A method for producing a pre-melted refining slag

Abstract

The application belongs to the technical field of steel metallurgy and solid waste resource utilization, and relates to a preparation method of pre-melting refining slag, which takes 30-50 parts of lithium ore smelting residue, 20-40 parts of calcium adjusting agent, 5-10 parts of magnesium adjusting agent, 5-20 parts of aluminum adjusting agent and 3-8 parts of binder as raw materials, and is prepared through mixing, pressing, high-temperature melting, cooling and crushing; the chemical composition of the obtained pre-melting refining slag is as follows in percentage by weight: CaO 35%-55%, Al2O3 20%-30%, SiO2 8%-18%, MgO 3%-8%, Na2O+K2O+Li2O>4%, and CaF2≤0.5%. The application realizes high-value utilization of lithium ore lithium extraction waste residue, does not need to add fluorite, has the advantages of low melting point of ≤1350 DEG C, good fluidity, high desulfurization efficiency, and is suitable for LF ladle refining and molten steel desulfurization.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy and solid waste resource utilization technology, and particularly relates to a method for preparing pre-melted refining slag. Background Technology

[0002] Pre-melted refining slag is a commonly used slag-forming material in the ladle refining (LF) process. It is formed by pre-melting and cooling the raw materials outside the furnace, followed by crushing. It features uniform composition, rapid melting speed, and good and stable slag-forming effect. During LF refining, the melting point, fluidity, and basicity of the refining slag affect the metallurgical effects of desulfurization, deoxidation, and inclusion adsorption. Traditional pre-melted refining slag is mainly composed of lime and bauxite, with fluorite (CaF2) added as a flux to lower the slag melting point and improve fluidity. However, fluorite reacts with the refractory materials in the furnace lining at high temperatures, accelerating the erosion rate of the lining and generating fluorine-containing gases, causing environmental pollution. On the other hand, lithium extraction from lithium ore generates a large amount of smelting residue containing SiO2, Al2O3, CaO, and alkali metal oxides such as K2O, Na2O, and Li2O. Stockpiling these lithium ore smelting residues occupies land resources and poses environmental pollution risks, while valuable components such as potassium, sodium, and lithium are not effectively utilized.

[0003] Various fluorine-free refining slags and their preparation methods have been disclosed in the prior art.

[0004] CN119614795A discloses a steelmaking method using fluorine-free refining slag in LF refining. The metallurgical properties of the slag sample are calculated using thermodynamic software, and the composition of the fluorine-free refining slag system to replace the fluorine-containing refining slag is calculated using phase diagrams. The slag system is then modified and adjusted twice, once in a converter and once in LF refining.

[0005] CN103849712A discloses a fluorine-free refining slag for 20Cr alloy structural steel and its preparation method. The slag system is mainly composed of CaO 55%~60%, SiO2 10%~16%, Al2O3 15%~20%, MgO 4%~6%, and B2O3 5%~10%, and is used after crushing and mixing the ore raw materials. CN101643822A discloses an ultra-high basicity low-alumina fluorine-free refining slag, which is composed of CaO 85%~95%, B2O3 2%~10%, MgO 2%~10%, and Al2O3 1%~10%.

[0006] CN102344997A discloses a high-calcium, high-alumina, fluorine-free refining slag for producing high-purity steel. Its chemical composition, by mass percentage, is CaO 30%~50%, MgO 5%~14.9%, Al₂O₃ 30%~45%, SiO₂ 5%~10%, with the balance being FeO and MnO. This slag system is based on high calcium and high aluminum, and its main purpose is to reduce non-metallic inclusions in steel.

[0007] CN102787214A discloses a fluorine-free pre-melted slag for ladle furnace refining, which utilizes 40%~60% spodumene powder, 30%~50% lime powder, and 5%~25% alumina powder to prepare a fluorine-free pre-melted refining slag containing lithium oxide. This method directly uses spodumene ore and mainly utilizes the fluxing effect of Li2O.

