Method for preparing calcined kaolin from coal gangue

Abstract

The invention relates to the technical field of coal gangue treatment, in particular to a method for preparing calcined kaolin from coal gangue, which at least comprises the following steps: S01, taking coal gangue, crushing, magnetically separating, wet-grinding, and pulping to obtain a pulped material; s02, taking the chemical slurry, adding acid to adjust the pH value, then adding a compound chelating agent for continuous treatment, then filtering, and drying a filtered and collected material to obtain a refined material; s03, taking the refined material, and performing calcination treatment to obtain calcined kaolin; the compound chelating agent is prepared by mixing the following raw materials in parts by mass: 20-30 parts of modified chitosan, 10-20 parts of erythorbic acid, 5-10 parts of oxalic acid, 20-30 parts of water and 3-5 parts of polyepoxysuccinic acid. When the compound chelating agent is used for treating coal gangue slurry, the removal rate of iron ions is greater than or equal to 95.7%, and the whiteness of the prepared calcined kaolin can reach 99.1%.

Description

Technical Field

[0001] This application relates to the field of coal gangue processing technology, and in particular to a method for preparing calcined kaolin from coal gangue. Background Technology

[0002] Coal gangue is a solid waste generated during coal mining and washing. Its main mineral components include kaolinite and quartz. With proper treatment, it can be transformed into high-value-added calcined kaolin, thereby realizing the reuse of waste resources.

[0003] The process of preparing calcined kaolin from coal gangue mainly includes crushing, grinding, impurity removal, calcination, and classification. However, coal gangue raw materials often contain iron impurities, which form colored oxides during high-temperature calcination, significantly reducing the whiteness of the product and affecting its application value. Therefore, iron removal is a key step in improving the quality of calcined kaolin.

[0004] Currently, commonly used industrial methods for iron removal include acid leaching and chemical reduction. Acid leaching uses acidic solutions such as hydrochloric acid, sulfuric acid, or oxalic acid to dissolve iron compounds, then removes iron ions through solid-liquid separation. Chemical reduction, on the other hand, uses sulfur-containing reducing agents such as sodium dithionite to reduce sparingly soluble ferric iron (Fe3+) to soluble ferrous iron (Fe2+), followed by washing to remove iron ions. However, the sulfur-containing reducing agents used in chemical reduction easily generate harmful gases such as sulfur dioxide, causing secondary pollution, and the wastewater treatment cost is high. In contrast, acid leaching is simple, environmentally friendly, and effectively removes iron impurities, making it the mainstream technology for iron removal from coal gangue.

[0005] Patent application CN110369457A discloses a method for processing coal gangue and its application. The method employs a combination of various mixed acids and mixed bacteria to biologically treat raw coal gangue ore, which can significantly reduce the iron content in the coal gangue, resulting in a coal gangue product with low iron content.

[0006] Although the above-mentioned scheme can significantly reduce the iron residue in coal gangue by combining biochemical and inorganic acid treatment, the mixed bacteria used in the scheme have a long iron removal cycle. This makes the free iron ions generated after iron removal easily attracted by the particles in the treatment liquid and undergo re-adsorption, which is detrimental to the iron removal process. Therefore, it is necessary to find a method for preparing calcined kaolin from coal gangue that can efficiently remove iron from coal gangue, inhibit iron ion re-adsorption, and improve the whiteness of calcined kaolin products. Summary of the Invention

[0007] In view of the shortcomings of the prior art described above, the purpose of this application is to provide a method for preparing calcined kaolin from coal gangue, which solves the problem of incomplete iron removal and low removal efficiency in the early stage of coal gangue in the prior art.

[0008] To achieve the above and other related objectives, this application is obtained through the following technical solution.

