A low-cost dephosphorization agent and a preparation method thereof

Abstract

The application discloses a low-cost dephosphorization agent and a preparation method thereof, relates to the technical field of steel refining, and is characterized in that the application takes, as core raw materials, slag cutting slag produced by a steel plant and low-concentration fluorine-containing wastewater treatment by-product calcium fluoride sludge, both of which are industrial solid wastes, thereby saving the purchase cost of purchased mineral raw materials such as iron ore, fluorite and lime, and greatly reducing the material transportation cost, on the basis of realizing the resource utilization of metallurgical solid wastes, fitting the green and low-carbon metallurgical development orientation, and significantly reducing the comprehensive use cost of the dephosphorization agent from the source.

Description

Technical Field

[0001] This invention relates to the field of steelmaking refining technology, specifically to a low-cost dephosphorizing agent and its preparation method. Background Technology

[0002] Phosphorus is a harmful impurity element in steel materials. It can significantly reduce the low-temperature toughness of steel, cause "cold brittleness", and deteriorate the plasticity and weldability of steel. Therefore, dephosphorization is one of the core processes in steelmaking.

[0003] Currently, oxygen blowing dephosphorization is commonly used in steelmaking. This process involves directly blowing oxygen into molten steel to oxidize phosphorus into phosphorus pentoxide, which is then removed through slag formation. However, the oxygen blowing dephosphorization process is violent, and the large amount of heat released by the oxidation reaction causes the temperature of the molten steel to rise rapidly. Under high-temperature conditions, the distribution ratio of phosphorus between slag and metal decreases, which is not only detrimental to the stable removal of phosphorus but also easily leads to phosphorus reversion. At the same time, the violent reaction can easily cause the molten steel to boil and splash, posing safety hazards and making process control difficult.

[0004] Commercially available oxidative dephosphorizing agents mostly use natural ores such as iron ore and manganese ore as oxidant components, resulting in high raw material procurement costs, which is inconsistent with the current development direction of cost reduction and efficiency improvement in the steel industry. Furthermore, existing dephosphorizing agent technologies still have many limitations: For example, the dephosphorizing agent disclosed in Chinese patent number 201410277321.6 is a reducing dephosphorizing agent, which mainly plays the role of slag formation and fluxing. It requires specific argon blowing process conditions in the electric heating station to achieve dephosphorization. There are many process restrictions, and it must rely on the front-end converter process to blow oxygen to oxidize the phosphorus in the molten steel into phosphorus pentoxide. Its application scenarios and applicable processes are obviously limited.

[0005] For example, the dephosphorizing agent disclosed in Chinese patent application No. 202511711868.7 uses iron oxide scale and lime as the main raw materials. The main component of iron oxide scale is FeO, and its effective oxygen content is much lower than that of high-valence iron oxides. In order to achieve the target dephosphorization effect, the amount of reagent added needs to be increased, which in turn increases the cost of use. At the same time, iron oxide scale is currently mostly used to produce coolant or to be combined with iron ore concentrate to prepare blast furnace pellets. The amount of resources that can be recovered for dephosphorizing agents is gradually decreasing, and the stability of raw material supply is insufficient.

[0006] In summary, developing a dephosphorizing agent that has a wide range of raw material sources, low cost, mild dephosphorization reaction, and stable dephosphorization effect is a practical problem that urgently needs to be solved in the steelmaking and refining field. Summary of the Invention

[0007] To address the shortcomings of existing dephosphorizing agents, such as high raw material costs, violent oxygen blowing dephosphorization reactions leading to phosphorus reversion, and insufficient molding performance and dephosphorization efficiency of solid waste-based dephosphorizing agents, this invention provides a low-cost dephosphorizing agent and its preparation method. Using industrial solid waste gas cutting slag and calcium fluoride sludge as core raw materials, this method achieves resource utilization of solid waste while ensuring excellent dephosphorization effect and pelletizing performance, thereby reducing the cost of the steelmaking dephosphorization process.

