Preparation of calcium sulphoaluminate cementitious material based on ternary solid waste subcritical hydrothermal-low temperature calcination coupling process system

Abstract

The application belongs to the technical field of solid waste resource utilization and low-carbon cementing material preparation, and particularly relates to a process system for preparing calcium sulphoaluminate cementing material based on ternary solid waste subcritical hydrothermal-low temperature calcination coupling. Steel slag, aluminum ash and desulfurization gypsum are pretreated, mixed, adjusted and boosted to enter a subcritical hydrothermal synthesis reaction unit, so that Ca, Al, Si and S components in the steel slag, aluminum ash and desulfurization gypsum are dissolved, activated, migrated and recombined to form a hydrothermal composite precursor; ammonia gas generated by hydrolysis of aluminum nitride in the aluminum ash is absorbed and recovered by an ammonia gas treatment and recovery unit. The hydrothermal product is separated by pressure gas-solid liquid separation, the liquid phase is recycled after treatment, and the solid phase is dried, low-temperature calcined, cooled and superfine ground to obtain calcium sulphoaluminate cementing material with anhydrous calcium sulphoaluminate and beta-type dicalcium silicate as main mineral phases. The application can realize collaborative resource utilization of steel slag, aluminum ash and desulfurization gypsum, and reduce the preparation temperature and energy consumption of calcium sulphoaluminate cementing material.

Description

Technical Field

[0001] This invention belongs to the field of solid waste resource utilization and low-carbon cementitious material preparation technology, specifically involving a process system for preparing calcium sulfoaluminate cementitious materials based on ternary solid waste subcritical hydrothermal-low temperature calcination coupling. Background Technology

[0002] Calcium sulfoaluminate cementitious materials possess characteristics such as early strength, rapid hardening, micro-expansion, and strong adaptability, making them suitable for applications in road base courses, mine filling, solid waste solidification, rapid-hardening repair, and low-carbon building materials. Traditional processes for preparing calcium sulfoaluminate cementitious materials mostly include a calcination unit, with temperatures reaching up to 1200℃. These processes primarily use limestone, bauxite, and natural gypsum as raw materials, resulting in high consumption of natural minerals, high energy consumption, and high carbon emissions.

[0003] Steel slag, aluminum ash, and desulfurized gypsum are all typical industrial solid wastes, containing calcium-silicon components, aluminum components, and calcium sulfate components, respectively. They can provide key elements such as Ca, Si, Al, and S for calcium sulfoaluminate cementitious materials. Therefore, steel slag, aluminum ash, and desulfurized gypsum can be used together as raw materials for calcium sulfoaluminate cementitious materials, achieving synergistic resource utilization while reducing the dependence of calcium sulfoaluminate cementitious materials on natural minerals.

[0004] However, when preparing calcium sulfoaluminate cementitious materials in synergy with steel slag, aluminum ash, and desulfurized gypsum, the free CaO, free MgO, and low-activity mineral phases in the steel slag easily lead to low cementitious activity and poor volume stability; AlN in aluminum ash easily releases NH3 when it comes into contact with water, posing environmental pollution and safety risks; and the existing utilization methods of desulfurized gypsum have low added value and limited disposal capacity.

[0005] Existing solid waste treatment processes are insufficient to address the aforementioned problems because: existing solid waste resource utilization systems primarily include simple grinding and blending, mechanical mixing, direct calcination, water washing for denitrification, and conventional alkali activation. Grinding and blending, and mechanical mixing, struggle to achieve sufficient homogenization and synergistic reactions among the multiple components; direct calcination relies on solid-phase diffusion, resulting in high target mineral formation temperatures and low reaction efficiency; water washing for denitrification easily generates saline wastewater and causes the loss of effective aluminum components; conventional alkali activation struggles to stably form cementitious materials with anhydrous calcium sulfoaluminate and β-type dicalcium silicate as the main mineral phases, and also fails to simultaneously achieve aluminum ash denitrification and liquid-phase reuse. While existing technologies have attempted to utilize industrial solid waste to prepare calcium sulfoaluminate cementitious materials, they generally utilize only one or two types of industrial solid waste, resulting in limited integrated utilization of solid waste materials. This makes them unsuitable for the synergistic preparation of calcium sulfoaluminate cementitious materials from steel slag, aluminum ash, and desulfurized gypsum, and still suffers from the problem of AlN in aluminum ash releasing NH3 upon contact with water.

[0006] Therefore, traditional process systems struggle to simultaneously achieve high-value utilization, low-energy preparation, and harmless treatment of ternary solid wastes, including steel slag, aluminum ash, and desulfurized gypsum. Summary of the Invention

[0007] The purpose of this invention is to provide a process system for preparing calcium sulfoaluminate cementitious materials based on subcritical hydrothermal-low temperature calcination coupling of ternary solid waste, so as to solve the problems of high consumption of natural mineral raw materials, high calcination temperature, high energy consumption, difficulty in the synergistic utilization of steel slag, aluminum ash and desulfurized gypsum, and the risk of ammonia release from direct utilization of aluminum ash in traditional processes for preparing calcium sulfoaluminate cementitious materials.

