Method for comprehensively utilizing high-aluminum coal gangue

Abstract

The invention belongs to the field of comprehensive utilization of bulk solid waste coal gangue, and particularly relates to a method for comprehensive utilization of high-aluminum coal gangue. According to the method, components such as sandstone, kaolinite rock and low-calorific-value coal are separated out through mineral separation of the high-alumina coal gangue, the kaolinite rock can be used as a raw material for calcining kaolin, mullite and the like, and economic benefits are improved; the low-calorific-value coal is roasted and activated to obtain high-alumina fly ash which is further used for producing aluminum oxide; sodium metasilicate pentahydrate can be further produced from a sodium silicate solution generated in the desilicication process, so that the added value of the product is improved; the silicon-calcium slag discharged in the process of producing aluminum oxide by a sintering method can be further used for producing cement, so that the cyclic utilization of wastes is realized. The method not only effectively solves the problem of comprehensive utilization of a large amount of solid waste of the high-alumina coal gangue and avoids serious pollution to the environment, but also can relieve the problem of insufficient supply of bauxite in China, and has remarkable economic and environmental benefits.

Description

Technical Field

[0001] The present invention belongs to the field of comprehensive utilization of bulk solid waste coal gangue, and in particular relates to a method for comprehensive utilization of high-aluminum coal gangue. Background Art

[0002] The Jungar coalfield in Inner Mongolia boasts abundant high-aluminum coal resources, with reserves reaching 23.7 billion tons. Coal mining produces a significant amount of gangue, accounting for approximately 25% of the total coal produced. After years of mining, the Jungar coalfield has accumulated hundreds of millions of tons of gangue. High-aluminum gangue is primarily composed of kaolin, sandstone, and low-calorific coal. The high-aluminum fly ash produced after calcination has an aluminum oxide content of approximately 35% to 53% and a silicon oxide content of approximately 37% to 55%, making it a resource with great development potential. However, currently, most of the gangue generated by coal mining in central and western Inner Mongolia is simply piled up or used in scattered locations as filler or construction materials. This not only pollutes the environment but also wastes resources. Existing technologies for the comprehensive utilization of high-aluminum gangue and alumina extraction suffer from harsh reaction conditions and low economic returns, resulting in extremely low comprehensive utilization rates for high-aluminum gangue and hindering large-scale application. my country faces a shortage of bauxite resources and a high degree of external dependence. In 2023, my country imported approximately 141 million tons of bauxite, accounting for over 70% of its annual consumption. Therefore, efficient separation and beneficiation of high-alumina coal gangue and the efficient extraction and utilization of valuable elements such as alumina have become key research challenges for researchers in this field. The comprehensive utilization of high-alumina coal gangue and the production of alumina not only safeguards the strategic security of my country's aluminum industry but also holds significant strategic significance for local environmental protection and economic development, contributing to the formation of a circular economy industry chain.

[0003] In recent years, researchers have been continuously improving the technology for extracting alumina from high-alumina coal gangue and fly ash. The main process options can be divided into pre-desiliconization-soda lime sintering method, acid method, ammonium sulfate sintering method, limestone sintering method, etc. Among them, the soda lime sintering method and limestone sintering method are representative, but the limestone sintering method has problems such as large slag phase flow and high energy consumption. Although the pre-desiliconization-soda lime sintering method is the only process method that has achieved industrial production, it still has problems such as a long process flow, high sintering energy consumption, and high alumina production cost.

[0004] Patent application number 202310010746.X proposes a method for producing aluminum hydroxide from coal gangue. This process does not beneficiate the gangue, resulting in high impurity content and high production costs. Furthermore, acid impregnation of the clinker, which has been calcined with the addition of Na2CO3, produces large amounts of salt, making it difficult to recycle the alkali.

[0005] Patent number CN 107758713 B proposes a method for preparing alumina using high-aluminum coal and high-aluminum coal gangue. This method has the problem of unselected gangue and uses a clinker self-pulverization process to produce alumina, resulting in a high impurity content in the gangue, low calorific value of the gangue, and high production costs.

[0006] Patent application number 202311537421.3 proposes a method and system for producing metallurgical-grade alumina using high-aluminum mixed coal. The patent does not sort the coal gangue, and the gangue has a high impurity content. The wet sintering process has high production costs, and when using a fluidized bed boiler to roast activated fly ash, there are problems such as low fly ash activation degree and poor activity.

[0007] The invention patent with publication number CN101941725A proposes a method for extracting alumina from coal gangue and co-producing active calcium silicate. Since the coal gangue has not been sorted and utilized, the impurity content is high and the efficiency is low. The method also does not consider the rational utilization of carbon and the full utilization of waste heat during the roasting and activation process of the coal gangue. At the same time, the traditional wet sintering process is used, resulting in poor technical and economic indicators and extremely high production costs, making it impossible to put it into application in the industry.

