A method for preparing a composite cement product using low-quality coal gangue

Abstract

The application discloses a method for preparing composite cement products by using low-quality coal gangue, and belongs to the technical field of building material production. The method comprises the following steps: heating normal-temperature coal gangue powder with a particle size less than a first target particle size to obtain heated coal gangue powder with a temperature not lower than a preset temperature, calcining the heated coal gangue powder in a suspension state to obtain high-temperature calcined coal gangue powder, and cooling the high-temperature calcined coal gangue powder to obtain calcined coal gangue raw material; preparing an active activator by mixing light-burned limestone with a decomposition rate of 20%-40% and fly ash according to a preset proportion; fully mixing cement clinker, desulfurization gypsum, the calcined coal gangue raw material, limestone powder and the active activator to obtain a mixture; and grinding the mixture to obtain a composite cement product. The application can obtain the technical effects that the quality proportion of active materials in various low-quality coal gangues with an Al2O3 content of only 20%-28% reaches 35%-45%, and the 28d compressive strength of the composite cement product is greater than 48 MPa.

Description

Technical Field

[0001] This application relates to the field of building materials production technology, and in particular to a method for preparing composite cement products using low-quality coal gangue. Background Technology

[0002] Coal gangue is the largest solid waste in China in terms of both emissions and stockpiles. The massive accumulation of coal gangue not only occupies arable land and pollutes the environment but also leads to resource waste. Therefore, the large-scale, high-value utilization of coal gangue is of great significance.

[0003] A significant proportion of my country's coal gangue resources are high-aluminum coal gangue, primarily composed of active clay minerals such as kaolinite, illite, montmorillonite, and chlorite. High-temperature calcination of this coal gangue removes its water of crystallization, producing gel materials with an amorphous silica-alumina mineral structure exhibiting gel activity. These materials can participate in the hydration reaction in the alkaline environment created during cement hydration, thereby contributing to the mechanical strength of the cement. Therefore, coal gangue can serve as a raw material for cement and other building materials. Consequently, the use of coal gangue in building materials is considered the most promising approach for large-scale, high-value utilization.

[0004] There are two main ways to use calcined coal gangue in cementitious materials: First, it can be used directly as an active material, that is, directly mixed and ground with cement clinker to prepare ordinary Portland cement. This method does not take into account the characteristics of calcined coal gangue and involves a reasonable component matching, failing to effectively utilize its activity. Therefore, the amount added to cement is generally below 10%, resulting in low utilization of coal gangue. Second, calcined coal gangue, limestone, and cement clinker can be mixed in a certain proportion to prepare composite cement products. In this method, due to a reasonable proportioning design, the activity of calcined coal gangue can be activated to a certain extent, thereby increasing the proportion of calcined coal gangue to 20%–40%, improving the utilization rate of coal gangue. Therefore, the preparation of composite cement products by mixing calcined coal gangue, limestone, and cement clinker is a promising application direction, which not only has the potential to achieve large-scale, high-value utilization of coal gangue but also significantly reduces energy consumption and carbon emissions in cement production.

[0005] However, despite the promising prospects of composite cement products prepared by mixing calcined coal gangue with limestone and cement clinker, several challenges remain in practical applications. Firstly, the activity of the calcined coal gangue significantly impacts the performance of the composite cement product. Higher quality coal gangue generally contains more than 80% active clay minerals, resulting in better activity after calcination. However, most coal gangue from certain regions is of low quality, with Al2O3 content below 30%, or even less than 20%, and consequently, a low content of active materials. Calcined coal gangue from such low-quality coal gangue exhibits poor activity, leading to unsatisfactory performance in composite cement products.

[0006] Secondly, the calcination process also has a significant impact on the activity of calcined coal gangue. Currently, processes such as vertical shaft furnaces, rotary kilns, and fluidized beds often suffer from problems of "over-calcination" or "under-calcination" in actual operation, both of which affect the activity of calcined coal gangue.

[0007] Finally, calcined coal gangue and limestone were mixed as active materials to replace a higher proportion of cement clinker. Since the hydration reaction of calcined coal gangue and limestone needs to be carried out in the alkaline environment formed by cement hydration, its hydration sequence is lagging behind that of cement hydration. If the added active materials cannot effectively participate in hydration, they cannot compensate for the strength loss caused by the higher proportion of cement clinker, which will lead to a decrease in the strength of the prepared cement, especially a decrease in the early strength of the cement.

