Method for preparing calcined kaolin clay for glass fiber from coal gangue

Abstract

The present application relates to coal gangue resource utilization field, specifically to a kind of coal gangue preparation calcined kaolin for glass fiber method, comprising: coal gangue is ground and homogenized, the obtained homogenized powder is made into concentration 30wt%-40wt% ore pulp, after magnetic separation impurity removal, add dilute acid leaching, then add complexing agent, solid-liquid separation, after drying the refined powder is calcined;Calcined powder is mixed with whitening agent, ground to particle size less than 325 mesh, that is, it is made into.The present application method controls the composition of powder in reasonable range by homogenization, combined with magnetic separation, leaching, complexing selective impurity removal, improve the whiteness of final product;The setting of calcination system can control the COD level of product and inhibit the generation of mullite, so that the product meets the standard of calcined kaolin for glass fiber, and the coal gangue can be used to prepare calcined kaolin for glass fiber at low cost.

Description

Technical Field

[0001] This invention relates to the field of coal gangue resource utilization, specifically to a method for preparing kaolin for glass fiber from coal gangue. Background Technology

[0002] Glass fiber, or simply glass fiber, is an important base material for modern composite materials, widely used in construction, transportation, electronics, wind power, and other fields. Calcined kaolin is used as a key functional filler in glass fiber, requiring calcined kaolin with a whiteness ≥90%, COD ≤350ppm, and mullite phase ≤5%, exhibiting extremely high requirements for purity, stability, and low impurities.

[0003] Coal gangue is a major industrial solid waste generated during coal mining and washing, with huge annual emissions. Long-term stockpiling of coal gangue occupies land and pollutes the environment. At the same time, coal gangue is rich in minerals such as kaolinite and illite, making it a potential high-quality raw material for the preparation of calcined kaolin. However, coal gangue itself contains many impurities, making it difficult to prepare calcined kaolin for glass fiber, which requires high purity. Moreover, over-burning during calcination can lead to excessive mullite content, while under-burning can result in high COD, making it difficult to meet the requirements of glass fiber. This restricts the high-value utilization and industrial promotion of coal gangue.

[0004] Existing technologies such as CN111533440A and CN108821459A mostly employ magnetic separation combined with calcination, resulting in products with COD generally higher than 350ppm and whiteness ≤88%, which is difficult to meet the needs of high-end glass fiber. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the above-mentioned defects of the prior art and provide a method for preparing calcined kaolin for glass fiber using coal gangue as raw material.

[0006] The technical solution adopted by this invention to solve its technical problem is as follows: A method for preparing calcined kaolin for glass fiber from coal gangue, comprising: grinding and homogenizing coal gangue to obtain homogenized powder of 200-325 mesh; preparing the homogenized powder into a slurry with a concentration of 30wt%-40wt%, removing impurities by magnetic separation, adding dilute acid for leaching, adding a complexing agent, separating the solid and liquid, and drying to obtain refined powder; calcining the refined powder to obtain calcined powder; mixing the calcined powder with a whitening agent and grinding it until the particle size is less than 325 mesh, thus obtaining the final product; The homogenized powder comprises SiO2: 44.0wt%–46.0wt%, Al2O3: 38.5wt%–40.5wt%, Fe2O3 content ≤0.6wt%, and loss on ignition of 11.0wt%–12.5wt%. Add dilute acid to adjust the pH of the slurry to 4.0~4.7; The calcination includes sequential low-temperature calcination and high-temperature calcination. The low-temperature calcination temperature is 650~850℃, and the oxygen content in the atmosphere is 8vol%~10vol%. The high-temperature calcination temperature is 850~1050℃, and the oxygen content in the atmosphere is 2vol%~4vol%. The whitening agent comprises zinc oxide and silicon dioxide.

[0007] Preferably, in the homogenized powder, the CaO content is ≤0.5wt%, the MgO content is ≤0.3wt%, the TiO2 content is ≤1.0wt%, the sum of the K2O and Na2O contents is ≤0.8wt%, and the moisture content is ≤1.5wt%.

[0008] Preferably, the magnetic field strength of the magnetic separation is 10T or higher.

[0009] Preferably, the dilute acid is dilute hydrochloric acid.

[0010] Preferably, the leaching temperature is 60–80°C.

[0011] Preferably, the leaching time is 1 to 2 hours.

