Preparation method of lime-free molybdenum tailings autoclaved aerated concrete

Abstract

The present invention discloses a method for preparing lime-free molybdenum tailings autoclaved aerated concrete. The raw materials of the autoclaved aerated concrete include 100-150 parts of molybdenum tailings, 40-60 parts of water-quenched slag, 30-50 parts of cement, 5-10 parts of waste slurry, 8-15 parts of gypsum, 2-6 parts of aluminum paste, 0.1-0.5 parts of water reducer, 0.5-1 parts of modifier, 0.5-1 parts of admixture, and 200-250 parts of water. The present invention uses molybdenum tailings and water-quenched slag instead of traditional siliceous materials such as river sand and fly ash to prepare autoclaved aerated concrete. This can solve the environmental problems caused by the storage of molybdenum tailings and realize the transformation of waste into treasure. At the same time, the water-quenched slag is rationally utilized to reduce production costs, which has a positive effect on the sustainable development of society. The prepared autoclaved aerated concrete has good water resistance, oil resistance, and compressive strength. At the same time, it has good resistance to seawater corrosion and can be used in marine environments.

Description

Technical Field

[0001] The invention relates to the technical field of autoclaved aerated concrete, in particular to a preparation method of lime-free molybdenum tailings autoclaved aerated concrete. Background Art

[0002] Autoclaved aerated concrete (AAC) is a lightweight, high-strength building material with excellent thermal and sound insulation properties. Due to its excellent performance, environmental friendliness, and affordability, it is widely used in the construction industry. It is a porous concrete product made from fly ash, lime, cement, gypsum, and slag as its primary raw materials, along with appropriate modifiers. The concrete is then batched, mixed, poured, allowed to stand, cut, and then autoclaved to create a porous concrete product. Compared to conventional concrete, AAC exhibits extremely low thermal conductivity, high compressive and flexural strength, and a very low weight. AAC can be made from a wide variety of raw materials, including industrial waste materials such as fly ash and slag.

[0003] Molybdenum tailings are a type of waste generated during the molybdenum mining process, typically consisting of residues, waste rock, and dust remaining after beneficiation. These tailings still contain a certain amount of molybdenum and other valuable metallic elements, but due to their low grade, they are no longer worth mining. This has led to mountains of molybdenum tailings, which not only occupy large amounts of land but also pollute and damage the environment. Their resource utilization urgently needs to be addressed. Molybdenum tailings are a silicon-containing solid waste that can be used as a siliceous raw material for autoclaved aerated concrete. Furthermore, the presence of certain metallic elements in molybdenum tailings can chemically react with certain components of cement, improving the concrete's performance and further enhancing its strength and durability.

[0004] CN106242613A discloses a molybdenum tailings and Yellow River sand autoclaved aerated concrete and its preparation method. The aerated concrete is made from dry materials and auxiliary materials, wherein the dry materials are composed of molybdenum tailings, Yellow River sand, construction waste, cement, quicklime, desulfurized gypsum, and waste. The aerated concrete uses solid waste—molybdenum tailings, construction waste, and inexpensive Yellow River sand—as its primary siliceous raw materials. This not only addresses the environmental issues caused by molybdenum tailings storage, but also produces concrete blocks with excellent physical and mechanical properties and durability, meeting national standards.

[0005] CN114455975A discloses a method for producing autoclaved aerated concrete products using molybdenum tailings slurry. Using molybdenum tailings, cement, lime, gypsum, and admixtures as raw materials, autoclaved aerated concrete blocks are produced. This invention uses molybdenum tailings slurry in place of traditional siliceous materials such as river sand and fly ash to produce autoclaved aerated concrete products. This allows for the processing and utilization of large quantities of molybdenum tailings slurry, addressing issues such as molybdenum tailings occupying land and polluting the environment. Summary of the Invention

[0006] This invention provides limeless molybdenum tailings autoclaved aerated concrete and its preparation method. Using molybdenum tailings and water-quenched slag as siliceous materials, this method addresses the land occupation and environmental pollution problems associated with molybdenum tailings. Furthermore, the rational use of water-quenched slag not only reduces production costs but also enables waste resource recycling. The resulting autoclaved aerated concrete exhibits excellent water and oil resistance, compressive strength, and good seawater corrosion resistance, making it suitable for use in marine environments.

