A method for producing cement clinker from phosphogypsum-based calcium slag and its application

Abstract

This application relates to a method for producing cement clinker using phosphogypsum-based calcium slag and its application. The steps include: preparing raw materials; grinding and pressing the raw materials to obtain raw meal; calcining the raw meal to obtain cement clinker. The raw materials, based on 100% by weight, include: limestone: 40%~70%; sandstone: 3%~8%; fly ash: 5~10%; iron powder: 1%~6%; calcium slag: 5%~35%. In the calcium slag, the mass fraction of calcium oxide is ≥70%, the mass fraction of sulfur trioxide is ≤3.5%, the mass fraction of P2O5 is ≤3.5%, and the mass fraction of fluoride ions is ≤1.5%. The cement clinker obtained by this application has an f-CaO content ≤1.5% and a main mineral composition ratio of 83%~95%, which meets national standards and has significant resource-saving and environmental protection value.

Description

Technical Field

[0001] This application relates to the field of solid waste resource utilization technology, and in particular to a method for producing cement clinker using phosphogypsum to produce acid calcium slag and its application. Background Technology

[0002] The production of cement clinker is highly dependent on limestone, which typically accounts for about 86% of the raw meal mix. However, limestone, as a non-renewable resource, is facing the dual pressures of increasingly scarce resources and tightening environmental constraints. Meanwhile, the large accumulation of phosphogypsum solid waste generated by the phosphate chemical industry has caused serious environmental pollution and land resource occupation problems. Utilizing phosphogypsum to produce acid and co-produce cement is one of the effective ways to solve these problems; the calcium slag produced from phosphogypsum acid production can be used as a calcium-based raw material for cement clinker.

[0003] In existing technologies, using phosphogypsum to produce calcareous slag as a substitute for limestone suffers from poor batch compatibility. Traditional batching schemes are designed based on the compositional characteristics of limestone, while the composition of calcareous slag differs significantly from that of limestone. Existing technologies lack batching schemes tailored to the characteristics of calcareous slag, resulting in poor adaptability of the batching schemes and affecting the clinker firing quality.

[0004] Therefore, developing a batching method that precisely matches the characteristics of calcareous slag is of great significance for promoting the resource utilization of phosphogypsum and the green development of the cement industry. Summary of the Invention

[0005] The main objective of this application is to provide a method for producing cement clinker using phosphogypsum-based calcium slag and its application. The technical problem to be solved is how to ensure that the performance of cement clinker produced using phosphogypsum-based calcium slag meets the standards by designing a special formula, thereby making it more suitable for practical use.

[0006] The objective of this application and the technical problem it solves are achieved through the following technical solution. A method for producing cement clinker using phosphogypsum to produce calcareous slag, according to this application, includes the following steps:

[0007] Prepare raw materials;

[0008] The aforementioned raw materials are ground and then pressed into shape to obtain raw meal;

[0009] The aforementioned raw materials are calcined to obtain cement clinker;

[0010] Based on the aforementioned raw material quality as 100%, the aforementioned raw materials include:

[0011] Limestone: 40%~70%;

[0012] Sandstone: 3%~8%;

[0013] Fly ash: 5~10%;

[0014] Iron powder: 1%~6%;

[0015] Calcium residue: 5%~35%;

[0016] In the aforementioned calcareous slag, the mass fraction of calcium oxide is ≥70%, the mass fraction of sulfur trioxide is ≤3.5%, the mass fraction of P2O5 is ≤3.5%, and the mass fraction of fluoride ions is ≤1.5%.

[0017] The purpose of this application and the technical problems to be solved can also be further achieved by the following technical measures.

[0018] Preferably, in the aforementioned method for producing cement clinker from phosphogypsum-based calcium carbonate slag, the raw materials include:

[0019] Limestone: 55%~65%;

[0020] Sandstone: 4%~5%;

[0021] Fly ash: 9~10%;

[0022] Iron powder: 4.5%~5.5%;

[0023] Calcium residue: 5%~35%.

