A method for synthesizing nontronite mesoporous materials using coal gangue leaching solution

Abstract

The present invention discloses a method for synthesizing nontronite mesoporous materials using coal gangue leaching solution. In this method, coal gangue is transformed into silicate minerals through calcination treatment, and then metal ions are dissolved out through acid etching treatment. While obtaining silicon oxide, a leaching solution containing various metal ions is obtained. By adjusting the ion composition and pH value, under the action of organic additives, the metal ions in the acid leaching solution can be transformed into nontronite mesoporous materials, ultimately achieving the goal of fully utilizing all components of coal gangue to prepare a variety of new products. The prepared nontronite mesoporous materials can be used for the adsorption of various substances such as mycotoxins, heavy metals, dyes, and antibiotics, and have broad application prospects in wastewater purification and adsorption separation.

Description

Technical Field

[0001] The present invention relates to a method for synthesizing nontronite mesoporous materials using coal gangue leaching solution, belonging to the technical fields of solid waste treatment, deep processing of non-metallic minerals, and synthesis of porous materials. Background Art

[0002] Coal gangue is a solid waste generated during coal production and processing. China is the largest coal-producing country in the world. The amount of coal gangue generated during coal production or coal washing each year reaches about 15% of the annual coal output. Currently, the cumulative stockpile has exceeded 7 billion tons, making it one of the largest industrial solid waste emissions in China. Due to the long-term stacking of coal gangue, it will occupy a large amount of land, and it will also cause harm to the ecological environment such as the atmosphere, water bodies, and soil due to spontaneous combustion, acid rain, and underground seepage. Currently, the treatment methods for coal gangue discharged from most coal mines are relatively simple, still mainly backfilling, stacking, or burying, which not only occupy land but also are prone to spontaneous combustion, posing a great threat to the normal production of mines and the production and living of surrounding residents. Therefore, it is urgent to develop new technologies for the resource utilization of coal gangue solid waste.

[0003] Coal gangue contains clay minerals represented by kaolinite (such as montmorillonite, illite, kaolinite, muscovite, quartz, feldspar, etc.), so coal gangue is also a natural mineral resource with rich reserves. In recent years, the development of coal gangue utilization technologies has been a research hotspot. Chinese Patent CN202110297963.2 discloses a leaching method for sintered products of coal measure kaolinite clay rock. By adding water to stir the sintered coal gangue, separating the water leaching residue and adding HCl solution, stirring, and separating the acid leaching residue and acid leaching filtrate, the leaching of rare metals and rare earth elements is completed. Chinese Patent CN113735131A discloses a method for efficiently preparing water glass using coal gangue. The water glass is prepared by activating coal gangue, acid leaching, separating and purifying silicon, and mixing with alkali solution for heating. The coal gangue is activated by mixing with potassium carbonate or potassium hydroxide under heating conditions. Most of the silicon can be dissolved in the acid leaching solution of coal gangue with a lower concentration of hydrochloric acid. In the process of separating and purifying silicon, potassium fluoride is selected to react with the acid leaching solution of coal gangue. Chinese Patent CN112978734A discloses a method for extracting carbon and silicon dioxide from coal gangue. The coal gangue is crushed and ground; the crushed and ground coal gangue is activated under supercritical water or subcritical water conditions; the activated coal gangue is separated by a separation device into an organic liquid phase and a solid slag phase; the solid slag phase is screened by a shaking table to separate out an enrichment containing carbon and silicon dioxide, as well as silicate and impurities; the enrichment containing carbon and silicon dioxide is subjected to electrostatic separation to obtain carbon and silicon dioxide products. These patented technologies utilize conventional methods such as blending, calcination, and acid leaching to utilize coal gangue, but the technology for fully utilizing all components of coal gangue to synthesize new materials is still very limited. From the analysis results of the mineral structure, the mineral components in coal gangue are composed of SiO4 Tetrahedron and MO 6 The octahedron is connected by Si-O-Si or Si-O-M bonds. That is, by changing the combination mode of the smallest structural units (i.e., Si-O-Si and Si-O-M), which is defined as the "gene" of the mineral, new materials with diverse morphologies and properties can be obtained. Through a large number of experimental studies, the applicant found that after acid leaching treatment of coal gangue, not only silica materials can be obtained, but also its leaching solution can be used to synthesize nontronite mesoporous materials, and this technical result has not been reported in the literature and there is no application precedent at present. Summary of the Invention

