Tailing-based autoclaved aggregate as well as preparation method and application thereof

Abstract

The invention discloses tailing-based autoclaved aggregate as well as a preparation method and application thereof, and belongs to the technical field of building materials. The tailing-based autoclaved aggregate is prepared from the following raw materials in percentage by mass based on the total weight of the dry basis of the aggregate: 66-70% of composite tailing powder, 21-25% of calcium-based solid waste and 5-9% of a composite adhesive, wherein the composite tailing powder is composed of iron tailings and gold tailings according to the mass ratio of 3: 4-1: 1, the composite adhesive comprises calcium sulfate dihydrate, hydroxypropyl modified starch and sodium polyacrylate, and the mass ratio of the three components is (3-6): (1-1.5): (1-1.5). The coarse aggregate for the concrete is prepared by compounding the gold tailings and the iron tailings together and adopting the composite adhesive composed of the calcium sulfate dihydrate, the hydroxypropyl modified starch and the sodium polyacrylate through the static pressure molding and autoclaved curing process, so that the problem that in the prior art, when tailing slag is adopted as the concrete aggregate, the coarse aggregate is not easy to deform can be effectively solved. And the strength and durability of the concrete cannot be ensured.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, and more specifically, relates to a tailings-based autoclaved aggregate, its preparation method, and its application. Background Technology

[0002] With the development of the construction industry, the amount of concrete used is increasing daily, leading to a growing demand for aggregates. Currently, there are two types of construction aggregates used: natural aggregates and artificial aggregates. Natural aggregates mainly rely on natural sand and gravel, but their extraction process damages the ecological environment, causing soil erosion, soil desertification, and a series of other ecological problems. As the country places greater emphasis on environmental and resource protection, the extraction of natural aggregates has faced increasing restrictions. Therefore, artificial aggregates, as a substitute for natural aggregates, have become particularly important.

[0003] Tailings slag is the residue left after ore beneficiation or smelting. It is a type of solid waste, and traditional treatment mainly involves stockpiling. Large-scale stockpiling not only impacts the environment but also wastes resources. Therefore, how to utilize tailings slag, this solid waste, has become a pressing issue in the mineral processing industry. Although existing technologies have explored using iron tailings and other tailings slag to prepare building aggregates, the resulting concrete still suffers from low strength and poor durability. Furthermore, some existing processes require the addition of large amounts of cement or chemical admixtures, leading to high production costs and potentially affecting aggregate stability. Summary of the Invention

[0004] This application provides a tailings-based autoclaved aggregate, its preparation method, and its application. By compounding gold tailings and iron tailings together and using a composite binder composed of calcium sulfate dihydrate, hydroxypropyl modified starch, and sodium polyacrylate, coarse aggregate for concrete is prepared through static pressing and autoclaving processes. This effectively solves the problem that the strength and durability of concrete cannot be guaranteed when tailings slag is used as concrete aggregate in the prior art, thus facilitating the resource utilization of tailings slag.

[0005] Specifically, to achieve the above objectives, the technical solution provided by this invention is as follows: The first aspect of the present invention provides a tailings-based autoclaved aggregate, wherein the raw materials comprise the following components by mass percentage based on the total dry weight of the aggregate: 66-70% composite tailings powder, 21-25% calcium-based solid waste, and 5-9% composite binder; The composite tailings powder is composed of iron tailings and gold tailings in a mass ratio of 3:4 to 1:1, and the composite binder contains calcium sulfate dihydrate, hydroxypropyl modified starch and sodium polyacrylate, with a mass ratio of (3~6):(1~1.5):(1~1.5).

[0006] In order to make resource utilization of tailings powder, existing studies have used iron tailings and other tailings slag as aggregates in concrete. However, existing studies mostly use iron tailings and other tailings as fine aggregates in concrete, and the structural strength and other mechanical properties and / or corrosion resistance of the resulting concrete products still need to be further improved, thus limiting the application of tailings powder in concrete.

[0007] Based on the above problems, this application proposes to use iron tailings and gold tailings together as coarse aggregate for concrete. The highly active SiO2 and Al2O3 in the iron tailings and gold tailings can react with calcium-based solid waste and composite binders to produce CSH gel and ettringite (AFt) hydration products, thus effectively ensuring the compactness and mechanical properties such as structural strength of the aggregate.

[0008] Specifically, by blending iron tailings and gold tailings together, on the one hand, since iron tailings are mainly composed of inert silicate minerals such as quartz and feldspar, these inert silicate minerals can form a stable framework; while gold tailings are rich in highly active SiO2 and Al2O3, which can provide sufficient hydration products to fill the voids. Therefore, the combination of the two can not only ensure the interfacial bonding strength, but also help improve the aggregate's resistance to deformation and reduce its crushing index.

