Process for preparing building cementing material by autogenous grinding, separation, calcination and activation of coal gangue

Abstract

The invention discloses a process for preparing a building cementing material by autogenous grinding, separation, calcination and activation of coal gangue, which comprises the following steps: putting preliminarily crushed coal gangue into a rod mill for crushing and screening to obtain undersize coal gangue and oversize coal gangue; washing the oversize coal gangue with water, drying the precipitate obtained in the washing process, and mixing the dried precipitate with the undersize coal gangue; preheating the mixed coal gangue, and calcining at a certain temperature to obtain a calcined product; putting the calcined product into a rod mill for mechanical grinding, and taking the ground product as an admixture; weighing the admixture, the cement and the fine sand according to a certain proportion, and uniformly stirring and mixing to obtain a product; the preparation method comprises the following steps: weighing a water reducing agent and water according to a certain ratio, mixing the water reducing agent and the water, stirring until the water reducing agent is fully dissolved, then pouring into an obtained product, and continuously stirring uniformly to obtain the final building cementing material. Coal gangue is calcined and ground by a rod mill to serve as an admixture to replace part of ordinary Portland cement.

Description

Technical Field

[0002] This invention belongs to the field of solid waste recycling technology. Specifically, this invention relates to a process for preparing building cementitious materials from coal gangue through auto-grinding, sorting, calcination, and activation. Background Technology

[0003] Coal gangue originates from waste rock generated during coal mining and washing. As a major solid waste produced in the coal, power, and aluminum industries, its long-term accumulation not only occupies vast amounts of land resources but also causes significant pollution to the ecological environment. The disposal of these wastes has long plagued the industrial sector. Traditional landfill and dumping methods are not only inefficient in resource utilization but can also cause soil, water, and air pollution, and even trigger geological disasters.

[0004] In recent years, with the rapid advancement of resource utilization technologies, the preparation of cementitious materials from these solid wastes has gradually become a research focus. As an indispensable building material in civil engineering and infrastructure construction, the traditional production process of cementitious materials consumes large amounts of limestone and clay resources and is accompanied by the emission of large amounts of carbon dioxide, putting significant pressure on the environment.

[0005] In view of this, existing technologies utilize coal gangue as a natural volcanic ash mixture material, which has a certain degree of activity. Its activity can be effectively improved through methods such as thermal activation, mechanical activation, and chemical activation, so that it can be better utilized as a resource in the field of building materials.

[0006] However, existing activation methods require cumbersome processes to treat coal gangue, which makes it difficult to avoid the possibility of secondary pollution. In order to address the above problems, this invention aims to develop a novel coal gangue activation method and to prepare building cementitious materials based on the coal gangue obtained by this method. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a novel method for activating coal gangue. The method involves crushing and separating coal gangue in a crusher to obtain brittle powdered coal gangue and hard, non-brittle block coal gangue. The block coal gangue is then washed with water. The precipitate obtained during the washing process is dried, preheated together with the powdered coal gangue, and calcined at a high temperature. The calcined product is then mechanically ground in a rod mill and used as an admixture. The admixture, cement, and fine sand are weighed in a specific ratio and mixed thoroughly to obtain a final product. A water-reducing agent and water are weighed in a specific ratio, mixed with water, and stirred until the water-reducing agent is fully dissolved. This mixture is then added to the final product and stirred until homogeneous, yielding the final building cementitious material. This method addresses the corresponding technical problems mentioned in the background section.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention relates to a process for preparing building cementitious materials from coal gangue through auto-grinding, sorting, calcination, and activation, the process specifically including the following steps: Step 1: After drying the raw coal gangue, it is initially crushed, and then the initially crushed coal gangue is put into a rod mill for crushing and screening to obtain undersize coal gangue and oversize coal gangue. Step 2: Wash the oversized coal gangue with water, dry the precipitate obtained during the washing process, and mix the dried precipitate with the undersized coal gangue obtained in Step 1. Step 3: After preheating the mixed coal gangue obtained in Step 2, calcine it at a certain temperature. After calcining for a certain time, take it out and place it in the air to cool down, and obtain the calcined product. Step 4: The calcined product is mechanically ground in a rod mill and used as an admixture; Step 5: Weigh the admixture, cement, and fine sand according to a certain ratio, and mix them evenly to obtain the product; Step Six: Weigh out the water-reducing agent and water in a certain ratio, mix the water-reducing agent and water and stir until the water-reducing agent is fully dissolved, then pour it into the product obtained in Step Five and continue to stir evenly to obtain the final building cementitious material.

[0009] Preferably, in step one, the rod mill is a three-roller four-cylinder rod mill with a rod-to-material ratio of 25:1, a 1mm standard sieve for screening, and a grinding time of 15-180 minutes, preferably 120 minutes.

[0010] Preferably, the calcination temperature is 450℃~850℃ and the calcination time is 0.5-4.0h, with the preferred calcination temperature being 650℃ and the calcination time being 2h.

[0011] Preferably, the cementitious material is a mixture of admixtures and cement; The mass ratio of the admixture to cement in the cementitious material is 15-45:100; preferably 25:100. The mass ratio of water to cementitious material, i.e., the water-cement ratio, is 0.44; The mass ratio of water-reducing agent to cementitious material is 1:100; The mass ratio of fine sand to the total mass of cementitious materials and water-reducing agent is 1:2.

[0012] Preferably, the cement is ordinary Portland cement.

[0013] Preferably, the water-reducing agent is a polycarboxylate-based water-reducing agent.

[0014] Preferably, the particle size of the fine sand is ≤2mm.

[0015] Preferably, the size of the admixture in step four is ground to ≤0.105mm.

