Preparation method of dry-mixed mortar by synergistically utilizing industrial solid waste

Abstract

The invention relates to the technical field of building materials and solid waste resource utilization, and discloses an industrial solid waste synergistic utilization dry-mixed mortar preparation method, which comprises Bayer process red mud, undisturbed phosphogypsum, sodium fluosilicate, light calcined magnesia, ordinary Portland cement, fine aggregate and an additive. The preparation method adopts a unique step-by-step mechanochemical ball milling process: S1, co-grinding the red mud and sodium fluosilicate, etching the surface of the red mud in a targeted manner, and curing free alkali; s2, adding ardealite and light calcined magnesia, continuously grinding, and inducing dephosphorization passivation and lattice reconstruction by utilizing fluorine ion migration to prepare modified composite gelling powder; and S3, mixing with other components. Through chemical regulation and control of a time sequence, the problems of saltpetering of the red mud and delayed coagulation of the ardealite are effectively solved, efficient synergistic utilization of two large solid wastes is realized, and the obtained mortar has excellent mechanical properties, volume stability and water resistance.

Description

Technical Field

[0001] This invention relates to the field of building materials and solid waste resource utilization technology, specifically a method for preparing dry-mixed mortar for the co-utilization of industrial solid waste. Background Technology

[0002] With the advancement of industrialization, the resource utilization of bulk industrial solid waste has become a critical issue that urgently needs to be addressed in the building materials industry. Among them, red mud, a highly alkaline waste residue produced by the alumina industry, and phosphogypsum, an acidic byproduct produced by the phosphate fertilizer industry, have always been difficult to utilize due to their huge emissions and significant environmental hazards.

[0003] Currently, the utilization of Bayer process red mud is mainly limited by its extremely high alkalinity and potential hydraulic cementitious inertness. The large amount of soluble sodium salts (such as sodium hydroxide and sodium carbonate) remaining in red mud not only leads to severe efflorescence, damaging the surface aesthetics and structural integrity of building materials, but also causes poor volume stability. Furthermore, the aluminosilicate minerals on the surface of red mud particles are usually encased in old carbonate or inert oxide films, making it difficult to participate in hydration reactions at room temperature. This results in it primarily existing as an inert filler in the cementing system, with a low contribution to activity.

[0004] Meanwhile, the resource utilization of phosphogypsum faces bottlenecks due to impurities and poor water resistance. Residual impurities in phosphogypsum, such as soluble phosphorus, fluorine, and organic matter, especially soluble phosphorus pentoxide, adsorb onto the surface of cement particles, forming an insoluble film that severely hinders the cement hydration process, resulting in abnormally prolonged setting time (retarded setting) and reduced early strength. Furthermore, untreated phosphogypsum-based materials have high porosity and a low softening coefficient, making them highly susceptible to strength degradation in humid environments, severely limiting their application in building mortars.

[0005] Although existing technologies attempt to combine red mud and phosphogypsum for composite utilization, aiming to neutralize these two solid wastes through acid-base neutralization, simple physical mixing cannot fundamentally alter their crystal structure and surface properties. In conventional mixing systems, the free alkali in red mud is not effectively solidified, still posing a risk of precipitation; while the phosphorus impurities in phosphogypsum are not completely passivated, still interfering with the cementitious reaction. Furthermore, due to the lack of effective activation methods, it is difficult to form dense chemical bonds between the solid waste components and the cement matrix, resulting in materials that typically require high doses of cement clinker to maintain basic strength, hindering truly low-carbon and high-content utilization. Therefore, developing a synergistic treatment technology that can simultaneously address the issues of red mud efflorescence, phosphogypsum's retarding and poor water resistance, and can activate the potential activity of both, is currently the key technology for achieving large-scale, high-value utilization of these two solid wastes. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for preparing dry-mixed mortar that utilizes industrial solid waste in a synergistic manner. This method solves the problems in existing technologies where Bayer red mud is prone to efflorescence and surface inertia due to its high alkalinity, and undisturbed phosphogypsum suffers from severe retardation and poor water resistance due to phosphorus impurities. As a result, these two materials cannot be efficiently utilized in large quantities, and the prepared mortar has insufficient mechanical properties and durability.

[0007] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a dry-mixed mortar for the co-utilization of industrial solid waste, employing the following technical solution: A dry-mixed mortar for the co-utilization of industrial solid waste is made from the following raw materials in parts by weight: modified powder precursor raw materials: 100 parts Bayer process red mud, 120-150 parts undisturbed phosphogypsum, 3-6 parts sodium fluorosilicate, and 6.5-12.5 parts lightly calcined magnesium oxide; regulating component raw materials: 25-45 parts ordinary silicate cement; aggregates and admixtures: 760-1250 parts fine aggregates and 1.5-4.0 parts functional admixtures.

