A geofixing agent for clayey tailings cemented filling and a method of using the same

Abstract

The present application relates to the technical field of tailings treatment, and particularly relates to a cementing agent for clay tailings cemented filling and a use method thereof, which comprises, in terms of weight fractions, 20-35 parts of fast-hardening sulphoaluminate cement, 8-15 parts of silica fume, 30-60 parts of activated slag powder, 10-20 parts of limestone powder, 5-15 parts of desulfurization gypsum, 6-10 parts of nano SiO2 / Al2O3 composite sol and 30-40 parts of magnesium phosphate-red mud activated microspheres; ions released by the magnesium phosphate-red mud activated microspheres destroy the interlayer hydrogen bonds of kaolinite, reduce the adsorption of free water by clay, cooperate with the fast-hardening sulphoaluminate cement to rapidly form a skeleton, solve the problem of insufficient hydration caused by the imbalance of the water-binder ratio of the cementing material, and meanwhile, the nano SiO2 / Al2O3 composite sol penetrates the clay gap by virtue of the nanoscale size and positive charge characteristics, and in combination with the silica fume and the slag powder, generates a gel in situ on the surface of the clay and constructs a cross-scale bonding network, so that the cementing material and the tailings particles are effectively bonded, the high-clay tailings are efficiently cemented, and the performance of the filling body is improved.

Description

Technical Field

[0001] This invention relates to the technical field of tailings treatment, and in particular to a cementing agent for cementing and backfilling clay tailings and its application method. Background Technology

[0002] With the expansion of mining operations, the treatment of high-kaolinite tailings has become a major challenge for the industry. Current technologies using ordinary Portland cement to treat such tailings have significant drawbacks: high water demand and high cementitious material content are required. Even so, the strength after 28 days of curing only reaches 1.5-2.1 MPa, which is insufficient to meet the strength requirements of mine backfill. Specific problems are as follows:

[0003] Firstly, the adsorption of free water by clay particles leads to the dilution of cementitious materials. Kaolinite has a unique layered structure and its surface is rich in hydroxyl groups, which have a strong adsorption capacity for free water. When ordinary silicate cement is used for bonding, a large amount of free water is adsorbed by kaolinite, resulting in an imbalance in the actual water-cement ratio of cement. The cement hydration reaction is insufficient, and a dense cementitious structure cannot be formed. The cement hydration products cannot effectively wrap and bind the tailing mineral particles, resulting in low strength of the cemented filling body. At the same time, problems such as slurry segregation and bleeding will also occur, affecting the construction performance and stability of the filling body.

[0004] Secondly, conventional materials cannot penetrate clay to form an effective hydration network. Ordinary silicate cement and commonly used auxiliary cementing materials such as silica fume and slag powder have particle sizes mostly in the micrometer range. However, there are a large number of nanometer-sized gaps between clay particles in kaolinite tailings. Conventional materials cannot penetrate these gaps and cannot fully contact the clay particles to undergo a hydration reaction. Therefore, they can only form a loose coating layer on the outside of the clay aggregates and cannot build a continuous and effective hydration network. This results in weak adhesion between the tailings particles and the cementing materials, which seriously restricts the improvement of the overall strength and durability of the backfill.

[0005] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the present invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a cementing agent for cemented backfilling of clay tailings and its application method. The agent utilizes ions released from magnesium phosphate-red mud activated microspheres to disrupt the interlayer hydrogen bonds of kaolinite, reducing the adsorption of free water by the clay. Combined with fast-hardening sulfoaluminate cement, this rapidly forms a framework, resolving the problem of insufficient hydration caused by an imbalance in the water-cement ratio of the cementing material. Simultaneously, the nanoscale size and positive charge of the nano-SiO2 / Al2O3 composite sol are utilized to penetrate the clay gaps, and in conjunction with silica fume and slag powder, a gel is generated in situ on the clay surface, constructing a cross-scale bonding network. This achieves effective bonding between the cementing material and tailings particles, resulting in efficient cementation of high-clay tailings and improved backfill performance.

[0007] The first objective of this invention is to provide a cementing agent for cemented backfilling of clay tailings, comprising, by weight: 20-35 parts of rapid-hardening sulfoaluminate cement, 8-15 parts of silica fume, 30-60 parts of activated slag powder, 10-20 parts of limestone powder, 5-15 parts of desulfurized gypsum, 6-10 parts of nano-SiO2 / Al2O3 composite sol, and 30-40 parts of magnesium phosphate-red mud activated microspheres;