[0008] This invention's process system includes a subcritical hydrothermal synthesis reaction unit. Utilizing subcritical hydrothermal technology, it achieves solid waste activation and reduces subsequent calcination temperatures. This subcritical hydrothermal technology differs from traditional hydrothermal curing, simple leaching, or single-raw-material liquid-phase activation. Traditional methods are often limited to hydration reactions, surface activation, or partial component dissolution. In contrast, this invention's subcritical hydrothermal process uses subcritical water as a medium. Under high temperature and pressure conditions with a water-controlled liquid phase, combined with an alkaline liquid-phase environment, components such as Ca, Si, Al, and S in steel slag, aluminum ash, and desulfurized gypsum undergo synergistic dissolution, migration, and recombination, forming a hydrothermal composite precursor with uniform component distribution and high reactivity. This hydrothermal composite precursor exhibits shorter solid-phase diffusion distances and higher reaction contact efficiency during subsequent calcination, thereby reducing the formation temperature of target minerals such as anhydrous calcium sulfoaluminate and β-type dicalcium silicate, and decreasing the high-temperature calcination energy consumption in the preparation of traditional calcium sulfoaluminate cementitious materials. Meanwhile, addressing the issue of AlN in aluminum ash decomposing upon contact with water and releasing ammonia, this invention incorporates it into a closed subcritical hydrothermal system for controlled hydrolysis. Controlled hydrolysis refers to adjusting the subcritical hydrothermal reaction temperature, pressure, alkali concentration, liquid-to-solid ratio, and reaction time to gradually hydrolyze AlN in the aluminum ash and release ammonia, avoiding the risk of ammonia escape due to rapid and disordered decomposition under open water conditions at room temperature. The ammonia generated during hydrolysis is collected and treated by an ammonia treatment and recovery unit. The liquid phase after the hydrothermal reaction is separated by a pressurized gas-solid-liquid separation unit and can be recycled for the hydrothermal activation process, thereby achieving ammonia removal, waste volume reduction, and resource recycling. Simultaneously, the aluminum-containing active components formed after AlN hydrolysis can further participate in the hydrothermal recombination of the Ca, Si, Al, and S system, which is beneficial for improving the precursor reactivity and promoting the formation of target minerals during subsequent low-temperature calcination.

[0009] This invention is specifically achieved through the following technical solutions: This invention provides a process system for preparing calcium sulfoaluminate cementitious materials based on subcritical hydrothermal-low-temperature calcination coupling of ternary solid waste, comprising: The mixing and homogenization unit is used to mix steel slag, aluminum ash, desulfurized gypsum, silica-alumina corrective agent, water and alkali activator to prepare an alkaline slurry; The mixing and homogenization unit is sequentially connected to a pressurization unit, a subcritical hydrothermal synthesis reaction unit, and a pressurized gas-solid-liquid separation unit. After being pressurized by the pressurization unit, the alkaline slurry enters the subcritical hydrothermal synthesis reaction unit, where it forms a hydrothermal composite precursor under a subcritical hydrothermal environment. The hydrothermal composite precursor then enters the pressurized gas-solid-liquid separation unit and is separated into an ammonia-containing gas phase, a liquid phase, and a solid phase. The liquid phase outlet of the pressurized gas-solid-liquid separation unit is connected to a liquid phase treatment and recovery unit, and the liquid phase is treated and reused to prepare an alkaline slurry. The ammonia-containing gas phase outlet of the pressurized gas-solid-liquid separation unit is connected to an ammonia treatment and recovery unit, which is used to convert the ammonia-containing gas phase into ammonium sulfate product. The solid phase outlet of the pressurized gas solid-liquid separation unit is sequentially connected to a drying and dehydration unit and a low-temperature calcination unit. After the solid phase enters the drying and dehydration unit to remove moisture, it enters the low-temperature calcination unit to calcine and generate a calcined product with anhydrous calcium sulfoaluminate and β-type dicalcium silicate as the main mineral phases. The calcined product is then cooled and ground by the post-processing unit to obtain the final product.

[0010] Preferably, the subcritical hydrothermal synthesis reaction unit is a horizontal or vertical hydrothermal reactor, a continuous tubular hydrothermal reactor, a stirred high-pressure reactor, or other reaction equipment capable of realizing hydrothermal activation of ternary solid waste and precursor construction.

[0011] The subcritical hydrothermal synthesis reaction adopts a segmented hydrothermal regime. In the first stage, ettringite formation is promoted at 100–160℃. In the second stage, aluminum nitride hydrolysis and denitrification in aluminum ash and dissolution and activation of the silicate phase in steel slag are promoted at 150–250℃. This causes the Ca, Al, Si, and S components in steel slag, aluminum ash, and desulfurized gypsum to dissolve, migrate, and recombine, forming a hydrothermal composite precursor containing ettringite, CSH gel, aluminum hydroxide, calcium hydroxide, and calcium sulfate.

[0012] It should be noted that in the subcritical hydrothermal synthesis reaction unit, the Ca, Al, Si, and S components in steel slag, aluminum ash, and desulfurized gypsum undergo dissolution, activation, hydration, migration, and recombination to form a hydrothermal composite precursor containing ettringite, CSH gel, aluminum hydroxide, calcium hydroxide, and calcium sulfate. Simultaneously, aluminum nitride in the aluminum ash undergoes hydrolysis and releases ammonia. This subcritical hydrothermal stage is used to achieve microscopic homogenization of the effective components of the ternary solid waste and the denitrification and harmless treatment of aluminum ash.