[0008] For the reasons mentioned above, although the preparation of composite cement products by mixing calcined coal gangue, limestone and cement clinker has good prospects, there are still some issues. Currently, the low-quality coal gangue and the poor activity of calcined coal gangue obtained by existing calcination processes, as well as the fact that mixing calcined coal gangue and limestone as an active material will lead to a decrease in the strength of the prepared cement, make the application effect of low-quality coal gangue in composite cement products unsatisfactory. Summary of the Invention

[0009] This application provides a method for preparing composite cement products using low-quality coal gangue. This method addresses the problems of poor activity in low-quality coal gangue and calcined coal gangue obtained by existing calcination processes, as well as the reduced strength of cement prepared by mixing calcined coal gangue with limestone as an active material. These issues result in unsatisfactory application effects of low-quality coal gangue in composite cement products.

[0010] To achieve the above objectives, the technical solution of this invention is as follows:

[0011] This invention provides a method for preparing composite cement products using low-quality coal gangue, comprising:

[0012] Room temperature coal gangue powder smaller than the first target particle size is heated to obtain heated coal gangue powder at a temperature not lower than the preset temperature. The heated coal gangue powder is then calcined in a suspension state to obtain high temperature calcined coal gangue powder. The high temperature calcined coal gangue powder is then cooled to obtain calcined coal gangue raw material.

[0013] An active activator is prepared by mixing lightly burned limestone with a decomposition rate of 20% to 40% with fly ash in a predetermined ratio.

[0014] The cement clinker, desulfurized gypsum, the calcined coal gangue raw material, limestone powder and active activator are thoroughly mixed to obtain a mixture;

[0015] The mixture is ground to obtain a composite cement product.

[0016] In one possible implementation, the first target particle size is 200 mesh;

[0017] The preset temperature is 550℃;

[0018] The furnace calcination temperature during suspension calcination is 800℃~950℃, the residence time in the furnace is 5s~15s, and the oxygen content is not less than 9%.

[0019] In one possible implementation, the preset ratio is 1:2 to 3.

[0020] In one possible implementation, before preparing the activation activator with the fly ash, the method further includes:

[0021] The fly ash is ultrafine ground to a specific surface area greater than 500 m². 2 Fineness of / g.

[0022] In one possible implementation, the method for preparing the lightly calcined limestone with a decomposition rate of 20% to 40% includes:

[0023] Limestone raw materials smaller than the second target particle size are suspended and calcined in a furnace at a temperature of 810℃ to 830℃ for 5s to 8s to obtain lightly calcined limestone with a decomposition rate of 20% to 40%.

[0024] In one possible implementation, the mass percentages of cement clinker, desulfurized gypsum, calcined coal gangue raw material, limestone powder, and active activator are 55%–60%, 4%–6%, 20%–26%, 10%–13%, and 3%–4%, respectively.

[0025] In one possible implementation, the 28-day compressive strength of the cement clinker is not less than 46 MPa.

[0026] In one possible implementation, the percentage of CaO in the limestone powder is not less than 44%.

[0027] In one possible implementation, heating room-temperature coal gangue powder smaller than the first target particle size to obtain heated coal gangue powder at a temperature not lower than a preset temperature includes:

[0028] Room temperature coal gangue powder with a particle size smaller than the first target size is subjected to multi-stage suspension heating to obtain heated coal gangue powder with a temperature not lower than the preset temperature.

[0029] In one possible implementation, cooling the high-temperature calcined coal gangue powder to obtain calcined coal gangue raw material includes:

[0030] The high-temperature calcined coal gangue powder is subjected to multi-stage suspension cooling to obtain calcined coal gangue raw material.

[0031] One or more technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages:

[0032] The method for preparing composite cement products using low-quality coal gangue provided in this invention involves heating room-temperature coal gangue powder with a particle size smaller than a first target size to obtain heated coal gangue powder at a temperature not lower than a preset temperature. This heated coal gangue powder is then subjected to suspension calcination to obtain high-temperature calcined coal gangue powder. Finally, the high-temperature calcined coal gangue powder is cooled to obtain calcined coal gangue raw material. This process effectively promotes the formation of active substances, resulting in highly active calcined coal gangue raw material. An activity activator is prepared by mixing lightly calcined limestone with a decomposition rate of 20%–40% and fly ash in a preset ratio. This activity activator promotes the hydration of the calcined coal gangue raw material, improving the hydration strength of the composite cement product. This significantly enhances the performance of the composite cement product prepared from cement clinker, calcined coal gangue raw material, and limestone powder, meeting the performance requirements for cement use. Using the method of this invention, various low-quality coal gangue with Al2O3 content of only 20% to 28% can achieve the technical effect of active material mass ratio of 35% to 45% and composite cement product 28d compressive strength greater than 48MPa. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 A flowchart illustrating a method for preparing composite cement products using low-quality coal gangue, provided in an embodiment of this application.

[0035] Figure 2 This is a graph showing the trend of flexural strength as a function of curing age in Example 1 of this application;

[0036] Figure 3 This is a graph showing the trend of compressive strength as a function of curing age in Example 2 of this application. Detailed Implementation

[0037] 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, not all, of the embodiments of the present invention. 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.

