Preparation method of high specific surface area phosphate-based polymer and application thereof

Abstract

The application provides a preparation method of a high specific surface area phosphate-based polymer, which comprises the following steps: mixing fly ash and slurry powder to obtain raw material A; mixing aluminum dihydrogen phosphate solution with a mass fraction of 35% with the raw material A, uniformly stirring, pouring into a mold, and performing room temperature curing to obtain the high specific surface area phosphate-based polymer. The application also provides an application for heavy metal adsorbents or contaminated site treatment. The phosphate-based polymer prepared by the application has a high specific surface area and is suitable for being used as heavy metal adsorbents or for contaminated site treatment.

Description

Technical Field

[0001] This invention belongs to the field of geopolymer technology, specifically relating to a method for preparing a high specific surface area phosphate-based polymer and its application. Background Technology

[0002] Geopolymers are amorphous materials that can be prepared from aluminosilicate sources or alkali activators, first reported by Professor David Witz in the 1970s. Alkali-activated geopolymers consist of Si-O-Si and Si-O-Al chains formed by three-dimensional cross-linked [SiO4] and [AlO4] units. Geopolymers are characterized by high mechanical strength, excellent durability, and low preparation cost. In recent years, a novel phosphate-based polymer prepared from aluminosilicates and phosphoric acid or phosphate activators has attracted widespread attention. Like alkali-activated materials, phosphate-based polymers can be prepared from industrial by-products such as fly ash, high-magnesium nickel slag, and iron silicate powder by-products from the copper industry, as well as clay minerals such as metakaolin and laterite. The matrix of phosphate-based geopolymers is a three-dimensional network structure composed of Si–O–Al–O–P, Al–O–P, Si–O–P, and Si-OS links, and its strength may be higher than that of alkali-activated geopolymers.

[0003] Phosphate-based polymers have numerous applications in engineering, including the preparation of pressed clay bricks, high-temperature ceramics, and Pb. 2+ Electrochemical sensors and geopolymer foams are used for detection. Phosphate-based geopolymers have a large surface area and contain mesopores that have a good adsorption effect on pollutants, making them suitable for the removal of heavy metal pollutants from wastewater. Njimoudengh et al. studied the specific surface area of ​​prepared alginate-phosphate geopolymer cement beads, finding it to be 8.3 ± 0.04 m². 2 / g. Liu et al. studied the use of metakaolin as raw material, hydrogen peroxide solution, and Triton X-100 (C2H4O). n C 14 H 22 O) was used as a pore-forming agent and foam stabilizer to prepare an adsorbent with a specific surface area of ​​7.25 m². 2 / g. Phosphate-based polymer adsorbents exhibit good removal efficiency for heavy metal ions in wastewater. Compared to some other adsorbents, phosphate-based polymer adsorbents are more effective; for example, sodium alginate-modified phosphate-based polymers are particularly effective for removing Pb. 2+ The maximum adsorption efficiency can reach 0.38 mmol / g. However, the specific surface area of ​​the adsorbent is a very important parameter, which has a significant impact on the adsorption effect of heavy metals. The larger the specific surface area of ​​the material, the better the adsorption effect of heavy metals. Currently, existing studies have shown that phosphate-based polymers have a specific surface area of ​​<10 m². 2 / g, its specific surface area is relatively low compared to many adsorbents. Phosphate-based polymers contain many mesopores and micropores, which are beneficial for the adsorption of heavy metals, such as Pb. 2+ With a radius of 0.175 nm, it easily diffuses into mesopores. Therefore, if suitable methods are found to increase the mesopore-to-micropore ratio of phosphate-based polymers, then phosphate-based polymers could potentially become an environmental treatment material.