[0007] One of the objects of the present invention is to provide a method for preparing lime-free molybdenum tailings autoclaved aerated concrete, which comprises the following steps:

[0008] (1) Grinding the molybdenum tailings and water-quenched slag into powder respectively;

[0009] (2) adding water to the molybdenum tailings and water-quenched slag powder ground in step (1), mixing and stirring, adding gypsum and waste slurry during the stirring process to obtain a mixed material, which is set aside;

[0010] (3) Cement, water reducing agent and modifier are added to the mixture obtained in step (2) and stirred to mix evenly, and then aluminum powder paste is added and stirred evenly for pouring. After pouring, the mixture is sent to a static curing room for static curing to thicken.

[0011] (4) After static curing, demoulding and cutting are carried out to obtain the green body of required specifications and sizes; the green body is then transferred to an autoclave for steam curing; after being taken out of the autoclave, it is inspected, packaged and stored, and naturally cured for 28 days to obtain the finished product of lime-molybdenum tailings autoclaved aerated concrete.

[0012] Preferably, the weight ratio of each raw material component is:

[0013] 100-150 parts of molybdenum tailings, 40-60 parts of water-quenched slag, 30-50 parts of cement, 5-10 parts of waste slurry, 8-15 parts of gypsum, 2-6 parts of aluminum powder paste, 0.1-0.5 parts of water reducer, 0.5-1 parts of modifier and 200-250 parts of water.

[0014] Preferably, in step (1), the molybdenum tailings and the water-quenched slag are respectively ground into powders with a 0.1 mm square hole sieve residue of no more than 15%;

[0015] Preferably, in step (2), the stirring temperature is 35-45° C., the stirring rate is 100-150 r / min, and the stirring time is 3-6 h.

[0016] Preferably, in step (3), the stirring temperature is 40-50° C., and the stirring rate is 600-800 r / min; the aluminum powder paste is added and stirred for 3-5 minutes before pouring, and after pouring, the mixture is sent to a static curing room for static curing. The static curing temperature is 40-50° C., the humidity is 50-70%, and the curing time is 3-5 hours.

[0017] Preferably, the water reducer in step (3) is a naphthalene-based high-efficiency water reducer powder; and the modifier is selected from at least one of stearic acid, 19-fluorodecanoic acid, perfluorooctanoic acid, and perfluorododecanoic acid.

[0018] More preferably, the modifier is prepared by mixing stearic acid and nonadecafluorodecanoic acid in a mass ratio of 2:3.

[0019] Preferably, the autoclave curing time in step (4) is 8 to 10 hours, the internal temperature of the autoclave is 185 to 195° C., and the pressure is 1.2 to 1.3 MPa.

[0020] Further preferably, step (3) can also be: adding cement, water reducing agent, modifier, and admixture to the mixture obtained in step (2) and stirring and mixing, then adding aluminum powder paste and stirring and mixing until uniform, then pouring, and after pouring, sending it to a quiescent chamber for quiescent curing to thicken it. More specifically, adding cement, water reducing agent, mixed modifier, and Ca-SLS-LDH nanocomposite material to the mixture obtained in step (2) at a stirring temperature of 40-50°C and a stirring rate of 600-800 r / min and stirring and mixing, then adding aluminum powder paste and stirring for 3-5 minutes until uniform, then pouring, and after pouring, sending it to a quiescent chamber for quiescent curing at a temperature of 40-50°C and a humidity of 50-70% for 3-5 hours to thicken it.

