Process for preparing silicon carbide from coal gangue and waste based on super-enthalpy calcination energy supply

Abstract

The present application relates to solid waste treatment technical field, disclose a kind of process for preparing silicon carbide based on super-enthalpy calcination energy supply of coal gangue and waste, comprising: coal gangue is crushed and sieved, while using the first part of recovery heat of calcining furnace backflow to preheat and send into furnace calcination;Calcination product is leached by hydrochloric acid, liquid phase extraction by-product aluminum salt, solid phase interception obtains silicon dioxide residue;Then, silicon dioxide residue is uniformly mixed with high-carbon waste;System dispatching second part of recovery heat provides high-temperature environment for downstream, drive mixture material to occur carbothermic reduction reaction, product is finally obtained after removing impurities by acid liquid step washing silicon carbide.The present application integrates heat cascade reuse and mineral phase chemical elution, reduces the cost of silicon-carbon source procurement and external heat consumption, and completes the high-value conversion of coal gangue and high-carbon waste.

Description

Technical Field

[0001] This invention relates to the field of solid waste treatment technology, specifically to a process for preparing silicon carbide from coal gangue and waste materials powered by superenthalpy calcination. Background Technology

[0002] Silicon carbide is an important industrial powder material. Traditional preparation processes typically rely on high-purity quartz sand and petroleum coke, resulting in high raw material procurement costs. In recent years, utilizing coal gangue and high-carbon solid waste as alternative silicon-carbon sources to prepare silicon carbide has become a resource-based approach with industrial economic value. However, existing waste residue preparation technologies still have shortcomings in energy utilization efficiency, reaction kinetics, and phase purity control.

[0003] In terms of energy allocation and thermodynamic management, existing preparation processes typically separate the initial calcination of coal gangue from the downstream carbothermic reduction into completely independent heating sections. Each process section relies on an external heat source for independent power supply, resulting in persistently high external energy consumption for the overall process. This cut-off approach leads to the complete loss of waste heat generated in the high-temperature furnace, preventing its reuse within the process flow. Furthermore, directly introducing unheated, cold materials into the high-temperature furnace can trigger thermal shock to the system, reducing the stability of production operations.

[0004] Regarding material conversion and reaction mechanisms, coal gangue contains a large amount of alumina byproducts. Current technologies fail to effectively integrate the dealuminization and purification of coal gangue with the mixed reduction of high-carbon waste, leading to direct loss of aluminum resources. More critically, due to the lack of pre-treatment chemical leaching to create pores, the ore matrix maintains a dense physical structure. When mixed with high-carbon waste, the effective contact area between silicon-carbon solid particles is limited, directly increasing the reaction resistance in the subsequent carbothermic reduction stage.

[0005] In terms of product crystal formation and post-purification processing, the cooling and elution methods after high-temperature reduction are relatively crude. During the conventional rapid cooling process, thermal stress inevitably accumulates within the newly formed silicon carbide lattice, leading to micro-cracks in the material. Simultaneously, single or conventional acid leaching processes cannot simultaneously address the dissolution of metallic impurities and the removal of incompletely converted silica matrix, resulting in a large amount of residual impurities within the system. This significantly hinders the final silicon carbide product from meeting the standards for structural integrity and phase purity. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a process for preparing silicon carbide from coal gangue and waste based on superenthalpy calcination. This process solves the problems of high energy consumption, low resource utilization rate of coal gangue and high-carbon waste, and lack of a comprehensive treatment approach that combines heat recovery in stages with silicon source purification and extraction.

[0007] To address the above problems, the present invention provides the following technical solution: This invention provides a process for preparing silicon carbide from coal gangue and waste materials based on superenthalpy calcination, employing the following technical solution: Coal gangue containing silica and alumina is crushed and screened to obtain screened coal gangue. Simultaneously, heat generated by the calcining furnace is recovered using a heat exchanger, the heat including a first part of recovered heat and a second part of recovered heat. The first portion of the recovered heat is returned to the preheating process for the screened coal gangue. The preheated coal gangue is fed into a calcining furnace for calcination to obtain calcined waste rock powder. After mixing and reacting calcined waste stone powder with hydrochloric acid aqueous solution, a separation operation is performed to obtain acid leachate and acid leachate residue whose main component is silicon dioxide. The acid leaching residue is uniformly mixed with high-carbon waste to obtain a reaction mixture; The second part of the recovered heat is transferred to the reaction mixture using a heat exchanger to provide a high-temperature environment, so that the reaction mixture undergoes a carbothermic reduction reaction and a multi-step washing and purification process in sequence, and finally silicon carbide is obtained.

[0008] By adopting the above technical solution, this invention does not employ the traditional high-energy-consuming independent preparation route, but instead deeply integrates waste treatment with the cascade utilization of thermal energy. At the front end of the process flow, the system uses a heat exchanger to comprehensively distribute the high-temperature waste heat generated by the calcining furnace. The first part of the recovered heat is refluxed to directly preheat the screened coal gangue. This operation not only reduces the absolute energy consumption of the calcination stage but also buffers the system thermal shock caused by the cold material entering the furnace. As the material enters the calcining furnace, the internal crystal structure of the coal gangue undergoes a phase transformation under thermal stress. In particular, the kaolinite component undergoes a dehydroxylation reaction, transforming into amorphous metakaolinite. During this process, the originally structurally inert alumina is transformed into a highly chemically active phase, which directly clears the reaction obstacles and provides favorable conditions for the subsequent acid leaching operation.

[0009] After the aforementioned thermal activation treatment, the material is then transferred to the liquid-solid phase acid leaching and elution stage. The activated alumina reacts rapidly with hydrochloric acid, and the resulting aluminum chloride dissolves in the aqueous phase to form the acid leaching solution. Meanwhile, the original silica from the coal gangue, due to its relatively stable crystal structure, remains primarily in the solid residue. Through conventional liquid-solid separation operations, the process can physically remove most of the aluminum impurities that affect the purity of subsequent preparations, thereby obtaining a high-purity silica framework with a certain degree of porosity as a precursor for subsequent reduction.