[0013] Preferably, in the low-temperature calcination unit, the calcination temperature is 600–800℃. Compared with the traditional calcination process of calcium sulfoaluminate cementitious materials, the calcination temperature is greatly reduced.

[0014] Preferably, the pressurized gas-solid-liquid separation unit includes, but is not limited to, plate and frame filter press, belt filter press, ceramic filter, centrifugal filter, continuous filter press or combination thereof, used to achieve gas phase, liquid phase and solid phase separation of subcritical hydrothermal products under the condition of maintaining system pressure or controlled pressure relief.

[0015] Preferably, the ammonia treatment and recovery unit is equipped with an acid absorption liquid storage tank, a spray absorption tower, a circulation pump, and a tail gas purification device. The acid absorption liquid is a sulfuric acid solution, which absorbs ammonia to form an ammonium sulfate solution or ammonium sulfate product, and then enters the ammonium sulfate collection unit, thereby realizing the resource utilization of ammonia gas, a by-product of aluminum nitride hydrolysis in aluminum ash.

[0016] Preferably, the liquid phase treatment and recovery unit is used to perform sedimentation, filtration, neutralization, desalination, or pH adjustment on the liquid phase obtained from the pressurized gas-solid-liquid separation unit.

[0017] Preferably, the process system of the present invention further includes: a steel slag storage and supply unit, an aluminum ash storage and supply unit, a desulfurized gypsum storage and supply unit, a raw material pretreatment unit, a silicon-aluminum corrective material storage and supply unit, an industrial water source unit, and an alkali activator storage and supply unit. The steel slag storage and supply unit is connected to the raw material pretreatment unit, which includes a crushing unit, an iron removal unit, and a screening unit connected in sequence. The discharge port of the steel slag storage and supply unit is connected to the crushing unit. The raw material pretreatment unit is used to crush, remove iron, and screen the steel slag to remove metallic iron and obtain steel slag particles or powder of suitable particle size. Aluminum ash and desulfurized gypsum can be directly fed into the mixing, blending, and homogenization unit according to their particle size and impurity content. The specific surface area of ​​the powder raw materials is sufficient to meet the fineness requirements of the subsequent subcritical hydrothermal reaction.

[0018] The crushing unit includes, but is not limited to, a jaw crusher, a hammer crusher, a roller crusher, or a combination thereof; the iron removal unit includes, but is not limited to, a magnetic separator, an iron remover, or an electromagnetic separator; the screening unit includes a vibrating screen, a drum screen, an air classifier, or a combination thereof.

[0019] The aluminum ash storage and supply unit, the desulfurized gypsum storage and supply unit, the discharge end of the screening unit, the silicon-aluminum corrective material storage and supply unit, the industrial water source unit, and the alkali activator storage and supply unit are respectively connected to the mixing, blending, and homogenization unit.

[0020] The liquid phase processed by the liquid phase treatment and recovery unit is returned to the alkaline activator storage and supply unit for recycling and preparation of alkaline slurry.

[0021] Preferably, the steel slag storage and supply unit is used to provide metallurgical solid waste including but not limited to converter steel slag, electric furnace steel slag, refined steel slag, or other calcium- and silicon-containing components.

[0022] The aluminum ash storage and supply unit is used to provide, but is not limited to, primary aluminum ash, secondary aluminum ash, pretreated aluminum ash, or other aluminum-containing industrial solid waste.

[0023] The desulfurized gypsum storage and supply unit is used to provide, but is not limited to, wet desulfurized gypsum, semi-dry desulfurized ash, or other solid waste containing calcium sulfate.

[0024] The silica-aluminate correction material storage and supply unit is used to meet the stoichiometric requirements for the synthesis of ettringite and anhydrous calcium sulfoaluminate in the system.

[0025] The alkaline activator storage and supply unit is used to provide sodium hydroxide, calcium hydroxide, water glass, sodium carbonate, lime milk, carbide slag slurry, or other alkaline regulators that can adjust the alkalinity of the slurry and promote the dissolution and activation of ternary solid waste.

[0026] Preferably, the mixing and homogenization unit is equipped with a metering device, a stirring device, and a pH adjustment device, used to meter, mix, blend, and homogenize steel slag, aluminum ash, desulfurized gypsum, silica-alumina corrective material, industrial water, and alkali activator to form an alkaline slurry; and to adjust the proportion of each component and the pH of the slurry as needed to control the generation of ettringite, CSH gel, and other composite precursor components in the subcritical hydrothermal stage.

[0027] The pressurization unit includes, but is not limited to, plunger pumps, diaphragm pumps, screw pumps, slurry pumps, or other pumping equipment capable of delivering alkaline slurry to the subcritical hydrothermal synthesis reaction unit and maintaining the subcritical hydrothermal reaction pressure; the pressurization unit is used to pressurize the alkaline slurry to any pressure capable of maintaining the subcritical hydrothermal reaction state.

