Technical method for preparing high-whiteness filler from coal gangue

Abstract

The invention discloses a preparation method of a high-whiteness filler, which comprises the following steps: calcining coal gangue as a raw material in an inert gas and carrying out immersion treatment by using dilute acid, reducing non-ferrous metals to avoid the generation of a stable spinel structure, and carrying out immersion treatment by using dilute acid to remove the non-ferrous metals to obtain the high-whiteness filler. And the requirements on production equipment and the production energy consumption are greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of ore powder processing into high-whiteness filler, and more specifically to a technical method for processing coal gangue into high-whiteness filler. Background Technology

[0002] Coal gangue refers to the main form of solid waste generated during coal mining and washing, typically accounting for 15%-20% of the total raw coal volume. It is a dark gray rock with a low carbon content, harder than coal, and occurs alongside coal seams during coal formation. Due to significant differences between mining areas and coal seams, its occurrence generally exhibits the characteristics of "two lows and one high": low carbon, low calorific value, and high hardness. Currently, China's coal gangue is primarily stored and disposed of. The historical cumulative stockpile of coal gangue has exceeded 7 billion tons and continues to increase at a rate of approximately 720 million tons per year. These massive coal gangue deposits cover an area of ​​over 70 square kilometers and are accompanied by various environmental pressures, including the release of harmful gases from spontaneous combustion, acid rain and groundwater pollution from rainwater leaching, siltation due to river channel obstruction, and even the potential for major geological disasters such as landslides and mudslides. Therefore, promoting the transformation of coal gangue from waste treatment to resource utilization, and achieving high-quality development through environmental protection and resource recycling, is crucial. Coal gangue, rich in high-value components such as silica and alumina, shows broad application prospects in resource utilization, especially in the field of filler materials. However, its complex mineral composition (carbonaceous materials, etc.) and the presence of coloring impurities (pyrite FeS2, hematite Fe2O3, manganese, chromium, and other colored minerals and trace elements) give coal gangue its inherent gray-black color or the corresponding trace element color. Consequently, whitening coal gangue is essential as a filler material, particularly in certain applications.

[0003] To date, various whitening methods, including high-temperature calcination, acid leaching, bleaching agent treatment, and whitening agent coating, have been reported, all of which can improve the whiteness of coal gangue powder to some extent. Calcination of coal gangue at high temperatures oxidizes and burns the organic carbonaceous matter within it. However, after high-temperature calcination, the iron, chromium, copper, and other metallic elements in the coal gangue often oxidize, exhibiting various colors such as red. Therefore, acid leaching methods using concentrated sulfuric acid, concentrated hydrochloric acid, or oxalic acid are commonly used to dissolve the metallic elements in the coal gangue, achieving whitening. Additionally, there are reports of using white substances such as calcium oxide and titanium dioxide to coat the surface of coal gangue for whitening, or of directly applying chemical bleaching agents (such as oxidizing or reducing agents) to the coloring substances on the surface of the coal gangue, causing them to decompose or transform into colorless substances. However, existing whitening technologies applied to coal gangue generally have limited whiteness improvement effects (e.g., the whiteness range after high-temperature calcination and decarbonization is 20-25 Wb, but the application of fillers requires greater than 60 Wb), complex operation processes (e.g., using whitening agents to coat powder), and high technical costs and risk factors (e.g., in acid leaching, because coal gangue has a highly stable crystal structure, high-concentration acid reagents are required).