[0010] To ensure the thoroughness of the reduction process, the purified silica is mixed with high-carbon waste. At this point, the second portion of recovered heat from the heat exchanger establishes the necessary high-temperature environment for the downstream reaction bed. Under these conditions, solid silica undergoes a carbothermic reduction reaction with the carbon source.

[0011] The above process directly absorbs and utilizes the sensible heat generated from the upstream process waste, completing the energy transfer and reuse within the system. After the reaction, the prepared primary silicon carbide crystals undergo multiple washing and purification steps to remove any incompletely converted deposits. Thus, the entire process line not only achieves resource utilization of waste but also ensures the efficient self-circulation of system energy.

[0012] Preferably, the coal gangue contains silicon dioxide and alumina, and contains 30% to 50% silicon dioxide and 15% to 25% alumina by mass percentage.

[0013] By adopting the above technical solution, coal gangue within this composition range can ensure sufficient aluminum salt conversion during the acid leaching stage. More importantly, the residual silica framework usually generates appropriate micropores in situ after acid washing and dealuminization. This associated porous structure improves the solid-solid contact mass transfer efficiency during subsequent mixing with the carbon source, thereby accelerating the carbothermic reduction reaction rate.

[0014] Preferably, after obtaining the acid leachate, the process further includes extracting the byproduct aluminum salt from the acid leachate by evaporation.

[0015] By adopting the above technical solution and solidifying the free aluminum ions in the waste liquid through the introduction of an evaporation and crystallization process, the process not only realizes the resource-based extraction of associated aluminum elements from coal gangue, but also reduces the difficulty and environmental burden of subsequent acidic waste liquid treatment.

[0016] Preferably, the high-carbon waste is one of waste tire residue, solid biochar, and kerosene co-refining residue.

[0017] By adopting the above technical solutions, all three types of waste can provide amorphous carbon sources after thermal pyrolysis. Compared with conventional crystalline carbon sources, amorphous carbon has a higher degree of atomic disorder and more microscopic defects on its surface, which can reduce the activation energy required for carbothermal reduction in actual reaction systems.

[0018] Preferably, the reaction mixture undergoes the following four processing steps in a high-temperature environment: first, a carbothermic reduction reaction occurs at a first temperature and in an inert gas atmosphere; then, a cooling treatment is performed at a second temperature and in an inert gas atmosphere; next, a washing treatment is performed using an aqueous hydrochloric acid solution; finally, a washing treatment is performed using an aqueous hydrofluoric acid solution to obtain silicon carbide.

[0019] By adopting the above technical solution, the staged heat treatment not only ensured the completion rate of the main reaction but also created conditions for the stable growth of the crystal form. In the subsequent elution stage, hydrochloric acid aqueous solution is preferentially used to dissolve and remove trace metal cations adsorbed in the system; then, hydrofluoric acid aqueous solution selectively dissolves the unreacted silica matrix through a coordination complexation mechanism. This stepwise dual-acid washing removes residual impurities in the product and effectively improves the purity of the final silicon carbide phase.

[0020] Preferably, the first temperature at which the carbothermic reduction reaction occurs is controlled between 1200°C and 1600°C.

[0021] By adopting the above technical solution and limiting the reaction temperature to 1200℃ to 1600℃, the system can be provided with sufficient energy input to overcome the strong endothermic characteristics of carbothermic reduction, thereby successfully driving the silicon-oxygen bond to break and reconstruct into a silicon-carbon bond.

[0022] Preferably, the second temperature for cooling is controlled between 650°C and 750°C.

[0023] By adopting the above technical solution and setting a medium-temperature annealing treatment of 650℃ to 750℃, the main purpose is to slow down the thermal stress accumulated in the newly formed silicon carbide lattice and avoid the risk of micro-cracks in the material during subsequent cooling.

[0024] Preferably, when using solid biochar as a high-carbon waste, the solid biochar is prepared through the following steps: selecting lignocellulose agricultural biomass as raw material, the lignocellulose agricultural biomass containing 10% to 25% lignin, 55% to 60% cellulose and 15% to 30% hemicellulose by mass percentage; hydrolyzing the lignocellulose agricultural biomass to produce fermentable sugars and residual organic waste, and then carbonizing the residual organic waste to convert it into solid biochar.

[0025] By employing the above technical solution, when using biomass with specific components for hydrolysis, the lignin in a defined ratio remains structurally stable during the hydrolysis stage, serving as the initial carbon skeleton in the remaining waste. Simultaneously, a high proportion of cellulose and hemicellulose, after being hydrolyzed and exfoliated, leaves numerous mesoporous channels in situ within the solid material. During subsequent carbonization, the solid biochar generated based on these pore structures possesses a high specific surface area, allowing it to be fully dispersed and encapsulate silica particles during the mixing process, thereby expanding the contact area for the solid-phase reaction.

[0026] Preferably, when using waste tire residue as a high-carbon waste, the waste tire residue is prepared by the following steps: selecting waste tires with high carbon content as raw materials; pyrolyzing and sintering the waste tires to recycle and obtain waste tire residue.

[0027] By adopting the above technical solution, waste tires that are difficult to degrade naturally are pyrolyzed and sintered, which not only effectively solves the environmental pollution problem caused by solid waste, but also recovers waste tire residue with high carbon content, providing a stable and low-cost high-quality carbon source for subsequent preparation processes.

[0028] Preferably, when using kerosene co-refining residue as a high-carbon waste, the carbon content of the kerosene co-refining residue is as high as 80%.

[0029] By adopting the above technical solution, the co-refining residue with this specific ratio not only provides a basic solid carbon source, but also allows the heavy hydrocarbon macromolecules generated within it to easily undergo secondary thermal decomposition during the heating period, releasing small-molecule reducing gases into the reaction bed. This gas-solid two-phase reduction environment, composed of decomposed gas and solid carbon, can shorten the overall carbothermic conversion process.

