Modified ardealite cement and method for preparing the same

Abstract

This invention relates to the fields of phosphogypsum resource utilization and cement technology, and provides a modified phosphogypsum cement and its preparation method. The modified phosphogypsum cement of this invention comprises Ca@SiO2-NH2 material, and its preparation method is as follows: mesoporous SiO2 is prepared using the sol-gel method, and Ca is loaded into the mesoporous SiO2 channels by impregnation. 2+ Active sites are formed by amino functionalizing the surface of 3-aminopropyltriethoxysilane; during hydration, the nanopores of mesoporous SiO2 provide high-density nucleation sites, promoting crystal formation and significantly improving early strength; simultaneously, the surface amino groups enhance the activity of PO4. 3‑ F ‑ The adsorption capacity of Ca, and with Ca 2+ A precipitation reaction occurs, Ca 2+ Enrichment promotes pollutant precipitation and improves solidification stability; the Ca@SiO2-NH2 material of this invention can achieve "strength enhancement + PO42-NH2" 3‑ F ‑ Collaborative optimization of "pollution solidification".

Description

Technical Field

[0001] This invention relates to the fields of phosphogypsum resource utilization and cement technology, and particularly to a modified phosphogypsum cement and its preparation method. Background Technology

[0002] Phosphogypsum is a typical bulk industrial solid waste generated during the wet-process phosphoric acid production process, with extremely high annual output and a massive stockpile. The long-term open-air storage of large quantities of phosphogypsum not only severely occupies land resources, but also, due to its high content of soluble phosphate and fluoride ions, these impurities are highly unstable and easily washed away and leached into the soil and groundwater system by rainwater, causing water and soil pollution, soil salinization, and other ecological problems, resulting in continuous harm to the regional ecological environment. Therefore, promoting the harmless treatment and high-value utilization of phosphogypsum is a key research direction in the fields of solid waste disposal and green building materials.

[0003] Currently, the mainstream method for large-scale utilization of phosphogypsum is to combine it with cement and other cementing materials to prepare cementitious materials. However, due to the low activity and high content of phosphate and fluoride ions in phosphogypsum, the materials have low early strength, loose structure, and significant environmental risks. Traditional phosphogypsum cementitious systems rely solely on lime or cement for alkaline activation, resulting in limited improvement in early strength; and for harmful pollutants such as phosphorus and fluoride, they rely only on physical encapsulation for barrier function, leading to poor curing stability.

[0004] In summary, given the limitations of traditional phosphogypsum cementation systems, such as limited early strength improvement, phosphorus and fluorine contaminants primarily being physically encapsulated, and poor curing stability, improvements are necessary. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a modified phosphogypsum cement and its preparation method. The modified phosphogypsum cement of this invention comprises a mesoporous structure and is loaded with Ca. 2+ The Ca@SiO2-NH2 material with surface amino functions is prepared by: using a sol-gel method to prepare mesoporous SiO2 as a support; and loading Ca into its pores by an impregnation method. 2+ Active sites are formed by amino functionalizing the surface of SiO2 with 3-aminopropyltriethoxysilane. During hydration, the nanopores of mesoporous SiO2 provide nucleation sites, promoting crystal formation and significantly improving early strength. The surface amino groups enhance the adsorption capacity for phosphorus and fluoride ions and react with Ca2+. 2+ A precipitation reaction occurs, improving curing stability; the Ca@SiO2-NH2 material of this invention can achieve "strength enhancement + PO4" 3- F - Collaborative optimization of "pollution solidification".

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a modified phosphogypsum cement, comprising phosphogypsum, slag, cement, Ca@SiO2-NH2 material, and water;

[0008] The preparation method of the Ca@SiO2-NH2 material includes the following steps:

[0009] Add hexadecyltrimethylammonium bromide to water, stir, and adjust the pH to 10-11 to obtain a hexadecyltrimethylammonium bromide solution;

[0010] Tetraethyl orthosilicate was added dropwise to a hexadecyltrimethylammonium bromide solution to obtain a suspension of mesoporous SiO2 precursor. The suspension was washed, dried, and calcined to obtain mesoporous SiO2.

[0011] Mesoporous SiO2 placed in Ca 2+ In solution, the reaction proceeds, followed by washing and drying to obtain the Ca@SiO2 intermediate product.

[0012] The Ca@SiO2 intermediate was modified with amino functionalization using 3-aminopropyltriethoxysilane to obtain Ca@SiO2-NH2 material.

[0013] Preferably, the Ca@SiO2 intermediate product is dispersed in ethanol, 3-aminopropyltriethoxysilane is added, and the mixture is refluxed at 70-80°C for 4-5 hours. After washing and drying, the Ca@SiO2-NH2 material is obtained.

[0014] Preferably, the hexadecyltrimethylammonium bromide solution is heated to 70-80 °C, and tetraethyl orthosilicate is added dropwise to the hexadecyltrimethylammonium bromide solution under stirring. After the addition is completed, the reaction continues for 1-3 hours to obtain a mesoporous SiO2 precursor suspension.

[0015] Preferably, the calcination temperature is 550~600℃ and the time is 4~6h.

[0016] Preferably, mesoporous SiO2 is placed in Ca 2+ The solution was stirred at 20-40℃ for 6-8 hours, washed, and dried to obtain the Ca@SiO2 intermediate product.

[0017] Preferably, the mass-to-volume ratio of hexadecyltrimethylammonium bromide, water, and tetraethyl orthosilicate is (10~15) g:(1250~1350) mL:(25~35) mL;

[0018] The mesoporous SiO2, Ca 2+ The mass-to-volume ratio of the solution is (2.5~3) g:(500~600) mL, wherein the Ca...2+ The solution includes CaCl2 solution or Ca(NO3)2 solution, wherein the Ca 2+ The solution concentration is 0.5~1 mol / L;

[0019] The mass-to-volume ratio of the Ca@SiO2 intermediate product to ethanol is (0.5~1)g:(500~600)mL, and the volume of the 3-aminopropyltriethoxysilane is 1~5% of the volume of ethanol.

