Method for preparing cement clinker from magnesium slag and carbide slag

Abstract

The invention relates to a method for preparing cement clinker from magnesium slag and carbide slag, and belongs to the technical field of cement materials.The cement clinker is prepared from carbide slag, modified magnesium slag, activated converter slag and coal gangue as main raw materials, the modified magnesium slag is an Mg3 (PO4) 2 protective layer formed by ball-milling modification of magnesium slag through a Mg (H2PO4) 2 aqueous solution and a ferulic acid ethanol solution, and the magnesium slag is a magnesium slag protective layer formed by ball-milling modification of activated converter slag and coal gangue. The activated converter slag is obtained by roasting and activating the converter slag and Na2CO3; the four raw materials are mixed according to a certain proportion, a Li2B4O7-CaF2 composite mineralizer is added for low-temperature calcination, a proper amount of SO2 is introduced to induce generation of a new three-phase system of gehlenite-dicalcium silicate-spinel, carbon emission can be effectively reduced, fuel energy consumption can be saved, and the obtained cement clinker has high early strength and can be widely applied to the field of cement materials. The early strength and the later strength stability are well balanced, cracking is not prone to occurring, and the sulfate corrosion resistance is excellent.

Description

Technical Field

[0001] The present invention belongs to the technical field of cement materials, and particularly relates to a method for preparing cement clinker by using magnesium slag and carbide slag. Background Art

[0002] Cement, as an indispensable basic material for modern construction, is widely used in various construction projects and plays an important role in promoting social development and economic construction. Among various cement varieties, Portland cement occupies the dominant position in the cement market due to its good performance and wide applicability, and Portland cement clinker is the key semi-finished product that determines the performance of Portland cement.

[0003] In the production process, Portland cement clinker uses calcareous materials (limestone accounts for about 80%) and siliceous materials as the main raw materials. After proportioning the raw materials appropriately, crushing, batching, and grinding them into raw meal, the raw meal is calcined in a cement kiln until partially melted and then cooled to obtain a product mainly composed of calcium silicate minerals. However, in the actual production process, the following problems exist: On the one hand, for some typical low-grade limestone mines, with the country's rectification of mining resources, the externally purchased limestone resources are becoming increasingly tense. It is urgent to find high-grade limestone or alternative materials, match them with the low-grade limestone from its own mines, reduce the waste discharge, and extend the service life of the mines; On the other hand, the process characteristics of the cement industry determine that its carbon emission problem is severe. Approximately 60% of the CO2 in traditional clinker production comes from the decomposition of limestone, causing serious environmental pollution; On the third hand, the temperature required for the decomposition of limestone (CaCO3) is above 900°C, the clinker burning temperature is high, generally around 1450°C, and the burning time is long, resulting in large fuel energy consumption; On the fourth hand, after traditional Portland cement clinker is prepared into cement, its early strength is poor, and the effect of quickly reaching the design strength to shorten the construction period cannot be achieved. Although there are early-strength cements available in the current market, they often have problems such as insufficient later strength development and easy cracking; and various cements generally have insufficient resistance to sulfate attack.

[0004] How to balance the early strength, later strength stability of cement, improve the resistance to sulfate attack, and achieve energy conservation, carbon reduction, and green transformation has become a technical problem to be solved urgently. Summary of the Invention

[0005] In view of the problems existing in the existing cement, such as the increasingly tight limestone resources, the serious problem of material carbon emissions, the large energy consumption of firing fuels, the poor early strength of cement, the difficulty in balancing the early strength and the late strength stability, easy cracking, and insufficient resistance to sulfate erosion. The present invention provides a method for preparing cement clinker by using magnesium slag and carbide slag. Using carbide slag, modified magnesium slag, activated converter slag and coal gangue as the main raw materials, adding a Li2B4O7-CaF2 composite mineralizer for low-temperature calcination, and appropriately introducing SO2 to induce the formation of a new three-phase system of calcium aluminofeldspar-dicalcium silicate-spinel, effectively reducing carbon emissions, saving fuel energy consumption, and the obtained cement clinker has high early strength, good balance between early strength and late strength stability, not easy to crack, and excellent resistance to sulfate erosion. The specific technical solution is as follows: A method for preparing cement clinker by using magnesium slag and carbide slag, comprising the following steps: S1: The carbide slag is dried and crushed to obtain carbide slag powder; S2: The magnesium slag is crushed to obtain magnesium slag powder, Mg(H2PO4)2 aqueous solution is added, ferulic acid ethanol solution is added, ball milled and dried, and a Mg3(PO4)2 protective layer is formed on the surface of the magnesium slag powder particles to obtain modified magnesium slag powder; S3: The converter slag is crushed to obtain converter slag powder, mixed with Na2CO3 and roasted to obtain activated converter slag powder; S4: The coal gangue is crushed to obtain coal gangue powder; S5: By mass, 50 parts to 60 parts of carbide slag powder, 25 parts to 30 parts of modified magnesium slag powder, 3 parts to 5 parts of activated converter slag powder, 12 parts to 15 parts of coal gangue powder and 5 parts to 8 parts of Li2B4O7-CaF2 composite mineralizer are mixed evenly, preheated at 800°C to 900°C for 20 min to 30 min, and at the same time, a CO2-H2O mixed gas is introduced; then calcined at 1100°C to 1200°C for 2 h to 3 h, and 0.3 vol% to 0.5 vol% SO2 is supplemented and introduced during the period of 50 min to 70 min of the holding calcination to induce the formation of a new three-phase system of calcium aluminofeldspar-dicalcium silicate-spinel; cooled to obtain cement clinker.

[0006] In S1 of the above method, the carbide slag is dried to a water content of less than 1 wt%; the particle size of the carbide slag powder is passed through a 200-mesh to 250-mesh sieve.

[0007] In S2 of the above method, the concentration of the Mg(H2PO4)2 aqueous solution is 3 wt% to 5 wt%; the addition amount of the Mg(H2PO4)2 aqueous solution is 10% to 20% of the mass of the magnesium slag powder; In S2 of the above method, the concentration of the ferulic acid ethanol solution is 6wt% - 8wt%; the addition amount of the ferulic acid ethanol solution is 5% - 10% of the mass of the magnesium slag powder; In S2 of the above method, the particle size of the magnesium slag powder is passed through a 250 - 325 mesh sieve; the ball milling is carried out at a rotational speed of 15r / min - 20r / min for 1.5h - 2h; the diameter of the grinding balls used in the ball milling is 8mm - 15mm, and the filling rate of the grinding balls is 30% - 40%; after drying, sieving is carried out to remove the grinding balls.

[0008] In S3 of the above method, the particle size of the converter slag powder is passed through a 150 - 200 mesh sieve; the addition amount of Na2CO3 is 4% - 6% of the mass of the converter slag powder; the roasting is carried out at 400°C - 500°C for 30min - 40min.

[0009] In S4 of the above method, the particle size of the coal gangue powder is passed through a 200 - 250 mesh sieve.

