Method for preparing white carbon black from coal gangue kaolin

Abstract

The invention provides a method for preparing white carbon black from coal gangue kaolin, relates to the technical field of inorganic non-metallic material preparation, and aims to solve the problems of pollution caused by stockpiling of coal gangue kaolin, low resource utilization rate and non-systematic separation of silicon and aluminum. And an integrated technical system of waste recycling, precise roasting, efficient silicon-aluminum separation and double-product synergistic preparation is innovatively constructed. According to the method, coal gangue kaolin is taken as a raw material, efficient separation of silicon and aluminum is realized through the steps of crushing, temperature-controlled roasting, hydrochloric acid leaching, solid-liquid separation, washing dehydration, high-temperature calcination and the like, white carbon black is prepared from a solid phase, and aluminum chloride crystal is recovered from a liquid phase and roasted to obtain aluminum oxide. The core innovation lies in precise control of a roasting phase, optimization of a silicon-aluminum directional separation process and adaptation of white carbon black roasting parameters. The method not only reduces environmental pollution, but also creates remarkable economic value, and the process is simple, easy to industrialize and suitable for large-scale solid waste resource utilization scenes.

Description

A method for preparing silica from coal gangue and kaolin Technical Field

[0001] This invention relates to the field of inorganic non-metallic material preparation technology, specifically a method for preparing silica from coal gangue kaolin. Background Technology

[0002] my country's coal gangue and kaolin stockpiles have exceeded 7 billion tons, with an annual increase of 300-500 million tons. This large-scale stockpiling not only occupies land resources but also easily leads to environmental problems such as dust pollution and groundwater contamination. The main components of coal gangue and kaolin are Al2O3 (43%-45%) and SiO2 (48%-52%), representing potentially valuable mineral resources. However, current utilization methods have significant drawbacks: low resource utilization rate: most coal gangue is simply disposed of as waste, with a small portion used for low-value-added applications such as brick making and backfilling, while core elements such as silicon and aluminum are not systematically utilized; incomplete silicon-aluminum separation: existing technologies struggle to achieve directional silicon-aluminum separation, or the separation process is complex and costly, hindering large-scale implementation; significant industrialization challenges: the process for preparing alumina has not been industrialized, and a synergistic "one waste, multiple products" model has not been established, resulting in limited economic benefits; environmental pollution risks: poor management during stockpiling can easily lead to heavy metal leakage and dust pollution, requiring substantial human and material resources for remediation.

[0003] Current methods for producing precipitated silica rely heavily on high-quality raw materials such as quartz sand and soda ash, which are costly and resource-intensive. Meanwhile, coal gangue resource utilization technologies focus on single products and have not achieved the synergistic recovery of silicon and aluminum.

[0004] Therefore, developing a simple, efficient, and industrially scalable method for preparing silica from coal gangue and kaolin has become crucial for solving solid waste pollution and resource waste. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing precipitated silica from coal gangue kaolin. Addressing the pain points of coal gangue kaolin stockpiling pollution, low resource utilization, and lack of systematic separation of silicon and aluminum, it innovatively constructs an integrated technology system of "waste resource utilization - precise roasting - efficient silicon-aluminum separation - synergistic preparation of dual products." This solves the problems of existing precipitated silica production relying heavily on high-quality raw materials such as quartz sand and soda ash, resulting in high costs and resource consumption; and the fact that coal gangue resource utilization technologies often focus on single products and fail to achieve synergistic recovery of silicon and aluminum.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing silica from coal gangue kaolin, comprising the following steps: Step 1: Raw material pretreatment. Coal gangue kaolin is selected as the raw material, and the SiO2 content in the raw material is controlled at 48%~52% and the Al2O3 content at 43%~45%. The raw material is pulverized to 200~500 mesh, and impurities are removed to obtain pretreated raw material; Step 2: Temperature-controlled roasting. The pretreated raw material is placed in a roasting device and roasted at 800℃~840℃ for 2~3 hours, controlling the unburned carbon content in the clinker to ≤1%, and preventing the formation of α-Al2O3 phase, to obtain roasted clinker; Step 3: Hydrochloric acid leaching and separation of silicon and aluminum. The roasted clinker is mixed with hydrochloric acid at a solid-liquid ratio of 1:3~1:5. The mixture is prepared at g / mL and reacted at 140℃~160℃ for 1.5~2.5h to dissolve metal oxides such as aluminum, iron, and potassium in the clinker, while silicon oxide remains in the solid phase. Solid filter residue and aluminum chloride-containing leachate are obtained by solid-liquid separation. Step 4: Filter residue washing and dehydration. The solid filter residue is washed with deionized water until pH=6~7 and dehydrated to a water content of 18%~22% to obtain a silicon-based precursor. Step 5: Preparation of silica and recovery of by-products. The silica-based precursor is calcined at 850℃~1000℃ for 25~35min, cooled, and pulverized to 300~500 mesh to obtain silica product. Simultaneously, the leachate from step 3 is concentrated and crystallized to obtain crystalline aluminum chloride. The crystalline aluminum chloride is then calcined to obtain alumina by-product.