[0008] By adopting the above technical solution, this invention utilizes a composite modification system composed of sodium fluorosilicate and lightly calcined magnesium oxide to achieve synergistic modification of highly alkaline Bayer process red mud and phosphorus-containing phosphogypsum. Specifically, a multi-mineralization network is constructed within the system: the fluorine source provided by sodium fluorosilicate converts free alkali in the red mud into insoluble fluoride salts, eliminating the risk of efflorescence; on the other hand, it works in conjunction with lightly calcined magnesium oxide to convert soluble phosphates in phosphogypsum into inert magnesium fluorophosphate minerals, eliminating the phosphorus retarding effect. Simultaneously, the active aluminum-silicon components in the red mud, the calcium sulfate in the phosphogypsum, and magnesium oxide and cement hydration products undergo a hydraulic cementitious reaction to generate dense MASH (magnesium-aluminum-silicon-hydrate) and calcium vanadium phase, endowing the mortar with excellent mechanical strength and water resistance.

[0009] Preferably, the raw materials are in the following weight proportions: 100 parts Bayer red mud; 130-140 parts unprocessed phosphogypsum; 4-5 parts sodium fluorosilicate; 8.0-10.0 parts lightly calcined magnesium oxide; 30-40 parts ordinary silicate cement; 800-1000 parts fine aggregate; and 2.0-3.0 parts functional admixtures.

[0010] By adopting the above technical solution, the proportions of each component are in the optimal synergistic range, which can maximize the filling effect and cementing activity of red mud and phosphogypsum, while ensuring the workability and volume stability of the mortar.

[0011] Preferably, the modified powder precursor raw material has the following characteristics: the pH value of the Bayer process red mud is 10.5-12.0; the pH value of the undisturbed phosphogypsum is 1.5-4.5, and it contains 0.2wt%-1.5wt% soluble phosphorus pentoxide.

[0012] By adopting the above technical solution, the acidity, alkalinity and impurity range of solid waste raw materials are limited, ensuring that the acid etching ability of sodium fluorosilicate matches the alkalinity of red mud, and that the amount of magnesium oxide added is sufficient to passivate phosphorus impurities in phosphogypsum.

[0013] Preferably, the functional additive is composed of hydroxypropyl methylcellulose and redispersible latex powder, and the weight ratio of hydroxypropyl methylcellulose to redispersible latex powder is 1:(2-4).

[0014] By adopting the above technical solutions, hydroxypropyl methylcellulose provides water retention and thickening effects to prevent mortar bleeding; redispersible latex powder forms a polymer film in the hardened body, enhancing interfacial adhesion and flexibility. The combination of the two improves the workability and construction properties of mortar with high solid waste content.

[0015] Preferably, the fine aggregate is natural river sand or manufactured sand, and its particle size distribution is a continuous gradation of 0-2.36 mm. By adopting the above technical solution, the continuously graded aggregate can construct a compact aggregate skeleton, reduce the filling voids of the cementitious material, and improve the density and compressive strength of the mortar.

[0016] Secondly, the present invention provides a method for preparing dry-mixed mortar for the co-utilization of industrial solid waste, which adopts the following technical solution: A method for preparing dry-mixed mortar for the co-utilization of industrial solid waste, comprising the following steps: S1. Targeted etching activation: Weighed Bayer red mud and sodium fluorosilicate are put into a ball mill for the first stage of grinding. The adsorbed water on the surface of the red mud induces the hydrolysis of sodium fluorosilicate, and the red mud particles are dealkalized and etched to obtain a primary activated powder. S2, Fluorine Migration and Reconstruction: Keep the activated powder in the ball mill without removing it, and continue to add the weighed original phosphogypsum and lightly calcined magnesium oxide to the ball mill for the second stage of grinding. Use the fluorine ions generated in step S1 to induce magnesium oxide to dephosphorize and passivate the phosphogypsum and reconstruct the crystal lattice to obtain the modified composite cementitious powder. S3. Finished dry-mixed mortar: The modified composite cementitious powder is exported and sent to a mixer, and weighed ordinary silicate cement, fine aggregate and functional admixture are added. The mixture is stirred and mixed evenly to obtain the dry-mixed mortar.

[0017] By adopting the above technical solution, this invention innovatively employs a stepwise mechanochemical ball milling process. Through strict control of the feeding sequence and grinding stages, it achieves directional regulation of the chemical reaction. The specific modification mechanism is as follows: Phase 1 (S1): Directed dealkalization and lattice activation During the first stage of grinding, sodium fluorosilicate undergoes a hydrolysis reaction with trace amounts of adsorbed water on the surface of the red mud under mechanical force, producing hydrofluoric acid and silica gel. Since no other competing alkaline substances (such as magnesium oxide) are present in the system at this stage, the acidic hydrolysis products target the alkaline sites (Na₂O₃) on the surface of the red mud particles. + The following chemical transformations occur during this process: Solidification and prevention of efflorescence: Soluble sodium ions in red mud combine with fluoride ions to form extremely insoluble sodium fluoride (NaF) or sodium fluoroaluminate precipitates, which thermodynamically block the migration path of sodium ions and completely solve the problem of efflorescence in red mud-based building materials.