[0012] Preferably, the complexing agent comprises a combination of citric acid and oxalic acid, wherein the amount of citric acid added is 0.3wt% to 0.8wt% of the mass of the homogenized powder, and the amount of oxalic acid added is 0.5wt% to 1.0wt% of the mass of the homogenized powder.

[0013] Preferably, the calcination time in the low-temperature section is 2 to 2.5 hours.

[0014] Preferably, the calcination time in the high-temperature section is 0.5~1.0h.

[0015] Preferably, during the calcination, the heating rate from the low-temperature section to the high-temperature section is 5~10℃ / min.

[0016] Preferably, the powder is preheated to 300–650°C before low-temperature calcination.

[0017] Preferably, after high-temperature calcination, the powder is cooled to ≤100℃.

[0018] Preferably, the whitening agent comprises a combination of zinc oxide and silicon dioxide, wherein the mass ratio of zinc oxide to silicon dioxide is 2~3:5~15.

[0019] Preferably, the whitening agent comprises a combination of zinc oxide and silicon dioxide, wherein the amount of zinc oxide added is 0.4wt% to 0.6wt% of the mass of the calcined powder, and the amount of silicon dioxide added is 1wt% to 3wt% of the mass of the calcined powder.

[0020] The present invention has the following beneficial effects: This invention's method controls the composition of the powder within a reasonable range through homogenization, combined with magnetic separation, leaching, and selective impurity removal via complexation, improving the whiteness of the final product while achieving an alumina loss rate of ≤3%. Calcination includes sequential low-temperature and high-temperature calcination. Low-temperature calcination removes carbon and organic matter, controlling the product's COD level, while high-temperature calcination inhibits mullite formation, ensuring the product's mullite content meets the standards for calcined kaolin used in glass fiber manufacturing. The whitening agent reduces the color of the iron-titanium oxide to a lower valence and lighter color through a reduction reaction. During glass fiber preparation, this inhibits mullite formation, improves the glass fiber's appearance, reduces bubble defects, and enhances melt drawing stability and mechanical insulation properties. Simultaneously, the whitening agent itself also has a whitening effect, thereby improving the quality of the calcined kaolin. This invention enables the production of calcined kaolin for glass fiber from coal gangue at a lower cost.

[0021] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The present invention will now be described in further detail. Detailed Implementation

[0022] To make the objectives, solutions, and beneficial technologies of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be noted that the embodiments described in this specification are merely illustrative of the invention and are not intended to limit the invention.

[0023] For simplicity, this paper only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an undefined range; and any lower limit can be combined with other lower limits to form an undefined range, just as any upper limit can be combined with any other upper limit to form an undefined range. Furthermore, although not explicitly stated, every point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can serve as its own lower or upper limit and be combined with any other point or individual value, or with other lower or upper limits, to form an undefined range.

[0024] In this description, it should be noted that, unless otherwise stated, "above" and "below" include the stated number, "multiple" in "one or more" means two or more, and "more than" in "one or more" means two or more.

[0025] An embodiment of the present invention provides a method for preparing calcined kaolin for glass fiber from coal gangue, comprising: grinding and homogenizing the coal gangue to obtain homogenized powder of 200-325 mesh; preparing the homogenized powder into a slurry with a concentration of 30wt%-40wt%, removing impurities by magnetic separation, leaching with dilute acid, adding a complexing agent, separating the solid and liquid, and drying to obtain refined powder; calcining the refined powder to obtain calcined powder; mixing the calcined powder with a whitening agent and grinding until the particle size is less than 325 mesh, thus obtaining the final product; The homogenized powder comprises SiO2: 44.0wt%–46.0wt%, Al2O3: 38.5wt%–40.5wt%, Fe2O3 content ≤0.6wt%, and loss on ignition of 11.0wt%–12.5wt%. Add dilute acid to adjust the pH of the slurry to 4.0~4.7; The calcination includes sequential low-temperature calcination and high-temperature calcination. The low-temperature calcination temperature is 650~850℃, and the oxygen content in the atmosphere is 8vol%~10vol%. The high-temperature calcination temperature is 850~1050℃, and the oxygen content in the atmosphere is 2vol%~4vol%. The whitening agent comprises zinc oxide and silicon dioxide.

