A method for preparing a continuous casting tundish covering agent using a lithium battery crucible.

Abstract

This invention belongs to the technical field of metallurgical functional refractory materials and high-value recycling of industrial solid waste. Specifically, it relates to a method for preparing a continuous casting tundish covering agent from used lithium battery crucibles, including raw material pretreatment, precise batching, efficient mixing, granulation, low-temperature curing, and finished product screening steps: Used aluminum-silicon lithium battery cathode material sintering crucibles are selected, and large impurities, metal debris, and unsintered waste are removed by manual sorting. A two-stage crushing process is adopted: first, the material is coarsely crushed to a particle size ≤10mm by a jaw crusher, and then medium crushed to a particle size ≤3mm by a cone crusher. The material is then fed into a planetary ball mill for dry ultrafine grinding. After grinding, the crucible powder with a particle size <74μm is obtained by negative pressure screening. Then, efficient mixing, granulation, low-temperature curing, and finished product processing are performed to obtain a tundish covering agent with uniform particle size distribution and good flowability.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical functional refractory materials and high-value recycling of industrial solid waste. Specifically, it relates to a method for directly preparing a green, fluorine-free, low-melting-point, high-spreading, and highly purifying continuous casting tundish covering agent using sintered crucibles of used aluminum-silicon lithium battery cathode material as the main raw material without high-temperature pre-melting. In particular, it relates to a preparation technology that utilizes the residual lithium components in the crucible to synergistically improve the melting rate, viscosity, heat preservation properties, and steel purification capacity of the covering agent. Background Technology

[0002] The tundish in continuous casting is a key functional container in the steelmaking-continuous casting process, responsible for buffering, diverting, temperature regulation, and removing non-metallic inclusions. Tundish covering agent is the core functional material ensuring stable tundish operation and improving the surface quality and internal cleanliness of the cast billet. Its main functions include: isolating molten steel from air to prevent secondary oxidation and the formation of brittle inclusions such as Al2O3 and MgAl2O4; rapidly melting and spreading on the surface of molten steel to form a continuous and uniform slag layer, reducing radiative heat loss and achieving stable casting at low temperatures; adsorbing fine inclusions floating in the molten steel and assimilating them into the slag phase, preventing inclusions from remaining inside the cast billet; and possessing a suitable viscosity and melting temperature range to prevent problems such as poor spreading due to excessive slag viscosity or slag entrapment and lining erosion due to excessively thin slag. Currently, industrially used tundish covering agents are mainly divided into three categories: the first category is carbonized rice husk-based carbonaceous materials. The first type is a covering agent, which has low raw material cost and good heat preservation effect, but it is prone to carbon oxidation at high temperatures, causing carbon increase in molten steel. It is not suitable for high-end steel grades that are sensitive to carbon content, such as ultra-low carbon steel, non-oriented silicon steel, and stainless steel. Moreover, it produces a lot of smoke and dust when burned, polluting the on-site environment. The second type is a magnesium-based alkaline covering agent, which uses magnesia and dolomite as the main raw materials. It has high alkalinity, but the raw material purity requirements are high and the cost is expensive. In addition, the melting point of magnesium oxide is too high, which leads to slow melting speed and poor spreading uniformity of the covering agent. It is easy to cause local crusting and exposed molten steel, which cannot meet the requirements of high-speed continuous casting. The third type is a fluorinated composite silicate covering agent, which introduces fluorides to lower the melting point and improve fluidity. However, fluorides are prone to volatilization at high temperatures to generate toxic gases such as HF, which corrode continuous casting equipment and crystallizers. After entering the secondary cooling water system, it causes water pollution and destroys the ozone layer, which is not in line with the development direction of green and low-carbon steelmaking.

[0003] With the explosive growth of the lithium-ion battery cathode material industry, the annual usage and scrap volume of aluminosilicate refractory saggers, as the core vessels for high-temperature sintering of cathode materials, continues to rise. The main mineral phases of lithium battery saggers are mullite, cordierite, corundum, spinel, and a small amount of glass phase, with Al2O3, SiO2, and MgO as the main chemical components. After repeated use, cathode material elements penetrate and adhere to the inner wall of the sagger. For example, the chemical composition of a 6-series sagger used in a cathode material production plant after it was broken is shown in Table 1.