[0009] This application provides a method for preparing calcined kaolin from coal gangue, comprising at least the following steps: S01. Take coal gangue, crush it, magnetically separate it, wet grind it, and then process it into a slurry to obtain a slurry material; S02. Take the slurry, add acid to adjust the pH, then add a compound chelating agent for further treatment, filter, and dry the filtrate to obtain the refined material; S03. Take refined materials, calcine them to obtain calcined kaolin; The compound chelating agent is prepared by mixing the following raw materials in parts by weight: 20-30 parts modified chitosan, 10-20 parts isoascorbic acid, 5-10 parts oxalic acid, 20-30 parts water, and 3-5 parts polyepoxysuccinic acid. In step S01, the magnetic separation magnetic field strength is set to 0.25-0.28T; The water-to-material ratio for the pulping process is controlled at (2-3):1; In step S02, the amount of compound chelating agent added is 200-220 mg / L; In step S03, the calcination treatment is performed by setting the temperature to 850-900℃ and treating for 3-4 hours.

[0010] By adopting the above technical solution, free ferric ions in the acidified slurry are reduced to more stable ferrous ions under the action of isoascorbic acid, which has a reducing effect. At the same time, isoascorbic acid is oxidized to obtain 2,3-diketone-L-gulonic acid, an open-ring oxidation product containing a carboxyl group. The isoascorbic acid oxidation product, combined with modified chitosan, can form a stable chelate structure with the reduced ferrous ions. The ferrous ions exist stably in the liquid phase of the slurry in the form of coordination compounds. In the subsequent filtration operation, the coordinated ferrous ions are removed from the crushed coal gangue with the partial overflow of the liquid phase. In addition, the chelate structure provides greater steric hindrance, which can inhibit the re-adsorption of ferrous ions caused by the attraction of slurry particles. In the calcined kaolin product, ferrous ions can be removed to the maximum extent.

[0011] In some embodiments of this application, the preparation steps of the modified chitosan include the following: (1). Take 4-hydroxyphenylboronic acid, disperse it with dimethyl sulfoxide, heat it and add epichlorohydrin, react it, then adjust the pH, extract it, and rotary evaporate it to obtain product A; (2). Take product A and ethylene glycol, add a mixed solvent to disperse, react, and then purify to obtain product B; (3). Take chitosan and disperse it in 3%-4% acetic acid to obtain solution C; (4) Take product B and disperse it in phosphate buffer to obtain solution D; (5) Mix solution C with solution D, heat to react, then readjust the pH, and purify to obtain modified chitosan; In step (1), the ratio of 4-hydroxyphenylboronic acid, dimethyl sulfoxide and epichlorohydrin is (1.38-1.67)g:(20-30)mL:(2.23-2.78)g; In step (2), the mixed solvent is prepared by mixing p-toluenesulfonic acid, acetic acid and toluene in a ratio of (0.5-0.6)g:(3-4)mL:(30-40)mL; The mass ratio of chitosan to product B is (3.24-4.86):(1.1-2.2).

[0012] By adopting the above technical solution, 4-hydroxyphenylboronic acid undergoes nucleophilic substitution with epichlorohydrin to generate epoxidized product A. Subsequently, the boric acid group on product A reacts with ethylene glycol in an acidic mixed solvent to obtain product B protected by borate ester group, so as to avoid the boric acid group on product A being consumed in the early stage of the reaction. The epoxy group of product B undergoes ring opening in step (5) and reacts with the alcohol hydroxyl group on chitosan. Finally, after deprotection, modified chitosan with boric acid group is obtained. The sterically hindered modified chitosan can react with the low sterically hindered oxidation product obtained after ring opening of isoascorbic acid. The deprotected boric acid group in its structure forms a complex with the terminal ortho-carbon dihydroxyl structure of the isoascorbic acid oxidation product. Through the combination of the carboxyl part on the complex and the amino group on the modified chitosan ring structure, the reduced ferrous ions are chelated to improve the efficiency of chelating ferrous ions.

[0013] In some embodiments of this application, in step (5), the heating reaction is as follows: set the temperature to 40-45°C, process for 3-4 hours, and then raise the temperature to 60-70°C and stir overnight; The pH was readjusted to 7.5-8.2.

[0014] By adopting the above technical solution, chitosan in solution C and product B in solution D form a composite structure in the early stage of the heating reaction. Subsequently, with further heating, under the action of heat and alkaline environment, the borate ester group is deprotected and the active boric acid group is exposed. This can be used to combine with the modified chitosan in the compound chelating agent component to enhance the chelating effect on iron ions.