[0008] Patent publication number CN101306826A discloses a method for extracting metallurgical-grade alumina from fly ash or slag. This method is applicable to fly ash or slag produced after coal combustion in thermal power plants. After screening, flotation, pre-desiliconization, and production of white carbon black, metallurgical-grade alumina can be obtained. Cement can also be co-produced, reducing the difficulty of waste slag treatment. However, this patent directly uses fly ash and slag as raw materials. The desiliconized fly ash after pre-desiliconization has a low aluminum-silicon ratio (A / S ≤ 2), which is significantly different from the existing traditional series and mixed sintering methods for producing alumina. Due to the low aluminum-silicon ratio, a large amount of limestone is required when using the sintering method to produce alumina. Furthermore, the production of alumina using the traditional wet process has the problems of high production costs and poor economic benefits. In addition, when co-producing white carbon black in this patented method, due to the strong adsorption of white carbon black, the white carbon black will absorb various impurities and alkali solution in the pre-desiliconization solution during the aging process, resulting in difficult washing and high impurity content in the white carbon black product. Therefore, this process has high production costs and poor economic benefits, making it difficult to achieve industrial production.

[0009] Patent publication number CN108275695A discloses a method for preparing 4A zeolite for detergent additives from high-aluminum coal gangue. This method involves crushing the high-aluminum coal gangue, adding an activator (aluminum hydroxide or an ore containing aluminum oxide), and calcining the mixture. The mixture is then pre-desiliconized using an alkaline method to produce a sodium silicate solution and desiliconized fly ash. The desiliconized fly ash is then treated using the Bayer process to produce a sodium aluminate solution, which can be used to prepare 4A zeolite. This method involves adding an activator (aluminum hydroxide or an ore containing aluminum oxide) to the high-aluminum coal gangue during calcination, significantly reducing the calorific value of the material during calcination. However, the addition of the activator increases raw material costs, making it suitable for producing 4A zeolite. However, the production of alumina presents high production costs.

[0010] Therefore, there is an urgent need for a new method that can effectively solve the above problems, so as to improve the comprehensive utilization rate of high-aluminum coal gangue, reduce production costs, and achieve efficient utilization of resources and sustainable development of the environment. Summary of the Invention

[0011] The purpose of the present invention is to provide a method for comprehensive utilization of high-aluminum coal gangue, which greatly improves the comprehensive utilization rate of high-aluminum coal gangue and improves the economic benefits of the process. It not only makes up for the defects of the existing technology, but also has a wide source of raw materials, low energy consumption and low production cost.

[0012] In order to achieve the above object, the present invention provides the following technical solutions:

[0013] A method for comprehensive utilization of high-aluminum coal gangue comprises the following steps:

[0014] S1: High-aluminum gangue beneficiation: sorting high-aluminum gangue to separate sandstone, kaolinite and low calorific value coal from the gangue;

[0015] S2: Calcination and activation of low calorific value coal: Calcination and activation of low calorific value coal to obtain high-aluminum fly ash;

[0016] S3: Pre-desiliconization of high-alumina fly ash: The high-alumina fly ash obtained by roasting and activation is mixed with sodium hydroxide lye to perform desiliconization, thereby obtaining desiliconized fly ash, which is used as raw material 1 for producing alumina;

[0017] S4: Suspension roasting to produce powdered quicklime: limestone powder is calcined in a suspension roaster to obtain powdered quicklime, which is used as a raw material for producing alumina.

[0018] S5: preparing raw materials and forming raw materials into balls: mixing raw materials for producing alumina with super absorbent resin, stirring to obtain raw material balls, wherein the raw materials for producing alumina include raw material 1 obtained in S3, raw material 2 obtained in S4, and raw material 3 sodium carbonate lye;

[0019] S6: Drying and breaking up the raw material: Drying and breaking up the raw material balls prepared in S5 to obtain dry raw material;

[0020] S7: Raw meal preheating and calcination outside the kiln: The dry raw meal from S6 is preheated by suspension preheating outside the kiln and then enters the rotary kiln for calcination to obtain alumina clinker;

[0021] S8: Alumina clinker production: Alumina clinker is sintered to produce metallurgical grade alumina, and calcium-silicon slag is discharged during the production process;

[0022] S9: Preparation of cement raw materials from calcium silicate slag: The calcium silicate slag discharged from S8 is dealkalized and dried to produce cement raw materials.

[0023] Furthermore, the separation described in S1 is carried out using a dry intelligent separator and ray separation equipment.

[0024] Furthermore, the coal gangue with a particle size of ≤70mm is sorted by a dry intelligent sorting machine, and the coal gangue with a particle size of >70mm is sorted by a ray mineral separation equipment.

[0025] Furthermore, the ray mineral processing equipment is X-ray mineral processing equipment.

[0026] Furthermore, the Al2O3 content in the sandstone described in S1 is ≤30%, and the SiO2 content is ≥40%.

[0027] Furthermore, the kaolinite in S1 has an Al2O3 content of 30-37%, a SiO2 content of 32-44%, a Fe2O3 content ≤1%, and an ignition loss ≤20%. The kaolinite is used to produce calcined kaolin, mullite refractory materials, etc.