[0016] Preferably, in step one, a jaw crusher is used to perform preliminary crushing of the raw coal gangue, and the particle size of the preliminary crushing is less than 6mm.

[0017] Secondly, this invention relates to a building cementing material, which is a building cementing material prepared by the process described above for preparing building cementing materials by self-grinding, sorting, calcining and activation of coal gangue.

[0018] Compared with the prior art, the beneficial effects of the present invention are: 1. In the technical solution of this invention, selective crushing of coal gangue is achieved by utilizing the hardness difference of coal gangue. The raw coal gangue is crushed by a jaw crusher and then separated by a rod mill. The brittle material under the screen and the coarse aggregate over the screen are obtained by screening. The coarse aggregate is washed with water, and the precipitate obtained in the washing process is filtered, dried and mixed with the brittle material under the screen. This achieves mechanical activation of the coal gangue, making the coal gangue particles finer, increasing the specific surface area and improving the reaction rate.

[0019] 2. Autogenous grinding separation of coal gangue is carried out based on the difference in hardness. The calorific value and ash content of the coal gangue after autogenous grinding separation are significantly different from those of the original coal gangue. After autogenous grinding separation for different time periods, XRF and XRD tests of the separated coal gangue are analyzed, and the effects and economic benefits of different autogenous grinding crushing and separation methods are comprehensively compared. It can be determined that the autogenous grinding method of coal gangue is a better method for crushing and separating coal gangue, and it also has the advantages of simple operation and no consumables.

[0020] 3. In the technical solution of this invention, the sorted coal gangue is activated by a thermo-chemical composite activation method. The mixed coal gangue powder material is calcined at a temperature of 450℃ to 850℃. The changes in its internal mineral composition are analyzed by XRD and XRF tests to obtain the optimal calcination conditions. The product of calcined coal gangue is used as an admixture and is mixed evenly with ordinary silicate cement, water, polycarboxylate-based high-efficiency water-reducing agent, fine sand, etc. to obtain a building cementitious material. The resulting high-performance concrete has the characteristics of good fluidity, non-segregation, good mechanical properties, and good durability. The process consumes a large amount of coal gangue, which effectively reduces the environmental pollution caused by coal gangue. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the preparation process in this invention; Figure 2 The XRD pattern of raw coal gangue in this invention; Figure 3The XRD patterns of the sorted coal gangue after autogenous grinding at different times in this invention are shown. Figure 4 The XRD patterns of the sorted coal gangue in this invention at different calcination temperatures are shown. Figure 5 The XRD patterns of calcined activated coal gangue at different calcination times in this invention are shown. Figure 6 The compressive strength of the building cementitious materials with different coal gangue content in this invention; Figure 7 The compressive strength of the building cementitious materials with different coal gangue content in this invention; Figure 8 The flexural strength of building cementitious materials at different calcination temperatures in this invention; Figure 9 The compressive strength of building cementitious materials at different calcination temperatures in this invention; Figure 10 This is a curve showing the compressive strength of the building cementitious material in this invention. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Unless otherwise specified, all raw materials used in the embodiments of the present invention are commercially available or obtainable by those skilled in the art; unless otherwise specified, all methods used in the embodiments of the present invention are methods mastered by those skilled in the art.

[0024] Coal gangue refers to solid waste generated during coal mining, washing, and processing. It is also a usable resource, exhibiting a dual nature. Coal gangue has become one of the largest accumulations and emissions of industrial solid waste in my country, accounting for approximately 15% of China's total solid waste.

[0025] Coal gangue is mostly stored in open-air piles, resulting in large coal gangue mountains. The harm these mountains cause to the surrounding ecological environment stems primarily from the following aspects: First, they occupy large amounts of arable land, preventing land resources from realizing their true value and damaging soil nutrients. Second, they cause air pollution; coal gangue contains combustible materials such as residual coal, carbonaceous mudstone, wood chips, and pyrite, posing a potential risk of spontaneous combustion in hot, dry summers. Furthermore, years of exposure to wind and sun cause weathering and decomposition, generating large amounts of dust that form smog, seriously affecting the health of residents in mining areas. Third, they pollute land and groundwater resources.

[0026] Coal gangue contains some heavy metal elements. Sulfides in coal gangue form acidic solutions under the scouring and leaching effects of atmospheric precipitation. During the infiltration and migration process, mercury, chromium, arsenic, copper, cadmium, lead, and other elements are dissolved and seep into the soil along with groundwater, thus polluting the soil and water resources. The higher the sulfide content in coal gangue, the easier it is for harmful elements to dissolve. Fourth, because the accumulation of coal gangue is relatively loose, its stability is not high, and it is very easy to cause geological disasters such as collapse, landslides, and debris flows in the rainy season.

[0027] Coal gangue, as a natural volcanic ash mixture, has a certain degree of activity. Its activity can be effectively improved through methods such as thermal activation, mechanical activation, and chemical activation, so that it can be better utilized in the field of building materials.

[0028] Secondly, statistics show that traditional cement production accounts for about 15% of global energy consumption. Under this immense energy pressure, there is an urgent need to find alternative materials to alleviate this burden. To address this, the paper proposes using coal gangue to prepare cement mortar, exploring ways to achieve large-scale, harmless, and sustainable consumption of coal gangue, while effectively alleviating the enormous energy pressure of traditional cement production. Finally, existing uses for coal gangue, primarily in power generation, fertilizer production, road construction materials, sintered bricks, and building ceramics, are difficult to scale up and still require complex processing methods, potentially leading to secondary pollution. Therefore, using coal gangue to prepare cement mortar effectively improves the utilization rate of coal gangue and is a simple, harmless, and sustainable green approach.

[0029] Based on this, the present invention proposes a novel method for activating coal gangue, and uses the coal gangue obtained by this method to prepare building cementitious materials.