[0007] Furthermore, in step one, the raw material is pulverized using an air jet mill or a Raymond mill, resulting in uniform particle size and ≤3% residue on the sieve. Magnetic separation is used to remove ferromagnetic impurities, ensuring a raw material purity of ≥95%.

[0008] Furthermore, in step two, the temperature-controlled roasting is carried out using a rotary kiln or a tunnel kiln, with a roasting heating rate of 5~10℃ / min. Air is introduced during the roasting process, with a ventilation volume of 0.5~1.0m³. 3 / h・kg, suppressing unburned char residue.

[0009] Furthermore, in step three, the mass concentration of hydrochloric acid is 20%~30%, the reaction is carried out in a high-pressure reactor at a pressure of 0.3~0.5MPa and a stirring rate of 100~200r / min to promote the full dissolution of the metal oxide.

[0010] Furthermore, in step four, the washing process adopts a countercurrent washing process, and the washing is carried out 3 to 4 times. The amount of washing liquid used each time is 2 to 3 times the mass of the filter residue. The dewatering is carried out using a plate and frame filter press or a centrifugal dewatering machine. After dewatering, the moisture content of the filter residue is precisely controlled at 20% ± 2%.

[0011] Furthermore, in step five, the calcination of silica is carried out in an electric or gas-fired kiln with an air atmosphere and a cooling rate of 8-12°C / min to prevent product agglomeration. The resulting pulverized silica particles have a particle size of 300-500 mesh and a specific surface area ≥150 m². 2 / g.

[0012] Furthermore, in step three, the leachate is concentrated using a vacuum distillation process at a concentration temperature of 80-100℃ and a pressure of -0.07--0.09MPa. After crystallization, crystalline aluminum chloride (AlCl3・6H2O) is obtained. The crystalline aluminum chloride is then calcined at 900-1000℃ for 2-3 hours to obtain alumina with a purity ≥98%.

[0013] Furthermore, the prepared silica product has the following specifications: purity ≥ 97%, whiteness ≥ 92%, and specific surface area 150~250m². 2 / g, oil absorption value ≥1.0mL / g; suitable for rubber reinforcement, coating filler, plastic modification and other fields. The alumina by-product is a first-grade product and is suitable for electrolytic aluminum raw materials.

[0014] This invention provides a method for preparing precipitated silica from coal gangue kaolin. It offers the following advantages: 1. This invention provides a method for preparing precipitated silica from coal gangue kaolin, using coal gangue kaolin as raw material, turning waste into treasure, and simultaneously producing two high-value products: precipitated silica and alumina. The residue is only 200 kg / 2.7 tons of clinker, achieving complete resource utilization. The calcination temperature is strictly controlled at 800℃~840℃ to avoid the formation of the α-Al2O3 phase (α-Al2O3 is difficult to leach with hydrochloric acid), ensuring efficient subsequent silicon-aluminum separation. The unburned carbon content is controlled to ≤1%, improving product purity.