[0015] As described above, the method for preparing calcined kaolin from coal gangue according to this application has the following beneficial effects: (1) This application uses isoascorbic acid in combination with modified chitosan to achieve the effect of removing residual iron ions in coal gangue slurry; wherein, isoascorbic acid can reduce ferric ions in slurry to obtain ring-opening oxidation products containing carboxyl groups, and through the combination of carboxyl groups in its structure with amino groups in modified chitosan, a chelating structure for chelating ferrous ions is formed. Through the steric hindrance of the chelating structure, the stability of iron ions in the liquid phase of slurry can be improved, and the re-adsorption behavior of particles in slurry for iron ions can be inhibited. Combined with filtration, iron ions in coal gangue can be removed efficiently.

[0016] (2) In this application, chitosan is modified to introduce boric acid groups, which can complex with the low-steric hind carbon hydroxyl structure on the oxidation product obtained by ring-opening oxidation of isoascorbic acid to form a complex, thereby reducing the influence of the slurry dispersion environment on the chelation combination effect and improving the iron removal efficiency of coal gangue.

[0017] (3) When the coal gangue slurry is treated with the compound chelating agent of this application, the removal rate of iron ions is ≥95.7%, and the whiteness of the calcined kaolin can reach 99.1%. Attached Figure Description

[0018] Figure 1 The following are the synthetic routes for modified chitosan shown in Examples 1-4 of this application.

[0019] Figure 2 The image shown is the hydrogen spectrum of product A obtained in Example 2 of this application.

[0020] Figure 3 The image shown is the hydrogen spectrum of product B obtained in Example 2 of this application.

[0021] Figure 4 The results shown are the iron removal rate test results of Examples 1-4 and Comparative Examples 1-2 of this application. Detailed Implementation

[0022] To make the inventive purpose, technical solution and beneficial technical effects of this application clearer, the following detailed description is provided in conjunction with embodiments. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0024] When using “including,” “having,” and “contains” as described herein, the intention is to cover non-exclusive inclusion, unless an explicit qualifying term such as “only,” “consisting of,” etc., is used, in which case another component may be added.

[0025] The terms "preferred," "more preferably," "better," and "even better" used in this application refer to embodiments of this application that provide certain beneficial effects under certain circumstances. However, other embodiments may also be preferred under the same or other circumstances. Furthermore, the description of one or more preferred embodiments does not imply that other embodiments are unavailable, nor is it intended to exclude other embodiments from the scope of this application. That is, in this application, "preferred," "more preferably," "better," and "even better" are merely descriptions of implementations or embodiments with better effects, but do not constitute a limitation on the scope of protection of this application.

[0026] In this application, terms such as "further," "even more," and "particularly" are used for descriptive purposes and indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0027] In this application, "at least one" means one or more, such as one, two, or more. "Multiple" or "several" means at least two, such as two, three, etc., and "multi-layered" means at least two layers, such as two layers, three layers, etc., unless otherwise explicitly specified. In the description of this application, "several" means at least one, such as one, two, etc., unless otherwise explicitly specified.

[0028] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0029] Unless otherwise specified, all steps in this application may be performed sequentially or randomly. For example, the method comprising steps (a) and (b) indicates that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc. Unless otherwise stated, singular terms may include plural forms and should not be construed as having a quantity of one.

[0030] In this application, "above" or "below" includes the number itself. For example, "below 1" includes 1.

[0031] In this application, room temperature refers to 0~40℃, including but not limited to 10~40℃, or further to 20~30℃.

[0032] The present application will be further illustrated by the following examples, but these examples do not limit the scope of the present application.

[0033] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in this application, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. All reagents or instruments whose manufacturers are not specified are conventional products that can be purchased commercially. In addition to the specific methods, equipment, and materials used in the embodiments, based on the knowledge of the prior art possessed by one of ordinary skill in the art and the description in this application, any prior art methods, equipment, and materials similar to or equivalent to those described, used, or made by the methods, equipment, and materials in the embodiments of this application may be used to implement this application.