[0038] It should be noted that all raw materials in the embodiments of the present invention can be purchased on the market or prepared by conventional methods known to those skilled in the art; the terms "first" and "second" in the embodiments of the present invention are used for descriptive purposes only and therefore should not be construed as indicating or implying relative importance; in the relevant descriptions of this embodiment, the terms "including," "containing," "possessing," etc. are all open terms and are generally understood to include but not be limited to; the term "at least one" is generally understood to mean one or more, wherein "multiple" refers to two or more; the term "at least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items, for example, "at least one of a, b or c", or "at least one of a, b and c", can all mean: a, b, c, ab (i.e. a and b), ac, bc, or abc, wherein a, b, and c can be single or multiple; the symbol "A / B" is used to describe the selection relationship of related objects and generally indicates an "or" relationship.

[0039] In the following description of the embodiments, the terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to limit the application. The singular forms "a" and "the" as used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0040] Those skilled in the art should understand that in the following description of the embodiments of this application, the sequence of numbers does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application. The numerical ranges in the embodiments of this application should be understood to specifically disclose each intermediate value between the upper and lower limits of the range. Each smaller range between any stated value or intermediate value within a stated range, as well as any other stated value or intermediate value within said range, is also included within the scope of this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0041] Unless otherwise stated, the technical / scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. While this application describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this application. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0042] like Figure 1 As shown, this embodiment of the invention provides a method for preparing composite cement products using low-quality coal gangue, including the following steps 1 to 4, where the step numbers do not represent the order of execution.

[0043] Step 1: Heating room-temperature coal gangue powder smaller than the first target particle size to obtain heated coal gangue powder at a temperature not lower than the preset temperature ensures that the heated coal gangue powder for subsequent reactions already has a certain temperature, greatly shortening the subsequent reaction time and preventing subsequent "over-calcination" or "under-calcination". This room-temperature coal gangue powder is prepared from low-quality coal gangue.

[0044] Heated coal gangue powder is calcined in suspension to obtain high-temperature calcined coal gangue powder. The high-temperature calcined coal gangue powder is then cooled to obtain calcined coal gangue raw material, thus obtaining highly active calcined coal gangue raw material, which effectively promotes the formation of active substances and can be used for subsequent applications.

[0045] Further, heating room-temperature coal gangue powder smaller than the first target particle size to obtain heated coal gangue powder at a temperature not lower than a preset temperature includes: multi-stage suspension heating of room-temperature coal gangue powder smaller than the first target particle size to obtain heated coal gangue powder at a temperature not lower than the preset temperature. In this embodiment, the room-temperature coal gangue powder is in powder form. Through multi-stage suspension heating, the room-temperature coal gangue can quickly reach the preset temperature, saving time and energy. For example, room-temperature coal gangue powder smaller than the first target particle size can be suspended and heated in two stages to obtain heated coal gangue powder at a temperature not lower than the preset temperature.

[0046] Furthermore, cooling high-temperature calcined coal gangue powder to obtain calcined coal gangue raw material includes: multi-stage suspension cooling of high-temperature calcined coal gangue powder to obtain calcined coal gangue raw material. In this embodiment, the high-temperature coal gangue powder is in powder form. Through multi-stage suspension cooling, the high-temperature coal gangue can be rapidly cooled and used, saving time and energy. For example, high-temperature calcined coal gangue powder can be subjected to three-stage suspension cooling to obtain calcined coal gangue raw material.

[0047] The first target particle size is 200 mesh. In actual operation, the coal gangue raw material is passed through a 200-mesh standard sieve. The coal gangue raw material below the standard sieve is the room temperature coal gangue powder below 200 mesh. This room temperature coal gangue powder is finer, which facilitates the suspension reaction of the powder during subsequent suspension calcination, thus resulting in a better activation effect.

[0048] The preset temperature is 550℃. If this preset temperature is too low, the temperature difference between the room-temperature coal gangue powder and the furnace calcination temperature will be too large, resulting in a high heat load during suspension calcination and significant interference with the suspension calcination process. Conversely, with a preset temperature of 550℃, the temperature difference between the room-temperature coal gangue powder and the furnace calcination temperature is smaller, resulting in a lower heat load during suspension calcination and less interference with the suspension calcination process.

[0049] The furnace calcination temperature during suspension calcination is 800℃~950℃ (typical but not limiting temperatures include 800℃, 820℃, 840℃, 860℃, 880℃, 900℃, 920℃, 940℃, and 950℃), and the furnace residence time is 5s~15s (typical but not limiting times include 5s, 6s, 7s, 8s, 9s, 10s, 11s, 12s, 13s, 14s, and 15s). Because the residence time of room-temperature coal gangue powder in the furnace is short, if the furnace calcination temperature is too low, the carbon cannot burn completely, resulting in an incomplete reaction. If the furnace calcination temperature is too high, the active clay minerals in the room-temperature coal gangue powder will crystallize, resulting in a loss of their activity.

