Potassium-containing coal gangue-based cementitious material and preparation method thereof

Abstract

The application discloses a kind of potassium-containing coal gangue-based cementitious materials and preparation method thereof, belong to building material technical field;Method includes: selecting potassium-containing coal gangue with potassium content ≥4%, crushing, grinding to 80 μm residue <10%;Potassium-containing coal gangue powder is preheated after 600 DEG C, and is suspended state calcination at 800 DEG C~950 DEG C 5s~15s, oxygen content ≥9%, multistage suspension cooling, obtain activated potassium-containing coal gangue;The activated potassium-containing coal gangue is mixed with cement clinker, desulfurization gypsum, limestone powder according to proportion, and grinding, to obtain potassium-containing coal gangue-based cementitious material;The application makes potassium-containing coal gangue in suspended state calcination white mica in it decompose and release active K + , and reacts with gypsum to form potassium gypsum (K2Ca(SO4)2·2H2O) during hydration, improving the micro-pore structure of the cementitious material. When the total amount of activated potassium-containing coal gangue and limestone is 25%, the 28d compressive strength of the cementitious material reaches 51.6MPa, which is comparable to the strength of pure cement. Each ton of cementitious material can consume 130kg-270kg of potassium-containing coal gangue raw material, and has both mechanical properties and resource and environmental benefits.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a potassium-containing coal gangue-based cementitious material and its preparation method. Background Technology

[0002] my country is rich in coal gangue resources, of which potassium-containing coal gangue accounts for a certain proportion. The mineral composition of this type of coal gangue is mainly composed of clay minerals such as kaolinite and illite, and muscovite (containing potassium aluminum silicate). Potassium is mainly contained in the crystal structure of muscovite. Through high-temperature calcination, the water of crystallization in the coal gangue is removed, the original clay mineral structure is destroyed, and it is transformed into amorphous silica-alumina active components. At the same time, the crystal structure of muscovite decomposes under heat, and the potassium element that was originally bound by the crystal lattice is released, providing the preconditions for its participation in subsequent hydration reactions. Therefore, using muscovite-type potassium-containing coal gangue to prepare cementitious materials is a research direction with dual value of resource utilization and performance regulation.

[0003] Currently, there are two main ways to use calcined coal gangue in cementitious materials: one is to directly add calcined coal gangue as a common active admixture to cement clinker for co-grinding to prepare ordinary silicate cement. This method does not target the characteristics of muscovite-type coal gangue for activation and component optimization, making it difficult to fully stimulate the cementitious activity of silica-alumina components and also failing to achieve effective release and utilization of potassium in muscovite, resulting in low resource utilization. The other method is to mix calcined coal gangue, limestone, and cement clinker in a certain proportion to prepare composite silicate cement products, thereby increasing the coal gangue content through mineral synergy. In addition, existing research mainly focuses on conventional phases such as hydrated calcium silicate gel (CSH), ettringite (AFt), and calcium hydroxide (CH), and has not yet paid in-depth attention to the behavior and fate of potassium in potassium-containing coal gangue during the hydration process.

[0004] However, muscovite has an extremely stable crystal structure, and existing conventional calcination equipment (such as vertical shaft furnaces and rotary kilns) generally suffers from uneven temperature distribution and low temperature control precision in actual production. Under conventional calcination conditions, muscovite is difficult to completely decompose, resulting in a low potassium release rate. Simultaneously, some low-quality muscovite-type coal gangue has a low content of active clay minerals, leading to insufficient silicon-aluminum activity after calcination. Existing processes struggle to achieve synergistic optimization of silicon-aluminum activation and potassium release. Furthermore, when the calcination temperature is too high or the holding time is too long, amorphous silicon-aluminum active components are prone to crystallization and deactivation, and the released potassium ions may precipitate as inert salts, thus reducing their usability. In cementitious materials, the potassium released from potassium-containing minerals... +Often considered as inert components that are not utilized, secondary hydration of silicon and aluminum components alone is insufficient to compensate for the strength loss caused by the reduction of clinker, especially resulting in a significant decrease in early strength. Furthermore, it fails to guide the directional reaction of potassium ions with calcium and sulfur components in the system to generate functional hydration products, thus missing a key approach to improve the performance of cementitious materials through product regulation. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a potassium-containing coal gangue-based cementitious material and its preparation method.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This application provides a method for preparing a potassium-containing coal gangue-based cementitious material, comprising: Coal gangue pretreatment steps: crush and grind potassium-containing coal gangue raw materials with a potassium content of not less than 4% to a preset fineness to obtain coal gangue powder; Calcination and activation step: The coal gangue powder is calcined in a suspension calcination device under an oxygen-containing atmosphere at a temperature of 800℃~950℃ for 5s~15s, and then cooled to obtain activated coal gangue. Mixing and grinding step: The activated coal gangue is mixed with silicate cement clinker, gypsum component and calcium carbonate component and then ground to the target specific surface area to obtain the potassium-containing coal gangue-based cementitious material.