[0024] Preferably, in the aforementioned method for producing cement clinker from phosphogypsum-based calcium slag, the calcination temperature of the raw material is (1450±20)℃, and the calcination time is 20~60min.

[0025] Preferably, in the aforementioned method for producing cement clinker from phosphogypsum-based calcium carbonate slag, the raw materials include:

[0026] Limestone: 45%~60%;

[0027] Sandstone: 5.5%~6%;

[0028] Fly ash: 5.5%~6.5%;

[0029] Calcium residue: 5%~35%;

[0030] Bauxite: 4%~4.5%;

[0031] Iron powder: 1.5%~1.6%;

[0032] Fluorite: 0~0.4%

[0033] Anhydrite: 6.5%~7.5%.

[0034] Preferably, in the aforementioned method for producing cement clinker from phosphogypsum-based calcium slag, the calcination temperature of the raw material is (1300±20)℃, and the calcination time is 20~60min.

[0035] Preferably, in the aforementioned method for producing cement clinker from phosphogypsum-based calcium slag, the raw meal is ground to a fineness of 4%-5% residue on a 0.080mm square-hole sieve.

[0036] The purpose of this application and the technical problem solved therein are also achieved by the following technical solution. A cement clinker according to this application is prepared by any of the aforementioned methods. In the aforementioned cement clinker, by mass percentage, the content of f-CaO is ≤1.5%, the content of C3S is 57%~75%, and the total content of C3S, C2S, C3A, and C4AF is 83%~95%.

[0037] The purpose of this application and the technical problem it solves are also achieved by the following technical solution. A cement according to this application comprises the aforementioned cement clinker, wherein the 28-day compressive strength of the aforementioned cement is greater than 50 MPa.

[0038] The purpose of this application and the solution to its technical problems are also achieved by the following technical solutions: the application of the aforementioned cement clinker in the field of building materials.

[0039] By employing the above technical solution, the method for producing cement clinker using phosphogypsum-based calcium slag and its application, as described in this application, has at least the following advantages:

[0040] (1) By strictly limiting the total amount of P2O5 and the content of water-soluble P2O5 in calcareous slag, the formation of harmful crystalline phases is prevented from the source, ensuring the normal generation of major minerals such as C3S.

[0041] (2) Two innovative cement clinker formulations were designed for the characteristics of calcareous slag, including silicate cement clinker and calcium sulfoaluminate modified silicate cement clinker, which solved the problem of poor compatibility of traditional batching schemes.

[0042] (3) The f-CaO content of the cement clinker produced by the method of this application is far lower than the national standard (≤1.5%), and can be as low as 0.2%, which ensures the firing quality of the cement clinker.

[0043] (4) The cement clinker produced by the method of this application has a main mineral composition (C3S, C2S, C3A, C4AF) content of 83% to 95% of the clinker, which meets the GB / T 21372-2008 standard and has the potential for stable industrial production.

[0044] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, the preferred embodiments of this application are described in detail below. Detailed Implementation

[0045] To further illustrate the technical means and effects adopted by this application to achieve its intended purpose, the following, in conjunction with preferred embodiments, details the specific implementation methods, structures, features, and effects of a method for producing cement clinker from phosphogypsum-based calcium slag according to this application. In the following description, different "embodiments" or "embodiments" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable manner.

[0046] This application discloses a method for producing cement clinker using phosphogypsum to produce acid calcareous slag, the steps of which include:

[0047] Step 1: Prepare the raw materials

[0048] Based on the raw material mass of 100%, the raw materials include: limestone: 40%~70%; sandstone: 3%~8%; fly ash: 5%~10%; iron powder: 1%~6%; and calcareous slag: 5%~35%. The calcareous slag in this application is a product obtained during the low-temperature decomposition of phosphogypsum to produce sulfuric acid, with calcium oxide as the main component, referred to as phosphogypsum-based sulfuric acid calcareous slag, or simply calcareous slag, with a calcium oxide mass fraction ≥70%.