[0008] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: A low-cost dephosphorizing agent is provided, wherein the raw material is composed of the following components in parts by weight: The mixture consists of 55-67 parts of gas cutting slag with a particle size of 1-3 mm, 10-16 parts of gas cutting slag with a particle size of less than 1 mm, 20-35 parts of calcium fluoride sludge with a particle size of -325 mesh, 1-1.5 parts of gelatinized starch with a particle size of -325 mesh, and water accounting for 5-8% of the total mass of solids.

[0009] Furthermore, the gas cutting slag is an oxidation byproduct generated by the reaction of high-temperature metal and oxygen during the gas cutting process of steel, and the gas cutting slag contains 55-65% Fe2O3 and 25-35% Fe3O4, with a high proportion of high-valence iron oxides, which can provide sufficient effective oxygen for dephosphorization reaction.

[0010] Furthermore, the calcium fluoride sludge is a byproduct generated by chemical precipitation of calcium compounds added during the treatment of low-concentration fluoride wastewater. The calcium fluoride sludge contains ≥50% CaF2 and ≥30% CaO, and can simultaneously replace the fluorite (CaF2) and lime (CaO) components in traditional dephosphorizing agents, while also having slag-forming and fluxing functions.

[0011] Furthermore, the gelatinized starch is obtained by gelatinization of corn starch or kudzu starch, with a gelatinization degree of ≥50%, and is used as a binder for cold-pressed pellets to improve the initial strength of the pellets and reduce breakage losses during molding and transportation.

[0012] This invention also provides a method for preparing the above-mentioned low-cost dephosphorizing agent, comprising the following steps: S1: Weigh each raw material according to the weight ratio and put them into the mixer to premix evenly; S2: Add water at 5-8% of the total mass of solids to the mixture and continue stirring until the material is fully mixed. S3: Feed the mixed material into a double roller briquetting machine to press it into pellets; S4: Dry the pellets until the moisture content is ≤3% to obtain the finished dephosphorizing agent.

[0013] Furthermore, the pellets obtained in step S3 are ellipsoidal, with pellets having a particle size > 5mm accounting for ≥ 90%, ensuring uniform particle size of the finished product and meeting the requirements for feeding into the high-level silo.

[0014] Furthermore, in step S4, the drying method is natural air drying or oven drying.

[0015] This invention also provides the application of the aforementioned low-cost dephosphorizing agent in the dephosphorization of molten steel during the electric heating refining process of steelmaking. In the electric heating refining process of steelmaking, the dephosphorizing agent is added to the molten steel as needed for dephosphorization treatment, based on the phosphorus content of the molten steel entering the plant and the target phosphorus content leaving the plant.

[0016] The beneficial effects of this invention are as follows: Compared to existing conventional dephosphorization materials and preparation technologies, this invention relies on steel plant-produced gas cutting slag and calcium fluoride sludge from the treatment of low-concentration fluoride-containing wastewater as core raw materials. Both types of materials are industrial solid waste, which not only saves the purchase expenditure of external mineral raw materials such as iron ore, fluorite, and lime, but also significantly reduces material transportation costs because the solid waste production site is adjacent to the steelmaking plant area. On the basis of realizing the resource utilization of metallurgical solid waste and conforming to the green and low-carbon metallurgical development orientation, it significantly reduces the comprehensive cost of dephosphorizing agent from the source. The gas cutting slag with a high proportion of Fe2O3 and Fe3O4 in the formula system can slowly decompose and release active oxygen to complete the oxidation of phosphorus. Compared with direct oxygen blowing dephosphorization, the reaction rhythm is easier to control, which can avoid the risk of violent splashing of molten steel. The gentle exothermic process can also reduce the temperature rise of molten steel, effectively suppress the problem of phosphorus return under high temperature conditions, and ensure that the dephosphorization process is stable and controllable. This invention constructs a reasonable aggregate filling gradation by combining coarse and fine-grained gas cutting slag, and synergistically improves the pelletizing performance with a gelatinized starch binding system. The resulting pellets have a stable pelletizing rate of over 90%, higher mechanical strength after forming, and significantly reduce pellet breakage losses during production and transfer, thus reducing additional losses from defective products. Industrial testing at a 220-ton converter refining station has verified that the overall dephosphorization efficiency of this invention can reach an average of 88.86%, which is far superior to the blank working condition and the comparative sample with unbalanced proportions. It can stably reduce the phosphorus impurity content in molten steel, fully adapting to the dephosphorization production requirements of the electric heating refining process in steelmaking, and has multiple advantages in terms of economy, environmental protection, and process application. Detailed Implementation