[0004] The object of the present invention is to provide a method for synthesizing nontronite mesoporous materials using the leaching solution of coal gangue. This method is to convert coal gangue into silicate minerals through calcination treatment, and then dissolve out metal ions through acid corrosion treatment. While obtaining silica, a leaching solution containing various metal ions is obtained. By adjusting the ion composition and pH value, and under the action of an organic assistant, the metal ions in the acid leaching solution can be transformed into nontronite mesoporous materials, ultimately achieving the goal of fully utilizing all components of coal gangue to prepare a variety of new products.

[0005] The present invention adopts the following technical solutions:

[0006] A method for synthesizing nontronite mesoporous materials using the leaching solution of coal gangue, comprising the following steps:

[0007] (1) Crushing coal gangue into powder, calcining at a temperature of 500 - 1000 °C for 1 - 10 h to obtain silicate minerals; the content of kaolinite in the silicate minerals is not less than 45%, and the content of Fe 2 O 3 is not less than 5%.

[0008] (2) Disperse the silicate minerals obtained in step (1) into an aqueous solution of acid according to a solid-liquid mass ratio of 1:3 - 1:30, and then pass through a vibrating screen with 120 - 800 meshes to remove large particles that are not dispersed, to obtain a uniform suspension; the acid is one of sulfuric acid, hydrobromic acid, hydrochloric acid, nitric acid, oxalic acid, phosphoric acid, citric acid, malic acid, tartaric acid, and the molar concentration of the aqueous solution of the acid is 0.1 - 5 mol / L.

[0009] (3) Transfer the suspension obtained in step (2) into a reaction kettle, react at a temperature of 100 - 300 °C and a pressure of 1 - 10 MPa for 4 - 36 h, and then perform solid-liquid separation to obtain solid silica and a leaching solution; the solid silica is collected as a product; the leaching solution is used to synthesize nontronite porous materials.

[0010] (4) Add a magnesium salt to the leaching solution obtained in step (3), adjust the pH value of the solution to 2 - 8, then add soluble silicate and an organic auxiliary agent, stir well, and conduct a hydrothermal reaction at a temperature of 100 - 300 °C for 2 - 24 h. Filter, wash and dry the obtained solid product to obtain a nontronite mesoporous material.

[0011] The magnesium salt is at least one of magnesium carbonate, magnesium hydroxide, magnesium oxide, basic magnesium carbonate, dolomite, magnesium chloride, magnesium stearate, magnesium sulfate, magnesium nitrate, and magnesium acetate, and the addition amount is 1.5 - 30% of the mass of the leaching solution.

[0012] The soluble silicate is at least one of sodium silicate, potassium silicate, lithium silicate, and sodium potassium silicate, and the addition amount is 50 - 300% of the total molar amount of the added alkaline metal compound and metal salt.

[0013] The organic auxiliary agent is at least one of tetramethylethylenediamine and tetramethylammonium hydroxide, and the addition amount is 1 - 10% of the molar amount of the soluble silicate.

[0014] The synthesis mechanism of the present invention: Through heat treatment, coal gangue is transformed into a silicate mineral containing kaolinite; on the premise of maintaining the silica skeleton structure and morphology unchanged, metal ions in the silicate mineral are dissolved out with acid to obtain silica nanosheets and an acid leaching solution rich in various metal ions. By adding an alkaline metal salt to neutralize the excessive acid in the leaching solution, adjusting the pH of the solution, then supplementing metal salts to regulate the metal ion composition in the solution, and then reacting with soluble silicate, under the assistance of an organic auxiliary agent, a nontronite mesoporous material is synthesized through a one-step hydrothermal reaction.

