Environment restoration material synergistically modified by ardealite and phosphorus tailings based on ettringite ion replacement and preparation method of environment restoration material

Abstract

The invention provides an ettringite ion replacement-based environment restoration material synergistically modified by phosphogypsum and phosphorus tailings and a preparation method of the environment restoration material, and belongs to the technical field of solid waste disposal. The filling material comprises the ardealite, the phosphorus tailings, the alkaline modifier, the aluminum source material, the dispersing agent and the pH regulator, and then the raw materials are mixed through specific steps, so that the synergistic effect among the raw materials is enhanced to the maximum extent, and the fixing of harmful ions and the strength of the repairing material are both improved to the maximum extent. According to the method disclosed by the invention, resource synergistic utilization of the phosphorus tailings and the phosphogypsum is realized through a CaSO4-Al-Si-OH synergistic reaction system. According to the method, generation of ettringite can be induced at normal temperature, efficient fixation and long-term stabilization of various harmful ions are achieved through ion replacement and solidification, the innovation direction of greenization, one-stage and synergistic interaction is reflected, and a new technical approach is provided for phosphorite solid waste recycling and environmental restoration.

Description

Technical Field

[0001] This invention relates to the field of solid waste disposal technology, specifically to an environmental remediation material based on the synergistic modification of phosphogypsum and phosphogypsum tailings using ettringite ion replacement, and its preparation method. Background Technology

[0002] Phosphate tailings and phosphogypsum are two major types of industrial solid waste generated during phosphate rock development and wet-process phosphoric acid production. Their emissions are enormous, their storage periods are long, and their burden on the ecological environment is increasingly prominent. According to statistics from the China Phosphate Chemical Industry Association, my country produces approximately 80 million tons of phosphogypsum and 20 million tons of phosphogypsum annually, with a cumulative stockpile exceeding 1 billion tons. Phosphate tailings mainly consist of quartz, feldspar, a small amount of apatite, and residual silicate minerals, containing trace amounts of heavy metal ions (such as Cr, Pb, and As). Phosphogypsum is primarily composed of calcium sulfate dihydrate (CaSO4·2H2O), accompanied by soluble phosphorus, fluorine, acidic residues, and heavy metal impurities. Due to their poor chemical stability, high acidity, and the presence of soluble harmful ions, direct stockpiling can lead to a series of environmental problems, including soil acidification, heavy metal migration, eutrophication of water bodies, and groundwater pollution.

[0003] Existing technologies for generating ettringite from phosphogypsum and phosphate tailings are essentially limited to conventional hydration reactions. The ettringite primarily functions as a cement and physical encapsulator, and its role in removing PO4 from the phosphogypsum is limited. 3- F - The chemical curing ability of harmful anions is relatively weak, and there is still a risk of delayed expansion of ettringite and secondary release of pollutants in the later stage of the material. Summary of the Invention

[0004] In view of the technical problems existing in the background art, this application provides an environmental remediation material based on chelate ion replacement of phosphogypsum and phosphate tailings synergistic modification and its preparation method, aiming to solve the problems of weak solidification ability of harmful ions in the existing solid waste treatment of phosphogypsum and phosphate tailings, delayed expansion of chelate in the later material affecting the strength and stability of the material, and secondary release of pollutants.

[0005] In a first aspect, embodiments of this application provide an environmental remediation material based on the synergistic modification of phosphogypsum and phosphorus tailings using ettringite ion replacement, characterized in that it comprises 40-60 parts of phosphogypsum, 20-30 parts of phosphorus tailings, 5-10 parts of alkaline modifier, 5-15 parts of aluminum source material, 0.1-0.5 parts of dispersant, and 0.5-2 parts of pH adjuster.

[0006] In the technical solution of this application embodiment, active Al is gradually released under alkaline conditions by constructing phosphorus tailings. 3+ With Si 4+ phosphogypsum provides calcium 2+With SO4 2- External aluminum source to supplement Al 3+ A multiphase dynamic equilibrium system was developed to achieve rapid nucleation and dense growth of ettringite without the need for any external crystal inducers; the more core innovation lies in the slow-release of active Al from phosphorus tailings. 3+ First, with PO4 in the system 3- F - Pre-complexes (Al-PO4, Al-F) are formed, which then act as "in-situ inductive factors" to guide SO4 formation during the formation of the ettringite lattice. 2- by PO4 3- and F - A controlled isomorphic substitution of 10-25% occurs, producing Ca6Al2(SO4). 3-x (PO4) x (OH) 12 ·26H2O and Ca6Al2(SO4) 3-y Fy(OH) 12 • Doped ettringite with 26H2O; simultaneously, Si released slowly from phosphorus tailings. 4+ Further polymerization forms a [Si-O-Al] secondary cross-linked network, structurally suppressing the delayed expansion of traditional ettringite. Completely different from existing technologies that rely solely on physical encapsulation and ordinary ettringite cementation, resulting in a curing rate of <95%, easy later expansion and cracking, and the need for large amounts of cement or slag, this application for the first time achieves a novel chemical curing mechanism of "in-situ induced lattice substitution + dual locking of secondary silicon-aluminum network," enabling PO4 to... 3- F - With a heavy metal solidification rate of ≥99.5%, a 28-day compressive strength of ≥2MPa, an expansion rate of <0.05%, and a total proportion of phosphogypsum and phosphate tailings of ≥95%, it truly achieves "waste treatment with waste, green ambient temperature, and integrated synergistic efficiency," providing a brand-new technical path for the large-scale resource utilization of phosphate mine associated solid waste.