[0050] An oxygen content of not less than 9% (for example, typical but not limiting contents such as 9%, 10%, 11%, 12%, 13%, 14%, 15%) can enable more complete suspension calcination of room temperature coal gangue powder and better reduction and decarbonization effect.

[0051] In this embodiment, room-temperature coal gangue powder with a mesh size of less than 200 is heated to a temperature not lower than 550°C. This heated coal gangue powder is then subjected to suspension calcination in a furnace at a temperature of 800°C–950°C, a residence time of 5–15 seconds, and an oxygen content not lower than 9%, resulting in high-temperature calcined coal gangue powder. The high-temperature calcined coal gangue powder is then cooled to obtain calcined coal gangue raw material. Under these conditions, the decomposition rate of active clay minerals in the calcined coal gangue raw material is greater than 98%, and the carbon content is less than 2.0%, resulting in an activity index of not less than 90%. The carbon content of the calcined coal gangue raw material is determined using a carbon-sulfur analyzer, and the decomposition rate of active clay minerals is calculated by subtracting the mass of carbon from the mass lost on ignition of the calcined coal gangue raw material.

[0052] Step 2: Prepare an activation agent by mixing lightly calcined limestone with a decomposition rate of 20%–40% with fly ash in a predetermined ratio. Lightly calcined limestone refers to partially decomposed limestone.

[0053] Furthermore, the preparation method of lightly calcined limestone with a decomposition rate of 20% to 40% includes:

[0054] Limestone raw materials smaller than the second target particle size are suspended and calcined in a furnace at a temperature of 810℃ to 830℃ for 5 to 8 seconds to obtain lightly calcined limestone with a decomposition rate of 20% to 40%. During suspension calcination, the airflow continuously tumbles the limestone raw materials, and the 5 to 8 seconds of suspension calcination time allows the limestone raw materials to achieve a decomposition rate of 20% to 40% to obtain lightly calcined limestone. The surface of this lightly calcined limestone is covered with a layer of CaO, which forms Ca(OH)2 upon hydration, increasing the alkalinity in the composite cement product. This helps to accelerate the hydration of active materials such as low-temperature calcined coal gangue and limestone powder. When the surface CaO is completely consumed, the surface has better adhesion to the limestone powder and cement product, which helps to improve the strength of the cement. Typical but non-limiting furnace calcination temperatures include 810℃, 815℃, 820℃, 825℃, and 830℃. The typical but not limiting time for suspension calcination is 5s, 6s, 7s, 8s, etc. The limestone raw material is in powder form. The second target particle size is 200 mesh. In actual operation, the limestone raw material is passed through a 200-mesh standard sieve; limestone raw material passing through the standard sieve is considered to be below 200 mesh.

[0055] The preset ratio is 1:2 to 3. Examples of typical but non-limiting preset ratios include 1:2, 1:2.5, and 1:3. The preferred ratio is 1:2, with a light-burned limestone grade of not less than 90%. A ratio of 1:3 is preferred when the light-burned limestone grade is less than 80%. This means that more fly ash is added when the light-burned limestone grade is low, thus ensuring the strength of the composite cement product after the addition of the active activator.

[0056] Before preparing the activation agent using fly ash, the following steps are also included:

[0057] Fly ash must meet the Class I fly ash standard, and the fly ash must be ultra-finely ground to a specific surface area greater than 500 m². 2 Fineness of / g.

[0058] Step 3: Thoroughly mix cement clinker, desulfurized gypsum, calcined coal gangue raw materials, limestone powder, and activator to obtain a mixture. This cement clinker is ordinary Portland cement clinker.

[0059] Furthermore, the mass percentages of cement clinker, desulfurized gypsum, calcined coal gangue raw material, limestone powder, and active activator are 55%–60%, 4%–6%, 20%–26%, 10%–13%, and 3%–4%, respectively. For example, the mass percentages of cement clinker are typically, but not limiting, at 55%, 57%, 59%, 61%, 63%, and 65%. The mass percentages of desulfurized gypsum are typically, but not limiting, at 4%, 4.5%, 5%, 5.5%, and 6%. The mass percentages of calcined coal gangue raw material are typically, but not limiting, at 20%, 21%, 22%, 23%, 24%, 25%, and 26%. The mass percentages of limestone powder are typically, but not limiting, at 10%, 11%, 12%, and 13%. Typical but non-limiting contents of the active activator by mass are 3%, 3.5%, 4%, 4.5%, and 5%.

