An iron-rich slag-derived additive and its preparation method and application

Abstract

This application discloses an iron-rich slag-derived additive, its preparation method, and application, relating to the field of building materials. The additive comprises slag extracted from iron-rich slag and nano-silica, forming a core-shell structure with the slag as the core and the nano-silica as the shell. This application separates the nano-silica from the iron-rich slag and then forms a core-shell structure with the slag as the core and the nano-silica as the shell. The nano-silica shell enhances the activity of the alkali-activated reaction and increases the degree of polymerization of the gel molecules. The slag core acts as a rigid skeleton to fill the pores of the matrix. The two synergistically optimize the microstructure of the gelled product, improving the compressive strength and elastic modulus of the resulting alkali-activated gelled material.

Description

Technical Field

[0001] The present application relates to the field of building materials, and in particular to an iron-rich slag-derived additive and a preparation method and application thereof. Background Art

[0002] Iron-rich slag is a metallurgical by-product produced in the production process of the metallurgical industry, including copper slag, steel slag, lead slag, zinc slag, nickel slag, etc. It contains a large amount of silica and iron oxides. The global annual output exceeds 50 million tons and is often used in the construction industry as cement raw materials, auxiliary cementitious materials and aggregates.

[0003] Alkali-activated cementitious materials are commonly used in the construction industry. Compared with ordinary Portland cement, they have higher mechanical strength, better chemical corrosion resistance and excellent high-temperature resistance. In addition, their manufacturing process reduces energy consumption by 30% to 50% and carbon emissions by 60% to 70%, making them sustainable. However, their elastic modulus is 10% to 20% lower than that of traditional Portland cement-based materials. This is mainly related to the high porosity and low degree of polymerization of C-(N)-ASH gel. This defect leads to insufficient elastic modulus of alkali-activated gel materials, which seriously limits their application in load-bearing structures with high deformation requirements.

[0004] Currently, to improve the mechanical properties or reduce the cost of alkali-activated cementitious materials, nanosilica or iron-rich slag is added as an auxiliary gelling material. However, traditional nanosilica preparation methods (such as vapor deposition and sol-gel methods) still face challenges such as high energy consumption, high raw material costs (such as tetraethyl orthosilicate), organic solvent contamination, and easy agglomeration. Direct addition of iron-rich slag, however, results in weak interfacial bonding with the gel due to its surface inertness, leading to microcracks forming in the interfacial region and a decrease in compressive strength. Summary of the Invention

[0005] In view of the shortcomings of the above-mentioned related technologies, the present application provides an iron-rich slag-derived additive, its preparation method, and application. By separating the nano-silica in the iron-rich slag from the slag, and then forming a core-shell structure with the slag as the core and the nano-silica as the shell, the nano-silica shell enhances the activity of the alkali-activated reaction and increases the degree of polymerization of the gel molecules. The slag core acts as a rigid skeleton to fill the pores of the matrix and increase the rigidity. The two synergistically optimize the microstructure of the gelled product, thereby improving the compressive strength and elastic modulus of the resulting alkali-activated gelled material.

[0006] In the first aspect, the present application provides an iron-rich slag-derived additive using the following technical solution:

[0007] An iron-rich slag derived additive consists of slag extracted from the iron-rich slag and nano-silicon dioxide, and has a core-shell structure formed by taking the slag as a core and the nano-silicon dioxide as a shell.

[0008] Preferably, the extraction of the slag and the nano-silica comprises the following steps: acid leaching the iron-rich slag, then allowing it to stand, separating the upper layer mixture for washing, filtering and drying to obtain the nano-silica, and recovering the bottom precipitate to obtain the slag.

[0009] Preferably, the shell structure formed by the nano-silica has a thickness of 0.4-0.8 μm.

[0010] Preferably, the shell structure formed by the nano-silica has a thickness of 0.5-0.7 μm.

[0011] Preferably, the iron-rich slag includes one or more of copper slag, nickel slag, lead slag, zinc slag and steel slag.

[0012] Preferably, the iron-rich slag is copper slag.