[0028] Furthermore, the low calorific value coal in S1 has an Al2O3 content of 30-38%, a SiO2 content of 33-42%, a loss on ignition ≥20%, a calorific value >400Kcal / kg, preferably 1600-2500Kcal / kg, and the low calorific value coal is used as a raw material for producing alumina.

[0029] The present invention first sorts the coal gangue, and the sorted kaolin is used as the raw material for calcining kaolin, mullite, etc., which can greatly improve the economic benefits of the project. At the same time, sandstone with low alumina content and high silicon oxide content is selected to reduce the consumption of alkali and calcium by sandstone in the process of producing alumina, and at the same time, the sandstone content in low calorific value coal can be further reduced. The calorific value of the sorted low calorific value coal is increased, and it can continue to spontaneously combust without adding additional fuel during the subsequent roasting and activation process, which greatly reduces the roasting and activation costs. The high-temperature flue gas generated by roasting is used for waste heat power generation, and the high-aluminum fly ash produced is used as the raw material for producing alumina. By sorting high-aluminum coal gangue, the added value of each product can be greatly increased, which is conducive to the large-scale comprehensive utilization of high-aluminum coal gangue.

[0030] Furthermore, in S2, a suspension roasting furnace or a rotary kiln is used for roasting and activation, and preferably a suspension roasting furnace is used for roasting and activation.

[0031] Furthermore, the temperature of the calcination activation in S2 is 900-1200° C., and the holding time is 5-40 minutes.

[0032] Furthermore, before the roasting and activation in S2, the low calorific value coal is crushed and ground into a particle size of 100 to 325 meshes, preferably 150 to 250 meshes.

[0033] Furthermore, the sodium hydroxide alkali solution in S3 is a sodium hydroxide aqueous solution with a mass concentration of 10 to 25%.

[0034] Furthermore, the mass ratio of the high-aluminum fly ash to the sodium hydroxide alkali solution in S3 is 1:2-8, the time for desiliconization by mixing the high-aluminum fly ash and the sodium hydroxide alkali solution is 60-300 minutes, and the desiliconization temperature is 60-100°C.

[0035] Furthermore, after the desiliconization described in S3 is completed, the mixture is subjected to liquid-solid separation, and the obtained liquid phase is a sodium silicate solution, and the solid phase is desiliconized fly ash. The sodium silicate solution is cooled and crystallized to obtain a sodium metasilicate product, and the solution after crystallization is further used for mixing with high-alumina fly ash for desiliconization.

[0036] Furthermore, the cooling temperature for the crystallization is 40-45° C., and the precipitated crystals are sodium metasilicate pentahydrate.

[0037] Furthermore, in the raw material 1 in S3, A / S=2-4, where A / S is the mass ratio of aluminum to silicon.

[0038] The high-alumina fly ash of the present invention can further increase its aluminum-silicon ratio after pre-desiliconization. The aluminum-silicon ratio of the high-alumina fly ash after high-alumina gangue roasting and activation is 0.8-1.0, and after desiliconization, the aluminum-silicon ratio can reach 2-4. This can significantly reduce lime consumption and the amount of silicon-calcium slag generated during the sintering process for alumina production, thereby improving the economic efficiency and feasibility of the project. The sodium silicate solution produced by desiliconization is further used to produce sodium metasilicate pentahydrate, which has the advantages of a short production process and low production costs. At the same time, sodium metasilicate pentahydrate is a standard market product with a large market capacity and high added value.

[0039] Furthermore, the calcination temperature in S4 is 800-1000° C., and the calcination time is 5-30 minutes.

[0040] Furthermore, the mass ratio of the sodium carbonates of raw material 1, raw material 2, and raw material 3 in S5 is 100:(40-50):(70-75); sodium carbonate is dissolved in water to obtain sodium carbonate lye, and the mass ratio of sodium carbonate to water is (25-35):100.

[0041] Furthermore, the super absorbent resin in S5 accounts for 0 to 30% of the dry mass of the total materials in the raw ball.

[0042] Superabsorbent resins are polymeric materials capable of absorbing and retaining tens to hundreds of times their own weight in water. In the present invention, superabsorbent resins are primarily used to improve the binding properties and ball stability of the raw material during ball formation. They also effectively regulate the rate of water release during drying, thereby improving the structural uniformity and molding quality of the raw material balls.

[0043] Types of super absorbent resins include, but are not limited to, sodium polyacrylates, polyacrylamides, modified starches, cellulose derivatives, polyvinyl alcohols, etc. The present invention does not impose any specific restrictions on the type of super absorbent resin used.

[0044] Furthermore, in the raw ball in S5, [N / R]=0.8-1.2, [C / S]=1.8-2.2, and moisture ≤45%; preferably, [N / R]=0.96-0.98, [C / S]=2.05-2.1, and moisture ≤42%.

[0045] The [N / R] is the molar ratio of sodium oxide to aluminum oxide and iron oxide in the material, and the [C / S] is the molar ratio of calcium oxide to silicon oxide and titanium oxide in the material.

[0046] Furthermore, the moisture content of the dry raw material in S6 is ≤15%, preferably ≤10%; the particle size of the dry raw material is 100-325 mesh, preferably 150-250 mesh.