[0060] The 28-day compressive strength of cement clinker is not less than 46 MPa, thus ensuring that the produced composite cement products meet the existing 42.5 grade cement factory requirements.

[0061] The CaO content in limestone powder should be no less than 44%, meaning the grade of the limestone powder should be no less than 78%. If the grade of the limestone powder is too low, its hydration activity will be affected.

[0062] Step 4: Grind the mixture to obtain the composite cement product. Specifically, place the mixture in a ball mill and grind it to a specific surface area of ​​350 m². 2 / g~380m 2 A fineness of / g is used to obtain composite cement products.

[0063] The composite cement product was tested for performance according to GB175-2023. The 28-day compressive strength was not less than 48MPa, which meets the 42.5 grade standard.

[0064] The method for preparing composite cement products using low-quality coal gangue provided in this embodiment of the invention includes step 1, in which heated coal gangue powder is calcined in a suspension state to obtain high-temperature calcined coal gangue powder. The suspension state calcination has the characteristics of high transfer efficiency, fast reaction rate, uniform temperature field and narrow residence time distribution range, so that the dehydroxylation reaction of active clay minerals in heated coal gangue powder and the combustion reaction of coal are fully completed within 15s, promoting the effective formation of activity in the high-temperature calcined coal gangue powder.

[0065] Specifically, in the suspension state, room-temperature coal gangue powder is fully dispersed in the airflow, resulting in a large gas-solid contact area. Compared to the calcination method using bulk particles, the effective gas-solid contact area is increased by more than 3000 times. Based on this, the heat transfer efficiency and reaction rate between gas and solid are improved by 3 to 4 orders of magnitude compared to the bulk state, allowing the dehydroxylation reaction of active clay minerals and the combustion reaction time of coal to be completed within 5 to 15 seconds, instead of more than 2 hours. In the suspension calcination furnace, the newly added room-temperature coal gangue powder rapidly rises to 800℃ to 950℃ within 0.05 seconds through heat exchange with the hot airflow, and then flows within the furnace with the airflow. All powder particles have similar effective residence times and reaction processes within the furnace, effectively avoiding the problems of "under-calcination" and "over-calcination" under appropriate calcination parameters. Furthermore, in the suspension calcination process, organic matter in the coal gangue powder and carbon in the coal can be fully removed, thereby eliminating their adverse effects on cement performance. Practice has shown that low-temperature coal gangue powder prepared by suspension calcination has higher activity compared to that prepared by vertical shaft furnace, rotary kiln, and fluidized bed processes. Therefore, suspension calcination can fully activate coal gangue powder to achieve high activity.

[0066] In steps 2-4, in the composite cement product prepared from cement clinker, calcined coal gangue raw materials, and limestone powder, to address the problem of cement strength loss caused by a high proportion of cement clinker replacement, this embodiment of the invention promotes the effective participation of active materials in hydration through a combination of reasonable ingredient proportioning and the addition of active activators, thereby enabling the composite cement product to form strength. This compensates for the strength loss reduced by the high proportion of cement clinker replacement, achieving the technical indicator of no reduction in cement performance even with a high admixture content of 35%-40% of active materials.

[0067] Furthermore, based on extensive experimental research, this invention continuously optimizes the mass ratio of each component in the composite cement product, ensuring that the added low-temperature calcined coal gangue and limestone powder, among other active materials, fully participate in hydration and develop strength, minimizing strength loss. Addressing the issue of insufficient alkalinity during hydration after a high proportion of cement clinker is replaced, which hinders the effective hydration of active materials like low-temperature calcined coal gangue and limestone powder, an activator is added to promote hydration. Through suspended calcination of limestone raw materials, the surface of the lightly calcined limestone particles in the activator is covered with a layer of CaO, forming Ca(OH)2 during hydration. This increases the alkalinity in the cement system, accelerating the hydration of active materials such as low-temperature calcined coal gangue and limestone powder. Ca(OH)2 is itself a product of cement hydration; therefore, the addition of lightly calcined limestone according to the designed mass ratio in this invention will not cause problems with cement stability. When the CaO on the surface of the lightly calcined limestone is completely consumed, the surface exhibits better adhesion to the limestone powder and the composite cement product, further contributing to increased cement strength.

[0068] In composite cement products, ultrafine fly ash has a smaller particle size than other powder particles, thus it can fill secondary pores between cement clinker, low-temperature calcined coal gangue particles, and limestone powder. The fly ash is ultrafine ground to a specific surface area greater than 500 m². 2 With a fineness of / g, ultrafine fly ash has a large specific surface area and hydrates quickly, acting as a binder between tiny powder particles. Whether filling voids or binding particles, it can improve the strength of composite cement products to a certain extent.

