A method for resourceful treatment of industrial solid waste

Abstract

The application provides a resource processing method of industrial solid waste, and particularly relates to a method for simultaneously extracting silicon and aluminum elements from graphite tailings, which comprises the following steps: mixing ammonium salt with the graphite tailings, and calcining the mixture at 250 DEG C to 500 DEG C for 0.5 h to 2.0 h to obtain a primary activated product; mixing the primary activated product with an alkaline activation additive, and calcining the mixture at 700 DEG C to 900 DEG C for 1.0 h to 3.0 h to obtain an alkali fusion product; immersing the alkali fusion product in an acid solution with a concentration of 3 mol / L to 9 mol / L, and stirring the mixture at 60 DEG C to 100 DEG C for 3.0 h to 8.0 h to obtain an acid leaching product; and filtering the acid leaching product to obtain an acid leaching filtrate rich in aluminum and an acid leaching residue rich in silicon. The application also relates to methods for preparing regenerated aluminum oxide based on the acid leaching filtrate and soil conditioner based on the acid leaching residue. The method can simultaneously realize efficient directional separation and recovery of silicon and aluminum components, and can further prepare mesoporous silicon powder which can be used as a soil conditioner to improve obstacle soil and high-purity aluminum oxide powder which can be used for refractory materials.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization, specifically to a method for the resource utilization of industrial solid waste graphite tailings, particularly a method for extracting silicon and aluminum from graphite tailings as raw materials and preparing mesoporous silica powder and soil conditioner, while simultaneously recovering alumina. Background Technology

[0002] With industrial development, graphite tailings, a byproduct of graphite beneficiation, have resulted in consistently high emissions. Long-term accumulation of this waste not only occupies significant land resources but also facilitates the release and migration of heavy metal ions through weathering, erosion, and rainwater leaching, polluting soil and water bodies and seriously endangering the balance of surrounding ecosystems and human health. Currently, the resource utilization of graphite tailings is relatively limited, mainly focusing on the preparation of building materials (such as non-fired bricks and concrete aggregates). However, this method of utilization has low added value and fails to fully tap the resource potential of graphite tailings. Simultaneously, the widespread and diverse nature of obstacle soils, due to deteriorating physical and chemical properties and micro-ecological imbalances, severely restricts the improvement of agricultural production quality and efficiency, urgently requiring low-cost, high-efficiency soil improvement technologies.

[0003] Studies have shown that graphite tailings mainly contain aluminosilicate minerals such as quartz, feldspar, and zeolite. Leveraging their abundant silica content, they can be used to prepare soil conditioners for high-value applications. Existing technologies for silica extraction from graphite tailings primarily focus on the preparation of silicon-based products. For example, CN 119976859 A discloses a method for preparing high-purity quartz. This method uses graphite tailings with a quartz content of over 40% as raw material, and sequentially processes it through multiple steps including flotation, high-temperature calcination, acid leaching, secondary calcination, and acid leaching to ultimately obtain high-purity quartz particles. The core of this process lies in deeply removing impurities and improving product purity through key steps such as adding mineralizing agents, high-temperature calcination, and multiple acid leaching. CN 106185961 A discloses a process for preparing fumed silica at low temperature using graphite tailings as raw material. This patent first processes the graphite tailings through pulping, grading, magnetic separation, precipitation, concentration, and dehydration to obtain graphite tailings powder. Then, alkali and alkaline earth metal elements are removed by hydrochloric acid, and feldspar and mica impurities are removed by flotation. Finally, high-value-added products such as fumed silica are produced through a gas-phase reaction using mixed acids. This technology suffers from problems such as sacrificing a large amount of metal elements from the tailings, complex process flow, and high energy consumption.

[0004] Furthermore, utilizing the silicon-rich elements in graphite tailings to prepare soil conditioners can achieve both tailings reduction and resource utilization. Technologies for preparing soil conditioners from industrial waste such as graphite tailings have also been reported. For example, CN118026737 A discloses a method for preparing high-purity silicon-based minerals and potassium sulfate liquid fertilizer from graphite tailings. This method uses waste sulfuric acid from expandable graphite production, hydrogen peroxide, and Tween 80 emulsifier to prepare an acid leaching solution. After high-pressure reaction with the graphite tailings, high-purity solid silicon-based minerals with approximately 90% purity are obtained. The acid leaching filtrate is then treated with ammonia water to adjust the pH and with a flocculant to obtain a potassium sulfate solution, which can be concentrated and used as potassium fertilizer. Although this invention achieves the extraction of silicon from graphite tailings and the preparation of liquid potassium fertilizer, it has shortcomings such as requiring the addition of multiple chemical reagents, the need for high-pressure reaction conditions, and the failure to recover valuable metal elements such as aluminum, leading to resource loss. CN111253945B discloses a graphite tailings-based soil conditioner for acidified soil and its preparation method: using natural flake graphite tailings powder as raw material, high-adsorption expanded graphite is obtained through concentrated nitric acid intercalation and high-temperature expansion at 900-1000℃, followed by soaking and drying with a mixture of calcium magnesium phosphate fertilizer and wood ash, and then mixed with limestone powder. However, the product is specifically designed for acidified soil, and the high-temperature intercalation process has high energy consumption and significant environmental impact.