[0030] 1. Raw materials The main raw materials include calcined coal gangue, cement, water, fine sand, release agent, and water-reducing agent. The specific models of the materials are shown in Table 1 below:

[0031] 2. Activation scheme for coal gangue: The activity of coal gangue refers to the property that its soluble components, such as SiO2 and Al2O3, can react with lime after adding water at room temperature to form cementitious hydration products. Activation pathways for coal gangue include thermal activation, mechanical activation, chemical activation, and combined activation.

[0032] (1) Mechanical activation: The purpose of mechanical activation is to refine the coal gangue particles, increase the specific surface area, and improve the reaction rate. Selective crushing is achieved through autogenous grinding and sorting of the coal gangue, allowing the harder parts (mainly calcium-containing gangue) to maintain their original particle size, while the softer parts (mainly containing clay minerals) are crushed into fine particles. The different hardnesses of the coal gangue are then separated by sieving.

[0033] (2) Thermal activation: The purpose of thermal activation is to use high temperatures to induce intense thermal motion in the microstructure of coal gangue and remove bound water from the minerals. After calcination, the layered structure of ultrafine kaolinite in coal gangue is destroyed due to dehydration, forming amorphous aluminum silicate, i.e., metakaolinite. Therefore, calcined coal gangue contains a large amount of active silica and aluminum oxide. Because the molecular arrangement of metakaolinite is irregular and it exhibits a thermodynamically metastable state, it possesses gelling properties after activation by reagents.

[0034] (3) Chemical activation: Chemical activation of coal gangue involves adding activators to enhance its pozzolanic activity. Activators serve two purposes: first, they provide a highly polar environment, disrupting the Si-O and Al-O bonds on the coal gangue surface, leading to structural disintegration; second, they participate in reactions to generate cementing substances. The main factors affecting the effectiveness of chemical activation are the type and amount of activator used.

[0035] (4) Composite activation: Composite activation refers to the simultaneous activation of two or more methods. Generally speaking, composite activation is more effective than single activation methods.

[0036] This invention utilizes a method of thermo-chemical composite activation of coal gangue after sorting to achieve the activation of coal gangue.

[0037] First, the separation technology for coal gangue was explored, utilizing its hardness differences to achieve selective crushing. Raw coal gangue was crushed to -6mm using a jaw crusher and then separated using a rod mill. The material was screened to obtain undersize (fragile material) and oversize (coarse aggregate). The coarse aggregate was washed with water, and the sediment obtained during the washing process was filtered and dried.

[0038] Secondly, the optimal calcination conditions for thermal activation of coal gangue were investigated. The washed and sieved fragile coal gangue powder was calcined together at a temperature of 450℃ to 850℃. Changes in the internal mineral composition were analyzed using XRD and XRF tests to determine the optimal calcination conditions.

[0039] Finally, the influence of different dosages of calcined coal gangue on the mechanical properties of building cementitious materials was investigated. Based on the above experiments, the product of calcined coal gangue was prepared, ground, and used as an admixture. By adding different amounts of the calcined coal gangue product, and mixing it evenly with ordinary silicate cement, water, polycarboxylate-based high-efficiency water-reducing agent, fine sand, etc., a building cementitious material was obtained. The resulting high-performance concrete has the characteristics of good fluidity, non-segregation, good mechanical properties, and good durability. The process consumes a large amount of coal gangue, effectively reducing the environmental pollution caused by coal gangue.

[0040] Specifically, high-performance concrete is prepared using coal gangue as the main raw material. The coal gangue is crushed and sorted in a crusher to obtain brittle powdered coal gangue and hard, non-brittle block coal gangue. The block coal gangue is washed with water. The precipitate obtained during the washing process is dried, preheated together with the powdered coal gangue, and calcined at a temperature of 450℃~850℃ to obtain the calcined product. The calcined product is mechanically ground in a rod mill and used as an admixture. The admixture, cement, and fine sand are weighed in a certain proportion and mixed evenly to obtain the final product. A water-reducing agent and water are weighed in a certain proportion, mixed with water, and stirred until the water-reducing agent is fully dissolved. This mixture is then poured into the obtained product and stirred evenly to obtain the final building cementitious material. A schematic diagram of the specific preparation method is shown below. Figure 1 As shown, cement mortar strength tests were conducted after 3, 7, and 28 days of curing to investigate the influence of calcined coal gangue content on the mechanical properties of building cementitious materials.

[0041] 3. Physicochemical properties of coal gangue: The coal gangue underwent full industrial analysis, sulfur content testing, and calorific value testing. The results of each test are shown in Table 2.

[0042] Table 2 shows the following industrial analysis, sulfur content analysis, and calorific value analysis of coal gangue: Moisture content 2.96%, Ash content 83.94%, Volatile matter 88.72%, Fixed carbon content 11.28%, Sulfur content 0.63%, and Calorific value 0.03 MJ / kg. The ash content of the undersize coal gangue is 80.95%, Fixed carbon content 10.50%, Sulfur content 0.86%, and Calorific value 2.29 MJ / kg. The ablation rate of the coal gangue is measured to be 18.68%. The changes in calorific value and ash content indicate that the carbon content of the undersize coal gangue is relatively higher than that of the main coal gangue.

[0043] The XRF analysis results of coal gangue are shown in Table 3:

[0044] According to Table 3, XRF testing analysis of coal gangue revealed that it mainly consists of SiO2 (44.40% of total), Al2O3 (19.70% of total), Fe2O3 (18.90% of total), TiO2 (7.24% of total), K2O (2.10% of total), and GaO (4.53% of total). After sorting, the content of SiO2 and Al2O3 on the sieve increased, while the content of SiO2 and Al2O3 on the undersize decreased, and the content of Fe2O3 increased. This demonstrates the feasibility of sorting coal gangue based on hardness differences.

