A method for producing a refining slag-making agent from casting slag

Abstract

The present invention discloses a method for making a refining slag-forming agent from casting slag, and relates to the technical field of steel manufacturing. The method for making a refining slag-forming agent from casting slag comprises the following steps: (1) selecting the casting slag as a calm steel casting slag. (2) crushing the selected casting slag and subjecting it to magnetic separation to remove metallic iron and control FeO within 5%. (3) the components of the refining slag-forming agent are: 40-50% of the casting slag after magnetic separation, 25-35% of calcium carbonate, 1-2% of industrial salt, 15-25% of silicon slag (8-10% of elemental silicon, SiO2: 80-90, and the rest are impurity elements), and a forming binder of 0.5%-1.5% of the total mass of the main raw materials; (4) dry mixing the materials, and preparing pellets by dry pressing using a strong pelletizing machine; screening, and selecting pellets with a particle size greater than 10 mm to prepare the refining slag-forming agent. The present invention realizes the comprehensive utilization of secondary resources, while improving the current situation where lime + fluorite slag is slow to produce and the effect is unstable.

Description

Technical Field

[0001] The invention relates to the field of iron and steel metallurgy, and in particular to a method for preparing a refining slagging agent from casting slag. Background Art

[0002] Currently, the main refining slag systems are CaO-Al2O3 and CaO-SiO2. CaO-Al2O3-based slags exhibit numerous metallurgical properties for off-line refining, including: 1) high basicity; 2) strong desulfurization capabilities; 3) low oxygen potential, enabling diffusion deoxidation; 5) strong inclusion absorption capabilities; and 6) low or no fluorine content, making them suitable for rapid refining operations and environmentally friendly requirements. CaO-Al2O3-based slags are not only used in off-line refining processes such as LF, RH, VAD, and VOD, but can also serve as a covering for molten steel in intermediate ladle applications during continuous casting. In terms of melting point and fluidity, CaO-Al2O3-based slags possess a high capacity for CaO and Al2O3, allowing the addition of large amounts of lime and foaming agents to form LF refining slags with strong desulfurization capabilities. Because of the aforementioned advantages, CaO-Al2O3-based refined slags are widely used in steelmaking. However, they also present some challenges: 1) High cost. To ensure rapid melting and slag formation, steel mills typically use pre-melted CaO-Al2O3-based refined slags, which cost nearly 3,000 yuan per ton and can generally only be used to produce high-quality, high-value-added products. 2) Simply using high-Al2O3-containing raw materials such as bauxite to supplement the Al2O3 content in refined slags is slightly less expensive, but the melting effect is poor, and slag-forming materials such as fluorite are often required. Given the environmental pollution of fluorite and its dwindling reserves, fluorite is rarely or essentially no longer used in the foreign steel and metallurgical industry. In China, similar policies are expected to be introduced to limit or reduce its use in the steel and metallurgical industry. Therefore, a refining slag-forming agent based on casting slag has been developed to improve this situation. After refining and slagging, the casting slag has the characteristics of rapid melting of pre-melted slag into slag. At the same time, according to the composition of the casting slag, appropriate addition of some components can achieve effective control of the steel grade composition. This type of refining slag-forming agent has the advantages of rapid slagging (second only to pre-melted slag), low cost (equivalent to the price of lime), and strong desulfurization ability.

[0003] Similar patented technologies mainly include the following:

[0004] CN202111208386 discloses a method for processing aluminum-iron alloy metallurgical slag used for steelmaking. The method involves removing iron from the slag left over from aluminum-iron smelting through magnetic separation, then separating the alloy through sorting. The remaining tailings are then reduced with limestone, coke, and other materials to produce iron, yielding calcium aluminate slag. This slag serves as a pre-melted slag that can be used as slag for steelmaking and refining. However, this method is costly and the raw materials are difficult to obtain.

