Iron-rich slag derivative additive as well as preparation method and application thereof

Abstract

The invention discloses an iron-rich slag derivative additive and a preparation method and application thereof, and relates to the field of building materials, the iron-rich slag derivative additive is composed of slag extracted from iron-rich slag and nano silicon dioxide, and the iron-rich slag derivative additive is of a core-shell structure formed by taking the slag as a core and the nano silicon dioxide as a shell. Nano silicon dioxide in the iron-rich slag is separated from the slag, then a core-shell structure is formed by taking the slag as a core and nano silicon dioxide as a shell, the nano silicon dioxide shell enhances the alkali-activated reaction activity and improves the degree of polymerization of gel molecules, the slag core is used as a rigid framework to fill matrix pores, and the core-shell structure of the iron-rich slag is improved. The two components cooperate with each other to optimize the microstructure of a gelling product, and the compressive strength and elastic modulus of the prepared alkali-activated gelling material are improved.

Description

Technical Field

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

[0002] Rich iron slag is a metallurgical by-product generated in the process of metallurgical industry production, including copper slag, steel slag, lead slag, zinc slag, nickel slag, etc. It contains a large amount of silicon dioxide and iron oxides, with a global annual output of more than 50 million tons, and is often used in the construction industry as cement raw materials, supplementary cementitious materials and aggregates, etc.

[0003] Alkali-activated cementitious materials are a commonly used cementitious material in the construction industry. Compared with ordinary Portland cement, they have higher mechanical strength, more excellent chemical erosion resistance durability and excellent high-temperature resistance performance. And the energy consumption in their manufacturing process is reduced by 30% - 50%, and the carbon emissions are reduced by 60% - 70%, showing sustainability. However, their elastic modulus decreases by 10% - 20% compared with traditional Portland cement-based materials, which is mainly related to the high porosity and low polymerization degree of C-(N)-A-S-H gel. This defect leads to insufficient elastic modulus of alkali-activated gel materials, severely restricting their application in load-bearing structures with high deformation requirements.

[0004] Currently, to improve the mechanical properties of alkali-activated cementitious materials or reduce the cost of alkali-activated cementitious materials, nano-silica or rich iron slag is added as an auxiliary gel material in alkali-activated cementitious materials. However, due to the traditional preparation methods of nano-silica (such as chemical vapor deposition, sol-gel method), they still face problems such as high energy consumption, high raw material costs (such as tetraethyl orthosilicate), organic solvent pollution, and easy agglomeration; while when rich iron slag is directly incorporated, due to its surface inertness, the bonding force between it and the gel interface is weak, and microcracks are easily formed in the interface area, resulting in a decrease in compressive strength. Summary of the Invention

[0005] In view of the above deficiencies in the related art, the present application provides an additive derived from rich iron slag and its preparation method and application. By separating nano-silica in rich iron slag from the slag material, and then forming a core-shell structure with the slag material as the core and nano-silica as the shell, the nano-silica shell enhances the alkali-activation reaction activity and improves the polymerization degree of gel molecules, and the slag material core fills the matrix pores as a rigid skeleton and improves the stiffness. The two cooperate to optimize the microstructure of the cementitious product and improve the compressive strength and elastic modulus of the prepared alkali-activated cementitious material.

[0006] In the first aspect, an additive derived from rich iron slag provided by the present application adopts the following technical solution: A ferric slag-derived additive consists of slag material extracted from ferric slag and nano-silica, and has a core-shell structure with the slag material as the core and the nano-silica as the shell.

[0007] Preferably, the extraction of the slag material and the nano-silica includes the following steps: acid-leaching the ferric slag, then standing still, separating the upper-layer mixture for washing, suction filtration and drying to obtain the nano-silica, and recovering the bottom precipitate to obtain the slag material.

[0008] Preferably, the thickness of the shell structure formed by the nano-silica is 0.4 - 0.8 μm.

[0009] Preferably, the thickness of the shell structure formed by the nano-silica is 0.5 - 0.7 μm.

[0010] Preferably, the ferric slag includes one or more of copper slag, nickel slag, lead slag, zinc slag and steel slag.

[0011] Preferably, the ferric slag is copper slag.