[0004] In contrast, the combined calcination and acid leaching method has a better whitening effect on coal gangue. However, this method requires high-concentration acid and heating to remove metal elements, resulting in harsh reaction conditions and high production equipment costs. Given the limitations of existing methods, it is essential to develop a whitening process for coal gangue materials. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing powder whitening technologies by providing a method for producing high-whiteness filler from coal gangue. This method not only effectively improves the whitening effect but also simplifies the process, enhances experimental safety, and reduces production costs, resulting in significant economic and environmental benefits. This technology involves calcining coal gangue powder under an inert N2 atmosphere, utilizing the coke within the powder to reduce the metallic minerals, followed by acid treatment under mild conditions, and finally, high-temperature calcination to remove remaining carbon impurities. Experimental results show that the whiteness of the coal gangue filler treated using this technology can reach over 60 Wb, an improvement of 2-3 times compared to traditional methods. Furthermore, the process is simplified, safety is improved, and production costs are reduced by approximately 40%, demonstrating significant economic and environmental benefits.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a method for preparing high-whiteness filler using coal gangue, characterized by comprising the following steps: S1. Inert gas reduction: Calcination of coal gangue powder under an inert atmosphere; thereby reducing some of the non-ferrous metal oxides in the coal gangue to elemental form, resulting in reduced powder; Surprisingly, the inventors discovered that non-ferrous metals such as iron in coal gangue can reconstruct the crystal lattice with other metals through solid-phase reactions at high temperatures, forming structurally stable spinel. This means that subsequent treatment with high-concentration acid is necessary to remove the non-ferrous metals, significantly increasing production costs.

[0007] Surprisingly, by calcining coal gangue raw materials under an inert atmosphere, the coke in the coal gangue itself acts as a reducing agent. After reducing the oxides of non-ferrous metals to their elemental form, the subsequent lattice reconstruction reaction of spinel structures formed by non-ferrous metals and aluminum is avoided. This greatly simplifies the subsequent removal process of non-ferrous metal elements and reduces the overall energy consumption and cost of the process.

[0008] S2. The reduced powder obtained in step S1 is treated with a dilute acid solution to obtain an acid-treated slurry; Surprisingly, by avoiding the lattice reconstruction reaction between non-ferrous metal elements and aluminum and the formation of spinel structures, acid treatment can be carried out using dilute acid, which greatly reduces the corrosion resistance requirements of production equipment.

[0009] Extraction and post-processing; High-temperature calcination to remove carbon.

[0010] Preferably, in step S1, the particle size of the coal gangue powder is less than 400 mesh.

[0011] Understandably, prior to the inert gas reduction step, to obtain coal gangue powder with a suitable particle size, processes such as crushing, ball milling, and sieving may be included to achieve the desired particle size. A suitable particle size can increase the reaction area and improve the efficiency of subsequent processes. The crushing, sieving, and ball milling processes are illustrated below: Crushing: The original lumpy coal gangue minerals are crushed into coal gangue powder by a crusher, and the crushing time is 0.5-5 minutes; Sieving: The coal gangue powder obtained above is sieved to remove coarser particles, resulting in coal gangue powder with a particle size of not less than 35 mesh. Ball milling: The coal gangue powder obtained above is ball milled into powder with a relatively smaller particle size. The ball milling time is 0.5-5 h. Sieving: The powder with a relatively smaller particle size obtained above is sieved to further subdivide the powder and obtain coal gangue fine powder with a particle size of not less than 400 mesh; Preferably, the non-ferrous metal oxide is Fe2O3.

[0012] Preferably, in the coal gangue, the molar ratio of carbon to iron is greater than 3:2; Understandably, in order to ensure the whitening effect, the amount of coke in the coal gangue should be excessive to ensure the removal efficiency of non-ferrous metals.

[0013] In step S2, the H in the dilute acid solution + The molar ratio with Fe is >6.

[0014] The corresponding dilute acid ranges for different types of acid solutions are as follows: hydrochloric acid 0.5-6 mol / L, sulfuric acid 0.5-2 mol / L, nitric acid 0.5-3 mol / L, phosphoric acid 1-5 mol / L, oxalic acid 0.5-5 mol / L, acetic acid 1-6 mol / L, and hydrofluoric acid 0.5-4.5 mol / L.

[0015] It is understandable that when other non-ferrous metals are present in coal gangue, adjusting the amount of acid according to the metal content is a conventional method in the field, and such adjustments should still be considered within the scope of protection of this application.

[0016] Step S3 includes solid-liquid separation and washing.

[0017] The solid-liquid separation in step S3 separates the powder from the solution in the acid-treated slurry obtained in step S2; Understandably, after acid treatment, the non-ferrous metals react with the acid and exist in the solution in the form of ions. After solid-liquid separation, the non-ferrous metal elements are completely separated from the coal gangue powder.