[0028] Preferably, the post-processing unit includes a cooling unit and an ultrafine grinding unit. The calcined product generated in the low-temperature calcination unit enters the cooling unit for cooling, and then enters the ultrafine grinding unit for grinding. The product is stored in a cementitious material storage silo to obtain the finished calcium sulfoaluminate cementitious material. The specific surface area of ​​the finished product is any fineness that can meet the requirements for use as road base material, mine filling material, solid waste solidification material, low-carbon building material, or fast-hardening repair material.

[0029] The drying and dehydration unit includes, but is not limited to, hot air dryers, belt dryers, flash dryers, vacuum dryers, or other drying equipment capable of reducing the moisture content of the hydrothermal composite precursor. The moisture content of the dried hydrothermal composite precursor includes, but is not limited to, less than 10%, or any moisture content suitable for subsequent low-temperature calcination.

[0030] The low-temperature calcination unit includes a rotary kiln, muffle furnace, tunnel kiln, roller kiln, fluidized bed calcination furnace, or other heat treatment equipment. The hydrothermal composite precursor, after drying, enters the low-temperature calcination unit and is calcined at 600–800°C; preferably, the calcination temperature is 650–750°C. During calcination, the ettringite, CSH gel, aluminum hydroxide, calcium hydroxide, and calcium sulfate in the hydrothermal composite precursor undergo dehydration, decomposition, and mineral reconstruction, generating a calcined product with anhydrous calcium sulfoaluminate and dicalcium silicate as the main mineral phases.

[0031] The cooling unit includes a natural cooling device, an air cooling device, a water-cooled jacket device, or a rotary cooler; the ultrafine grinding unit includes a ball mill, a vertical mill, an air jet mill, a stirred mill, or a roller press.

[0032] Compared with the prior art, the present invention has the following beneficial effects: The process system of this invention includes a subcritical hydrothermal synthesis reaction unit. Using subcritical water as the medium, the subcritical hydrothermal reaction promotes the dissolution, migration, and recombination of Ca, Al, Si, and S components in steel slag, aluminum ash, and desulfurized gypsum, forming a highly active composite precursor containing ettringite and CSH gel. This precursor exhibits higher reactivity than conventional mechanically mixed materials, significantly shortening the solid-phase diffusion distance during subsequent calcination. This significantly reduces the formation temperature of target minerals such as anhydrous calcium sulfoaluminate and β-dicalcium silicate, thereby lowering the calcination temperature and preparation energy consumption. Simultaneously, the subcritical hydrothermal process promotes the hydration and recombination of free calcium oxide and active calcium phases in steel slag, which is beneficial for improving volume stability.

[0033] The process system of this invention includes an ammonia treatment and recovery unit and a liquid phase treatment and recovery unit. AlN in aluminum ash undergoes hydrolysis in a subcritical hydrothermal synthesis reaction unit, generating aluminum-containing hydration products and releasing NH3. These aluminum-containing hydration products can continue to participate in the formation of hydrothermal composite precursors. The released NH3 is absorbed and treated by the ammonia treatment and recovery unit before entering the ammonium sulfate collection unit, achieving the harmless treatment and resource utilization of the nitrogen-containing components in the aluminum ash. Simultaneously, the liquid phase separated by the pressurized gas-solid-liquid separation unit enters the liquid phase treatment and recovery unit, recovering alkaline components and soluble ions from the liquid phase, reducing the consumption of fresh water and alkaline activators, and minimizing wastewater discharge. This achieves synergistic coupling of aluminum ash denitrification, liquid phase reuse, and cementitious material synthesis processes.

[0034] The process system of this invention uses steel slag, aluminum ash and desulfurized gypsum as the main raw materials, and utilizes their calcium-silicon components, aluminum components and calcium sulfate components respectively to construct a CaO-Al2O3-SiO2-SO3 system, realizing the synergistic utilization of the three industrial solid wastes in the same cementitious material system, and reducing the consumption of natural limestone, bauxite and natural gypsum. Attached Figure Description

[0035] Figure 1 The flowchart of the process system for preparing calcium sulfoaluminate cementitious materials based on subcritical hydrothermal-low temperature calcination coupling of ternary solid waste provided by the present invention is shown.

[0036] Explanation of reference numerals in the attached figures: 1. Steel slag storage and supply unit; 2. Aluminum ash storage and supply unit; 3. Desulfurized gypsum storage and supply unit; 4. Raw material pretreatment unit; 4a. Crushing unit; 4b. Iron removal unit; 4c. Screening unit; 5. Silica-alumina corrective material storage and supply unit; 6. Industrial water source unit; 7. Alkali activator storage and supply unit; 8. Mixing, blending and homogenization unit; 9. Pressurization unit; 10. Subcritical hydrothermal synthesis reaction unit; 11. Pressurized gas solid-liquid separation unit; 12. Liquid phase treatment and recovery unit; 13. Ammonia treatment and recovery unit; 14. Ammonium sulfate collection unit; 15. Drying and dehydration unit; 16. Low-temperature calcination unit; 17. Cooling unit; 18. Ultrafine grinding unit; 19. Cementitious material storage silo. Detailed Implementation

[0037] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below with reference to specific embodiments and accompanying drawings. However, the embodiments described are not intended to limit the present invention. Unless otherwise specified, the experimental methods and detection methods described in the following embodiments are conventional methods; unless otherwise specified, the reagents and materials described are commercially available.

