Magnesite-based cement and green building material product and method for manufacturing the same

Abstract

This invention provides a magnesite-based cement and a green building material product, as well as a method for preparing the same, belonging to the field of building materials technology. In the method for preparing the magnesite-based cement, step S1 involves crushing, grinding, and then washing low-grade magnesite ore to remove surface impurities. Step S2 involves calcining and activating a mixture of low-grade magnesite powder and a first and second activator to improve the activity of the low-grade magnesite powder, resulting in a significant improvement in the performance of the subsequently prepared building material product, such as strength and durability. Step S3 uses the activated low-grade magnesite powder as the main raw material, employing environmentally friendly processing methods and additives and auxiliary ingredients to reduce environmental pollution, aligning with the concept of green development. The method for preparing magnesite-based cement in this invention effectively utilizes low-grade magnesite resources, reduces production costs, and improves resource utilization, resulting in good economic and social benefits.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a magnesium oxide-based cement and green building material products and their preparation methods. Background Technology

[0002] Low-grade magnesite refers to magnesite ore with low magnesium oxide content and high impurity content. Its main chemical component is magnesium carbonate, but it also contains numerous impurities such as compounds of silicon, iron, calcium, and aluminum. The presence of these impurities reduces the grade of the magnesite, affecting its properties and applications. Low-grade magnesite is mostly white or grayish-white in color, while iron-bearing magnesite is yellow to brown. It has a vitreous luster, and its crystals belong to the trigonal crystal system, usually occurring as granular or cryptocrystalline massive crystals. Porcelain-like magnesite exhibits conchoidal fracture. The reasons for the formation of low-grade magnesite are as follows: (1) Sedimentary metamorphism: During geological history, magnesium-containing solutions react with other substances in a specific sedimentary environment to form magnesite deposits. During the sedimentation process, due to changes in geological conditions, more impurities may be mixed into the ore, resulting in low-grade magnesite; (2) Hydrothermal replacement: Magnesium ions in hydrothermal fluids react with minerals in the surrounding rocks to form magnesite. If the composition of the hydrothermal fluids is complex or the replacement process is incomplete, low-grade magnesite may be formed.

[0003] my country is one of the world's richest countries in magnesite resources. However, after years of mining, high-grade magnesite resources are gradually decreasing, making the development and utilization of low-grade magnesite increasingly important. In low-grade magnesite, valuable minerals and gangue minerals often coexist closely, with fine grain sizes, making it difficult to effectively liberate them into individual particles during beneficiation, thus affecting subsequent separation efficiency. Furthermore, due to the high variety and content of impurities in low-grade magnesite, and their similar physicochemical properties to magnesite, traditional beneficiation methods are insufficient for efficient separation, leading to increased beneficiation costs and difficulty in improving concentrate grade and recovery rate.

[0004] After purification and processing, low-grade magnesite can be used to produce refractory materials such as refractory bricks and refractory castables, which can then be used as linings for high-temperature industrial kilns in steel, cement, and glass industries. Alternatively, it can be used as an admixture or aggregate in concrete production to improve the durability and corrosion resistance of concrete. In addition, it can be used to produce magnesite-based cement products such as wall panels, flooring, and decorative panels.

[0005] The reason why low-grade magnesite can be used to prepare green building materials is mainly due to its chemical and physical properties, as well as its advantages in resource utilization and environmental protection. Current methods for preparing green building materials from low-grade magnesite generally involve impurity removal using ammonium salt methods, carbonation methods, and acid leaching methods. These reaction processes are complex and result in low production efficiency. Therefore, it is necessary to design a magnesite-based cement and green building materials, as well as their preparation method. This method can utilize low-grade magnesite to produce high-quality magnesite-based cement and green building materials, and the preparation process is simple and highly efficient. Summary of the Invention

[0006] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention provide a magnesium oxychloride-based cement and a green building material product, as well as a method for preparing the same.

[0007] In a first aspect, embodiments of the present invention provide a method for preparing magnesium oxychloride-based cement, comprising the following steps:

[0008] S1. The low-grade magnesite ore is crushed and ground to obtain low-grade magnesite powder; the low-grade magnesite powder is then washed, the washing process including sequential water washing, magnetic separation and flotation, to obtain pre-purified low-grade magnesite powder.

[0009] S2. The pre-purified low-grade magnesite powder is mixed with the first activator to obtain a premix; under a weak oxidizing atmosphere, the premix is ​​first heated to 400℃-500℃ at a heating rate of 5℃ / min-8℃ / min and held for 30min-45min, then heated to 750℃-850℃ at a heating rate of 8℃ / min-10℃ / min, and the second activator is sprayed into the premix by spraying, controlling the atomization pressure to be 0.2-0.4MPa and the spraying rate to be 4-6mL / min to obtain a mixture, which is then held at 750℃-850℃ for 60min-90min to obtain activated low-grade magnesite powder; wherein, the first activator is ferrous sulfate, and the second activator is a compound of magnesium sulfate and sodium carbonate;

[0010] S3. The activated low-grade magnesite powder is mixed with additives and auxiliary ingredients to obtain magnesite-based cement; wherein the additives include a compound of reinforcing fiber materials, curing agents and waterproofing agents, and the auxiliary ingredients include a compound of fly ash, metakaolin and slag powder.

[0011] The advantages and technical effects of the preparation method of magnesium-based cement in this invention are as follows:

[0012] (1) This invention involves calcining and activating low-grade magnesite powder. The first activator is ferrous sulfate, which weakens chemical bonds and forms active sites. It also acts as a catalyst, altering the reaction pathway and reducing the activation energy by forming intermediate complexes with reactants and products. The second activator, magnesium sulfate, decomposes at high temperatures, generating sulfate ions that invade the magnesite lattice, forcing it to distort and creating lattice defects. This increases the diffusion channels for magnesium ions, making them more easily migrated, thus significantly enhancing the activity of the low-grade magnesite powder. Sodium carbonate in the activator can reduce the activation energy of the calcination process. At high temperatures, it reacts chemically with low-grade magnesite powder, causing the magnesite crystal structure to rearrange, making it more likely to participate in subsequent reactions and enhancing its activity. High temperatures destroy the relatively stable crystal structure of magnesite, causing the internal chemical bonds to break and recombine. As the temperature rises, the thermal motion of atoms in the crystal intensifies, the crystal structure gradually becomes disordered, and the specific surface area increases. This not only increases the contact area between magnesite and external substances, but also exposes the internal active sites, greatly improving its activity and significantly enhancing the performance of the prepared building materials.