[0018] It is understood that this application does not specifically limit the method of solid-liquid separation. Without departing from the inventive concept of this application, any known solid-liquid separation means can be used in this application. It is merely an illustrative example and not a limitation on the scope of protection. The solid-liquid separation method can be one or more of centrifugal separation, filtration, sedimentation, and membrane separation.

[0019] Preferably, in step S3, the washing is a water wash; Preferably, in step S3, the water is washed until neutral; Preferably, step S3 further includes a drying process at a temperature of 100-120°C.

[0020] Preferably, in step S4, the calcination temperature is 600-800 ℃.

[0021] The second aspect of this application relates to high whiteness fillers prepared using the method described above.

[0022] Due to the adoption of the above technical solution, the present invention has the following beneficial effects: compared with the traditional high-temperature calcination whitening technology, the whiteness effect is improved by 2-3 times; compared with the whitening agent coating technology, the process flow is simplified; compared with the high-concentration acid reagent leaching technology, the experimental safety is improved, the production cost is reduced, and the final whiteness of coal gangue powder is improved to more than 60 Wb, which meets the production requirements of filler application and has significant economic and environmental benefits. Detailed Implementation

[0023] To make the technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be described in more detail below with reference to the embodiments of the present invention. Of course, the described embodiments are only some embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0024] Example 1: Crushing: The original lumpy coal gangue minerals are crushed into coal gangue powder by a crusher, and the crushing time is 3 minutes; Sieving: The coal gangue powder obtained above is sieved to remove coarser particles, resulting in coal gangue powder with a particle size of not less than 35 mesh. Ball milling: The coal gangue powder obtained above is ball milled into powder with a relatively smaller particle size for 3 hours; Sieving: The powder with a relatively smaller particle size obtained above is sieved to further subdivide the powder and obtain coal gangue fine powder with a particle size of not less than 400 mesh; Inert gas reduction: The fine powder obtained above is placed in a tube furnace and calcined under an inert gas N2 atmosphere. The carbon component serves as the heat source and reducing agent in this reaction process, reacting with oxygen in Fe2O3 at high temperature to generate CO2. Simultaneously, iron coloring impurities are reduced to elemental iron, yielding reduced powder. The inert gas flow rate is 30 mL / min, the calcination temperature is 700 ℃, and the calcination time is 1 h. Acid leaching to remove iron: Prepare 6 mol / L dilute hydrochloric acid solutions respectively, take a certain amount of the above-mentioned reducing powder and mix it with each acid solution at a stoichiometric ratio of 1:6, place them in a three-necked flask, and acid wash for 40 min in a constant temperature oil bath environment of 80 ℃ and a stirring rate of 500 r / min. Solid-liquid separation: The acid-washed solution and powder in the three-necked flask were transferred to centrifuge tubes and placed in a centrifuge to separate the solution and powder, obtaining the acid-washed powder. The centrifugation speed was 8000 r / min, and the centrifugation time was 40 min. Filtration: The above-mentioned acid-washed powder is subjected to vacuum filtration, and the powder is washed with deionized water until neutral; Drying: Place the filter cake obtained after the above filtration into a vacuum oven, set the oven temperature to 100 ℃, and the drying time to 7 h; High-temperature decarbonization: The dried filter cake is placed in a muffle furnace for calcination to remove carbon impurities from the powder. The calcination temperature is 800 ℃, the heating rate is 5 ℃ / min, and the calcination time is 3 h, resulting in a high-whiteness filler.

