Lightweight ceramic granules, method for their production and use

Abstract

The present application relates to the technical field of ceramsite preparation, in particular to a light ceramsite and a preparation method and application thereof.The technical scheme of the present application is as follows: the light ceramsite comprises, from inside to outside, a core layer, an intermediate layer and an outer shell layer; the preparation method comprises the following steps: the core layer: mixing lithium mica tailings, an organic pore-forming agent and a fluxing agent, grinding, wet mixing, granulating, drying, sintering, forming a porous matrix, cooling to room temperature, and obtaining the core layer; the intermediate layer: coating a mixture of an aluminosilicate mineral conversion agent, a hydrogen phosphate solidifying agent, a dispersing agent and water on the core layer, drying, and obtaining the intermediate layer; and the outer shell layer: coating a mixture of a low-melting fluxing agent, a dispersing agent and water on the intermediate layer, drying, sintering, cooling to room temperature, forming a dense glassy outer shell, and obtaining the outer shell layer.The main use of the present application is to realize efficient utilization of lithium mica tailings and long-term and stable solidification of heavy metals, and to provide a new option for preparation of light ceramsite.

Description

Technical Field

[0001] This invention belongs to the field of lithium slag resource utilization technology, specifically relating to a lightweight ceramsite, its preparation method, and its application. Background Technology

[0002] With the rapid development of industry, heavy metal pollution (such as Cd) has become increasingly prominent. 2+ Pb 2+ 、Tl + Heavy metals (such as sodium chloride, sodium thiosulfate ...

[0003] Meanwhile, the resource utilization of industrial solid waste is a key link in achieving a circular economy and sustainable development. Lithium mica tailings, a solid waste generated during the processing of lithium mica ore to extract valuable metals such as lithium, rubidium, and cesium, are produced in huge quantities. Its chemical composition is rich in SiO2 and Al2O3, and also contains significant amounts of Na2O, K2O, TiO2, and CaO, as well as small amounts of SO3, Fe2O3, and MgO. However, according to GB 5086.1-1997 "Solid Waste Leaching Toxicity Leaching Method - Turnover Method," toxicity leaching of the raw tailings revealed that the levels of thallium, cadmium, and lead in the tailings exceeded the limits specified in the Technical Specification for the Use of Lithium Slag in Highway Subgrade Engineering (DB36 / T 1968-2024), posing a significant environmental hazard. Long-term stockpiling or improper disposal not only occupies substantial land resources but also causes significant environmental damage, resulting in secondary pollution through leaching and other methods. Currently, there are still significant limitations in the high-value utilization technology of lepidolite tailings, making it difficult to achieve efficient and environmentally friendly resource-based disposal.

[0004] Existing technologies for solidifying heavy metals mostly focus on simple physical encapsulation or chemical fixation, which suffers from insufficient solidification stability and poor long-term effectiveness. Furthermore, the utilization of lepidolite tailings is largely limited to low-value applications and fails to effectively integrate with heavy metal pollution control. Therefore, developing a technology that enables high-value utilization of lepidolite tailings while simultaneously achieving long-term, stable solidification of toxic heavy metals has become a pressing technical problem in this field.

[0005] In the field of ceramsite production, traditional processes primarily use natural minerals such as clay and shale as raw materials. However, with the over-exploitation of these resources, the industry faces the problem of increasingly depleted natural resources. Furthermore, the extraction process damages the ecological environment, including surface vegetation and soil structure, contradicting the concept of sustainable development. Therefore, how to effectively utilize industrial waste such as silicon-aluminum based slag to prepare ceramsite, achieving resource recycling of waste and reducing dependence on natural resources, has become an urgent technical problem to be solved in this field.

[0006] In summary, developing a technology that enables high-value utilization of lepidolite tailings, long-term and stable solidification of toxic heavy metals, and provides new raw materials for ceramsite production has become an urgent technical problem to be solved in this field. Summary of the Invention

[0007] In view of the problems existing in the prior art, the purpose of this invention is to provide a lightweight ceramsite, its preparation method and application, so as to solve the problem of disposal of lepidolite tailings, as well as the problems of unstable and short-lasting solidification of toxic heavy metals, and the problem of over-reliance on natural resources in the preparation of lightweight ceramsite.

[0008] The technical solution of the present invention is as follows:

[0009] This invention provides a lightweight ceramic aggregate, which comprises, from the inside out, a core layer, an intermediate layer, and an outer shell layer.

[0010] The raw materials for the core layer include lithium mica tailings, organic pore-forming agents, and fluxing agents;

[0011] The raw materials for the intermediate layer include aluminosilicate mineral conversion agent, hydrogen phosphate curing agent, and dispersant;

[0012] The raw materials for the outer shell layer include low-melting-point flux and dispersant.

[0013] Through a multi-layered structural design, this method achieves efficient utilization of lepidolite tailings and long-term, stable solidification of heavy metals; it realizes the resource-based reuse of waste, reducing dependence on natural resources; and it provides a new option for the preparation of lightweight ceramsite. The three-layer structure design achieves the fixation and encapsulation of heavy metals. The core layer forms a porous silica-alumina framework through organic pore-forming agents and alkaline earth metal oxides; the middle layer fixes heavy metals through mineral transformation and phosphate solidification agents; and the outer shell forms a dense shell through vitrification, further improving the material's environmental stability. This method solves the problem of lepidolite tailings disposal, achieves high-value utilization of lepidolite tailings, provides a new approach to heavy metal pollution control, solves the problems of unstable and short-lasting solidification of toxic heavy metals, and addresses the issue of excessive reliance on natural resources in the preparation of lightweight ceramsite.

[0014] Furthermore, in the raw materials of lightweight ceramsite, the mass percentage of the lepidolite tailings is 70-75%, the mass percentage of the organic pore-forming agent is 5-8%, the mass percentage of the flux is 3-5%, the mass percentage of the aluminosilicate mineral conversion agent is 10-15%, the mass percentage of the hydrogen phosphate curing agent is 2-3%, the mass percentage of the dispersant in the intermediate layer is 0.5-0.8%, the mass percentage of the dispersant in the outer shell layer is 0.5-0.8%, and the mass percentage of the low-melting-point flux is 4-5%.

[0015] Furthermore, the chemical composition of the lepidolite tailings, by mass percentage, includes: 46.42% SiO2, 22.75% Al2O3, 0.61% Fe2O3, 2.14% CaO, 0.25% MgO, 0.07% SO3, 9.52% Na2O, 4.02% K2O, 3.39% TiO2, and 10.71% other impurities; the loss on ignition of the lepidolite tailings is 0.12%.

[0016] And / or, the organic pore-forming agent is a starch-based material, the starch-based material is corn starch and sugarcane bagasse, and the mass ratio of corn starch to sugarcane bagasse is 0~1:0~1;

[0017] And / or, the flux is an alkaline earth metal oxide, wherein the alkaline earth metal oxide is CaO or MgO;

[0018] And / or, the aluminosilicate mineral conversion agent is modified metakaolin, wherein the modified metakaolin comprises 53% SiO2, 45% Al2O3 and 1.5% impurities, and the loss on ignition of the modified metakaolin is 0.5%;

[0019] And / or, the hydrogen phosphate curing agent is potassium dihydrogen phosphate or sodium dihydrogen phosphate;

[0020] And / or, the dispersant of the intermediate layer is sodium polyacrylate;

[0021] And / or, the dispersant of the outer shell layer is water glass;

[0022] And / or, the low-melting-point flux is a borax-feldspar-alkaline earth metal oxide composite system, wherein the components of the borax-feldspar-alkaline earth metal oxide composite system are borax, feldspar and alkaline earth metal oxide, the mass ratio of borax, feldspar and alkaline earth metal oxide is 7~9:1~2:1~2, and the alkaline earth metal oxide is one or two of MgO and CaO.

