A red mud-based nanometer flame retardant, a preparation method and application thereof

Abstract

This invention belongs to the field of flame retardant technology, specifically relating to a red mud-based nano-flame retardant, its preparation method, and its application. The invention involves mixing red mud with a carbon-containing reducing agent and subjecting it to reduction roasting. Iron oxides in the red mud are reduced to metallic iron. Then, the metallic iron is dissociated through crushing and grinding. Magnetic separation is then used to separate the magnetic product (metallic iron) and the non-magnetic product (aluminum-rich slag, mainly containing alumina). The aluminum-rich slag, magnesium additives, and water undergo a mechanochemical reaction in a CO2 atmosphere. Under mechanochemical action, the alumina in the aluminum-rich slag and the magnesium in the magnesium additives react with water and carbon dioxide to form magnesium aluminum carbonate-type hydrotalcite, resulting in a red mud-based nano-flame retardant containing hydrotalcite components.

Description

Technical Field

[0001] This invention belongs to the field of flame retardant technology, specifically relating to a red mud-based nano flame retardant, its preparation method, and its application. Background Technology

[0002] Red mud is an industrial solid waste discharged after refining alumina from bauxite. The production of 1 ton of alumina generates 1.0 to 1.8 tons of red mud as a byproduct. Large-scale stockpiling of red mud not only occupies land resources but also severely impacts the surrounding environment. Currently, there are many methods for the comprehensive recycling and utilization of red mud. Research on the utilization of red mud in building materials, road construction materials, and insulation materials has been applied in practice and has achieved certain results. However, the above-mentioned comprehensive utilization methods of red mud also have certain problems. For example, when using red mud to make building materials, the presence of radioactive elements in the red mud requires the addition of other substances to reduce its hazards, increasing production costs. Furthermore, the finished building materials may develop salt seepage and efflorescence on the surface after prolonged storage, affecting strength and performance. Therefore, to better dispose of red mud, it is necessary to study new approaches for its comprehensive recycling and utilization. Summary of the Invention

[0003] In view of this, the purpose of this invention is to provide a red mud-based nano flame retardant, its preparation method and application. The preparation method provided by this invention can not only recover metallic iron from red mud, but also make red mud into a red mud-based nano flame retardant with excellent flame retardant properties, thus realizing the efficient resource conversion and utilization of red mud.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] This invention provides a method for preparing a red mud-based nano flame retardant, comprising the following steps:

[0006] Red mud and a carbon-containing reducing agent are mixed and subjected to reduction roasting to obtain the roasted product;

[0007] The roasted product is sequentially crushed, ground, and magnetically separated to obtain aluminum-rich slag.

[0008] The aluminum-rich slag, magnesium additive, and water are mixed and subjected to a mechanochemical reaction in a CO2 atmosphere to obtain a red mud-based nano flame retardant.

[0009] Preferably, the red mud contains 20-50% Fe2O3, 30-60% Al2O3, 1-10% MgO, and 5-20% SiO2 by mass.

[0010] Preferably, the carbon-containing reducing agent includes one or more of coke, coal and graphite; the mass ratio of the carbon-containing reducing agent to red mud is (3-8):100.

[0011] Preferably, the reduction calcination temperature is 1100–1200°C and the time is 30–90 min.

[0012] Preferably, the mass of the grinding product with a fineness of ≤0.043mm is 70-80% of the total grinding product mass; the magnetic field strength of the magnetic separation is 800-1200GS.

[0013] Preferably, the magnesium additive includes one or more of MgO, MgCO3 and Mg(OH)2; the mass ratio of the magnesium additive to the aluminum-rich slag is (5-10):100.

[0014] Preferably, the mechanochemical reaction is carried out under ball milling conditions; the ball milling speed is 450-600 rpm; and the ball milling time is 60-120 min.

[0015] Preferably, the volume concentration of CO2 in the CO2 atmosphere is 80-100%.

[0016] The present invention also provides a red mud-based nano flame retardant prepared by the preparation method described above, wherein the red mud-based nano flame retardant comprises magnesium aluminum carbonate type hydrotalcite.