[0013] (2) The present invention activates low-grade magnesite powder, which not only improves its activity but also changes its crystal structure. The increased activity allows the magnesite to react more fully with the additives in subsequent reactions, generating stable and high-strength products. The addition of additives such as reinforcing fiber materials, curing agents and waterproofing agents significantly improves the performance of building materials. The reinforcing fiber materials are uniformly dispersed inside the building materials, playing a role in reinforcing the skeleton. In the preparation process, environmentally friendly treatment methods and additives are used, reducing environmental pollution and conforming to the concept of green development. This method can effectively utilize low-grade magnesite resources, reduce production costs, improve resource utilization, and has good economic and social benefits.

[0014] (3) This invention has a high resource utilization rate, effectively utilizes a large amount of idle low-grade magnesite, improves the overall utilization rate of magnesite resources, reduces resource waste, and can meet the various usage requirements of the construction industry. In the preparation process, the method reduces energy consumption and waste generation through reasonable process design. It also uses industrial waste such as fly ash and slag powder as auxiliary ingredients. Fly ash is rich in active ingredients such as silicon, aluminum, and calcium. In an alkaline environment, it can undergo a volcanic ash reaction to generate hydration products with cementing properties. These products intertwine with the hydration products of magnesite, enhancing the density and strength of the internal structure of the building materials. Slag powder also has potential hydraulic activity. Its main components include calcium oxide, magnesium oxide, aluminum oxide, and silicon oxide. After grinding, under the action of an activator, it can significantly improve the later strength and durability of building materials, realize the resource utilization of industrial waste, reduce environmental pollution, and conform to the development direction of green building materials.

[0015] In some embodiments, in step S1, the specific surface area of ​​the low-grade magnesite powder is 350 m². 2 / kg-450m 2 / kg, with an average particle size of 10μm-20μm.

[0016] In some embodiments, in step S2, the amount of the first activator added is 3wt%-5wt% of the mass of the pre-purified low-grade magnesite powder; and / or, the amount of magnesium sulfate added is 5wt%-10wt% of the mass of the pre-purified low-grade magnesite powder; and / or, the amount of sodium carbonate added is 5wt%-10wt% of the mass of the pre-purified low-grade magnesite powder.

[0017] In some embodiments, in step S2, the pre-purified low-grade magnesite powder and the first activator are mixed by stirring, the stirring speed is 300 r / min-500 r / min, and the stirring time is 30 min-60 min.

[0018] In some embodiments, during step S2, when the second activator is added by spray, the atomization pressure is controlled to be 0.2-0.4 MPa and the spray rate is 4-6 mL / min.

[0019] In some embodiments, in step S3, the total mass of the magnesite-based cement is 100wt%, wherein the amount of activated low-grade magnesite powder added is 17wt%-46wt%, the amount of reinforcing fiber material added is 5wt%-10wt%, the amount of curing agent added is 3wt%-5wt%, the amount of waterproofing agent added is 1wt%-3wt%, the amount of fly ash added is 20wt%-30wt%, the amount of metakaolin added is 10wt%-15wt%, the amount of slag powder added is 15wt%-20wt%, and the remainder is activated low-grade magnesite powder.

[0020] In some embodiments, in step S3, the activated low-grade magnesite powder is mixed with additives and auxiliary ingredients by stirring. The stirring speed is 800 r / min-1000 r / min, and the stirring time is 15 min-20 min.

[0021] Secondly, embodiments of the present invention provide a magnesium oxychloride-based cement, obtained by the preparation method of the magnesium oxychloride-based cement described in the first aspect.

[0022] The advantages and technical effects of the magnesium-based cement in this invention are as follows:

[0023] Because the preparation method of magnesium-based cement described in the first aspect is adopted, the magnesium-based cement of the present invention significantly improves the strength and durability of green building materials.

[0024] Thirdly, embodiments of the present invention provide a method for preparing green building materials, comprising the following steps:

[0025] S4. The magnesium-based cement described in the second aspect is mixed with water and a modifier, and then subjected to a hydration reaction under stirring conditions to obtain a mixture; wherein the modifier is an organosilicon emulsion;

[0026] S5. The mixture is placed into a mold for molding to obtain a building material blank;

[0027] S6. The building material blank is cured to obtain green building material products.

[0028] The advantages and technical effects of the preparation method of green building materials products in this invention are as follows:

[0029] Because the magnesium-based cement described in the second aspect is used, the green building material products obtained by the preparation method of the green building material products in the embodiments of the present invention have high strength and water resistance and other properties.

[0030] In some embodiments, in step S4, the amount of the modifier added is 1wt%-2wt% of the mass of the magnesium oxychloride cement; the ratio of the magnesium oxychloride cement to water is in the range of 1:(1.02-1.03); and the hydration reaction time is 30min-45min.

[0031] Fourthly, embodiments of the present invention provide a green building material product, which is obtained by the preparation method of the green building material product described in the third aspect.

[0032] The advantages and technical effects of the green building materials products of this invention are as follows:

[0033] Because the green building material product preparation method described in the third aspect is adopted, the green building material product of the present invention has high strength and water resistance and other properties. Attached Figure Description

[0034] Figure 1 XRD pattern of low-grade magnesite powder;

[0035] Figure 2 The image shows the XRD pattern of the floor tiles prepared in Example 1.

[0036] Figure 3 SEM image of the floor tiles prepared in Example 1;

[0037] Figure 4The image shows the XRD pattern of the floor tiles prepared in Example 3.

