A mudstone-based portland cement clinker and a method for producing the same

Abstract

This invention discloses a silicate cement clinker based on marl and its preparation method, relating to the field of cement technology. The method includes first crushing, grinding, and drying natural marl, then activating it by spraying with a mixed impregnation solution containing sodium hydroxide, lanthanum nitrate, and cerium nitrate, followed by drying and low-temperature calcination to obtain modified marl powder; mixing this powder with calcium carbonate, quartz powder, iron oxide, gypsum dihydrate, calcium fluoride, and barium carbonate, and pressing it into a green body; finally, subjecting the green body to a two-stage mineralization calcination process, with oxygen-enriched air introduced during the heat preservation stage for continued calcination, and obtaining cement clinker after cooling. This invention utilizes marl as the main raw material, and through impregnation activation and multi-stage calcination processes, the resulting cement clinker exhibits excellent resistance to sulfate attack.

Description

Technical Field

[0001] This invention relates to the field of cement technology, specifically to a silicate cement clinker based on marl and its preparation method. Background Technology

[0002] Silicate cement, as the most widely used cementitious material in the construction engineering field, plays a core role in various projects such as housing construction, bridges and roads, marine engineering, and underground tunnels due to its advantages of high strength, rapid setting and hardening, and strong adaptability. However, in sulfate-eroded environments such as marine environments, salt lake areas, underground sulfur-bearing strata, and sewage treatment facilities, cement hydration products (such as calcium hydroxide and calcium aluminate hydrate) easily react with sulfates in the environment to generate ettringite, gypsum, and other volume-expanding products. This leads to internal stress, structural cracking, and reduced strength within the cement stone, and in severe cases, even structural failure, greatly shortening the service life of the project. This problem has become a key bottleneck restricting the application of silicate cement in corrosive environments. To solve the above problems, various solutions to improve the sulfate resistance of cement have been proposed in existing technologies. For example, by optimizing the mineral composition of clinker, the content of tricalcium aluminate, which readily reacts with sulfates, can be reduced, while the proportion of tetracalcium aluminoferrite can be increased. The anti-corrosion properties of tetracalcium aluminate hydration products can then be utilized to improve overall performance. Alternatively, mineral admixtures such as slag, fly ash, and silica fume can be added to cement to refine the pore structure of the cement stone through secondary hydration reactions, thereby reducing the penetration rate of corrosive media. Other technologies employ chemical admixtures such as nanogels and organic rust inhibitors to block the reaction pathway between sulfates and hydration products. Furthermore, some solutions attempt to replace some clinker raw materials with industrial waste (such as steel slag and blast furnace slag), reducing costs while utilizing the active components in the waste to optimize anti-corrosion performance. However, existing technologies still have many shortcomings that need to be addressed: Firstly, the preparation of high-sulfur-resistant cement clinker largely relies on high-purity chemical raw materials such as calcium oxide and silicon dioxide or specific industrial waste residues, which are costly and geographically limited. Marl, as a natural mineral raw material with abundant reserves and wide distribution, is mainly composed of calcium carbonate and clay minerals, containing core elements such as silicon, aluminum, and calcium required for cement clinker. However, due to its dense natural mineral structure, low reactivity, and uneven component distribution, when directly used in cement production, the clinker mineral phases are not fully formed and the stability is poor, making it difficult to meet the requirements for resistance to sulfate attack. As a result, this inexpensive natural resource has not been effectively developed and utilized. Summary of the Invention

[0003] The purpose of this invention is to provide a silicate cement clinker based on marl and its preparation method, thereby solving the technical problems mentioned in the background section. The silicate cement clinker based on marl prepared by this invention exhibits excellent resistance to sulfate attack.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] A method for preparing silicate cement clinker based on marl includes the following steps:

[0006] (1) Natural marl is crushed, ground and dried to obtain marl powder;

[0007] (2) Prepare a mixed impregnation solution by mixing sodium hydroxide solution, lanthanum nitrate, cerium nitrate and water;

[0008] (3) Spray the mixed impregnation solution evenly onto the marl powder, let it stand to activate, and obtain activated powder;

[0009] (4) The activated powder is dried and calcined at low temperature, and then the calcined product is ground to obtain modified marl powder;

[0010] (5) The modified marl powder is mixed with calcium carbonate, quartz powder, iron oxide, gypsum dihydrate, calcium fluoride and barium carbonate, and pressed into shape to obtain a green body;

[0011] (6) The billet is subjected to two-stage mineralization calcination;

[0012] (7) Keep warm and introduce oxygen-rich air, continue calcining, and cool after calcination to obtain the product.