[0009] On the other hand, since there are differences in the particle size distribution between iron tailings and gold tailings, with gold tailings being mainly composed of fine particles and iron tailings containing more coarse particles, the combination of the two can also optimize the gradient gradation inside the aggregate, which is beneficial to reducing the porosity inside the aggregate and increasing the apparent density.

[0010] More preferably, the particle size distribution of the iron tailings is: Dv(50) is 30~50μm, Dv(90) is 200~350μm; the particle size distribution of the gold tailings is: Dv(50) is 10~20μm, Dv(90) is 60~80μm.

[0011] It should be noted that the aggregate greens made from tailings powder are prone to breakage during autoclaving, which affects the yield. Therefore, this application further optimizes the composition of the binder. By compounding three different components, not only can the bonding effect be guaranteed, but it is also beneficial to improve the early strength of the aggregate and avoid breakage during autoclaving.

[0012] Specifically, calcium sulfate dihydrate, acting as an inorganic cementitious core, can undergo a hydration reaction with the active components in calcium-based solid waste and tailings powder to generate ettringite (AFt) and CSH gel, thus providing a foundation for aggregate strength. Simultaneously, the hydration rate of calcium sulfate dihydrate is moderate (initial setting time 2-3 hours, final setting time 4-6 hours), making it perfectly compatible with subsequent autoclaving processes and preventing internal stress cracking caused by excessively rapid early strength development.

[0013] Hydroxypropyl-modified starch can serve as an organic-inorganic interfacial bridging agent, optimizing the interfacial bonding between binders and tailings particles; furthermore, the hydroxyl groups (-OH) on its molecular chain can react with Ca in the calcium sulfate dihydrate hydration products. 2+ It forms coordination bonds, while the hydrophobic group at the other end can be adsorbed onto the surface of tailings particles, reducing the porosity and cracks in the interface transition zone, thus helping to further improve the interfacial bonding strength.

[0014] Sodium polyacrylate not only improves the workability and stability of the binder slurry, but its anionic groups (-COONa) can also adsorb onto the surface of calcium sulfate dihydrate and tailings particles, forming electrostatic repulsion to prevent particle agglomeration and ensure that the binder uniformly coats the tailings particles. In addition, the hydrophilicity of its polymer chains can lock in free water, preventing slurry cracking caused by excessive evaporation of water before autoclaving and providing sufficient water for the hydration reaction.

[0015] In summary, the combination of these three components achieves a synergistic effect of "1+1+1>3," ultimately ensuring the realization of the aggregate's performance goals of high strength and low porosity. Specifically, calcium sulfate dihydrate provides a strong framework, improving the early strength of the aggregate and compensating for the insufficient strength of the organic components (modified starch and sodium polyacrylate); hydroxypropyl modified starch strengthens interfacial bonding, ensuring a tight bond between the hydration products of calcium sulfate dihydrate and tailings particles, preventing strength loss and improving adhesion; and sodium polyacrylate optimizes slurry properties, allowing calcium sulfate dihydrate and modified starch to be evenly distributed, thus creating conditions for hydration reactions and interfacial bonding.

[0016] Furthermore, the chemical environment of composite tailings is more stable. The ettringite produced by the reaction of dihydrate gypsum with Al2O3 in gold tailings can form hydrogen bonds with the hydroxyl groups on the surface of iron tailings, and the dispersing effect of modified starch and sodium polyacrylate is fully utilized, further optimizing the uniformity of aggregate microstructure.

[0017] Furthermore, this application optimizes the mass ratio of the three components in the composite adhesive, thereby effectively ensuring both the early strength of the resulting aggregate and the bonding effect on tailings particles.

[0018] In some cases, insufficient addition of calcium sulfate dihydrate results in inadequate gelling cores, low hydration product formation, and an inability to fill the gaps between tailings particles, leading to low aggregate strength and increased crushing index. Excessive addition of calcium sulfate dihydrate causes overly vigorous hydration, generating a large amount of ettringite, resulting in volume expansion, internal stress in the aggregate, and a tendency to crack. Insufficient addition of modified starch leads to insufficient interfacial bridging, resulting in a weak bond between the binder and tailings particles, causing increased porosity and crushing index in the interfacial transition zone. Excessive addition of modified starch creates a weak organic layer within the aggregate, reducing its rigidity and compressive strength; simultaneously, the organic components readily absorb water and soften, increasing water absorption. Insufficient addition of sodium polyacrylate leads to binder slurry agglomeration, uneven coating of tailings particles, and localized loose areas within the aggregate, increasing porosity. Excessive addition of sodium polyacrylate significantly increases water absorption and reduces compressive strength.