[0015] 2. This invention provides a method for preparing silica from coal gangue kaolin. By precisely matching the concentration of hydrochloric acid, reaction temperature and pressure, metal oxides such as aluminum and iron are fully dissolved, while silicon oxide is selectively retained in the solid phase with a separation efficiency of ≥95%. By optimizing the washing and dehydration parameters and calcination conditions, the silica purity is ensured to be ≥97% and the specific surface area is ≥150m² / g, meeting the requirements of industrial applications.

[0016] 3. This invention provides a method for preparing silica from coal gangue kaolin. The method has a simple process and uses conventional equipment, such as a crusher, calcining kiln, reaction vessel, and filter press. The parameters are easy to control and it is suitable for large-scale continuous production. Attached Figure Description

[0017] Figure 1 is a process flow diagram of preparing silica from coal gangue kaolin according to the present invention; Figure 2 is an XRD pattern of the calcined clinker of the present invention; Figure 3 is a scanning electron microscope (SEM) image of the silica product of the present invention. Detailed Implementation

[0018] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0019] In the description of this invention, unless otherwise explicitly specified and limited, the terms "connected," "linked," and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0020] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0021] In the description of this embodiment, the terms "upper," "lower," "right," etc., refer to the orientation or positional relationship shown in the accompanying drawings. They are used only for ease of description and simplification of operation, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention. In addition, the terms "first" and "second" are used only for distinction in description and have no special meaning.

[0022] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0023] As shown in Figure 1, this embodiment of the invention provides a method for preparing silica from coal gangue kaolin. The raw material selection for this method is as follows: raw material: coal gangue kaolin, requiring SiO2 content of 50% and Al2O3 content of 44%, free from impurities such as large gravel and metal slag, and a storage time of ≤3 years (to avoid compositional fluctuations caused by weathering); key indicators: raw material moisture content ≤10%, loss on ignition ≤8%, to ensure calcination efficiency and product quality stability.

[0024] The preparation method includes the following steps: Step 1: Raw material pretreatment and screening: The raw materials are screened manually or mechanically to remove impurities such as gravel and metal blocks with a particle size >5cm; Crushing: The raw materials are crushed to 200~500 mesh using an air jet mill or Raymond mill, and the proportion of particles passing through a 500 mesh standard sieve is ≥97% to ensure sufficient reaction in the subsequent roasting and leaching process; Magnetic separation: A dry magnetic separator with a magnetic field strength of 1200Gs is used to remove ferromagnetic impurities and reduce the iron content in the product.

[0025] Step Two: Temperature-Controlled Calcination and Loading: The pretreated raw materials are evenly spread into the rotary kiln, with a layer thickness of 8cm. Calcination: The temperature is increased to 820℃ at a rate of 8℃ / min, and held for 2.5 hours. Air is introduced during the calculation process at a ventilation rate of 0.8m³. 3 / h・kg, to promote the combustion and removal of unburned carbon; discharge cooling: after roasting, it is naturally cooled to room temperature to obtain roasted clinker. The unburned carbon content in the clinker is required to be ≤1%, and no α-Al2O3 characteristic peak is detected by X-ray diffraction (XRD), as shown in Figure 2.

[0026] Step 3: Hydrochloric acid leaching and silicon-aluminum separation: Prepare a 25% hydrochloric acid solution and add the roasted clinker and hydrochloric acid solution to a high-pressure reactor at a solid-liquid ratio of 1:4 g / mL; Reaction: Seal the reactor, heat to 150℃, control the pressure at 0.4 MPa, stir at 150 r / min, and react for 2.0 h to allow the metal oxides such as Al2O3, Fe2O3, and K2O in the clinker to react with the hydrochloric acid to generate soluble chlorides; Solid-liquid separation: After the reaction, use a plate and frame filter press or centrifuge to separate the solid and liquid components, obtaining solid filter residue (mainly SiO2) and leachate (mainly containing AlCl3).

[0027] Step 4: Filter cake washing and dehydration. Washing: The solid filter cake is washed four times with deionized water using a countercurrent washing process. The amount of washing liquid used each time is three times the mass of the filter cake, until the pH of the washing liquid is 6.5, to remove chloride impurities adsorbed on the surface of the filter cake. Dehydration: The washed filter cake is sent to a plate and frame filter press for dehydration. The moisture content of the filter cake after dehydration is controlled at 20% to obtain the silicon-based precursor.