[0038] This invention proposes a process system for preparing calcium sulfoaluminate cementitious materials from ternary solid waste, which is based on subcritical hydrothermal reaction and coupled with low-temperature calcination. This system aims to solve problems such as insufficient activation of solid waste, high formation temperature of target minerals, and difficulty in coordinating denitrification and resource utilization of aluminum ash in traditional processes.

[0039] This invention provides a process system for preparing calcium sulfoaluminate cementitious materials based on subcritical hydrothermal-low-temperature calcination coupling of ternary solid waste, such as... Figure 1 As shown, it includes a steel slag storage and supply unit 1, an aluminum ash storage and supply unit 2, a desulfurized gypsum storage and supply unit 3, a raw material pretreatment unit 4, a silicon-aluminum corrective material storage and supply unit 5, an industrial water source unit 6, an alkali activator storage and supply unit 7, a mixing, blending and homogenization unit 8, a pressurization unit 9, a subcritical hydrothermal synthesis reaction unit 10, a pressurized gas-solid-liquid separation unit 11, a liquid phase treatment and recovery unit 12, an ammonia treatment and recovery unit 13, an ammonium sulfate collection unit 14, a drying and dehydration unit 15, a low-temperature calcination unit 16, a cooling unit 17, an ultrafine grinding unit 18, and a cementitious material storage silo 19.

[0040] The steel slag storage and supply unit 1 is connected to the raw material pretreatment unit 4, which includes a crushing unit 4a, an iron removal unit 4b, and a screening unit 4c, used for crushing, removing iron, and screening the steel slag. The pretreated steel slag material, along with aluminum ash from the aluminum ash storage and supply unit 2, desulfurized gypsum from the desulfurized gypsum storage and supply unit 3, silica-alumina corrective material from the silica-alumina corrective material storage and supply unit 5, industrial water from the industrial water source unit 6, and alkali activator from the alkali activator storage and supply unit 7, enters the mixing, blending, and homogenization unit 8. After metering, mixing, pH adjustment, and homogenization, an alkaline slurry is formed.

[0041] After being mixed and homogenized, the alkaline slurry is pressurized by pressurization unit 9 and then enters subcritical hydrothermal synthesis reaction unit 10. In subcritical hydrothermal synthesis reaction unit 10, the Ca, Al, Si, and S components in steel slag, aluminum ash, and desulfurized gypsum undergo dissolution, activation, hydration, migration, and recombination in a liquid-phase hydrothermal environment, forming a hydrothermal composite precursor containing ettringite, CSH gel, aluminum hydroxide, calcium hydroxide, and calcium sulfate. Simultaneously, aluminum nitride in the aluminum ash undergoes hydrolysis and releases ammonia gas. This subcritical hydrothermal stage is a crucial process for forming the AFt / CSH composite precursor and achieving the harmless treatment of AlN.

[0042] The hydrothermal product stream generated by the subcritical hydrothermal synthesis reaction unit 10 enters the pressurized gas-solid-liquid separation unit 11. The pressurized gas-solid-liquid separation unit 11 separates the hydrothermal product stream into an ammonia-containing gas phase, a liquid phase, and a solid phase. The ammonia-containing gas phase enters the ammonia treatment and recovery unit 13 for absorption, purification, and resource recovery, and further enters the ammonium sulfate collection unit 14 to form ammonium sulfate products; the liquid phase enters the liquid phase treatment and recovery unit 12, and after treatment, returns to the alkali activator storage and supply unit 7 for recycling; the solid phase enters the drying and dehydration unit 15 to remove moisture, and then enters the low-temperature calcination unit 16.

[0043] In the low-temperature calcination unit 16, the hydrothermal composite precursor undergoes dehydration, decomposition, and mineral reconstruction to generate a calcined product with anhydrous calcium sulfoaluminate and dicalcium β-silicate as the main mineral phases. After being cooled by the cooling unit 17 and ground by the ultrafine grinding unit 18, the calcined product enters the cementitious material storage silo 19 to obtain the finished calcium sulfoaluminate cementitious material.

[0044] The above-described process system of the present invention will be further described below.

[0045] A process system for preparing calcium sulfoaluminate cementitious materials based on subcritical hydrothermal-low-temperature calcination coupling of ternary solid waste is as follows: Figure 1 As shown.

[0046] Steel slag storage and supply unit 1 quantitatively delivers steel slag to raw material pretreatment unit 4. Aluminum ash storage and supply unit 2 quantitatively delivers aluminum ash to mixing, blending, and homogenizing unit 8, and desulfurized gypsum storage and supply unit 3 quantitatively delivers desulfurized gypsum to mixing, blending, and homogenizing unit 8. The steel slag includes, but is not limited to, converter steel slag, electric furnace steel slag, or refined steel slag; the aluminum ash includes, but is not limited to, primary aluminum ash, secondary aluminum ash, or pretreated aluminum ash; and the desulfurized gypsum includes, but is not limited to, wet desulfurization gypsum, semi-dry desulfurization ash, or other solid waste containing calcium sulfate.

