Low-magnetism cement and industrial production process thereof

Abstract

The invention discloses low-magnetism cement and an industrial production process thereof, and belongs to the technical field of materials. The process comprises the following steps: S1, performing magnetic separation on each raw material, and then performing raw material proportioning; grinding the mixture obtained by burdening, performing magnetic separation again, homogenizing, preheating, and calcining in a rotary kiln; high-temperature clinker obtained through calcination directly enters a bleaching machine to be quenched, then enters a cooling machine to be subjected to forced air cooling and drying, and low-magnetism cement clinker is obtained; s2, after gypsum powder is ground, magnetism is detected, and if the requirement is met, low-magnetism gypsum powder is obtained; otherwise, carrying out magnetic separation until the requirements are met; preparing low-magnetism fly ash by the same method; s3, mixing the low-magnetism clinker, the low-magnetism gypsum powder, the low-magnetism fly ash and the functional additive to obtain a clinker mixture; and S4, grinding the clinker mixture, performing magnetic separation, and keeping the residual magnetic field intensity of the magnetically-separated cement in a 30mT magnetic field after continuous magnetization for 10s to be less than or equal to 10nT. The cement prepared by the industrial production process disclosed by the invention is low in magnetism and excellent in mechanical property, and can meet the strength requirement of engineering application.

Description

Technical Field

[0001] This invention belongs to the field of materials technology, specifically relating to a low-magnetic cement and its industrial production process. Background Technology

[0002] Cement, as a fundamental material in modern construction engineering, is widely used in various construction projects. However, conventional cement products are typically rich in ferromagnetic mineral components, such as ferric oxide and ferrous oxide. These substances may become magnetic under the influence of a magnetic field, leading to magnetic interference problems. With technological advancements, in recent years, higher demands have been placed on the magnetic concealment performance of buildings and structures in specialized fields such as marine engineering, defense engineering, and precision engineering. These structures not only need to avoid magnetic interference with the surrounding environment but also need to possess good concealment under existing magnetic detection technologies to address potential safety and functional risks. Based on these needs, the concept of low-magnetic cement has emerged and plays an important role in several key areas. Specifically:

[0003] (1) In marine engineering, the use of magnetic materials may interfere with the normal operation of navigation and detection equipment. Therefore, in projects such as submarine cable laying, pipeline construction, and offshore platforms, the use of low-magnetic cement can significantly reduce such interference and improve the reliability of facility operation. (2) In defense engineering, military facilities, especially those involving radar, communication equipment, and other magnetic field-sensitive devices, must minimize the impact of materials on the magnetic field to ensure the normal operation of the equipment and enhance the anti-attack capability of important underground facilities. Low-magnetic cement can be used in the construction of such facilities to effectively achieve magnetic concealment targets. (3) In the construction of scientific research infrastructure, for places involving high-precision magnetic field measurement or magnetic field control experiments, such as particle accelerators and nuclear magnetic resonance imaging (MRI) equipment laboratories, the use of low-magnetic cement can help maintain a stable magnetic field environment, thereby improving the accuracy and repeatability of experimental data. (4) In the manufacturing and installation of precision instruments, in the manufacturing and installation of precision instruments involving high-precision magnetic field control, the relevant infrastructure can be constructed using low-magnetic cement to ensure that the magnetic field environment required for its operation meets technical standards.

[0004] In conclusion, the research and application of low-magnetic cement not only meets the functional requirements of specific engineering fields, but also provides a new material solution for the technological upgrading of modern construction engineering.

[0005] Currently, research on low-magnetic cement is still in its early stages, and there are no publicly reported cases of large-scale industrial production of low-magnetic cement. This field remains largely unexplored. Therefore, developing a cement material with low magnetic properties and achieving its industrial-scale mass production has become a pressing technical problem for those skilled in the art. Summary of the Invention

[0006] The purpose of this invention is to provide an industrial production process for low-magnetic cement. Cement prepared by this method has low magnetic properties and excellent mechanical properties, which can meet the strength requirements of engineering applications.

[0007] The second objective of this invention is to provide a low-magnetic cement prepared by the above-mentioned industrial production process.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] The first aspect of this invention discloses an industrial production process for low-magnetic cement, comprising the following steps:

[0010] S1. Magnetic separation is performed on each raw material before raw material batching; the magnetically separated raw materials should meet the following conditions: the residual magnetic field strength after being magnetized in a 30mT magnetic field for 10 seconds is ≤10nT; and the iron oxide content in the raw material is ≤10nT.