[0013] In a second aspect, the present application provides a method for preparing an iron-rich slag-derived additive using the following technical solution:

[0014] A preparation method of an iron-rich slag-derived additive comprises the following steps: preparing slag and nano-silicon dioxide into suspensions respectively, adding a complexing agent to the slag suspension and stirring evenly to obtain a transition liquid, adding the nano-silicon dioxide suspension to the transition liquid, stirring and filtering to obtain a precipitate, and drying and grinding the precipitate to obtain the iron-rich slag-derived additive.

[0015] Preferably, the weight ratio of the slag material to the nano-silicon dioxide is 1:0.8-1.2.

[0016] Preferably, the weight ratio of the slag material to the nano-silicon dioxide is 1:1.

[0017] Preferably, the weight ratio of the slag material to the complexing agent is 8-12:1.

[0018] Preferably, the weight ratio of the slag material to the complexing agent is 10:1.

[0019] Preferably, the complexing agent includes one or more of polyvinyl pyrrolidone, polyethylene glycol, and polyacrylic acid.

[0020] Preferably, the complexing agent is polyvinyl pyrrolidone.

[0021] In a third aspect, the present application provides an application of an iron-rich slag-derived additive in the preparation of alkali-activated cementitious materials.

[0022] Preferably, the alkali-activated cementitious material is made of the following components in parts by weight: 1 to 3 parts of iron-rich slag-derived additive, 40 to 60 parts of blast furnace iron-rich slag, 40 to 60 parts of fly ash, and 3 to 6 parts of alkaline activator; the water-cement ratio is 0.35 to 0.37.

[0023] Preferably, the alkali-activated cementitious material is made of the following components in parts by weight: 2 parts of iron-rich slag-derived additive, 50 parts of blast furnace iron-rich slag, 50 parts of fly ash, and 4 parts of alkaline activator; and the water-cement ratio is 0.36.

[0024] Preferably, the alkaline activator includes one or more of sodium oxide, water glass, sodium phosphate and sodium hydroxide.

[0025] In summary, this application includes at least one of the following beneficial technical effects:

[0026] 1. The present application separates the nano-silica in the iron-rich slag from the slag, and then forms a core-shell structure with the slag as the core and the nano-silica as the shell, thereby reducing the degree of agglomeration of the nano-silica, enhancing the alkali-activated reaction activity of the iron-rich slag, optimizing the microstructure of the cementitious product, and improving the compressive strength and elastic modulus of the alkali-activated cementitious material.

[0027] 2. The nano-silica shell structure of the core-shell structure of the iron-rich slag-derived additive of the present application dissolves rapidly in the early stage, accelerating the initial release of silicate ions, but inhibiting the excessive early hydration reaction process. At the same time, the undissolved slag particles serve as heterogeneous nucleation sites for the formation of NASH gel, promoting the acceleration of secondary hydration and avoiding the shrinkage and microcracks of the alkali-activated gel material caused by early excessive hydration. The overall hydration heat is slightly increased, generating more dense hydration products, which is conducive to the improvement of mechanical strength.

[0028] 3. The core-shell structure of the iron-rich slag-derived additive in this application implements a multi-scale pore-filling strategy and optimizes the pore structure. Micron-sized slag particles act as a rigid framework to fill the macropores. The nanosilica shell enhances the activity of the alkali-activated reaction, increasing the gel content and thus the proportion of gel pores. This maximizes the pore size distribution and reduces the proportion of harmful pores (pore diameter > 100 nm) in the alkali-activated gel material.

[0029] 4. The core-shell structure of the iron-rich slag-derived nanostructured additives described in this application enhances the degree of polymerization (DOP) of the gel. The nanosilica shells are rich in hydroxyl groups, which rapidly release active silicate groups in an alkaline environment. These hydroxyl groups act as a supplemental silicon source to participate in the polycondensation reaction, extending the silicon-oxygen chain and strengthening the crosslinking network. Furthermore, the nanoparticles act as heterogeneous nucleation sites, inducing the orderly arrangement of aluminosilicate units, increasing the number of high-DOP structural units, and ultimately improving the DOP.