[0049] The calcium residue from phosphogypsum acid production contains trace elements such as P2O5, S, and F. The mass fraction of SO3 in the calcium residue is strictly limited to ≤3.5%, the mass fraction of P2O5 is ≤3.5%, and the mass fraction of fluoride ions is ≤1.5% to avoid the impurities from adversely affecting the clinker performance.

[0050] Trace amounts of sulfur trioxide can delay cement setting and increase its strength. It can also act as a mineralizer during cement calcination, helping to lower the temperature at which the liquid phase appears, promote the formation of tricalcium silicate, accelerate cement calcination, and save energy. However, excessive sulfur trioxide will react with tricalcium aluminate to form more ettringite, causing volume expansion and compromising stability. When the SO3 content in the raw meal ranges from 0% to 1.5%, the f-CaO content in the cement clinker gradually decreases, and sulfur significantly improves burnability and lowers the clinker's firing temperature. When the SO3 content in the raw meal is greater than 1.5%, both compressive and flexural strength decrease significantly with increasing SO3 content, with a maximum reduction of 10% at 28 days. In silicate cement clinker, when the SO3 content is less than 1.8%, it significantly promotes the growth of alite crystals, which is beneficial for the formation of large crystal particles. In calcium sulfoaluminate modified silicate cement clinker, an SO3 content of 1.8% to 3.5% is conducive to the formation of anhydrous calcium sulfoaluminate 4CaO·3Al2O3·SO3. In this application, the SO3 mass fraction of the calcareous slag is limited to ≤3.5%, and more preferably, the SO3 mass fraction of the calcareous slag is ≤1.8%.

[0051] When the P2O5 content in cement raw materials increases, it preferentially replaces SiO2 in C3S through solid solution, inhibiting the formation of allite crystals, leading to a decrease in early clinker strength and a prolonged setting time. When the P2O5 content in the raw meal exceeds approximately 0.5%, the C3S content decreases, while the C2S content increases, resulting in a 5%–10% decrease in 28-day compressive strength. Generally, the P2O5 content in the raw meal is controlled at ≤0.8% to maintain clinker performance and cement stability. When the P2O5 content in the raw meal ranges from 0% to 0.9%, the f-CaO content in the clinker gradually decreases, phosphorus significantly improves burnability, and lowers the clinker's firing temperature. When the P2O5 content in the raw meal exceeds 0.9%, with increasing P2O5 content, the clinker setting time gradually lengthens, and early strength, especially compressive strength, decreases significantly, while later strength remains relatively consistent. Taking a calcareous slag content of 30% as an example, when the P2O5 content in the calcareous slag is less than 1%, the clinker compressive strength is slightly higher than that of the blank sample; while when the P2O5 content in the calcareous slag is 2%, the clinker compressive strength is basically the same as that of the blank sample. In this application, the mass fraction of P2O5 in the calcareous slag is limited to ≤3.5%, and more preferably, the mass fraction of P2O5 in the calcareous slag is limited to ≤1.6%.

[0052] Fluoride ions (F) in cement raw materials - During calcination, a low-melting-point eutectic is formed, with an appropriate amount of F. - (0.2%~0.4%) can lower the clinker formation temperature, promote C3S formation, and improve early strength; when F -When the concentration exceeds 1%, the liquid phase viscosity increases sharply, hindering C3S crystal development, leading to decreased clinker strength in the later stages, abnormal setting time, and a tendency to form rings and crusts within the kiln. Therefore, F in limestone raw materials... - The typical limit is ≤0.6%. When the fluoride ion content in the raw meal ranges from 0% to 0.24%, the f-CaO content in cement clinker gradually decreases, and fluoride significantly improves burnability and lowers the clinker's firing temperature. As the fluoride ion content increases, the strength of the cement clinker decreases. When the fluoride ion content in the raw meal is less than 0.1%, the compressive strength of the cement clinker is not significantly different from the blank sample; however, when the fluoride ion content in the raw meal is 0.2%, the compressive strength of the cement clinker is lower than the blank sample. Considering that the mineralization effect of fluoride ions can significantly reduce the clinker firing temperature and effectively reduce the standard coal consumption for clinker, and considering that the maximum amount of calcareous slag replacing limestone raw materials is 30%, the fluoride ion content of the calcareous slag is specified to be no more than 0.4%.