[0011] ≤0.25WT%;

[0012] The mixture obtained from the batching process, i.e., the raw material mixture, is ground and then magnetically separated again. After homogenization and preheating, it is calcined in a rotary kiln.

[0013] The high-temperature clinker obtained from calcination is directly fed into a bleaching machine, where it is water-quenched and rapidly cooled at the feed end. Then it enters a cooling machine for forced air cooling and drying to obtain low-magnetic cement clinker.

[0014] S2. Magnetic testing of gypsum powder after grinding: If the residual magnetic field strength after being magnetized in a 30mT magnetic field for 10s is ≤10nT, then it meets the requirements and low-magnetic gypsum powder is obtained; otherwise, it is prepared by magnetic separation to meet the requirements; low-magnetic fly ash is prepared by the same method.

[0015] S3. Mix low-magnetic clinker, low-magnetic gypsum powder, low-magnetic fly ash and functional additives to obtain clinker mixture;

[0016] S4. After grinding the clinker mixture, the cement is qualified if it meets the following condition: the residual magnetic field strength after being magnetized in a 30mT magnetic field for 10s is ≤10nT.

[0017] In some embodiments of the present invention, in step S1, raw ore from mines and / or industrial waste are used as iron-based corrective materials, aluminum-based corrective materials, calcium-based raw materials, and silicon-based raw materials for cement calcination.

[0018] In some embodiments of the present invention, in step S1, the raw materials after magnetic separation are mixed in the following mass percentages: 75.0-85.0% calcium raw material, 10.0-20.0% silicon raw material, 3.0-6.0% iron correcting raw material, and 2.0-5.0% aluminum correcting raw material.

[0019] In some embodiments of the present invention, the raw materials are crushed, ground, and then water is added to form a slurry. The slurry is then subjected to multiple wet magnetic separations with increasing magnetic field strength. The separated powder slurry is then dried. Preferably, three wet magnetic separations are performed, with magnetic field strengths of 120-200 kA / m, 200-600 kA / m, and 600-2600 kA / m, respectively.

[0020] Preferably, the ground raw materials are mixed with 40-60% water by their own weight to form a slurry;

[0021] Preferably, the particle size of the crushed raw material is ≤5mm.

[0022] In this invention, a weak magnetic wet magnetic separator is first used for primary magnetic separation to preferentially remove high-grade magnetic minerals (magnetite, titanomagnetite, etc.), reducing the load on subsequent strong magnetic separation and avoiding excessive interference of the strong magnetic field on the weak magnetic minerals. The powder slurry that has undergone primary magnetic separation is then fed into a medium magnetic wet magnetic separator with a magnetic field strength of 200-600 kA / m for secondary magnetic separation to optimize the magnetic field gradient for the graded removal of magnetic materials. Finally, the powder slurry that has undergone secondary magnetic separation is fed into a strong magnetic wet magnetic separator with a magnetic field strength of 600-2600 kA / m for tertiary magnetic separation to separate fine-grained weak magnetic minerals (hematite, limonite, siderite, etc.) through a high-gradient magnetic field, thereby comprehensively improving the removal rate of magnetic materials.

[0023] The raw material mixture is ground and then subjected to two stages of dry magnetic separation; the magnetic field strengths are 120-200 kA / m and 600-2600 kA / m, respectively.

[0024] The high-temperature clinker obtained from calcination is rapidly cooled to 550-600°C by water quenching at the feed end of a bleaching machine, and then enters a cooling machine for forced air cooling and drying to obtain low-magnetic cement clinker.

[0025] In some embodiments of the present invention, in step S1, the homogenized raw material mixture is preheated to 750-820°C and then fed into a decomposition furnace;

[0026] Preferably, the homogenized raw material mixture is blown into a five-stage preheating and decomposition system to be preheated to 750-820°C, and then enters the decomposition furnace;

[0027] More preferably, the five-stage preheating decomposition system consists of five cyclones connected in series from C1 to C5. After the homogenized raw material mixture enters from C1, it is heated step by step through four cyclones, finally reaching 750-820°C at the C4 stage outlet, and then enters the decomposition furnace.

[0028] This invention first uses a dry magnetic separator to apply a weak magnetic field with an intensity of 120-200 kA / m to the raw material mixture powder for magnetic separation, with the aim of preferentially removing the high-grade magnetic minerals newly exposed after re-grinding; secondly, a strong magnetic field with an intensity of 600-2600 kA / m is applied to the raw material mixture powder for magnetic separation again, with the aim of further separating fine-grained weakly magnetic minerals.