[0030] 5. The iron-rich slag derivative additive of the present application, on the one hand, fully utilizes the components in the iron-rich slag and reduces the cost. On the other hand, it is used in the form of a core-shell structure, which improves the mechanical properties of the alkali-activated gel material while optimizing the pore structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a comparison chart of the X-ray diffraction patterns of the nano-silica obtained in the preparation process of Example 1 of the present application and commercial nano-silica.

[0032] Figure 2 This is a comparison chart of the infrared spectra of the nano-silica obtained in the preparation process of Example 1 of the present application and the commercial nano-silica.

[0033] Figure 3 This is a transmission electron microscope image of nano-silicon dioxide obtained during the preparation process of Example 1 of the present application.

[0034] Figure 4 This is the EDS energy spectrum of nano-silicon dioxide obtained in the preparation process of Example 1 of the present application.

[0035] Figure 5 This is a transmission electron microscope image of the iron-rich slag-derived additive of Example 1 of the present application.

[0036] Figure 6 This is the EDS spectrum of the iron-rich slag-derived additive in Example 1 of the present application.

[0037] Figure 7 This is a comparison chart of the XPS spectra of the iron-rich slag-derived additive and the slag in Example 1 of the present application.

[0038] Figure 8 This is a comparison chart of the compressive strength of the alkali-activated gelling materials of Application Example 1 and Comparative Examples 1 to 4 of the present application over time.

[0039] Figure 9 It is a comparison diagram of the stress-strain diagrams of the alkali-activated gelling materials of Application Example 1 and Comparative Examples 1 to 4 of the present application.

[0040] Figure 10 This is a comparison diagram of the compressive strength-elastic modulus diagram of the alkali-activated gelling materials of Application Example 1 and Comparative Examples 1 to 4 of the present application.

[0041] Figure 11 It is a comparison diagram of the pore distribution diagrams of the alkali-activated gelling materials of Application Example 1 and Comparative Examples 1 to 4 of the present application.

[0042] Figure 12 This is a comparison diagram of the heat flow-time curves of the alkali-activated gelling materials of Application Example 1 and Comparative Examples 1 to 3 of the present application.

[0043] Figure 13 This is a comparison diagram of the cumulative heat-time curves of the alkali-activated gelling materials of Application Example 1 and Comparative Examples 1 to 3 of the present application.

[0044] Figure 14 It is a comparison diagram of the heat flow-time curves of the alkali-activated gelling materials of Application Example 1, Comparative Example 1 and Comparative Example 4 of the present application.

[0045] Figure 15 It is a comparison diagram of the cumulative heat-time curves of the alkali-activated gelling materials of Application Example 1, Comparative Example 1 and Comparative Example 4 of the present application.

[0046] Figure 16 The alkali-activated gelling material of Application Example 1, Comparative Example 1 and Comparative Example 4 of this application is 29 Solid-state NMR deconvolution spectrum of Si.

[0047] Figure 17 The alkali-activated gelling material of Application Example 1, Comparative Example 1 and Comparative Example 4 of this application is 27 Solid-state NMR deconvolution spectrum of Al. DETAILED DESCRIPTION

[0048] The present application is described in further detail below with reference to the examples. The following examples are intended to illustrate the present invention only and should not be construed as limiting the scope of the present invention. In the following examples, if specific conditions are not specified, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. The methods used are conventional methods well known in the art unless otherwise specified, and the consumables and reagents used are commercially available unless otherwise specified. Unless otherwise indicated, the professional and scientific terms used herein have the same meaning as those familiar to those skilled in the art. In addition, any method or material similar or equivalent to the described content may also be applied to the present invention. The raw materials used in the examples and comparative examples can be obtained commercially.