[0047] Furthermore, the preheating temperature in S7 is 400-1000°C, preferably 800-900°C.

[0048] Furthermore, the calcination temperature in S7 is 1100-1300° C., preferably 1250-1300° C.; the calcination time is 10-90 min, preferably 30-40 min.

[0049] The present invention prepares alumina raw materials into raw material balls, which are dried and crushed, and then preheated outside the kiln before entering the rotary kiln for calcining into clinker. The drying cost of the raw materials can be greatly reduced. The raw materials preheated outside the kiln are calcined in the rotary kiln, which can greatly reduce the energy consumption of clinker production by more than 30%, increase the production capacity of the rotary kiln system by more than 30%, greatly reduce the production cost of alumina clinker firing, and improve the economic benefit of producing alumina clinker by sintering method.

[0050] Furthermore, the sintering method described in S8 is a conventional method for producing alumina.

[0051] Furthermore, the sintering method described in S8 includes dissolution of alumina clinker, separation of silicon-calcium slag, desiliconization, decomposition, evaporation, separation and washing of aluminum hydroxide, and roasting of aluminum hydroxide.

[0052] Furthermore, during the dealkalization treatment in S9, 2-8% of the dry mass of the calcium silicate slag, preferably 4-6% of quicklime, is added to the calcium silicate slag, the reaction temperature is 60-130° C., preferably 90-95° C., and the reaction time is 30-180 min, preferably 60-90 min. The dealkalized calcium silicate slag is subjected to liquid-solid separation and then dried to a moisture content of ≤10% and sent to a cement plant as a raw material for cement production.

[0053] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0054] 1. The present invention provides a large-scale, high-value-added process technology solution for the comprehensive utilization of high-aluminum coal gangue, which can solve the current problem of comprehensive utilization of large-scale solid waste of high-aluminum coal gangue, and can avoid occupying a large amount of land and serious pollution to the environment. The method of the present invention can make comprehensive utilization of high-aluminum coal gangue, and the kaolinite produced by sorting can be used as a raw material for calcining kaolin, mullite, etc., which can greatly improve the economic benefits of the project. After roasting low-calorific value coal, it is preheated to generate electricity or steam. The high-aluminum fly ash produced after roasting low-calorific value coal is used as a raw material for producing alumina, which can effectively alleviate the problem of insufficient bauxite supply in my country. The sodium silicate solution produced in the desiliconization process is further used to produce sodium metasilicate pentahydrate, and the product has high added value. The calcium silicate slag discharged during the sintering process of producing alumina is further used to produce cement, which not only effectively reduces the discharge of industrial waste and reduces the risk of environmental pollution, but also provides part of the raw materials for cement production, saves resources, and improves economic benefits.

[0055] 2. The present invention has good economic and social benefits. Practice has proven that 1 ton of coal gangue can produce approximately 150 kg of kaolinite, 600 kg of low calorific value coal, and 250 kg of sandstone. Roasting the low calorific value coal can produce 360 kg of high-aluminum fly ash, and when producing alumina, 143 kg of alumina can be produced. Combustion of 1 ton of low calorific value coal can generate 800 kWh of electricity and co-produce steam. The kaolinite obtained from the beneficiation process is sold as a raw material for calcining kaolin and mullite. It has been calculated that the production cost of alumina using this process is 2,000 yuan / ton, while the current market price of alumina is 5,000 yuan / ton. This process has good economic and social benefits and completely solves the global technical problem of comprehensive utilization of high-aluminum coal gangue. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1This is a schematic diagram of the process flow for comprehensive utilization of high-aluminum coal gangue of the present invention. DETAILED DESCRIPTION

[0057] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0058] Example 1

[0059] This embodiment provides a method for comprehensive utilization of high-aluminum coal gangue. Figure 1 The process shown includes the following steps:

[0060] S1: High-aluminum gangue beneficiation: The high-aluminum gangue produced by the coal mine is first screened with a sieve hole size of 7 cm. The gangue larger than 7 cm is beneficiated by X-ray beneficiation equipment, and the kaolinite and sandstone in the large high-aluminum gangue are sorted, and the rest is low calorific value coal; the gangue less than or equal to 7 cm is sorted by dry intelligent sorting equipment to obtain heavy component sandstone and light component kaolinite; the low calorific value coal obtained by X-ray beneficiation is mixed with the light component kaolinite obtained by the dry intelligent sorting equipment as raw materials for roasting.

[0061] In this embodiment, the calorific value of the low calorific value coal obtained by beneficiation was 1735 kcal / kg. Industrial analysis and composition testing of the low calorific value coal revealed the following: Al2O3: 31.23%, SiO2: 33.19%, and loss on ignition: 36.24%. The kaolinite obtained by X-ray beneficiation had a composition of Al2O3: 32.68%, SiO2: 36.71%, Fe2O3: 0.3%, and loss on ignition: 18.57%. The sandstone obtained by X-ray beneficiation had a composition of Al2O3: 18.89% and SiO2: 69.56%.