[0053] Preferably, the loss on ignition (LOI) of the calcareous slag should not exceed 1.0%. Excessive LOI in the calcareous slag indicates a higher content of sulfates, organic matter, or bound water in components such as calcium oxide. This necessitates additional heat absorption during decomposition in the kiln, lowering the clinker formation temperature and reducing the liquid phase content. This results in insufficient C3S formation, decreased early strength, and increased fly ash, ring formation, and energy consumption due to the escape of decomposition gases. Calcium slag is a product obtained from the low-temperature (1100℃) decomposition of phosphogypsum to produce sulfuric acid, and its LOI is generally low. According to experimental results, the LOI of calcareous slag obtained from phosphogypsum sulfuric acid production varies between 0% and 1% in different regions.

[0054] Preferably, the moisture content of the calcareous slag should not exceed 1.0%. Excessive moisture content in cement raw materials will reduce the grinding efficiency of raw materials and increase the energy consumption for conveying and homogenization. After entering the kiln, the evaporation of moisture will absorb heat, causing the temperature of the firing zone to drop and the amount of liquid phase to decrease, which will hinder the formation of C3S, reduce the strength of clinker, make it easy for the kiln tail to form a crust, and limit the output.

[0055] During the batching process, each raw material is batched according to the set proportions and measured using a weighing meter with a measurement accuracy of 0.01g to ensure the accuracy of the batching. Afterwards, a test ball mill is used to grind the batched raw materials to a fineness of 4%~5% residue on a 0.080mm square-hole sieve to ensure the uniformity and reactivity of the raw materials.

[0056] Step 2: Prepare raw materials

[0057] Add 7% to 10% water by weight of the aforementioned raw materials and mix evenly. Press the mixture into shape under a pressure of 20 to 30 MPa, and then dry it at 105±5℃ for more than 60 minutes to ensure that the moisture content meets the requirements of the subsequent firing process, thus obtaining raw material.

[0058] Step 3: Firing Control

[0059] The dried raw meal is placed on a platinum sheet and calcined in a muffle furnace. After calcination, it is quickly removed and rapidly cooled with a fan to obtain cement clinker. By mass percentage, the aforementioned cement clinker contains ≤1.5% f-CaO, 57%~75% C3S, and a total content of 83%~95% for C3S, C2S, C3A, and C4AF. Cement made from the aforementioned cement clinker exhibits a 28-day compressive strength greater than 50 MPa, meeting the quality requirements.

[0060] Preferably, the aforementioned raw materials include: limestone: 55%~65%; sandstone: 4%~5%; fly ash: 9%~10%; iron powder: 4.5%~5.5%; and calcareous slag: 5%~35%. Under this formulation, the calcination temperature of the raw meal is (1450±20)℃, and the calcination time is 20~60min. This formulation can improve the C3S content in ordinary silicate cement clinker, thereby increasing the strength of the cement clinker.

[0061] Preferably, the aforementioned raw materials include: limestone: 45%~60%; sandstone: 5.5%~6%; fly ash: 5.5%~6.5%; calcareous slag: 5%~35%; bauxite: 4%~4.5%; iron powder: 1.5%~1.6%; fluorite: 0~0.4%; and anhydrite: 6.5%~7.5%. Under this formulation, the calcination temperature of the raw meal is (1300±20)℃, and the calcination time is 20~60min. This formulation can improve the burnability of calcium sulfoaluminate modified silicate cement clinker and reduce the difficulty of calcination.

[0062] This application proposes a type of cement comprising the aforementioned cement clinker, wherein the 28-day compressive strength of the aforementioned cement is greater than 50 MPa.

[0063] The aforementioned application of cement clinker in the field of building materials is presented in this application.