[0021] Further preferably, the weight ratio of each raw material component is:

[0022] 100-150 parts of molybdenum tailings, 40-60 parts of water-quenched slag, 30-50 parts of cement, 5-10 parts of waste slurry, 8-15 parts of gypsum, 2-6 parts of aluminum powder paste, 0.1-0.5 parts of water reducer, 0.5-1 parts of modifier, 0.5-1 parts of admixture and 200-250 parts of water.

[0023] The admixture is a Ca-SLS-LDH nanocomposite material.

[0024] Further preferably, the preparation method of the Ca-SLS-LDH nanocomposite material is as follows: Ca(NO3)2·4H2O and Al(NO3)3·9H2O are added to boiling water, mixed and stirred to obtain solution A; NaNO3 and NaOH are added to boiling water, mixed and stirred to obtain solution B; solution A and solution B are ultrasonically dispersed respectively, and the ultrasonicated solution A and solution B are evenly mixed with sodium lignin sulfonate to obtain a mixed solution; the mixed solution is vigorously stirred in a water bath to obtain a suspension; the suspension is directly transferred to a hydrothermal reactor and aged at high temperature to obtain a precipitate; after deep filtering the precipitate, it is washed with boiled water, and the washed precipitate is placed in a vacuum oven and dried at high temperature to obtain a dry powder, i.e., the Ca-SLS-LDH nanocomposite material.

[0025] Specifically, the preparation method of the Ca-SLS-LDH nanocomposite material is as follows: 25.6g Ca(NO3)2·4H2O and 18.75g Al(NO3)39H2O are added to 200mL boiling water, mixed and stirred to obtain solution A; 17g NaNO3 and 12g NaOH was added to 100 mL of boiling water, and the mixture was stirred to obtain solution B; solution A and solution B were ultrasonically dispersed for 15 to 25 minutes respectively, and the ultrasonicated solution A and solution B were evenly mixed with 1 g of sodium lignin sulfonate to obtain a mixed solution; the mixed solution was vigorously stirred in a water bath at 60 to 65° C. for 30 to 50 minutes to obtain a suspension; the suspension was directly transferred to a hydrothermal reactor and aged at 100 to 120° C. for 20 to 24 hours to obtain a precipitate; the precipitate was deep filtered and washed with boiled water, and the washed precipitate was placed in a vacuum oven at 80 to 90° C. and dried for 20 to 24 hours to obtain a dry powder, i.e., a Ca-SLS-LDH nanocomposite material.

[0026] The second object of the present invention is to provide a lime-free molybdenum tailings autoclaved aerated concrete prepared by the above method.

[0027] Beneficial effects of the present invention:

[0028] 1. Compared with the prior art, the present invention introduces a modifier composed of a mixture of stearic acid and nonadecafluorodecanoic acid into concrete to modify the concrete. The low surface energy CH and CF groups contained in the stearic acid and nonadecafluorodecanoic acid are grafted onto the -OH groups on the concrete surface to form hydrophobic and oleophobic chains. At the same time, the hydration product calcium hydroxide can react with the stearic acid and nonadecafluorodecanoic acid to produce a product with long hydrophobic and oleophobic chains, which creates hydrophobic and oleophobic properties on the concrete surface, thereby reducing the surface free energy of the concrete. In addition, the strong repulsive effect of the CH and CF groups promotes the accumulation of fluorine-containing groups with low surface free energy on the concrete surface, resulting in the modified autoclaved aerated concrete exhibiting superhydrophobic and oleophobic properties. At the same time, because concrete is unsaturated during use, the entry of water and corrosive ions is mainly controlled by capillary tension. The addition of the modifier reduces the surface tension of the concrete pore structure, making the concrete pore structure denser and reducing pores and cracks. This constitutes a barrier to the penetration of water and corrosive ions. Therefore, water and corrosive ions cannot come into contact with the concrete, reducing corrosion to the concrete. The modifier composed of a mixture of stearic acid and 19-fluorodecanoic acid can react with the calcium hydroxide in the concrete. At the same time, due to the introduction of Ca-SLS-LDH, it enables them to better react with the minerals in the concrete, forming more stable calcium soap crystals, thereby improving the pore structure of the concrete and enhancing the concrete's resistance to seawater corrosion.