[0062] S2: Calcination and activation of low calorific value coal: In order to meet the roasting and activation requirements of the suspension roaster for low calorific value coal, large pieces of low calorific value coal are crushed, and small pieces of light kaolin and the crushed large pieces of low calorific value coal are homogenized together. The homogenized material is ground and the particle size of the material is controlled to be less than 10% on a 200-mesh standard sieve. The material then enters the fluidized suspension roaster for roasting and activation. The temperature of the fluidized suspension roaster is controlled to be 1030°C, and the residence time of the material in the roaster retention tank is controlled to be 30 minutes. After roasting and activation, activated fly ash is obtained, which is high-aluminum fly ash.

[0063] After the calcination and activation, the chemical composition of the high-aluminum fly ash obtained after calcination was detected, including Al2O3: 43.16%, SiO2: 52.87%, CaO: 1.53%, Fe2O3: 1.47%;

[0064] The high-temperature flue gas discharged from the fluidized suspension roasting furnace is treated in accordance with national environmental protection standards and discharged after the waste heat boiler generates electricity and steam.

[0065] S3: Pre-desiliconization of high-aluminum fly ash: Take the above-mentioned high-aluminum fly ash, and carry out pre-desiliconization under the conditions of liquid-solid ratio L / S=4, NaOH mass concentration of 18%, desiliconization time of 120min, and desiliconization temperature of 95°C. After desiliconization, the mixture is subjected to liquid-solid separation to obtain a liquid phase of sodium silicate solution and a solid phase of desiliconized fly ash; the desiliconized fly ash contains Al2O3:68.32%, SiO2:24.72%, its A / S is 2.76, the yield of desiliconized fly ash is 71.33%, and the moisture content is 43.58%; the NaOH concentration in the sodium silicate solution after desiliconization is 16.32%, and the SiO2 concentration is 70.72g / L. The sodium silicate solution is cooled to 45°C for crystallization to obtain a sodium metasilicate pentahydrate product.

[0066] S4: Suspension roasting to produce powdered quicklime: limestone powder is calcined in a suspension roaster to obtain powdered quicklime. The calcination temperature is 986°C and the calcination time is 15 minutes. The total calcium content of the quicklime obtained after calcination is 96.32%.

[0067] S5: preparing raw material and forming raw material balls: using the above-mentioned desiliconized fly ash, powdered quicklime, and sodium carbonate to prepare ingredients, and adding super absorbent resin, the super absorbent resin accounting for 2% of the total material dry basis weight, and the ingredients are prepared according to [N / R] = 1, [C / S] = 2, and the obtained raw material is stirred into balls;

[0068] The mass ratio of the desiliconized fly ash dry basis, powdered quicklime and sodium carbonate is 100:47.91:71.24:10, wherein the sodium carbonate is dissolved in water, and the mass ratio of sodium carbonate to water is 71.24:240.

[0069] S6: Drying and breaking up the raw material: Dry the raw material after being formed into balls in S5, use a drying and breaking up machine to further break up the raw material and then dry it. The moisture content of the raw material after drying is 5.32%.

[0070] S7: Preheating and calcination of raw meal outside the kiln: The dried raw meal is preheated by a suspension preheater outside the kiln. The hot air comes from the rotary kiln for subsequent calcination. The material temperature after preheating is 780℃. After preheating, the raw meal enters the rotary kiln for calcination. The calcination temperature is 1240℃ and the calcination residence time in the high temperature section is 35 minutes. After calcination, the raw meal is converted into alumina clinker.

[0071] S8: Alumina production from alumina clinker: The above alumina clinker is reused to produce alumina by the existing soda-lime sintering method, which mainly includes clinker dissolution, silicon-calcium slag separation, one and two stage desiliconization, decomposition, evaporation, aluminum hydroxide separation and washing, aluminum hydroxide roasting and other process steps to produce metallurgical grade alumina.

[0072] The specific operations are as follows:

[0073] Clinker dissolution: Alumina clinker is mixed with sodium hydroxide solution to dissolve the alumina to form sodium aluminate solution, while impurities such as silicate-calcium slag remain undissolved;

[0074] Calcium-silicon slag separation: The insoluble calcium-silicon slag is separated from the sodium aluminate solution through solid-liquid separation technology. The calcium-silicon slag can be further used in cement production.

[0075] One- and two-stage desiliconization: The sodium aluminate solution is desiliconized twice to further remove silicon impurities in the solution;

[0076] Decomposition: The desiliconized sodium aluminate solution is heated to 70°C. At the same time, carbon dioxide is introduced or seed crystals are added to decompose the sodium aluminate into aluminum hydroxide and alkali.

[0077] Evaporation: Evaporation and concentration of the decomposed solution to increase the concentration of alkali in the solution;

[0078] Aluminum hydroxide separation and washing: Aluminum hydroxide precipitate is separated from the solution by filtration and washed to obtain relatively pure aluminum hydroxide;

[0079] Aluminum hydroxide roasting: The washed aluminum hydroxide is roasted at high temperature to dehydrate it and convert it into alumina, ultimately obtaining metallurgical grade alumina products.