[0025] Example 2: Crushing: The original lumpy coal gangue minerals are crushed into coal gangue powder by a crusher, and the crushing time is 3 minutes; Sieving: The coal gangue powder obtained above is sieved to remove coarser particles, resulting in coal gangue powder with a particle size of not less than 35 mesh. Ball milling: The coal gangue powder obtained above is ball milled into powder with a relatively smaller particle size for 3 hours; Sieving: The powder with a relatively smaller particle size obtained above is sieved to further subdivide the powder and obtain coal gangue fine powder with a particle size of not less than 400 mesh; Inert gas reduction: The fine powder obtained above is placed in a tube furnace and calcined under an inert gas N2 atmosphere. The carbon component serves as the heat source and reducing agent in this reaction process, reacting with oxygen in Fe2O3 at high temperature to generate CO2. Simultaneously, iron coloring impurities are reduced to elemental iron, yielding reduced powder. The inert gas flow rate is 30 mL / min, the calcination temperature is 700 ℃, and the calcination time is 1 h. Acid leaching to remove iron: Prepare 1 mol / L sulfuric acid solutions respectively, take a quantitative amount of the above-mentioned reducing powder and mix it with each acid solution at a stoichiometric ratio of 1:6, place them in a three-necked flask, and acid wash for 30 min in a constant temperature oil bath environment of 40 ℃ and a stirring rate of 500 r / min. Solid-liquid separation: The acid-washed solution and powder in the three-necked flask were transferred to centrifuge tubes and placed in a centrifuge to separate the solution and powder, obtaining the acid-washed powder. The centrifugation speed was 8000 r / min, and the centrifugation time was 40 min. Filtration: The above-mentioned acid-washed powder is subjected to vacuum filtration, and the powder is washed with deionized water until neutral; Drying: Place the filter cake obtained after the above filtration into a vacuum oven, set the oven temperature to 100 ℃, and the drying time to 7 h; High-temperature decarbonization: The dried filter cake is placed in a muffle furnace for calcination to remove carbon impurities from the powder. The calcination temperature is 600 ℃, the heating rate is 5 ℃ / min, and the calcination time is 3 h, resulting in a high-whiteness filler.

[0026] Example 3: Crushing: The original lumpy coal gangue minerals are crushed into coal gangue powder by a crusher, and the crushing time is 3 minutes; Sieving: The coal gangue powder obtained above is sieved to remove coarser particles, resulting in coal gangue powder with a particle size of not less than 35 mesh. Ball milling: The coal gangue powder obtained above is ball milled into powder with a relatively smaller particle size for 3 hours; Sieving: The powder with a relatively smaller particle size obtained above is sieved to further subdivide the powder and obtain coal gangue fine powder with a particle size of not less than 400 mesh; Inert gas reduction: The fine powder obtained above is placed in a tube furnace and calcined under an inert gas N2 atmosphere. The carbon component serves as the heat source and reducing agent in this reaction process, reacting with oxygen in Fe2O3 at high temperature to generate CO2. Simultaneously, iron coloring impurities are reduced to elemental iron, yielding reduced powder. The inert gas flow rate is 30 mL / min, the calcination temperature is 700 ℃, and the calcination time is 1 h. Acid leaching to remove iron: Prepare 2 mol / L dilute nitric acid solutions respectively, take a certain amount of the above-mentioned reducing powder and mix it with each acid solution at a stoichiometric ratio of 1:6, place them in a three-necked flask, and acid wash for 50 min in a constant temperature oil bath environment of 50 ℃ and a stirring rate of 500 r / min. Solid-liquid separation: The acid-washed solution and powder in the three-necked flask were transferred to centrifuge tubes and placed in a centrifuge to separate the solution and powder, obtaining the acid-washed powder. The centrifugation speed was 8000 r / min, and the centrifugation time was 40 min. Filtration: The above-mentioned acid-washed powder is subjected to vacuum filtration, and the powder is washed with deionized water until neutral; Drying: Place the filter cake obtained after the above filtration into a vacuum oven, set the oven temperature to 100 ℃, and the drying time to 7 h; High-temperature decarbonization: The dried filter cake was placed in a muffle furnace for calcination to remove carbon impurities from the powder. The calcination temperature was 680 ℃, the heating rate was 5 ℃ / min, and the calcination time was 3 h, resulting in a high-whiteness filler.

