A method for preparing alumina from kaolin and coal gangue and removing chlorine ions

Abstract

This invention provides a method for preparing alumina and removing chloride ions from kaolin and coal gangue, relating to the fields of inorganic chemical production and solid waste resource utilization. The method uses kaolin and coal gangue as raw materials, which are crushed and ground, calcined at high temperature, leached with hydrochloric acid, separated from aluminum and silicon, concentrated and crystallized with aluminum chloride, and calcined at low temperature to obtain acid-process alumina. Residual chloride ions are then removed through a precisely temperature-controlled water leaching dechlorination process, ultimately producing alumina superior to first-grade alumina via the Bayer process. The activity and dissolution rate of the acid-process alumina are ensured by controlling the calcination temperature of the aluminum chloride crystals at 730℃~780℃. A dechlorination process using 5~7 times the amount of water and constant temperature stirring at 95℃ for 45 minutes reduces the chloride ion content from 1%~2% to approximately 0.015%. This invention achieves full resource utilization of kaolin and coal gangue solid waste, efficient separation of aluminum and silicon components, and co-production of silica from the sludge. The process is simple, energy-efficient, and produces high-quality products, making it suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention relates to the field of inorganic chemical production and solid waste resource utilization technology, specifically a method for preparing alumina and removing chloride ions using kaolin and coal gangue. Background Technology

[0002] Kaolin and coal gangue are both mineral / industrial solid wastes rich in aluminum and silicon components, with high aluminum oxide content, making them high-quality and inexpensive raw materials for alumina production. Currently, the industry commonly uses an acid-base combined method to produce alumina from kaolin and coal gangue: the raw materials react with hydrochloric acid, while silicon does not react; aluminum, iron, titanium, and other metal oxides are converted into chlorides and enter the liquid phase, achieving aluminum-silicon separation; after solid-liquid separation, the liquid phase is an aluminum chloride solution, which is concentrated, crystallized, and calcined to obtain acid-process alumina.

[0003] The existing technology has the following core defects: Excessive chloride ion residue: When crystalline aluminum chloride is calcined at 730℃~780℃, some chlorides cannot be completely decomposed, resulting in a chloride ion content as high as 1%~2% in acid-processed alumina; Severe equipment corrosion: When high chloride ion acid alumina enters the alkali dissolution process, it will cause severe corrosion to the reaction equipment and pipelines, shorten the service life of the equipment, and increase production costs. Product grade not meeting standards: Excessive chloride ion content prevents the production of national standard grade 1 alumina, limiting product application scenarios; Insufficient utilization of solid waste: Some processes only extract aluminum components, and silicon-based sludge is not utilized efficiently, resulting in serious waste of resources.

[0004] Therefore, developing a preparation method that can efficiently remove chloride ions from acid-processed alumina, while simultaneously achieving the resource utilization of all components of kaolin and coal gangue and ensuring the quality of alumina products, has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing alumina and removing chloride ions using kaolin and coal gangue, achieving efficient chloride removal, full utilization of solid waste, product optimization, and low-energy production. It solves the problems of high chloride ion residue, equipment corrosion from alkali dissolution, low alumina grade, and insufficient utilization of solid waste in existing technologies for acid-process alumina.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing alumina and removing chloride ions using kaolin and coal gangue includes the following steps: Step S1: Raw material pretreatment Kaolin and coal gangue are mixed, crushed, and ground to obtain powder. Step S2: Clinker Preparation The powder obtained in step S1 is calcined at high temperature to obtain calcined clinker; Step S3: Hydrochloric acid leaching and separation The roasted clinker is reacted with hydrochloric acid to achieve aluminum-silicon separation. After solid-liquid separation, a leachate containing aluminum chloride and silicon-based sludge are obtained. Step S4: Concentration and Crystallization The leaching solution containing aluminum chloride is concentrated and crystallized to obtain crystalline aluminum chloride; Step S5: Preparation of Acid-Based Alumina Crystalline aluminum chloride is calcined to obtain acid-processed alumina; Step S6: Water immersion for dechlorination Acid-processed alumina is added to water, heated and stirred for water immersion treatment, and solid-liquid separation is performed to obtain dechlorinated alumina. Step S7: Bayer process purification High-purity alumina is prepared by feeding the dechlorinated alumina into the Bayer process.