[0015] In summary, the present invention uses the acid leaching waste liquid of solid waste coal gangue as the main raw material, under the condition of precisely controlling the ion ratio and pH value, and through a simple one-step hydrothermal reaction, the enriched metal elements are transformed into pure-phase nontronite with a honeycomb shape. The nontronite has good batch stability and uniform particle size, and the preparation process is simple, which can effectively convert coal gangue solid waste into high-value-added products, achieving a new goal of converting solid waste into materials. And the prepared nontronite mesoporous material can be used for the adsorption of various substances such as mycotoxins, heavy metals, dyes, and antibiotics, and has broad application prospects in wastewater purification and adsorption separation. Description of the Drawings

[0016] Figure 1 It is the XRD pattern of the calcined coal gangue used in the present invention, the nontronite mesoporous material synthesized in Example 2, and the nontronite mesoporous material synthesized in Example 3.

[0017] Figure 2 It is the SEM image of the nontronite mesoporous material prepared in Example 2 of the present invention.

[0018] Figure 3SEM image of the nontronite mesoporous material prepared in Example 3 of the present invention

[0019] Figure 4 Adsorption - desorption isotherm and pore structure distribution curve of the nontronite mesoporous material prepared in Example 2 of the present invention Detailed implementation manners

[0020] The present invention will be further explained below with reference to the accompanying drawings and specific embodiments.

[0021] Example 1

[0022] (1) Coal gangue (kaolinite content not less than 45%; Fe 2 O 3 content not less than 5%) was crushed into powder and calcined at 500 °C for 1 h to obtain layered silicate minerals.

[0023] (2) 4.0 g of the calcined silicate minerals were dispersed in an aqueous solution of 0.1 mol / L citric acid according to a solid - liquid mass ratio of 1:3, and then passed through a 120 - mesh vibrating sieve to remove undispersed large particles, obtaining a uniform suspension.

[0024] (3) The obtained suspension was transferred to a reaction kettle and reacted at 100 °C and 1 MPa for 4 h to obtain a mixed product containing solids and liquids.

[0025] (4) The above - obtained mixed product was subjected to solid - liquid separation. The solid was collected as the product, and the liquid was used as the precursor solution and reaction medium for synthesizing nontronite.

[0026] (5) 0.24 g of magnesium nitrate was added to 12.0 g of the leaching solution, the pH value of the solution was adjusted to 2, and then 0.36 g of sodium potassium silicate and 0.02 g of tetramethylethylenediamine were added. After stirring evenly, the reaction was carried out at 100 °C for 2 h. The obtained solid product was collected, washed, and dried to obtain nontronite mesoporous material.

[0027] Example 2

[0028] (1) Coal gangue (kaolinite content not less than 45%; Fe 2 O 3 content not less than 5%) was crushed into powder and calcined at 800 °C for 4 h to obtain layered silicate minerals.

[0029] (2) 4.0 g of the calcined silicate minerals were dispersed in an aqueous solution of 2.0 mol / L hydrochloric acid according to a solid - liquid mass ratio of 1:15, and then passed through a 200 - mesh vibrating sieve to remove undispersed large particles, obtaining a uniform suspension.

[0030] (3) Transfer the obtained suspension into a closed reactor, and react it at a temperature of 160 °C and a pressure of 6 MPa for 8 h to obtain a mixed product containing solids and liquids.

[0031] (4) Separate the solid and liquid of the above-obtained mixed product. Collect the solid as the product, and use the liquid as the precursor solution and reaction medium for synthesizing nontronite.