[0064] The present application will be further described below with reference to specific embodiments, but this should not be construed as a limitation on the scope of protection of the present application. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present application are still within the scope of protection of the present application.

[0065] Unless otherwise specified, all materials and reagents mentioned below are commercially available products well known to those skilled in the art; unless otherwise specified, all methods described are methods known in the art. Unless otherwise defined, the technical or scientific terms used should have the ordinary meaning understood by one of ordinary skill in the art to which this application pertains.

[0066] In the following examples, calcareous slag produced by the phosphogypsum acid production line was used, and its composition is shown in Table 1. In the following examples and comparative examples, the compositions of limestone, sandstone, fly ash, and iron powder are shown in Table 2. All raw materials were dried and ground to meet the required fineness.

[0067] Table 1. Chemical composition of calcareous slag (wt%)

[0068]

[0069] Table 2 Chemical composition of cement raw materials (unit: wt%)

[0070]

[0071] In the following examples and comparative examples, KH, SM, IM, PM, and K represent the percentage values ​​of cement clinker. KH is the lime saturation coefficient; SM is the silica ratio; IM is the aluminum ratio; PM is the phosphoric acid ratio; and K is the alkalinity coefficient.

[0072] In the following examples and comparative examples, the raw meal content refers to the mass fraction of calcareous slag in the raw meal. Substitution content = mass of calcareous slag / (mass of calcareous slag + mass of limestone).

[0073] Example 1:

[0074] This embodiment provides a silicate cement clinker produced from phosphogypsum-based calcium slag, its preparation method, and its application.

[0075] Ingredients: According to the ingredient ratio in Table 3, accurately weigh 1000g of calcareous slag 1, limestone, sandstone, fly ash, and iron powder to obtain the raw materials. The content of each component is expressed as a percentage by mass.

[0076] Table 3 Raw Material Formulation Scheme / %

[0077]

[0078] Raw material preparation: The prepared raw materials were put into a test ball mill and ground until 4.5% residue was found on a 0.080mm sieve. 80g of water was added and mixed well. The mixture was pressed into raw material with a diameter of 50mm under 25MPa and dried at 105℃ for 70 minutes.

[0079] Firing: The raw material is placed in a muffle furnace and heated to 1450℃ at a rate of 20℃ / min. The temperature is maintained for 1 hour. After being removed, it is immediately cooled by a fan to obtain silicate cement clinker.

[0080] The f-CaO content in the silicate cement clinker was found to be 0.147%. XRD analysis showed that the main mineral composition of the silicate cement clinker was C3S, C2S, C3A, and C4AF, with C3S accounting for 70.84% ​​and the total content of C3S, C2S, C3A, and C4AF being 96.06% (see Table 4 for details).

[0081] Table 4. Clinker Ratio and Potential Mineral Composition of Silicate Cement (%)

[0082]

[0083] Silicate cement clinker is mixed with gypsum to obtain silicate cement; the silicate cement clinker content is 95% based on 100% of the mass of silicate cement. Ordinary Portland cement is mixed with silicate cement clinker, sandstone, fly ash, etc.; the silicate cement clinker content is 80% based on 100% of the mass of ordinary Portland cement. The physical properties of silicate cement and ordinary Portland cement were tested, and the results are shown in Table 5.

[0084] Table 5 Physical properties of silicate cement and ordinary silicate cement in Example 1

[0085]

[0086] Example 2:

[0087] This embodiment provides a silicate cement clinker produced from phosphogypsum-based calcium slag, its preparation method, and its application.

[0088] Ingredients: According to the ingredient ratio in Table 6, accurately weigh 1000g of calcareous slag 2, limestone, sandstone, fly ash, and iron powder to obtain the raw materials. The content of each component is expressed as a percentage by mass.

[0089] Table 6 Raw Material Formulation Scheme / %

[0090]

[0091] Raw material preparation: The prepared raw materials were put into a test ball mill and ground until 4.5% residue was found on a 0.080mm sieve. 80g of water was added and mixed well. The mixture was pressed into raw material with a diameter of 50mm under 25MPa and dried at 105℃ for 70 minutes.