[0007] Furthermore, in step S1, the mass ratio of kaolin and coal gangue is 1:1 to 3:1, and the particle size of the powder after grinding is 200 to 500 mesh.

[0008] Furthermore, the high-temperature roasting temperature in step S2 is 750℃~820℃, and the roasting time is 60~90 minutes.

[0009] Further, in step S3, the concentration of hydrochloric acid is 18%~22%, the liquid-solid ratio is 3:1~5:1, the leaching temperature is 85℃~95℃, and the leaching time is 90~120 minutes. The silicon-based sludge is used to prepare silica.

[0010] Furthermore, in step S5, the calcination temperature of the crystalline aluminum chloride is 730℃~780℃, the calcination time is 50~70 minutes, and the acid-processed alumina dissolution rate is 100%.

[0011] Furthermore, in step S6, the amount of water added during immersion is 5 to 7 times the mass of the acid-processed alumina, and deionized water or industrial pure water is used.

[0012] Furthermore, the water immersion heating temperature in step S6 is controlled at 93℃~97℃, preferably 95℃.

[0013] Furthermore, the stirring and soaking time in step S6 is 40-50 minutes, preferably 45 minutes, and the stirring speed is 120-180 r / min.

[0014] Furthermore, the chloride ion content in the alumina obtained by the dechlorination method in step S6 is ≤0.015%, and the purity of the alumina obtained in step S7 is better than that of the national standard grade 1 alumina.

[0015] This invention provides a method for preparing alumina and removing chloride ions using kaolin and coal gangue. It has the following beneficial effects: 1. This invention combines kaolin and coal gangue in a certain proportion, and activates the aluminum component by precise roasting at 750℃~820℃, which greatly improves the leaching efficiency and realizes the efficient synergistic utilization of the two aluminum and silicon solid wastes.

[0016] 2. This invention limits the calcination temperature of crystalline aluminum chloride to 730℃~780℃, taking into account both chloride decomposition and alumina activity, achieving 100% dissolution rate, and avoiding alumina crystal transformation and activity reduction caused by high temperature.

[0017] 3. This invention employs a precise dechlorination process using 5-7 times the water volume, a constant temperature of 95°C, and 45 minutes of stirring to reduce chloride ions to below 0.015%, thereby fundamentally solving the problems of equipment corrosion and product exceeding standards.

[0018] 4. This invention prepares high-purity alumina from aluminum components and precipitated silica from silicon components, with no waste residue emissions, meeting the requirements of a circular economy. All process parameters are quantifiable and controllable. It can be used in conjunction with traditional acid-base combined methods and Bayer processes, requiring low investment and quick production, making it suitable for upgrading existing enterprises. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the process flow for preparing alumina and removing chloride ions from kaolin and coal gangue according to the present invention. Detailed Implementation

[0020] 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.

[0021] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0022] Raw materials and testing methods Raw materials: Kaolin (Al2O3 38.2%), coal gangue (Al2O3 32.5%), industrial hydrochloric acid (31%); Chloride ion detection: silver nitrate titration method (GB / T 3051-2000); Alumina purity testing: EDTA titration method (GB / T 6609.1-2018); Dissolution rate: Calculated by gravimetric method of alkali dissolution. Example 1