[0004] Li2O is a highly effective fluxing component in metallurgical slag systems. It can significantly reduce the melting temperature of silicate melts, regulate high-temperature viscosity, and improve glass formation ability. Its effects can completely replace traditional fluorides. However, currently, used lithium battery crucibles are not effectively utilized, and the performance of recycled products is unstable due to heavy metal and lithium salt residues. A large number of scrapped crucibles are still mainly stockpiled and landfilled, causing serious waste of resources and environmental safety hazards.

[0005] While there are existing reports on the preparation of metallurgical covering agents using solid waste, they generally suffer from the following drawbacks: First, they rely on high-temperature pre-melting processes, which result in high energy consumption, large equipment investment, and long production cycles, limiting their industrial-scale promotion; second, they do not specifically explore the in-situ fluxing and interface modification mechanisms of lithium components in the used lithium battery crucible, thus limiting their ability to improve the adsorption and purification of inclusions; and third, their formulation systems are unreasonable, failing to simultaneously achieve multiple functions such as rapid melting, uniform spreading, long-term heat preservation, and deep purification, making them difficult to adapt to the continuous casting production needs of various steel grades.

[0006] Based on the aforementioned industry pain points, this invention provides a method for preparing a continuous casting tundish covering agent that does not require pre-melting and uses used lithium battery crucibles as the main raw material. This method fully releases the functional value of lithium components in the covering agent, achieving multiple goals such as solid waste disposal, cost reduction, performance upgrade, and green environmental protection. It has significant theoretical value and promising industrial application prospects. Summary of the Invention

[0007] The purpose of this invention is to overcome the defects of existing tundish covering agents, such as carbon increase, fluorine pollution, poor melting and spreading performance, and insufficient purification effect. At the same time, it solves the problems of low resource utilization rate of used lithium battery crucibles, lithium resource waste, and high disposal costs. This invention provides a method for preparing a continuous casting tundish covering agent using used lithium battery crucibles. This method does not involve high-temperature pre-melting. Using used lithium battery crucibles as the main raw material, it fully utilizes the fluxing, viscosity reduction, interface modification, and inclusion assimilation effects of lithium components through reasonable component ratio and particle size distribution. This results in a fluorine-free, environmentally friendly, rapidly slag-forming, heat-insulating, and highly efficient purification tundish covering agent.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a continuous casting tundish covering agent using a lithium battery crucible includes the following steps: raw material pretreatment, precise batching, efficient mixing, granulation, low-temperature curing, and finished product sieving. The details are as follows: 1) Raw material pretreatment: Used aluminum-silicon lithium battery cathode material sintering crucibles were selected and manually sorted to remove large impurities, metal debris and unsintered waste. A two-stage crushing process was adopted: first, the material was coarsely crushed to a particle size ≤10mm by a jaw crusher, and then medium crushed to a particle size ≤3mm by a cone crusher. Subsequently, the material was sent to a planetary ball mill for dry ultrafine grinding. After grinding, the crucible powder with a particle size <74μm was obtained by negative pressure screening. 2) Precise ingredient proportioning: The ingredients are shown in the table below, by weight percentage, total weight 100%;

[0009] 3) High-efficiency mixing, granulation molding, low-temperature curing, and finished product: Follow these steps: (1) Dry mixing stage: Add the pretreated crucible powder, quartz sand powder, lightly calcined magnesium oxide powder, sodium carbonate powder, cenospheres and carbon black into a high-speed high-power mixer according to the ratio, and dry mix at 600~800r / min for 20~30min to ensure that each solid component is evenly dispersed and free from agglomeration and segregation; (2) Wet mixing stage: Slowly add water-soluble inorganic binder and deionized water to the dry-mixed mixture, and continue wet mixing at 400~600r / min for 20~40min to form a mixture with uniform moisture content and moderate plasticity. (3) Granulation and curing: The wet mixture is fed into a centrifugal rolling ball granulator for molding and granulation, and the particle size is controlled between 0.25 and 1.25 mm. After granulation, it is sent into a hot air curing oven and dried and cured at 120-150℃ for 2.5-4.0 h to remove free water and ensure that the particle strength is ≥15N. (4) Screening the finished product: The solidified particles are screened in two stages to remove fine powder and oversized particles, and the intermediate package covering agent with uniform particle size distribution and good flowability is obtained.