[0034] The synthetic routes of modified chitosan in Examples 1-4 and the proton NMR spectra of products A and B in Example 2 are shown below. Figure 1-3 As shown.

[0035] The main chemical composition of the coal gangue used in Examples 1-4 and Comparative Examples 1-2 of this application is shown in Table 1.

[0036] Table 1. Main chemical composition of coal gangue from Examples 1-4 and Comparative Examples 1-2 Preparation Example 1 4-hydroxyphenylboronic acid (1.38 g, 10 mmol) and potassium carbonate (1.66 g, 12 mmol) were mixed and dispersed in 20 mL of dimethyl sulfoxide. The mixture was bubbled with argon for 10 min, and then the argon atmosphere was maintained. The temperature was adjusted to 90 °C, and the magnetic stirring speed was 50 rpm for 10 min. Then, epichlorohydrin (2.23 g, 24 mmol) was added to the system, and the mixture was refluxed for 1 h. After that, the heating was stopped and the system was allowed to cool naturally to room temperature. The pH of the system was then adjusted to 3, and 30 mL of ethyl acetate was added. The mixture was shaken for 5 min and allowed to stand for separation. The upper organic phase was then collected and dried with anhydrous sodium sulfate (0.5 g, 3.5 mmol). The product A was then obtained by rotary evaporation under reduced pressure at 50 °C.

[0037] Take 30 mL of toluene, add 3 mL of acetic acid and p-toluenesulfonic acid (0.5 g, 2.9 mmol), adjust the temperature to 25 °C, and treat with magnetic stirring at 200 rpm for 1 min to obtain a mixed solvent.

[0038] Product A (1.94 g, 10 mmol) and ethylene glycol (0.75 g, 12 mmol) were dissolved in 20 mL of mixed solvent and reacted at 35 °C for 2 h. The mixture was then extracted with 30 mL of dichloromethane, concentrated by rotary evaporation under reduced pressure at 40 °C, washed twice with saturated sodium bicarbonate solution, dried with anhydrous sodium sulfate (0.5 g, 3.5 mmol), and filtered to obtain product B.

[0039] Preparation Example 2 4-Hydroxyphenylboronic acid (1.38 g, 10 mmol) and potassium carbonate (1.8 g, 13 mmol) were mixed and dispersed in 25 mL of dimethyl sulfoxide. The mixture was bubbled with argon for 10 min, and then the argon atmosphere was maintained. The temperature was adjusted to 100 °C, and the magnetic stirring speed was 100 rpm for 10 min. Then, epichlorohydrin (2.5 g, 26.9 mmol) was added to the system, and the mixture was refluxed for 1 h. After that, the heating was stopped and the mixture was allowed to cool naturally to room temperature. The pH of the system was then adjusted to 3.5, and 40 mL of ethyl acetate was added. The mixture was shaken for 5 min and allowed to stand for separation. The upper organic phase was then collected, dried with anhydrous sodium sulfate (0.5 g, 3.5 mmol), and then rotary evaporated under reduced pressure at 50 °C to obtain product A.

[0040] Take 35 mL of toluene, add 3 mL of acetic acid and p-toluenesulfonic acid (0.6 g, 3.5 mmol), adjust the temperature to 30 °C, and treat with magnetic stirring at 300 rpm for 5 min to obtain a mixed solvent.

[0041] Product A (1.94 g, 10 mmol) and ethylene glycol (0.8 g, 13 mmol) were dissolved in 30 mL of mixed solvent and reacted at 35 °C for 3 h. The mixture was then extracted with 30 mL of dichloromethane, concentrated by rotary evaporation under reduced pressure at 50 °C, washed three times with saturated sodium bicarbonate solution, dried with anhydrous sodium sulfate (0.5 g, 3.5 mmol), and filtered to obtain product B.