[0023] Furthermore, the modified metakaolin is a product obtained by adding 9% acid modifier to natural kaolin and then thermally activating it at 800°C.

[0024] Furthermore, the acid modifier is a mixture of hydrochloric acid and nitric acid.

[0025] The mass percentages of each raw material show that using lithium mica tailings as the main raw material not only realizes the resource utilization of solid waste, but also regulates the lightweight properties through organic pore-forming agents. Various additives work synergistically, with fluxes and low-melting-point fluxes promoting sintering and densification, aluminosilicate mineral conversion agents optimizing the structure, hydrogen phosphate curing agents stabilizing heavy metals, and the appropriate proportions of dispersants in different layers ensuring a uniform layered structure. This approach balances the lightweight, structural stability, and environmental safety of the ceramsite, achieving both economic and environmental benefits.

[0026] This invention also provides a method for preparing lightweight ceramsite, characterized by comprising the following steps:

[0027] S1. Preparation of the core layer: Lithium mica tailings, organic pore-forming agent and flux are mixed, ground, wet-mixed, granulated, dried and sintered to form a porous matrix. The core layer is then cooled to room temperature.

[0028] S2. Preparation of the intermediate layer: A mixture of aluminosilicate mineral conversion agent, hydrogen phosphate curing agent, dispersant and water is coated on the outside of the core layer and dried to obtain the intermediate layer;

[0029] S3. Preparation of the outer shell layer: A mixture of low-melting-point flux, dispersant and water is coated on the outside of the intermediate layer, dried, sintered and cooled to room temperature to form a dense glassy shell, thus obtaining the outer shell layer.

[0030] Furthermore, after the sintering described in step S3 is completed, the intermediate layer described in step S2 will form an aluminosilicate network structure.

[0031] Using lepidolite tailings as the main material, organic pore-forming agents and fluxes are added. Dry ball milling is used to refine the material to <150µm (approximately 100 mesh) to ensure the uniformity and efficiency of subsequent reactions. The ball-milled material is then wet-mixed to a plastic state, granulated, dried at low temperature, and preheated to decompose the pore-forming agent, forming a porous structure. After cooling to room temperature, modified metakaolin and phosphate curing agent are ball-milled with water to form a suspension slurry. This slurry is then impregnated onto the porous core surface, forming an interlocking structure through capillary action. After low-temperature drying, it is cooled to room temperature. A borax-feldspar-alkaline earth metal oxide mixed powder is used to prepare the outer shell layer powder. The impregnated intermediate layer material is conveyed via a conveyor belt and coated with the outer shell layer slurry using an automatic glazing machine. The coated green body is then dried at low temperature and sintered at high temperature, followed by cooling to room temperature. The final product is a three-layer ceramic aggregate with physical sealing and chemical bonding. The core pores are solidified with heavy metals, the intermediate layer enhances stability, and the glass shell provides an inert barrier to ensure long-term safety.

[0032] Further, in step S1, the grinding time is 60-90 minutes; the wet mixing includes adding water, which accounts for 18-22% of the core layer raw material by mass percentage, and the wet mixing time is 15 minutes; the drying temperature is 100-150°C, and the drying time is 10-12 hours; the sintering includes: heating to the preheating temperature, preheating and holding, the heating rate is 2-5°C / min, the preheating temperature is 400°C, and the holding time is 30-40 minutes; the cooling rate is 3-5°C / min.

[0033] And / or, in step S2, the drying temperature is 100~150℃ and the drying time is 8~10h.

[0034] And / or, in step S3, the drying temperature is 100~150℃, and the drying time is 8~10h; the sintering includes: heating to the conversion end-sealing temperature, conversion end-sealing and holding at the temperature, the heating rate is 5~10℃ / min, the conversion end-sealing temperature is 1100~1200℃, and the holding time is 40~50min; the cooling rate is 2~3℃ / min, and the thickness of the dense glassy shell is 1~2mm.

[0035] The carbonization and pore-forming process is completed through sintering (heat treatment) in step S1. Then, the surface vitrification is carried out in step S3, which enables the lightweight ceramic particles to have a porous effect.

[0036] Furthermore, in step S1, a disc granulator is used for granulation. The tilt angle of the disc granulator is adjusted to 45~55° and the rotation speed is 15~25 r / min. By adjusting the tilt angle and rotation speed, the particle size of the core preform is controlled to be between 5~8 mm.

[0037] And / or, in step S2, the mixture is prepared by mixing aluminosilicate mineral conversion agent, hydrogen phosphate curing agent, dispersant and water, and grinding them into a suspension slurry;

[0038] And / or, in step S3, the mixture is prepared by mixing a low-melting-point flux, a dispersant and water, and grinding them into a slurry.

[0039] Furthermore, in step S2, the grinding is ball milling, the ball milling concentration is 66%~80%, and the ball milling time is 30~40 min;

[0040] And / or, in step S3, the grinding is ball milling, the ball milling concentration is 66%~80%, and the ball milling time is 20~30 min.

[0041] Furthermore, in step S2, the coating is performed using an impregnation coating method, and the coating thickness is 1 to 1.5 mm;

[0042] And / or, in step S3, the coating is carried out by spraying, the spraying is carried out by an automatic glazing machine, the spraying pressure of the automatic glazing machine is 0.4 to 0.8 MPa, the moving speed of the spray gun is 400 to 600 mm / min, the rotation speed of the intermediate layer is 200 to 300 rpm, the number of glazing sprays is 2 to 3, and the thickness of each glaze spray is 0.5 to 0.7 mm.

[0043] In the preparation of lightweight ceramsite, refining each step offers several significant advantages: It enables efficient utilization of solid waste and component stability through precise control of raw material ratios (such as the proportion of lepidolite tailings and the dosage of various additives); it also allows for the finer control of granulation parameters (tilt angle, rotation speed) to regulate the uniformity of the core green body particle size, ensuring consistent sintering. The layered process and synergistic effect of additives in the sintering stage (such as the proportion of different layers of dispersants and fluxes) precisely optimize the porous structure inside the ceramsite and the density of the outer shell, balancing lightweight properties with mechanical strength. Furthermore, the refined step-by-step action of functional components such as hydrogen phosphate curing agents enhances the fixation effect of heavy metals, improving environmental safety. This overall refinement of the process creates synergistic advantages for ceramsite in terms of raw material utilization, product performance (lightweight, strength, stability), and environmental friendliness, ensuring the stability of mass production and controllable product quality, thus achieving both economic and ecological benefits.

[0044] Furthermore, the bulk density of the lightweight ceramsite is 480~511 kg / m³. 3 The cylinder compressive strength is >9MPa.

[0045] The present invention also provides the application of the above-mentioned lightweight expanded clay aggregate in construction.

[0046] Furthermore, the applications of the lightweight expanded clay aggregate in construction include: use as thermal insulation materials, as lightweight aggregate, as a floor subbase, as floor backfill, and in the production of lightweight partition boards.