[0005] In summary, existing technologies have significant limitations: they either focus on the single preparation of graphite tailings-based silicon materials, making it difficult to simultaneously achieve the synergistic extraction and recovery of multiple elements such as silicon and aluminum; or they sacrifice process simplicity in pursuit of product purity. These technological approaches not only have high energy consumption but also waste valuable metal resources such as aluminum in graphite tailings, failing to fully exploit their potential value. These shortcomings are even more pronounced in the application of graphite tailings in the preparation of soil conditioners: firstly, silicon is mostly present in stable crystalline forms such as quartz, and direct utilization or simple acid leaching is insufficient to effectively activate its activity, thus hindering the conditioner's ability to regulate soil salinity and improve soil structure; secondly, the lack of mesoporous structures during preparation results in conditioners with weak adsorption properties, failing to effectively enrich soil nutrients and hindering the achievement of long-term soil improvement goals. Summary of the Invention

[0006] To address the technical problems in existing graphite tailings resource utilization technologies, such as the inability to efficiently and synergistically extract silicon and aluminum elements and the difficulty in meeting high-value applications, the present invention aims to propose a novel graphite tailings resource utilization method that can simultaneously and efficiently recover silicon and aluminum elements contained in graphite tailings, thereby enabling the recovered silicon and aluminum materials to meet the requirements for high-value utilization. To achieve the above objective, the present invention proposes a graphite tailings treatment scheme that can be termed "asynchronous alkali fusion-low-temperature acid leaching-step precipitation." This scheme aims to achieve precise adaptation through differentiated control of alkali fusion reaction parameters, combined with the synergistic dissolution effect of low-temperature acid leaching and stepwise precipitation technology with precise pH control. This not only simultaneously achieves efficient and directional separation and recovery of silicon and aluminum components, but also further prepares mesoporous silica powder that can be used as a soil conditioner to improve obstacle soils, and high-purity alumina powder that can be used in refractory materials.

[0007] To achieve the above objectives, the present invention employs the following technical solutions:

[0008] In a first aspect, the present invention provides a method for simultaneously extracting silicon and aluminum elements from graphite tailings, comprising:

[0009] 1) Asynchronous alkaline melting:

[0010] The first stage is low-temperature calcination: ammonium salt is mixed with graphite tailings and calcined at 250℃~500℃ for 0.5h~2.0h to obtain primary activated product a;

[0011] The second stage of high-temperature calcination: the primary activated product a is mixed with an alkaline activating agent and calcined at 700℃~900℃ for 1.0 h~3.0 h to obtain the alkali fusion product b;

[0012] 2) Low temperature acid leaching:

[0013] The alkaline fusion product b obtained in 1) is immersed in an acid solution with a concentration of 3 mol / L to 9 mol / L and stirred at 60℃ to 100℃ for 3.0 h to 8.0 h to obtain the acid leaching product c.

[0014] 3) Solid-liquid separation:

[0015] The acid leaching product c obtained in 2) is separated by filtration to obtain an aluminum-rich acid leaching filtrate and a silicon-rich acid leaching residue.

[0016] In the method described in this invention, industrial solid waste graphite tailings mainly consist of silicates and aluminosilicates. The activation principle of the asynchronous alkali fusion process for graphite tailings described in this invention is as follows: First, the tailings are initially activated using HCl gas generated from the pyrolysis of ammonium salts at ≥350℃. This process disrupts the crystal structure of silicates and aluminates on one hand, and reacts with Ca in the crystal lattice on the other. 2+ Mg 2+ Fe3+ The metal cations react to form soluble chlorides. This process creates a loose, porous structure on the surface of the tailings particles, increasing surface roughness and thus increasing the contact area between the subsequent alkali fusion reagent and the mineral. After initial activation, an alkaline activating agent is used to further react with the silicon and aluminum components in the initially activated tailings, disrupting the silicon-oxygen tetrahedron and aluminum-oxygen tetrahedron network structure in the minerals, generating soluble sodium silicate and sodium aluminate. The CO2 gas released during the reaction can further expand the pores, causing deep disintegration of silicate and aluminosilicate crystals, achieving efficient dissociation of the target components.

[0017] In the method described in this invention, the ammonium salt in step 1) first stage low-temperature calcination can be any one or a mixture of two or more of ammonium chloride, ammonium sulfate, and ammonium bicarbonate; ammonium chloride is preferred.

[0018] In a further preferred embodiment of the present invention, the ammonium salt calcined in the first stage of step 1) is ammonium chloride, and the mass ratio of ammonium chloride to graphite tailings is controlled at (0.3 - 0.8):1; in a more preferred embodiment, the mass ratio of ammonium chloride to graphite tailings is controlled at (0.4-0.6):1.

[0019] In the preferred embodiment of the present invention, the specific scheme of the first stage of low-temperature calcination in step 1) is calcination at 350℃~420℃ for 0.5h~2.0h; more preferably, calcination at 350℃~400℃ for 0.5h~1.0h.

[0020] In the method described in this invention, the alkaline activating agent in the second stage of high-temperature calcination in step 1) can be any one or a mixture of two or more of sodium carbonate, sodium hydroxide, calcium hydroxide, or calcium carbonate; sodium carbonate is preferred.

[0021] In a further preferred embodiment of the present invention, the alkaline activating agent in the second stage of high-temperature calcination in step 1) is sodium carbonate, and the mass ratio of sodium carbonate to primary activation product a is controlled at (0.6-1.5):1; in a more preferred embodiment, the mass ratio of sodium carbonate to primary activation product a is controlled at (0.8-1.2):1.

[0022] In the preferred embodiment of the present invention, the specific scheme of the second stage of high-temperature calcination in step 1) is calcination at 750℃~830℃ for 1.0 h~3.0 h; more preferably, calcination at 800℃~820℃ for 1.5 h~2.5 h.

[0023] In the method described in this invention, step 2) low-temperature acid leaching uses an acid solution that can be any one or a mixture of two or more of hydrochloric acid, sulfuric acid, hydrofluoric acid, or nitric acid; hydrochloric acid is preferred.

[0024] In a further preferred embodiment of the present invention, the acid solution in step 2) low-temperature acid leaching is hydrochloric acid, and the mass-to-volume ratio of the alkali fusion product b to hydrochloric acid is 1:(2-10) g / mL; more preferably 1:(3-6) g / mL.