[0010] In S5 of the above method, the Li2B4O7 - CaF2 composite mineralizer is a mixture of Li2B4O7 and CaF2 in a mass ratio of (1.5 - 3):(1 - 2); the volume ratio of the CO2 - H2O mixed gas is CO2:H2O = (3 - 4):(1 - 1.2); the feeding amount of the CO2 - H2O mixed gas is 0.8L / min - 1.2L / min per kilogram of the material.

[0011] In S5 of the above method, the MgO content in the cement clinker is ≤5wt%; the SO3 content in the clinker is <1wt%.

[0012] In the above method, the cement clinker is used in combination with an auxiliary agent, and the auxiliary agent includes, but is not limited to, 5wt% - 8wt% of gypsum powder, 2wt% - 4wt% of silica fume, 0.1wt% - 0.2wt% of polyacrylamide, and 1wt% - 2wt% of polycarboxylate superplasticizer powder based on the cement clinker.

[0013] A method for preparing cement clinker using magnesium slag and carbide slag provided by the present invention has the following beneficial effects: I. Modification of magnesium slag powder Adding an appropriate amount of aqueous solution of Mg(H2PO4)2 will form a Mg3(PO4)2 protective layer on the surface of magnesium slag powder particles. This protective layer can prevent components such as magnesium oxide in magnesium slag from reacting with other substances too quickly and from hydrating and swelling, enabling magnesium slag to play a more stable and continuous role in the formation process of cement clinker. At the same time, adding an appropriate amount of ethanol solution of ferulic acid can improve the surface properties of magnesium slag particles, activate the activity of magnesium slag, and enhance its compatibility with other materials. Ferulic acid in the appropriate amount of ethanol solution of ferulic acid adsorbs on the surface of magnesium slag particles, reducing the surface energy between particles and reducing the agglomeration phenomenon of particles, enabling magnesium slag particles to be more evenly dispersed during the ball milling process, thereby improving the ball milling efficiency and modification effect. During the ball milling process, the ethanol solution of ferulic acid helps to further mill and refine magnesium slag particles, improve their activity, enable magnesium slag to better participate in the formation reaction of cement clinker, and ultimately improve the quality and performance of cement clinker.

[0014] II. Mixed roasting of converter slag powder and Na2CO3 Na2CO3 will react with some components in the converter slag during the roasting process, reducing the melting point of the converter slag and causing solid-phase reactions in the converter slag at a lower temperature, thereby improving the activity of the converter slag. The activated converter slag powder can provide more active components for the formation of cement clinker, including tetracalcium ferroaluminate, etc., which helps to improve the mineral composition of cement clinker and enhance the strength and other properties of cement.

[0015] III. Using carbide slag, magnesium slag, converter slag, and coal gangue in a specific ratio can effectively improve the early strength of cement, balance the early strength and the stability of later strength, be not prone to cracking, and have good sulfate erosion resistance. The Li2B4O7-CaF2 composite mineralizer is mixed in a specific mass ratio and added to the raw materials, which can significantly reduce the firing temperature of cement clinker, enabling the materials to react fully at a relatively low temperature, promoting the formation and development of minerals. This can not only save energy but also reduce the wear of equipment during high-temperature calcination. At the same time, the composite mineralizer helps to induce the formation of a new three-phase system of calcium aluminosilicate - dicalcium silicate - spinel, improving the mineral composition of cement clinker, and thus enhancing the early strength, later strength, and durability and other properties of cement.

[0016] IV. Passing a CO2-H2O mixed gas during preheating to adjust the reaction atmosphere of the materials, promoting the decomposition of some carbonates, making carbonates such as calcium carbonate more easily decompose into calcium oxide, providing an adequate calcium source for the formation of minerals in the subsequent cement clinker. At the same time, the CO2-H2O mixed gas can also react with some components in the materials, improving the reaction activity of the materials, making the reaction more sufficient and efficient during the subsequent heat preservation and calcination, being conducive to the formation of minerals and the development of crystals, and thus improving the quality of cement clinker.

[0017] V. Supplementing and introducing a trace amount of SO2 during a suitable period of heat preservation calcination can induce the formation of a new three-phase system of calcium aluminosilicate - dicalcium silicate - spinel, optimizing the mineral composition of cement clinker. At the same time, SO2 can adjust the sulfur content in the clinker, and an appropriate amount of sulfur can react with other components in the cement to improve the setting time of the cement, enabling the cement to better meet the construction requirements during use. In addition, precise control can avoid excessive introduction of sulfur elements.

[0018] The formation of calcium aluminosilicate (C2AS) and spinel (MA) mainly occurs in the early and middle stages of calcination. Supplementing and introducing 0.3vol% - 0.5vol% SO2 during the period of 50min - 70min of heat preservation calcination can significantly reduce the risk of sulfur residue in the clinker, while still effectively inducing the formation of the target mineral phases; sulfur is mainly fixed by forming sulfoaluminate (precursor of ettringite) or dissolving in silicate minerals; the oxidation atmosphere of SO2 can adjust the Fe 3+ / Fe 2+ ratio and stabilize the spinel structure. Without introducing SO2 in the later stage, it can avoid sulfur interfering with the polymorphic transformation of C2S. If SO2 is introduced throughout the heat preservation calcination process, excessive sulfur will form free CaSO4 or unreacted sulfur oxides, resulting in a residue risk. By limiting the SO2 introduction time to the key stage of mineral formation (including the nucleation period of calcium aluminosilicate and spinel), the amount of sulfur participating in the reaction can be precisely controlled, avoiding excessive sulfur introduction in the later stage and causing later expansion (delayed formation of ettringite).

[0019] VI. According to the characteristics of cement clinker, the present invention designs additives with specific components and proportions. An appropriate amount of gypsum is used as a retarder to adjust the setting time and participate in the hydration reaction of C3A to avoid flash setting. An appropriate amount of silica fume, a highly active siliceous material, fills the pores and promotes the development of later strength. An appropriate amount of polyacrylamide improves the particle dispersibility and reduces the risk of cracking. An appropriate amount of polycarboxylate superplasticizer reduces the water - cement ratio and improves the density. The components are used in combination to assist the cement clinker in improving various properties of the cement.

[0020] VII. Regulating the mineral composition: Controlling the MgO content in the magnesium slag ≤ 5wt%. On the one hand, it can prevent excessive hydration expansion, and on the other hand, it can partially replace CaO in the clinker, promoting the formation of silicate minerals (C3S, C2S) and the intermediate phase (including C4AF), and at the same time generating a small amount of minerals such as forsterite (Mg2SiO4), optimizing the early strength and sulfate resistance of the clinker.

[0021] VIII. Improving the burnability: The highly active CaO in carbide slag and trace elements (including Fe, Al) in magnesium slag can reduce the liquid phase formation temperature of raw meal, accelerate the formation reaction of clinker minerals, and shorten the firing time.

