carbide slag and red mud, the expanding agent is steel slag, and the reinforcing agent is desulfurized gypsum. S3. Mix the iron tailings powder and part of the solid waste cementitious material, crush and stir evenly to obtain a mixture; S4. The mixture is rolled and sprayed with water to obtain iron tailings microspheres with a diameter of 1-4 mm; S5. Add the remaining solid waste cementitious material to the iron tailings microspheres for rolling treatment, so that the solid waste cementitious material coats the surface of the iron tailings microspheres to obtain core-shell structured composite particles. S6. The core-shell structured composite particles are cured to obtain artificial fine aggregate of iron tailings.

2. The method for preparing non-fired, non-steam-cured, solid waste-type artificial fine aggregate from iron tailings according to claim 1, characterized in that, The weight ratio of the iron tailings powder to the solid waste cementitious material is 1:0.2-0.

5.

3. The method for preparing non-fired, non-steam-cured, solid waste-type artificial fine aggregate from iron tailings according to claim 1, characterized in that, In step S1: The iron tailings are composed of silicon dioxide, ferric oxide, and aluminum oxide; and / or When drying the iron tailings, the moisture content of the iron tailings is less than 0.5 wt%, the drying temperature is 80-120℃, and the drying time is 1-2 hours.

4. The method for preparing non-fired, non-steam-cured, solid waste-type artificial fine aggregate from iron tailings according to claim 1, characterized in that, In step S2: The weight ratio of the volcanic ash material, the activator, the expanding agent, and the reinforcing agent is 1:0.5-1.0:0.1-0.2:0.05-0.1; and / or The S95 grade mineral powder is an amorphous or microcrystalline silicate and aluminate; and / or The Class II fly ash is composed of amorphous silica and aluminum oxide; and / or The weight ratio of the S95 grade mineral powder to the II grade fly ash is 1:0.2-0.4; and / or The alkaline residue is composed of calcium oxide, sodium oxide, and potassium oxide; and / or The carbide slag is calcium hydroxide; and / or The red mud is composed of ferric oxide, aluminum oxide, silicon dioxide, and sodium oxide; and / or The weight ratio of the alkaline residue, the carbide slag, and the red mud is 1:0.8-1.2:0.1-0.5; and / or The steel slag is composed of free calcium oxide and free magnesium oxide; and / or The specific surface area of ​​the steel slag is greater than or equal to 400 m². 2 / kg.

5. The method for preparing non-fired, non-steam-cured, solid waste-type artificial fine aggregate from iron tailings according to claim 1, characterized in that, In step S2: The volcanic ash material, the activator, the expansion agent, and the reinforcing agent are placed in a planetary mixing vessel for mixing. The planetary mixing vessel uses the rotation and revolution of the agitator to perform multi-dimensional and all-round shearing, mixing, and diffusion of the material. The mixing time is 2-4 minutes.

6. The method for preparing non-fired, non-steam-cured, solid waste-type artificial fine aggregate from iron tailings according to claim 1, characterized in that, In step S3: The amount of the solid waste cementitious material added is 70-85 wt% of the total weight of the solid waste cementitious material; and / or The iron tailings powder and 70-85 wt% of the total solid waste cementitious material are placed in a roller mill for compaction and mixing, and the compaction and mixing time is 4-6 minutes.

7. The method for preparing non-fired, non-steam-cured, solid waste-type artificial fine aggregate from iron tailings according to claim 1, characterized in that, In step S4: The mixture is poured into a disc pelletizer, and the tilt angle and speed of the disc pelletizer are adjusted for rolling. At the same time, water accounting for 2-6% of the total mass of the mixture is sprayed evenly through a precision spraying system for 3-6 minutes to obtain iron tailings microspheres with a diameter of 1-4 mm.

8. The method for preparing non-fired, non-steam-cured, solid waste-type artificial fine aggregate from iron tailings according to claim 7, characterized in that, In step S5: The remaining solid waste cementitious material is added to the disc pelletizer for rolling treatment. The rolling continues for 2-5 minutes, so that the solid waste cementitious material coats the surface of the iron tailings microspheres, thus obtaining the core-shell structured composite particles.

9. The method for preparing non-fired, non-steam-cured, solid waste-type artificial fine aggregate from iron tailings according to claim 1, characterized in that, In step S6: The core-shell structured composite particles were placed in an environment with a temperature of 15-30℃ and a relative humidity of over 90% for 28 days to cure them, thus obtaining the artificial fine aggregate of iron tailings.

10. A non-fired, non-steam-cured, solid waste-type artificial fine aggregate for iron tailings, characterized in that, The artificial fine aggregate of iron tailings is prepared by the preparation method of the non-fired and non-steam-cured solid waste type artificial fine aggregate of iron tailings as described in any one of claims 1-9.

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