[0019] According to any of the technical solutions described in the first aspect of the present invention, the calcium content in the calcium-based solid waste is not less than 35% based on CaO; more preferably, the calcium content in the calcium-based solid waste is 35-55% based on CaO, the SiO2 content is 20-30%, and the Al2O3 content is 5-10%.

[0020] Since the calcium-based solid waste in this application is mainly used to provide a calcium source for the hydration reaction, the active CaO in the calcium-based solid waste will, on the one hand, undergo a hydrothermal reaction with SiO2 and Al2O3 in the tailings under autoclaving conditions to generate high-strength hydration products such as tobermorite and CSH gel. The platy crystals of tobermorite interweave to form a dense network structure, which is a key source of aggregate strength. On the other hand, it will also synergistically react with calcium sulfate dihydrate in the composite binder to generate ettringite (AFt), further filling the pores and improving the density. In addition, OH- released during the hydration process of the calcium-based solid waste... - It can also provide an alkaline environment for the activation of inert SiO2 in tailings.

[0021] Therefore, this application imposes high requirements on the component content of calcium-based solid waste, especially the CaO content. When the CaO content is too low (<35%), the amount of tobermorite and CSH gel generated by the hydration reaction is insufficient, which cannot fully fill the pores, resulting in a decrease in the compressive strength of the aggregate and an increase in the crushing index. When the CaO content is too high (>55%), the excess CaO will react with water to generate Ca(OH)2, resulting in volume expansion, microcracks inside the aggregate, increased water absorption, and decreased corrosion resistance.

[0022] This application further optimizes the SiO2 and Al2O3 content in the calcium-based solid waste, forming a reasonable ratio among the three to ensure the optimal ratio of tobermorite to CSH gel in the hydration products, balancing strength and durability. It should be noted that this application mainly specifies requirements for the content of CaO, SiO2, and Al2O3 in the calcium-based solid waste. As long as the aforementioned quality requirements are met, it is acceptable. That is, if the quality requirements of the concentrated components can be met, only one type of calcium-based solid waste can be used. However, when one type of calcium-based solid waste cannot simultaneously meet the quality requirements of the above components, different substances can be used in combination.

[0023] Specifically, according to some embodiments of the present invention, the calcium-based solid waste may be one or more of fly ash, slag, steel slag, carbide slag, and cement.

[0024] More preferably, the specific surface area of ​​the calcium-based solid waste is 350-450 m² / kg, which can further optimize the particle size distribution. The calcium-based solid waste can fill the tiny gaps between iron tailings particles, which is beneficial to further reduce the internal porosity of the aggregate.

[0025] According to any of the technical solutions described in the first aspect of the present invention, the aggregate product is prepared by a process of raw material pretreatment-static pressing-autoclaving, and the compressive strength of the cylinder after autoclaving is 23~25 MPa and the crushing index is 1.5~1.9%.

[0026] By further subjecting the aggregates to separate autoclaving treatment beforehand, the internal hydration reaction of the aggregates can be more complete, resulting in a sufficient amount of tobermorite formation. This effectively improves the compressive strength of the finished aggregate product, and also results in higher density and a tighter interface with the cement paste. The aggregates of this application can be prefabricated and stored, which also helps to shorten the concrete mixing cycle.

[0027] The second aspect of the present invention also provides a method for preparing tailings-based autoclaved aggregate as described in the first aspect of the present invention, comprising: Mix all raw materials with water until homogeneous to obtain a raw material slurry; The raw material slurry is subjected to static pressing molding to obtain aggregate green body; The obtained aggregate greens are subjected to autoclaving and curing, and then crushed and screened to obtain coarse aggregate finished products with a particle size of more than 5mm.

[0028] According to any of the technical solutions described in the second aspect of the present invention, the step of mixing and stirring all raw materials with water to obtain a raw material slurry specifically involves: first, dry mixing all raw materials for 3-5 minutes, then adding water and mixing for 5-8 minutes until the slump is 15-20 mm, thereby obtaining the raw material slurry.

[0029] According to any of the technical solutions described in the second aspect of the present invention, the pressure of the static pressing process is 20~30MPa, and the pressure is held for 60~80s.

[0030] According to any of the technical solutions described in the second aspect of the present invention, the conditions for the autoclaving treatment include: an autoclaving temperature of 180~200℃, a pressure of 1.0~1.2MPa, an autoclaving time of 4~10 hours, and then cooling to below 50℃ before being removed from the autoclave.