[0030] This invention provides a process for preparing silicon carbide from coal gangue and waste materials using superenthalpy calcination as the energy source. It has the following beneficial effects: 1. This invention utilizes heat exchangers to recover heat generated in the calcining furnace and then stages it back for preheating coal gangue at the front end and providing a heat source for the downstream carbothermic reduction reaction, thus changing the high-energy-consuming mode of independent heating in each reaction stage in traditional processes. This coordinated allocation of heat energy not only reduces the overall external energy consumption of the process but also buffers the system thermal shock caused by the direct input of cold materials into the furnace, achieving effective heat recovery within the process flow.

[0031] 2. This invention integrates the dealuminization and purification of coal gangue with the reduction and utilization of high-carbon waste. In the initial stage, aluminum is removed from the coal gangue by elution with hydrochloric acid aqueous solution, and aluminum salts are extracted as a byproduct. This process, while achieving resource extraction of associated metals, also generates a silica framework with microporous structures in situ in the dealuminized residue. This framework expands the solid-solid contact area when subsequently mixed with amorphous high-carbon waste, thereby reducing the reaction resistance in the carbothermic reduction stage.

[0032] 3. This invention incorporates a cooling process under an inert gas atmosphere after high-temperature carbothermal reduction, coupled with a stepwise washing process using hydrochloric acid and hydrofluoric acid. The cooling process at the intermediate temperature stage can alleviate the thermal stress accumulated inside the newly formed silicon carbide lattice, preventing micro-cracks from forming in the product during subsequent cooling. Subsequently, the product is washed with hydrochloric acid aqueous solution and hydrofluoric acid aqueous solution respectively. Relying on the dissolving properties of the two acids, residual metal impurities and incompletely converted silicon dioxide matrix are removed from the system in sequence, effectively ensuring the structural integrity and phase purity of the final silicon carbide. Attached Figure Description

[0033] Figure 1This is a schematic diagram of the process flow for preparing silicon carbide from coal gangue and waste materials based on superenthalpy calcination energy supply according to the present invention. Figure 2 The graphs are comparative diagrams of the heat redistribution verification test of the superenthalpy combustion system of the present invention. Among them, (a) is a line graph comparing the energy distribution of the reaction system, and (b) is a line graph showing the relationship between the temperature response and external energy supply of each group of objects. Figure 3 The diagram shows a comparison of the phase state of the target product and the recovery verification test of the by-products of the present invention. (a) is a line graph showing the intensity of the main diffraction peak of the final product hexagonal silicon carbide and the number of characteristic peaks of the impurity phases, and (b) is a bar graph showing the comparison of the recovery amount of aluminum salt by-products. Figure 4 The following is an energy consumption tracking and evaluation chart for the comprehensive energy consumption comparison test of the system of the present invention, wherein (a) is a line graph of the total comprehensive energy consumption and the equivalent energy consumption of each item for generating a unit mass of silicon carbide product for each test object, and (b) is a matchstick graph for evaluating the energy-saving benefits of the superenthalpy heat cycle. Figure 5 The evaluation charts are for the purity and impurity stripping comparison test of the silicon carbide product of the present invention. Among them, (a) is a line graph comparing the absolute purity of the final product silicon carbide, and (b) is a quantitative evaluation chart of the residual level of various impurities. Figure 6 This is an evaluation chart comparing the waste resource conversion and environmental benefits of this invention. Detailed Implementation

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] Please see the appendix Figure 1 , Figure 1 This is a schematic diagram of the process flow for preparing silicon carbide from coal gangue and waste materials based on ultraenthalpic calcination. The entire process mainly integrates the cascade recovery of heat with the chemical washing of mineral phases to achieve material conversion.

[0036] Preparation Examples 1-4: Preparation Example 1: This preparation example provides a method for preparing biochar, including the following steps: Lignocellulose agricultural biomass is selected as raw material. Lignocellulose agricultural biomass contains 10% lignin, 60% cellulose and 30% hemicellulose by mass percentage. The above-mentioned lignocellulose agricultural biomass is hydrolyzed to produce fermentable sugars, and the remaining organic waste is then carbonized to convert it into solid biochar.

[0037] Preparation Example 2: This preparation example provides a method for preparing biochar, including the following steps: Lignocellulose agricultural biomass is selected as raw material. The lignocellulose agricultural biomass contains 20% lignin, 55% cellulose and 25% hemicellulose by mass percentage. The above-mentioned lignocellulose agricultural biomass is hydrolyzed to produce fermentable sugars, and the remaining organic waste is then carbonized to convert it into solid biochar.

[0038] Preparation Example 3: This preparation example provides a method for preparing biochar, including the following steps: Lignocellulose agricultural biomass is selected as raw material. Lignocellulose agricultural biomass contains 25% lignin, 60% cellulose and 15% hemicellulose by mass percentage. The above-mentioned lignocellulose agricultural biomass is hydrolyzed to produce fermentable sugars, and the remaining organic waste is then carbonized to convert it into solid biochar.

[0039] Preparation Example 4: This preparation example provides a method for preparing waste tire residue, including the following steps: Waste tires with high carbon content were selected as raw materials; The waste tires are subjected to pyrolysis and sintering to recover waste tire residue. Examples 1-6: Example 1:

[0040] This embodiment provides a process for preparing silicon carbide from coal gangue and waste materials based on superenthalpy calcination, including the following steps: Coal gangue containing 50% silica and 25% alumina by weight percentage will be crushed and screened. The heat generated by the calcining furnace is recovered using a heat exchanger, and the first part of the recovered heat is recycled back to preheat the screened coal gangue. The preheated coal gangue is fed into a calcining furnace for calcination, and calcined waste rock powder is output.

[0041] The calcined waste stone powder is mixed with hydrochloric acid aqueous solution (HCl) and reacted. The acid leachate was separated and the byproduct aluminum salt was extracted by evaporation; At the same time, acid leaching residues, whose main component is silicon dioxide, were separated.