[0023] like Figure 1As shown, this embodiment of the invention provides a method for preparing alumina and removing chloride ions using kaolin and coal gangue, comprising the following steps: Step S1: Raw material pretreatment Kaolin and coal gangue were mixed at a mass ratio of 1:1, and then coarsely crushed by a jaw crusher and finely ground by a ball mill to control the powder particle size to 200 mesh, ensuring sufficient subsequent roasting and leaching reactions. Step S2: Clinker Preparation The pretreated powder is fed into a rotary kiln and calcined at 750°C for 90 minutes to remove the water of crystallization, organic matter, and activated aluminum components from the raw material, thereby obtaining a highly reactive calcined clinker. Step S3: Hydrochloric acid leaching and separation The calcined clinker was mixed with 18% hydrochloric acid at a liquid-to-solid ratio of 3:1 and leached at 85°C for 120 minutes. The aluminum component was converted into aluminum chloride and entered the liquid phase, while the silicon component remained in the solid phase as silicon oxide. The solid and liquid components were separated by a filter press to obtain aluminum chloride leachate and silicon-based sludge. The silicon-based sludge can be directly used to prepare silica, realizing the resource utilization of silicon components. Step S4: Concentration and Crystallization The aluminum chloride leaching solution was sent into a vacuum concentrator and concentrated to a supersaturated state under a negative pressure of 0.08 MPa and a temperature of 85°C. After cooling and crystallization, crystalline aluminum chloride was obtained. Step S5: Preparation of Acid-Based Alumina Crystalline aluminum chloride was fed into a calcining furnace and calcined at 730°C for 70 minutes to decompose and obtain acid-processed alumina. Step S6: Water immersion for dechlorination Acid-processed alumina is placed in a sealed tank with a stirrer, and five times its weight of deionized water is added. The tank is heated to 93°C and stirred at 120 r / min for 50 minutes. The residual chloride ions are fully dissolved in the water. The solid and liquid are separated by centrifugation to obtain dechlorinated alumina with a chloride ion content reduced to about 0.015%. Step S7: Bayer process purification Alumina produced by the dechlorination process is fed into the Bayer process production system, where it undergoes alkali dissolution, decomposition, and calcination to obtain an alumina product with a purity superior to the national standard grade 1 product.

[0024] The test results are as follows: the chloride ion content of the acid-process alumina before dechlorination is 1.85%, and after dechlorination it is 0.0148%; the alumina leaching rate is 100%; the purity of the final product alumina is 99.23%, which is better than that of Grade I products. Example 2

[0025] A method for preparing alumina and removing chloride ions using kaolin and coal gangue includes the following steps: Step S1: Raw material pretreatment Kaolin and coal gangue were mixed at a mass ratio of 2:1, and then coarsely crushed by a jaw crusher and finely ground by a ball mill to control the powder particle size to 350 mesh, ensuring sufficient subsequent roasting and leaching reactions. Step S2: Clinker Preparation The pretreated powder is fed into a rotary kiln and calcined at 780°C for 75 minutes to remove the water of crystallization, organic matter, and activated aluminum components from the raw material, thereby obtaining a highly reactive calcined clinker. Step S3: Hydrochloric acid leaching and separation The calcined clinker was mixed with 20% hydrochloric acid at a liquid-to-solid ratio of 4:1 and leached at 90°C for 105 minutes. The aluminum component was converted into aluminum chloride and entered the liquid phase, while the silicon component remained in the solid phase as silicon oxide. The solid and liquid components were separated by a filter press to obtain aluminum chloride leachate and silicon-based sludge. The silicon-based sludge can be directly used to prepare silica, realizing the resource utilization of silicon components. Step S4: Concentration and Crystallization The aluminum chloride leaching solution was sent into a vacuum concentrator and concentrated to a supersaturated state under a negative pressure of 0.085 MPa and a temperature of 80°C. After cooling and crystallization, crystalline aluminum chloride was obtained. Step S5: Preparation of Acid-Based Alumina Crystalline aluminum chloride was fed into a calcining furnace and calcined at 750°C for 60 minutes to decompose and obtain acid-processed alumina. Step S6: Water immersion for dechlorination Acid-processed alumina is placed in a sealed tank with a stirrer, and six times its weight of deionized water is added. The tank is heated to 95°C and stirred at 150 r / min for 45 minutes. The residual chloride ions are fully dissolved in the water. The solid and liquid are separated by centrifugation to obtain dechlorinated alumina with a chloride ion content reduced to about 0.015%. Step S7: Bayer process purification Alumina produced by the dechlorination process is fed into the Bayer process production system, where it undergoes alkali dissolution, decomposition, and calcination to obtain an alumina product with a purity superior to the national standard grade 1 product.