[0029] In some embodiments of the present invention, the temperature of the decomposition furnace is maintained at 820-900°C, and the raw material mixture is kept in the decomposition furnace for 4-10 seconds in order to complete 85%-95% of the CaCO3 decomposition reaction.

[0030] In some embodiments of the present invention, the raw meal mixture that has been preliminarily decomposed in the decomposition furnace is fed into the rotary kiln. In the transition zone between the rotary kiln and the C5-grade cyclone separator, the temperature is controlled at 850-950°C. The raw meal mixture stays in the transition zone for 20-40 minutes to ensure that the CaCO3 decomposition efficiency is stable at over 90%.

[0031] Preferably, during calcination, the temperature of the raw material mixture rises from 950°C to 1450°C within 20–30 minutes, and is held at 1450°C for 20–40 minutes.

[0032] In some embodiments of the present invention, the magnetic separation in step S2 is a two-stage dry magnetic separation; the magnetic field strengths are 120-200 kA / m and 600-2600 kA / m, respectively.

[0033] In some embodiments of the present invention, step S4 involves multiple stages of dry magnetic separation based on magnetic field strength, from low to high.

[0034] Preferably, a dry magnetic separator is used for three-stage dry magnetic separation; the magnetic field strengths are 120-200 kA / m, 200-600 kA / m and 600-2600 kA / m respectively.

[0035] In some embodiments of the present invention, non-magnetic materials are used for material conveying in the process;

[0036] Ceramic ball media are used during grinding.

[0037] Preferably, in step S4, the clinker mixture is crushed by a tungsten carbide roller press and then ground.

[0038] In some embodiments of the present invention, the fineness of the powder after grinding the raw material mixture and the powder after grinding the clinker mixture is controlled to be 8-12% residue on a 0.08mm square hole sieve, preferably 10% or less than 1.0% residue on a 0.20mm hole sieve.

[0039] In some embodiments of the present invention, the exhaust air from the cooler is used as secondary air for the rotary kiln head and tertiary air for the decomposition furnace;

[0040] Preferably, the water vapor generated after the high-temperature clinker in the bleaching machine is sprayed with water is used to recover heat through a heat exchanger to preheat the cold air to above 200°C for use in coal mill drying.

[0041] The second aspect of the present invention discloses a low-magnetic cement produced using the above-described process.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] This invention is scientifically designed and ingeniously conceived. The cement prepared by the water-based production process of this invention has low magnetic properties and excellent mechanical properties, which can meet the strength requirements of engineering applications.

[0044] The method of this invention first performs graded crushing and grinding of mineral raw materials to effectively expose the naturally occurring magnetic substances in the minerals, laying the foundation for subsequent efficient separation.

[0045] In the wet processing stage, this invention employs wet-grade magnetic separation. By setting up three magnetic fields—weak, medium, and strong—not only can minerals with different magnetic properties be efficiently separated, but magnetic materials can also be recycled in a classified manner, significantly improving mineral utilization. This process also brings significant environmental benefits, such as reducing carbon emissions and promoting the comprehensive utilization of tailings.

[0046] To rapidly and accurately assess the magnetism of materials, this invention introduces a convenient method for measuring remanence. This method uses the magnetizing magnetic field strength and magnetization time as key variables, and directly determines the strength of the magnetism by measuring the material's remanence. The entire processing and measurement process takes only about 2 to 8 minutes, offering advantages such as convenience, speed, and efficiency, significantly saving the time and resources required for conventional magnetic measurements.

[0047] Meanwhile, to minimize the risk of ferrous impurities contaminating the final product during processing and affecting its magnetic properties, this invention implements strict iron-free contamination control at every stage of material transportation and handling. Specific measures include: using a tungsten carbide roller press for crushing, a ceramic media ball mill for grinding, using a canvas inclined chute for airflow conveying, and using a rubber belt for transport, ensuring that the material avoids contact with ferrous materials throughout the entire process.

[0048] In the dry processing stage, the dry magnetic separator also employs a gradient magnetic field. While ensuring the material's activity, this equipment can grade and magnetically separate residual magnetic minerals from the material, thereby effectively reducing the magnetic strength of the final product.

[0049] The clinker cooling process of this invention has also been specifically optimized. This invention adopts a cooling method combining a bleaching machine and a cooling machine: the water cooling stage can quickly reduce the clinker temperature and isolate air, effectively shortening the residence time of magnetic materials (such as γ-Fe2O3) in its generation temperature range; the subsequent waste heat air cooling combined with rapid drying helps to reduce the excessive hydration of active materials (such as C3A) in the clinker, ensuring product quality.

