A concrete containing smelted furnace slag and a method for producing the same

Abstract

This invention relates to a solid waste concrete containing slag from a melting furnace, prepared from the following raw materials in parts by weight: 170-220 parts slag from a melting furnace, 170-220 parts steel slag, 60-80 parts desulfurized gypsum, 750-900 parts ultrafine iron tailings, 860-110 parts waste rock, 150-200 parts water, and 0.5-1 parts water-reducing agent. The solid waste concrete containing slag from a melting furnace provided by this invention uses 100% industrial solid waste as raw material, without adding any cement or cement clinker, thus reducing the economic cost of concrete and achieving good economic benefits. Furthermore, by adjusting the 28-day compressive strength to above 30 MPa, this solid waste concrete can be applied to various non-load-bearing building materials, such as roads, walls, and slope protection.

Description

Technical Field

[0001] This invention belongs to the fields of industrial solid waste resource utilization and building materials technology, and specifically relates to a concrete containing slag from a melting furnace and its preparation method. Background Technology

[0002] Currently, waste incineration is the primary method for disposing of municipal solid waste in my country. During incineration, 2% to 15% of the total raw waste is generated as fly ash. Because this fly ash contains heavy metals such as Pb, Zn, As, and Cr, soluble salts, and substances like dioxins, it is classified as HW18 hazardous waste in my country. Simultaneously, with the development of the steel industry and the improvement of productivity, the consumption of resources and energy, as well as the emission of metallurgical waste, have become increasingly serious problems. Currently, the treatment of metallurgical solid waste and waste incineration fly ash mostly involves stockpiling. Stockpiling not only occupies a large amount of land resources but also causes environmental problems such as dust pollution and contamination of surface water, groundwater, and soil. Even with melting treatment and comprehensive utilization methods, it is difficult to digest all the waste residue, easily generating secondary waste that pollutes the environment.

[0003] Metallurgical dust is rich in valuable elements such as Fe, C, Zn, Pb, K, and Na. The metallic substances in this dust have a higher grade than those in natural minerals. Resource recycling of metallurgical dust reduces the environmental damage caused by mining and solves the problem of dust storage. Currently, the main treatment methods for metallurgical dust include physical methods, sintering methods, hydrometallurgical processes, and pyrometallurgical processes. However, none of these methods can fully utilize the resources available for metallurgical dust.

[0004] The slag from the melting furnace comes from the flue gas magnetization melting furnace co-processing production line of the steel solid waste treatment company, which uses fly ash from waste incineration and metallurgical dust. Figure 1 This diagram illustrates the generation of slag in a smelting furnace. In this process, the different gasification temperatures of valuable elements in metallurgical dust and waste incineration fly ash are utilized. The metallurgical dust is scientifically proportioned and mixed according to the elements of iron, zinc, potassium, sodium, and carbon, and then fed into a hot agglomerator for high-temperature melting and gasification reactions to obtain hot agglomerates and potassium ash. The hot agglomerates are then fed into the smelting furnace in a specific ratio with coke, undergoing high-temperature oxidation-reduction and gasification reactions to obtain recycled pig iron, rare and precious metal alloys, zinc oxide powder, and slag. All products except the slag can be separated and purified to ensure the valuable utilization of all elements and directly yield finished products. Smelting furnace slag is a secondary solid waste characterized by low activity and difficulty in utilization. Therefore, it is necessary to find a simple and high-value-added resource utilization pathway for slag to achieve zero-waste disposal of metallurgical dust and waste incineration fly ash throughout the entire process.

[0005] The slag from the melting furnace is black and granular. XRD analysis shows that the slag is amorphous. Mechanical activation through grinding not only increases the specific surface area but also generates microcracks on the surface of the glassy particles. This facilitates the entry of molecules or ions from the solution into the interior of the glassy structure, thereby promoting ion dissolution and hydration reaction rates and enhancing hydration activity. Furthermore, the microparticles also have a filling effect, reducing the porosity of the internal structure and increasing the overall compressive strength of the specimen.

[0006] Low-carbon concrete is mainly achieved through two approaches: First, by using industrial solid waste as a cementing material to reduce the use of cement clinker in concrete, directly reducing the large amount of CO2 generated during cement calcination; second, by using tailings, waste rock, and other solid waste as aggregates to reduce the mining of natural sand and gravel, conserve natural resources, and indirectly reduce CO2 emissions.

[0007] CN104860584A discloses a method for preparing concrete from waste incineration power plant slag. The method involves replacing coarse aggregate in the concrete with waste incineration slag through pretreatment processes such as washing, crushing and screening, magnetic separation, buoyancy separation, and sieving. The slag is then combined with raw materials such as cement, sand, gravel, water-reducing agent, acrylic resin, and GCY activator to produce concrete with a strength grade of C15-40. While the slag replaces 50-70% of the aggregate in this method, the pretreatment process is complex, requiring the addition of a large amount of cement clinker, resulting in high concrete preparation costs. Furthermore, the utilization of the slag from the melting furnace is relatively simple, failing to leverage the pozzolanic activity of the slag and improve its comprehensive utilization value.

[0008] CN106687424A discloses a method for preparing solid slag particles from a molten slag composition. The method includes: (a) providing the molten slag composition; (b) converting the molten slag composition into solid slag particles in a dispersion device; and (c) sorting the solid slag particles according to shape in a separator to prepare multiple fractions with different sphericities. Granular slag products include proppant, roofing granules, and catalyst carriers. However, this method requires sorting the solid slag particles according to shape and density in a separator, and the processing technology is complex, failing to achieve full-scale utilization of the slag. Furthermore, proppant products require the slag to have specific strength, size, properties, and compositional properties, which limits the effectiveness of this method.

[0009] CN113526896A discloses a method for treating fly ash from waste incineration and using it to prepare solid waste-based gel materials. In this method, slag discharged from the melting furnace is quenched in water and ground to obtain slag powder, which is then mixed with solid waste and water to obtain solid waste-based gel materials.