[0020] Preferably, tetraethyl orthosilicate is added dropwise to the hexadecyltrimethylammonium bromide solution over a period of 10 to 30 minutes.

[0021] Preferably, the modified phosphogypsum cement comprises the following raw materials in parts by weight: 20-25 parts phosphogypsum, 75-80 parts slag, 5-10 parts cement, 1-2 parts Ca@SiO2-NH2 material, and 40-45 parts water.

[0022] Secondly, the present invention also provides a method for preparing the modified phosphogypsum cement, comprising the following steps:

[0023] A dry mix is ​​prepared by mixing phosphogypsum, slag, cement, and Ca@SiO2-NH2 materials.

[0024] Add water to the dry mixture and stir to obtain a slurry;

[0025] After the slurry is placed in a mold and allowed to solidify, it is demolded and then cured according to standard conditions to obtain modified phosphogypsum cement.

[0026] Preferably, the slurry is placed in a mold and allowed to stand and cure at 20~25℃ for 48~58 hours. After demolding, it is transferred to a standard curing box for standard curing to obtain modified phosphogypsum cement. The standard curing temperature is 18~22℃ and the relative humidity is ≥95%.

[0027] The modified phosphogypsum cement and its preparation method of the present invention have the following advantages over the prior art:

[0028] The modified phosphogypsum cement of the present invention comprises Ca@SiO2-NH2 material, and its preparation method is as follows: mesoporous SiO2 is prepared by sol-gel method as a carrier, and Ca is loaded into the mesoporous SiO2 channels by impregnation method. 2+ Active sites are formed by amino functionalizing the surface of 3-aminopropyltriethoxysilane. During hydration, the nanopores of mesoporous SiO2 provide high-density nucleation sites, promoting crystal formation. Crystal growth is limited by the pore structure, thus forming a dense microstructure that significantly improves early strength. Simultaneously, the surface amino groups enhance the activity of PO4+. 3- F - The adsorption capacity of Ca, and with Ca2+ A precipitation reaction occurs, Ca 2+ Enrichment promotes pollutant precipitation and improves solidification stability; the Ca@SiO2-NH2 material of this invention can achieve "strength enhancement + PO42-NO2 concentration". 3- F - Collaborative optimization of "pollution solidification". Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art 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.

[0030] Figure 1 The results show the changes in phosphate leaching concentration in phosphogypsum cement in Comparative Examples 1 (EX), 2 (S1), 4 (S3), 6 (S5), 2 (S7), 7 (S9), 8 (S10), and 9 (S11).

[0031] Figure 2 The results show the changes in fluoride ion leaching concentration in phosphogypsum cement in Comparative Examples 1 (EX), 2 (S1), 4 (S3), 6 (S5), 2 (S7), 7 (S9), 8 (S10), and 9 (S11).

[0032] Figure 3 Microscopic morphology images of phosphogypsum cement in Comparative Example 1 (EX), Comparative Example 6 (S5), and Example 2 (S7) after standard curing for 28 days;

[0033] Figure 4 The images show the Fourier transform infrared (FTIR) spectra of the mesoporous SiO2 prepared in Example 1, the Ca@SiO2-NH2 material prepared in Example 1, and the Ca@SiO2-NH2 material after adsorption of F and P. Detailed Implementation

[0034] The present invention will now be clearly and completely described with reference to specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] To better understand the invention and not to limit its scope, all figures indicating amounts, percentages, and other numerical values ​​used in this application should, in all cases, be understood to be modified by the word "approximately." Therefore, unless specifically stated otherwise, the numerical parameters listed in the specification and appended claims are approximate values ​​and may vary depending on the desired properties being sought. Each numerical parameter should at least be considered as obtained based on reported significant figures and through conventional rounding methods.

[0036] It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of embodiments. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single digits within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0037] This invention provides a modified phosphogypsum cement, comprising phosphogypsum, slag, cement, Ca@SiO2-NH2 material, and water;

[0038] Mesoporous SiO2 was prepared from Ca@SiO2-NH2 material using a hexadecyltrimethylammonium bromide (CTAB) template method. 2+ Solution impregnation loaded with Ca 2+ Then, it is aminated using 3-aminopropyltriethoxysilane. Specifically, the preparation method of Ca@SiO2-NH2 material includes the following steps:

[0039] S1. Add hexadecyltrimethylammonium bromide to water, stir, and adjust the pH to 10-11 to obtain a hexadecyltrimethylammonium bromide solution;

[0040] S2. Tetraethyl orthosilicate (TEOS) is added dropwise to a hexadecyltrimethylammonium bromide solution to react and obtain a suspension of mesoporous SiO2 precursor. The suspension is washed, dried, and calcined to remove the template agent CTAB, resulting in mesoporous SiO2 with a regular pore structure.

[0041] S3, Place mesoporous SiO2 in Ca 2+ In solution, the reaction causes Ca to... 2+The Ca2+ enters the mesoporous SiO2 channels through diffusion and is adsorbed and loaded onto the active sites inside the channels and on the surface. After the reaction, the product is filtered and washed with deionized water to remove unloaded free Ca2+. 2+ Subsequently, it was dried to obtain the Ca@SiO2 intermediate product;

[0042] S4. The Ca@SiO2 intermediate was modified with amino functionalization using 3-aminopropyltriethoxysilane to obtain Ca@SiO2-NH2 material.

