Method for preparing autoclaved aerated concrete from unburned coal gangue

Abstract

The present invention relates to the technical field of decarbonization, modification and activation treatment of unburned coal gangue and preparation of autoclaved aerated concrete. The unburned coal gangue decarbonization modifier is any one of nitrate, potassium permanganate, H2O2, etc. A method for decarbonization, modification and activation of unburned coal gangue, comprising: physical decarbonization, mechanical activation, chemical decarbonization, modification and activation and other composite decarbonization, modification and activation. An autoclaved aerated concrete prepared from unburned coal gangue, the material of which contains more than 50% of the above-mentioned decarbonization, modification and activation gangue material. The present invention improves the tolerance of the product to the carbon content of coal gangue, stimulates the activity of the coal gangue raw material, is conducive to promoting the full progress of the hydrothermal reaction, and can produce a multi-mineral cementitious material composed of several hydrated calcium silicates and other hydrated minerals, thereby obtaining a denser microcrystalline structure, and is also conducive to the formation of a microporous structure in the pore wall, so that the product obtains good physical properties.

Description

Technical Field

[0001] The invention relates to a technology for chemically decarbonizing, modifying and activating coal gangue, and a technology for preparing autoclaved aerated concrete by using the decarbonized modified coal gangue. Background Art

[0002] Since the beginning of the new century, many diligent and intelligent individuals, driven by the benefits of waste utilization and environmental protection, or policies to save energy, reduce emissions, and improve building functions, have adopted new technologies and even imported foreign production technology and equipment to produce a wave of new energy-saving building materials. These include hollow bricks, sand-lime bricks, (waste-blended) concrete bricks, lightweight concrete blocks, aerated concrete blocks, lightweight composite insulation blocks, composite panels, EPS insulation boards, phenolic boards, XPS extruded boards, polyurethane boards, foamed cement, rock wool boards, foam glass, and many other new building materials.

[0003] It's undeniable that many new building materials have made significant contributions to the comprehensive utilization of waste, energy conservation and emission reduction, and even the development of modern construction technology. However, some materials also suffer from drawbacks such as high water absorption, flammability, susceptibility to aging, flaking, and high thermal conductivity, resulting in significant losses to the national economy and to people's lives and property, and have become a common criticism of these new energy-saving materials.

[0004] According to statistics, my country's total building area has reached over 60 billion square meters, and is growing at a rate of approximately 2 billion square meters per year. Building energy consumption accounts for 27.5% of total energy consumption, not including energy consumed during building material production and construction. Therefore, building energy conservation is a key national initiative and a key policy.

[0005] Building energy conservation refers to minimizing energy consumption while meeting the same needs or achieving the same goals during the production of building materials, construction of buildings and structures, and their use. This is typically achieved by improving the thermal insulation and sealing properties of building envelopes, such as walls, doors, windows, and roofs, while reducing the energy consumption of heating and air conditioning systems, thereby improving the living environment and conserving energy.

[0006] While short-term energy conservation goals have been achieved, a comprehensive evaluation of energy conservation throughout a building's lifecycle must be critical. The overall goals of "health, comfort, aesthetics, durability, safety, economy, and environmental protection" must not be compromised. Therefore, ideal new energy-saving, environmentally friendly, and ecological building materials should combine lightweight, high-strength, fireproof, non-combustible, waterproof, breathable, thermally insulating, sound-absorbing, weather-resistant, durable, and economical, environmentally friendly features.

[0007] Obviously, autoclaved aerated concrete ecological building materials are the most excellent new ecological materials with this comprehensive feature.

[0008] Autoclaved aerated concrete is a recognized green ecological wall material with the advantages of light weight, heat insulation, thermal insulation, sound insulation, fire resistance, impermeability, earthquake resistance, environmental protection, durability, economy, and convenient construction. It plays an irreplaceable role in the field of wall innovation and energy-saving construction.

[0009] Steam-pressurized concrete is a porous silicate product made from siliceous and calcareous materials as the main raw materials, mixed with gas-generating agents, and manufactured through processes such as raw material preparation, batching and pouring, gasification and stabilization, cutting and shaping, autoclaving and curing, sorting and packaging. Its typical feature is that the pores in the product are formed by chemical reactions.

[0010] The raw materials used in the production of autoclaved aerated concrete are categorized into four main groups: base materials, gas-generating materials, regulating materials, and structural materials. Base materials are the primary components of autoclaved aerated concrete, accounting for over 95% of the product's total weight. These materials include siliceous materials (primarily SiO2) and calcareous materials (primarily CaO). Siliceous materials are generally derived from quartz sand and account for 55-65% of the product's weight. Calcium materials, primarily cement and lime, contribute over 30% of the product's weight.

[0011] Since sand is a non-renewable mineral resource, its cost is not only high but also subject to strict state regulation. Meanwhile, the combined content of inorganic SiO2 and Al2O3 in coal gangue is generally over 70%, sometimes exceeding 90%. The SiO2 content is generally over 50%, sometimes reaching 80%. This shows that coal gangue, as a siliceous material, is inherently suitable for use in autoclaved aerated concrete production. Therefore, developing coal gangue as a siliceous material not only provides an effective way to save energy, soil, waste, and protect the environment, but also offers a sustainable path for autoclaved aerated concrete manufacturers to reduce costs and improve efficiency.

[0012] However, compared to other minerals with pozzolanic activity (including power plant fly ash), the minerals that make up gangue tend to be better crystallized, with a high degree of order and close arrangement of chemical molecules, resulting in a relatively stable chemical structure. Therefore, the pozzolanic activity of raw gangue is very low. Furthermore, the fact that gangue generally contains combustible carbon presents certain obstacles to its direct utilization. Class I and Class II gangues have a carbon content of 6% or less (with a lower calorific value below 420 kcal / kg); Class III gangue has a carbon content of 6% to 20%, falling between Class II and Class IV gangues; and Class IV gangue has a carbon content of 20% or more and a higher calorific value (lower calorific value ≥1400 kcal / kg).

[0013] Because of the above reasons, the current use and research of coal gangue in the field of autoclaved aerated concrete generally uses coal gangue after spontaneous combustion, or uses combustion method to pre-treat the coal gangue.

[0014] After spontaneous combustion of gangue, the carbon content issue has been largely resolved, and the activation of the raw materials has also been improved to a certain extent. Data indicates that 237 gangue mines in my country have experienced spontaneous combustion, and 134 gangue heaps are still experiencing varying degrees of spontaneous combustion. However, spontaneous combustion of gangue not only wastes precious coal resources, but also emits carbon dioxide, sulfur dioxide, nitrogen oxides, and soot, seriously polluting the atmosphere and endangering the health of residents in mining areas. Furthermore, spontaneous combustion of gangue is highly regional, specific, and incomplete. Therefore, researchers have conducted the following research on the autoclaved aeration of spontaneously combusted gangue.

[0015] Combustion of coal gangue not only eliminates the impact of carbon on product quality but also decomposes minerals such as calcite and illite, increasing the gangue's volcanic ash activity. This effectively addresses both the carbon content and raw material activity issues inherent in the comprehensive utilization of coal gangue. However, thermal activation not only consumes a high amount of energy, but also results in secondary energy waste if the heat generated by combustion is not effectively utilized. Furthermore, the high-temperature calcination process releases chemicals that are harmful to the human body and pollute the environment. The application process is cumbersome and uneconomical, increasing carbon emissions and not in line with current development trends in my country. Therefore, research on the preparation of autoclaved aerated concrete using thermally activated coal gangue has remained confined to the laboratory. Application to large-scale industrial production is not only environmentally unfriendly and uneconomical, but also carries certain technical risks.

[0016] Professor Wang Changlong and Qiao Chunyu from Beijing University of Science and Technology and Hebei University of Engineering conducted an experimental study on the preparation of autoclaved aerated concrete using coal gangue and iron tailings. The amount of coal gangue in the optimized scheme was 20% (the amount of iron tailings was 40%). The method was as follows: (1) Pretreatment of raw materials: the coal gangue was crushed to <2mm and then dried to a moisture content of less than 1%. Then, a SMS 500mm×500mm laboratory ball mill was used with a charge of 5kg. The fineness of the coal gangue after grinding was less than 8% of the residue on a 0.08mm square hole sieve. The coal gangue was calcined and activated in a CD-1400X muffle furnace at a calcination temperature of 600℃ for 4h. The calcined coal gangue was water quenched and cooled to room temperature. After drying the iron tailings, the coal gangue was ground using a SMS 500mm×500mm laboratory ball mill to a fineness of less than 7.5% on a 0.08mm square hole sieve. (2) Material preparation: The calcined coal gangue and finely ground iron tailings were used as the main siliceous raw materials for the batching. The final optimized batching scheme was (mass fractions): coal gangue / iron tailings / lime / gypsum = 20 / 40 / 25 / 10 / 5, the aluminum powder paste content was 0.06% of the total weight of the blank, the water addition amount was 0.60 of the total dry material, the pouring temperature was 55°C, and the static curing temperature was 55°C. The autoclave curing conditions were: heating for 2h, constant temperature and pressure for 8h (temperature 185°C, maximum pressure 1.25Mpa), and cooling for 2h. The products meet the requirements of A3.5 and B06 grade qualified products in "Autoclaved Aerated Concrete Blocks" (GB 11968-2006).