[0017] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0018] The raw materials used in this embodiment of the invention are: gas cutting slag, which is an oxidation byproduct generated from the gas cutting process of steelmaking plants, wherein Fe2O3 is 55-65% and Fe3O4 is 25-35%; calcium fluoride sludge, which is a byproduct generated from the treatment of low-concentration hydrofluoric acid wastewater with lime precipitation, wherein CaF2 is ≥50% and CaO is ≥30%; and gelatinized starch, which is corn starch obtained by gelatinization process, with a gelatinization degree of 50% and a particle size of -325 mesh.

[0019] Example 1 Weigh 55 parts of gas cutting slag with a particle size of 1-3 mm, 10 parts of gas cutting slag with a particle size of less than 1 mm, 35 parts of calcium fluoride sludge with a particle size of -325 mesh, and add 1.2 parts of gelatinized starch. Put them into a planetary mixer and mix for 1 minute. Then add water at 8% of the total mass of solids and continue mixing for 3 minutes until the material is uniform. Send the mixed material to a double roller briquetting machine through a belt and press it into ellipsoidal pellets. Let the pellets air dry naturally for 3 days until the moisture content drops to below 3%. After passing the inspection, they are put into storage.

[0020] Example 2 Weigh 60 parts of gas cutting slag with a particle size of 1-3 mm, 10 parts of gas cutting slag with a particle size of less than 1 mm, 30 parts of calcium fluoride sludge with a particle size of -325 mesh, and add 1.1 parts of gelatinized starch. Put them into a planetary mixer and mix for 1 minute. Then add water at 7% of the total mass of solids and continue mixing for 3 minutes until the material is uniform. Send the mixed material to a double roller briquetting machine through a belt and press it into ellipsoidal pellets. Let the pellets air dry naturally for 3 days until the moisture content drops to below 3%. After passing the inspection, they are put into storage.

[0021] Example 3 Weigh 65 parts of gas cutting slag with a particle size of 1-3 mm, 10 parts of gas cutting slag with a particle size of less than 1 mm, 25 parts of calcium fluoride sludge with a particle size of -325 mesh, and add 1.2 parts of gelatinized starch. Put them into a planetary mixer and mix for 1 minute. Then add water at 6% of the total mass of solids and continue mixing for 3 minutes until the material is uniform. The mixed material is fed into a double roller briquetting machine through a belt and pressed into ellipsoidal pellets. The pellets are naturally dried for 3 days until the moisture content drops to below 3%. After passing the inspection, they are put into storage.

[0022] Example 4 Weigh 60 parts of gas cutting slag with a particle size of 1-3 mm, 15 parts of gas cutting slag with a particle size of less than 1 mm, 25 parts of calcium fluoride sludge with a particle size of -325 mesh, and add 1.2 parts of gelatinized starch. Put them into a planetary mixer and mix for 1 minute. Then add water at 7% of the total mass of solids and continue mixing for 3 minutes until the material is uniform. Send the mixed material to a double roller briquetting machine through a belt and press it into ellipsoidal pellets. Let the pellets air dry naturally for 3 days until the moisture content drops to below 3%. After passing the inspection, they are put into storage.

[0023] Comparative Example 1 The difference between this comparative example and Example 1 is that the raw materials used are 60 parts of gas cutting slag with a particle size of 1~3mm, 40 parts of calcium fluoride sludge with a particle size of -325 mesh, and 1.4 parts of gelatinized starch.

[0024] Comparative Example 2 The difference between this comparative example and Example 1 is that the raw materials used are 50 parts of gas cutting slag with a particle size of less than 1 mm, 50 parts of calcium fluoride sludge with a particle size of -325 mesh, and 1.5 parts of gelatinized starch.