[0045] XRD analysis of coal gangue: Figure 2 The images show mineral composition analysis of coal gangue under different conditions using a LabXXRD-1600 X-ray diffractometer. The scanning speed was 2° / s, the scanning step size was 0.02°, and the scanning angle ranged from 10° to 80°. XRD analysis is the most common method for analyzing phase transitions in materials and is indispensable for analyzing the phase transitions of coal gangue before and after calcination and activation under different conditions.

[0046] 4. Coal gangue sorting technology (mechanical activation): The pre-crushed coal gangue is placed in a rod mill for crushing and screening. The principle is to separate different mineral components through ball milling of the coal gangue. The main influencing factor is the grinding time. Within a certain range, the selective crushing and separation effect improves with increasing grinding time; however, excessively long grinding times can also crush hard materials, leading to poorer crushing selectivity.

[0047] The coal gangue was crushed to a particle size of less than 6mm using a jaw crusher of model EP-II. The coal gangue was then dried using an electric heating blast drying oven and subsequently put into a three-roller four-cylinder rod mill for auto-grinding. The ground product was screened and sorted using screening tools. The hard aggregate was washed, dried, and set aside for later use. The washed and dried aggregate was then mixed with the undersized, easily broken coal gangue for later use.

[0048] Specifically, when the material-to-bar ratio is 25:1, the coal gangue is dry-ground using a three-roller four-cylinder rod mill, and then screened using a 1mm standard sieve. The quality of the products on and off the sieve is weighed separately.

[0049] The experiment investigated the relationship between the sieve ratio and the grinding time. By designing grinding times of 15 min, 30 min, 60 min, 120 min and 180 min, the mass ratio of the undersize to the oversize of the product was calculated. The relationship between the mass ratio of the undersize to the oversize and the grinding time was examined, and the optimal grinding time was obtained. Table 4 shows the sieve ratio for different grinding times.

[0050]

[0051] The maximum mass ratios for each grinding process are shown in Table 4. Raw coal gangue was auto-ground using a three-roller four-cylinder rod mill at different times. Based on the formula: mass ratio = mass of undersize material / mass of oversize material, the maximum mass ratios were obtained (products at five different auto-grinding times: 15 min, 30 min, 60 min, 120 min, and 180 min). From the mass ratios at different auto-grinding times, it can be seen that when the grinding time is 120 min, the grinding mass ratio is 0.32; when the grinding time is 180 min, the mass ratio is 0.34. The mass ratio gradually stabilizes; therefore, from an economic perspective, this invention selects 120 min as the optimal grinding time.

[0052] Analysis of the properties of coal gangue under different autogenous grinding times: Coal gangue is rich in various elements, and its mineral composition varies greatly depending on its formation and origin. However, it is generally rich in silicon, aluminum, iron, titanium, and calcium. To understand the effect of high-temperature calcination on the activity of sorted coal gangue, it is necessary to analyze the chemical composition of the raw coal gangue.

[0053] The chemical composition of coal gangue at different autogenous grinding times was analyzed by X-ray fluorescence spectroscopy, as shown in Table 5:

[0054] When the autogenous grinding process lasted 120 min, the main chemical components in the coal gangue were SiO2 (decreased from 44.40% to 42.30%), Al2O3 (decreased from 19.7% to 18.00%), and Fe2O3 (increased from 18.90% to 23.20%).

[0055] XRD analysis of the phase composition of coal gangue at different autogenous grinding times, such as Figure 3 As shown: Depend on Figure 3 The XRD patterns of the autogenous grinding of coal gangue at different times show that when the diffraction angle is 26.68° and the autogenous grinding time is 120 min, the diffraction peaks of quartz and kaolinite are the lowest compared to other autogenous grinding times, and the diffraction peaks of quartz and kaolinite are lower than those of raw coal gangue.

[0056] Autogenous grinding of coal gangue, based on differences in hardness, results in significant variations in calorific value and ash content compared to the original gangue. After autogenous grinding for different durations, XRF and XRD analyses of the separated gangue, along with a comprehensive comparison of the crushing and separation effects and economic benefits of different autogenous grinding methods, confirm that autogenous grinding is a superior method for crushing and separating coal gangue, offering advantages such as simple operation and no consumables. Experiments show that grinding time significantly impacts the crushing and separation effect of coal gangue, with a suitable grinding time of 120 minutes. Therefore, the autogenous grinding time in this invention is 120 minutes.

[0057] 5. Thermal activation technology for coal gangue: Thermal activation involves calcining coal gangue at high temperatures to enhance its pozzolanic activity. This process simultaneously activates the pozzolanic activity and removes organic matter and other substances introduced during coal mining that are detrimental to its cementitious properties.

[0058] This invention utilizes high-temperature calcination to activate the minerals in coal gangue. High-temperature calcination causes lattice distortion and disrupts saturated Si-O and Al-O bonds, thereby altering the mineral structure and chemical composition of the coal gangue. Scientific research shows that the abundant kaolinite in coal gangue undergoes dehydration at temperatures between 500℃ and 700℃, resulting in highly reactive metakaolinite minerals and further enhancing the activity of the coal gangue. However, above a certain temperature range, silicon dioxide combines with aluminum oxide to form inactive mullite. Therefore, this invention selects five high-temperature calcination activation points within the 400℃–900℃ range: 450℃, 550℃, 650℃, 750℃, and 850℃.

