Mine tailings grading and activation treatment method and application thereof in water permeable building materials

Abstract

The application relates to the technical fields of solid waste resource utilization and building materials, and discloses a mine tailings grading and activating treatment method and application of the mine tailings grading and activating treatment method in water-permeable building materials, which comprises the following steps: grading mine tailings to obtain fine powder components and coarse aggregate components; co-grinding the fine powder components with water, sodium hydroxide and an ethylenediamine tetramethylene phosphonic acid sodium working solution to prepare a masking precursor slurry; adding a sodium metaaluminate aqueous solution and propylene carbonate under heating and stirring conditions to make the pH value of the slurry drop to a critical alkaline interval, so as to obtain a critical-state precursor slurry; and making the coarse aggregate components contact with the sodium hydroxide aqueous solution and making the critical-state precursor slurry coat the surfaces of the coarse aggregates to obtain a mine tailings mixture. The method is favorable for improving the rheological stability of the slurry and the interface bonding state of the coarse aggregates, and the obtained mixture can be used for preparing water-permeable building materials.

Description

Technical Field

[0001] This invention relates to the fields of solid waste resource utilization and building materials technology, and in particular to a method for graded activation treatment of mine tailings and its application in permeable building materials. Background Technology

[0002] Mine tailings are a large amount of solid waste generated during mineral resource extraction and beneficiation. Their main components typically include silicates, aluminosilicates, and small amounts of metal oxides such as calcium, iron, and magnesium. With the expansion of mining operations, the amount of tailings stockpiled continues to increase, occupying land resources and potentially posing risks to dust, leachate, and the surface environment. Using mine tailings in the preparation of building materials is one of the important directions for achieving large-scale disposal and resource utilization of these materials.

[0003] Permeable building materials have a certain interconnected pore structure, allowing rainwater to infiltrate and drain within the material. They are suitable for permeable paving, ecological roads, and sponge city projects. After grading, the coarse particles of mine tailings can be used as a skeleton material, while the silicon and aluminum components in the fine powder have certain reactivity under alkaline conditions. Therefore, they possess the basic conditions for preparing permeable building materials.

[0004] In existing technologies, the preparation of permeable building materials from mine tailings typically involves direct activation with strong alkali or simple mixing of tailings with cement and alkali activators. While these methods can induce a certain degree of gelation in the fine powder of the tailings, the fine powder components are prone to rapid dissolution, precipitation, and gelation in a highly alkaline environment, leading to increased slurry viscosity and affecting the stability of the conveying, spraying, and molding processes. Furthermore, the interfacial transition zone between the coarse aggregate surface and the gelled coating layer is usually relatively weak, easily becoming a crack propagation site during compression or bending, thus limiting the improvement of the mechanical properties of the permeable building materials.

[0005] Furthermore, permeable building materials need to retain interconnected pores to meet drainage performance requirements, but the presence of interconnected pores weakens the overall load-bearing structure of the material. Increasing strength by filling the pores with cementitious materials can easily reduce permeability. Therefore, how to improve the interfacial bonding state of coarse aggregate while retaining permeable channels is a problem that needs to be solved in the preparation of permeable building materials from mine tailings.

[0006] On the other hand, sodium ions are usually introduced into the alkali activation system. If the gel structure is not formed sufficiently or sodium ions remain mainly in a migratory state in the pore liquid and pore wall surface, sodium ions are prone to migrate to the material surface during subsequent immersion, wet-dry cycles or water evaporation, and react with carbon dioxide or other anions in the air to form alkali efflorescence, affecting the appearance of the product and its long-term stability.

[0007] Therefore, it is necessary to provide a graded activation treatment method for mine tailings, so that the fine powder and coarse aggregate of the tailings can be treated separately. Through slurry rheology regulation, aluminum source supply, programmed alkali reduction and coarse aggregate interface activation process, the coating and molding performance, interfacial bonding state and control ability of migratable alkali metal ions of the mine tailings mixture can be improved, thereby meeting the needs of permeable building material preparation. Summary of the Invention

[0008] The technical problem solved by this invention is that when mine tailings are used to prepare permeable building materials, the fine powder of the tailings is prone to rapid gelation under high alkaline conditions, which leads to a decrease in the transportability and coating uniformity of the slurry; the interfacial bonding between the coarse aggregate and the cementitious coating layer is insufficient, which affects the mechanical properties of the permeable building materials; at the same time, sodium ions introduced in the high-alkali activation system are prone to remain in the pore liquid or pore wall surface in a migratory state, which poses a risk of efflorescence during later service.

[0009] To address the above problems, the present invention provides the following technical solution:

[0010] In a first aspect, the present invention provides a method for graded activation treatment of mine tailings, comprising the following steps:

[0011] The tailings from the mine are graded to obtain fine powder components and coarse aggregate components;

[0012] The fine powder component is mixed with water, sodium hydroxide is added to adjust the pH of the slurry to 12.8-13.2, sodium ethylenediaminetetramethylenephosphonate working solution is added, and wet co-milling is performed to obtain the masking precursor slurry.

[0013] Under heating and stirring conditions, sodium aluminate aqueous solution and propylene carbonate were added to the masking precursor slurry, and the pH value of the slurry was controlled to decrease to 11.7-11.9 to obtain a critical state precursor slurry with a pH value of 11.7-11.9.

[0014] The surface of the coarse aggregate component is brought into contact with an aqueous sodium hydroxide solution, and then the critical state precursor slurry is coated onto the surface of the coarse aggregate component treated with the aqueous sodium hydroxide solution to obtain a mine tailings mixture after graded activation treatment.

[0015] By adopting the above technical solution, the fine powder component and coarse aggregate component in the mine tailings play different roles. The fine powder component has a higher specific surface area and is more likely to dissolve silica and aluminum components under alkaline conditions, serving as the main reaction source for the formation of the cementitious phase; the coarse aggregate component retains the particle skeleton structure and can serve as the skeleton material in permeable building materials. First, the fine powder component is wet-milled with water, sodium hydroxide, and sodium ethylenediaminetetramethylenephosphonate working solution. This promotes surface activation of the tailings fine powder under mechanical shearing and high alkalinity conditions, and allows sodium ethylenediaminetetramethylenephosphonate to coordinate with calcium, magnesium, iron, and other metal ions in the system, thereby reducing the degree to which metal ions prematurely form disordered precipitation in a high alkaline environment. The above coordination process can be represented by the following general formula:

[0016] M n+ +L→ML;

[0017] Among them, M n+ The symbols represent calcium, magnesium, iron, or aluminum ions released from mine tailings. L represents the phosphonate coordination structure in sodium ethylenediaminetetramethylenephosphonate, and ML represents the corresponding coordination product.

[0018] Based on this, adding an aqueous solution of sodium aluminate to the masking precursor slurry can replenish the aluminum source in the system that can participate in the formation of aluminosilicate gels. Sodium aluminate can form aluminate or tetrahydroxyaluminate in the aqueous phase, and the process can be represented as follows:

[0019] NaAlO2 + 2H2O → Na + +[Al(OH)4] - ;

[0020] Upon the addition of propylene carbonate, the propylene carbonate undergoes hydrolysis under alkaline conditions, gradually producing carbonate ions and consuming some of the alkalinity. This process can be represented as follows:

[0021] C4H6O3 + 2OH - →C3H8O2+CO3 2- ;

[0022] By simultaneously supplementing aluminum with sodium aluminate and reducing alkalinity with propylene carbonate, the slurry's pH value is gradually lowered from the high-alkalinity range of 12.8–13.2 to the critical range of 11.7–11.9. This process reduces the risk of rapid thickening of the slurry in the reactor, ensuring it remains flowable before coating the coarse aggregate. Simultaneously, the carbonate ions generated from the hydrolysis of propylene carbonate react with calcium ions in the system to form calcium carbonate crystals, a process that can be represented as follows:

[0023] Ca 2+ +CO3 2- →CaCO3↓;

[0024] The simultaneous formation of the carbonate and the subsequent formation of the aluminosilicate gel structure is beneficial for improving the structural continuity of the gel matrix.