[0049] Example 1

[0050] Example 1 of the present application provides an iron-rich slag-derived additive, which is prepared by the following steps:

[0051] Preparation of nano-silica and slag: Copper slag (mainly composed of fayalite and magnetite) with a particle size of 0.21-0.42 mm was ball-milled to a particle size of less than 10 μm. The slag was then mixed with a 10 wt% hydrochloric acid solution by magnetic stirring for 30 minutes for acid leaching. The following reactions occurred during this process:

[0052] ;

[0053] After acid leaching, the mixture was allowed to stand, and the upper layer was separated by decantation, with the unreacted residue at the bottom being recovered. The upper layer was then washed and filtered to separate a silica cake with a solid content of approximately 25%. This was dried at 40°C for 4 hours and thoroughly ground to produce powdered nano-silica.

[0054] Preparation of core-shell structure: 10 g of slag and deionized water were prepared into a suspension, 1 g of polyvinylpyrrolidone (PVP, (C6H9NO) n , analytically pure, with an average molecular weight of 10,000) and the slag suspension were added to a magnetic stirrer and stirred at 900 r / min for 1 hour. 10 g of nano-silica and deionized water were prepared into a suspension and ultrasonically treated for 15 minutes. The suspension was then added to a magnetic stirrer and stirred at 900 r / min for 1 hour. Finally, the precipitate was collected by filtration, dried in a vacuum oven at 60°C for 4 hours, and then ground for 2 minutes to obtain a gray powdery iron-rich slag-derived additive.

[0055] Example 2

[0056] Example 2 of the present application provides an iron-rich slag-derived additive. The difference between Example 2 and Example 1 is that Example 2 uses nickel slag instead of copper slag.

[0057] Example 3

[0058] Example 3 of the present application provides an iron-rich slag-derived additive. The difference between Example 3 and Example 1 is that Example 3 uses steel slag instead of copper slag.

[0059] Application Example 1

[0060] Application Example 1 of the present application provides an alkali-activated gelling material, which is prepared by the following method:

[0061] 5 parts by weight of iron-rich blast furnace slag, 5 parts by weight of fly ash, and 0.2 parts by weight of the iron-rich slag derivative from Example 1 were mixed in a blender for 2 minutes, with a water-binder ratio of 0.36. Tap water and 0.4 parts by weight of an alkali activator (Na2O, modulus 2.0) were then added to the blender and stirred slowly for 1 minute and rapidly for 3 minutes. The freshly mixed slurry was poured into a mold and vibrated for 20 seconds to produce a sample. The sample was cured in an environmental chamber at 20°C and a relative humidity (RH) ≥ 95% for 24 hours, followed by an additional 28 days of curing in the same chamber to produce an alkali-activated cementitious material.

[0062] Application Example 2

[0063] Application Example 2 of the present application provides an alkali-activated gel material. The difference between Application Example 2 and Application Example 1 is that Application Example 2 uses the iron-rich slag derivative of Example 2.

[0064] Application Example 3

[0065] Application Example 3 of the present application provides an alkali-activated gel material. The difference between Application Example 3 and Application Example 1 is that Application Example 3 uses the iron-rich slag derivative of Example 3.

[0066] Comparative Example 1

[0067] Comparative Example 1 of the present application provides an alkali-activated gelling material. The difference between Comparative Example 1 and Application Example 1 is that the iron-rich slag derivative additive of Example 1 is not added in Comparative Example 1.

[0068] Comparative Example 2

[0069] Comparative Example 2 of the present application provides an alkali-activated gelling material. The difference between Comparative Example 2 and Application Example 1 is that the slag extracted from Example 1 is used in Comparative Example 2 to replace the iron-rich slag derivative additive in Example 1.

[0070] Comparative Example 3

[0071] Comparative Example 3 of the present application provides an alkali-activated gelling material. The difference between Comparative Example 3 and Application Example 1 is that in Comparative Example 3, nano-silica extracted from Example 1 is used to replace the iron-rich slag-derived additive in Example 1.

[0072] Comparative Example 4

[0073] Comparative Example 4 of the present application provides an alkali-activated gelling material. The difference between Comparative Example 4 and Application Example 1 is that in Comparative Example 4, nano-silica and slag extracted from Example 1 are used to replace the iron-rich slag-derived additives of Example 1, with the nano-silica being 0.13 parts by weight and the slag being 0.07 parts by weight.

