Preparation method of low-cost solid waste-based sulphoaluminate cement

Abstract

The invention discloses a preparation method of low-cost solid-waste-based sulphoaluminate cement, and relates to the technical field of cement preparation.The preparation method comprises the steps of solid waste pretreatment, ingredient design, raw material preparation, low-temperature calcination, clinker quenching and cement powdering.By means of the scheme design, high-aluminum / sulfur-rich solid waste such as red mud, desulfurized gypsum and fly ash is used for replacing 70% or above of natural raw materials, and the low-cost solid-waste-based sulphoaluminate cement is obtained; for example, expensive alumina, natural gypsum and the like, the cost of the raw materials can be directly reduced by more than 40%. Wherein the red mud is used as the waste residue of the aluminum oxide industry, the original treatment cost is very high, and the red mud is converted into an effective aluminum source nowadays, so that negative-cost raw material utilization is realized, and the waste residue treatment cost is also saved; the desulfurized gypsum is used as a power plant waste material to completely replace natural gypsum, so that the sulfur source cost is reduced by 60%. Through comprehensive calculation, the production cost of the clinker is reduced by 30-35% compared with that of the traditional sulphoaluminate cement.

Description

Technical Field

[0001] This invention relates to the field of cement preparation technology, specifically to a method for preparing low-cost solid waste-based sulfoaluminate cement. Background Technology

[0002] Sulfoaluminate cement (SAC) is widely used in special engineering fields due to its early strength, corrosion resistance, and good low-temperature adaptability. Traditional production processes mainly use bauxite, limestone, and natural gypsum as raw materials, calcined at 1350-1400℃. In recent years, to reduce costs and environmental pressures, some studies have attempted to incorporate solid waste to replace natural raw materials; however, due to the large fluctuations in the composition of solid waste and the presence of many harmful impurities, industrial application still faces significant bottlenecks.

[0003] However, the price of high-quality bauxite (Al2O3≥50%) in existing technologies is as high as 800-1000 yuan / ton, and the cost of natural gypsum accounts for more than 15% of the total raw material cost, resulting in the production cost of traditional SAC clinker being about 40% higher than that of silicate cement (OPC). Although attempts have been made to incorporate solid waste, the low activity and unstable composition of solid waste usually result in a substitution rate of less than 50%, which cannot substantially reduce costs. At the same time, the calcination temperature of traditional SAC is 1350-1400℃ (although slightly higher than the 1450℃ of OPC, it is still significant), and the heat consumption per unit clinker is ≥4000kJ / kg. In addition, the decomposition of limestone produces a large amount of CO2 (about 0.5 tons per ton of clinker), coupled with high fuel consumption, the carbon emission intensity is more than 20% higher than that of OPC.

[0004] Furthermore, harmful components in industrial solid waste such as red mud (alkali content 6-10%), phosphogypsum (P2O5 content 1-3%), and steel slag (composition fluctuation ±5%) can easily disrupt mineral formation. Existing batching technologies cannot effectively control the coagulation abnormalities caused by high-alkali red mud, and phosphates in phosphogypsum inhibit the formation of C4A3Š, leading to a decrease in clinker strength of more than 30%, thus forcing the solid waste content to be limited to within 50%.

[0005] Based on the above problems, a low-cost method for preparing solid waste-based sulfoaluminate cement is proposed to solve these problems. Summary of the Invention

[0006] In view of this, the technical problem to be solved by the present invention is to provide a low-cost method for preparing solid waste-based sulfoaluminate cement, so as to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing low-cost solid waste-based sulfoaluminate cement, comprising: S1, Solid waste pretreatment: The selected industrial solid waste is treated, including drying, crushing, grinding and impurity removal, so that the treated solid waste meets the requirements of subsequent batching and reaction. S2, Ingredient Design: Based on the target mineral composition (C4A3Š and C2S), calculate and optimize the proportions of each solid waste and supplementary raw material, and control the key rate values ​​(LSF, A / S, A / Si). S3, Raw material preparation: The pretreated solid waste is accurately weighed according to the design ratio, thoroughly mixed, and then ground to the required fineness; S4, Low-temperature calcination: Raw materials are calcined at a relatively low temperature of 1250-1350℃ in a rotary kiln or vertical kiln to promote the formation of target minerals; S5, Clinker Rapid Cooling: Rapidly cooling the high-temperature clinker after calcination to stabilize the mineral phase; S6, Cement Grinding: Cooled clinker is ground together with an appropriate amount of solid waste gypsum (such as desulfurized gypsum) and possible regulators to a specified fineness to produce finished cement.