[0029] 2. The present invention prepares autoclaved aerated concrete, introduces a modifier composed of a mixture of stearic acid and 19-fluorodecanoic acid to modify the concrete, and also introduces a Ca-SLS-LDH nanocomposite material, which greatly improves the situation in which the compressive strength of the concrete is reduced due to the addition of the modifier, so that the prepared autoclaved aerated concrete not only has good water resistance, oil resistance and seawater corrosion resistance, but also has good compressive resistance. Since the CF group and CH group in the modifier have low surface free energy, the hydration reaction between cement and water is hindered, resulting in a reduction in the compressive strength of the concrete. The present invention introduces the Ca-SLS-LDH nanocomposite material, which contains hydroxide ions in its layered structure and has a high interlayer ion exchange capacity, and can be well exchanged with calcium ions in cement. This exchange releases more calcium ions, thereby accelerating the hydration reaction of the cement. At the same time, Ca-SLS-LDH has a high specific surface area and large interlayer distance, which enables them to better react with minerals such as silicates and aluminates in concrete to generate hydration products with high strength and durability. These hydration products can fill the pores in the concrete, increase the density and strength of the concrete, and make the prepared autoclaved aerated concrete have better compressive strength.

[0030] 3. The present invention uses molybdenum tailings and water-quenched slag as raw materials, replacing traditional siliceous materials such as river sand and fly ash, to produce autoclaved aerated concrete. This solves the environmental problems caused by molybdenum tailings storage, turning waste into valuable resources. Furthermore, the rational use of water-quenched slag reduces production costs, contributing positively to sustainable social development. The resulting autoclaved aerated concrete exhibits excellent water and oil resistance, compressive strength, and resistance to seawater corrosion, making it suitable for use in marine environments. DETAILED DESCRIPTION

[0031] In the following embodiments, the molybdenum tailings are taken from the Luanchuan molybdenum mining area in Henan Province, and the SiO2 content is about 70%, the Al2O3 content is about 13%, the Fe2O3 content is about 1%, the CaO content is about 6.6%, and the MgO content is about 1.1%, all of which refer to weight percentages;

[0032] The water-quenched slag is taken from Henan Wugang Iron and Steel Company, with a SiO2 content of more than 40%, a CaO content of more than 42%, and a Na2O content of less than 1%;

[0033] The cement is PO 42.5 cement;

[0034] The waste slurry is the waste slurry produced by adding water after cutting waste materials during the production process of autoclaved aerated concrete;

[0035] The aluminum powder paste is passed through a 0.075mm sieve with a sieve residue of no more than 3%;

[0036] Naphthalene-based high-efficiency water-reducing agent powder: brown powder, manufactured by Anhui Shengyuan Chemical Co., Ltd., item number: SY-4.

[0037] Example 1

[0038] A method for preparing lime-free molybdenum tailings autoclaved aerated concrete comprises the following steps:

[0039] (1) Grind 120 kg of molybdenum tailings and 60 kg of water-quenched slag separately until the residue on a 0.1 mm square sieve is no more than 15% of the powder;

[0040] (2) The molybdenum tailings and water-quenched slag ground in step (1) were added with 220 kg of water and stirred at a stirring temperature of 40 ° C. and a stirring rate of 130 r / min for 5 h. During the stirring process, 8 kg of gypsum and 10 kg of waste slurry were added to obtain a mixed material, which was set aside;

[0041] (3) 40 kg of cement and 0.2 kg of naphthalene-based high-efficiency water-reducing agent powder are added to the mixture obtained in step (2) at a stirring temperature of 45 ° C. and a stirring rate of 700 r / min, and then 4 kg of aluminum powder paste is added and stirred for 5 min until the mixture is uniform, and then poured. After pouring, the mixture is sent to a static room at a temperature of 45 ° C. and a humidity of 50% for 5 h to allow it to thicken;

[0042] (4) After static curing, the green body is demoulded and cut to obtain the required specifications and sizes; then the green body is transferred to an autoclave for steam curing, the autoclave curing time is 8 hours, the internal temperature of the autoclave is 190 ° C, and the pressure is 1.2 MPa; after being taken out of the autoclave, it is inspected, packaged and stored, and naturally cured for 28 days to obtain the finished product of lime-molybdenum tailings autoclaved aerated concrete.