[0042] The acid leaching residue and the waste tire residue obtained in Preparation Example 4 were uniformly mixed at a molar ratio of silicon dioxide to carbon of 1:3 to obtain a reaction mixture.

[0043] The second portion of recovered heat is transferred downstream using a heat exchanger to provide a high-temperature environment, allowing the reaction mixture to undergo four processing steps sequentially: A carbothermic reduction reaction occurs at 1450℃ in an inert gas atmosphere; Cooling treatment was carried out at 700℃ in an inert gas atmosphere; Washing treatment was performed using hydrochloric acid aqueous solution; Silicon carbide (SiC) is finally obtained by washing with an aqueous solution of hydrofluoric acid (HF). Example 2:

[0044] This embodiment provides a process for preparing silicon carbide from coal gangue and waste materials based on superenthalpy calcination, including the following steps: Coal gangue containing 50% silica and 25% alumina by weight percentage will be crushed and screened. The heat generated by the calcining furnace is recovered using a heat exchanger, and the first part of the recovered heat is recycled back to preheat the screened coal gangue. The preheated coal gangue is fed into a calcining furnace for calcination, and calcined waste rock powder is output.

[0045] The calcined waste stone powder is mixed with hydrochloric acid aqueous solution and reacted. The acid leachate was separated and the byproduct aluminum salt was extracted by evaporation; At the same time, acid leaching residues, whose main component is silicon dioxide, were separated.

[0046] The acid leaching residue and the waste tire residue obtained in Preparation Example 4 were uniformly mixed at a molar ratio of silicon dioxide to carbon of 1:3 to obtain a reaction mixture.

[0047] The second portion of recovered heat is transferred downstream using a heat exchanger to provide a high-temperature environment, allowing the reaction mixture to undergo four processing steps sequentially: A carbothermic reduction reaction occurs at 1200℃ in an inert gas atmosphere; Cooling treatment was carried out at 650℃ in an inert gas atmosphere; Wash with hydrochloric acid aqueous solution; Silicon carbide was finally obtained by washing with an aqueous solution of hydrofluoric acid. Example 3:

[0048] This embodiment provides a process for preparing silicon carbide from coal gangue and waste materials based on superenthalpy calcination, including the following steps: Coal gangue containing 50% silica and 25% alumina by weight percentage will be crushed and screened. The heat generated by the calcining furnace is recovered using a heat exchanger, and the first part of the recovered heat is recycled back to preheat the screened coal gangue. The preheated coal gangue is fed into a calcining furnace for calcination, and calcined waste rock powder is output.

[0049] The calcined waste stone powder is mixed with hydrochloric acid aqueous solution and reacted. The acid leachate was separated and the byproduct aluminum salt was extracted by evaporation; At the same time, acid leaching residues, whose main component is silicon dioxide, were separated.

[0050] The acid leaching residue and the waste tire residue obtained in Preparation Example 4 were uniformly mixed at a molar ratio of silicon dioxide to carbon of 1:3 to obtain a reaction mixture.

[0051] The second portion of recovered heat is transferred downstream using a heat exchanger to provide a high-temperature environment, allowing the reaction mixture to undergo four processing steps sequentially: A carbothermic reduction reaction occurs at 1600℃ in an inert gas atmosphere; Cooling treatment was carried out at 750℃ in an inert gas atmosphere; Wash with hydrochloric acid aqueous solution; Silicon carbide was finally obtained by washing with an aqueous solution of hydrofluoric acid. Example 4:

[0052] This embodiment provides a process for preparing silicon carbide from coal gangue and waste materials based on superenthalpy calcination, including the following steps: Coal gangue containing 50% silica and 25% alumina by weight percentage will be crushed and screened. The heat generated by the calcining furnace is recovered using a heat exchanger, and the first part of the recovered heat is recycled back to preheat the screened coal gangue. The preheated coal gangue is fed into a calcining furnace for calcination, and calcined waste rock powder is output.

[0053] The calcined waste stone powder is mixed with hydrochloric acid aqueous solution and reacted. The acid leachate was separated and the byproduct aluminum salt was extracted by evaporation; At the same time, acid leaching residues, whose main component is silicon dioxide, were separated.

[0054] The acid leaching residue was mixed uniformly with the solid biochar prepared in Preparation Example 1 at a molar ratio of silicon dioxide to carbon of 1:3 to obtain a reaction mixture.

[0055] The second portion of recovered heat is transferred downstream using a heat exchanger to provide a high-temperature environment, allowing the reaction mixture to undergo four processing steps sequentially: A carbothermic reduction reaction occurs at 1450℃ in an inert gas atmosphere; Cooling treatment was carried out at 700℃ in an inert gas atmosphere; Wash with hydrochloric acid aqueous solution; Silicon carbide was finally obtained by washing with an aqueous solution of hydrofluoric acid. Example 5:

[0056] This embodiment provides a process for preparing silicon carbide from coal gangue and waste materials based on superenthalpy calcination, including the following steps: Coal gangue containing 50% silica and 25% alumina by weight percentage will be crushed and screened. The heat generated by the calcining furnace is recovered using a heat exchanger, and the first part of the recovered heat is recycled back to preheat the screened coal gangue. The preheated coal gangue is fed into a calcining furnace for calcination, and calcined waste rock powder is output.

[0057] The calcined waste stone powder is mixed with hydrochloric acid aqueous solution and reacted. The acid leachate was separated and the byproduct aluminum salt was extracted by evaporation; At the same time, acid leaching residues, whose main component is silicon dioxide, were separated.

[0058] The acid leaching residue and the kerosene co-refining residue with a carbon content of up to 80% were uniformly mixed at a molar ratio of silicon dioxide to carbon of 1:3 to obtain a reaction mixture.