[0027] Example 4: Crushing: The original lumpy coal gangue minerals are crushed into coal gangue powder by a crusher, and the crushing time is 3 minutes; Sieving: The coal gangue powder obtained above is sieved to remove coarser particles, resulting in coal gangue powder with a particle size of not less than 35 mesh. Ball milling: The coal gangue powder obtained above is ball milled into powder with a relatively smaller particle size for 3 hours; Sieving: The powder with a relatively smaller particle size obtained above is sieved to further subdivide the powder and obtain coal gangue fine powder with a particle size of not less than 400 mesh; Inert gas reduction: The fine powder obtained above is placed in a tube furnace and calcined under an inert gas N2 atmosphere. The carbon component serves as the heat source and reducing agent in this reaction process, reacting with oxygen in Fe2O3 at high temperature to generate CO2. Simultaneously, iron coloring impurities are reduced to elemental iron, yielding reduced powder. The inert gas flow rate is 30 mL / min, the calcination temperature is 700 ℃, and the calcination time is 1 h. Acid leaching to remove iron: Prepare 4 mol / L dilute phosphoric acid solutions respectively, take a certain amount of the above-mentioned reducing powder and mix it with various acid solutions at a stoichiometric ratio of 1:6, place them in a three-necked flask, and acid wash the reaction for 90 min in a constant temperature oil bath environment of 20 ℃ and a stirring rate of 500 r / min. Solid-liquid separation: The acid-washed solution and powder in the three-necked flask were transferred to centrifuge tubes and placed in a centrifuge to separate the solution and powder, obtaining the acid-washed powder. The centrifugation speed was 8000 r / min, and the centrifugation time was 40 min. Filtration: The above-mentioned acid-washed powder is subjected to vacuum filtration, and the powder is washed with deionized water until neutral; Drying: Place the filter cake obtained after the above filtration into a vacuum oven, set the oven temperature to 100 ℃, and the drying time to 7 h; High-temperature carbon removal: The dried filter cake is placed in a muffle furnace for calcination to remove carbon impurities from the powder. The calcination temperature is 700 ℃, the heating rate is 5 ℃ / min, and the calcination time is 3 h, resulting in a high-whiteness filler.

[0028] Example 5: Crushing: The original lumpy coal gangue minerals are crushed into coal gangue powder by a crusher, and the crushing time is 3 minutes; Sieving: The coal gangue powder obtained above is sieved to remove coarser particles, resulting in coal gangue powder with a particle size of not less than 35 mesh. Ball milling: The coal gangue powder obtained above is ball milled into powder with a relatively smaller particle size for 3 hours; Sieving: The powder with a relatively smaller particle size obtained above is sieved to further subdivide the powder and obtain coal gangue fine powder with a particle size of not less than 400 mesh; Inert gas reduction: The fine powder obtained above is placed in a tube furnace and calcined under an inert gas N2 atmosphere. The carbon component serves as the heat source and reducing agent in this reaction process, reacting with oxygen in Fe2O3 at high temperature to generate CO2. Simultaneously, iron coloring impurities are reduced to elemental iron, yielding reduced powder. The inert gas flow rate is 30 mL / min, the calcination temperature is 700 ℃, and the calcination time is 1 h. Acid leaching to remove iron: Prepare 5 mol / L oxalic acid solutions respectively, take a quantitative amount of the above-mentioned reducing powder and mix it with each acid solution at a stoichiometric ratio of 1:6, place them in a three-necked flask, and acid wash for 70 min in a constant temperature oil bath environment of 70 ℃ and a stirring rate of 500 r / min. Solid-liquid separation: The acid-washed solution and powder in the three-necked flask were transferred to centrifuge tubes and placed in a centrifuge to separate the solution and powder, obtaining the acid-washed powder. The centrifugation speed was 8000 r / min, and the centrifugation time was 40 min. Filtration: The above-mentioned acid-washed powder is subjected to vacuum filtration, and the powder is washed with deionized water until neutral; Drying: Place the filter cake obtained after the above filtration into a vacuum oven, set the oven temperature to 100 ℃, and the drying time to 7 h; High-temperature decarbonization: The dried filter cake is placed in a muffle furnace for calcination to remove carbon impurities from the powder. The calcination temperature is 750 ℃, the heating rate is 5 ℃ / min, and the calcination time is 3 h, resulting in a high-whiteness filler.