[0032] (5) Add 0.9 g of magnesium oxide to 60.0 g of the leaching solution, adjust the pH value of the solution to 4, then add 1.58 g of sodium silicate and 0.04 g of tetramethylethylenediamine, stir well, react at a temperature of 180 °C for 8 h, collect the obtained solid product, wash it, and dry it to obtain nontronite mesoporous material.

[0033] Example 3

[0034] (1) Crush the coal gangue (the content of kaolinite is not less than 45%; the content of Fe 2 O 3 is not less than 5%) into powder, and calcine it at a temperature of 800 °C for 4 h to obtain layered silicate minerals.

[0035] (2) Disperse 4.0 g of the calcined silicate minerals into an aqueous solution of 2.0 mol / L oxalic acid according to a solid-liquid mass ratio of 1:15, and then pass it through a 200-mesh vibrating screen to remove the undispersed large particles to obtain a uniform suspension.

[0036] (3) Transfer the obtained suspension into a closed reactor, and react it at a temperature of 160 °C and a pressure of 6 MPa for 8 h to obtain a mixed product containing solids and liquids.

[0037] (4) Separate the solid and liquid of the above-obtained mixed product. Collect the solid as the product, and use the liquid as the precursor solution and reaction medium for synthesizing nontronite.

[0038] (5) Add 0.9 g of magnesium oxide to 60.0 g of the leaching solution, adjust the pH value of the solution to 4, then add 1.58 g of sodium silicate and 0.04 g of tetramethylethylenediamine, stir well, react at a temperature of 180 °C for 8 h, collect the obtained solid product, wash it, and dry it to obtain nontronite mesoporous material.

[0039] Example 4

[0040] (1) Crush the coal gangue (the content of kaolinite is not less than 45%; the content of Fe 2 O 3 is not less than 5%) into powder, and calcine it at a temperature of 900 °C for 8 h to obtain layered silicate minerals.

[0041] (2) Disperse 4.0 g of the calcined silicate mineral into an aqueous solution of 3.0 mol / L oxalic acid according to a solid-liquid mass ratio of 1:22, and then pass it through a 500-mesh vibrating screen to remove the undispersed large particles, obtaining a homogeneous suspension.

[0042] (3) Transfer the obtained suspension into a closed reactor and react it at a temperature of 160 °C and a pressure of 8 MPa for 25 h to obtain a mixed product containing solid and liquid.

[0043] (4) Perform solid-liquid separation on the above-obtained mixed product, collect the solid as the product, and use the liquid as the precursor solution and reaction medium for synthesizing nontronite.

[0044] (5) Add 3.6 g of magnesium oxide to 90.0 g of the leaching solution, adjust the pH value of the solution to 6, and then add 93.6 g of potassium silicate and 2.19 g of tetramethylethylenediamine, stir well, and react at a temperature of 100 °C for 15 h. Collect, wash, and dry the obtained solid product to obtain nontronite mesoporous material.

[0045] Example 5

[0046] (1) Crush coal gangue (kaolinite content not less than 45%; Fe 2 O 3 content not less than 5%) into powder, and calcine it at a temperature of 1000 °C for 10 h to obtain a layered silicate mineral.

[0047] (2) Disperse 4.0 g of the calcined silicate mineral into an aqueous solution of 4.0 mol / L sulfuric acid according to a solid-liquid mass ratio of 1:30, and then pass it through a 700-mesh vibrating screen to remove the undispersed large particles, obtaining a homogeneous suspension.

[0048] (3) Transfer the obtained suspension into a closed reactor and react it at a temperature of 200 °C and a pressure of 8 MPa for 30 h to obtain a mixed product containing solid and liquid.

[0049] (4) Perform solid-liquid separation on the above-obtained mixed product, collect the solid as the product, and use the liquid as the precursor solution and reaction medium for synthesizing nontronite.

[0050] (5) Add 20 g of magnesium carbonate to 100.0 g of the leaching solution, adjust the pH value of the solution to 4, and then add 360 g of lithium silicate and 7.29 g of tetramethylammonium hydroxide, stir well, and react at a temperature of 200 °C for 20 h. Collect, wash, and dry the obtained solid product to obtain nontronite mesoporous material.

