Phosphoric acid excited large-volume steel slag-based geopolymer and forming method thereof

Abstract

The invention relates to the technical field of solid waste resource utilization and building materials, in particular to a phosphoric acid excited large-dosage steel slag-based geopolymer and a forming method thereof. The phosphoric acid excited large-dosage steel slag-based geopolymer is prepared from the following raw materials in parts by mass: 0 to 30 parts of metakaolin, 50 to 80 parts of steel slag powder, 20 parts of mineral powder, 10 parts of organic acid, 5 to 20 parts of phosphoric acid solution and 20 parts of water. The forming method provided by the invention is compression forming. According to the method, the structural defect caused by insufficient fluidity in a pouring method is overcome, and the engineering application scene of the geopolymer is expanded; according to the invention, the problem of component segregation caused by sedimentation in a pouring method is solved, and uniform compounding of steel slag particles and a matrix is realized; compared with a traditional pouring forming method, the method has the advantages that the steel slag doping proportion is remarkably increased, meanwhile, the strength of the synchronous energizing material is greatly increased, and a new path for efficient resource utilization of the steel slag is successfully unlocked.

Description

Technical Field

[0001] This invention relates to the fields of solid waste resource utilization and building materials technology, and in particular to a phosphoric acid-activated high-volume steel slag-based polymer and its molding method. Background Technology

[0002] Geopolymers are amorphous to semi-crystalline inorganic materials composed of a three-dimensional network of AlO4 and SiO4 tetrahedra. They possess excellent mechanical properties, corrosion resistance, and high-temperature resistance, and can utilize solid waste as raw materials, making them widely used in building materials, sealing, and refractory materials. Steel slag, the second largest industrial solid waste with an annual output exceeding 100 million tons, mainly contains CaO, SiO2, and Al2O3. Current utilization methods include internal recycling (sintered ore solvent) and external resource recovery (cement, road construction materials, etc.), but the comprehensive utilization rate is less than 30%. The bottleneck lies in the poor material stability caused by the expansion of free calcium oxide (f-CaO) and magnesium oxide (f-MgO) in steel slag upon contact with water, and the strong alkaline substances generated by the hydration of f-CaO easily pollute the environment. Currently, the large-scale stockpiling of steel slag not only occupies land but also poses a continuous threat to the ecological environment, urgently requiring the development of new and efficient resource recovery technologies to overcome stability limitations and expand large-scale application scenarios.

[0003] In the traditional field of geopolymer preparation, casting is a commonly used method. However, for phosphoric acid-activated steel slag-based geopolymers, casting has several limitations: 1. Casting relies on the slurry's own weight to fill the mold; even with vibration, air bubbles remain inside, resulting in high porosity, low compressive strength, and poor durability. 2. To ensure slurry fluidity, the water-to-solid ratio needs to be increased. Due to the low activity of steel slag, its content is usually limited to no more than 30% to ensure high strength, restricting the large-scale resource utilization of steel slag. 3. Slurry stratification is significant; steel slag particles easily settle, causing component segregation, weakening the interfacial bonding of the product, resulting in low strength and easy crack propagation later. 4. After casting, it needs to be allowed to cure for 24 hours before demolding, increasing the complexity of the preparation process. Casting makes it difficult to precisely control the microstructure of the material, leading to uneven distribution of pores inside the material, affecting its mechanical properties and durability. Moreover, cast products have poor surface smoothness, making subsequent processing complex. With the continuous improvement of material performance requirements, a new molding method is urgently needed. Summary of the Invention

[0004] Based on the above, this invention provides a phosphoric acid-activated high-volume steel slag-based polymer and its compression molding method. This invention uses metallurgical industrial solid waste steel slag as the main raw material, phosphoric acid as the activator, and organic acids as modifiers, employing a compression molding process to prepare a high-volume steel slag-based polymer.

[0005] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of this invention is a phosphoric acid-activated high-volume steel slag-based polymer, comprising, by mass parts: 0-30 parts metakaolin, 50-80 parts steel slag powder, 20 parts mineral powder, 10 parts organic acid, 5-20 parts phosphoric acid solution and 20 parts water.

[0006] Optionally, in the raw materials for the phosphoric acid-activated high-volume steel slag-based polymer, the amount of phosphoric acid solution added can be any value between 5 and 20.