[0047] The beneficial effects of this invention are as follows: This invention provides a lightweight ceramsite, its preparation method, and its applications. Through a multi-layered structural design, it achieves efficient utilization of lepidolite tailings and long-term, stable solidification of heavy metals; it realizes the resource-based reuse of waste, reducing dependence on natural resources; and it provides a new option for the preparation of lightweight ceramsite. The three-layered structural design achieves the fixation and sealing of heavy metals. The core layer forms a porous silica-alumina framework through organic pore-forming agents and alkaline earth metal oxides; the middle layer achieves heavy metal fixation through mineral transformation and phosphate solidification agents; and the outer shell forms a dense shell through vitrification, further improving the environmental stability of the material. This method solves the problem of lepidolite tailings disposal, realizes high-value utilization of lepidolite tailings, provides a new approach to heavy metal pollution control, solves the problems of unstable and short-lasting solidification of toxic heavy metals, and addresses the issue of excessive reliance on natural resources in the preparation of lightweight ceramsite.

[0048] Using lepidolite tailings as the main material, organic pore-forming agents and fluxes are added. Dry ball milling is used to refine the material to <150µm (approximately 100 mesh) to ensure the uniformity and efficiency of subsequent reactions. The ball-milled material is then wet-mixed to a plastic state, granulated, dried at low temperature, and preheated to decompose the pore-forming agent, forming a porous structure. After cooling to room temperature, modified metakaolin and phosphate curing agent are ball-milled with water to form a suspension slurry. This slurry is then impregnated onto the porous core surface, forming an interlocking structure through capillary action. After low-temperature drying, it is cooled to room temperature. A borax-feldspar-alkaline earth metal oxide mixed powder is used to prepare the outer shell layer powder. The impregnated intermediate layer material is conveyed via a conveyor belt and coated with the outer shell layer slurry using an automatic glazing machine. The coated green body is then dried at low temperature and sintered at high temperature, followed by cooling to room temperature. The final product is a three-layer ceramic aggregate with physical sealing and chemical bonding. The core pores are solidified with heavy metals, the intermediate layer enhances stability, and the glass shell provides an inert barrier to ensure long-term safety.

[0049] The core of this invention lies in using a strategy combining "physical enclosure" and "chemical fixation" to stably encapsulate heavy metals within a ceramic aggregate matrix, providing a highly promising technical solution for the high-value utilization of lepidolite tailings and the remediation of heavy metal pollution. This solution is based on the mineral phase gradient transformation theory and designs a three-layer structure ceramic aggregate preparation process for lepidolite lithium extraction tailings. The core idea of ​​this technical solution is to construct a multi-layered protection system with functional gradients. Each layer has a unique function, and through synergistic effects, ultimately achieves a "double-insurance" fixation of heavy metals. Attached Figure Description

[0050] Figure 1 This is a SEM image of the product's internal structure.

[0051] Figure 2The image shows the XRD diffraction pattern of the lightweight ceramsite product. The horizontal axis represents the diffraction angle (2θ), and the vertical axis represents the diffraction intensity.

[0052] Figure 3 SEM image of the product particles of the three-layer ceramsite (III);

[0053] Figure 4 SEM image of the product particles of two-layer ceramsite (I);

[0054] Figure 5 SEM image of the product particles of the two-layer ceramic aggregate (II);

[0055] Figure 6 SEM image of the product particles of traditional lithium mica tailings lightweight ceramic particles. Detailed Implementation

[0056] The present invention will be further described in detail below through embodiments, but in no way is the invention limited.

[0057] The main chemical composition of the lepidolite tailings used in the following embodiments and comparative examples of the present invention, by mass percentage, includes: 46.42% SiO2, 22.75% Al2O3, 0.61% Fe2O3, 2.14% CaO, 0.25% MgO, 0.07% SO3, 9.52% Na2O, 4.02% K2O, 3.39% TiO2, and 10.71% other impurities. The loss on ignition rate of the lepidolite tailings is 0.12%.

[0058] The modified metakaolin used in the following embodiments and comparative examples of the present invention comprises, by mass percentage: 53% SiO2, 45% Al2O3, and 1.5% impurities, with a loss on ignition rate of 0.5%. The 1.5% impurities include: Fe2O3, K2O, Na2O, TiO2, CaO, MgO, MnO2, and P2O5. The content of each impurity is generally low, and the total content of all impurities is 1.5%. The modified metakaolin is a product obtained by thermally activating natural kaolin with 9% acid modifier at 800°C. The acid modifier is a mixture of hydrochloric acid and nitric acid.

[0059] The technical mechanism of the present invention is as follows:

[0060] (1) Core layer: Construction of porous silicon-aluminum framework

[0061] The core layer is the main body and skeleton of the entire solidified structure, and its design goal is to provide sufficient structural strength and containment space.

[0062] Main framework material: Lepidolite tailings (70-75 wt%). Lepidolite tailings are an ideal matrix material, with high SiO2 and Al2O3 content as their main chemical components. These components form the basis for the formation of stable silicate and aluminosilicate network structures. Lithium extraction tailings from lepidolite are typically rich in quartz and feldspar, which provide the necessary framework structure for high-temperature sintering. Furthermore, the lithium slag itself has a porous structure and is easy to grind; its specific surface area increases with grinding time, which is beneficial for the uniformity of subsequent material mixing and improved reactivity. Using it as the main raw material not only achieves large-scale disposal of industrial solid waste but also significantly reduces raw material costs.

[0063] Organic pore-forming agent: Starch-based materials (5-8 wt%) are used as the organic pore-forming agent. These materials include readily available and inexpensive biomass materials such as corn starch or sugarcane bagasse. Specifically, this invention uses corn starch or sugarcane bagasse as the organic pore-forming agent. Its key function is that at a relatively low preheating temperature (approximately 400°C), these organic macromolecules undergo thermal decomposition, generating gases such as CO2 and H2O that escape. This gas escape forms a large number of uniformly distributed micron-sized pores within the ceramsite body. These pores not only provide channels and sites for the subsequent penetration and reaction of the intermediate layer solidifying agent but also provide space for the carrying capacity of heavy metal wastewater.

[0064] Low-temperature flux: Alkaline earth metal oxides (CaO / MgO, 3~5wt%) are introduced as fluxes during the sintering of ceramic aggregates. Their main purpose is to promote the formation of a liquid phase at lower temperatures (e.g., below 1000℃). The presence of the liquid phase can significantly accelerate material migration and diffusion, thereby reducing the overall sintering densification temperature and saving energy. Note: Although alkaline earth metal oxides have relatively high melting points, they may exhibit lower melting points or fluidity under specific conditions (such as high temperatures or eutectic melting with other substances).

[0065] (2) Intermediate layer: chemical transformation and stabilization of heavy metals

[0066] The intermediate layer is the core functional layer for achieving the chemical fixation of heavy metals. Its design goal is to transform the heavy metal ions that have migrated here into a thermodynamically stable crystal structure through chemical reactions.