[0074] Test and Inspection

[0075] (1) X-ray diffraction was performed on the nano-silica prepared from the iron-rich slag obtained in the preparation process of Example 1 and the commercial nano-silica to obtain a comparison of the X-ray diffraction patterns as shown below: Figure 1 As shown; the nano-silicon dioxide prepared from the iron-rich slag obtained in the preparation process of Example 1 and the commercial nano-silicon dioxide were subjected to infrared spectroscopy testing to obtain a comparison of infrared spectra as shown in FIG. Figure 2 The commercial nano-silica is S817575 nano-silica produced by McLean.

[0076] (2) The transmission electron microscope image of the nano-silicon dioxide obtained in the preparation process of Example 1 was obtained. Figure 3 As shown, and the EDS spectrum is detected, the EDS spectrum is obtained as shown Figure 4 shown.

[0077] (4) The purity of the nano-silica obtained in the preparation process of Example 1 was detected by inductively coupled plasma emission spectrometry and was found to be 99%. The pore volume of the nano-silica obtained in the preparation process of Example 1 was detected by a fully automatic specific surface and pore size analyzer using a specific surface area test method and was found to be 0.75 cm³ / g and 358 m² / g, respectively.

[0078] (5) The scanning electron microscope image of the iron-rich slag-derived additive of Example 1 of the present application was obtained, as shown in FIG. Figure 5 As shown; detect the EDS spectrum, such as Figure 6 Detection of the XPS spectrum of the iron-rich slag derived additive in Example 1 and detection of the XPS spectrum of the slag to obtain an XPS spectrum comparison diagram, as shown Figure 7 As shown in Figure 2, the slag is labeled as CS and the iron-rich slag-derived additive is labeled as CS@PVP@NS.

[0079] (6) The compressive strength of the alkali-activated cementitious materials of Application Example 1 and Comparative Examples 1 to 4 was tested on the 3rd, 7th and 28th days of curing, and a comparison graph of the compressive strength versus time was obtained, as shown in FIG. Figure 8 The results of Application Example 1 are labeled CS@PVP@NS2, the results of Comparative Example 1 are labeled CS0NS0, the results of Comparative Example 2 are labeled CS2, the results of Comparative Example 3 are labeled NS2, and the results of Comparative Example 4 are labeled CS0.7NS1.3. The compressive strength of the alkali-activated cementitious materials of Application Examples 2 and 3 was tested on the 28th day of curing, and the results are shown in Table 1 below.

[0080] Table 1:

[0081]

[0082] (7) The stress-strain diagram comparison of the alkali-activated cementitious materials of Application Example 1 and Comparative Examples 1 to 4 is obtained, as shown in FIG. Figure 9 The comparison diagram of the compressive strength-elastic modulus diagram of the alkali-activated cementitious materials and cement paste (42.5 ordinary Portland cement) of Application Example 1 and Comparative Examples 1 to 4 was obtained, as shown in FIG. Figure 10 shown.

[0083] (8) The comparison diagram of the pore distribution of the alkali-activated gelling materials of Application Example 1 and Comparative Examples 1 to 4 is obtained, as shown in FIG. Figure 11 shown.

[0084] (9) The heat flow-time curve comparison of the alkali-activated gelling materials of Comparative Examples 1 to 3 is shown in the figure below: Figure 12 The comparison diagram of the cumulative heat-time curve is shown in the figure below. Figure 13The comparison of the heat flow-time curves of the alkali-activated gelling materials of Application Example 1, Comparative Example 1 and Comparative Example 4 is shown in FIG. Figure 14 The comparison diagram of the cumulative heat-time curve is shown in the figure below. Figure 15 shown.