[0059] The second portion of recovered heat is transferred downstream using a heat exchanger to provide a high-temperature environment, allowing the reaction mixture to undergo four processing steps sequentially: A carbothermic reduction reaction occurs at 1450℃ in an inert gas atmosphere; Cooling treatment was carried out at 700℃ in an inert gas atmosphere; Wash with hydrochloric acid aqueous solution; Silicon carbide was finally obtained by washing with an aqueous solution of hydrofluoric acid. Example 6:

[0060] This embodiment provides a process for preparing silicon carbide from coal gangue and waste materials based on superenthalpy calcination, including the following steps: Coal gangue containing 30% silica and 15% alumina by weight percentage will be crushed and screened. The heat generated by the calcining furnace is recovered using a heat exchanger, and the first part of the recovered heat is recycled back to preheat the screened coal gangue. The preheated coal gangue is fed into a calcining furnace for calcination, and calcined waste rock powder is output.

[0061] The calcined waste stone powder is mixed with hydrochloric acid aqueous solution and reacted. The acid leachate was separated and the byproduct aluminum salt was extracted by evaporation; At the same time, acid leaching residues, whose main component is silicon dioxide, were separated.

[0062] The acid leaching residue and the waste tire residue obtained in Preparation Example 4 were uniformly mixed at a molar ratio of silicon dioxide to carbon of 1:3 to obtain a reaction mixture.

[0063] The second portion of recovered heat is transferred downstream using a heat exchanger to provide a high-temperature environment, allowing the reaction mixture to undergo four processing steps sequentially: A carbothermic reduction reaction occurs at 1450℃ in an inert gas atmosphere; Cooling treatment was carried out at 700℃ in an inert gas atmosphere; Wash with hydrochloric acid aqueous solution; Silicon carbide was finally obtained by washing with an aqueous solution of hydrofluoric acid.

[0064] Comparative Examples 1-4: Comparative Example 1: Compared with Example 1, the difference is that the heat generated by the calcining furnace was not recovered by the heat exchanger for heat recirculation, the first part of the recovered heat was not used to preheat the coal gangue, and the second part of the recovered heat was not used to transport it downstream to provide a high-temperature environment. The entire process uses external independent heating, and everything else is the same.

[0065] Comparative Example 2: Compared with Example 1, the difference is that coal gangue and waste tire residue are not used. Instead, commercially available petroleum coke and high-purity quartz sand are used as carbon and silicon sources for the mixed reaction. All other aspects are the same.

[0066] Comparative Example 3: Compared with Example 1, the difference is that after calcination, the coal gangue is directly and uniformly mixed with waste tire residue at a molar ratio of silicon dioxide to carbon of 1:3, skipping the steps of mixing and reacting the calcined waste stone powder with hydrochloric acid aqueous solution and separating them. All other steps are the same.

[0067] Comparative Example 4: Compared with Example 1, the difference is that after the reaction mixture is treated at 700°C and in an inert gas atmosphere, the reaction is directly terminated, and the subsequent washing treatment with hydrochloric acid aqueous solution and hydrofluoric acid aqueous solution is omitted. All other steps are the same.

[0068] Test Examples 1-5: Test Example 1: The pre-proportioned reactants from Examples 1 to 6 and Comparative Example 1 were used as test objects. High-temperature thermocouples and high-precision heat flow sensors were arranged at key energy transmission nodes in the reaction system. The monitoring points covered the calcining furnace outlet, the front-end reflux channel of the heat exchange system, and the outer wall of the downstream carbothermic reduction reaction zone.

[0069] The system inputs ignition energy to start the system. After the furnace reaches a stable combustion state, the external ignition source is cut off. The data acquisition system then synchronously records the total heat generated by the system during the complete reaction stage of 1 kg of reference mass material.

[0070] The flow state of the working medium in the heat exchanger and the temperature gradient changes at the inlet and outlet are dynamically monitored. The amount of preheating retained back to the front end to enhance the preheating enthalpy of coal gangue is calculated and recorded. At the same time, the amount of downstream energy supplied to the carbothermic reduction reaction system is calculated.

[0071] Record the peak temperature reached in the carbothermic reduction reaction zone. For test objects that have not reached the target conversion temperature, turn on the external auxiliary heating source to supplement energy until the target is reached, and record the cumulative amount of external auxiliary heating consumed when the system reaches steady state.

[0072] Table 1. Test data on heat distribution and temperature response of the reaction system like Figure 2 As shown, it contains two sub-graphs, one above the other. Figure 2 (a) is a line graph comparing the energy distribution of the reaction system, which highlights the differences in the absolute values ​​of the total heat generated by the system, the amount of preheating at the front end and the amount of energy supplied downstream in Examples 1 to 6 and Comparative Example 1. Figure 2 (b) is a line graph showing the relationship between the temperature response and external energy supply of each group of objects, which intuitively shows the relationship between the peak temperature of the reaction zone under the self-heating condition of the system and the amount of external auxiliary heating required to reach the target environment in Examples 1 to 6 and Comparative Example 1.

[0073] In the engineering research of high-value treatment of solid waste, energy consumption control indicators are key to evaluating technical feasibility. According to the data in Table 1, if the heat energy released by coal gangue and high-carbon waste during the calcination stage is not internally recovered, the high-temperature waste heat will be lost outward, increasing the energy consumption of the subsequent high-temperature reduction stage. Comparative Example 1 is in a state without heat exchanger intervention, lacking a reflux preheating and energy redistribution mechanism. The peak temperature of the downstream carbothermic reduction reaction zone is 582℃, which does not meet the high-temperature conditions required for silicon carbide preparation. The system needs to supplement 15.65 MJ of auxiliary heat source to maintain the reaction. After introducing the heat exchange system, the high-temperature waste heat is guided back to the front end of the system, increasing the initial preheating enthalpy of the screened coal gangue. The total enthalpy of the system becomes the superposition of the chemical reaction release enthalpy and the preheating enthalpy. The thermal circulation network plays a role in interception and heat redistribution in the system's energy transmission path. The intercepted heat supports the preheating of the front-end materials and delivers distributed energy in the range of 11 to 14 MJ to the downstream of the process. The convergence of the internal self-circulating energy flow enables Examples 1 to 6 to achieve an internal operating temperature range of 1200°C to 1600°C without relying on external primary energy supply. In a stable, high-temperature environment, the highly active carbon provided by waste tire residue or biochar reacts with residual silica, releasing oxygen as carbon monoxide gas, and carbon-silicon bonding forms hexagonal silicon carbide. Through closed-loop heat transfer before and after the process, using recovered waste heat as the primary energy source, the dependence of traditional carbothermal reduction processes on fossil fuels for maintaining high-temperature operation is reduced, achieving self-consistent energy operation of the preparation process.