[0018] Surface etching and exposure: Acid etching destroys the old carbonate and aluminosilicate inert shells on the surface of red mud particles, exposing fresh, highly active aluminum-silicon-oxygen tetrahedral sites inside, providing nuclei for subsequent hydration reactions.

[0019] Phase 2 (S2): Fluoride ion relay migration and phosphorus removal reconstruction While keeping the S1 product intact, phosphogypsum and lightly calcined magnesium oxide are introduced. At this point, the free fluoride ions generated in the S1 stage and the unreacted active fluorides act as chemical shuttles, initiating a cascade reaction: Phosphorus removal and passivation: Fluoride ions induce the reaction between soluble phosphorus pentoxide (P2O5) in phosphogypsum and magnesium oxide, which is rapidly converted into insoluble and chemically stable magnesium fluorophosphate or magnesium phosphate minerals, thus removing the shielding and retarding effect of soluble phosphorus on cement hydration.

[0020] Dual gel network construction: Lightly calcined magnesium oxide undergoes an in-situ mineralization reaction with the active aluminum-silicon components of red mud exposed in the S1 stage under mechanical stimulation, generating MASH (magnesium-aluminum-silicon-hydrate) gel. This gel phase interweaves with the ettringite phase generated by the hydration of phosphogypsum, constructing a dense microstructure that endows the material with excellent water resistance and mechanical strength.

[0021] Preferably, in step S1, the Bayer red mud and undisturbed phosphogypsum are pre-treated by drying, and the moisture content of the Bayer red mud entering the mill is controlled to be 0.5wt%-2.0wt%, and the moisture content of the undisturbed phosphogypsum entering the mill is controlled to be 0.1wt%-1.0wt%.

[0022] By adopting the above technical solutions, strictly controlling the moisture content can prevent the material from agglomerating or sticking to the wall during ball milling, thus ensuring grinding efficiency. On the other hand, retaining trace amounts of adsorbed water (0.5%-2.0%) in the red mud is a necessary condition for inducing the hydrolysis of sodium fluorosilicate to start the etching reaction, while controlling the low moisture content of gypsum can prevent the cementitious material from prematurely hydrating and failing during storage.

[0023] Preferably, the specific process parameters for steps S1 and S2 are as follows: the ball-to-material mass ratio for the first stage of grinding is (8-12):1, the rotation speed is 350-500 r / min, and the grinding time is 15-25 minutes; the second stage of grinding maintains the same ball-to-material mass ratio as the first stage of grinding, the rotation speed is 300-400 r / min, and the grinding time is 15-20 minutes.

[0024] By employing the above technical solution, the mechanical energy provided by high-energy ball milling causes lattice distortion and defects in solid particles, reducing the activation energy of the chemical reaction. The phased control of rotation speed and time ensures sufficient etching of the red mud in the first stage while avoiding excessive grinding in the second stage that could lead to excessive damage to the phosphogypsum crystal structure and reduced strength, thus achieving a balance between energy consumption and performance.

[0025] Preferably, in step S2, the fineness of the modified composite gel powder is controlled as follows: specific surface area of ​​450-650 m2 / kgm2 / kg, and particle size distribution D90 of 45-75 μm.

[0026] By adopting the above technical solution, controlling the specific surface area range ensures that the modified powder has suitable hydration reactivity. If it is too low, the early strength will be insufficient; if it is too high, the water demand will increase dramatically, leading to mortar shrinkage and cracking. The particle size distribution allows the modified powder to effectively fill the voids caused by the cement particle gradation, exerting the micro-aggregate filling effect.

[0027] Preferably, in step S3, the mixing is performed using a twin-shaft blade zero-gravity mixer or a plow mixer, and the mixing time is 180-300 seconds until the material has no visible color difference.

[0028] By adopting the above technical solution, selecting powerful mixing equipment and controlling the mixing time, the uniform dispersion of trace amounts of additives and high amounts of solid waste powder at both the macroscopic and microscopic scales is ensured, thus guaranteeing the consistency and stability of the finished mortar performance.

[0029] This invention provides a method for preparing dry-mixed mortar for the co-utilization of industrial solid waste. It has the following beneficial effects: 1. This invention employs a unique stepwise mechanochemical ball milling process, achieving targeted synergistic modification of Bayer process red mud and undisturbed phosphogypsum through strict control of the feeding sequence. In the first stage, sodium fluorosilicate preferentially etches the inert shell layer on the surface of the red mud and solidifies the free alkali. In the second stage, fluoride ions migrate through intermediate channels to induce magnesium oxide for dephosphorization and passivation of the phosphogypsum. This process completely solves two major industry problems: the high alkali content of red mud leading to efflorescence and the phosphorus-containing impurities in phosphogypsum causing delayed coagulation. This allows these two major industrial solid wastes to replace cement clinker at a very high proportion, achieving efficient synergistic utilization of solid waste resources.