[0059] After sorting, the fragile coal gangue is ground in a rod mill and then calcined and activated in a muffle furnace. Each calcination cycle is 500g of coal gangue. The muffle furnace temperature is initially set to 650℃ for activation. Once the temperature reaches and stabilizes at 650℃, it is held for 30, 60, 90, 120, 180, and 240 minutes, respectively, and then removed after natural cooling. The muffle furnace temperature is then set to 450℃, 550℃, 650℃, 750℃, and 850℃ for further activation. Once the temperature reaches the set value, it is held for 120 minutes, and then removed after natural cooling.

[0060] Analysis of the properties of coal gangue activated at different calcination temperatures: Table 6 shows the results of inorganic component content at different calcination temperatures after 120 min;

[0061] Table 6 shows that when the calcination time is 120 min and the calcination temperature is 650℃, the Al2O3 content decreases from 18.8% in the uncalcined coal gangue under the sorting sieve to 18.50%, and the Si2O chemical composition content decreases from 42.8% to 41.90%. The data indicate that the activation effect on the sorted coal gangue is significant when calcined for 120 min at 650℃.

[0062] like Figure 4 The image shows the XRD patterns of sorted coal gangue at different temperatures. Figure 4 XRD analysis of sorted coal gangue at different temperatures showed that the quartz peaks in the sorted coal gangue gradually decreased with increasing temperature. At scanning angles of 39.56° and 50.18°, the diffraction peaks of quartz disappeared after the calcination temperature exceeded 550°C.

[0063] At a scanning angle of 29.50° and a temperature equal to or higher than 450°C, and at an angle of 31.80° and a temperature higher than 550°C, the diffraction peak of hydrated calcium sulfate disappeared. At an angle of 12.22° and a temperature higher than 450°C, the diffraction peak of kaolin disappeared. At a scanning angle of 26.92°, when the temperature exceeded 450°C, the quartz diffraction peak gradually decreased relative to the uncalcined coal gangue under the original sorting sieve as the temperature increased, and the quartz peak tended to stabilize after 650°C. Therefore, from an economic perspective, this invention selects 650°C for calcining and activating coal gangue.

[0064] Analysis of the properties of coal gangue activated by different heat preservation times: Table 7 shows the chemical composition content results at 650℃ for different calcination times;

[0065] As shown in Table 7, when the calcination temperature is 650℃ and the calcination time is 120 min, the chemical composition content of Al2O3 decreased from 18.80% in the uncalcined coal gangue under the sorting sieve to 18.50%, and the chemical composition content of SiO2 decreased from 42.80% to 43.60%. Therefore, it can be concluded that the activity of coal gangue after sorting and calcination is significantly improved.

[0066] like Figure 5 The image shows the XRD patterns of calcined activated coal gangue at different times. Figure 5 XRD pattern analysis of coal gangue calcined and activated at different times revealed that, with increasing calcination time, the diffraction peaks of kaolin disappeared at a scanning angle of 32.56° and a calcination temperature of 30 min or more. At a scanning angle of 26.52°, the diffraction peaks of quartz decreased with increasing calcination time, and tended to stabilize after 120 min of calcination.

[0067] Comparative analysis with the XRD patterns of sorted coal gangue revealed a sharp decrease in the diffraction peaks of quartz and kaolinite at different times and temperatures when the scanning angle was 26.6°. This analysis indicates that calcination activation of coal gangue is relatively better at temperatures above 650℃ and for 120 minutes.

[0068] By investigating the effects of different calcination activation temperatures (holding time of 120 min) and different holding times (calcination temperature of 650℃) on the activation effect of sorted coal gangue, XRD and XRF tests show that the optimal calcination activation conditions are calcination at 650℃ and holding time of 120 min.

[0069] 6. Test Analysis: A process for preparing building cementitious materials from coal gangue through auto-grinding, sorting, calcination, and activation, the process specifically includes the following steps: Step 1: After drying the raw coal gangue, it is initially crushed, and then the initially crushed coal gangue is put into a rod mill for crushing and screening to obtain undersize coal gangue and oversize coal gangue. Step 2: Wash the oversized coal gangue with water, dry the precipitate obtained during the washing process, and mix the dried precipitate with the undersized coal gangue obtained in Step 1. Step 3: After preheating the mixed coal gangue obtained in Step 2, calcine it at a certain temperature. After calcining for a certain time, take it out and place it in the air to cool down, and obtain the calcined product. Step 4: The calcined product is mechanically ground in a rod mill and used as an admixture; Step 5: Weigh the admixture, cement, and fine sand according to a certain ratio, and mix them evenly; Step 6: Weigh out the water-reducing agent and water in a certain ratio, mix the water-reducing agent and water and stir until the water-reducing agent is fully dissolved, then pour it into the product obtained in Step 5 and continue to stir evenly to obtain the final building cementitious material. In step one, the rod mill is a three-roller four-cylinder rod mill with a rod-to-material ratio of 25:1, a 1mm standard sieve for screening, and a grinding time of 120 minutes.

[0070] The cement is ordinary Portland cement, the water-reducing agent is polycarboxylate-based water-reducing agent, the particle size of the fine sand is ≤2mm, the size of the admixture in step four is ground to ≤0.105mm, and in step one, a jaw crusher is used to pre-crush the raw coal gangue, and the particle size of the pre-crushed material is below 6mm. The cement mortar specimens required for the experiment of this invention were prepared according to the mix proportions designed in Table 8 below; the calcination temperature was 650℃ and the calcination time was 2h; the cementitious material was a mixture of admixtures and cement; the mass ratio of water to cementitious material, i.e., the water-cement ratio, was 0.44; the mass ratio of water-reducing agent to cementitious material was 1:100; and the mass ratio of fine sand to the total mass of cementitious material and water-reducing agent was 1:2.

[0071] The mass ratio of the admixture to cement in the cementitious material is the amount of calcined coal gangue added. The calcined coal gangue content in Example 1 is 0%, in Example 2 it is 15%, in Example 3 it is 25%, in Example 4 it is 35%, and in Example 5 it is 45%. As shown in Table 8, these are the cement mortar mix proportions at T=650℃.