[0013] In the technical solution of this invention, the sulfate resistance of marl silicate cement clinker is improved synergistically from the following two aspects: Firstly, ball milling increases the specific surface area of ​​marl and disrupts the long-range ordered structure of minerals, increasing surface active sites. Combined with the micro-etching effect of equal-volume alkali impregnation, chemical activation of particle surface is achieved without loss of active silicon and aluminum components, improving the uniformity of mineral phase formation during subsequent calcination. Trace rare earth elements are precisely anchored at the active sites of raw materials through ion exchange or chemical adsorption. Their polarization effect can stabilize the subsequently generated C3S crystal form and refine the grains, reducing internal defects in minerals. Low-temperature static dehydration not only transforms clay minerals into amorphous active substances but also avoids premature decomposition of CaCO3 leading to cracking of the green body, ensuring the initial combination of rare earth elements with the silicon and aluminum matrix, further optimizing the uniformity of raw material composition. The entire process improves the physical activity, chemical homogeneity, and compositional stability of raw materials, thereby reducing unstable mineral phases and structural defects in clinker that are prone to reacting with sulfates from the source, enhancing the intrinsic erosion resistance of mineral phases, and providing a high-quality raw material foundation for subsequent enhancement of sulfate resistance.

[0014] On the other hand, CaCO3 serves as the core calcium supply substance, providing sufficient material support for the formation of high-content C3S (alite) in clinker. C3S is not only a core contributor to clinker strength, but it also possesses excellent intrinsic properties against sulfate attack. Its high proportion directly enhances the basic ability of clinker to resist attack. The introduction of iron oxide can optimize the ratio of aluminum and iron elements in clinker, inhibit the formation of the attack-sensitive phase C3A, which readily reacts with sulfate to form expansive ettringite, and promote the formation of iron phase minerals (such as C4AF) with better sulfate attack resistance, thereby reducing the reaction targets of sulfate attack from the source of mineral composition. By introducing gypsum dihydrate as a safe sulfur source and combining it with a two-stage heating and calcination process, the maximum calcination temperature is controlled at 1380℃. This avoids excessive volatilization of sulfur due to high temperatures and utilizes the mineralization effect of sulfur to reduce the viscosity of the liquid phase during calcination, promoting the full development and uniform distribution of beneficial mineral phases such as C3S. At the same time, it allows the rare earth ions introduced in the first aspect to be smoothly embedded into the C3S lattice, further enhancing the stability of the mineral crystal form. The oxygen-rich micro-positive pressure atmosphere effectively inhibits the high-temperature decomposition and volatilization of CaSO4 by strengthening the oxidation environment, causing sulfur to be fixed in situ in the clinker in the form of solid solution or trace amounts of calcium sulfoaluminate, forming a chemical barrier at the mineral micropores and interfaces, hindering the penetration and diffusion of sulfate erosion media. Finally, through rapid forced cooling, not only is the reverse reaction decomposition of C3S avoided during slow cooling, ensuring the stability of high-content C3S, but the remaining small amount of unstable components such as C3S are also frozen in the glassy state, reducing their activity in reacting with sulfates. Combined with the grinding process to control the specific surface area of ​​the clinker, the structural density is further optimized. The entire process achieves a significant improvement in the clinker's resistance to sulfate attack through multiple synergistic effects of mineral composition optimization, structural densification, erosion path blocking, and mineral phase stabilization.

[0015] Preferably, in step (1), the natural marl is ground to a particle size ≤75um.

[0016] Preferably, in step (2), the mass ratio of lanthanum nitrate to cerium nitrate is 5:(2-4).

[0017] Preferably, in step (3), the static activation time is 2 to 4 hours.

[0018] Preferably, in step (4), the calcination temperature is 550-600℃ and the calcination time is 2-3h.

[0019] Preferably, in step (5), the mass ratio of modified marl powder to calcium carbonate is 9:(11-12).

[0020] Preferably, in step (5), the mass ratio of calcium fluoride to barium carbonate is 1:(2-4).