[0047] The raw material pretreatment unit 4 includes a crushing unit 4a, an iron removal unit 4b, and a screening unit 4c. After being crushed, iron removed, and screened sequentially, the steel slag yields steel slag particles or powder suitable for subsequent subcritical hydrothermal reactions. Depending on the raw material particle size, moisture content, and impurity content, aluminum ash and desulfurized gypsum can be directly fed into the mixing and homogenization unit 8, or they can be pretreated before entering the mixing and homogenization unit 8. The fineness of the raw materials can be adjusted as needed.

[0048] The pretreated steel slag, aluminum ash, desulfurized gypsum, and the aluminosilicate corrective material supplied by the aluminosilicate corrective material storage and supply unit 5 enter the mixing, blending, and homogenization unit 8, where they are mixed with industrial water supplied by the industrial water source unit 6 and alkali activator supplied by the alkali activator storage and supply unit 7. The aluminosilicate corrective material storage and supply unit 5 is used to meet the stoichiometric requirements for the synthesis of ettringite and anhydrous calcium sulfoaluminate in the system; the alkali activator storage and supply unit 7 provides sodium hydroxide, calcium hydroxide, water glass, sodium carbonate, lime slurry, carbide slag slurry, or other alkaline regulators that can adjust the alkalinity of the slurry and promote the dissolution and activation of ternary solid waste. The mixing, blending, and homogenization unit 8 is equipped with a metering device, a stirring device, and a pH adjustment device to adjust the slurry composition, pH, and solid-liquid ratio. Steel slag mainly provides calcium and silicon sources, aluminum ash mainly provides aluminum sources, desulfurized gypsum mainly provides sulfur sources and some calcium sources, and the aluminosilicate corrective material is used to adjust the ratio of silicon and aluminum components in the system. The formation of ettringite, CSH gel, and other composite precursor components in the subcritical hydrothermal stage can be controlled by adjusting the above ratios and the pH of the system, according to actual needs.

[0049] The homogenized alkaline slurry enters the pressurization unit 9, and after pressurization, it enters the subcritical hydrothermal synthesis reaction unit 10. The pressurization unit 9 can be a plunger pump, diaphragm pump, screw pump, slurry pump, or other pumping equipment capable of conveying slurries with high solids content. The pressurization pressure is controlled to any pressure that can maintain the subcritical hydrothermal reaction state in the liquid phase, for example, the pressurization pressure can be controlled to be 0.2 to 5.0 MPa.

[0050] The subcritical hydrothermal synthesis reaction unit 10 can be a horizontal hydrothermal reactor, a vertical hydrothermal reactor, a continuous tubular hydrothermal reactor, or a stirred high-pressure reactor. The alkaline slurry undergoes a subcritical hydrothermal reaction within the subcritical hydrothermal synthesis reaction unit 10, with the reaction temperature controlled between 100 and 250°C. During the subcritical hydrothermal reaction, the Ca, Al, Si, and S components in the ternary solid waste dissolve, migrate, and recombine, forming a hydrothermal composite precursor. The subcritical hydrothermal synthesis reaction employs a segmented hydrothermal regime. In the first stage, at 100–160°C, the formation of ettringite is promoted. In the second stage, at 150–250°C, the hydrolysis and denitrification of aluminum nitride in aluminum ash and the dissolution and activation of the silicate phase in steel slag are promoted. This causes the Ca, Al, Si, and S components in the steel slag, aluminum ash, and desulfurized gypsum to dissolve, migrate, and recombine, forming a hydrothermal composite precursor containing ettringite, CSH gel, aluminum hydroxide, calcium hydroxide, and calcium sulfate.

[0051] The product outlet of the subcritical hydrothermal synthesis reaction unit 10 is connected to the pressurized gas solid-liquid separation unit 11. Aluminum nitride in the aluminum ash undergoes hydrolysis during the subcritical hydrothermal stage, releasing ammonia. The ammonia-containing gas phase is separated by the pressurized gas solid-liquid separation unit 11 and then enters the ammonia treatment and recovery unit 13. The ammonia treatment and recovery unit 13 is equipped with an acid absorption liquid storage tank, a spray absorption tower, a circulating pump, and a tail gas purification device. The acid absorption liquid is a sulfuric acid solution, which is discharged or recovered after condensation absorption, acid absorption, water washing absorption, or tail gas purification treatment. Preferably, the ammonia-containing gas phase enters the ammonium sulfate collection unit 14 after acid absorption, forming ammonium sulfate byproducts.

[0052] The pressurized gas-solid-liquid separation unit 11 can be a plate and frame filter press, belt filter press, ceramic filter, centrifugal filter, or continuous filter press device, used to separate the hydrothermal reaction product stream into an ammonia-containing gas phase, liquid phase, and solid phase under maintained system pressure or controlled pressure relief conditions. The pressurized gas-solid-liquid separation pressure can be controlled from 0.2 to 5.0 MPa, or controlled to any condition that enables gas-solid-liquid separation while maintaining the activity of the precursor.