[0080] S9: Preparation of cement raw materials from calcium silicate slag: When calcium silicate slag is dealkalized to produce cement, the reaction temperature is 85°C, the reaction time is 150 min, and quicklime is added at 8% of the dry weight of the calcium silicate slag. After dealkalization, the sodium oxide content in the calcium silicate slag is ≤1.2%. The dealkalized calcium silicate slag is subjected to liquid-solid separation and then dried until the moisture content is ≤8%. It is then sent to a cement plant as a raw material for cement production.

[0081] The alumina prepared in this embodiment can meet the first-class product standard in GB / T 24487-2022 "Alumina".

[0082] The sodium silicate solution and sodium aluminate solution produced in this embodiment can also be used to produce other chemical substances, such as aluminum oxide.

[0083] According to the method of Example 1, 1 ton of coal gangue can produce about 150kg of kaolinite, 600kg of low calorific value coal, and 250kg of sandstone. After roasting, the low calorific value coal can produce 360kg of high-aluminum fly ash, and 143kg of alumina can be produced when producing alumina. When burning 1 ton of low calorific value coal, 800kwh of electricity can be generated, and steam can be co-produced at the same time. The kaolinite obtained by mineral processing is sold as a raw material for calcined kaolin and mullite. It is calculated that the production cost of alumina by this process is 2,000 yuan / ton, while the current market price of alumina reaches 5,000 yuan / ton, which has good economic and social benefits, and completely solves the world's technical problem of comprehensive utilization of high-aluminum coal gangue.

[0084] Example 2

[0085] This embodiment provides a method for comprehensive utilization of high-aluminum coal gangue. Figure 1 The process shown includes the following steps:

[0086] S1: High-aluminum gangue beneficiation: The high-aluminum gangue produced by the coal mine is first screened with a sieve hole size of 7 cm. The gangue larger than 7 cm is beneficiated by X-ray beneficiation equipment, and the kaolinite and sandstone in the large high-aluminum gangue are sorted, and the rest is low calorific value coal; the gangue less than or equal to 7 cm is sorted by dry intelligent sorting equipment to obtain heavy component sandstone and light component kaolinite; the low calorific value coal obtained by X-ray beneficiation is mixed with the light component kaolinite obtained by the dry intelligent sorting equipment to obtain low calorific value coal.

[0087] In this example, the low-calorific value coal obtained by beneficiation has a calorific value of 1957 kcal / kg. Industrial analysis and composition testing of the low-calorific value coal revealed the following: Al2O3: 29.23%, SiO2: 31.19%, and loss on ignition: 39.24%. Kaolinite obtained by X-ray beneficiation has a composition of Al2O3: 31.72%, SiO2: 35.94%, Fe2O3: 0.5%, and loss on ignition: 19.21%. Sandstone obtained by X-ray beneficiation has a composition of Al2O3: 21.32% and SiO2: 68.79%.

[0088] S2: Calcination and activation of low calorific value coal: In order to meet the roasting and activation requirements of the suspension roaster for low calorific value coal, large pieces of low calorific value coal are crushed and homogenized together with small pieces of light kaolin and the crushed large pieces of low calorific value coal. The homogenized material is ground and the particle size of the material is controlled to be less than 15% on a 180-mesh standard sieve. The material then enters the fluidized suspension roaster for roasting and activation. The temperature of the fluidized suspension roaster is controlled to be 1060°C and the residence time of the material in the roaster retention tank is controlled to be 20 minutes. After roasting and activation, activated fly ash is obtained, which is high-aluminum fly ash.

[0089] After the calcination and activation, the chemical composition of the high-aluminum fly ash obtained after calcination was detected, including Al2O3: 48.78%, SiO2: 44.56%, CaO: 1.83%, Fe2O3: 1.92%;

[0090] The high-temperature flue gas discharged from the fluidized suspension roasting furnace is treated in accordance with national environmental protection standards and discharged after the waste heat boiler generates electricity and steam.

[0091] S3: Pre-desiliconization of high-aluminum fly ash: Take high-aluminum fly ash and carry out pre-desiliconization under the conditions of liquid-solid ratio L / S=6, NaOH mass concentration of 20%, desiliconization time of 240min and desiliconization temperature of 75°C. After desiliconization, the mixture is subjected to liquid-solid separation to obtain a liquid phase of sodium silicate solution and a solid phase of desiliconized fly ash. The desiliconized fly ash contains Al2O3:72.46%, SiO2:19.32%, its A / S is 3.75, the yield of desiliconized fly ash is 64.28%, and the moisture content is 44.39%. After desiliconization, the NaOH concentration in the sodium silicate solution is 17.93%, and the SiO2 concentration is 55.87g / L. The sodium silicate solution is cooled to 45°C for crystallization to obtain a sodium metasilicate pentahydrate product.

[0092] S4: Suspension roasting to produce powdered quicklime: limestone powder is calcined in a suspension roaster to obtain powdered quicklime. The calcination temperature is 980°C and the calcination time is 20 minutes. The total calcium content of the quicklime obtained after calcination is 97.08%.