[0038] Figure 5 This is a SEM image of the floor tiles prepared in Example 3. Detailed Implementation

[0039] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0040] In a first aspect, embodiments of the present invention provide a method for preparing magnesium oxychloride-based cement, comprising the following steps:

[0041] S1. The low-grade magnesite ore is crushed and ground to obtain low-grade magnesite powder; the low-grade magnesite powder is then washed, the washing process including sequential water washing, magnetic separation and flotation, to obtain pre-purified low-grade magnesite powder.

[0042] S2. The pre-purified low-grade magnesite powder is mixed with the first activator to obtain a premix; under a weak oxidizing atmosphere, the premix is ​​first heated to 400℃-500℃ at a heating rate of 5℃ / min-8℃ / min and held for 30min-45min, then heated to 750℃-850℃ at a heating rate of 8℃ / min-10℃ / min, and the second activator is sprayed into the premix by spraying, controlling the atomization pressure to be 0.2-0.4MPa and the spraying rate to be 4-6mL / min to obtain a mixture, which is then held at 750℃-850℃ for 60min-90min to obtain activated low-grade magnesite powder; wherein, the first activator is ferrous sulfate, and the second activator is a compound of magnesium sulfate and sodium carbonate;

[0043] S3. The activated low-grade magnesite powder is mixed with additives and auxiliary ingredients to obtain magnesite-based cement; wherein the additives include a compound of reinforcing fiber materials, curing agents and waterproofing agents, and the auxiliary ingredients include a compound of fly ash, metakaolin and slag powder.

[0044] In the preparation method of this invention, the crushing and grinding processes in step S1 are to obtain low-grade magnesite powder so that the subsequent reaction can proceed fully; the washing process of the low-grade magnesite powder is to remove impurities on its surface and achieve a preliminary purification effect.

[0045] In some embodiments, the cleaning process specifically includes the following three steps: "water washing-magnetic separation-flotation": first, the low-grade magnesite powder is washed with deionized water at a liquid-to-solid ratio of 3:1 to remove soluble salts adhering to the surface; then, ferromagnetic impurities are separated by a permanent magnet drum separator; finally, dodecylamine is used as a collector for flotation to separate siliceous impurities, thereby reducing the total impurity content and increasing the purity of magnesium oxide in the preliminarily purified low-grade magnesite powder.

[0046] In the preparation method of this invention, step S2 requires calcination activation in a weak oxidizing atmosphere to prevent over-oxidation. A strong oxidizing atmosphere would generate byproducts, such as magnesium oxides. An inert atmosphere would result in insufficient combustion efficiency, incomplete decomposition of low-grade magnesite powder, and insufficient strength in the activated low-grade magnesite powder.

[0047] In the preparation method of this invention embodiment, in step S2, the low-grade magnesite powder to be pre-purified is mixed evenly with the first activator, ferrous sulfate, and pre-mixed. The role of the first activator is to improve the activity of the low-grade magnesite powder. Then, the obtained premixed material is placed in a high-temperature furnace and calcined and activated under a specific temperature and a weak oxidizing atmosphere. During the calcination process, an appropriate amount of the second activator is added. The second activator selected in this process is a mixture of magnesium sulfate and sodium carbonate. The amount of magnesium sulfate and sodium carbonate added is similar, which can further improve the activity of the low-grade magnesite powder.

[0048] In the preparation method of this invention, the first activator in step S2 is added by pre-mixing it with low-grade magnesite powder before calcination activation treatment. The second activator, however, requires heating the pre-mixed material to 750℃-850℃ and then adding it via spraying. The reason for adding the second activator during calcination activation, rather than pre-mixing it like the first activator, is that the second activator undergoes side reactions at low temperatures, easily leading to raw material waste or impurity generation. Therefore, the second activator must be added only when the temperature reaches above 750℃.

[0049] Specifically, the first activator is ferrous sulfate, which can weaken chemical bonds and form active sites. Ferrous sulfate undergoes hydrolysis in aqueous solution, producing some positively charged hydrolysis products. The effect of ferrous sulfate is to make the atomic arrangement on the surface of low-grade magnesite powder particles more disordered, increasing the surface energy. During the mixing and stirring process with low-grade magnesite powder, ferrous sulfate will form a special ionic environment around the low-grade magnesite powder particles. Under the stirring action, ferrous sulfate and low-grade magnesite powder are in full contact, and the temperature and concentration distribution in the system are more uniform, which is conducive to the diffusion of ions. Ferrous ions in ferrous sulfate have variable oxidation states and can undergo redox reactions under certain conditions to produce free radicals. In some chemical reactions involving low-grade magnesite powder, ferrous sulfate can act as a catalyst, changing the reaction pathway and reducing the activation energy of the reaction by forming intermediate complexes with reactants and products.

[0050] The magnesium sulfate in the second activator decomposes at temperatures above 750°C, producing sulfate ions that invade the magnesite crystal lattice. Due to the large radius of the sulfate ions, this forces the magnesite lattice to distort, creating lattice defects. These defects increase the diffusion channels for magnesium ions, making them more easily migrated and significantly enhancing the activity of low-grade magnesite powder. The sodium carbonate in the second activator reacts with the magnesium oxide on the magnesite surface at temperatures above 750°C, forming a new phase that alters the atomic arrangement on the crystal surface, increasing the number of active sites on the surface of low-grade magnesite powder.

[0051] In the preparation method of this invention, step S2 involves two stages of calcination activation treatment. During the heat preservation stage of 400℃-500℃, such as 400℃, 420℃, 440℃, 460℃, 480℃, 500℃, etc., the adsorbed water, crystal water, and some impurities such as carbonates and sulfates in the low-grade magnesite powder begin to decompose. During the heat preservation stage of 750℃-850℃, such as 750℃, 770℃, 790℃, 810℃, 830℃, 850℃, etc., the effective components in the low-grade magnesite powder begin to activate.