[0007] Furthermore, in the calcination activation step, the calcination temperature is 900℃~950℃, and the calcination time is 8s~12s.

[0008] Furthermore, in the mixing and grinding step, the mass percentage of each raw material is as follows: silicate cement clinker 55%~75%, activated coal gangue 13.3%~26.7%, calcium carbonate component 6.7%~13.3%, and gypsum component 4%~5%.

[0009] Furthermore, in the mixing and grinding step, the target specific surface area is 300m² / kg to 380m² / kg.

[0010] Furthermore, in the calcination activation step, the oxygen volume content in the oxygen-containing atmosphere is not less than 9%.

[0011] Furthermore, in the calcination activation step, a multi-stage suspension cooling system is used to cool the calcined material to below 100°C to inhibit the recrystallization of amorphous silicon-aluminum components and the conversion of potassium ions into inert salts.

[0012] Furthermore, in the coal gangue pretreatment step, the preset fineness is that the residue on an 80μm square-hole sieve is less than 10%.

[0013] Furthermore, in the calcination activation step, before the coal gangue powder is fed into the suspension calcination device, the coal gangue powder is preheated to 600℃±20℃ in a multi-stage suspension preheating system.

[0014] Furthermore, the activated coal gangue has a strength activity index greater than 90% when tested according to GB / T2847-2022 standard.

[0015] A potassium-containing coal gangue-based cementitious material is prepared by the above method; the 28-day compressive strength of the cementitious material is not less than 42.5 MPa, and its hydration products include potassium gypsum, the chemical formula of which is K2Ca(SO4)2·2H2O.

[0016] Compared with the prior art, this application has the following beneficial effects: This invention proposes a potassium-containing coal gangue-based cementitious material and its preparation method. Through suspension-state high-temperature short-time calcination, the decomposition efficiency of muscovite and the release rate of potassium are significantly improved. Furthermore, multi-stage suspension cooling effectively inhibits the recrystallization of amorphous silica-alumina components and the conversion of released potassium ions into inert potassium silicate or potassium aluminate. For the first time, a directional potassium ion conversion pathway is constructed in a coal gangue-based cementitious material system, enabling the release of active potassium ions during hydration. + The product reacts with gypsum and calcium components in the system to generate potassium gypsum (K2Ca(SO4)2·2H2O). This product can effectively fill the pores inside the slurry and optimize the microstructure. As a result, when the total content of activated coal gangue and limestone reaches 25%, its 28-day compressive strength can reach 51.6 MPa, which is comparable to the strength of pure cement. This effectively makes up for the strength loss caused by the reduction of cement clinker. Moreover, each ton of cementitious material can consume 130~270 kg of potassium-containing coal gangue raw materials. It has both excellent mechanical properties and significant environmental benefits, providing a new technical path for the large-scale and high-value utilization of muscovite-type potassium-containing coal gangue. Attached Figure Description

[0017] Figure 1 This is a process flow diagram of the method for preparing potassium-containing coal gangue-based cementitious materials according to the present invention.

[0018] Figure 2 This is a graph showing the variation of flexural strength of cementitious materials at different ages under different mix proportions.

[0019] Figure 3 This is a graph showing the variation of compressive strength of cementitious materials at different ages under different mix proportions.

[0020] Figure 4 X-ray diffraction pattern of the hydration products of cementitious materials after 28 days. Detailed Implementation

[0021] 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.