[0021] In the experiments of this invention, it was found that even after controlling the maximum calcination temperature at 1380℃ to retain sulfur, the liquid phase viscosity remained relatively high. This resulted in insufficient diffusion kinetics for rare earth ions (such as lanthanum and cerium) pre-loaded on the raw material surface, making it difficult for them to fully penetrate the depths of the Alite mineral lattice, leading to ineffective enrichment at grain boundaries. Furthermore, the generated sulfur phase exhibited a clump-like distribution, failing to construct a uniform and continuous chemical barrier against sulfur corrosion within the micropores. To further address this technical problem, this invention introduces calcium fluoride and barium carbonate into the preform. The fluoride ions in calcium fluoride significantly lower the temperature at which the liquid phase appears and drastically reduce the liquid phase viscosity, effectively creating a high-speed channel for the migration of rare earth ions and sulfur components, greatly accelerating the diffusion process of rare earths from the surface to the lattice core. Simultaneously, the barium ions in barium carbonate, due to their larger radius than calcium ions, cause moderate expansion and distortion upon entering the mineral lattice. This creates ample solid solution space for the also large-radius rare earth ions, thereby significantly improving the solid solubility of rare earths. Furthermore, barium ions have an extremely strong affinity for sulfur, combining with in-situ sulfur components to form a highly thermally stable barium-sulfur composite mineral phase, firmly anchoring sulfur within the microstructure. Through the synergistic effect of fluorine and barium, the former solves the problems of rare earth element migration and dispersion with sulfur, while the latter solves the problems of rare earth element containment and sulfur fixation. This results in a superstable structure within the clinker, where deeply solid-solution-modified alite nuclei of rare earth elements intertwine with a dense, continuous chemical barrier constructed by the barium-sulfur composite phase, further enhancing the clinker's resistance to sulfate attack.

[0022] Preferably, in step (6), the calcination temperature of the first stage of mineralization calcination is 950℃ and the calcination time is 45min; the calcination temperature of the second stage of mineralization calcination is 1380℃ and the calcination time is 30min.

[0023] Preferably, in step (7), the oxygen content of the oxygen-enriched air is 25% to 30%.

[0024] A silicate cement clinker based on marl is prepared by the method described above.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] 1. By crushing, grinding, and activating the marl with alkali-rare earth equal-volume impregnation, atomic-level dispersion and anchoring of rare earth elements (lanthanum and cerium) on the surface of the raw material were achieved. After low-temperature calcination, the rare earth elements were initially combined with the silicon-aluminum matrix, which not only greatly improved the uniformity and reactivity of the raw material composition, but also laid the foundation for the deep embedding of rare earth ions into the alite (C3S) lattice in subsequent calcination. This stabilized the mineral crystal form from the source, refined the grains, and reduced internal defects, significantly improving the intrinsic sulfate resistance of the clinker mineral phase.

[0027] 2. By introducing calcium fluoride and barium carbonate into the feedstock, the synergistic effect of fluoride ions strongly reducing liquid phase viscosity and barium ions expanding the crystal lattice and anchoring sulfur elements was utilized to simultaneously solve the problems of rare earth ion diffusion barriers and uneven sulfur phase distribution at a relatively low firing temperature (1380℃). Ultimately, an ultra-stable and dense structure was formed inside the clinker, intertwined with rare earth deeply solid-solution modified Alite crystal nuclei and a barium-sulfur composite continuous barrier with extremely high thermal stability. This achieved multiple synergies of mineral composition optimization, erosion path blocking, and phase stabilization, significantly improving the clinker's resistance to sulfate attack. Attached Figure Description

[0028] Figure 1 This is a SEM image of the silicate cement clinker prepared in Example 4 of the present invention.

[0029] Figure 2 The image shows the XPS spectrum of the silicate cement clinker prepared in Example 4 of this invention. Detailed Implementation

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0031] Example 1

[0032] A method for preparing silicate cement clinker based on marl includes the following steps:

[0033] (1) Take 100g of natural marl, crush it with a jaw crusher, grind it with a planetary ball mill until the particle size is ≤75μm, and place the ground marl powder in an oven at 105℃ for 5 hours to dry it continuously to obtain dry marl powder.