[0031] Under the above conditions of autoclaving, the activity of water molecules is enhanced, which breaks through the inert layer on the surface of tailings particles, promotes the hydrothermal reaction of SiO2 and CaO, and generates a large amount of tobermorite (the source of strength), thereby reducing the porosity of aggregate and improving its compressive strength; at the same time, high temperature and high pressure increase the crystallinity of hydration products, making the structure more stable and significantly enhancing corrosion resistance.

[0032] According to any of the technical solutions described in the second aspect of the present invention, the method further includes: before mixing and stirring all raw materials with water evenly, mixing iron tailings and gold tailings evenly and performing steam pre-hydration treatment. Steam pre-hydration can activate the early hydration reaction of composite tailings and calcium-based solid waste in advance, generating a small amount of CSH gel "binding" particles, laying the foundation for subsequent autoclaving.

[0033] Furthermore, the pre-hydration involves placing the mixed material at 18-25°C and 90-95% humidity for 10-12 hours.

[0034] A third aspect of the present invention also provides an application of the tailings-based autoclaved aggregate as coarse aggregate in concrete.

[0035] According to any of the technical solutions described in the third aspect of the present invention, the tailings-based autoclaved aggregate is used to replace part of the crushed stone as coarse aggregate in concrete. The percentage of the tailings-based autoclaved aggregate added is 5-30% of the total coarse aggregate, more preferably 10-30%, and even more preferably 20-30%. This ensures the performance of the resulting concrete while maximizing the resource utilization rate of tailings slag.

[0036] The autoclaved aggregate of this application can directly replace some of the natural coarse aggregates such as crushed stone in existing concrete, reduce the consumption of natural sand and gravel, ensure the mechanical properties and corrosivity of the resulting concrete, and realize the resource utilization of tailings slag. At the same time, its overall preparation process is simple.

[0037] According to any of the technical solutions described in the third aspect of the present invention, the coarse aggregate in the concrete comprises aggregate particles with a particle size of 5-10 mm and a particle size of 10-19 mm, and the mass ratio of the two particle sizes of aggregate is 2:3 to 1:1.

[0038] According to any of the technical solutions described in the third aspect of the present invention, the 28-day compressive strength of the concrete is 55.6-58.3 MPa.

[0039] In summary, by adopting the technical solution provided by this invention, the following beneficial effects can be achieved compared with the prior art: (1) In this invention, composite tailings powder composed of iron tailings and gold tailings is used together with calcium-based solid waste and composite binder to make coarse aggregate for concrete. The highly active SiO2 and Al2O3 in the composite tailings powder can react with calcium-based solid waste and composite binder in the subsequent autoclaving process to generate high-strength hydration products such as CSH gel, tobermorite and ettringite (AFt). Therefore, the compactness and mechanical properties of the aggregate, such as structural strength, can be guaranteed, which solves the problem that the strength and durability of concrete cannot be effectively guaranteed when tailings slag is used as concrete aggregate in the prior art.

[0040] (2) The present invention uses a composite binder composed of calcium sulfate dihydrate, hydroxypropyl modified starch and sodium polyacrylate, which can improve the early strength of the obtained aggregate and avoid breakage during subsequent autoclaving. At the same time, it can effectively ensure the interfacial bonding strength between the particles inside the aggregate and make the binder uniformly dispersed and coated on the surface of tailings powder and calcium-based solid waste, further enhancing the bonding effect.

[0041] (3) This invention uses iron tailings and gold tailings together to prepare coarse aggregate for concrete. On the one hand, it can effectively utilize the stabilizing skeleton of inert silicate minerals in iron tailings and the higher content of active SiO2 and Al2O3 in gold tailings, which is conducive to further improving the deformation resistance of aggregate and reducing its crushing index. On the other hand, it can also optimize the gradient distribution inside the aggregate, which is conducive to reducing the porosity inside the aggregate and increasing the apparent density.

[0042] (4) This application further optimizes and controls the mass ratio of each component, thereby achieving the best combination of mechanical properties such as structural strength, interfacial bonding properties and water absorption of aggregate.

[0043] (5) In preparing the aggregate, this application involves static pressing and autoclaving of the raw material slurry, which is a mixture of raw materials. This allows for the hydrothermal reaction of SiO2 and CaO during the autoclaving process, resulting in a more complete reaction and the generation of a large amount of tobermorite. Consequently, the porosity of the aggregate is effectively reduced, its compressive strength is increased, and the aggregate cured by autoclaving alone has a higher density and a tighter interface with the cement paste. Furthermore, the high-temperature and high-pressure curing process can also improve the crystallinity of the hydration products, making the structure more stable and thus enhancing its corrosion resistance.