[0067] Aluminosilicate mineral conversion agent (10~15 wt%): Modified metakaolin is a product obtained by adding 9% acid modifier to natural kaolin and then thermally activating it at 800℃. It has highly amorphous and highly active SiO2 and Al2O3. At a sintering temperature of 1100~1200℃, these highly active components undergo a dissolution-recrystallization process, interdiffusion and reaction with the silicon-aluminum framework of the core layer, forming a denser and more stable [AlO4]-[SiO4] tetrahedral network structure, thereby enhancing the mechanical strength and chemical stability of the entire solidified body. Note: During the preparation process, the intermediate layer is only impregnated and coated, and is not sintered separately. Instead, it is sintered together with the outer shell layer for 40~50 minutes after preparation. After sintering, the intermediate layer will form an aluminosilicate network structure.

[0068] Hydrogen phosphate curing agent: Hydrogen phosphate (Magnesium Potassium Phosphate, 2-3 wt%) is the key active component of the intermediate layer. The hydrogen phosphate curing agent is a hydrogen phosphate such as potassium dihydrogen phosphate or sodium dihydrogen phosphate. Preferred potassium dihydrogen phosphate (KH₂PO₄) reacts with magnesium or calcium salts in the system to ultimately form a calcium phosphate or magnesium phosphate structure. Calcium phosphate or magnesium phosphate crystals have highly reactive surfaces, and their structure possesses excellent ion exchange capacity, enabling efficient capture and fixation of heavy metal ions. The curing mechanism is mainly an ion substitution reaction; for example, Ca in the crystal lattice... 2+ It can be replaced by heavy metal ions with similar radius or charge (such as Cd). 2+ Pb 2+ 、Tl + Substitution. The reaction mechanism is shown in equations (I), (II), and (III):

[0069] 3Ca 2+ +2KH2PO4→Ca3(PO4)2+2K + +4H + (I)

[0070] Ca3(PO4)2+(Cd 2+ Pb 2+ )→Ca2(Cd,Pb)(PO4)2+Ca 2+ (II)

[0071] Ca3(PO4)2+4Tl + →CaTl4(PO4)2 +2Ca 2+ (III)

[0072] The heavy metal-containing calcium phosphate or magnesium phosphate salts generated by the reaction are highly stable mineral phases with extremely low solubility in the natural environment, thus achieving chemical locking of heavy metals and preventing their migration and diffusion in the environment.

[0073] (3) Outer shell: a dense, glassy physical enclosure

[0074] The outer shell is the last physical barrier, and its goal is to form a completely dense, non-porous glassy shell that completely seals in any unreacted or potentially leached heavy metals that may be present inside.

[0075] Low-melting-point flux (4-5 wt%): The borax-feldspar-alkaline earth metal oxide composite system is a composite flux composed of borax (Na2B4O7), feldspar (KAlSi3O8), and alkaline earth metal oxides (MgO, CaO, etc.). This composite flux is used as a low-melting-point flux for the outer shell layer. Borax has a low melting point (approximately 800-1150℃), which can significantly reduce the melting temperature of silicate systems. Alkaline earth metal oxides can disrupt the Si-O tetrahedral bond structure, reducing the system viscosity and generating a liquid phase, which also helps to lower the sintering temperature of the glass. Feldspar provides the alkali metals and aluminum required for the glass network at high temperatures (1100-1200℃) and promotes the formation of the glass phase. The role of alkaline earth metal oxides in low-melting-point fluxes is mainly reflected in their fluxing properties, including lowering the melting point, promoting liquid phase formation, improving sintering efficiency, and improving material properties. By precisely adjusting the proportion of flux, molten glass with appropriate viscosity can be formed within a relatively low temperature range of 1100~1200℃. This molten glass can uniformly cover the surface of the solidified body and form a relatively dense glassy outer shell after cooling, effectively isolating the solidified body from the exchange of substances with the external environment.

[0076] This technology employs a smart sintering furnace programmed temperature rise sintering process: first, organic matter is released at 400℃, then the intermediate mineral phase transformation is achieved at 1100℃~1200℃, and the outer shell is formed by sintering. See Table 1 for details.

[0077] Table 1. Sintering process and parameters of intelligent sintering furnace with programmed heating.

[0078]

[0079] Example 1

[0080] A method for preparing lightweight ceramsite:

[0081] Using lepidolite tailings as the main material, organic pore-forming agents and fluxes are added. The mixture is dry-ball-milled to a fineness of <150µm (approximately 100 mesh) to ensure the uniformity and efficiency of subsequent reactions. The ball-milled material is then wet-mixed in a mixer until it reaches a plastic state. It is then granulated using a disc granulator, dried at low temperature, and preheated to decompose the pore-forming agent, forming a porous structure. After cooling to room temperature, modified metakaolin and phosphate curing agent are ball-milled with water to form a suspension slurry. This slurry is then impregnated onto the porous core surface, forming an interlocking structure through capillary action. After low-temperature drying, it is cooled to room temperature. A borax-feldspar-alkaline earth metal oxide mixed powder is used to prepare the outer shell layer powder. The impregnated intermediate layer material is conveyed via a conveyor belt and coated with the outer shell layer slurry using an automatic glazing machine. The coated green body is then dried at low temperature and sintered at high temperature, followed by cooling to room temperature. The final product is a three-layer ceramic aggregate with physical sealing and chemical bonding. The core pores are solidified with heavy metals, the intermediate layer enhances stability, and the glass shell provides an inert barrier to ensure long-term safety.

[0082] (1) Preparation and preprocessing of the kernel layer

[0083] Raw material mixing and ball milling:

[0084] Weigh precisely according to the following proportions: 70-75 wt% lepidolite tailings, 5-8 wt% organic pore-forming agent (corn starch / bagasse powder), and 3-5 wt% flux (CaO / MgO powder).

[0085] Grind all powdered raw materials (lithium mica tailings, organic pore-forming agent, flux) for 60-90 minutes using a dry ball mill to ensure the uniformity and efficiency of the subsequent reaction.

[0086] Granulation and molding:

[0087] Add the ball-milled material to a mixer, and slowly spray in 18-22 wt% water (this 18-22 wt% water percentage is based on all raw materials in the core layer). Wet mix for 15 minutes to ensure the material is uniformly mixed and in a plastic state. Then, granulate the material using a disc granulator at an inclination angle of 45-55° and a rotation speed of 15-25 r / min. By adjusting the inclination angle and rotation speed, control the particle size of the raw material balls (core blanks) to be between 5-8 mm. Dry at a low temperature of 100-150℃ for 10-12 hours to remove moisture.

[0088] Low-temperature preheating (hole creation):

[0089] The dried core blank is placed in a sintering furnace for sintering. It is heated to 400°C at a slow heating rate (2~5°C / min) and held at that temperature for 30~40 min. It is then cooled to room temperature at a cooling rate (3~5°C / min) to obtain the core layer.

[0090] (2) Application and transformation of intermediate layers

[0091] Slurry preparation:

[0092] 10–15 wt% modified metakaolin, 2–3 wt% hydrogen phosphate curing agent (such as KH₂PO₃ / NaH₂PO₃), 0.5–0.8 wt% dispersant (such as sodium polyacrylate), and water are mixed and ball-milled to prepare a suspension slurry with suitable viscosity and stability. The ball-milling concentration is 66%–80%, and the ball-milling time is 30–40 min.

[0093] The pre-fired, porous core layer is immersed in the intermediate layer slurry using an impregnation coating method. After coating, it is dried at a low temperature of 100~150℃ for 8~10 hours to remove moisture, thus obtaining the intermediate layer.