[0026] In some embodiments of the present invention, the homogenized powder contains ≤0.5wt% CaO, ≤0.3wt% MgO, ≤1.0wt% TiO2, ≤0.8wt% K2O and Na2O, and ≤1.5wt% moisture. CaO, MgO, K2O, Na2O, etc., are harmful impurities in the raw materials, and their content should not be too high.

[0027] In some embodiments of the present invention, the magnetic field strength of the magnetic separation is 10T or higher. Magnetic separation with a magnetic field strength of 10T or higher can remove fine iron and titanium impurities, and has a good impurity removal effect; high gradient superconducting magnetic separation is preferred.

[0028] In some embodiments of the present invention, the dilute acid is dilute hydrochloric acid.

[0029] In some embodiments of the present invention, the dilute acid is 0.5 to 1.5 mol / L dilute hydrochloric acid.

[0030] In some embodiments of the present invention, the amount of dilute acid added is 0.5wt% to 1wt% of the slurry mass.

[0031] In some embodiments of the present invention, the leaching temperature is 60–80°C.

[0032] In some embodiments of the present invention, the leaching time is 1 to 2 hours.

[0033] In some embodiments of the present invention, the complexing agent comprises a combination of citric acid and oxalic acid, wherein the amount of citric acid added is 0.3wt% to 0.8wt% of the mass of the homogenized powder, and the amount of oxalic acid added is 0.5wt% to 1.0wt% of the mass of the homogenized powder.

[0034] In some embodiments of the present invention, the moisture content of the refined powder is ≤1 wt%. Low moisture content facilitates the smooth progress of subsequent calcination.

[0035] In some embodiments of the present invention, the calcination time in the low-temperature section is 2 to 2.5 hours.

[0036] In some embodiments of the present invention, the calcination time in the high-temperature section is 0.5~1.0h.

[0037] In some embodiments of the present invention, during the calcination, the heating rate from the low-temperature section to the high-temperature section is 5~10℃ / min.

[0038] In some embodiments of the present invention, the powder is preheated to 650-800°C before low-temperature calcination.

[0039] In some embodiments of the present invention, after high-temperature calcination, the powder is cooled to ≤100°C.

[0040] In this invention, preheating before calcination in the low-temperature section removes free water and some organic matter, stabilizing the powder composition. The low-temperature calcination uses a lower temperature and a strong oxidizing atmosphere, which decarbonizes and removes organic matter, reducing COD content. The high-temperature calcination uses a higher temperature and a weak oxidizing atmosphere, which inhibits mullite formation. By controlling the calcination conditions, the controllability of calcination is improved, making it suitable for large-scale industrial production. This avoids the problems of over-burning and under-burning (even occurring simultaneously in a single batch) caused by the incomplete uniformity of the temperature field inside the kiln in conventional large-batch calcination.

[0041] In some embodiments of the present invention, preheating is performed using multi-stage cyclone preheating.

[0042] In some embodiments of the present invention, calcination is carried out using a variable diameter rotary kiln.

[0043] In some embodiments of the present invention, cooling is achieved using multi-stage cyclone cooling. The recovered hot air can be reused as tertiary air, further reducing manufacturing costs.

[0044] In some embodiments of the present invention, the whitening agent comprises a combination of zinc oxide and silicon dioxide, wherein the mass ratio of zinc oxide to silicon dioxide is 2~3:5~15.

[0045] In some embodiments of the present invention, the whitening agent comprises a combination of zinc oxide and silicon dioxide, wherein the amount of zinc oxide added is 0.4wt% to 0.6wt% of the mass of the calcined powder, and the amount of silicon dioxide added is 1wt% to 3wt% of the mass of the calcined powder.

[0046] In some embodiments of the present invention, the silica in the whitening agent is quartz powder.

[0047] Example The following examples describe the disclosure of this invention in more detail. These examples are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of this disclosure. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on weight. Unless otherwise stated, all reagents used in the examples are available commercially or synthesized using conventional methods and are ready for use without further processing. Unless otherwise stated, all instruments used in the examples are available commercially.

[0048] Example 1 The coal gangue raw materials in this embodiment come from Pinglu County in Shanxi Province, Huairen County in Shanxi Province, and northern Anhui Province. After homogenization, a powder with uniform and stable composition is obtained.