[0030] 2. The dry-mixed mortar prepared by this invention exhibits excellent volume stability and water resistance. The sparingly soluble sodium fluoride and fluoroaluminate generated in the reaction system thermodynamically block the migration path of sodium ions, eliminating the efflorescence problem of traditional red mud-based building materials. Simultaneously, the activated aluminum-silicon components in the red mud react in situ with magnesium oxide to generate a dense MASH (magnesium-aluminum-silicon-hydrate) gel. This gel phase interweaves with the calcium vanadate crystals to construct a highly water-resistant microstructure, improving the material's softening coefficient and enabling it to adapt to the construction requirements in humid environments.

[0031] 3. This invention induces lattice distortion and defects in solid particles through mechanochemical action, reducing the activation energy of the chemical reaction and endowing the composite powder with independent and high hydraulic cementitious activity. Even with a reduced amount of ordinary Portland cement, the resulting mortar still achieves and exceeds the M15-M25 grade standard in 28 days. Furthermore, by controlling the specific surface area and particle size distribution (D90) of the modified powder, the particle size distribution is optimized, and the micro-aggregate filling effect further enhances the density and mechanical properties of the hardened body. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.

[0033] Preparation Examples 1-3: Preparation Example 1: 100.0 parts of dried and pretreated Bayer red mud and 4.5 parts of sodium fluorosilicate were added to a planetary ball mill. Zirconia balls were used as the grinding medium, and the ball-to-material mass ratio was controlled at 10:1. The first stage of grinding was carried out for 20 minutes at a speed of 400 r / min to obtain a primary activated powder. The primary activated powder was kept in the ball mill jar without being removed. 135.0 parts of undisturbed phosphogypsum and 9.0 parts of lightly calcined magnesium oxide were added to the jar. The same ball-to-material ratio and speed were maintained, and the second stage of grinding was carried out for 20 minutes. After grinding, the powder was discharged. All of the obtained powder passed through a 0.08 mm square hole sieve, and the sieve residue was less than 8.0%, which yielded modified composite cementitious powder A1.

[0034] Preparation Example 2: 100.0 parts of dried and pretreated Bayer red mud and 3.0 parts of sodium fluorosilicate were added to a planetary ball mill. Zirconia balls were used as the grinding medium, and the ball-to-material mass ratio was controlled at 8:1. The first stage of grinding was carried out for 15 minutes at a speed of 350 r / min to obtain a primary activated powder. The primary activated powder was kept in the ball mill jar without being removed. 120.0 parts of undisturbed phosphogypsum and 6.6 parts of lightly calcined magnesium oxide were added to the jar. The same ball-to-material ratio and speed were maintained, and the second stage of grinding was carried out for 15 minutes. After grinding, the powder was discharged. All of the obtained powder passed through a 0.08 mm square hole sieve, and the sieve residue was less than 8.0%, which yielded modified composite cementitious powder A2.

[0035] Preparation Example 3: 100.0 parts of dried and pretreated Bayer red mud and 6.0 parts of sodium fluorosilicate were added to a planetary ball mill. Zirconia balls were used as the grinding medium, and the ball-to-material mass ratio was controlled at 12:1. The first stage of grinding was carried out for 25 minutes at a speed of 500 r / min to obtain a primary activated powder. The primary activated powder was kept in the ball mill jar without being removed. 150.0 parts of undisturbed phosphogypsum and 12.5 parts of lightly calcined magnesium oxide were added to the jar. The same ball-to-material ratio and speed were maintained, and the second stage of grinding was carried out for 20 minutes. After grinding, the powder was discharged. All of the obtained powder passed through a 0.08 mm square hole sieve, and the sieve residue was less than 8.0%, which yielded modified composite cementitious powder A3.

[0036] Examples 1-4: Example 1: This example provides a dry-mixed mortar based on the co-utilization of industrial solid waste, the raw material components of which include, by weight: The modified composite cementitious powder A1 obtained in Preparation Example 1 consisted of 248.5 parts, ordinary silicate cement 35.0 parts, natural river sand 850.0 parts, hydroxypropyl methylcellulose 0.8 parts, and redispersible latex powder 2.0 parts.

[0037] The preparation method of this dry-mixed mortar includes the following steps: accurately weighed modified composite cementitious powder A1 is added to a biaxial blade zero-gravity mixer, followed by ordinary silicate cement, natural river sand, hydroxypropyl methylcellulose and redispersible latex powder in sequence. The mixer is started and stirred for 180 seconds at a spindle speed of 50 r / min until the material is evenly dispersed and there is no visible color difference. After sampling and testing, the mortar is packaged at the valve port to obtain the finished product.

[0038] Example 2: This example provides a dry-mixed mortar based on the co-utilization of industrial solid waste, the raw material components of which include, by weight: The modified composite cementitious powder A2 obtained in Preparation Example 2 consisted of 229.6 parts, ordinary silicate cement 25.0 parts, natural river sand 760.0 parts, hydroxypropyl methylcellulose 0.5 parts, and redispersible latex powder 1.0 parts.