[0028] Step 5: Preparation of Silica and By-product Recovery Calcination: The silicon-based precursor is fed into an electric kiln or gas kiln and calcined at 900℃ for 30 min to remove residual moisture and volatile impurities, promoting SiO2 crystallization and grading; Pulverization and Classification: After cooling, it is pulverized to 400 mesh using an air jet mill to obtain silica product. The scanning electron microscope (SEM) image of the silica product is shown in Figure 3, with a magnification of 50,000x; By-product Recovery: The leachate from Step 3 is sent to a vacuum distillation apparatus and concentrated and crystallized at 90℃ and -0.08MPa to obtain crystalline aluminum chloride (AlCl3・6H2O); The crystalline aluminum chloride is calcined at 950℃ for 2.5 h to decompose and obtain first-grade alumina with a purity ≥98%. Example 1:

[0029] Raw materials: Kaolin from coal gangue in Jungar Banner, Ordos, Inner Mongolia was selected. The SiO2 content was 50.2%, Al2O3 content was 44.3%, moisture content was 8.5%, and loss on ignition was 6.8%.

[0030] The preparation steps are as follows: Step 1: Raw material pretreatment: screening to remove impurities, Raymond milling to 300 mesh, 2.1% residue on 500 mesh sieve, magnetic separation to remove ferromagnetic impurities, obtaining pretreated raw material; Step 2: Temperature-controlled calcination: heating to 820℃ in a rotary kiln at 8℃ / min, holding for 2.5h, ventilation rate 0.8m³ / min. 3 / (h・kg), after cooling, calcined clinker was obtained with an unburned carbon content of 0.8% and no α-Al2O3 phase detected by XRD; Step 3: Leaching with 30% hydrochloric acid solution, solid-liquid ratio 1:4 g / mL, reaction in a high-pressure reactor at 150℃, 0.4MPa, and 150r / min for 2h, solid-liquid separation by plate and frame filter press to obtain solid filter residue and leachate; Step 4: Washing and dehydration, countercurrent washing 4 times, washing solution pH=6.5, plate and frame filter press dehydration to 20% water content to obtain silicon-based precursor; Step 5: Preparation of silica, calcined at 900℃ for 30min, air-jet pulverized to 400 mesh to obtain silica product; concentrated and crystallized leachate under reduced pressure to obtain crystalline aluminum chloride, calcined at 950℃ for 2.5h to obtain alumina.

[0031] The silica and alumina byproducts prepared in Example 1 were tested, and the results are shown in the table below: Product Index Silica Alumina Purity 97.5% 98.3% Specific Surface Area (m² / g) 168 - Whiteness (%) 93.2 - Main Impurity Content (%) Fe₂O₃≤0.5, CaO≤0.3 Fe₂O₃≤0.4, SiO₂≤0.8 Product Grade Industrial Grade 1 Electrolytic Aluminum Grade 1 Table of Material Output and Economic Benefits: Raw Material Consumption: 2.7 tons of coal gangue kaolin clinker; Product Output: 1 ton of alumina, with an output value of 3,000 yuan; 1.5 tons of silica, with an output value of 7,500 yuan; Residue: 200 kg, which can be used for brick making or roadbed filler; Overall Benefits: Each ton of raw material generates an output value of approximately 4,000 yuan. After deducting production costs, the economic benefits are significant, while also reducing storage and environmental remediation costs.

[0032] The above practical verification shows that 2.7 tons of coal gangue kaolin clinker can produce 1 ton of first-grade alumina with a purity ≥98% and 1.5 tons of high-quality silica with a purity ≥97% and a specific surface area ≥150m². 2 / g, with a residue of only 200 kg, achieving "complete utilization" of raw materials, which not only reduces environmental pollution but also creates significant economic value.

[0033] The following points should be noted in this article: 1. The accompanying drawings of the embodiments disclosed herein only involve structures related to the embodiments disclosed herein; other structures can refer to general designs.

[0034] 2. Where there is no conflict, the embodiments of this disclosure and the features in the embodiments can be combined with each other to obtain new embodiments.