[0025] After the surface of the coarse aggregate component is pre-contaminated with an aqueous sodium hydroxide solution, a localized alkaline liquid phase exists in the microcracks, pores, and rough regions of the coarse aggregate surface. When the critical-state precursor slurry with a pH of 11.7–11.9 comes into contact with the coarse aggregate surface, the alkalinity of the interfacial region locally increases, promoting further condensation of the dissolved silicate and aluminate structural units in the slurry. This process mainly involves the formation of silicon-oxygen bonds and silicon-aluminum-oxygen bonds, which can be represented as follows:

[0026] Si-OH + HO-Si → Si-O-Si + H2O;

[0027] Si-OH + HO-Al → Si-O-Al + H2O;

[0028] Through the above process, the critical-state precursor slurry can form a coating layer on the surface of coarse aggregate and form an aluminosilicate gel structure connected to the cementitious matrix in the interface region of coarse aggregate. Thus, the reactivity of the fine powder component, the skeletal role of the coarse aggregate component, and the alkali-triggered process at the interface work together to enable the mine tailings mixture to be used for the subsequent molding and curing of permeable building materials.

[0029] Preferably, the mine tailings are iron tailings or copper tailings; the fine powder component has a particle size of less than 0.15 mm and a specific surface area of ​​395 m². 2 / kg~410m 2 / kg; the particle size of the coarse aggregate component is 2.36mm to 4.75mm.

[0030] By adopting the above technical solution, the fine powder component with a particle size of less than 0.15 mm has a high reaction contact area, making it suitable for wet co-milling and surface activation under alkaline conditions; the coarse aggregate component with a particle size of 2.36 mm to 4.75 mm can form a particle skeleton in the subsequent molding process and provide a basis for the formation of water-permeable channels. Using iron tailings or copper tailings as the source of mine tailings, the silicon, aluminum, calcium, iron and other components can be utilized to participate in alkali activation and subsequent gel structure formation.

[0031] Preferably, the amount of water used in the fine powder component is 25 to 35 parts by weight per 100 parts by weight, the amount of sodium ethylenediaminetetramethylenephosphonate working solution is 0.8 to 1.5 parts by weight, and the solid content of the sodium ethylenediaminetetramethylenephosphonate working solution is 45.0 wt% to 55.0 wt%.

[0032] By adopting the above technical solution, the amount of water added can meet the liquid phase conditions required for wet co-milling and ion migration of the fine powder components; the amount of sodium ethylenediaminetetramethylenephosphonate working solution added can provide a multidentate coordination structure in the high-alkali system, which can be used to regulate the release and precipitation behavior of metal ions such as calcium, magnesium, and iron. The solid content is controlled within the range of 45.0 wt% to 55.0 wt%, which facilitates metering and addition, and is beneficial to achieving uniform contact between the masking agent and the tailings fine powder during the co-milling process.

[0033] Preferably, the rotation speed of the wet co-milling process is 300 r / min to 450 r / min, and the processing time is 45 minutes to 60 minutes.

[0034] By adopting the above technical solution, wet co-milling can simultaneously achieve mechanical activation, alkaline wetting, and masking agent dispersion of fine powder components. Controlling the co-milling speed and time within the aforementioned range can promote surface activation of the fine powder and adsorption and dispersion of the masking agent, while avoiding excessive grinding that would cause the slurry viscosity to increase too rapidly.

[0035] Preferably, the sodium ethylenediaminetetramethylenephosphonate working solution is prepared by the following method: diluting a 50.0 wt% sodium ethylenediaminetetramethylenephosphonate aqueous solution with water, filtering to remove impurities, or concentrating under reduced pressure to obtain a sodium ethylenediaminetetramethylenephosphonate working solution with a solid content of 45.0 wt% to 55.0 wt%.

[0036] By adopting the above technical solution, the solid content of the sodium ethylenediaminetetramethylenephosphonate working solution can be adjusted according to different process parameters. Diluting with water can obtain a working solution with a lower solid content, filtration to remove impurities can improve the stability of the working solution, and vacuum concentration can obtain a working solution with a higher solid content, thus adapting to different tailings fine powder activities and different co-grinding conditions.

[0037] Preferably, the molar concentration of the sodium aluminate aqueous solution, calculated as NaAlO2, is 1.5 mol / L to 2.5 mol / L; and the amount of sodium aluminate aqueous solution added is 15.0 L to 25.0 L per 100 kg of fine powder component.

[0038] By adopting the above technical solution, sodium aluminate aqueous solution can supplement the system with reactive aluminum source, allowing the silicate structural units dissolved in the tailings fine powder to participate in the formation of aluminosilicate gel structure together with the added aluminum source. Controlling the concentration and amount of sodium aluminate within the above range helps reduce insufficient gel network formation caused by insufficient aluminum source, and also helps reduce local precipitation and slurry thickening caused by excessive aluminum source.

[0039] Preferably, the heating and stirring conditions are: temperature 78℃~82℃, stirring speed 120r / min~180r / min; the addition time of the sodium aluminate aqueous solution and propylene carbonate is 40 minutes~50 minutes; the cumulative addition amount of propylene carbonate is 0.95kg~2.45kg per 100kg of fine powder component; after the pH value of the slurry drops to 11.7~11.9, it is cooled to below 40℃ to obtain the critical state precursor slurry.

[0040] By adopting the above technical solution, the heating conditions can improve the hydrolysis rate of propylene carbonate and the migration rate of silicon and aluminum components, while the stirring conditions can maintain the homogeneity of the slurry. The sodium aluminate aqueous solution and propylene carbonate are added within 40 to 50 minutes, allowing the aluminum supplementation and alkali reduction processes to proceed simultaneously, gradually bringing the slurry pH value into the range of 11.7 to 11.9. Subsequent cooling to below 40°C reduces the rate of further reaction and thickening of the slurry, ensuring that the critical precursor slurry remains operable before entering the coarse aggregate coating step.

[0041] Preferably, the fine powder component is in the amount of 300 to 500 parts by mass per 100 parts by mass; the sodium hydroxide aqueous solution has a mass fraction of 0.8 wt% to 1.2 wt% and an amount of 3 to 10 parts by mass; the mixing time after the coarse aggregate component comes into contact with the sodium hydroxide aqueous solution is 3 to 5 minutes; and the mixing time after the critical state precursor slurry comes into contact with the coarse aggregate component is 8 to 12 minutes.

[0042] By adopting the above technical solution, the amount of coarse aggregate component can meet the requirements for the formation of the permeable building material skeleton, and the sodium hydroxide aqueous solution can provide a local alkaline liquid phase on the surface of the coarse aggregate. The mixing time after the coarse aggregate comes into contact with the sodium hydroxide aqueous solution is controlled at 3 to 5 minutes, which is conducive to the distribution of the alkaline solution on the surface of the coarse aggregate; the mixing time after the critical state precursor slurry comes into contact with the coarse aggregate component is controlled at 8 to 12 minutes, which is conducive to the formation of a continuous coating layer on the surface of the coarse aggregate.

[0043] Secondly, the present invention provides an application of a mine tailings mixture obtained by a graded activation treatment method for mine tailings in the preparation of permeable building materials. The mine tailings mixture obtained by the graded activation treatment method for mine tailings described in the first aspect is shaped, thermo-cured and maintained to obtain a finished permeable building material.

[0044] By adopting the above technical solution, in the mine tailings mixture obtained in the first aspect, the surface of the coarse aggregate component is coated with a gelled coating layer formed by a critical-state precursor slurry. This gelled coating layer originates from the activation of the tailings fine powder under alkaline conditions, aluminum supplementation with sodium aluminate, alkali reduction by propylene carbonate, and the interfacial reaction process after alkaline treatment of the coarse aggregate surface. After the mine tailings mixture is formed and then thermosetting, the gelled coating layer can continue to undergo aluminosilicate condensation reaction, forming a connecting structure between the coarse aggregates, thereby obtaining a permeable building material product with permeable channels and a mechanical load-bearing structure.