[0050] This cooling process also achieves efficient energy recovery and cascade utilization. The heat dissipated during the clinker water cooling process is recovered and used to dry the coal mill raw materials; while the heat dissipated in the air cooling process is used as secondary hot air for the kiln and tertiary hot air for the decomposition furnace, fully demonstrating the advantages of comprehensive energy utilization.

[0051] This invention successfully prepared a low-magnetic cement product that meets stringent magnetic performance requirements. After magnetization in a 30mT magnetic field for 10 seconds, the residual magnetism of this product is less than 10nT; after magnetization in a 12mT magnetic field for 10 seconds, the residual magnetism is also less than 10nT, and its low-magnetic characteristics are far superior to those of conventional products. Attached Figure Description

[0052] Appendix Figure 1 This is a flowchart of the production process of the present invention. Detailed Implementation

[0053] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. All kinds of raw materials used in the embodiments of the present invention should comply with the relevant provisions of the following standards: "Industrial By-product Gypsum for Cement" (GB / T 21271), "Lead-Zinc and Iron Tailings Powder for Cement and Concrete" (T / CECS10103-2020), "Silicon-Ferrous Blend for Cement Clinker Production" (T / CECS10133-2021), and "Specifications for Geological Exploration of Limestone and Dolomite, Cement Raw Material Minerals in Metallurgy and Chemical Industry" (DZ / T 0213-2002), etc.

[0054] Example 1

[0055] This embodiment discloses an industrial production method for low-magnetic cement of the present invention, specifically including the following steps:

[0056] Step (1). Raw material selection: Select and prepare mine raw ore and industrial waste that meet the relevant national standards as iron correction material, aluminum correction material, calcium raw material and silicon raw material for cement calcination; pre-treat each raw material, magnetically separate and magnetically test it before batching, as shown in steps (2) to (4).

[0057] Step (2). Raw material pretreatment: First, use a jaw crusher to crush the raw material obtained in step (1) to a particle size ≤ 5mm. Then, put the crushed granules into a horizontal closed sand mill for grinding. After grinding, put the powder into a vibrating screen for screening to ensure that the fineness of the powder is controlled at about 10% of the residue on a 0.08mm square hole screen or less than 1.0% on a 0.20mm hole screen to avoid over-grinding. Finally, the powder that meets the requirements is put into a wet premixing tank, and the granules that do not meet the requirements are returned to the horizontal closed sand mill for further grinding.

[0058] Step (3). Raw material magnetic separation: First, add 50% of the mass of water to the powder in the wet premixing tank and stir evenly to make a slurry; then send it to a weak magnetic wet magnetic separator with a magnetic field strength of 150kA / m for primary magnetic separation. The purpose is to remove high-grade magnetic minerals (magnetite, titanomagnetite, etc.) first, reduce the load of subsequent strong magnetic separation, and avoid excessive interference of strong magnetic field on weak magnetic minerals; then send the powder slurry that has completed primary magnetic separation to a medium magnetic wet magnetic separator with a magnetic field strength of 350kA / m for secondary magnetic separation. The purpose is to optimize the magnetic field gradient for graded removal of magnetic materials; then send the powder slurry that has completed secondary magnetic separation to a strong magnetic wet magnetic separator with a magnetic field strength of 1200kA / m for tertiary magnetic separation. The purpose is to separate fine-grained weak magnetic minerals (hematite, limonite, siderite, etc.) through a high gradient magnetic field, and comprehensively improve the removal rate of magnetic materials; finally, dry the powder slurry that has passed through the three-stage magnetic separation.

[0059] Step (4). Magnetic detection of raw materials: Apply a 30mT magnetic field to the dry raw materials obtained by three-stage magnetic separation in step (3) and continue for 10s. After the magnetic field is removed, immediately measure the magnetization remanence of the dry raw materials. If the magnetization remanence is ≤10nt, then classify and store them in different storage bins according to the raw material category; if the magnetization remanence is >10nt, return to step (1).

[0060] Step (5). Raw meal batching: The stored raw meal materials are batched by mass percentage using a rubber conveyor belt, with 82.0% calcium raw materials, 13.0% silica raw materials, 3.0% iron correcting raw materials, and 2.0% aluminum correcting raw materials. However, the total iron oxide content must be strictly controlled to ≤0.25% using a neutron-activated raw meal batching system. After grinding, the raw meal is homogenized in a homogenization silo to obtain cement raw meal.