[0004] The adsorption capacity of phosphate-based polymer adsorbents is significantly affected by surface area and pore volume. A larger specific surface area results in better adsorption of pollutants. Therefore, increasing the specific surface area of ​​phosphate-based polymers is of great significance for their environmental remediation. High-moisture-content mud is difficult to compact and exhibits low strength and high compressibility. In most cases, ultra-high-moisture-content mud contains high levels of clay and silt (typically >50%), leading to very low permeability. Dehydration and consolidation under gravity are extremely slow, making direct application in engineering difficult. Traditional methods for disposing of high-moisture-content mud involve direct disposal, inevitably consuming land resources and causing environmental pollution and safety hazards. High-moisture-content mud, after drying and crushing, yields powder with a high specific surface area, fine particles, and abundant SiO2. The clay and powder particles effectively fill the pores created by the phosphate-based polymer. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing a high specific surface area phosphate-based polymer and its application, which addresses the shortcomings of the prior art. The phosphate-based polymer prepared by this method has a high specific surface area and is suitable for use as a heavy metal adsorbent or for the treatment of contaminated sites.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for preparing a high specific surface area phosphate-based polymer, the method being as follows:

[0007] S1. Mix fly ash and slurry powder to obtain raw material A;

[0008] S2. After mixing the 35% aluminum dihydrogen phosphate solution with the raw material A obtained in S1 and stirring evenly, pour the mixture into a mold and cure it at room temperature to obtain a high specific surface area phosphate-based polymer.

[0009] Preferably, the mass fraction of mud powder in raw material A in S1 is 10% to 50%.

[0010] Preferably, the fly ash in S1 is 5000 mesh fly ash.

[0011] Preferably, the particle size of the mud powder in S1 is less than 100 μm; the mud powder is dried from mud with a moisture content of 110%; the mud powder contains the following mass fractions: SiO2 36.41%, MgO 26.46%, CaO 12.35%, Fe2O3 11.88%, Al2O3 8.03%, SO3 1.15%, MnO 0.97%, K2O 0.95%, ZnO 0.74%, P2O5 0.55%, and TiO2 0.32%.

[0012] Preferably, the mass ratio of the 35% aluminum dihydrogen phosphate solution in S2 to the raw material A is 0.381:1.

[0013] Preferably, the curing period for room temperature curing described in S2 is 7 days to 28 days.

[0014] Preferably, when the curing period is 7 days, the specific surface area of ​​the high specific surface area phosphate-based polymer is 63.05 m². 2 / g~311.66m 2 / g; When the curing period is 28 days, the specific surface area of ​​the high specific surface area phosphate-based polymer is 40.24 m². 2 / g~63.246m 2 / g.

[0015] The present invention also provides the application of the high specific surface area phosphate-based polymer prepared by the above preparation method, wherein the high specific surface area phosphate-based polymer is used as a heavy metal adsorbent or for the treatment of contaminated sites.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] 1. The phosphate-based polymer prepared by this invention is a mesoporous material. At a curing age of 7 days, the specific surface area of ​​the high specific surface area phosphate-based polymer prepared by this invention reaches 63.05 m². 2 / g~311.66m 2 / g, with a curing period of 28 days, the specific surface area reaches 40.24m². 2 / g~63.246m 2 / g has great potential in the adsorption and solidification / stabilization of pollutants.

[0018] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. Attached Figure Description

[0019] Figure 1 shows the SEM images of the raw materials and the phosphate-based polymers prepared in Examples 1-2 and Comparative Examples 1-2.

[0020] Figure 2 The percentage of various pore types in the phosphate-based polymer in Example 7.

[0021] Figure 3 shows the effect of mud powder content and curing age on geopolymer strength in Example 7. Detailed Implementation

[0022] The fly ash powder used in the following examples and its main chemical components and contents are shown in Tables 1 and 2.

[0023] Table 1. Main Chemical Components and Contents of Fly Ash Powder

[0024]

[0025] Table 2. Chemical composition of mud powder

[0026]

[0027] Table 1 shows other components in fly ash powder, including trace chemical substances such as ZrO2, V2O5, and PbO.