[0043] Example 2

[0044] A method for preparing lime-free molybdenum tailings autoclaved aerated concrete comprises the following steps:

[0045] (1) Grind 120 kg of molybdenum tailings and 60 kg of water-quenched slag separately until the residue on a 0.1 mm square sieve is no more than 15% of the powder;

[0046] (2) The molybdenum tailings and water-quenched slag ground in step (1) were added with 220 kg of water and stirred at a stirring temperature of 40 ° C. and a stirring rate of 130 r / min for 5 h. During the stirring process, 8 kg of gypsum and 10 kg of waste slurry were added to obtain a mixed material, which was set aside;

[0047] (3) 40 kg of cement, 0.2 kg of naphthalene-based high-efficiency water-reducing agent powder, and 0.5 kg of modifier are added to the mixture obtained in step (2) at a stirring temperature of 45 ° C. and a stirring rate of 700 r / min, and then 4 kg of aluminum powder paste is added and stirred for 5 min until the mixture is uniform, and then poured. After pouring, the mixture is sent to a static room at a temperature of 45 ° C. and a humidity of 50% for static curing for 5 h to thicken.

[0048] (4) After static curing, the green body is demoulded and cut to obtain the required specifications and sizes; then the green body is transferred to an autoclave for steam curing, the autoclave curing time is 8 hours, the internal temperature of the autoclave is 190 ° C, and the pressure is 1.2 MPa; after being taken out of the autoclave, it is inspected, packaged and stored, and naturally cured for 28 days to obtain the finished product of lime-molybdenum tailings autoclaved aerated concrete.

[0049] The modifier is a mixed modifier, and its preparation method is as follows: 0.4 g of stearic acid and 0.6 g of 19-fluorodecanoic acid are added to 15 mL of anhydrous ethanol, and stirred evenly to form a mixed solution, thereby obtaining the mixed modifier.

[0050] Example 3

[0051] A method for preparing lime-free molybdenum tailings autoclaved aerated concrete is disclosed. The method differs from Example 1 in that the modifier is a mixed modifier. The preparation method comprises the following steps: adding 0.4 g of stearic acid and 0.6 g of perfluorooctanoic acid to 15 mL of anhydrous ethanol, stirring uniformly to form a mixed solution, and obtaining the mixed modifier.

[0052] Example 4

[0053] A method for preparing lime-free molybdenum tailings autoclaved aerated concrete is disclosed, which differs from Example 1 in that the modifier is a mixed modifier. The preparation method comprises the following steps: adding 0.4 g of stearic acid and 0.6 g of perfluorododecanoic acid to 15 mL of anhydrous ethanol, stirring uniformly to form a mixed solution, and obtaining the mixed modifier.

[0054] Example 5

[0055] A method for preparing lime-free molybdenum tailings autoclaved aerated concrete comprises the following steps:

[0056] (1) Grind 120 kg of molybdenum tailings and 60 kg of water-quenched slag separately until the residue on a 0.1 mm square sieve is no more than 15% of the powder;

[0057] (2) The molybdenum tailings and water-quenched slag ground in step (1) were added with 220 kg of water and stirred at a stirring temperature of 40 ° C. and a stirring rate of 130 r / min for 5 h. During the stirring process, 8 kg of gypsum and 10 kg of waste slurry were added to obtain a mixed material, which was set aside;