[0005] CN201910228821 A method for controlling the pulverization and recycling of steelmaking refined slag. For the reductive refined slag outside the furnace, a CaO-Al2O3-based slag system is used in the slag shape. The composition of the refined slag is controlled so that the refined slag contains, by mass percentage, the following: CaO 50%-66%, SiO2 8%-12%, Al2O3 21%-42%, MgO 7.6%-10%, and FeO+MnO 0.7%-3%. The R of the refined slag is ≥4. The refined slag after the controlled pulverization is reused according to the steel slag cascade utilization process or recycled in the refining process. During the reuse process, the temperature of the refined slag does not exceed 500 degrees Celsius. Although the method can effectively reduce the pulverization of steelmaking refined slag, it does not require the addition of additional conditioning substances, facilitates its return and reuse, prevents dust from being dispersed during transportation caused by pulverization, and improves the operating environment. Reusing steel slag reduces slag-making material consumption and slag discharge, offering high economic and environmental value. This method also recycles casting slag, but is relatively simple and can only be used for partially reducing slag. It is highly specific to specific steel grades and cannot be used for all killed steel grades. It also significantly impacts on on-site operations.

[0006] CN201110192283 discloses a method for producing high-basicity steelmaking slag for use in the off-line refining process. This method addresses the issues of slow hydration of lime powder and slow melting of added lime blocks. The method involves crushing and grinding freshly burned lime from a lime kiln, placing the ground lime powder into a fluidized bed at 650-750°C, introducing waste gas and water vapor from the lime kiln's lime burning process. The lime surface is passivated and waterproofed using CO₂ in the waste gas, and the water vapor accelerates the CO₂ passivation of the lime surface. The passivated lime powder is then mixed with flux powder, pelletized by a wet or dry process, and sieved. The slag has the characteristics of high basicity, fast melting rate, good spreadability, low cost, and long storage life. It can shorten off-line refining time and improve the desulfurization and dephosphorization rates of molten steel in the off-line refining process. It also utilizes the CO₂ waste gas emitted from the lime kiln's lime burning process. However, the basicity of the refined slag produced is too high, and the slag components have limited ability to absorb inclusions, resulting in high costs. Summary of the Invention

[0007] The purpose of the present invention is to provide a method for making a refining slag-making agent from casting slag, thereby realizing the comprehensive utilization of secondary resources and improving the current situation in which lime+fluorite slag is slow to produce and the effect is unstable.

[0008] The purpose of the present invention is achieved through the following technical solutions:

[0009] A method for preparing a refining slagging agent from casting slag comprises the following steps:

[0010] The components of the refining slag-making agent include main raw materials and auxiliary materials. The main raw materials are calculated by mass fraction as follows: 40-50% of casting slag after magnetic separation, 25-35% of calcium carbonate, 1-2% of industrial salt (NaCl), and 15-25% of silicon slag. The silicon slag is mainly used to adjust the alkalinity and reduce the oxidizability of the steel slag by using elemental silicon. The auxiliary material is a forming binder, which accounts for 0.5%-1.5% of the total mass of the main raw materials.

[0011] Step 1: dry mix the main raw material dry material and stir for 5-7 minutes to mix evenly, then add the auxiliary material forming binder dry material and stir for 3-5 minutes until uniform, to prepare a dry mix;

[0012] Step 2: Use a strong ball press to dry-press the balls to prepare pellets with a size (diameter) of 20-35 mm;

[0013] Step 3: Screening: Use a sieve with a 10 mm mesh to screen the pellets, and select pellets with a particle size greater than 10 mm to prepare a refining slag-making agent.

[0014] Based on the above technical solution, preferably, the casting slag is a killed steel casting slag, and its composition range is calculated by mass fraction:

[0015] CaO: 35-45%, SiO2: 25-40%, Al2O3: 3-10%, FeO: 3-8%, MgO: 7-12%, and the rest are some metallic iron and impurities.

[0016] Based on the above technical solution, preferably, the casting slag is crushed and then subjected to magnetic separation to remove metallic iron and control FeO within 5%.

[0017] Based on the above technical solution, preferably, the particle size of the pulverized casting slag is 0-3 mm.

[0018] Based on the above technical solution, preferably, the silicon slag has a composition range of 8-10% elemental silicon, 80-90% SiO2, and the rest are impurity elements, calculated by mass fraction.