[0008] In summary, existing fluorine-free premelted refining slag preparation methods either use fluxes such as B2O3 to replace fluorite, resulting in high raw material costs, or directly use spodumene ore without utilizing the lithium extraction waste as a resource. Furthermore, current technologies do not fully consider the synergistic fluxing and metallurgical promoting effects of K2O, Na2O, and Li2O in lithium ore smelting residues. Therefore, a low-cost, environmentally friendly, and metallurgically superior premelted refining slag preparation method using lithium ore smelting residues as the main raw material is proposed. Summary of the Invention

[0009] The purpose of this invention is to provide a method for preparing pre-melted refining slag that uses smelting residue generated after lithium extraction from lithium ore as the main raw material. This method has the functions of high-value utilization of solid waste, fluorine-free environmental protection, low melting point, good fluidity, and high desulfurization efficiency. It solves the problems of environmental pollution caused by the stockpiling of lithium ore smelting residue, furnace lining corrosion and fluorine emission pollution caused by the reliance on fluorite flux for traditional pre-melted refining slag, and the high cost of raw materials and underutilization of alkali metal resources in existing fluorine-free refining slag.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The present invention provides a method for preparing pre-melted refining slag, comprising the following steps: mixing 30-50 parts by weight of lithium ore smelting residue, 20-40 parts by calcium regulator, 5-10 parts by magnesium regulator, 5-20 parts by aluminum regulator and 3-8 parts by binder, and then pressing, high-temperature melting, cooling and crushing to obtain pre-melted refining slag;

[0011] The chemical composition of the pre-melted refining slag, by weight percentage, includes CaO 35%-55%, Al2O3 20%-30%, SiO2 8%-18%, MgO 3%-8%, Na2O+K2O+Li2O > 4%, and unavoidable balance impurities. The CaF2 content of the pre-melted refining slag is ≤0.5%.

[0012] Specifically, the chemical composition of the lithium ore smelting residue, by weight percentage, includes 30%-40% SiO2, 15%-25% Al2O3, 15%-30% CaO, 2%-6% K2O, 2%-10% Na2O, and 0.2%-0.5% Li2O.

[0013] Specifically, the calcium regulator is industrial lime and / or limestone, the magnesium regulator is magnesium oxide, and the aluminum regulator is bauxite; the binder is water glass with a modulus of 2.2-2.5.

[0014] Specifically, the mass ratio of CaO to Al2O3 in the pre-melted refining slag is 1.2-2.75, and the Li2O content is ≥0.05%; the particle size of the pre-melted refining slag is 5-40mm, the melting point is ≤1350℃, the sulfur content is ≤0.1%, and the phosphorus content is ≤0.05%.

[0015] Specifically, it includes the following steps:

[0016] Step 1: Crush and grind the lithium ore smelting residue, calcium regulator, magnesium regulator, and aluminum regulator separately to a particle size of less than 200 mesh, and dry them to a moisture content of less than 1%.

[0017] Step 2: Weigh the pretreated raw materials according to the proportion, add the binder, mix evenly, and obtain the mixture;

[0018] Step 3: Press the mixture into pellets or blocks with a diameter of 20-50mm;

[0019] Step 4: Melt the molding material at 1400℃-1550℃ in a reducing or inert atmosphere for 30-90 minutes;

[0020] Step 5: Quickly cool the molten slag with air, crush and screen it to obtain a pre-melted refining slag product with a particle size of 5-40mm.

[0021] Specifically, in step 4, the melting temperature is 1450℃-1500℃, and the melting time is 45-60 minutes.

[0022] Specifically, in step 5, rapid air cooling yields a product including a glassy phase, which, after crushing, has a particle size of 5-30 mm.

[0023] Specifically, the pre-melted refining slag is used for LF ladle refining or molten steel desulfurization.

[0024] Specifically, the amount of pre-melted refining slag added is 5-30 kg per ton of molten steel, the refining temperature is 1550℃-1650℃, and the refining time is 30-60 minutes.