[0007] In a preferred embodiment of the present invention, the specific surface area of ​​the metakaolin is 350–450 m². 2 / g; the specific surface area of ​​the steel slag powder is 320-400 m² / g. 2 / g; the specific surface area of ​​the mineral powder is 400-500m². 2 / g.

[0008] In a preferred embodiment of the present invention, the organic acid is citric acid.

[0009] In a preferred embodiment of the present invention, the mass fraction of the phosphoric acid solution is 50% to 70%.

[0010] The second technical solution of the present invention is a molding method for the above-mentioned phosphoric acid-activated high-volume steel slag-based polymer, comprising the following steps: The metakaolin, steel slag powder, mineral powder and organic acid are mixed in proportion to mass to obtain a mixture. The phosphoric acid solution was mixed with water and then sprayed onto the mixture to obtain a wet powder. The wet powder is pressed into shape and then cured to obtain the phosphoric acid-activated high-dosage steel slag-based polymer.

[0011] In a preferred embodiment of the present invention, the spraying process is carried out while stirring; the stirring speed is 200-600 r / min.

[0012] In a preferred embodiment of the present invention, the pressing pressure is 6-15 MPa, and the pressure is reached and the pressure is allowed to stand still for 10 seconds.

[0013] In a preferred embodiment of the present invention, the curing temperature is 60°C and the curing time is 72 hours.

[0014] In a preferred embodiment of the present invention, before mixing metakaolin, steel slag powder, mineral powder and organic acid, a step of drying metakaolin and mineral powder is included; the drying temperature is 105°C and the drying time is 12 hours.

[0015] In a preferred embodiment of the present invention, the method for preparing the steel slag powder includes the following steps: drying the steel slag, crushing it, passing it through a 4.75mm square hole sieve, and then ball milling it to obtain steel slag powder.

[0016] The mechanism involved in this invention is as follows: (1) Mechanism of mineral powder inhibiting expansion: After the addition of mineral powder, the cementitious products are reconstructed, the silica-alumina ratio of the products is increased, the crystal water content of the crystallized products is reduced, and the "volume expansion effect" is weakened. In the phosphoric acid-activated steel slag-meta-kaolin system, the H in phosphoric acid + Phosphoric acid attacks the mineral structure of steel slag and metakaolin, promoting the dissolution and release of calcium, silicon, and aluminum ions into the system. These ions then polymerize with phosphate ions, forming a calcium-silicon-aluminum-phosphate composite gel phase (such as calcium phosphate, silicon-aluminum-phosphorus amorphous phase, aluminophosphate, etc.). On one hand, the bulk density of the resulting composite gel phase is significantly lower than that of the reactants. According to the law of conservation of mass, if the mass remains unchanged before and after the reaction, the decrease in product density inevitably leads to an increase in volume. On the other hand, most phosphate products contain water of crystallization. The embedding of this water in the crystal lattice leads to an increase in lattice spacing, macroscopically manifested as volume expansion. These two aspects are the main reasons why phosphoric acid induces the expansion of the steel slag-metakaolin system. After the addition of mineral powder, the mineral powder weakens the "volume expansion effect" through competitive reactions with the active components: the glassy structure of the mineral powder is more easily affected by the H+ ions of phosphate than metakaolin. + During depolymerization, the released active silicon and aluminum preferentially combine with calcium and phosphate ions released from steel slag to form a multi-component composite gel phase. Since the Si / Al ratio in the mineral powder is higher than that in metakaolinite, the Si / Al and P / Al ratios in the system are increased. The silicon-aluminum tetrahedra form more -Si-O-Al-OP- bonds and -Al-OPO-Si- bonds with multiple phosphorus-oxygen tetrahedra by sharing oxygen atoms. The proportion of Si-OP bonds increases, forming a denser silicon-aluminum-phosphorus three-dimensional network structure. Calcium reacts with phosphate to generate calcium phosphate (such as hydroxyapatite) precursors, further enhancing the structural density while reducing the crystal water content in the product, avoiding "volume expansion caused by loose accumulation".

[0017] (2) Acid-base neutralization reaction: H in phosphoric acid + It reacts with alkaline substances in steel slag to form phosphates, while releasing active silicon, aluminum, iron and other components.