[0019] Based on the above technical solution, preferably, the molding binder, by mass fraction, has a composition range of: bentonite 40-60%, sodium carboxymethyl cellulose 2%, gluten 10-20%, and cement 20-30%.

[0020] Based on the above technical solution, preferably, the cement is 425 cement.

[0021] The refining slag-forming agent of the present invention is applied to converter tapping or refining process. When the refining slag-forming agent is applied to converter tapping, the amount of the refining slag-forming agent added is 4-6 kg / t steel. When the refining slag-forming agent is applied to the refining process, lime is added according to the desulfurization requirement, and the refining slag-forming agent is added at 1 / 2 of the added amount. After desulfurization is completed, the refining slag-forming agent is added in an amount equal to the amount of lime added to adjust the binary basicity of the slag system. 2-4 kg / t steel of the refining slag is added in the furnaces that do not require desulfurization to meet the submerged arc requirement.

[0022] The beneficial effects of the present invention are as follows: the casting slag-based refining slag-making agent of the present invention can realize the recovery of casting slag of all killed steel grades, the raw materials are easy to obtain, the comprehensive utilization of secondary resources is realized, the cost is low, the slagging condition is good, and at the same time, the current situation of slow slagging and unstable effect of lime + fluorite is improved. DETAILED DESCRIPTION

[0023] The following non-limiting examples may enable those skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0024] Example 1

[0025] A method for preparing a casting slag-based refining slagging agent comprises the following steps:

[0026] (1) The casting slag is selected as the killed steel casting slag, and its composition is:

[0027] CaO: 40%, SiO2: 33%, Al2O3: 7%, FeO: 5%, MgO: 9%, and the rest is some metallic iron and impurities.

[0028] (2) The selected casting slag is crushed and then subjected to magnetic separation to remove metallic iron and control FeO within 5%.

[0029] (3) The components of the refining slag-making agent are: 46% of the casting residue after magnetic separation, 32% of calcium carbonate, 2% of industrial salt (NaCl), 20% of silicon slag (9% of elemental silicon, 85% of SiO2, and the rest are impurity elements. The main purpose is to adjust the alkalinity and use elemental silicon to reduce the oxidizing property of the steel slag), and the molding binder is 1% of the total mass of the main raw materials;

[0030] (4) further comprising the following steps:

[0031] Step 1: dry mix the main raw material dry material and stir for 5-7 minutes to mix evenly, then add the auxiliary material forming binder dry material and stir for 3-5 minutes until uniform, to prepare a dry mix;

[0032] Step 2: Use a strong ball press to dry-press the balls to prepare pellets with a size of 20-35 mm;

[0033] Step 3: Screening: Use a sieve with a 10 mm mesh to screen the pellets, and select pellets with a particle size greater than 10 mm to prepare a refining slag-making agent.

[0034] Example 2

[0035] A method for preparing a casting slag-based refining slagging agent comprises the following steps:

[0036] (1) The casting slag is selected as the killed steel casting slag, and its composition is:

[0037] CaO: 45%, SiO2: 25%, Al2O3: 8%, FeO: 6%, MgO: 10%, and the rest is some metallic iron and impurities.

[0038] (2) The selected casting slag is crushed and then subjected to magnetic separation to remove metallic iron and control FeO within 5%.

[0039] (3) The components of the refining slag-making agent are: 50% of the casting residue after magnetic separation, 28% of calcium carbonate, 1% of industrial salt (NaCl), 21% of silicon slag (9% of elemental silicon, 85% of SiO2, and the rest are impurity elements. The main purpose is to adjust the alkalinity and use elemental silicon to reduce the oxidizing property of the steel slag), and the molding binder is 1.5% of the total mass of the main raw materials;

[0040] (4) further comprising the following steps:

[0041] Step 1: dry mix the main raw material dry material and stir for 5-7 minutes to mix evenly, then add the auxiliary material forming binder dry material and stir for 3-5 minutes until uniform, to prepare a dry mix;

[0042] Step 2: Use a strong ball press to dry-press the balls to prepare pellets with a size of 20-35 mm;

[0043] Step 3: Screening: Use a sieve with a 10 mm mesh to screen the pellets, and select pellets with a particle size greater than 10 mm to prepare a refining slag-making agent.