[0008] Mg released by magnesium phosphate-red mud activated microspheres 2+ Fe 3+ Coordination with hydroxyl groups on the kaolinite surface disrupts interlayer hydrogen bonds and promotes lattice disintegration. This reduces the adsorption of free water by the clay, while releasing active SiO2 and Al2O3, which provide raw materials for the cementation reaction. Among these, Fe... 3+ Catalytic activation breaks the Al-O-Si bonds in slag powder, synergistically promoting the Si carried by nano-SiO2 / Al2O3 composite sol. 3 + Al 3+ Ions accelerate the dissolution of active components in slag powder in a weakly acidic microenvironment. Meanwhile, the nano-SiO2 / Al2O3 composite sol, with its nanoscale size and positive charge, overcomes the negative charge repulsion on the clay surface, penetrating deep into the nanoscale gaps of clay aggregates. This allows for the in-situ generation of CSH and CASH gels on the activated kaolinite surface, achieving chemical bonding through Si-O-Al bonds. Simultaneously, Mg in the magnesium phosphate-red mud activated microspheres... 2+ SO4 with desulfurized gypsum 2- Synergistically, it accelerates the hydration of fast-hardening sulfoaluminate cement to generate ettringite skeleton, which is supported by the "nano-bridging-micron filling" cross-scale bonding network induced by nano-sol. This not only weakens the water absorption capacity of clay from the source, but also builds a strong chemical bond cementing system that runs through the inside and outside of clay particles. This upgrades the interface between cementing material and clay from physical adsorption to molecular-level bonding, significantly improving the hydration reaction depth and the compactness of the filling body. It systematically solves the problems of interface bonding and hydration efficiency in the cementation of high clay tailings.

[0009] Mg 2+The ionic radius is relatively large (Fe 3+ Ionic radius approximately Mg 2+ Ionic radius approximately If there is no Fe 3+ Pre-disruption of the tight interlayer structure of kaolinite, Mg 2+ Difficult to enter directly, Fe 3+ With its high +3 charge density and small ionic radius, Fe can form strong coordination bonds with hydroxyl groups on the kaolinite surface (such as inner-sphere coordination). Through strong electrostatic interactions and polarization effects, it disrupts interlayer hydrogen bonds and induces lattice distortion. 3+ The initial cracks that break hydrogen bonds are Mg 2+ The entry provides a channel, while Mg 2+ After the interlayer structure was opened up, more Fe was exposed. 3+ The two interact through a cycle of “destruction-expansion-re-destruction”, which greatly increases the lattice disintegration rate compared to the action of a single ion and greatly increases the amount of interlayer active SiO2 dissolution, providing sufficient raw materials for subsequent gelation reactions.

[0010] Limestone powder primarily functions as a filler and auxiliary cementitious agent, improving the particle size distribution of cementitious materials, filling voids between tailings particles, and increasing slurry density. It may also participate in some hydration reactions, further enhancing cementitious strength. Desulfurized gypsum, as a major source of sulfate ions, reacts with Mg released from magnesium phosphate-red mud activated microspheres. 2+ Synergistically, it accelerates the hydration of fast-hardening sulfoaluminate cement, promotes the formation of ettringite skeleton, reduces slurry segregation and bleeding, and enhances the density and early strength of cementitious structure.

[0011] As a preferred embodiment of the present invention, the preparation method of nano-SiO2 / Al2O3 composite sol includes:

[0012] Tetraethyl orthosilicate (TEOS) was dissolved in anhydrous ethanol, and then deionized water and hydrochloric acid were added dropwise. The mixture was stirred at room temperature to obtain a silicon precursor solution containing a silanol intermediate. More specifically, tetraethyl orthosilicate (TEOS) was dissolved in anhydrous ethanol and hydrochloric acid and deionized water were added dropwise. TEOS was hydrolyzed to generate a silanol intermediate (Si-OH) through acidic catalysis (pH≈2-3). At the same time, excessive condensation of silanol to form an oligomer solution was inhibited, ensuring uniform mixing with the aluminum source in the subsequent process. The ethanol solvent prevented local high concentrations from causing agglomeration, providing a stable and dispersed active silicon source for constructing a silicon-aluminum composite network.

[0013] Aluminum isopropoxide is dissolved in anhydrous ethanol and heated and stirred until completely dissolved to form an aluminum source solution. More specifically, aluminum isopropoxide undergoes alcoholysis in anhydrous ethanol under heating (60-80℃) to generate a soluble aluminum alkoxide intermediate, avoiding direct hydrolysis to form Al(OH)3 precipitate. Heating enhances the coordination between the solvent and the aluminum alkoxide, regulates the chemical environment of the aluminum species, and lays the foundation for the subsequent formation of Si-O-Al bonds with silicon precursors through condensation reaction.

[0014] The aluminum source solution is slowly added to the silicon precursor solution to form a silicon-aluminum composite precursor solution; more specifically, the aluminum source solution is slowly dripped into the silicon precursor solution, and Si-O-Al bonds are formed through the co-condensation reaction of silanol and aluminum alkoxide, thereby achieving uniform mixing of silicon-aluminum components at the nanoscale.

[0015] A cationic surfactant was added to the silicon-aluminum composite precursor solution, stirred and dissolved, and the pH was adjusted to 8-9 with ammonia. Then, the solution was ultrasonically dispersed to obtain a nano-SiO2 / Al2O3 composite sol. More specifically, the cationic surfactant adsorbed onto the surface of the sol particles, imparting a positive charge. This positive charge was overcome by electrostatic attraction, which helped the sol penetrate into the nanoscale gaps. Ammonia provided an alkaline environment, which accelerated the condensation reaction of silanol and aluminum alcohol groups.