[0093] S5: preparing raw meal and forming raw meal into balls: using the above-mentioned desiliconized fly ash, powdered quicklime, and sodium carbonate to prepare ingredients, and adding super absorbent resin, the super absorbent resin accounting for 5% of the total material dry basis weight, the ingredients are prepared according to [N / R] = 1.05, [C / S] = 2.05, and the obtained raw meal is stirred into balls;

[0094] The mass ratio of the desiliconized fly ash dry basis, powdered quicklime and sodium carbonate is 100:48.75::72.53:5. Sodium carbonate is dissolved in water, and the mass ratio of sodium carbonate to water is 72.53:250.

[0095] S6: Drying and breaking up the raw material: Dry the raw material after being formed into balls in S5, use a drying and breaking up machine to further break up the raw material and then dry it. The moisture content of the raw material after drying is 4.74%.

[0096] S7: Preheating and calcination of raw meal outside the kiln: The dried raw meal is preheated by a suspension preheater outside the kiln. The hot air comes from the rotary kiln for subsequent calcination. The material temperature after preheating is 680℃. After preheating, the raw meal enters the rotary kiln for calcination. The calcination temperature is 1260℃ and the calcination residence time in the high temperature section is 30 minutes. After calcination, the raw meal is converted into alumina clinker.

[0097] S8: Alumina clinker production of alumina: The above alumina clinker is reused to produce alumina by the existing soda-lime sintering method, which mainly includes clinker dissolution, red mud separation and washing, one and two stage desiliconization, decomposition, evaporation, aluminum hydroxide separation and washing, aluminum hydroxide roasting and other process steps to produce metallurgical grade alumina.

[0098] The specific operations are as follows:

[0099] Clinker dissolution: Alumina clinker is mixed with sodium hydroxide solution to dissolve the alumina to form sodium aluminate solution, while impurities such as silicate-calcium slag remain undissolved;

[0100] Calcium-silicon slag separation: The insoluble calcium-silicon slag is separated from the sodium aluminate solution through solid-liquid separation technology. The calcium-silicon slag can be further used in cement production.

[0101] One- and two-stage desiliconization: The sodium aluminate solution is desiliconized twice to further remove silicon impurities in the solution;

[0102] Decomposition: The desiliconized sodium aluminate solution is heated to 70°C. At the same time, carbon dioxide is introduced or seed crystals are added to decompose the sodium aluminate into aluminum hydroxide and alkali.

[0103] Evaporation: Evaporation and concentration of the decomposed solution to increase the concentration of alkali in the solution;

[0104] Aluminum hydroxide separation and washing: Aluminum hydroxide precipitate is separated from the solution by filtration and washed to obtain relatively pure aluminum hydroxide;

[0105] Aluminum hydroxide roasting: The washed aluminum hydroxide is roasted at high temperature to dehydrate it and convert it into alumina, ultimately obtaining metallurgical grade alumina products.

[0106] S9: Preparation of cement raw materials from calcium silicate slag: When calcium silicate slag is dealkalized to produce cement, the reaction temperature is 90°C, the reaction time is 120 min, and quicklime is added at 5% of the dry weight of the calcium silicate slag. After dealkalization, the sodium oxide content in the calcium silicate slag is ≤1.5%. The dealkalized calcium silicate slag is subjected to liquid-solid separation and then dried until the moisture content is ≤10% and is sent to the cement plant as raw material for cement production.

[0107] The alumina prepared in this embodiment can meet the first-grade product standard in GB / T 24487-2022 "Alumina", and can also produce ultrafine, high-white, low-sodium and other chemical alumina.

[0108] The sodium silicate solution and sodium aluminate solution produced in this embodiment can also be used to produce other chemical substances, such as aluminum oxide.

[0109] Comparative Example 1

[0110] This comparative example provides a method for comprehensive utilization of high-aluminum coal gangue, which differs from Example 1 in that the S1 high-aluminum coal gangue beneficiation step is not performed, and the rest is the same as Example 1.

[0111] The chemical composition of high-aluminum fly ash obtained by calcining and activating high-aluminum coal gangue includes: Al2O3: 33.3%, SiO2: 35.2%, CaO: 0.12%, Fe2O3: 0.43%, and loss on ignition: 34.6%;

[0112] In Comparative Example 1, since no mineral processing was performed, the kaolinite in the high-aluminum coal gangue was not separated and could not be used as a high-value-added raw material for calcining kaolin, mullite, etc., resulting in the loss of this part of the economic benefits. Low calorific value coal is mixed with a large amount of impurities such as sandstone, and has a low calorific value, and additional fuel needs to be added during the roasting and activation process. The Al2O3 content in high-aluminum fly ash is low and the SiO2 content is high, which leads to a decrease in the desiliconization efficiency of the subsequent desiliconization step. The alumina finally produced in Comparative Example 1 can only meet the third-grade product standard in the metallurgical grade alumina GB / T 24487-2022 "Alumina".