[0053] The liquid phase outlet of the pressurized gas-solid-liquid separation unit 11 is connected to the liquid phase treatment and recovery unit 12. After sedimentation, filtration, pH adjustment, or purification, the liquid phase is returned to the alkali activator storage and supply unit 7 for recycling. The solid phase outlet of the pressurized gas-solid-liquid separation unit 11 is connected to the drying and dehydration unit 15. The solid hydrothermal composite precursor enters the drying and dehydration unit 15 for drying. The drying and dehydration unit 15 can be a hot air dryer, belt dryer, flash dryer, or vacuum dryer. The moisture content of the dried hydrothermal composite precursor is controlled within a range suitable for subsequent calcination.

[0054] The dried hydrothermal composite precursor enters the low-temperature calcination unit 16. The low-temperature calcination unit 16 can be a rotary kiln, muffle furnace, tunnel kiln, roller kiln, or fluidized bed calcination furnace. The calcination temperature can be controlled at 600–800℃, preferably 650–750℃.

[0055] The calcined products sequentially enter the cooling unit 17 and the ultrafine grinding unit 18. After cooling and grinding, the material enters the cementitious material storage silo 19 to obtain the finished calcium sulfoaluminate cementitious material. The cooling unit 17 can be a natural cooling device, an air cooling device, a water-cooled jacket device, or a rotary cooler; the ultrafine grinding unit 18 can be a ball mill, a vertical mill, an air jet mill, a stirred mill, or a roller press. The specific surface area of ​​the finished product is controlled to any fineness that meets the requirements for use as road base material, mine filling material, solid waste solidification material, low-carbon building material, or fast-hardening repair material.

[0056] Through the above process system, steel slag, aluminum ash, desulfurized gypsum and silica-alumina corrective material are successively processed through raw material storage and pretreatment, mixing and homogenization, pressurized hydrothermal synthesis, pressurized gas solid-liquid separation, ammonia treatment and recovery, liquid phase treatment and reuse, precursor drying, low-temperature calcination, cooling grinding and storage, forming a continuous ternary solid waste subcritical hydrothermal-low-temperature calcination coupled preparation route.

[0057] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from the spirit and scope of the invention. Therefore, it is intended to include any modifications and variations of this invention that fall within the scope of the claims and their equivalents.

Claims

1. A process system for preparing calcium sulfoaluminate cementitious materials based on subcritical hydrothermal-low-temperature calcination coupling of ternary solid waste, characterized in that, include: The mixing and homogenization unit (8) is used to mix steel slag, aluminum ash, desulfurized gypsum, silica-alumina corrective material, water and alkali activator to prepare an alkaline slurry; Downstream of the mixing and homogenization unit (8) are a pressurization unit (9), a subcritical hydrothermal synthesis reaction unit (10), and a pressurized gas-solid-liquid separation unit (11); after being pressurized by the pressurization unit (9), the alkaline slurry enters the subcritical hydrothermal synthesis reaction unit (10) and forms a hydrothermal composite precursor in a subcritical hydrothermal environment. The hydrothermal composite precursor enters the pressurized gas-solid-liquid separation unit (11) and is separated into an ammonia-containing gas phase, a liquid phase, and a solid phase. The liquid phase outlet of the pressurized gas-solid-liquid separation unit (11) is connected to a liquid phase treatment and recovery unit (12), and the liquid phase is treated and reused to prepare the alkaline slurry. The ammonia-containing gas phase outlet of the pressurized gas-solid-liquid separation unit (11) is connected to an ammonia treatment and recovery unit (13), which is used to convert the ammonia-containing gas phase into ammonium sulfate product. The solid phase outlet of the pressurized gas solid-liquid separation unit (11) is sequentially connected to a drying and dehydration unit (15) and a low-temperature calcination unit (16). After the solid phase enters the drying and dehydration unit (15) to remove moisture, it enters the low-temperature calcination unit (16) to calcine and generate a calcined product with anhydrous calcium sulfoaluminate and β-type dicalcium silicate as the main mineral phases. The calcined product is then cooled and ground by a post-processing unit to obtain the final product.

2. The process system for preparing calcium sulfoaluminate cementitious materials based on subcritical hydrothermal-low-temperature calcination coupling of ternary solid waste according to claim 1, characterized in that, The subcritical hydrothermal synthesis reaction unit (10) is a hydrothermal reactor, a continuous tubular hydrothermal reactor, or a stirred high-pressure reactor. The subcritical hydrothermal synthesis reaction adopts a segmented hydrothermal regime. In the first stage, ettringite formation is promoted at 100–160℃. In the second stage, aluminum nitride hydrolysis and denitrification in aluminum ash and dissolution and activation of the silicate phase in steel slag are promoted at 150–250℃. This causes the Ca, Al, Si, and S components in steel slag, aluminum ash, and desulfurized gypsum to dissolve, migrate, and recombine, forming a hydrothermal composite precursor containing ettringite, CSH gel, aluminum hydroxide, calcium hydroxide, and calcium sulfate.

3. The process system for preparing calcium sulfoaluminate cementitious materials based on subcritical hydrothermal-low-temperature calcination coupling of ternary solid waste according to claim 1, characterized in that, In the low-temperature calcination unit (16), the calcination temperature is 600-800℃.

