Acid-activated steel slag-based geopolymer and preparation method thereof

Abstract

The present invention relates to the technical field of steel slag resource utilization, and specifically to an acid-activated steel slag-based geopolymer and a preparation method thereof. The specific technical solution is: an acid-activated steel slag-based geopolymer, which comprises, by mass, 55 to 70 parts of metakaolin, 30 to 45 parts of steel slag powder, 8 to 12 parts of organic acid and 87 to 223 parts of phosphoric acid solution. The present invention utilizes the acidity of phosphoric acid and organic acid to solve the problem that steel slag is difficult to be comprehensively utilized in the fields of building materials due to the presence of f-CaO and f-MgO, and provides a new direction for the resource utilization of steel slag. At the same time, the added organic acid forms a complex with the calcium ions dissolved in the steel slag, avoiding the phenomenon that the slurry is rapidly solidified and cannot be formed due to a large amount of heat released simply due to the acid-base neutralization reaction.

Description

Technical Field

[0001] The present invention relates to the technical field of steel slag resource utilization, and in particular to an acid-activated steel slag-based geopolymer and a preparation method thereof. Background Art

[0002] Geopolymers are inorganic polymers with a three-dimensional network structure composed of AlO₄ and SiO₄ tetrahedral structural units. They are inorganic non-metallic materials ranging from amorphous to semi-crystalline. They possess excellent mechanical properties and resistance to acids, alkalis, fire, and high temperatures. They can be made from solid waste and construction debris, and are therefore used in construction materials, high-strength materials, solid waste materials, sealing materials, and high-temperature resistant materials.

[0003] Steel slag, a byproduct of the steelmaking industry, produces over 100 million tons annually, making it the second largest typical industrial solid waste after blast furnace slag. Steel slag, a multi-mineral solid solution, primarily consists of CaO, SiO2, Al2O3, MgO, Fe2O3, MnO, and P2O5. Steel slag resource utilization is primarily divided into internal recycling within steel companies and external resource utilization. Internal utilization primarily involves serving as a solid solvent for sintered ore and a solvent in blast furnaces or cupola furnaces, but usage is limited. External utilization primarily involves use as a raw material for cement, concrete, road materials, and for water and flue gas treatment. Currently, utilization is primarily concentrated in civil engineering applications such as construction and roads. However, the presence of free calcium oxide (f-CaO) and free magnesium oxide (f-MgO) in steel slag results in poor stability, limiting its large-scale application in construction and road construction. At present, the comprehensive utilization rate of steel slag in my country is still less than 30%, resulting in serious stockpiling of legacy steel slag. Moreover, the f-CaO in the steel slag reacts with water to form Ca(OH)2, which can easily cause strong alkaline pollution, endanger the surrounding environment, and put great pressure on the surrounding ecological environment. Therefore, there is an urgent need to find a practical and effective way to utilize steel slag resources. Summary of the Invention

[0004] In view of the deficiencies in the prior art, the present invention provides an acid-activated steel slag-based geopolymer and a preparation method thereof.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0006] The invention discloses an acid-activated steel slag-based geopolymer, which comprises, by mass, 55-70 parts of metakaolin, 30-45 parts of steel slag powder, 8-12 parts of organic acid and 87-223 parts of phosphoric acid solution.

[0007] Preferably, the organic acid is any one or more of citric acid, malic acid, lactic acid and oxalic acid.

[0008] Preferably, the concentration of the phosphoric acid solution is 40-70%.

[0009] Preferably, the specific surface area of ​​the steel slag powder is 300-400 kg / m 3 .

[0010] Accordingly, a method for preparing an acid-activated steel slag-based geopolymer comprises the following steps: uniformly mixing metakaolin, steel slag powder and an organic acid, adding the mixture into a phosphoric acid solution, and stirring the mixture sufficiently to form a uniform acid-activated steel slag-based geopolymer slurry.

[0011] Preferably, the acid-activated steel slag-based geopolymer slurry is poured into a mold, vibrated, cured, and demoulded. The acid-activated steel slag-based geopolymer is obtained by curing it to a certain age.

[0012] Preferably, the stirring speed is 200-600 r / min and the stirring time is 2-4 min.

[0013] Preferably, the curing condition is constant temperature sealed curing at 60°C for 48 hours.

[0014] The present invention has the following beneficial effects:

[0015] 1. The acid-activated steel slag-based geopolymer prepared by the present invention uses steel slag to partially replace metakaolin as raw material, thereby reducing the production cost of the acidic geopolymer. Utilizing the acidity of phosphoric acid and organic acid, on the one hand, the problem of difficulty in comprehensive utilization of steel slag in building materials and other fields due to the presence of f-CaO and f-MgO in the slag is solved, thus providing a new direction for the resource utilization of steel slag. On the other hand, the added organic acid forms a complex with calcium and magnesium ions dissolved in the steel slag, thereby avoiding the phenomenon that the slurry cannot be formed due to the acid-base neutralization reaction between phosphoric acid and alkaline substances in the steel slag powder, which releases a large amount of heat.