[0022] In summary, carbide slag replaces limestone to reduce carbon emissions from CaCO3 decomposition. Modified magnesium slag introduces MgO, but the expansion of free MgO is inhibited by the magnesium phosphate protective layer. Activated converter slag provides Al2O3 and Fe2O3 to promote the formation of calcium aluminosilicate (C2AS). The Li2B4O7-CaF2 composite mineralizer reduces the liquid phase formation temperature and synergistically promotes the mineral phase reconstruction with SO2. The formulation design takes into account resource utilization, process optimization and performance balance, and has good practical value. Detailed implementation mode

[0023] Example 1: A method for preparing cement clinker using magnesium slag and carbide slag, comprising the following steps: S1: The carbide slag is dried, crushed, and passed through a 200-mesh sieve to obtain carbide slag powder. S2: The magnesium slag is crushed, passed through a 250-mesh sieve to obtain magnesium slag powder, 3wt% concentration Mg(H2PO4)2 aqueous solution of 10% of the mass of the magnesium slag powder is added, 6wt% concentration ferulic acid ethanol solution of 5% of the mass of the magnesium slag powder is added, and ball milling is carried out. The diameter of the grinding balls is 8mm, the filling rate of the grinding balls is 30%, and after ball milling at 15r / min for 1.5h, it is dried and sieved to remove the grinding balls. A Mg3(PO4)2 protective layer is formed on the surface of the magnesium slag powder particles to obtain modified magnesium slag powder. S3: The converter slag is crushed, passed through a 150-mesh sieve to obtain converter slag powder, 4% of the mass of the converter slag powder is added with Na2CO3 and roasted at 400°C for 30min to obtain activated converter slag powder. S4: The coal gangue is crushed, passed through a 200-mesh sieve to obtain coal gangue powder. S5: By mass, 50 parts of carbide slag powder, 25 parts of modified magnesium slag powder, 3 parts of activated converter slag powder, 12 parts of coal gangue powder and 5 parts of Li2B4O7-CaF2 composite mineralizer are mixed evenly, preheated at 800°C for 20min, and CO2-H2O mixed gas is introduced at the same time; then calcined at 1100°C for 2h, and 0.3vol% SO2 is supplemented and introduced during the 50min - 70min period of the calcination to induce the formation of a new three-phase system of calcium aluminosilicate - dicalcium silicate - spinel; cooled to obtain cement clinker, the MgO content in the clinker is 4.3wt%, and the SO3 content in the clinker is 0.4wt%. Among them, the Li2B4O7-CaF2 composite mineralizer is a mixture of Li2B4O7 and CaF2 in a mass ratio of 1.5:1; the volume ratio of the CO2-H2O mixed gas is CO2:H2O = 3:1; the introduction amount of the CO2-H2O mixed gas is 0.8L / min per kilogram of the material.

[0024] Example 2: A method for preparing cement clinker using magnesium slag and carbide slag, comprising the following steps: S1: The carbide slag is dried, crushed, and passed through a 200-mesh sieve to obtain carbide slag powder; S2: The magnesium slag is crushed and passed through a 325-mesh sieve to obtain magnesium slag powder. Add a 5wt% concentration of Mg(H2PO4)2 aqueous solution accounting for 10% of the mass of the magnesium slag powder, and add a 6.5wt% concentration of ferulic acid ethanol solution accounting for 5% of the mass of the magnesium slag powder. Then carry out ball milling. The diameter of the grinding balls is 8mm, the filling rate of the grinding balls is 40%, and ball milling is carried out at a rotation speed of 15r / min for 2h and then dried. After sieving to remove the grinding balls, a Mg3(PO4)2 protective layer is formed on the surface of the magnesium slag powder particles to obtain modified magnesium slag powder; S3: The converter slag is crushed and passed through a 150-mesh sieve to obtain converter slag powder. Mix it with Na2CO3 accounting for 6% of the mass of the converter slag powder and calcine it at 400°C for 40min to obtain activated converter slag powder; S4: The coal gangue is crushed and passed through a 200-mesh sieve to obtain coal gangue powder; S5: By mass, 60 parts of carbide slag powder, 25 parts of modified magnesium slag powder, 5 parts of activated converter slag powder, 12 parts of coal gangue powder and 8 parts of Li2B4O7-CaF2 composite mineralizer are mixed evenly, preheated at 800°C for 30min, and at the same time, a CO2-H2O mixed gas is introduced; then keep it at 1100°C for heat preservation and calcination for 3h, and supplement and introduce 0.3vol% SO2 during the 50min - 70min period of heat preservation and calcination to induce the formation of a new three-phase system of calcium aluminofeldspar-dicalcium silicate-spinel; cool to obtain cement clinker. The MgO content in the clinker is 3.4wt%, and the SO3 content in the clinker is 0.5wt%; Among them, the Li2B4O7-CaF2 composite mineralizer is a mixture of Li2B4O7 and CaF2 in a mass ratio of 3:1; the volume ratio of the CO2-H2O mixed gas is CO2:H2O = 4:1; the introduction amount of the CO2-H2O mixed gas is 1.2L / min per kilogram of the material.

[0025] Example 3: A method for preparing cement clinker using magnesium slag and carbide slag, including the following steps: S1: The carbide slag is dried, crushed, and passed through a 200-mesh sieve to obtain carbide slag powder; S2: The magnesium slag is crushed and passed through a 325-mesh sieve to obtain magnesium slag powder. Add a 4wt% concentration of Mg(H2PO4)2 aqueous solution accounting for 15% of the mass of the magnesium slag powder, and add a 7wt% concentration of ferulic acid ethanol solution accounting for 8% of the mass of the magnesium slag powder. Then carry out ball milling. The diameter of the grinding balls is 10mm, the filling rate of the grinding balls is 35%, and ball milling is carried out at a rotation speed of 20r / min for 1.5h and then dried. After sieving to remove the grinding balls, a Mg3(PO4)2 protective layer is formed on the surface of the magnesium slag powder particles to obtain modified magnesium slag powder; S3: The converter slag is crushed and passed through a 200-mesh sieve to obtain converter slag powder, 5% of the mass of the converter slag powder is added with Na2CO3, and the mixture is calcined at 450°C for 35 minutes to obtain activated converter slag powder; S4: crushing the coal gangue and passing it through a 200-mesh sieve to obtain coal gangue powder; S5: Calculated by weight, 55 parts of carbide slag powder, 28 parts of modified magnesium slag powder, 4 parts of activated converter slag powder, 13 parts of coal gangue powder and 7 parts of Li2B4O7-CaF2 composite mineralizer are mixed evenly, preheated at 850℃ for 25min, and a CO2-H2O mixed gas is introduced at the same time; then, the mixture is kept at 1150℃ for 2.5h, and 0.4vol% SO2 is added during the 50min-70min period of the calcination to induce the formation of a new three-phase system of calcite-dicalcium silicate-spinel; cooled to obtain cement clinker, wherein the MgO content in the clinker is 4.1wt%, and the SO3 content in the clinker is 0.7wt%; Among them, the Li2B4O7-CaF2 composite mineralizer is a mixture of Li2B4O7 and CaF2 in a mass ratio of 2:1.5; the volume ratio of the CO2-H2O mixed gas is CO2:H2O=3.5:1; the amount of CO2-H2O mixed gas introduced is 1.0L / min per kilogram of material.