[0018] (3) Curing reaction: H in phosphoric acid + The process disrupts the glassy structure in slag and metakaolin, releasing active silicon, aluminum, and other components. The active silicon and aluminum released from steel slag, slag, and metakaolin undergo a condensation reaction with phosphate ions, forming a three-dimensional network structure, i.e., a geopolymer, with silicon-oxygen tetrahedra, aluminum-oxygen tetrahedra, and phosphorus-oxygen tetrahedra as basic structural units. Under suitable silicon-aluminum and phosphorus-aluminum ratios, this network structure exhibits high strength and stability.

[0019] (4) Compression molding: By applying external pressure, the particles in the mixture are brought closer together and squeezed, expelling air and moisture from the pores and increasing the density of the mixture. At the same time, the compression process can also promote the polymerization reaction, making the structure of the geopolymer more compact.

[0020] Compared with the prior art, the present invention has the following beneficial effects: 1) Low water-to-solid ratio and increased steel slag content enable efficient resource utilization of industrial solid waste; 2) Compression molding can eliminate air bubbles, reduce porosity, increase the interfacial bonding strength of the cured product, and improve its compressive strength. 3) After reaching the set pressure during pressing and molding, let it stand for 10 seconds, then unload and demold, which simplifies the process and increases output. 4) It avoids the settling of steel slag particles and significantly enhances the uniformity of component distribution; 5) The raw material ratio and pressing parameters are precisely controllable, reducing the fluctuation rate of finished product performance and adapting to the needs of continuous industrial production; 6) The high strength and low porosity of the prepared geopolymer make it suitable for high-end fields such as underground engineering impermeable structures and marine anti-corrosion coatings, breaking through the performance limitations of casting-based products. Attached Figure Description

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

[0022] Figure 1 The image shows the XRD pattern of the raw materials and phosphoric acid-activated high-volume steel slag-based polymer (YZPG-50, Example 1) in Example 1. In the image, SS represents steel slag powder, MK represents metakaolin, and GGBFS represents granulated blast furnace slag powder (i.e., mineral powder). Detailed Implementation

[0023] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0024] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0025] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0026] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0027] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0028] This invention provides a method for preparing phosphoric acid-activated high-volume steel slag-based geopolymers using a compression molding process. Steel slag powder, mineral powder, and metakaolin are used as raw materials. A 50%–70% (w / w) phosphoric acid solution is used as an activator, synergistically modified with organic acids. After mixing, a wet powder is formed. The wet powder is placed in a mold and pressed (6–15 MPa) to form the polymer. After demolding, it is cured at 60°C for 72 hours. The organic acid acts as a modifier, synergistically reacting with phosphoric acid and active substances in steel slag, mineral slag, and metakaolin to generate crystalline and amorphous gels, forming a three-dimensional network structure. Combined with the densification effect of pressure, a high steel slag content (50%–80%, referring to the percentage of steel slag powder in the total mass of metakaolin, steel slag powder, and mineral powder) is achieved, with a compressive strength of not less than 48 MPa after 3 days of curing. This method features high steel slag content, low energy consumption, no pollution, and high added value, making it suitable for the manufacture of building blocks, corrosion-resistant engineering materials, and solid waste storage materials. This invention uses a compression molding method to prepare geopolymers. This method can greatly increase the amount of steel slag incorporated, while the strength of the resulting products is significantly higher than that of casting. Moreover, the compression molding process is simple, low-cost, and suitable for industrial production. It can be widely used in building blocks, corrosion-resistant engineering, solid waste storage and other fields, and is especially suitable for municipal engineering and industrial solid waste resource utilization scenarios with strict requirements for environmental protection and durability.

[0029] This invention represents a significant advancement over existing technologies, as detailed below: 1. To address structural defects caused by insufficient fluidity in the casting method and expand the engineering application scenarios of geopolymers; 2. Overcome the problem of component segregation caused by settlement in the casting method and achieve uniform composite of steel slag particles and matrix; 3. Utilizing the initial structural strength generated by high pressure, combined with the phosphoric acid-activated reaction to form a crystalline and gel-like three-dimensional network structure, rapid self-hardening is achieved; 4. Geopolymers are prepared by compression molding, which forcibly removes gas from the material gaps and achieves microstructural densification. This overcomes the physical limitations of casting methods that rely on self-weight filling and can effectively improve their compressive strength. 5. Low water-to-solid ratio significantly reduces free water content, inhibits activator loss, and increases the amount of steel slag incorporated; 6. Compared with the traditional casting method, the amount of steel slag incorporated can be increased, and a large amount of steel slag can be effectively utilized (the steel slag content in the phosphoric acid-activated high-volume steel slag-based geopolymer prepared by compression molding is 50% to 80%, the strength of the geopolymer is significantly improved, and the resource utilization rate of steel slag is high).