[0017] This invention also provides the application of the red mud-based nano flame retardant described in the above technical solution in the field of flame retardancy.

[0018] This invention provides a method for preparing a red mud-based nano flame retardant, comprising the following steps: mixing red mud and a carbon-containing reducing agent, and performing reduction roasting to obtain a roasted product; sequentially crushing, grinding, and magnetically separating the roasted product to obtain aluminum-rich slag; mixing the aluminum-rich slag, magnesium additive, and water, and performing a mechanochemical reaction in a CO2 atmosphere to obtain the red mud-based nano flame retardant.

[0019] The mechanochemical treatment in this invention exposes Al on the surface of the aluminum-rich slag. 3+ Magnesium-containing reagents have exposed Mg on their surface. 2+ With the addition of water and CO2, a chemical reaction occurs under mechanochemical action, ultimately producing magnesium aluminum carbonate type hydrotalcite; the preparation process of the magnesium aluminum carbonate type hydrotalcite involves the following chemical transformations:

[0020]

[0021] This invention involves mixing red mud with a carbon-containing reducing agent and then subjecting it to reduction roasting to reduce iron oxides in the red mud to metallic iron. The metallic iron is then dissociated through crushing and grinding, and a non-magnetic product, alumina-rich slag (mainly composed of alumina), is obtained through magnetic separation. The alumina-rich slag, magnesium additives, and water undergo a mechanochemical reaction in a CO2 atmosphere. Under this mechanochemical action, the alumina-rich slag and magnesium additives undergo physical changes such as splitting, breaking, deformation, and volume refinement. Furthermore, the particle size gradually decreases and the specific surface area continuously increases under mechanical action, resulting in energy conversion and the generation of atomic groups and excited electrons. This activates the alumina in the alumina-rich slag and the magnesium in the magnesium additives, causing the alumina and magnesium to react with water and carbon dioxide to form magnesium aluminum carbonate-type hydrotalcite, yielding a red mud-based nano-flame retardant containing hydrotalcite components. Hydrotalcite contains bicarbonate ions, which decompose upon heating in a fire, releasing carbon dioxide and water, thus blocking air and reducing heat, achieving flame retardancy. Moreover, the magnesium oxide and alumina contained in hydrotalcite are non-combustible materials and also contribute to flame retardancy. This invention not only recovers metallic iron from red mud but also transforms it into a red mud-based nano-flame retardant with excellent flame-retardant properties, achieving efficient resource conversion and utilization of industrial solid waste red mud. Furthermore, the raw material components are refined through a mechanochemical process, enabling the nanoscale preparation of the red mud-based flame retardant. Moreover, the prepared red mud-based nano-flame retardant is a halogen-free, environmentally friendly flame retardant with excellent flame-retardant effects and good compatibility with polymer materials. Attached Figure Description

[0022] Figure 1 This is a flowchart of the preparation method of the red mud-based nano flame retardant in this invention;

[0023] Figure 2 XRD pattern of the red mud-based nano flame retardant prepared in Example 2;

[0024] Figure 3 The image shows the XRD pattern of the red mud used in Example 2.

[0025] Figure 4 The image shows the XRD pattern of magnesium aluminum carbonate hydrotalcite. Detailed Implementation

[0026] This invention provides a method for preparing a red mud-based nano flame retardant, comprising the following steps:

[0027] Red mud and a carbon-containing reducing agent are mixed and subjected to reduction roasting to obtain the roasted product;

[0028] The roasted product is sequentially crushed, ground, and magnetically separated to obtain aluminum-rich slag.

[0029] The aluminum-rich slag, magnesium additive, and water are mixed and subjected to a mechanochemical reaction in a CO2 atmosphere to obtain a red mud-based nano flame retardant.

[0030] Unless otherwise specified, the present invention does not have special requirements on the source of the raw materials used in the preparation, and commercially available products well known to those skilled in the art can be used.

[0031] This invention involves mixing red mud with a carbon-containing reducing agent and then subjecting it to reduction roasting to obtain the roasted product.