[0028] Table 2 shows other components in the mud powder, including trace chemical substances such as MoO3, Bi2O3, and Cr2O3. The mud powder in this invention is obtained by drying mud with a moisture content of 110%.

[0029] The aluminum dihydrogen phosphate [Al(H2PO4)3] solution used had a pH of 1.4, a mass fraction of 35%, and a relative density of 1.44, and was classified as an industrial-grade product.

[0030] Example 1

[0031] The method for preparing the high specific surface area phosphate-based polymer in this embodiment is as follows:

[0032] S1. Mix fly ash and mud powder to obtain raw material A; the mass ratio of fly ash to mud powder in raw material A is 1:1.

[0033] S2. Mix the 35% (w / w) aluminum dihydrogen phosphate solution with raw material A obtained in S1, stir for 60 seconds, and after stirring evenly, pour into a container with dimensions of 40×40×40m. 3 In a rigid mold of d, it was cured at room temperature for 7 days to obtain a phosphate-based polymer with high specific surface area.

[0034] In this embodiment, the mass ratio of the 35% aluminum dihydrogen phosphate solution to raw material A is 1:0.381 (denoted as L / S).

[0035] The fly ash in this embodiment is 5000 mesh fly ash.

[0036] In this embodiment, the particle size of the mud powder is less than 100 μm.

[0037] Comparative Example 1

[0038] The modified geopolymer preparation method of this comparative example is the same as that of Example 1, except that the mass ratio of fly ash and slurry powder in raw material A in step S1 is 1:0, and the modified geopolymer is prepared.

[0039] After curing at room temperature for 7 days, the specific surface area of ​​the high specific surface area phosphate-based polymer prepared in this example was 311.66 m². 2 / g, while in Comparative Example 1, no mud powder was added, and the specific surface area of ​​the modified geopolymer prepared was 42.074 m². 2 Compared to / g, the specific surface area is significantly improved after adding high-content cement slurry powder. This is because slurry powder also has pozzolanic activity, but the activity of slurry powder is different from that of fly ash. Under the action of aluminum dihydrogen phosphate activator, fly ash and slurry powder will undergo dealuminization and dissolution. Since slurry powder has lower reactivity and fly ash has higher reactivity, the addition of slurry powder can reduce the rate of geopolymerization, reduce the number of macropores in the geopolymer, and increase the specific surface area of ​​the geopolymer.

[0040] Example 2

[0041] The method for preparing the high specific surface area phosphate-based polymer in this embodiment is the same as in Example 1, except that it is cured at room temperature for 28 days.

[0042] Comparative Example 2

[0043] The modified geopolymer preparation method of this comparative example is the same as that of Example 2, except that the mass ratio of fly ash and slurry powder in raw material A in step S1 is 1:0, and the modified geopolymer is prepared.

[0044] After curing at room temperature for 28 days, the specific surface area of ​​the high specific surface area phosphate-based polymer prepared in this example was 63.246 m². 2 / g, while in Comparative Example 2, no mud powder was added, and the specific surface area of ​​the modified geopolymer prepared was 34.128 m². 2 / g, compared to the previous method, the addition of high-cement-content slurry powder resulted in a significant increase in specific surface area.

[0045] Example 3

[0046] The preparation method of high specific surface area phosphate-based polymer in this embodiment is the same as that in Example 1, except that the mass fraction of mud powder in raw material A is 10% in step S1, and the curing is carried out at room temperature for 7 days and 28 days in step S2.

[0047] After curing at room temperature for 7 days, the specific surface area of ​​the high specific surface area phosphate-based polymer prepared in this example was 63.05 m². 2 / g.

[0048] After curing at room temperature for 28 days, the specific surface area of ​​the high specific surface area phosphate-based polymer prepared in this example was 40.24 m². 2 / g.

[0049] Example 4

[0050] The preparation method of high specific surface area phosphate-based polymer in this embodiment is the same as that in Example 1, except that the mass fraction of mud powder in raw material A in step S1 is 20%, and the curing is carried out at room temperature for 7 days and 28 days in step S2.