[0017] Cong Xinyu and others from Harbin Institute of Technology used self-igniting coal gangue from a coal mine in Dalianhe Town, Heilongjiang Province to conduct experiments on autoclaved aerated concrete. They found that under the condition of taking both compressive strength and dry density into consideration, the optimal mix ratio of coal gangue / quicklime / cement / gypsum is 54 / 23 / 20 / 3, and the aluminum powder content is 1.3‰ of the total amount of the matrix material. At this time, the calcium-silicon ratio of the matrix material is 0.82.

[0018] In the aforementioned related technologies, the amount of gangue used in combustion treatment is only 20%. While the amount used in spontaneous combustion gangue reaches 54%, due to the insufficiency and unevenness of spontaneous combustion gangue, it is not suitable for industrial production. Therefore, the low amount used in resource utilization cannot be achieved on a large scale. Furthermore, the use of combustion to treat gangue not only wastes precious coal resources but also emits carbon dioxide, sulfur dioxide, nitrogen oxides, and smoke during the combustion process, seriously polluting the atmosphere. Summary of the Invention

[0019] After extensive research, the inventors discovered that coal in gangue undergoes oxidation under the action of an oxidant. The oxidation process progresses from surface oxidation to mild oxidation, moderate oxidation, deep oxidation, and finally complete oxidation. The molecular structure of the oxidation product decreases from complex to simple as the oxidation temperature increases, the stronger the oxidant, and the longer the oxidation time. The product progresses from complex humic acid to simple low-molecular-weight acids, ultimately being completely oxidized to carbon dioxide and water.

[0020] It was further discovered that the oxidation conditions for coal carbon in coal gangue are:

[0021] It can be oxidized in a strong oxidant (such as nitric acid) solution at 60-100℃;

[0022] 100-200℃ can be oxidized by air and oxygen in alkaline solution;

[0023] It can be oxidized by direct air and oxygen at 100-300℃;

[0024] It can be oxidized by air oxygen in pressurized alkaline solution at 200-300℃.

[0025] At all stages, increasing the oxidant strength, increasing the oxidant dosage, extending the reaction time, increasing the oxidation temperature, increasing the stirring measures, and increasing the reaction pressure can promote the speed and efficiency of oxidation.

[0026] The inventors' experimental research has found that oxidizing gangue with 7% H₂O₂ at 60°C to 80°C for 12 hours completely destroys the carbon structure in the gangue, with over 90% of the carbon in the original gangue undergoing moderate to deep oxidation, converting large molecules into small ones. With the addition of cement and lime alkaline materials, and even after the gangue autoclaved aerated concrete body is further pressurized and heated in the autoclave, the residual carbon and its oxidation products (such as small molecule acids) in the body undergo further oxidation and decomposition, until they are completely oxidized into CO₂ and H₂O. After the CO₂ and H₂O evaporate, the space occupied by these products partially becomes the micropores in the pore walls of the gangue autoclaved aerated concrete.

[0027] The study also found that as the carbon in the gangue is continuously oxidized, its mineral structure, such as calcite and illite, disintegrates and decomposes as the gangue is stripped away, promoting the depolymerization and activation of elements like SiO2 and CaO in the gangue. Based on the pore structure theory of autoclaved aerated concrete, it is known that maintaining the porosity constant, reducing the pore content, and increasing the capillary and micropore content can improve the strength of autoclaved aerated concrete. Therefore, the micropores formed by the small molecular products produced by oxidation of gangue with strong oxidants provide an auxiliary means of reducing the pore size and improving the strength of autoclaved aerated concrete. Furthermore, oxidation of gangue with strong oxidants disintegrates and decomposes its mineral components, promoting the depolymerization and activation of elements like SiO2 and CaO, and enhancing the hydration reaction of autoclaved aerated concrete, a development we welcome. Therefore, the strong oxidant introduced in the preparation process of gangue autoclaved aerated concrete not only becomes a decarbonization modifier for gangue, but also becomes a performance activation stimulator for elements such as SiO2 and CaO in gangue.

[0028] The present invention aims to solve the key problems existing in the process of preparing autoclaved aerated concrete using coal gangue, and provides a method for improving the tolerance of the carbon content of coal gangue in the preparation of autoclaved aerated concrete. It also provides a coal gangue decarbonization, modification and activation treatment technology with an environmentally friendly coal gangue decarbonization treatment method, less coal gangue treatment equipment and high treatment efficiency, and a technology for preparing autoclaved aerated concrete using the above-mentioned coal gangue.

[0029] In view of the above-mentioned limitations, the present invention proposes an unburned coal gangue decarbonization modification activator, a decarbonization modification activation method and autoclaved aerated concrete prepared therefrom.

[0030] An unburned coal gangue decarbonization modification activator, the unburned coal gangue chemical decarbonization modification activator comprising:

[0031] Group 1: Nitrates;

[0032] and / or, in the second group, peroxides or percarbonates;

[0033] and / or, in the third group, permanganate;

[0034] The amount of the unburned gangue decarbonization modification activator used accounts for 1% to 7% of the total mass of the gangue.

[0035] Further: the nitrate includes: at least one of sodium nitrate, calcium nitrate, and calcium ammonium nitrate;

[0036] The percarbonate comprises at least one of sodium percarbonate and calcium percarbonate;

[0037] The peroxide comprises: H2O2;

[0038] The permanganate includes potassium permanganate.

[0039] Further: If the unburned coal gangue decarbonization modification activator is only nitrate, the amount of nitrate used accounts for 1% of the coal gangue

[0040] Total mass, by mass:

[0041] For coal gangue with carbon content of 0% to 5%, use 1% to 3%;

[0042] For gangue with 5% to 10% carbon content, use 2% to 5%;

[0043] For coal gangue with a carbon content of 10% to 15%, use 3% to 6%;

[0044] For coal gangue with a carbon content of 15% to 20%, 4% to 7% is used.

[0045] A method for decarbonizing, modifying and activating unburned coal gangue includes: chemical decarbonizing, modifying and activating treatment, wherein the chemical decarbonizing, modifying and activating treatment comprises: treating the unburned coal gangue with the unburned coal gangue decarbonizing, modifying and activating agent to obtain decarbonizing, modifying and activated gangue slurry.

[0046] Furthermore: the method also includes: physical decarbonization and / or mechanical activation, and the coal gangue is first treated with physical decarbonization and / or mechanical activation, and then chemical decarbonization modification and activation treatment is performed after treatment.

[0047] Furthermore: the physical decarbonization is to separate the coal and the gangue by photoelectric separation, and / or to adopt at least one of screening, wet separation and gravity separation, so that the carbon content of the gangue is the first carbon content;

[0048] The mechanical activation is to hammer the gangue and then grind it to make the gangue particle size into the first particle size;

[0049] After the chemical decarbonization, modification and activation treatment, the carbon content of the gangue in the decarbonization, modification and activation gangue slurry obtained is made to be the second carbon content.

[0050] Furthermore: the first carbon content is less than 20%; the second carbon content is less than 3%;

[0051] The milling and refining process uses dry milling or wet milling;

[0052] The first particle size is: 180 mesh sieve residue ≤ 15%.

[0053] Furthermore: the chemical decarbonization modification and activation treatment is to add the unburned coal gangue decarbonization modification activator to the unburned coal gangue according to the above-mentioned usage amount, and stir it at a temperature of 60°C to 80°C until it is fully reacted to obtain the decarbonization modification activated gangue slurry with a carbon content of less than 3%, and the decarbonization modification activated gangue slurry contains 30% to 90% silicon oxide, 0.2% to 45% aluminum oxide, and 0.05% to 20% calcium oxide.

[0054] A kind of autoclaved aerated concrete prepared from unburned coal gangue, the ingredients of the autoclaved aerated concrete prepared from unburned coal gangue are:

[0055] Using decarbonized modified activated gangue slurry with a mass content of 50% or more, wherein the decarbonized modified activated gangue slurry is obtained by the method;

[0056] The calcium / silicon ratio of the ingredients is 0.5-1.0.

[0057] Furthermore, the hydrothermal synthesis product contained in the autoclaved aerated concrete prepared from the unburned coal gangue comprises hydrated mineral crystals, wherein the hydrated mineral crystals include any combination of CSH(I), tobermorite, aluminum-substituted tobermorite, hydrogarnet, xonotlite, and hydrated calcium sulfoaluminate.

[0058] Furthermore, the autoclaved aerated concrete prepared from the unburned coal gangue forms a heterogeneous solid-liquid-gas multiphase aggregate structure with a core particle of siliceous material as a skeleton, hydrated silicate as a colloid, connected and supported by crystal intergrowths, and including a variety of micropores.