[0022] Furthermore, in this invention, an element referred to as fixed to or disposed on another element may be directly disposed on the other element, or there may be an intermediate element. When an element is considered to be connected to another element, it may be directly connected to the other element, or there may be an intermediate element present simultaneously. The terms vertical, horizontal, left, right, and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0023] The following is in conjunction with the appendix Figures 1 to 4 The present invention will be further described with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0024] Step 1: Pretreatment of potassium-containing coal gangue Potassium-containing coal gangue (uncalcined raw material) with a potassium (K) content ≥4% by mass was selected as raw material. To ensure the accuracy of the batching, the potassium content was determined quantitatively by X-ray fluorescence spectrometry (XRF). The potassium-containing coal gangue raw material was subjected to coarse crushing and grinding in sequence: first, it was crushed to a particle size ≤5mm using a jaw crusher or hammer crusher; then, the coarsely crushed material was fed into a ball mill and ground for 30min~45min to make the fineness of the powder reach <10% residue on an 80μm square hole sieve; then, it was sieved using an 80μm square hole sieve, and the material under the sieve was taken as potassium-containing coal gangue raw material powder, while the material over the sieve was returned to the grinding process.

[0025] Step 2: Activation of potassium-containing coal gangue by suspension calcination The potassium-containing coal gangue raw material powder obtained in step 1 (at room temperature) is subjected to gas-solid heat exchange through a multi-stage suspension preheating system (3-5 stage cyclone preheaters), and the temperature is gradually increased to 600℃±20℃. The material is in a suspended state, and the preheating residence time is 1s~3s.

[0026] The preheated material is fed into a suspension calcination furnace (such as a flash calcination furnace or a suspension calcination system with a decomposition furnace); the core parameters of the calcination process are controlled as follows: the furnace temperature is 800℃~950℃, preferably 900℃~950℃; the calcination time of the material in the furnace is 5s~15s, preferably 8s~12s; the oxygen volume content in the furnace is ≥9% by controlling the amount of combustion air or oxygen-enriched combustion; the system pressure is a slight negative pressure of -100Pa~-300Pa.

[0027] The key technology in this step is the synergistic effect of suspended high-temperature short-time calcination and multi-stage suspension rapid cooling. First, the suspended reaction allows the coal gangue powder to fully contact the high-temperature airflow within the furnace, resulting in an exponential increase in heat and mass transfer rates. This enables deep dissociation of the muscovite crystal structure within a very short time (8-12 seconds), avoiding the crystallization and deactivation of amorphous silicon-aluminum components caused by prolonged calcination in traditional rotary kilns. Second, the calcined material (800℃-950℃) immediately enters a multi-stage suspension cooling system (3-4 stages of cyclone coolers) for rapid cooling using cold air as the medium, causing the material temperature to plummet to below 100℃. This rapid cooling step effectively inhibits the recrystallization of amorphous silicon-aluminum components and successfully prevents the release of active K+ at high temperatures. + During the cooling process, it recombines with other components to form inert, insoluble potassium silicate or potassium aluminate, thus ensuring that the potassium element in the activation product exists as highly active, soluble K. + It exists in its original form; according to GB / T 2847-2022, the strength activity index of the activated potassium-containing coal gangue prepared in this step is >90%.

[0028] Step 3: Batching and grinding of cementitious materials Prepare auxiliary raw materials: Cement clinker is ordinary Portland cement clinker with a 28-day compressive strength of not less than 42.5 MPa; Desulfurization gypsum is a by-product of wet desulfurization in power plants, which is dihydrate gypsum (CaSO4·2H2O) with an SO3 mass fraction ≥45% and an attached water content ≤10%; Limestone powder is obtained by crushing and grinding natural limestone, with a CaO mass fraction ≥44% and an 80μm sieve residue <15%.

[0029] The following ingredients are proportioned by weight (total of all components is 100%): cement clinker 55%~75%, activated potassium-containing coal gangue 13.3%~26.7%, limestone powder 6.7%~13.3%, and desulfurized gypsum 4%~5%. The four materials, weighed according to the proportions, are premixed in a high-efficiency mixer for 5~10 minutes. The mixture is then fed into a ball mill or a combined roller press and ball mill grinding system for grinding. The specific surface area of ​​the finished product is controlled to be 300m² / kg~380m² / kg, thus obtaining the potassium-containing coal gangue-based cementitious material.

[0030] Step 4: Product performance verification and mechanism analysis The potassium-containing coal gangue-based cementitious material prepared by the above method has a 28-day compressive strength of not less than 42.5 MPa, and the characteristic peak of potassium gypsum (K2Ca(SO4)2·2H2O) can be detected in the hydration products by X-ray diffraction analysis.