[0044] Example 3

[0045] After tapping the converter, 4 kg / t steel of the refining slag-making agent prepared in Example 1 was added, and argon was blown on a small platform for 3 minutes. The steel slag was basically melted and had good spreadability.

[0046] According to the sulfur content of the small platform (0.005%), LF does not require desulfurization treatment when entering the station. During the refining process, only 2kg / t steel is added. After the converter is tapped, 2kg / t steel of the refining slag-making agent is added. After heating and slagging for 3 minutes, the slag is completely melted, with good spreadability and a desulfurization rate of 13.7%.

[0047] Example 4

[0048] After tapping the converter, 5 kg / t steel of the refining slag-making agent prepared in Example 1 was added, and argon was blown on a small platform for 4 minutes. The steel slag was basically melted and had good spreadability.

[0049] According to the sulfur content of the small platform (0.008%), LF needs to be desulfurized to within 0.006% when entering the station. 4kg / t steel lime is added for desulfurization. The sulfur content after desulfurization is 0.006%. After desulfurization, 2kg / t steel refined slag is added to adjust the slag basicity. The desulfurization rate is 25%.

[0050] Example 5

[0051] After tapping the converter, 6 kg / t steel of the refining slag-making agent prepared in Example 1 was added, and argon was blown on a small platform for 5 minutes. The steel slag was basically melted and had good spreadability.

[0052] LF enters the station and needs to be desulfurized to within 0.006% according to the sulfur content of the small platform (0.010%). 6kg / t steel lime is added for desulfurization treatment. The sulfur content after desulfurization is 0.005%. After desulfurization, 3kg / t steel refined slag is added to adjust the slag basicity, and the desulfurization rate is 50%.

[0053] Anyone skilled in the art will be able to utilize the above-disclosed technical content to make many possible changes and modifications to the technical solution of the present invention, or to modify it into equivalent embodiments with equivalent changes, without departing from the scope of the technical solution of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention that do not depart from the content of the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a refining slag-forming agent from casting slag, characterized in that: The following steps are involved: The refining slag-making agent includes a main raw material and auxiliary materials. The main raw materials are calculated by mass fraction as follows: 40-50% of magnetic separation casting residue, 25-35% of calcium carbonate, 1-2% of industrial salt, and 15-25% of silicon slag. The auxiliary material is a forming binder, which accounts for 0.5%-1.5% of the total mass of the main raw materials. The casting slag is a killed steel casting slag, and its composition by mass fraction is: CaO: 35-45%, SiO2: 25-40%, Al2O3: 3-10%, FeO: 3-8%, MgO: 7-12%, and the rest is metallic iron and impurities; The industrial salt is NaCl; Step 1: dry mix the main raw material dry material and stir for 5-7 minutes to mix evenly, then add the auxiliary material forming binder dry material and stir for 3-5 minutes until uniform, to prepare a dry mix; Step 2: Use a strong ball press to dry-press the balls to prepare pellets with a size of 20-35 mm; Step 3: Screening: Use a sieve with a 10 mm mesh to screen the pellets, and select pellets with a particle size greater than 10 mm to prepare a refining slag-making agent.

2. The method according to claim 1, characterized in that The casting slag is crushed and then subjected to magnetic separation to remove metallic iron and control FeO within 5%.

3. The method according to claim 1, characterized in that The particle size of the casting slag is 0-3 mm.

4. The method according to claim 1, wherein Calculated by mass fraction, the silicon slag comprises: elemental silicon 8-10%, SiO2: 80-90%, and the rest are impurity elements.

5. The method according to claim 1, wherein Calculated by mass fraction, the molding binder comprises the following components: 40-60% bentonite, 2% sodium carboxymethyl cellulose, 10-20% gluten, and 20-30% cement.

6. The method according to claim 5, characterized in that The cement is 425 cement.