[0012] In a second aspect, a preparation method of a ferric slag-derived additive provided by the present application adopts the following technical solution: A preparation method of a ferric slag-derived additive includes the following steps: separately preparing suspensions of the slag material and the nano-silica, adding a complexing agent to the slag material suspension and stirring evenly to obtain a transition liquid, adding the nano-silica suspension to the transition liquid, filtering after stirring to obtain a precipitate, and drying and grinding the precipitate to obtain the ferric slag-derived additive.

[0013] Preferably, the weight ratio of the slag material to the nano-silica is 1:0.8 - 1.2.

[0014] Preferably, the weight ratio of the slag material to the nano-silica is 1:1.

[0015] Preferably, the weight ratio of the slag material to the complexing agent is 8 - 12:1.

[0016] Preferably, the weight ratio of the slag material to the complexing agent is 10:1.

[0017] Preferably, the complexing agent includes one or more of polyvinylpyrrolidone, polyethylene glycol, and polyacrylic acid.

[0018] Preferably, the complexing agent is polyvinylpyrrolidone.

[0019] In a third aspect, an application of a ferric slag-derived additive provided by the present application in preparing an alkali-activated cementitious material.

[0020] Preferably, the alkali-activated cementitious material is made of components including the following parts by weight: 1-3 parts of 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 alkaline activator; the water-binder ratio is 0.35-0.37.

[0021] Preferably, the alkali-activated cementitious material is made of components including the following 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; the water-binder ratio is 0.36.

[0022] Preferably, the alkaline activator includes one or more of sodium oxide, water glass, sodium phosphate, and sodium hydroxide.

[0023] In summary, the present application includes at least one of the following beneficial technical effects: 1. In the present application, nano-silica in the iron-rich slag is separated from the slag material, and then a core-shell structure is formed with the slag material as the core and nano-silica as the shell, reducing the agglomeration degree of nano-silica, enhancing the alkali-activation reactivity 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.

[0024] 2. The nano-silica shell structure of the iron-rich slag-derived additive with a core-shell structure in 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 N-A-S-H gel, promoting the acceleration of secondary hydration and avoiding the shrinkage and microcracks of the alkali-activated cementitious material caused by excessive early hydration. The overall hydration heat is slightly increased, generating more dense hydration products, which is beneficial to the improvement of mechanical strength.

[0025] 3. The iron-rich slag-derived additive with a core-shell structure in the present application realizes a multi-scale pore filling strategy and optimizes the pore structure. The slag particles with micron size serve as a rigid skeleton to fill the macro pores. The nano-silica shell improves the alkali-activation reactivity, increases the gel content, and thus increases the proportion of gel pores, maximizing the refinement of the pore size distribution and reducing the proportion of harmful pores (pore diameter > 100 nm) in the alkali-activated gel material.

[0026] 4. The core-shell type nano-additive of the iron-rich slag with a core-shell structure in the present application improves the gel polymerization degree. The surface of the nano-silica shell is rich in hydroxyl groups, which rapidly release reactive silicate radicals in an alkaline environment, participate in the polycondensation reaction as a supplementary silicon source, extend the silicon-oxygen chain, and strengthen the network cross-linking. At the same time, the nano-particles serve as heterogeneous nucleation points, inducing the ordered arrangement of silicate-aluminate units, increasing the high-polymerization-degree structural units, and improving the polymerization degree.

[0027] 5. On the one hand, the iron-rich slag-derived additive of the present application makes full use of the components in the iron-rich slag, reducing costs. 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 and optimizes the pore structure at the same time. Description of the Drawings

[0028] Figure 1 It is a comparison diagram of the X-ray diffraction patterns of the nano-silica obtained during the preparation process of Example 1 of the present application and commercial nano-silica.

[0029] Figure 2 It is a comparison diagram of the infrared spectra of the nano-silica obtained during the preparation process of Example 1 of the present application and commercial nano-silica.

[0030] Figure 3 It is a transmission electron microscope image of the nano-silica obtained during the preparation process of Example 1 of the present application.

[0031] Figure 4 It is an EDS energy spectrum diagram of the nano-silica obtained during the preparation process of Example 1 of the present application.

[0032] Figure 5 It is a transmission electron microscope image of the iron-rich slag-derived additive of Example 1 of the present application.