[0034] (2) Weigh 32 mL of sodium hydroxide solution with a concentration of 0.75 mol / L, add 0.5 g of lanthanum nitrate and 0.35 g of cerium nitrate to it and stir evenly to prepare a mixed impregnation solution.

[0035] (3) The above mixed impregnation liquid was evenly sprayed into 100g of dried marl powder using an ultrasonic spraying device, with mechanical stirring during the process. After the material was added, the material was placed in a sealed container and allowed to stand for 3.5h to activate, thus obtaining activated powder.

[0036] (4) The activated powder is dried at 150℃ for 3 hours, then placed in a muffle furnace and heated to 580℃ at a heating rate of 5℃ / min and kept at that temperature for 2.5 hours. After the temperature inside the furnace naturally cools to room temperature, it is taken out and ground in a planetary ball mill until the particle size is ≤75μm to obtain modified marl powder.

[0037] (5) Weigh 90g of the above modified marl powder, add 118g of calcium carbonate, 17.5g of high-purity quartz powder, 12.5g of ferric oxide, 4.5g of gypsum dihydrate, 0.5g of calcium fluoride and 1.8g of barium carbonate in sequence and mix them. After dry mixing the mixture in a ball mill for 1 hour, add 6% of the total mass of deionized water and press it into shape on a pressure testing machine at a pressure of 25MPa to obtain a round cake blank.

[0038] (6) The billet is placed in a rotary kiln with an airtight opening for two-stage mineralization calcination. In the first stage, the temperature is increased from room temperature to 950℃ at a rate of 10℃ / min and held for 45min. In the second stage, the temperature is increased to 1380℃ at a rate of 5℃ / min and held for 30min.

[0039] (7) During the 1380℃ heat preservation stage, continue to introduce oxygen-enriched air with an oxygen content of 28% into the kiln and maintain the kiln pressure at 0.02MPa, and continue calcining for 30 minutes. After calcination, quickly open the kiln door to take out the clinker and use a high-pressure cold air blower to force rapid cooling to below 500℃ within 2 minutes. Then, let it cool naturally to room temperature, and finally put it into a planetary ball mill to grind to a particle size ≤45μm, thus obtaining high sulfur-resistant silicate cement clinker based on marl.

[0040] Example 2

[0041] A method for preparing silicate cement clinker based on marl includes the following steps:

[0042] (1) Take 100g of natural marl, crush it with a jaw crusher, grind it with a planetary ball mill until the particle size is ≤75μm, and place the ground marl powder in an oven at 105℃ for 5 hours to dry it continuously to obtain dry marl powder.

[0043] (2) Weigh 32 mL of sodium hydroxide solution with a concentration of 0.75 mol / L, add 0.5 g of lanthanum nitrate and 0.25 g of cerium nitrate to it and stir evenly to prepare a mixed impregnation solution.

[0044] (3) The above mixed impregnation liquid was evenly sprayed into 100g of dried marl powder using an ultrasonic spraying device, with mechanical stirring during the process. After the material was added, it was placed in a sealed container and allowed to stand for 2.5h to activate, thus obtaining activated powder.

[0045] (4) The activated powder is dried at 150℃ for 3 hours, then placed in a muffle furnace and heated to 580℃ at a heating rate of 5℃ / min and kept at that temperature for 2.5 hours. After the temperature inside the furnace naturally cools to room temperature, it is taken out and ground in a planetary ball mill until the particle size is ≤75μm to obtain modified marl powder.

[0046] (5) Weigh 90g of the above modified marl powder, add 112g of calcium carbonate, 17.5g of high-purity quartz powder, 12.5g of ferric oxide, 4.5g of gypsum dihydrate, 0.5g of calcium fluoride and 1.3g of barium carbonate in sequence and mix them. After dry mixing the mixture in a ball mill for 1 hour, add 6% of the total mass of deionized water and press it into shape on a pressure testing machine at a pressure of 25MPa to obtain a round cake blank.

[0047] (6) The billet is placed in a rotary kiln with an airtight opening for two-stage mineralization calcination. In the first stage, the temperature is increased from room temperature to 950℃ at a rate of 10℃ / min and held for 45min. In the second stage, the temperature is increased to 1380℃ at a rate of 5℃ / min and held for 30min.