[0059] Compared with the related art, the present invention has the following advantages:

[0060] In one aspect of the present invention, an unburned coal gangue decarbonization modification and activation agent, utilizing the modified agent claimed herein, not only increases the tolerance of the autoclaved aerated concrete manufacturing process for the carbon content of the coal gangue material, but also effectively stimulates and enhances the activity of the coal gangue raw material, improving the hydrothermal synthesis reaction efficiency of the product, generating sufficient hydration products, and promoting an increase in the micropore content of the pore walls of the autoclaved aerated concrete. This facilitates process control for reducing the large pore content while maintaining a constant porosity, resulting in a product with excellent performance. Furthermore, the modified agent can achieve decarbonization, activation, and micropore creation in a single step, thus possessing significant innovative significance. The chemical decarbonization modification agent can achieve a coal gangue content exceeding 60%, with high reaction efficiency and no need for additional equipment, thus reducing construction investment. In the preparation of the autoclaved aerated concrete of the present invention, coal gangue is used as the primary raw material for the siliceous material, with a coal gangue content exceeding 60%. This high-proportion resource utilization can significantly address the problem of coal gangue accumulation. After being treated with the modifier or method of the present invention, the coal gangue raw material for preparing autoclaved aerated concrete can reach more than 60%, which has an unexpected technical effect.

[0061] Another aspect of the present invention relates to a method for decarbonizing, modifying, and activating unburned coal gangue, and another aspect relates to autoclaved aerated concrete prepared from unburned coal gangue. By combining physical decarbonization, mechanical activation, and chemical decarbonization, modification, and activation, the present invention improves the utilization rate of the coal gangue and increases its usage in autoclaved aerated concrete, thereby effectively recycling the coal gangue and resolving the environmental issues associated with its storage. Furthermore, the present invention enhances the activity of the coal gangue, significantly improving the physical properties of the autoclaved aerated concrete products. By using the above-mentioned decarbonization modification activator to chemically decarbonize gangue, the tolerance of the autoclaved aerated concrete manufacturing process for the carbon content of the gangue raw material is expanded, making it possible to use Class III gangue in autoclaved aerated concrete, thereby increasing the processing ratio of gangue; at the same time, the carbon content of Class I and Class II gangue can be further reduced to obtain higher-quality autoclaved aerated concrete products. It also effectively stimulates and increases the activity of the gangue raw material, further improving the hydrothermal synthesis reaction effect of the product, promoting the increase in the micropore content of the autoclaved aerated concrete, and thus improving the physical properties of the autoclaved aerated concrete product. The method combines the functions of decarbonization, activation, and promotion of micropore content in a single step, thus having significant innovative significance. The gangue content after treatment by the method of the present invention can reach over 60%, and the reaction efficiency is high. No additional equipment is required, reducing economic investment. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1-1The samples of Experimental Example 1 and Experimental Example 2 were prepared by adding chemical modifiers to 1# coal gangue raw material. In Experimental Example 2, other modifiers were added to further improve the strength of the product.

[0063] Figure 1-2 The samples of Experimental Example 3 (H3) and Experimental Example 4 (H4) were prepared by adding chemical modifiers to 2# coal gangue raw material. In Experimental Example 4 (H4), other modifiers were added to further improve the strength of the product.

[0064] Figure 1-3 The sample (15-2) of Experimental Example 5 was prepared by adding a chemical modifier to the 3# coal gangue raw material;

[0065] Figure 1-4 The sample of Experiment 6 was prepared by adding other regulators to the raw material of 3# coal gangue on the basis of Experiment 5;

[0066] Figure 2 This is a 40-fold magnified observation photo of 2# coal gangue raw material, in which the black particles are carbon particles;

[0067] Figure 3 The raw material was 3# coal gangue with a carbon content of about 15.4%. No chemical modification activator was added. After batching, stirring, pouring, pausing, and demoulding, the appearance inspection showed that the sample was unqualified. The mechanical strength was poor and there was uneven bubble distribution. Therefore, no further subsequent processing and testing were carried out.

[0068] Figure 4 This is an XRD diffraction pattern of an autoclaved aerated concrete experimental sample prepared from 1# coal gangue in another embodiment of the present invention;

[0069] Figure 5 This is a SEM image of an experimental sample of autoclaved aerated concrete prepared with 1# coal gangue according to another embodiment of the present invention. DETAILED DESCRIPTION

[0070] To make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below. However, it should be understood that the description herein is only for explaining the present invention and is not intended to limit the scope of the present invention.

[0071] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art to which this invention pertains. The terms used in this specification are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The characterization methods used herein can be found in the relevant descriptions in the prior art and will not be elaborated upon herein.

[0072] In order to further understand the present invention, the present invention is further described in detail below in conjunction with the best embodiment.

[0073] During long-term research, the inventors discovered that coal gangue is an aggregate of various sedimentary rocks, each composed of different diagenetic minerals. The carbon in the gangue is largely intermingled, interwoven, and encapsulated with various minerals within the gangue, such as quartz, alumina, and carbonates, or mixed within various carbonate mineral phases, such as calcite, mica, kaolinite, and illite. Therefore, one of the main research objectives of the present invention is to determine how to process the gangue to enhance the activity of elements such as silicon oxide and silicon dioxide within the gangue.

[0074] Example 1

[0075] An unburned coal gangue decarbonization modification activator, the unburned coal gangue decarbonization modification activator comprising:

[0076] Group 1: Nitrates;

[0077] and / or, in the second group, peroxides or percarbonates;

[0078] and / or, in the third group, permanganate;

[0079] The amount of the unburned coal gangue decarbonization modification activator used is 1% to 7% of the total mass of the coal gangue, and can be, for example, 1%, 2%, 3%, 4%, 5%, 6%, or 7%. The present invention is not limited to the listed values, and other values ​​not listed within this numerical range are also applicable.

[0080] Further: the nitrate includes: at least one of sodium nitrate, calcium nitrate, and calcium ammonium nitrate;

[0081] The percarbonate comprises at least one of sodium percarbonate and calcium percarbonate;

[0082] The peroxide comprises: H2O2;

[0083] The permanganate includes potassium permanganate.

[0084] Further: If the unburned coal gangue decarbonization modification activator is only nitrate, the amount of nitrate used in the total mass of coal gangue is calculated by mass as follows:

[0085] For gangue with a carbon content of 0% to 5%, 1% to 3% is used; for example, 1%, 2%, or 3% may be used. The present invention is not limited to the values ​​listed, and other values ​​not listed within the range are also applicable.

[0086] For gangue with a carbon content of 5% to 10%, 2% to 5% is used; for example, 2%, 3%, 4%, or 5% can be used. The present invention is not limited to the values ​​listed above, and other values ​​not listed within the range are also applicable.

[0087] 3% to 6% is used for coal gangue with a carbon content of 10% to 15%; for example, it can be 3%, 4%, 5%, or 6%. The present invention is not limited to the values ​​listed, and other values ​​not listed within the numerical range are also applicable.

[0088] The coal gangue with a carbon content of 15% to 20% uses 4% to 7%, for example, 4%, 5%, 6%, 7%. The present invention is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0089] Coal is a reducing agent and easily reacts with oxidants. Coal oxidation not only destroys its structure but also produces new substances (including CO2, H2, O2) and other gases. Studies have shown that when coal is oxidized with H2O2, H2O2 breaks covalent bonds, such as Ar-OH, Ar-O-Ar, and replaces carbon, and then generates -COOH, C-O-C, and R-OH. The hydrogen and oxygen absorbed during coal oxidation primarily enter the carbon structure in the form of -OH. First, the weak C-O bond breaks, producing a large number of water-soluble macromolecules and CO2. The macromolecules gradually decompose into small molecules such as fatty acids. Experiments have shown that at relatively low temperatures (100°C), coal can undergo various oxidation reactions with air, oxygen, or other strong oxidants. Although the conditions are relatively mild, the coal structure can still be destroyed.

[0090] Coal oxidation is the process by which the molecular structure of coal is transformed from complex to simple under the action of an oxidant. The higher the oxidation temperature, the stronger the oxidant, and the longer the oxidation time, the simpler the molecular structure of the oxidation product, from the complex humic acid to the simple phenylcarboxylic acid, until it is completely oxidized to carbon dioxide and water. When coal is oxidized with H2O2 at 60°C for 2 hours, 90% is converted into small molecules such as phenylcarboxylic acid, fatty acids, and oxalic acid. 17% of the product is soluble in water, leaving only 10% of the residual coal. At this point, the coal structure is completely destroyed. In alkaline environments, such as those with Ca(OH)2, especially under autoclaved conditions, products such as oxalic acid will continue to undergo oxidation reactions, forming nano-scale calcium oxalate crystals, or even being completely oxidized to form carbon dioxide and water.

[0091] Based on the above findings, the inventors conducted further experiments and added an appropriate strong oxidant to the gangue to disrupt the structure of the coal in the gangue. Oxidation then resulted in the emission of some of the coal-generated gases, thereby reducing the coal content and impact. The other small molecules generated by oxidation, such as carboxylic acids and oxalic acid, not only are less likely to cause concentrated damage to the finished product, but are even completely oxidized to carbon dioxide and water after exposure to an alkaline environment, as curing time, pressure, and temperature increase. Furthermore, this oxidation reaction strips the coal from other minerals, altering the physical and chemical properties of the original minerals (such as illite, mica, and impurity-rich minerals in coal interbedded gangue), and depolymerizing them into highly active components such as silicon oxide, aluminum oxide, and calcium oxide, which facilitate their participation in the hydrothermal synthesis reaction of the finished product. Furthermore, the oxidation process breaks Al-O and Si-O bonds, enhancing the gangue's pozzolanic activity and addressing the problem of low gangue pozzolanic activity. Furthermore, the chemically modified activator has no other adverse effects on the inorganic mineral raw materials in the gangue.