[0051] After curing at room temperature for 7 days, the specific surface area of ​​the high specific surface area phosphate-based polymer prepared in this example was 90.34 m². 2 / g.

[0052] After curing at room temperature for 28 days, the specific surface area of ​​the high specific surface area phosphate-based polymer prepared in this example was 46.24 m². 2 / g.

[0053] Example 5

[0054] The preparation method of high specific surface area phosphate-based polymer in this embodiment is the same as that in Example 1, except that the mass fraction of mud powder in raw material A is 30% in step S1, and the curing is carried out at room temperature for 7 days and 28 days in step S2.

[0055] After curing at room temperature for 7 days, the specific surface area of ​​the high specific surface area phosphate-based polymer prepared in this example was 176.32 m². 2 / g.

[0056] After curing at room temperature for 28 days, the specific surface area of ​​the high specific surface area phosphate-based polymer prepared in this example was 48.36 m². 2 / g.

[0057] Example 6

[0058] The preparation method of high specific surface area phosphate-based polymer in this embodiment is the same as that in Example 1, except that the mass fraction of mud powder in raw material A is 40% in step S1, and the curing is carried out at room temperature for 7 days and 28 days in step S2.

[0059] After curing at room temperature for 7 days, the specific surface area of ​​the high specific surface area phosphate-based polymer prepared in this example was 280.32 m². 2 / g.

[0060] After curing at room temperature for 28 days, the specific surface area of ​​the high specific surface area phosphate-based polymer prepared in this example was 56.25 m². 2 / g.

[0061] Example 7

[0062] This embodiment compares the performance of different reaction parameters in the preparation method of high specific surface area phosphate-based polymers.

[0063] (I) SEM morphology performance

[0064] Figure 1a It is mud powder;

[0065] Figure 1b It is fly ash;

[0066] Figure 1c The modified geopolymer prepared in Comparative Example 1;

[0067] Figure 1d The high specific surface area phosphate-based polymer of Example 1;

[0068] Figure 1e The modified geopolymer prepared in Comparative Example 2;

[0069] Figure 1f The high specific surface area phosphate-based polymer is from Example 2.

[0070] Figure 1a Figure b shows the SEM images of mud powder and fly ash. It can be observed that the mud powder particles are mainly slender strips, elongated strips, and thin plates, and irregular clumps formed by the accumulation of thin plate-like particles are also observed. The fly ash particles are mainly spherical hollow microspheres, which exhibit high reactivity. At 7 days, the SEM images of fly ash and the phosphate-based polymer prepared from fly ash + mud powder are shown below. Figure 1c , Figure 1dSEM images of geopolymers prepared from fly ash show numerous undissolved hollow fly ash microspheres, along with some formed geopolymer matrix and shrinkage cracks. The undissolved hollow fly ash microspheres are also observed to be bound together by a cementing substance. These cracks may be due to the vacuum drying process of the sample. After incorporating slurry powder (fly ash to slurry powder mass ratio 1:1), the geopolymer matrix undergoes significant changes, becoming looser, with some fine strips of unreacted slurry powder dispersed within it. When the curing period increases to 28 days, the number of undissolved hollow fly ash microspheres decreases significantly in the SEM images of both fly ash and fly ash + slurry powder geopolymers, and the geopolymer matrix becomes denser. However, undissolved porous fly ash microspheres and reacted slurry powder are still observed in the fly ash + slurry powder geopolymer, which has a looser structure than the fly ash-prepared geopolymer.

[0071] (ii) Porosity

[0072] Figure 2 The porosity of various types of geopolymers prepared in Example 1, Comparative Example 1, Example 2 and Comparative Example 2 were tested respectively.

[0073] Figure 2 FA: fly ash; FA+Mud: fly ash + high moisture content mud in a 1:1 mass ratio.

[0074] Micropore: a pore size <2nm;

[0075] Mesopore: mesopores, with a pore size of 2-50nm;

[0076] Macropore: Large pore size, pore diameter > 50nm.