[0033] Figure 6 It is an EDS energy spectrum diagram of the iron-rich slag-derived additive of Example 1 of the present application.

[0034] Figure 7 It is a comparison diagram of the XPS energy spectra of the iron-rich slag-derived additive and the slag material of Example 1 of the present application.

[0035] Figure 8 It is a comparison diagram of the compressive strength-time variation diagrams of the alkali-activated cementitious materials of Application Example 1 and Comparative Examples 1 to 4 of the present application.

[0036] Figure 9 It is a comparison diagram of the stress-strain diagrams of the alkali-activated cementitious materials of Application Example 1 and Comparative Examples 1 to 4 of the present application.

[0037] Figure 10 It is a comparison diagram of the compressive strength-elastic modulus diagrams of the alkali-activated cementitious materials of Application Example 1 and Comparative Examples 1 to 4 of the present application.

[0038] Figure 11 It is a comparison diagram of the pore distribution diagrams of the alkali-activated cementitious materials of Application Example 1 and Comparative Examples 1 to 4 of the present application.

[0039] Figure 12 It is a comparison diagram of the heat flow-time curves of the alkali-activated cementitious materials of Application Example 1 and Comparative Examples 1 to 3 of the present application.

[0040] Figure 13 It is a comparison chart of the cumulative heat - time curves of the alkali - activated cementitious materials in Application Example 1 and Comparative Examples 1 - 3 of the present application.

[0041] Figure 14 It is a comparison chart of the heat flow - time curves of the alkali - activated cementitious materials in Application Example 1, Comparative Example 1 and Comparative Example 4 of the present application.

[0042] Figure 15 It is a comparison chart of the cumulative heat - time curves of the alkali - activated cementitious materials in Application Example 1, Comparative Example 1 and Comparative Example 4 of the present application.

[0043] Figure 16 It is the 29 Solid - state NMR deconvolution spectrum of Si of the alkali - activated cementitious materials in Application Example 1, Comparative Example 1 and Comparative Example 4 of the present application.

[0044] Figure 17 It is the 27 Solid - state NMR deconvolution spectrum of Al of the alkali - activated cementitious materials in Application Example 1, Comparative Example 1 and Comparative Example 4 of the present application. Detailed implementation manners

[0045] The following further elaborates on the present application in conjunction with examples. The following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. For those conditions not specified in the following examples, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. The methods used, unless otherwise specified, are all conventional methods well - known in the art. The consumables and reagents used, unless otherwise specified, are all commercially available. Unless otherwise stated, 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 can also be applied to the present invention. The raw materials used in the examples and comparative examples can all be obtained commercially.

[0046] Example 1 Example 1 of the present application provides an iron - rich slag - derived additive, which is prepared by the following steps: Obtaining nano - silica and slag material: Copper slag with a particle size of 0.21 - 0.42 mm (mainly composed of fayalite and magnetite) is ball - milled to a particle size below 10 μm by a ball mill, and then mixed with a 10 wt% hydrochloric acid solution through magnetic stirring for 30 min for acid leaching. The following reactions mainly occur in this process: ; After acid leaching, let it stand still, and use the decantation method to separate the upper mixture, and retain and recycle the unreacted residue at the bottom. Subsequently, the upper mixture is subjected to combined treatment of washing and suction filtration to separate a silica cake with a solid content of about 25%. It is dried at 40 °C for 4 hours and ground thoroughly to obtain powdered nano-silica.

[0047] Preparation of core-shell structure: Make a suspension of 10 g of the residue and deionized water. Add 1 g of polyvinylpyrrolidone (PVP, (C6H9NO) n , analytical pure, with an average molecular weight of 10,000) and the residue suspension to a magnetic stirrer and stir at a speed of 900 r / min for 1 hour. Take 10 g of nano-silica and deionized water to make a suspension, ultrasonically treat it for 15 minutes, then add it to the magnetic stirrer and stir at a speed of 900 r / min for 1 hour. Finally, filter and collect the precipitate, dry the precipitate in a vacuum oven at 60 °C for 4 hours, and then grind it for 2 minutes to obtain an iron-rich slag-derived additive in the form of gray powder.

[0048] Example 2 Example 2 of this application provides an iron-rich slag-derived additive. The difference between Example 2 and Example 1 is that in Example 2, nickel slag is used to replace copper slag.