[0025] In a preferred embodiment of the present invention, step 2) low-temperature acid leaching involves stirring at 75°C to 95°C for 3.0 h to 8.0 h; more preferably, stirring at 80°C to 90°C for 4.0 h to 5.0 h.

[0026] Secondly, based on the method described in the first aspect above, the present invention also provides a method for preparing a soil conditioner using graphite tailings as raw material, comprising:

[0027] A. Using graphite tailings as raw material, the silicon-rich acid leaching residue is prepared according to the method described in the first aspect of the present invention. The acid leaching residue is washed to neutral and dried, and then pulverized to a fineness of not less than 200 mesh to obtain mesoporous silica powder.

[0028] B. Mix the mesoporous silica powder obtained in A with calcium hydroxide to obtain a calcium-silicon mixture. Control the molar ratio of calcium to silicon in the calcium-silicon mixture to be 0.3-0.5:1. Then add water to the calcium-silicon mixture and carry out a hydrothermal reaction at a temperature of 150℃~200℃ and a pressure of 0.2-0.5MPa for 3~10 h to obtain a calcium-silicon based soil conditioner.

[0029] In a preferred embodiment of the present invention, the temperature of the hydrothermal reaction in step B is 160℃~180℃, and the hydrothermal reaction time is 4~7 h.

[0030] In a preferred embodiment of the present invention, the water in step B is deionized water, and the amount added is 10% to 20% of the mass of the silicon-calcium mixture.

[0031] Thirdly, based on the method described in the first aspect above, the present invention also provides a method for preparing alumina from graphite tailings as raw material, comprising: using graphite tailings as raw material, first preparing the aluminum-rich acid leaching filtrate according to the method described in the first aspect of the present invention; then precipitating and separating the acid leaching filtrate by a step-by-step precipitation method to obtain solid aluminum hydroxide; and then calcining the obtained solid aluminum hydroxide at high temperature to obtain alumina powder.

[0032] This invention focuses on a process for the simultaneous and efficient extraction of silicon and aluminum from graphite tailings, effectively solving the problem that graphite tailings, a type of solid waste, is difficult to utilize for high-value applications. Compared with existing technologies, the beneficial effects of this invention are mainly reflected in the following aspects: ① The asynchronous alkali fusion in the method of this invention is a key activation process, which can not only promote the conversion of aluminum silicate minerals into soluble salts, but also reduce the overall energy consumption through low-temperature-high-temperature synergistic calcination; ② The acid leaching residue obtained by the low-temperature acid leaching treatment described in this invention is not only rich in silicon elements, but also has a rich mesoporous structure. The mesoporous silica powder obtained after drying can be used to prepare soil conditioners. The silica powder can not only supplement the soil with silicon and promote soil aggregation to improve air and water permeability, but more importantly, the conditioner prepared by the silica powder has a typical mesoporous structure with a large specific surface area. The mesoporous channels can delay nutrient leaching and realize slow-release nutrient supply, which can further improve fertilizer utilization;  The acid leaching filtrate obtained by the low-temperature acid leaching treatment described in this invention is rich in aluminum ions. Through step precipitation and calcination with precise control of pH changes, high-value-added recycled alumina can be produced, so that the resource utilization of graphite tailings can take into account both economic and environmental benefits.

[0033] Experiments have shown that the method of this invention can achieve a silicon extraction efficiency of over 94% in graphite tailings, while simultaneously regenerating alumina with a purity of approximately 80%, thus solving the problems of low tailings utilization and resource waste in traditional technologies.

[0034] In summary, this invention uses industrial solid waste graphite tailings as the core raw material, which is inexpensive and highly feasible for large-scale production. It not only solves the environmental problem of graphite tailings accumulation but also provides a low-cost solution for soil remediation, while producing high-value-added recycled alumina. This achieves multiple goals of "solid waste reduction, resource recycling, and soil remediation," aligning with the concept of green development. The entire process of this invention is simple, easy to operate, has low energy consumption, and produces no secondary pollution. It achieves efficient utilization of all components of graphite tailings, solves the pollution problem caused by graphite tailings accumulation, and has significant economic, environmental, and social benefits. It is also easy to promote and apply on a large scale. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the process flow for a specific embodiment of the present invention.

[0036] Figure 2 This is an electron microscope image of the surface morphology of the graphite tailings used as raw material in Example 1.

[0037] Figure 3 and Figure 4 This is an electron microscope image of the surface morphology of the silicon powder after acid leaching in Example 1. Detailed Implementation

[0038] This invention provides a method for extracting silicon and aluminum from industrial solid waste graphite tailings and further preparing mesoporous silica powder, soil conditioner, and recycled alumina. Figure 1 As shown, it includes the following steps:

[0039] Raw material pretreatment: Graphite tailings are used as raw materials. The graphite tailings are passed through a square hole sieve with a diameter of 1.25 mm, and then placed in a drying oven and dried at 105-110℃ for 3-6 hours to remove moisture and set aside for later use.

[0040] The microstructure of the graphite tailings raw material is as follows: Figure 2 As shown, the main chemical components are SiO2, Al2O3, CaO, Fe2O3, K2O, MgO, Na2O, TiO2, etc., and the mineral composition is mainly quartz, feldspar, diopside, calcite, zeolite, pyrite, and chlorite. The tailings have a complex mineral composition and close intergrowth relationships, making the separation and recovery of the silicon and aluminum components difficult. Because the silicon and aluminum components are bound within a stable mineral lattice structure, traditional separation processes such as single alkali fusion and conventional acid leaching are insufficient to achieve selective dissociation and efficient dissolution of the silicon and aluminum components. Therefore, this invention proposes a targeted technical solution to achieve efficient recovery and high-value utilization of the silicon and aluminum components in the tailings.