[0092] Therefore, the use of this chemical modifier not only expands the tolerance for carbon content in coal gangue, enabling the use of Class III coal gangue in autoclaved aerated concrete, thereby increasing the proportion of coal gangue that can be processed. It also further reduces the carbon content of Class I and Class II coal gangue, enabling the use of coal gangue to reach 50-70% by weight. Furthermore, the modifier effectively stimulates and enhances the hydrothermal activity of the coal gangue raw material, further improving the hydrothermal synthesis reaction efficiency of the product. This facilitates the formation of a microcrystalline structure composed of hard, multi-mineral and cementitious materials, including hydration products such as tobermorite, aluminum-substituted tobermorite, CSH, xenosilicate, and hydrated calcium sulfoaluminate, during the autoclaved curing process. This also promotes the formation of a microporous structure in the autoclaved aerated concrete, thereby improving the physical properties of the concrete product. This single-step process combines decarbonization, activation, and microporous structure formation, making it a highly innovative process. In the preparation of autoclaved aerated concrete, gangue is used as the primary siliceous material, with the gangue content exceeding 60%. This high proportion of resource utilization significantly addresses the problem of gangue accumulation. Treatment with the reagents or methods of the present invention allows the raw material content of concrete to exceed 60%, resulting in unexpected technical benefits.

[0093] Example 2

[0094] On the basis of Example 1, a method for decarbonization, modification and activation of unburned coal gangue is provided, which includes: chemical decarbonization, modification and activation treatment, wherein the chemical decarbonization, modification and activation treatment is: treating the unburned coal gangue with the unburned coal gangue decarbonization modification activator to obtain decarbonization, modification and activation gangue slurry.

[0095] Furthermore: the method also includes: physical decarbonization and / or mechanical activation, and the coal gangue is first treated with physical decarbonization and / or mechanical activation, and then chemical decarbonization modification and activation treatment is performed after treatment.

[0096] Preferably, the method may include any one of the following:

[0097] 1.① First carry out physical decarburization, then mechanical activation, and finally chemical decarburization modification activation;

[0098] Or, ② first carry out mechanical activation, and then carry out chemical decarburization modification activation;

[0099] Further: the physical decarbonization is to separate the coal and the gangue with a carbon content of the first carbon content by photoelectric separation, or to obtain the gangue with a carbon content of the first carbon content by screening, wet separation, gravity separation, etc.;

[0100] The mechanical activation is to hammer the gangue and then further grind and refine it to obtain activated gangue material with a first particle size;

[0101] The chemical decarbonization modification and activation is to use the coal gangue chemical decarbonization modification activator to carry out chemical decarbonization modification and activation treatment; after the chemical decarbonization modification and activation, a modified and activated low-carbon gangue slurry with a carbon content of the second carbon content is obtained.

[0102] The mechanical activation is to hammer and ball-mill the first carbon content gangue obtained after physical decarbonization of Class I, Class II, Class III coal gangue and photoelectric separation, or screening, wet separation, gravity separation, etc., to achieve activated gangue material with a first particle size.

[0103] Chemical decarbonization modification and activation: using the chemical decarbonization modification activator described in Example 1, performing a decarbonization modification and activation treatment on the activated gangue of the first particle size obtained after physical decarbonization; after the chemical decarbonization modification and activation, obtaining activated low-carbon gangue with a carbon content of the second carbon content;

[0104] The most important factors influencing the physical properties of autoclaved aerated concrete prepared from coal gangue are the carbon content of the raw material and the activity of its mineral components such as silicon oxide, aluminum oxide, and calcium oxide. Therefore, it is necessary not only to reduce the carbon content of the coal gangue, but also to modify and activate the coal gangue as much as possible.

[0105] In the above method, if the carbon content of the gangue raw material already meets the first carbon content, the mechanical activation + chemical decarbonization modification activation treatment method can be directly used, and photoelectric separation, or physical decarbonization methods such as screening, wet separation, gravity separation, and flotation are no longer required.

[0106] The three types of coal gangue with higher carbon content can also be directly treated by chemical decarbonization modification and activation methods, but direct treatment cannot recover coal with higher carbon content, which will cause waste of energy resources.

[0107] The screening, wet separation, gravity separation and flotation methods can adopt but are not limited to conventional methods, which will not be described in detail here.

[0108] The following specific implementation steps are used as examples to illustrate the method of the present invention, but should not be regarded as limiting the present invention:

[0109] ① Physical decarbonization: Physical treatment methods to reduce the carbon content of coal gangue include electro-optical separation, screening, wet separation, gravity separation, flotation and other conventional physical decarbonization methods.

[0110] ② Mechanical activation: The coal gangue with the first carbon content is hammered and then subjected to deep fine grinding to achieve a first particle size; the deep fine grinding is carried out by dry grinding or wet grinding; the first particle size is 180 mesh sieve residue ≤15%.

[0111] Uncalcined gangue has very low volcanic ash activity. Ball milling mechanically activates gangue activity. During ball milling, intense mechanical impact, shearing, grinding, and interparticle compression and collision refine the gangue's mineral crystals. Furthermore, mechanical forces create microcracks on and within the particles, creating surface defects that allow polar molecules or ions to more easily enter the internal voids of the crystal structure, promoting the depolymerization of silica and alumina in the gangue. The most obvious effect is particle refinement and an increase in specific surface area, significantly improving the efficiency and effectiveness of hydrothermal synthesis reactions.

[0112] ③ Chemical decarbonization modification and activation: The mechanically finely ground activated coal gangue slurry of the first carbon content and the first particle size is treated with one of the strong oxidants, including but not limited to sodium nitrate, calcium nitrate, H2O2, etc., to chemically oxidize the organic carbon in the coal gangue mineral crystals, so that the coal carbon is separated from other mineral bodies. Some of the generated gases, such as CO2, H2, and O2, are volatilized, and some of the generated small molecules are dispersed in the raw materials, and some are even completely oxidized to form carbon dioxide and water, thereby changing the physical and chemical properties of the original minerals, especially the mineral crystals with a large amount of impurities such as illite, mica, and coal-bed gangue, so that they are excited and depolymerized into highly active components such as silicon oxide, aluminum oxide, and calcium oxide, which are conducive to increasing solubility and participating in the hydrothermal synthesis reaction of the product. In addition, the chemical modification activator has no other adverse effects on the inorganic mineral raw materials in the coal gangue.

[0113] Therefore, the chemical modification and activation method not only expands the tolerance for carbon content in coal gangue but also effectively stimulates and enhances the activity of the raw material, further improving the efficiency of the hydrothermal synthesis reaction in the product and promoting the improvement of the microporous structure of the autoclaved aerated concrete, thereby improving the physical properties of the autoclaved aerated concrete product. This method combines decarbonization, activation, and the improvement of the microporous structure in the product in a single step, making it of great innovative significance.

[0114] The unburned coal gangue decarbonization, modification and activation method of the present invention, by combining physical decarbonization, mechanical activation, chemical decarbonization, modification and activation and other composite decarbonization, modification and activation methods, on the one hand, improves the utilization rate of coal gangue and increases the amount of coal gangue used in autoclaved aerated concrete, thereby enabling the effective resource utilization of coal gangue, saving the raw material cost of autoclaved aerated concrete, and solving the environmental problems of coal gangue stacking. On the other hand, it expands the tolerance of the autoclaved aerated concrete manufacturing process for the carbon content of coal gangue materials, effectively stimulates and increases the activity of coal gangue raw materials, further improves the hydrothermal synthesis reaction effect of the product, promotes the increase in the content of the microporous structure of the product, and thus improves the physical properties of the autoclaved aerated concrete product. It combines the functions of decarbonization treatment, activation treatment and promotion of the increase in the content of the microporous structure of the product in one step, and therefore has great innovative significance.

[0115] Example 3

[0116] On the basis of Example 1 or 2, further: the first carbon content is less than 20%; for example, it can be 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%. The present invention is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable;

[0117] The second carbon content is less than 3%, for example, it can be 1%, 1.5%, 2%, 2.5%, 3%. The present invention is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable;

[0118] In the mechanical activation, the grinding and refining adopts dry grinding or wet grinding; the first particle size is: 180 mesh sieve residue ≤ 15%.

[0119] Uncalcined gangue is inactive or has very low activity. The ball milling refinement process uses mechanical stimulation and mechanical-chemical combined stimulation to stimulate the activity of gangue. During the ball milling process, the gangue mineral crystal particles are refined through intense mechanical impact, shearing, grinding, and the mutual compression and collision between particles. In addition, the mechanical force causes microcracks on the surface and interior of the particles, resulting in surface defects, making it easier for polar molecules or ions to enter the internal voids of the crystal structure, promoting the depolymerization of silica, calcium oxide, and aluminum oxide in the gangue. The most obvious effect is the refinement of the particles and the increase in specific surface area, which greatly improves the efficiency and effectiveness of the hydrothermal synthesis reaction.

[0120] By using the method of chemical decarbonization modification and activation, the silicon oxide, aluminum oxide, calcium oxide and other components contained in the gangue can be fully activated. These activated components can fully participate in the hydrothermal reaction of the product, thereby improving the physical properties of the concrete products.