[0026] Embodiment 4: A method for preparing cement clinker using magnesium slag and carbide slag, comprising the following steps: S1: drying and crushing the carbide slag, and passing it through a 250-mesh sieve to obtain carbide slag powder; S2: The magnesium slag is crushed and passed through a 250-mesh sieve to obtain magnesium slag powder, and a 3wt% Mg(H2PO4)2 aqueous solution with a concentration of 20% by mass of the magnesium slag powder is added, and a 7.5wt% ferulic acid ethanol solution with a concentration of 10% by mass of the magnesium slag powder is added, and ball milling is performed. The diameter of the grinding ball is 15 mm, and the filling rate of the grinding ball is 30%. The ball milling is performed at a speed of 20 r / min for 1.5 h, and then the grinding balls are dried, and the grinding balls are removed by sieving. A Mg3(PO4)2 protective layer is formed on the surface of the magnesium slag powder particles to obtain modified magnesium slag powder; S3: The converter slag is crushed and passed through a 200-mesh sieve to obtain converter slag powder, 4% of the mass of the converter slag powder is added with Na2CO3, and the mixture is calcined at 500°C for 30 minutes to obtain activated converter slag powder; S4: crushing the coal gangue and passing it through a 250-mesh sieve to obtain coal gangue powder; S5: By mass fraction, 50 parts of carbide slag powder, 30 parts of modified magnesium slag powder, 3 parts of activated converter slag powder, 15 parts of coal gangue powder and 5 parts of Li2B4O7-CaF2 composite mineralizer are mixed evenly, preheated at 900 °C for 20 min, and at the same time, a CO2-H2O mixed gas is introduced; then calcined at 1200 °C for 2 h, and 0.5 vol% SO2 is supplemented and introduced during the period of 50 min to 70 min of heat preservation calcination to induce the formation of a new three-phase system of calcium aluminofeldspar-dicalcium silicate-spinel; cooled to obtain cement clinker, the MgO content in the clinker is 5.0 wt%, and the SO3 content in the clinker is 0.9 wt%. Among them, the Li2B4O7-CaF2 composite mineralizer is a mixture of Li2B4O7 and CaF2 in a mass ratio of 1.5:2; the volume ratio of the CO2-H2O mixed gas is CO2:H2O = 3:1.2; the introduction amount of the CO2-H2O mixed gas is 0.8 L / min per kilogram of material.

[0027] Example 5: A method for preparing cement clinker by using magnesium slag and carbide slag, comprising the following steps: S1: The carbide slag is dried, crushed, and passed through a 250-mesh sieve to obtain carbide slag powder; S2: The magnesium slag is crushed, passed through a 325-mesh sieve to obtain magnesium slag powder, 5 wt% concentration Mg(H2PO4)2 aqueous solution accounting for 20% of the mass of the magnesium slag powder is added, 8 wt% concentration ferulic acid ethanol solution accounting for 10% of the mass of the magnesium slag powder is added, and ball milling is carried out. The diameter of the grinding balls is 15 mm, the filling rate of the grinding balls is 40%, and after ball milling at 20 r / min for 2 h, it is dried and sieved to remove the grinding balls, and a Mg3(PO4)2 protective layer is formed on the surface of the magnesium slag powder particles to obtain modified magnesium slag powder; S3: The converter slag is crushed, passed through a 200-mesh sieve to obtain converter slag powder, mixed with 6% of Na2CO3 by the mass of the converter slag powder, and calcined at 500 °C for 40 min to obtain activated converter slag powder; S4: The coal gangue is crushed, passed through a 250-mesh sieve to obtain coal gangue powder; S5: By mass fraction, 60 parts of carbide slag powder, 30 parts of modified magnesium slag powder, 5 parts of activated converter slag powder, 15 parts of coal gangue powder and 8 parts of Li2B4O7-CaF2 composite mineralizer are mixed evenly, preheated at 900 °C for 30 min, and at the same time, a CO2-H2O mixed gas is introduced; then calcined at 1200 °C for 3 h, and 0.5 vol% SO2 is supplemented and introduced during the period of 50 min to 70 min of heat preservation calcination to induce the formation of a new three-phase system of calcium aluminofeldspar-dicalcium silicate-spinel; cooled to obtain cement clinker, the MgO content in the clinker is 3.9 wt%, and the SO3 content in the clinker is 0.8 wt%. Among them, the Li2B4O7-CaF2 composite mineralizer is a mixture of Li2B4O7 and CaF2 with a mass ratio of 3:2; the volume ratio of the CO2-H2O mixed gas is CO2:H2O = 4:1.2; the input amount of the CO2-H2O mixed gas is 1.2 L / min per kilogram of the material.

[0028] The cement clinkers prepared in the above-mentioned respective examples are used in combination with additives. The additives include, but are not limited to, gypsum powder accounting for 5wt% - 8wt% of the cement clinker, silica fume accounting for 2wt% - 4wt%, polyacrylamide accounting for 0.1wt% - 0.2wt%, and polycarboxylate superplasticizer powder accounting for 1wt% - 2wt% of the cement clinker.

[0029] For the comparability of sample testing, in the cement samples of each example, the additives are gypsum powder accounting for 6wt% of the cement clinker, silica fume accounting for 3wt%, polyacrylamide accounting for 0.15wt%, and polycarboxylate superplasticizer powder accounting for 1.5wt% to prepare cement.

[0030] The sources of the raw materials in the above-mentioned respective examples are as follows: The carbide slag is from Shaanxi Jintai Chlor-Alkali Chemical Co., Ltd. The magnesium slag is from Jixian Hengsheng Magnesium Industry Co., Ltd. in Shaanxi Province. The supplier of the converter slag is Shanxi Hongmo Logistics Co., Ltd., and the manufacturer is Shanxi Gaoyi Iron & Steel Co., Ltd. The supplier of the coal gangue is Yulin Jinshunhui Transportation Co., Ltd., and the manufacturer is Zizhou Yongxing Coal Industry Co., Ltd. Mg(H2PO4)2 is from Zhengzhou Shengfeng Chemical Products Co., Ltd. with a purity of 98%. Ferulic acid is from Shaanxi Yinuo Biotechnology Co., Ltd., model YN-01, with a purity of 98%. Na2CO3 is from Weifang Haizhiyuan Chemical Co., Ltd. Li2B4O7 is from Henan Wanshan New Material Technology Co., Ltd. with a purity of 99%. CaF2 is from Hebei Guanting Building Materials Technology Co., Ltd. with a purity of 97%. The gypsum powder is from Zaozhuang Yicheng Jinhai Gypsum Products Factory, model jh-001. The silica fume is from Lingshou Muchen New Material Technology Co., Ltd. with a silicon content of 96% and a particle size of 1200 mesh. The polyacrylamide is from Henan Hangrui Environmental Protection Technology Co., Ltd., model anionic 16 million. The polycarboxylate superplasticizer powder is from Wuhan Huaxuan High-Tech Co., Ltd., model PC-1006.