[0058] (3) 40 kg of cement, 0.2 kg of naphthalene-based high-efficiency water-reducing agent powder, 0.5 kg of modifier, and 0.5 kg of Ca-SLS-LDH nanocomposite material are added to the mixture obtained in step (2) at a stirring temperature of 45 ° C. and a stirring rate of 700 r / min, and then 4 kg of aluminum powder paste is added and stirred for 5 min until the mixture is uniformly stirred, and then poured. After pouring, the mixture is sent to a static room at a temperature of 45 ° C. and a humidity of 50% for static curing for 5 h to thicken it;

[0059] (4) After static curing, the green body is demoulded and cut to obtain the required specifications and sizes; then the green body is transferred to an autoclave for steam curing, the autoclave curing time is 8 hours, the internal temperature of the autoclave is 190 ° C, and the pressure is 1.2 MPa; after being taken out of the autoclave, it is inspected, packaged and stored, and naturally cured for 28 days to obtain the finished product of lime-molybdenum tailings autoclaved aerated concrete.

[0060] The modifier is a mixed modifier, and its preparation method is the same as that of Example 2.

[0061] The preparation method of the Ca-SLS-LDH nanocomposite material is as follows: 25.6g Ca(NO3)2·4H2O and 18.75g Al(NO3)39H2O are added to 200mL of boiling water, mixed and stirred to obtain solution A; 17g NaNO3 and 12g NaOH are added to 100mL of boiling water, mixed and stirred to obtain solution B; solution A and solution B are ultrasonically dispersed for 15 minutes respectively, and the ultrasonicated solution A and solution B are evenly mixed with 1g of sodium lignin sulfonate to obtain a mixed solution; the mixed solution is vigorously stirred in a 65°C water bath for 30 minutes to obtain a suspension; the suspension is directly transferred to a hydrothermal reactor and aged at 120°C for 24 hours to obtain a precipitate; after deep filtering the precipitate, it is washed with boiled water, and the washed precipitate is placed in a vacuum oven at 85°C and dried for 24 hours to obtain a dry powder, i.e., the Ca-SLS-LDH nanocomposite material.

[0062] Test Example 1

[0063] Anti-seepage performance test

[0064] The lime-free molybdenum tailings autoclaved aerated concrete prepared in Examples 1-5 was tested for water resistance and oil resistance.

[0065] The water resistance performance is tested by applying a water pressure of 0.3MPa on one side of the concrete sample and testing the time required for water to begin to penetrate the concrete sample. The oil resistance performance is tested by spraying ordinary motor oil at a pressure of 0.3MPa on one side of the concrete sample and testing the time required for the motor oil to begin to penetrate the concrete sample.

[0066] The test results are shown in Table 1.

[0067] Compressive strength test

[0068] Referring to the standard "GB / T11969-2020 Autoclaved Aerated Concrete Performance Test Method", the compressive strength of the concrete of Examples 1-5 was tested.

[0069] Three samples were tested in each embodiment, and the average value was taken. The test results are shown in Table 1.

[0070] Table 1 Anti-penetration performance and compressive strength test of each embodiment

[0071]

[0072]

[0073] As can be seen from Table 1, compared with Examples 1-5, the time for the concrete of Examples 2-5 to resist water penetration and oil penetration is significantly longer than that of Example 1, indicating that the water and oil resistance of the modified concrete is improved. Among them, the time for the resistance to water penetration and oil penetration of Examples 2 and 5 is significantly longer than that of Examples 3-4, and the time of Examples 2 and 5 is comparable. This is because the low surface energy CH and CF groups contained in stearic acid and 19-fluorodecanoic acid are grafted onto the -OH groups on the concrete surface to form hydrophobic and oleophobic chains. At the same time, the hydration product calcium hydroxide can react with stearic acid and 19-fluorodecanoic acid to obtain a product with long hydrophobic and oleophobic chains, which forms hydrophobic and oleophobic properties on the concrete surface, thereby reducing the surface free energy of the concrete. In addition, since CH and CF groups have a strong repulsive effect, this promotes the accumulation of fluorine-containing groups on the concrete surface. Therefore, due to the accumulation of low surface free energy groups on the surface, the modified concrete exhibits super hydrophobic and oleophobic properties.