[0041] Asynchronous alkali fusion treatment: Based on the intercalation characteristics of mineral components in graphite tailings, asynchronous alkali fusion technology is used to achieve efficient preliminary dissociation of graphite tailings. Using ammonium salts and alkaline reagents as activating agents, the calcination temperature can be reduced, thus decreasing energy consumption.

[0042] Specific implementation: First, ammonium salt and graphite tailings are mixed evenly in a specific ratio. After a first-stage controlled-temperature calcination treatment, a preliminary activated product is obtained. Then, an alkaline reagent is added and thoroughly mixed, followed by a second-stage controlled-temperature calcination to obtain an alkali-fused product. This technology introduces ammonium salt and alkaline flux into the system in stages to exert a synergistic activation effect, thereby achieving the preliminary activation and dissociation of a stable mineral lattice structure.

[0043] The first-stage activation aid described in this invention is ammonium chloride. Ammonium chloride is mixed with graphite tailings in a certain proportion and then calcined to obtain primary activation product a.

[0044] The mass ratio of ammonium chloride to graphite tailings is (0.3 - 0.8):1, for example, it can be 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, or 0.8:1. This mass ratio is preferably (0.4-0.6):1. When the amount of ammonium chloride used is less than 0.3:1, the amount of HCl and other gases produced by its decomposition is insufficient, making it impossible to effectively etch the surface of the graphite tailings minerals, and the activation effect does not meet the requirements for subsequent applications.

[0045] The first stage of temperature-controlled calcination is at a temperature of 250℃ to 500℃, for example, 250℃, 300℃, 350℃, 400℃, 450℃, or 500℃, or other values ​​besides those mentioned above. The preferred temperature is 350℃ to 420℃.

[0046] The calcination activation time for the first stage is 0.5h to 2.0h.

[0047] The second-stage activation aid described in this invention is sodium carbonate. Sodium carbonate is widely available, inexpensive, and readily accessible. The calcined product a is mixed uniformly with sodium carbonate in a certain proportion, calcined at a certain temperature, and then cooled to room temperature to obtain the alkali-fused product b.

[0048] The mass ratio of sodium carbonate to the first-stage activation product a is (0.6-1.5):1. For example, it can be 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, or 1.5:1, as well as other values ​​besides those mentioned above. The preferred mass ratio is (0.8-1.2):1.

[0049] The second-stage controlled calcination temperature is 700℃~900℃, for example, it can be 700℃, 750℃, 800℃, 850℃, or 900℃, or other values ​​besides the above. The preferred temperature is 750℃~830℃. The activation temperature is a key variable for controlling the activation effect. Below 700℃, the activation reaction is insufficient and cannot deeply destroy the crystal structure of the mineral; above 900℃, the melting point of sodium carbonate is exceeded, resulting in a molten state, inducing excessive reaction, and easily causing equipment wear and increased energy consumption.

[0050] The calcination activation time for the second stage is 1.0 h to 3.0 h.

[0051] Low temperature acid leaching

[0052] In this invention, the product b, activated by alkali fusion, is placed in an acid solution of a specific concentration and subjected to a constant-temperature stirring leaching reaction under set temperature conditions. After the reaction is completed, a solid-liquid separation operation is performed to obtain the acid leaching solution and the acid leaching filter residue, respectively. Under the condition of preliminary activation of graphite tailings, the acid leaching reaction achieves the directional migration of aluminum and the solid-phase retention of silicon, laying a key foundation for the subsequent recovery of aluminum components. The dilute acid reacts with the sodium silicate in the alkali-activated product to generate active silicon, while the soluble aluminum salts in the product enter the liquid phase for efficient dissolution. In addition, the acid leaching process can further open up the internal pores of the product, realizing the formation of a mesoporous structure.

[0053] In this invention, the acid used is hydrochloric acid, and its concentration is controlled between 3 mol / L and 9 mol / L. For example, it can be 3 mol / L, 4 mol / L, 5 mol / L, 7 mol / L, 8 mol / L, or 9 mol / L, as well as other values ​​besides those mentioned above. The preferred concentration is 4 mol / L to 8 mol / L.

[0054] The above-mentioned preferred acid concentration can ensure that the soluble aluminate in the activation product reacts fully with hydrochloric acid to achieve efficient dissolution of aluminum components; it can also allow sodium silicate to react with hydrochloric acid to generate active silicon dioxide and avoid excessive dissolution of active silicon, while taking into account both reaction rate and production cost.

[0055] According to the present invention, the mass-to-volume ratio of the alkali-activated product to the acid solution is 1:(2-10) g / mL, for example, it can be 1:2 g / mL, 1:3 g / mL, 1:4 g / mL, 1:5 g / mL, 1:6 g / mL, 1:7 g / mL, 1:8 g / mL, 1:9 g / mL, or 1:10 g / mL, as well as other values ​​other than those mentioned above. This mass-to-volume ratio is preferably 1:(3-6) g / mL.

[0056] According to the present invention, the acid leaching reaction temperature is 60°C to 100°C, for example, 60°C, 70°C, 80°C, 90°C, or 100°C, as well as other values ​​besides those mentioned above. The preferred temperature is 75°C to 95°C.

[0057] According to the present invention, the acid leaching reaction time is 3.0 h to 8.0 h, for example, it can be 3.0 h, 4.0 h, 5.0 h, 6.0 h, 7.0 h or 8.0 h, as well as other values ​​other than those mentioned above. The reaction time is preferably 4.0 h to 6.0 h.

[0058] According to the present invention, in order to avoid raw material loss and environmental risks caused by acid volatilization during the acid leaching reaction, a condensation reflux device is provided.

[0059] Mesoporous silica powder (silica powder)

[0060] According to the present invention, after the acid leaching reaction is completed, the mixture is filtered to obtain acid leaching filtrate and acid leaching residue. The obtained acid leaching residue is washed with deionized water until neutral, and then dried at 105-120°C for more than 2 hours. After drying, it is pulverized to 200-300 mesh to obtain silicon powder.