[0061] Step (6). Raw material grinding: After the batching is completed, the raw material mixture is fed into the ceramic ball media vertical ball mill for grinding using a rubber belt. After grinding is completed, the resulting powder is fed into the classifier 1 to ensure that the fineness of the powder is controlled at about 10% of the residue on a 0.08mm square hole sieve or less than 1.0% of the residue on a 0.20mm hole sieve, to avoid over-grinding. Particles that do not meet the fineness requirements are put back into the ceramic mill for further grinding, while the raw material mixture powder that meets the fineness requirements is blown into the dry magnetic separator through the inclined airflow of the canvas material.

[0062] Step (7). Magnetic separation of raw meal powder: A fourth magnetic separation is performed on the raw meal mixture powder by applying a weak magnetic field with an intensity of 180 kA / m using a dry magnetic separator. The purpose is to preferentially remove the high-grade magnetic minerals newly exposed after the second grinding. Then, a fifth magnetic separation is performed on the raw meal mixture powder by applying a strong magnetic field with an intensity of 1800 kA / m. The purpose is to further separate fine-grained weak magnetic minerals.

[0063] Step (8). Raw material preheating: The raw material mixture powder that has completed the fifth magnetic separation is sent to the raw material homogenization silo via a rubber belt for further homogenization. After homogenization, the raw material mixture is blown into the five-stage preheating and decomposition system. The system consists of five cyclones connected in series from C1 to C5. After entering from C1, the raw material mixture is heated step by step through four cyclones, and finally reaches 750-820°C at the C4 stage outlet, and then enters the decomposition furnace.

[0064] Step (9). Clinker calcination: Fine coal powder is used as fuel to ensure that the temperature of the decomposition furnace is maintained at 820-900℃. The raw meal mixture only needs to stay in the decomposition furnace for 4-10 seconds to complete 85%-95% of the CaCO3 decomposition reaction (CaCO3→CaO3+CO2↑). The raw meal mixture that has completed the initial decomposition reaction is fed into the rotary kiln through C5. In the transition zone between the rotary kiln's firing zone and C5, it may undertake a small amount of decomposition work, and fine coal powder is still used as fuel. To provide heat to the rotary kiln, the transition zone temperature is maintained at 850–950℃. The raw meal mixture needs to remain in the transition zone for approximately 30 minutes to ensure that the CaCO3 decomposition efficiency remains stable above 90%. The decomposed raw meal mixture is then fed into the calcination zone of the rotary kiln, where fine coal powder continues to be used as fuel to provide heat. This ensures that the raw meal mixture temperature rises from 950℃ to 1450℃ within 25 minutes, and is held at 1450℃ for 30 minutes to obtain cement clinker. It is important to note that the supply of fine coal powder and the proportion of primary air should be adjusted in real time to control the flame length (4–6 m) and temperature distribution, avoiding localized overheating.

[0065] Step (10). Cement clinker cooling: The high-temperature clinker obtained from calcination, i.e., the high-temperature clinker exiting the kiln, is directly fed into the bleaching machine through the feeding chamber and rapidly cooled by water quenching at the feed end of the bleaching machine. A cold air valve is installed on the discharge hood of the bleaching machine to control the amount of cold air entering the bleaching machine. The temperature of the clinker exiting the bleaching machine is controlled at 550-600℃, and then it enters the cooler for forced air cooling. The residual air from the cooler is used as secondary air for the rotary kiln head and tertiary air for the decomposition furnace. After the air cooling is completed, the clinker needs to be further dried. It should be noted that a large amount of water vapor will be generated after the high-temperature clinker is sprayed with water in the bleaching machine. After this part of the water vapor is extracted, the cold air is preheated to above 200℃ through a heat pipe heat exchanger and used for drying in the coal mill (roller mill).

[0066] Step (11). Selection of low magnetic admixtures: The dried clinker is sent to the storage silo via a rubber belt. At the same time, the gypsum is ground using an air jet mill. The gypsum powder and fly ash admixtures are tested for magnetization remanence. If the residual magnetism after magnetization for 10s under a magnetic field strength of 30mt is <10nt, it meets the requirements for use and can be stored directly for later use. If the magnetization remanence index cannot be met, the gypsum powder and fly ash are subjected to secondary magnetic separation in step (7).

[0067] Step (12). Selection of demagnetizing additives: Purchase and store other demagnetizing mixtures such as citric acid, sodium dodecylbenzenesulfonate, and octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate.

[0068] Step (13). Cement batching: Clinker, gypsum powder, fly ash, and other demagnetizing admixtures are fed into the clinker batching system via a rubber conveyor belt. The system batches the clinker at a mass percentage of 70.0-85.0%, gypsum powder at 3.0-5.0%, fly ash at 1%-26.7%, and other demagnetizing admixtures at 0.3%-2%. The other demagnetizing admixtures are a premix of octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate: sodium dodecylbenzene sulfonate: citric acid = 1:2:1 (mass ratio).