4. The process system for preparing calcium sulfoaluminate cementitious materials based on subcritical hydrothermal-low-temperature calcination coupling of ternary solid waste according to claim 1, characterized in that, The pressurized gas-solid-liquid separation unit (11) is a plate and frame filter press, a belt filter press, a ceramic filter, a centrifugal filter, a continuous filter press or a combination thereof, used to achieve gas phase, liquid phase and solid phase separation of hydrothermal products under the condition of maintaining system pressure or controlled pressure relief.

5. The process system for preparing calcium sulfoaluminate cementitious materials based on subcritical hydrothermal-low-temperature calcination coupling of ternary solid waste according to claim 1, characterized in that, The ammonia treatment and recovery unit (13) is equipped with an acid absorption liquid storage tank, a spray absorption tower, a circulation pump and a tail gas purification device. The acid absorption liquid is a sulfuric acid solution, which absorbs ammonia to form an ammonium sulfate solution or ammonium sulfate product, and enters the ammonium sulfate collection unit (14).

6. The process system for preparing calcium sulfoaluminate cementitious materials based on subcritical hydrothermal-low-temperature calcination coupling of ternary solid waste according to claim 1, characterized in that, The liquid phase treatment and recovery unit (12) is used to perform sedimentation, filtration, neutralization, desalination or pH adjustment on the liquid phase obtained from the pressurized gas-solid-liquid separation unit (11).

7. The process system for preparing calcium sulfoaluminate cementitious materials based on subcritical hydrothermal-low-temperature calcination coupling of ternary solid waste according to claim 1, characterized in that, Also includes: Steel slag storage and supply unit (1), aluminum ash storage and supply unit (2), desulfurized gypsum storage and supply unit (3), raw material pretreatment unit (4), silicon-aluminum corrective material storage and supply unit (5), industrial water source unit (6) and alkali activator storage and supply unit (7). The raw material pretreatment unit (4) includes a crushing unit (4a), an iron removal unit (4b) and a screening unit (4c) connected in sequence, and the discharge port of the steel slag storage and supply unit (1) is connected to the crushing unit (4a). The aluminum ash storage and supply unit (2), the desulfurized gypsum storage and supply unit (3), the discharge end of the screening unit (4c), the silicon-aluminum corrective material storage and supply unit (5), the industrial water source unit (6) and the alkali activator storage and supply unit (7) are respectively connected to the mixing, blending and homogenization unit (8). The liquid phase processed by the liquid phase treatment and recovery unit (12) is returned to the alkaline activator storage and supply unit (7) for recycling.

8. The process system for preparing calcium sulfoaluminate cementitious materials based on subcritical hydrothermal-low-temperature calcination coupling of ternary solid waste according to claim 7, characterized in that, The steel slag storage and supply unit (1) is used to provide metallurgical solid waste including converter steel slag, electric furnace steel slag, refined steel slag or other calcium- and silicon-containing components; The aluminum ash storage and supply unit (2) is used to provide primary aluminum ash, secondary aluminum ash, pretreated aluminum ash or other aluminum-containing industrial solid waste; The desulfurized gypsum storage and supply unit (3) is used to provide wet desulfurized gypsum, semi-dry desulfurized ash or other solid waste containing calcium sulfate; The silicon-aluminate correction material storage and supply unit (5) is used to meet the stoichiometric relationship required for the synthesis of ettringite and anhydrous calcium sulfoaluminate in the system; The alkaline activator storage and supply unit (7) is used to provide sodium hydroxide, calcium hydroxide, water glass, sodium carbonate, lime milk, carbide slag slurry or other alkaline regulators that can adjust the alkalinity of the slurry and promote the dissolution and activation of ternary solid waste.

9. The process system for preparing calcium sulfoaluminate cementitious materials based on subcritical hydrothermal-low-temperature calcination coupling of ternary solid waste according to claim 1, characterized in that, The mixing, blending and homogenizing unit (8) is equipped with a metering device, a stirring device and a pH adjustment device, which are used to meter, mix, blend and homogenize steel slag, aluminum ash, desulfurized gypsum, silica-alumina corrective material, industrial water and alkaline activator to form an alkaline slurry. The pressurization unit (9) is a plunger pump, diaphragm pump, screw pump, slurry pump or other pumping equipment that can transport alkaline slurry to the subcritical hydrothermal synthesis reaction unit (10) and pressurize it to the subcritical hydrothermal reaction pressure.

10. The process system for preparing calcium sulfoaluminate cementitious materials based on subcritical hydrothermal-low-temperature calcination coupling of ternary solid waste according to claim 1, characterized in that, The post-processing unit includes a cooling unit (17) and an ultrafine grinding unit (18). The calcined product generated in the low-temperature calcination unit (16) enters the cooling unit (17) for cooling, and then enters the ultrafine grinding unit (18) for grinding. The product enters the cementitious material storage silo (19) for storage. The drying and dehydration unit (15) is a hot air dryer, a belt dryer, a flash dryer, or a vacuum dryer; The low-temperature calcination unit (16) is a rotary kiln, muffle furnace, tunnel kiln, roller kiln or fluidized bed calcination furnace; The cooling unit (17) is a natural cooling device, an air cooling device, a water-cooled jacket device, or a rotary cooler; The ultrafine grinding unit (18) is a ball mill, vertical mill, air jet mill, stirred mill or roller press.

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