[0008] Preferably, the mineral composition described in S2 includes anhydrous calcium sulfoaluminate (C4A3Š) and belite (C2S), and the key rate values ​​include: Lime saturation factor (LSF): LSF = CaO / (2.8 SiO2 + 1.18 Al2O3 + 0.65 Fe2O3 + 1.5 SO3-bound CaO). The lime saturation factor is between 0.8 and 1.0, which is lower than that of ordinary Portland cement (~0.9-1.0). This ensures that there is enough CaO to form C4A3Š and C2S, but without excessive formation of free lime (f-CaO).

[0009] Aluminum-sulfur ratio (A / S): A / S = Al2O3 / SO3 (mass ratio), which is the key to controlling the formation of C4A3Š. The mass ratio is 3.5-4.5. Too low a ratio will result in excess SO3, which may lead to the formation of too much anhydrite or delay the setting of solids; too high a ratio will result in insufficient formation of C4A3Š.

[0010] Aluminum-silicon ratio (A / Si): A / Si = Al2O3 / SiO2 (mass ratio), which affects the content and flammability of C2S. It is determined based on the target ratio of C4A3Š to C2S and the characteristics of the solid waste used. The optimal ratio of various solid wastes and supplementary raw materials is determined by using the chemical composition of the raw materials and the set target rate value, either through calculation software or manual calculation.

[0011] As a preferred embodiment, S4 specifically includes: S4.1 Calcination equipment: Rotary kilns are mainly used (wet, semi-dry or dry preheating and predecomposition kilns are all acceptable, with dry kilns being more energy-efficient), and mechanized vertical kilns can also be used (which have higher requirements for scale and technical control).

[0012] S4.2, Calcination Temperature: The calcination temperature should be controlled between 1250°C and 1350°C. This is significantly lower than the approximately 1450°C required for ordinary Portland cement (OPC). Excessively high temperatures (>1400°C) will cause the decomposition of the key mineral C4A3Š (C4A3Š → C3A + CaO + SO2↑).

[0013] S4.3, Calcination atmosphere: Maintain a weakly oxidizing or neutral atmosphere.

[0014] S4.4, Holding time: Sufficient time (usually 20-60 minutes) is required at the target temperature to ensure complete reaction of raw materials and full formation of C4A3Š and C2S.

[0015] S4.5, Mineralizing Agent Role: Certain components in solid waste (such as Fe2O3, CaF2, P2O5, etc.) may act as mineralizing agents, reducing the temperature and viscosity of the liquid phase, promoting mineral formation, and helping to achieve good calcination at lower temperatures.

[0016] As a preferred embodiment, S5 specifically includes: S5.1 Cooling equipment: mainly adopts high-efficiency grate coolers, including push-type, reciprocating type or third-generation controlled flow grate coolers.

[0017] S5.2 Cooling requirements: Rapidly cool from the calcination temperature of 1250-1350°C to the ambient temperature, and cool the high-temperature clinker to below 600°C within 6-10 minutes.

[0018] To prevent C4A3Š decomposition: During slow cooling, C4A3Š will decompose into C3A, CaO and gaseous SO2.

[0019] Maintaining C2S activity: Slow cooling will cause the hydraulically active γ-C2S to transform into the hydraulically inactive β-C2S or even inert γ-C2S. Rapid cooling can freeze it in the highly active β-C2S crystal form.

[0020] Improved grindability: Rapid cooling generates internal stress and microcracks in the clinker, which helps with subsequent grinding.

[0021] Heat recovery: The high-temperature hot air discharged from the grate cooler can be used to dry raw materials or generate electricity.