[0049] Example 3 Example 3 of this application provides an iron-rich slag-derived additive. The difference between Example 3 and Example 1 is that in Example 3, steel slag is used to replace copper slag.

[0050] Application Example 1 Application Example 1 of this application provides an alkali-activated cementitious material, which is prepared by the following method: Take 5 parts by weight of blast furnace iron-rich slag, 5 parts by weight of fly ash, and 0.2 parts by weight of the iron-rich slag derivative of Example 1 and place them in a blender to mix and stir for 2 minutes. Control the water-binder ratio to be 0.36. Mix tap water and 0.4 parts by weight of an alkali activator (Na2O, modulus 2.0) and add them to the blender, stir slowly for 1 minute, and stir quickly for 3 minutes. Pour the fresh slurry into a mold and vibrate for 20 seconds to obtain a sample. Cure the sample in an environmental chamber at a temperature of 20 °C and a relative humidity (RH) ≥ 95% for 24 hours, and then carry out an additional 28-day cure in the same environmental chamber to obtain the alkali-activated cementitious material.

[0051] Application Example 2 Application Example 2 of this application provides an alkali-activated gel material. The difference between Application Example 2 and Application Example 1 is that in Application Example 2, the iron-rich slag derivative of Example 2 is used.

[0052] Application Example 3 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.

[0053] Comparative Example 1 Comparative Example 1 of the present application provides an alkali-activated cementitious material. The difference between Comparative Example 1 and Application Example 1 is that in Comparative Example 1, the iron-rich slag-derived additive of Example 1 is not added.

[0054] Comparative Example 2 Comparative Example 2 of the present application provides an alkali-activated cementitious material. The difference between Comparative Example 2 and Application Example 1 is that in Comparative Example 2, the slag material obtained by extraction in Example 1 is used to replace the iron-rich slag-derived additive of Example 1.

[0055] Comparative Example 3 Comparative Example 3 of the present application provides an alkali-activated cementitious material. The difference between Comparative Example 3 and Application Example 1 is that in Comparative Example 3, the nano-silica obtained by extraction in Example 1 is used to replace the iron-rich slag-derived additive of Example 1.

[0056] Comparative Example 4 Comparative Example 4 of the present application provides an alkali-activated cementitious material. The difference between Comparative Example 4 and Application Example 1 is that in Comparative Example 4, the nano-silica and slag material obtained by extraction in Example 1 are used to replace the iron-rich slag-derived additive of Example 1, with 0.13 parts by weight of nano-silica and 0.07 parts by weight of slag material.

[0057] Test and Detection (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 commercial nano-silica, and the comparison diagram of the X-ray diffraction patterns is as shown in Figure 1 ; infrared spectroscopy was performed on the nano-silica prepared from the iron-rich slag obtained in the preparation process of Example 1 and commercial nano-silica, and the comparison diagram of the infrared spectra is as shown in Figure 2 . Among them, the commercial nano-silica is S817575 nano-silica from Macklin.

[0058] (2) The transmission electron microscope image of the nano-silica obtained in the preparation process of Example 1 was detected, as shown in Figure 3 , and the EDS energy spectrum was detected, and the EDS energy spectrum diagram is as shown in Figure 4 .

[0059] (4) The purity of the nano-silica obtained during the preparation process of Example 1 was detected by an inductively coupled plasma emission spectrometer to be 99%; using a fully automatic specific surface and pore size analyzer and the specific surface test method, the pore volume of the nano-silica obtained during the preparation process of Example 1 was detected to be 0.75 cm³ / g, and the specific surface area was 358 m² / g.

[0060] (5) The scanning electron microscope image of the iron-rich slag-derived additive of Example 1 of the present application was detected, as shown in Figure 5 ; the EDS energy spectrum diagram was detected, as shown in Figure 6 ; the XPS energy spectrum diagram of the iron-rich slag-derived additive of Example 1 was detected and the XPS energy spectrum diagram of the slag material was detected to obtain a comparative XPS energy spectrum diagram, as shown in Figure 7 ; among them, the slag material was marked as CS, and the iron-rich slag-derived additive was marked as CS@PVP@NS.