[0069] The method for preparing composite cement products using low-quality coal gangue provided in this invention involves heating room-temperature coal gangue powder with a particle size smaller than a first target size to obtain heated coal gangue powder at a temperature not lower than a preset temperature. This heated coal gangue powder is then subjected to suspension calcination to obtain high-temperature calcined coal gangue powder. Finally, the high-temperature calcined coal gangue powder is cooled to obtain calcined coal gangue raw material. This process effectively promotes the formation of active substances, resulting in highly active calcined coal gangue raw material. An activity activator is prepared by mixing lightly calcined limestone with a decomposition rate of 20%–40% and fly ash in a preset ratio. This activity activator promotes the hydration of the calcined coal gangue raw material, improving the hydration strength of the composite cement product. This significantly enhances the performance of the composite cement product prepared from cement clinker, calcined coal gangue raw material, and limestone powder, meeting the performance requirements for cement use. Using the method of this invention, various low-quality coal gangue with Al2O3 content of only 20% to 28% can achieve technical effects such as an active content of 35% to 45% and a 28-day compressive strength of composite cement products greater than 48 MPa.

[0070] To enable those skilled in the art to clearly understand the above-described implementation details and operations, and to highlight the significant advancements of the method for preparing composite cement products using low-quality coal gangue in the embodiments of this application, the following examples illustrate the above technical solutions.

[0071] Example 1

[0072] The chemical composition of low-quality coal gangue from a certain area is shown in Table 1.

[0073] Table 1 Chemical Analysis of a Low-Quality Coal Gangue

[0074]

[0075] The active clay mineral in this coal gangue is mainly kaolinite, and the Al2O3 content is only 21.31%, classifying it as low-quality coal gangue. Using this low-quality coal gangue as raw material, composite cement products are prepared according to the method described in this embodiment of the invention.

[0076] A method for preparing composite cement products using low-quality coal gangue specifically includes the following steps:

[0077] Low-quality coal gangue powder (smaller than 200 mesh) was prepared by two-stage suspension heating to obtain heated coal gangue powder at 565℃. This heated coal gangue powder was then subjected to suspension calcination to obtain high-temperature calcined coal gangue powder. The furnace calcination temperature during suspension calcination was 800℃–940℃, the residence time in the furnace was 5–8 seconds, and the oxygen content was 12%–14%. The high-temperature calcined coal gangue powder was then subjected to three-stage suspension cooling to obtain calcined coal gangue raw material. The decomposition rate of active clay minerals in this calcined coal gangue raw material was measured to be 99.7%, and the carbon content was 1.87%. Based on an active material content of 30%, the activity index was 91.7%.

[0078] Limestone raw material with a mesh size of less than 200 was suspended and calcined in a furnace at a temperature of 810℃ to 830℃ for 5s to 8s to obtain lightly calcined limestone with a decomposition rate of 36.7%.

[0079] Grade I fly ash was ultrafine ground to a specific surface area of ​​517 m². 2 Fineness of / g.

[0080] An active activator was prepared by mixing lightly burned limestone with a decomposition rate of 36.7% with fly ash at a ratio of 1:3.

[0081] The mixture is prepared by mixing cement clinker, desulfurized gypsum, calcined coal gangue raw material, limestone powder, and an active activator. The specific batching scheme is shown in Table 2, where the mass percentage of the active material is the sum of the mass percentages of the calcined coal gangue raw material, limestone powder, and active activator.

[0082] Table 2 Ingredient Recipe (by weight, %)

[0083]

[0084] The mixture was ground in a ball mill until the specific surface area reached 378.6 m². 2 A fineness of / g is used to obtain composite cement products.

[0085] The composite cement product was tested for performance according to GB175-2023, and the 28-day flexural strength and compressive strength are shown in Table 3.

[0086] Table 3. 28-day flexural strength and compressive strength of composite cement products (%)

[0087]

[0088] The trend graphs of flexural strength and compressive strength with curing age, as shown in Table 3, are as follows: Figure 2 and Figure 3 As stated above.