[0042] Preparation Example 3 4-hydroxyphenylboronic acid (1.67 g, 12 mmol) and potassium carbonate (2.07 g, 15 mmol) were mixed and dispersed in 30 mL of dimethyl sulfoxide. The mixture was bubbled with argon for 10 min, and then the argon atmosphere was maintained. The temperature was adjusted to 105 °C, and the magnetic stirring speed was 100 rpm for 30 min. Then, epichlorohydrin (2.78 g, 30 mmol) was added to the system, and the mixture was refluxed for 2 h. After that, the heating was stopped and the system was allowed to cool naturally to room temperature. The pH of the system was then adjusted to 4, and 50 mL of ethyl acetate was added. The mixture was shaken for 10 min and allowed to stand for separation. The upper organic phase was then collected, dried with anhydrous sodium sulfate (0.5 g, 3.5 mmol), and then rotary evaporated under reduced pressure at 50 °C to obtain product A.

[0043] Take 40 mL of toluene, add 4 mL of acetic acid and p-toluenesulfonic acid (0.6 g, 3.5 mmol), adjust the temperature to 30 °C, and treat with magnetic stirring at 300 rpm for 5 min to obtain a mixed solvent.

[0044] Product A (1.94 g, 10 mmol) and ethylene glycol (0.93 g, 15 mmol) were dissolved in 30 mL of mixed solvent and reacted at 40 °C for 3 h. The mixture was then extracted with 30 mL of dichloromethane, concentrated by rotary evaporation under reduced pressure at 50 °C, washed three times with saturated sodium bicarbonate solution, dried with anhydrous sodium sulfate (0.5 g, 3.5 mmol), and filtered to obtain product B. Example 1

[0045] Chitosan (3.24 g, 20 mmol) (98% deacetylation) was dissolved in 20 mL of 3% acetic acid solution, and the pH was adjusted to 3.2 to obtain solution C. Product B (1.1 g, 5 mmol) was dissolved in 5 mL of phosphate buffer (pH=5.8) to obtain solution D. Solution C and solution D were then mixed and treated at 40 °C for 3 h under a nitrogen atmosphere. The system temperature was then increased to 60 °C, the pH was readjusted to 7.5, and the mixture was stirred overnight. Finally, modified chitosan was obtained by column chromatography purification and elution.

[0046] Mix 10g isoascorbic acid, 5g oxalic acid, 20g deionized water, and 3g polyepoxysuccinic acid. Adjust the magnetic stirring speed to 200rpm and the temperature to 30℃, and stir for 10min. Then add 20g modified chitosan, reduce the stirring speed to 100rpm, and continue stirring for 3min to obtain the compound chelating agent.

[0047] Take 20 kg of coal gangue and process it in a crusher to obtain crushed particles with a particle size ≤ 2 mm. Then transfer it to a magnetic separator and set the magnetic field strength to 0.25 T for magnetic separation. Then use zirconium oxide as abrasive and control the water-to-material ratio to 5:1 for wet grinding. After drying the wet grinding product, obtain powder. Set the water-to-material ratio to 2:1 and re-slurry the powder to obtain slurry. Then use 15% hydrochloric acid to adjust the pH of the system to 2.4 and the temperature to 45℃. Add a compound chelating agent to the system with an effective component content of 200 mg / L and continue stirring for 3 hours. Then let it stand for 8 hours. After the clear liquid overflows, take the sediment, dry it, re-crush it and sieve it to obtain refined material with a particle size ≤ 0.038 mm. Then transfer the refined material to a high-temperature furnace and set the temperature to 850℃ for 3 hours to obtain calcined kaolin.

[0048] In this embodiment, product B was prepared from preparation example 1. Example 2

[0049] Chitosan (4.86 g, 30 mmol) (98% deacetylation) was dissolved in 20 mL of 4% acetic acid solution, and the pH was adjusted to 3.7 to obtain solution C. Product B (1.5 g, 6.8 mmol) was dissolved in 10 mL of phosphate buffer (pH=6.1) to obtain solution D. Solution C and solution D were then mixed and treated at 40 °C for 4 h under a nitrogen atmosphere. The system temperature was then increased to 65 °C, the pH was readjusted to 7.8, and the mixture was stirred overnight. Finally, modified chitosan was obtained by column chromatography purification and elution.