[0043] The modified phosphogypsum cement of the present invention comprises Ca@SiO2-NH2 material, and its preparation method is as follows: mesoporous SiO2 is prepared by sol-gel method as a carrier, and Ca is loaded into the mesoporous SiO2 channels by impregnation method. 2+ Active sites are formed by amino functionalizing the surface of 3-aminopropyltriethoxysilane. During hydration, the nanopores of mesoporous SiO2 provide high-density nucleation sites, promoting crystal formation. Crystal growth is limited by the pore structure, thus forming a dense microstructure that significantly improves early strength. Simultaneously, the surface amino groups enhance the activity of PO4+. 3- F - The adsorption capacity of Ca, and with Ca 2+ A precipitation reaction occurs, Ca 2+ Enrichment promotes pollutant precipitation and improves solidification stability; the Ca@SiO2-NH2 material of this invention can achieve "strength enhancement + PO42-NO2 concentration". 3- F - Collaborative optimization of "pollution solidification".

[0044] In some embodiments, hexadecyltrimethylammonium bromide is added to water, stirred, and then NaOH is added to adjust the pH to 10-11 to obtain a hexadecyltrimethylammonium bromide solution.

[0045] In some embodiments, the Ca@SiO2 intermediate product is dispersed in ethanol, and 3-aminopropyltriethoxysilane (APTES) is added. The mixture is refluxed at 70-80°C for 4-5 hours to allow the aminosilane to graft onto the surface of the Ca@SiO2 intermediate product. After the reaction is complete, the product is centrifuged and repeatedly washed with anhydrous ethanol to remove unreacted organic matter. The washed product is then dried at 60-80°C to obtain the Ca@SiO2-NH2 material.

[0046] In some embodiments, a hexadecyltrimethylammonium bromide solution is heated to 70-80 °C, and tetraethyl orthosilicate is added dropwise to the hexadecyltrimethylammonium bromide solution under stirring. After the addition is complete, the reaction continues for 1-3 h to obtain a mesoporous SiO2 precursor suspension. The obtained suspension is filtered and washed with deionized water until neutral, dried at 60-80 °C, and then calcined at 550-600 °C for 4-6 h to remove the template agent, thereby obtaining mesoporous SiO2 with a regular pore structure.

[0047] In some embodiments, mesoporous SiO2 is placed in Ca 2+ In the solution, stir at 20-40℃ for 6-8 hours to allow Ca to... 2+ The product enters the pores and is loaded onto the SiO2 surface. After the reaction is complete, the product is filtered and washed with deionized water to remove unloaded free Ca. 2+ The product was then dried at 60-80 °C to obtain the Ca@SiO2 intermediate.

[0048] In some embodiments, the mass-to-volume ratio of hexadecyltrimethylammonium bromide, water, and tetraethyl orthosilicate is (10~15) g:(1250~1350) mL:(25~35) mL;

[0049] Mesoporous SiO2, Ca 2+ The mass-to-volume ratio of the solution is (2.5~3) g : (500~600) mL, Ca 2+ The solutions include CaCl2 solution or Ca(NO3)2 solution, Ca 2+ The solution concentration is 0.5~1 mol / L;

[0050] The mass-to-volume ratio of Ca@SiO2 intermediate product to ethanol is (0.5~1)g:(500~600)mL, and the volume of 3-aminopropyltriethoxysilane is 1~5% of the volume of ethanol.

[0051] In some embodiments, tetraethyl orthosilicate is added dropwise to a hexadecyltrimethylammonium bromide solution over a period of 10 to 30 minutes, i.e., the addition time of tetraethyl orthosilicate is 10 to 30 minutes.

[0052] In some embodiments, modified phosphogypsum cement comprises the following raw materials in parts by weight: 20-25 parts phosphogypsum, 75-80 parts slag, 5-10 parts cement, 1-2 parts Ca@SiO2-NH2 material, and 40-45 parts water.

[0053] Based on the same inventive concept, the present invention also provides a method for preparing the above-mentioned modified phosphogypsum cement, comprising the following steps:

[0054] A dry mix is ​​prepared by mixing phosphogypsum, slag, cement, and Ca@SiO2-NH2 materials.

[0055] Add water to the dry mixture and stir to obtain a slurry;

[0056] After the slurry is placed in a mold and allowed to solidify, it is demolded and then cured according to standard conditions to obtain modified phosphogypsum cement.

[0057] In some embodiments, the slurry is placed in a mold and allowed to stand and cure at 20~25°C for 48~58 hours. After demolding, it is transferred to a standard curing chamber for standard curing to obtain modified phosphogypsum cement. The standard curing temperature is 18~22°C and the relative humidity is ≥95%.

[0058] The modified phosphogypsum cement and its preparation method of the present invention are further illustrated below with specific embodiments. This section further illustrates the content of the present invention in conjunction with specific embodiments, but should not be construed as limiting the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the art.

[0059] The slag used in the following examples and comparative examples is commercially available S95 grade blast furnace slag; the cement is P·O 42.5 ordinary Portland cement, purchased from Shandong Shanshui Cement Group Co., Ltd.; and the phosphogypsum is provided by Hubei Liuguo Chemical Co., Ltd.

[0060] Example 1

[0061] This embodiment provides a modified phosphogypsum cement, comprising the following raw materials in parts by weight: 20 parts phosphogypsum, 75 parts slag, 5 parts cement, 1 part Ca@SiO2-NH2 material, and 40 parts water (the water-cement ratio is 0.4, i.e., the ratio of the mass of water to the sum of the masses of phosphogypsum, slag, and cement).

[0062] The preparation method of Ca@SiO2-NH2 material includes the following steps:

[0063] S1. Add 10g of hexadecyltrimethylammonium bromide to 1250mL of deionized water and stir at 300r / min at room temperature (25℃) until completely dissolved. Then add NaOH solution to adjust the pH of the system to 11 to obtain hexadecyltrimethylammonium bromide solution.