[0074] Test Example 2: The final solid powders prepared in Examples 1 to 6 and Comparative Example 3 were collected, and the solid substances obtained after evaporation and crystallization of the acid leaching solution in Examples 1 to 6 were also collected as test objects.

[0075] The collected solid powder was thoroughly ground in an agate mortar and passed through a 200-mesh standard sieve to prepare a standard powder sample for X-ray diffraction testing. The standard powder sample was scanned using an X-ray diffractometer within a diffraction angle range of 20 to 80 degrees, and the positions and relative intensities of characteristic diffraction peaks were recorded to confirm the hexagonal silicon carbide phase and count the number of characteristic peaks of impurity phases.

[0076] Collect and weigh the actual mass of aluminum salt crystal solids corresponding to each test object, and calculate the mass of aluminum salt by-products that can be recovered from each kilogram of initial coal gangue raw material consumed.

[0077] Table 2. Product phase characteristics and by-product recovery test data like Figure 3 As shown, it contains two sub-graphs, one above the other. Figure 3(a) is a line graph showing the difference between the intensity of the main diffraction peak of the final product hexagonal silicon carbide and the number of characteristic peaks of the impurity phase, illustrating the differences between Examples 1 to 6 and Comparative Example 3 in terms of the growth and development of the target crystal and the purity of the phase state. Figure 3 (b) is a bar chart comparing the recovery of aluminum salt by-products, which visually shows the actual output effect of aluminum extraction operations in Examples 1 to 6 and the blank state of Comparative Example 3 without extraction operations.

[0078] According to the data in Table 2, the alumina content in the coal gangue raw material affects the preparation of silicon carbide. In the high-temperature solid-phase reaction system, aluminum metal impurities and silicon sources easily form aluminosilicate phases at high temperatures, or exist as ash on the surface of reactant particles, affecting the gas-solid mass transfer of the carbothermic reduction reaction. Analysis of the X-ray diffraction results of the final products of Examples 1 to 6 shows that the main peak intensity of hexagonal silicon carbide is in the range of 7000 to 9000, with fewer characteristic peaks of impurity phases, reflecting the integrity of the crystal structure of the product. This is related to the hydrochloric acid aqueous solution reaction step introduced earlier, which strips excess aluminum elements to the liquid phase. Data on the recovery of aluminum salt by-products shows that the example using raw materials with medium alumina content produced more than 400 grams of aluminum salt crystals, while Example 6 using raw materials with low alumina content had an aluminum salt conversion of 251.4 grams. In Comparative Example 3, which did not undergo acid leaching and separation treatment, five characteristic peaks of impurity phases were observed, with the main peak intensity of silicon carbide at a relatively low level of 3145. Residual impurities reduced the effective concentration of reactants, affecting the formation environment of silicon carbide nuclei. Introducing an aluminum extraction step into the preparation process eliminated the interference of aluminum on the subsequent high-temperature carbonization process, increased the reaction concentration of silicon dioxide, and simultaneously enabled the recovery and utilization of the byproduct aluminum salt, verifying the rationality of the material transformation and resource recovery in the chemical mechanism.

[0079] Test Example 3: The technical solutions of Examples 1 to 6 and Comparative Example 1 were selected as test objects. A full-process energy consumption monitoring platform was built, and high-precision smart meters and gas mass flow controllers were connected to the power input end of the reaction equipment and the fuel supply pipeline, respectively.

[0080] Start the continuous material feeding program. After the entire reaction network reaches thermal equilibrium and enters a stable continuous production mode, record the initial operating readings of all monitoring instruments and set the production of 1 kg of purified final solid silicon carbide product as the unified energy consumption calculation benchmark.

[0081] During the continuous testing period, the electrical energy consumed by mechanical equipment (including crushers, screening machines and pumps at all levels) and heating components is tracked and accumulated. The total equivalent of primary fossil fuel energy consumed during the initial ignition stage of the calciner and the maintenance of the auxiliary heat source is simultaneously captured and calculated.

[0082] The collected and compiled power and fuel data will be converted into standard coal equivalent indicators according to the current national energy conversion standards. The overall system energy consumption will be verified and the actual relative energy saving rate of the superenthalpy combustion system will be calculated.

[0083] Table 3. System Comprehensive Energy Consumption Test Calculation Data Note: In Table 3, "-" indicates that Comparative Example 1 is used as the benchmark for calculation in this "Relative Energy Saving Rate" indicator, and there is no energy saving data relative to itself. Since the core logic of this indicator is to quantify the percentage decrease in the total system energy consumption of each embodiment relative to Comparative Example 1, and Comparative Example 1 itself belongs to the traditional high-energy-consumption original state without adopting the superenthalpy combustion heat distribution mechanism, this cell is left blank with "-" to anchor the reference benchmark for the entire energy saving assessment.

[0084] like Figure 4 As shown, it contains two sub-graphs, one above the other. Figure 4 (a) Generate a line graph for the total energy consumption and the equivalent energy consumption of each unit mass of silicon carbide product for each test object, which visually shows the huge absolute differences in electricity expenditure, fuel consumption and final total energy burden between Examples 1 to 6 and Comparative Example 1, which uses external independent heating. Figure 4 (b) is a matchstick diagram for evaluating the energy-saving benefits of the superenthalpy heat cycle, highlighting and comparing the relative energy-saving rates achieved by Examples 1 to 6 compared to Comparative Example 1 in reducing total primary energy dissipation.