[0052] Specifically, during the 400℃-500℃ holding stage, adsorbed water and crystal water in low-grade magnesite powder can be removed. Some impurities in low-grade magnesite powder, such as carbonates and sulfates, will begin to decompose within this temperature range. During this temperature range, the crystal structure of magnesite undergoes subtle changes. Meanwhile, magnesium carbonate, the main component of low-grade magnesite powder, decomposes violently at 750-850℃, producing magnesium oxide and carbon dioxide. Higher temperatures and appropriate holding times are beneficial to the growth and development of magnesium oxide crystals. During this high-temperature stage, a large number of active sites form on the surface of the magnesium oxide produced by the decomposition of magnesite.

[0053] In step S2, the temperature is increased to 400℃-500℃ at a heating rate of 5℃ / min-8℃ / min, for example, 400℃, 420℃, 440℃, 460℃, 480℃, 500℃, etc. This stage uses a relatively low heating rate to decompose more than 80% of the adsorbed water and crystal water in the magnesite powder, while also avoiding excessive decomposition of impurities.

[0054] In step S2, the temperature is increased to 750℃-850℃ at a heating rate of 8℃ / min-10℃ / min, such as 8℃ / min, 8.5℃ / min, 9℃ / min, 9.5℃ / min, 10℃ / min, etc., for example, 750℃, 780℃, 800℃, 820℃, 850℃, etc. A lower heating rate helps to adjust and stabilize the magnesite crystal structure, avoiding defects caused by drastic structural changes due to rapid heating.

[0055] In step S2, when adding the second activator via spray, the atomization pressure is controlled at 0.2-0.4 MPa and the spray rate is 4-6 mL / min. This ensures uniform dispersion of the second activator and reduces local side reactions.

[0056] In the preparation method of this invention embodiment, step S3 involves mixing the activated low-grade magnesite powder with additives and auxiliary ingredients to obtain magnesite-based cement; wherein the additives include a compound of reinforcing fiber materials, curing agents and waterproofing agents, and the auxiliary ingredients include a compound of fly ash, metakaolin and slag powder.

[0057] Specifically, the reinforcing fiber material, evenly dispersed within the building material, acts as a reinforcing skeleton. When the building material is subjected to external forces, the reinforcing fiber material can share the stress, preventing the generation and propagation of cracks, thereby improving the strength of the building material. The curing agent can reasonably control the curing reaction rate of magnesium oxychloride cement, promote the curing reaction of magnesium oxychloride cement, accelerate the formation of the internal structure, and enable magnesium oxychloride cement to complete curing within an appropriate time, making the structure of the building material more compact and improving its strength and durability. The waterproofing agent can form a continuous and dense waterproof protective film on or inside the magnesium oxychloride cement, effectively preventing the penetration and intrusion of water, reducing the water absorption rate of the building material, improving the waterproof performance of the building material, and enabling the building material to maintain good performance in humid or wet environments.

[0058] Fly ash contains abundant active components such as silicon and aluminum, which can undergo a secondary reaction with calcium hydroxide produced during cement hydration under alkaline conditions. Furthermore, the predominantly spherical shape and smooth surface of fly ash particles act as ball bearings in magnesia-based cement, reducing inter-particle friction and improving the fluidity of the cement paste. Metakaolin exhibits high pozzolanic activity and reacts rapidly with calcium hydroxide, generating cementitious products that refine the pore structure of the material, improving both early and late-stage strength of building materials, particularly enhancing early strength. Slag powder, under the influence of alkaline activators, undergoes a hydration reaction, generating numerous hydration products that increase the amount of cementitious material in magnesia-based cement, thereby improving the overall strength of building materials and positively impacting their long-term strength development. Therefore, the aforementioned auxiliary ingredients can optimize the performance of magnesia-based cement and enhance the strength of building materials.

[0059] In addition, among the auxiliary ingredients, the spherical particles of fly ash can exert a "ball effect," reducing friction within the system. Simultaneously, the SiO2 and Al2O3 contained in fly ash can react with potential impurities in the activator to form iron-aluminum silicate gel. The pozzolanic activity of metakaolin can accelerate the hydration reaction, generating MSH gel to fill the pores. The CaO and SiO2 in the slag powder can react with Na... + The reaction produces sodium calcium silicate, which inhibits salting out.

[0060] In some embodiments, in step S1, the specific surface area of ​​the low-grade magnesite powder is 350 m². 2 / kg-450m 2 / kg, for example, 350m 2 / kg, 380m 2 / kg, 400m 2 / kg, 420m 2 / kg, 450m 2 The average particle size is 10μm-20μm, such as 10μm, 12μm, 14μm, 16μm, 18μm, and 20μm. After crushing and grinding, low-grade magnesite particles become smaller, significantly increasing their specific surface area. In subsequent chemical reactions, the contact area between reactants is significantly increased, allowing reactant molecules to contact and collide more fully, thereby accelerating the reaction rate and improving the completeness of the reaction. During the calcination and activation process of low-grade magnesite, smaller particle size allows for more complete contact between the ore and hot air, resulting in more complete decomposition of impurities such as calcium carbonate, which is beneficial for improving the purity of subsequent products. Furthermore, the reduced particle size after crushing and grinding lowers the diffusion resistance of reactants, resulting in more uniform material mixing, which is beneficial for subsequent separation and purification.

[0061] In some embodiments, in step S2, the amount of the first activator added is 3wt%-5wt% of the mass of the pre-purified low-grade magnesite powder, for example, 3wt%, 3.2wt%, 3.4wt%, 3.6wt%, 3.8wt%, 4wt%, 4.2wt%, 4.4wt%, 4.6wt%, 4.8wt%, 5wt%, etc.; and / or, the amount of magnesium sulfate added is 5wt%-10wt% of the mass of the pre-purified low-grade magnesite powder, for example, 5wt%, 5.5wt%, 6wt%, 6.5wt%, 7wt%, 7.5wt%, 8wt%, 8.5wt%, 9wt%, 9.5wt%, 10wt%, etc.; and / or, the amount of sodium carbonate added is 5%-10% of the mass of the pre-purified low-grade magnesite powder, for example, 5wt%, 5.5wt%, 6wt%, 6.5wt%, 7wt%, 7.5wt%, 8wt%, 8.5wt%, 9wt%, 9.5wt%, 10wt%, etc. Adding the first activator and / or the second activator within the above range is beneficial to fully activate the low-grade magnesite powder after preliminary purification and improve the activity of the low-grade magnesite powder.

