Cement reinforcing agent reinforced cement prepared through co-catalysis of waste plastic gasified red mud and preparation method of cement reinforcing agent reinforced cement

Abstract

The invention discloses cement reinforcing agent reinforced cement prepared through co-catalysis of waste plastic gasified red mud and a preparation method of the cement reinforcing agent reinforced cement, and the preparation method comprises the following steps: adding a red mud-based carbon nanotube reinforcing agent and a water reducing agent into water, carrying out ultrasonic treatment to obtain a dispersion solution, uniformly mixing the dispersion solution with reference cement, and carrying out curing maintenance to obtain final cement, wherein the red mud-based carbon nanotube reinforcing agent is formed by in-situ deposition of carbon nanotubes on the surface of red mud through red mud catalytic plastic pyrolysis gas. According to the method, the compressive strength of the cement can be enhanced by using the reinforcing agent derived from the red mud and the plastic waste.

Description

Technical Field

[0001] The present invention belongs to the fields of solid waste resource utilization and building materials, and particularly relates to a method for enhancing cement by using waste plastics and gasified red mud as co-catalysts to prepare a cement enhancer and its preparation method. Background Art

[0002] Red mud, as a large amount of industrial waste generated during the processing of bauxite, has an astonishing annual output, reaching hundreds of millions of tons. Behind this huge number are severe environmental and resource challenges.

[0003] Red mud has high alkalinity, with a pH value usually between 10 and 13. This strong alkaline characteristic makes it difficult to be easily neutralized in the natural environment. At the same time, red mud also contains various heavy metal elements such as iron, aluminum, titanium, calcium, etc., as well as some toxic and harmful elements such as gallium, scandium, chromium, etc. These heavy metal elements are not only difficult to degrade but may also enter the ecosystem through ways such as rainwater scouring and soil infiltration, causing pollution to the soil, water body, and atmospheric environment and endangering the health of animals, plants, and humans.

[0004] Due to the above characteristics, red mud is traditionally difficult to be directly applied to other fields. To prevent it from harming the environment, a large amount of resources are often required for harmless treatment. This includes using complex processes for acid-base neutralization, heavy metal separation, etc. A large amount of manpower, material resources, and financial resources are required during the process. Moreover, the treated red mud also needs to be safely stored, building special storage sites and taking measures such as anti-seepage and anti-dispersion, which further increases costs and resource consumption.

[0005] The invention patent with the publication number CN117602907A proposes a steel slag - red mud - cement-based composite mortar and its preparation method. It aims to solve the problems that the landfill and stockpile treatment of red mud and steel slag in the prior art cause serious pollution to the ecological environment, and at the same time solve the technical problem that the single addition of steel slag in the field of gel materials will significantly reduce the mechanical properties and durability of cement mortar. The present invention includes 16.25% - 20% of Portland cement, 2.50% - 4.38% of red mud, 2.50% - 4.37% of fine steel slag, and the rest is 75% of aggregate; the water-binder ratio of the steel slag - red mud - cement-based composite mortar is 0.5. This scheme uses red mud, etc. as cement admixtures to improve the physical properties of cement and concrete, proving the potential of red mud in the application of building materials. However, this method only utilizes the soluble alkali in red mud to promote the potential hydration activity of steel slag, and its own gelling activity is poor, and the mechanical properties are not significantly improved, still less than 42.5 MPa.

[0006] The invention patent application with the publication number CN117049802A discloses a red mud-based low-carbon composite cement and its preparation method. The raw materials of this red mud-based low-carbon composite cement include red mud, supplementary cementitious materials, gypsum-based solid waste, alkali activators, retarders, and interfacial enhancers. It has a compressive strength equivalent to or even higher than that of 425 cement or 525 cement. The red mud content is ≥ 30 wt%, and the dosage of the alkali activator is as low as 3 wt% - 8 wt%. It not only realizes the large-scale resource utilization of red mud but also significantly reduces the production cost. At the same time, the hydration products of this cement have a good shielding effect on radioactivity, and the radioactivity of the obtained cement after hardening can still meet the national standards while a large amount of red mud is incorporated. However, there is still room for further improvement in the compressive strength of the cement prepared by this method.