[0025] Compared with the prior art, the advantages and positive effects of the present invention are as follows:

[0026] 1. This invention uses the smelting residue generated after lithium extraction from lithium ore as the main raw material to realize the resource utilization of bulk solid waste, effectively reduce the raw material cost of pre-melted refining slag, and at the same time alleviate the land occupation and environmental pollution problems caused by the stockpiling of lithium ore smelting residue, turning waste into treasure.

[0027] 2. This invention does not add fluorite, and the CaF2 content in the resulting pre-melted refining slag is ≤0.5%, which avoids the erosion of the furnace lining and the emission of fluorine-containing gases by traditional fluorine-containing refining slag, and meets the requirements of green metallurgy and environmentally friendly production.

[0028] 3. This invention fully utilizes the naturally occurring alkali metal oxides such as K2O, Na2O, and Li2O in lithium ore smelting residues to synergistically aid melting. The resulting pre-melted refining slag has a melting point ≤1350℃, good fluidity, improves the desulfurization efficiency of the LF refining process, and has excellent metallurgical performance.

[0029] 4. The present invention adopts a process route of pressing-high temperature melting-air quenching-crushing, and the resulting pre-melted refining slag has a uniform composition with glass phase as the main component, stable quality, and is easy to store, transport and industrialize. Detailed Implementation

[0030] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described below with reference to embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0031] Numerous specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways than those described herein, and therefore the invention is not limited to the specific embodiments disclosed in the following specification.

[0032] A method for preparing pre-melted refining slag, wherein the typical components of the raw materials used in the following examples are as follows:

[0033] Lithium ore smelting residue: SiO2 35%, Al2O3 18%, CaO 18%, K2O 4%, Na2O 8%, Li2O 0.3%, with the remainder being small amounts of impurities such as Fe2O3, TiO2, and MgO;

[0034] Industrial lime: CaO 92%, MgO 1.5%, SiO2 1.0%, loss on ignition 4%, other impurities;

[0035] Limestone: CaCO3 95%, MgO 0.5%, SiO2 0.5%, sulfur, phosphorus and other impurities <1%;

[0036] Magnesium oxide: MgO 95%, CaO 1%, SiO2 0.5%, other impurities <1.5%;

[0037] Bauxite: Al2O3 70%, SiO2 10%, Fe2O3 10%, TiO2 5%, the remainder 5%;

[0038] Water glass: Modulus M=2.3, SiO2 30%, Na2O 13%, water 57%, based on aqueous solution content.

[0039] All of the above raw materials are industrial-grade commercial products, and the lithium ore smelting residue was taken from the waste slag yard of a lithium spodumene extraction company.

[0040] Test method:

[0041] Melting point test: The hemispherical method was used. The slag sample was made into a φ3mm×3mm cylinder and heated at 10℃ / min. The temperature at which the sample height dropped to 1 / 2 of the original height was recorded as the melting point.

[0042] Viscosity test: The viscosity of the slag was measured using a rotational viscometer at 1500℃ under argon protection.

[0043] Desulfurization rate test: LF refining was simulated in an induction furnace using industrial pure iron as raw material. FeS was added to achieve an initial sulfur content of 0.020%, the slag-to-steel mass ratio was 1:10, the refining temperature was 1600℃, the stirring time was 40 min, and argon protection was applied. After refining, steel samples were taken to analyze the sulfur content, and the desulfurization rate was calculated using the following formula:

[0044] Desulfurization rate = (Initial sulfur content - Sulfur content after refining) / Initial sulfur content × 100%

[0045] CaF2 content determination: Quantitative analysis was performed using X-ray fluorescence spectrometry (XRF).

[0046] Example 1: This example provides a method for preparing pre-melted refining slag, including the following steps:

[0047] Step 1: Crush and grind 30kg of lithium ore smelting residue, 30kg of industrial lime, 10kg of limestone, 5kg of magnesium oxide, and 20kg of bauxite separately until the particle size is less than 200 mesh (i.e., 0.074mm), and dry them at 150℃ until the moisture content is less than 1%.