[0062] In some embodiments, in step S2, the pre-purified low-grade magnesite powder and the first activator are mixed by stirring. The stirring speed is 300 r / min-500 r / min, for example, 300 r / min, 350 r / min, 400 r / min, 450 r / min, 500 r / min, etc., and the stirring time is 30 min-60 min, for example, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, etc. These stirring conditions ensure that the first activator and the low-grade magnesite powder are thoroughly and evenly mixed, achieving sufficient contact and thus improving the activity of the low-grade magnesite powder.

[0063] In some embodiments, in step S2, the weak oxidizing atmosphere is a mixture of oxygen and an inert gas, for example, the ratio of the oxygen flow rate to the inert gas flow rate is 1:(2-5), such as 1:2, 1:3, 1:4, 1:5, etc.

[0064] In some embodiments, in step S3, with the total mass of the magnesite-based cement being 100 wt%, the amount of activated low-grade magnesite powder added is 17 wt%-46 wt%, for example, 17 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 46 wt%, etc.; the amount of reinforcing fiber material added is 5 wt%-10 wt%, for example, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, etc.; the amount of curing agent added is 3 wt%-5 wt%, for example, 3 wt%, 3.2 wt%, 3.5 wt%, 3.8 wt%, 4 wt%, 4.2 wt%, 4.5 wt%, 4.8 wt%, 5 wt%, etc.; and the amount of waterproofing agent added is 1 wt%. The components of the magnesium oxychloride-based cement are 1 wt%, 1.2 wt%, 1.4 wt%, 1.6 wt%, 1.8 wt%, 2 wt%, 2.2 wt%, 2.4 wt%, 2.6 wt%, 2.8 wt%, 3 wt%, etc. The amount of fly ash added is 20 wt%-30 wt%, such as 20 wt%, 22 wt%, 24 wt%, 26 wt%, 28 wt%, 30 wt%, etc. The amount of metakaolin added is 10 wt%-15 wt%, such as 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, etc. The amount of slag powder added is 15 wt%-20 wt%, such as 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, etc. When the components of the magnesium oxychloride-based cement are within the above ranges, the resulting magnesium oxychloride-based cement significantly improves the strength and durability of green building materials.

[0065] In some embodiments, in step S3, the activated low-grade magnesite powder is mixed with additives and auxiliary materials by stirring. The stirring speed is 800 r / min-1000 r / min, for example, 800 r / min, 850 r / min, 900 r / min, 950 r / min, 1000 r / min, etc., and the stirring time is 15 min-20 min, for example, 15 min, 16 min, 17 min, 18 min, 19 min, 20 min, etc. These stirring conditions ensure that the additives and auxiliary materials are fully and evenly mixed with the activated low-grade magnesite powder, achieving sufficient contact and improving the uniformity of the magnesite-based cement.

[0066] In some embodiments, in step S3, the reinforcing fiber material is glass fiber and / or carbon fiber. These reinforcing fiber materials can effectively improve the tensile strength, tear strength, and impact resistance of magnesium oxychloride-based cement, giving it better flexibility and ductility, reducing the brittleness of building materials, and enhancing the ability of building materials to resist repeated loads, thus reducing the possibility of fatigue damage during long-term use and extending the service life of building materials.

[0067] Secondly, embodiments of the present invention provide a magnesium oxychloride-based cement, obtained by the preparation method of the magnesium oxychloride-based cement described in the first aspect.

[0068] Because the preparation method of magnesium-based cement described in the first aspect is adopted, the magnesium-based cement of the present invention significantly improves the strength and durability of green building materials.

[0069] Thirdly, embodiments of the present invention provide a method for preparing green building materials, comprising the following steps:

[0070] S4. The magnesium-based cement described in the second aspect is mixed with water and a modifier, and then subjected to a hydration reaction under stirring conditions to obtain a mixture; wherein the modifier is an organosilicon emulsion;

[0071] S5. The mixture is placed into a mold for molding to obtain a building material blank;

[0072] S6. The building material blank is cured to obtain green building material products.

[0073] In the preparation method of the green building material product of this invention, the modifier used in step S4 is an organosilicon emulsion, which can form a continuous hydrophobic film on and inside the magnesium oxychloride-based cement, significantly reducing the surface energy of the material, making it difficult for water to adhere to and penetrate the material surface, thereby significantly improving the waterproof performance of the material, effectively preventing the intrusion of external moisture, and extending its service life. In step S5, molding methods such as pressing and casting can be used. The curing treatment used in step S6 can be natural curing or steam curing.

[0074] In some embodiments, in step S5, for board-type building materials, pressing can be used; or for block-type building materials, casting can be used. The specific method used to form the desired shape of the building material blank in step S5 depends on the desired shape. For example, for board-type building materials, pressing can be used. Pressing, through the action of molds and pressure, subjects the board to uniform external force during the forming process, thereby ensuring high surface flatness and accurate dimensions. This meets the stringent requirements of different construction projects for board specifications, facilitating installation and use. The pressing process also makes the internal structure of the board denser, with tighter bonding between fibers, particles, and other materials, thereby increasing the board's density and strength, enhancing its load-bearing capacity and resistance to deformation, and improving its quality and durability. Different textures or patterns can be designed on the mold surface as needed, and pressing creates corresponding decorative effects on the board surface, increasing its aesthetics and decorative properties to meet the needs of different architectural styles.

[0075] In some embodiments, in step S4, the mass ratio of the magnesium oxychloride cement to water is 1:(1.02-1.03). A suitable water-cement ratio can meet the needs of the hydration reaction of the magnesium oxychloride cement without increasing the porosity of the material due to excessive water, thus ensuring that the material has good density and high strength. A suitable water-cement ratio can give the material good fluidity and plasticity, which is convenient for construction operations such as mixing, pouring, and vibration. An appropriate water-cement ratio helps to form a reasonable pore structure, reduce the permeability of the material, and make it difficult for external moisture, gas and harmful substances to penetrate, thereby improving the material's impermeability, frost resistance and chemical erosion resistance, and enhancing the material's durability.