[0032] In this invention, the mass percentage of Fe2O3 in the red mud is preferably 20-50%, more preferably 20-40%, the mass percentage of Al2O3 is preferably 30-60%, more preferably 30-58%, the mass percentage of MgO is preferably 1-10%, more preferably 1-5%, and the mass percentage of SiO2 is preferably 5-20%, more preferably 10-15%.

[0033] Before mixing the red mud and the carbon-containing reducing agent, the present invention preferably washes, filters, and dries the red mud sequentially. In the present invention, the washing is preferably water washing; the washing is preferably performed until the washed red mud is neutral as measured by pH test paper; the drying method is preferably oven drying; the drying temperature is preferably 50–80°C, more preferably 50–70°C, and the drying time is preferably 30–120 min, more preferably 30–100 min. The present invention does not specifically limit the filtration process; a filtration process well known in the art can be used.

[0034] In this invention, the carbon-containing reducing agent preferably includes one or more of coke, coal, and graphite, more preferably coke, coal, or graphite; the mass ratio of the carbon-containing reducing agent to red mud is preferably (3-8):100, more preferably (3-5):100. This invention does not impose any particular limitation on the mixing process of the red mud and the carbon-containing reducing agent; a mixing process well-known in the art can be used to ensure uniform mixing of the materials.

[0035] In this invention, the equipment for reduction roasting is preferably a clay crucible and a muffle furnace; the temperature for reduction roasting is preferably 1100-1200℃, more preferably 1100-1150℃, and the time is preferably 30-90 min, more preferably 30-70 min; the reduction roasting process preferably involves placing the mixed material into a clay crucible and then placing it in a muffle furnace for roasting; after reduction roasting is completed, the clay crucible is preferably removed from the muffle furnace, allowed to cool naturally, and then the roasted product is removed from the clay crucible.

[0036] After obtaining the roasted product, the present invention sequentially crushes, grinds and magnetically separates the roasted product to obtain metallic iron and aluminum-rich slag.

[0037] The present invention involves crushing the roasted product to obtain the crushed roasted product.

[0038] The present invention does not specifically limit the crushing process; any crushing process well known in the art can be used.

[0039] After obtaining the crushed roasted product, the present invention grinds the crushed roasted product to obtain the ground roasted product.

[0040] Preferably, the mass of the grinding product with a fineness ≤0.043mm is 70-80% of the total grinding product mass, more preferably 71-79%; the grinding process preferably involves mixing the crushed roasted product with water to obtain grinding feed; grinding the grinding feed; the mass percentage of the crushed roasted product in the grinding feed is preferably 50-60%, more preferably 50-55%; the grinding time is preferably 15 minutes.

[0041] After obtaining the roasted product after grinding, the present invention performs magnetic separation on the roasted product after grinding to obtain magnetic products of metallic iron and non-magnetic products.

[0042] In this invention, the magnetic field strength of the magnetic separation is preferably 800-1200 GS, more preferably 800-1000 GS; the magnetic separation device is preferably a magnetic separator tube.

[0043] The present invention preferably involves filtering and drying the non-magnetic product sequentially to obtain aluminum-rich slag.

[0044] The present invention does not impose any particular limitation on the filtration process; any filtration process well known in the art can be used.

[0045] In this invention, the drying method is preferably oven drying; the drying temperature is preferably 50-80°C, more preferably 50-70°C, and the drying time is preferably 30-120 min, more preferably 30-100 min.

[0046] After obtaining the aluminum-rich slag, the present invention mixes the aluminum-rich slag, magnesium additive and water, and carries out a mechanochemical reaction in a CO2 atmosphere to obtain a red mud-based nano flame retardant.

[0047] In this invention, the magnesium additive preferably includes one or more of MgO, MgCO3, and Mg(OH)2, more preferably MgO, MgCO3, or Mg(OH)2; the mass ratio of the magnesium additive to the aluminum-rich slag is preferably (5-10):100, more preferably (5-8):100; the mass ratio of the water to the aluminum-rich slag is preferably (2-8):100, more preferably (2-6):100. This invention does not impose any particular limitation on the mixing process of the aluminum-rich slag, magnesium additive, and water; a mixing process well-known in the art can be used to ensure uniform mixing of the materials.