[0007] In some embodiments, the phosphogypsum is calcium sulfate dihydrate, an industrial byproduct, with a purity ≥85% and a pH value of 3-4.

[0008] In this embodiment, the synergistic effect of phosphogypsum providing sulfate source CaSO4 and phosphogypsum tailings providing silicate buffer and auxiliary aluminum source induces the orderly formation of ettringite crystals.

[0009] In some embodiments, the phosphate tailings are typical phosphate mine tailings with a SiO2 content of 5-15% and an Al2O3 content of 0.8-3.0%.

[0010] In this embodiment, the phosphate tailings are low-silica-alumina tailings. The silicates and aluminosilicates in the phosphate tailings act as buffers and auxiliary Al sources, synergistically forming ettringite with CaSO4 in phosphogypsum. The slow-release ions from the silicates in the phosphate tailings form a chemically complementary reaction system with CaSO4 in the phosphogypsum, enhancing the ettringite formation rate and stability. The silica-alumina components and alkaline modifiers participate in the formation of AFt. The active Al released by the phosphate tailings under alkaline conditions is thus utilized. 3+ With Si 4+ As an in situ inductive factor, it causes some SO4 in the generated ettringite lattice to... 2- by PO4 3- and F - Controllable replacement (replacement rate 10~25%) enables the fixation of harmful ions.

[0011] In some embodiments, the alkaline modifier is lime or quicklime powder.

[0012] In this embodiment, lime dissolves a large amount of Ca(OH)2 when it comes into contact with water, providing an alkaline environment and calcium source for the formation of ettringite.

[0013] In some embodiments, the aluminum source material is granulated blast furnace slag or crushed aluminum foil waste, with an Al2O3 content ≥14%.

[0014] In this embodiment, an aluminum source is added to provide the main source of aluminum ions for the formation of ettringite, thereby promoting the formation of ettringite.

[0015] In some embodiments, the dispersant is sodium hexametaphosphate or sodium dodecyl sulfate.

[0016] In this embodiment, a dispersant is added to promote the dispersion of ions and the uniformity of the reaction in the reaction system.

[0017] In some embodiments, the pH adjuster is sodium hydroxide or sodium carbonate.

[0018] In this embodiment, the main function of the pH adjuster is to precisely control and stabilize the reaction system within the pH range of 8.0 to 9.0 over a long period. This range is conducive to the rapid nucleation and dense growth of ettringite crystals and the reduction of SO42-. 2- by PO4 3- / F - The optimal window for controllable lattice replacement; at the same time, neutralizing the residual acidity of phosphogypsum to prevent early pH from being too low, which would lead to the dissolution or slow formation of ettringite; during aging and long-term service, the pH adjuster and the slow-released silica-alumina components of the phosphogypsum tailings work synergistically to ensure that the overall pH of the material is eventually stabilized within the safe range of 7.0 to 9.0, avoiding the risk of delayed expansion or secondary release of harmful ions caused by pH drift in traditional ettringite materials.

[0019] Secondly, embodiments of this application provide a method for preparing an environmental remediation material based on the synergistic modification of phosphogypsum and phosphogypsum tailings using ettringite ion replacement, comprising the following steps: S1. Raw material pretreatment: Dry phosphogypsum and phosphogypsum tailings at 60℃ until the moisture content is <5%, grind them to a particle size of <2mm, stir them evenly, and obtain matrix mixture slurry; S2. Electret-induced formation and targeted solidification of harmful substances: Add an alkaline modifier and aluminum source material to the matrix mixture slurry, then add water at a solid-liquid ratio of 1:0.4, stir at 300 rpm for 1.5 h, then add a dispersant and pH adjuster to adjust the pH value to 8.0~9.0, and continue stirring for 30~60 min to obtain the mixture slurry; S3. Aging and Stabilization: The mixed slurry is placed in a ventilated environment for aging for 7-14 days, and turned over every 3-5 days to obtain the aged slurry; wherein the pH value is stabilized at 7.5-8.5 during the aging process; S4. Drying and molding: The aged slurry is dried at 50°C until the moisture content is <10%, and then pulverized through a 100-mesh sieve to obtain the environmental remediation material.