[0121] Furthermore, the chemical decarbonization modification and activation method is to add the coal gangue chemical decarbonization modification agent to the slurry of the activated gangue material of the first particle size according to the above usage amount, and stir it at a temperature of 60-80° C. until it undergoes a sufficient oxidation reaction to obtain the modified activated low-carbon gangue slurry;

[0122] The amount of the activation agent for chemical decarbonization modification of coal gangue is 1% to 7% of the total mass of the coal gangue before addition. For example, it can be 1%, 2%, 3%, 4%, 5%, 6%, or 7%. The present invention is not limited to the listed values, and other values ​​not listed within this range are also applicable.

[0123] Furthermore: the chemical decarbonization, modification and activation method is to use one of the strong oxidants including but not limited to sodium nitrate, calcium nitrate, H2O2, etc. on the mechanically finely ground activated coal gangue slurry with a carbon content still at the first carbon content and a particle size of the first particle size according to the above usage amount, and stir at a temperature of 60 to 80°C until sufficient reaction occurs to obtain the decarbonized, modified and activated gangue slurry, which generally requires stirring for more than 60 minutes. The obtained decarbonized, modified and activated gangue slurry can be stored in a slurry tank for standby use. It needs to be stirred during storage to avoid precipitation. At the same time, the incompletely oxidized organic carbon in the slurry and the small molecular organic matter produced by carbon oxidation continue to be oxidized in the slurry tank until they are completely decomposed into CO2 and H2O.

[0124] Furthermore, the chemical decarbonization modification and activation treatment is to add the unburned coal gangue decarbonization modification activator to the unburned coal gangue according to the above-mentioned usage amount, and stir it at a temperature of 60°C to 80°C until it is fully reacted to obtain the decarbonization modification activated gangue slurry with a carbon content of less than 3%, and the decarbonization modification activated gangue slurry contains:

[0125] Silicon oxide 30% to 90%, for example, can be 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%. The present invention is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable;

[0126] Aluminum oxide 0.2% to 45%, for example, can be 1%, 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%. The present invention is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable;

[0127] Calcium oxide is 0.05% to 20%, for example, it can be 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%. The present invention is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0128] The carbon content below 3% may be, for example, 1%, 1.5%, 2%, 2.5%, or 3%. The present invention is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0129] Example 4

[0130] On the basis of any one of Examples 1-3, an autoclaved aerated concrete prepared from unburned coal gangue is provided, wherein the ingredients of the autoclaved aerated concrete prepared from unburned coal gangue are:

[0131] A decarbonized modified activated gangue slurry having a mass content greater than or equal to 50% is used, and the decarbonized modified activated gangue slurry is obtained by the method described in Example 3; the mass content is greater than or equal to 50%, for example, it can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, etc. The present invention is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0132] The calcium / silicon ratio of the ingredients is 0.5 to 1.0; for example, it can be 0.5, 0.6, 0.7, 0.8, 0.9, or 1. The present invention is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0133] When the pores in autoclaved aerated concrete are small and evenly distributed, they generally have a better ability to resist external loads, which is manifested as high compressive strength of the product. On the contrary, if the pores are large (such as greater than 2mm) and unevenly distributed, they are prone to stress concentration under external loads, causing premature damage to certain pore wall structures in the product and reducing the product strength. Therefore, while maintaining the same porosity, reducing the pore content (macro, visible) and increasing the micropore content is an effective way to improve the strength of autoclaved aerated concrete.

[0134] The porosity of B07 grade products is 68% to 71%, the porosity of B06 products is 72% to 76%, and the porosity of B05 grade products is 77% to 80%. The presence of these pores changes the density of the product, which will lead to a decrease in strength, but improve thermal insulation and frost resistance.

[0135] The porosity of autoclaved aerated concrete is primarily determined by the amount of aluminum powder added, which in turn determines its dry density. In the present invention, the amount of aluminum powder used is reduced by approximately 10% compared to conventional formulations. However, the density of the final product shows no reduction in porosity, demonstrating that the unburned coal gangue decarbonization modification and activator of the present invention increases porosity.

[0136] Through experimental observation, it can be found that the pores formed by the pore wall material inside the autoclaved aerated concrete can be divided into two categories: macropores and micropores.

[0137] Large pores, also called macropores, are visible to the naked eye and are formed by bubbles, hence the common term "stomata." These pores are formed by gassing materials, such as aluminum powder, within the slurry. These pores gradually harden and become fixed within the blank during the static process. Their size ranges from approximately 2 mm to under 0.8 mm.

[0138] Micropores, also known as microscopic pores, exist within the pore walls and can only be clearly observed under microscopes or electron microscopes. They include capillary pores, gel pores, and intercrystalline pores. Under electron or scanning electron microscopy, intracrystalline pores between gel particles, known as ultramicropores, can also be seen. Capillary pores typically have a radius of 100 μm to 5 nm and are formed by the evaporation of capillary water. Gel pores and intercrystalline pores, on the other hand, exist between colloid and crystal particles at smaller sizes, typically between 1 and 5 nm, due to particle discontinuity. Ultramicropores are even smaller, typically below the scale of colloidal particles, and are caused by the uneven internal structure of colloidal particles. Except for the water in pores above the capillary, which can evaporate (hence the term condensed water), the water in other micropores often participates in the formation of the pore wall structure to some extent or becomes part of it. This includes adsorbed water (or gel water) and interlayer water, which are non-evaporable water. Loss of this water would disrupt the internal structure of the material and cause damage. Furthermore, the hydrothermal synthesis product contained in the autoclaved aerated concrete prepared from the unburned coal gangue comprises hydrated mineral crystals, wherein the hydrated mineral crystals include any combination of CSH(I), tobermorite, aluminum-substituted tobermorite, hydrogarnet, xonotlite, and hydrated calcium sulfoaluminate, such as Figure 5 shown.

[0139] The role of coal gangue in autoclaved aerated concrete is to provide siliceous material for the hydrothermal synthesis reaction. At room temperature, the crystal structure of siliceous material is stable, in a state of minimum internal energy, and is an inert material. During high-temperature hydrothermal treatment, the solubility of the siliceous material (SiO2) in the coal gangue increases, and it reacts with the calcium material CaO in the raw materials (cement, lime) to form hydration products such as calcium silicate hydrate (CSH). Calcium silicate hydrate is a calcium silicate hydrate mineral with the chemical formula Ca5Si6O 16 (OH)·4H2O. CSH(I) is one of the most important hydrates in silicate concrete. It is a monobasic calcium silicate hydrate with low crystallinity and high compressive strength. It can be synthesized in a short time from lime and quartz sand or lime and silica gel under autoclaving conditions at 125-175°C (lime and silica gel can also be synthesized over a longer time at room temperature). Due to the presence of various impurities in the main raw materials, the resulting cementitious material cannot be a pure hydration product of CSH(I), but rather a mixed phase or continuous phase of various hydration products, including calcium silicate hydrate, calcium aluminate, and calcium sulfoaluminate hydrate. Under autoclaving curing conditions (175-195°C, 0.9-1.4 MPa saturated steam curing), the single-crystal CSH(I) is largely converted into coarse tobermorite, thereby stabilizing and improving the product's performance.

[0140] From the perspective of product strength and the microscopic perspective of intergrowths, the mineral composition of autoclaved aerated concrete products prepared from unburned coal gangue is characterized by the presence of more low-alkalinity calcium silicates (such as tobermorite, xonotlite, orthorhombic mortar, and CSH single crystals) with extremely small crystal sizes, large specific surface areas, numerous intergrowth contact points, and strong connections between particles, while the presence of less high-alkalinity calcium silicate hydrates (such as C6S3H, C3S2H, C2SH, and C3SH2) with coarse crystals and few intergrowth contact points is reduced. Furthermore, a multi-mineral cementitious material composed of two or more calcium silicate hydrates and other hydrated minerals can be formed, resulting in a denser microcrystalline structure and better product strength and durability. This is the reason why the autoclaved aerated concrete products prepared from unburned coal gangue of the present invention achieve high strength and long-term durability.

[0141] Furthermore, the autoclaved aerated concrete prepared from the unburned coal gangue forms a heterogeneous solid-liquid-gas multiphase aggregate structure with a core particle of siliceous material as a skeleton, hydrated silicate as a colloid, connected and supported by crystal intergrowths, and including a variety of micropores.

[0142] Example 5

[0143] The following is a method for preparing autoclaved aerated concrete using decarbonized unburned coal gangue according to the present invention, using specific steps:

[0144] (1) Mixing ingredients: The modified activated gangue slurry described in Example 4 is mixed with lime, cement, and other calcium materials, and conditioning materials according to a preset formula to prepare a mixed slurry, wherein the mixed slurry contains more than 50% of the activated gangue material described above; and the calcium / silicon ratio in the mixed slurry is 0.5 to 1.0;

[0145] (2) Pouring and stopping: continue to stir the slurry and add the gas generating agent, quickly inject it into the steel mold, and send it into the constant temperature and humidity box to generate gas and stop;

[0146] (3) Cutting and demoulding: After removing the bread head that is higher than the mold with steel wire cutting, demoulding is performed to obtain the green body;

[0147] (4) Pre-curing before the autoclave: the green body is sent to a constant temperature and humidity chamber for pre-curing before the autoclave;

[0148] (5) Autoclave curing: The green body that has been pre-cured in the autoclave is sent to the autoclave for autoclave curing.