[0045] Preferably, the molding process includes vibration molding with a vibration time of 30 seconds; the thermosetting temperature is 75°C and the thermosetting time is 24 hours; after thermosetting, the material is demolded and cured for 28 days at a temperature of 20±2°C and a relative humidity of 95% or higher.

[0046] By adopting the above technical solutions, vibration compaction molding enables the mine tailings mixture to form a relatively stable particle accumulation structure in the mold, reducing local voids or discontinuous areas of coating. 75℃ thermosetting increases the rate of aluminosilicate polycondensation, allowing the cementitious coating layer to acquire initial structural strength in a shorter time. Demolding after 24 hours of thermosetting and continued standard curing to 28 days promotes further development of the cementitious matrix, resulting in stable mechanical and permeable properties in the finished permeable building material.

[0047] In summary, the present invention has at least one of the following beneficial technical effects:

[0048] 1. This invention classifies mine tailings into fine powder components and coarse aggregate components, and activates and utilizes them separately. The fine powder components are activated by alkali, masked co-grinding and aluminum supplementation to form a source of cementitious reaction, while the coarse aggregate components are used as skeleton materials for permeable building materials, thereby improving the utilization efficiency of different particle size components of mine tailings.

[0049] 2. In this invention, sodium ethylenediaminetetramethylenephosphonate working solution is added during the wet co-milling stage of the fine powder component. This can regulate the release and precipitation behavior of metal ions such as calcium, magnesium, and iron in the system, reduce the risk of rapid thickening of the slurry under high alkalinity conditions, and facilitate the stable operation of subsequent aluminum source replenishment, propylene carbonate alkali reduction, and slurry coating.

[0050] 3. This invention supplements the aluminum source with sodium aluminate and utilizes the hydrolysis of propylene carbonate under alkaline conditions to generate carbonate ions, thereby reducing the pH value of the slurry from the high alkaline range to the critical alkaline range. This maintains the workability of the slurry while providing conditions for the subsequent formation of aluminosilicate gel structure and carbonate crystal phase.

[0051] 4. In this invention, the surface of coarse aggregate is pre-contaminated with sodium hydroxide aqueous solution, and then the critical state precursor slurry is coated on the surface of coarse aggregate. This can cause a local alkalinity rebound in the interface area, promote the formation and development of the cementitious coating layer on the surface of coarse aggregate, thereby improving the interfacial bonding state of permeable building materials and improving the mechanical properties of the finished product while maintaining permeability. Attached Figure Description

[0052] Figure 1 This is a graph showing the pH value change trend of the precursor slurry obtained in Examples 1, 2, 3 and 4 of the present invention during the isothermal dripping stage at 80°C.

[0053] Figure 2 This is a graph showing the change trend of apparent viscosity of the precursor slurry obtained in Examples 1, 2, 3 and 4 of the present invention during the isothermal dripping stage at 80°C.

[0054] Figure 3 The graph shows the response change trend of the critical state precursor slurry obtained in Example 1 of the present invention before and after alkaline triggering; wherein, (a) is the trend trend of hydration heat release rate; and (b) is the trend trend of storage modulus G'.

[0055] Figure 4 The XRD and FTIR spectra of the cementitious matrix powder of the permeable building material finished product obtained in Example 1 and Comparative Example 1 of the present invention at 28 days of age are shown; wherein, (a) is the XRD spectrum and (b) is the FTIR spectrum. Detailed Implementation

[0056] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The implementation of the present invention will be described in detail below with reference to specific embodiments. Those skilled in the art should understand that these embodiments are only used to clearly explain the technical solutions of the present invention and should not be used to limit the scope of protection of the present invention.

[0057] The sources and specifications of the main raw materials and reagents used in the following examples and comparative examples are as follows. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0058] Iron tailings were obtained from flotation tailings in a mineral processing plant and naturally dried. The main chemical components were determined to be: SiO2 65.4 wt%, Al2O3 12.3 wt%, Fe2O3 8.5 wt%, CaO 4.2 wt%, and loss on ignition 2.1 wt%. Before use, the tailings were mechanically vibrated and screened to select particles with a diameter between 2.36 mm and 4.75 mm as coarse aggregate, with particles smaller than 0.15 mm and a specific surface area of ​​410 m² being selected. 2 / kg of powder is used as the fine powder component.

[0059] The copper tailings were obtained from the flotation tailings of a copper ore beneficiation plant and naturally dried. Analysis showed that their main chemical components (mass fractions) were: SiO2 58.7 wt%, Al2O3 13.6 wt%, Fe2O3 10.8 wt%, CaO 5.1 wt%, MgO 2.4 wt%, CuO 0.32 wt%, and loss on ignition 2.8 wt%. Before use, the tailings were mechanically vibrated and screened to select particles with a diameter between 2.36 mm and 4.75 mm as coarse aggregate, and particles smaller than 0.15 mm with a specific surface area of ​​395 m² were selected. 2 / kg of powder is used as the fine powder component.

[0060] Sodium hydroxide has the CAS number 1310-73-2, the molecular formula is NaOH, and the purity is 99.0 wt%.

[0061] Sodium ethylenediaminetetramethylenephosphonate (EDTA) has the CAS number 1429-50-1. It is a commercially available industrial-grade aqueous solution, appearing as a yellowish-brown transparent liquid. The active ingredient, sodium ethylenediaminetetramethylenephosphonate, has a mass fraction of 50.0 wt%. The density of this aqueous solution at 20°C is 1.42 g / cm³. 3 Its 1wt% aqueous solution has a pH value of 10.5.

[0062] Sodium aluminate has the CAS number 11138-49-1, the molecular formula is NaAlO2, the purity is 98.0 wt%, and the mass fraction of Al2O3 on a dry basis is greater than 50.0 wt%.

[0063] Propylene carbonate, commonly known as 1,2-propanediol carbonate, has the CAS number 108-32-7, the molecular formula C4H6O3, a purity of 99.5 wt%, and a density of 1.20 g / cm³ at 20°C. 3 .

[0064] Sodium hexametaphosphate has the CAS number 10124-56-8, the molecular formula is (NaPO3)6, and the total phosphate content is 68.0 wt% based on the P2O5 mass fraction.

[0065] Preparation Example 1:

[0066] This preparation example provides a method for preparing an aluminum source replenishment solution with a molar concentration of 1.5 mol / L based on NaAlO2, including the following steps:

[0067] Weigh 10.0g of sodium hydroxide solid and add it to a mixing tank. Add 800mL of deionized water and stir to dissolve and form an alkaline base solution. Then weigh 125.5g of sodium aluminate solid powder and slowly add it to the base solution. Stir mechanically at 200r / min for 30 minutes at room temperature until the powder is completely dissolved and the solution is clear and transparent. Make up to 1000mL with deionized water and let stand to remove bubbles to obtain an aqueous solution of sodium aluminate with a NaAlO2 molar concentration of 1.5mol / L.

[0068] Preparation Example 2:

[0069] This preparation example provides a method for preparing an aluminum source replenishment solution with a molar concentration of 2.0 mol / L (based on NaAlO2), including the following steps:

[0070] Weigh 15.0g of sodium hydroxide solid and add it to a mixing tank. Add 800mL of deionized water and stir to dissolve and form an alkaline base solution. Then weigh 167.3g of sodium aluminate solid powder and slowly add it to the base solution. Stir mechanically at 200r / min for 30 minutes at room temperature until the powder is completely dissolved and the solution is clear and transparent. Make up the volume to 1000mL with deionized water. After standing to remove bubbles, a sodium aluminate aqueous solution with a NaAlO2 molar concentration of 2.0mol / L is obtained.