[0064] S2. The hexadecyltrimethylammonium bromide solution was heated to 80 °C, and 25 mL of tetraethyl orthosilicate was added dropwise to the hexadecyltrimethylammonium bromide solution over 20 min while stirring at 300 r / min. After the addition was completed, the reaction was continued at 80 °C for 2 h to obtain a mesoporous SiO2 precursor suspension. The obtained suspension was filtered and washed with deionized water until neutral, dried at 80 °C for 2 h, and then calcined at 550 °C for 4 h to obtain mesoporous SiO2 with a regular pore structure.

[0065] S3. Place 2.5g of mesoporous SiO2 in 500mL of 0.5mol / L CaCl2 aqueous solution and stir at 300r / min for 6h at room temperature to allow CaCl2 to react. 2+ The Ca2+ enters the mesoporous SiO2 channels through diffusion and is adsorbed and loaded onto the active sites inside the channels and on the surface. After the reaction, the product is filtered and washed with deionized water to remove unloaded free Ca2+. 2+ Subsequently, it was dried to obtain the Ca@SiO2 intermediate product;

[0066] S4. Disperse 0.5g of Ca@SiO2 intermediate product in 500mL of ethanol, add 15mL of 3-aminopropyltriethoxysilane (3% of the ethanol volume), and reflux at 80℃ for 4h to allow aminosilane to graft onto the surface of the Ca@SiO2 intermediate product. After the reaction is complete, centrifuge the product and wash it with anhydrous ethanol to remove unreacted organic matter. Dry the washed product at 80℃ to obtain Ca@SiO2-NH2 material.

[0067] The preparation method of the above-mentioned modified phosphogypsum cement includes the following steps:

[0068] S1. Mix phosphogypsum, slag, cement, and Ca@SiO2-NH2 materials to obtain a dry mix;

[0069] S2. Add water to the dry mixture and stir to obtain a slurry;

[0070] S3. Place the slurry in a mold and let it stand at 25°C for 48 hours to cure. Then demold it and transfer it to a standard curing chamber for standard curing to obtain modified phosphogypsum cement. The standard curing temperature is 20°C and the relative humidity is 98%. After standard curing for 3 days, 7 days and 28 days, take it out for compressive strength testing.

[0071] Example 2

[0072] This embodiment provides a modified phosphogypsum cement, comprising the following raw materials in parts by weight: 20 parts phosphogypsum, 75 parts slag, 5 parts cement, 1.5 parts Ca@SiO2-NH2 material, and 40 parts water;

[0073] The preparation method of Ca@SiO2-NH2 material is the same as in Example 1:

[0074] The preparation method of the above-mentioned modified phosphogypsum cement includes the following steps:

[0075] S1. Mix phosphogypsum, slag, cement, and Ca@SiO2-NH2 materials to obtain a dry mix;

[0076] S2. Add water to the dry mixture and stir to obtain a slurry;

[0077] S3. Place the slurry in a mold and let it stand at 25°C for 48 hours to cure. Then demold it and transfer it to a standard curing chamber for standard curing to obtain modified phosphogypsum cement. The standard curing temperature is 20°C and the relative humidity is 98%. After standard curing for 3 days, 7 days and 28 days, take it out for compressive strength testing.

[0078] Example 3

[0079] This embodiment provides a modified phosphogypsum cement, comprising the following raw materials in parts by weight: 20 parts phosphogypsum, 75 parts slag, 5 parts cement, 2 parts Ca@SiO2-NH2 material, and 40 parts water.

[0080] The preparation method of Ca@SiO2-NH2 material is the same as in Example 1:

[0081] The preparation method of the above-mentioned modified phosphogypsum cement includes the following steps:

[0082] S1. Mix phosphogypsum, slag, cement, and Ca@SiO2-NH2 materials to obtain a dry mix;

[0083] S2. Add water to the dry mixture and stir to obtain a slurry;

[0084] S3. Place the slurry in a mold and let it stand at 25°C for 48 hours to cure. Then demold it and transfer it to a standard curing chamber for standard curing to obtain modified phosphogypsum cement. The standard curing temperature is 20°C and the relative humidity is 98%. After standard curing for 3 days, 7 days and 28 days, take it out for compressive strength testing.

[0085] Comparative Example 1

[0086] This comparative example provides a phosphogypsum cement, comprising the following raw materials in parts by weight: 20 parts phosphogypsum, 75 parts slag, 5 parts cement, and 40 parts water.

[0087] The above-mentioned method for preparing phosphogypsum cement includes the following steps:

[0088] S1. Mix phosphogypsum, slag, and cement to obtain a dry mix;

[0089] S2. Add water to the dry mixture and stir to obtain a slurry;

[0090] S3. Place the slurry in a mold and let it stand at 25°C for 48 hours to cure. Then demold it and transfer it to a standard curing chamber for standard curing to obtain phosphogypsum cement. The standard curing temperature is 20°C and the relative humidity is 98%. After standard curing for 3 days, 7 days and 28 days, take it out for compressive strength testing.

[0091] Comparative Example 2

[0092] This comparative example provides a phosphogypsum cement, comprising the following raw materials in parts by weight: 20 parts phosphogypsum, 75 parts slag, 5 parts cement, 3 parts quicklime (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., item number C141333), and 40 parts water.

[0093] The above-mentioned method for preparing phosphogypsum cement includes the following steps:

[0094] S1. Mix phosphogypsum, slag, cement, and quicklime to obtain a dry mix;

[0095] S2. Add water to the dry mixture and stir to obtain a slurry;

[0096] S3. Place the slurry in a mold and let it stand at 25°C for 48 hours to cure. Then demold it and transfer it to a standard curing chamber for standard curing to obtain phosphogypsum cement. The standard curing temperature is 20°C and the relative humidity is 98%. After standard curing for 3 days, 7 days and 28 days, take it out for compressive strength testing.