[0031] Comparative Example 1 In S2, the modified magnesium slag powder is replaced with magnesium slag powder (without modification); other parameters and methods are the same as those in Example 1.

[0032] Comparative Example 2 In S2, the ferulic acid ethanol solution is not added; other parameters and methods are the same as those in Example 1.

[0033] Comparative Example 3 In S2, the concentration of the ferulic acid ethanol solution is 15wt%, and the addition amount is 10% of the mass of the magnesium slag powder; other parameters and methods are the same as those in Example 1.

[0034] Comparative Example 4 In S2, the concentration of the Mg(H2PO4)2 aqueous solution was 15 wt%, and the addition amount was 20% of the mass of the magnesium slag powder; other parameters and methods were the same as those in Example 1.

[0035] Comparative Example 5 In S2, the modified magnesium slag powder was replaced with magnesium slag powder (without modification), and 0.5% of Mg3(PO4)2 powder by the mass of the magnesium slag powder was directly added and dry-mixed evenly; other parameters and methods were the same as those in Example 1.

[0036] Comparative Example 6 In S3, the activated converter slag powder was replaced with converter slag powder (without activation); other parameters and methods were the same as those in Example 1.

[0037] Comparative Example 7 In S3, the roasting temperature was 300 °C; other parameters and methods were the same as those in Example 1.

[0038] Comparative Example 8 In S5, the Li2B4O7-CaF2 composite mineralizer was not added; other parameters and methods were the same as those in Example 1.

[0039] Comparative Example 9 In S5, the composite mineralizer was all Li2B4O7; other parameters and methods were the same as those in Example 1.

[0040] Comparative Example 10 In S5, the composite mineralizer was all CaF2; other parameters and methods were the same as those in Example 1.

[0041] Comparative Example 11 In S5, the addition amount of the Li2B4O7-CaF2 composite mineralizer was 15 parts; other parameters and methods were the same as those in Example 1.

[0042] Comparative Example 12 In S5, there were 25 parts of carbide slag powder and 50 parts of modified magnesium slag powder; other parameters and methods were the same as those in Example 1.

[0043] Comparative Example 13 In S5, there were 15 parts of activated converter slag powder and 5 parts of coal gangue powder; other parameters and methods were the same as those in Example 1.

[0044] Comparative Example 14 In S5, there were 25 parts of carbide slag powder, 50 parts of modified magnesium slag powder, 15 parts of activated converter slag powder, and 5 parts of coal gangue powder; other parameters and methods were the same as those in Example 1.

[0045] Comparative Example 15 In S5, within the time period of 50 min to 70 min during heat preservation calcination, SO2 is not introduced; other parameters and methods are the same as those in Example 1.

[0046] Due to the changes in the composition or process of each comparative example, the contents of MgO and SO3 in the cement clinker product are different from those in Example 1.

[0047] I. Setting time determination: According to the "Test Methods for Water Requirement of Normal Consistency, Setting Time and Soundness of Cement" GB / T 1346, it is measured using a Vicat apparatus. The cement clinker and water are mixed at a water-cement ratio of 0.45 to make cement paste, which is filled into a test mold. The test rod is lowered to the surface of the paste, and the time required for the test rod to sink into the paste and be 6 mm ± 1 mm away from the bottom plate is recorded as the initial setting time; when the test needle sinks into the test specimen by 0.5 mm, that is, when the annular attachment can no longer leave a mark on the test specimen, it is the final setting time. The experimental environment temperature is 20 °C and the relative humidity is 60%.

[0048] II. Strength determination: The cement sample includes cement clinker and additives (the additives are gypsum powder at 6 wt% of the cement clinker, silica fume at 3 wt%, polyacrylamide at 0.15 wt%, and polycarboxylate superplasticizer powder at 1.5 wt%); first, the cement clinker is ground to a specific surface area of 350 ± 10 m² / kg, and then mixed with other additives in a planetary mixer at a rotation speed of 120 r / min for 5 min to make the materials fully mixed evenly, obtaining the cement sample.

[0049] According to the "Test Methods for Strength of Cement Mortar (ISO Method)" GB / T 17671, cement mortar specimens with dimensions of 40 mm × 40 mm × 160 mm are prepared. The mortar mix ratio is cement sample (including additives): standard sand: water = 1:3:0.5. They are cured for 3 days and 28 days respectively under standard curing conditions (temperature 20 °C, relative humidity 90%), and then the compressive strength test is carried out using a compression testing machine.

[0050] III. Cracking detection: According to the formulation preparation method for strength detection, thin plate specimens with dimensions of 400 mm × 400 mm × 60 mm are made. After curing for 28 days under standard curing conditions, a crack width gauge is used to observe the crack situation on the surface of the specimen, and the number of cracks and the maximum width of the cracks are recorded.

[0051] IV. Detection of sulfate resistance performance: According to the formula preparation method detected by strength, prepare cement mortar specimens with dimensions of 40mm×40mm×160mm. According to the "Test Method for Resistance of Cement to Sulfate Attack" GB / T 749, soak the cement mortar specimens cured under standard conditions for 28 days in a sodium sulfate solution with a concentration of 5wt%, take them out after 90 days, observe the appearance changes (spalling, swelling, cracks, etc.) of the specimens, measure their compressive strength, and calculate the strength loss rate.

[0052] Table 1 Performance Test Results

[0053] From the above results, it can be seen that the cement clinkers of Examples 1 to 5 can not only avoid adding a large amount of limestone, effectively reduce carbon emissions, have a low calcination temperature, save fuel energy, but also have a relatively fast setting time, shorten the construction period, and have high early strength of the cement, stable early strength and later strength, are not easy to crack, and have better resistance to sulfate attack.

[0054] In Comparative Example 1, when the modified magnesium slag powder was replaced with magnesium slag powder, the chemical reaction rate during the calcination process with other raw materials was relatively slow when the magnesium slag was not modified. During the cement hydration process, due to the lack of special structures and active substances formed by modification, the formation rate of hydration products was slowed down. In the initial stage of cement hydration, the formation rate of hydration products such as ettringite became slower, resulting in a longer time required for the cement paste to transform from a plastic state to a solid state with a certain strength. Magnesium oxide was more likely to hydrate to form magnesium hydroxide during the cement hydration process, with a high volume expansion rate, and both the initial setting time and the final setting time were prolonged. The strength mainly comes from the dense structure formed by the interweaving of various hydration products generated by cement hydration. The unmodified magnesium slag has insufficient activity and cannot fully participate in the reaction to form high-strength mineral phases during the calcination process, resulting in a relatively reduced content of effective strength contributing phases (including minerals such as calcium silicate) in the cement clinker. During the cement hydration process, due to the lack of the promoting effect brought by modification, both the quantity and quality of hydration products were affected. The generation amount of C-S-H gel (the main strength contributing substance of cement hydration) decreased, and its structure was not dense enough, making the cement stone more likely to be damaged when bearing external forces. The addition of unmodified magnesium slag made the uniformity of the internal structure of the cement stone worse, magnesium oxide was prone to expand, and microcracks were more likely to occur. Sulfate ions in the sulfate solution will react with certain components in the cement stone (including calcium hydroxide, tricalcium aluminate, etc.) to generate expansive products (including secondary formation of ettringite, gypsum crystallization). Unmodified magnesium slag affects the uniformity and compactness of the overall structure of the cement and cannot effectively inhibit the occurrence and development of these harmful reactions, resulting in the expansion and cracking of the cement stone, an increase in the strength loss rate, and a decline in the resistance to sulfate attack.