[0072]

[0073] The effect of different coal gangue admixtures on the strength of cement mortar: Before producing calcined activated coal gangue cement mortar, to ensure the uniformity of the produced cement mortar, a dry-mixing followed by wet-mixing method was adopted during the experimental mixing process. First, the calcined activated coal gangue and fine sand, weighed using an ACS-6kg electronic scale, were poured into a test tray and mixed thoroughly with a mixer. Then, cement, the cementitious material, was added and mixed until homogeneous. Next, the amount of water-reducing agent was weighed using an electronic balance, and the required amount of water was measured using a graduated cylinder. The water-reducing agent and the measured water were poured into a 1000mL beaker and stirred continuously until the water-reducing agent was fully dissolved. This solution was then poured into the homogeneously mixed calcined coal gangue cement mortar and stirred continuously.

[0074] Subsequently, a 40cm×40cm×160cm triple mold was brushed with release agent. After the mixture was thoroughly and evenly mixed, cement mortar was poured into the mold, and the mold filled with cement mortar mixture was placed in a cement paste mixer for mixing and shaping. While vibrating, surface air bubbles were broken up with a shovel to reduce air bubbles inside and on the surface of the cement mortar mixture. After vibration, the surface was smoothed to ensure that the height difference between the surface of the cement mortar specimen and the edge of the mold was no more than 0.5mm. The shaped cement mortar specimen was covered with a plastic film to prevent excessive moisture evaporation, which would affect the test results. After standing for one day, the mold was removed, and the specimens were classified, numbered, and labeled, and the specimen conditions were recorded in detail. For specimens with different curing times of 3d, 7d, and 28d, the specimens were cured and maintained in accordance with GB / T17671-1999 "Test Method for Strength of Cement Mortar (ISO Method)" standard, and the flexural and compressive strength tests of the cement mortar specimens were conducted using a WAW-600C universal testing machine.

[0075] Table 9 shows the test results of flexural and compressive strength of cement mortar samples under different coal gangue content and mix proportions.

[0076]

[0077] Flexural strength of cement mortar with different admixtures: as shown in Table 9 and Figure 6 The comparison shows that the flexural strength of the standard cement mortar specimens at 3d, 7d, and 28d is 10.0 MPa, 13.0 MPa, and 33.0 MPa, respectively. The variation trend of the flexural strength of cement mortar prepared with different coal gangue contents at a calcination activation temperature of 650℃ is also examined. Compared with the standard sample, the strength initially decreases, then increases sharply at a calcined coal gangue content of 25%, reaching a maximum before decreasing again. When the calcined coal gangue content is 25%, the flexural strength of the cement mortar at 3d, 7d, and 28d is 11 MPa, 13 MPa, and 26 MPa, respectively.

[0078] Compressive strength of cement mortar with different admixtures: as shown in Table 9 and Figure 7 The comparison shows that when the calcination activation temperature is 650℃, the compressive strength of cement mortar prepared with different calcined coal gangue contents increases slowly at first, reaching a maximum when the calcined coal gangue content is 25%, and then gradually decreases. When the calcined coal gangue content is 0%, the compressive strength of the standard cement mortar specimens at 3d, 7d, and 28d is 20.0 MPa, 33.0 MPa, and 39.0 MPa, respectively.

[0079] Comparison with standard parts shows that when the calcination temperature is 650℃ and the holding time is 120min, the compressive strength of cement mortar test blocks prepared by adding different amounts of calcined activated and sorted coal gangue first increases and then decreases with the continuous increase of the amount of calcined coal gangue. When the amount of calcined activated and sorted coal gangue is 25%, the compressive strength reaches the maximum value. The compressive strengths at 3d, 7d, and 28d are 28.5MPa, 36.0MPa, and 80.0MPa, respectively.

[0080] When the calcination temperature of activated coal gangue is 650℃ and the holding time is 120min, the compressive strength of the sorted and calcined activated coal gangue cement mortar first increases and then decreases with increasing calcination temperature; and with increasing coal gangue content, its compressive strength first increases and then decreases. When the calcination temperature is 650℃, the holding time is 120min, and the calcined coal gangue content is 25%, the maximum flexural strength of the cement mortar at 3d, 7d, and 28d is 26MPa; the maximum compressive strength is 80MPa.

[0081] A process for preparing building cementitious materials from coal gangue through auto-grinding, sorting, calcination, and activation, the process specifically includes the following steps: Step 1: After drying the raw coal gangue, it is initially crushed, and then the initially crushed coal gangue is put into a rod mill for crushing and screening to obtain undersize coal gangue and oversize coal gangue. Step 2: Wash the oversized coal gangue with water, dry the precipitate obtained during the washing process, and mix the dried precipitate with the undersized coal gangue obtained in Step 1. Step 3: After preheating the mixed coal gangue obtained in Step 2, calcine it at a certain temperature. After calcining for a certain time, take it out and place it in the air to cool down, and obtain the calcined product. Step 4: The calcined product is mechanically ground in a rod mill and used as an admixture; Step 5: Weigh the admixture, cement, and fine sand according to a certain ratio, and mix them evenly; Step 6: Weigh out the water-reducing agent and water in a certain ratio, mix the water-reducing agent and water and stir until the water-reducing agent is fully dissolved, then pour it into the product obtained in Step 5 and continue to stir evenly to obtain the final building cementitious material. In step one, the rod mill is a three-roller four-cylinder rod mill with a rod-to-material ratio of 25:1, a 1mm standard sieve for screening, and a grinding time of 120 minutes.