[0044] (6) The tailings-based autoclaved aggregate of the present invention can directly replace 10-30% of natural coarse aggregate in concrete without changing the original structure of concrete, realizing the dual benefits of large-scale industrial solid waste disposal and partial replacement of natural aggregate, with significant economic and environmental value. Moreover, its overall preparation process is simple to operate and does not require overall autoclaving treatment of concrete. Attached Figure Description

[0045] Figure 1 The XRD pattern of the iron tailings powder used in the embodiments of the present invention; Figure 2 The XRD pattern of the gold tailings powder used in the embodiments of the present invention; Figure 3 The particle size distribution of the iron tailings powder used in the embodiments of the present invention; Figure 4 This is the particle size distribution of the gold tailings powder used in the embodiments of the present invention. Detailed Implementation

[0046] To further understand the content of this invention, the invention will be described in detail below with reference to specific embodiments. However, the embodiments do not limit the invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in this invention are conventional reagents, methods, and equipment in this technical field. The essential features and significant effects of this invention can be seen from the following embodiments. The described embodiments are some embodiments of this invention, but not all embodiments. Therefore, they do not limit the invention in any way. Non-essential improvements and adjustments made by those skilled in the art based on the content of this invention are all within the protection scope of this invention.

[0047] It should also be understood that, for clarity, certain features of this disclosure may be described herein in the context of individual embodiments, but may also be provided in combination with each other in individual embodiments. That is, unless obviously incompatible or specifically excluded, each individual embodiment is considered to be combinable with any other embodiment, and such combination is considered to represent another different embodiment. Conversely, for brevity, various features of this disclosure described in the context of individual embodiments may also be provided individually or in any sub-combination. Finally, while a particular embodiment may be described as part of a series of steps or part of a more general structure, each step or substructure may also be considered an independent embodiment in itself.

[0048] Furthermore, all numerical ranges in this application should be interpreted as including not only the numerical values ​​explicitly stated as the limits of the range, but also all individual numerical values ​​or sub-ranges covered within the range, as if each numerical value and sub-range were explicitly stated. For example, the numerical range of approximately 66 to 70% should be interpreted as including not only the explicitly stated limit value of 66 to 70%, but also individual numbers (such as 66%, 68%, 69.5%, 70%) and sub-ranges (such as 66 to 68%, 68 to 70%, etc.).

[0049] Example 1 The method for preparing tailings-based autoclaved aggregate in this embodiment includes the following steps: (1) Raw material pretreatment and mixing: Dry iron tailings powder and gold tailings powder to a moisture content of ≤3%, and screen to remove impurities with a particle size >0.15mm; dry mix iron tailings powder (32%), gold tailings powder (35%), saponification waste (25%) and composite binder (8%) (containing 6% calcium sulfate dihydrate, 1% hydroxypropyl modified starch and 1% sodium polyacrylate) for 5 minutes according to the mass ratio, and then add water and mix for 8 minutes until the slump is about 20mm to obtain raw material slurry.

[0050] Specifically, the oxide content analysis of iron tailings powder and gold tailings powder in this embodiment is shown in Tables 1 and 2, respectively. XRD analysis was performed on them, and the results are as follows: Figure 1 , Figure 2 As shown, combined with Figure 1 , Figure 2 It can be seen that the iron tailings powder in this embodiment contains 86% quartz and 9% hematite, with quartz as the main component; the gold tailings powder in this embodiment contains 25% quartz, 18% plagioclase, 11% microcline, 8% calcite, 5% chlorite, 13% dolomite, 8% illite, 12% amphibole, etc.

[0051] Table 1. Analysis Results of Oxide Content in Iron Tailings Powder

[0052] Table 2 Oxide Content Analysis of Gold Tailings Powder

[0053] The particle size distributions of the iron tailings powder and gold tailings powder in this embodiment are as follows: Figure 3 , Figure 4As shown, the specific surface area of ​​iron tailings powder is 776.6 m² / kg, Dv(10) is 2.76 μm, Dv(50) is 43.5 μm, and Dv(90) is 286 μm; the specific surface area of ​​gold tailings powder is 1220 m² / kg, Dv(10) is 1.91 μm, Dv(50) is 14.0 μm, and Dv(90) is 73.1 μm.