[0020] In the technical solution of this application embodiment, the process of the environmental remediation material includes raw material pretreatment, ettringite formation induction, targeted solidification of harmful substances, aging and stabilization, drying and molding, all completed at room temperature without the need for water washing or high-temperature calcination. During aging, the pH value is stably maintained within the range of 7.5 to 8.5, which ensures that the ettringite crystals continue to grow in an orderly manner and complete the PO4 formation. 2- F - The lattice substitution solidification method avoids the transformation of ettringite to monosulfide-type hydrated calcium sulfoaluminate at pH above 9.0 or the crystal dissolution at pH below 7.0, ensuring continuous strength growth and optimal long-term stability after 28 days. The resulting repair material exhibits long-term stability (heavy metal leaching <0.01 mg / L at pH 4-10), and its compressive strength consistently reaches over 2 MPa after 28 days. Furthermore, it achieves a total content of over 95% for phosphogypsum and phosphate tailings, eliminating the need for additional cement or slag. By constructing a "Ca-Al-Si-SO4 multiphase reaction system," the entire process of ion replacement, structure formation, and stabilization is completed at room temperature and pressure, achieving environmentally friendly treatment with no calcination, low water consumption, and high fixation rate.

[0021] In some embodiments, the amount of the dispersant is 0.1 to 0.5 wt% of the mass of the mixed slurry.

[0022] In some embodiments, the amount of pH adjuster is 0.5 to 2 wt% of the mass of the mixed slurry.

[0023] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, specific embodiments of this application are given below.

[0024] In this application, unless otherwise specified, all parts are by weight and all percentages are by mass percentage. Detailed Implementation

[0025] The embodiments of the technical solution of this application will be described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion.

[0027] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0028] To address the problems of weak coagulation capacity of harmful ions in existing phosphogypsum and phosphogypsum tailings solid waste treatment, delayed expansion of ettringite in later-stage materials affecting material strength and stability, and secondary release of pollutants, this application provides an environmental remediation material based on ettringite ion replacement and synergistic modification of phosphogypsum and phosphogypsum tailings, and its preparation method. The environmental remediation material in this application includes: phosphogypsum, phosphogypsum tailings, an alkaline modifier, an aluminum source material, a dispersant, and a pH adjuster. This invention utilizes the silicates and aluminosilicates in phosphogypsum tailings as buffers and auxiliary Al sources, synergistically generating ettringite (AFt) with CaSO4 in phosphogypsum. Phosphogypsum tailings, rich in SiO2 and Al2O3, can serve as a natural silicon-aluminum source and buffer, providing the necessary reaction conditions (Ca-Al-SO4) for ettringite formation. 2-(Si system equilibrium environment). Furthermore, the silicates in the phosphate tailings can slowly release Si-O-Al complex ions under alkaline conditions, forming a "secondary framework" structure, improving the density and dissolution resistance of ettringite crystals. The slowly released silicate ions in the phosphate tailings form a chemically complementary reaction system with CaSO4 in phosphogypsum, enhancing the formation rate and stability of ettringite. The silicon-aluminum components and alkaline modifiers participate in the formation of AFt. The alkaline modifier and pH adjuster stabilize the pH between 8.0 and 9.0, which is a necessary environment for the stable formation of ettringite crystals. The actual reaction is a multiphase dynamic equilibrium process. The active silicon and aluminum provided by the phosphate tailings participate in the formation of a secondary framework cross-linked with silicon-oxygen tetrahedra and aluminum-oxygen tetrahedra. The main reaction is as follows: 3CaSO4 + 2[Al(OH)4] - (Slow-release phosphorus tailings) + 3Ca(OH)₂ + nSi(OH)₄ (Slow-release phosphorus tailings) + 26H₂O → Ca₆Al₂(SO₄)₃(OH)₂ 12 ·26H2O (ettringite main phase) + n{Si-O-Al} secondary network framework + OH - This promotes crystal densification and homogenization, increasing its structural stability by more than 20%, and improving the chemical equilibrium of the multiphase system (Ca, Al, Si, SO4). 2- (The stoichiometric balance between them), which is a prerequisite for the rapid nucleation and growth of ettringite into a dense network structure; through the gradient slow release of active Al from phosphate tailings under alkaline conditions 3+ With Si 4+ As an in situ inductive factor, it causes some SO4 in the generated ettringite lattice to... 2- by PO4 3- and F - Controllable replacement (replacement rate 10~25%) utilizes the channel encapsulation effect of the layered structure of ettringite to embed harmful ions into the crystal lattice. Permanent fixation is achieved through a triple mechanism of "replacement-adsorption-complexation," forming a doped ettringite-silicate composite phase with a more stable structure and significantly increased active sites. This modified phase not only increases the chemical solidification rate of heavy metals and phosphorus and fluorine to over 98%, but also fundamentally inhibits the delayed expansion of traditional ettringite. The 28-day compressive strength stably reaches over 2 MPa, and the pH value of the material remains stable within the range of 7.0~9.0 during long-term service and leaching environments. Furthermore, it achieves a total content of over 95% for phosphogypsum and phosphate tailings, eliminating the need for external cement or slag. This synergistic mechanism provides a new approach for the resource utilization of phosphate tailings, increasing the comprehensive resource utilization rate to >85%.