[0025] Comparative Example 3 The difference between this comparative example and Example 1 is that the raw materials used are 60 parts of gas cutting slag with a particle size of 1-3 mm, 40 parts of gas cutting slag with a particle size of less than 1 mm, and 1.5 parts of gelatinized starch.

[0026] Comparative Example 4 The blank control group did not add any dephosphorizing agent during the refining process.

[0027] The pelletizing rate of the dephosphorizing agents prepared in the above embodiments and comparative examples was statistically analyzed, and actual dephosphorizing production was carried out in a 220-ton converter of a steel plant. The phosphorus content (%) of molten steel entering the station, the phosphorus content (%) of molten steel leaving the station, and the dephosphorizing efficiency (%) were statistically analyzed, and the results are shown in Table 1 below; Table 1

[0028] Among them, the ball formation rate of Comparative Example 4 is / , meaning that it is impossible to form a ball.

[0029] As shown in Table 1, the pelletizing rate of the dephosphorizing agent prepared in the embodiments of the present invention can reach over 90%, which is much higher than that of the comparative examples. This fully demonstrates that the optimized two-stage particle size gas cutting slag ratio of the present invention can significantly improve the cold-pressed pelletizing performance, effectively reduce the output of defective products during the production process, and reduce the overall processing cost. The dephosphorizing efficiency of each embodiment of the present invention is higher than 87%, with an average dephosphorizing efficiency of 88.86%, which is much higher than the blank condition without dephosphorizing agent and the comparative sample with unbalanced ratio. Among them, the dephosphorizing effect of the comparative sample without calcium fluoride sludge is significantly reduced, which confirms that CaO and CaF2 in calcium fluoride sludge can synergistically complete slag formation, reduce the melting point of molten slag, and promote the stable migration of phosphorus elements to the slag phase. They are the core components to ensure efficient dephosphorization. The raw materials of the whole formula work together to stably reduce the phosphorus impurity content in molten steel, which fully meets the dephosphorization production requirements of the electric heating refining process in steelmaking.

Claims

1. A low-cost dephosphorizing agent, characterized in that, By weight, the raw material consists of the following components: The mixture consists of 55-67 parts of gas cutting slag with a particle size of 1-3 mm, 10-16 parts of gas cutting slag with a particle size of less than 1 mm, 20-35 parts of calcium fluoride sludge with a particle size of -325 mesh, 1-1.5 parts of gelatinized starch with a particle size of -325 mesh, and water accounting for 5-8% of the total mass of solids.

2. The low-cost dephosphorizing agent according to claim 1, characterized in that, The gas cutting slag is an oxidation byproduct generated by the reaction of high-temperature metal and oxygen during the gas cutting process of steel, and the gas cutting slag contains 55-65% Fe2O3 and 25-35% Fe3O4.

3. The low-cost dephosphorizing agent according to claim 1, characterized in that, The calcium fluoride sludge is a byproduct generated by chemical precipitation of calcium compounds added during the treatment of low-concentration fluoride wastewater, and the calcium fluoride sludge contains ≥50% CaF2 and ≥30% CaO.

4. The low-cost dephosphorizing agent according to claim 1, characterized in that, The gelatinized starch is obtained from corn starch or kudzu starch through a gelatinization process, with a gelatinization degree ≥50%.

5. A method for preparing a low-cost dephosphorizing agent according to any one of claims 1 to 4, characterized in that, Includes the following steps: S1: Weigh each raw material according to the weight ratio and put them into the mixer to premix evenly; S2: Add water at 5-8% of the total mass of solids to the mixture and continue stirring until the material is fully mixed. S3: Feed the mixed material into a double roller briquetting machine to press it into pellets; S4: Dry the pellets until the moisture content is ≤3% to obtain the finished dephosphorizing agent.

6. The preparation method according to claim 5, characterized in that, The pellets obtained in step S3 are ellipsoidal, with pellets having a particle size > 5 mm accounting for ≥ 90%.

7. The preparation method according to claim 5, characterized in that, In step S4, the drying method is natural air drying or oven drying.

8. The application of the low-cost dephosphorizing agent as described in any one of claims 1 to 4 in the dephosphorization of molten steel in the electric heating refining process of steelmaking.

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