[0026] The test results are as follows: the chloride ion content of the acid-process alumina before dechlorination is 1.52%, and after dechlorination it is 0.0135%; the alumina leaching rate is 100%; the purity of the final product alumina is 99.31%, which is better than that of Grade I products. Example 3

[0027] A method for preparing alumina and removing chloride ions using kaolin and coal gangue includes the following steps: Step S1: Raw material pretreatment Kaolin and coal gangue were mixed at a mass ratio of 3:1, and then coarsely crushed by a jaw crusher and finely ground by a ball mill to control the powder particle size to 500 mesh, ensuring sufficient subsequent roasting and leaching reactions. Step S2: Clinker Preparation The pretreated powder is fed into a rotary kiln and calcined at 820°C for 60 minutes to remove the water of crystallization, organic matter, and activated aluminum components from the raw material, thereby obtaining a highly reactive calcined clinker. Step S3: Hydrochloric acid leaching and separation The calcined clinker was mixed with 22% hydrochloric acid at a liquid-to-solid ratio of 5:1 and leached at 95°C for 90 minutes. The aluminum component was converted into aluminum chloride and entered the liquid phase, while the silicon component remained in the solid phase as silicon oxide. The solid and liquid components were separated by a filter press to obtain aluminum chloride leachate and silicon-based sludge. The silicon-based sludge can be directly used to prepare silica, realizing the resource utilization of silicon components. Step S4: Concentration and Crystallization The aluminum chloride leaching solution was sent into a vacuum concentrator and concentrated to a supersaturated state under a negative pressure of 0.09 MPa and a temperature of 75°C. After cooling and crystallization, crystalline aluminum chloride was obtained. Step S5: Preparation of Acid-Based Alumina Crystalline aluminum chloride was fed into a calcining furnace and calcined at 780°C for 50 minutes to decompose and obtain acid-processed alumina. Step S6: Water immersion for dechlorination Acid-processed alumina is placed in a sealed tank with a stirrer, and seven times its weight of deionized water is added. The tank is heated to 97°C and stirred at 180 r / min for 40 minutes. The residual chloride ions are fully dissolved in the water. The solid and liquid are separated by centrifugation to obtain dechlorinated alumina with a chloride ion content reduced to about 0.015%. Step S7: Bayer process purification Alumina produced by the dechlorination process is fed into the Bayer process production system, where it undergoes alkali dissolution, decomposition, and calcination to obtain an alumina product with a purity superior to the national standard grade 1 product.

[0028] The test results are as follows: the chloride ion content of acid-processed alumina before dechlorination is 1.10%, and after dechlorination it is 0.0129%; the alumina leaching rate is 100%; the purity of the final product alumina is 99.37%, which is better than that of Grade I products.

[0029] Comparative Example 1: The process parameters are the same as in Example 2, but the water immersion dechlorination step S6 is omitted, and the acid-processed alumina is directly fed into the Bayer process.

[0030] The test results were as follows: the chloride ion content of acid-processed alumina was 1.52%; the corrosion rate of the alkaline dissolution equipment increased by 8 to 10 times; and the purity of the final product alumina was 97.15%, which did not meet the first-grade standard.

[0031] Comparative Example 2: The process parameters are the same as in Example 2, with the amount of water added for water immersion being 3 times that of acid-process alumina, the temperature being 80°C, and stirring for 20 minutes.

[0032] The test results showed that the chloride ion content of alumina produced by the dechlorination method was 0.125%, which still exceeded the standard; the product purity was 98.02%, which did not meet the first-grade standard.

[0033] Compared to Comparative Examples 1 and 2, the high-purity alumina prepared by the methods in Examples 1-3 all met the standard of Grade 1, while the alumina prepared by the methods in Comparative Examples 1 and 2 did not meet the standard of Grade 1. Therefore, it can be seen that the acid-process alumina prepared by the present invention has high activity and a 100% dissolution rate. The final product is superior to the national standard Grade 1 alumina and can solve the problems of equipment corrosion and substandard product quality caused by excessive chloride ion concentration in acid-process alumina.