[0010] Currently, there is limited research on slag from smelting furnaces. As a secondary slag produced after resource utilization, the slag is black and granular after cooling. Chemical composition analysis of the slag after grinding reveals that its main components are SiO2, CaO, Al2O3, and MgO, which are very similar to those of slag powder. The typical slag structure is mainly composed of a calcium aluminosilicate glass phase, and also contains trace amounts of TiO2 and Ca. 2+ and Mg 2+ The existence of [AlO4] makes 5- The charge balance facilitates the depolymerization of silica. Therefore, slags with higher CaO and MgO content typically exhibit greater depolymerization and contain more unbridged oxygen bonds, theoretically making them more reactive.

[0011] Smelting furnace slag, as the final product of co-processing metallurgical dust and waste incineration fly ash in smelting furnaces, has an annual output of up to 360,000 tons. However, currently it can only be sold to cement plants and brick factories as raw materials at relatively low prices. However, capacity reduction in these sectors and the low added value of the products limit the high-value utilization of smelting furnace slag. On the other hand, because metallurgical dust and waste incineration fly ash contain a large amount of active substances such as Ca, Si, and Al, the extensive utilization methods fail to fully realize the potential of these active substances in the slag, resulting in a certain degree of resource waste. If the activity of the slag can be fully activated, then the high-value resource utilization of the entire process of co-processing metallurgical dust and waste incineration fly ash can be achieved, maximizing the value of resource utilization by-products in the local economy. This will provide reference and guidance for the treatment of large quantities of metallurgical dust and waste incineration fly ash in my country. Therefore, it is necessary to study the properties of smelting furnace slag. Summary of the Invention

[0012] This invention aims to at least partially solve one of the aforementioned technical problems in the prior art. This invention provides a method for processing slag from a melting furnace that is simple, economically efficient, and can fully and effectively utilize it. It not only uses the currently low-value-added slag from melting furnaces as a cementing material, but also comprehensively utilizes industrial solid wastes such as steel slag, desulfurization gypsum, tailings sand, and waste rock. The cementing material used completely replaces cement clinker in the process of utilizing solid wastes such as slag from melting furnaces, reducing the cost of concrete preparation. The composition of slag from melting furnaces is similar to that of S95 mineral powder, containing a relatively high amount of Si and Al, which can replace the more expensive S95 mineral powder. Based on the tetracoordination and double salt effects of silicon, it produces mineral phases such as ettringite, hydrated calcium silicate gel, and zeolite-like phases that are beneficial to concrete strength, thereby enabling the preparation of high-performance all-solid-waste concrete.

[0013] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0014] A solid waste concrete containing slag from a melting furnace is prepared from the following raw materials in parts by weight: 170-220 parts slag from a melting furnace, 170-220 parts steel slag, 60-80 parts desulfurized gypsum, 750-900 parts ultrafine iron tailings, 860-110 parts waste rock, 150-200 parts water, and 0.5-1 parts water-reducing agent.

[0015] The specific surface area of ​​the slag in the melting furnace is 450–505 m². 2 / kg. This invention utilizes mechanical grinding to activate its activity, grinding slag to a specific surface area of ​​450–505 m². 2 / kg. The inventors discovered that the specific surface area of ​​the slag in the melting furnace is crucial to the quality of the resulting concrete. Only at 450–505 m² / kg. 2 Only with a specific surface area of ​​ / kg can concrete with satisfactory strength be obtained. The larger the surface area, the finer the fineness of the slag from the melting furnace, which is beneficial to promoting the early hydration reaction. The finer slag can act as micro-aggregate in the concrete system, effectively filling the voids inside the system and improving the density of the concrete. In addition, the slag from the melting furnace is fully activated during the mechanical grinding process, causing the slag particles to form an amorphous structure that is more easily hydrated.

[0016] The slag containing molten material is Figure 1 The metallurgical dust and sludge are generated in the co-processing route of the smelting furnace shown. Metallurgical dust and sludge account for 3-5 wt% of the total mass of waste incineration fly ash and metallurgical dust and sludge. Specifically, 3-5 wt% of waste incineration fly ash and 95-97 wt% of metallurgical dust and sludge are batched and mixed, then fed into a hot agglomeration workshop for high-temperature melting and gasification reactions to obtain hot agglomerates and potassium ash. The potassium ash is further separated and purified in a purification workshop. The hot agglomerates and coke are fed into a pyrometallurgical enrichment and separation furnace, undergoing high-temperature oxidation-reduction and gasification reactions to obtain recycled pig iron, rare and precious metal alloys, zinc oxide powder, and smelting furnace slag.

[0017] This invention scientifically proportions metallurgical dust and sludge from waste incineration fly ash with elements such as iron, zinc, potassium, sodium, and chlorine. The resulting slag from the melting furnace has an alkalinity coefficient of 1.1-1.2, for example, 1.18, and an activity coefficient of 0.6-0.7, for example, 0.65. The ratio of non-bridging oxygen (NBO) to tetrahedral ions (T) (NBO / T) is 1.5-2, preferably 1.6-1.7, for example, 1.65, 1.70, or 175.

[0018] Currently, there is limited research on slag from smelting furnaces. As a secondary slag produced after resource utilization, the slag is black and granular after cooling. Chemical composition analysis of the slag after grinding reveals that its main components are SiO2, CaO, and Al2O3, which are very similar to those of blast furnace slag powder. The typical slag structure is mainly composed of a calcium aluminosilicate glass phase, and also contains some MgO and trace amounts of TiO2 and Ca.2+ and Mg 2+ The existence of [AlO4] makes 5- The charge balance facilitates the depolymerization of silica. Therefore, slags with higher CaO and MgO content typically exhibit greater depolymerization and contain more unbridged oxygen bonds, theoretically resulting in higher reactivity. However, proper combination with other components is necessary to fully realize the application of slag from melting furnaces in concrete.

[0019] This invention obtains highly active slag from a melting furnace by adjusting the ratio of fly ash from waste incineration and metallurgical dust. Combined with specific proportions of steel slag, desulfurization gypsum, tailings sand, and waste rock, the resulting concrete exhibits excellent performance.