[0097] Comparative Example 3

[0098] This comparative example provides a phosphogypsum cement, comprising the following raw materials in parts by weight: 20 parts phosphogypsum, 75 parts slag, 5 parts cement, 1 part nano-SiO2 (purchased from Hubei Huifu Nanomaterials Co., Ltd., model: HF-200), and 40 parts water.

[0099] The above-mentioned method for preparing phosphogypsum cement includes the following steps:

[0100] S1. Mix phosphogypsum, slag, cement, and nano-SiO2 to obtain a dry mix;

[0101] S2. Add water to the dry mixture and stir to obtain a slurry;

[0102] S3. Place the slurry in a mold and let it stand at 25°C for 48 hours to cure. Then demold it and transfer it to a standard curing chamber for standard curing to obtain phosphogypsum cement. The standard curing temperature is 20°C and the relative humidity is 98%. After standard curing for 3 days, 7 days and 28 days, take it out for compressive strength testing.

[0103] Comparative Example 4

[0104] This comparative example provides a phosphogypsum cement, comprising the following raw materials in parts by weight: 20 parts phosphogypsum, 75 parts slag, 5 parts cement, 1.5 parts nano-SiO2 (purchased from Hubei Huifu Nanomaterials Co., Ltd., model: HF-200), and 40 parts water.

[0105] The above-mentioned method for preparing phosphogypsum cement includes the following steps:

[0106] S1. Mix phosphogypsum, slag, cement, and nano-SiO2 to obtain a dry mix;

[0107] S2. Add water to the dry mixture and stir to obtain a slurry;

[0108] S3. Place the slurry in a mold and let it stand at 25°C for 48 hours to cure. Then demold it and transfer it to a standard curing chamber for standard curing to obtain phosphogypsum cement. The standard curing temperature is 20°C and the relative humidity is 98%. After standard curing for 3 days, 7 days and 28 days, take it out for compressive strength testing.

[0109] Comparative Example 5

[0110] This comparative example provides a phosphogypsum cement, comprising the following raw materials in parts by weight: 20 parts phosphogypsum, 75 parts slag, 5 parts cement, 2 parts nano-SiO2 (purchased from Hubei Huifu Nanomaterials Co., Ltd., model and specification: HF-200), and 40 parts water.

[0111] The above-mentioned method for preparing phosphogypsum cement includes the following steps:

[0112] S1. Mix phosphogypsum, slag, cement, and nano-SiO2 to obtain a dry mix;

[0113] S2. Add water to the dry mixture and stir to obtain a slurry;

[0114] S3. Place the slurry in a mold and let it stand at 25°C for 48 hours to cure. Then demold it and transfer it to a standard curing chamber for standard curing to obtain phosphogypsum cement. The standard curing temperature is 20°C and the relative humidity is 98%. After standard curing for 3 days, 7 days and 28 days, take it out for compressive strength testing.

[0115] Comparative Example 6

[0116] This comparative example provides a phosphogypsum cement, comprising the following raw materials in parts by weight: 20 parts phosphogypsum, 75 parts slag, 5 parts cement, 3 parts quicklime (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., item number C141333), 1.5 parts nano SiO2 (purchased from Hubei Huifu Nanomaterials Co., Ltd., model: HF-200), and 40 parts water.

[0117] The above-mentioned method for preparing phosphogypsum cement includes the following steps:

[0118] S1. Mix phosphogypsum, slag, cement, quicklime, and nano-SiO2 to obtain a dry mix;

[0119] S2. Add water to the dry mixture and stir to obtain a slurry;

[0120] S3. Place the slurry in a mold and let it stand at 25°C for 48 hours to cure. Then demold it and transfer it to a standard curing chamber for standard curing to obtain phosphogypsum cement. The standard curing temperature is 20°C and the relative humidity is 98%. After standard curing for 3 days, 7 days and 28 days, take it out for compressive strength testing.

[0121] Comparative Example 7

[0122] This comparative example provides a modified phosphogypsum cement, comprising the following raw materials in parts by weight: 20 parts phosphogypsum, 75 parts slag, 5 parts cement, 1.5 parts SiO2-NH2 material, and 40 parts water.

[0123] The preparation method of SiO2-NH2 material includes the following steps:

[0124] S1. Add 10g of hexadecyltrimethylammonium bromide to 1250mL of deionized water and stir at 300r / min at room temperature (25℃) until completely dissolved. Then add NaOH solution to adjust the pH of the system to 11 to obtain hexadecyltrimethylammonium bromide solution.

[0125] S2. The hexadecyltrimethylammonium bromide solution was heated to 80 °C, and 25 mL of tetraethyl orthosilicate was added dropwise to the hexadecyltrimethylammonium bromide solution over 20 min while stirring at 300 r / min. After the addition was completed, the reaction was continued at 80 °C for 2 h to obtain a mesoporous SiO2 precursor suspension. The obtained suspension was filtered and washed with deionized water until neutral, dried at 80 °C for 2 h, and then calcined at 550 °C for 4 h to obtain mesoporous SiO2 with a regular pore structure.

[0126] S3 and 0.5 g of mesoporous SiO2 were dispersed in 500 mL of ethanol, and 15 mL of 3-aminopropyltriethoxysilane (3% of the volume of ethanol) was added. The mixture was refluxed at 80 °C for 4 h. After the reaction was completed, the product was centrifuged and washed with anhydrous ethanol to remove unreacted organic matter. The washed product was dried at 80 °C to obtain SiO2-NH2 material.