[0085] According to the data in Table 3, the overall system energy consumption of Examples 1 to 6 ranges from 3.19 to 3.89 kgce / kg. In the energy accounting of industrial reaction systems, maintaining a high-temperature reduction environment above 1200°C typically requires a large amount of fuel, which is a major constraint on the large-scale preparation of related materials. Comparative Example 1 uses a fully external independent heating mode, with a fuel thermal equivalent of 14.66 kg standard coal equivalent and an overall system energy consumption of 19.28 kg standard coal equivalent. The superenthalpy combustion heat distribution mechanism used in the examples optimizes the energy consumption structure. Waste heat from the reaction is collected through a heat flow cross-linking network, recycled for preheating of materials, and provides heat energy to the carbothermic reduction reaction zone. The chemical network maintains operation through internal heating, reducing the process chain's dependence on external energy. The breakdown data shows that internal heat conduction replaces some of the fuel consumption required to maintain the high temperature, while the electrical load of related auxiliary heating equipment decreases. The system's self-consistent energy operation mechanism improves energy utilization efficiency, achieving a relative energy saving rate of approximately 80%, indicating that the superenthalpy combustion technology can reduce the overall energy cost of carbothermal reduction while ensuring reaction output, and has good potential for industrial application.

[0086] Test Example 4: The final solid products prepared by Examples 1 to 6, Comparative Example 3 (which skipped the aluminum separation step), and Comparative Example 4 (which omitted the subsequent acid washing step) were selected as test objects. All solid products were ground and dried to constant weight under the same constant temperature and humidity environment.

[0087] Accurately weigh an appropriate amount of dried solid powder sample, and use a mixture of sodium carbonate and boric acid flux to perform alkaline melting digestion on the powder sample at high temperature. After adjusting the volume, use inductively coupled plasma atomic emission spectrometry to determine the absolute concentration of aluminum, iron, calcium and magnesium metal elements in the digestion solution. The total content of metal impurities per kilogram of product is calculated by conversion and summation.

[0088] Based on conventional chemical analysis methods for silicon carbide, the amount of free carbon residue in each group of samples was determined by combustion titration, the total amount of unreacted silicon dioxide and silicate residue was determined by hydrofluoric acid volatilization gravimetric method, and the absolute purity percentage of silicon carbide in the final product was calculated by the total element difference subtraction method.

[0089] Table 4. Test data on purity and residual impurities of silicon carbide products like Figure 5 As shown, it contains two sub-graphs, one above the other. Figure 5 (a) is a line graph comparing the absolute purity of the final product silicon carbide, which visually shows the fundamental difference in the target product compliance rate between Examples 1 to 6 and the two different comparative examples; Figure 5 (b) is a quantitative assessment chart of the residual levels of various impurities. The left axis uses a bar chart with light and dark gray groups to compare the residual percentages of free carbon, unreacted silica and silicates. The right axis uses a line graph in a logarithmic coordinate system to accurately reveal the increase of metal impurities after skipping the purification step.

[0090] Product purity is a crucial dimension for evaluating the industrial application value of non-metallic materials. High-temperature solid-phase reaction systems often face challenges in conversion rate and byproduct separation, making impurity stripping a practically significant process design. According to Table 4, different process routes exhibit varying levels of impurity control effectiveness. Observing the test results of Comparative Example 3, without the front-end acid leaching separation step, aluminum, iron, and other metallic elements in the raw materials entered the high-temperature reaction zone. Metal ions readily participate in side reactions at temperatures above 1400℃, resulting in the final product containing 12.56% unreacted silica and silicate phases, with a total metallic impurity content of 32145.8 mg / kg and a silicon carbide purity of 81.35%. In Comparative Example 4, the system implemented a front-end aluminum extraction operation but omitted the subsequent washing and purification steps. Unreacted carbon sources and silica adhered to the product surface, forming a non-metallic impurity coating, resulting in a product purity of 91.12%. Examples 1 to 6 employed a pre- and post-purification mechanism. Before the preparation stage, metal ions were transferred to the liquid phase using hydrochloric acid aqueous solution to obtain a silicon-rich substrate. After the high-temperature reaction, washing was performed using a combination of hydrochloric acid and hydrofluoric acid. The hydrofluoric acid dissolved unreacted silica and silicate residues, while the hydrochloric acid removed residues from the free carbon surface. This multi-step purification process reduced the amount of non-metallic residues in the final solid powder, controlled metallic impurities within the range of two to three hundred milligrams, and maintained the silicon carbide purity above 98%, verifying the role of the multi-stage purification steps in impurity separation.

[0091] Test Example 5: A unified reaction output benchmark was set, with the continuous and stable production of 1000 grams of target silicon carbide powder that meets the purity standard as the accounting boundary. The absolute dry basis mass of coal gangue, waste tire residue, solid biochar and other high-carbon wastes that participated in the chemical transformation in the input reaction network of Examples 1 to 6 were weighed and statistically analyzed.

[0092] For Comparative Example 2, which uses commercially available high-purity quartz sand and petroleum coke as pure silicon-carbon sources, the absolute dry basis total amount of industrial-grade pure raw materials that must be consumed to achieve the same 1000g output target was monitored and recorded simultaneously.

[0093] Based on the law of conservation of mass, the total mass of the hexagonal silicon carbide main product and the recovered aluminum salt byproduct output from each test group is summarized and divided by the total mass of the initial solid waste put into the system. The high-value conversion rate of waste that has transitioned from physical mass to valuable products is then calculated.

[0094] The actual purchase guidance prices of bulk industrial raw materials in the experimental period and the relevant solid waste disposal subsidy conversion standards were retrieved. The raw material cost per kilogram of product corresponding to the production of unit mass silicon carbide product was comprehensively and quantitatively calculated, and the total load of solid waste disposal corresponding to the production was statistically analyzed.