[0029] On one hand, this application provides an environmental remediation material based on the synergistic modification of phosphogypsum and phosphorus tailings by ettringite ion replacement, comprising 40-60 parts of phosphogypsum, 20-30 parts of phosphorus tailings, 5-10 parts of alkaline modifier, 5-15 parts of aluminum source material, 0.1-0.5 parts of dispersant, and 0.5-2 parts of pH adjuster.

[0030] In the technical solution of this application embodiment, silicates and aluminosilicates in phosphogypsum are used as buffers and auxiliary Al sources to synergistically generate ettringite (AFt) with CaSO4 in phosphogypsum. Phosphogypsum tailings are rich in SiO2 and Al2O3, which can serve as natural silicon-aluminum sources and buffers, providing the necessary reaction conditions (Ca-Al-SO4) for ettringite formation. 2- (Si system equilibrium environment). Furthermore, the silicates in the phosphate tailings can slowly release Si-O-Al complex ions under alkaline conditions, forming a "secondary framework" structure, improving the density and dissolution resistance of ettringite crystals. The slowly released silicate ions in the phosphate tailings form a chemically complementary reaction system with CaSO4 in phosphogypsum, enhancing the formation rate and stability of ettringite. The silicon-aluminum components and alkaline modifiers participate in the formation of AFt. The alkaline modifier and pH adjuster stabilize the pH between 8.0 and 9.0, which is a necessary environment for the stable formation of ettringite crystals. The actual reaction is a multiphase dynamic equilibrium process. The active silicon and aluminum provided by the phosphate tailings participate in the formation of a secondary framework cross-linked with silicon-oxygen tetrahedra and aluminum-oxygen tetrahedra. The main reaction is as follows: 3CaSO4 + 2[Al(OH)4] - (Slow-release phosphorus tailings) + 3Ca(OH)₂ + nSi(OH)₄ (Slow-release phosphorus tailings) + 26H₂O → Ca₆Al₂(SO₄)₃(OH)₂ 12 ·26H2O (ettringite main phase) + n{Si-O-Al} secondary network framework + OH - This promotes crystal densification and homogenization, increasing its structural stability by more than 20%, and improving the chemical equilibrium of the multiphase system (Ca, Al, Si, SO4). 2- (The stoichiometric balance between them), which is a prerequisite for the rapid nucleation and growth of ettringite into a dense network structure; through the gradient slow release of active Al from phosphate tailings under alkaline conditions 3+ With Si 4+ As an in situ inductive factor, it causes some SO4 in the generated ettringite lattice to... 2- by PO4 3- and F -Controllable replacement (replacement rate 10~25%) utilizes the channel encapsulation effect of the layered structure of ettringite to embed harmful ions into the crystal lattice. Permanent fixation is achieved through a triple mechanism of "replacement-adsorption-complexation," forming a doped ettringite-silicate composite phase with a more stable structure and significantly increased active sites. This modified phase not only increases the chemical solidification rate of heavy metals and phosphorus and fluorine to over 98%, but also fundamentally inhibits the delayed expansion of traditional ettringite. The 28-day compressive strength stably reaches over 2 MPa, and the pH value of the material remains stable within the range of 7.0~9.0 during long-term service and leaching environments. Furthermore, it achieves a total content of over 95% for phosphogypsum and phosphate tailings, eliminating the need for external cement or slag. This synergistic mechanism provides a new approach for the resource utilization of phosphate tailings, increasing the comprehensive resource utilization rate to >85%.