[0092] Firing: The raw material is placed in a muffle furnace and heated to 1450℃ at a rate of 20℃ / min. The temperature is maintained for 45 minutes. After being removed, it is immediately cooled by a fan to obtain silicate cement clinker.

[0093] The f-CaO content in the silicate cement clinker was found to be 0.188%. XRD analysis showed that the main mineral composition of the silicate cement clinker was C3S, C2S, C3A, and C4AF, with C3S accounting for 73.72% and the total content of C3S, C2S, C3A, and C4AF being 95.83% (see Table 7 for details).

[0094] Table 7. Clinker Ratio and Potential Mineral Composition of Silicate Cement (%)

[0095]

[0096] Silicate cement clinker is mixed with gypsum to obtain silicate cement; the silicate cement clinker content is 95% based on 100% of the mass of silicate cement. Ordinary Portland cement is mixed with silicate cement clinker, sandstone, fly ash, etc.; the silicate cement clinker content is 80% based on 100% of the mass of ordinary Portland cement. The physical properties of silicate cement and ordinary Portland cement were tested, and the results are shown in Table 8.

[0097] Table 8 Physical properties of silicate cement and ordinary silicate cement in Example 2

[0098]

[0099] Example 3:

[0100] This embodiment provides a method for preparing calcium sulfoaluminate modified silicate cement clinker produced from phosphogypsum-based calcium slag, and its application.

[0101] Ingredients: According to the ingredient plan in Table 9, accurately weigh 1000g of calcareous slag 3, limestone, sandstone, fly ash, bauxite, iron powder, fluorite, and anhydrite to obtain the raw materials. The content of each component is expressed as a percentage by mass.

[0102] Table 9 Raw Material Formulation Scheme / %

[0103]

[0104] Raw material preparation: The prepared raw materials were put into a test ball mill and ground until 4.5% residue was found on a 0.080mm sieve. 80g of water was added and mixed well. The mixture was pressed into raw material with a diameter of 50mm under 25MPa and dried at 105℃ for 70 minutes.

[0105] Firing: The raw material is placed in a muffle furnace and heated to 1320℃ at a rate of 20℃ / min. The temperature is maintained for 40 minutes. After being removed, it is immediately cooled by a fan to obtain calcium sulfoaluminate modified silicate cement clinker.

[0106] The f-CaO content in the calcium sulfoaluminate modified silicate cement clinker was found to be 0.15%. XRD analysis showed that the mineral composition of the calcium sulfoaluminate modified silicate cement clinker was mainly C3S, C2S, C3A, and C4AF, with C3S accounting for 64.46% and the total content of C3S, C2S, C3A, and C4AF being 83.94% (see Table 10 for details).

[0107] Table 10. Clinker ratio and potential mineral composition (%) of calcium sulfoaluminate modified silicate cement

[0108]

[0109] Cement was obtained by mixing calcium sulfoaluminate modified silicate cement clinker with sandstone, fly ash, etc.; the content of calcium sulfoaluminate modified silicate cement clinker was 80% based on the mass of cement (100%). The physical properties of calcium sulfoaluminate modified silicate cement clinker and cement were tested, and the results are shown in Table 11.

[0110] Table 11 Physical properties of calcium sulfoaluminate modified silicate cement clinker and cement in Example 3

[0111]

[0112] Example 4:

[0113] This embodiment provides a method for preparing calcium sulfoaluminate modified silicate cement clinker produced from phosphogypsum-based calcium slag, and its application.

[0114] Ingredients: According to the ingredient plan in Table 12, accurately weigh 1000g of calcareous slag 3, limestone, sandstone, fly ash, bauxite, iron powder, fluorite, and anhydrite to obtain the raw materials. The content of each component is expressed as a percentage by mass.