[0007] These solutions are limited to the alternative application of red mud materials. Due to the poor self-cementitious activity of red mud, the direct incorporation of red mud does not bring a significant improvement in mechanical properties. Therefore, how to fully explore the synergistic effect of red mud in building materials has become an urgent technical problem to be solved. Carbon nanotube enhancement technology has a significant effect on enhancing the performance of cement-based materials, but it is often limited by the high cost of commercial materials. Developing a technical solution that synergistically converts plastics and red mud into carbon nanotube reinforcement materials using the catalytic effect of red mud can not only solve the two environmental problems of plastic waste and red mud but also provide new ideas for the preparation of cement and concrete with excellent enhancement effects. Summary of the Invention

[0008] The present invention proposes a preparation method for enhancing cement by using waste plastic gasification and red mud co-catalysis to prepare a cement enhancer, which can use red mud and plastic waste-derived carbon nanotube enhancer to improve the compressive strength of cement.

[0009] The present invention provides a preparation method for enhancing cement by using waste plastic gasification and red mud co-catalysis to prepare a cement enhancer, including:

[0010] Adding the red mud-based carbon nanotube enhancer and water reducer into water, and obtaining a dispersion solution by ultrasonic treatment. Mixing the dispersion solution with reference cement uniformly, and curing and maintaining to obtain the final cement;

[0011] Among them, the red mud-based carbon nanotube enhancer is in-situ loading of carbon nanotubes on the surface of red mud by catalyzing the pyrolysis of plastics with red mud.

[0012] The present invention uses the Fe and Al components in red mud to promote the formation of ettringite. The formed ettringite and carbon nanotubes overlap with each other, refine the pore structure, improve the microstructural integrity of the composite material, and thus improve the compressive strength.

[0013] Preferably, in the final cement, the mass percentage of carbon nanotubes is 0.025 wt% to 0.4 wt%. On the one hand, the carbon nanotubes act as nucleation sites to accelerate the cement hydration reaction; on the other hand, the carbon nanotubes and ettringite overlap with each other to jointly refine the pore structure, thereby improving the compressive strength of the cement.

[0014] More preferably, in the final cement, the mass percentage of carbon nanotubes is 0.025 wt% to 0.1 wt%. By further controlling the content of carbon nanotubes in the present invention, the carbon nanotubes are more uniformly dispersed, reducing aggregation and avoiding the decrease in the compressive strength of the cement caused by the addition of excessive carbon nanotubes.

[0015] Preferably, in the red mud-based carbon nanotube enhancer, the mass ratio of red mud to carbon nanotubes is 15 to 50 wt% of the carbon nanotubes in the red mud-based carbon nanotube enhancer. The present invention is achieved by controlling and regulating the pyrolysis process of plastics by red mud, ensuring the synergistic strengthening effect of red mud and carbon nanotubes in cement.

[0016] Preferably, the preparation method of the red mud-based carbon nanotube enhancer includes:

[0017] (1) Calcining, pressing, crushing and screening the red mud to obtain red mud particles with a target particle size;

[0018] (2) Placing the plastic and the red mud particles obtained in step (1) in the pyrolysis section and the catalytic section of a two-stage fixed-bed reactor respectively. Under an inert atmosphere, when the catalytic section reaches a preset temperature, pyrolyze the plastic so that the plastic pyrolysis gas contacts and reacts with the red mud particles, and finally obtain a cement enhancer in the catalytic section.

[0019] The present invention utilizes the volatiles after plastic pyrolysis to be able to transform and deposit on the surface of red mud to generate carbon nanotubes, making full use of waste plastics and red mud to obtain carbon nanotubes in a green and environmentally friendly manner.

[0020] Preferably, the calcination is carried out at a temperature of 600 to 800 °C in an air atmosphere for 2 to 3 h. The present invention controls the calcination temperature and time to remove organic impurities and improve the catalyst stability and activity.