[0094] (3) Application and vitrification of the outer shell layer

[0095] Powder preparation:

[0096] Borax-feldspar-alkaline earth metal oxide is a composite flux composed of borax, feldspar, and alkaline earth metal oxide in an optimized mass ratio of 7~9:1~2:1~2; the alkaline earth metal oxide is one or both of MgO and CaO.

[0097] 4-5 wt% of borax-feldspar-alkaline earth metal oxide powder, 0.5-0.8 wt% of dispersant (such as water glass), and water are mixed and ball-milled to prepare a slurry with suitable viscosity and stability. The ball milling concentration is 66%-80%, and the ball milling time is 20-30 minutes to ensure uniform mixing of the materials, thus producing the outer shell layer slurry.

[0098] Coating method and sintering temperature control:

[0099] The dried intermediate layer is conveyed via a conveyor belt and then coated with an outer shell layer slurry using an automatic glazing machine. The glazing pressure is 0.4~0.8MPa, the spray gun moving speed is 400~600mm / min, the intermediate layer rotation speed is 200~300 rpm, the number of glazing passes is 2~3, and the thickness of each glaze pass is 0.5~0.7mm.

[0100] The coated preform is dried at a low temperature of 100~150℃ for 8~10 hours to remove moisture. It is then placed in a sintering furnace for sintering, heated to 1100℃~1200℃ at a slow heating rate (5℃~10℃ / min) and held at that temperature for 40~50 minutes. After cooling to room temperature, a dense vitreous outer shell is formed, resulting in the outer shell layer. A programmed slow cooling rate (2℃~3℃ / min) is used to release thermal stress and prevent cracking of the finished product due to mismatches in the coefficients of thermal expansion (TCE) of the layers.

[0101] Lightweight ceramic particles were finally prepared through the preparation and pretreatment of the core layer, the application and transformation of the intermediate layer, and the application and vitrification of the outer shell layer.

[0102] Example 2

[0103] Preparation of three-layer ceramsite:

[0104] S1. Using 70 wt% lepidolite tailings as the main material, add 7 wt% organic pore-forming agent corn starch and 5 wt% fluxing agent CaO powder, and dry ball mill for 60 min. Add the ball-milled material to a mixer, spray with 18% water and wet mix for 15 min, then granulate using a disc granulator at an inclination angle of 45° and a rotation speed of 15 r / min, controlling the particle size of the core blank to 5 mm. After drying at 100℃ for 10 h, place the dried core blank in a sintering furnace, heat to 400℃ at a heating rate of 3℃ / min, hold for 30 min, and cool to room temperature at a cooling rate of 3℃ / min to obtain the core layer;

[0105] S2. 11 wt% modified metakaolin, 2 wt% phosphate curing agent KH2PO3, and 0.5 wt% dispersant sodium polyacrylate were ball-milled with water for 30 min to a grinding concentration of 66%, forming a suspension slurry. This slurry was then applied to the porous core surface of the core layer using an impregnation coating method, forming an interlocking structure through capillary action. After coating, the intermediate layer preform was dried at 100℃ for 8 hours to obtain the intermediate layer.

[0106] S3. Mix 4 wt% borax-feldspar-CaO powder, 0.5 wt% water glass dispersant, and water, and ball mill to prepare a slurry with suitable viscosity and stability. The ball milling concentration is 66%, and the milling time is 20 minutes to ensure uniform mixing of the materials, thus forming the outer shell layer slurry. The 4 wt% borax-feldspar-CaO powder is a composite flux composed of borax, feldspar, and CaO in an optimized mass ratio of 7:1:2.

[0107] S4. The dried intermediate layer is conveyed via a conveyor belt and coated with the outer shell layer slurry using an automatic glazing machine. The glazing pressure is 0.4 MPa, the spray gun moving speed is 400 mm / min, the intermediate layer rotation speed is 200 rpm, the number of glazing passes is 2, and the thickness of each glaze pass is 0.5 mm.

[0108] The coated blank is dried at 100℃ for 8 hours. The blank is then heated to 1100℃ at a heating rate of 5℃ and sintered at a high temperature for 30 minutes. It is then cooled to room temperature at a rate of 2℃ / min to form a dense glassy outer shell, thus obtaining the outer shell layer.

[0109] Through the preparation of steps S1, S2, S3 and S4, the final product is a physically sealed and chemically bonded three-layer ceramic aggregate, named three-layer ceramic aggregate (I).

[0110] Example 3

[0111] Preparation of three-layer ceramsite:

[0112] S1. Using 70 wt% lepidolite tailings as the main material, add 6.5 wt% organic pore-forming agent bagasse and 4.5 wt% fluxing agent MgO powder, and dry ball mill for 80 min. Add the ball-milled material to a mixer, spray with 20% water and wet mix for 15 min, then granulate using a disc granulator at an inclination angle of 50° and a rotation speed of 20 r / min, controlling the particle size of the core blank to 6 mm. After drying at 120℃ for 11 h, place the dried core blank in a sintering furnace, heat to 400℃ at a heating rate of 4℃ / min, hold for 35 min, and cool to room temperature at a cooling rate of 4℃ / min to obtain the core layer;

[0113] S2. 11 wt% modified metakaolin, 2.5 wt% phosphate curing agent NaH2PO3, and 0.5 wt% dispersant sodium polyacrylate were ball-milled with water for 35 min to a grinding concentration of 70%, forming a suspension slurry. This slurry was then applied to the porous core surface of the core layer using an impregnation coating method, forming an interlocking structure through capillary action. After coating, the intermediate layer preform was dried at 120℃ for 9 h to obtain the intermediate layer.

[0114] S3. Mix 4.5 wt% borax-feldspar-CaO powder, 0.5 wt% water glass dispersant, and water, and ball mill to prepare a slurry with suitable viscosity and stability. The ball milling concentration is 70%, and the milling time is 25 minutes to ensure uniform mixing of the materials, thus forming the outer shell layer slurry. The 4.5 wt% borax-feldspar-CaO powder is a composite flux composed of borax, feldspar, and CaO in an optimized mass ratio of 7:2:1.

[0115] S4. The dried intermediate layer is conveyed via a conveyor belt and coated with the outer shell layer slurry using an automatic glazing machine. The glazing pressure is 0.6 MPa, the spray gun moving speed is 500 mm / min, the intermediate layer rotation speed is 350 rpm, the number of glazing passes is 2, and the thickness of each glaze is 0.6 mm.

[0116] The coated blank is dried at 120℃ for 9 hours. The blank is then heated to 1150℃ at a heating rate of 8℃ and sintered at that temperature for 35 minutes. It is then cooled to room temperature at 3℃ / min to form a dense glassy outer shell, thus obtaining the outer shell layer.

[0117] Through the preparation of steps S1, S2, S3 and S4, the final product is a physically sealed and chemically bonded three-layer ceramic aggregate, named three-layer ceramic aggregate (II).

[0118] Example 4

[0119] Preparation of three-layer ceramsite:

[0120] S1. Using 74wt% lepidolite tailings as the main material, add 5wt% organic pore-forming agent and 3wt% flux powder, and dry ball mill for 90 min. Add the ball-milled material to a mixer, spray with 20% water and wet mix for 15 min, then granulate using a disc granulator at an inclination angle of 55° and a rotation speed of 25 r / min, controlling the particle size of the core blank to 6 mm. After drying at 120℃ for 12 h, place the dried core blank in a sintering furnace, heat to 400℃ at a heating rate of 5℃ / min, hold for 40 min, and cool to room temperature at a cooling rate of 5℃ / min to obtain the core layer; wherein, the 5wt% organic pore-forming agent is prepared from corn starch and bagasse in a 1:1 mass ratio, and the 3wt% flux powder is prepared from CaO and MgO in a 1:1 mass ratio.