[0076] In some embodiments, in step S4, the amount of modifier added is 1wt%-2wt% of the mass of the magnesium oxide-based cement, for example, 1wt%, 1.2wt%, 1.4wt%, 1.6wt%, 1.8wt%, 2wt%, etc. In humid environments, adding the above-mentioned amounts of modifier allows the silicone emulsion to form a hydrophobic film that prevents moisture from penetrating the interior of building materials, avoiding structural damage due to water erosion, significantly improving the waterproof performance of green building materials, and extending the service life of building materials.

[0077] In some embodiments, in step S4, the hydration reaction is carried out under stirring conditions. The stirring speed can be 200 r / min-600 r / min, and the stirring time can be 30 min-45 min. The above stirring conditions are conducive to the full progress of the hydration reaction.

[0078] In some embodiments, in step S5, the molding temperature is 30℃-35℃, such as 30℃, 31℃, 32℃, 33℃, 34℃, 35℃, etc., and the molding time is 1.5h-2h, such as 1.5h, 1.6h, 1.7h, 1.8h, 1.9h, 2h, etc. Under the molding conditions described above, the building material blank can be rapidly molded.

[0079] In some embodiments, in step S6, the building material blank is naturally cured for 7 to 14 days, for example, 7, 8, 10, 12, or 14 days, in an environment with a temperature of 20°C-25°C (e.g., 20°C, 21°C, 22°C, 23°C, 24°C, 25°C) and a relative humidity of 80%-90% (e.g., 80%, 82%, 84%, 86%, 88%, 90%). This curing treatment allows the building material blank to fully solidify, improving its strength and stability, thereby further enhancing the strength and performance of the building material product.

[0080] Specifically, magnesium oxide-based cement particles undergo a series of complex chemical reactions with water to generate hydration products. These hydration products continuously fill the pores inside the building materials, thereby continuously improving the strength of the building materials. Under suitable temperature and humidity conditions, the crystals generated during the curing process have sufficient time and conditions to grow more completely and regularly. During natural curing, the bonding performance of the interface transition zone between aggregates and cementitious materials is continuously enhanced under suitable temperature and humidity, reducing drying shrinkage cracks, stabilizing the microstructure, and reducing internal stress.

[0081] Fourthly, embodiments of the present invention provide a green building material product, which is obtained by the preparation method of the green building material product described in the third aspect.

[0082] Because the green building material product preparation method described in the third aspect is adopted, the green building material product of the present invention has high strength and water resistance and other properties.

[0083] In some embodiments, the green building material is artificial marble, fireproof board, or floor tile, etc.

[0084] The green building materials products of this invention meet the following technical indicators: 28-day compressive strength ≥ 55 MPa, 28-day flexural strength ≥ 9 MPa, and 28-day softening coefficient ≥ 0.6.

[0085] The present invention will now be described in detail with reference to the embodiments and accompanying drawings.

[0086] Example 1

[0087] A green, low-grade magnesite preparation method for building materials based on activation treatment includes the following steps:

[0088] S1. Raw material pretreatment: Select low-grade magnesite ore with a magnesium oxide content of 30wt%, and crush it to a specific surface area of ​​400m². 2 Low-grade magnesite powder was obtained by rinsing the powder with deionized water at a liquid-to-solid ratio of 3:1 to remove soluble salts adhering to the surface. Ferromagnetic impurities were then separated using a permanent magnet drum separator (magnetic field strength 12000 Gs). Finally, dodecylamine was used as a collector for flotation to separate siliceous impurities, resulting in pre-purified low-grade magnesite powder. Compared to the original low-grade magnesite powder, the pre-purified low-grade magnesite powder had a lower total impurity content and higher magnesium oxide purity.

[0089] S2. Calcination and activation treatment:

[0090] The pre-purified low-grade magnesite powder was mixed evenly with the first activator and stirred at 400 r / min for 40 min in a stirring device to obtain a premix. The first activator was ferrous sulfate, added at 3 wt% of the mass of the pre-purified low-grade magnesite powder. Oxygen at a flow rate of 300 mL / min and inert gas at a flow rate of 900 mL / min were introduced into the high-temperature furnace to create a weakly oxidizing atmosphere. The premixed material was placed in a high-temperature furnace and heated from room temperature to 450°C at a rate of 6°C / min, and held for 40 min. Then, a second activator was added to the premixed material in the high-temperature furnace by spraying to obtain a mixture. The mixture was then heated to 800°C at a rate of 9°C / min and held for 80 min to obtain activated low-grade magnesite powder. The second activator was selected from magnesium sulfate and sodium carbonate. The amount of magnesium sulfate added was 5 wt% of the mass of the pre-purified low-grade magnesite powder, and the amount of sodium carbonate added was 5 wt% of the mass of the pre-purified low-grade magnesite powder. When spraying the second activator, the atomization pressure was controlled at 0.3 MPa and the spraying rate was 5 mL / min.

[0091] S3. Mixing of Additives and Auxiliary Materials: The activated low-grade magnesite powder is mixed with additives and auxiliary materials in a mixing device at a speed of 900 r / min for 18 min to obtain magnesite-based cement. The additives consist of reinforcing fiber materials, curing agents, and waterproofing agents, while the auxiliary materials consist of fly ash, metakaolin, and slag powder. The total mass of the magnesite-based cement is 100 wt%, of which the amount of reinforcing fiber materials added is 8 wt%, the amount of curing agent added is 4 wt%, the amount of waterproofing agent added is 2 wt%, the amount of fly ash added is 25 wt%, the amount of metakaolin added is 12 wt%, the amount of slag powder added is 18 wt%, and the remainder is activated low-grade magnesite powder.

[0092] S4: Hydration reaction: Add water and modifier to magnesium oxychloride cement, stir at 400 r / min for 40 min, and carry out hydration reaction while mixing the above materials evenly to obtain the mixture; wherein, the mass ratio of magnesium oxychloride cement to water is 1:1.02, the modifier is an organosilicon emulsion, and the amount of modifier added is 1.5 wt% of the total mass of magnesium oxychloride cement.

