Polyacrylic acid assisted red mud-phosphogypsum-cement ternary system gelling material and preparation method thereof

Abstract

The present invention belongs to the technical field of plugging leaks in coal mine goafs in underground engineering projects, and in particular relates to a polyacrylic acid-assisted red mud-phosphogypsum-cement ternary system cementitious material and a preparation method thereof. A method for preparing a polyacrylic acid-assisted red mud-phosphogypsum-cement ternary system cementitious material comprises the following steps: drying the red mud, crushing and screening it; weighing the red mud, phosphogypsum, cement, polyacrylic acid and water respectively, and stirring the red mud, phosphogypsum, cement and water to prepare a composite material; adding polyacrylic acid to the composite material and stirring it to prepare a multicomponent system cementitious material; pouring the multicomponent system cementitious material into a mold, vibrating it, demolding it, and curing it. The multicomponent system gel material prepared by the present invention can achieve a flexural strength of 6.1MPa, a compressive strength of 12.5MPa, and a total pore volume of 11.971×10 ‑2 mL / g, pore sizes below 50 nm account for 60.9%, and pore sizes above 50 nm account for 39.1%, which can provide a basis for underground space wall plugging materials and solve the problem of resource utilization of red mud.

Description

Technical Field

[0001] The invention belongs to the technical field of plugging leakage in coal mine goafs in underground engineering projects, and in particular relates to a polyacrylic acid-assisted red mud-phosphogypsum-cement ternary system gelling material and a preparation method thereof. Background Art

[0002] Red mud is an industrial solid waste produced during the extraction of alumina by the aluminum industry. China is the world's leading alumina producer, and approximately 1.0 to 1.8 tons of red mud are emitted for every ton of alumina produced, totaling hundreds of millions of tons annually. Furthermore, with the development of the alumina industry, my country's red mud production continues to increase dramatically year by year.

[0003] Due to its strong alkalinity, fine particles, and complex mineral composition, red mud's resource utilization is difficult. Currently, most of my country's red mud is stored in dumps, which not only consumes precious land resources, but also causes the strong alkalinity and heavy metal ions of red mud to gradually seep into the ground, causing significant pollution to the surrounding soil and groundwater resources.

[0004] Cement, a common alkaline solidifying agent, stimulates alkalinity during the red mud solidification process, further increasing the alkalinity of the leachate from the solidified red mud. Phosphogypsum, a byproduct of the industrial production of phosphoric acid, is stable and has a dealkalizing effect. Phosphogypsum is only effective in solidifying red mud when combined with inorganic binders such as cement.

[0005] Therefore, it is necessary to research and develop a suitable cementitious material so that the underground space wall sealing material can meet the flexural strength and compressive strength performance and have economic benefits. This can not only improve the utilization rate of industrial red mud waste, realize the resource utilization of large amounts of solid waste, and achieve sustainable development, but also replace traditional building materials such as cement, sand and gravel, reduce the consumption of natural resources and environmental pollution, and have significant economic advantages. Summary of the Invention

[0006] The invention provides a polyacrylic acid-assisted red mud-phosphogypsum-cement ternary system gelling material and a preparation method thereof, which solves the red mud pollution problem and provides a new material for plugging underground leaks.

[0007] The technical solution of the polyacrylic acid-assisted red mud-phosphogypsum-cement ternary system cementitious material of the present invention is as follows:

[0008] The polyacrylic acid-assisted red mud-phosphogypsum-cement ternary system cementitious material comprises red mud, phosphogypsum, cement, polyacrylic acid and water.

[0009] The technical solution of the present invention for a method for preparing a polyacrylic acid-assisted red mud-phosphogypsum-cement ternary system cementitious material is as follows:

[0010] A method for preparing a polyacrylic acid-assisted red mud-phosphogypsum-cement ternary system cementitious material comprises the following steps:

[0011] (1) Pretreatment: drying the red mud, crushing it, and then screening it; aging the phosphogypsum with 5% calcium chloride;

[0012] (2) mixing and stirring: weighing red mud, phosphogypsum, cement, polyacrylic acid and water respectively, pouring the weighed red mud, phosphogypsum and cement into a mortar mixer, adding water and stirring to prepare a composite material;

[0013] (3) adding polyacrylic acid to the composite material by an external doping method and then continuing to stir to obtain a multi-component system gelling material;

[0014] (4) Moulding and curing: Pour the above multi-component system cementitious material into a 40mm×40mm×160mm triple mould, compact it with a mortar vibrating table, demould it after 24 hours, and cure it at a temperature of 25±3℃ and a humidity of >95%.