[0121] S2. 10 wt% modified metakaolin, 2 wt% phosphate curing agent NaH2PO3, and 0.5 wt% dispersant sodium polyacrylate were ball-milled with water for 40 min to a grinding concentration of 80%, forming a suspension slurry. This slurry was then applied to the porous core surface of the core layer using an impregnation coating method, forming an interlocking structure through capillary action. After coating, the intermediate layer preform was dried at 120℃ for 10 h to obtain the intermediate layer.

[0122] S3. Mix 5 wt% borax-feldspar-CaO powder, 0.5 wt% water glass dispersant, and water, and ball mill to prepare a slurry with suitable viscosity and stability. The ball milling concentration is 80%, and the milling time is 30 minutes to ensure uniform mixing of the materials, thus forming the outer shell layer slurry. The 5 wt% borax-feldspar-CaO powder is a composite flux composed of borax, feldspar, and CaO in an optimized mass ratio of 8:1:1.

[0123] S4. The dried intermediate layer is conveyed via a conveyor belt and coated with the outer shell layer slurry using an automatic glazing machine. The glazing pressure is 0.7 MPa, the spray gun moving speed is 550 mm / min, the intermediate layer rotation speed is 300 rpm, the number of glazing passes is 3, and the thickness of each glaze pass is 0.7 mm.

[0124] The coated blank is dried at 130℃ for 10 hours. The blank is then heated to 1200℃ at a heating rate of 10℃ and sintered at that temperature for 20 minutes. It is then cooled to room temperature at a rate of 3℃ / min to form a dense glassy outer shell, thus obtaining the outer shell layer.

[0125] Through the preparation of steps S1, S2, S3 and S4, the final product is a three-layer ceramic aggregate that is physically sealed and chemically bonded, named three-layer ceramic aggregate (III).

[0126] Comparative Example 1

[0127] Preparation of two layers of ceramsite:

[0128] S1. Using 80wt% lepidolite tailings as the main material, add 7wt% organic pore-forming agent and 3wt% flux powder, and dry ball mill for 90 min. Add the ball-milled material to a mixer, spray with 20% water and wet mix for 15 min, then granulate using a disc granulator at an inclination angle of 55° and a rotation speed of 25 r / min, controlling the particle size of the core blank to 8 mm. After drying at 120℃ for 12 h, place the dried core blank in a sintering furnace, heat to 400℃ at a heating rate of 5℃ / min, hold for 40 min, and cool to room temperature at a cooling rate of 5℃ / min to obtain the core layer; wherein, the 7wt% organic pore-forming agent is prepared from corn starch and bagasse in a 1:1 mass ratio, and the 3wt% flux powder is prepared from CaO and MgO in a 1:1 mass ratio.

[0129] S2. Mix 9.5 wt% borax-feldspar-CaO powder, 0.5 wt% water glass dispersant, and water, and ball mill to prepare a slurry with suitable viscosity and stability. The ball milling concentration is 80%, and the milling time is 30 minutes to ensure uniform mixing of the materials, thus forming the outer shell layer slurry. The 9.5 wt% borax-feldspar-CaO powder is a composite flux composed of borax, feldspar, and CaO in an optimized mass ratio of 8:1:1.

[0130] S3. The core layer is transported via conveyor belt, and the outer shell layer slurry is evenly coated onto the surface using an automatic glazing machine. The glazing pressure is 0.7 MPa, the spray gun moving speed is 550 mm / min, the intermediate layer rotation speed is 300 rpm, the number of glazing passes is 3, and the thickness of each glaze pass is 0.7 mm.

[0131] The coated green body was dried at 130℃ for 10 hours. The green body was then heated to 1200℃ at a heating rate of 10℃ and sintered at a high temperature for 40 minutes. It was then cooled to room temperature at a rate of 3℃ / min. The final product was a physically sealed two-layer ceramsite, named two-layer ceramsite (I).

[0132] Comparative Example 2

[0133] Preparation of two layers of ceramsite:

[0134] S1. Using 79wt% lepidolite tailings as the main material, add 5wt% organic pore-forming agent and 3wt% flux powder, and dry ball mill for 90 min. Add the ball-milled material to a mixer, spray with 20% water and wet mix for 15 min, then granulate using a disc granulator at an inclination angle of 55° and a rotation speed of 25 r / min, controlling the particle size of the core blank to 7 mm. After drying at 120℃ for 12 h, place the dried core blank in a sintering furnace, heat to 400℃ at a heating rate of 5℃ / min, hold for 40 min, and cool to room temperature at a cooling rate of 5℃ / min to obtain the core layer; wherein, the 5wt% organic pore-forming agent is prepared from corn starch and bagasse in a 1:1 mass ratio, and the 3wt% flux powder is prepared from CaO and MgO in a 1:1 mass ratio.

[0135] S2. 10 wt% modified metakaolin, 2.5 wt% phosphate curing agent NaH2PO3, and 0.5 wt% dispersant sodium polyacrylate were ball-milled with water for 40 min to a grinding concentration of 80%, forming a suspension slurry. This slurry was then impregnated onto the porous core surface of the core layer, forming an interlocking structure through capillary action. After impregnation, an intermediate layer preform was obtained and dried at 120℃ for 10 h. The dried intermediate layer preform was placed in a sintering furnace and heated to 1200℃ at a heating rate of 10℃ / min, held for 40 min, and then cooled to room temperature at a cooling rate of 3℃ / min. The final product was a chemically bonded two-layer ceramsite, named two-layer ceramsite (II).

[0136] Comparative Example 3

[0137] Preparation of lightweight ceramsite from traditional lepidolite tailings:

[0138] Using 68wt% lepidolite tailings as the main material, along with 10wt% cement, 8wt% quicklime, 3wt% alkali activator, 1wt% silicon carbide foaming agent, and 10wt% water, the mixture was dry-milled for 90 min. The milled material was then added to a mixer, wet-mixed with 20% water for 15 min, and granulated using a disc granulator at a 55° inclination angle and a rotation speed of 25 r / min, controlling the core blank particle size to 6 mm. After drying at 120℃ for 12 h, the dried core blank was placed in a sintering furnace and heated to 1300℃ at a heating rate of 5℃ / min, held for 40 min, and then cooled to room temperature at a cooling rate of 5℃ / min. The final product was traditional lepidolite tailings lightweight ceramsite.

[0139] Detection and analysis:

[0140] The lightweight ceramsite product, three-layer ceramsite (I), was finally prepared using the preparation method described in Example 2. The product prepared by the method described in Example 2 was observed using scanning electron microscopy (SEM) and X-ray diffraction (XRD).

[0141] 1. Mineral phase gradient transformation theory: Through a three-layer structural design, heavy metals are fixed and sealed. The core layer forms a porous matrix, the middle layer forms an aluminosilicate network structure, and the outer shell forms a dense glassy shell.