[0030] Unless otherwise specified, the technical solutions described in this invention are all conventional solutions in the field, and the reagents or raw materials used are all purchased from commercial channels or are publicly available unless otherwise specified.

[0031] The metakaolin used in this embodiment of the invention has a specific surface area of ​​400 m². 2 / g; The specific surface area of ​​the ball-milled steel slag powder is 350m². 2 / g, with an activity index of 80% after 28 days; the mineral powder is of type S95, with a specific surface area of ​​450m². 2 / g.

[0032] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0033] Example 1 A phosphoric acid-activated high-volume steel slag-based polymer, by mass fraction, consists of 30 parts metakaolin, 50 parts steel slag powder, 20 parts mineral powder, 10 parts citric acid, 13 parts 70% phosphoric acid solution, and 20 parts water.

[0034] The preparation method of the above-mentioned phosphoric acid-activated high-volume steel slag-based polymer comprises the following steps: Step 1, Powder Refining: Dry the steel slag in an oven at 105℃ for 12 hours. After cooling to room temperature, pass it through a 4.75mm square hole sieve. Crush the material on the sieve to a fineness of less than 4.75mm using a crusher. Then, put the sieved steel slag into a ball mill and ball mill for 60 minutes to obtain steel slag powder.

[0035] Step 2, powder drying: Place the metakaolin and mineral powder in an oven at 105℃ for 12 hours and then cool to room temperature.

[0036] Step 3, Preparation of mixture: Place the above steel slag powder, metakaolin, mineral powder and citric acid in a mixer and mechanically mix them at 300 r / min for 10 min to obtain the mixture.

[0037] Step 4, preparing wet material: After mixing phosphoric acid solution and water, spray the mixture into the mixture while stirring to obtain wet powder; Step 5, molding and curing: The wet powder is filled into a steel mold, pressed under 15MPa pressure for 10s, unloaded and demolded, the test block is covered and sealed, and cured at 60℃ for 72h to obtain phosphoric acid activated high-dosage steel slag-based polymer.

[0038] Example 2 The preparation process of Example 2 is the same as that of Example 1, except that the raw materials consist of 0 parts metakaolin, 80 parts steel slag powder, 20 parts mineral powder, 10 parts citric acid, 13 parts phosphoric acid solution with a mass fraction of 70% and 20 parts water.

[0039] Example 3 The preparation process of Example 3 is the same as that of Example 1, except that the raw materials consist of 10 parts metakaolin, 70 parts steel slag powder, 20 parts mineral powder, 10 parts citric acid, 5 parts 50% phosphoric acid solution and 20 parts water.

[0040] Example 4 The preparation process of Example 4 is the same as that of Example 1, except that the raw materials consist of 10 parts metakaolin, 70 parts steel slag powder, 20 parts mineral powder, 10 parts citric acid, 13 parts phosphoric acid solution with a mass fraction of 70% and 20 parts water.

[0041] Example 5 The preparation process of Example 5 is the same as that of Example 1, except that the raw materials consist of 10 parts metakaolin, 70 parts steel slag powder, 20 parts mineral powder, 10 parts citric acid, 13 parts phosphoric acid solution with a mass fraction of 70% and 20 parts water, and the pressing pressure in step 5 is 6 MPa.

[0042] Example 6 The preparation process of Example 6 is the same as that of Example 1, except that the raw materials consist of 10 parts metakaolin, 70 parts steel slag powder, 20 parts mineral powder, 10 parts citric acid, 13 parts phosphoric acid solution with a mass fraction of 70% and 20 parts water, and the pressing pressure in step 5 is 12 MPa.

[0043] The compressive strength of the steel slag-based polymers prepared in Examples 1-6 after 3 days of curing is shown in Table 1. Table 1 shows that the steel slag-based polymers prepared by compression molding have high compressive strength.

[0044] Table 1 Compressive strength of steel slag-based polymers prepared in each example

[0045] Figure 1 The XRD patterns of the raw materials and phosphoric acid-activated high-volume steel slag-based polymers in Example 1 are shown. Figure 1 It can be seen that the peaks in metakaolin and steel slag have disappeared, while in addition to amorphous matter, there are also crystalline phases of calcium phosphate (CaPO3(OH)) and aluminum hydroxyphosphate (AlP3O8(OH)2) in the geopolymer.