[0071] Preparation Example 3:

[0072] This preparation example provides a method for preparing an aluminum source replenishment solution with a molar concentration of 2.5 mol / L (based on NaAlO2), including the following steps:

[0073] Weigh 20.0g of sodium hydroxide solid and add it to a mixing tank. Add 800mL of deionized water and stir to dissolve and form an alkaline base solution. Then weigh 209.1g of sodium aluminate solid powder and slowly add it to the base solution. Stir mechanically at 200r / min for 30 minutes at room temperature until the powder is completely dissolved and the solution is clear and transparent. Make up the volume to 1000mL with deionized water. After standing to remove bubbles, a sodium aluminate aqueous solution with a NaAlO2 molar concentration of 2.5mol / L is obtained.

[0074] Preparation Example 4:

[0075] This preparation example provides a method for preparing a masking agent working solution with a solid content of 45.0 wt%, including the following steps:

[0076] Weigh 900.0g of commercially available sodium ethylenediaminetetramethylenephosphonate aqueous solution with a mass fraction of 50.0wt%, add 100.0g of deionized water, stir at 150r / min for 15 minutes at room temperature, and after mixing evenly, obtain a sodium ethylenediaminetetramethylenephosphonate working solution with a solid content of 45.0wt%.

[0077] Preparation Example 5:

[0078] This preparation example provides a method for preparing a masking agent working solution with a solid content of 50.0 wt%, including the following steps:

[0079] Take a commercially available sodium ethylenediaminetetramethylenephosphonate aqueous solution with a mass fraction of 50.0 wt%, filter it through a precision filter with a pore size of 10 μm to remove insoluble mechanical impurities, and collect the filtrate to directly use as a working solution of sodium ethylenediaminetetramethylenephosphonate with a solid content of 50.0 wt%.

[0080] Preparation Example 6:

[0081] This preparation example provides a method for preparing a masking agent working solution with a solid content of 55.0 wt%, including the following steps:

[0082] Weigh 1100.0g of a commercially available sodium ethylenediaminetetramethylenephosphonate aqueous solution with a mass fraction of 50.0wt%, place it in a reactor equipped with a vacuum decompression device, and concentrate it under reduced pressure at 50℃ and a vacuum degree of -0.08MPa. Evaporate 100.0g of water, and stop heating when the total mass of the material is 1000.0g. After cooling to room temperature, a sodium ethylenediaminetetramethylenephosphonate working solution with a solid content of 55.0wt% is obtained.

[0083] Example 1:

[0084] This embodiment provides a method for graded activation treatment of mine tailings, including the following steps:

[0085] (1) Preparation of masking precursor slurry: 100.0 kg of fine iron tailings powder after physical classification and 30.0 kg of deionized water were weighed and put into a wet ball mill. Solid sodium hydroxide was slowly added and the initial pH value of the liquid phase was adjusted to 13.0 by monitoring with an online pH meter. Then, 1.2 kg of sodium ethylenediaminetetramethylenephosphonate working solution with a solid content of 50.0 wt% prepared in Preparation Example 5 was added into the ball mill. The ball mill was closed and the ball mill speed was set to 380 r / min. The ball mill was continuously co-milled at room temperature for 50 minutes to obtain the masking precursor slurry.

[0086] (2) Preparation of critical precursor slurry: The above-mentioned masked precursor slurry was pumped into a reactor equipped with a jacketed heating and mechanical stirring device. Stirring was started and the speed was set to 150 r / min. The temperature of the slurry in the reactor was raised to 80°C at a constant rate and kept constant. Two high-precision metering pumps were started for synchronous dripping. Pump A dripped 20.0 L of sodium aluminate aqueous solution with a molar concentration of 2.0 mol / L prepared in Preparation Example 2 at a constant rate. Pump B dripped liquid propylene carbonate at the same time. The cumulative amount of liquid propylene carbonate added by pump B was 1.60 kg. The dripping speed of pump B was adjusted by feedback from the online pH meter to control the pH value of the slurry in the reactor to gradually decrease from the initial 13.0 to the critical value of 11.8 within 45 minutes and maintain this value at the end of the dripping. After the two dripping was completed, cooling water was immediately introduced into the reactor jacket to rapidly reduce the system temperature to below 40°C within 10 minutes, thus obtaining the critical precursor slurry.

[0087] (3) Activation and coating of coarse aggregate interface: 400.0 kg of physically classified iron tailings coarse aggregate components were put into the drum granulator, the tumbling was started, and 4.0 kg of sodium hydroxide aqueous solution with a mass fraction of 1.0 wt% was sprayed onto the surface of the coarse aggregate through the atomizing nozzle. The mixture was continuously tumbled and mixed for 4 minutes to fully wet the microcracks on the surface of the coarse aggregate with alkaline solution. Then, the critical state precursor slurry prepared above was atomized and sprayed into the granulator through the mud pump. The mixture was continuously tumbled and mixed for 10 minutes to make the slurry undergo a secondary pH jump on the surface of the aggregate and form a uniform coating layer. Finally, the activated mine tailings mixture was obtained.

[0088] Example 2:

[0089] This embodiment provides a method for graded activation treatment of mine tailings, including the following steps:

[0090] (1) Preparation of masking precursor slurry: 100.0 kg of fine iron tailings powder after physical classification and 25.0 kg of deionized water were weighed and put into a wet ball mill. Solid sodium hydroxide was slowly added and the initial pH of the liquid phase was adjusted to 12.8 by monitoring with an online pH meter. Then, 0.8 kg of sodium ethylenediaminetetramethylenephosphonate working solution with a solid content of 45.0 wt% prepared in Preparation Example 4 was added. The ball mill speed was set to 300 r / min and the mixture was continuously co-milled at room temperature for 45 minutes to obtain the masking precursor slurry.

[0091] (2) Preparation of critical precursor slurry: The masked precursor slurry was pumped into the reactor, the stirring was turned on, the stirring speed was set to 120 r / min, the temperature was raised to 78℃ and kept constant; the metering pump was started to add 15.0 L of 1.5 mol / L sodium aluminate aqueous solution prepared in Preparation Example 1 was added by pump A, and propylene carbonate was added by pump B. The cumulative amount of liquid propylene carbonate added by pump B was 0.95 kg. The pH value of the slurry in the reactor was controlled to gradually decrease from 12.8 to 11.9 within 40 minutes and maintained at this critical value; after the addition was completed, cooling water was introduced and the temperature was lowered to below 40℃ within 10 minutes to obtain the critical precursor slurry.

[0092] (3) Activation and coating of coarse aggregate interface: 300.0 kg of iron tailings coarse aggregate component is added to the granulator, tumbled and sprayed with 3.0 kg of sodium hydroxide aqueous solution with a mass fraction of 0.8 wt%, and continuously tumbled and mixed for 3 minutes; then critical state precursor slurry is sprayed and continuously tumbled and mixed for 8 minutes to obtain the activated mine tailings mixture.

[0093] Example 3:

[0094] This embodiment provides a method for graded activation treatment of mine tailings, including the following steps:

[0095] (1) Preparation of masking precursor slurry: Weigh 100.0 kg of fine iron tailings powder after physical classification and add it together with 35.0 kg of deionized water into a wet ball mill. Slowly add solid sodium hydroxide to adjust the initial pH of the liquid phase to 13.2. Add 1.5 kg of sodium ethylenediaminetetramethylenephosphonate working solution with a solid content of 55.0 wt% prepared in Preparation Example 6. Set the ball mill speed to 450 r / min and continuously co-mill at room temperature for 60 minutes to obtain the masking precursor slurry.

[0096] (2) Preparation of critical precursor slurry: The above-mentioned masked precursor slurry was pumped into the reactor, the stirring was turned on, the stirring speed was set to 180 r / min, the temperature was raised to 82℃ and kept constant; the metering pump was started, pump A added 25.0 L of 2.5 mol / L sodium aluminate aqueous solution prepared in Preparation Example 3, and pump B added propylene carbonate simultaneously. The cumulative amount of liquid propylene carbonate added by pump B was 2.45 kg. The pH value was controlled to gradually decrease from 13.2 to 11.7 within 50 minutes and maintained at this critical value; after the addition was completed, cooling water was introduced and the temperature was lowered to below 40℃ within 15 minutes to obtain the critical precursor slurry.