[0021] Preferably, the target particle size of the red mud particles is 40 to 60 mesh, and the proportion of the active component Fe2O3 is 30 to 40%. By controlling the target particle size, the catalyst bed particles are ensured to have a suitable porosity and specific surface area to avoid blocking the gas path.

[0022] Preferably, the plastic is one kind of polyolefin plastics, avoiding the presence of chlorine-containing substances causing the deactivation and sintering of red mud and leading to a rapid decrease in the carbon nanotube yield.

[0023] Preferably, the mass ratio of the plastic to the red mud is 1:2 to 4:1, which helps to ensure that an appropriate amount of red mud catalyst participates in the reaction, promoting the efficient conversion of pyrolysis products and facilitating the growth of carbon nanotubes on the surface of the red mud.

[0024] Preferably, the temperature of the catalytic section is 750 - 850 °C, ensuring that the pyrolysis volatiles of the plastic can be efficiently converted and deposited on the surface of the red mud to form carbon nanotubes. Too low a temperature will not initiate the catalytic reaction and is not conducive to the growth of carbon nanotubes; while too high a temperature will cause catalyst deactivation and damage to the carbon structure.

[0025] Preferably, during the plastic pyrolysis process, the temperature is raised from room temperature to 500 - 600 °C at a heating rate of 10 - 20 °C / min and held for 10 - 15 min to ensure complete pyrolysis of the plastic. The temperature of the catalytic section is 750 - 850 °C to ensure a favorable temperature for the conversion of plastic pyrolysis products into carbon nanotubes.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] (1) Utilizing the catalytic effect of the active component Fe2O3 in the red mud, the plastic waste and red mud are synergistically converted into high - value - added carbon nanotube / red mud composites, realizing the resource utilization of waste and reducing environmental pollution.

[0028] (2) Utilizing the synergistic effect of the red mud and carbon nanotubes in the red mud - based carbon nanotube reinforcing agent to promote the improvement of the compressive strength of cement. Fe and Al in the red mud promote the formation of ettringite in the cement. The carbon nanotubes serve as nucleation sites, promoting the cement hydration reaction. At the same time, they overlap with the formed ettringite, refining the pore structure and enhancing the compressive strength of the cement.

[0029] (3) Solving the problem of insignificant improvement in mechanical properties due to the low cementitious activity of red mud;

[0030] (4) Using inexpensive red mud as a catalyst carrier, reducing the production cost of carbon nanotubes and having good economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of the preparation device for the red mud - based carbon nanotube reinforcing agent provided by a specific embodiment of the present invention;

[0032] In the figure: 1 - inert gas cylinder (gas source); 2 - mass flow controller; 3 - pyrolysis section; 4 - catalytic section; 5 - hanging basket; 6 - quartz perforated plate; 7, 8 - temperature controller; 9 - condensation device; 10 - gas bag; 11 - gas chromatograph.

[0033] Figure 2Provide the electron microscopy image of the red mud-based carbon nanotube enhancer for Example 1;

[0034] Figure 3 Provide the electron microscopy image of the cement-based material prepared for Comparative Example 1;

[0035] Figure 4 Provide the electron microscopy image of the cement-based material prepared for Example 1;

[0036] Figure 5 Provide the electron microscopy image of the cement-based material prepared for Comparative Example 2. Detailed implementation manners

[0037] The following will combine specific embodiments to elaborate on the content of the present invention in detail. The following embodiments are only listed as implementation cases of the present invention and do not limit the present invention. Any modifications and optimizations based on the essence and concept of the present invention fall within the protection scope of the present invention.

[0038] To solve the deficiencies in the prior art, the present invention proposes a preparation method for enhancing cement based on carbon nanotubes derived from red mud plastics.

[0039] The technical solution of the present invention includes the following steps:

[0040] (1) Calcinate red mud in an air atmosphere at 600 - 800 °C for 2 - 3 h. After calcination, press and form it with a tablet press, crush it and then screen it to retain red mud particles with a mesh size of 40 - 60.