[0095] Table 5. Test data on waste resource conversion and environmental economic benefits Note: The "-" in Table 5 indicates that there is no corresponding data for Comparative Example 2 in the "Waste High-Value Conversion Rate" indicator. Since Comparative Example 2 uses commercially available high-purity quartz sand and petroleum coke as pure sources and does not add any solid waste to the reaction system, the waste disposal base is zero. Therefore, it is impossible to calculate the rate of waste conversion to valuable materials. The cell is left blank with a horizontal line to match the actual material flow logic.

[0096] like Figure 6 As shown, the data comprehensively compares the amount of waste disposed of, the rate of high-value conversion, and the economic input of core raw materials. The bar chart quantifies the absolute weight of solid waste consumed to generate 1 kg of target product, while the line chart simultaneously displays the ratio of physical waste to chemical phases and the corresponding changes in the economic input of core raw materials, intuitively revealing the difference in upfront capital expenditure between relying on natural pure mineral sources and adopting waste substitution routes.

[0097] The preparation of industrial-grade solid powders often faces the problem of high costs for upstream mineral resources. Conventional solid-phase reduction systems often require pure reactants. In Comparative Example 2, the cost of commercially available high-purity quartz sand and refined petroleum coke, after mining and purification, was calculated to be RMB 28.45 per kilogram of silicon carbide. According to the statistics in Table 5, Examples 1 to 6, while producing the target phase, consumed an average of 5.45 to 8.34 kilograms of mixed solid waste. Based on the system heat recovery and multi-stage acid leaching network settings of the aforementioned test examples, it can be inferred that the synergy between system thermal energy and chemical treatment promoted the reconstruction of low-grade silicon-carbon sources, resulting in 21.36% to 35.22% of the waste residue in the test group being physically converted into silicon carbide crystals and byproduct aluminum salts. Using waste residue instead of pure minerals reduced the costs of conventional mining and high-purity purification, allowing the raw material procurement cost per kilogram of target product in each example to be controlled within the range of RMB 1.54 to 2.12. Comparing the cost data and waste conversion rate of the two sets of raw materials, it is shown that it is feasible to co-melt low-quality coal gangue and high-carbon waste residue. This not only partially alleviates the environmental pressure caused by waste stockpiling, but also demonstrates clear industrial economic value in reducing raw material procurement costs.

Claims

1. A process for preparing silicon carbide from coal gangue and waste materials using superenthalpy calcination as the energy source, characterized in that, include: Coal gangue containing silica and alumina is crushed and screened to obtain screened coal gangue. Simultaneously, heat generated by the calcining furnace is recovered using a heat exchanger, the heat including a first part of recovered heat and a second part of recovered heat; The first portion of recovered heat is recycled back to preheat the screened coal gangue. The preheated coal gangue is fed into the calcining furnace for calcination to obtain calcined waste rock powder; The calcined waste stone powder is mixed with hydrochloric acid aqueous solution and then separated to obtain acid leachate and acid leachate residue whose main component is silicon dioxide. The acid leaching residue is uniformly mixed with high-carbon waste to obtain a reaction mixture; The heat exchanger is used to transfer the second portion of recovered heat to the reaction mixture, providing a high-temperature environment so that the reaction mixture undergoes a carbothermal reduction reaction and multiple washing and purification processes in sequence, ultimately obtaining silicon carbide.

2. The process for preparing silicon carbide from coal gangue and waste based on superenthalpy calcination energy supply according to claim 1, characterized in that, The coal gangue containing silicon dioxide and alumina contains 30% to 50% silicon dioxide and 15% to 25% alumina by mass percentage.

3. The process for preparing silicon carbide from coal gangue and waste based on superenthalpy calcination energy supply according to claim 1, characterized in that, After obtaining the acid leachate, the process further includes extracting the byproduct aluminum salt from the acid leachate by evaporation.

4. The process for preparing silicon carbide from coal gangue and waste based on superenthalpy calcination energy supply according to claim 1, characterized in that, The high-carbon waste is one of the following: waste tire residue, solid biochar, and kerosene co-refining residue.

5. The process for preparing silicon carbide from coal gangue and waste based on superenthalpy calcination energy supply according to claim 1, characterized in that, The reaction mixture is subjected to the following four processing steps in sequence in the high-temperature environment: First, the carbothermic reduction reaction occurs at a first temperature and in an inert gas atmosphere; Subsequently, a cooling process was carried out at a second temperature in an inert gas atmosphere; Next, the mixture was washed with a hydrochloric acid solution. Finally, the silicon carbide is obtained by washing with an aqueous solution of hydrofluoric acid.

6. The process for preparing silicon carbide from coal gangue and waste based on superenthalpy calcination energy supply according to claim 5, characterized in that, The first temperature at which the carbothermic reduction reaction occurs is controlled between 1200°C and 1600°C.

7. The process for preparing silicon carbide from coal gangue and waste based on superenthalpy calcination energy supply according to claim 5, characterized in that, The second temperature for the cooling process is controlled between 650°C and 750°C.

8. The process for preparing silicon carbide from coal gangue and waste based on superenthalpy calcination energy supply according to claim 4, characterized in that, When the solid biochar is used as the high-carbon waste, the solid biochar is prepared through the following steps: Lignocellulose agricultural biomass is selected as raw material, wherein the lignocellulose agricultural biomass contains 10% to 25% lignin, 55% to 60% cellulose and 15% to 30% hemicellulose by mass percentage. The lignocellulose agricultural biomass is hydrolyzed to produce fermentable sugars and residual organic waste. The residual organic waste is then carbonized to convert it into solid biochar.

9. The process for preparing silicon carbide from coal gangue and waste based on superenthalpy calcination energy supply according to claim 4, characterized in that, When the waste tire residue is used as the high-carbon waste, the waste tire residue is prepared through the following steps: Waste tires with high carbon content were selected as raw materials; The waste tires are subjected to pyrolysis and sintering to recover the waste tire residue.

10. The process for preparing silicon carbide from coal gangue and waste based on superenthalpy calcination energy supply according to claim 4, characterized in that, When the kerosene co-refining residue is used as the high-carbon waste, the carbon content of the kerosene co-refining residue is as high as 80%.

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