[0069] Step (14). Cement grinding: The clinker mixture with the completed batching is fed into the tungsten carbide roller press through a rubber belt to crush the clinker particles. After crushing, the clinker mixture is fed into the ceramic ball media clinker mill for grinding. After grinding, the resulting powder is fed into the classifier 2 to ensure that the fineness of the powder is controlled at about 10% of the residue on the 0.08mm square hole sieve and less than 1.0% of the residue on the 0.20mm hole sieve to avoid over-grinding. The particles that do not meet the fineness requirements are put back into the ceramic mill for further grinding, while the clinker mixture powder (cement) that meets the fineness requirements is blown into the dry magnetic separator by the inclined airflow of the canvas material.

[0070] Step (15). Cement magnetic separation: The dry magnetic separator first applies a weak magnetic field with an intensity of 200 kA / m to the cement for the sixth magnetic separation, the purpose of which is to preferentially remove high-grade magnetic minerals present in the clinker; then, a medium magnetic field with an intensity of 600 kA / m is applied to the cement for the seventh magnetic separation, the purpose of which is to optimize the magnetic field gradient for the graded removal of magnetic materials, so as to remove magnetic materials in the cement more comprehensively; finally, a strong magnetic field with an intensity of 2600 kA / m is applied to the cement for the eighth magnetic separation, the purpose of which is to further separate fine-grained weakly magnetic minerals.

[0071] Step (16). Detection of remanent magnetization properties of cement: The cement that has completed magnetic separation is fed into a 30mT magnetic field via a rubber conveyor belt and continuously magnetized for 10s. After the magnetic field is removed, the remanent magnetization of the cement is measured immediately. The measurement results are shown in DC1 to DC3 in Table 1. It should be noted that if the remanent magnetization is >10nt, return to step (15); if the remanent magnetization is ≤10nt and meets the set index, the finished low-magnetic cement is obtained, and the low-magnetic cement is sent into the cement silo via a rubber conveyor belt for storage and later use.

[0072] Comparative Example 1

[0073] Comparative Example 1 uses a cement production method in the existing technology, as follows:

[0074] Step (1). Raw material batching: The existing calcium raw materials, silica raw materials, iron correcting materials and alumina correcting materials of ordinary silicate cement are batched according to the following mass percentages: calcium raw materials 82.0%, silica raw materials 13.0%, iron correcting materials 3.0% and alumina correcting materials 2.0%, respectively. The batches are then fed into a traditional steel ball media vertical ball mill for grinding. After grinding, the batches are homogenized in a homogenization silo to obtain cement raw materials.

[0075] Step (2). Clinker calcination: The raw material obtained in step (1) is fed into a rotary kiln for calcination. During clinker calcination, the calcination temperature is 1450℃ and the holding time is 30 minutes to obtain cement clinker. In addition, the clinker is cooled using a grate cooler.

[0076] Step (3). Cement grinding: The clinker and gypsum obtained in step (2) are fed into a traditional steel roller press and a vertical ball mill with steel ball media for grinding. After grinding, the cement is sent to the cement silo.

[0077] Step (4). Detection of remanent magnetic properties of cement magnetization: Three batches of finished cement products prepared using this comparative method were randomly selected, with a sampling base of 10m³ for each batch. 3Then, a magnetic field of 30 mT was applied to the cement using a building material magnetizer and magnetized for 10 seconds. After the magnetization time ended, residual magnetism was immediately tested using a building material magnetic detector. The measurement results are shown in Tables 1-3. It should be noted that the measurement accuracy of this building material magnetic detector is ≤0.01%, the signal noise is ≤0.3 nT, and the measurement range must be within ±100 μT.

[0078] Comparative Example 2

[0079] Compared with Example 1, steps (1) to (4) are the same in this comparative example, but the steps after raw material preparation are different, as follows:

[0080] Steps (1) to (4): Same as steps (1) to (4) in Example 1.

[0081] Step (5). Raw material batching: The stored raw materials are batched by means of a rubber belt, with the following mass percentages: 82.0% calcium raw material, 13.0% silica raw material, 3.0% iron correcting material, and 2.0% aluminum correcting material. However, the total iron oxide content must be strictly controlled to be ≤0.25% by a neutron-activated raw material batching system. After batching, the raw material mixture is fed into a ceramic ball media vertical ball mill for grinding using a rubber belt. After grinding, it is homogenized in a homogenization silo to obtain cement raw meal.