[0074] Comparing Examples 1-5, the compressive strength of the concrete of Examples 2-4 is significantly lower than that of Example 1, while that of Example 5 is higher than that of Example 1, indicating that the compressive strength of the modified concrete is affected. Compared with Example 1, the compressive strength of the concrete of Examples 2-4 decreases, while that of Example 5 increases. This is because the CF and CH groups in the modifier have low surface free energy, which hinders the hydration reaction between cement and water, resulting in a decrease in the compressive strength of the concrete. The Ca-SLS-LDH nanocomposite material introduced into the concrete contains hydroxide ions in its layered structure and has a high interlayer ion exchange capacity, which can effectively exchange with calcium ions in the cement. This exchange releases more calcium ions, thereby accelerating the hydration reaction of the cement. At the same time, Ca-SLS-LDH has a high specific surface area and a large interlayer distance, which enables them to better react with minerals such as silicates and aluminates in concrete to generate hydration products with high strength and durability. These hydration products can fill the pores in the concrete and increase the density and strength of the concrete. Therefore, the introduction of Ca-SLS-LDH nanocomposites has effectively solved the problem of the decrease in the compressive strength of concrete due to the modifier hindering the hydration reaction between cement and water.

[0075] Test Example 2

[0076] Corrosion resistance

[0077] The concrete prepared in Examples 1-5 was immersed in a high-concentration seawater solution, and the mechanical properties of the concrete columns were tested on the 0th, 60th, and 100th day after immersion. The test method was based on the "GB / T11969-2020 Autoclaved Aerated Concrete Performance Test Method" standard, and the compressive strength of the concrete was tested. In order to accelerate the corrosion intensity of seawater and reduce the experimental time, the present invention uses a high-concentration seawater solution with the following concentrations: sodium chloride 68g / 1000g, magnesium chloride 9.5g / 1000g, magnesium sulfate 4.1g / 1000g, and sodium sulfate 5.3g / 1000g.

[0078] The test results are shown in Table 2.

[0079] Table 2 Changes in compressive strength of various examples after seawater immersion

[0080] 0 day (MPa) 60 days (MPa) 100 days (MPa) Example 1 4.33 3.01 2.23 Example 2 3.82 3.76 3.69 Example 3 3.23 2.82 2.43 Example 4 3.81 3.64 2.57 Example 5 4.83 4.75 4.68

[0081] As shown in Table 2, the compressive strength of the autoclaved aerated concrete prepared in Examples 1-5, when immersed in seawater, shows a significant downward trend in the compressive strength of Examples 1 and 3-4 with increasing immersion time, while the compressive strength of Examples 2 and 5 shows no significant change. This indicates that Examples 2 and 5 have superior seawater corrosion resistance to Examples 1 and 3-4. This is because concrete is unsaturated during use, and the entry of water and corrosive ions is primarily controlled by capillary tension. The addition of the modifier reduces the surface tension of the concrete pore structure, making it denser and reducing pores and cracks. This creates a barrier to the penetration of water and corrosive ions, preventing them from contacting the concrete and reducing corrosion. The modifier, composed of a mixture of stearic acid and 19-fluorodecanoic acid, reacts with the calcium hydroxide in the concrete. Furthermore, the introduction of Ca-SLS-LDH enables them to react better with the minerals in the concrete, forming more stable calcium soap crystals, thereby improving the concrete's pore structure. Therefore, the addition of the modifier can improve the seawater corrosion resistance of autoclaved aerated concrete, so that the prepared autoclaved aerated concrete can be used in marine environments.