[0048] In this invention, the mechanochemical reaction is preferably carried out under ball milling conditions; the ball milling speed is preferably 450-600 rpm, more preferably 450-550 rpm; the ball milling time is preferably 60-120 min, more preferably 60-100 min; the ball milling is preferably carried out in a CO2 atmosphere; the volume concentration of CO2 in the CO2 atmosphere is preferably 80-100%, more preferably 80-90%.

[0049] In this invention, the ball milling equipment is preferably a planetary ball mill and grinding balls; the grinding balls are preferably made of zirconium oxide; the diameter of the grinding balls is preferably 3-15 mm, more preferably 3 mm, 10 mm and 15 mm, and the mass ratio of the 3 mm, 10 mm and 15 mm grinding balls is preferably 4:2:4; the mass ratio of the grinding balls to the material obtained by mixing aluminum-rich slag, magnesium additives and water is preferably (5-10):1, more preferably (5-8):1; the ball milling is preferably carried out by alternating forward and reverse rotation; the ball milling method is preferably intermittent ball milling; the intermittent ball milling is preferably stopped for 0.5-2 minutes after each 3-5 minute milling.

[0050] After the mechanochemical reaction is completed, the present invention preferably centrifuges and dries the mechanochemical reaction products sequentially; the centrifugation equipment is preferably a centrifuge; the centrifugation speed is preferably 3000-6000 rpm, more preferably 4000-6000 rpm; the centrifugation time is preferably 4-8 min, more preferably 5-8 min; the drying temperature is preferably 60-70℃, more preferably 60-65℃; the drying time is preferably 35-60 min, more preferably 35-50 min.

[0051] Mechanochemistry utilizes mechanical force to generate numerous lattice defects, dislocations, and vacancies, inducing structural changes, altering reactivity, and triggering chemical reactions that cannot occur under normal conditions. Mechanical force can enhance the activity of solids. Generally, mechanochemical processes generate lattice defects or distortions, increasing specific surface area and newly formed surfaces after pulverization, producing atomic groups and externally excited electrons (on the surfaces of metals and metal oxides), thereby activating solid materials and increasing their reactivity. For inorganic materials, due to their brittle nature, the small particle size during mechanical pulverization easily leads to lattice distortion and collapse. The surface crystal structure is severely disrupted, forming an amorphous layer. As the activation process progresses, the entire inorganic particle gradually becomes amorphous, increasing its solubility, decreasing its density, and enhancing its ion exchange capacity and surface adsorption capacity. Mechanical activation is an effective way to improve inorganic materials and prepare composite inorganic materials. Under mechanochemical action, aluminum-rich slag and magnesium additives undergo physical changes such as splitting, breaking, deformation, and volume refinement. Moreover, under mechanical action, the particle size gradually decreases and the specific surface area continuously increases, resulting in energy conversion. This generates atomic groups and externally excited electrons, which activate the alumina in the aluminum-rich slag and the magnesium in the magnesium additives. As a result, the alumina and magnesium react with water and carbon dioxide to form magnesium aluminum carbonate type hydrotalcite, yielding a red mud-based nano flame retardant containing hydrotalcite components.

[0052] The present invention also provides a red mud-based nano flame retardant prepared by the preparation method described above, wherein the red mud-based nano flame retardant comprises magnesium aluminum carbonate type hydrotalcite.

[0053] In this invention, the content of magnesium aluminum carbonate hydrotalcite in the red mud-based nano flame retardant is preferably 30-85%, more preferably 40-83%; the particle size of the red mud-based nano flame retardant is preferably ≤100nm.

[0054] Hydrotalcite contains bicarbonate ions, which can decompose when heated in a fire to release carbon dioxide and water, blocking air and reducing heat, thus achieving the purpose of flame retardancy. Moreover, hydrotalcite contains high levels of magnesium oxide and aluminum oxide, which are non-combustible materials and can also play a role in flame retardancy.