[0055] In Comparative Example 2, the ethanol solution of ferulic acid was not added. The ethanol solution of ferulic acid plays an important role in the modification process of magnesium slag. It can act as a surfactant and a dispersant to improve the dispersibility and adsorption of the Mg(H2PO4)2 aqueous solution on the surface of magnesium slag powder, enabling the Mg3(PO4)2 protective layer to form more uniformly and densely on the surface of magnesium slag powder particles. When the ethanol solution of ferulic acid is not added, the formation of the Mg(H2PO4)2 protective layer is not ideal, and the active sites on the surface of some magnesium slag powder particles are not fully exposed, resulting in a reduced degree of reaction with other raw materials during the calcination process, thereby affecting the formation and quality of mineral phases in the cement clinker. Due to the lack of the action of the ethanol solution of ferulic acid, the crystal morphology and growth mode of the cement hydration products will change, and the connection between crystals is not tight enough, leading to a slight decrease in the strength of the cement stone. In terms of resistance to sulfate erosion, due to the slight change in the internal structure of the cement stone, the sulfate solution is more likely to penetrate into the interior of the cement stone and react with the components of the cement stone. Although this effect is relatively small, it will still cause a decrease in the sulfate erosion resistance performance.

[0056] In Comparative Example 3, the concentration of the ethanol solution of ferulic acid was 15 wt%, and the addition amount was 10% of the mass of magnesium slag powder. An ethanol solution of ferulic acid with too high a concentration will form an overly thick adsorption layer on the surface of magnesium slag powder. Although this adsorption layer can protect magnesium slag powder to a certain extent, it will hinder the full reaction of the Mg(H2PO4)2 aqueous solution with magnesium slag powder, inhibiting the formation process of the Mg3(PO4)2 protective layer and resulting in insufficient formation amount and non-ideal structure of the protective layer. During the calcination process, the overly thick adsorption layer will decompose to produce some gases and other by-products, which will form tiny pores and defects inside the cement clinker, affecting the microstructure of the cement clinker. These changes in the microstructure have a negative impact on the strength and erosion resistance of the cement. The presence of pores will reduce the density of the cement stone, making the cement stone more vulnerable to external erosion media (such as sulfate solution).

[0057] In Comparative Example 4, the concentration of the Mg(H₂PO₄)₂ aqueous solution was 15 wt%, and the addition amount was 20% of the mass of the magnesium slag powder. An Mg(H₂PO₄)₂ aqueous solution with too high a concentration and addition amount would cause too much Mg₃(PO₄)₂ to form on the surface of the magnesium slag powder. Too much Mg₃(PO₄)₂ would form an overly dense protective layer on the surface of the magnesium slag powder. Although this dense protective layer could protect the magnesium slag powder to a certain extent, it would seriously hinder the chemical reaction between the magnesium slag powder and other raw materials during the calcination process. Because chemical reactions require sufficient contact and material exchange between raw materials, the overly dense protective layer makes it difficult for other raw materials to react with the active components inside the magnesium slag powder, resulting in the inhibition of the formation of some important mineral phases (including calcium silicate, calcium aluminate, etc.) in the cement clinker. Too much Mg₃(PO₄)₂ would affect the release and migration of ions during the cement hydration process, interfering with the normal progress of the hydration reaction; it would affect the release rate and diffusion path of calcium ions, resulting in a decrease in the amount of hydration products such as C-S-H gel and a poor crystal form, thus reducing the strength of the cement stone. In terms of resistance to sulfate attack, due to the change in the mineral composition and structure inside the cement stone, the ability of the cement stone to resist sulfate attack decreases. The sulfate solution is more likely to react with the unstable components in the cement stone, generating more expansive products and accelerating the destruction of the cement stone, resulting in poor resistance to sulfate attack.

[0058] In Comparative Example 5, the modified magnesium slag powder was replaced with magnesium slag powder, and Mg₃(PO₄)₂ powder with a content of 0.5% of the mass of the magnesium slag powder was directly added. When directly dry-mixing and adding Mg₃(PO₄)₂ powder, it could not adhere tightly to the surface of the magnesium slag powder particles like the in-situ generated Mg₃(PO₄)₂ protective layer, and the distribution was uneven. Its performance was equivalent to that of unmodified magnesium slag powder.

[0059] In Comparative Example 6, the activated converter slag powder was replaced with converter slag powder. When the converter slag was not activated, its internal active components (including vitreous phase, some unstable mineral phases) were in a relatively stable state and were difficult to fully participate in the reaction during the cement clinker calcination process. During the calcination process, the chemical reaction degree between the unactivated converter slag and other raw materials (such as carbide slag, magnesium slag, etc.) was low, and it could not effectively promote the formation and optimization of mineral phases in the cement clinker, resulting in a decrease in the content of mineral phases that contribute effectively to the strength in the cement clinker. The unactivated converter slag had a weak ability to release active ions during the cement hydration process and could not provide sufficient promotion for cement hydration, resulting in a decrease in the amount of hydration products and a poor quality. It could not efficiently promote the growth and development of C-S-H gel, leading to a reduction in the strength of the cement stone. In terms of resistance to sulfate attack, due to the defects in the mineral composition and structure inside the cement stone, the ability of the cement stone to resist sulfate attack decreased. The unactivated converter slag could not effectively inhibit the harmful reaction between sulfate and the components in the cement stone, resulting in the cement stone being more likely to expand and crack.

[0060] In Comparative Example 7, the calcination temperature is 300°C. The calcination temperature is crucial in the activation process of converter slag. The calcination temperature of 300°C is too low to cause sufficient destruction and reorganization of the crystal structure inside the converter slag, nor to fully activate the active components in the converter slag. At a lower temperature, some chemical bonds in the converter slag fail to break, and the active sites cannot be fully exposed, resulting in limited improvement in the activity of the converter slag and a decline in various indicators.

[0061] In Comparative Example 8, Li2B4O7-CaF2 composite mineralizer is not added. Li2B4O7-CaF2 composite mineralizer plays an important mineralization role in the cement clinker calcination process. It can reduce the temperature of cement clinker mineral formation and promote the formation and development of various mineral phases. When the composite mineralizer is not added, the reaction between the raw materials during the cement clinker calcination process requires a higher temperature and a longer time to achieve the desired reaction degree. Under actual calcination conditions, due to the lack of the promotion effect of the mineralizer, the formation of some important mineral phases (including tricalcium silicate, tricalcium aluminate, etc.) is inhibited, resulting in a reduction in the content of these high-strength mineral phases in the cement clinker.