[0039] The preparation method of this dry-mixed mortar includes the following steps: accurately weighed modified composite cementitious powder A2 is added to a biaxial blade zero-gravity mixer, followed by ordinary silicate cement, natural river sand, hydroxypropyl methylcellulose and redispersible latex powder in sequence. The mixer is started and stirred for 240 seconds at a spindle speed of 45 r / min until the material is evenly dispersed and there is no visible color difference. After sampling and testing, the mortar is packaged at the valve port to obtain the finished product.

[0040] Example 3: This example provides a dry-mixed mortar based on the co-utilization of industrial solid waste, the raw material components of which include, by weight: The modified composite cementitious powder A3 obtained in Preparation Example 3 consisted of 268.5 parts, ordinary silicate cement 45.0 parts, natural river sand 1250.0 parts, hydroxypropyl methylcellulose 1.0 part, and redispersible latex powder 3.0 parts.

[0041] The preparation method of this dry-mixed mortar includes the following steps: accurately weighed modified composite cementitious powder A3 is added to a biaxial blade zero-gravity mixer, followed by ordinary silicate cement, natural river sand, hydroxypropyl methylcellulose and redispersible latex powder in sequence. The mixer is started and stirred for 300 seconds at a spindle speed of 60 r / min until the material is evenly dispersed and there is no visible color difference. After sampling and testing, the mortar is packaged at the valve port to obtain the finished product.

[0042] Example 4: This example provides a dry-mixed mortar based on the co-utilization of industrial solid waste, the raw material components of which, by weight, include: The modified composite cementitious powder A1 obtained in Preparation Example 1 consisted of 248.5 parts, ordinary silicate cement 30.0 parts, natural river sand 975.0 parts (mortar-to-sand ratio approximately 1:3.5), 0.9 parts, hydroxypropyl methylcellulose, and 2.5 parts, redispersible latex powder.

[0043] The preparation method of this dry-mixed mortar includes the following steps: accurately weighed modified composite cementitious powder A1 is added to a plow mixer, followed by ordinary silicate cement, natural river sand, hydroxypropyl methylcellulose and redispersible latex powder in sequence. The mixer is started and stirred for 200 seconds at a spindle speed of 55 r / min until the material is evenly dispersed and there is no visible color difference. After sampling and testing, the mortar is packaged at the valve port to obtain the finished product.

[0044] Comparative Examples 1-5: Comparative Example 1: Compared with Example 1, the difference lies in the preparation process of the modified composite cementitious powder A1. This comparative example adopts a one-step mixing ball milling method, specifically: 100.0 parts of Bayer red mud, 4.5 parts of sodium fluorosilicate, 135.0 parts of undisturbed phosphogypsum and 9.0 parts of lightly calcined magnesium oxide are all added to a planetary ball mill at one time and continuously ground at the same speed for 40 minutes. There is no step feeding operation involved, and everything else is the same.

[0045] Comparative Example 2: Compared with Example 1, the difference is that component C (sodium fluorosilicate) was not added when preparing the modified composite gel powder A1, and only red mud was put into the ball mill for grinding in the first stage, while the rest were the same.

[0046] Comparative Example 3: Compared with Example 1, the difference is that no component F (lightly calcined magnesium oxide) was added when preparing the modified composite gel powder A1, and only phosphogypsum was added to the ball mill jar for co-grinding in the second stage, while the rest were the same.

[0047] Comparative Example 4: Compared with Example 1, the difference is that the feeding sequence in the preparation process of modified composite gel powder A1 was changed. Specifically, in the first stage, phosphogypsum and sodium fluorosilicate were mixed and ground for 20 minutes. In the second stage, red mud and lightly calcined magnesium oxide were added and ground for another 20 minutes. The rest were the same.

[0048] Comparative Example 5: Compared with Example 1, the difference is that the modified composite gel powder A1 was not modified by mechanochemical ball milling, but was directly mixed by simple physical stirring in a twin-shaft blade zero-gravity mixer according to the proportion of Example 1, with red mud, sodium fluorosilicate, phosphogypsum and lightly calcined magnesium oxide. All other aspects were the same.

[0049] Test Example 1-3: Test Example 1: Basic Physical and Mechanical Properties Test Experimental description: This test aims to verify the physical and mechanical properties of the dry-mixed mortars prepared in Examples 1 to 4 under standard working conditions and to evaluate whether they meet the application requirements of building mortar. The test procedure is carried out in accordance with JGJ / T70-2009 "Standard for Test Methods of Basic Performance of Building Mortar" and GB / T25181-2019 "Premixed Mortar".

[0050] The specific operating steps are as follows: Sample preparation: Take the finished dry-mixed mortars from Examples 1 to 4 respectively, add metered tap water to a mixer, and mix for 180 seconds. The amount of water used is determined based on the mortar consistency, which is controlled within the range of 80mm-90mm.

[0051] Consistency and water retention rate test: After mixing, the settling degree of the mixture was immediately measured using a mortar consistency meter; then the water retention rate of the mortar was measured by vacuum filtration and the data were recorded.