[0055] This invention also provides the application of the red mud-based nano flame retardant described above in the field of flame retardancy. This invention does not impose any particular limitation on the application method of the red mud-based nano flame retardant in flame retardancy; any application method well-known in the art can be used.

[0056] Figure 1 This is a flowchart illustrating the preparation method of the red mud-based nano flame retardant in this invention. Figure 1As shown, the present invention obtains neutral red mud by irrigating and drying red mud, then mixes it evenly with a reducing agent and performs reduction roasting, followed by crushing, grinding and magnetic separation to obtain metallic iron and aluminum-rich slag. The aluminum-rich slag, magnesium-containing reagent and water are mixed and subjected to mechanochemical reaction in CO2 atmosphere, centrifuged and dried to obtain nanocomposite flame retardant.

[0057] This invention not only recovers metallic iron from red mud, but also produces red mud-based nano flame retardants with excellent flame retardant properties, realizing the efficient resource conversion and utilization of industrial solid waste red mud.

[0058] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments thereof.

[0059] Example 1

[0060] 30g of red mud (containing 29.45% Fe2O3, 41.27% Al2O3, 4.88% MgO, and 18.93% SiO2) was washed with water. After pH testing, the washed red mud was found to be neutral. It was then filtered and dried at 50℃ for 120min to obtain 23.57g of dried red mud. The dried red mud was then mixed evenly with 4% (by weight) of anthracite coal, placed in a clay crucible, and then subjected to reduction in a muffle furnace at 1150℃. The initial roasting time was 60 minutes. After roasting, the crucible was removed from the muffle furnace and allowed to cool naturally. The roasted product was then removed from the crucible and crushed. The crushed roasted product was mixed with water to obtain a grinding feed (the grinding feed contained 50% by mass of the crushed roasted product). Grinding was performed for 15 minutes until the mass content of the grinding product with a fineness ≤0.043mm was 79%. Magnetic separation was then performed using a magnetic separator at 900GS to obtain magnetic products. The product is a mixture of metallic iron and non-magnetic products. The non-magnetic product is filtered and dried at 50℃ for 120 min to obtain aluminum-rich slag. The aluminum-rich slag, 5% MgO (by mass of the aluminum-rich slag), and 4% water (by mass of the aluminum-rich slag) are then mixed evenly and placed in a planetary ball mill containing 3-15 mm (3 mm, 10 mm, and 15 mm grinding balls in a mass ratio of 4:2:4) (the mass ratio of the grinding balls to the mixture of aluminum-rich slag, magnesium additives, and water is 8:1). The mixture is ball-milled at 500 rpm for 70 min, using intermittent ball milling with alternating forward and reverse rotation. The milling process involves 3 min of grinding followed by a 1 min stop, and CO2 gas is introduced during the milling process. After the milling is completed, the mixture is centrifuged at 6000 rpm for 4 min and then dried at 60℃ for 35 min to obtain a red mud-based nano flame retardant (67% by mass of magnesium aluminum carbonate type hydrotalcite with a particle size ≤100 nm).