[0061] (6) The compressive strength of the alkali-activated cementitious materials of Application Example 1 and Comparative Examples 1 to 4 was detected on the 3rd, 7th, and 28th days of curing, and a comparative diagram of the compressive strength vs. time change diagram was obtained, as shown in Figure 8 . Among them, the result of Application Example 1 was marked as CS@PVP@NS2, the result of Comparative Example 1 was marked as CS0NS0, the result of Comparative Example 2 was marked as CS2, the result of Comparative Example 3 was marked as NS2, and the result of Comparative Example 4 was marked as CS0.7NS1.3. The compressive strength of the alkali-activated cementitious materials of Application Examples 2 to 3 was detected on the 28th day of curing, and the results are shown in Table 1 below.

[0062] Table 1:

[0063] (7) A comparative diagram of the stress-strain diagrams of the alkali-activated cementitious materials of Application Example 1 and Comparative Examples 1 to 4 was detected, as shown in Figure 9 . A comparative diagram of the compressive strength-elastic modulus diagrams of the alkali-activated cementitious materials of Application Example 1 and Comparative Examples 1 to 4 and neat cement paste (42.5 ordinary Portland cement) was detected, as shown in Figure 10 .

[0064] (8) A comparative diagram of the pore distribution diagrams of the alkali-activated cementitious materials of Application Example 1 and Comparative Examples 1 to 4 was detected, as shown in Figure 11 .

[0065] (9) A comparative diagram of the heat flow-time curves of the alkali-activated cementitious materials of Comparative Examples 1 to 3 was detected, as shown in Figure 12 and a comparative diagram of the cumulative heat-time curves, as shown in Figure 13 . A comparative diagram of the heat flow-time curves of the alkali-activated cementitious materials of Application Example 1 and Comparative Examples 1 and 4 was detected, as shown in Figure 14The comparison chart with the shown and cumulative heat - time curves is as Figure 15 shown.

[0066] (10) Detect and calculate the 29 solid - state NMR deconvolution spectra of Si in the alkali - activated cementitious materials of Application Example 1, Comparative Example 1, and Comparative Example 4, as Figure 16 shown. Detect and calculate the MCL data obtained from the NMR test for the alkali - activated cementitious materials of Application Example 1, Comparative Example 1, and Comparative Example 4 27 solid - state NMR deconvolution spectra of Al, as Figure 17 shown. Detect and calculate the 29 comparative table of quantitative calculation of solid - state NMR deconvolution of Si in the alkali - activated cementitious materials of Application Example 1, Comparative Example 1, and Comparative Example 4, as shown in Table 2 below. The results of the average chain length and silica - alumina ratio of the reaction products of Application Example 1, Comparative Example 1, and Comparative Example 4 are shown in Table 3 below. Detect and calculate the 27 comparative table of quantitative calculation of solid - state NMR deconvolution of Al in the alkali - activated cementitious materials of Application Example 1, Comparative Example 1, and Comparative Example 4, as shown in Table 4 below. The calculation formulas are as follows: The calculation formulas for the average molecular chain length (MCL) and the silica - alumina ratio of C - A - S - H and N - A - S - H gels are calculated according to the following formulas: ; ; ; where and represent the silica - alumina ratios of C - A - S - H and N - A - S - H gels respectively; where Q n (mAl) has the following meaning: Q n : represents the degree of polymerization of silicon - oxygen tetrahedra (SiO4), n is the number of bridging oxygen atoms (i.e., the number of oxygen atoms shared with other tetrahedra), Q 1 : dimer or terminal structure (1 bridging oxygen), Q 2 : chain - like structure (2 bridging oxygen), Q 4 : three - dimensional network structure (4 bridging oxygen); Q 1 and Q 2 are low - degree polymerization structures, reflecting early reaction products or unreacted silicon sources (such as silicate phases in fly ash and blast furnace slag), Q 4 (mAl): high - degree polymerization aluminosilicate network, indicating the structural substitution of aluminum for the silicon - oxygen network, affecting the mechanical properties of the material; (mAl): m represents the number of aluminum - oxygen tetrahedra (AlO4) connected around the silicon - oxygen tetrahedron, Q 4 (0Al): the silicon tetrahedron is in a three - dimensional network and is surrounded by 4 silicon tetrahedra, Q 4(1Al): The silicon tetrahedra are in a three-dimensional network and are adjacent to 1 aluminum-oxygen tetrahedron, and the remaining 3 are silicon tetrahedra, Q 4 (2Al): The silicon tetrahedra are in a three-dimensional network and are adjacent to 2 aluminum-oxygen tetrahedra, and the remaining 2 are silicon tetrahedra, Q 4 (3Al): The silicon tetrahedra are in a three-dimensional network and are adjacent to 3 aluminum-oxygen tetrahedra, and the remaining 1 is silicon tetrahedron, Q4(4Al): The silicon tetrahedron is surrounded by 4 aluminum-oxygen tetrahedra.