[0016] 2. The invention incorporates a high amount of steel slag, which reduces environmental problems caused by steel slag storage. At the same time, the generated geopolymer can seal heavy metals in the steel slag, which is highly environmentally safe. Under acidic conditions, the active SiO2, Al2O3, Fe2O3, etc. dissolved from the steel slag participate in the formation of the geopolymer network, resulting in a dense structure and high strength of the geopolymer. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 FT-IR spectra of metakaolin, steel slag and acid-activated steel slag-based geopolymer in Example 1. DETAILED DESCRIPTION

[0018] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0019] Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0020] Acid-activated geopolymers have many advantages over alkali-activated geopolymers. Acid-activated geopolymers have higher strength, which makes them have better application potential in environments with heavy loads and stress concentration; acid-activated geopolymers will not undergo alkali-aggregate reaction with the active components in the aggregate, so they have better durability and stability; acid-activated geopolymers have stronger resistance to acid erosion, which enables them to maintain good stability and performance in acidic environments.

[0021] The present invention uses phosphoric acid and an organic acid to synergistically activate steel slag and metakaolin to prepare geopolymers. This synergistic use of phosphoric acid and organic acids not only eliminates the potential risk of poor volume stability in building materials caused by free calcium oxide and free magnesium oxide in the steel slag, but also addresses the problem of excessive steel slag incorporation causing rapid coagulation and molding failure due to acid-base neutralization reactions, further improving the resource utilization of steel slag. The present invention utilizes steel slag as a raw material, and the active SiO2, Al2O3, and Fe2O3 dissolved from the steel slag under acidic conditions participate in the formation of the geopolymer network, resulting in a denser structure and higher compressive strength for the geopolymer.

[0022] Specifically: The present invention discloses an acid-activated steel slag-based geopolymer, which comprises, by weight, 55 to 70 parts of metakaolin, 30 to 45 parts of steel slag powder, 8 to 12 parts of an organic acid, and 87 to 223 parts of a phosphoric acid solution. The organic acid is any one or more of citric acid, malic acid, lactic acid, and oxalic acid. The concentration of the phosphoric acid solution is 40 to 70%. The specific surface area of ​​the steel slag powder is 300 to 400 kg / m 3 .

[0023] Furthermore, the phosphoric acid solution includes 51 to 73 parts of water and 36 to 150 parts of concentrated phosphoric acid, calculated by weight, and is prepared by mixing water and concentrated phosphoric acid.

[0024] The present invention also discloses a method for preparing an acid-activated steel slag-based geopolymer. The solid raw materials (metakaolin, steel slag powder, and organic acid) are uniformly mixed according to the aforementioned proportions, added to a phosphoric acid solution, and stirred thoroughly to form a uniform acid-activated steel slag-based geopolymer slurry. The stirring speed is 200 to 600 rpm for 2 to 4 minutes. The acid-activated steel slag-based geopolymer slurry is poured into a mold, vibrated, cured, and demolded. The acid-activated steel slag-based geopolymer is obtained by curing for a certain age. The curing conditions are constant temperature, sealed curing, and curing at 60°C for 72 hours.

[0025] Furthermore, the amount of phosphoric acid solution added is 79-115% of the solid raw material. When the amount of phosphoric acid solution added is too low, the water content is too low and the material cannot be formed; when the amount of phosphoric acid solution added is too high, it will bring more free water, forming pores inside the material, thereby affecting the strength of the acid-activated steel slag-based geopolymer.

[0026] The present invention will be further described below with reference to specific embodiments.

[0027] Unless otherwise specified, the reagents and raw materials used in the following examples were purchased from commercial sources or are publicly available.

[0028] In the following examples, metakaolin was of industrial grade. The main chemical composition of the steel slag is shown in Table 1: Concentrated phosphoric acid (85 wt.%, analytical grade); organic acid, analytical grade.

[0029] Table 1 Chemical composition of solid raw materials (%)

[0030] Element CaO <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> MgO <![CDATA[TiO2]]> MnO steel slag 39.73 17.23 4.60 24.32 7.25 0.25 5.12 Metakaolin - 55.06 44.12 0.8 - - -

[0031] Example 1

[0032] The invention discloses an acid-activated steel slag-based geopolymer, which comprises the following components in parts by mass: 30 parts of steel slag, 70 parts of metakaolin, 10 parts of citric acid, 67 parts of concentrated phosphoric acid and 57 parts of water.

[0033] The preparation process includes the following steps:

[0034] Powder refinement: The steel slag is dried in an oven at 105°C for 12 hours, cooled to room temperature, and passed through a 4.75mm square hole sieve. The sieved material is crushed to a fineness of less than 4.75mm using a crusher. The sieved steel slag is then placed in a ball mill and ball milled for 60 minutes to obtain steel slag powder.

[0035] Powder drying: The metakaolin was dried in an oven at 105°C for 12 hours and then cooled to room temperature to obtain the metakaolin raw material.

[0036] Preparation of a mixture: placing the above-mentioned steel slag powder, metakaolin and citric acid in a mixer and mechanically mixing them at 300 r / min for 10 minutes to obtain a mixture.