[0085] (10) The alkali-activated gelling materials of Application Example 1, Comparative Example 1 and Comparative Example 4 were obtained by detection and calculation. 29 Solid-state NMR deconvolution spectrum of Si, such as Figure 16 The MCL data obtained by NMR test was detected and calculated to be the alkali-activated gelling materials of Application Example 1, Comparative Example 1 and Comparative Example 4. 27 The solid-state NMR deconvolution spectrum of Al, such as Figure 17 The alkali-activated gelling materials of Application Example 1, Comparative Example 1 and Comparative Example 4 were obtained by detection and calculation. 29 The solid-state nuclear magnetic deconvolution quantitative calculation comparison table of Si is shown in Table 2 below. The average chain length and silicon-aluminum ratio of the reaction products of Application Example 1, Comparative Example 1 and Comparative Example 4 are detected and calculated, as shown in Table 3 below. 27 The comparison table of quantitative calculation of solid-state nuclear magnetic deconvolution of Al is shown in Table 4 below. The calculation formula is as follows:

[0086] The average molecular chain length (MCL), the Si-Al ratio of CASH and NASH gels were calculated according to the following formula: ; ; ;

[0087] in and represent the Si-Al ratios of CASH and NASH gels, respectively;

[0088] where Q n (mAl) has the following meanings:

[0089] Q n : represents the degree of polymerization of silicon-oxygen tetrahedron (SiO4), n is the number of bridging oxygens (i.e. the number of oxygen atoms shared with other tetrahedrons), Q 1 : dimer or terminal structure (1 bridging oxygen), Q 2 :chain structure (2 bridging oxygens), Q 4 : three-dimensional network structure (4 bridging oxygen); Q 1 and Q 2 It is a low-polymerization structure, reflecting the early reaction product or incomplete reaction of silicon source (such as the silicate phase in fly ash and blast furnace slag). 4 (mAl): A highly polymerized aluminosilicate network, indicating the structural substitution of aluminum on the silicon-oxygen network, which affects the mechanical properties of the material;

[0090] (mAl): m represents the number of aluminum oxide tetrahedra (AlO4) connected around the silicon oxide tetrahedron, Q 4 (0Al): Silicon tetrahedron is in a three-dimensional network and is surrounded by four silicon tetrahedrons, Q 4 (1Al): Silicon tetrahedron is in a three-dimensional network and is adjacent to one aluminum oxide tetrahedron. The remaining three are silicon tetrahedrons, Q 4 (2Al): Silicon tetrahedron is in a three-dimensional network and is adjacent to two aluminum oxide tetrahedrons. The remaining two are silicon tetrahedrons, Q 4 (3Al): The silicon tetrahedron is in a three-dimensional network and is adjacent to three aluminum-oxygen tetrahedrons, and the remaining one is a silicon tetrahedron. Q4(4Al): The silicon tetrahedron is surrounded by four aluminum-oxygen tetrahedrons.

[0091] also, 29 The quantification of Si-O-Si and Al-O-Si bonds in Si MAS NMR analysis can be calculated by the following method: ; ; ;

[0092] in Indicates the amount of Si-O-Si bonds, Indicates the amount of Si-O-Al bonds, Represents the total amount of Si-O-Si bonds and Si-O-Al bonds.

[0093] The relative proportions of Si-O-Si and Al-O-Si bonds are calculated using the following expression: ; ;

[0094] in Indicates the relative proportion of Si-O-Si bonds, Indicates the relative proportion of Al-O-Si bonds.

[0095] Table 2: Samples 29 Si MAS NMR spectrum deconvolution results

[0096]

[0097] Table 3: Average chain length and Si / Al ratio of reaction products

[0098]

[0099] Table 4: 27 Al MAS NMR spectrum deconvolution results

[0100]

[0101] Among them, Al(IV): tetracoordinate aluminum (AlO4), usually replaces Si in the silicon-oxygen network to form [AlO4] - tetrahedral, reflecting the structural aluminum in the aluminosilicate network;

[0102] Al(V): pentacoordinate aluminum (AlO5), usually associated with amorphous phases or reaction intermediates;

[0103] Al(VI): Hexacoordinated aluminum (AlO6), usually from unreacted crystalline phase or free Al 3+ , such as corundum in fly ash, or layered structures (such as aluminum hydroxide in hydration products).

[0104] Result Analysis

[0105] The following combination Figures 1 to 17 The experimental results provided in Tables 1 to 4 are used to describe this application in detail.