[0067] In addition, 29 The quantification of Si-O-Si and Al-O-Si bonds in Si MAS NMR analysis can be calculated by the following methods: ; ; ; where represents the amount of Si-O-Si bonds, represents the amount of Si-O-Al bonds, represents the total amount of Si-O-Si and Si-O-Al bonds.

[0068] The relative ratios of Si-O-Si and Al-O-Si bonds are calculated by the following expressions: ; ; where represents the relative ratio of Si-O-Si bonds, represents the relative ratio of Al-O-Si bonds.

[0069] Table 2: Samples 29 Results of deconvolution of Si MAS NMR spectra

[0070] Table 3: Calculation of average chain length and silicon-aluminum ratio of reaction products

[0071] Table 4: 27 Results of deconvolution of Al MAS NMR spectra

[0072] where Al(IV): tetracoordinated aluminum (AlO4), usually replaces Si in the silicon-oxygen network to form [AlO4] - tetrahedron, reflecting the structural aluminum in the silicate network; Al(V): pentacoordinated aluminum (AlO5), usually associated with amorphous phases or reaction intermediates; Al(VI): hexacoordinated aluminum (AlO6), usually from unreacted crystalline phases or free Al3+ , such as corundum in fly ash or layered structures (such as aluminum hydroxide in hydration products).

[0073] Result Analysis The following combines Figures 1 to 17 with the experimental results provided in Tables 1 to 4 to elaborate on this application in detail.

[0074] Referring to Figures 1 to 4 , it can be seen from Figure 1 , Figure 2 and Figure 3 that nano-silica with the same amorphous state as commercial nano-silica is prepared ( Figure 1 Verify the amorphous state; Figure 2 Verify that the obtained is silica; Figure 3 Verify that the particle size of silica is 10 - 30 nm, belonging to the nano-scale), indicating that this application has successfully separated the slag material in copper slag and nano-silica without heating and high-temperature treatment. Figure 4 It is further verified that the obtained is silica and the residual metal elements are extremely few, which is consistent with the result that the purity of nano-silica obtained in the preparation process of Example 1 detected by inductively coupled plasma emission spectrometer is 99%. And the pore volume of the obtained nano-silica is 0.75 cm³ / g, presenting a mesoporous structure, and the specific surface area is as high as 358 m² / g. Compared with the traditional method for preparing nano-silica, this method can reduce the comprehensive cost by about 60% - 70% and enhance its reaction activity for geopolymers.

[0075] Referring to Figures 5 to 7 , a uniform nano-silica shell layer is formed on the core of the slag material for the iron-rich slag-derived additive obtained in Example 1. The particle size of the slag material is 2.8 μm, and the thickness of the nano-silica shell is about 0.5 - 0.7 μm. Figure 7 From the XPS energy spectrum diagram of

[0076] Referring to Figure 8In the early stage of geopolymerization, the 3-day compressive strength of the alkali-activated gelling material of Application Example 1 is lower than that of the alkali-activated gelling material of Comparative Examples 1 to 3, which delays early hydration and avoids the shrinkage and microcracks of the alkali-activated gelling material caused by early excessive hydration as much as possible. The 28-day compressive strength of the alkali-activated gelling material of Application Example 1 is 21.3% (54.3 MPa) higher than that of the alkali-activated gelling material of Comparative Example 1, and is superior to the alkali-activated gelling material of the single addition group of Comparative Examples 2 to 3 and the alkali-activated gelling material of the physical mixing group of Comparative Example 4, indicating 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. At the same time, referring to Table 1, the 28-day compressive strength of the alkali-activated gelling material of Application Examples 2 to 3 reaches a level close to the 28-day compressive strength of the alkali-activated gelling material of Application Example 1, indicating that the use of iron-rich slags such as nickel slag, steel slag and copper slag as raw materials to make iron-rich slag derived additives is beneficial to improving the compressive strength of alkali-activated gelling materials.