[0010] This invention does not rely on high-temperature pre-melting, but directly activates the multiple functions of residual Li2O in the used lithium battery crucible, thereby improving the performance of the covering agent from three aspects: slag physicochemistry, interfacial wetting behavior, and inclusion assimilation kinetics. (1) Fluorine-free fluxing and rapid slag formation mechanism: Li2O is a strong network modifier, which can react with SiO2 in the sagger. Al2O3 forms a low eutectic system in situ, with the lowest eutectic point dropping to 1120~1230℃, far lower than that of traditional magnesium covering agents. Under the action of high temperature (1500~1580℃) of molten steel in the tundish, the covering agent can quickly absorb heat and melt without external pre-melting, and spread out completely within 5~10 seconds to form a continuous closed liquid slag layer, completely eliminating secondary oxidation caused by exposed molten steel, while avoiding defects such as local crusting and pores. (2) High-temperature viscosity precise control mechanism: Li⁺ ions have small ionic radius and high charge density, which can effectively break the Si-O-Si and Al-O-Al network structures, reduce the degree of polymerization of molten slag, and make the high-temperature viscosity of the covering agent stably controlled in the range of 0.15~0.35 Pa・s at 1500℃; this viscosity range can ensure good slag flowability and avoid slag entrapment and erosion of the lining caused by excessively low viscosity, thus achieving a dynamic balance between lubrication and slag stabilization. (3) Mechanism of deep purification and inclusion assimilation of molten steel: Li₂O can significantly increase the basicity and interfacial activity of the slag phase, reduce the slag-steel interfacial tension, and enhance the wetting and adsorption capacity of non-metallic inclusions such as Al₂O₃, CaO·Al₂O₃, and MnO·SiO₂ in molten steel; at the same time, Li⁺ can enter the interior of the inclusion lattice, change its morphology and physical properties, and promote the collision, aggregation, coarsening and rapid floating of fine inclusions into the slag phase. After treatment with this covering agent, the total oxygen content T[O] of molten steel is reduced by 25%~38%, the number of large inclusions is reduced by more than 60%, and the cleanliness of the billet interior is significantly improved; (4) Synergistic enhancement mechanism of heat preservation performance: The Al2O3-SiO2-MgO system in the sagger forms a porous and lightweight structure with the cenospheres. Combined with the dense glassy slag film formed after lithium modification, it double blocks heat conduction and heat radiation, so that the temperature drop rate of molten steel is controlled at 0.5~1.0℃ / min, which meets the temperature stability requirements under long-term transportation and multi-furnace continuous casting conditions.

[0011] The present invention proposes a method for preparing a continuous casting tundish covering agent using a lithium battery crucible. Employing the above-mentioned technical solution, this method has the following beneficial effects: (1) The high-temperature pre-melting process is eliminated throughout the process, which reduces energy consumption, shortens the production process, and significantly reduces equipment investment and operating costs, making it more suitable for industrial continuous production.

[0012] (2) Using used lithium battery crucibles as the main raw material, the solid waste utilization rate reaches more than 62%, realizing the in-situ efficient utilization of multi-component resources such as lithium, aluminum, silicon and magnesium, and solving the solid waste disposal problem in the lithium battery industry.

[0013] (3) Completely replace fluorides with Li2O to achieve fluorine-free green production, avoid fluorine pollution and equipment corrosion, and meet the requirements of ultra-low emissions and low-carbon steelmaking.