[0097] (3) Activation and coating of coarse aggregate interface: 500.0 kg of iron tailings coarse aggregate component is added to the granulator, tumbled and sprayed with 10.0 kg of sodium hydroxide aqueous solution with a mass fraction of 1.2 wt%, and tumbled and mixed for 5 minutes; then critical state precursor slurry is sprayed, tumbled and mixed for 12 minutes to obtain the activated mine tailings mixture.

[0098] Example 4:

[0099] This embodiment provides a method for graded activation treatment of mine tailings, including the following steps:

[0100] (1) Preparation of masking precursor slurry: The raw material was replaced with copper tailings that had been dried, chemically analyzed and physically classified as described above. 100.0 kg of copper tailings fine powder and 30.0 kg of deionized water were weighed and put into a wet ball mill. Solid sodium hydroxide was added to adjust the initial pH value to 13.0. 1.2 kg of sodium ethylenediaminetetramethylenephosphonate working solution with a solid content of 50.0 wt% prepared in Preparation Example 5 was added. The mixture was continuously co-milled at 380 r / min for 50 minutes to obtain the masking precursor slurry.

[0101] (2) Preparation of critical precursor slurry: The masked precursor slurry was pumped into the reactor, stirred at 150 r / min and kept at a constant temperature of 80°C; 20.0 L of 2.0 mol / L sodium aluminate aqueous solution prepared in Preparation Example 2 was added dropwise by pump A, and propylene carbonate was added dropwise by pump B. The cumulative amount of liquid propylene carbonate added by pump B was 1.70 kg. The pH value was controlled to gradually decrease from 13.0 to 11.8 within 45 minutes and maintained; after the addition was completed, the temperature was lowered to below 40°C to obtain the critical precursor slurry.

[0102] (3) Activation and coating of coarse aggregate interface: 400.0 kg of copper tailings coarse aggregate component is added to the granulator, and 4.0 kg of sodium hydroxide aqueous solution with a mass fraction of 1.0 wt% is sprayed and continuously rolled and mixed for 4 minutes; the above-mentioned critical state precursor slurry is sprayed and continuously rolled and mixed for 10 minutes to obtain the activated mine tailings mixture.

[0103] Comparative Example 1:

[0104] Compared with Example 1, the difference is that sodium ethylenediaminetetramethylenephosphonate working solution was not added in step one, liquid propylene carbonate was not added simultaneously via pump B in step two, and sodium hydroxide aqueous solution was not sprayed onto the surface of the coarse aggregate for wetting treatment in step three. The remaining raw material dosage, sodium aluminate aqueous solution added via pump A, temperature, stirring and granulation conditions are the same as in Example 1.

[0105] Comparative Example 2:

[0106] Compared with Example 1, the difference is that the sodium ethylenediaminetetramethylenephosphonate working solution is replaced by an aqueous solution of sodium hexametaphosphate with the same solid content. The aqueous solution of sodium hexametaphosphate is prepared by mixing sodium hexametaphosphate solid with deionized water and has a solid content of 50.0 wt%. All other aspects are the same.

[0107] Comparative Example 3:

[0108] Compared with Example 1, the difference is that pump B was turned off in the reactor and liquid propylene carbonate was not added simultaneously, so that the pH value of the slurry in the reactor was maintained at around 13.0 throughout the dropping stage, and no programmed alkali reduction occurred. 20.0L of 2.0mol / L sodium aluminate aqueous solution prepared in Preparation Example 2 was still added dropwise through pump A. All other aspects were the same.

[0109] Comparative Example 4:

[0110] Compared with Example 1, the difference lies in the increased dripping amount and rate of liquid propylene carbonate from pump B in the reactor. The cumulative dripping amount of liquid propylene carbonate from pump B is 3.20 kg, which is 2.0 times the cumulative dripping amount in Example 1. This causes the pH value of the slurry in the reactor to drop to about 11.0 after 30 minutes, and further drop to a low-alkali range of about 10.5 after 45 minutes, forming excessive alkali reduction conditions. All other aspects are the same.

[0111] Comparative Example 5:

[0112] Compared with Example 1, the difference is that in the drum granulator, the sodium hydroxide aqueous solution sprayed onto the surface of the coarse aggregate is replaced with deionized water by the same mass, and a high-concentration alkaline environment is not constructed at the interface; otherwise, they are the same.

[0113] Test Example 1:

[0114] The testing steps are as follows:

[0115] (1) A simulated reaction evaluation device with a constant temperature water bath jacket was built. The device is equipped with a rotary rheological testing component and a high-temperature resistant composite electrode online pH meter. Before the test, the device temperature was preset to 80℃ and kept constant during the test. At the same time, the pH meter was calibrated and the rheological testing component was calibrated under no-load conditions.

[0116] (2) Take 500.0g of the precursor slurry obtained at the end of step one of the preparation process of Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4 respectively, add them to the above-mentioned simulated reaction evaluation device, turn on mechanical stirring, and set the stirring speed to 150r / min so that the slurry remains in a uniform suspension state during the test.

[0117] (3) Following the aluminum source replenishment solution, propylene carbonate dripping method, and pH control target set in step two of Examples 1, 2, 3, and 4, the dripping amounts of aluminum source replenishment solution A and propylene carbonate B were proportionally reduced according to the ratio of the test slurry mass to the original process slurry mass, and a micro-injection pump was used for the dripping operation. Specifically, in Examples 1 and 2, aluminum source replenishment solution A and propylene carbonate B were dripped simultaneously according to their corresponding processes; in Comparative Example 3, only aluminum source replenishment solution A was dripped, and propylene carbonate B was not dripped; in Comparative Example 4, while dripping aluminum source replenishment solution A, the cumulative dripping amount and dripping rate of propylene carbonate B were increased according to its corresponding process.

[0118] (4) During the dropping process, the pH value and apparent viscosity data of the system were continuously collected. The apparent viscosity was tested using rotational rheology testing mode, the test temperature was 80℃, and the shear rate was set to 50s. -1 Data was recorded after the readings stabilized at each monitoring time point. Real-time pH and apparent viscosity data of the system were recorded at 0, 10, 20, 30, 40, and 45 minutes during the dropping process.

[0119] The test results are shown in Table 1.

[0120] Table 1. Rheological properties and pH monitoring data of the precursor slurry during the isothermal dripping stage:

[0121]

[0122] Based on the data in Table 1 and in conjunction with Figure 1 and Figure 2 It can be seen that in Example 1, during the 45-minute dropping cycle, the pH value of the system gradually decreased from 13.01 to 11.78, with a relatively gentle overall decrease. Simultaneously, the apparent viscosity increased from 123.6 mPa·s to 196.7 mPa·s, remaining at a relatively low level. These results indicate that under the temperature, aluminum source supply, and propylene carbonate dropping conditions set in this example, the alkalinity of the system can gradually decrease during the dropping process, and the slurry maintains good flow during the dropping stage. This suggests that the introduction of propylene carbonate is beneficial for improving the rheological stability of the high-alkali activated system during the aluminum source supply process.

[0123] Compared to Example 1, Comparative Example 2 showed a similar trend in pH value change, both gradually decreasing to around 11.8 during the dropwise addition process; however, combined with... Figure 2It can be seen that the apparent viscosity of Comparative Example 2 increased significantly after 20 minutes, reaching 6350.2 mPa·s at 45 minutes. This result indicates that, under similar pH control conditions, replacing sodium ethylenediaminetetramethylenephosphonate with sodium hexametaphosphate resulted in a more significant increase in viscosity in a high-temperature alkaline environment, suggesting that the type of masking agent has a significant impact on the rheological stability of the slurry during the dropwise addition stage.