[0029] In Comparative Examples 1-2, the whiteness of coal gangue powder was improved by acid leaching with different types of acid solutions.

[0030] Comparative Example 1 Crushing: The original lumpy coal gangue minerals are crushed into coal gangue powder by a crusher for 3 minutes; Sieving: The coal gangue powder obtained above is sieved to remove coarser particles, resulting in coal gangue powder with a particle size of not less than 35 mesh. Ball milling: The coal gangue powder obtained above is ball milled into powder with a relatively smaller particle size for 3 hours; Sieving: The powder with a relatively smaller particle size obtained above is sieved to further subdivide the powder and obtain coal gangue fine powder with a particle size of not less than 400 mesh; Acid leaching to remove iron: Prepare an 8 mol / L acetic acid solution, take a quantitative amount of the above fine powder and mix it with the two acid solutions at a stoichiometric ratio of 1:6, place them in a three-necked flask, and acid wash for 80 min in a constant temperature oil bath at 80℃ and a stirring rate of 500 r / min. Solid-liquid separation: Transfer the acid-washed solution and powder from the three-necked flask to a centrifuge tube and place it in a centrifuge to separate the solution and powder, obtaining the acid-washed powder. The centrifugation speed is 8000-8000 r / min, and the centrifugation time is 40 min. Filtration: The above-mentioned acid-washed powder is subjected to vacuum filtration, and the powder is washed with deionized water until neutral; Drying: Place the filter cake obtained after the above filtration into a vacuum oven, set the oven temperature to 100 ℃, and the drying time to 7 h; High-temperature decarbonization: The dried filter cake is placed in a muffle furnace for roasting to remove carbon impurities from the powder. The roasting temperature is 750 ℃, the heating rate is 5 ℃ / min, and the roasting time is 2-3 h, resulting in coal gangue filler with high whiteness.

[0031] Comparative Example 2: Crushing: The original lumpy coal gangue minerals are crushed into coal gangue powder by a crusher, and the crushing time is 3 minutes; Sieving: The coal gangue powder obtained above is sieved to remove coarser particles, resulting in coal gangue powder with a particle size of not less than 35 mesh. Ball milling: The coal gangue powder obtained above is ball milled into powder with a relatively smaller particle size for 3 hours; Sieving: The powder with a relatively smaller particle size obtained above is sieved to further subdivide the powder and obtain coal gangue fine powder with a particle size of not less than 400 mesh; Inert gas reduction: The fine powder obtained above is placed in a tube furnace and calcined under an inert gas N2 atmosphere. The carbon component serves as the heat source and reducing agent in this reaction process, reacting with oxygen in Fe2O3 at high temperature to generate CO2. Simultaneously, iron coloring impurities are reduced to elemental iron, yielding reduced powder. The inert gas flow rate is 30 mL / min, the calcination temperature is 700 ℃, and the calcination time is 1 h. Acid leaching to remove iron: Prepare 10 mol / L hydrofluoric acid solutions respectively, take a certain amount of the above-mentioned reducing powder and mix it with each acid solution at a stoichiometric ratio of 1:6, place them in a three-necked flask, and acid wash for 90 min in a constant temperature oil bath environment of 100 ℃ and a stirring rate of 500 r / min. Solid-liquid separation: The acid-washed solution and powder in the three-necked flask were transferred to centrifuge tubes and placed in a centrifuge to separate the solution and powder, obtaining the acid-washed powder. The centrifugation speed was 8000 r / min, and the centrifugation time was 40 min. Filtration: The above-mentioned acid-washed powder is subjected to vacuum filtration, and the powder is washed with deionized water until neutral; Drying: Place the filter cake obtained after the above filtration into a vacuum oven, set the oven temperature to 100 ℃, and the drying time to 7 h; High-temperature decarbonization: The dried filter cake is placed in a muffle furnace for calcination to remove carbon impurities from the powder. The calcination temperature is 800 ℃, the heating rate is 5 ℃ / min, and the calcination time is 3 h, resulting in a high-whiteness filler.