[0052] Setting time determination: The premixed mortar is loaded into a frustum-shaped container and measured using a penetration resistance meter at a laboratory temperature of 20±2℃. The time when the penetration resistance reaches 0.5MPa is the initial setting time, and the time when it reaches 3.5MPa is the final setting time.

[0053] Mechanical strength test: The mixed mortar was poured into a triple steel mold (40mm×40mm×160mm) and compacted on a vibrating table. The specimens were cured in the mold for 24 hours in a standard curing room (temperature 20±2℃, relative humidity ≥90%), then demolded and cured further until the specified curing age (7 days and 28 days). After reaching the specified curing age, the flexural and compressive strengths of the specimens were determined using a flexural and compressive strength testing machine.

[0054] Test results: Table 1. Test data of physical and mechanical properties of dry-mixed mortar in Examples 1-4 Testing items Example 1 Example 2 Example 3 Example 4 Water consumption (wt%) 15.2 14.8 15.6 15.1 Consistency (mm) 86 84 88 85 Water retention rate (%) 92.4 91.1 93.6 91.8 Initial setting time (min) 255 238 285 260 Final setting time (min) 390 365 425 405 7-day flexural strength (MPa) 3.4 2.9 3.6 2.5 7-day compressive strength (MPa) 14.2 11.5 15.1 9.8 28-day flexural strength (MPa) 5.8 4.7 6.1 4.1 28-day compressive strength (MPa) 23.8 19.4 25.3 16.7 Results analysis: Table 1 shows that the dry-mixed mortars prepared in Examples 1 to 4 all meet or exceed the standard requirements of ordinary dry-mixed masonry mortars of grades M10 to M25 in terms of various physical and mechanical properties.

[0055] Data shows that despite the introduction of large amounts of red mud and phosphogypsum industrial solid waste into the formulation, the setting time of the samples was still controlled within the allowable range for normal construction (initial setting > 4 hours, final setting < 8 hours). This confirms that in the stepwise ball milling process, the lightly calcined magnesium oxide introduced in the second stage, under the catalysis of free fluoride ions generated in the first stage, effectively reacts chemically with the soluble phosphates in phosphogypsum to generate insoluble fluorophosphate minerals, thereby removing the shielding effect of phosphorus impurities on cement hydration.

[0056] Meanwhile, the sample samples exhibited high compressive strength (16.7-25.3 MPa) at 28 days. This strength development stemmed from the directional etching of the red mud surface by sodium fluorosilicate in the first stage. The exposed active aluminum-silicon components underwent a synergistic mineralization reaction with the subsequently added magnesium oxide and cement hydration products, constructing a dense MASH (magnesium-aluminum-silicon-hydrate) and CSH (calcium silicate hydrate) dual gel network within the system. Example 4 maintained acceptable strength indicators even with reduced cement content, indicating that the modified solid waste composite powder possesses independent hydraulic cementitious activity.

[0057] Test Example 2: Durability and Special Performance Tests Experimental description: This test addresses the technical characteristics of red mud-based materials being prone to efflorescence and phosphogypsum-based materials having poor water resistance. It designs an efflorescence degree assessment and a water resistance (softening coefficient) test to verify the durability of the samples from Examples 1 to 4.

[0058] Alkali bloom assessment: An accelerated test was conducted using a semi-immersion method. Specimens (40mm×40mm×160mm) cured for 7 days were placed vertically in a rectangular water tank, and distilled water was added to 1 / 3 of the specimen's height (approximately 50mm). The room temperature was maintained at 23±2℃, relative humidity at 50±5%, and there was no wind interference. After immersion for 7 days, the surface condition of the un-immersed portions was observed.

[0059] The evaluation criteria are as follows: None: The surface is dry, retains its original color, and has no visible exudate.

[0060] Slight: Scattered white spots appear on edges or localized areas, covering less than 5% of the total surface area.

[0061] Obvious: A continuous white crystalline layer or powder appears on the surface, covering an area of ​​5%-50%.

[0062] Severe: The surface is covered by a thick layer of white substance, covering more than 50% of the area, or accompanied by surface peeling.

[0063] Water resistance test (softening coefficient): Six specimens from each of the embodiments, cured to 28 days of age, were divided into two groups. The first group was dried in a 60℃ oven to constant weight, cooled to room temperature, and then its dry compressive strength was measured. The second group was completely immersed in water at 20±2℃ for 48 hours. After being removed and dried, the water absorption saturated compressive strength was measured. .

[0064] Softening coefficient According to the formula This index is calculated to reflect the strength retention rate of a material in a humid environment.

[0065] Test results: Table 2. Test data on alkali efflorescence and water resistance of dry-mixed mortars in Examples 1-4 Testing items Example 1 Example 2 Example 3 Example 4 28-day dry compressive strength (MPa) 24.1 19.8 25.6 17.2 28-day saturated compressive strength (MPa) 21.3 16.5 23.4 13.5 Softening coefficient (K) 0.88 0.83 0.91 0.78 Semi-immersion efflorescence assessment none none none none Surface condition description Smooth surface and uniform color No precipitation on the surface, intact edges The surface is dense and free of white spots. No precipitation was observed on the surface; the surface appeared slightly rough. Results analysis: Table 2 shows that all the sample samples prepared using the method of this invention were rated as alkali-free in the semi-immersion accelerated test, and the softening coefficient remained between 0.78 and 0.91, which is better than the water resistance level of ordinary gypsum-based materials.