[0020] The desulfurization gypsum is a flue gas desulfurization gypsum that meets the requirements of Grade II or above in GB / T 37785-2019 "Flue Gas Desulfurization Gypsum" and whose main component is calcium sulfate dihydrate (CaSO4·2H2O).

[0021] The steel slag is converter steel slag as specified in YB / T 022-2008 "Steel Slag Used in Cement".

[0022] Mechanical activation has a certain effect on enhancing the activity of slag, with a specific surface area of ​​450-505 m². 2 Slag with an activity index of around [value missing] kg has a high activity index, but mechanical activation alone is insufficient to fully realize its activity potential. Experiments on slag activity enhancement using different hydration systems revealed that the combined effect of a ternary system with a specific ratio of steel slag, desulfurized gypsum (alkaline activation, sulfate activation) resulted in the best activity enhancement. The synergistic effect of steel slag and desulfurized gypsum effectively enhanced the slag's hydration activity. The addition of steel slag provided a high-alkalinity reaction environment, promoting the continuous dissolution of [SiO4] from the glassy phase of the slag. 4- With [AlO4] 5- The addition of desulfurized gypsum provided the system with sufficient SO4. 2- SO4 2- [AlO4] produced by hydrolysis of slag 5- The reaction forms ettringite (AFt). In the later stages of hydration, a greater number of long-chain CASH gels are generated in the slag-based cementitious material. Hydration products are continuously generated, contributing to the strength of the slag-steel slag-desulfurized gypsum-based cementitious system.

[0023] The water-reducing agent is a polycarboxylate water-reducing agent.

[0024] The present invention also provides a method for preparing the above-mentioned all-solid-waste concrete, comprising the following steps:

[0025] (1) Pretreatment of cementitious materials: Dry and grind the slag from the melting furnace, steel slag and desulfurized gypsum to the required fineness respectively;

[0026] (2) Preparation of cementitious materials: The cementitious materials in step (1) are mixed in proportion to obtain the cementitious materials;

[0027] (3) Add cementitious materials and aggregates to water-reducing agent and water, and mix them according to the proportion of all solid waste concrete to obtain all solid waste concrete.

[0028] Furthermore, after obtaining the all-solid-waste concrete, the following steps are also included:

[0029] (4) The solid waste concrete is poured into the mold and then cured. The curing temperature is 20±5℃ and the curing humidity is ≥98% relative humidity.

[0030] The beneficial effects of this invention are:

[0031] 1. The solid waste concrete containing slag from the melting furnace provided by this invention uses 100% industrial solid waste as raw material and does not add any cement or cement clinker, which reduces the economic cost of concrete and has good economic benefits.

[0032] 2. The solid waste concrete containing slag from a melting furnace provided by this invention achieves zero-waste emission throughout the entire process of metallurgical dust and sludge and waste incineration fly ash treatment, promotes the resource utilization of metallurgical dust and sludge and waste incineration fly ash, and solves the problems of solid waste storage occupying land and polluting the environment.

[0033] 3. The solid waste concrete containing slag from a melting furnace provided by this invention utilizes ultra-fine iron tailings and waste rock as aggregates, effectively improving the utilization rate of difficult-to-utilize fine-grained tailings; by adjusting the sand ratio, the performance of the concrete can be optimized.

[0034] 4. The solid waste concrete containing slag from the melting furnace provided by the present invention can achieve a compressive strength of more than 30 MPa after 28 days, and more than 40 MPa in the preferred embodiment. It can be applied to a variety of non-load-bearing building materials, such as roads, walls and slope protection. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the slag production process in a melting furnace.

[0036] Figure 2 It is the XRD pattern of the slag from the melting furnace.

[0037] Figure 3 It is a curve showing the relationship between the fineness of the slag from the melting furnace and the grinding time.

[0038] Figure 4 It refers to the morphological characteristics and cumulative particle size distribution of slag from melting furnaces with different fineness.

[0039] Figure 5 XRD comparison charts of slag from melting furnaces with different fineness

[0040] Figure 6 This is a comparison of the activity index of slag from the melting furnace and S95 slag.

[0041] Figure 7 These are the results of the stability test of the slag from the melting furnace.

[0042] Figure 8 These are SEM images of static grout test blocks from different systems cured for 3 days.

[0043] Figure 9 These are SEM images of static grout test blocks from different systems after 28 days of curing.

[0044] Figure 10 These are SEM images of the paste test blocks from Example 1 and Comparative Example 4 at different curing times.

[0045] Figure 11 These are EDS spectra of the paste test blocks from Example 1 and Comparative Example 4 at different curing times (a, b, c, d). Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. The following embodiments are provided to better understand this invention, but do not limit the invention. Unless otherwise specified, the experimental methods in the following embodiments are conventional methods.

[0047] Unless otherwise specified, "parts" in the embodiments of the present invention refers to parts by mass, and "%" refers to percentage by mass unless otherwise specified.

[0048] The water-reducing agent was purchased from polycarboxylate superplasticizer, which is a white powder with a water reduction rate of 34%.

[0049] The gradation ratio of the waste rock is as follows, based on the cumulative percentage of sieve residue: ≥25mm: 0%, ≥20mm: 6.1%, ≥16mm: 22.0%, ≥10mm: 95.2%, ≥5mm: 99.1%, ≥2.5mm: 99.9%.

[0050] The composition of the steel slag used in this invention is shown in Table 1 below. The main components of the steel slag are CaO and Fe2O3, accounting for approximately 65.53% in total. The basicity of the steel slag is medium-alkaline, which meets the alkalinity requirements for preparing concrete.

[0051] Table 1 Chemical composition of steel slag (wt.%)

[0052] Element CaO <![CDATA[Fe2O3]]> <![CDATA[SiO2]]> MgO MnO <![CDATA[P2O5]]> <![CDATA[Al2O3]]> <![CDATA[TiO2]]> Wt% 34.29 31.24 14.10 9.9 4.39 2.68 2.50 0.80

[0053] The chemical composition of desulfurized gypsum is shown in Table 2 below.