[0054] (2) Molding: The raw material slurry is injected into the mold and a pressure of 25MPa is applied and held for 75 seconds to obtain the aggregate green body; (3) Autoclaving: After the aggregate green body is left to stand at room temperature for 24 hours, the green body is transferred to an autoclave and autoclaved at 190℃ and 1.2MPa for 6 hours. Then the temperature is reduced to 50℃ and the green body is removed from the autoclave and covered with film for 24 hours. (4) Screening and grading: Defective products are removed by vibrating screen, and the cured aggregate particles are graded into 5-10mm and 10-20mm for later use.

[0055] Comparative Example 1 The preparation method of the tailings-based autoclaved aggregate in this comparative example differs from that in Example 1. The tailings powder in this comparative example uses only iron tailings, that is, the mass ratio of iron tailings is 67%.

[0056] Comparative Example 2 The preparation method of the tailings-based autoclaved aggregate in this comparative example differs from that in Example 1. The tailings powder in this comparative example uses only gold tailings, that is, the mass ratio of gold tailings is 67%.

[0057] Comparative Example 3 The preparation method of tailings-based autoclaved aggregate in this comparative example differs from that in Example 1, as only calcium sulfate dihydrate is used as a binder in this comparative example.

[0058] Comparative Example 4 The preparation method of tailings-based autoclaved aggregate in this comparative example differs from that in Example 1, as only hydroxypropyl modified starch is used as a binder in this comparative example.

[0059] Comparative Example 5 The preparation method of tailings-based autoclaved aggregate in this comparative example differs from that in Example 1. In this comparative example, calcium sulfate dihydrate + hydroxypropyl modified starch is used as a binder.

[0060] Comparative Example 6 The preparation method of tailings-based autoclaved aggregate in this comparative example differs from that in Example 1, as calcium sulfate dihydrate and sodium polyacrylate are used as binders in this comparative example.

[0061] Comparative Example 7 The preparation method of tailings-based autoclaved aggregate in this comparative example differs from that in Example 1. In this comparative example, hydroxypropyl modified starch + sodium polyacrylate is used as a binder.

[0062] Comparative Example 8 The preparation method of tailings-based autoclaved aggregate in this comparative example differs from that in Example 1, in which anhydrous gypsum is used instead of dihydrate gypsum.

[0063] The relevant performance parameters of the aggregates obtained in Example 1 and Comparative Examples 1-8 are shown in Table 1 below. As can be seen from Table 1, when only iron tailings, only gold tailings, or only a portion of the components in the composite binder are used, at least one performance parameter of the resulting aggregates fails to meet the requirements.

[0064] Table 1 Comparison of relevant performance parameters of aggregates obtained in Example 1 and Comparative Examples 1-8

[0065] Example 2 The method for preparing tailings-based autoclaved aggregate in this embodiment includes the following steps: (1) Raw material pretreatment and mixing: Dry iron tailings powder and gold tailings powder to a moisture content of ≤3%, and screen to remove impurities with a particle size >0.15mm; dry mix iron tailings powder (35%), gold tailings powder (35%), cement (10%), carbide slag (15%) and 5% composite binder (3% calcium sulfate dihydrate, 1% hydroxypropyl modified starch and 1% sodium polyacrylate) for 3 minutes according to the mass ratio, and then add water and mix for 5 minutes until the slump is about 15mm to obtain raw material slurry; (2) Molding: The raw material slurry is injected into the mold, and a pressure of 20MPa is applied and held for 80 s to obtain the aggregate green body; (3) Autoclaving: After the aggregate green body is left to stand at room temperature for 24 hours, the green body is transferred to an autoclave and autoclaved at 200℃ and 1.5MPa for 4 hours. Then the temperature is reduced to 50℃ and the green body is removed from the autoclave and covered with film for 24 hours. (4) Screening and grading: Defective products were removed using a vibrating screen, and the cured aggregate particles were graded into 5-10mm and 10-20mm sizes for later use. The apparent density of the aggregate prepared in this embodiment was 2238 kg / m³. 3 The water absorption rate is 12.4%, the crushing index is 1.5%, and the cylinder compressive strength is 25.0 MPa.