[0016] As a preferred embodiment of the present invention, the zeta potential of the nano-SiO2 / Al2O3 composite sol is +35±5mV. Kaolinite particles, due to their layered structure and rich hydroxyl content on their surface, are prone to dissociation in aqueous media to form a negatively charged surface (the zeta potential is typically -20 to -40mV), resulting in strong adsorption of free water and repulsion of external cementing components. However, the nano-SiO2 / Al2O3 composite sol, through modification with a cationic surfactant (such as hexadecyltrimethylammonium bromide), carries a stable positive charge on the particle surface. This potential can overcome the negative charge repulsion of the kaolinite surface through electrostatic attraction, prompting the sol particles to actively adsorb and penetrate into the nanoscale gaps between the kaolinite tailings particles, while avoiding particle agglomeration that may be caused by excessively high positive potential, thus ensuring good dispersion of the sol in the tailings slurry.

[0017] As a preferred embodiment of the present invention, the cationic surfactant is one or more of hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, dodecyltrimethylammonium bromide, and octadecyltrimethylammonium bromide. All of the above substances contain trimethylammonium cations, which can be firmly adsorbed onto the surface of nano-SiO2 / Al2O3 composite sol particles under alkaline conditions, imparting a significant positive charge. Furthermore, the long-chain alkyl groups (dodecyl, hexadecyl, octadecyl) of the above substances form a hydrophobic bridging effect between the sol particles and the clay surface. On the one hand, this reduces the surface energy of the particles, inhibits sol aggregation, and ensures nanoscale dispersion. On the other hand, the steric hindrance effect of the alkyl chains can stabilize the sol particles, ensuring their uniform distribution in the tailings slurry, increasing the probability of contact with the hydroxyl groups on the kaolinite surface, and promoting the subsequent chemical bonding of Si-O-Al bonds with the active sites of the clay.

[0018] As a preferred embodiment of the present invention, the method for preparing magnesium phosphate-red mud activated microspheres includes:

[0019] molar ratio Mg 2+ :H2PO4 - =1:1.2-1.5, weigh magnesium oxide and potassium dihydrogen phosphate, add deionized water, and stir evenly at 50-60℃ to form magnesium phosphate slurry; more specifically, potassium dihydrogen phosphate (KH2PO4) dissociates in water to release H + It reacts with magnesium oxide (MgO) to form Mg 2+ and HPO4 2- This forms a magnesium phosphate precursor solution. In this formulation, the phosphorus source is in excess, promoting the formation of magnesium phosphate precursor solution. 2+ It stabilizes and dissolves Mg(OH)2 and inhibits the formation of Mg(OH)2 precipitate;

[0020] The activated red mud is slowly added to the magnesium phosphate slurry at a mass ratio of 3-5:5-7, and mixed thoroughly to form a mixture. This uniform mixing ensures that the activated red mud particles are fully dispersed and evenly coated by the magnesium phosphate slurry, guaranteeing the formation of uniformly distributed nascent microspheres during subsequent atomization and drying processes. This facilitates the release of magnesium phosphate from the magnesium phosphate-red mud activated microspheres within the binder. 2+ Fe 3+ It lays the foundation for active SiO2, Al2O3 and other components to play a synergistic gelling role;

[0021] The mixture is atomized into droplets and dried in hot air to form nascent microspheres. Atomizing the mixture into droplets and drying it in hot air allows the mixture of activated red mud and magnesium phosphate slurry to be evenly dispersed into fine droplets during the atomization process. The hot air quickly evaporates the moisture, causing the material to shrink into spherical particles under the action of surface tension, forming nascent microspheres with a porous structure. This lays the foundation for the uniform release of components and the stability of the microsphere structure during subsequent curing.

[0022] The nascent microspheres were placed in a curing chamber with humidity ≥90% and temperature 25±5℃ for 24-48 hours to obtain magnesium phosphate-red mud activated microspheres. More specifically, during the curing process, the mineral phases (such as Fe2O3) in the red mud formed complexes with magnesium phosphate, regulating the Mg content. 2+ Fe 3+ The release rate allows it to continue to exert its activating effect for 7-14 days, matching the cement hydration process and avoiding flash condensation caused by excessively high early ion concentrations.

[0023] As a preferred embodiment of the present invention, the method for preparing activated red mud includes:

[0024] After calcining and cooling the red mud, sulfuric acid was added for acid etching. After filtration and drying, it was mixed with 0.5-1.3% CaF2 by mass and ground until the particle size was ≤75μm.

[0025] After red mud is calcined, the lattice structure of its internal inert mineral phases (such as aluminosilicates and iron-titanium oxides) is destroyed, and active components such as SiO2 and Al2O3 are exposed. These active components can directly combine with the hydroxyl groups on the surface of kaolinite through hydrogen bonding or condensation reaction, reducing the adsorption sites of free water on the surface of kaolinite.

[0026] Sulfuric acid etching can dissolve some of the metal oxides in red mud, forming a porous and rough structure on the particle surface, which significantly increases the specific surface area. The porous structure allows the red mud particles to be more tightly embedded in the nanoscale gaps between kaolinite tailings particles, breaking through the limitations of conventional micron-sized materials, and directly contacting the surface of clay particles, providing more active sites for subsequent cementation reactions.