[0031] Example 1 Potassium-containing coal gangue (uncalcined raw material) from the Panzhihua area was used, and its chemical composition is shown in Table 1.

[0032] Table 1. Chemical analysis (mass fraction) of a certain low-quality coal gangue. Potassium-containing coal gangue-based cementitious materials are prepared according to the following steps: Potassium-containing coal gangue was crushed to less than 5 mm, ball-milled for 30 min, and passed through an 80 μm sieve. The residue on the sieve was <10%, thus obtaining potassium-containing coal gangue raw material powder.

[0033] Potassium-containing coal gangue raw material powder was preheated to 600℃ through multi-stage suspension, and then calcined at 950℃ for 10s in a suspension calcination furnace with an oxygen volume content of 10%. After multi-stage suspension cooling to below 100℃, activated potassium-containing coal gangue was obtained. According to GB / T2847-2022, its strength activity index was 92%.

[0034] According to the precise proportions shown in Table 2, the activated potassium-containing coal gangue obtained in step 2 was mixed with cement clinker (P·I 42.5 grade), desulfurized gypsum (SO3 content 46%), and limestone powder (CaO content 48%), and ground to a specific surface area of ​​350 m² / kg to obtain each group of potassium-containing coal gangue-based cementitious materials.

[0035] Table 2. Batching scheme for activated potassium-containing coal gangue-based composite materials (mass fraction %) Each group of cementitious materials was used to prepare mortar specimens according to GB / T 17671-2021. The ratio of cementitious material: standard sand: water was 1:3:0.5. The curing temperature was 20℃±1℃ and the relative humidity was ≥90%. After demolding for 24 hours, the specimens were cured in water to the specified age and then tested for flexural and compressive strength.

[0036] The effects of Example 1 will be analyzed and explained in conjunction with the accompanying drawings: Flexural strength ( Figure 2 ) and compressive strength ( Figure 3 Effect analysis: by Figure 2 and Figure 3It can be seen that with the increase of activated potassium-containing coal gangue content, the strength of the cementitious material generally shows a trend of first increasing and then decreasing. Particularly noteworthy is the M2 group (25% total content of activated potassium-containing coal gangue and limestone), which exhibits peak mechanical properties at all ages. The 28-day flexural strength of the M2 group reaches 13.1 MPa, and the 28-day compressive strength is as high as 51.6 MPa; while the 28-day compressive strength of the baseline group M0 (pure cement, 100% clinker) is only 50.4 MPa. This indicates that the 28-day compressive strength of the M2 group is 2.38% higher than that of the baseline group M0. This result fully demonstrates the unexpected technical effect of this invention: when cement clinker is largely replaced (total replacement reaches 25%), the release of potassium ions through a specific activation process to generate potassium gypsum not only compensates for the strength loss but also achieves a strength reversal, which is completely unattainable by existing technologies.

[0037] XRD analysis of hydration products ( Figure 4 ): Figure 4 The X-ray diffraction patterns of the cementitious material's 28-day hydration products are shown. It is clearly observed that characteristic diffraction peaks of potassium gypsum (K₂Ca(SO₄)₂·2H₂O) were detected in groups M1 to M5 (corresponding to diffraction peaks at approximately 2θ=9° and 31° in the patterns), while these characteristic peaks were not present in the pattern of the baseline group M0. This result directly proves that only when the suspended short-time high-temperature calcination + rapid cooling process of this invention is used can the potassium gypsum in coal gangue be reduced. + Only after being successfully activated and released can potassium react with gypsum in the cement hydration environment; if it is not activated by calcination according to the present invention, potassium will always be trapped in the muscovite lattice and cannot form potassium gypsum.

[0038] The formation of potassium gypsum is attributed to the release of potassium from activated potassium-containing coal gangue. + With SO4² in the system - and Ca² + The reaction, the reaction formula is as follows: K + +SO4² - +Ca² + +H₂O→K₂Ca(SO₄)₂·2H₂O This product can effectively fill the interconnected pores inside the slurry, optimize the microporous structure of the cementitious material, and improve the density and mechanical properties of the system. Therefore, group M2 is the optimal formulation of this invention; taking group M2 as an example, each ton of potassium-containing coal gangue-based cementitious material contains 166.7 kg of activated potassium-containing coal gangue. Considering the mass loss during the calcination process (approximately 15%), the corresponding potassium-containing coal gangue raw material consumed is approximately 196 kg; considering the overall range of this embodiment, each ton of cementitious material consumes 130 kg to 270 kg of potassium-containing coal gangue raw material.