[0127] The preparation method of the above-mentioned modified phosphogypsum cement includes the following steps:

[0128] S1. Mix phosphogypsum, slag, cement, and SiO2-NH2 materials to obtain a dry mix;

[0129] S2. Add water to the dry mixture and stir to obtain a slurry;

[0130] S3. Place the slurry in a mold and let it stand at 25°C for 48 hours to cure. Then demold it and transfer it to a standard curing chamber for standard curing to obtain modified phosphogypsum cement. The standard curing temperature is 20°C and the relative humidity is 98%. After standard curing for 3 days, 7 days and 28 days, take it out for compressive strength testing.

[0131] Comparative Example 8

[0132] This comparative example provides a modified phosphogypsum cement, comprising the following raw materials in parts by weight: 20 parts phosphogypsum, 75 parts slag, 5 parts cement, 1.5 parts Ca@SiO2 material, and 40 parts water.

[0133] The preparation method of Ca@SiO2 material is as follows: Ca@SiO2 intermediate product is prepared according to the method in steps S1 to S3 of Example 1, which is Ca@SiO2 material;

[0134] The preparation method of the above-mentioned modified phosphogypsum cement includes the following steps:

[0135] S1. Mix phosphogypsum, slag, cement, and Ca@SiO2 materials to obtain a dry mix;

[0136] S2. Add water to the dry mixture and stir to obtain a slurry;

[0137] S3. Place the slurry in a mold and let it stand at 25°C for 48 hours to cure. Then demold it and transfer it to a standard curing chamber for standard curing to obtain modified phosphogypsum cement. The standard curing temperature is 20°C and the relative humidity is 98%. After standard curing for 3 days, 7 days and 28 days, take it out for compressive strength testing.

[0138] Comparative Example 9

[0139] This comparative example provides a modified phosphogypsum cement, comprising the following raw materials in parts by weight: 20 parts phosphogypsum, 75 parts slag, 5 parts cement, 1.5 parts mesoporous SiO2, and 40 parts water.

[0140] The preparation method of mesoporous SiO2 material is as follows: mesoporous SiO2 is prepared according to the method in steps S1~S2 of Example 1;

[0141] The preparation method of the above-mentioned modified phosphogypsum cement includes the following steps:

[0142] S1. Mix phosphogypsum, slag, cement, and mesoporous SiO2 to obtain a dry mix;

[0143] S2. Add water to the dry mixture and stir to obtain a slurry;

[0144] S3. Place the slurry in a mold and let it stand at 25°C for 48 hours to cure. Then demold it and transfer it to a standard curing chamber for standard curing to obtain modified phosphogypsum cement. The standard curing temperature is 20°C and the relative humidity is 98%. After standard curing for 3 days, 7 days and 28 days, take it out for compressive strength testing.

[0145] Examples 1-3 are designated as S6, S7, and S8, respectively; Comparative Examples 1-6 are designated as EX, S1, S2, S3, S4, and S5, respectively; Comparative Examples 7-8 are designated as S9-S10, respectively; and Comparative Example 9 is designated as S11. The test results of the compressive strength of each group are shown in Table 1 below.

[0146] Table 1 - Compressive strength of phosphogypsum cement obtained in different embodiments and comparative examples

[0147]

[0148] As shown in Table 1, the blank group EX in Comparative Example 1 had the worst mechanical properties, with compressive strengths of only 9.48 MPa, 25.36 MPa, and 39.29 MPa at 3d, 7d, and 28d, respectively. This indicates that the unmodified phosphogypsum system had low hydration, numerous structural defects, and extremely poor strength development. In Comparative Examples 2-6, the strength of phosphogypsum cement was improved after modification with quicklime and nano-SiO2, either alone or in combination. Comparative Example 6 showed the best strength after modification with a combination of quicklime and nano-SiO2, with strengths of 39.53 MPa, 56.36 MPa, and 68.43 MPa at 3d, 7d, and 28d, respectively, but the strength improvement was limited. In contrast, the modified phosphogypsum cement in Examples 1-3 had superior strengths compared to all comparative examples. In Example 1, with a Ca@SiO2-NH2 material content of 1wt%, the modified phosphogypsum cement achieved a 28-day strength of 73.42 MPa. MPa; In Example 2, the Ca@SiO2-NH2 material content was 1.5wt%, and the modified phosphogypsum cement had the best strength, with compressive strengths of 46.27 MPa, 65.39 MPa, and 79.94 MPa at 3d, 7d, and 28d, respectively; In Example 3, the Ca@SiO2-NH2 material content was increased to 2wt%, and the strength of the modified phosphogypsum cement decreased slightly, but was still significantly higher than that of the traditional modified group; Furthermore, the mesoporous SiO2 in Comparative Example 9 was not treated in any way, and the mesoporous SiO2 in Comparative Example 7 was only modified with 3-aminopropyltriethoxysilane without Ca loading. 2+ Comparative Example 8: Mesopores of SiO2 only loaded with Ca 2+ Without modification with 3-aminopropyltriethoxysilane, the compressive strength of all samples was lower than that of Example 2, indicating that Ca 2+ Both the loading and surface amino grafting processes are indispensable in the preparation; only by simultaneously loading Ca into the mesoporous SiO2 channels can the desired results be achieved. 2+ By forming active sites and functionalizing the surface with 3-aminopropyltriethoxysilane, Ca@SiO2-NH2 can simultaneously achieve multiple effects, including hydration activity activation, hydration direction regulation, and stable adsorption of phosphorus and fluoride ions, thus maximizing compressive strength. The Ca@SiO2-NH2 material of this invention can effectively improve hydration disorder and dense matrix structure through confined nucleation, activity activation, and synergistic effects of amino adsorption, significantly improving both early and late-stage strength of the material. Traditional quicklime and nano-SiO2 modification can only improve the performance of phosphogypsum cementitious materials to a limited extent, failing to fundamentally solve the defects of low early-stage strength and loose microstructure. In contrast, the Ca@SiO2-NH2 material of this invention shows significantly better modification effects than traditional methods, efficiently optimizing the hydration structure and greatly improving mechanical strength at all ages, demonstrating outstanding modification advantages.