[0051] Example 6

[0052] (1) Coal gangue (kaolinite content not less than 45%; Fe 2O 3 with a content of not less than 5%) is pulverized into powder and calcined at 1000 °C for 10 h to obtain a layered silicate mineral.

[0053] (2) 4.0 g of the calcined silicate mineral is dispersed in an aqueous solution of 5.0 mol / L citric acid according to a solid-liquid mass ratio of 1:30, and then passed through an 800-mesh vibrating sieve to remove undispersed large particles to obtain a uniform suspension.

[0054] (3) The obtained suspension is transferred into a closed reactor and reacted at 300 °C and 10 MPa for 36 h to obtain a mixed product containing solid and liquid.

[0055] (4) The above-obtained mixed product is subjected to solid-liquid separation, and the solid is collected as the product, and the liquid is used as the precursor solution and reaction medium for synthesizing nontronite.

[0056] (5) 36 g of magnesium sulfate is added to 120.0 g of the leaching solution, the pH value of the solution is adjusted to 8, and then 624 g of potassium silicate and 22.89 g of tetramethylammonium hydroxide are added, stirred well, and reacted at 300 °C for 24 h. The obtained solid product is collected, washed, and dried to obtain nontronite mesoporous material.

[0057] Comparative Example 1

[0058] The difference between Comparative Example 1 and Example 2 is only that: sodium silicate is not added in Comparative Example 1, and the other parameters are the same.

[0059] Comparative Example 2

[0060] The difference between Comparative Example 2 and Example 2 is only that: magnesium salt is not added in Comparative Example 2, and the other parameters are the same.

[0061] The comparison of the adsorption effects of the products prepared in Examples 1-6 and Comparative Examples 1-2 on different pollutants is shown in Table 1 below:

[0062] Table 1 Saturated adsorption capacities (mg / g) of the products prepared in Examples 1-6 and Comparative Examples 1-2 for methylene blue, Pb(II), Cu(II), doxycycline hydrochloride, and phosphate

[0063]

[0064] As can be seen from Table 1, the adsorption capacity of the nontronite mesoporous material prepared by the present invention for the organic dye methylene blue reaches 349.21 - 387.82 mg / g, the adsorption capacity for the heavy metal Pb(II) reaches 420.12 - 453.98 mg / g, the adsorption capacity for Cu(II) reaches 219.86 - 229.54 mg / g, the adsorption capacity for doxycycline hydrochloride reaches 456.39 - 486.19 mg / g, and the adsorption capacity for phosphate reaches 287.89 - 298.67 mg / g. These adsorption capacities are significantly higher than those of the calcined coal gangue and the products prepared in Comparative Example 1 and Comparative Example 2. This proves that the nontronite mesoporous material prepared by the present invention has high adsorption performance and is effective in treating environmental pollutants.

[0065] Taking the pure-phase nontronite prepared in Example 2 as an example, the structure of the nontronite synthesized by the present invention will be analyzed and described below.

[0066] Figure 1 XRD patterns of the calcined coal gangue, the nontronite mesoporous material synthesized in Example 2, and the nontronite mesoporous material synthesized in Example 3 are shown. From Figure 1 It can be seen that the main mineral components of the calcined coal gangue are quartz and mullite. After acid treatment and hydrothermal synthesis reaction, the diffraction peaks of quartz and mullite disappear, and the obtained product is a pure crystalline phase of nontronite. The XRD pattern shows that the 2θ values of the characteristic diffraction peaks of nontronite are 19.54°, 34.21°, and 60.40°.