[0034] The raw materials used in this invention are kaolin and industrial solid waste coal gangue, which are widely available and inexpensive. The process is fully compatible with existing rotary kilns, thickeners, roasting furnaces, and Bayer process production equipment, requiring no large-scale equipment modification. The process produces no toxic or harmful byproducts, and silicon-based sludge can be used to co-produce silica, achieving zero solid waste discharge.

[0035] This invention can be widely applied to alumina production enterprises, solid waste resource treatment plants, and inorganic chemical enterprises. It is suitable for large-scale industrial production and has environmental, economic, and social benefits, making it highly practical for industrial applications.

[0036] The following points should be noted in this article: 1. The accompanying drawings of the embodiments disclosed herein only relate to the structures involved in the embodiments disclosed herein; other structures can be referred to in a general design.

[0037] 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.

[0038] 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 alumina and removing chloride ions using kaolin and coal gangue, characterized in that, Includes the following steps: Step S1: Raw material pretreatment Kaolin and coal gangue are mixed, crushed, and ground to obtain powder. Step S2: Clinker Preparation The powder obtained in step S1 is calcined at high temperature to obtain calcined clinker; Step S3: Hydrochloric acid leaching and separation The roasted clinker is reacted with hydrochloric acid to achieve aluminum-silicon separation. After solid-liquid separation, a leachate containing aluminum chloride and silicon-based sludge are obtained. Step S4: Concentration and Crystallization The aluminum chloride-containing leachate is concentrated and crystallized to obtain crystalline aluminum chloride; Step S5: Preparation of Acid-Based Alumina Crystalline aluminum chloride is calcined to obtain acid-processed alumina; Step S6: Water immersion to remove chlorine Acid-processed alumina is added to water, heated and stirred for water immersion treatment, and solid-liquid separation is performed to obtain dechlorinated alumina. Step S7: Bayer process purification High-purity alumina is prepared by feeding the dechlorinated alumina into the Bayer process.

2. The method for preparing alumina and removing chloride ions using kaolin and coal gangue according to claim 1, characterized in that, The mass ratio of kaolin and coal gangue in step S1 is 1:1 to 3:1, and the particle size of the powder after grinding is 200 to 500 mesh.

3. The method for preparing alumina and removing chloride ions using kaolin and coal gangue according to claim 1, characterized in that, The high-temperature roasting temperature in step S2 is 750℃~820℃, and the roasting time is 60~90 minutes.

4. The method for preparing alumina and removing chloride ions using kaolin and coal gangue according to claim 1, characterized in that, In step S3, the hydrochloric acid concentration is 18%~22%, the liquid-solid ratio is 3:1~5:1, the leaching temperature is 85℃~95℃, and the leaching time is 90~120 minutes. The silicon-based sludge is used to prepare silica.

5. The method for preparing alumina and removing chloride ions using kaolin and coal gangue according to claim 1, characterized in that, In step S5, the calcination temperature of the crystalline aluminum chloride is 730℃~780℃, the calcination time is 50~70 minutes, and the acid-processed alumina dissolution rate is 100%.

6. The method for preparing alumina and removing chloride ions using kaolin and coal gangue according to claim 1, characterized in that, The amount of water added during the water immersion process in step S6 is 5 to 7 times the mass of the acid-processed alumina, and deionized water or industrial pure water is used.

7. The method for preparing alumina and removing chloride ions from kaolin and coal gangue according to claim 1, characterized in that, The water immersion heating temperature in step S6 is controlled at 93℃~97℃, preferably 95℃.

8. The method for preparing alumina and removing chloride ions using kaolin and coal gangue according to claim 1, characterized in that, The stirring and soaking time in step S6 is 40-50 minutes, preferably 45 minutes, and the stirring speed is 120-180 r / min.

9. The method for preparing alumina and removing chloride ions using kaolin and coal gangue according to claim 1, characterized in that, The chloride ion content in the alumina obtained by the dechlorination method in step S6 is ≤0.015%, and the purity of the alumina obtained in step S7 is better than that of the national standard grade 1 alumina.

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