[0082] The cement is ordinary Portland cement, the water-reducing agent is polycarboxylate-based water-reducing agent, the particle size of the fine sand is ≤2mm, the size of the admixture in step four is ground to ≤0.105mm, and in step one, a jaw crusher is used to pre-crush the raw coal gangue, and the particle size of the pre-crushed material is below 6mm. The cement mortar specimens required for the experiment of this invention were prepared according to the mix proportions designed in Table 10 below; the cementitious material is a mixture of admixture and cement; wherein, the mass ratio of the admixture to cement in the cementitious material is 25:100; the mass ratio of water to cementitious material, i.e., the water-cement ratio, is 0.44; the mass ratio of water-reducing agent to cementitious material is 1:100; and the mass ratio of fine sand to the total mass of cementitious material and water-reducing agent is 1:2.

[0083] The calcination temperature is 450℃~850℃, and the calcination time is 2h.

[0084] The calcination temperature in Example 6 was 450℃, the calcination temperature in Example 7 was 550℃, the calcination temperature in Example 8 was 650℃, the calcination temperature in Example 9 was 750℃, and the calcination temperature in Example 10 was 850℃. The cement mortar mix ratio at T=650℃ is shown in Table 10.

[0085]

[0086] Effect of coal gangue content at different calcination temperatures: Before producing calcined activated coal gangue cement mortar, to ensure the uniformity of the produced cement mortar, a dry-mixing followed by wet-mixing method was adopted during the experimental mixing process. First, the calcined activated coal gangue and fine sand, weighed using an ACS-6kg electronic scale, were poured into a test tray and mixed thoroughly with a mixer. Then, cement, the cementitious material, was added and mixed until homogeneous. Next, the amount of water-reducing agent was weighed using an electronic balance, and the required amount of water was measured using a graduated cylinder. The water-reducing agent and the measured water were poured into a 1000mL beaker and stirred continuously until the water-reducing agent was fully dissolved. This solution was then poured into the homogeneously mixed calcined coal gangue cement mortar and stirred continuously.

[0087] Subsequently, a 40cm×40cm×160cm triple mold was brushed with release agent. After the mixture was thoroughly and evenly mixed, cement mortar was poured into the mold, and the mold filled with cement mortar mixture was placed in a cement paste mixer for mixing and shaping. While vibrating, surface air bubbles were broken up with a shovel to reduce air bubbles inside and on the surface of the cement mortar mixture. After vibration, the surface was smoothed to ensure that the height difference between the surface of the cement mortar specimen and the edge of the mold was no more than 0.5mm. The shaped cement mortar specimen was covered with a plastic film to prevent excessive moisture evaporation, which would affect the test results. After standing for one day, the mold was removed, and the specimens were classified, numbered, and labeled, and the specimen conditions were recorded in detail. For specimens with different curing times of 3d, 7d, and 28d, the specimens were cured and maintained in accordance with GB / T17671-1999 "Test Method for Strength of Cement Mortar (ISO Method)" standard, and the flexural and compressive strength tests of the cement mortar specimens were conducted using a WAW-600C universal testing machine.

[0088] Table 11 shows the test results of flexural and compressive strength of cement mortar samples under different temperatures and coal gangue content ratios.

[0089]

[0090] Flexural strength of cement mortar at different calcination temperatures: as shown in Table 11 and Figure 8 Combining these findings, we can deduce the changes in flexural strength of cement mortar prepared after calcination and activation at different temperatures when the coal gangue content is 25%. The strength of the cement mortar initially increases and then decreases sharply, reaching its maximum value at 650℃. The flexural strengths at 3d, 7d, and 28d are 10MPa, 12MPa, and 26MPa, respectively.

[0091] Compressive strength of cement mortar at different calcination temperatures: as shown in Table 11 and Figure 9Combined, it can be seen that when the admixture content is 25%, the compressive strength of cement mortar prepared from coal gangue after calcination and activation at different temperatures first increases and then decreases. At 650℃, the compressive strength at 3d, 7d, and 28d all reach the maximum value under the same conditions, which are 28.5MPa, 36MPa, and 80MPa, respectively.

[0092] Figure 10 The compressive strength curve of the building cementitious material with 25% calcined coal gangue and a calcination temperature of 650℃ is shown.

[0093] The relationship between the amount of coal gangue calcined at different temperatures and the flexural and compressive strength of the samples at 3d, 7d, and 28d was analyzed. The results show that when the coal gangue content is 25%, the flexural and compressive strengths of the samples gradually increase before reaching 650℃ due to the continuous increase in temperature, but decrease sharply when the calcination temperature exceeds 650℃. The graphs clearly show that the cement mortar prepared from sorted, calcined, and activated coal gangue reaches its maximum flexural and compressive strength at 3d, 7d, and 28d when the calcination temperature is 650℃ and the holding time is 120min. This is mainly because the activation degree of coal gangue is relatively optimal at around 650℃.

[0094] The results showed that, using coal gangue from the Liupanshui area as raw material, the changes in the cementitious properties of coal gangue after rod mill separation and subsequent thermal composite activation were investigated. Coal gangue active powder material was prepared as an admixture after thermal activation of the rod-milled coal gangue. The changes in the mineral composition of the coal gangue before and after activation were analyzed, thus exploring its activation mechanism. The activity level was evaluated through comparative analysis. The active powder coal gangue prepared under optimal activation conditions was used as a cement mortar admixture. After being mixed evenly with ordinary silicate cement, fine sand, polycarboxylate superplasticizer, and water, cement mortar specimens were obtained. The mechanical properties were tested after curing for 3 days, 7 days, and 28 days according to GB / T17617-1999 "Test Method for Strength of Cement Mortar (ISO Method)" to explore the changes in its mechanical properties. The above research leads to the following conclusions: (1) Through testing and analysis of the sorted coal gangue, it was found that the ash content of the undersize gangue after auto-grinding decreased from 83.94% to 80.95% compared to the coal gangue, while the calorific value increased from 0.03 MJ / kg to 2.29 MJ / kg. The changes in calorific value and ash content indicate that the carbon content of the undersize gangue is relatively high compared to the coal gangue. XRD and XRF spectrum analysis of the undersize gangue after auto-grinding showed that the diffraction peaks of quartz and kaolinite decreased significantly after 120 min of auto-grinding, indicating that auto-grinding of coal gangue is of certain significance.