[0061] The solid-liquid separation operation described in this invention can be implemented using conventional solid-liquid separation methods in the art, such as filtration, pressure filtration, or vacuum filtration. This invention does not limit the specific methods used.

[0062] Compared to other preparation methods, the silica powder prepared by this invention has significant advantages, with a silica purity of up to 95.8%, an average pore size of 3.8 nm, and a specific surface area as high as 332 m² / g. This silica powder exhibits a mesoporous structure, which can both fill the gaps between soil particles and promote soil particle aggregation through its mesoporous properties, rapidly breaking down the dense soil layer and significantly improving soil aeration and permeability. It is particularly suitable for improving saline-alkali and compacted farmland.

[0063] Regenerated alumina

[0064] The present invention treats the acid leaching filtrate obtained above by a stepwise precipitation method. By precisely controlling the pH value of the system in multiple stages, high-purity aluminum hydroxide precipitate is obtained through stepwise solid-liquid separation. The aluminum hydroxide precipitate is then calcined at high temperature to obtain alumina powder.

[0065] Pretreatment of acid leaching filtrate: Take the acid leaching filtrate after the above hydrochloric acid leaching and filter it through a precision filter (filter membrane pore size 0.45 μm) to remove suspended impurities and set it aside for later use; at this time, the filtrate mainly contains AlCl3, and is accompanied by a small amount of impurity salts such as FeCl3, CaCl2, and MgCl2.

[0066] Primary precipitation: Add sodium hydroxide solution dropwise to the acid leaching filtrate at a rate of 1~2 mL / min while stirring (200~250 r / min) to adjust the pH of the system to 3.0-3.5, stir for 30~60 min, let stand for more than 2 h, and then perform solid-liquid separation to remove precipitated impurities.

[0067] Deep precipitation: Add sodium hydroxide solution to the filtrate after removing impurities, adjust the pH of the system to 6.5-7.5, maintain the stirring rate, and stir for 40-90 min to allow aluminum ions to fully precipitate. Then perform solid-liquid separation to obtain aluminum hydroxide precipitate.

[0068] Aging and purification: Stop stirring and let the reaction system stand for 4~24 hours to age, so that the aluminum hydroxide crystals grow completely and the particle size distribution is uniform.

[0069] Alumina: Aluminum hydroxide precipitate was separated by filtration. The filter cake was washed multiple times with deionized water until no white precipitate formed upon addition of silver nitrate solution to the washing liquid (i.e., no residue). The washed filter cake was placed in an oven and dried at 105-120℃ for at least 2 hours to obtain dried aluminum hydroxide powder. The aluminum hydroxide powder was calcined at 800-900℃ for 2-3 hours to obtain alumina with a purity of up to 80%.

[0070] In this invention, the mass concentration of the sodium hydroxide solution is 5% to 30%. When precipitation is performed, a mass concentration of 15% to 25% of the sodium hydroxide solution is preferred. When the pH value is close to that required for titration, a mass concentration of 5% to 10% of the sodium hydroxide solution is used.

[0071] Soil conditioner preparation

[0072] Take the mesoporous silica powder prepared above and mix it with calcium hydroxide in a mixing device according to a specific mass ratio. Add a certain amount of deionized water to the mixture and stir until the system forms a uniform slurry without obvious particles. Transfer the slurry to a high-pressure reactor and control the temperature and other parameters inside the reactor to the preset conditions. Keep the reactor warm and pressurized to complete the hydrothermal reaction. After filtering and drying, the reaction product is used to obtain the finished product of silicon-calcium based soil conditioner.

[0073] According to the present invention, the calcium hydroxide is an industrial grade or analytical grade product;

[0074] According to the present invention, the mixing ratio of the mesoporous silica powder and calcium hydroxide is such that the molar ratio of calcium to silicon contained therein is 0.3:1 to 0.5:1;

[0075] According to the present invention, the mass ratio of deionized water added is 10% to 20%;

[0076] According to the present invention, the temperature of the hydrothermal reaction is 150°C to 200°C, more preferably 160°C to 180°C;

[0077] According to the present invention, the hydrothermal reaction time is 3 to 10 h, more preferably 4 to 7 h.

[0078] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0079] Example 1

[0080] A method for extracting silicon and aluminum from industrial solid waste graphite tailings and further preparing mesoporous silica powder includes the following steps:

[0081] Raw material pretreatment: Pretreatment of materials with microstructures such as... Figure 2 The graphite tailings shown (main chemical components: SiO2≥55%, Al2O3≥6.0%) were passed through a square-hole sieve with a diameter of 1.25 mm to obtain graphite tailings powder; then the graphite tailings powder was dried at 105℃ for 3.0 h to remove moisture and was ready for use.

[0082] First step activation: The pretreated graphite tailings powder and ammonium chloride are mixed evenly at a mass ratio of 1:0.5, placed in a muffle furnace, and calcined at 350℃ for 1 h to obtain the calcined product;

[0083] The second step of activation: The product from the first step of calcination is mixed with sodium carbonate at a mass ratio of 1:1, placed in a muffle furnace, and calcined at 800℃ for 1.5 h to obtain the alkali fusion product;

[0084] Hydrochloric acid leaching: The alkaline fusion product is added to a 6 mol / L hydrochloric acid solution, the liquid-solid ratio is controlled at 4:1, and the mixture is stirred and leached at 80℃ for 4.5 h. After leaching, the solid and liquid are separated by vacuum filtration to obtain acid leaching residue and acid leaching filtrate.