[0027] CaF2 can significantly reduce the hardness and agglomeration of materials during the grinding process after red mud calcination, and the F in CaF2... - Ions can chemically react with components such as aluminum and calcium in red mud, forming highly active sites on the surface of red mud particles. These active sites can accelerate the hydration reaction of cementitious materials, especially promote the dissolution and recombination of aluminate and silicate phases, generating more cementitious products such as CSH gel and CASH gel. For the hydroxyl groups on the surface of kaolinite, the active sites can reduce their adsorption of free water through chemical bonding or physical adsorption, alleviate the water-cement ratio imbalance problem, make cement hydration more complete, and form a denser cementitious structure.

[0028] As a preferred embodiment of the present invention, the specific surface area of ​​the rapid-hardening sulfoaluminate cement is ≥400 m². 2 / kg, tricalcium aluminate content is 10-20wt%, dicalcium silicate content is 40-60wt%;

[0029] The high specific surface area gives cement particles a larger reaction interface, accelerates early hydration, rapidly consumes free water, reduces the ineffective adsorption of water by kaolinite, and alleviates the problems of water-cement ratio imbalance and slurry segregation. Tricalcium aluminate and desulfurized gypsum synergistically generate a large number of ettringite needle-like crystals, forming a rigid framework to maintain the stability of the slurry structure and resist clay expansion. The nanoscale CSH gel generated by dicalcium silicate hydration can penetrate the nanoscale gaps between kaolinite particles and enhance the interfacial bonding between tailings and cementitious materials through chemical bonding.

[0030] As a preferred embodiment of the present invention, the method for preparing activated slag powder includes:

[0031] CO2 microbubbles are introduced into the slag powder under a pressure of 0.3-0.5 MPa for 15-20 minutes to form a surface carbonation layer.

[0032] CO2 reacts with components such as CaO and Al2O3 on the surface of slag powder under pressure to form a microlayer of calcium carbonate and bicarbonate. These polar groups can directly bind to the hydroxyl groups on the surface of kaolinite through hydrogen bonds or ionic bonds, reducing the adsorption sites of hydroxyl groups for free water.

[0033] The carbonation layer changes the zeta potential of the slag powder surface from negative to weakly positive, forming a gradient charge distribution with the strong positive charge of the nano-SiO2 / Al2O3 composite sol. This enhances the adsorption of the negatively charged surface of kaolinite through electrostatic synergy, further weakening the clay's competitive adsorption capacity for water.

[0034] A second object of the present invention is to provide a method of using the above-mentioned cementing agent for cemented backfilling of clay tailings, comprising:

[0035] Mix rapid-hardening sulfoaluminate cement, activated slag powder, limestone powder, magnesium phosphate-red mud activated microspheres, and desulfurized gypsum to form basic cementitious materials;

[0036] The nano-SiO2 / Al2O3 composite sol is mixed with silica fume, and then 5-10% anhydrous ethanol (by mass of the nano-SiO2 / Al2O3 composite sol) is added. The mixture is then ultrasonically dispersed to form a pretreated sol. More specifically, the nano-SiO2 / Al2O3 composite sol is prone to local agglomeration due to surface tension when directly added to dry powder. By premixing it with silica fume and adding a small amount of ethanol, a stable dispersion system of "solid carrier-liquid sol" is formed. This system facilitates uniform adhesion to the surface of cement, slag powder, and other particles during the dry mixing stage, avoiding the "agglomeration" problem caused by traditional direct addition. Furthermore, ethanol, as a dispersion medium, evaporates during wet mixing, and the remaining small amount of ethanol does not participate in the gelation reaction, only playing a temporary dispersion role, which meets the safety requirements for building material preparation.

[0037] The pretreated sol is sprayed into the base cementitious material and mixed to form a cementitious agent.

[0038] Curing is carried out after mixing tailings, solidifying agent, water and water-reducing agent.

[0039] The method of this invention forms a basic cementitious material through multi-component dry mixing, which allows the fast-hardening hydration components, long-lasting activated microspheres, and filler materials to work synergistically and uniformly, inhibiting water absorption by kaolinite from the source and activating interlayer activity. The nano-sol and silica fume are dispersed in ethanol to form a stable system, avoiding agglomeration and achieving uniform encapsulation of cementitious material particles with the help of a solid carrier. Its positive charge characteristics enhance interfacial bonding activity, and there is no need to pre-treat tailings. The fluidity of the slurry is directly adjusted by water-reducing agent, which promotes the synergistic effect of ionic debonding, nano-bridging, and micron-filling functions in the cementitious agent during mixing and curing, forming a dense cementitious network that penetrates the inside and outside of the clay. This significantly improves the strength of the filling body and the convenience of construction, and effectively solves the problems of weak interfacial bonding and insufficient hydration in traditional cementing processes.

[0040] As a preferred embodiment of the present invention, the mass ratio of tailings to solidifying agent is 5-8:1. At this ratio, the amount of nano-SiO2 / Al2O3 composite sol and magnesium phosphate-red mud activated microspheres in the solidifying agent is sufficient to cover the surface and nano-interstic gaps of kaolinite particles in the tailings. Through electrostatic attraction, interlayer debonding and other effects, the adsorption of free water by clay is weakened, and CSH gel, ettringite framework and other cementing networks are formed inside and outside the tailings particles, avoiding the problem of weak interfacial bonding caused by insufficient solidifying agent.