[0062] Due to the unsatisfactory mineral composition of cement clinker, the quantity and quality of hydration products generated during cement hydration are reduced. The production of major strength-contributing substances such as CSH gel is greatly reduced, and its loose structure makes cement paste more easily damaged when subjected to external forces, and its strength is greatly reduced. In terms of crack resistance, due to the increase in defects and unevenness in the internal structure of cement paste, microcracks are more likely to occur during the hardening process. These microcracks provide channels for corrosive media. In the sulfate corrosion test, sulfate solution is more likely to enter the interior of cement paste and react with the components in cement paste to generate a large amount of expansive products, causing cement paste to expand and crack, increase strength loss rate, and deteriorate crack resistance and sulfate corrosion resistance.

[0063] In Comparative Example 9, the composite mineralizer is entirely Li2B4O7. Li2B4O7 has different mechanisms of action in the composite mineralizer, and they need to cooperate with each other to achieve the best mineralization effect. When only Li2B4O7 is used, although it can reduce the temperature of the formation of cement clinker minerals to a certain extent, it cannot provide the unique effect brought by CaF2. CaF2 promotes the formation of certain mineral phases (including tricalcium silicate), changes the crystal form and size of the minerals, making the mineral crystals finer and more uniform, thus improving the microstructure of the cement stone. Without the effect of CaF2, the formation and development of cement clinker minerals are affected, and the quantity and quality of some important mineral phases decline, resulting in a reduction in the quality of the cement clinker. Due to the changes in the mineral composition and structure of the cement clinker, the formation and development of hydration products are also affected. The crystal form and growth mode of hydration products such as C-S-H gel change, and the connection between the crystals is not tight enough, causing the strength of the cement stone to decrease. In terms of resistance to sulfate attack, due to the defects in the microstructure of the cement stone, sulfate solutions are more likely to penetrate into the interior of the cement stone and react with the components of the cement stone, resulting in poor resistance to sulfate attack.

[0064] In Comparative Example 10, the composite mineralizer is entirely CaF2. Although CaF2 has a certain mineralization effect in the calcination of cement clinker, using it alone cannot fully replace the effect of the Li2B4O7-CaF2 composite mineralizer. Li2B4O7 regulates the properties of the liquid phase during the formation of cement clinker minerals, promotes the dissolution and recrystallization of certain mineral phases, and also has a certain regulating effect on properties such as the setting time of the cement. When only CaF2 is used, the lack of the synergistic effect of Li2B4O7 during the calcination of cement clinker leads to imperfect formation and development of mineral phases, and some minerals beneficial to strength and durability (including the optimized formation of calcium aluminate minerals) are affected, resulting in a reduction in the content of the effective strength-contributing phases in the cement clinker, and all indicators also decline.

[0065] In Comparative Example 11, the addition amount of the Li2B4O7-CaF2 composite mineralizer was 15 parts. When the addition amount of the composite mineralizer was excessive, although it could promote the formation of mineral phases to a certain extent, it would lead to an excessive amount of liquid phase and a change in the properties of the liquid phase during the calcination process of cement clinker. The excessive mineralizer would interfere with the crystallization process of some mineral phases, resulting in coarse and uneven mineral crystallization, and destroying the microstructure of cement clinker. It would cause the growth of tricalcium silicate crystals to be too large, and the bonding force between the crystals to be weakened, affecting the strength of the cement stone. Due to the change in the microstructure of cement clinker, the formation and development of hydration products were also affected. Although the hydration reaction would be accelerated at the initial stage due to the action of the mineralizer, in the later stage, due to structural defects, the connection between hydration products was not tight enough, resulting in a limited increase in the strength of the cement stone and a slight decrease in strength. In terms of resistance to sulfate erosion, due to the defects in the microstructure of the cement stone, sulfate solution was more likely to penetrate into the interior of the cement stone and react with the components of the cement stone, resulting in a slight reduction in the resistance to sulfate erosion.

[0066] In Comparative Example 12, there were 25 parts of carbide slag powder and 50 parts of modified magnesium slag powder. The change in the ratio of carbide slag to modified magnesium slag led to significant changes in the chemical composition and mineral composition of the raw material system. Carbide slag was the main raw material providing calcium, and its reduction would cause the supply of calcium element in cement clinker to be relatively insufficient, affecting the formation of important mineral phases such as calcium silicate and calcium aluminate. While the proportion of modified magnesium slag was too high, it would introduce excessive components such as magnesium element. If these components could not react and balance well with other components during the calcination process of cement clinker, it would lead to an unreasonable mineral composition of cement clinker. Due to the change in mineral composition, the process and products of the hydration reaction were affected. The insufficient calcium content would affect the formation of hydration products such as C-S-H gel, resulting in a decrease in its production amount and quality, thus reducing the strength of the cement stone. The unreasonable mineral composition made the internal structure of the cement stone uneven, and microcracks were more likely to occur during the hardening process. These microcracks became channels for erosion medium to enter. In the sulfate resistance test, sulfate solution was more likely to enter the interior of the cement stone and react with the components in the cement stone, resulting in a decrease in crack resistance and sulfate resistance.

[0067] In Comparative Example 13, there were 15 parts of activated converter slag powder and 5 parts of coal gangue powder. The change in the ratio of activated converter slag powder to coal gangue powder affected the chemical reactions and mineral formation during the calcination of cement clinker. If there was too much activated converter slag powder and too little coal gangue powder, the proportion of certain components in the raw material system would be unbalanced. Activated converter slag powder mainly provided some active components and trace elements, while coal gangue powder provided components such as silica. The imbalance in proportion would affect the formation of mineral phases in cement clinker, change the composition and structure of calcium silicate minerals, and was not conducive to the formation and stability of high-strength mineral phases. Due to the change in the mineral composition of cement clinker, the generation and development of hydration products were affected. The quantity and quality of hydration products such as C-S-H gel decreased, resulting in a reduction in the strength of the cement stone. Due to the imbalance in the ratio of activated converter slag powder to coal gangue powder, the internal microstructure of the cement stone became more complex and uneven. This non-uniformity would cause stress concentration and local damage more easily when the cement stone was subjected to external stress and erosion. During the anti-sulfate erosion process, the sulfate solution was more likely to penetrate along the weak parts of the structure, accelerating the erosion of the cement stone.

[0068] At the same time, the ratio change could also affect the stability of cement hydration products. When the content of coal gangue powder was insufficient, it could not provide enough silica components to form a stable C-S-H gel structure, weakening the anti-erosion ability of the gel body. And too much activated converter slag powder would introduce excessive active components, which were more likely to generate expansive products (including the secondary formation of ettringite) when reacting with sulfates. These expansive products would cause large expansive stresses inside the cement stone, promoting the expansion of microcracks, and thus reducing the strength of the cement stone and significantly decreasing its anti-sulfate erosion performance.