[0022] Compared with existing technologies, the present invention provides a low-cost method for preparing solid waste-based sulfoaluminate cement, which has the following advantages: I. Significantly reduced raw material costs, resulting in substantial economic benefits: By using high-alumina / sulfur-rich solid wastes such as red mud, desulfurized gypsum, and fly ash to replace more than 70% of natural raw materials, including expensive bauxite and natural gypsum, raw material costs can be reduced by more than 40%. Red mud, a waste residue from the alumina industry, originally had high treatment costs; now, it is transformed into an effective aluminum source, achieving "negative cost" raw material utilization and saving on waste disposal fees. Desulfurized gypsum, a power plant waste, completely replaces natural gypsum, reducing sulfur source costs by 60%. Overall, clinker production costs are reduced by 30% to 35% compared to traditional sulfoaluminate cement. II. Significant Energy Conservation and Emission Reduction Effects: This production method lowers the calcination temperature to 1250-1350℃, while traditional silicate cement requires 1450℃, and traditional SAC (Solid Cement) is approximately 1350-1400℃. Combined with mineralizing agents in solid waste, such as Fe2O3 from steel slag, energy consumption can be further reduced. This results in a 20%-25% reduction in calcination energy consumption. Actual measurements show that the heat consumption per unit clinker is ≤3100kJ / kg, compared to ≥4000kJ / kg with traditional processes. Simultaneously, CO2 emissions are reduced by 30%, partly due to lower fuel consumption from low-temperature calcination and partly because the utilization of solid waste avoids limestone decomposition emissions. It's worth noting that each ton of limestone decomposition releases approximately 0.44 tons of CO2. III. Enhanced process adaptability and high solid waste compatibility: An innovative "multi-solid-waste co-processing" technology was developed, which solves the problem of composition fluctuation by controlling the ratio values ​​(A / S, LSF, A / Si), and is compatible with the challenges of high alkalinity in red mud and phosphorus content in phosphogypsum. After pretreatment of red mud by "water washing and dealkalization + low-temperature calcination", the alkali content (Na2O+K2O) is reduced from 6% to <1%, avoiding abnormal cement setting. When desulfurized gypsum is used directly, the "calcination-rapid cooling" process suppresses the agglomeration problem caused by the dehydration of dihydrate gypsum. In addition, the solid waste utilization rate reaches 80%~85%, while the traditional process is ≤50%, and the composition fluctuation tolerance is improved by ±2%. When Al2O3 fluctuates, it can be compensated by dynamically adjusting the steel slag / limestone. Attached Figure Description

[0023] Figure 1 This is a flowchart illustrating the steps of a low-cost solid waste-based sulfoaluminate cement preparation method according to the present invention. Detailed Implementation The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0025] For an example, please refer to... Figure 1 As shown: To address the problems mentioned in the technical solutions, this application provides a low-cost method for preparing solid waste-based sulfoaluminate cement. Step 1: Solid waste pretreatment; First, continue the process of dealkalizing the red mud. Take 500g of red mud and add deionized water at a solid-liquid ratio of 1:5. Stir for 30 minutes, then let it stand to settle. Discard the supernatant. Repeat this operation three times. Next, dry the treated red mud at 105℃ for 24 hours, then ball mill it at 45 rpm for 2 hours until the red mud particles reach a residue of ≤10% on an 80μm sieve. Then, the desulfurized gypsum was dried at 80°C for 12 hours until the moisture content was <1%. After that, it was ball-milled to ensure that the residue on the 80μm sieve was ≤5%. Further activation of the steel slag was initiated by placing the steel slag in a calcination device and heating it to 800°C at a heating rate of 10°C / min. The slag was then calcined at this temperature for 1 hour. After calcination, the slag was subjected to rapid cooling and then ball-milled until the residue on an 80μm sieve was ≤15%. Step 2: Ingredient design and calculation; The target mineral composition must meet the following requirements: C4A3Š≥55%, C2S 25-30%; the ratio value should be controlled as follows: aluminum-sulfur ratio (A / S) 3.8–4.0, lime saturation coefficient (LSF) 0.90, and aluminum-silicon ratio (A / Si) 4.5. Example of ingredient calculation (based on 1000g of raw material): 350g red mud (providing Al2O3), 200g desulfurized gypsum (providing SO3), 150g fly ash (providing SiO2 / Al2O3), 150g steel slag (providing CaO / Fe2O3), and 150g limestone (supplementing CaO). Step 3: Raw material preparation; Weigh each raw material according to the above formula, ensuring the weighing accuracy is within ±0.1g. Place the weighed raw materials in a mixer and mix at 60rpm for 1 hour. Add 5% water to the mixed raw materials to form raw material sheets with a diameter of 30mm × 5mm. Then dry them at 105℃ for 2 hours to prevent cracking during subsequent calcination. Step 4: Low-temperature calcination; Starting from room temperature, heat to 800°C at a rate of 10°C / min and hold at 800°C for 30 minutes (for decarburization); then heat from 800°C to 1300°C at a rate of 5°C / min and hold at 1300°C for 40 minutes. Air must be circulated through the high-temperature furnace at a flow rate of 1L / min to maintain a weakly oxidizing atmosphere; the raw material sheets must be placed in a corundum crucible and covered with raw material powder of the same proportion to prevent sticking. Step 5: Rapid cooling of clinker; After calcination, immediately remove the crucible and pour the red-hot calcined material onto a copper plate. Then, spray with liquid nitrogen (-196℃) to cool it until the temperature drops below 100℃ (cooling time must be <3 minutes). During the operation, asbestos gloves and a face mask must be worn to prevent heat burns. Step 6: Cement preparation and performance testing; The clinker was mixed with 6% desulfurized gypsum (ensuring a total SO3 content of approximately 2.5%) and ball-milled until the specific surface area reached 380±10 m². 2 / kg. Tested according to GB / T1346 standard method, the target value is initial setting ≥25min, final setting ≤3h; 3-day compressive strength tested according to GB / T17671 standard method, the target value is ≥40MPa; 28-day compressive strength tested according to GB / T17671 standard method, the target value is ≥60MPa; f-CaO content tested using the glycerol-ethanol method, the target value is ≤1.0%.