[0031] Furthermore, in some embodiments, the phosphogypsum is calcium sulfate dihydrate, an industrial byproduct, with a purity ≥85% and a pH value of 3-4.

[0032] In the technical solution of this application embodiment, the synergistic effect of phosphogypsum providing sulfate source CaSO4 and phosphogypsum tailings providing silicate buffer and auxiliary aluminum source induces the orderly formation of ettringite crystals.

[0033] Furthermore, in some embodiments, the phosphorus tailings are typical phosphate rock tailings with a SiO2 content of 5-15% and an Al2O3 content of 0.8-3.0%.

[0034] In the technical solution of this application embodiment, the phosphate tailings are low-silica-alumina tailings. The silicates and aluminosilicates in the phosphate tailings act as buffers and auxiliary Al sources, synergistically forming ettringite with CaSO4 in phosphogypsum. The slow-release ions from the silicates in the phosphate tailings form a chemically complementary reaction system with CaSO4 in the phosphogypsum, enhancing the ettringite formation rate and stability. The silica-alumina components and alkaline modifiers participate in the formation of AFt. The active Al released by the phosphate tailings under alkaline conditions is thus utilized. 3+ With Si 4+ As an in situ inductive factor, it causes some SO4 in the generated ettringite lattice to... 2- by PO4 3- and F - Controllable replacement (replacement rate 10~25%) enables the fixation of harmful ions.

[0035] Furthermore, in some embodiments, the alkaline modifier is lime or quicklime powder.

[0036] In the technical solution of this application embodiment, lime dissolves a large amount of Ca(OH)2 when it comes into contact with water, providing an alkaline environment and calcium source for the formation of ettringite.

[0037] Furthermore, in some embodiments, the aluminum source material is granulated blast furnace slag or crushed aluminum foil waste, with an Al2O3 content ≥14%.

[0038] In the technical solution of this application embodiment, an aluminum source is added to provide the main source of aluminum ions for the formation of ettringite, thereby promoting the formation of ettringite.

[0039] Furthermore, in some embodiments, the dispersant is sodium hexametaphosphate or sodium dodecyl sulfate.

[0040] In the technical solution of this application embodiment, a dispersant is added to promote the dispersion of ions and the uniformity of the reaction in the reaction system.

[0041] Furthermore, in some embodiments, the pH adjuster is sodium hydroxide or sodium carbonate.

[0042] In the technical solution of this application embodiment, slow-release Si is constructed by constructing phosphorus tailings. 4+ / Al 3+ A dynamic chemical equilibrium system with phosphogypsum (CaSO4) within the pH range of 8.0–9.0 enables rapid nucleation and dense network growth of ettringite. Simultaneously, the active silica-alumina components released gradient from the phosphogypsum tailings form a [Si-O-Al] secondary cross-linked framework, structurally inhibiting the delayed expansion of traditional ettringite. More importantly, within the uniform microenvironment formed by the dispersant, the phosphogypsum tailings slowly release Al... 3+ Priority and PO4 in the system 3- F - The formation of a pre-complex followed by SO4 formation during the nucleation process of ettringite lattice 2- by PO4 3- / F - Controllable lattice substitution (substitution rate 10~25%) produces Ca6Al2(SO4). 3-x (PO4) x (OH) 12 ·26H2O and Ca6Al2(SO4) 3-y Fy(OH) 12 The doped ettringite-silicate composite phase of ·26H2O makes PO4 3- F - The heavy metal ions are completely transformed from the soluble state to the lattice covalent state, the curing rate is increased to over 99.5%, the 28-day compressive strength is stably above 2MPa, and the pH of the material remains stable at 7.0-9.0 in long-term leaching at pH 4-10 and in a 100-year accelerated aging simulation environment. The release rate of heavy metals and phosphorus and fluorine is less than 0.8%, which completely solves the problem of later strength reduction and secondary release of pollutants caused by physical encapsulation in existing technologies, and achieves true chemical curing and permanent stabilization.

[0043] Secondly, embodiments of this application provide a method for preparing an environmental remediation material based on the synergistic modification of phosphogypsum and phosphogypsum tailings using ettringite ion replacement, comprising the following steps: S1. Raw material pretreatment: Dry phosphogypsum and phosphogypsum tailings at 60℃ until the moisture content is <5%, grind them to a particle size of <2mm, stir them evenly, and obtain matrix mixture slurry; S2. Electret-induced formation and targeted solidification of harmful substances: Add an alkaline modifier and aluminum source material to the matrix mixture slurry, then add water at a solid-liquid ratio of 1:0.4, stir at 300 rpm for 1.5 h, then add a dispersant and pH adjuster to adjust the pH value to 8.0~9.0, and continue stirring for 30~60 min to obtain the mixture slurry; S3. Aging and Stabilization: The mixed slurry is placed in a ventilated environment for aging for 7-14 days, and turned over every 3-5 days to obtain the aged slurry; wherein the pH value is stabilized at 7.5-8.5 during the aging process; S4. Drying and molding: The aged slurry is dried at 50°C until the moisture content is <10%, and then pulverized through a 100-mesh sieve to obtain the environmental remediation material.