[0149] Figure 1The results show the changes in phosphate leaching concentration in phosphogypsum cement in Comparative Examples 1 (EX), 2 (S1), 4 (S3), 6 (S5), 2 (S7), 7 (S9), 8 (S10), and 9 (S11).

[0150] Figure 2 The results show the changes in fluoride ion leaching concentration in phosphogypsum cement in Comparative Examples 1 (EX), 2 (S1), 4 (S3), 6 (S5), 2 (S7), 7 (S9), 8 (S10), and 9 (S11).

[0151] Specifically, Figures 1-2 The determination methods for phosphate and fluoride ions in phosphogypsum cement in different embodiments and comparative examples are as follows: Phosphogypsum cement cured for 28 days is crushed and ground into powder. 1g of the obtained powder is added to 10mL of deionized water, shaken for 24 hours and allowed to stand. The supernatant is taken and filtered through a 0.45 μm filter membrane. The leaching concentrations of phosphorus (phosphate) and fluoride in the filtrate are tested.

[0152] from Figures 1-2 As can be seen from the data, in Comparative Example 1 (EX), the leaching concentrations of phosphate and fluoride ions were the highest among all groups (PO4). 3- The concentrations of phosphate and fluoride ions were approximately 0.68 mg / L and F was approximately 11.3 mg / L, indicating that the unmodified system had no effective curing ability for phosphorus and fluoride ions and posed the greatest environmental risk. In Comparative Example 2 (S1), the leaching concentrations of phosphate and fluoride ions decreased significantly (PO4 ≈ 0.68 mg / L, F ≈ 11.3 mg / L). 3- (≈0.32 mg / L, F≈4.0 mg / L), indicating that an alkaline environment can achieve partial solidification by generating sparingly soluble salts, but the effect is limited; in Comparative Example 4 (S3), the leaching concentrations of phosphate and fluoride ions rebounded (PO4 ≈0.32 mg / L, F≈4.0 mg / L). 3- The concentrations of phosphate and fluoride ions decreased again in Comparative Example 6 (S5) (≈0.49 mg / L, F≈7.8 mg / L), indicating that the direct curing effect of single nanomaterials on phosphorus and fluoride ions through physical encapsulation is weak and the effect is unstable. 3- The concentrations of P and F in Example 2 (S7) were approximately 0.29 mg / L and 2.4 mg / L, respectively, which were superior to single modification, demonstrating the synergistic effect of alkaline activation by quicklime and nano-SiO2, but there is still room for improvement. In Example 2 (S7), the leaching concentrations of P and F were reduced to the lowest (P≈0.18 mg / L, F≈1.0 mg / L), and the curing effect was far superior to all traditional methods. Furthermore, in Comparative Example 7 (S9, without calcium ion loading), PO4... 3- ≈0.40 mg / L, F≈5.1 mg / L; Comparative Example 8 (S10, without amino grafting modification), PO4 3-≈0.23 mg / L, F≈1.8 mg / L; Comparative Example 9 (S11, mesoporous SiO2 without any treatment), PO4 3- ≈0.43 mg / L, F≈7.2 mg / L; the phosphorus and fluorine leaching concentrations in Comparative Examples 7-9 were all higher than those in Example 2, indicating that only when Ca is simultaneously loaded within the mesoporous SiO2 channels... 2+ To simultaneously improve the curing effect of phosphorus and fluoride, active sites must be formed and the surface of the material must be functionalized with amino groups using 3-aminopropyltriethoxysilane. Traditional modification methods can only achieve partial and unstable curing of phosphorus and fluoride ions. However, the Ca@SiO2-NH2 material of this invention achieves efficient and stable curing of phosphorus and fluoride ions through multiple synergistic effects of amino adsorption, calcium ion precipitation and dense hydration product encapsulation. This significantly reduces the environmental risk of phosphogypsum solid waste and verifies the significant advantages of the technical solution in pollution control.

[0153] Figure 3 The images show the microstructures of phosphogypsum cement in Comparative Example 1 (EX), Comparative Example 6 (S5), and Example 2 (S7) after standard curing for 28 days. Among them, (a) and (b) are SEM images of phosphogypsum cement in Comparative Example 1 (EX) at different magnifications, (c) and (d) are SEM images of phosphogypsum cement in Comparative Example 6 (S5) at different magnifications, and (e) and (f) are SEM images of phosphogypsum cement in Example 2 (S7) at different magnifications.

[0154] Depend on Figure 3 The 28-day SEM microstructure shows that the EX sample without Ca@SiO2-NH2 material has a relatively loose internal structure, with obvious cracks and pores, numerous pores and unreacted particles, discontinuous distribution of hydration products, and ettringite mainly exhibiting a localized dispersion state, with limited C-(A)-SH gel filling. In contrast, the S5 sample shows a significant increase in gel-like hydration products and ettringite, with some pore filling, indicating that nano-SiO2 and alkaline components can promote the hydration reaction. In the S7 sample with Ca@SiO2-NH2 material, the matrix structure is the densest, with the interparticle spaces filled by a large amount of C-(A)-SH gel, and the ettringite densely interwoven in the gel phase to form a continuous network, with a significant reduction in the number of pores. This indicates that the surface and nanopores of the Ca@SiO2-NH2 material provide abundant heterogeneous nucleation sites, promoting the in-situ nucleation, growth, and accumulation of hydration products such as CSH gel and ettringite on its surface, thereby increasing the density of hydration product formation and improving the compactness of the microstructure. This microstructural change is consistent with the result of the highest 28-day compressive strength of the S7 sample, indicating that the Ca@SiO2-NH2 material plays a role in promoting the nucleation and growth of hydration products and enhancing the compactness of the matrix structure.