[0035] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for preparing silica from coal gangue and kaolin, characterized in that, Includes the following steps: Step 1: Raw Material Pretreatment. Coal gangue and kaolin are selected as raw materials. The SiO2 content is controlled at 48%~52%, and the Al2O3 content at 43%~45%. The raw materials are pulverized to 200~500 mesh to remove impurities, resulting in pretreated raw materials. Step 2: Temperature-Controlled Roasting. The pretreated raw materials are placed in a roasting device and roasted at 800℃~840℃ for 2~3 hours. The unburned carbon content in the clinker is controlled to be ≤1%, and no α-Al2O3 phase is formed, resulting in roasted clinker. Step 3: Hydrochloric Acid Leaching and Silicate-Aluminum Separation. The roasted clinker is mixed with hydrochloric acid at a solid-liquid ratio of 1:3~1:5 g / mL. The reaction is carried out at 140℃~160℃ for 1.5~2.5h to dissolve the metal oxides such as aluminum, iron, and potassium in the clinker, while silicon oxide remains in the solid phase. After solid-liquid separation, solid filter residue and aluminum chloride-containing leachate are obtained; Step 4: Filter residue washing and dehydration. The solid filter residue is washed with deionized water until pH=6~7 and dehydrated to a water content of 18%~22% to obtain a silicon-based precursor; Step 5: Preparation of silica and by-product recovery. The silica-based precursor is calcined at 850℃~1000℃ for 25~35min, cooled, and pulverized to 300~500 mesh to obtain silica product; Simultaneously, the leachate from step three is concentrated and crystallized to obtain crystalline aluminum chloride, which is then calcined to obtain alumina as a byproduct.

2. The method for preparing silica from coal gangue and kaolin according to claim 1, characterized in that, In step one, the raw material is pulverized using an air jet mill or Raymond mill. After pulverization, the particle size is uniform and the residue on the sieve is ≤3%. Magnetic separation is used to remove ferromagnetic impurities to ensure that the purity of the raw material is ≥95%.

3. The method for preparing silica from coal gangue and kaolin according to claim 1, characterized in that, In step two, temperature-controlled roasting is performed using a rotary kiln or tunnel kiln, with a roasting heating rate of 5~10℃ / min. Air is introduced during the roasting process, with a ventilation volume of 0.5~1.0m³. 3 / h・kg, suppressing unburned char residue.

4. The method for preparing silica from coal gangue and kaolin according to claim 1, characterized in that, In step three, the hydrochloric acid has a mass concentration of 20% to 30%, and the reaction is carried out in a high-pressure reactor at a pressure of 0.3 to 0.5 MPa and a stirring rate of 100 to 200 r / min to promote the complete dissolution of the metal oxide.

5. The method for preparing silica from coal gangue and kaolin according to claim 1, characterized in that, In step four, the washing process adopts a countercurrent washing process, and the washing is carried out 3 to 4 times. The amount of washing liquid used each time is 2 to 3 times the mass of the filter residue. The dewatering is carried out using a plate and frame filter press or a centrifugal dewatering machine. After dewatering, the moisture content of the filter residue is precisely controlled at 20% ± 2%.

6. The method for preparing silica from coal gangue and kaolin according to claim 1, characterized in that, In step five, the silica calcination is performed in an electric or gas-fired kiln under an air atmosphere. The cooling rate is 8-12°C / min to prevent product agglomeration. After pulverization, the silica particles have a particle size of 300-500 mesh and a specific surface area ≥150 m². 2 / g.

7. The method for preparing silica from coal gangue and kaolin according to claim 1, characterized in that, In step three, the leachate is concentrated using a vacuum distillation process at a concentration temperature of 80-100℃ and a pressure of -0.07-0.09 MPa. After crystallization, crystalline aluminum chloride is obtained. The crystalline aluminum chloride is then calcined at 900-1000℃ for 2-3 hours to obtain alumina with a purity ≥98%.

8. The method for preparing silica from coal gangue and kaolin according to claim 1, characterized in that, The prepared silica product has the following specifications: purity ≥ 97%, whiteness ≥ 92%, and specific surface area 150~250 μm². 2 / g, oil absorption value ≥1.0mL / g.

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