[0124] Comparative Example 3 did not introduce propylene carbonate during the dropwise addition process, thus combining... Figure 1 It can be seen that its pH value is basically maintained around 13.0; combined with Figure 2 It was observed that the apparent viscosity continuously increased over time, reaching 28540.0 mPa·s at 45 minutes. This result indicates that under continuously high alkalinity conditions, the slurry is more prone to rapid thickening during aluminum source replenishment, which is detrimental to subsequent conveying, spraying, and coating operations. Compared to Example 1, in-situ alkalinity reduction treatment helps reduce the risk of rapid viscosity increase in the slurry during the dripping stage.

[0125] In Comparative Example 4, the pH value of the system decreased to 11.42 after 20 minutes and further decreased to 10.48 after 45 minutes; its apparent viscosity exhibited an unstable change characteristic of first increasing, then locally decreasing, and then increasing again. This result indicates that when the alkalinity decreases too much, the rheological state of the system is prone to fluctuation, which is not conducive to the formation of a stable precursor slurry. (See Table 1 for details.) Figure 1 and Figure 2 The results show that controlling the pH value at the droplet addition endpoint within the range of approximately 11.7 to 11.9 is beneficial for balancing the low viscosity and fluidity of the slurry with the stability of the system components, thus providing a more suitable process window for subsequent atomization spraying and aggregate surface coating.

[0126] Test Example 2:

[0127] The testing steps are as follows:

[0128] (1) Weigh two portions of the critical precursor slurry prepared in step two of Example 1, each weighing 50.0g. Place one portion in the sample reaction cup of an isothermal calorimeter with an in-situ injection port to test the hydration exothermic rate of the system; place the other portion on the parallel plate test platform of a rotational rheometer to test the storage modulus G' of the system. Before the test, the temperature of both test environments was set to 25°C and kept constant.

[0129] (2) Start the isothermal calorimeter and rotational rheometer. During the initial stage of 0 min to 5 min, do not add any additional substances to the critical precursor slurry. Record the hydration heat release rate and storage modulus G' of the system during this stage. The rotational rheometer adopts the small amplitude oscillation test mode, the test frequency is 1 Hz, and the shear amplitude is 0.05%.

[0130] (3) When the test is in progress for 5 minutes, 1.0 g of sodium hydroxide aqueous solution with a mass fraction of 1.0 wt% is added to the slurry sample in the sample reaction cup of the isothermal calorimeter and the parallel plate test area of ​​the rotational rheometer through a micro-injector, respectively, to simulate the local alkalinity recovery state after the critical state precursor slurry comes into contact with the alkaline wettment layer on the surface of coarse aggregate.

[0131] (4) After injecting the sodium hydroxide aqueous solution, the hydration exothermic rate and storage modulus G' data were collected at 25°C. The rotational rheometer was kept at a test frequency of 1 Hz and a shear amplitude of 0.05% for 30 min to obtain the exothermic and rheological response data of the critical precursor slurry before and after alkaline triggering.

[0132] The test results are shown in Table 2.

[0133] Table 2. Data on changes in hydration heat release rate and storage modulus before and after triggering of critical state precursor slurry:

[0134]

[0135] Based on the data in Table 2 and in conjunction with Figure 3 It can be seen that during the non-triggered phase of 0 min to 5 min, the hydration exothermic rate of the critical precursor slurry prepared in step two of Example 1 remained between 0.02 mW / g and 0.03 mW / g, and the storage modulus G' remained between 42 Pa and 46 Pa, both of which were at a low level. This result indicates that, without the introduction of additional alkali solution, the reaction exothermics and elastic structure development of the critical precursor slurry were relatively slow in the initial stage of the test, and the slurry as a whole was in a relatively stable low reactivity state.

[0136] After adding an aqueous sodium hydroxide solution at 5 min, both the hydration exothermic rate and the storage modulus G' of the system showed significant changes. Figure 3 Part (a) shows that the hydration exothermic rate increases to 8.95 mW / g at 8 min and then gradually decreases; Figure 3 Part (b) shows that the storage modulus G' increases to 215 Pa at 5.5 min and continues to increase during subsequent tests, reaching 26120 Pa at 30 min. This result indicates that the critical-state precursor slurry can produce a significant exothermic response and elastic structure growth under local alkalinity recovery conditions.

[0137] Combined with Table 2 and Figure 3The changing trend shows that the addition of sodium hydroxide aqueous solution can transform the critical precursor slurry from a low-reactivity state to a faster structure-forming state. This experimental result, from the perspectives of reaction kinetics and rheology, demonstrates that precursor slurries in the critical pH range, upon contact with an alkaline wetting environment, tend to be further activated and undergo gel structure growth, thus providing experimental evidence for the interfacial pH secondary transition and interfacial pre-anchoring effect proposed in this application.

[0138] Test Example 3:

[0139] The testing steps are as follows:

[0140] (1) The activated mine tailings mixtures obtained in Example 1 and Comparative Example 1 were respectively loaded into test molds and compacted using a vibrating table for 30 seconds. After molding, the molds were placed in a constant temperature curing chamber at 75°C and relative humidity not less than 90% for 24 hours for heat curing. After heat curing, the molds were removed and the specimens were transferred to a standard curing room at 20±2°C and relative humidity above 95% for continued curing until 28 days of age, thus obtaining the corresponding permeable building material products. Subsequently, the 28-day-old permeable building material products obtained in Example 1 and Comparative Example 1 were crushed and peeled off, and the cementitious matrix was collected and ground in an agate mortar until it all passed through a 200-mesh standard sieve (particle size less than 74μm).

[0141] (2) The sieved powder sample was soaked in anhydrous ethanol for 24 hours to terminate the subsequent reaction, and then dried in a vacuum drying oven at 60°C for 24 hours. After being taken out, it was sealed and stored in a desiccator as the matrix powder sample to be tested.

[0142] (3) The crystal structure of the matrix powder sample to be tested was determined using an X-ray diffractometer. The test conditions were set as follows: copper target Kα radiation, tube voltage 40kV, tube current 40mA, scanning range 2θ 10°~60°, step size 0.02°, and scanning speed 5° / min. All samples were tested using the same test parameters, and the data on the diffraction intensity as a function of the diffraction angle were recorded.

[0143] (4) Fourier transform infrared spectroscopy was used to analyze the chemical bond structure of the matrix powder sample. The potassium bromide pellet method was used for sample preparation. The powder sample and dry potassium bromide powder were mixed evenly at a mass ratio of 1:100 and pressed into transparent thin sheets. The mixture was then subjected to infrared spectroscopy at 400 cm⁻¹. -1 ~2000cm -1 Infrared spectral scanning was performed within the wavenumber range, with a resolution set to 4 cm⁻¹. -1 Record data on transmittance as a function of wavenumber.

[0144] The test results are shown in Table 3.

[0145] Table 3. XRD diffraction peaks and FTIR main absorption band characteristics of the finished cementitious matrix powder of permeable building materials at 28 days of age:

[0146]

[0147] Based on the data in Table 3 and in conjunction with Figure 4 It can be seen that the matrix powders of both Example 1 and Comparative Example 1 showed characteristic quartz diffraction peaks at approximately 26.6° 2θ, indicating that both samples retained the quartz phase from the original mineral components of the tailings. Compared with Comparative Example 1, Example 1 showed a characteristic calcite diffraction peak at 29.43° 2θ with a diffraction intensity of 1245 counts, while Comparative Example 1 did not show a significant calcite diffraction peak at the corresponding position. This result indicates that a detectable calcium carbonate crystalline phase exists in the sample of Example 1, while the calcium carbonate crystalline phase characteristics are not obvious in the sample of Comparative Example 1.

[0148] Based on the process analysis of Example 1, the propylene carbonate introduced in Example 1 hydrolyzes under alkaline conditions to produce carbonate ions. These carbonate ions can react with the calcium components in the system, thereby promoting the formation of the calcium carbonate crystalline phase. This result indicates that the in-situ alkalinity reduction treatment of propylene carbonate used in this application can not only participate in the pH regulation process but may also affect the subsequent formation of the carbonate crystalline phase.