[0069] In Comparative Example 14, there were 25 parts of carbide slag powder, 50 parts of modified magnesium slag powder, 15 parts of activated converter slag powder, and 5 parts of coal gangue powder. The simultaneous change in the proportions of multiple raw materials caused a huge change in the chemical composition of the entire raw material system, seriously deviating from the appropriate ratio range. The reduction in carbide slag led to insufficient calcium source, unable to meet the demand for forming sufficient amounts of main mineral phases such as calcium silicate and calcium aluminate; the proportion of modified magnesium slag was too high, introducing excessive components such as magnesium elements, exceeding the balance tolerance of the system; too much activated converter slag powder and too little coal gangue powder further exacerbated the imbalance in the proportions of elements such as silicon, aluminum, and iron, causing the disorder in the mineral formation process of cement clinker and a serious decline in various properties.

[0070] In Comparative Example 15, SO2 was not introduced during the period of heat preservation calcination from 50 min to 70 min. The purpose of introducing SO2 is to induce the formation of a new three-phase system of calcium aluminosilicate - dicalcium silicate - spinel. When SO2 is not introduced, this special three-phase system cannot be efficiently formed, so that the mineral composition of the cement clinker is mainly limited to traditional silicate minerals and other conventional mineral phases. Compared with the cement clinker containing the new three-phase system, the cement clinker lacking this three-phase system has defects in mineral composition, and some mineral phases with special properties are missing, resulting in a decline in the overall performance of the cement clinker. During the cement hydration process, the calcium aluminosilicate - dicalcium silicate - spinel three-phase system can interact synergistically to promote the formation and development of strength-contributing phases such as C-S-H gel. Without this three-phase system, the quantity and quality of the cement hydration products are both affected. The amount of C-S-H gel formed decreases, and the crystal structure is not dense enough, making the cement stone more likely to be damaged when subjected to external forces. Some minerals (including spinel) in the calcium aluminosilicate - dicalcium silicate - spinel three-phase system have a certain resistance to sulfate attack and can inhibit the harmful reactions of sulfate ions with other components in the cement stone. The lack of these key anti-corrosion mineral phases in the cement stone makes it easier for the sulfate solution to react with components such as calcium hydroxide and tricalcium aluminate in the cement stone, resulting in a significant decline in the sulfate resistance performance.

Claims

1. A method for preparing cement clinker by using magnesium slag and carbide slag, characterized in that, It includes the following steps: S1: The carbide slag is dried and crushed to obtain carbide slag powder; S2: The magnesium slag is crushed to obtain magnesium slag powder, an aqueous solution of Mg(H2PO4)2 is added, an ethanol solution of ferulic acid is added, ball milling is carried out, and then drying is performed. A Mg3(PO4)2 protective layer is formed on the surface of the magnesium slag powder particles to obtain modified magnesium slag powder; S3: The converter slag is crushed to obtain converter slag powder, mixed with Na2CO3, and calcined to obtain activated converter slag powder; S4: The coal gangue is crushed to obtain coal gangue powder; S5: By mass, 50 parts to 60 parts of carbide slag powder, 25 parts to 30 parts of modified magnesium slag powder, 3 parts to 5 parts of activated converter slag powder, 12 parts to 15 parts of coal gangue powder and 5 parts to 8 parts of Li2B4O7-CaF2 composite mineralizer are mixed evenly, preheated at 800°C to 900°C for 20 min to 30 min, and at the same time, a CO2-H2O mixed gas is introduced; then heat preservation calcination is carried out at 1100°C to 1200°C for 2 h to 3 h, and 0.3 vol% to 0.5 vol% of SO2 is supplemented and introduced during the 50 min to 70 min period of heat preservation calcination to induce the formation of a new three-phase system of calcium aluminofeldspar-dicalcium silicate-spinel; after cooling, cement clinker is obtained.

2. The method for preparing cement clinker by using magnesium slag and carbide slag according to claim 1, wherein, In S1, the carbide slag is dried to a water content of less than 1 wt%; the particle size of the carbide slag powder is below 200 mesh to 250 mesh sieve.

3. A method for preparing cement clinker using magnesium slag and carbide slag according to claim 1, characterized in that, In S2, the concentration of the aqueous solution of Mg(H2PO4)2 is 3 wt% to 5 wt%; the addition amount of the aqueous solution of Mg(H2PO4)2 is 10% to 20% of the mass of the magnesium slag powder.

4. A method for preparing cement clinker using magnesium slag and carbide slag according to claim 1, characterized in that, In S2, the concentration of the ethanol solution of ferulic acid is 6 wt% to 8 wt%; the addition amount of the ethanol solution of ferulic acid is 5% to 10% of the mass of the magnesium slag powder.

5. A method for preparing cement clinker using magnesium slag and carbide slag according to claim 1, characterized in that, In S2, the particle size of the magnesium slag powder is below 250 mesh to 325 mesh sieve; the ball milling is carried out at a rotation speed of 15 r / min to 20 r / min for 1.5 h to 2 h; the diameter of the grinding balls used for ball milling is 8 mm to 15 mm, and the filling rate of the grinding balls is 30% to 40%; after drying, sieving is carried out to remove the grinding balls.

6. A method for preparing cement clinker using magnesium slag and carbide slag according to claim 1, characterized in that, In S3, the particle size of the converter slag powder is below 150 mesh to 200 mesh sieve; the addition amount of Na2CO3 is 4% to 6% of the mass of the converter slag powder; the calcination is carried out at 400°C to 500°C for 30 min to 40 min.

7. A method for preparing cement clinker using magnesium slag and carbide slag according to claim 1, characterized in that, In S4, the particle size of the coal gangue powder is below 200 mesh to 250 mesh sieve.

8. A method for preparing cement clinker using magnesium slag and carbide slag according to claim 1, characterized in that, In S5, the Li2B4O7-CaF2 composite mineralizer is a mixture of Li2B4O7 and CaF2 in a mass ratio of (1.5 to 3):(1 to 2); the volume ratio of the CO2-H2O mixed gas is CO2:H2O = (3 to 4):(1 to 1.2); the introduction amount of the CO2-H2O mixed gas is 0.8 L / min to 1.2 L / min per kilogram of the material.

9. A method for preparing cement clinker using magnesium slag and carbide slag according to claim 1, characterized in that, In S5, the MgO content in the cement clinker is ≤5 wt%; the SO3 content in the clinker is <1 wt%.

10. A method for preparing cement clinker using magnesium slag and carbide slag according to claim 1, characterized in that, The cement clinker is used in combination with an auxiliary agent, and the auxiliary agent includes, but is not limited to, gypsum powder accounting for 5wt% to 8wt% of the cement clinker, silica fume accounting for 2wt% to 4wt%, polyacrylamide accounting for 0.1wt% to 0.2wt%, and polycarboxylate superplasticizer powder accounting for 1wt% to 2wt%.

Images