[0115] Table 12 Raw Material Formulation Scheme / %

[0116]

[0117] Raw material preparation: The prepared raw materials were put into a test ball mill and ground until 4.5% residue was found on a 0.080mm sieve. 80g of water was added and mixed well. The mixture was pressed into raw material with a diameter of 50mm under 25MPa and dried at 105℃ for 70 minutes.

[0118] Firing: The raw material is placed in a muffle furnace and heated to 1320℃ at a rate of 20℃ / min. The temperature is maintained for 35 minutes. After being removed, it is immediately cooled by a fan to obtain calcium sulfoaluminate modified silicate cement clinker.

[0119] The f-CaO content in the calcium sulfoaluminate modified silicate cement clinker was found to be 0.386%. XRD analysis showed that the mineral composition of the calcium sulfoaluminate modified silicate cement clinker was mainly C3S, C2S, C3A, and C4AF, with C3S accounting for 63.79% and the total content of C3S, C2S, C3A, and C4AF being 83.96% (see Table 13 for details).

[0120] Table 13 Clinker Ratio and Potential Mineral Composition (%) of Calcium Sulfoaluminate Modified Silicate Cement

[0121]

[0122] Cement was obtained by mixing calcium sulfoaluminate modified silicate cement clinker with sandstone, fly ash, etc.; the content of calcium sulfoaluminate modified silicate cement clinker was 80% based on the mass of cement (100%). The physical properties of calcium sulfoaluminate modified silicate cement clinker and cement were tested, and the results are shown in Table 14.

[0123] Table 14 Physical properties of calcium sulfoaluminate modified silicate cement clinker and cement in Example 4

[0124]

[0125] Comparative Example 1

[0126] Ingredients: Accurately weigh 1000g of calcareous slag, limestone, sandstone, fly ash, and iron powder according to the ingredient ratio in Table 15 to obtain the raw materials. The content of each component is expressed as a percentage by mass. The content of each component in the calcareous slag is shown in Table 16.

[0127] Table 15 Raw Material Formulation Scheme / %

[0128]

[0129] Table 16 Chemical composition of calcareous slag (wt%)

[0130]

[0131] Raw material preparation: The prepared raw materials were put into a test ball mill and ground until 4.5% residue was found on a 0.080mm sieve. 80g of water was added and mixed well. The mixture was pressed into raw material with a diameter of 50mm under 25MPa and dried at 105℃ for 70 minutes.

[0132] Firing: The raw materials are placed in a muffle furnace and heated to 1450℃ at a rate of 20℃ / min. The temperature is maintained for 50 minutes. After being removed, the materials are immediately cooled by a fan to obtain cement clinker.

[0133] Tests showed that the f-CaO content in the cement clinker was as high as 2.5%. The XRD analysis results are shown in Table 17.

[0134] Table 17 Clinker Ratio and Potential Mineral Composition of Silicate Cement (%)

[0135]

[0136] Cement clinker is mixed with gypsum to obtain silicate cement; the clinker content is 95% based on 100% of the mass of silicate cement. Ordinary Portland cement is mixed with silicate cement clinker, sandstone, fly ash, etc.; the clinker content is 80% based on 100% of the mass of ordinary Portland cement. Physical property tests on silicate cement and ordinary Portland cement revealed abnormal setting times and low early strength, as shown in Table 18.

[0137] Table 18 Physical properties of silicate cement and ordinary silicate cement in Comparative Example 1

[0138]

[0139] Comparative Example 2

[0140] Ingredients: Accurately weigh limestone, sandstone, fly ash, and iron powder according to the ingredient plan in Table 19, with a total mass of 1000g, to obtain the raw materials. The content of each component is expressed as a percentage by mass.

[0141] Table 19 Raw Material Proportioning Scheme / %

[0142]

[0143] Raw material preparation: The prepared raw materials were put into a test ball mill and ground until 4.5% residue was found on a 0.080mm sieve. 80g of water was added and mixed well. The mixture was pressed into raw material with a diameter of 50mm under 25MPa and dried at 105℃ for 70 minutes.