[0049] This embodiment describes a method for preparing calcined kaolin for glass fiber from coal gangue, including: (1) Raw material grinding and batching homogenization: The coal gangue raw material is crushed to 50-80mm; gangue is removed by near-infrared photoelectric combined with gravity separation, and the particle composition is quickly detected by X-ray diffraction. The raw materials are batched and ground to obtain homogenized powder with the following composition: SiO2 45.2wt%, Al2O3 38.5wt%, Fe2O3 0.6wt%, CaO 0.47wt%, MgO 0.15wt%, TiO2 0.82wt%, K2O and Na2O content sum of 0.66wt%, loss on ignition of 12.1wt%, moisture content ≤1.5wt%, and particle size of 325 mesh. (2) Composite impurity removal: The homogenized powder was mixed with water to prepare a slurry with a concentration of 35wt%. Fine iron and titanium impurities were removed by high gradient superconducting magnetic separation with a magnetic field strength of 12T. The pH value of the slurry was adjusted to 4.5 by adding 1.0mol / L hydrochloric acid, and the slurry was heated to 70℃ and leached for 1.5h. Then, 0.4wt% of citric acid and 0.5wt% of oxalic acid were added. After filtration, the precipitate was dried to a water content of 0.8wt% to obtain refined powder. The iron content in the refined powder was found to be 0.08wt%, and the aluminum loss was 2.5% (relative to the total aluminum loss). (3) Segmented calcination: The refined powder is preheated, calcined in a low-temperature section, calcined in a high-temperature section, and cooled to obtain calcined powder. The preheating is carried out by a multi-stage cyclone preheater to 600℃. The temperature of the low-temperature section is 800℃, the oxygen content of the atmosphere is 9vol%, and the holding time is 2h. Then the temperature is increased to the target temperature of the high-temperature section at a rate of 8℃ / min. The temperature of the high-temperature section is 950℃, the oxygen content of the atmosphere is 3vol%, and the holding time is 1h. The cooling is carried out by a multi-stage cyclone cooler to 80℃. The hot air is recovered as tertiary air for reuse, and the waste heat utilization rate is 85%. (4) Performance control: The obtained calcined powder is mixed with the whitening agent, ground, and passed through a 325-mesh sieve with a residue of 0.6%, to obtain calcined kaolin for glass fiber; the whitening agent is a combination of ZnO and SiO2, with ZnO added at 0.5wt% of the mass of the calcined powder and SiO2 added at 3wt% of the mass of the calcined powder.

[0050] Example 2 The coal gangue raw materials in this embodiment come from Pinglu County in Shanxi Province, Huairen County in Shanxi Province, and northern Anhui Province. After homogenization, a powder with uniform and stable composition is obtained.

[0051] This embodiment describes a method for preparing calcined kaolin for glass fiber from coal gangue, including: (1) Raw material grinding and batching homogenization: The coal gangue raw material is crushed to 60-100mm; gangue is removed by near-infrared photoelectric combined with gravity separation, and the particle composition is quickly detected by X-ray diffraction. The raw material is batched and ground to obtain homogenized powder with the following composition: SiO2 45.8wt%, Al2O3 39.2wt%, Fe2O3 0.6wt%, CaO 0.33wt%, MgO 0.21wt%, TiO2 0.91wt%, K2O and Na2O content sum of 0.52wt%, loss on ignition of 11.6wt%, moisture content ≤1.5wt%, and particle size of 200 mesh. (2) Composite impurity removal: The homogenized powder was mixed with water to prepare a slurry with a slurry concentration of 40wt%. Fine iron and titanium impurities were removed by high gradient superconducting magnetic separation with a magnetic field strength of 12T. The pH value of the slurry was adjusted to 4.6 by adding 0.8mol / L hydrochloric acid, and the slurry was heated to 65℃ and leached for 2h. Then, 0.6wt% citric acid and 0.8wt% oxalic acid were added by mass of the homogenized powder. After filtration, the precipitate was dried to a water content of 0.9wt% to obtain refined powder. The iron content in the refined powder was found to be 0.09wt%, and the aluminum loss was 2.8% (relative to the total aluminum loss). (3) Segmented calcination: The refined powder is preheated, calcined in a low-temperature section, calcined in a high-temperature section, and cooled to obtain calcined powder. The preheating is carried out by a multi-stage cyclone preheater to 500℃. The temperature of the low-temperature section is 700℃, the oxygen content of the atmosphere is 8.5 vol%, and the holding time is 2.5 h. Then, the temperature is increased to the target temperature of the high-temperature section at a rate of 6℃ / min. The temperature of the high-temperature section is 900℃, the oxygen content of the atmosphere is 2.5 vol%, and the holding time is 0.5 h. The cooling is carried out by a multi-stage cyclone cooler to 90℃. The hot air is recovered as tertiary air for reuse, and the waste heat utilization rate is 82%. (4) Performance control: The obtained calcined powder is mixed with the whitening agent, ground, and passed through a 325-mesh sieve with a residue of 0.8%, to obtain calcined kaolin for glass fiber; the whitening agent is a combination of ZnO and SiO2, with ZnO added at 0.4wt% of the mass of the calcined powder and SiO2 added at 2wt% of the mass of the calcined powder.