[0149] Preferably, the static temperature is 50-65°C, the humidity is 90-95°C, and the time is 2.5-4.5 hours.

[0150] Preferably, the pre-curing temperature before the autoclave is 60-80°C, the humidity is 90-95 degrees, and the time is 2-4 hours.

[0151] Preferably, the autoclave curing conditions are:

[0152] The first stage: the temperature is raised from room temperature to 105℃ at a constant speed for 10 minutes; the second stage: the temperature is raised from 105 to 125℃ at a constant speed for 75 minutes

[0153] Since the laboratory uses a small autoclave, steam is generated by gradually heating room-temperature water with an electric heating tube. Air is trapped inside the autoclave, and the equipment lacks a vacuum pump, requiring the air to be expelled for optimal performance. Therefore, it takes 10 minutes to heat the autoclave from room temperature to 105°C. The third stage: curing the temperature at a constant rate from 125°C to 190°C for 75 minutes.

[0154] The fourth stage: maintain the kettle at a constant temperature of 190℃ and a pressure of 1.30MPa for 8 to 12 hours, then exhaust and reduce the pressure and temperature at a uniform rate for 2 hours until the pressure in the kettle drops to 0, and then take the kettle out after the temperature in the kettle drops to a safe temperature below 60℃.

[0155] The aeration pause is a process that ensures the slurry undergoes a series of physical changes, including aeration, thickening, and initial setting, to form a green body with suitable strength. Pre-curing in the autoclave prevents heat dissipation and cooling of the green body after demolding and cutting, before entering the autoclave for autoclave curing, thereby improving its strength upon entry. Autoclave curing is a specific method and means of promoting the completion of the necessary physical and chemical changes in the green body—the hydrothermal synthesis reaction—to generate the required new minerals, resulting in the product having excellent physical and mechanical properties. The biggest difference between aerated concrete and conventional concrete is that the hydration reaction is essentially completed in the autoclave, and the autoclave curing time determines the final development of the inherent properties of aerated concrete.

[0156] During the autoclaving and curing process, SiO2, Al2O3, and CaO in the modified and activated low-carbon gangue slurry of the present invention undergo a hydrothermal reaction to produce various hydration products. These hydration products are key factors in the performance of the finished autoclaved aerated concrete products. Due to the treatment with the chemical decarbonization modification and activation reagent of the present invention, the activity of SiO2, Al2O3, and CaO is made higher, which further enhances the effect of the above-mentioned hydrothermal reaction, thereby obtaining a denser microcrystalline structure and achieving better performance levels such as strength and durability of the products.

[0157] The autoclave curing temperature system is based on the temperature conditions required for the hydrothermal synthesis reaction of the main components of CaO, SiO2, Al2O3, and CaSO4 in silicate concrete and their products. It follows the specific control system of temperature, pressure and time formulated for the full and effective curing of the autoclaved aerated concrete body, so as to achieve full and reasonable curing of the body, so that the product can obtain the best strength in a shorter time, while minimizing the damage that may be suffered to the body.

[0158] Example 6

[0159] Experimental Example 1 (Formula and preparation process of 1# raw material + chemically modified activator):

[0160] 1# raw material: carbon content 3.7%, calorific value 260kcal / kg; formula C / S=0.82;

[0161] (1) Chemical decarbonization modification and activation treatment: 62 parts of 1# material, 2% calcium nitrate by mass fraction of gangue, 0.65 parts of 60℃ warm water, and stirring for 60 minutes;

[0162] (2) While stirring continuously, quickly add 17 parts of lime, 18 parts of cement, and 3 parts of gypsum and continue stirring for 2.5 minutes;

[0163] (3) Add 0.09 parts of aluminum powder while stirring continuously and stir for 40 seconds;

[0164] (4) After stopping stirring, quickly inject the stirred slurry into the steel mold prepared in advance;

[0165] (5) The poured mold is then placed in a constant temperature and humidity chamber at 60°C and 95% relative humidity for 3.0 to 4.0 hours to complete the static processes of foaming, shaping, and solidification;

[0166] (6) Then use a wire saw to cut off the bread head that is higher than the mold and demould it;

[0167] (7) The demoulded green body is sent to a constant temperature and humidity chamber at a temperature of 80°C and a relative humidity of 95% for further pre-curing (pre-kettle pre-curing) for 4 hours;

[0168] (8) The pre-cured green body is quickly transferred to a small autoclave for autoclave curing. The curing system is as follows: uniform temperature rise from room temperature to 105°C for 10 minutes (during which the vent valve is open to discharge the air in the autoclave), uniform temperature rise from 105 to 125°C for 75 minutes, uniform temperature rise from 125 to 190°C for 75 minutes, constant temperature at 190°C (autoclave pressure 1.3 MPa) for 8 hours, uniform exhaust and depressurization for 2 hours until the autoclave pressure drops to 0. The green body is removed from the autoclave after the humidity in the autoclave drops to a safe temperature below 60°C.

[0169] The absolute dry density is 534kg / m 3 Its compressive strength reaches 2.76Mpa, which is greater than the average value requirement of national standard strength level A2.5 and dry density level B05.

[0170] Note: Step (1) can be carried out independently. The obtained decarbonized modified activated gangue slurry can be stored and used as a raw material for preparing autoclaved aerated concrete. After 60 minutes of reaction in step (1), the subsequent steps can be carried out. Alternatively, the slurry can be stored in a slurry storage tank and kept stirred in the slurry storage tank. The modification and activation reaction of the slurry will continue.

[0171] Experimental Example 2 (Formula and preparation process of 1# raw material + 2% chemical modification activator + 3% silica fume):

[0172] 1# raw material: carbon content 3.7%, calorific value 260kcal / kg; formula C / S = 0.80;

[0173] (1) Chemical decarbonization modification and activation treatment: 59 parts of 1# material, 2% calcium nitrate by mass of gangue, 3 parts of silica fume, and 0.65 parts of 60℃ warm water were added and stirred for 90 minutes;

[0174] (2) While stirring continuously, quickly add 17 parts of lime, 18 parts of cement, and 3 parts of gypsum and continue stirring for 2.5 minutes;

[0175] (3) Add 0.09 parts of aluminum powder while stirring continuously and stir for 40 seconds;

[0176] (4) After stopping stirring, quickly inject the stirred slurry into the steel mold prepared in advance;

[0177] (5) The poured mold is then placed in a constant temperature and humidity chamber at 50°C and 95% relative humidity for 2.5 to 3.0 hours to complete the static processes of foaming, shaping, and solidification;

[0178] (6) Then use a wire saw to cut off the bread head that is higher than the mold and demould it;

[0179] (7) The demoulded green body is sent to a constant temperature and humidity chamber at a temperature of 80°C and a relative humidity of 95% for further pre-curing (pre-kettle pre-curing) for 3 hours;

[0180] (8) The pre-cured green body is quickly transferred to a small autoclave for autoclave curing. The curing system is as follows: uniform temperature rise from room temperature to 105°C for 10 minutes (during which the vent valve is in the open state to discharge the air in the autoclave), uniform temperature rise from 105 to 125°C for 75 minutes, uniform temperature rise from 125 to 190°C for 75 minutes, constant temperature at 190°C (autoclave pressure 1.3 MPa) for 8 hours, uniform exhaust and depressurization for 2 hours until the autoclave pressure drops to 0. The autoclave is removed from the autoclave after the humidity in the autoclave drops to a safe temperature below 60°C.

[0181] The absolute dry density is 537kg / m 3 Its compressive strength reaches 2.89Mp, which is greater than the average value requirement of national standard strength level A2.5 and dry density level B05.

[0182] Experimental Example 3 (Formula and preparation process of 2# raw material + 3% chemically modified activator):

[0183] 2# raw material: carbon content 7.5%, calorific value 525kcal / kg; formula C / S = 0.92.

[0184] (1) Chemical decarbonization modification and activation treatment: 64.5 parts of 2# raw material, 3% sodium nitrate by mass fraction of gangue, 0.75 parts of 60℃ warm water were added and stirred for 120 minutes;

[0185] (2) While stirring continuously, quickly add 20 parts of lime, 12 parts of cement, and 3.5 parts of gypsum and continue stirring for 2.5 minutes;

[0186] (3) Add 0.09 parts of aluminum powder while stirring continuously and stir for 40 seconds;

[0187] (4) After stopping stirring, quickly inject the stirred slurry into the steel mold prepared in advance;

[0188] (5) The poured mold is then placed in a constant temperature and humidity chamber at 60°C and 95% relative humidity for 3.5 to 4.0 hours to complete the static stop processes of foaming, shaping, and solidification;

[0189] (6) Then use a wire saw to cut off the bread head that is higher than the mold and demould it;

[0190] (7) The demoulded green body is sent to a constant temperature and humidity chamber at a temperature of 80°C and a relative humidity of 95% for further pre-curing (pre-kettle pre-curing) for 4 hours;

[0191] (8) The pre-cured green body is quickly transferred to a small autoclave for autoclave curing. The curing system is as follows: uniform temperature rise from room temperature to 105°C for 10 minutes (during which the vent valve is in the open state to discharge the air in the autoclave), uniform temperature rise from 105 to 125°C for 75 minutes, uniform temperature rise from 125 to 190°C for 75 minutes, constant temperature at 190°C (autoclave pressure 1.30 MPa) for 8 hours, uniform exhaust and depressurization for 2 hours until the autoclave pressure drops to 0. The autoclave is removed from the oven after the humidity in the autoclave drops to a safe temperature below 60°C.