[0050] Mix 15g isoascorbic acid, 10g oxalic acid, 25g deionized water, and 5g polyepoxysuccinic acid. Adjust the magnetic stirring speed to 250rpm and the temperature to 40℃, and stir for 10min. Then add 30g modified chitosan, reduce the stirring speed to 100rpm, and continue stirring for 5min to obtain the compound chelating agent.

[0051] Take 20 kg of coal gangue and process it in a crusher to obtain crushed particles with a particle size ≤ 2 mm. Then transfer it to a magnetic separator and set the magnetic field strength to 0.28 T for magnetic separation. Then use zirconium oxide as abrasive and control the water-to-material ratio to 5:1 for wet grinding. After drying the wet grinding product, obtain powder. Set the water-to-material ratio to 3:1 and re-slurry the powder to obtain slurry. Then use 15% hydrochloric acid to adjust the pH of the system to 2.5 and the temperature to 50℃. Add a compound chelating agent to the system with an effective component content of 220 mg / L and continue stirring for 3 hours. Then let it stand for 10 hours. After the clear liquid overflows, take the sediment, dry it, re-crush it and sieve it to obtain refined material with a particle size ≤ 0.038 mm. Then transfer the refined material to a high-temperature furnace and set the temperature to 900℃ for 3 hours to obtain calcined kaolin.

[0052] In this embodiment, product B was prepared from preparation example 2. Example 3

[0053] Chitosan (4.86 g, 30 mmol) (98% deacetylation) was dissolved in 20 mL of 4% acetic acid solution, and the pH was adjusted to 4 to obtain solution C. Product B (2.2 g, 10 mmol) was dissolved in 10 mL of phosphate buffer (pH=6.5) to obtain solution D. Solution C and solution D were then mixed and treated at 45 °C for 4 h under a nitrogen atmosphere. The system temperature was then increased to 70 °C, the pH was readjusted to 8.2, and the mixture was stirred overnight. Finally, modified chitosan was obtained by column chromatography purification and elution.

[0054] Mix 20g isoascorbic acid, 10g oxalic acid, 30g deionized water, and 5g polyepoxysuccinic acid. Adjust the magnetic stirring speed to 250rpm and the temperature to 40℃, and stir for 30min. Then add 30g modified chitosan, reduce the stirring speed to 100rpm, and continue stirring for 5min to obtain the compound chelating agent.

[0055] Take 20 kg of coal gangue and process it in a crusher to obtain crushed particles with a particle size ≤ 2 mm. Then transfer it to a magnetic separator and set the magnetic field strength to 0.28 T for magnetic separation. Then use zirconium oxide as abrasive and control the water-to-material ratio to 5:1 for wet grinding. After drying the wet grinding product, obtain powder. Set the water-to-material ratio to 3:1 and re-slurry the powder to obtain slurry. Then use 15% hydrochloric acid to adjust the pH of the system to 2.7 and the temperature to 50℃. Add a compound chelating agent to the system with an effective component content of 220 mg / L and continue stirring for 4 hours. Then let it stand for 10 hours. After the clear liquid overflows, take the sediment, dry it, re-crush it and sieve it to obtain refined material with a particle size ≤ 0.038 mm. Then transfer the refined material to a high-temperature furnace and set the temperature to 900℃ for 4 hours to obtain calcined kaolin.

[0056] In this embodiment, product B was prepared from preparation example 3. Example 4

[0057] Chitosan (4.86 g, 30 mmol) (98% deacetylation) was dissolved in 20 mL of 3% acetic acid solution, and the pH was adjusted to 4 to obtain solution C. Product B (1.7 g, 7.7 mmol) was dissolved in 10 mL of phosphate buffer (pH=6.5) to obtain solution D. Solution C and solution D were then mixed and treated at 45 °C for 4 h under a nitrogen atmosphere. The system temperature was then increased to 70 °C, the pH was readjusted to 8, and the mixture was stirred overnight. Finally, modified chitosan was obtained by column chromatography purification and elution.