[0144] Firing: The raw materials are placed in a muffle furnace and heated to 1450℃ at a rate of 20℃ / min. The temperature is maintained for 45 minutes. After being removed, the materials are immediately cooled by a fan to obtain cement clinker.

[0145] Tests showed that the f-CaO content in the cement clinker was as high as 0.83%. The XRD analysis results are shown in Table 20.

[0146] Table 20 Clinker Ratio and Potential Mineral Composition of Silicate Cement (%)

[0147]

[0148] Cement clinker was mixed with gypsum to obtain silicate cement; the clinker content was 95% based on 100% of the mass of silicate cement. Ordinary Portland cement was obtained by mixing silicate cement clinker with sandstone, fly ash, etc.; the clinker content was 80% based on 100% of the mass of ordinary Portland cement. The physical properties of silicate cement and ordinary Portland cement were tested, and the results are shown in Table 21.

[0149] Table 21 Physical properties of silicate cement and ordinary silicate cement in Comparative Example 1

[0150]

[0151] In summary, the calcination method for producing cement clinker using phosphogypsum-based calcium slag provided in this application successfully overcomes the shortcomings of existing technologies through systematic raw material control, a dedicated batching scheme, and an optimized calcination process. It achieves high-value utilization of solid waste and stable production of cement clinker, and has extremely high industrial application value and environmental benefits.

[0152] The technical features in the claims and / or specification of this application can be combined, and the combination is not limited to the combinations obtained through reference in the claims. Technical solutions obtained by combining the technical features in the claims and / or specification are also within the scope of protection of this application.

[0153] The above description is merely a preferred embodiment of this application and is not intended to limit this application in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of this application shall still fall within the scope of the technical solution of this application.

Claims

1. A method for producing cement clinker using phosphogypsum to produce acid-calcium slag, characterized in that, The steps include: Prepare raw materials; The raw materials are ground and then pressed into shape to obtain raw material; The raw materials are calcined to obtain cement clinker; Based on the raw material mass of 100%, the raw material includes: Limestone: 40%~70%; Sandstone: 3%~8%; Fly ash: 5~10%; Iron powder: 1%~6%; Calcium residue: 5%~35%; In the calcareous slag, the mass fraction of calcium oxide is ≥70%, the mass fraction of sulfur trioxide is ≤3.5%, the mass fraction of P2O5 is ≤3.5%, and the mass fraction of fluoride ions is ≤1.5%.

2. The method according to claim 1, characterized in that, The raw materials include: Limestone: 55%~65%; Sandstone: 4%~5%; Fly ash: 9~10%; Iron powder: 4.5%~5.5%; Calcium residue: 5%~35%.

3. The method according to claim 2, characterized in that, The calcination temperature of the raw material is (1450±20)℃, and the calcination time is 20~60min.

4. The method according to claim 1, characterized in that, The raw materials include: Limestone: 45%~60%; Sandstone: 5.5%~6%; Fly ash: 5.5%~6.5%; Calcium residue: 5%~35%; Bauxite: 4%~4.5%; Iron powder: 1.5%~1.6%; Fluorite: 0~0.4% Anhydrite: 6.5%~7.5%.

5. The method according to claim 4, characterized in that, The calcination temperature of the raw material is (1300±20)℃, and the calcination time is 20~60min.

6. The method according to claim 1, characterized in that, The raw materials are ground to a fineness such that 4%-5% residue remains on a 0.080mm square-hole sieve.

7. The method according to claim 1, characterized in that, The raw materials are calcined and then cooled by air cooling to obtain cement clinker.

8. Cement clinker, prepared by the method according to any one of claims 1-7, wherein, by mass percentage, the content of f-CaO in the cement clinker is ≤1.5%, the content of C3S is 57%~75%, and the total content of C3S, C2S, C3A, and C4AF is 83%~95%.

9. A type of cement, characterized in that, It comprises the cement clinker of claim 8, wherein the cement has a 28-day compressive strength greater than 50 MPa.

10. The application of the cement clinker according to claim 8 in the field of building materials.

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