[0089] As shown in Table 3, Figure 2 and Figure 3As shown, Formula A0, containing only pure cement clinker and desulfurized gypsum (as a control example), yields cement with 28-day flexural and compressive strengths of 12.4 MPa and 48.9 MPa, respectively. Formula A1 consists of cement clinker, desulfurized gypsum, and calcined coal gangue. Adding 30% calcined coal gangue to the cement clinker reduces the 28-day flexural and compressive strengths of the composite cement product to 10.7 MPa and 44.6 MPa, respectively. Formula A2 consists of cement clinker, desulfurized gypsum, calcined coal gangue, and limestone powder. Increasing the mass percentage of active materials (calcined coal gangue and limestone powder) to 36% results in 28-day flexural and compressive strengths of the composite cement product of 9.9 MPa and 43.8 MPa, respectively. Compared to A1, with a 6% increase in the proportion of active materials, the 28-day flexural strength and compressive strength of the composite cement product only slightly decreased, both by 0.8 MPa. A3 is a formulation based on A2 with the addition of only ultrafine fly ash. Results show that with the addition of 3% ultrafine fly ash, the 28-day flexural strength of the A3 composite cement product is similar to that of A2, but the 28-day compressive strength is significantly improved, increasing by 4.4 MPa. The A4 formulation, based on A3, further adds 1% lightly calcined limestone, meaning the active activator is a 1:3 ratio of lightly calcined limestone to fly ash. Compared to A3, the 28-day flexural strength and compressive strength of the A4 composite cement product are significantly improved, with increases of 1.5 MPa and 1.9 MPa respectively, meeting the requirements for 42.5 grade cement. These experiments confirm that the addition of lightly calcined limestone and ultrafine fly ash is effective in improving the performance of composite cement products.

[0090] The method for preparing composite cement products using low-quality coal gangue according to embodiments of the present invention involves preparing room-temperature coal gangue powder from low-quality coal gangue with an Al2O3 content of only 21.31%. After suspension calcination, the active clay mineral decomposition rate of the calcined coal gangue raw material is 99.7%, the carbon content is 1.87%, and the activity index is 91.7%. The decomposition rate of the prepared lightly calcined limestone is 36.7%, and the primary fly ash is ultrafine ground to a specific surface area of ​​517 m². 2The fineness of the limestone was determined by mixing lightly calcined limestone with fly ash in a 1:3 ratio to obtain an active activator. Cement clinker, desulfurized gypsum, calcined coal gangue raw materials, limestone powder, and the active activator were thoroughly mixed to obtain a mixture. The composite cement product was prepared according to the batching scheme in Table 2. With the active materials (calcined coal gangue raw materials, limestone powder, and active activator) accounting for as much as 39-40% of the total mass, the 28-day compressive strength of the composite cement product was 48.2 MPa and 50.1 MPa, respectively, meeting the 42.5 composite cement product standard. The method of this invention can effectively improve the activity of calcined coal gangue raw materials, providing technical support for the preparation of composite cement products from coal gangue (especially low-quality coal gangue).

[0091] Example 2

[0092] The chemical composition of low-quality coal gangue from a certain area is shown in Table 4.

[0093] Table 4 Chemical Analysis of a Low-Quality Coal Gangue

[0094]

[0095] The active clay mineral in this coal gangue is mainly kaolinite, with an Al2O3 content of 26.80%, classifying it as low-quality coal gangue. Composite cement products are prepared using this low-quality coal gangue as raw material through the method described in this embodiment of the invention.

[0096] A method for preparing composite cement products using low-quality coal gangue specifically includes the following steps:

[0097] Low-quality coal gangue powder (smaller than 200 mesh) was prepared by two-stage suspension heating to obtain heated coal gangue powder at 565℃. This heated coal gangue powder was then subjected to suspension calcination to obtain high-temperature calcined coal gangue powder. The furnace calcination temperature during suspension calcination was 860℃–950℃, the residence time in the furnace was 6–9 seconds, and the oxygen content was 13%–15%. The high-temperature calcined coal gangue powder was then subjected to three-stage suspension cooling to obtain calcined coal gangue raw material. The decomposition rate of active clay minerals in this calcined coal gangue raw material was measured to be 99.37%, and the carbon content was 1.93%. Based on an active material content of 30%, the activity index was 103.8%.

[0098] Limestone raw material with a mesh size of less than 200 was calcined in suspension at a furnace temperature of 810℃~820℃ for 5s~6s to obtain lightly calcined limestone with a decomposition rate of 32.6%.

[0099] Grade I fly ash was ultrafine ground to a specific surface area of ​​543 m². 2 Fineness of / g.

[0100] An active activator was prepared by mixing lightly burned limestone with a decomposition rate of 32.6% with fly ash at a ratio of 1:3.

[0101] The cement clinker, desulfurized gypsum, calcined coal gangue raw material, limestone powder, and active activator are mixed to obtain the mixture. The specific batching scheme is shown in Table 5, where the mass ratio of the active material is the sum of the mass ratios of the calcined coal gangue raw material, limestone powder, and active activator.

[0102] Table 5 Ingredient Recipe (by weight, %)

[0103]

[0104] The mixture was ground in a ball mill until the specific surface area reached 383.1 m². 2 A fineness of / g is used to obtain composite cement products.

[0105] The composite cement product was tested for performance according to GB175-2023, and the 28-day flexural strength and compressive strength are shown in Table 6.