[0015] Preferably, in step (1), the red mud is first dried in an electric blast drying oven, then crushed using a pulverizer and sieved using a sieve with a pore size of 0.16 mm; the moisture content of the red mud is 48.44%, wherein the drying temperature is 105-110°C.

[0016] Preferably, in step (2), the mass ratio of the red mud to the phosphogypsum is 1:3; and the cement content accounts for 20 to 70% of the sum of the mass of the red mud and the phosphogypsum.

[0017] Preferably, in step (2), the amount of polyacrylic acid added is 0.25 to 0.75% of the total mass of red mud, phosphogypsum and cement.

[0018] Preferably, in step (2), the ratio of the sum of the mass of the red mud, phosphogypsum and cement to the mass of water is 5:2.

[0019] Further preferably, the main components of the red mud are Fe2O3, SiO2, Al2O3 and Na2O, wherein the semi-quantitative content of Fe2O3 is 55.8%.

[0020] Preferably, the main components of the phosphogypsum are Ca(SO4)(H2O)2, Ca(SO4)(H2O) 0.5 , and the content of phosphogypsum is 91.9%.

[0021] Preferably, the cement is PI42.5 ordinary Portland cement, and the main components of the cement are CaO, SiO2, Al2O3, MgO and Fe2O3.

[0022] Beneficial effects:

[0023] The present invention uses Bayer red mud and phosphogypsum as auxiliary cementing materials, adds polyacrylic acid, and combines with cement to prepare a new green and low-carbon red mud and other solid waste cementing material. The multi-component system gel material prepared by the present invention can achieve a flexural strength of 6.1MPa, a compressive strength of 12.5MPa, and a total pore volume of 11.971×10 -2 mL / g, with pore sizes below 50nm accounting for 60.9% and pore sizes above 50nm accounting for 39.1%. This can provide a basis for underground space wall plugging materials and solve the problem of resource utilization of red mud. The alkalinity of red mud combined with the acidity of phosphogypsum can effectively solve the problem of strong alkalinity of red mud. At the same time, when using large amounts of red mud, the mechanical properties and pore structure of the gel material meet the requirements of underground space wall plugging materials, and have high economic and green environmental benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The compressive and compression strength diagrams of different cement and polyacrylic acid dosages for this application;

[0025] Figure 2 This is the XRD pattern of the gelling material in Example 6 of the present application;

[0026] Figure 3 This is a pie chart showing the pore size distribution of the gelling material in Example 6 of the present application;

[0027] Figure 4 This is the FTIR spectrum of the gelling material in Example 6 of the present application;

[0028] Figure 5 Thermogravimetric analysis diagrams of the gelling materials in Examples 4 and 6 of the present application;

[0029] Figure 6 This is the SEM image of the gelling material in Example 6 of the present application. DETAILED DESCRIPTION

[0030] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0031] 1. The specific embodiment of the preparation method of the polyacrylic acid-assisted red mud-phosphogypsum-cement ternary system cementitious material of the present invention is as follows:

[0032] Example 1

[0033] A method for preparing a polyacrylic acid-assisted red mud-phosphogypsum-cement ternary system cementitious material comprises the following steps:

[0034] (1) Pretreatment: The red mud is first dried in an electric blast drying oven, then crushed in a pulverizer, and then sieved through a 0.16 mm pore size sieve; phosphogypsum is aged for 24 h using 5% calcium chloride. Calcium chloride is a good activator for phosphogypsum activation and can also effectively promote the transformation of dihydrate gypsum to hemihydrate gypsum. When the calcium chloride content is 5%, the strength of the phosphogypsum is the highest. After calcium chloride activates the phosphogypsum, the optimal aging time is 24 h.