[0054] Table 2 Chemical composition of desulfurized gypsum (wt.%)

[0055] Element CaO <![CDATA[SiO2]]> <![CDATA[Al2O3]]> MgO <![CDATA[SO3]]> <![CDATA[TiO2]]> MnO <![CDATA[Fe2O3]]> Wt% 41.88 5.04 1.61 1.30 46.40 0.23 0.02 0.74

[0056] The fineness modulus of the ultrafine iron tailings is 0.8-1.0, and its main component is quartz. The particle size distribution is shown in Table 3 below.

[0057] Table 3

[0058]

[0059]

[0060] The testing method and equipment of this invention are as follows:

[0061] (1) Strength measurement

[0062] According to the relevant provisions of GB / T 50107-2010 "Standard for Testing and Evaluation of Concrete Strength", the strength of concrete test blocks and neat cement paste test blocks in the test were determined separately.

[0063] (2) X-ray diffraction analysis

[0064] X-ray diffraction analysis was performed using a Ultima IV rotating anode diffractometer with a Cu target as the X-ray source, λ = 1.5406 Å. The operating voltage was 40 kV, the operating current was 150 mA, and the detector was a Ni-filtered one-dimensional detector.

[0065] (3) Analysis of heavy metal ion leaching concentration

[0066] Heavy metal ion leaching concentration analysis: The analytical instrument was a Thermo Fisher Scientific ICP-RQ inductively coupled plasma mass spectrometer, with a detection range of 5–260 amu, a detection limit of <0.1 ppt, a detector count range of 1–10⁹, and a resolution of <1 amu, used for the analysis of trace elements without polarity.

[0067] (4) Scanning electron microscopy analysis

[0068] The scanning electron microscope (SEM) instrument used was a Suppatm 55 field emission scanning electron microscope with an accelerating voltage of 0.02–30 kV, and the energy dispersive spectrometer (EDS) was used with the field emission electron microscope.

[0069] (5) X-ray fluorescence spectroscopy

[0070] The XRD data was measured using an XRF-1800 X-ray fluorescence spectrometer manufactured by Huarda Science and Trade Institute, and the data were determined using a 721 spectrophotometer and the EDTA dissolution method.

[0071] (6) Thermogravimetric analysis

[0072] Thermogravimetric analysis (TGA) data were obtained using thermogravimetric analysis and differential scanning calorimetry (instrument: Netzsch STA449C, Germany). The temperature range was 20–1000 °C, the heating rate was 10 °C / min, and nitrogen was used as the gas medium.

[0073] (7) Laser particle size analysis

[0074] Laser particle size analysis data were analyzed using an LMS-30 laser particle size distribution analyzer manufactured by Shinsei Corporation of Japan.

[0075] (8) Infrared analysis

[0076] Infrared data were obtained using a Nexus 70 Fourier transform infrared spectrometer (350–7000 cm⁻¹). -1 ), resolution 3cm -1 Operating conditions: Temperature 27℃, humidity 68%, voltage 220~240V, frequency 56~60Hz.

[0077] (9) Specific surface area test

[0078] Specific surface area was determined according to national standard GB / T 208-2014, using a Leebow bottle to test the density of steel slag, furnace slag, and desulfurized gypsum. The required weight of raw material was calculated based on the density, and the sample was loaded into the specific surface area analyzer, compacted to achieve the required volume. The vacuum switch was turned on until the liquid level on the right side of the U-tube reached above the graduation mark, then the vacuum system was turned off. A thin layer of Vaseline was applied to the outer wall of the Blaine tube for sealing. The Blaine tube was then installed on the specific surface area analyzer, and the measurement was started, recording the time and calculating the specific surface area.

[0079] The slag raw material for the smelting furnace of this invention is 5 wt% waste incineration fly ash and 95 wt% metallurgical dust and sludge. Figure 1 The process yielded chemical composition tests on the slag from the melting furnace, and the results are shown in Table 4 below.

[0080] Table 4 Chemical composition of slag from the melting furnace (wt.%)

[0081] Element CaO <![CDATA[SiO2]]> <![CDATA[Al2O3]]> MgO <![CDATA[SO3]]> <![CDATA[TiO2]]> <![CDATA[Na2O]]> MnO <![CDATA[Fe2O3]]> Cl <![CDATA[K2O]]> Wt% 37.87 25.59 16.67 12.02 2.58 1.77 1.07 0.91 6.24 0.06 0.61

[0082] Based on the chemical composition of the slag, its various performance indicators were calculated: the basicity coefficient ((CaO+MgO) / (SiO2+Al2O3)) was calculated to be 1.18, and the activity rate (Al2O3 / SiO2) was 0.65; simultaneously, the chemical activity of the slag can be expressed by the mass ratio of unbridged oxygen (NBO) to tetrahedral ions (T), calculated using the following formula:

[0083]

[0084] The NBO / T ratio of the slag in the melting furnace is 1.65. The higher the NBO / T value, the higher the degree of depolymerization of the glassy structure of the slag and the greater the reactivity.

[0085] Figure 2 The image shows the XRD pattern of the slag from the melting furnace. It can be seen that the slag is a typical glassy material, with the main phase composition being amorphous. There is only one crystalline peak, which is calcium aluminum feldspar, and there are no obvious crystalline phases in other areas.