[0106] Table 6. 28-day flexural strength and compressive strength of composite cement products (%)

[0107]

[0108]

[0109] The method for preparing composite cement products using low-quality coal gangue according to embodiments of the present invention involves preparing room-temperature coal gangue powder from low-quality coal gangue with an Al2O3 content of 26.80%. After suspension calcination, the decomposition rate of active clay minerals in the calcined coal gangue raw material is 99.37%, the carbon content is 1.93%, and the activity index is 103.8%. The decomposition rate of lightly calcined limestone is 32.6%, and primary fly ash is ultrafine ground to a specific surface area of ​​543 m². 2 The fineness of the limestone was determined by mixing lightly calcined limestone and fly ash in a 1:3 ratio to obtain an active activator. Cement clinker, desulfurized gypsum, calcined coal gangue raw materials, limestone powder, and the active activator were thoroughly mixed to obtain a mixture. The composite cement product was prepared according to the batching scheme in Table 5. With the active materials (calcined coal gangue, limestone, and active activator) accounting for as much as 43-44% of the mass, the 28-day compressive strength of the composite cement product was 51.6 MPa and 53.4 MPa, respectively, meeting the 42.5 composite cement product standard. The method of this invention can effectively improve the activity of calcined coal gangue, providing technical support for the preparation of composite cement products from coal gangue (especially low-quality coal gangue).

[0110] The various embodiments in this specification are described in a progressive manner. For the same or similar parts between the various embodiments, please refer to each other. Each embodiment focuses on describing the differences from other embodiments.

[0111] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of this application.

Claims

1. A method for preparing composite cement products using low-quality coal gangue, characterized in that, include: Room temperature coal gangue powder smaller than the first target particle size is heated to obtain heated coal gangue powder at a temperature not lower than the preset temperature. The heated coal gangue powder is then calcined in a suspension state to obtain high temperature calcined coal gangue powder. The high temperature calcined coal gangue powder is then cooled to obtain calcined coal gangue raw material. An active activator is prepared by mixing lightly burned limestone with a decomposition rate of 20% to 40% with fly ash in a predetermined ratio. The cement clinker, desulfurized gypsum, the calcined coal gangue raw material, limestone powder and active activator are thoroughly mixed to obtain a mixture; The mixture is ground to obtain a composite cement product.

2. The method for preparing composite cement products using low-quality coal gangue according to claim 1, characterized in that, The first target particle size is 200 mesh; The preset temperature is 550℃; The furnace calcination temperature during suspension calcination is 800℃~950℃, the residence time in the furnace is 5s~15s, and the oxygen content is not less than 9%.

3. The method for preparing composite cement products using low-quality coal gangue according to claim 1, characterized in that, The preset ratio is 1:2 to 3.

4. The method for preparing composite cement products using low-quality coal gangue according to claim 1 or 3, characterized in that, Before using the fly ash to prepare the activation activator, the method further includes: The fly ash is ultrafine ground to a specific surface area greater than 500 m². 2 Fineness of / g.

5. The method for preparing composite cement products using low-quality coal gangue according to claim 1, characterized in that, The method for preparing the lightly calcined limestone with a decomposition rate of 20% to 40% includes: Limestone raw materials smaller than the second target particle size are suspended and calcined in a furnace at a temperature of 810℃ to 830℃ for 5s to 8s to obtain lightly calcined limestone with a decomposition rate of 20% to 40%.

6. The method for preparing composite cement products using low-quality coal gangue according to claim 1, characterized in that, The mass percentages of cement clinker, desulfurized gypsum, calcined coal gangue raw material, limestone powder, and active activator are 55%–60%, 4%–6%, 20%–26%, 10%–13%, and 3%–4%, respectively.

7. The method for preparing composite cement products using low-quality coal gangue according to claim 1 or 6, characterized in that, The 28-day compressive strength of the cement clinker shall not be less than 46 MPa.

8. The method for preparing composite cement products using low-quality coal gangue according to claim 1 or 6, characterized in that, The percentage of CaO in the limestone powder is not less than 44%.

9. The method for preparing composite cement products using low-quality coal gangue according to claim 1, characterized in that, The step of heating room-temperature coal gangue powder smaller than the first target particle size to obtain heated coal gangue powder at a temperature not lower than a preset temperature includes: Room temperature coal gangue powder with a particle size smaller than the first target size is subjected to multi-stage suspension heating to obtain heated coal gangue powder with a temperature not lower than the preset temperature.

10. The method for preparing composite cement products using low-quality coal gangue according to claim 1, characterized in that, The process of cooling the high-temperature calcined coal gangue powder to obtain calcined coal gangue raw material includes: The high-temperature calcined coal gangue powder is subjected to multi-stage suspension cooling to obtain calcined coal gangue raw material.

Images