[0035] (2) Mixing and stirring: Use an electronic scale to weigh the ingredients, pour the weighed red mud, phosphogypsum, and cement into a mortar mixer, add water and stir, wherein the mass ratio of red mud to phosphogypsum is 1:3, the cement content accounts for 70% of the mass of the red mud-phosphogypsum binary system cementitious material; and the water-solid ratio is 0.4;

[0036] (3) Adding polyacrylic acid: add 0.25% polyacrylic acid to the stirred material by external mixing method and continue stirring;

[0037] (4) Mold filling and curing: pour the material mixed evenly in step 3 into a 40mm×40mm×160mm triple mold, vibrate it on a mortar vibrating table, demould it after 24 hours, and cure it at a temperature of 25℃ (±3℃) and a humidity of >95% for 7 days.

[0038] Examples 2 to 9

[0039] A method for preparing a polyacrylic acid-assisted red mud-phosphogypsum-cement ternary system cementitious material comprises the following steps:

[0040] The specific method is the same as that of Example 1, and the addition amount of each raw material is shown in Table 1.

[0041] Comparative Examples 1 to 3

[0042] A method for preparing a polyacrylic acid-assisted red mud-phosphogypsum-cement ternary system cementitious material comprises the following steps: The specific method is the same as that in Example 1, and the addition amount of each raw material is shown in Table 1.

[0043] Table 1 Statistics of raw materials of Examples 1 to 9 and Comparative Examples 1 to 3

[0044]

[0045]

[0046] Note: (1) The percentage of cement content is the percentage of the sum of the mass of red mud and phosphogypsum; the percentage of polyacrylic acid content is the percentage of the sum of the mass of red mud, phosphogypsum and cement; (3) The "solid" in the water-solid ratio refers to the sum of the mass of red mud, phosphogypsum and cement.

[0047] 2. Specific examples of the polyacrylic acid-assisted red mud-phosphogypsum-cement ternary system cementitious material of the present invention are as follows:

[0048] Example 10

[0049] A polyacrylic acid-assisted red mud-phosphogypsum-cement ternary system cementitious material, comprising the following components:

[0050] 5 kg of red mud, 15 kg of phosphogypsum, 14 kg of cement, 85 g of polyacrylic acid, and 13.6 kg of water, wherein the phosphogypsum is activated for 24 hours.

[0051] Examples 11 to 18 and Comparative Examples 4 to 6

[0052] A polyacrylic acid-assisted red mud-phosphogypsum-cement ternary system cementitious material, the amount of the cementitious material is shown in Table 2.

[0053] Table 2 Statistics of raw materials for Examples 10 to 18 and Comparative Examples 4 to 6

[0054]

[0055]

[0056] 3. Results and Analysis

[0057] The bending and compression tests of Examples 1 to 9 and Comparative Examples 1 to 3 were carried out using a bending and compression testing machine. The results are shown in Table 3.

[0058] Table 3 Flexural and compression test results of Examples 1 to 9 and Comparative Examples 1 to 3

[0059]

[0060] Figure 1 The compressive and compressive strength diagrams of different cement and polyacrylic acid dosages for this application are shown in Figure 1. Figure 1 As shown in Table 3, the compressive and flexural strengths decrease with decreasing cement content, while increasing with increasing polyacrylic acid content leads to an initial increase followed by a decrease. When the cement content remains constant, the mechanical properties are optimized at 0.5% polyacrylic acid. At 70% cement content, the compressive strength at 7 days is 39.6 MPa, and the flexural strength is 10.7 MPa.

[0061] The raw materials and sample samples were dried and ground, and then subjected to XRD ray diffraction for qualitative analysis of Example 6. The results are as follows: Figure 2 As shown, the raw material phase composition ratio, the phase composition of the hydration product and the phase change are obtained.

[0062] Depend on Figure 2It can be seen that the hydration reaction in the cementitious material produces Ca(SO)4(H2O) 0.5 、NaKZrSi3O9(H2O)2、Ca 0.857 Na 0.285 (SO4)(H2O) 0.473 、C 12 H 12 O4 and other hydration products, among which the dihydrate gypsum contained in the phosphogypsum is basically completely converted into hemihydrate gypsum and further undergoes hydration reaction. Due to the addition of polyacrylic acid and metal ions, organic high molecular polymers are generated.