[0142] A portion of the lightweight ceramsite product was taken as a sample for testing. The sample was loaded into the cutting stage and calibrated using a coarse calibrator. After successful calibration, the sample was placed in the working chamber, the cutting mode was selected, and the argon ion gun was used to cut the sample. The polished sample was fixed on the electron microscope stage using conductive adhesive, and the cross-sectional morphology and pore structure changes were observed under a scanning electron microscope (SEM). Observing the internal morphology of the sample further verifies the uniformity and integrity of the material structure. After high-temperature sintering, the porous core, intermediate layer, and outer layer fused together, but a three-layer structure could still be observed, such as... Figure 1 As shown, SEM observation further verifies the effectiveness of the multi-layer structure design in this technical solution. The porous structure of the core layer helps improve the material's lightweight properties, while the dense glassy structure of the outer shell enhances the material's environmental stability. The SEM observation results further verify the feasibility and effectiveness of the technical solution of this invention.

[0143] 2. Ion substitution-lattice embedding mechanism: Heavy metals are fixed in the lattice in the intermediate layer by aluminosilicate mineral conversion agent and phosphate curing agent.

[0144] The lightweight ceramsite product is crushed, ground, and subjected to XRD analysis, such as... Figure 2 As shown in the figure, the diffraction peaks of the lightweight ceramsite product mainly represent the phases of SiO2, aluminosilicate, and CaSO4. In addition, diffraction peaks of the stable apatite phase were also observed. This indicates that a chemical reaction occurred in the intermediate layer after sintering. The intermediate layer is the core functional layer for achieving the chemical fixation of heavy metals, and its design goal is to transform the heavy metal ions that migrate here into a thermodynamically extremely stable crystal structure through chemical reactions. The generated calcium phosphate salt can achieve chemical locking of heavy metals, preventing their migration and diffusion in the environment.

[0145] The physical properties of the products prepared in Examples 2, 3, 4, Comparative Examples 1, 2, and 3 are shown in Table 2; the heavy metal toxicity leaching properties of the products prepared in Examples 2, 3, 4, Comparative Examples 1, 2, and 3 are shown in Table 3.

[0146] Table 2 Physical performance indicators of the products

[0147]

[0148] Table 3 Heavy metal leaching performance indicators of the products

[0149]

[0150] Analysis of the physical properties and heavy metal leaching performance of three-layer ceramsite (I) to three-layer ceramsite (III) shows that the bulk density of the three-layer lightweight ceramsite is approximately 480~510 kg / m³. 3 The compressive strength of the cylinders is greater than 9 MPa, the leaching concentration of heavy metals is lower than the limit of DB36 / T 1968-2024, and when the amount of phosphate curing agent added is ≥2.0 wt%, the heavy metal fixation rate reaches more than 97.5%, which fully complies with the GB / T 17431.1 standard for lightweight ceramsite for construction.

[0151] Comparing three-layer ceramsite (III) and two-layer ceramsite (I), it can be seen that the three-layer lightweight ceramsite, which has undergone chemical fixation and physical sealing, has a 12.9% higher compressive strength, a 23.8% lower bulk density, and a 3.6% higher heavy metal fixation rate than the two-layer lightweight ceramsite, which only uses physical sealing. Comparing three-layer ceramsite (III) and two-layer ceramsite (II), the three-layer lightweight ceramsite, which has undergone chemical fixation and physical sealing, has a 19.9% ​​higher compressive strength, a 21.9% lower bulk density, and a 4.8% higher heavy metal fixation rate than the two-layer lightweight ceramsite, which only uses chemical fixation. Comparing three-layer ceramsite (III) and traditional lithium mica tailings lightweight ceramsite, the three-layer lightweight ceramsite, which has undergone chemical fixation and physical sealing, has a 55.9% higher compressive strength, a 44.3% lower bulk density, and a 20% higher heavy metal fixation rate than the traditional lightweight ceramsite. Furthermore, in Comparative Example 3, the traditional method for preparing lightweight ceramsite from lithium mica tailings resulted in a heavy metal fixation rate of only 78.4%, and the thallium content in the toxic leachate only met the emission standards for general solid waste, failing to meet the standards of the Technical Specification for the Utilization of Lithium Slag in Highway Subgrade Engineering (DB36 / T 1968-2024).

[0152] SEM morphology of the three-layer ceramsite (III) product particles, as shown in the figure. Figure 3 As shown; SEM morphology of the product particles from the two layers of ceramsite (I), as follows. Figure 4 As shown; SEM morphology of the product particles from the two layers of ceramsite (II), as follows. Figure 5 As shown; SEM image of traditional lithium mica tailings lightweight ceramic particles, as shown. Figure 6As shown; analysis reveals that the three-layer ceramsite (III) product particles have a highly dense microstructure, with relatively tight bonding between particles. This structural characteristic significantly enhances the physical protective performance of the material, effectively inhibiting the leaching and diffusion of heavy metal ions, thereby enhancing the environmental stability and safety of the product. In contrast, the coating degree of the two-layer ceramsite (I) product particles is slightly weaker; the coating layer structure of the two-layer ceramsite (II) product particles is relatively loose, and the particle surface is not completely wrapped by the glassy material, resulting in areas of incomplete fusion during the fusion process. This not only affects the cylinder compressive strength of the product but also weakens its barrier ability against heavy metals; Comparative Example 3 uses traditional lithium mica tailings lightweight ceramsite prepared by conventional processes, and the particles exhibit a porous structure with a large number of micropores and cracks on the surface. This structure is easily eroded by moisture, reducing the water resistance and mechanical strength of the material, while also exacerbating the migration of heavy metals and further increasing the risk of environmental pollution.

[0153] In summary, the method for preparing lightweight ceramsite provided by this invention has the following advantages:

[0154] First, through a multi-layered structural design, the efficient utilization of lepidolite tailings and the long-term, stable solidification of heavy metals are achieved; this enables the resource-based reuse of waste, reducing dependence on natural resources; and provides a new option for the preparation of lightweight ceramsite. The three-layer structure design achieves the fixation and encapsulation of heavy metals. The core layer forms a porous silica-alumina framework through organic pore-forming agents and alkaline earth metal oxides; the middle layer fixes heavy metals through mineral transformation and phosphate solidification agents; and the outer shell forms a dense shell through vitrification, further improving the material's environmental stability. This method solves the problem of lepidolite tailings disposal, achieves high-value utilization of lepidolite tailings, provides a new approach to heavy metal pollution control, solves the problems of unstable and short-lasting solidification of toxic heavy metals, and addresses the issue of excessive reliance on natural resources in the preparation of lightweight ceramsite.

[0155] Secondly, using lepidolite tailings as the main material, organic pore-forming agents and fluxes are added. Dry ball milling is used to refine the material to <150µm (approximately 100 mesh) to ensure the uniformity and efficiency of subsequent reactions. The ball-milled material is then wet-mixed to a plastic state, granulated, dried at low temperature, and preheated to decompose the pore-forming agent, forming a porous structure. After cooling to room temperature, modified metakaolin and phosphate curing agent are ball-milled with water to form a suspension slurry. This slurry is then impregnated onto the porous core surface, forming an interlocking structure through capillary action. After low-temperature drying, it is cooled to room temperature. A borax-feldspar-alkaline earth metal oxide mixed powder is used to prepare the outer shell layer powder. The impregnated intermediate layer material is transported via conveyor belt and coated with the outer shell layer slurry using an automatic glazing machine. The coated green body is then dried at low temperature and sintered at high temperature, followed by cooling to room temperature. The final product is a three-layer ceramic aggregate with physical sealing and chemical bonding. The core pores are solidified with heavy metals, the intermediate layer enhances stability, and the glass shell provides an inert barrier to ensure long-term safety.