[0048] Step 2: Weigh the pretreated raw materials according to the above proportions, add 5 kg of water glass, and mix evenly in a mixer to obtain a mixture;

[0049] Step 3: Press the mixture into pellets with a diameter of 30mm using a briquetting machine;

[0050] Step 4: Add the pellet material to the electric arc furnace and melt it at 1500℃ under an argon protective atmosphere for 60 minutes to allow all components to react fully and form a homogeneous melt;

[0051] Step 5: The molten slag is rapidly cooled with air to obtain a product mainly composed of glass phase. The product is then crushed and screened to obtain a pre-melted refining slag product with a particle size of 5-30 mm.

[0052] According to the test, the chemical composition of the pre-melted refining slag obtained in this embodiment is as follows by weight percentage: CaO 44%, Al2O3 21%, SiO2 15.5%, MgO 8%, Na2O 3.0%, K2O 1.6%, Li2O 0.2%, Na2O+K2O+Li2O total 4.8%, CaF2 0.03%, and the balance is unavoidable impurities such as Fe2O3 and TiO2.

[0053] Performance test results: melting point 1320℃; viscosity at 1500℃ 0.32 Pa·s; desulfurization rate 89% (sulfur content after refining 0.0022%).

[0054] Example 2 differs from Example 1 in the raw material ratio: 40 kg of lithium ore smelting residue, 35 kg of industrial lime, 5 kg of magnesium oxide, 15 kg of bauxite, and 5 kg of water glass. The remaining steps and process parameters are the same as in Example 1.

[0055] The chemical composition of the obtained pre-melted refining slag by weight percentage is as follows: CaO 46.5%, Al2O3 20.5%, SiO2 14.8%, MgO 6.2%, Na2O 3.4%, K2O 1.8%, Li2O 0.25%, Na2O+K2O+Li2O total 5.45%, CaF2 0.02%, with the balance being unavoidable impurities.

[0056] Performance test results: melting point 1290℃; viscosity at 1500℃ 0.28 Pa·s; desulfurization rate 92% (sulfur content after refining 0.0016%).

[0057] Example 3 differs from Example 1 in the raw material ratio: 50 kg of lithium ore smelting residue, 20 kg of industrial lime, 5 kg of limestone, 8 kg of magnesium oxide, 10 kg of bauxite, and 7 kg of water glass. The remaining steps and process parameters are the same as in Example 1.

[0058] The chemical composition of the obtained pre-melted refining slag by weight percentage is as follows: CaO 38.5%, Al2O3 24%, SiO2 17.2%, MgO 7.5%, Na2O 4.5%, K2O 2.2%, Li2O 0.4%, Na2O+K2O+Li2O total 7.1%, CaF2 0.05%, with the balance being unavoidable impurities.

[0059] Performance test results: melting point 1260℃; viscosity at 1500℃ 0.25 Pa·s; desulfurization rate 93% (sulfur content after refining 0.0014%).

[0060] Example 4 differs from Example 1 in that: in step 4, the melting temperature is 1400℃ and the melting time is extended to 90 minutes; in step 5, after crushing and sieving, a product with a particle size of 5-40mm is obtained. The remaining proportions and process parameters are the same as in Example 1.

[0061] The chemical composition of the obtained pre-melted refining slag by weight percentage is as follows: CaO 43.8%, Al2O3 21.2%, SiO2 15.6%, MgO 7.8%, Na2O 3.1%, K2O 1.5%, Li2O 0.2%, Na2O+K2O+Li2O total 4.8%, CaF2 0.03%, with the balance being unavoidable impurities.

[0062] Performance test results: melting point 1330℃; viscosity at 1500℃ 0.35 Pa·s; desulfurization rate 87% (sulfur content after refining 0.0026%).

[0063] Example 5 differs from Example 1 in that a reducing atmosphere (a mixture of nitrogen and a small amount of CO, with a CO volume fraction of 5%) is used in step 4, the melting temperature is 1550°C, and the melting time is 30 minutes. The remaining proportions and process parameters are the same as in Example 1.