[0058] In this embodiment, product B was prepared from preparation example 2.

[0059] The remaining steps are the same as in Example 1.

[0060] Comparative Example 1 The difference between this comparative example and Example 1 is that the preparation steps of product B are as follows: 4-Nitrophenol (1.39 g, 10 mmol) and potassium carbonate (1.66 g, 12 mmol) were mixed and dispersed in 20 mL of dimethyl sulfoxide. The mixture was bubbled with argon for 10 min, and then the argon atmosphere was maintained. The temperature was adjusted to 90 °C, and the magnetic stirring speed was 50 rpm for 10 min. Then, epichlorohydrin (2.23 g, 24 mmol) was added to the system, and the mixture was refluxed for 1 h. After that, the heating was stopped and the system was allowed to cool naturally to room temperature. The pH of the system was then adjusted to 3, and 30 mL of ethyl acetate was added. The mixture was shaken for 5 min and allowed to stand for separation. The upper organic phase was then collected and dried with anhydrous sodium sulfate (0.5 g, 3.5 mmol). The product A was then obtained by rotary evaporation under reduced pressure at 50 °C.

[0061] Take 30 mL of toluene, add 3 mL of acetic acid and p-toluenesulfonic acid (0.5 g, 2.9 mmol), adjust the temperature to 25 °C, and treat with magnetic stirring at 200 rpm for 1 min to obtain a mixed solvent.

[0062] Product A (1.94 g, 10 mmol) and ethylene glycol (0.75 g, 12 mmol) were dissolved in 20 mL of mixed solvent and reacted at 35 °C for 2 h. The mixture was then extracted with 30 mL of dichloromethane, concentrated by rotary evaporation under reduced pressure at 40 °C, washed twice with saturated sodium bicarbonate solution, dried with anhydrous sodium sulfate (0.5 g, 3.5 mmol), and filtered to obtain product B.

[0063] The remaining steps are the same as in Example 1.

[0064] Comparative Example 2 The difference between this comparative example and Example 1 is that the preparation steps of the compound chelating agent are as follows: Take 40g sodium metabisulfite, 10g oxalic acid, 30g deionized water, and 5g polyepoxysuccinic acid, mix them, adjust the magnetic stirring speed to 250rpm, the temperature to 40℃, and stir for 30min to obtain the compound chelating agent.

[0065] The remaining steps are the same as in Example 1.

[0066] Performance testing 1. Appearance properties Table 2 Apparent performance test items of Examples 1-4 and Comparative Examples 1-2 Table 3. Test results of apparent properties of calcined kaolin from Examples 1-4 and Comparative Examples 1-2 2. Iron removal rate test Take 20g each of the magnetic separation powder and refined material from Examples 1-4 and Comparative Examples 1-2, and place them in 100mL of 15% hydrochloric acid aqueous solution. Adjust the magnetic stirring speed to 200rpm and stir for 2-3h for acid leaching. After standing for 6h, take the clear liquid and repeat the acid leaching 3 times. Mix the clear liquid of each group of refined materials to obtain test samples, which are recorded as Y1, Y2, Y3, Y4, Y5, and Y6 respectively. Similarly, obtain the test samples of each group of magnetic separation powder, which are recorded as X1, X2, X3, X4, X5, and X6 respectively.

[0067] Referring to the relevant test methods in the national standard GB / T14563-2020, test samples from groups X1-X6 and Y1-Y6 were taken for iron ion content determination, according to the formula: W=(X n -Y n ) / X n ×100%; n = 1, 2, 3, 4, 5, 6; Test results are as follows Figure 4 As shown.

[0068] Take Examples 1-4 and Comparative Examples 1-2, and refer to Tables 2-3 and... Figure 4 It can be seen that the apparent properties of the calcined kaolin prepared using the example scheme are all within the test index range, meeting the requirements for industrial use.