[0061] Example 2

[0062] 30g of red mud (containing 20.14% Fe2O3, 55.87% Al2O3, 9.16% MgO, and 10.22% SiO2) was washed with water. After pH testing, the washed red mud was found to be neutral. It was then filtered and dried at 65℃ for 60 min to obtain 23.09g of dried red mud. The dried red mud was then mixed evenly with 3% graphite by weight and placed in a clay crucible. The mixture was then placed in a muffle furnace and reduced-calcined at 1200℃ for 30 min. After roasting, remove the crucible from the muffle furnace and allow it to cool naturally. Then, remove the roasted product from the crucible and crush it. Mix the crushed roasted product with water to obtain a grinding feed (the grinding feed contains 55% crushed roasted product by mass). Grind the feed for 15 minutes until the mass content of the grinding product with a fineness ≤0.043mm is 79%. Perform magnetic separation at 800GS using a magnetic separator to obtain magnetic iron and non-magnetic products. Non-magnetic products are filtered and dried at 65℃ for 60 min to obtain aluminum-rich slag. Then, the aluminum-rich slag, 5% Mg(OH)2 (by mass of the aluminum-rich slag), and 8% water (by mass of the aluminum-rich slag) are mixed evenly and placed into a planetary ball mill containing 3-15 mm (3 mm, 10 mm, and 15 mm grinding balls in a mass ratio of 4:2:4) (the mass ratio of the grinding balls to the mixture of aluminum-rich slag, magnesium additives, and water is 5:1). The mixture is ball-milled at 600 rpm for 60 min, using intermittent ball milling with alternating forward and reverse rotation. After each 3 min of ball milling, the mixture is stopped for 0.5 min. CO2 gas (with a volume concentration of 90%) is introduced during the ball milling process. After the ball milling is completed, the mixture is centrifuged at 3000 rpm for 8 min and then dried at 70℃ for 35 min to obtain a red mud-based nano flame retardant (magnesium aluminum carbonate type hydrotalcite with a mass percentage of 83% and a particle size ≤100 nm).

[0063] Example 3

[0064] 30g of red mud (containing 48.89% Fe2O3, 30.55% Al2O3, 1.89% MgO, and 6.74% SiO2) was washed with water. After pH testing, the washed red mud was found to be neutral. It was then filtered and dried at 80℃ for 30 minutes to obtain 31.28g of dried red mud. The dried red mud was then mixed evenly with 8% coke by weight of the red mud, placed in a clay crucible, and then placed in a muffle furnace for reduction roasting at 1100℃ for 90 minutes. After roasting, the crucible is removed from the muffle furnace and allowed to cool naturally. The roasted product is then removed from the crucible and crushed. The crushed roasted product is mixed with water to obtain grinding feed (the grinding feed contains 60% crushed roasted product by mass). Grinding is performed for 15 minutes until the mass content of the grinding product with a fineness ≤0.043mm is 71%. Magnetic separation is then performed using a magnetic separator at 1200GS to obtain magnetic products (iron metal) and non-magnetic products. The non-magnetic product was filtered and dried at 80℃ for 30 min to obtain aluminum-rich slag. Then, the aluminum-rich slag, 10% MgCO3 (by mass of the aluminum-rich slag), and 2% water (by mass of the aluminum-rich slag) were mixed evenly and placed into a planetary ball mill containing 3-15 mm (3 mm, 10 mm, and 15 mm grinding balls in a mass ratio of 4:2:4) (the mass ratio of the grinding balls to the mixture of aluminum-rich slag, magnesium additives, and water was 10:1). The mixture was ball-milled at 450 rpm for 120 min, using intermittent ball milling with alternating forward and reverse rotation. The milling process involved 4 min of ball milling followed by a 2 min stop. CO2 gas (80% by volume) was introduced during the ball milling process. After the ball milling was completed, the mixture was centrifuged at 6000 rpm for 4 min and then dried at 65℃ for 60 min to obtain a red mud-based nano flame retardant (41% by mass of magnesium aluminum carbonate type hydrotalcite with a particle size ≤100 nm).

[0065] Comparative Example 1

[0066] Pure ethylene-vinyl acetate copolymer without added flame retardants was used as Comparative Example 1.

[0067] Comparative Example 2

[0068] A composite material made of red mud and ethylene-vinyl acetate copolymer is used as a flame retardant material, wherein the percentage of red mud is 50%.

[0069] Performance testing

[0070] (1) The red mud-based nano-flame retardant prepared in Example 2 was characterized by XRD, and the results are as follows: Figure 2 As shown. Figure 3 XRD pattern of red mud. Figure 4 The image shows the XRD pattern of pure magnesium aluminum carbonate type hydrotalcite (LDHs).

[0071] Depend on Figure 2 It can be seen that the XRD pattern of the red mud-based nano-flame retardant prepared by the method provided in this invention is significantly different from that of the original red mud. The main components of the original red mud are SiO2, Al2O3, Al(OH)3, and Fe2O3, etc. The red mud-based nano-flame retardant prepared by the method provided in this invention mainly shows the diffraction peaks of LDHs, and is similar to... Figure 4 Compared to pure LDHs, the results are essentially similar. This demonstrates that the preparation method of this invention can yield a red mud-based nano-flame retardant containing magnesium aluminum carbonate type hydrotalcite.