[0052] Example 3 The coal gangue raw materials in this embodiment come from Pinglu County in Shanxi Province, Huairen County in Shanxi Province, and northern Anhui Province. After homogenization, a powder with uniform and stable composition is obtained.

[0053] This embodiment describes a method for preparing calcined kaolin for glass fiber from coal gangue, including: (1) Raw material grinding and batching homogenization: The coal gangue raw material is crushed to 50-100mm; gangue is removed by near-infrared photoelectric combined with gravity separation, and the particle composition is quickly detected by X-ray diffraction. The raw material is batched and ground to obtain homogenized powder with the following composition: SiO2 44.5wt%, Al2O3 40.1wt%, Fe2O3 0.5wt%, CaO 0.23wt%, MgO 2.5wt%, TiO2 0.84wt%, K2O and Na2O content sum of 0.71wt%, loss on ignition of 12.4wt%, moisture content ≤1.5wt%, and particle size of 200 mesh. (2) Composite impurity removal: The homogenized powder was mixed with water to prepare a slurry with a concentration of 30wt%. Fine iron and titanium impurities were removed by high gradient superconducting magnetic separation with a magnetic field strength of 12T. The pH value of the slurry was adjusted to 4.1 by adding 0.8mol / L hydrochloric acid, and the slurry was heated to 75℃ and leached for 1h. Then, 0.8wt% of citric acid and 0.6wt% of oxalic acid were added. After filtration, the precipitate was dried to a water content of 0.9wt% to obtain refined powder. The iron content in the refined powder was found to be 0.08wt%, and the aluminum loss was 2.6% (relative to the total aluminum loss). (3) Segmented calcination: The refined powder is preheated, calcined in a low-temperature section, calcined in a high-temperature section, and cooled to obtain calcined powder. The preheating is carried out by a multi-stage cyclone preheater to 400℃. The temperature of the low-temperature section is 750℃, the oxygen content of the atmosphere is 9.5 vol%, and the holding time is 2.5h. Then, the temperature is increased to the target temperature of the high-temperature section at a rate of 5℃ / min. The temperature of the high-temperature section is 1000℃, the oxygen content of the atmosphere is 3.5 vol%, and the holding time is 1h. The cooling is carried out by a multi-stage cyclone cooler to 90℃. The hot air is recovered as tertiary air for reuse, and the waste heat utilization rate is 81%. (4) Performance control: The obtained calcined powder is mixed with the whitening agent, ground, and passed through a 325-mesh sieve with a residue of 0.6%, to obtain calcined kaolin for glass fiber; the whitening agent is a combination of ZnO and SiO2, with ZnO added at 0.6 wt% of the mass of the calcined powder and SiO2 added at 1.5 wt% of the mass of the calcined powder.

[0054] Comparative Example 1 This comparative example uses the same coal gangue raw material as Example 1.

[0055] This comparative example uses conventional methods to prepare calcined kaolin from coal gangue, including: (1) Raw material processing: The raw materials are sorted and batched manually and ground into powder with a particle size of 325 mesh; (2) Impurity removal: The powder is mixed with water to prepare a slurry with a concentration of 35wt%. The impurities are removed by conventional magnetic separation. After filtration, the precipitate is dried to a moisture content of 0.8wt% to obtain refined powder. (3) Oxidation and calcination: The refined powder is preheated, conventionally oxidized and calcined, and cooled to obtain calcined powder. The preheating is carried out by a multi-stage cyclone preheater to 600℃. The oxidation and calcination temperature is 1000℃, the oxygen content of the atmosphere is 9 vol%, and the holding time is 3 hours. The cooling is carried out by a multi-stage cyclone cooler to 80℃, and the hot air is recovered as tertiary air for reuse. (4) Performance control: The obtained calcined powder is ground and passed through a 325-mesh sieve to obtain calcined kaolin.