[0026] This solution has the following advantages over existing technologies: I. Raw material costs have been significantly reduced, resulting in significant economic benefits. By using high-alumina / sulfur-rich solid wastes such as red mud, desulfurized gypsum, and fly ash to replace more than 70% of natural raw materials, such as expensive bauxite and natural gypsum, raw material costs can be reduced by more than 40%. Red mud, a waste residue from the alumina industry, originally had high treatment costs; now, it is transformed into an effective aluminum source, achieving "negative cost" raw material utilization and saving on waste disposal fees. Desulfurized gypsum, a power plant waste, completely replaces natural gypsum, reducing sulfur source costs by 60%. Overall, clinker production costs are reduced by 30% to 35% compared to traditional sulfoaluminate cement. II. Significant Energy Conservation and Emission Reduction Effects This production method lowers the calcination temperature to 1250-1350℃, while traditional silicate cement requires 1450℃, and traditional SAC (Solid Cement) is approximately 1350-1400℃. Combined with mineralizing agents in solid waste, such as Fe2O3 from steel slag, energy consumption can be further reduced. This results in a 20%-25% reduction in calcination energy consumption. Actual measurements show that the heat consumption per unit clinker is ≤3100kJ / kg, compared to ≥4000kJ / kg with traditional processes. Simultaneously, CO2 emissions are reduced by 30%, partly due to lower fuel consumption from low-temperature calcination and partly because the utilization of solid waste avoids limestone decomposition emissions. It's worth noting that each ton of limestone decomposition releases approximately 0.44 tons of CO2. Third, it has stronger process adaptability and higher solid waste compatibility. An innovative "multi-solid-waste co-processing" technology was developed, which solves the problem of composition fluctuation by controlling the ratio values ​​(A / S, LSF, A / Si), and is compatible with the challenges of high alkalinity in red mud and phosphorus content in phosphogypsum. After pretreatment of red mud by "water washing and dealkalization + low-temperature calcination", the alkali content (Na2O+K2O) is reduced from 6% to <1%, avoiding abnormal cement setting. When desulfurized gypsum is used directly, the "calcination-rapid cooling" process suppresses the agglomeration problem caused by the dehydration of dihydrate gypsum. In addition, the solid waste utilization rate reaches 80%~85%, while the traditional process is ≤50%, and the composition fluctuation tolerance is improved by ±2%. When Al2O3 fluctuates, it can be compensated by dynamically adjusting the steel slag / limestone. IV. Superior product performance expands application scenarios The Fe2O3 and CaF2 components in the solid waste act as mineralizers, promoting the formation of highly active minerals (β-C2S, C4A3Š) at low temperatures, thereby improving the early strength of the cement. This cement has a 3-day compressive strength ≥40MPa, while the national standard ≥32.5 grade only requires 30MPa; its 28-day strength ≥60MPa. It exhibits outstanding rapid-hardening characteristics, with initial setting in 25-40 minutes and final setting in 1.5-2.5 hours, compared to ≥4 hours for traditional OPC, making it suitable for emergency repair projects. Simultaneously, its corrosion resistance is also improved. Due to the high proportion of low-calcium minerals (C2S) in the solid waste, its sulfate erosion resistance coefficient K ≥0.90, compared to ≤0.80 for traditional OPC. V. Achieving a win-win situation for both environmental and social benefits Based on a cement production capacity of 200,000 tons, each production line can handle up to 100,000 tons of solid waste annually, reducing stockpiling pollution. This process solves the problem of highly alkaline red mud pollution, consuming only 0.35 tons of red mud per ton of cement, thus preventing the risk of groundwater pollution from its leachate. Simultaneously, it reduces the consumption of natural resources, saving 0.25 tons of bauxite and 0.15 tons of natural gypsum per ton of cement. Furthermore, it creates a circular economy model, enabling power plants (desulfurization gypsum), steel plants (steel slag), aluminum plants (red mud), and cement plants to form a regional solid waste collaborative treatment network, reducing overall industrial pollution costs.