[0077] Reference Figures 9 to 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.

[0078] Reference Figure 11 The proportion of harmful pores (>100 nm) in the alkali-activated gelling material of Application Example 1 was reduced from 16.98% to 8.85% compared with the proportion of harmful pores (>100 nm) in the alkali-activated gelling material of Comparative Example 1. The analysis shows that the core-shell structure of the iron-rich slag-derived additive of Example 1 optimized the pore structure during the reaction process of the geopolymerization of the alkali-activated gelling material of Application Example 1. The micron-sized slag particles serve as a rigid skeleton to fill the macroscopic pores, while the nano-silica shell increases the gel content by increasing the activity of the alkali-activated reaction, thereby increasing the proportion of gel pores and refining the pore size distribution to the maximum extent.

[0079] Reference Figures 12 to 15, the iron-rich slag-derived additive in Example 1 regulated the hydration process of the alkali-activated cementitious material, delayed the early hydration, accelerated the late hydration, and the overall heat of hydration was increased. The analysis is that the nano-silica shell structure of the iron-rich slag-derived additive in Example 1 dissolved 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 served as heterogeneous nucleation sites for the formation of N-A-S-H gel, promoting the acceleration of secondary hydration and avoiding the shrinkage and microcracks of the alkali-activated cementitious material caused by excessive early hydration. The overall heat of hydration increased slightly, generating more dense hydration products, which was beneficial to the improvement of mechanical strength.

[0080] Referring to Figure 16 and Tables 1-2, the proportions of Q 4 (4Al) and Q 4 (3Al), the average molecular chain length, and the proportion of Al-O-Si bonds in the alkali-activated cementitious material of Application Example 1 were all increased compared with Comparative Example 1 and Comparative Example 4. The analysis is that the nano-silica shell with a core-shell structure in Application Example 1 increased the degree of Al substitution in the silicon-oxygen tetrahedron framework, promoted the formation and crosslinking of long-chain structures, enhanced the crosslinking density, and formed a long-range ordered network structure.

[0081] Referring to Figure 17 and Table 3, the proportion of Al(Ⅵ)+Al(Ⅴ) in the alkali-activated cementitious material of Application Example 1 was decreased compared with Comparative Example 1 and Comparative Example 4, and the chemical shift of Al(Ⅳ) was increased by 3.70 ppm and 2.93 ppm respectively compared with Comparative Example 1 and Comparative Example 4. The analysis is that the nano-silica shell with a core-shell structure in Application Example 1 improved the reaction activity of the alkali-activated material and promoted the proportion of aluminum in the four-coordinate network. The upward shift of the Al(IV) resonance peak indicates the transformation of the gel composition from N-A-S-H gel to C-A-S-H gel, which is beneficial to the improvement of the elastic modulus.

Claims

1. An iron-rich slag derived additive, characterized in that: The invention is composed of slag extracted from iron-rich slag and nano silicon dioxide, and has a core-shell structure with the slag as a core and the nano silicon dioxide as a shell.

2. The iron-rich slag-derived additive according to claim 1, characterized in that: The extraction of the slag and the nano-silicon dioxide comprises the following steps: acid leaching the iron-rich slag, then standing it, separating the upper layer mixture, washing, filtering and drying it to obtain the nano-silicon dioxide, and recovering the bottom precipitate to obtain the slag.

3. 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.

4. 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.

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

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

2.

7. The method for preparing an iron-rich slag-derived additive according to claim 5, characterized in that: The weight ratio of the slag material to the complexing agent is 8-12:

1.

8. The method for preparing an iron-rich slag-derived additive according to claim 5, characterized in that: The complexing agent includes one or more of polyvinyl pyrrolidone, polyethylene glycol, and polyacrylic acid.

9. Use of the iron-rich slag derived additive according to any one of claims 1 to 4 in the preparation of alkali-activated cementitious materials.

10. The use of an iron-rich slag-derived additive in the preparation of alkali-activated cementitious materials according to claim 9, 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-to-cement ratio is 0.35~0.37.

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