[0048] (7) During the 1380℃ heat preservation stage, continue to introduce oxygen-enriched air with an oxygen content of 28% into the kiln and maintain the kiln pressure at 0.02MPa, and continue calcining for 30 minutes. After calcination, quickly open the kiln door to take out the clinker and use a high-pressure cold air blower to force rapid cooling to below 500℃ within 2 minutes. Then, let it cool naturally to room temperature, and finally put it into a planetary ball mill to grind to a particle size ≤45μm, thus obtaining high sulfur-resistant silicate cement clinker based on marl.

[0049] Example 3

[0050] A method for preparing silicate cement clinker based on marl includes the following steps:

[0051] (1) Take 100g of natural marl, crush it with a jaw crusher, grind it with a planetary ball mill until the particle size is ≤75μm, and place the ground marl powder in an oven at 105℃ for 5 hours to dry it continuously to obtain dry marl powder.

[0052] (2) Weigh 32 mL of sodium hydroxide solution with a concentration of 0.75 mol / L, add 0.5 g of lanthanum nitrate and 0.3 g of cerium nitrate to it and stir evenly to prepare a mixed impregnation solution.

[0053] (3) The above mixed impregnation liquid was evenly sprayed into 100g of dried marl powder using an ultrasonic spraying device, with mechanical stirring during the process. After the material was added, it was placed in a sealed container and allowed to stand for 3 hours to activate, thus obtaining activated powder.

[0054] (4) The activated powder is dried at 150℃ for 3 hours, then placed in a muffle furnace and heated to 580℃ at a heating rate of 5℃ / min and kept at that temperature for 2.5 hours. After the temperature inside the furnace naturally cools to room temperature, it is taken out and ground in a planetary ball mill until the particle size is ≤75μm to obtain modified marl powder.

[0055] (5) Weigh 90g of the above modified marl powder, add 115g of calcium carbonate, 17.5g of high-purity quartz powder, 12.5g of ferric oxide, 4.5g of gypsum dihydrate, 0.5g of calcium fluoride and 1.5g of barium carbonate in sequence and mix them. After dry mixing the mixture in a ball mill for 1 hour, add 6% of the total mass of deionized water and press it into shape on a pressure testing machine at a pressure of 25MPa to obtain a round cake blank.

[0056] (6) The billet is placed in a rotary kiln with an airtight opening for two-stage mineralization calcination. In the first stage, the temperature is increased from room temperature to 950℃ at a rate of 10℃ / min and held for 45min. In the second stage, the temperature is increased to 1380℃ at a rate of 5℃ / min and held for 30min.

[0057] (7) During the 1380℃ heat preservation stage, continue to introduce oxygen-enriched air with an oxygen content of 28% into the kiln and maintain the kiln pressure at 0.02MPa, and continue calcining for 30 minutes. After calcination, quickly open the kiln door to take out the clinker and use a high-pressure cold air blower to force rapid cooling to below 500℃ within 2 minutes. Then, let it cool naturally to room temperature, and finally put it into a planetary ball mill to grind to a particle size ≤45μm, thus obtaining high sulfur-resistant silicate cement clinker based on marl.

[0058] Example 4

[0059] A method for preparing silicate cement clinker based on marl includes the following steps:

[0060] (1) Take 100g of natural marl, crush it with a jaw crusher, grind it with a planetary ball mill until the particle size is ≤75μm, and place the ground marl powder in an oven at 105℃ for 5 hours to dry it continuously to obtain dry marl powder.

[0061] (2) Weigh 32 mL of sodium hydroxide solution with a concentration of 0.75 mol / L, add 0.5 g of lanthanum nitrate and 0.4 g of cerium nitrate to it and stir evenly to prepare a mixed impregnation solution.

[0062] (3) The above mixed impregnation liquid was evenly sprayed into 100g of dried marl powder using an ultrasonic spraying device, with mechanical stirring during the process. After the material was added, it was placed in a sealed container and allowed to stand for 4 hours to activate, thus obtaining activated powder.

[0063] (4) The activated powder is dried at 150℃ for 3 hours, then placed in a muffle furnace and heated to 600℃ at a heating rate of 5℃ / min and kept at that temperature for 3 hours. After the temperature inside the furnace naturally cools to room temperature, it is taken out and ground in a planetary ball mill until the particle size is ≤75μm to obtain modified marl powder.