[0086] Mechanical activation of slag from a melting furnace was performed. During mechanical grinding, collisions and friction occur between solid particles and between the solid particles and the grinding media, causing physical and chemical changes in the particles to activate their activity. The slag from the melting furnace is granular and was ground using a ball mill to activate it. A small ball mill was used in the experiment, with steel segments (2-5 cm in diameter, 4-8 cm in length) as the grinding media, and a 5 kg feed rate was maintained per grinding cycle. Samples were taken after grinding the slag for 40, 60, 80, 95, and 110 minutes to test the specific surface area of ​​the slag powder. The results are as follows: Figure 3 As shown in the figure, the specific surface area of ​​the slag from the smelting furnace increases with longer grinding time. The specific surface areas of the slag after grinding for 40 min, 60 min, 80 min, 95 min, and 110 min are 207 m², respectively. 2 / kg, 320m 2 / kg, 450m 2 / kg and 505m 2 / kg, 550m 2 / kg, as the grinding test time increased, the fineness of the slag gradually increased. In the initial stage of grinding, the specific surface area of ​​the slag increased rapidly, but as the grinding time was continuously extended to 80 minutes, the specific surface area reached 450m². 2 At a certain temperature (kg), the rate of increase in slag fineness gradually slows down, and the curve tends to flatten. Continuing to extend the grinding time further makes it difficult to guarantee good grinding efficiency and reasonable energy consumption. Although powder particles with a larger specific surface area are beneficial to promoting the early hydration reaction, the specific surface area does not have too much of an impact. Otherwise, excessive fluidity will affect the workability of concrete, causing severe bleeding and segregation in the concrete, which will affect the subsequent concrete strength. Moreover, carbonation caused by excessive grinding is also detrimental to concrete performance.

[0087] Select a specific surface area of ​​320m² 2 / kg, 450m 2 / kg, 505m 2The slag from the melting furnace, weighing approximately [weight] kg, was designated A, B, and C. The particle size distribution of the three slag powders was measured using a Malvern laser particle size analyzer, and their morphological characteristics were observed using SEM. The particle size distribution, cumulative particle size distribution, and morphological characteristics of the three slag powders are shown in [reference needed]. Figure 4 As the slag grinding time increases, the characteristic particle size of slag powder of different fineness gradually decreases; the SEM images show obvious changes in the particle size geometry. With the increase of grinding time, the number of fine particles gradually increases, and their proportion increases significantly, and the specific surface area of ​​the powder also increases rapidly. Table 5 shows the characteristic particle size of slag from melting furnaces of different fineness.

[0088] Table 5. Characteristic particle size of slag powder with different fineness

[0089]

[0090] Fine-grained slag from melting furnaces can act as micro-aggregates in concrete systems, effectively filling internal voids and improving concrete density. Furthermore, the mechanical grinding process fully activates the slag, causing the Si-O bonds within its glassy structure to break, promoting lattice changes in the slag particles and resulting in a more easily hydrated amorphous structure. Therefore, it is necessary to compare the phase composition of slags with different specific surface areas. Figure 5 The XRD patterns of slag from melting furnaces with different fineness show that after grinding for different times, the main phases of slag with different specific surface areas also differ to some extent. At 320 μm... 2 / kg, 450m 2 / kg, 505m 2 In the XRD patterns of the slag at / kg, diffraction peaks of C2AS were observed in all samples, indicating that this is the main phase of the slag, calcium aluminum feldspar. Simultaneously, it was found that the diffraction peaks of C2S in the three samples weakened with increasing specific surface area, suggesting that the crystal structure of C2S was disrupted, transforming towards an amorphous state. Upon contact with water, it readily reacts to form Ca(OH)2, increasing the alkalinity of the system. At 505m... 2 CaCO3 was found in the XRD curve of / kg, which may be due to carbonization caused by excessive grinding. Therefore, attention should be paid to selecting an appropriate specific surface area of ​​the slag in the melting furnace.

[0091] To investigate the activation effect of mechanical activation on slag from a melting furnace, and to study the hydration characteristics of slags with different specific surface areas, an activity exploration experiment was conducted on the slags according to the appendix of standard GB / T 18046-2008. The specific surface areas of slags 1 to 4 were 320 m² and 320 m², respectively. 2 / kg, 450m 2 / kg, 505m 2 / kg, 550m 2 / kg, 42.5 silicate cement was selected as the control group, and the activity of slag with different grinding fineness and commercial slag powder (S95) was compared to conduct an activity exploration experiment. The experimental mix proportions are shown in Table 6, and the results are shown in the table below. Figure 6 .

[0092] Table 6. Activity Exploration Experiment Formulation

[0093]

[0094] The slags in groups 2 and 3 showed the best activity, with little difference in activity indices between the two groups. The activity indices of group 2 at 7d, 28d and P.O42.5 cement reached 100.94% and 103.7% respectively, while the activity indices of group 3 reached 101.88% and 104.2% respectively, all higher than the activity index of S95 slag.

[0095] The fluidity was also tested, and it was found that the fluidity increased with the increase of the specific surface area of ​​the slag, and was higher than that of cement and S95 slag. The fluidity of group 4 was the largest. However, if slag 4 is used to prepare high-performance concrete, the excessive fluidity will affect the workability of the concrete, resulting in severe bleeding and segregation, which will affect the subsequent concrete strength. Therefore, slag with a moderate specific surface area should be selected to prepare all-solid waste cementitious materials.

[0096] Example 1

[0097] The specific implementation method of a solid waste concrete containing slag from a melting furnace and its preparation method is as follows:

[0098] Prepare concrete according to the concrete formula in Table 7: (Material usage per cubic meter of concrete: kg / m³) 3 The specific surface area of ​​the slag in the melting furnace is 450 m². 2 / kg.

[0099] Table 7 Concrete Formula

[0100]

[0101] For the solid waste concrete, the raw materials are weighed according to the mix proportions shown in the table above. The raw materials are put into a concrete mixer and mixed evenly for no less than 240 seconds. Then, the concrete is poured into a 150mm×150mm×150mm plastic triple mold, placed on a concrete vibrating table and vibrated to form the concrete. After curing for 24 hours under the conditions of ambient temperature of 20±5℃ and curing humidity of >50%, the concrete is demolded. Then, the concrete is placed in the conditions of ambient temperature of 20±2℃ and curing humidity of ≥98% for continued curing.

[0102] According to the concrete mix design shown in the table above, the compressive strengths of the concrete test blocks after mixing, molding, and curing at 1 day, 3 days, 7 days, and 28 days are 11.48 MPa, 24.36 MPa, 26.52 MPa, and 43.95 MPa, respectively.