[0039] Example 2 The steps are the same as in Example 1, except that in step 2, the calcination temperature is 850℃, the calcination time is 12s, and the oxygen content is 12%; in step 3, the proportions are: 60% cement clinker, 5% desulfurized gypsum, 23.33% activated potassium-containing coal gangue, and 11.67% limestone. The obtained potassium-containing coal gangue-based cementitious material has a 28-day compressive strength of 46.8MPa, and potassium gypsum can still be detected in the hydration products; this indicates that even when the temperature and time parameters fluctuate to a certain extent, the core technical route of this invention can still achieve the generation of potassium gypsum and the effective increase in strength.

[0040] Comparative Example In the comparative example, the suspension calcination in step 2 was omitted. The potassium-containing coal gangue raw material (same as in Example 1, K2O content 5.38%) that had not been calcined was directly mixed and ground with cement clinker, desulfurized gypsum and limestone according to the M2 group ratio. The resulting potassium-containing coal gangue-based cementitious material had a 28-day compressive strength of only 32.1 MPa, and no potassium gypsum was detected in its hydration products.

[0041] This comparative example fully demonstrates the necessity of the core innovation of this invention: without suspension calcination and activation, the muscovite lattice cannot be dissociated, and the potassium-containing coal gangue cannot exert the activity of volcanic ash, nor can the potassium element in it participate in the hydration reaction to generate potassium gypsum, resulting in a 28-day compressive strength that is far lower than the 51.6 MPa of this invention, with extremely serious losses.

[0042] Therefore, the specific suspension-state calcination activation process of the present invention is an absolutely necessary condition for realizing potassium release, generating potassium gypsum and improving strength.

[0043] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0044] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing a potassium-containing coal gangue-based cementitious material, characterized in that, include: Coal gangue pretreatment steps: crush and grind potassium-containing coal gangue raw materials with a potassium content of not less than 4% to a preset fineness to obtain coal gangue powder; Calcination and activation step: The coal gangue powder is calcined in a suspension calcination device under an oxygen-containing atmosphere at a temperature of 800℃~950℃ for 5s~15s, and then cooled to obtain activated coal gangue. Mixing and grinding step: The activated coal gangue is mixed with silicate cement clinker, gypsum component and calcium carbonate component and then ground to the target specific surface area to obtain the potassium-containing coal gangue-based cementitious material.

2. The method according to claim 1, characterized in that, In the calcination activation step, the calcination temperature is 900℃~950℃ and the calcination time is 8s~12s.

3. The method according to claim 1, characterized in that, In the mixing and grinding step, the mass percentage of each raw material is as follows: silicate cement clinker 55%~75%, activated coal gangue 13.3%~26.7%, calcium carbonate component 6.7%~13.3%, and gypsum component 4%~5%.

4. The method according to claim 1, characterized in that, In the mixing and grinding step, the target specific surface area is 300m² / kg to 380m² / kg.

5. The method according to claim 1, characterized in that, In the calcination and activation step, the oxygen volume content in the oxygen-containing atmosphere is not less than 9%.

6. The method according to claim 1, characterized in that, In the calcination activation step, a multi-stage suspension cooling system is used to cool the calcined material to below 100°C to inhibit the recrystallization of amorphous silicon-aluminum components and the conversion of potassium ions into inert salts.

7. The method according to claim 1, characterized in that, In the coal gangue pretreatment step, the preset fineness is that the residue on an 80μm square hole sieve is less than 10%.

8. The method according to claim 1, characterized in that, In the calcination and activation step, before the coal gangue powder is fed into the suspension calcination device, the coal gangue powder is preheated to 600℃±20℃ in a multi-stage suspension preheating system.

9. The method according to claim 1, characterized in that, The activated coal gangue, tested according to GB / T2847-2022 standard, has a strength activity index greater than 90%.

10. A potassium-containing coal gangue-based cementitious material, characterized in that, The cementitious material is prepared by any one of claims 1 to 9; the 28-day compressive strength of the cementitious material is not less than 42.5 MPa, and its hydration products contain potassium gypsum, wherein the chemical formula of the potassium gypsum is K2Ca(SO4)2·2H2O.

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