[0064] The chemical composition of the obtained pre-melted refining slag by weight percentage is as follows: CaO 44.2%, Al2O3 20.8%, SiO2 15.3%, MgO 8.1%, Na2O 3.0%, K2O 1.6%, Li2O 0.2%, Na2O+K2O+Li2O total 4.8%, CaF2 0.03%, with the balance being unavoidable impurities.

[0065] Performance test results: melting point 1315℃; viscosity at 1500℃ 0.30 Pa·s; desulfurization rate 90% (sulfur content after refining 0.0020%).

[0066] Comparative Example 1: This comparative example uses traditional fluorite-containing refining slag, whose chemical composition by weight percentage is: CaO 50%, Al2O3 20%, SiO2 15%, MgO 5%, CaF2 10%. The preparation method is: the raw materials are crushed and then directly mechanically mixed without high-temperature pre-melting treatment.

[0067] Performance test results: melting point 1380℃; viscosity at 1500℃ 0.55 Pa·s; under the same simulated LF refining conditions, desulfurization rate 75% (sulfur content after refining 0.005%).

[0068] Comparative Example 2 differs from Example 1 in that it uses spodumene ore powder instead of lithium ore smelting residue, with a ratio of 50 kg spodumene powder, 30 kg lime, and 20 kg aluminum ash powder (according to CN102787214A). No lithium ore smelting residue is added. The remaining steps and process parameters are the same as in Example 1.

[0069] The chemical composition of the obtained refining slag by weight percentage is as follows: CaO 42%, Al2O3 25%, SiO2 18%, MgO 4%, Li2O 0.5%, Na2O+K2O+Li2O total 2.1%, CaF2 0.02%, with the balance being unavoidable impurities.

[0070] Performance test results: melting point 1420℃; viscosity at 1500℃ 0.68 Pa·s; desulfurization rate 80% (sulfur content after refining 0.004%).

[0071] Comparative Example 3 differs from Example 1 in that the raw material ratio is adjusted so that the total amount of Na2O + K2O + Li2O is less than 4%. The specific ratio is: 20 kg of lithium ore smelting residue, 40 kg of industrial lime, 10 kg of limestone, 5 kg of magnesium oxide, 20 kg of bauxite, and 5 kg of water glass. The remaining steps and process parameters are the same as in Example 1.

[0072] The chemical composition of the obtained refining slag by weight percentage is as follows: CaO 52%, Al2O3 22%, SiO2 13%, MgO 6%, Na2O 1.8%, K2O 0.8%, Li2O 0.1%, Na2O+K2O+Li2O total 2.7%, CaF2 0.02%, with the balance being unavoidable impurities.

[0073] Performance test results: melting point 1410℃; viscosity at 1500℃ 0.62 Pa·s; desulfurization rate 78% (sulfur content after refining 0.0044%).

[0074] Performance Test Results Summary Table

[0075]

[0076] It can be seen from the above table:

[0077] (1) The melting point of the pre-melted refining slag obtained in each embodiment of the present invention is ≤1350℃, and the viscosity at 1500℃ is ≤0.35Pa·s. The fluidity is significantly better than that of the traditional fluorite-containing slag of Comparative Example 1 (viscosity 0.55 Pa·s) and Comparative Examples 2 and 3 (viscosity >0.6Pa·s).

[0078] (2) The desulfurization rates of the embodiments of the present invention are all above 87%, with the highest reaching 93%, which is significantly higher than 75% in Comparative Example 1, 80% in Comparative Example 2 and 78% in Comparative Example 3. Among them, the desulfurization rate of 89% in Example 1 is 18.7% higher than that of 75% in Comparative Example 1, which meets the requirement of an increase of at least 15%.

[0079] (3) The CaF2 content in the products of the embodiments of the present invention is ≤0.05%, while the CaF2 content in Comparative Example 1 is 10%, which is much lower than that in traditional fluorite slag, indicating that the present invention achieves fluorine-free treatment and avoids fluorine emissions and furnace lining corrosion problems.