[0149] In the FTIR test results, the Si-OT stretching vibration peak of Example 1 is located at 1004.2 cm⁻¹. -1 The corresponding peak in Comparative Example 1 is located at 1028.5 cm⁻¹. -1 In Example 1, the characteristic peak shifts towards lower wavenumbers compared to Comparative Example 1, indicating a difference in the chemical environment of the aluminosilicate structural units in the two samples. This peak position change is generally related to the formation and reconstruction process of the aluminosilicate gel network structure, suggesting that the aluminosilicate structure in the matrix obtained in Example 1 may have more complete reaction and rearrangement characteristics.

[0150] Furthermore, in Example 1, at 1422.6 cm... -1 An absorption peak related to the stretching vibration of carbonate CO was detected at [location missing], and the corresponding peak in Comparative Example 1 was located at 1455.1 cm⁻¹. -1 Based on the XRD results showing the detection of calcite characteristic peaks in Example 1, it can be concluded that the carbonate-related structural features in the Sample 1 are more clearly defined. This result corresponds to the process by which propylene carbonate hydrolyzes to produce carbonate ions, which then participate in the formation of the carbonate crystal phase.

[0151] The combined XRD and FTIR test results show that the gel matrix obtained in Example 1 differs from that in Comparative Example 1 in both crystal phase composition and aluminosilicate structural characteristics. These structural differences are related to the ethylenediaminetetramethylphosphonate sodium masking, propylene carbonate programmed alkali reduction, and carbonate competitive nucleation process in this application, and can provide structural characterization support for the subsequent improvement in mechanical properties and reduction in free alkali leaching observed in Example 1.

[0152] Test Example 4:

[0153] The testing steps are as follows:

[0154] (1) Referring to the molding and thermosetting conditions described in step (1) of Test Example 3, the activated mine tailings mixtures obtained in Examples 1-4 and Comparative Examples 1, 4, and 5 were respectively prepared into permeable building materials. Among them, the compressive strength test used a 100mm×100mm×100mm cubic specimen, the flexural strength test used a 100mm×100mm×400mm prism specimen, and the permeability coefficient test used a cylindrical specimen with a diameter of 100mm and a height of 50mm. After demolding, all specimens were placed in a standard curing room with a temperature of 20±2℃ and a relative humidity of 95% or higher for continued curing until 28 days.

[0155] (2) In accordance with GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete", 28-day-old cubic specimens were placed in the center of a compression testing machine and continuously and uniformly loaded at a loading rate of 0.5 MPa / s until the specimen failed. The ultimate failure load was recorded and the 28-day compressive strength of the finished product was calculated. Prism specimens were placed on a flexural testing fixture and tested using a three-point loading method at a loading rate of 0.05 MPa / s until the specimen broke. The 28-day flexural strength of the finished product was calculated. Three specimens of each group of compressive strength and flexural strength specimens were tested in parallel, and the arithmetic mean was taken as the final test result.

[0156] (3) Referring to the constant head method specified in CJJ / T 135-2009 "Technical Specification for Permeable Cement Concrete Pavement", the cylindrical specimen used for permeability coefficient testing is placed into the sealing sleeve of the permeability coefficient tester. The gap between the outer wall of the specimen and the inner wall of the sleeve is sealed with sealant to reduce the impact of edge leakage on the results during the test.

[0157] (4) Start the permeability testing device and fill the water supply tank with water to keep the test head difference constant. After the water flow at the outlet reaches a stable state, use a graduated cylinder and stopwatch to collect and record the volume of water flowing through the specimen within the set time interval. Combine the specimen height, water flow cross-sectional area and stable head difference to calculate the permeability coefficient of each group of samples. Three specimens of each group of permeability coefficients are tested in parallel, and the arithmetic mean is taken as the final test result.

[0158] The test results are shown in Table 4.

[0159] Table 4. Test data of mechanical properties and permeability coefficient of permeable building materials:

[0160]

[0161] According to the data in Table 4, the permeable building materials prepared in Examples 1-4 exhibit compressive strengths of 38.6 MPa to 45.1 MPa, flexural strengths of 5.81 MPa to 6.89 MPa, and permeability coefficients of 2.64 mm / s to 3.12 mm / s after 28 days of use. These results indicate that, under different process parameters or tailings types, the samples from these examples can maintain a certain level of permeability while achieving high mechanical strength, demonstrating that the treatment method described in this application has a certain improving effect on the comprehensive performance of permeable building materials made from mine tailings.

[0162] Compared with Example 1, Comparative Example 1 did not include sodium ethylenediaminetetramethylenephosphonate working solution and propylene carbonate, and the surface of the coarse aggregate was not wetted with sodium hydroxide aqueous solution. Table 4 shows that the compressive strength of Comparative Example 1 was 22.4 MPa, the flexural strength was 2.84 MPa, and the permeability coefficient was 1.95 mm / s, all lower than that of Example 1. This result indicates that in the absence of a masking agent, in-situ alkali reduction treatment, and alkaline wetting treatment at the aggregate interface, the mechanical properties and permeability of the resulting product are reduced, suggesting that the above treatment steps have a synergistic effect on improving the overall performance of the finished product.

[0163] In Comparative Example 4, the increased amount and rate of propylene carbonate addition caused the pH of the system to drop to 10.48 at 45 min, entering the low-alkali range. Table 4 shows that the compressive strength and flexural strength of Comparative Example 4 were 2.1 MPa and 0.31 MPa, respectively, significantly lower than those of Example 1; its permeability coefficient was 4.35 mm / s, higher than that of Example 1. These results indicate that when the pH decreases too much, although the finished product exhibits a high permeability coefficient, its mechanical strength is significantly insufficient, suggesting that excessive alkali reduction is not conducive to the formation of an effective gel coating and load-bearing structure.

[0164] The main difference between Comparative Example 5 and Example 1 is that the surface of the coarse aggregate was not sprayed with sodium hydroxide aqueous solution, but instead replaced with deionized water by an equal mass. Table 4 shows that the compressive strength of Comparative Example 5 is 34.2 MPa and the flexural strength is 3.45 MPa, both lower than that of Example 1; its permeability coefficient is 2.98 mm / s, which is similar to that of Example 1. This result indicates that, under conditions where the permeability is not significantly different, alkaline wetting treatment of the coarse aggregate surface has a significant impact on the mechanical properties of the finished product, especially the flexural strength. Combined with the results of Test Example 2, the alkaline environment on the coarse aggregate surface may be conducive to further structural growth of the critical state precursor slurry in the interfacial region, thereby improving the interfacial bonding state between the cementitious coating layer and the coarse aggregate.

[0165] The results in Table 4 show that the samples in this application, while maintaining a certain permeability coefficient, improve the mechanical load-bearing capacity of the finished product through processes such as slurry rheological control, interface triggering, and nucleation structure adjustment. Therefore, the solution in this application is beneficial for achieving a better balance between permeability and structural strength.

[0166] Test Example 5:

[0167] The testing steps are as follows:

[0168] (1) Referring to the molding, thermosetting, and standard curing conditions described in step (1) of Test Example 3, the activated mine tailings mixtures obtained in Examples 1-4 and Comparative Examples 1 and 2 were prepared into 28-day-old permeable building materials. The above-mentioned 28-day-old permeable building materials were crushed using a jaw crusher, and then graded and screened using a standard vibrating screen. Particle samples with a particle size between 4.75 mm and 9.50 mm were collected as extraction masterbatch.

[0169] (2) Weigh 100.0g of each group of sieved particle samples accurately and place them in a clean and dry 500mL polyethylene high-density plastic bottle. Then add 500.0mL of deionized water to each bottle so that the solid-liquid mass-volume ratio is 100.0g:500.0mL. Ensure that the liquid completely submerges the solid particles and tighten the bottle cap to reduce liquid evaporation during the extraction process.

[0170] (3) Place the polyethylene plastic bottle containing the sample and deionized water into a constant temperature air bath shaking box with a set temperature of 60±1℃, adjust the horizontal oscillation frequency to 120r / min, and continuously oscillate and extract for 24h to allow the migratable sodium ions in the sample to enter the aqueous phase.