[0066] Example 3 The method for preparing tailings-based autoclaved aggregate in this embodiment includes the following steps: (1) Raw material pretreatment and mixing: Dry iron tailings powder and gold tailings powder to a moisture content of ≤3%, and screen to remove impurities with a particle size >0.15mm; dry mix iron tailings powder (30%), gold tailings powder (38%), cement (7%), carbide slag (18%), and composite binder (4% calcium sulfate dihydrate, 1.5% modified starch and 1.5% sodium polyacrylate) for 4 minutes according to the mass ratio, and then add water and mix for 7 minutes until the slump is about 18mm to obtain raw material slurry; (2) Molding: The raw material slurry is injected into the mold and a pressure of 30 MPa is applied and held for 60 seconds to obtain the aggregate green body; (3) Autoclaving: After the aggregate green body is left to stand at room temperature for 24 hours, the green body is transferred to an autoclave and autoclaved at 180℃ and 1.0MPa for 10 hours. Then the temperature is reduced to 50℃ and the green body is removed from the autoclave and covered with film for 24 hours. (4) Screening and grading: Defective products were removed using a vibrating screen, and the cured aggregate particles were graded into 5-10mm and 10-20mm sizes for later use. The apparent density of the aggregate prepared in this embodiment was 2243 kg / m³. 3 The water absorption rate is 12.7%, the crushing index is 1.7%, and the cylinder compressive strength is 23.2 MPa.

[0067] The aggregates obtained in Examples 1-3 were used in concrete tests, that is, the autoclaved aggregates in Examples 1-3 were used to directly replace part of the crushed stone in the control concrete samples as coarse aggregates. The amount of autoclaved aggregate replacing crushed stone was preferably 10-30%, such as 10%, 15%, 20%, 25%, 30%, etc. Here, we take replacing 30% of crushed stone as an example for explanation. The concrete mix proportions are shown in Table 2 below.

[0068] After conducting concrete mix design tests, the test results are shown in Table 3 below. According to the test results, when the autoclaved aggregate prepared by this invention is applied to concrete, the physical and mechanical properties of the resulting concrete meet the requirements and are superior to those of the comparative sample. Therefore, it can directly replace some natural aggregates in concrete production.

[0069] Table 2 Concrete mix proportions (unit: kg / m³) 3 )

[0070] Table 3. Results of concrete performance tests on comparative samples and example samples (30% admixture).

[0071] Comparative Example 9 Unlike Example 1, this comparative example does not perform separate autoclaving treatment on the aggregates, but instead performs overall autoclaving treatment on the concrete.

[0072] The results show that when only overall autoclaving is performed, the reaction inside the aggregate is incomplete because the cement hydration and aggregate reaction compete for water and heat. Therefore, the compressive strength of the resulting aggregate is significantly insufficient, only about 38.5 MPa. Furthermore, the high porosity of the overall autoclaved aggregate makes it easy to form weak interfacial areas, which also causes the 28-day strength of the concrete to fail to meet the requirements.

[0073] Example 4 The method for preparing tailings-based autoclaved aggregate in this embodiment includes the following steps: (1) Raw material pretreatment and mixing: Dry iron tailings powder and gold tailings powder to a moisture content of ≤3%, and screen to remove impurities with a particle size >0.15mm; dry mix iron tailings powder (30%), gold tailings powder (40%), cement (4%), carbide slag (4%), slag (13%), and composite binder 9% (6% calcium sulfate dihydrate, 1.5% modified starch and 1.5% sodium polyacrylate) for 3.5min according to the mass ratio, and then add water and mix for 8min until the slump is about 19mm to obtain raw material slurry; (2) Molding: The raw material slurry is injected into the mold and a pressure of 28 MPa is applied and held for 65 seconds to obtain the aggregate green body; (3) Autoclaving: After the aggregate green body is left to stand at room temperature for 24 hours, the green body is transferred to an autoclave and autoclaved at 193℃ and 1.3MPa for 7.5 hours. Then the temperature is reduced to 50℃ and the green body is removed from the autoclave and covered with film for 24 hours. (4) Screening and grading: Defective products were removed using a vibrating screen, and the cured aggregate particles were graded into 5-10mm and 10-20mm sizes for later use. The apparent density of the aggregate prepared in this embodiment was 2245 kg / m³. 3 It has a water absorption rate of 13.1%, a crushing index of 1.6%, a cylinder compressive strength of 23.6 MPa, and a porosity of 10.5%.