[0103] Example 2

[0104] The specific implementation method of a solid waste concrete containing slag from a melting furnace and its preparation method is as follows:

[0105] Prepare concrete according to the concrete formula in Table 8: (Material usage per cubic meter of concrete: kg / m³) 3 )

[0106] Table 8 Concrete Formula

[0107]

[0108] The curing conditions were the same as in Example 1. According to the concrete mix proportions shown in Table 8, the compressive strengths of the concrete test blocks after mixing, molding, and curing were 10.51 MPa, 22.44 MPa, 26.23 MPa, and 40.45 MPa after 1 day, 3 days, 7 days, and 28 days, respectively.

[0109] Example 3

[0110] The specific implementation method of a solid waste concrete containing slag from a melting furnace and its preparation method is as follows:

[0111] Prepare concrete according to the concrete formula in Table 9: (Material usage per cubic meter of concrete: kg / m³) 3 )

[0112] Table 9 Concrete Formula

[0113]

[0114] The curing conditions were the same as in Example 1. According to the concrete mix proportions shown in Table 9, the compressive strengths of the concrete test blocks after mixing, molding, and curing were 13.81 MPa, 23.49 MPa, 24.47 MPa, and 36.78 MPa after 1 day, 3 days, 7 days, and 28 days, respectively.

[0115] Example 4

[0116] Other conditions and materials are the same as in Example 1, the difference being that the specific surface area of ​​the slag in the melting furnace is 505 m². 2 / kg, according to the concrete mix proportions shown in Table 8, the compressive strengths of the concrete test blocks after mixing, molding and curing were 11.26MPa, 23.95MPa and 26.38MPa, 41.72MPa after 1 day, 3 days, 7 days and 28 days respectively.

[0117] Example 5

[0118] Other formulations are consistent with Table 6 of Example 1, with the total amount of gel material remaining unchanged (total amount of slag from melting furnace, steel slag, and desulfurization gypsum is 450 kg / m³). 3 The water-to-gel ratio is 0.32, and the difference is that the gel material is prepared according to Table 10 below.

[0119] Table 10 Concrete gel material formulation and 28-day strength

[0120]

[0121] Application examples

[0122] The cementitious materials in Examples 1-5 above were tested for soundness using the pat test method. The soundness test was performed according to GB / T1346-2011 "Standard Consistency Water Requirement, Setting Time and Soundness Test Method for Cement". The soundness test results are as follows: Figure 7 As shown, the test cakes had no cracks on their surfaces and all met national standards.

[0123] Comparative Example 1

[0124] The only difference between this example and Example 1 is the fineness of the slag grinding in the melting furnace: the specific surface area of ​​the slag in the melting furnace is 320 m². 2 / kg.

[0125] The compressive strengths of the cured concrete test blocks after 3 days, 7 days, and 28 days were 13.22 MPa, 19.33 MPa, and 21.54 MPa, respectively.

[0126] Comparative Example 2

[0127] The only difference between this example and Example 1 is the fineness of the slag grinding in the melting furnace: the specific surface area of ​​the slag in the melting furnace is 550 m². 2 / kg.

[0128] The compressive strengths of the cured concrete test blocks after 3 days, 7 days, and 28 days were 18.55 MPa, 24.68 MPa, and 31.85 MPa, respectively.

[0129] Comparative Example 3

[0130] Other formulations are consistent with Table 6 of Example 1, with the total amount of gel material remaining unchanged (total amount of slag from melting furnace, steel slag, and desulfurization gypsum is 450 kg / m³). 3 The water-to-gel ratio is 0.32, and the difference is that the gel material is prepared according to Table 11 below.

[0131] Table 11 Concrete gel material formulation and 28-day strength

[0132]

[0133] By comparing the data in Table 11 with the data in Example 1, it can be found that in the unary hydration system of No. A1, the slag from the melting furnace is used as a separate cementing material. The slurry test blocks after 3d, 7d and 28d of slag hydration alone have a good effect, indicating that the slag has high activity.

[0134] Comparing the data from B1 to B5 with Example 1, the hydration effect of the binary hydration system was poor, with the compressive strength of the paste specimens generally low, none exceeding 4 MPa, far inferior to the effect of hydration of the slag alone in the melting furnace. Observation of the compressive strength change trend revealed a negative correlation between compressive strength and steel slag content; the higher the steel slag content, the lower the compressive strength of the paste specimens. The higher the steel slag content, the greater the negative impact on early strength. The main role of steel slag in the system is to increase the alkalinity of the environment and gradually promote slag hydrolysis, but it is difficult to improve the early system strength. In addition, the mold damage problems in groups B3 and B2 during demolding at 3 days also indicate that excessive steel slag addition leads to a prolonged final setting time, which is not conducive to early strength growth. Although the strength of the system slightly recovers in the later stages, the poor internal structure of the early paste specimens may lead to a high internal porosity. Even if the amount of hydration products increases in the later stages, it is difficult to fill the internal pores, so the later strength is not ideal. The addition of steel slag did not have a positive effect on the hydration effect of the binary system. Since the main strength improvement stage of slag hydration is between 7 and 28 days, the strength growth in the early stage is relatively weak. The addition of steel slag made the early hydration effect even worse, resulting in the long-term hydration effect of the binary system being much lower than that of the uni-system. This shows that it is difficult to activate the activity of slag by steel slag alone.

[0135] Comparing the data in Tables 9 and 10, it can be seen that the hydration effect of the ternary hydration system is superior to that of the binary and unary systems. The compressive strength of the slurry specimens is generally higher, indicating that the ternary system is more reasonable and can effectively activate the activity of the slag in the melting furnace, while also promoting the synergistic hydration of various solid wastes. Observation of the strength change curves reveals a positive correlation between the amount of desulfurized gypsum and the early strength of the slurry specimens. The higher the amount of desulfurized gypsum, the greater the 3-day compressive strength. When the amount of desulfurized gypsum is 20%, the early hydration strength reaches its highest value of 13.5 MPa. The improvement of early strength of the paste system by desulfurized gypsum can be attributed to two aspects. Firstly, desulfurized gypsum acts as a sulfate activator within the system. It reacts with active alumina or silica in the slag to generate micro-expanded calcium vanadate and some calcium silicate gel. These hydration products fill the pores within the paste system. Simultaneously, unhydrated desulfurized gypsum can also act as fine aggregate to fill the gaps between system particles, further refining the pore size and improving interfacial bonding, thereby reducing the porosity of the paste sample. Secondly, desulfurized gypsum mutually promotes the hydration process with steel slag and furnace slag, reacting to generate AFt, resulting in volume expansion. This compensates for the shrinkage deformation caused in the early stages of hydration. Therefore, the ternary hydration system can compensate for the deficiencies of mono- and binary systems, improving early hydration while ensuring the long-term stable growth of the system's internal compressive strength.