[0069] Regarding whiteness, the whiteness of calcined kaolin products can indirectly indicate their iron content. The whiteness value of the example solution is significantly higher than that of the comparative solution, indicating that the calcined kaolin in the example solution has a lower iron content. This is related to... Figure 4The iron removal results of each test scheme were consistent. Regarding the iron ion removal rate, in Comparative Example 1, because the modified chitosan did not introduce boric acid groups that could complex with the ring-opening oxidation products of isoascorbic acid, the mechanical dispersion of the compound chelating agent after its addition to the slurry system made it difficult for the chelating agent components with chelating effects to combine and work together. This made it easier for iron ions in the slurry to be re-adsorbed, resulting in incomplete iron ion removal. In contrast, Comparative Example 2 used sodium metabisulfite, which can only reduce iron ions but does not have the ability to chelate and stabilize iron ions in the slurry system. As a result, a large number of iron ions remained in the refined coal gangue, and the iron ion removal effect was the worst in the test.

[0070] The above embodiments are merely illustrative of the principles and effects of this application and are not intended to limit this application. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of this application. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in this application should still be covered by the claims of this application.

Claims

1. A method for preparing calcined kaolin from coal gangue, characterized in that, It should include at least the following steps: S01. Take coal gangue, crush it, magnetically separate it, wet grind it, and then process it into a slurry to obtain a slurry material; S02. Take the slurry, add acid to adjust the pH, then add a compound chelating agent for further treatment, filter, and dry the filtrate to obtain the refined material; S03. Take refined materials, calcine them to obtain calcined kaolin; The compound chelating agent is prepared by mixing the following raw materials in parts by weight: 20-30 parts modified chitosan, 10-20 parts isoascorbic acid, 5-10 parts oxalic acid, 20-30 parts water, and 3-5 parts polyepoxysuccinic acid.

2. The method for preparing calcined kaolin from coal gangue according to claim 1, characterized in that, In step S01, the magnetic separation magnetic field strength is set to 0.25-0.28T; The water-to-material ratio for the pulping process is controlled at (2-3):

1.

3. The method for preparing calcined kaolin from coal gangue according to claim 1, characterized in that, In step S02, the amount of compound chelating agent added is 200-220 mg / L.

4. The method for preparing calcined kaolin from coal gangue according to claim 1, characterized in that, In step S03, the calcination treatment is performed by setting the temperature to 850-900℃ and treating for 3-4 hours.

5. A method for preparing calcined kaolin from coal gangue according to claim 1, characterized in that, The preparation steps of the modified chitosan include the following: (1). Take 4-hydroxyphenylboronic acid, disperse it with dimethyl sulfoxide, heat it and add epichlorohydrin, react it, then adjust the pH, extract it, and rotary evaporate it to obtain product A; (2). Take product A and ethylene glycol, add a mixed solvent to disperse, react, and then purify to obtain product B; (3). Take chitosan and disperse it in 3%-4% acetic acid to obtain solution C; (4) Take product B and disperse it in phosphate buffer to obtain solution D; (5) Mix solution C with solution D, heat the mixture to react, then readjust the pH and purify to obtain modified chitosan.

6. A method for preparing calcined kaolin from coal gangue according to claim 5, characterized in that, In step (1), the ratio of 4-hydroxyphenylboronic acid, dimethyl sulfoxide and epichlorohydrin is (1.38-1.67)g:(20-30)mL:(2.23-2.78)g.

7. A method for preparing calcined kaolin from coal gangue according to claim 5, characterized in that, In step (2), the mixed solvent is prepared by mixing p-toluenesulfonic acid, acetic acid and toluene in a ratio of (0.5-0.6)g:(3-4)mL:(30-40)mL.

8. A method for preparing calcined kaolin from coal gangue according to claim 5, characterized in that, The mass ratio of chitosan to product B is (3.24-4.86):(1.1-2.2).

9. A method for preparing calcined kaolin from coal gangue according to claim 5, characterized in that, In step (5), the heating reaction is as follows: set the temperature to 40-45℃, process for 3-4 hours, and then raise the temperature to 60-70℃ and stir overnight.

10. A method for preparing calcined kaolin from coal gangue according to claim 5, characterized in that, In step (5), the pH is readjusted to 7.5-8.2.

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