[0192] The absolute dry density is 598kg / m 3 Its compressive strength reaches 3.12Mpa, meeting the minimum requirements of national standard strength level A3.5 and dry density level B06.

[0193] Experimental Example 4 (Formula and preparation process of 2# raw material + 3% chemical modification activator + 3% silica fume):

[0194] 2# raw material: carbon content 7.5%, calorific value 525kcal / kg; formula C / S = 0.88.

[0195] (1) Chemical decarbonization modification and activation treatment: add 61.5 parts of 2# raw material, 3% sodium nitrate based on the mass of gangue, 3 parts of silica fume, 0.75 parts of 60℃ warm water and stir for 120 minutes;

[0196] (2) While stirring continuously, quickly add 20 parts of lime, 12 parts of cement, and 3.5 parts of gypsum and continue stirring for 2.5 minutes;

[0197] (3) Add 0.08 parts of aluminum powder while stirring continuously and stir for 40 seconds;

[0198] (4) After stopping stirring, quickly inject the stirred slurry into the steel mold prepared in advance;

[0199] (5) The poured mold is then placed in a constant temperature and humidity chamber at 60°C and 95% relative humidity for 3.0 to 4.0 hours to complete the static processes of foaming, shaping, and solidification;

[0200] (6) Then use a wire saw to cut off the bread head that is higher than the mold and demould it;

[0201] (7) The demoulded green body is sent to a constant temperature and humidity chamber at a temperature of 80°C and a relative humidity of 95% for further pre-curing (pre-kettle pre-curing) for 4 to 6 hours;

[0202] (8) The pre-cured green body is quickly transferred to a small autoclave for autoclave curing. The curing system is as follows: uniform temperature rise from room temperature to 105°C for 10 minutes (during which the vent valve is in the open state to discharge the air in the autoclave), uniform temperature rise from 105 to 125°C for 75 minutes, uniform temperature rise from 125 to 190°C for 75 minutes, constant temperature at 190°C (autoclave pressure 1.30 MPa) for 8 hours, uniform exhaust and depressurization for 2 hours until the autoclave pressure drops to 0. The autoclave is removed from the oven after the humidity in the autoclave drops to a safe temperature below 60°C.

[0203] The absolute dry density is 630kg / m 3 Its compressive strength reaches 3.57Mpa, meeting the national standard strength level A3.5 and dry density level B06 average value requirements.

[0204] Experimental Example 5 (Formula and preparation process of 3# raw material + 5% chemically modified activator):

[0205] 3# raw material: carbon content 15.4%, calorific value 1080kcal / kg; formula C / S = 0.88

[0206] (1) Chemical decarbonization modification and activation treatment: 60 parts of 3# raw material, 6 parts of silica fume, 5% sodium percarbonate by mass fraction of gangue, 0.75 parts of 60℃ warm water, and stirring for 120 minutes;

[0207] (2) While stirring continuously, quickly add 16 parts of lime, 16 parts of cement, and 2.0 parts of gypsum and continue stirring for 2.5 minutes;

[0208] (3) Add 0.08 parts of aluminum powder while stirring continuously and stir for 40 seconds;

[0209] (4) After stopping stirring, quickly inject the stirred slurry into the steel mold prepared in advance;

[0210] (5) The poured mold is then placed in a constant temperature and humidity chamber at 60°C and 95% relative humidity for 2.5 to 3.5 hours to complete the static processes of foaming, shaping, and solidification;

[0211] (6) Then use a wire saw to cut off the bread head that is higher than the mold and demould it;

[0212] (7) The demoulded green body is sent to a constant temperature and humidity chamber at a temperature of 80°C and a relative humidity of 95% for further pre-curing (pre-kettle pre-curing) for 2 to 4 hours;

[0213] (8) The pre-cured green body is quickly transferred to a small autoclave for autoclave curing. The curing system is as follows: uniform temperature rise from room temperature to 105°C for 10 minutes (during which the vent valve is in the open state to discharge the air in the autoclave), uniform temperature rise from 105 to 125°C for 75 minutes, uniform temperature rise from 125 to 190°C for 75 minutes, constant temperature at 190°C (autoclave pressure 1.30 MPa) for 8 hours, uniform exhaust and depressurization for 2 hours until the autoclave pressure drops to 0. The autoclave is removed from the oven after the humidity in the autoclave drops to a safe temperature below 60°C.

[0214] The absolute dry density is 634kg / m 3 Its compressive strength reaches 3.02Mpa, meeting the minimum requirements of national standard strength level A3.5 and dry density level B06.

[0215] Experimental Example 6 (Formula and preparation process of 3# raw material + 5% chemical modified activator + 8# silica fume):

[0216] 3# raw material: carbon content 15.4%, calorific value 1080kcal / kg; formula C / S = 0.86.

[0217] (1) Chemical decarbonization modification and activation treatment: 58 parts of 3# raw material, 8 parts of silica fume, 5% hydrogen peroxide by mass fraction of gangue, 0.75 parts of 60℃ warm water, and stirring for 120 minutes;

[0218] (2) While stirring continuously, quickly add 16 parts of lime, 16 parts of cement, and 2 parts of gypsum and continue stirring for 2.5 minutes;

[0219] (3) Add 0.08 parts of aluminum powder while stirring continuously and stir for 40 seconds;

[0220] (4) After stopping stirring, quickly inject the stirred slurry into the steel mold prepared in advance;

[0221] (5) The poured mold is then placed in a constant temperature and humidity chamber at 60°C and 95% relative humidity for 2.5 to 3.0 hours to complete the static processes of foaming, shaping, and solidification;

[0222] (6) Then use a wire saw to cut off the bread head that is higher than the mold and demould it;

[0223] (7) The demoulded green body is sent to a constant temperature and humidity chamber at a temperature of 80°C and a relative humidity of 95% for further pre-curing (pre-kettle pre-curing) for 2 to 4 hours;

[0224] (8) The pre-cured green body is quickly transferred to a small autoclave for autoclave curing. The curing system is as follows: uniform temperature rise from room temperature to 105°C for 10 minutes (during which the vent valve is in the open state to discharge the air in the autoclave), uniform temperature rise from 105 to 125°C for 75 minutes, uniform temperature rise from 125 to 190°C for 75 minutes, constant temperature at 190°C (autoclave pressure 1.30 MPa) for 8 hours, uniform exhaust and depressurization for 2 hours until the autoclave pressure drops to 0. The autoclave is removed from the oven after the humidity in the autoclave drops to a safe temperature below 60°C.

[0225] The absolute dry density is 650kg / m 3 Its compressive strength reaches 3.63Mpa, meeting the national standard strength level A3.5 and dry density level B06 average value requirements.

[0226] Comparative Example 1:

[0227] The steps of Experimental Example 1 are the same as those of Experimental Example 1 except that the gangue slurry is not treated with modified activator. 3 When the compressive strength reaches 2.32Mpa, it is lower than the compressive strength of the product in Example 1.

[0228] Comparative Example 2:

[0229] The steps of Experimental Example 3 are the same as those of Experimental Example 3 except that the gangue slurry is not treated with modified activator. 3 When the compressive strength reaches 2.01Mpa, it is lower than the compressive strength of the product in Example 3.

[0230] Comparative Example 3:

[0231] The steps of Experimental Example 5 are the same as those of Experimental Example 5 except that the gangue slurry is not treated with modified activator. 3 When the compressive strength reaches 1.66Mpa, it is lower than the compressive strength of the product in Example 5.

[0232] Table 1 Relationship between autoclaved aerated concrete performance and process

[0233]

[0234]

[0235] From Table 1 we can see that:

[0236] Experimental Example 1 uses the chemical decarbonization modification method of the present invention. Compared with Example 1 which does not use the chemical decarbonization modification method under the same conditions, the compressive strength of the autoclaved aerated concrete obtained is significantly improved, and the specific strength is increased by 20.10%; and in Experimental Example 2 in which the regulator silica fume is added on the basis of Experiment 1, the compressive strength is further improved, and the specific strength is increased by 3.58% on the basis of Experimental Example 1; the specific strength of Experimental Example 2 is increased by 25.05% on the basis of Comparative Example 1.

[0237] Experimental Example 3 uses the chemical decarbonization modification method of the present invention. Compared with Example 2 in which the chemical decarbonization modification method is not used under the same conditions, the compressive strength of the autoclaved aerated concrete obtained is significantly improved, and the specific strength is increased by 42.74%; and in Experimental Example 4 in which the regulating agent silica fume is added on the basis of Experiment 3, the compressive strength is further improved, and the specific strength is increased by 8.63% on the basis of Experimental Example 3; the specific strength of Experimental Example 4 is increased by 55.05% on the basis of Comparative Example 2.

[0238] Experimental Example 5 uses the chemical decarbonization modification method of the present invention. Compared with the comparative example 3 in which the chemical decarbonization modification method is not used under the same conditions, the compressive strength of the autoclaved aerated concrete obtained is significantly improved, and the specific strength is increased by 76.73%; and in Experimental Example 6 in which the regulating agent silica sol is added on the basis of Experiment 5, the compressive strength is further improved, and the specific strength is increased by 17.26% on the basis of Experiment 5; the specific strength of Experimental Example 6 is increased by 107.24% on the basis of Comparative Example 3, indicating that the combined use of multiple regulating agents can further improve the strength of the product.