[0072] (2) To test the flame-retardant effect of the red mud-based nano flame retardant obtained in each embodiment, it was prepared into a flame-retardant composite material with ethylene-vinyl acetate copolymer (the percentage of red mud-based nano flame retardant was 50%). The specific preparation method of the composite material was as follows: an appropriate amount of ethylene-vinyl acetate material was placed in a mixer and mixed at 130°C and 35 r / min. After it was completely melted, an equal mass of red mud-based nano flame retardant was added to the mixer and mixed for 18 min. The composite material obtained by the mixer was placed in the mold of a tablet press and hot-pressed at 130°C and 15 MPa for 15 min. Then, it was cold-pressed for 5 min under the same pressure. The sample was then cut into a cone-shaped calorimeter for experimental testing. The size was 100 mm × 100 mm square with a thickness of 10 mm. In addition, the pure ethylene-vinyl acetate copolymer, the composite material prepared by ethylene-vinyl acetate and red mud were used as comparative examples. The flame retardant properties of the flame retardant materials of Examples 1-3 and Comparative Examples 1-2 were tested using a Stanton Redcroft cone calorimeter according to ISO 5660 standard (including ignition time, average heat release rate (AHRR), peak heat release rate (PHRR), total heat release (THR), and burning time). The test results are shown in Table 1.

[0073] Table 1. Flame retardant properties of flame retardant materials in Examples 1-3 and Comparative Examples 1-2

[0074]

[0075] As shown in Table 1, the red mud-based nano flame retardant prepared in this invention has a longer ignition time, a lower average heat release rate, a lower peak heat release and total heat release, and a longer combustion time compared to the composite material prepared from pure ethylene-vinyl acetate copolymer and red mud and ethylene-vinyl acetate copolymer. This indicates that the red mud-based nano flame retardant prepared in this invention has superior flame retardant properties.

[0076] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a red mud-based nano flame retardant, characterized in that, Includes the following steps: Red mud and a carbon-containing reducing agent are mixed and subjected to reduction roasting to obtain the roasted product; The red mud contains 20-50% Fe2O3, 30-60% Al2O3, 1-10% MgO, and 5-20% SiO2 by mass. The roasted product is sequentially crushed, ground, and magnetically separated to obtain aluminum-rich slag. The aluminum-rich slag, magnesium additive and water are mixed and subjected to a mechanochemical reaction in a CO2 atmosphere to obtain a red mud-based nano flame retardant. The magnesium additive includes one or more of MgO, MgCO3 and Mg(OH)2; the mass ratio of the magnesium additive to the aluminum-rich slag is (5-10):100; the mass ratio of the water to the aluminum-rich slag is (2-8):

100. The mechanochemical reaction is carried out under ball milling conditions; the ball milling speed is 450-600 rpm; the ball milling time is 60-120 min.

2. The preparation method according to claim 1, characterized in that, The carbon-containing reducing agent includes one or more of coke, coal and graphite; the mass ratio of the carbon-containing reducing agent to red mud is (3-8):

100.

3. The preparation method according to claim 1, characterized in that, The reduction calcination temperature is 1100–1200℃, and the time is 30–90 min.

4. The preparation method according to claim 1, characterized in that, The mass of the grinding product with a fineness of ≤0.043mm is 70-80% of the total grinding product mass; the magnetic field strength of the magnetic separation is 800-1200GS.

5. The preparation method according to claim 1, characterized in that, The volume concentration of CO2 in the CO2 atmosphere is 80-100%.

6. The red mud-based nano-flame retardant prepared by the preparation method according to any one of claims 1 to 5, characterized in that, The red mud-based nano flame retardant comprises magnesium aluminum carbonate-type hydrotalcite.

7. The application of the red mud-based nano flame retardant according to claim 6 in the field of flame retardancy.

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