[0046] Comparative Example 1 The only difference from Example 1 is that, by mass, the raw materials for the geopolymer consist of 30 parts steel slag, 70 parts metakaolin, 10 parts citric acid, 67 parts 85 wt.% phosphoric acid solution, and 57 parts water.

[0047] Results: Geopolymers prepared according to the compression molding method of Example 1 could not be compressed and molded.

[0048] Comparative Example 2 A phosphoric acid-activated geopolymer with a high content of steel slag as the base material, by mass, consists of 50 parts metakaolin, 50 parts steel slag powder, 10 parts citric acid, 13 parts 70% phosphoric acid solution, and 20 parts water. Results: The geopolymer prepared according to the compression molding method of Example 1 showed significant expansion in the middle part of the test block, with a linear expansion rate of 1.4%.

[0049] Table 2 shows the results of Si / Al and P / Al ratios of the steel slag-based polymer prepared in Example 1 and Comparative Example 2. As can be seen from Table 2, compared with Comparative Example 2, Example 1 has a higher Si / Al and P / Al ratio. That is, the silicon-aluminum tetrahedra of the steel slag-based polymer with added mineral powder form more -Si-O-Al-OP- bonds and -Al-OPO-Si- bonds with multiple phosphorus-oxygen tetrahedra through shared oxygen atoms. The proportion of -Si-OP- bonds is increased, forming a denser silicon-aluminum-phosphorus three-dimensional network structure.

[0050] In addition, the water of crystallization content of the geopolymer prepared in Example 1 (16.64%) was lower than that in Comparative Example 2 (19.08%).

[0051] Based on the above results, Example 1 with added mineral powder has a higher Si / Al and P / Al ratio, a corresponding increase in the silicon and phosphorus content in the geopolymer network, and a lower water of crystallization content, resulting in a more compact structure and avoiding "volume expansion caused by loose accumulation." In other words, the incorporation of mineral powder changes the composition and structure of the product.

[0052] Table 2. Si / Al and P / Al ratios of steel slag-based polymers prepared in Example 1 and Comparative Example 2

[0053] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A phosphoric acid-activated mass-volume steel slag-based geopolymer, characterized by, The raw materials include, by mass fraction: 0-30 parts of metakaolin, 50-80 parts of steel slag powder, 20 parts of mineral powder, 10 parts of organic acid, 5-20 parts of phosphoric acid solution and 20 parts of water.

2. The phosphonic acid-activated mass-volume steel slag-based geopolymer according to claim 1, characterized by, said metakaolin has a specific surface area comprised between 350 and 450 m 2 / g; said steel slag powder has a specific surface area comprised between 320 and 400 m 2 / g; said mineral powder has a specific surface area comprised between 400 and 500 m 2 / g. 3.The phospho-activated mass fly ash and steel slag-based geopolymer according to claim 1, characterized in that, The organic acid is citric acid.

4. The phosphonic acid-activated mass-volume steel slag-based geopolymer according to claim 1, characterized by, The mass fraction of the phosphoric acid solution is 50-70%.

5. A method for forming a phosphonic acid-activated massif steel slag-based geopolymer according to any one of claims 1 to 4, characterized in that, The method comprises the following steps: Mixing metakaolin, steel slag powder, mineral powder and organic acid uniformly by mass fraction to obtain a mixture; Spraying the mixture of phosphoric acid solution and water to obtain wet powder; Curing the wet powder after compression molding to obtain the phosphoric acid-activated large-dosage steel slag-based geopolymer.

6. The molding method according to claim 5, characterized by The spraying process is accompanied by stirring at a speed of 200-600 r / min.

7. The molding method according to claim 5, wherein The compression molding pressure is 6-15 MPa, and the pressure is maintained for 10 s after the compression molding pressure is reached.

8. The molding method according to claim 5, wherein The curing temperature is 60 DEG C, and the curing time is 72 h.

9. The molding method according to claim 5, wherein Before mixing metakaolin, steel slag powder, mineral powder and organic acid uniformly, the method further comprises the step of drying metakaolin and mineral powder; the drying temperature is 105 DEG C, and the drying time is 12 h.

10. The molding method according to claim 5, characterized by The preparation method of the steel slag powder comprises the following steps: drying steel slag, crushing, ball milling after passing through a 4.75 mm square hole sieve to obtain steel slag powder.

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