[0063] The chemical bonds and functional group compositions of Example 6 were determined by FTIR analysis. Example 6 was subjected to infrared scanning by Fourier transform infrared spectrometer to study the changes in its functional groups. The results are as follows: Figure 4 As shown. Figure 4 It can be seen that after adding cement, 3553cm -1 The absorption peaks on the left and right correspond to the stretching vibration region of -OH in the association reaction, 3441 cm -1 The absorption peaks on the left and right correspond to the stretching vibration region of -NH of the association effect, 1620cm -1 The absorption peaks on the left and right correspond to the stretching vibration region of the benzene ring -C=C-, 1483cm -1 and 1426cm -1 The absorption peaks around 1153 cm correspond to the stretching vibration region of OH bending vibration. -1 The absorption peaks around 660cm -1 The absorption peaks on the left and right correspond to the CH stretching vibration region of the association effect.

[0064] The JW-BK112 specific surface area and void analyzer produced by Beijing Jingwei Gaobo Science and Technology Co., Ltd. was used to perform liquid nitrogen adsorption on Example 6 to explore the void structure of the sample, such as pore distribution, pore volume, characteristic pore diameter, and porosity. The results are as follows: Figure 3 shown.

[0065] Depend on Figure 3 It can be seen that the pore size range of 2nm to 50nm accounts for 60.9%, large capillary pores account for 30.2%, and pores >50nm account for 39.1%. This is because the stable and dense polymer complex generated by the reaction of polyacrylic acid with the metal ions in the gelling material and the hydrated calcium silicate gel generated by hydration have a significant filling effect on the medium capillary pores and capillary macropores, reducing the void ratio of the material, improving the density of the gelling material, and making the gelling material denser.

[0066] The microstructure of Example 6 was observed using a Guoyi Quantum SEM3200 scanning electron microscope. Figure 6As shown. Figure 6 It can be seen that after the addition of polyacrylic acid and cement, the sample's structure became more compact, and a large amount of calcium hydroxide generated by hydration reactions appeared on the surface. The cement, along with components such as aluminum oxide and calcium oxide in the red mud, combined with calcium sulfate in the phosphogypsum, gradually forming needle-shaped ettringite with higher strength, which intertwined with a large amount of hydrated calcium silicate (SCH) gel. The gel covered the surface of the ettringite and tightly wrapped it. Polyacrylic acid molecules contain a large number of active carboxyl groups. During the hydration process, these carboxyl groups break their hydrogen-oxygen bonds and combine with water-soluble metal ions in the cementitious material to form a high-molecular complex. This complex interspersed between the gel and the ettringite, further connecting the already intertwined phases through organic matter, effectively filling the pores.

[0067] The mass variation of Example 4 and Example 6 with temperature was analyzed using a Setline STA / STA+ synchronous thermal analyzer. The results are as follows: Figure 5 As shown. Figure 5 It can be seen that during the heating process, the hydration products within the two groups of samples continuously reduced their mass as the temperature continued to rise. Both groups of samples reached maximum weight loss at around 700°C. Example 4 has three main weight loss ranges: the first range from 60°C to 200°C shows a mass loss of 4.93%; the second range from 400°C to 500°C shows a mass loss of 2.06%; and the third range from 540°C to 700°C shows a mass loss of 1.2%. Example 6 has three main weight loss ranges: the first range from 80°C to 200°C shows a mass loss of 4.46%; the second range from 300°C to 500°C shows a mass loss of 1.06%; and the third range from 560°C to 691°C shows a mass loss of 1.10%.

[0068] The mass loss across the three ranges indicates that the hydration product in the first range is the loss of bound water from ettringite and CSH gel, the hydration product in the second range is primarily the decomposition of Ca(OH)2, and the decomposition of carbonates in the third range is due to the decomposition of the samples. Mass loss analysis indicates that the amount of ettringite and CSH gel produced in both samples (Example 4) exceeds that in Example 6, which is consistent with the mechanical strength results. This indirectly indicates that the total amount of Ca(OH)2 in both samples (Example 4) exceeds that in Example 6. Ca(OH)2 is an intermediate product in the hydration process, formed when calcium ions react with alkaline substances in the red mud. Therefore, the mass loss in the second range indicates that the reaction level in Example 6 is higher.

[0069] Cement and red mud components such as alumina and calcium oxide combine with calcium sulfate in phosphogypsum, gradually forming stronger, needle-rod-shaped ettringite, which interlocks with a large amount of hydrated calcium silicate (SCH) gel. The gel covers the surface of the ettringite and tightly envelops it. Polyacrylic acid molecules contain numerous active carboxyl groups. During hydration, these hydroxyl bonds are broken, combining with water-soluble metal ions in the cementitious material to form a high-molecular complex. This complex is interspersed between the gel and the ettringite, further connecting the already intertwined phases through organic matter, effectively filling the pores.