[0066] Regarding the efflorescence performance, none of the examples exhibited the sodium salt precipitation phenomenon commonly seen in red mud-based materials. The underlying mechanism lies in the chemical precipitation reaction between sodium fluorosilicate and soluble alkalis (sodium hydroxide, sodium carbonate) in the red mud during the first-stage ball milling process, under an acidic microenvironment. This reaction transforms the reactive free sodium ions into extremely insoluble sodium fluoride (NaF) and fluoroaluminate microcrystals. This chemical sodium fixation mechanism thermodynamically reduces the likelihood of sodium ions migrating to the mortar surface with moisture, thereby eliminating efflorescence.

[0067] Regarding water resistance, the sample in the example exhibits a high softening coefficient. This is because the magnesium oxide introduced in the second stage undergoes an in-situ mineralization reaction with the active aluminosilicate components exposed by etching in the first stage, generating a water-resistant MASH (magnesium aluminosilicate) gel phase. This gel phase, together with the generated magnesium fluorophosphate precipitate, fills the micropores of the hardened body, blocking the channels for water intrusion, allowing the material to maintain high structural strength even under long-term water immersion. The slightly lower softening coefficient (0.78) in Example 4 is mainly attributed to the relatively increased total porosity of the matrix due to the reduced cement content, but it still meets the requirements for use in general humid environments. Test Example 3: Comparative Analysis Test Experimental description: This test aims to verify the impact of key technical features such as step-by-step ball milling, sodium fluorosilicate etchant, and lightly calcined magnesium oxide reconstructing agent on the final performance of dry-mixed mortar by comparing the performance differences between Example 1 and various comparative samples.

[0068] The test subjects included Example 1 (preferred scheme) and Comparative Examples 1 to 5. The test methods were consistent with those of Example 1 and Example 2, focusing on four key indicators: setting time, 28-day compressive strength, softening coefficient, and degree of efflorescence.

[0069] Test results: Table 3. Performance comparison test data of Example 1 and Comparative Examples 1-5 Group Initial setting / final setting time (min) 28-day compressive strength (MPa) Softening coefficient Assessment of the degree of efflorescence Example 1 255 / 390 23.8 0.88 none Comparative Example 1 270 / 415 11.4 0.62 obvious Comparative Example 2 245 / 380 7.2 0.45 serious Comparative Example 3 >2880 (not frozen) — (Unable to be demolded) — — Comparative Example 4 265 / 400 9.6 0.54 obvious Comparative Example 5 480 / 650 4.8 0.38 serious Note: "—" indicates that subsequent testing could not be performed because the sample had not solidified or its strength was too low.

[0070] Results analysis: Based on the data in Table 3, the reaction mechanism is analyzed as follows: The decisive role of process sequence: The compressive strength of Example 1 is higher than that of Comparative Example 1 (one-step ball milling) and Comparative Example 4 (gypsum grinding first). Comparative Example 1 uses mixed ball milling, where sodium fluorosilicate preferentially reacts with alkaline lightly calcined magnesium oxide in an acid-base neutralization reaction, consuming the fluorine source. This results in the aluminosilicate shell on the surface of the red mud not being effectively etched, and the activity not being released. At the same time, because sodium fluorosilicate fails to react with the free alkali in the red mud, significant efflorescence occurs in the product. Comparative Example 4 changes the feeding sequence. Sodium fluorosilicate is co-milled with acidic phosphogypsum in the first stage, preferentially combining with calcium ions to form inert calcium fluoride, similarly losing its subsequent activation ability for the red mud. Data confirms that a process sequence of red mud etching first, followed by component reconstruction, must be followed to ensure that the chemical reaction proceeds according to the preset path.

[0071] The etching and sodium fixation functions of sodium fluorosilicate: In Comparative Example 2, without the addition of sodium fluorosilicate, the 28-day compressive strength was only 7.2 MPa, and the efflorescence assessment was severe. This indicates that in the absence of acidic fluoride etching, the red mud remains in an inert state and cannot participate in the gelation reaction; furthermore, the large amount of soluble sodium ions carried by the red mud are not chemically fixed and migrate to the surface with moisture for precipitation. Sodium fluorosilicate is not only an activator but also a key component in inhibiting efflorescence.

[0072] The phosphorus removal and synergistic effects of magnesium oxide: In Comparative Example 3, without the addition of lightly calcined magnesium oxide, the sample remained in a plastic state (unset) after 48 hours. This indicates that treatment with sodium fluorosilicate alone cannot eliminate the inhibitory effect of soluble phosphorus in phosphogypsum on cement hydration. The magnesium oxide introduced in the second stage, with the assistance of fluoride ions, converts soluble phosphorus into insoluble magnesium phosphate or magnesium fluorophosphate minerals, which is a necessary condition for ensuring normal setting of the mortar.