[0044] In the technical solution of this application embodiment, the process of the environmental remediation material includes raw material pretreatment, ettringite formation induction, targeted solidification of harmful substances, aging and stabilization, drying and molding, all completed at room temperature without the need for water washing or high-temperature calcination. During aging, the pH value is stably maintained within the range of 7.5 to 8.5, which ensures that the ettringite crystals continue to grow in an orderly manner and complete the PO4 formation. 2- F - The lattice substitution solidification method avoids the transformation of ettringite to monosulfide-type hydrated calcium sulfoaluminate at pH above 9.0 or the crystal dissolution at pH below 7.0, ensuring continuous strength growth and optimal long-term stability after 28 days. The resulting repair material exhibits long-term stability (heavy metal leaching <0.01 mg / L at pH 4-10), and its compressive strength consistently reaches over 2 MPa after 28 days. Furthermore, it achieves a total content of over 95% for phosphogypsum and phosphogypsum tailings, eliminating the need for additional cement or slag. By constructing a "Ca-Al-Si-SO4 multiphase reaction system," the entire process of ion replacement, structure formation, and stabilization is completed at room temperature and pressure, achieving environmentally friendly treatment with no calcination, low water consumption, and high fixation rate.

[0045] Furthermore, in some embodiments, the amount of the dispersant is 0.1 to 0.5 wt% of the mass of the mixed slurry.

[0046] Furthermore, in some embodiments, the amount of the pH adjuster is 0.5 to 2 wt% of the mass of the mixed slurry.

[0047] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0048] Example 1 This embodiment provides a method for preparing an environmental remediation material based on the synergistic modification of phosphogypsum and phosphogypsum tailings using ettringite ion replacement, specifically including the following steps: (1) Weigh the required raw materials according to the following weight proportions: 50 parts phosphogypsum, 25 parts phosphogypsum tailings, 8 parts lime, 10 parts shredded aluminum foil waste, 0.3 parts sodium hexametaphosphate, and 1 part sodium hydroxide; (2) Raw material pretreatment: Dry phosphogypsum and phosphogypsum tailings at 60°C to a moisture content of 4%, grind them to a particle size of 1 mm, stir them evenly, and obtain matrix mixture slurry; (3) Calcium alum induction and targeted solidification of harmful substances: Lime and crushed aluminum foil waste were added to the matrix mixture slurry, and then water was added at a solid-liquid ratio of 1:0.4. The mixture was stirred at 300 rpm for 1.5 h, then sodium hexametaphosphate and sodium hydroxide were added to adjust the pH value to 8.5. The mixture was stirred for 50 min to obtain the mixed slurry. (4) Aging and stabilization: The mixed slurry was placed in a ventilated environment for 14 days and turned over every 5 days to obtain the aged slurry; (5) Drying and molding: The aged slurry is dried at 50°C to a moisture content of 8%, and then crushed through a 100-mesh sieve to obtain environmental remediation material.

[0049] The sources and performance parameters of each raw material are as follows: Phosphogypsum is an industrial byproduct of wet-process phosphoric acid production, specifically calcium sulfate dihydrate (CaSO4·2H2O), supplied by Yunnan Phosphate Group Co., Ltd. Its main phase is calcium sulfate dihydrate, accompanied by small amounts of Ca(H2PO4)2·H2O and CaSO4·0.5H2O. Its chemical composition is shown in Table 1.

[0050] Table 1 Chemical composition of phosphogypsum Phosphogypsum: It is derived from calcium sulfate dihydrate, a byproduct of wet-process phosphoric acid production at Yunnan Phosphate Group Jin Co., Ltd., with a purity of 92.6%, a pH value of 3.4, and contains 0.619% soluble phosphorus (calculated as P2O5) and 0.21% soluble fluorine.

[0051] Phosphate tailings: Taken from the beneficiation tailings of Yunnan Phosphate Group Co., Ltd., with SiO2 content of 9.13%, Al2O3 content of 1.16%, loss on ignition of 3.9%, and fineness (<0.075mm percentage) of 81%.

[0052] Alkaline modifier: Industrial quicklime powder produced by a chemical company in Hunan Province, with CaO content ≥92% and fineness 200 mesh.