[0037] Prepare the pure slurry: add the mixture to the phosphoric acid solution and continue mixing and stirring for 3 minutes to obtain the pure slurry;

[0038] Molding and curing: The slurry is poured into a steel mold for forming. The mold is then coated and sealed, and then placed in a cement rapid curing box for constant temperature curing at 60°C for 24 hours. After demolding, the mold is coated and sealed, and then cured in a cement rapid curing box for constant temperature curing at 60°C for 48 hours to obtain an acid-activated steel slag-based geopolymer.

[0039] Example 2

[0040] The invention discloses an acid-activated steel slag-based geopolymer, which comprises the following components in parts by mass: 40 parts of steel slag, 60 parts of metakaolin, 8 parts of citric acid, 67 parts of concentrated phosphoric acid and 57 parts of water.

[0041] The preparation process is the same as that of Example 1.

[0042] Example 3

[0043] The invention discloses an acid-activated steel slag-based geopolymer, which comprises the following components in parts by mass: 30 parts of steel slag, 70 parts of metakaolin, 10 parts of citric acid, 36 parts of concentrated phosphoric acid and 51 parts of water.

[0044] The preparation process is the same as that of Example 1.

[0045] Example 4

[0046] The invention discloses an acid-activated steel slag-based geopolymer gelling material, wherein the contents of the components thereof are respectively as follows, calculated by weight: 30 parts of steel slag, 70 parts of metakaolin, 10 parts of malic acid, 67 parts of concentrated phosphoric acid and 57 parts of water.

[0047] The preparation process is the same as that of Example 1.

[0048] Example 5

[0049] The invention discloses an acid-activated steel slag-based geopolymer gelling material, wherein the contents of the components thereof are respectively as follows, calculated by weight: 30 parts of steel slag, 70 parts of metakaolin, 10 parts of lactic acid, 67 parts of concentrated phosphoric acid and 57 parts of water.

[0050] The preparation process is the same as that of Example 1.

[0051] Example 6

[0052] The invention discloses an acid-activated steel slag-based geopolymer, which comprises the following components in parts by mass: 30 parts of steel slag, 70 parts of metakaolin, 10 parts of oxalic acid, 67 parts of concentrated phosphoric acid and 57 parts of water.

[0053] The preparation process is the same as that of Example 1.

[0054] The compressive strength of each example was tested at the same age (72 hours). The test standard was based on the cement mortar strength test method (ISO method) GB / T 17671-2021. The test results of each example are shown in Table 2.

[0055] Table 2 Strength of acid-activated steel slag-based geopolymers in various examples

[0056]

[0057] As shown in Table 2, the acid-activated steel slag-based geopolymers prepared in each embodiment have excellent mechanical properties. A comparison of the six groups of embodiments shows that the strength of embodiment 1 is the highest, which is 27.0 MPa.

[0058] Figure 1 The FT-IR spectra of metakaolin, steel slag and the acid-activated steel slag-based geopolymer of Example 1 are shown in Figure 1. The steel slag sample is located at 1482 cm -1 , 715cm -1 、588cm -1 and 519cm -1 The absorption peaks at 1056 cm are caused by the bending and stretching vibrations of O-Si-O, Si-O, Al-O-Si and Si-O-Si respectively. -1 , 810cm -1 and 465cm -1 The absorption peaks at 553 cm are caused by the stretching vibration of Si-O-Si(Al), Si-O-Al and Si-O-Si bending vibrations. Compared with steel slag and metakaolin, the curve of acid-activated steel slag-based geopolymer is at 553 cm -1 、468cm -1 、801cm -1 New peaks appeared at 40° and 45°, which are attributed to the symmetrical stretching of the Si-O-Al bond, the bending vibration of the Si-O-Si bond, and the PO-Si(Al) bond. The appearance of these new peaks indicates that after acid excitation, both steel slag and metakaolin participated in the solidification reaction, forming a geopolymer.

[0059] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. An acid-activated steel slag-based geopolymer, characterized by: The invention comprises, by weight, 55 to 70 parts of metakaolin, 30 to 45 parts of steel slag powder, 8 to 12 parts of organic acid, and 87 to 223 parts of phosphoric acid solution; the organic acid is any one or more of citric acid, malic acid, lactic acid, and oxalic acid; the concentration of the phosphoric acid solution is 40 to 70%; the specific surface area of ​​the steel slag powder is 300 to 400 kg / m 3 .

2. A method for preparing an acid-activated steel slag-based geopolymer according to claim 1, characterized in that: After uniformly mixing metakaolin, steel slag powder and organic acid, the mixture is added to a phosphoric acid solution and stirred thoroughly to form a uniform acid-activated steel slag-based geopolymer slurry; the stirring speed is 200 to 600 r / min and the stirring time is 2 to 4 minutes. The curing condition is constant temperature sealed curing at 60°C for 72 hours.

3. The preparation method according to claim 2, wherein: The acid-activated steel slag-based geopolymer slurry is poured into a mold for vibration molding, curing, and demoulding. The acid-activated steel slag-based geopolymer is obtained by curing to a certain age.

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