[0106] Reference Figures 1 to 4 ,Depend on Figure 1 、 Figure 2 and Figure 3 It can be seen that the prepared nano-silica is the same as the commercial nano-silica in amorphous state ( Figure 1 Verify amorphous state; Figure 2 Verify that the product is silicon dioxide; Figure 3 It was verified that the silica particle size was 10-30 nm, which is nanoscale), indicating that the present application successfully separated the slag and nano-silica in the copper slag without heating and high-temperature treatment. Figure 4 Further verification confirmed that the resulting nanosilica was pure silicon dioxide with minimal residual metal elements, consistent with the 99% purity of the nanosilica obtained during the preparation process of Example 1, as determined by inductively coupled plasma optical emission spectrometry. Furthermore, the resulting nanosilica had a pore volume of 0.75 cm³ / g, exhibiting a mesoporous structure and a specific surface area of 358 m² / g. Compared to traditional methods for preparing nanosilica, this method can reduce overall costs by approximately 60% to 70% and enhance its reactivity for geopolymerization reactions.

[0107] Reference Figures 5-7 The iron-rich slag-derived additive obtained in Example 1 forms a uniform nano-silica shell on the slag core. The particle size of the slag is 2.8 μm, and the thickness of the nano-silica shell is about 0.5-0.7 μm. Figure 7 The XPS spectrum shows that the main elements in the slag are iron, oxygen, calcium and silicon. By comparison, the Fe signal in the iron-rich slag-derived additive obtained in Example 1 disappears, indicating that the nano-silica shell covers the core surface of the slag to form a core-shell structure.

[0108] Reference Figure 8 In the early stages of the geopolymerization reaction, the 3-day compressive strength of the alkali-activated gelling material of Application Example 1 was lower than that of the alkali-activated gelling materials of Comparative Examples 1-3, delaying early hydration and minimizing the shrinkage and microcracks of the alkali-activated gelling material caused by early overhydration. The 28-day compressive strength of the alkali-activated gelling material of Application Example 1 was 21.3% higher (54.3 MPa) than that of the alkali-activated gelling material of Comparative Example 1, and was superior to that of the alkali-activated gelling materials of the single-addition group of Comparative Examples 2-3 and the alkali-activated gelling material of the physical mixing group of Comparative Example 4. This demonstrates that the iron-rich slag-derived additive obtained in Example 1 exhibits an excellent synergistic effect on the compressive strength of the alkali-activated gelling material. Furthermore, referring to Table 1, the 28-day compressive strength of the alkali-activated gelling materials of Application Examples 2-3 reached a level close to that of the alkali-activated gelling material of Application Example 1, indicating that using iron-rich slags such as nickel slag, steel slag, and copper slag as raw materials to produce iron-rich slag-derived additives can improve the compressive strength of alkali-activated gelling materials.

[0109] Reference Figures 9 and 10 The elastic modulus of the alkali-activated cementitious material of Application Example 1 (12.11 GPa) is higher than the elastic modulus of the alkali-activated cementitious material of Comparative Examples 1 to 4, especially the elastic modulus of the alkali-activated cementitious material of Comparative Example 1 is increased by 26.37%, and is higher than the elastic modulus of cement paste (42.5 ordinary Portland cement) of the same strength.

[0110] Reference Figure 11 The proportion of harmful pores (>100 nm) in the alkali-activated cementitious material of Application Example 1 was reduced from 16.98% to 8.85% compared to the alkali-activated cementitious material of Comparative Example 1. This analysis suggests that the core-shell structure of the iron-rich slag-derived additive in Example 1 optimized the pore structure during the geopolymerization reaction of the alkali-activated cementitious material of Application Example 1. The micron-sized slag particles acted as a rigid framework to fill the macropores, while the nanosilica shells increased the gel content by enhancing the activity of the alkali-activated reaction, thereby increasing the proportion of gel pores and maximally refining the pore size distribution.