[0095] (2) XRD pattern analysis of coal gangue under different conditions after calcination showed that when the calcination temperature was 650℃ (holding time was 120min) and the holding time was 120min (calcination temperature was 650℃), the quartz diffraction peak decreased sharply and the kaolin diffraction peak disappeared when the scanning angle was 26.6°. This indicates that the coal gangue had the best activation effect under the activation conditions.

[0096] (3) The results of the influence of different temperatures on the mechanical properties of cement mortar showed that when the amount of calcined activated coal gangue was 25% and the holding time was 120 min, the flexural and compressive strengths of the cement mortar specimens under different activation temperatures first increased and then decreased compared with the standard specimens. When the calcination temperature was 650℃, the flexural and compressive strengths of the cement mortar prepared by sorting and calcining activated coal gangue reached their maximum values ​​at 3d, 7d, and 28d. The flexural strengths were 10MPa, 12MPa, and 26MPa, respectively; and the compressive strengths were 28.5MPa, 36MPa, and 80MPa, respectively.

[0097] (4) The effect of different amounts of gangue under the autogenous grinding screen on the mechanical properties of cement mortar showed that when the calcination temperature was 650℃ and the holding time was 120min, the flexural strength and compressive strength of cement mortar specimens prepared by adding different amounts of calcined and activated sorted gangue first increased and then decreased with the increase of the amount of gangue. When the amount of sorted and calcined activated gangue was 25%, both the flexural and compressive strengths reached their peak values. The flexural strengths at 3d, 7d, and 28d were 11MPa, 13MPa, and 26MPa, respectively, and the compressive strengths were 28.5MPa, 36.0MPa, and 80.0MPa, respectively.

[0098] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A process for preparing building cementitious materials from coal gangue through auto-grinding, sorting, calcination, and activation, characterized in that, The process specifically includes the following steps: Step 1: After drying the raw coal gangue, it is initially crushed, and then the initially crushed coal gangue is put into a rod mill for crushing and screening to obtain undersize coal gangue and oversize coal gangue. Step 2: Wash the oversized coal gangue with water, dry the precipitate obtained during the washing process, and mix the dried precipitate with the undersized coal gangue obtained in Step 1. Step 3: After preheating the mixed coal gangue obtained in Step 2, calcine it at a certain temperature. After calcining for a certain time, take it out and place it in the air to cool down, and obtain the calcined product. Step 4: The calcined product is mechanically ground in a rod mill and used as an admixture; Step 5: Weigh the admixture, cement, and fine sand according to a certain ratio, and mix them evenly to obtain the product; Step Six: Weigh out the water-reducing agent and water in a certain ratio, mix the water-reducing agent and water and stir until the water-reducing agent is fully dissolved, then pour it into the product obtained in Step Five and continue to stir evenly to obtain the final building cementitious material.

2. The process for preparing building cementitious materials from coal gangue through autogenous grinding, sorting, calcination, and activation as described in claim 1, characterized in that, In step one, the rod mill is a three-roller four-cylinder rod mill with a rod-to-material ratio of 25:

1. The sieving uses a 1mm standard sieve, and the grinding time is 15-180 minutes, preferably 120 minutes.

3. The process for preparing building cementitious materials from coal gangue through autogenous grinding, sorting, calcination, and activation as described in claim 1, characterized in that, The calcination temperature is 450℃~850℃, and the calcination time is 0.5-4.0h, preferably 650℃ and 2h.

4. The process for preparing building cementitious materials from coal gangue through auto-grinding, sorting, calcination, and activation as described in claim 1, characterized in that, The cementitious material is a mixture of admixtures and cement; The mass ratio of the admixture to cement in the cementitious material is 15-45:100; preferably 25:

100. The mass ratio of water to cementitious material, i.e., the water-cement ratio, is 0.44; The mass ratio of water-reducing agent to cementitious material is 1:100; The mass ratio of fine sand to the total mass of cementitious materials and water-reducing agent is 1:

2.

5. The process for preparing building cementitious materials from coal gangue through auto-grinding, sorting, calcination, and activation according to claim 4, characterized in that, The cement is ordinary Portland cement.

6. The process for preparing building cementitious materials from coal gangue through autogenous grinding, sorting, calcination, and activation according to claim 4, characterized in that, The water-reducing agent is a polycarboxylate-based water-reducing agent.

7. The process for preparing building cementitious materials from coal gangue through auto-grinding, sorting, calcination, and activation according to claim 4, characterized in that, The particle size of the fine sand is ≤2mm.

8. The process for preparing building cementitious materials from coal gangue through autogenous grinding, sorting, calcination, and activation according to claim 1, characterized in that, In step four, the size of the admixture is ground to ≤0.105mm.

9. The process for preparing building cementitious materials from coal gangue through autogenous grinding, sorting, calcination, and activation according to claim 1, characterized in that, In step one, a jaw crusher is used to perform preliminary crushing of the raw coal gangue, with the particle size of the preliminary crushed material being less than 6mm.

10. A building cementitious material, characterized in that, Cement mortar material prepared by the process of preparing building cementitious materials by self-grinding, sorting, calcination and activation of coal gangue as described in any one of claims 1-9.

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