[0136] Figure 8These are SEM images of slurry specimens from different systems cured for 3 days. (a) is the unary hydration system (A1), (b) is the binary hydration system (B1), and (c) and (d) are the ternary hydration systems (C4). In (a), many large, blocky particles can be observed. Since the unary system only contains slag from the melting furnace, these are identified as raw material particles of the slag. This indicates that in the early stages of hydration, slag hydration alone is insufficient to fully deagglomerate the slag particles. The lack of external environmental stimulation makes it difficult for the active components of the slag to function, consistent with the insufficient early strength observed when slag is hydrated alone. In (b), a small number of rod-shaped crystals can be observed, identified as AFt. However, the crystals are relatively fine and difficult to form a stable structure. The presence of many raw material particles within the system indicates that there are many unhydrated raw material particles of steel slag and furnace slag in the system, and few hydration products. In (c), clusters of AFt were observed to form within the pores. Compared to the binary system, the AFt was longer, more numerous, and significantly thicker, indicating that the ternary system exhibited good mechanical properties in the early stages of hydration. In (d), a network-like structure formed later was observed, within which needle-like AFt crystals grew. Based on the morphology, the network-like structure was likely CSH gel, with the gel and AFt interwoven and the AFt embedded within the gel. The ternary system formed a good network structure in the early stages of hydration, indicating that the slag, after being co-activated by desulfurized gypsum and steel slag, exhibited good activity in the ternary system.

[0137] Figure 9 These are SEM images of static slurry test blocks from different systems after 28 days of curing. Among them, (a) is the unary hydration system numbered A1, (b) is the binary hydration system numbered B1, and (c) and (d) are the ternary hydration systems numbered C4. It can be observed that there are more needle-like AFt crystals in the unary system, and the raw material particles are also reduced compared with the ternary hydration system, which is consistent with the result that the strength of the unary system increases significantly in the later stage; (b) In the binary hydration system, a large number of hexagonal plate-like substances can be found, which is a typical morphological feature of Ca(OH)2. This indicates that there are more unreacted Ca(OH)2 in the binary cementitious material, indicating that the steel slag content is too high and the activation effect on the slag is not good; In the ternary hydration systems in (c) and (d), a large number of AFt crystals are found in the ternary system, which are coarser than those in the unary system. In (d), it is observed that the roots of the AFt crystals are covered with a large amount of gel, making the structure of the cement paste more compact. The hydration products intertwine and fill the pores of the paste. AFt plays a supporting role in the structure, thus enabling the strength of the ternary system to continue to increase.

[0138] In summary, the hydration mechanism analysis of the unary system revealed that the early hydration effect of slag hydration alone was good, indicating that slag hydration alone in the melting furnace has a good early effect, but the degree of hydration is lower in the later stages. The poor hydration effect of the slag-steel slag-based binary cementitious system was found, possibly because the addition of steel slag caused a rapid increase in the alkalinity of the solution in the early stages, but the lack of SO4... 2- Regarding the consumption of metal cations, excessive Ca in the system 2+ The diffusion of ions in the solution was inhibited, leading to incomplete hydration in the early stages. Therefore, although the addition of steel slag has a certain alkaline activation effect on the slag and can promote slag dissociation, it cannot fully utilize the slag's activity. The ternary cementitious system of slag-steel slag-desulfurized gypsum in the melting furnace showed the best hydration effect. The main driving force of the hydration reaction in the system is the synergistic effect of multiple solid wastes and the double salt effect among the raw materials. A significant AFt characteristic peak was observed in the XRD pattern of the ternary system, which gradually increased with increasing curing time. FTIR analysis revealed a symmetric stretching vibration band of the Si-O-Al bond in the ternary system. This absorption peak only exists in the ternary system, possibly due to the large number of aluminum (silicon) oxygen tetrahedra in the ternary system. After depolymerization, the Al... 3+ Substitute Si in CSH gel 2+ This process leads to the formation of CASH gel. XPS analysis of the binding energies of Al 2p and Ca 2p revealed that the ternary system produced Al-containing hydration products (AFt) and long-chain CASH gels in the later stages of hydration, consistent with FTIR findings. Within the ternary system, the addition of steel slag provided a high-alkalinity hydration environment for the slag, increasing its hydration rate and promoting the continuous dissolution of [SiO4] through depolymerization. 4- With [AlO4] 5- The addition of desulfurized gypsum provided the system with sufficient SO4. 2- SO4 2- [AlO4] produced by hydrolysis of slag 5- The reaction forms AFt, and thus, under the synergistic reaction of steel slag, desulfurized gypsum, and furnace slag, hydration products are continuously generated, providing sustained strength to the ternary system, thereby reflecting that the activity of the furnace slag is fully activated.

[0139] Comparative Example 4

[0140] Other conditions and operations were the same as in Example 1, except that the slag from the melting furnace was replaced with an equal mass of S95 slag powder. After testing, the compressive strengths of the concrete in Comparative Example 4 at 3d, 7d, and 28d were 24.73 MPa, 28.66 MPa, and 32.34 MPa, respectively.