[0085] Silicon powder preparation: The acid leaching filter residue was washed with deionized water until neutral, and then dried at 108℃ for 4.0 h to obtain silicon powder (its silicon dioxide content was found to be 95.8%), and its microstructure is as follows. Figure 3 and Figure 4 As shown. (Through) Figure 2 and Figure 3 and Figure 4 The comparison shows that Figure 2 The graphite tailings particles are predominantly plate-like, with tight packing and exhibiting a relatively regular lamellar aggregation characteristic, lacking obvious pore structure and rough interfaces. After modification treatment by asynchronous alkali fusion activation-low-temperature acid leaching process, the microstructure of the prepared silicon powder undergoes a significant transformation (Figures 3 and 4). The silicon powder surface is rough and loose, forming a large number of interconnected pore structures, exhibiting typical porous morphological characteristics. Nitrogen adsorption-desorption (BET) test results show that the specific surface area of ​​this silicon powder can reach over 330 m² / g, with an average pore size of 4.0 nm, meeting the structural criteria for mesoporous materials and confirming that it possesses a typical mesoporous structure. The formation of the porous mesoporous structure of the silicon powder originates from the lattice destruction of aluminosilicate minerals in the tailings during the alkali fusion process, and the dissolution of soluble impurities by the subsequent acid leaching reaction.

[0086] Example 2

[0087] A method for extracting silicon and aluminum from industrial solid waste graphite tailings and further preparing mesoporous silica powder includes the following steps:

[0088] Raw material pretreatment: Graphite tailings (main chemical components: SiO2≥55%, Al2O3≥6.0%) are passed through a square-hole sieve with a diameter of 1.25mm to obtain graphite tailings powder; then the graphite tailings powder is dried at 105℃ for 3.0h to remove moisture and is ready for use.

[0089] First step activation: The pretreated graphite tailings powder and ammonium chloride were mixed evenly at a mass ratio of 1:0.6, placed in a muffle furnace, and calcined at 370℃ for 1 h to obtain the calcined product;

[0090] The second step of activation: The product from the first step of calcination is mixed with sodium carbonate at a mass ratio of 1:0.9, placed in a muffle furnace, and calcined at 780℃ for 1.5 h to obtain the alkali fusion product;

[0091] Hydrochloric acid leaching: The alkaline fusion product is added to a 7 mol / L hydrochloric acid solution, the liquid-solid ratio is controlled at 5:1, and the mixture is stirred and leached at 90℃ for 4.0 h. After leaching, the solid and liquid are separated by vacuum filtration to obtain acid leaching residue and acid leaching filtrate.

[0092] Silicon powder preparation: The acid leaching filter residue was washed with deionized water until neutral, and then dried at 105℃ for 4.0h to obtain silicon powder.

[0093] According to the test results, the silicon dioxide content in the silicon powder in this embodiment is 94.3%.

[0094] Example 3

[0095] Using the same process conditions as in Example 1, graphite tailings were subjected to pretreatment, asynchronous alkali fusion activation, and low-temperature acid leaching in sequence. Subsequently, the acid leaching residue and acid leaching filtrate obtained after acid leaching were subjected to further treatment.

[0096] Preparation of silica powder and soil conditioner:

[0097] The acid leaching residue was washed with deionized water until neutral, and then dried at 108℃ for 4.0 h to obtain silica powder (purity 95.8%). The silica powder and calcium hydroxide were thoroughly mixed at a molar ratio of 1:0.3, and 15% of the total mass of the mixture was added with deionized water. The mixture was stirred until a uniform slurry without obvious particle agglomeration was formed. The slurry was transferred to a high-pressure reactor and heated to 180℃. The reaction was maintained at the temperature and pressure for 5 h. After the reaction was completed, the solid-liquid separation, water washing, and drying were performed to obtain the target soil conditioner.

[0098] Regenerated alumina:

[0099] Primary precipitation: Add 20% sodium hydroxide solution at a rate of 1.0 mL / min to the acid leaching filtrate, adjust the pH of the solution to 3.0, stir for 30 min, let stand for 2 h, and then perform solid-liquid separation to remove precipitated impurities;

[0100] Deep precipitation: Add sodium hydroxide solution to the filtrate after removing impurities at a rate of 1.0 mL / min, adjust the pH of the solution to 6.8, stir for 60 min, let stand for 4 h to allow aluminum ions to fully precipitate, and then perform solid-liquid separation and water washing to obtain aluminum hydroxide precipitate;

[0101] Alumina: Aluminum hydroxide precipitate was first dried at 105℃ for 2.5 h, and then calcined at 850℃ for 2.5 h to obtain alumina product; the purity of the product was tested to be 80.1%.

[0102] The soil conditioner prepared in this embodiment was found to contain 18.3% available silicon.

[0103] Example 4

[0104] A method for extracting silicon and aluminum from industrial solid waste graphite tailings and further preparing mesoporous silica powder, soil conditioner, and recycled alumina includes the following steps:

[0105] Includes the following steps:

[0106] Raw material pretreatment: Graphite tailings (main chemical components: SiO2≥55%, Al2O3≥6.0%) are passed through a square-hole sieve with a diameter of 1.25mm to obtain graphite tailings powder; then the graphite tailings powder is dried at 105℃ for 3.0h to remove moisture and is ready for use.

[0107] First stage activation: The pretreated graphite tailings powder and ammonium chloride were mixed evenly at a mass ratio of 1:0.6, placed in a muffle furnace, and calcined at 400℃ for 1 h to obtain the calcined product;

[0108] Second stage activation: The first step alkali fusion product and sodium carbonate are mixed evenly at a mass ratio of 1:0.9, placed in a muffle furnace, and calcined at 760℃ for 2.0h to obtain the second alkali fusion product;

[0109] Hydrochloric acid leaching: Add the solution to a hydrochloric acid solution with a concentration of 8 mol / L, control the liquid-solid ratio to 5:1, stir and leach at 90℃ for 4.0 h. After leaching, use vacuum filtration to separate the solid and liquid, and obtain acid leaching residue and acid leaching filtrate.