[0027] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0028] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing low-cost solid waste-based sulfoaluminate cement, characterized in that, include: S1, Solid waste pretreatment: The selected industrial solid waste is treated, including drying, crushing, grinding and impurity removal, so that the treated solid waste meets the requirements of subsequent batching and reaction. S2, Ingredient Design: Based on the target mineral composition, calculate and optimize the proportions of each solid waste and supplementary raw material, and control the key rate values; S3, Raw material preparation: The pretreated solid waste is accurately weighed according to the design ratio, thoroughly mixed, and then ground to the required fineness; S4, Low-temperature calcination: Raw materials are calcined at a relatively low temperature of 1250-1350℃ in a rotary kiln or vertical kiln to promote the formation of target minerals; S5, Clinker Rapid Cooling: Rapidly cooling the high-temperature clinker after calcination to stabilize the mineral phase; S6, Cement Grinding: Cooled clinker is ground together with an appropriate amount of solid waste gypsum and regulators to a specified fineness to produce finished cement.

2. The method for preparing low-cost solid waste-based sulfoaluminate cement according to claim 1, characterized in that, The mineral composition described in S2 includes anhydrous calcium sulfoaluminate and belite, and the key rate values ​​include: Lime saturation factor (LSF): LSF = CaO / (2.8 SiO2 + 1.18 Al2O3 + 0.65 Fe2O3 + 1.5 SO3-bound CaO), the lime saturation factor is between 0.8 and 1.0; Aluminum-sulfur ratio: A / S = Al2O3 / SO3, i.e., mass ratio, is the key to controlling the formation of C4A3Š, and the mass ratio is 3.5-4.5; Aluminum-silicon ratio (A / Si): A / Si = Al2O3 / SiO2, a mass ratio that affects the content and flammability of C2S. It is determined based on the target ratio of C4A3Š to C2S and the characteristics of the solid waste used. The optimal ratio of various solid wastes and supplementary raw materials is determined by using the chemical composition of the raw materials and the set target rate value, either through calculation software or manual calculation.

3. The method for preparing low-cost solid waste-based sulfoaluminate cement according to claim 1, characterized in that, S4 specifically includes: S4.1 Calcination equipment: mainly rotary kilns, including wet, semi-dry or dry preheating and precalcination kilns, and mechanized vertical kilns can also be used; S4.2, Calcination temperature: The calcination temperature is controlled between 1250°C and 1350°C; S4.3, Calcination atmosphere: Maintain a weakly oxidizing or neutral atmosphere; S4.4, Holding time: Sufficient time must be maintained at the target temperature to ensure complete reaction of raw materials and full formation of C4A3Š and C2S; S4.5, Role of mineralizers: Components in solid waste, including Fe2O3, CaF2, and P2O5, act as mineralizers, reducing the temperature and viscosity of the liquid phase, promoting mineral formation, and facilitating good calcination at lower temperatures.

4. The method for preparing low-cost solid waste-based sulfoaluminate cement according to claim 1, characterized in that, S5 specifically includes: S5.1 Cooling equipment: mainly adopts high-efficiency grate coolers, including push-type, reciprocating type or third-generation controlled flow grate coolers; S5.2 Cooling requirements: Rapidly cool from the calcination temperature of 1250-1350°C to the ambient temperature, and cool the high-temperature clinker to below 600°C within 6-10 minutes.

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