[0171] (4) After the extraction is completed, remove the plastic bottle and let it cool naturally to about 25°C at room temperature. After standing, take the supernatant and filter it using a water-based needle filter with a pore size of 0.45μm. Discard the initial filtrate and collect the subsequent filtrate as the extract to be tested.

[0172] (5) Inductively coupled plasma atomic emission spectrometry (ICP-AES) was used to analyze sodium ions (Na+) in the extract to be tested. + The Na concentration was determined. Each sample group was measured in triplicate, with values ​​recorded to an accuracy of 0.01 mg / L. The arithmetic mean was taken as the Na concentration for that sample group. + Leaching mass concentration.

[0173] The test results are shown in Table 5.

[0174] Table 5. Monitoring data on the leaching concentration of free sodium ions in permeable building materials:

[0175]

[0176] According to the data in Table 5, the permeable building materials obtained in Examples 1-4 contain Na. + The average leaching concentration ranged from 11.60 mg / L to 18.29 mg / L, which was generally at a low level. Specifically, the Na in Example 3... + The average leaching concentration was 11.60 mg / L, the lowest among the samples in all examples. This result indicates that the leaching amount of migratable sodium ions in the finished product obtained in this application is low, suggesting that the migration tendency of soluble alkali metal ions within it is suppressed to a certain extent.

[0177] Free Na + Leaching concentration can be used to evaluate the release level of migratable alkali metal ions in materials. Typically, Na... + A higher leaching concentration indicates a higher content of migratable alkali metal ions in the pore fluid or pore wall surface, and a higher likelihood of these ions migrating to the product surface during subsequent wet-dry cycles or water evaporation. Therefore, this indicator can be used as a reference for evaluating the potential efflorescence risk of permeable building materials.

[0178] Compared to Example 1, Comparative Example 1 did not include sodium ethylenediaminetetramethylenephosphonate working solution and propylene carbonate, and the surface of the coarse aggregate was not wetted with sodium hydroxide aqueous solution. Table 5 shows that the Na content in Comparative Example 1... + The average leaching concentration was 245.37 mg / L, significantly higher than that in Example 1. This result indicates that, in the absence of a masking agent, in-situ alkali reduction treatment, and interfacial alkali wetting treatment, the content of migratable sodium ions in the final product increased significantly, suggesting that the matrix structure formed under traditional strong alkali direct activation conditions has a relatively insufficient restrictive effect on alkali metal ions.

[0179] Comparative Example 2 replaced the sodium ethylenediaminetetramethylenephosphonate working solution with an equal mass of sodium hexametaphosphate aqueous solution with the same solid content. Table 5 shows that the Na content of Comparative Example 2... +The average leaching concentration was 186.08 mg / L, significantly higher than in Examples 1-4. This result indicates that, under similar alkali reduction conditions, the type of masking agent affects the leaching level of migratable sodium ions in the final product. Compared to sodium hexametaphosphate, sodium ethylenediaminetetramethylenephosphonate is more beneficial for subsequent alkali reduction and nucleation processes, forming a matrix structure that restricts the migration of alkali metal ions.

[0180] As can be seen from the results in Table 5, the Na content of the samples in the embodiments of this application is... + The leaching concentration was significantly lower than that of the comparative sample, indicating that the multi-toothed chelate masking, in-situ alkali reduction process of propylene carbonate, and subsequent structural regulation process adopted in this application are beneficial to reducing the release level of migratable sodium ions in the permeable building material, thereby reducing the potential risk of efflorescence caused by the migration of alkali metal ions in the later stage.

[0181] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method of beneficiating and activating mine tailings, characterized by, Includes the following steps: (1) The tailings of the mine are graded to obtain fine powder components and coarse aggregate components; (2) The fine powder component is mixed with water, sodium hydroxide is added to adjust the pH of the slurry to 12.8-13.2, sodium ethylenediaminetetramethylenephosphonate working solution is added, and wet co-milling is performed to obtain the masking precursor slurry; (3) Under heating and stirring conditions, sodium aluminate aqueous solution and propylene carbonate are added to the masking precursor slurry to control the pH value of the slurry to drop to 11.7-11.9, so as to obtain a critical state precursor slurry with a pH value of 11.7-11.9; (4) The surface of the coarse aggregate component is brought into contact with an aqueous sodium hydroxide solution, and then the critical state precursor slurry is coated on the surface of the coarse aggregate component after being treated with an aqueous sodium hydroxide solution to obtain a mine tailings mixture after graded activation treatment.

2. The mine tailings fractional activation treatment method of claim 1, wherein, The mine tailings are iron tailings or copper tailings; the fine powder component has a particle size of less than 0.15 mm and a specific surface area of ​​395 m². 2 / kg~410m 2 / kg; the particle size of the coarse aggregate component is 2.36mm to 4.75mm.

3. The mine tailings fractional activation treatment method of claim 1, wherein, In step (2), the amount of water used is 25 to 35 parts by mass per 100 parts by mass of fine powder component, the amount of sodium ethylenediaminetetramethylenephosphonate working solution is 0.8 to 1.5 parts by mass, and the solid content of sodium ethylenediaminetetramethylenephosphonate working solution is 45.0 wt% to 55.0 wt%.

4. The mine tailings fractional activation treatment method of claim 1, wherein, In step (2), the rotation speed of the wet co-milling process is 300 r / min to 450 r / min, and the processing time is 45 minutes to 60 minutes.

5. The mine tailings fractional activation treatment method of claim 1, wherein, The sodium ethylenediaminetetramethylenephosphonate working solution is prepared by the following method: diluting a 50.0 wt% sodium ethylenediaminetetramethylenephosphonate aqueous solution with water, filtering to remove impurities, or concentrating under reduced pressure to obtain a sodium ethylenediaminetetramethylenephosphonate working solution with a solid content of 45.0 wt% to 55.0 wt%.

6. The mine tailings fractional activation treatment method of claim 1, wherein, In step (3), the molar concentration of the sodium aluminate aqueous solution, calculated as NaAlO2, is 1.5 mol / L to 2.5 mol / L; and the amount of sodium aluminate aqueous solution added is 15.0 L to 25.0 L per 100 kg of fine powder component.

7. The mine tailings fractional activation treatment method of claim 1, wherein, In step (3), the heating and stirring conditions are a temperature of 78℃~82℃ and a stirring speed of 120r / min~180r / min; the addition time of the sodium aluminate aqueous solution and propylene carbonate is 40 minutes~50 minutes; the cumulative addition amount of propylene carbonate is 0.95kg~2.45kg based on 100kg of fine powder component; after the pH value of the slurry drops to 11.7~11.9, it is cooled to below 40℃ to obtain the critical state precursor slurry.

8. The mine tailings fractional activation treatment method of claim 1, wherein, In step (4), based on 100 parts by mass of fine powder component, the amount of coarse aggregate component is 300 parts by mass to 500 parts by mass; the mass fraction of sodium hydroxide aqueous solution is 0.8wt% to 1.2wt%, and the amount of sodium hydroxide aqueous solution is 3 parts by mass to 10 parts by mass; the mixing time after the coarse aggregate component comes into contact with the sodium hydroxide aqueous solution is 3 minutes to 5 minutes, and the mixing time after the critical state precursor slurry comes into contact with the coarse aggregate component is 8 minutes to 12 minutes.

9. The use of the mine tailings mixture obtained by the mine tailings classified activation treatment method according to any one of claims 1 to 8 in the preparation of a water permeable building material, characterized in that, The mine tailings mixture is shaped, heat-cured, and maintained to obtain a permeable building material product.

10. Use according to claim 9, characterized in that, The molding process includes vibration molding with a vibration time of 30 seconds; the thermosetting temperature is 75°C and the thermosetting time is 24 hours; after thermosetting, the product is demolded and cured for 28 days at a temperature of 20±2°C and a relative humidity of 95% or higher.

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