[0074] Example 5 The method for preparing tailings-based autoclaved aggregate in this embodiment includes the following steps: (1) Raw material pretreatment and mixing: Dry iron tailings powder and gold tailings powder to a moisture content of ≤3%, and screen to remove impurities with a particle size >0.15mm; dry mix iron tailings powder (32%), gold tailings powder (37%), cement (5%), carbide slag (7%), slag (11%), and composite binder 8% (5.5% calcium sulfate dihydrate, 1.2% modified starch and 1.3% sodium polyacrylate) for 4.5min according to the mass ratio, and then add water and mix for 6.5min until the slump is about 18mm to obtain raw material slurry; (2) Molding: The raw material slurry is injected into the mold and a pressure of 27.5 MPa is applied and held for 72 seconds to obtain the aggregate green body; (3) Autoclaving: After the aggregate green body is left to stand at room temperature for 24 hours, the green body is transferred to an autoclave and autoclaved at 184℃ and 1.2MPa for 8.5 hours. Then the temperature is reduced to 50℃ and the green body is removed from the autoclave and covered with film for 24 hours. (4) Screening and grading: Defective products were removed using a vibrating screen, and the cured aggregate particles were graded into 5-10mm and 10-20mm sizes for later use. The apparent density of the aggregate prepared in this embodiment was 2241 kg / m³. 3 It has a water absorption rate of 12.9%, a crushing index of 1.7%, a cylinder compressive strength of 24.1 MPa, and a porosity of 10.1%.

[0075] In summary, since the autoclaved aggregate prepared from iron tailings powder of the present invention uses tailings as raw material, it can not only reduce costs, but also improve the natural environment, meet the environmental protection requirements for carbon reduction, promote the sustainable development of mining resources, and is of great significance to environmental protection.

Claims

1. A tailings-based autoclaved aggregate, characterized in that, The raw materials include the following components in terms of mass percentage: 66-70% of composite tailings powder, 21-25% of calcium-based solid waste, and 5-9% of composite binder, based on the total weight of the dry aggregate base; The composite tailings powder is composed of iron tailings and gold tailings in a mass ratio of 3:4-1:1, and the composite binder includes calcium sulfate dihydrate, hydroxypropyl modified starch, and sodium polyacrylate, with a mass ratio of (3-6):(1-1.5):(1-1.5).

2. The tailings-based autoclaved aggregate according to claim 1, wherein, The particle size distribution of the iron tailings is Dv(50) of 30-50 μm and Dv(90) of 200-350 μm, and the particle size distribution of the gold tailings is Dv(50) of 10-20 μm and Dv(90) of 60-80 μm. The calcium content in the calcium-based solid waste is 35-55% in terms of CaO, the SiO2 content is 20-30%, and the Al2O3 content is 5-10%.

3. The tailings-based autoclaved aggregate according to claim 2, wherein, The calcium-based solid waste is made of one or more of fly ash, slag, steel slag, saponification slag, carbide slag, and cement.

4. The tailings-based autoclaved aggregate according to any one of claims 1 to 3, wherein, The aggregate product is prepared by the process of raw material pretreatment, static pressure forming, and autoclaved curing, with a cylinder compressive strength of 23-25 MPa and a crushing index of 1.5-1.9%.

5. A method of producing a tailings-based autoclaved aggregate according to any one of claims 1 to 4, characterised in that, It comprises: Mixing and stirring all raw materials with water to obtain a raw material slurry; Performing static pressure forming treatment on the raw material slurry to obtain a green aggregate; Performing autoclaved curing treatment on the obtained green aggregate, and then crushing and screening to obtain coarse aggregate products with a particle size of more than 5 mm.

6. The method of producing a tailings-based autoclaved aggregate according to claim 5, wherein The mixing and stirring of all raw materials with water to obtain a raw material slurry is specifically: first dry-mixing all raw materials for 3-5 min, and then adding water and mixing for 5-8 min until the slump is 15-20 mm, thereby obtaining the raw material slurry; The pressure of the static pressure forming treatment is 20-30 MPa, and the pressure is maintained for 60-80 s; The autoclaved curing treatment conditions include: autoclaved curing temperature of 180-200 ℃, pressure of 1.0-1.5 MPa, autoclaved time of 4-10 hours, and then cooling to below 50 ℃ before discharging; The method further comprises: before mixing and stirring all raw materials with water, first mixing the iron tailings and gold tailings uniformly and performing steam pre-hydration treatment.

7. Use of the tailings-based autoclaved aggregate as claimed in any one of claims 1-4, or prepared by the method of claim 5 or 6, as a coarse aggregate for concrete.

8. Use according to claim 7, characterized in that, The tailings-based autoclaved aggregate is used as a coarse aggregate for concrete instead of part of the gravel, and the addition amount of the tailings-based autoclaved aggregate accounts for 10-30% of the total amount of coarse aggregate.

9. Use according to claim 8, characterized in that, The coarse aggregate in the concrete includes aggregate particles with a particle size of 5-10 mm and a particle size of 10-19 mm, and the mass ratio of the two kinds of particle size aggregates is 2:3-1:

1.

10. Use according to any one of claims 7 to 9, characterized in that, The 28d compressive strength of the concrete is 55.6-58.3 MPa.

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