[0053] Aluminum source material: Granulated blast furnace slag (Al2O3≥14%) recovered from a steel company in Henan Province, ball-milled to a specific surface area of ​​420 m² 2 / kg, Al2O3 equivalent (determined by alkali leaching method) 19.4%, particle size <0.15mm.

[0054] Dispersant: Sodium hexametaphosphate, analytical grade, produced by a chemical reagent company in Hebei Province.

[0055] pH adjuster: Sodium hydroxide, analytical grade, produced by a chemical reagent company in Hebei Province.

[0056] Examples 2-3 and Comparative Examples 1-8 Examples 2-3 and Comparative Examples 1-8 respectively provide an environmental remediation material based on phosphogypsum and phosphogypsum tailings synergistic modification by ettringite ion replacement and its preparation method. Compared with Example 1, the difference lies in the different proportions of phosphogypsum, phosphogypsum tailings, lime, shredded aluminum foil waste, sodium hexametaphosphate and sodium hydroxide in the material. The specific amounts are shown in Table 2. Other steps are roughly the same as in Example 1 and will not be repeated here.

[0057] Table 2 shows the component proportions of the materials in Examples 2-3 and Comparative Examples 1-8. The compressive strength of the repair materials in Examples 1-3 and Comparative Examples 1-8 was determined according to GB / T 50081-2019 for 28 days. The solidification rate and leaching concentration of harmful substances were determined according to HJ / T 557-2010 "Leaching Toxicity of Solid Waste - Horizontal Oscillation Method". The volume expansion rate was determined according to GB / T 2419-2005 for 56 days. Leaching tests were conducted according to HJ / T 557-2010 (leachate pH 4-10 simulated environment) and stability tests were conducted under simulated geological conditions (pH 4-10, 100-year accelerated aging). The test results are shown in Table 3.

[0058] Table 3. Performance test results of the repair materials in Examples 1-3 and Comparative Examples 1-8 As can be seen from the results in Table 3, the environmental remediation materials prepared in Examples 1-3 of this application have an ettringite content of 40-52%, and exhibit good resistance to Cr, Pb, As, and PO4. 2- F - The solidification rate of harmful substances was above 98.5%, the pH was stable at 7.5~8.0, the compressive strength reached 2.2~2.8 MPa at 28 days, the volume expansion rate was ≤0.05% at 56 days, the phosphorus concentration after accelerated leaching was <0.5mg / L at 180 days, and the heavy metal release rate was less than 0.8%. The performance was significantly better than that of comparative examples 1~8.

[0059] Comparative Examples 1 and 2 resulted in insufficient ettringite formation and decreased curing rate due to the proportion of phosphogypsum or phosphate tailings exceeding the scope of the claims. Comparative Examples 3, 5, and 7 resulted in excessive pH of the system due to excessive alkaline modifier or pH adjuster, leading to excessive ettringite formation, delayed expansion, and a significant decrease in strength. Comparative Examples 4 and 6 resulted in insufficient ettringite formation due to insufficient alkaline modifier or aluminum source, failing to effectively cure harmful ions. Comparative Example 8 did not add a dispersant, resulting in poor material dispersion, uneven reaction, and a significant reduction in overall performance. The above comparisons fully demonstrate the necessity and superiority of the limited proportion range specified in this application.

[0060] In summary, this application provides an environmental remediation material based on the synergistic modification of phosphogypsum and phosphogypsum tailings using ettringite ion replacement, and its preparation method. Its core innovation lies in the fact that, unlike existing technologies that rely solely on the conventional physical encapsulation and cementing effects of ettringite, this application is the first to propose and realize a "slow-release Si from phosphogypsum tailings" method. 4+ / Al 3+ Gradient regulation—SO4 in ettringite lattice 2- by PO4 2- The triple synergistic solidification mechanism of "controllable substitution—formation of doped ettringite-silicate composite phase" is as follows: (1) Utilizing the gradient slow-release characteristics of low-silica-alumina tailings of collophane (SiO2 content 5~15%, Al2O3 content 0.8~3.0%) under alkaline conditions of pH 8.0~9.0, a continuous supply of active Si is provided. 4+ Al 3+ It forms a dynamic equilibrium of Ca-Al-Si-SO4 with CaSO4 in phosphogypsum. 2- The system not only significantly improves the formation rate and crystallinity of ettringite, but also significantly suppresses the delayed expansion of traditional ettringite through the Si-O-Al secondary framework network (the 28-day strength is increased to over 2 MPa, and the expansion rate is <0.05%). (2) Under the action of the dispersant, the microenvironment of the system is uniform, and the slow-release of Al from the phosphorus tailings is achieved. 3+ Priority over PO4 2- F - The formation of a pre-complex followed by SO4 formation during ettringite nucleation.2- Lattice substitution (substitution rate 10~25%) produces Ca6Al2(SO4). 3-x (PO4)x(OH) 12 ·26H2O and Ca6Al2(SO4) 3-y F y (OH) 12 The doping of ettringite with 26H2O makes PO4 2- F - The solidification rate is over 99.5%, which is far higher than the current technology level of less than 95%, as it transforms from a soluble state to a lattice covalent state. (3) The total amount of phosphorus tailings and phosphogypsum accounts for more than 95%, and no additional cement is needed, thus achieving the true meaning of "using waste to treat waste, green and normal temperature, and synergistic efficiency".