[0080] (4) Comparative Example 2 used spodumene ore, which had a total alkali metal oxide content of only 2.1%, a melting point as high as 1420℃, and a desulfurization rate of 80%. This shows that the excellent performance of the present invention cannot be obtained without utilizing K2O and Na2O in the lithium ore smelting residue. Comparative Example 3 had a total alkali metal content of 2.7%, and its performance was also poor, proving that the limitation of Na2O+K2O+Li2O>4% is the key to obtaining low melting point, high fluidity, and high desulfurization rate.

[0081] (5) The present invention uses lithium ore smelting residue as the main raw material, and the amount of its addition is 30-50 parts. While ensuring excellent performance, it disposes of a large amount of solid waste, reduces raw material costs, and realizes resource utilization.

[0082] Contents not described in detail in this specification are existing technologies known to those skilled in the art. The above descriptions are merely preferred embodiments of the present invention and are not intended to limit the invention in any other way. Any person skilled in the art may utilize the disclosed technical content to make changes or modifications to create equivalent embodiments for application in other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the scope of the present invention, shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing pre-melted refining slag, characterized in that, The process includes the following steps: mixing 30-50 parts by weight of lithium ore smelting residue, 20-40 parts by calcium regulator, 5-10 parts by magnesium regulator, 5-20 parts by aluminum regulator and 3-8 parts by binder, and then pressing, high-temperature melting, cooling and crushing to obtain pre-melted refining slag. The chemical composition of the pre-melted refining slag, by weight percentage, includes CaO 35%-55%, Al2O3 20%-30%, SiO2 8%-18%, MgO 3%-8%, Na2O+K2O+Li2O>4%, and unavoidable balance impurities. The CaF2 content of the pre-melted refining slag is ≤0.5%.

2. The method for preparing pre-melted refining slag according to claim 1, characterized in that, The chemical composition of the lithium ore smelting residue, by weight percentage, includes 30%-40% SiO2, 15%-25% Al2O3, 15%-30% CaO, 2%-6% K2O, 2%-10% Na2O, and 0.2%-0.5% Li2O.

3. The method for preparing pre-melted refining slag according to claim 1, characterized in that, The calcium regulator is industrial lime and / or limestone, the magnesium regulator is magnesium oxide, and the aluminum regulator is bauxite; the binder is water glass with a modulus of 2.2-2.

5.

4. The method for preparing pre-melted refining slag according to claim 1, characterized in that, The pre-melted refining slag has a CaO to Al2O3 mass ratio of 1.2-2.75 and a Li2O content of ≥0.05%; the pre-melted refining slag has a particle size of 5-40 mm, a melting point of ≤1350℃, a sulfur content of ≤0.1%, and a phosphorus content of ≤0.05%.

5. The method for preparing pre-melted refining slag according to claim 1, characterized in that, Includes the following steps: Step 1: Crush and grind the lithium ore smelting residue, calcium regulator, magnesium regulator, and aluminum regulator separately to a particle size of less than 200 mesh, and dry them to a moisture content of less than 1%. Step 2: Weigh the pretreated raw materials according to the proportion, add the binder, mix evenly, and obtain the mixture; Step 3: Press the mixture into pellets or blocks with a diameter of 20-50mm; Step 4: Melt the molding material at 1400℃-1550℃ in a reducing or inert atmosphere for 30-90 minutes; Step 5: Quickly cool the molten slag with air, crush and screen it to obtain a pre-melted refining slag product with a particle size of 5-40mm.

6. The method for preparing pre-melted refining slag according to claim 5, characterized in that, In step 4, the melting temperature is 1450℃-1500℃ and the melting time is 45-60 minutes.

7. The method for preparing pre-melted refining slag according to claim 5, characterized in that, In step 5, rapid air cooling yields a product including a glassy phase, which, after crushing, has a particle size of 5-30 mm.

8. A method for preparing pre-melted refining slag according to any one of claims 1-7, characterized in that, The pre-melted refining slag is used for LF ladle refining or molten steel desulfurization.

9. The method for preparing pre-melted refining slag according to claim 8, characterized in that, The amount of pre-melted refining slag added is 5-30 kg per ton of molten steel, the refining temperature is 1550℃-1650℃, and the refining time is 30-60 minutes.

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