[0064] (5) Weigh 90g of the above modified marl powder, add 120g of calcium carbonate, 17.5g of high-purity quartz powder, 12.5g of ferric oxide, 4.5g of gypsum dihydrate, 0.5g of calcium fluoride and 2.0g of barium carbonate in sequence and mix them. After dry mixing the mixture in a ball mill for 1 hour, add 6% of the total mass of deionized water and press it into shape on a pressure testing machine at a pressure of 25MPa to obtain a round cake blank.

[0065] (6) The billet is placed in a rotary kiln with an airtight opening for two-stage mineralization calcination. In the first stage, the temperature is increased from room temperature to 950℃ at a rate of 10℃ / min and held for 45min. In the second stage, the temperature is increased to 1380℃ at a rate of 5℃ / min and held for 30min.

[0066] (7) During the 1380℃ heat preservation stage, continue to introduce oxygen-enriched air with an oxygen content of 30% into the kiln and maintain the kiln pressure at 0.02MPa, and continue calcining for 30min. After calcination, quickly open the kiln door to take out the clinker and use a high-pressure cold air blower to force rapid cooling to below 500℃ within 2min. Then, let it cool naturally to room temperature, and finally put it into a planetary ball mill to grind to a particle size ≤45μm, thus obtaining high sulfur-resistant silicate cement clinker based on marl.

[0067] like Figure 1 and Figure 2 As shown, Figure 1 The SEM microstructure images show that the silicate cement clinker prepared in Example 4 formed a dense and interpenetrating microstructure, which directly verifies that under the synergistic effect of fluoride and barium ions, the liquid phase viscosity was significantly reduced, promoting the full development of mineral phases in the clinker and constructing a dense and continuous chemical barrier against sulfur erosion. Meanwhile, Figure 2 The XPS spectrum not only showed the characteristic peaks of conventional cement-based mineral components such as Ca, Si, O, Al, and Fe, but also clearly detected the characteristic peaks of doped elements such as La, Ce, Ba, F, and S. This strongly confirms that through impregnation activation and the introduction of specific ingredients, rare earth elements (lanthanum and cerium) have overcome diffusion resistance to achieve deep solid solution and embed into the alite crystal nucleus. Furthermore, barium ions have successfully combined with in-situ sulfur components to generate a stable barium-sulfur composite phase. This explains the intrinsic ultra-stable and dense structure mechanism of the clinker with excellent sulfate resistance from both the microstructure and elemental chemical composition perspectives.

[0068] Example 5

[0069] A method for preparing silicate cement clinker based on marl includes the following steps:

[0070] (1) Take 100g of natural marl, crush it with a jaw crusher, grind it with a planetary ball mill until the particle size is ≤75μm, and place the ground marl powder in an oven at 105℃ for 5 hours to dry it continuously to obtain dry marl powder.

[0071] (2) Weigh 32 mL of sodium hydroxide solution with a concentration of 0.75 mol / L, add 0.5 g of lanthanum nitrate and 0.2 g of cerium nitrate to it and stir evenly to prepare a mixed impregnation solution.

[0072] (3) The above mixed impregnation liquid was evenly sprayed into 100g of dried marl powder using an ultrasonic spraying device, with mechanical stirring during the process. After the material was added, the material was placed in a sealed container and allowed to stand for 2 hours to activate, thus obtaining activated powder.

[0073] (4) The activated powder is dried at 150℃ for 3 hours, then placed in a muffle furnace and heated to 550℃ at a heating rate of 5℃ / min and kept at that temperature for 2 hours. After the temperature inside the furnace naturally cools to room temperature, it is taken out and ground in a planetary ball mill until the particle size is ≤75μm to obtain modified marl powder.

[0074] (5) Weigh 90g of the above modified marl powder, add 110g of calcium carbonate, 17.5g of high-purity quartz powder, 12.5g of ferric oxide, 4.5g of gypsum dihydrate, 0.5g of calcium fluoride and 1.0g of barium carbonate in sequence and mix them. After dry mixing the mixture in a ball mill for 1 hour, add 6% of the total mass of deionized water and press it into shape on a pressure testing machine at a pressure of 25MPa to obtain a round cake blank.

[0075] (6) The billet is placed in a rotary kiln with an airtight opening for two-stage mineralization calcination. In the first stage, the temperature is increased from room temperature to 950℃ at a rate of 10℃ / min and held for 45min. In the second stage, the temperature is increased to 1380℃ at a rate of 5℃ / min and held for 30min.