[0082] Step (6). Clinker calcination: The raw material obtained in step (5) is fed into a rotary kiln for calcination. During clinker calcination, the firing zone temperature is 1450℃ to obtain cement clinker. In addition, the clinker is cooled using a grate cooler.

[0083] Step (7). Cement grinding: The clinker and gypsum obtained in step (2) are fed into a traditional steel roller press and a vertical ball mill with steel ball media for grinding. After grinding, the mixture is sent to the cement silo.

[0084] Step (8). Detection of remanent magnetic properties of cement magnetization: Randomly select three batches of finished cement materials, with a sampling base of 10m for each batch. 3 Then, a magnetic field of 30mT strength was applied to the cement using a building material magnetizer and magnetized for 10 seconds. After the magnetization time ended, the residual magnetism was immediately tested using a building material magnetic detector. The measurement results are shown in Table 1, S1 to S3.

[0085] Comparative Example 3

[0086] Compared with Example 1, Comparative Example 3 has the same steps (1) to (9), but the steps after clinker firing are different. Specifically:

[0087] Steps (1) to (9): Same as steps (1) to (9) in Example 1;

[0088] Step (10): Cool the clinker using a grate cooler for later use.

[0089] Step (11). Cement grinding: The clinker and gypsum obtained in step (10) are fed into a tungsten carbide roller press and a ceramic ball media vertical ball mill for grinding in sequence using a rubber belt. After grinding, the mixture is sent to the cement silo.

[0090] Step (12). Detection of remanent magnetic properties of cement magnetization: Randomly select three batches of finished cement materials, with a sampling base of 10m for each batch. 3 Then, a magnetic field of 30mT strength was applied to the cement using a building material magnetizer and magnetized for 10 seconds. After the magnetization time ended, the residual magnetism was immediately tested using a building material magnetic detector. The measurement results are shown in Table 1, ST1 to ST3.

[0091] Comparative Example 4

[0092] Compared with Example 1, Comparative Example 4 has the same steps (1) to (9), but the steps after clinker firing are different. Specifically:

[0093] Steps (1) to (9): Same as steps (1) to (9) in Example 1;

[0094] Step (10): Cool the clinker using a grate cooler for later use.

[0095] Step (11) Cement batching: Clinker, gypsum powder, fly ash, and other demagnetizing admixtures are fed into the clinker batching system via a rubber conveyor belt. The system batches the clinker at a weight percentage of 70.0%–85.0%, gypsum powder at 3.0%–5.0%, fly ash at 10%–26.7%, and other demagnetizing admixtures at 0.3%–2%. It should be noted that the other demagnetizing admixtures are a premix of octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate: sodium dodecylbenzene sulfonate: citric acid = 1:2:1.

[0096] Step (12) Cement grinding: The clinker mixture obtained in step (11) is fed into a tungsten carbide roller press and a ceramic ball media vertical ball mill for grinding using a rubber belt. After grinding, it is sent to the cement silo.

[0097] Step (13) Detection of remanent magnetic properties of cement magnetization: Randomly select three batches of finished cement materials, with a sampling base of 10m for each batch. 3 Then, a magnetic field of 30mT strength was applied to the cement using a building material magnetizer and magnetized for 10 seconds. After the magnetization time ended, the residual magnetism was immediately tested using a building material magnetic detector. The measurement results are shown in Table 1, STS1-3.

[0098] Table 1. Remanence of cement magnetization after 10 s in a 30 mT magnetic field.

[0099]

[0100] In addition, physical inspections were conducted on three randomly selected batches of low-magnetic cement finished products, and the results are shown in Table 2.

[0101] Table 2. Physical inspection results of finished low-heat, low-magnetic cement.

[0102]

[0103] As shown in Tables 1 and 2, the low-magnetic cement prepared using the industrial production method of this invention exhibits excellent low-magnetic properties. After testing, it shows that after continuous magnetization in a 30mT magnetic field for 10 seconds, the residual magnetic field strength does not exceed 10nT. Further analysis of Table 1 reveals that multiple stages in the production process positively contribute to reducing the final magnetic properties of the cement. These include multi-stage magnetic separation of raw materials and clinker, grinding using ceramic balls as grinding media, material conveying using rubber belts and canvas chutes, rapid water cooling of the clinker, addition of other demagnetizing admixtures, and magnetic separation of the finished cement. Furthermore, the data in Table 2 shows that the 28-day compressive strength of this low-magnetic cement reaches or exceeds 42.5MPa, indicating excellent mechanical properties that meet the strength requirements for engineering applications.