[0155] Figure 4 The mesoporous SiO2 prepared in Example 1, the Ca@SiO2-NH2 material prepared in Example 1, and the Ca@SiO2-NH2 material after adsorption of F and P ( Figure 4 The Fourier transform infrared (FTIR) spectrum of Ca@SiO2-NH2 material after adsorption of F and P is shown below. The preparation method of Ca@SiO2-NH2 material after adsorption of F and P is as follows: 50 mL of 0.05 mol / L NaF aqueous solution and 50 mL of 0.05 mol / L KH2PO4 aqueous solution are mixed to obtain a mixed solution; 0.5 g of Ca@SiO2-NH2 prepared in Example 1 is added to the mixed solution, shaken at 25 ℃ for 12 h, filtered, washed, and dried to obtain Ca@SiO2-NH2 material after adsorption of P and F.

[0156] from Figure 4 As can be seen, the mesoporous SiO2 sample exhibits typical Si-O-Si framework vibrational peaks and surface OH absorption peaks, indicating the successful formation of a mesoporous silica-oxygen network. (The text abruptly ends here, likely due to an incomplete translation or missing information.) 2+ After loading and APTES modification, the Ca@SiO2-NH2 material exhibits a -CH2- stretching vibration peak and a -NH2-related vibration peak, indicating that aminopropylsilane was successfully grafted onto the material surface. After P / F adsorption, the -NH2-related peak changes, and a Ca-F / PO-related absorption peak appears in the low wavenumber region, indicating that the surface amino groups participate in the PO44- adsorption. 3- and F - Adsorption and enrichment of Ca, while loading Ca 2+ It may undergo precipitation and fixation reactions with P and F.

[0157] It is understood that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0158] The above are merely preferred embodiments of this application, and only specifically describe the technical principles of this application. These descriptions are only for explaining the principles of this application and should not be construed as limiting the scope of protection of this application in any way. Based on this explanation, any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application, as well as other specific embodiments of this application that can be conceived by those skilled in the art without creative effort, should be included within the scope of protection of this application.

Claims

1. A modified phosphogypsum cement, characterized in that, Modified phosphogypsum cement comprises the following raw materials in parts by weight: 20-25 parts phosphogypsum, 75-80 parts slag, 5-10 parts cement, 1-2 parts Ca@SiO2-NH2 material, and 40-45 parts water. The preparation method of the Ca@SiO2-NH2 material includes the following steps: Add hexadecyltrimethylammonium bromide to water, stir, and adjust the pH to 10-11 to obtain a hexadecyltrimethylammonium bromide solution; Tetraethyl orthosilicate was added dropwise to a hexadecyltrimethylammonium bromide solution to obtain a suspension of mesoporous SiO2 precursor. The suspension was washed, dried, and calcined to obtain mesoporous SiO2. Mesoporous SiO2 placed in Ca 2+ In solution, the reaction proceeds, followed by washing and drying to obtain the Ca@SiO2 intermediate product. The Ca@SiO2 intermediate was dispersed in ethanol, 3-aminopropyltriethoxysilane was added, and the mixture was refluxed at 70-80℃ for 4-5 h. After washing and drying, the Ca@SiO2-NH2 material was obtained. The mass-to-volume ratio of hexadecyltrimethylammonium bromide, water, and tetraethyl orthosilicate is (10~15) g:(1250~1350) mL:(25~35) mL; The mesoporous SiO2, Ca 2+ The mass-to-volume ratio of the solution is (2.5~3) g:(500~600) mL, wherein the Ca... 2+ The solution includes CaCl2 solution or Ca(NO3)2 solution, wherein the Ca 2+ The solution concentration is 0.5~1 mol / L; The mass-to-volume ratio of the Ca@SiO2 intermediate product to ethanol is (0.5~1)g:(500~600)mL, and the volume of the 3-aminopropyltriethoxysilane is 1~5% of the volume of ethanol.

2. The modified phosphogypsum cement as described in claim 1, characterized in that, Hexadecyltrimethylammonium bromide solution was heated to 70-80 °C, and tetraethyl orthosilicate was added dropwise to the hexadecyltrimethylammonium bromide solution under stirring. After the addition was completed, the reaction was continued for 1-3 h to obtain a mesoporous SiO2 precursor suspension.

3. The modified phosphogypsum cement as described in claim 1, characterized in that, The calcination temperature is 550~600℃ and the time is 4~6h.

4. The modified phosphogypsum cement as described in claim 1, characterized in that, Mesoporous SiO2 placed in Ca 2+ The solution was stirred at 20-40℃ for 6-8 hours, washed, and dried to obtain the Ca@SiO2 intermediate product.

5. The modified phosphogypsum cement as described in claim 2, characterized in that, Tetraethyl orthosilicate was added dropwise to the hexadecyltrimethylammonium bromide solution over a period of 10 to 30 minutes.

6. A method for preparing modified phosphogypsum cement as described in any one of claims 1 to 5, characterized in that, Includes the following steps: A dry mix is ​​prepared by mixing phosphogypsum, slag, cement, and Ca@SiO2-NH2 materials. Add water to the dry mixture and stir to obtain a slurry; After the slurry is placed in a mold and allowed to solidify, it is demolded and then cured according to standard conditions to obtain modified phosphogypsum cement.

7. The method for preparing modified phosphogypsum cement as described in claim 6, characterized in that, The slurry is placed in a mold and allowed to stand and cure at 20~25℃ for 48~58 hours. After demolding, it is transferred to a standard curing box for standard curing to obtain modified phosphogypsum cement. The standard curing temperature is 18~22℃ and the relative humidity is ≥95%.

Images