[0070] To maximize solid waste utilization and achieve resource utilization, and in combination with practical applications, a 7-day flexural strength of 6.1 MPa and a compressive strength of 12.5 MPa were achieved when the red mud to phosphogypsum mass ratio was 1:3, the cement content was 20%, and the polyacrylic acid content was 0.5%. These mechanical properties meet the mechanical requirements for plugging leaks in underground walls, and the substantial utilization of solid waste is consistent with resource utilization.

[0071] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples without contradiction.

[0072] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A polyacrylic acid-assisted red mud-phosphogypsum-cement ternary system cementitious material, comprising red mud, phosphogypsum, cement, polyacrylic acid and water, wherein the phosphogypsum is aged with 5% calcium chloride, the mass ratio of the red mud to the phosphogypsum is 1:3, the cement content is 20-70% of the sum of the mass of the red mud and the phosphogypsum, the polyacrylic acid content is 0.25-0.75% of the sum of the mass of the red mud, phosphogypsum and cement, and the mass ratio of the sum of the mass of the red mud, phosphogypsum and cement to the mass of water is 5:

2.

2. The method for preparing the polyacrylic acid-assisted red mud-phosphogypsum-cement ternary system gelling material according to claim 1, characterized in that: The following steps are involved: (1) Pretreatment: dry the red mud, crush it, and then screen it; use 5% calcium chloride to age the phosphogypsum; (2) Mixing and stirring: weigh red mud, phosphogypsum, cement, polyacrylic acid and water respectively, pour the weighed red mud, phosphogypsum and cement into a mortar mixer, add water and stir to prepare a composite material; (3) adding polyacrylic acid to the composite material by an external doping method and then continuing to stir to obtain a multi-component system gelling material; (4) Moulding and curing: Pour the above multi-component system cementitious material into a 40mm×40mm×160mm triple mould, compact it with a mortar vibrating table, demould it after 24 hours, and cure it at a temperature of 25±3℃ and a humidity of >95%.

3. The method for preparing the polyacrylic acid-assisted red mud-phosphogypsum-cement ternary system gelling material according to claim 2, characterized in that: In step (1), the red mud is first dried in an electric blast drying oven, then crushed by a pulverizer and sieved using a sieve with an aperture of 0.16 mm; the moisture content of the red mud is 48.44%.

4. The method for preparing the polyacrylic acid-assisted red mud-phosphogypsum-cement ternary system gelling material according to claim 2, characterized in that: In step (2), the mass ratio of the red mud to the phosphogypsum is 1:3; and the cement content is 20-70% of the sum of the mass of the red mud and the phosphogypsum.

5. The method for preparing the polyacrylic acid-assisted red mud-phosphogypsum-cement ternary system gelling material according to claim 2, characterized in that: In step (2), the amount of polyacrylic acid added is 0.25-0.75% of the sum of the mass of red mud, phosphogypsum and cement.

6. The method for preparing the polyacrylic acid-assisted red mud-phosphogypsum-cement ternary system gelling material according to claim 2, characterized in that: In step (2), the ratio of the sum of the mass of the red mud, phosphogypsum and cement to the mass of water is 5:

2.

7. The method for preparing the polyacrylic acid-assisted red mud-phosphogypsum-cement ternary system gelling material according to any one of claims 2 to 6, characterized in that: The main components of the red mud are Fe2O3, SiO2, Al2O3 and Na2O, among which the semi-quantitative content of Fe2O3 is 55.8%.

8. The method for preparing the polyacrylic acid-assisted red mud-phosphogypsum-cement ternary system gelling material according to claim 2, characterized in that: The main components of the phosphogypsum are Ca(SO4)(H2O)2, Ca(SO4)(H2O) 0.5 , and the content of phosphogypsum is 91.9%.

9. The method for preparing the polyacrylic acid-assisted red mud-phosphogypsum-cement ternary system gelling material according to claim 2, characterized in that: The cement is PI 42.5 ordinary Portland cement, and the main components of the cement are CaO, SiO2, Al2O3, MgO and Fe2O3.

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