[0077] Figure 2 The study presents the volume percentages of various pore types in the prepared phosphate-based geopolymers. It shows that mesopores account for the largest proportion, while micropores account for the smallest, less than 1% under different conditions. With increasing mud powder content and curing age, the proportion of macropores in the geopolymer decreases, while the proportion of mesopores increases, and the micropores remain relatively unchanged. Furthermore, the porosity of the prepared high specific surface area geopolymer is closely related to its strength.

[0078] (III) Compressive Strength

[0079] (1) Unconfined compressive strength tests were conducted on high specific surface area phosphate-based polymers with room temperature curing ages of 7d, 14d, and 28d.

[0080] In the preparation of high specific surface area phosphate-based polymers, the mass ratios of mud powder and fly ash in raw material A in step S1 are 0:1, 1:9, 2:8, 3:7, 4:6, and 1:1, respectively, which means that the doping amount of mud powder (Mud) is 0%, 10%, 20%, 30%, 40%, and 50%, respectively.

[0081] Test procedure: The strength test was conducted using a micro-controlled electronic compression and flexural strength testing machine manufactured by Shenzhen Sanwei Zongheng Technology Co., Ltd. (UTM7305300kN). The loading rate was kept constant at 1 mm / min during the test, and each test was repeated 3 times. The test results are shown in Figure 3.

[0082] Figure 3a The study showed the effect of mud powder content on the strength of geopolymers at 7, 14, 21, and 28-day curing ages. With increasing mud powder content, the strength of the geopolymer decreased at 7, 14, and 21 days, but increased at 28 days when the mud powder content was 10%. When the mud powder content exceeded 10% (i.e., 200%–50%), the geopolymer strength decreased by nearly 40% compared to the control group with 10% mud powder content. However, when the mud powder content exceeded 10%, further increases to 50% did not decrease the strength but rather slightly increased it. Compared to geopolymers with a 20% mud powder content, geopolymers with 30%, 40%, and 50% mud powder content showed improved strength. This is because the phosphoric acid-based geopolymerization reaction is exothermic; when fly ash is used alone, the geopolymerization reaction is too rapid, resulting in more pores. When a larger amount of mud powder is added, the low activity of the mud powder reduces the geopolymerization reaction rate, decreasing the pore volume and number in the geopolymer matrix. Simultaneously, the fine-grained mud powder has a filling effect on the geopolymer pores.

[0083] The reason is that the mud fills some of the pores generated during the phosphate-based polymerization reaction, increasing the density of the geopolymer. When the mud powder content exceeds 20%, the strength of the geopolymer not only does not decrease with increasing mud powder content, but also slightly increases. This may also be related to the filling effect of the mud powder; the addition of mud powder can reduce the proportion of large pores in the geopolymer. However, with excessive mud powder addition, the low activity of the mud powder will greatly weaken the geopolymer reaction rate, resulting in a reduction in the formation of geopolymer gel and further reducing the strength of the geopolymer. When the mud powder content exceeds 20%, the strength of the geopolymer is reduced compared to that without added mud powder, due to the low reactivity of the mud powder, resulting in low geopolymer strength. Fly ash is an industrial by-product after high-temperature calcination and has high pozzolanic activity. However, although mud powder has a large specific surface area and a fineness similar to fly ash, its activity is poor due to the lack of high-temperature treatment, far inferior to fly ash, making it difficult for mud particles to dissolve under the action of phosphate activators. The increased strength of phosphate-based polymers primarily relies on the formation of amorphous cementitious substances. Generally, phosphate-based polymers prepared from materials that have not undergone high-temperature treatment have lower strength. For example, phosphate-based polymers prepared using bentonite have low strength, reaching only 758 kPa after 8 months. In contrast, phosphate-based polymers prepared using a mixture of uncalcined clay and calcined clay show that a 20% increase in calcined clay content leads to an increase in polymer strength from 17 MPa to 38 MPa. This is because calcined clay contains more active substances that promote the geopolymerization reaction.