[0113] Comparative Example 2

[0114] This comparative example provides a method for comprehensive utilization of high-aluminum coal gangue. The difference from Example 1 is that in the S3 high-aluminum fly ash pre-desiliconization step, NaOH is replaced by 10% sulfuric acid solution, the desiliconization time is 120 minutes, and the desiliconization temperature is 60°C.

[0115] The resulting desiliconized fly ash contained 55.58% Al2O3 and 37.91% SiO2, yielding a 62.45% yield. Using sulfuric acid as a desiliconizing agent is less effective than using sodium hydroxide, resulting in alumina that only meets the secondary standard for metallurgical-grade alumina, as specified in GB / T 24487-2022, "Alumina."

[0116] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for comprehensive utilization of high-aluminum coal gangue, comprising the following steps: S1: High-aluminum gangue beneficiation: sorting high-aluminum gangue to separate sandstone, kaolinite and low calorific value coal from the gangue; S2: Calcination and activation of low calorific value coal: Calcination and activation of low calorific value coal to obtain high-aluminum fly ash; S3: Pre-desiliconization of high-alumina fly ash: The high-alumina fly ash obtained by roasting and activation is mixed with sodium hydroxide lye to perform desiliconization, thereby obtaining desiliconized fly ash, which is used as raw material 1 for producing alumina; S4: Suspension roasting to produce powdered quicklime: limestone powder is calcined in a suspension roaster to obtain powdered quicklime, which is used as a raw material for producing alumina. S5: preparing raw materials and forming raw materials into balls: mixing raw materials for producing alumina with super absorbent resin, stirring to obtain raw material balls, wherein the raw materials for producing alumina include raw material 1 obtained in S3, raw material 2 obtained in S4, and raw material 3 sodium carbonate lye; S6: Drying and breaking up the raw material: Drying and breaking up the raw material balls prepared in S5 to obtain dry raw material; S7: Raw meal preheating and calcination outside the kiln: The dry raw meal from S6 is preheated by suspension preheating outside the kiln and then enters the rotary kiln for calcination to obtain alumina clinker; S8: Alumina clinker production: Alumina clinker is sintered to produce metallurgical grade alumina, and calcium-silicon slag is discharged during the production process; S9: Preparation of cement raw materials from calcium silicate slag: The calcium silicate slag discharged from S8 is dealkalized and dried to produce cement raw materials.

2. The method according to claim 1, wherein: The Al2O3 content of the sandstone described in S1 is ≤30%, and the SiO2 content is ≥40%; the Al2O3 content of the kaolin is 30-37%, the SiO2 content is 32-44%, the Fe2O3 content is ≤1%, and the loss on ignition is ≤20%; the Al2O3 content of the low calorific value coal is 30-38%, the SiO2 content is 33-42%, the loss on ignition is ≥20%, and the calorific value is >400Kcal / kg.

3. The method according to claim 1, wherein: The temperature of the calcination activation in S2 is 900-1200° C., and the holding time is 5-40 minutes.

4. The method according to claim 1, wherein: The sodium hydroxide alkali solution in S3 is a sodium hydroxide aqueous solution with a mass concentration of 10-25%, the mass ratio of the high-alumina fly ash to the sodium hydroxide alkali solution is 1:2-8, the time for mixing the high-alumina fly ash and the sodium hydroxide alkali solution for desiliconization is 60-300 minutes, and the desiliconization temperature is 60-100°C; after the desiliconization in S3 is completed, the mixture is subjected to liquid-solid separation, and the obtained liquid phase is a sodium silicate solution, and the sodium silicate solution is cooled to 40-45°C for crystallization to obtain sodium metasilicate.

5. The method according to claim 1, wherein: The calcination temperature in S4 is 800-1000° C., and the calcination time is 5-30 minutes.

6. The method according to claim 1, wherein: The mass ratio of the sodium carbonates of raw material 1, raw material 2, and raw material 3 in S5 is 100:(40-50):(70-75); sodium carbonate is dissolved in water to obtain sodium carbonate lye, and the mass ratio of sodium carbonate to water is (25-35):100; the super absorbent resin accounts for 0-30% of the dry weight of the total material in the raw ball, and the raw ball has [N / R]=0.8-1.2, [C / S]=1.8-2.2, and moisture ≤45%.

7. The method according to claim 1, wherein: The moisture content of the dry raw material in S6 is ≤15%, and the particle size of the dry raw material is 100-325 meshes.

8. The method according to claim 1, wherein: The preheating temperature in S7 is 400-1000° C., the calcination temperature is 1100-1300° C., and the calcination time is 10-90 minutes.

9. The method according to claim 1, wherein: The sintering method described in S8 includes dissolution of alumina clinker, separation of silicon-calcium slag, desiliconization, decomposition, evaporation, separation and washing of aluminum hydroxide, and roasting of aluminum hydroxide.

10. The method according to claim 1, wherein: During the dealkalization treatment in S9, 2-8% of quicklime by dry weight of the calcium silicate slag is added to the calcium silicate slag, the reaction temperature is 60-130° C., and the reaction time is 30-180 min.

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