[0041] (2) Load the pretreated red mud particles into the catalytic section of a two-stage fixed-bed reactor, and place polyolefin plastic powder in the pyrolysis section; introduce nitrogen into the reactor, replace the air and then continuously maintain an inert atmosphere; set the temperature of the catalytic section to 750 - 850 °C. After the temperature stabilizes, heat the pyrolysis section at a rate of 10 - 20 °C / min to 500 - 600 °C, and keep it warm for 10 - 15 min to fully pyrolyze the plastic; the generated pyrolysis gas (containing olefins, alkanes, etc.) enters the catalytic section under the drive of the carrier gas and undergoes a catalytic cracking reaction with the red mud particles. Finally, carbon nanotubes are loaded on the surface of the red mud to obtain a cement enhancer.

[0042] (3) Mix the enhancer, water reducer and water into a dispersion liquid and then add it to the cement-based material, where:

[0043] The addition amounts of carbon nanotubes (determine the amount of the enhancer according to the increase amount of carbon nanotubes), water reducer, and water (compared with the amount of the reference cement) are 0.025 - 0.1 wt%, 1.5 wt%, and 40 wt% respectively. After the mixed slurry is stirred, formed and cured, the compressive strength is measured.

[0044] The following uses examples to further describe the present invention, which is not used to limit the present invention.

[0045] In the following embodiments, the red mud selected was the Bayer red mud from a company in Yantai, and the main chemical element composition after its pretreatment was obtained by X-ray fluorescence spectroscopy.

[0046]

[0047] The cement used was P.I 42.5 reference cement, and the water reducer was a polycarboxylate superplasticizer.

[0048] Example 1:

[0049] (1) The red mud was calcined at 800 °C for 2 h in an air atmosphere. After calcination, it was pressed into tablets by a tablet press, crushed and sieved, and the red mud particles with a size of 40 - 60 mesh were retained.

[0050] (2) 1 g of polyethylene plastic and 2 g of pretreated red mud particles were respectively loaded into the pyrolysis section and the catalytic section of a two-stage fixed-bed reactor.

[0051] (3) Nitrogen was introduced into the reactor, and after replacing the air, an inert atmosphere was continuously maintained.

[0052] (4) The temperature of the catalytic section was set at 850 °C. After the temperature was stable, the pyrolysis section was heated to 500 °C at a rate of 15 °C / min and held for 10 min to fully pyrolyze the plastic.

[0053] (5) The pyrolysis gas generated during the process was carried by the carrier gas into the catalytic section and underwent a catalytic cracking reaction with the red mud particles. Finally, carbon nanotubes were loaded on the surface of the red mud to obtain a cement enhancer.

[0054] (6) 0.1 g of carbon nanotubes (i.e., 0.4 g of the cement enhancer) and 0.15 g of the water reducer were added to 40 mL of water and ultrasonicated for 30 min to obtain a dispersion solution.

[0055] (7) The dispersion solution was added to 100 g of the reference cement, stirred evenly, poured into a mold for curing, and after 28 days of curing, the compressive strength was measured to be 63.32 MPa.

[0056] Example 2

[0057] The difference between this example and Example 1 is that the amount of carbon nanotubes added in step (6) was 0.025 g, and the compressive strength measured after 28 days of curing was 59.20 MPa.

[0058] Example 3

[0059] The difference between this example and Example 1 is that the amount of carbon nanotubes added in step (6) was 0.2 g, and the compressive strength measured after 28 days of curing was 56.44 MPa.

[0060] Example 4

[0061] The difference between this example and Example 1 is that the amount of carbon nanotubes added in step (6) is 0.4 g, and the compressive strength measured after 28 days of curing is 52.76 MPa.

[0062] Comparative Example 1

[0063] Without adding a cement enhancer, 40 mL of water was directly added to 100 g of reference cement, stirred evenly, poured into a mold for curing, and cured for 28 days. The measured compressive strength was 45.44 MPa.