[0104] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. An industrial production process for low-magnetic cement, characterized in that, Includes the following steps: S1. Magnetic separation of each raw material is performed before raw material batching; the raw materials after magnetic separation should meet the following conditions: the residual magnetic field strength after being magnetized in a 30mT magnetic field for 10s is ≤10nT; and the iron oxide content in the raw material is ≤0.25WT%. The mixture obtained from the batching process, i.e., the raw material mixture, is ground and then magnetically separated again. After homogenization and preheating, it is calcined in a rotary kiln. The high-temperature clinker obtained from calcination is directly fed into a bleaching machine, where it is water-quenched and rapidly cooled at the feed end. Then it enters a cooling machine for forced air cooling and drying to obtain low-magnetic cement clinker. S2. Magnetic testing of gypsum powder after grinding: If the residual magnetic field strength after being magnetized in a 30mT magnetic field for 10s is ≤10nT, then it meets the requirements and low-magnetic gypsum powder is obtained; otherwise, it is prepared by magnetic separation to meet the requirements; low-magnetic fly ash is prepared by the same method. S3. Mix low-magnetic clinker, low-magnetic gypsum powder, low-magnetic fly ash and functional additives to obtain clinker mixture; S4. After grinding the clinker mixture, magnetic separation is performed. The residual magnetic field strength of the separated cement after being magnetized in a 30mT magnetic field for 10 seconds should be ≤10nT.

2. The industrial production process of low-magnetic cement according to claim 1, characterized in that, In step S1, raw ore from the mine and / or industrial waste are used as iron-based corrective materials, aluminum-based corrective materials, calcium-based raw materials, and silicon-based raw materials for cement calcination.

3. The industrial production process of low-magnetic cement according to claim 1, characterized in that, In step S1, the raw materials after magnetic separation are mixed according to the following mass percentages: 75.0-85.0% calcium raw material, 10.0-20.0% silicon raw material, 3.0-6.0% iron correcting raw material, and 2.0-5.0% aluminum correcting raw material.

4. The industrial production process of low-magnetic cement according to claim 1, characterized in that, The ground raw materials are mixed with water to form a slurry, which is then subjected to multiple wet magnetic separations according to the magnetic field strength from low to high. The magnetically separated powder slurry is then dried. Preferably, three wet magnetic separations are performed, with magnetic field strengths of 120-200 kA / m, 200-600 kA / m, and 600-2600 kA / m, respectively. Preferably, the ground raw materials are mixed with 40-60% water by their own weight to form a slurry. The raw material mixture is ground and then subjected to two stages of dry magnetic separation; the magnetic field strengths are 120-200 kA / m and 600-2600 kA / m, respectively. The high-temperature clinker obtained from calcination is rapidly cooled to 550-600°C by water quenching at the feed end of a bleaching machine, and then enters a cooling machine for forced air cooling and drying to obtain low-magnetic cement clinker.

5. The industrial production process of low-magnetic cement according to claim 1, characterized in that, The magnetic separation described in step S2 is a two-stage dry magnetic separation; the magnetic field strengths are 120-200 kA / m and 600-2600 kA / m, respectively.

6. The industrial production process of low-magnetic cement according to claim 1, characterized in that, In step S4, multiple stages of dry magnetic separation are performed according to the magnetic field strength from low to high. Preferably, a dry magnetic separator is used for three-stage dry magnetic separation; the magnetic field strengths are 120-200 kA / m, 200-600 kA / m and 600-2600 kA / m respectively.

7. The industrial production process of low-magnetic cement according to any one of claims 1-6, characterized in that, In the aforementioned process, non-magnetic materials are used for material conveying. Ceramic ball media are used during grinding. Preferably, in step S4, the clinker mixture is crushed by a tungsten carbide roller press and then ground.

8. The industrial production process of low-magnetic cement according to any one of claims 1-6, characterized in that, The fineness of the powder after grinding the raw material mixture and the powder after grinding the clinker mixture is controlled to be 8-12% residue on a 0.08mm square hole sieve, preferably 10%, or less than 1.0% residue on a 0.20mm hole sieve.

9. The industrial production process of low-magnetic cement according to any one of claims 1-5, characterized in that, The exhaust air from the cooler is used as secondary air at the rotary kiln head and tertiary air in the decomposition furnace. Preferably, the water vapor generated after the high-temperature clinker in the bleaching machine is sprayed with water is used to recover heat through a heat exchanger to preheat the cold air to above 200°C for use in coal mill drying.

10. A low-magnetic cement, characterized in that, It is produced using the process described in any one of claims 1-9.

Images