[0056] Comparative Example 2 This comparative example uses the same coal gangue raw material as Example 1.

[0057] The method for preparing calcined kaolin from coal gangue in this comparative example differs from that in Example 1 in that the oxygen content in the atmosphere during high-temperature calcination is higher at 9 vol%, while other process parameters remain consistent with Example 1. The specific preparation method includes: (1) Raw material grinding and batching homogenization: The coal gangue raw material is crushed to 50-80mm; gangue is removed by near-infrared photoelectric combined with gravity separation, and the particle composition is quickly detected by X-ray diffraction. The raw materials are batched and ground to obtain homogenized powder with the following composition: SiO2 45.2wt%, Al2O3 38.5wt%, Fe2O3 0.6wt%, CaO 0.47wt%, MgO 0.15wt%, TiO2 0.82wt%, K2O and Na2O content sum of 0.66wt%, loss on ignition of 12.1wt%, moisture content ≤1.5wt%, and particle size of 325 mesh. (2) Composite impurity removal: The homogenized powder is mixed with water to prepare a slurry with a slurry concentration of 35wt%. Fine iron and titanium impurities are removed by high gradient superconducting magnetic separation with a magnetic field strength of 12T. The pH value of the slurry is adjusted to 4.5 by adding 1.0mol / L hydrochloric acid, and the slurry is heated to 70℃ and leached for 1.5h. Then, 0.4wt% of citric acid and 0.5wt% of oxalic acid are added by the homogenized powder. After filtration, the precipitate is dried to a water content of 0.8wt% to obtain refined powder. (3) Segmented calcination: The refined powder is preheated, calcined in a low-temperature section, calcined in a high-temperature section, and cooled to obtain calcined powder. The preheating is carried out by a multi-stage cyclone preheater to 600℃. The temperature of the low-temperature section is 800℃, the oxygen content of the atmosphere is 9 vol%, and the holding time is 2h. Then the temperature is increased to the target temperature of the high-temperature section at a rate of 8℃ / min. The temperature of the high-temperature section is 950℃, the oxygen content of the atmosphere is 9 vol%, and the holding time is 1h. The cooling is carried out by a multi-stage cyclone cooler to 80℃, and the hot air is recovered as tertiary air for reuse. (4) Performance control: The obtained calcined powder is mixed with the whitening agent, ground, and passed through a 325-mesh sieve with a residue of 0.6%, to obtain calcined kaolin for glass fiber; the whitening agent is a combination of ZnO and SiO2, with ZnO added at 0.5wt% of the mass of the calcined powder and SiO2 added at 3wt% of the mass of the calcined powder.

[0058] Comparative Example 3 This comparative example uses the same coal gangue raw material as Example 1.

[0059] The method for preparing calcined kaolin from coal gangue in this comparative example differs from that in Example 1 in that the oxygen content in the atmosphere during low-temperature calcination is lower, at 3 vol%, while other process parameters remain consistent with Example 1. The specific preparation method includes: (1) Raw material grinding and batching homogenization: The coal gangue raw material is crushed to 50-80mm; gangue is removed by near-infrared photoelectric combined with gravity separation, and the particle composition is quickly detected by X-ray diffraction. The raw materials are batched and ground to obtain homogenized powder with the following composition: SiO2 45.2wt%, Al2O3 38.5wt%, Fe2O3 0.6wt%, CaO 0.47wt%, MgO 0.15wt%, TiO2 0.82wt%, K2O and Na2O content sum of 0.66wt%, loss on ignition of 12.1wt%, moisture content ≤1.5wt%, and particle size of 325 mesh. (2) Composite impurity removal: The homogenized powder is mixed with water to prepare a slurry with a slurry concentration of 35wt%. Fine iron and titanium impurities are removed by high gradient superconducting magnetic separation with a magnetic field strength of 12T. The pH value of the slurry is adjusted to 4.5 by adding 1.0mol / L hydrochloric acid, and the slurry is heated to 70℃ and leached for 1.5h. Then, 0.4wt% of citric acid and 0.5wt% of oxalic acid are added by the homogenized powder. After filtration, the precipitate is dried to a water content of 0.8wt% to obtain refined powder. (3) Segmented calcination: The refined powder is preheated, calcined in a low-temperature section, calcined in a high-temperature section, and cooled to obtain calcined powder. The preheating is carried out by a multi-stage cyclone preheater to 600℃. The temperature of the low-temperature section is 800℃, the oxygen content of the atmosphere is 3vol%, and the holding time is 2h. Then the temperature is increased to the target temperature of the high-temperature section at a rate of 8℃ / min. The temperature of the high-temperature section is 950℃, the oxygen content of the atmosphere is 3vol%, and the holding time is 1h. The cooling is carried out by a multi-stage cyclone cooler to 80℃, and the hot air is recovered as tertiary air for reuse. (4) Performance control: The obtained calcined powder is mixed with the whitening agent, ground, and passed through a 325-mesh sieve with a residue of 0.6%, to obtain calcined kaolin for glass fiber; the whitening agent is a combination of ZnO and SiO2, with ZnO added at 0.5wt% of the mass of the calcined powder and SiO2 added at 3wt% of the mass of the calcined powder.