[0014] (4) It integrates rapid slag formation, uniform spreading, long-term heat preservation and deep purification, and can be adapted to the continuous casting needs of various steel types such as ultra-low carbon steel, silicon steel, low alloy steel and stainless steel, and the surface and internal quality of the billet are significantly improved.

[0015] (5) The raw materials are stable, the formula cost is low, the particles have good flowability, and it is easy to use, with significant economic, environmental and social benefits. Detailed Implementation

[0016] The present invention will be described in detail with reference to specific embodiments: Example 1: Ingredient ratio (mass fraction): 76% sagger powder, 6% quartz sand powder, 3% lightly calcined magnesium oxide powder, 2% sodium carbonate powder, 5% cenospheres, 1% carbon black, 2% dextrin, and 5% deionized water.

[0017] Process parameters: dry mix for 20 min, wet mix for 20 min, cure at 135℃ for 3 h, finished particle size 0.3~1.0 mm.

[0018] Performance testing: melting point 1175℃, viscosity 0.22 Pa・s at 1500℃, spreading time 7 s.

[0019] Example 2: Ingredient ratio (mass fraction): 62% sagger powder, 14% quartz sand powder, 7% light-burned magnesium oxide powder, 5% sodium carbonate powder, 5.7% cenospheres, 0.8% carbon black, 1.5% pulp, and 4% deionized water.

[0020] Process parameters: dry mix for 25 min, wet mix for 30 min, cure at 120℃ for 2.5 h.

[0021] Performance testing: melting point 1205℃, viscosity 0.28 Pa・s at 1500℃, spreading time 9 s. Example 3:

[0022] Ingredient ratio (mass fraction): 62.4% sagger powder, 6.2% quartz sand powder, 3.2% lightly calcined magnesia powder, 2.2% sodium carbonate powder, 11% cenospheres, 1.8% carbon black, 3.0% dextrin, and 10% deionized water.

[0023] Process parameters: dry mix for 30 min, wet mix for 40 min, cure at 150℃ for 4 h.

[0024] Performance testing: melting point 1195℃, viscosity 0.25 Pa·s at 1500℃, spreading time 8 s.

Claims

1. A method for preparing a continuous casting tundish covering agent using a lithium battery crucible, characterized in that: The process includes raw material pretreatment, precise batching, efficient mixing, granulation and molding, low-temperature curing, and finished product screening, as detailed below: 1) Raw material pretreatment: Used aluminum-silicon lithium battery cathode material sintering crucibles were selected and manually sorted to remove large impurities, metal debris and unsintered waste. A two-stage crushing process was adopted: first, the material was coarsely crushed to a particle size ≤10mm by a jaw crusher, and then medium crushed to a particle size ≤3mm by a cone crusher. Subsequently, the material was sent to a planetary ball mill for dry ultrafine grinding. After grinding, the crucible powder with a particle size <74μm was obtained by negative pressure screening. 2) Precise ingredient proportioning: The ingredients are shown in the table below, by weight percentage, total weight 100%; ； 3) High-efficiency mixing, granulation molding, low-temperature curing, and finished product: Follow these steps: (1) Dry mixing stage: Add the pretreated crucible powder, quartz sand powder, lightly calcined magnesium oxide powder, sodium carbonate powder, cenospheres and carbon black into a high-speed high-power mixer according to the ratio, and dry mix at 600~800r / min for 20~30min to ensure that each solid component is evenly dispersed and free from agglomeration and segregation; (2) Wet mixing stage: Slowly add water-soluble inorganic binder and deionized water to the dry-mixed mixture, and continue wet mixing at 400~600r / min for 20~40min to form a mixture with uniform moisture content and moderate plasticity. (3) Granulation and curing: The wet mixture is fed into a centrifugal rolling ball granulator for molding and granulation, and the particle size is controlled between 0.25 and 1.25 mm. After granulation, it is sent into a hot air curing oven and dried and cured at 120-150℃ for 2.5-4.0 h to remove free water and ensure that the particle strength is ≥15N. (4) Screening the finished product: The solidified particles are screened in two stages to remove fine powder and oversized particles, and the intermediate package covering agent with uniform particle size distribution and good flowability is obtained.

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