[0064] Comparative Example 2

[0065] Without adding a cement enhancer, 30 g of red mud and 70 g of reference cement were dry-mixed, 40 mL of water was added to the mixture, stirred evenly, poured into a mold for curing, and cured for 28 days. The measured compressive strength was 32.80 MPa.

[0066] Performance analysis:

[0067] Comparing with the cement compressive strength results obtained in Comparative Example 1, it was found that the addition of the carbon nanotube / red mud composite material as an enhancer in Examples 1-4 could significantly improve the compressive strength. When the addition amount of carbon nanotubes was 0.1 g (0.1 wt%), the strength improvement effect reached the best, and the strength improvement rate was 39.4%. When exceeding this addition amount, although the improvement effect was still shown within the test range, the effect had begun to decline.

[0068] Comparing the cement compressive strength results obtained in Comparative Example 1 and Comparative Example 2, it was found that the partial replacement of cement with red mud could not improve the cement strength and could not achieve the expected effect.

[0069] Through the detailed analysis of the cement-based materials in Example 1 and Comparative Example 1, it was found that carbon nanotubes served as nucleation sites, accelerated the hydration reaction, and increased the polymerization degree of the calcium silicate hydrate gel; in addition, the Fe and Al components in red mud promoted the formation of ettringite, and the ettringite and carbon tubes overlapped with each other, refined the pore structure, and improved the microstructural integrity of the composite material, thereby enhancing the strength. It shows that by synergistically converting plastic waste and red mud into a high-value-added carbon nanotube / red mud composite material, the resource utilization of waste is realized, and at the same time, under the synergistic action of carbon nanotubes and red mud, the compressive strength of cement is improved. Therefore, this invention is a technology for the collaborative disposal and resource utilization of plastic waste and red mud with industrial application and economic benefit prospects.

[0070] As Figure 1As shown, the device is a two-stage fixed-bed reaction system for the red mud-based carbon nanotube enhancer provided by the specific embodiment. 1 is an inert gas cylinder to ensure an anaerobic condition during the reaction; 2 is a mass flow controller to regulate the inert gas velocity, thereby regulating the catalytic reaction of plastic pyrolysis volatiles on the surface of red mud; 3 is a pyrolysis section for the gradual pyrolysis of plastics; 4 is a catalytic section where plastic pyrolysis volatiles are converted and deposited on the surface of red mud filled herein to form carbon nanotubes; 5 is a hanging basket for loading plastics; 6 is a quartz perforated plate for loading red mud; 7 and 8 are temperature controllers for the pyrolysis stage and the catalytic stage respectively to regulate the temperatures at both ends; 9 is a condensation device to collect the liquid-phase components of the reaction; 10 is a gas bag to collect the gas-phase components of the reaction; 11 is a gas chromatograph to analyze the composition of the gas-phase products. After the reaction, the material collected at position 6 is the red mud-based carbon nanotube enhancer described above.

[0071] As Figure 2 shown, it is the electron micrograph of the red mud-based carbon nanotube enhancer provided for Example 1. It can be seen that slender and clustered carbon nanotubes are formed on the surface of red mud particles.

[0072] As Figure 3 shown, it is the electron micrograph of the cement-based material prepared in Comparative Example 1. It can be seen that when no red mud-based carbon nanotube enhancer is added, the pore structure of the cement-based material is very loose and there are many large pores. After magnification, it can be seen that the large pores are mainly hydrated calcium silicate gel products and a small amount of ettringite, and the pores cannot be filled densely.

[0073] As Figure 4 shown, it is the electron micrograph of the cement-based material prepared in Example 1. It can be seen that when the red mud-based carbon nanotube enhancer is added, the pore structure of the cement-based material is refined and there are no obvious large pores. After magnification, it can be seen that there is an effective overlap between carbon nanotubes and ettringite, filling the pores, which also improves the compressive strength of the cement-based material.