[0067] Figure 2 SEM image of the nontronite mesoporous material prepared in Example 2 is shown. From Figure 2 It can be seen that the obtained product is a pure-phase nontronite with a honeycomb-like morphology. Comparing Figure 2 the SEM image of the chlorite mesoporous material shown with the SEM image of the product prepared in Example 3 (using oxalic acid as the etching solution, Figure 3 ), it is found that the nontronite mesoporous material synthesized using oxalic acid etching solution as the raw material does not have a honeycomb-like morphology, the specific surface area of the material is relatively small (175.069 m 2 / g), and the exposed adsorption sites are fewer.

[0068] Figure 4 Nitrogen adsorption - desorption isotherm and pore size distribution curve of the nontronite mesoporous material prepared in Example 2 are shown. It can be seen that the pore structure of the nontronite mesoporous material is mainly mesoporous, the center position of the pore size distribution peak is at 4.06 nm, and it is a mesoporous material. After calculation, the specific surface area of the nontronite mesoporous material is 304.95 m 2 / g, and the pore volume is 0.27 cm 3 / g, with an average pore size of 3.48 nm. The porous structure is conducive to the ability of nontronite to quickly and efficiently capture organic molecules or ions, improving the adsorption rate and adsorption capacity of nontronite for target molecules or ions.

[0069] In summary, the present invention uses the acid leaching waste liquid of solid waste coal gangue as the main raw material. Under the condition of precisely controlling the ion ratio and pH value, the enriched metal elements are transformed into pure-phase nontronite with a honeycomb structure through a simple one-step hydrothermal reaction. The nontronite has good batch stability and uniform particle size. The preparation process is simple, which can effectively convert coal gangue solid waste into high-value-added products, achieving a new goal of converting solid waste into materials.

Claims

1. A method for synthesizing nontronite mesoporous materials using coal gangue leaching solution, characterized in that, it includes the following steps: (1) Crush coal gangue into powder, calcine it at a temperature of 500 - 1000 °C for 1 - 10 h to obtain silicate minerals; (2) Disperse the silicate minerals obtained in step (1) into an aqueous solution of acid according to a solid-liquid mass ratio of 1:3 - 1:30, and then pass through a 120 - 800 mesh vibrating screen to remove undispersed large particles to obtain a uniform suspension; (3) Transfer the suspension obtained in step (2) into a reaction kettle, react at a temperature of 100 - 300 °C and a pressure of 1 - 10 MPa for 4 - 36 h, and then perform solid-liquid separation to obtain solid silica and leaching solution; (4) Add magnesium salt to the leaching solution obtained in step (3), adjust the pH value of the solution to 2 - 8, then add soluble silicate and organic additives, stir well, perform hydrothermal reaction at a temperature of 100 - 300 °C for 2 - 24 h, filter, wash and dry the obtained solid product to obtain nontronite mesoporous materials; The magnesium salt is at least one of magnesium carbonate, magnesium hydroxide, magnesium oxide, basic magnesium carbonate, magnesium chloride, magnesium stearate, magnesium sulfate, magnesium nitrate, magnesium acetate, and the addition amount is 1.5 - 30% of the mass of the leaching solution; The soluble silicate is at least one of sodium silicate, potassium silicate, lithium silicate, potassium sodium silicate, and the addition amount is 50 - 300% of the total molar amount of the added alkaline metal compounds and metal salts; The organic additive is at least one of tetramethylethylenediamine, tetramethylammonium hydroxide, and the addition amount is 1 - 10% of the molar amount of the soluble silicate.

2. The method for synthesizing nontronite mesoporous materials using coal gangue leaching solution as described in claim 1, characterized in that, The content of kaolinite in the silicate minerals obtained after calcining the coal gangue is not less than 45%, and the content of Fe 2 O 3 is not less than 5%.

3. The method for synthesizing nontronite mesoporous materials using coal gangue leaching solution as described in claim 1, characterized in that, The acid is at least one of sulfuric acid, hydrobromic acid, hydrochloric acid, nitric acid, oxalic acid, phosphoric acid, citric acid, malic acid, tartaric acid, and the molar concentration of the aqueous solution of the acid is 0.1 - 5 mol / L.

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