[0093] S5. Molding and processing: The mixture is placed into a mold and shaped by pressing to form a sheet blank;

[0094] S6. Curing treatment: The board blank is cured by natural curing. The building material blank is cured for 7 days in an environment with a temperature of 20℃ and a relative humidity of 85% to obtain floor tiles.

[0095] Example 2

[0096] The method in this embodiment is the same as that in embodiment 1, except that in step S2, the amount of ferrous sulfate added is 5 wt% of the mass of the pre-purified low-grade magnesite powder, the amount of magnesium sulfate added is 10 wt% of the mass of the pre-purified low-grade magnesite powder, and the amount of sodium carbonate added is 10 wt% of the mass of the pre-purified low-grade magnesite powder.

[0097] Example 3

[0098] The method in this embodiment is the same as that in embodiment 1, except that in step S2, the amount of ferrous sulfate added is 4 wt% of the mass of the pre-purified low-grade magnesite powder, the amount of magnesium sulfate added is 7.5 wt% of the mass of the pre-purified low-grade magnesite powder, and the amount of sodium carbonate added is 7.5 wt% of the mass of the pre-purified low-grade magnesite powder.

[0099] Example 4

[0100] The method in this embodiment is the same as that in embodiment 1, except that in step S3, the total mass of the magnesite-based cement is 100wt%, wherein the amount of reinforcing fiber material added is 5wt%, the amount of curing agent added is 3wt%, the amount of waterproofing agent added is 1wt%, the amount of fly ash added is 20wt%, the amount of metakaolin added is 10wt%, the amount of slag powder added is 15wt%, and the balance is activated low-grade magnesite powder.

[0101] Example 5

[0102] The method in this embodiment is the same as that in embodiment 1, except that in step S3, the total mass of the magnesite-based cement is 100wt%, wherein the amount of reinforcing fiber material added is 10wt%, the amount of curing agent added is 5wt%, the amount of waterproofing agent added is 3wt%, the amount of fly ash added is 30wt%, the amount of metakaolin added is 15wt%, the amount of slag powder added is 20wt%, and the balance is activated low-grade magnesite powder.

[0103] Comparative Example 1

[0104] The method of this comparative example is the same as that of Example 1, except that in step S2, sodium carbonate is used as the second activator, and the amount of sodium carbonate added is 10 wt% of the mass of the low-grade magnesite powder after preliminary purification.

[0105] Comparative Example 2

[0106] The method of this comparative example is the same as that of Example 1, except that in step S2, magnesium sulfate is used as the second activator, and the amount of magnesium sulfate added is 10 wt% of the mass of the low-grade magnesite powder after preliminary purification.

[0107] Comparative Example 3

[0108] The method for this comparative example is the same as that for Example 1, except that in step S2, the first activator, ferrous sulfate, is not added. Comparative Example 4

[0109] The method of this comparative example is the same as that of Example 1, except that in step S2, the premix is ​​placed in a high-temperature furnace, heated from room temperature to 450°C at a rate of 6°C / min, held at that temperature for 40 minutes, and then a second activator is added to the premix in the high-temperature furnace to obtain a mixture. This mixture is then held at 450°C for 80 minutes to obtain activated low-grade magnesite powder. Comparative Example 5

[0110] The method of this comparative example is the same as that of Example 1, except that in step S2, the premixed material is placed in a high-temperature furnace and heated from room temperature to 800°C at a heating rate of 9°C / min, and held for 40 minutes. Then, a second activator is added to the premixed material in the high-temperature furnace to obtain the mixture. After that, it is held at 800°C for another 80 minutes to obtain activated low-grade magnesite powder.

[0111] Performance testing:

[0112] (1) The active MgO content of the activated low-grade magnesite powder obtained in step S2 of the above embodiments was determined by EDTA complexometric titration.

[0113] (2) Referring to GB / T12957-2005 "Granulated blast furnace slag powder for cement admixtures", the activity index of the activated low-grade magnesite powder obtained in step S2 of the above embodiments was tested.

[0114] (3) The water-soluble impurity content of the magnesium-based cement prepared in the above embodiments was tested using the GB / T176-2017 standard.

[0115] (4) After crushing the floor tiles prepared in the above embodiments, take a portion of the sample, grind and crush the sample in a mortar and pass it through a 0.075 mm sieve to ensure that the sample is uniform. Press the powder sample into the sample holder or spread it on a glass slide to form a flat surface. Then, use a German Bruker D8 Advance X-ray diffractometer to measure the XRD pattern. The scanning angle is 5~90°, the scanning speed is 5° / min, the step size is 0.02°, the test target is a copper target, the working voltage is 40 kV, and the power is 4 kW.

[0116] (5) Take a core sample of 0.5 cm to 1.0 cm from the floor tiles prepared in the above embodiments, and polish its surface with a sander. Soak it in anhydrous ethanol for 3 days to stop hydration and dry it at 60 ℃ for 48 h. Use a German ZEISS Sigma 300 scanning electron microscope for SEM test. Before the test, the test surface is sprayed with gold (30mA, 150 s). Ensure a vacuum environment during the test.

[0117] (6) The building material blanks prepared in the above embodiments were cured for 28 days in an environment with a temperature of 20°C and a relative humidity of 85%. The mechanical properties (compressive strength and flexural strength) of the obtained floor tile samples were tested according to the GB / T17671-2021 standard.

[0118] (7) The building material blanks prepared in the above embodiments were cured for 28 days in an environment with a temperature of 20℃ and a relative humidity of 85%, and the water resistance (softening coefficient) of the obtained floor tile samples was tested according to GB / T24129-2009 standard.

[0119] Table 1. Process parameters of the preparation methods of green building materials products in the above embodiments

[0120]

[0121] Table 2. Process parameters for the preparation methods of the green building materials products in the above comparative examples.

[0122]

[0123] In the activated low-grade magnesite powder obtained in step S2 of the above embodiments, the active MgO content is ≥80wt%, especially in Example 3, it reaches 82wt%, which meets the activity requirements of cementitious materials.