[0141] Figure 10These are SEM images of the paste test blocks from Example 1 and Comparative Example 4 at different curing times. Figure 11 These are EDS spectra of the cement paste test blocks from Example 1 and Comparative Example 4 at different curing times (a, b, c, and d). Group L represents the slag-steel slag-desulfurized gypsum-based cementitious system (Example 1), and Group K represents the S95 slag-steel slag-desulfurized gypsum-based cementitious system (Comparative Example 4). It can be seen that typical columnar gypsum can be observed in both K-3d and L-3d during the early hydration stage (3d). However, the gypsum crystals in the L system exhibit significant cleavage, with numerous needle-like crystals clustered within the cracks. EDS energy dispersive spectroscopy analysis confirmed that these crystals are hydration products, specifically AFt. This indicates that hydration was relatively deep by 3d, but the generated AFt crystals were small and few in number, making it difficult to fill the voids in the system and form a dense structure. In contrast, the gypsum surface in the K group showed cracks but remained largely intact, indicating that the desulfurized gypsum in the K group system could not participate well in hydration in the early stages. A small number of prismatic and needle-like crystals were also observed in the voids next to the desulfurized gypsum, which were identified as AFt based on their morphology. This suggests that the K group system had begun hydration by 3d, but the gypsum was not fully involved. When hydration reached 7 days, large raw material particles were observed in K-7d. Energy dispersive spectroscopy (EDS) analysis of point b revealed that the mineral mainly consisted of elements such as Ca, Si, and Al, indicating that the raw material particles were likely from slag. This suggests that the raw materials from group K did not fully participate in the reaction during the early stages of hydration. A small amount of amorphous flocculent matter was found in point a, which is likely CASH gel. In L-7d, a large number of spherical substances were observed cemented together and attached to the unreacted material. EDS analysis of point c revealed that the main elements contained in this point were Ca, Si, O, Al, and Mg. Based on the atomic percentage, Ca / (Si+Al) ≈ 1:1, indicating that it was CASH gel, possibly due to the high content of Al2O3 and [AlO4] in the slag. 5- For [SiO4] in the CSH phase 4- More AFt crystals are replaced, transforming into the CASH phase, consistent with FTIR results, thus significantly increasing the intensity of the L group in the later stages. At hydration 28 days, the number of AFt crystals in the K-28d system increased and became coarser, with cubic crystals also observed. Based on morphological characteristics, these are presumed to be CaO crystals, likely intermediate products from the steel slag in the raw materials. The presence of CaO crystals at 28 days of hydration indicates that the raw materials in the K group did not fully participate in the reaction, resulting in a lower degree of hydration. 2+The contribution to the formation of hydration products such as CSH gel was relatively low. L-28d showed good hydration effect of group L. A large number of AFt crystals were cemented together by the network material. EDS energy dispersive spectroscopy analysis of the network material showed that the main elements contained in point d were Ca, Si, O, Al and Mg, which were identified as gel phase. The network C-(A)SH gel and the needle-like AFt crystals were intertwined and tightly wrapped. The pores in the cement paste system were filled by the hydration products, which reduced the porosity and promoted the strength increase of the cementitious material of group L in the later stage of hydration. This is consistent with the result of XPS that a CASH gel phase was formed, which provides a theoretical basis for the significant improvement of the compressive strength of group L in the later stage.

[0142] Mechanism comparison studies were conducted on the slag-steel slag-desulfurized gypsum-based cementitious system (L) and the slag-steel slag-desulfurized gypsum-based cementitious system (K). XRD patterns revealed that hydration in the K system was more concentrated in the early stages, and the insufficient strength in the later stages was likely due to the lack of gel phase encapsulation. In contrast, hydration reactions continued in the L system. Weight loss analysis showed that the weight loss rate of the L group was about 5% higher than that of the K group in the later stages of hydration, indicating that the L group produced more hydration products than the K group. XPS analysis revealed a significant increase in the Al 2p binding energy and the area under the curve in the L group at 28 days, indicating that the L group continuously generated Al-containing hydration products (AFt) and longer CASH gel chains in the later stages of hydration. These findings suggest that the slag-steel slag-desulfurized gypsum-based cementitious system exhibits superior hydration performance.

Claims

1. A type of all-solid waste concrete containing slag from a melting furnace, characterized in that, The material was prepared from the following raw materials in parts by weight: 191.25 parts slag from a melting furnace, 191.25 parts steel slag, 67.5 parts desulfurization gypsum, 817.8 parts ultrafine iron tailings, 922.2 parts waste rock, 160 parts water, and 0.3% water-reducing agent for concrete; the specific surface area of ​​the slag from the melting furnace was 450~505 m². 2 / kg, with an alkalinity coefficient of 1.1-1.2, an activity coefficient of 0.6-0.7, and a NBO / T ratio of 1.6-1.7 for non-bridging oxygen (NBO) to tetrahedral ions (T). The slag from the melting furnace is obtained by a method including the following steps: 5 wt% of waste incineration fly ash and 95 wt% of metallurgical dust are mixed and fed into a hot agglomeration workshop for high-temperature hot melting and gasification reaction to obtain hot agglomerates and potassium ash. The potassium ash is further separated and purified in a purification workshop. The hot agglomerates and coke are fed into a melting furnace for pyrometallurgical enrichment and separation. After high-temperature oxidation-reduction and gasification reaction, recycled pig iron, rare and precious metal alloys, zinc oxide powder, and melting furnace slag are obtained.

2. The all-solid-waste concrete according to claim 1, characterized in that, The water-reducing agent is a polycarboxylate water-reducing agent, and the fineness of the ultrafine iron tailings is 0.8-1.

0.

3. The method for preparing all-solid-waste concrete according to claim 1 or 2, characterized in that, Includes the following steps: (1) Pretreatment of cementitious materials: Dry and grind the slag from the melting furnace, steel slag and desulfurized gypsum to the required fineness respectively; (2) Preparation of cementitious materials: The cementitious materials in step (1) are mixed in proportion to obtain the cementitious materials; (3) Add cementitious materials and aggregates, water-reducing agent and water, and mix them according to the proportion of solid waste concrete to obtain solid waste concrete.

4. The construction method of the all-solid waste concrete as described in claim 1 or 2, characterized in that, The process includes the following steps: pouring solid waste concrete into a mold, curing the poured solid waste concrete at a temperature of 20±5℃ and a relative humidity of ≥98%.

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