[0084] Figure 3b The study showed the effect of curing age on the strength of phosphate-based geopolymers with mud powder content ranging from 0% to 50%. It was observed that the strength of the geopolymer increased with increasing curing age, but the rate of increase varied depending on the mud powder content. Specifically, the strength of the geopolymer without added mud powder increased slowly, while the geopolymer with 10% mud powder content, although initially weak, showed a continuous increase in strength with increasing curing age. The rate of increase in strength of the phosphate-based geopolymer was generally consistent for other formulations. Furthermore, the increase in geopolymer strength with increasing curing age indicates that although the mud powder has a low reactivity level, it still possesses weak pozzolanic activity. With increasing curing age, more cementing materials such as AlPO4 and amorphous matrices composed of Si–O–P, Si–O–Al–O–P, and Al–O–P units are continuously formed, thus increasing the geopolymer strength. However, when phosphate-based polymers are prepared by adding mud powder, some of the mud powder absorbs water and adheres to the surface of fly ash in the early stages, hindering the dissolution of fly ash particles in an acidic environment, thereby reducing the early strength of the polymer.

[0085] In summary, the geopolymer exhibits high strength when the mud powder content is 10%. Although the strength decreases slightly as the mud powder content increases to 50%, it remains relatively high. As a suitable cementitious material for pollutant treatment, specific surface area is paramount; therefore, a mud powder content of 50% is recommended. The phosphate-based geopolymer prepared in this invention is a mesoporous material. Mud powder can increase the specific surface area of ​​the geopolymer, which increases significantly with increasing mud powder content. At a 7-day curing period, with a mud powder content of 50%, the specific surface area of ​​the geopolymer increases from 42.074 m² / m³. 2 / g increased to 311.66m 2 The surface area of ​​the gelling material prepared in this invention is significantly higher than that of many existing adsorbents. The high surface area gelling material has great potential in pollutant adsorption and solidification / stabilization treatment. The high surface area phosphate-based polymer prepared in this invention can be used as a heavy metal adsorbent or for contaminated site treatment.

[0086] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a high specific surface area phosphate-based polymer, characterized in that, The method is as follows: S1. Fly ash and mud powder are mixed to obtain raw material A; the mass fraction of mud powder in raw material A in S1 is 10% to 50%; the particle size of mud powder in S1 is less than 100 μm; the mud powder is dried from mud with a moisture content of 110%; the mass fraction of SiO2 in the mud powder is 36.41%, the mass fraction of MgO is 26.46%, the mass fraction of CaO is 12.35%, the mass fraction of Fe2O3 is 11.88%, the mass fraction of Al2O3 is 8.03%, the mass fraction of SO3 is 1.15%, the mass fraction of MnO is 0.97%, the mass fraction of K2O is 0.95%, the mass fraction of ZnO is 0.74%, the mass fraction of P2O5 is 0.55%, and the mass fraction of TiO2 is 0.32%. S2. A 35% aluminum dihydrogen phosphate solution is mixed with raw material A obtained in S1, stirred evenly, and then poured into a mold for room temperature curing to obtain a high specific surface area phosphate-based polymer. The mass ratio of the 35% aluminum dihydrogen phosphate solution to raw material A in S2 is 0.381:

1. The curing period at room temperature in S2 is 7 days to 28 days. When the curing period is 7 days, the specific surface area of ​​the high specific surface area phosphate-based polymer is 63.05 m² / g to 311.66 m² / g. When the curing period is 28 days, the specific surface area of ​​the high specific surface area phosphate-based polymer is 40.24 m² / g to 63.246 m² / g. The high specific surface area phosphate-based polymer is used as a heavy metal adsorbent or for the treatment of contaminated sites.

2. The method for preparing a high specific surface area phosphate-based polymer according to claim 1, characterized in that, The fly ash mentioned in S1 is 5000 mesh fly ash.

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