[0041] Compared with the prior art, the beneficial effects of the present invention are: 1) The magnesium phosphate-red mud activated microspheres in the binder release Mg 2+ Fe 3+ Coordinating with hydroxyl groups on the kaolinite surface disrupts interlayer hydrogen bonds and promotes lattice disintegration, reducing the adsorption of free water by the clay and alleviating the water-cement ratio imbalance problem at its source; the released active SiO2 and Al2O3 provide raw materials for the cementation reaction, and Fe... 3+ Catalytic activation breaks the Al-O-Si bonds in slag powder, synergistically promoting the Si carried by nano-SiO2 / Al2O3 composite sol. 3+ Al 3+ Ions accelerate the dissolution of active components in slag powder. The nanocomposite sol, with its +35±5mV positive charge characteristics and nanoscale size, overcomes the negative charge repulsion on the clay surface, penetrates into the nanoscale gaps, and generates CSH and CASH gels in situ on the kaolinite surface. Through Si-O-Al bonds, chemical bonding is achieved, upgrading the interfacial bonding between cementing materials and clay from physical adsorption to molecular-level bonding, significantly improving the depth of hydration reaction and the density of the filling body.

[0042] 2) After calcination, sulfuric acid etching, and CaF2 modification, the activated red mud's crystal structure is disrupted, forming a porous and rough surface that exposes active SiO2 and Al2O3 components. These components, with a particle size ≤75μm, can be embedded in the nano-interstices of kaolinite, providing more cementation reaction sites. CaF2 promotes the formation of highly active sites on the red mud surface, accelerating the dissolution and recombination of aluminate and silicate phases, generating more cementation products. Magnesium phosphate-red mud activated microspheres form a porous structure through atomized drying, and Mg is regulated by moist heat curing. 2+ Fe 3+ It is continuously released over 7-14 days, matching the cement hydration process; the activated slag powder is treated with CO2 microbubbles to form a surface carbonation layer, which enhances the adsorption capacity on the clay surface, and works synergistically with fast-hardening sulfoaluminate cement and desulfurized gypsum to form an ettringite skeleton, thereby improving the 28-day strength of the filling body. Attached Figure Description

[0043] Figure 1 This is a schematic flowchart illustrating the method of using the cementing agent for cemented backfilling of clay tailings according to the present invention. Detailed Implementation

[0044] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0045] In the specific implementation method, all raw materials are sourced from market purchases;

[0046] Example 1:

[0047] A cementing agent for cementing and backfilling clay tailings, comprising, by weight:

[0048] Rapid-hardening sulfoaluminate cement: 25 parts (specific surface area 420 m²) 2 / kg, tricalcium aluminate content 12wt%, dicalcium silicate content 55wt%)

[0049] Silica fume: 12 parts (average particle size 1.5μm, SiO2 content ≥96%)

[0050] Activated slag powder: 40 parts

[0051] Limestone powder: 18 parts (particle size ≤ 40 μm, CaCO3 content ≥ 92%)

[0052] Desulfurized gypsum: 8 parts (CaSO4·2H2O content ≥93%)

[0053] Nano-SiO2 / Al2O3 composite sol: 7 parts

[0054] Magnesium phosphate-red mud activated microspheres: 32 parts;

[0055] The preparation method of activated slag powder is as follows:

[0056] The slag powder was placed in a pressure reactor, and CO2 microbubbles were introduced under a pressure of 0.35 MPa for 18 minutes to obtain activated slag powder with surface carbonation.

[0057] The preparation method of magnesium phosphate-red mud activated microspheres is as follows:

[0058] molar ratio Mg 2 +:H2PO4 - A ratio of 1:1.3 was used to weigh magnesium oxide and potassium dihydrogen phosphate, which were then added to deionized water. The mixture was stirred at 55°C for 60 minutes to allow the potassium dihydrogen phosphate to dissociate into H+ in the water. + It reacts with magnesium oxide to form Mg 2+ and HPO4 2- This forms a uniform and stable magnesium phosphate slurry;

[0059] The activated red mud was slowly added to the magnesium phosphate slurry at a mass ratio of 4:6. The mixture was stirred at 200 r / min for 30 min to fully disperse the activated red mud particles and coat them evenly with the magnesium phosphate slurry, thus forming a mixture.

[0060] The mixture is atomized into droplets by a pressure atomizer, and the droplets enter a hot air drying tower for drying in hot air. The hot air temperature is set to 120℃. The droplets rapidly evaporate moisture in the hot air and shrink into spherical particles under the action of surface tension, forming nascent microspheres with a porous structure.

[0061] The nascent microspheres were placed in a curing chamber at 95% humidity and 25℃ for 36 hours to allow the mineral phases (such as Fe2O3) in the red mud to form complexes with magnesium phosphate, thereby regulating the Mg content. 2+ Fe 3+ The release rate was determined to obtain magnesium phosphate-red mud activated microspheres.