[0074] As Figure 5 shown, it is the electron micrograph of the cement-based material prepared in Comparative Example 2. After the addition of red mud, it can be seen that ettringite is formed in the cement-based material, but its compressive strength is not as good as that of ordinary cement. It can be seen that without the combined effect of carbon nanotubes to refine the pores, the mechanical properties of the pure red mud cement-based material are poor.

[0075] In addition, after reading the above description of the present invention, various types of applications, supplements, modifications, and variations made by those skilled in the art to the present invention without departing from the connotation and scope of the present invention shall fall within the scope defined by the appended claims of this application.

Claims

1. A preparation method for enhancing cement by using waste plastic gasification and red mud co-catalysis to prepare a cement enhancer, characterized in that, Including: Adding a red mud-based carbon nanotube enhancer and a water reducer into water, ultrasonically obtaining a dispersion solution, mixing the dispersion solution with reference cement evenly, and obtaining the final cement after curing and maintenance; Wherein, the red mud-based carbon nanotube enhancer is obtained by in-situ depositing carbon nanotubes on the surface of red mud by catalyzing the pyrolysis gas of plastic with red mud.

2. The preparation method of enhancing cement by using waste plastic gasification red mud co-catalysis to prepare a cement enhancer according to claim 1, characterized in that, In the finally obtained cement, the mass percentage of carbon nanotubes is 0.025wt% to 0.4wt%.

3. The preparation method of enhancing cement by using waste plastic gasification red mud co-catalysis to prepare a cement enhancer according to claim 2, characterized in that In the finally obtained cement, the mass percentage of carbon nanotubes is 0.025wt% to 0.1wt%.

4. The preparation method of enhancing cement by using waste plastic gasification red mud co-catalysis to prepare a cement enhancer according to claim 1, characterized in that, In the red mud-based carbon nanotube enhancer, the mass ratio of carbon nanotubes in the red mud-based carbon nanotube enhancer is 15 to 50wt%.

5. The preparation method of enhancing cement by using waste plastic gasification red mud co-catalysis to prepare a cement enhancer according to claim 1, characterized in that, The preparation method of the red mud-based carbon nanotube enhancer includes: (1) Calcining, tablet-pressing, crushing and screening red mud to obtain red mud particles with a target particle size; (2) Placing plastic and the red mud particles obtained in step (1) in the pyrolysis section and the catalytic section of a two-stage fixed-bed reactor respectively. Under an inert atmosphere, when the catalytic section reaches a preset temperature, pyrolyzing the plastic so that the pyrolysis gas of the plastic contacts and reacts with the red mud particles, and finally obtaining a cement enhancer in the catalytic section.

6. The preparation method of enhancing cement by using waste plastic gasification red mud co-catalysis to prepare a cement enhancer according to claim 5, characterized in that The temperature for calcining the red mud is 600 to 800°C, and it is calcined in an air atmosphere for 2 to 3 hours.

7. The preparation method of enhancing cement by using waste plastic gasification red mud co-catalysis to prepare a cement enhancer according to claim 5, characterized in that, The target particle size of the red mud particles is 40 to 60 mesh, and the proportion of the active component Fe2O3 is 30 to 40%.

8. The preparation method of enhancing cement by using waste plastic gasification red mud co-catalysis to prepare a cement enhancer according to claim 5, characterized in that, The plastic is one kind of polyolefin plastics, and the mass ratio of plastic to red mud is 1:2 to 4:

1.

9. The preparation method of enhancing cement by using waste plastic gasification red mud co-catalysis to prepare a cement enhancer according to claim 5, characterized in that The plastic pyrolysis is heated from room temperature to 500 to 600°C at a rate of 10 to 20°C / min and kept warm for 10 to 15 minutes; the temperature of the catalytic section is 750 to 850°C.

10. A cement prepared by the method for preparing cement enhanced by using a waste plastic gasification red mud co-catalyst to prepare a cement enhancer as described in any one of claims 1-9, wherein the compressive strength of the cement is 52.76 to 63.32 MPa.

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