[0111] Reference Figures 12-15The iron-rich slag-derived additive of Example 1 regulates the hydration process of the alkali-activated cementitious material, delays early hydration, accelerates late hydration, and improves the overall hydration heat. The analysis is that the nano-silica shell structure of the iron-rich slag-derived additive of Example 1 dissolves rapidly in the early stage, accelerates the initial release of silicate ions, but inhibits the excessive early hydration reaction process. At the same time, the undissolved slag particles serve as heterogeneous nucleation sites for the formation of NASH gel, which promotes the acceleration of secondary hydration and avoids the shrinkage and microcracks of the alkali-activated cementitious material caused by early excessive hydration. The overall hydration heat is slightly increased, and more dense hydration products are generated, which is beneficial to the improvement of mechanical strength.

[0112] Reference Figure 16 and Table 1~2, Q in the alkali activated gelling material of Application Example 1 4 (4Al) and Q 4 The proportion of (3Al), the average molecular chain length, and the proportion of Al-O-Si bonds are all increased compared to Comparative Example 1 and Comparative Example 4. Analysis shows that the core-shell structured nano-silica shell in Application Example 1 increases the degree of Al substitution in the silicon-oxygen tetrahedral framework, promotes the formation and cross-linking of long-chain structures, enhances the cross-linking density, and forms a long-range ordered network structure.

[0113] Reference Figure 17 As shown in Table 3, the ratio of Al(VI) + Al(V) in the alkali-activated gelling material of Application Example 1 is lower than that of Comparative Examples 1 and 4, while the chemical shift of Al(IV) increases by 3.70 ppm and 2.93 ppm, respectively, compared to Comparative Examples 1 and 4. Analysis suggests that the core-shell nanosilica shell in Application Example 1 enhances the reactivity of the alkali-activated material and increases the proportion of aluminum in the tetracoordinate network. The upward shift of the Al(IV) resonance peak indicates a transition from NASH gel to CASH gel, which contributes to an increase in the elastic modulus.

Claims

1. An iron-rich slag-derived additive, characterized by: The invention comprises slag extracted from iron-rich slag and nano-silica, and has a core-shell structure with the slag as a core and the nano-silica as a shell. The extraction of the slag and the nano-silica comprises the following steps: ball-milling the iron-rich slag to a particle size of less than 10 μm, then acid-leaching the slag, and then allowing the slag to stand, separating the upper layer mixture, washing, filtering, and drying the mixture to obtain the nano-silica, and recovering the precipitate at the bottom to obtain the slag.

2. The iron-rich slag-derived additive according to claim 1, characterized in that: The thickness of the shell structure formed by the nano-silicon dioxide is 0.4-0.8 μm.

3. The iron-rich slag-derived additive according to claim 1, characterized in that: The iron-rich slag includes one or more of copper slag, nickel slag, lead slag, zinc slag and steel slag.

4. A method for preparing the iron-rich slag-derived additive according to any one of claims 1 to 3, characterized in that: The following steps are involved: Slag and nano-silica are prepared into suspensions respectively, a complexing agent is added to the slag suspension and stirred evenly to obtain a transition liquid, the nano-silica suspension is added to the transition liquid, stirred and filtered to obtain a precipitate, and the precipitate is dried and ground to obtain the iron-rich slag derivative additive.

5. The method for preparing an iron-rich slag-derived additive according to claim 4, characterized in that: The weight ratio of the slag material to the nano-silicon dioxide is 1:0.8-1.

2.

6. The method for preparing an iron-rich slag-derived additive according to claim 4, characterized in that: The weight ratio of the slag material to the complexing agent is 8-12:

1.

7. The method for preparing an iron-rich slag-derived additive according to claim 4, characterized in that: The complexing agent includes one or more of polyvinyl pyrrolidone, polyethylene glycol, and polyacrylic acid.

8. Use of the iron-rich slag-derived additive according to any one of claims 1 to 3 in the preparation of alkali-activated cementitious materials.

9. The use of an iron-rich slag-derived additive in the preparation of alkali-activated gelling materials according to claim 8, characterized in that: The alkali-activated gelling material is made of the following components in parts by weight: 1-3 parts of an iron-rich slag-derived additive, 40-60 parts of blast furnace iron-rich slag, 40-60 parts of fly ash, and 3-6 parts of an alkaline activator; The water-cement ratio is 0.35~0.37.

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