[0060] Comparative Example 4 The coal gangue raw materials used in this comparative example came from Pinglu and Huairen in Shanxi Province, and northern Anhui Province. After homogenization, a powder with uniform and stable composition was obtained.

[0061] The method for preparing calcined kaolin from coal gangue in this comparative example differs from Example 1 in that the homogenized powder standards were adjusted: SiO2 43.7wt% and Al2O3 41.0wt%, while other process parameters remained consistent with Example 1. The specific preparation method includes: (1) Raw material grinding and batching homogenization: The coal gangue raw material is crushed to 50-80mm; gangue is removed by near-infrared photoelectric combined with gravity separation, and the particle composition is quickly detected by X-ray diffraction. The raw material is batched and ground to obtain homogenized powder with the following composition: SiO2 43.7wt%, Al2O3 41.0wt%, Fe2O3 0.6wt%, CaO 0.47wt%, MgO 0.15wt%, TiO2 0.82wt%, K2O and Na2O content sum 0.66wt%, loss on ignition 12.1wt%, moisture content ≤1.5wt%, and particle size 325 mesh. (2) Composite impurity removal: The homogenized powder is mixed with water to prepare a slurry with a slurry concentration of 35wt%. Fine iron and titanium impurities are removed by high gradient superconducting magnetic separation with a magnetic field strength of 12T. The pH value of the slurry is adjusted to 4.5 by adding 1.0mol / L hydrochloric acid, and the slurry is heated to 70℃ and leached for 1.5h. Then, 0.4wt% of citric acid and 0.5wt% of oxalic acid are added by the homogenized powder. After filtration, the precipitate is dried to a water content of 0.8wt% to obtain refined powder. (3) Segmented calcination: The refined powder is preheated, calcined in a low-temperature section, calcined in a high-temperature section, and cooled to obtain calcined powder. The preheating is carried out by a multi-stage cyclone preheater to 600℃. The temperature of the low-temperature section is 800℃, the oxygen content of the atmosphere is 9 vol%, and the holding time is 2h. Then the temperature is increased to the target temperature of the high-temperature section at a rate of 8℃ / min. The temperature of the high-temperature section is 950℃, the oxygen content of the atmosphere is 3 vol%, and the holding time is 1h. The cooling is carried out by a multi-stage cyclone cooler to 80℃, and the hot air is recovered as tertiary air for reuse. (4) Performance control: The obtained calcined powder is mixed with the whitening agent, ground, and passed through a 325-mesh sieve with a residue of 0.6%, to obtain calcined kaolin for glass fiber; the whitening agent is a combination of ZnO and SiO2, with ZnO added at 0.5wt% of the mass of the calcined powder and SiO2 added at 3wt% of the mass of the calcined powder.

[0062] Detection and Analysis The calcined kaolin products of each embodiment and comparative example were tested and analyzed, and the quality of each product was evaluated by comparing them with the standard for calcined kaolin for glass fiber.