[0110] Preparation of silica powder and soil conditioner:

[0111] The acid leaching residue was washed with deionized water until neutral, and then dried at 105°C for 4 h to obtain silicon powder (purity 94.9%).

[0112] Mix silica powder and calcium hydroxide thoroughly at a molar ratio of 1:0.4, add 15% of the total mass of deionized water, and stir until a uniform slurry without obvious particle agglomeration is formed. Transfer the slurry to a high-pressure reactor and heat it to 175°C. Maintain the temperature and pressure for 5 hours. After the reaction is completed, separate the solid and liquid, wash with water, and dry to obtain the target soil conditioner.

[0113] Primary precipitation: Add 20% sodium hydroxide solution to the acid leaching filtrate at a rate of 1.0 mL / min, adjust the pH of the solution to 3.0, stir for 40 min, and then perform solid-liquid separation to remove precipitated impurities;

[0114] Deep precipitation: Add 15% sodium hydroxide solution to the filtrate after removing impurities at a rate of 1.0 mL / min, adjust the pH of the solution to 6.8, stir for 75 min, let stand for 4 h to allow aluminum ions to fully precipitate, and then perform solid-liquid separation and water washing to obtain aluminum hydroxide precipitate.

[0115] Alumina: Aluminum hydroxide precipitate was first dried at 105℃ for 2.5 h, and then calcined at 820℃ for 3.0 h to obtain the alumina product.

[0116] The purity of alumina in this embodiment was 79.4%; the effective silicon content in the prepared soil conditioner was 17.5%.

[0117] Example 5

[0118] A method for extracting silicon and aluminum from industrial solid waste graphite tailings and further preparing mesoporous silica powder, soil conditioner, and recycled alumina includes the following steps:

[0119] Raw material pretreatment: Graphite tailings (main chemical components: SiO2≥55%, Al2O3≥6.0%) are passed through a square-hole sieve with a diameter of 1.25mm to obtain graphite tailings powder; then the graphite tailings powder is dried at 105℃ for 3.0h to remove moisture and is ready for use.

[0120] First step activation: The pretreated graphite tailings powder and ammonium chloride are mixed evenly at a mass ratio of 1:0.5, placed in a muffle furnace, and calcined at 380℃ for 40 min to obtain the calcined product;

[0121] The second step of activation: The product activated in the first step is mixed with sodium carbonate at a mass ratio of 1:1.1, placed in a muffle furnace, and calcined at 810℃ for 1.5 h to obtain the alkali fusion product;

[0122] Hydrochloric acid leaching: The alkaline fusion product is added to a 7 mol / L hydrochloric acid solution, the liquid-solid ratio is controlled at 4:1, and the mixture is stirred and leached at 90℃ for 4.0 h. After leaching, the solid and liquid are separated by vacuum filtration to obtain acid leaching residue and acid leaching filtrate.

[0123] Preparation of silica powder and soil conditioner: The acid leaching filter residue was washed with deionized water until neutral, and then dried at 110℃ for 4.0h to obtain silica powder (purity 95.1%).

[0124] Mix silica powder and calcium hydroxide thoroughly at a molar ratio of 1:0.4, add 18% of the total mass of deionized water, and stir until a uniform slurry without obvious particle agglomeration is formed. Transfer the slurry to a high-pressure reactor and heat it to 170°C. Maintain the temperature and pressure for 6 hours. After the reaction is completed, separate the solid and liquid, wash with water, and dry to obtain the target soil conditioner.

[0125] Regenerated alumina:

[0126] Primary precipitation: Add 20% sodium hydroxide solution to the acid leaching filtrate at a rate of 1.0 mL / min, adjust the pH of the solution to 3.2, stir for 30 min, let stand for 3 h, and then perform solid-liquid separation to remove precipitated impurities;

[0127] Deep precipitation: Add sodium hydroxide solution to the filtrate after removing impurities at a rate of 1.0 mL / min, adjust the pH of the solution to 6.6, stir for 50 min, let stand for 12 h to allow aluminum ions to fully precipitate, and then perform solid-liquid separation and water washing to obtain aluminum hydroxide precipitate;

[0128] Alumina: Aluminum hydroxide precipitate was first dried at 110℃ for 3.0 h, and then calcined at 830℃ for 2.0 h to obtain alumina product; the purity of the product was tested to be 80.7%.

[0129] The soil conditioner prepared in this embodiment was found to contain 18.7% available silicon.

[0130] Comparative Example 1

[0131] The difference from Example 1 is that in the asynchronous alkaline fusion activation process, the mass ratio of ammonium chloride to graphite tailings in the first stage of initial activation is 0.2:1, while other conditions remain unchanged.

[0132] The purity of the obtained silicon powder was 89.3%.

[0133] Comparative Example 2

[0134] The difference from Example 1 is that the asynchronous alkali fusion activation is not used; instead, sodium carbonate is used for activation. Specifically, sodium carbonate is directly added to the graphite tailings, and the sodium carbonate and graphite tailings are mixed evenly at a mass ratio of 1:1. The mixture is then calcined at 800°C for 1.5 h to obtain the alkali fusion product. All other conditions are the same.

[0135] The purity of the obtained silicon powder was 85.4%.

[0136] Comparative Example 3

[0137] The difference from Example 2 is that when sodium carbonate is used for alkali fusion activation in asynchronous alkali fusion activation, the activation temperature is 650°C, while all other conditions are the same.

[0138] The purity of the obtained silicon powder was 88.1%.

[0139] Comparative Example 4

[0140] The difference from Example 2 is that the concentration of hydrochloric acid in the low-temperature acid leaching is 2 mol / L, while all other conditions are the same.

[0141] The purity of the obtained silicon powder was 75.9%.