[0076] (7) During the 1380℃ heat preservation stage, continue to introduce oxygen-enriched air with an oxygen content of 25% into the kiln and maintain the kiln pressure at 0.02MPa, and continue calcining for 30 minutes. After calcination, quickly open the kiln door to take out the clinker and use a high-pressure cold air blower to force rapid cooling to below 500℃ within 2 minutes. Then, let it cool naturally to room temperature, and finally put it into a planetary ball mill to grind to a particle size ≤45μm, thus obtaining high sulfur-resistant silicate cement clinker based on marl.

[0077] Comparative Example 1: The difference between Comparative Example 1 and Example 4 is that the conventional cement clinker preparation process is used, which aims to compare the overall effect of the low-temperature mineralization and formula optimization technology of the present invention. Natural marl, calcium carbonate and quartz powder of the same mass ratio as in Example 1 are mixed. After the mixture is dry-mixed in a ball mill for 1 hour, 6% of the total mass of deionized water is added. The mixture is then pressed into a round cake blank at a pressure of 25 MPa on a pressure testing machine. In step (6), conventional high-temperature calcination at 1450℃ is used.

[0078] Comparative Example 2: The difference between Comparative Example 2 and Example 4 is that lanthanum nitrate and cerium nitrate are not added to the mixed impregnation solution in step (2). This comparative example aims to verify the role of rare earth elements (lanthanum, cerium) in stabilizing mineral crystal structure and refining grain size.

[0079] Comparative Example 3: The difference between Comparative Example 3 and Example 4 is that sodium hydroxide is not added in step (2). This comparative example aims to verify the effect of sodium hydroxide micro-etching on the activation of the raw material surface and the uniformity of component distribution.

[0080] Comparative Example 4: The difference between Comparative Example 4 and Example 4 is that oxygen-enriched air is not introduced in step (7) (calcination is carried out directly under normal air atmosphere). This comparative example aims to verify the importance of an oxygen-enriched micro-positive pressure environment for in-situ sulfur fixation and preventing the high-temperature decomposition and volatilization of sulfur.

[0081] Comparative Example 5: The difference between Comparative Example 5 and Example 4 is that calcium fluoride and barium carbonate are not added in step (5). This comparative example aims to verify the synergistic effect of calcium fluoride and barium carbonate in assisting rare earth diffusion and in-situ sulfur fixation barrier construction.

[0082] Performance testing:

[0083] 1. Sulfate Erosion Resistance Test: The sulfate erosion resistance coefficient was used as the evaluation index. Clinker prepared in the examples and comparative examples was processed into 40mm×40mm×160mm mortar specimens according to the test method of GB / T 748-2023 and cured for 28 days under standard curing conditions. The specimens were divided into two groups: one group was cured in clean water at 20℃, and the other group was immersed in a 5% Na2SO4 solution. After immersion for 180 days, the compressive strength of both groups was measured, and the sulfate erosion resistance coefficient was calculated (strength after 180 days of immersion / strength after the same age cured in clean water). The closer the coefficient is to 1.0, the better the sulfate erosion resistance. The test results are shown in Table 1.

[0084] 2. Compressive Strength Test: Following the test method in GB / T 17671-2021, clinker and gypsum were mixed and ground to prepare standard cement. This cement was then mixed with standard sand and water in a specific ratio to form mortar specimens. The compressive strength of the specimens was tested at 3 days (3d) and 28 days (28d) to assess the basic mechanical properties of the clinker and the development of its early and later strengths, ensuring that it meets the basic strength requirements while improving sulfur resistance. The test results are shown in Table 1.

[0085] 3. Clinker Sulfur Fixation Rate Test: The total sulfur content in clinker was determined using ion chromatography combined with high-temperature tubular furnace incineration. First, a measured amount of raw meal mixture (before proceeding to step 6) was weighed to determine the initial sulfur content. After calcination, a measured amount of clinker powder was weighed to determine the final sulfur content. Sulfur fixation rate = (total sulfur content in clinker / total sulfur content in raw meal) × 100%. This indicator was used to verify the technical effectiveness of the oxygen-enriched micro-positive pressure environment and barium ion anchoring in preventing high-temperature sulfur volatilization. The test results are shown in Table 1.