[0063] Table 1. Inspection results of calcined kaolin products from each example and comparative example. As can be seen from the results in Table 1, the products of Examples 1-3 met the standards for calcined kaolin for glass fiber in all aspects. Comparative Examples 1-4 used the same raw materials as Example 1. The comparative examples adopted a more conventional process, and their products failed to meet the standards for calcined kaolin for glass fiber in terms of whiteness, COD, mullite phase content, and iron content, resulting in poor quality. Compared with Example 1, Comparative Example 2 had a higher oxygen content in the atmosphere during high-temperature calcination, resulting in an excessively high mullite phase in the product, making it unsuitable for glass fiber manufacturing. Compared with Example 1, Comparative Example 3 had a lower oxygen content in the atmosphere during low-temperature calcination, resulting in excessive COD in the product. Compared with Example 1, Comparative Example 4 adjusted the homogenization powder standard, with a higher Al content and a lower Si content, resulting in an excessively high mullite phase in the product, insufficient activity, and unsuitability for glass fiber manufacturing.

Claims

1. A method for preparing calcined kaolin from coal gangue for glass fiber production, characterized in that, include: The coal gangue was ground and homogenized to obtain homogenized powder of 200-325 mesh. The homogenized powder is prepared into a slurry with a concentration of 30wt% to 40wt%. After magnetic separation to remove impurities, dilute acid is added for leaching. Then, a complexing agent is added, and solid-liquid separation is performed. After drying, refined powder is obtained. The refined powder is calcined to obtain calcined powder. The calcined powder is mixed with a whitening agent and ground until the particle size is less than 325 mesh. The homogenized powder comprises SiO2: 44.0wt%–46.0wt%, Al2O3: 38.5wt%–40.5wt%, Fe2O3 content ≤0.6wt%, and loss on ignition of 11.0wt%–12.5wt%. Add dilute acid to adjust the pH of the slurry to 4.0~4.7; The calcination includes sequential low-temperature calcination and high-temperature calcination. The low-temperature calcination temperature is 650~850℃, and the oxygen content in the atmosphere is 8vol%~10vol%. The high-temperature calcination temperature is 850~1050℃, and the oxygen content in the atmosphere is 2vol%~4vol%. The whitening agent comprises zinc oxide and silicon dioxide.

2. The method for preparing calcined kaolin for glass fiber from coal gangue according to claim 1, characterized in that, The homogenized powder contains ≤0.5wt% CaO, ≤0.3wt% MgO, ≤1.0wt% TiO2, ≤0.8wt% K2O and Na2O, and ≤1.5wt% moisture.

3. The method for preparing calcined kaolin for glass fiber from coal gangue according to claim 1 or 2, characterized in that, The magnetic field strength of the magnetic separator is above 10T.

4. The method for preparing calcined kaolin for glass fiber from coal gangue according to claim 1 or 2, characterized in that, The dilute acid is dilute hydrochloric acid; the leaching temperature is 60-80℃; and the leaching time is 1-2 hours.

5. The method for preparing calcined kaolin for glass fiber from coal gangue according to claim 1 or 2, characterized in that, The complexing agent comprises a combination of citric acid and oxalic acid, wherein the amount of citric acid added is 0.3wt% to 0.8wt% of the mass of the homogenized powder, and the amount of oxalic acid added is 0.5wt% to 1.0wt% of the mass of the homogenized powder.

6. The method for preparing calcined kaolin for glass fiber from coal gangue according to claim 1, characterized in that, The calcination time in the low-temperature section is 2~2.5h; the calcination time in the high-temperature section is 0.5~1.0h; during the calcination, the heating rate from the low-temperature section to the high-temperature section is 5~10℃ / min.

7. The method for preparing calcined kaolin for glass fiber from coal gangue according to claim 1 or 6, characterized in that, Before calcining in the low-temperature section, the powder is preheated to 300-650℃.

8. The method for preparing calcined kaolin for glass fiber from coal gangue according to claim 1 or 6, characterized in that, After high-temperature calcination, the powder is cooled to ≤100℃.

9. The method for preparing calcined kaolin for glass fiber from coal gangue according to claim 1, characterized in that, The whitening agent comprises a combination of zinc oxide and silicon dioxide, wherein the mass ratio of zinc oxide to silicon dioxide is 2~3:5~15.

10. The method for preparing calcined kaolin for glass fiber from coal gangue according to claim 1 or 9, characterized in that, The whitening agent comprises a combination of zinc oxide and silicon dioxide, wherein the amount of zinc oxide added is 0.4wt% to 0.6wt% of the calcined powder mass, and the amount of silicon dioxide added is 1wt% to 3wt% of the calcined powder mass.

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