[0062] The preparation method of nano-SiO2 / Al2O3 composite sol is as follows:

[0063] 40 g of tetraethyl orthosilicate was dissolved in 180 mL of anhydrous ethanol, and then 45 mL of deionized water and 4 mL of hydrochloric acid (37%) were added dropwise. The mixture was stirred at 300 r / min for 2.5 h at room temperature. The tetraethyl orthosilicate was hydrolyzed to generate silanol intermediate (Si-OH) by acid catalysis, and the excessive condensation of silanol to form oligomer solution was inhibited, thus obtaining a silicon precursor solution containing silanol intermediate.

[0064] Dissolve 25g of aluminum isopropoxide in 120mL of anhydrous ethanol, heat to 65℃, and stir at 250r / min until completely dissolved to allow aluminum isopropoxide to undergo alcoholysis reaction, generating a soluble aluminum alkoxide intermediate, avoiding direct hydrolysis to generate Al(OH)3 precipitate, and forming an aluminum source solution.

[0065] The aluminum source solution was slowly added dropwise to the silicon precursor solution, with the addition time controlled at 30 min. After the addition was completed, the mixture was stirred continuously for 4 h to allow the silanol and aluminum alkoxide to undergo a co-condensation reaction to form Si-O-Al bonds, thereby achieving uniform mixing of silicon and aluminum components at the nanoscale and forming a silicon-aluminum composite precursor solution.

[0066] 1.8 g of cetyltrimethylammonium chloride was added to the silicon-aluminum composite precursor solution, stirred and dissolved, and the pH was adjusted to 8.8 with ammonia water. Then, ultrasonic dispersion was performed at a frequency of 40 kHz for 18 min to obtain nano-SiO2 / Al2O3 composite sol.

[0067] The preparation method of activated red mud is as follows:

[0068] The red mud was placed in a muffle furnace and heated to 750°C for 2 hours, then naturally cooled to room temperature.

[0069] Add a 12% sulfuric acid solution to the cooled red mud and acid etch it at 50°C for 3 hours. Stir continuously during the acid etching process to dissolve some of the metal oxides in the red mud with sulfuric acid. After the reaction is complete, filter the mixture and wash it with deionized water until neutral. Then dry it at 105°C for 12 hours.

[0070] The dried red mud was mixed with 1.0% CaF2 by mass and ground in a ball mill. The grinding time was controlled so that the red mud particle size was ≤75μm to obtain activated red mud.

[0071] The above-mentioned method of using the cementing agent for cemented backfilling of clay tailings includes:

[0072] Rapid-hardening sulfoaluminate cement, activated slag powder, limestone powder, magnesium phosphate-red mud activated microspheres and desulfurized gypsum are put into a horizontal mixer and dry-mixed at 280 r / min for 10 min to ensure that each component is evenly dispersed.

[0073] The nano-SiO2 / Al2O3 composite sol was mixed with silica fume, and anhydrous ethanol accounting for 8% of the mass of the nano-SiO2 / Al2O3 composite sol was added. The mixture was ultrasonically dispersed for 12 min to form a pretreated sol.

[0074] The pretreated sol was evenly sprayed into the base cementitious material and stirred for 12 minutes at 220 r / min using a planetary mixer to make the nano-SiO2 / Al2O3 composite sol evenly coat the dry powder particles to form a cementitious agent.

[0075] Take 560 parts of kaolinite tailings, 80 parts of the above-mentioned cementitious agent, 70 parts of water, and water-reducing agent (polycarboxylate-based, dosage 0.6%), and put them into a twin-shaft mixer and mix at 350 r / min for 6 min to form a uniform slurry. Pour the slurry into a mold and place it in a curing chamber with 92% humidity and 24±1℃ for 28 days.

[0076] Example 2:

[0077] A cementing agent for cementing and backfilling clay tailings, comprising, by weight:

[0078] Rapid-hardening sulfoaluminate cement: 32 parts (specific surface area 410 m²) 2 / kg, tricalcium aluminate content 18wt%, dicalcium silicate content 48wt%)

[0079] Silica fume: 14 parts (average particle size 1.5μm, SiO2 content ≥96%)

[0080] Activated slag powder: 55 parts

[0081] Limestone powder: 13 parts (particle size ≤ 40 μm, CaCO3 content ≥ 92%)

[0082] Desulfurized gypsum: 12 parts (CaSO4·2H2O content ≥93%)

[0083] Nano-SiO2 / Al2O3 composite sol: 9 parts

[0084] Magnesium phosphate-red mud activated microspheres: 38 parts;

[0085] The preparation methods of activated slag powder, magnesium phosphate-red mud activated microspheres, nano SiO2 / Al2O3 composite sol and activated red mud are the same as in Example 1;

[0086] The method of using the cementing agent described above for cementing and backfilling clay tailings is the same as in Example 1.