[0073] The necessity of mechanochemical activation: Comparative Example 5, which only underwent physical mixing, exhibited the lowest performance indicators. This confirms that simple component superposition cannot achieve the synergistic utilization of solid waste. The performance improvement described in this scheme does not stem from a simple filling effect of the raw materials, but rather from the lattice distortion, chemical bond breaking, and subsequent mineral phase reconstruction induced during high-energy ball milling.

Claims

1. A dry-mixed mortar for the co-utilization of industrial solid waste, characterized in that, Made from the following ingredients in parts by weight: Modified powder precursor raw materials: 100 parts Bayer process red mud; 120-150 parts raw phosphogypsum; 3-6 parts sodium fluorosilicate; 6.5-12.5 parts lightly calcined magnesium oxide; Adjusting component raw materials: 25-45 parts of ordinary Portland cement; Aggregates and admixtures: 760-1250 parts fine aggregates; 1.5-4.0 parts functional admixtures.

2. The dry-mixed mortar for the co-utilization of industrial solid waste according to claim 1, characterized in that, The weight parts of the raw materials are: 100 parts Bayer red mud; 130-140 parts unprocessed phosphogypsum; 4-5 parts sodium fluorosilicate; 8.0-10.0 parts lightly calcined magnesia; 30-40 parts ordinary silicate cement; 800-1000 parts fine aggregate; 2.0-3.0 parts functional admixtures.

3. The dry-mixed mortar for the co-utilization of industrial solid waste according to claim 1, characterized in that, The modified powder precursor raw material has the following characteristics: The pH value of the Bayer red mud is 10.5-12.0; The undisturbed phosphogypsum has a pH of 1.5-4.5 and contains 0.2wt%-1.5wt% soluble phosphorus pentoxide.

4. The dry-mixed mortar for the co-utilization of industrial solid waste according to claim 1, characterized in that, The functional additive is composed of hydroxypropyl methylcellulose and redispersible latex powder, and the weight ratio of hydroxypropyl methylcellulose to redispersible latex powder is 1:(2-4).

5. The dry-mixed mortar for the co-utilization of industrial solid waste according to claim 1, characterized in that, The fine aggregate is natural river sand or manufactured sand, and the particle size distribution is a continuous gradation of 0-2.36 mm.

6. A method for preparing dry-mixed mortar for the co-utilization of industrial solid waste, characterized in that, The method for preparing a dry-mixed mortar for the co-utilization of industrial solid waste as described in any one of claims 1-5 comprises the following steps: S1. Targeted etching activation: Weighed Bayer red mud and sodium fluorosilicate are put into a ball mill for the first stage of grinding. The adsorbed water on the surface of the red mud induces the hydrolysis of sodium fluorosilicate, and the red mud particles are dealkalized and etched to obtain a primary activated powder. S2, Fluorine Migration and Reconstruction: Keep the activated powder in the ball mill without removing it, and continue to add the weighed original phosphogypsum and lightly calcined magnesium oxide to the ball mill for the second stage of grinding. Use the fluorine ions generated in step S1 to induce magnesium oxide to dephosphorize and passivate the phosphogypsum and reconstruct the crystal lattice to obtain the modified composite cementitious powder. S3. Finished dry-mixed mortar: The modified composite cementitious powder is exported and sent to a mixer, and weighed ordinary silicate cement, fine aggregate and functional admixture are added. The mixture is stirred and mixed evenly to obtain the dry-mixed mortar.

7. The method for preparing dry-mixed mortar for the co-utilization of industrial solid waste according to claim 6, characterized in that, In step S1, the Bayer red mud and undisturbed phosphogypsum are pre-treated by drying, and the moisture content of the Bayer red mud entering the mill is controlled to be 0.5wt%-2.0wt%, and the moisture content of the undisturbed phosphogypsum entering the mill is controlled to be 0.1wt%-1.0wt%.

8. The method for preparing dry-mixed mortar for the co-utilization of industrial solid waste according to claim 6, characterized in that, The specific process parameters for steps S1 and S2 are as follows: The mass ratio of balls to material in the first stage of grinding is (8-12):1, the rotation speed is 350-500 r / min, and the grinding time is 15-25 minutes; The second stage of grinding maintains the same ball-to-material mass ratio as the first stage, with a rotation speed of 300-400 r / min and a grinding time of 15-20 minutes.

9. The method for preparing dry-mixed mortar for the co-utilization of industrial solid waste according to claim 6, characterized in that, In step S2, the fineness of the modified composite gelling powder is controlled as follows: Specific surface area is 450-650 m² 2 / kg, and the particle size distribution D90 is 45-75μm.

10. The method for preparing dry-mixed mortar for the co-utilization of industrial solid waste according to claim 6, characterized in that, In step S3, the mixing is carried out using a twin-shaft blade zero-gravity mixer or a plow mixer, and the mixing time is 180-300 seconds until there is no visible color difference in the material.