[0124] The activated low-grade magnesite powder obtained in step S2 of the above embodiments has an activity index of 0.65-0.70, which is better than that of ordinary lightly calcined MgO (around 0.63), proving that the activation effect is significant.

[0125] The magnesia-based cement prepared in Example 1 has a water-soluble impurity content of ≤0.5%. The magnesia-based cement prepared in Example 3 has a water-soluble impurity content of ≤0.4%.

[0126] Figure 1 XRD pattern of low-grade magnesite powder; Figure 2 The image shows the XRD pattern of the floor tiles prepared in Example 1. Figure 4 The image shows the XRD pattern of the floor tile prepared in Example 3. In the XRD patterns of the floor tile samples prepared in the above examples, only characteristic peaks of magnesium oxychloride 518 phase (2θ=23.1°) and magnesium oxysulfide 318 phase (2θ=27.5°) appeared, while impurity peaks such as Fe2O3 (2θ=33.1°) and Na2SO4 (2θ=25.8°) were absent.

[0127] Figure 3 SEM image of the floor tiles prepared in Example 1; Figure 5 The image shows the SEM image of the floor tile prepared in Example 3. The SEM images of the floor tiles prepared in the above examples show that the matrix is ​​dense, and magnesium oxysulfate whiskers (5-10 μm in length and 0.5-1 μm in diameter) are closely intertwined with the gel phase. The matrix has no obvious pores or free impurity particles, and the density is significantly improved.

[0128] The technical performance indicators of the floor tile sample obtained after 28 days of curing in Example 1 are as follows: 28-day compressive strength is 56.8 MPa, 28-day flexural strength is 9.3 MPa, and 28-day softening coefficient is 0.62.

[0129] The technical performance indicators of the floor tile sample obtained after 28 days of curing in Example 3 are as follows: 28-day compressive strength is 58.2 MPa, 28-day flexural strength is 9.6 MPa, and 28-day softening coefficient is 0.65. The performance is improved compared with Example 1, which proves that the optimization of the ratio of activator and auxiliary ingredients can further improve the product performance.

[0130] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0131] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing magnesium oxychloride-based cement, characterized in that, Includes the following steps: S1. The low-grade magnesite ore is crushed and ground to obtain low-grade magnesite powder; the low-grade magnesite powder is then washed, the washing process including sequential water washing, magnetic separation and flotation, to obtain pre-purified low-grade magnesite powder. S2. The pre-purified low-grade magnesite powder is mixed with the first activator to obtain a premix; under a weak oxidizing atmosphere, the premix is ​​first heated to 400℃-500℃ at a heating rate of 5℃ / min-8℃ / min and held for 30min-45min, then heated to 750℃-850℃ at a heating rate of 8℃ / min-10℃ / min, and the second activator is sprayed into the premix by spraying, controlling the atomization pressure to be 0.2-0.4MPa and the spraying rate to be 4-6mL / min to obtain a mixture, which is then held at 750℃-850℃ for 60min-90min to obtain activated low-grade magnesite powder; wherein, the first activator is ferrous sulfate, and the second activator is a compound of magnesium sulfate and sodium carbonate; S3. The activated low-grade magnesite powder is mixed with additives and auxiliary ingredients to obtain magnesite-based cement; wherein the additives include a compound of reinforcing fiber materials, curing agents and waterproofing agents, and the auxiliary ingredients include a compound of fly ash, metakaolin and slag powder.

2. The method for preparing magnesium-based cement according to claim 1, characterized in that, In step S1, the specific surface area of ​​the low-grade magnesite powder is 350 m². 2 / kg-450m 2 / kg, with an average particle size of 10μm-20μm.

3. The method for preparing magnesium-based cement according to claim 1, characterized in that, In step S2, the amount of the first activator added is 3wt%-5wt% of the mass of the pre-purified low-grade magnesite powder; and / or, the amount of magnesium sulfate added is 5wt%-10wt% of the mass of the pre-purified low-grade magnesite powder; and / or, the amount of sodium carbonate added is 5wt%-10wt% of the mass of the pre-purified low-grade magnesite powder.

4. The method for preparing magnesium-based cement according to claim 1, characterized in that, In step S2, the pre-purified low-grade magnesite powder and the first activator are mixed by stirring. The stirring speed is 300 r / min-500 r / min and the stirring time is 30 min-60 min.

5. The method for preparing magnesium-based cement according to claim 1, characterized in that, In step S3, with the total mass of the magnesite-based cement being 100wt%, the following amounts are added: the activated low-grade magnesite powder is added at 17wt%-46wt%, the reinforcing fiber material is added at 5wt%-10wt%, the curing agent is added at 3wt%-5wt%, the waterproofing agent is added at 1wt%-3wt%, the fly ash is added at 20wt%-30wt%, the metakaolin is added at 10wt%-15wt%, and the slag powder is added at 15wt%-20wt%.

6. The method for preparing magnesium-based cement according to claim 1, characterized in that, In step S3, the activated low-grade magnesite powder is mixed with additives and auxiliary ingredients by stirring. The stirring speed is 800 r / min-1000 r / min and the stirring time is 15 min-20 min.

7. A magnesium oxychloride-based cement, characterized in that, It is obtained by the preparation method of magnesium-based cement according to any one of claims 1-6.

8. A method for preparing a green building material product, characterized in that, Includes the following steps: S4. The magnesium-based cement of claim 7 is mixed with water and a modifier, and then subjected to a hydration reaction under stirring conditions to obtain a mixture; wherein the modifier is an organosilicon emulsion; S5. The mixture is placed into a mold for molding to obtain a building material blank; S6. The building material blank is cured to obtain green building material products.

9. The method for preparing green building materials according to claim 8, characterized in that, In step S4, the amount of modifier added is 1wt%-2wt% of the mass of the magnesium oxychloride cement; the mass ratio of the magnesium oxychloride cement to water is 1:(1.02-1.03); and the hydration reaction time is 30min-45min.

10. A green building material product, characterized in that, Obtained by the method for preparing green building materials as described in claim 8 or 9.

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