[0087] Example 3:

[0088] A cementing agent for cementing and backfilling clay tailings, comprising, by weight:

[0089] Rapid-hardening sulfoaluminate cement: 20 parts (specific surface area 405 m²) 2 / kg, tricalcium aluminate content 10wt%, dicalcium silicate content 60wt%)

[0090] Silica fume: 8 parts (average particle size 1.5μm, SiO2 content ≥96%)

[0091] Activated slag powder: 30 parts

[0092] Limestone powder: 20 parts (particle size ≤ 40 μm, CaCO3 content ≥ 92%)

[0093] Desulfurized gypsum: 5 parts (CaSO4·2H2O content ≥93%)

[0094] Nano-SiO2 / Al2O3 composite sol: 6 parts

[0095] Magnesium phosphate-red mud activated microspheres: 30 parts;

[0096] The preparation methods of activated slag powder, magnesium phosphate-red mud activated microspheres, nano SiO2 / Al2O3 composite sol and activated red mud are the same as in Example 1;

[0097] The method of using the cementing agent described above for cementing and backfilling clay tailings is the same as in Example 1.

[0098] Comparative Example 1: The difference from Example 1 is that no nano-SiO2 / Al2O3 composite sol was added.

[0099] Comparative Example 2: The difference from Example 1 is that magnesium phosphate-red mud activated microspheres were not added.

[0100] Comparative Example 3: The difference from Example 1 is that iron-containing mineral microspheres were used instead of magnesium phosphate-red mud activated microspheres in equal parts by weight;

[0101] Methods for preparing iron-containing mineral microspheres include:

[0102] Fe2O3 powder (particle size ≤ 45 μm) was mixed with potassium dihydrogen phosphate at a mass ratio of 1:2, water was added to make a slurry, the slurry was atomized and dried, and then calcined at 600℃ for 2 hours to form porous microspheres.

[0103] Comparative Example 4: The difference from Example 1 is that magnesium mineral microspheres were used instead of magnesium phosphate-red mud activated microspheres in equal parts by weight;

[0104] Methods for preparing magnesium mineral microspheres include:

[0105] MgO powder and potassium dihydrogen phosphate were mixed at a mass ratio of 1:1.5, atomized and dried, and then calcined at 500℃ for 1.5h.

[0106] The tailings treated in Examples 1-3 and Comparative Examples 1-4 were tested, and the tests included:

[0107] The compressive strength test standard is GB / T 17671;

[0108] Porosity was measured using the mercury intrusion porosimetry method (ASTM C1723).

[0109] Slurry segregation rate: The test standard is GB / T 50080;

[0110] The data obtained after the above tests are shown in Table 1.

[0111] Table 1. Test results of Examples 1-3 and Comparative Examples 1-4

[0112] Compressive strength (MPa) Porosity (%) Slurry segregation rate (%) Example 1 4.8 26 8 Example 2 4.6 24 7 Example 3 4.7 28 9 Comparative Example 1 2.5 38 18 Comparative Example 2 2.2 42 28 Comparative Example 3 2.4 32 12 Comparative Example 4 2.7 30 10

[0113] In the above embodiments, the Mg released by the magnesium phosphate-red mud activated microspheres 2+ Fe 3+ Through a cyclic mechanism of "strong bond breaking + interlayer expansion" (Fe) 3+ Strong coordination disrupts the interlayer hydrogen bonds of kaolinite, Mg 2+ Hydrated ions expand the interlayer structure, greatly improving the efficiency of lattice disintegration and significantly increasing the amount of active SiO2 dissolved from the interlayer. The nano-SiO2 / Al2O3 composite sol, with its +35±5mV positive charge and nanoscale size, overcomes the negative charge repulsion of the clay surface and deeply penetrates the nanoscale gaps to generate CSH and CASH gels in situ. It achieves molecular-level bonding through Si-O-Al bonds, upgrading the interfacial adhesion from physical adsorption to chemical bonding, thus reducing the porosity to 24-28%.

[0114] Fe 3+ Catalytic activation of Al-O-Si bond breaking in slag powder, synergistically affecting Si in sol 3+ Al 3+ Ions accelerate the dissolution of active components, forming a multi-scale network of "nano-bridging - micron-filling (activated slag / silica fume) - macroscopic framework (ettringite)," thus enabling desulfurized gypsum and Mg... 2+ Synergistically accelerates the hydration of fast-hardening sulfoaluminate cement, generates an ettringite needle-like crystal framework, and reduces slurry segregation;

[0115] In Comparative Example 1, due to the lack of composite sol with nanoscale size and +35±5mV positive charge, it was unable to overcome the negative charge repulsion on the surface of kaolinite. The cementing material could only be physically adsorbed on the outside of the clay aggregates and could not penetrate into the nanoscale gaps to generate CSH / CASH gel and Si-O-Al bonds in situ, resulting in weak interfacial bonding, increased porosity, and aggravated slurry segregation.

[0116] Comparative Example 2 lacking Mg 2+ Fe 3+ The synergistic debonding effect did not disrupt the interlayer hydrogen bonds of kaolinite, leading to an increase in the adsorbed free water rate of clay, a severe imbalance in the water-cement ratio, and no release of active SiO2 / Al2O3 or Fe. 3+ Catalytic slag activation, insufficient raw materials for the cementation reaction, and incomplete hydration lead to a significant decrease in the strength of the filling body, an increase in porosity, and a substantial increase in the segregation rate.