[0156] Third, the core of this invention lies in using a strategy combining "physical sealing" and "chemical fixation" to stably encapsulate heavy metals within a ceramic aggregate matrix, providing a highly promising technical solution for the high-value utilization of lepidolite tailings and the remediation of heavy metal pollution. This solution is based on the mineral phase gradient transformation theory and designs a three-layer structure ceramic aggregate preparation process for lepidolite lithium extraction tailings. The core idea of ​​this technical solution is to construct a multi-layered protection system with functional gradients. Each layer has a unique function, and through synergistic effects, ultimately achieves a "double-insurance" fixation of heavy metals.

Claims

1. A lightweight ceramsite, characterized in that, From the inside out, it includes: kernel layer, intermediate layer, and outer shell layer; The raw materials for the core layer include lithium mica tailings, organic pore-forming agents, and fluxing agents; The raw materials for the intermediate layer include aluminosilicate mineral conversion agent, hydrogen phosphate curing agent, and dispersant; The raw materials for the outer shell layer include low-melting-point fluxing agents and dispersants; The aluminosilicate mineral conversion agent is modified metakaolin; the modified metakaolin is a product obtained by adding 9% acid modifier to natural kaolin and then thermally activating it at 800℃. The intermediate layer will form an aluminosilicate network structure; The outer shell is a physically enclosed, dense glassy layer; The heavy metal fixation rate of the lightweight ceramsite is ≥97.5%; In the raw materials of lightweight ceramsite, the mass percentage of lepidolite tailings is 70-75%, the mass percentage of organic pore-forming agent is 5-8%, the mass percentage of flux is 3-5%, the mass percentage of aluminosilicate mineral conversion agent is 10-15%, the mass percentage of hydrogen phosphate curing agent is 2-3%, the mass percentage of dispersant in the intermediate layer is 0.5-0.8%, the mass percentage of dispersant in the outer shell layer is 0.5-0.8%, and the mass percentage of low-melting-point flux is 4-5%.

2. The lightweight ceramsite according to claim 1, characterized in that, The chemical composition of the lepidolite tailings, by mass percentage, includes: 46.42% SiO2, 22.75% Al2O3, 0.61% Fe2O3, 2.14% CaO, 0.25% MgO, 0.07% SO3, 9.52% Na2O, 4.02% K2O, 3.39% TiO2, and 10.71% other impurities. The loss on ignition of the lepidolite tailings is 0.12%. And / or, the organic pore-forming agent is a starch-based material, the starch-based material is corn starch and sugarcane bagasse, and the mass ratio of corn starch to sugarcane bagasse is 0~1:0~1; And / or, the flux is an alkaline earth metal oxide, wherein the alkaline earth metal oxide is CaO or MgO; And / or, the modified metakaolin has a composition of 53% SiO2, 45% Al2O3 and 1.5% impurities, and the loss on ignition of the modified metakaolin is 0.5%; And / or, the hydrogen phosphate curing agent is potassium dihydrogen phosphate or sodium dihydrogen phosphate; And / or, the dispersant of the intermediate layer is sodium polyacrylate; And / or, the dispersant of the outer shell layer is water glass; And / or, the low-melting-point flux is a borax-feldspar-alkaline earth metal oxide composite system, wherein the components of the borax-feldspar-alkaline earth metal oxide composite system are borax, feldspar and alkaline earth metal oxide, the mass ratio of borax, feldspar and alkaline earth metal oxide is 7~9:1~2:1~2, and the alkaline earth metal oxide is one or two of MgO and CaO.

3. The lightweight ceramsite according to claim 1 or 2, characterized in that, The bulk density of the lightweight ceramsite is 480~511 kg / m³, and the cylinder compressive strength is >9MPa.

4. The method for preparing lightweight ceramsite according to claim 1 or 2, characterized in that, Includes the following steps: S1. Preparation of the core layer: Lithium mica tailings, organic pore-forming agent and flux are mixed, ground, wet-mixed, granulated, dried and sintered to form a porous matrix. The core layer is then cooled to room temperature. S2. Preparation of the intermediate layer: A mixture of aluminosilicate mineral conversion agent, hydrogen phosphate curing agent, dispersant and water is coated on the outside of the core layer and dried to obtain the intermediate layer; S3. Preparation of the outer shell layer: A mixture of low-melting-point flux, dispersant and water is coated on the outside of the intermediate layer, dried, sintered and cooled to room temperature to form a dense glassy shell, thus obtaining the outer shell layer.

5. The preparation method according to claim 4, characterized in that, In step S1, the grinding time is 60-90 min; the wet mixing includes adding water, which accounts for 18-22% of the core layer raw material by mass percentage, and the wet mixing time is 15 min; the drying temperature is 100-150℃, and the drying time is 10-12 h; the sintering includes: heating to the preheating temperature, preheating and holding, the heating rate is 2-5℃ / min, the preheating temperature is 400℃, the holding time is 30-40 min; the cooling rate is 3-5℃ / min. And / or, in step S2, the drying temperature is 100~150℃ and the drying time is 8~10h; And / or, in step S3, the drying temperature is 100~150℃, and the drying time is 8~10h; the sintering includes: heating to the conversion end-sealing temperature, conversion end-sealing and holding at the temperature, the heating rate is 5~10℃ / min, the conversion end-sealing temperature is 1100~1200℃, and the holding time is 40~50min; the cooling rate is 2~3℃ / min, and the thickness of the dense glassy shell is 1~2mm.

6. The preparation method according to claim 4, characterized in that, in step S1, a disc granulator is used for granulation, the tilt angle of the disc granulator is adjusted to 45~55° and the rotation speed is 15~25 r / min, and the particle size of the core preform is controlled to be between 5~8 mm by adjusting the tilt angle and the rotation speed; And / or, in step S2, the mixture is prepared by mixing aluminosilicate mineral conversion agent, hydrogen phosphate curing agent, dispersant and water, and grinding them into a suspension slurry; And / or, in step S3, the mixture is prepared by mixing a low-melting-point flux, a dispersant, and water, and then grinding them into a slurry; And / or, in step S2, the coating is performed by an impregnation coating method, and the thickness of the coating is 1 to 1.5 mm; And / or, in step S3, the coating is carried out by spraying, the spraying is carried out by an automatic glazing machine, the spraying pressure of the automatic glazing machine is 0.4 to 0.8 MPa, the moving speed of the spray gun is 400 to 600 mm / min, the rotation speed of the intermediate layer is 200 to 300 rpm, the number of glazing sprays is 2 to 3, and the thickness of each glaze spray is 0.5 to 0.7 mm.

7. The preparation method according to claim 6, characterized in that, In step S2, the grinding is ball milling, the ball milling concentration is 66%~80%, and the ball milling time is 30~40 min; And / or, in step S3, the grinding is ball milling, the ball milling concentration is 66%~80%, and the ball milling time is 20~30 min.

8. The lightweight ceramsite prepared by the preparation method according to any one of claims 4 to 7, characterized in that, The bulk density of the lightweight ceramsite is 480~511 kg / m³, and the cylinder compressive strength is >9MPa.

9. The application of the lightweight ceramsite according to claim 1 or 2, or the lightweight ceramsite prepared by the preparation method according to any one of claims 3 to 6, in construction.

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