[0086] 4. Free Calcium Oxide (f-CaO) Content Test: The content was determined using the glycerol-ethanol titration method. A clinker sample ground to a certain fineness was weighed, and a mixture of glycerol and anhydrous ethanol was added. The mixture was heated in a boiling water bath with constant stirring to allow the free calcium oxide to react with the glycerol to form calcium glycerol. Phenolphthalein was then used as an indicator, and the solution was titrated with a standard solution until the red color disappeared. This indicator is used to evaluate the degree of calcination of the clinker and the sufficiency of mineral phase formation. Generally, the lower the f-CaO content, the more complete the calcination reaction and the more stable the clinker quality. The test results are shown in Table 1.

[0087] Table 1:

[0088]

[0089] The sulfate resistance coefficients of the examples were all above 0.92, significantly higher than those of the comparative examples, indicating that the synergistic modification of the present invention greatly enhances the clinker's resistance to corrosion. In the examples, under oxygen-enriched micro-positive pressure and barium ion anchoring at 1380℃, the sulfur fixation rate remained above 84%, while the sulfur fixation rates of Comparative Example 1 (high temperature and no additives) and Comparative Example 4 (no oxygen-enriched environment) were extremely low, confirming the necessity of the present invention in constructing a sulfur fixation barrier. Comparative Example 5 shows that, in the absence of calcium fluoride and barium carbonate, despite the addition of rare earth elements and sulfur, the corrosion resistance coefficient (0.88) and sulfur fixation rate (55.3%) were unsatisfactory due to the lack of diffusion dynamics and a stable anchoring structure, fully demonstrating the crucial role of fluorine and barium introduction in improving the solubility of rare earth elements and the uniformity of sulfur phase distribution.

[0090] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for the production of a mudstone-based Portland cement clinker, characterized in that, Includes the following steps: (1) Natural marl is crushed, ground and dried to obtain marl powder; (2) Prepare a mixed impregnation solution by mixing sodium hydroxide solution, lanthanum nitrate and cerium nitrate; (3) Spray the mixed impregnation solution evenly onto the marl powder, let it stand to activate, and obtain activated powder; (4) The activated powder is dried and calcined at low temperature, and then the calcined product is ground to obtain modified marl powder; (5) The modified marl powder is mixed with calcium carbonate, quartz powder, iron oxide, gypsum dihydrate, calcium fluoride and barium carbonate, and pressed into shape to obtain a green body; (6) The billet is subjected to two-stage mineralization calcination; (7) Keep warm and introduce oxygen-rich air, continue calcining, and cool after calcination to obtain the product.

2. A method of manufacturing a silicate cement clinker based on marl according to claim 1, characterized in that, In step (1), the natural marl is ground to a particle size ≤75um.

3. The method for preparing silicate cement clinker based on marl according to claim 1, characterized in that, In step (2), the mass ratio of lanthanum nitrate to cerium nitrate is 5:(2-4).

4. A method of manufacturing a silicate cement clinker based on marl, according to claim 1, characterized in that, In step (3), the static activation time is 2 to 4 hours.

5. A method of manufacturing a silicate cement clinker based on marl, according to claim 1, characterized in that, In step (4), the roasting temperature is 550-600℃ and the roasting time is 2-3h.

6. A method of manufacturing a silicate cement clinker based on marl, according to claim 1, characterized in that, In step (5), the mass ratio of modified marl powder to calcium carbonate is 9:(11-12).

7. A method of manufacturing a silicate cement clinker based on marl, according to claim 1, characterized in that, In step (5), the mass ratio of calcium fluoride to barium carbonate is 1:(2-4).

8. A method of manufacturing a silicate cement clinker based on marl, according to claim 1, characterized in that, In step (6), the calcination temperature of the first stage of mineralization calcination is 950℃ and the calcination time is 45min; The second stage of mineralization calcination was carried out at a calcination temperature of 1380℃ for 30 minutes.

9. A method of manufacturing a silicate cement clinker based on marl, according to claim 1, characterized in that, In step (7), the oxygen content of the oxygen-enriched air is 25% to 30%.

10. A lime mud based Portland cement clinker, characterized in that, It is prepared by the method described in any one of claims 1 to 9 above.

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