[0032] Comparative Example 3 In Comparative Example 3, the whiteness of the coal gangue powder was improved primarily through high-temperature roasting to remove carbon. This included the following steps: Crushing: The original lumpy coal gangue minerals are crushed into coal gangue powder by a crusher, and the crushing time is 3 minutes; Sieving: The coal gangue powder obtained above is sieved to remove coarser particles, resulting in coal gangue powder with a particle size of not less than 35 mesh. Ball milling: The coal gangue powder obtained above is ball milled into powder with a relatively smaller particle size for 3 hours; Sieving: The powder with a relatively smaller particle size obtained above is sieved to further subdivide the powder and obtain coal gangue fine powder with a particle size of not less than 400 mesh; High-temperature decarbonization: The above-mentioned fine coal gangue powder is placed in a muffle furnace for roasting to remove carbon impurities from the powder. The roasting temperature is 700 ℃, the heating rate is 5 ℃ / min, and the roasting time is 1 h, resulting in coal gangue filler with improved whiteness.

[0033] Whiteness test: After the powders from the final calcination in the above embodiments and comparative examples have cooled naturally, the whiteness of the coal gangue powder with improved product whiteness is obtained. The whiteness of the powder is tested using a whiteness tester (SN-WSB-2) and recorded as follows; Table 1. Whiteness Improvement Effects of Examples and Comparative Examples In the table above, the acid leaching method used in Comparative Examples 1 and 2 is the same as the acid leaching method used in this process. The core mechanism of the whitening agent coating used in Comparative Example 3 is to mix PCC (precipitated calcium carbonate), coal gangue powder, and water evenly, so that PCC adheres to the powder. By cooking the mixture, the gelatinized and dried starch is used as a binder to fix the PCC. Then, grinding is used to obtain PCC-coated coal gangue powder.

[0034] Through detailed analysis and comparison of the data in the table above, the best whiteness improvement effect of coal gangue powder was achieved when the N2 reduction-acid leaching method was used, with the acid leaching solution being hydrochloric acid at a concentration of 6 mol / L, the acid leaching temperature at 80 ℃, the acid leaching time at 40 min, and the calcination temperature at 800 ℃. This not only significantly improved the whiteness index of the coal gangue powder, enabling it to meet the expected application standards, but also effectively balanced economic and environmental benefits during use.

[0035] The above process is merely an exemplary explanation of the coal gangue powder whitening technology. It is understood that this application does not specifically limit the above process parameters, that is, the embodiments are not intended to limit the scope of the patent application of this invention. All equivalent changes or modifications made under the technical spirit of this invention should fall within the patent scope covered by this invention.

Claims

1. A method for preparing high-whiteness filler using coal gangue, characterized in that, Includes the following steps: S1. Inert gas reduction: Calcination of coal gangue powder under an inert atmosphere; thereby reducing some of the non-ferrous metal oxides in the coal gangue to elemental form, resulting in reduced powder; S2. The reduced powder obtained in step S1 is treated with a dilute acid solution to obtain an acid-treated slurry. S3. Extraction and post-processing; S4. High-temperature calcination to remove carbon.

2. The method according to claim 1, characterized in that, In step S1, the particle size of the coal gangue powder is less than 400 mesh.

3. The method according to claim 1, characterized in that, The non-ferrous metal oxide is Fe2O3.

4. The method according to claim 3, characterized in that, In step S2, the H in the dilute acid solution + The molar ratio with Fe is >6.

5. The method according to claim 1, characterized in that, Step S3 includes solid-liquid separation and washing.

6. The method according to claim 5, characterized in that, The solid-liquid separation in step S3 separates the powder from the solution in the acid-treated slurry obtained in step S2; Preferably, the solid-liquid separation includes one or more of centrifugal separation, filtration, sedimentation, and membrane separation.

7. The method according to claim 5, characterized in that, In step S3, the washing is a water wash; preferably, in step S3, the water wash continues until the solution is neutral.

8. The method according to claim 5, characterized in that, Step S3 also includes a drying process, with a drying temperature of 100-120 ℃.

9. The method according to claim 8, characterized in that, In step S4, the calcination temperature is 600-800 ℃.

10. A high whiteness filler, which is prepared by any one of claims 1-9.

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