Claims

1. A method for preparing lime-free molybdenum tailings autoclaved aerated concrete, characterized in that: The following steps are involved: (1) Grind the molybdenum tailings and water-quenched slag into powder respectively; (2) Add water to the molybdenum tailings and water-quenched slag powder ground in step (1), mix and stir, add gypsum and waste slurry during the stirring process, and obtain a mixed material for standby use; (3) Add cement, water reducing agent and modifier to the mixture obtained in step (2) and stir to mix evenly, then add aluminum powder paste and stir evenly before pouring. After pouring, send it to the static curing room for static curing to thicken it; (4) After static curing, demoulding and cutting are carried out to obtain the green body of required specifications and sizes; the green body is then transferred to the autoclave for steam curing; after being taken out of the autoclave, it is inspected, packaged and stored, and naturally cured for 28 days to obtain the finished product of lime-molybdenum tailings autoclaved aerated concrete; The weight ratio of each raw material component is: 100-150 parts of molybdenum tailings, 40-60 parts of water-quenched slag, 30-50 parts of cement, 5-10 parts of waste slurry, 8-15 parts of gypsum, 2-6 parts of aluminum paste, 0.1-0.5 parts of water reducer, 0.5-1 parts of modifier, 0.5-1 parts of admixture, and 200-250 parts of water; The admixture is a Ca-SLS-LDH nanocomposite material; The preparation method of the Ca-SLS-LDH nanocomposite material is as follows: 25.6g of Ca(NO3)2•4H2O and 18.75g of Al(NO3)39H2O are added to 200mL of boiling water, mixed and stirred to obtain solution A; 17g of NaNO3 and 12g of NaOH are added to 100mL of boiling water, mixed and stirred to obtain solution B; Solution A and solution B were ultrasonically dispersed for 15 minutes respectively, and the ultrasonicated solutions A and B were mixed evenly with 1 g of sodium lignin sulfonate to obtain a mixed solution; the mixed solution was vigorously stirred in a 65°C water bath for 30 minutes to obtain a suspension; the suspension was directly transferred to a hydrothermal reactor and aged at 120°C for 24 hours to obtain a precipitate; the precipitate was deep filtered and washed with boiling water, and the washed precipitate was placed in a vacuum oven at 85°C for 24 hours to obtain a dry powder, namely, the Ca-SLS-LDH nanocomposite material; The water reducer is a naphthalene-based high-efficiency water reducer powder; The modifier is prepared by mixing stearic acid and 19-fluorodecanoic acid in a mass ratio of 2:

3.

2. The method for preparing lime-free molybdenum tailings autoclaved aerated concrete according to claim 1, wherein: In the step (1), the molybdenum tailings and the water-quenched slag are respectively ground into powders with a 0.1 mm square hole sieve residue of no more than 15%.

3. The method for preparing lime-free molybdenum tailings autoclaved aerated concrete according to claim 1, characterized in that: In step (2), the stirring temperature is 35-45° C., the stirring rate is 100-150 r / min, and the stirring time is 3-6 h.

4. The method for preparing lime-free molybdenum tailings autoclaved aerated concrete according to claim 1, wherein: In the step (3), the stirring temperature is 40-50°C, and the stirring rate is 600-800 r / min; the aluminum powder paste is added and stirred for 3-5 minutes before pouring, and after pouring, the mixture is sent to a static curing room for static curing. The static curing temperature is 40-50°C, the humidity is 50-70%, and the curing time is 3-5 hours.

5. The method for preparing lime-free molybdenum tailings autoclaved aerated concrete according to claim 1, characterized in that: The autoclave curing time in step (4) is 8 to 10 hours, the internal temperature of the autoclave is 185 to 195° C., and the pressure is 1.2 to 1.3 MPa.

6. The method for preparing lime-free molybdenum tailings autoclaved aerated concrete according to claim 1, characterized in that: The step (3) is as follows: adding cement, water reducing agent, modifier and admixture to the mixture obtained in step (2) and stirring to mix evenly, then adding aluminum powder paste and stirring evenly before pouring, and after pouring, sending it into a static curing room for static curing to thicken it.

7. A lime-free molybdenum tailings autoclaved aerated concrete, characterized in that: Prepared by the method according to any one of claims 1 to 6.

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