[0239] The products prepared by the method of the present invention can all meet the compressive strength requirements of the corresponding dry density levels in the national standard GB / T11968-2020 (see Table 4). At the same time, under the same treatment method of chemical modification, the lower the carbon content of the original gangue material, the better the compressive strength of the prepared autoclaved aerated concrete after chemical modification, which illustrates the importance of decarbonization treatment. For raw materials 3# with a higher carbon content (carbon content of about 15.4%), qualified products cannot be prepared without chemical modification. For gangue with a carbon content of about 10%, the chemical decarbonization modification method of the present invention makes it possible to use the gangue with the above carbon content as a raw material for autoclaved aerated concrete, and achieves a higher proportion of utilization for the resource application of gangue.

[0240] Figure 1-1 The samples of Experimental Example 1 and Experimental Example 2 were prepared by adding chemical modifiers to 1# coal gangue raw material. In Experimental Example 2, other modifiers were added to further improve the strength of the product.

[0241] Figure 1-2 The samples of Experimental Example 3 (H3) and Experimental Example 4 (H4) were prepared by adding chemical modifiers to 2# coal gangue raw material. In Experimental Example 4 (H4), other modifiers were added to further improve the strength of the product.

[0242] Figure 1-3 The sample (15-2) of Experimental Example 5 was prepared by adding a chemical modifier to the 3# coal gangue raw material.

[0243] Figure 1-4 The sample of Experiment 6 was prepared by adding other regulators to the 3# coal gangue raw material on the basis of Experiment 5.

[0244] Figure 2 This is a 40-fold magnified observation photo of 2# coal gangue raw material, in which the black particles are carbon particles.

[0245] Figure 3 The raw material was 3# coal gangue with a carbon content of approximately 15.4%. No chemical modification or activator was added. After batching, stirring, pouring, stabilization, and demolding, the sample failed visual inspection due to poor mechanical strength and uneven bubble distribution. Therefore, no further processing or testing was performed.

[0246] The chemical compositions of No. 1, No. 2 coal, and No. 3 coal gangue used in the present invention are shown in Table 2, and the mineral compositions are shown in Table 3.

[0247] Table 2 The chemical composition of the gangue raw material after the chemical decarbonization modification and activation treatment of the present invention is as follows:

[0248] coal gangue <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> CaO MgO <![CDATA[Na2O]]> <![CDATA[K2O]]> <![CDATA[SO3]]> C 1#(％) 61.79 10.28 5.84 9.07 4.44 0.62 1.80 2.06 3.7 2#(％) 49.23 18.65 7.72 6.20 3.61 0.59 1.74 4.27 7.5 3#(％) 45.25 14.16 6.96 9.05 2.45 0.54 1.90 1.05 15.4

[0249] Table 3 The mineral composition of the gangue raw material treated by chemical decarbonization modification of the present invention is as follows:

[0250]

[0251] Table 4 Compressive strength and dry density requirements

[0252]

[0253] The composition of the calcium raw materials of the autoclaved aerated concrete of the present invention is shown in Table 5.

[0254] Table 5 Chemical composition of calcium raw materials of autoclaved aerated concrete of the present invention

[0255]

[0256] Preparation of other raw materials for autoclaved aerated concrete:

[0257] Other materials used in the present invention are as follows:

[0258] plaster:

[0259] This experiment uses sintered masonry desulfurized gypsum.

[0260] Aluminum powder:

[0261] This test uses metallic aluminum powder, which is still in normal use in most autoclaved aerated concrete companies, as the gas-generating agent.

[0262] Silica fume:

[0263] Provided by a company in Ningxia, SiO2 content ≥93%, specific surface area ≥18m 2 / g

[0264] Modifier:

[0265] The modifiers used in the present invention are industrial-grade modifiers purchased online, including sodium nitrate, ammonium nitrate, calcium nitrate, sodium percarbonate, and H2O2.

[0266] Figure 4 This is the XRD pattern of a No. 1 coal gangue experimental sample provided by one embodiment of the present invention. The XRD pattern shows the main hydration products and unreacted mineral compositions. As can be seen from the figure, the main mineral compositions in the sample are tobermorite, CSH gel, anhydrite, quartz, dolomite, calcite, scawtite, pseudowollastonite, halloysite, and other minerals. Figure 5This is a SEM electron microscope photograph of a No. 1 coal gangue experimental sample provided by an embodiment of the present invention; the photograph shows the microstructure of the coal gangue experimental sample, wherein the flakes are mineral structures such as tobermorite, the needles are hydration products such as CSH gel, which are beneficial to improving the strength of the product, and the particles are residual minerals such as quartz, dolomite, and calcite that have not reacted completely, and are relatively evenly distributed.

[0267] The present invention has the following significant innovations:

[0268] (1) Gangue with low carbon content of Class I or II (carbon content 6%) or less can be used in autoclaved aerated concrete without further sorting, but the addition of modifiers will further improve its performance;

[0269] (2) The core innovation is to treat the gangue with chemical modifiers, which not only reduces the carbon content of the gangue by oxidation, but also depolymerizes the mineral structure of the gangue, thereby activating chemical elements such as SiO2, Al2O3, and CaO in the mineral, which is beneficial to their activity in participating in the hydrothermal reaction; at the same time, it was found that the chemical oxidation of the gangue can promote the formation of micropores in the gangue autoclaved aerated concrete products, thereby achieving the purpose of improving the physical properties of the products.

[0270] (3) The core innovation is to apply the chemically modified and activated coal gangue to autoclaved aerated concrete instead of siliceous materials, which has achieved significant industrial success. The performance of the prepared autoclaved aerated concrete meets the national standards and solves a problem that has not been solved in the industry.

[0271] (4) Significance: It has found a feasible way for the comprehensive high-value resource utilization of coal gangue; it has reduced the dependence on mineral resources such as silica sand for the production of autoclaved aerated concrete green ecological building materials.

[0272] The above description is merely a representative embodiment of the present invention and is not necessarily the optimal formulation. Therefore, it is not intended to limit the present invention. Any modifications, equivalent substitutions, or improvements made by any person skilled in the art within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. An autoclaved aerated concrete prepared from unburned coal gangue, characterized in that: The ingredients are: decarbonized modified activated gangue slurry, calcium material, regulating material and gas generating agent; the calcium material is lime and cement, the regulating material is gypsum and / or silica fume, and the gas generating agent is aluminum powder; The decarbonized modified activated gangue slurry is mixed with a calcium material and a regulating material to prepare a mixed slurry, and the mixed slurry is further stirred and a gas generating agent is added; In the mixed slurry, the amount of the decarbonized modified activated gangue slurry is greater than or equal to 50% by mass; The decarbonized modified activated gangue slurry is obtained by adding water to unburned coal gangue and stirring at a temperature of 60° C. to 80° C. until the mixture is fully reacted by any one of the following unburned coal gangue decarbonization modified activating agents: 1) Calcium nitrate accounting for 2% of the total mass of coal gangue; 2) Sodium nitrate accounting for 3% of the total mass of coal gangue; 3) Sodium percarbonate accounting for 5% of the total mass of coal gangue; The calcium / silicon ratio of the ingredients is 0.5 to 1.0; The decarbonized modified activated gangue slurry has a carbon content of less than 3%, a silicon oxide content of 30% to 90%, an aluminum oxide content of 0.2% to 45%, and a calcium oxide content of 0.05% to 20%.

2. An autoclaved aerated concrete prepared from unburned coal gangue, characterized in that: The ingredients are: decarbonized modified activated gangue slurry, calcium material, regulating material and gas generating agent; the calcium material is lime and cement, the regulating material is gypsum and / or silica fume, and the gas generating agent is aluminum powder; The decarbonized modified activated gangue slurry is mixed with a calcium material and a regulating material to prepare a mixed slurry, and the mixed slurry is further stirred and a gas generating agent is added; In the mixed slurry, the amount of the decarbonized modified activated gangue slurry is greater than or equal to 50% by mass; The decarbonized modified activated gangue slurry is obtained by adding water to an unburned gangue decarbonization modification activator and unburned gangue at a temperature of 60° C. to 80° C. and stirring until the unburned gangue is fully reacted. If the unburned gangue decarbonization modification activator is only nitrate, the amount of nitrate used is any one of the following based on the total mass of the gangue: For gangue with 0%~5% carbon content, use 1%~3%; For gangue with a carbon content of 5% to 10%, use 2% to 5%; Gangue with a carbon content of 10% to 15% uses 3% to 6%; For coal gangue with a carbon content of 15% to 20%, 4% to 7% is used.

3. The autoclaved aerated concrete prepared from unburned coal gangue according to claim 1 or 2, characterized in that: The hydrothermal synthesis product contained in the autoclaved aerated concrete prepared from the unburned coal gangue comprises hydrated mineral crystals, and the hydrated mineral crystals include any combination of CSH(I), tobermorite, aluminum-substituted tobermorite, hydrogarnet, xonotlite, and hydrated calcium sulfoaluminate.

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