[0061] The above mechanism enables the material to simultaneously possess three major breakthroughs: high strength (>2MPa), ultra-high curing rate (≥98.5%), and long-term stability (accelerated aging release rate <0.8% over 100 years), providing a brand-new technical path for the large-scale resource utilization of phosphate rock solid waste.

[0062] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. An environmental remediation material based on the synergistic modification of phosphogypsum and phosphogypsum tailings using ettringite ion replacement, characterized in that, It includes 40-60 parts of phosphogypsum, 20-30 parts of phosphorus tailings, 5-10 parts of alkaline modifier, 5-15 parts of aluminum source material, 0.1-0.5 parts of dispersant, and 0.5-2 parts of pH adjuster.

2. The environmental remediation material based on chelate ion exchange of phosphogypsum and phosphogypsum tailings synergistic modification according to claim 1, characterized in that, The phosphogypsum is calcium sulfate dihydrate, an industrial byproduct, with a purity of ≥85% and a pH value of 3~4.

3. The environmental remediation material based on the synergistic modification of phosphogypsum and phosphogypsum tailings using ettringite ion replacement according to claim 1, characterized in that, The phosphate tailings are typical phosphate mine tailings, with SiO2 content of 5-15% and Al2O3 content of 0.8-3.0%.

4. The environmental remediation material based on the synergistic modification of phosphogypsum and phosphogypsum tailings using ettringite ion replacement according to claim 1, characterized in that, The alkaline modifier is lime or quicklime powder.

5. The environmental remediation material based on the synergistic modification of phosphogypsum and phosphogypsum tailings using ettringite ion replacement according to claim 1, characterized in that, The aluminum source material is granulated blast furnace slag with an Al2O3 content of ≥14%.

6. The environmental remediation material based on the synergistic modification of phosphogypsum and phosphogypsum tailings using ettringite ion replacement according to claim 1, characterized in that, The dispersant is sodium hexametaphosphate or sodium dodecyl sulfate.

7. The environmental remediation material based on the synergistic modification of phosphogypsum and phosphogypsum tailings using ettringite ion replacement according to claim 1, characterized in that, The pH adjuster is sodium hydroxide or sodium carbonate.

8. A method for preparing an environmental remediation material based on the synergistic modification of phosphogypsum and phosphogypsum tailings using ettringite ion replacement, characterized in that, Includes the following steps: S1. Raw material pretreatment: Dry phosphogypsum and phosphogypsum tailings at 60℃ until the moisture content is <5%, grind them to a particle size of <2mm, stir them evenly, and obtain matrix mixture slurry; S2. Electret-induced formation and targeted solidification of harmful substances: Add an alkaline modifier and aluminum source material to the matrix mixture slurry, then add water at a solid-liquid ratio of 1:0.4, stir at 300 rpm for 1.5 h, then add a dispersant and pH adjuster to adjust the pH value to 8.0~9.0, and continue stirring for 30~60 min to obtain the mixture slurry; S3. Aging and Stabilization: The mixed slurry is placed in a ventilated environment for aging for 7-14 days, and turned over every 3-5 days to obtain the aged slurry; wherein the pH value is stabilized at 7.5-8.5 during the aging process; S4. Drying and molding: The aged slurry is dried at 50°C until the moisture content is <10%, and then pulverized through a 100-mesh sieve to obtain the environmental remediation material.

9. The method for preparing environmental remediation materials based on the synergistic modification of phosphogypsum and phosphogypsum tailings using ettringite ion replacement according to claim 8, characterized in that, The amount of the dispersant is 0.1 to 0.5 wt% of the mass of the mixed slurry.

10. The method for preparing environmental remediation materials based on the synergistic modification of phosphogypsum and phosphogypsum tailings using ettringite ion replacement according to claim 8, characterized in that, The amount of pH adjuster used is 0.5~2wt% of the mass of the mixed slurry.

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