[0117] In Comparative Example 3, only Fe3+ The "destruction-expansion" synergistic mechanism cannot be achieved; although it can disrupt surface hydrogen bonds, it lacks Mg. 2+ The interlayer structure is stretched open, the lattice disintegration is limited to the surface, the amount of active SiO2 dissolution is insufficient, and the porous structure of the unactivated red mud is embedded in the clay gaps, reducing the cementation reaction sites, resulting in lower strength, density and slurry stability than in the example.

[0118] In Comparative Example 4, only Mg 2+ Fe deficiency 3+ The strong coordination disruption effect of Fe cannot effectively break Si-O bonds and induce lattice distortion, resulting in limited interlayer expansion, no significant improvement in the agglomeration state of clay particles, and the absence of Fe. 3+ The activation of catalytic slag resulted in insufficient dissolution of active Al2O3, failing to construct a "nano-bridging-micron-filling" cross-scale network, thus limiting performance improvement.

[0119] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A cementing agent for cementing and backfilling clay tailings, characterized in that, By weight, it includes: 20-35 parts of rapid-hardening sulfoaluminate cement, 8-15 parts of silica fume, 30-60 parts of activated slag powder, 10-20 parts of limestone powder, 5-15 parts of desulfurized gypsum, 6-10 parts of nano-SiO2 / Al2O3 composite sol, and 30-40 parts of magnesium phosphate-red mud activated microspheres.

2. The cementing agent for cemented backfilling of clayey tailings as described in claim 1, characterized in that, The preparation method of the nano-SiO2 / Al2O3 composite sol includes: Tetraethyl orthosilicate was dissolved in anhydrous ethanol, and then deionized water and hydrochloric acid were added dropwise. The mixture was stirred at room temperature to obtain a silicon precursor solution containing silanol intermediates. Aluminum isopropoxide is dissolved in anhydrous ethanol and heated and stirred until completely dissolved to form an aluminum source solution. The aluminum source solution is slowly added to the silicon precursor solution to form a silicon-aluminum composite precursor solution; A cationic surfactant was added to the silicon-aluminum composite precursor solution, stirred and dissolved, and the pH was adjusted to 8-9 with ammonia. Then, the solution was ultrasonically dispersed to obtain the nano-SiO2 / Al2O3 composite sol.

3. The cementing agent for cemented backfilling of clayey tailings as described in claim 2, characterized in that, The zeta potential of the nano-SiO2 / Al2O3 composite sol is +35±5mV.

4. The cementing agent for cementing and backfilling clay tailings as described in claim 2, characterized in that, The cationic surfactant is one or more of hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, dodecyltrimethylammonium bromide, and octadecyltrimethylammonium bromide.

5. The cementing agent for cemented backfilling of clayey tailings as described in claim 1, characterized in that, The preparation method of the magnesium phosphate-red mud activated microspheres includes: molar ratio Mg 2+ :H2PO4 - =1∶1.2-1.5, weigh magnesium oxide and potassium dihydrogen phosphate, add deionized water, and stir evenly at 50-60℃ to form magnesium phosphate slurry; The activated red mud is slowly added to the magnesium phosphate slurry at a mass ratio of 3-5:5-7, and mixed evenly to form a mixture. The mixture is atomized into droplets and dried in hot air to form nascent microspheres; The nascent microspheres were placed in a curing chamber with humidity ≥90% and temperature 25±5℃ for 24-48 hours to obtain the magnesium phosphate-red mud activated microspheres.

6. The cementing agent for cemented backfilling of clayey tailings as described in claim 5, characterized in that, The method for preparing the activated red mud includes: After calcining and cooling the red mud, sulfuric acid was added for acid etching. After filtration and drying, it was mixed with 0.5-1.3% CaF2 by mass and ground until the particle size was ≤75μm.

7. The cementing agent for cemented backfilling of clayey tailings as described in claim 1, characterized in that, The specific surface area of ​​the rapid-hardening sulfoaluminate cement is ≥400 m². 2 / kg, tricalcium aluminate content is 10-20wt%, dicalcium silicate content is 40-60wt%.

8. The cementing agent for cemented backfilling of clayey tailings as described in claim 1, characterized in that, The method for preparing the activated slag powder includes: CO2 microbubbles are introduced into the slag powder under a pressure of 0.3-0.5 MPa for 15-20 minutes to form a surface carbonation layer.

9. The method of using the cementing agent for cemented backfilling of clayey tailings as described in any one of claims 1-8, characterized in that, include: The rapid-hardening sulfoaluminate cement, the activated slag powder, the limestone powder, the magnesium phosphate-red mud activated microspheres, and the desulfurized gypsum are mixed to form the basic cementitious material; The nano-SiO2 / Al2O3 composite sol is mixed with the silica fume, and then 5-10% anhydrous ethanol (by mass of the nano-SiO2 / Al2O3 composite sol) is added and ultrasonically dispersed to form a pretreated sol. The pretreated sol is sprayed into the base cementitious material and mixed to form the cementitious agent; After mixing the tailings, the cementing agent, water, and water-reducing agent, the mixture is cured.

10. The method of using the cementing agent for cemented backfilling of clayey tailings as described in claim 9, characterized in that, The mass ratio of the tailings to the cementing agent is 5-8:1.

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