[0142] Comparative Example 5

[0143] The preparation of soil conditioner using silica powder was carried out under hydrothermal conditions. A comparative analysis was also conducted on preparations not carried out in a high-pressure reactor, i.e., preparations under normal pressure conditions. The difference from Example 5 is that when preparing soil conditioner using silica powder and calcium hydroxide, the process was directly refluxed at 170°C in an oil bath; all other conditions were the same as in Example 5.

[0144] The obtained soil conditioner has an effective silicon content of <10%.

Claims

1. A method for simultaneously extracting silicon and aluminum from graphite tailings, comprising: 1) Asynchronous alkaline melting: The first stage is low-temperature calcination: ammonium salt is mixed with graphite tailings and calcined at 250℃~500℃ for 0.5h~2.0h to obtain primary activated product a; The second stage of high-temperature calcination: the primary activated product a is mixed with an alkaline activating agent and calcined at 700℃~900℃ for 1.0 h~3.0 h to obtain the alkali fusion product b; 2) Low temperature acid leaching: The alkaline fusion product b obtained in 1) is immersed in an acid solution with a concentration of 3 mol / L to 9 mol / L and stirred at 60℃ to 100℃ for 3.0 h to 8.0 h to obtain the acid leaching product c. 3) Solid-liquid separation: The acid leaching product c obtained in 2) is separated by filtration to obtain an aluminum-rich acid leaching filtrate and a silicon-rich acid leaching residue.

2. The method as described in claim 1, characterized in that: Step 1) The ammonium salt used in the first stage of low-temperature calcination is any one or a mixture of two or more of ammonium chloride, ammonium sulfate, and ammonium bicarbonate; in a preferred embodiment, the ammonium salt used in the first stage of low-temperature calcination is ammonium chloride, and the mass ratio of ammonium chloride to graphite tailings is controlled at (0.3 - 0.8):1; in a more preferred embodiment, the mass ratio of ammonium chloride to graphite tailings is controlled at (0.4-0.6):

1.

3. The method as described in claim 1, characterized in that: Step 1) The specific scheme for the first stage of low-temperature calcination is to calcine at 350℃~420℃ for 0.5h~2.0h; preferably, calcination at 350℃~400℃ for 0.5h~1.0h.

4. The method as described in claim 1, characterized in that: In step 1), the alkaline activating agent used in the second stage of high-temperature calcination is any one or a mixture of two or more of sodium carbonate, sodium hydroxide, calcium hydroxide, or calcium carbonate; in a preferred embodiment, the alkaline activating agent used in the second stage of high-temperature calcination is sodium carbonate, and the mass ratio of sodium carbonate to primary activation product a is controlled at (0.6-1.5):1; in a more preferred embodiment, the mass ratio of sodium carbonate to primary activation product a is controlled at (0.8-1.2):

1.

5. The method as described in claim 1, characterized in that: Step 1) The specific scheme for the second stage of high-temperature calcination is to calcine at 750℃~830℃ for 1.0 h~3.0 h; more preferably, to calcine at 800℃~820℃ for 1.5 h~2.5 h.

6. The method as described in claim 1, characterized in that: Step 2) Low-temperature acid leaching: The acid solution is any one or a mixture of two or more of hydrochloric acid, sulfuric acid, hydrofluoric acid or nitric acid; in a preferred embodiment, the acid solution in step 2) low-temperature acid leaching is hydrochloric acid, and the mass-volume ratio of the hydrochloric acid to the alkali fusion product b is 1:(2-10) g / mL; more preferably 1:(3-6) g / mL.

7. The method as described in claim 1, characterized in that: Step 2) Low-temperature acid leaching: The proposed method is to stir and react at 75℃~95℃ for 3.0 h~8.0 h; preferably, stir and react at 80℃~90℃ for 4.0 h~5.0 h.

8. A method for preparing a soil conditioner using graphite tailings as raw material, characterized in that, include: A. Using graphite tailings as raw material, an acid leaching residue rich in silicon is prepared according to any one of claims 1-7. The acid leaching residue is washed until neutral and dried, and then pulverized to a fineness of not less than 200 mesh to obtain mesoporous silica powder. B. Mix the mesoporous silica powder obtained in A with calcium hydroxide to obtain a calcium-silicon mixture. Control the molar ratio of calcium to silicon in the calcium-silicon mixture to be 0.3-0.5:

1. Then add water to the calcium-silicon mixture and carry out a hydrothermal reaction at a temperature of 150℃~200℃ (preferably 160℃~180℃) and a pressure of 0.2-0.5MPa for 3~10 h (preferably 4~7 h) to obtain a calcium-silicon based soil conditioner.

9. A method for preparing alumina from graphite tailings, characterized in that: First, using graphite tailings as raw material, an aluminum-rich acid leaching filtrate is prepared according to the method described in any one of claims 1-7; then, aluminum hydroxide solid is obtained by precipitation and separation using a stepwise precipitation method; and finally, the obtained aluminum hydroxide solid is calcined at high temperature to obtain alumina powder.

10. The method as described in claim 9, characterized in that, The process of obtaining solid aluminum hydroxide by precipitation and separation via a step-by-step precipitation method includes: Primary precipitation: Add sodium hydroxide solution dropwise to the acid leaching filtrate at a rate of 1-2 mL / min while stirring at a speed of 200-250 r / min. Adjust the pH of the system to 3.0-3.5, stir for 30-60 min, let stand for more than 2 h, and then perform solid-liquid separation to remove precipitated impurities. Deep precipitation: Add sodium hydroxide solution to the filtrate after removing impurities, adjust the pH of the system to 6.5-7.5, maintain the stirring rate, and stir for 40-90 min to allow aluminum ions to fully precipitate. Then perform solid-liquid separation to obtain aluminum hydroxide precipitate.

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