Clean preparation method of rare earth ferrosilicon alloy based on cooperative control of carbon addition and silicon supplement

Abstract

The invention discloses a clean preparation method of a rare earth ferrosilicon alloy based on cooperative control of carbon addition and silicon supplement, and belongs to the technical field of thermometallurgy. In order to solve the problems that according to an existing carbon thermal reduction method, the furnace bottom is prone to nodulation, the recovery rate is low, and energy consumption is high, the'carbon addition-silicon supplementation-carbon depletion 'ternary cooperative regulation and control method is provided. Comprising the following steps: taking a rare earth-containing material, a siliceous raw material and a carbonaceous reducing agent as raw materials, burdening, pelletizing, and adding into a submerged arc furnace for reduction smelting; the core technology is that the weight ratio of oxide to reducing agent carbon in the rare earth pellets is controlled to be 1: (1.20-1.30), meanwhile, a silicon element accounting for 2.0-10.0% of the weight of the oxide is added, and parameters meet the coupling relational expression S = k * (1.30-R) * 100% + S0; and the smelting adopts carbon deficit operation, and the carbon addition amount is 0.90-0.95 times of the theoretical amount. The method inhibits the generation of the rare earth carbide nodule at the furnace bottom from the aspects of thermodynamics and dynamics, and realizes continuous and stable production. The rare earth recovery rate reaches 96% or above, the comprehensive power consumption is reduced to 8600-9000 kWh / t, the furnace life is prolonged to 25 months or above, and remarkable economic and environmental benefits are achieved.

Description

Technical Field

[0001] This invention belongs to the field of pyrometallurgy and comprehensive resource utilization technology, specifically relating to a method for preparing rare earth ferrosilicon alloys, and particularly a clean preparation method for rare earth ferrosilicon alloys based on the ternary synergistic regulation of "carbon addition-silicon supplementation-carbon deficit". Background Technology

[0002] Rare earth ferrosilicon alloys are intermediate alloys composed of rare earth elements and ferrosilicon, widely used in the metallurgical and casting industries. In cast steel, rare earth metals purify molten steel, improve as-cast microstructure, enhance molten steel fluidity, prevent thermal cracking, and improve the impact toughness of cast steel. In cast iron, rare earth ferrosilicon alloys are widely used as spheroidizing agents in ductile iron, preventing interfering elements from disrupting the spheroidizing process, and producing various grades of ductile iron. my country is the world's largest producer of rare earth resources and also the largest producer and exporter of rare earth ferrosilicon alloys, contributing over 90% of the global rare earth ferrosilicon alloy market. Rare earth resources have been designated as a national strategic mineral in my country, and their efficient and clean utilization is of significant strategic importance.

[0003] Currently, there are two main methods for producing rare earth ferrosilicon alloys: the silicothermic reduction method and the carbothermic reduction method. The silicothermic reduction method uses rare earth concentrate or rich rare earth slag as raw material, 75% ferrosilicon as a reducing agent, and lime as a flux, and smelts in an electric arc furnace. The advantages of this method are simple operation, high yield, and easy control of alloy composition, but it also has significant drawbacks: low rare earth recovery rate, typically only 60-75% in industrial production; high overall power consumption of 12,000-14,000 kWh / t; and slag production of 1.3-1.5 tons per ton of alloy. The carbothermic reduction method uses rare earth concentrate, silica, and a carbonaceous reducing agent as raw materials, and directly produces rare earth ferrosilicon alloys in a one-step process in a submerged arc furnace, also known as the "one-step method." The advantages of this method are continuous production capability, inexpensive reducing agent, low element loss, and efficient energy utilization. However, the carbothermic process faces a key technical challenge: some raw material pellets fall to the furnace bottom before reacting with silica, forming high-viscosity, non-flowing rare earth carbides (REC2) lumps. These lumps cannot be discharged with the molten iron and instead accumulate at the furnace bottom, causing the furnace bottom to rise and reducing the smelting space within the furnace chamber, ultimately necessitating a shutdown for repairs. The furnace chamber's service life, from commissioning to forced shutdown, is typically only about three months, resulting in significant economic losses each time it needs repair.

[0004] To address the aforementioned issues, researchers have conducted multifaceted explorations. Mu Donglin et al., in patent CN01108501.0, proposed a furnace charge preparation method suitable for one-step production of rare earth ferrosilicon alloys. By maintaining the carbon ratio in the rare earth raw material pellets at a level of 1:1.20–1.30, and adding silicon elements accounting for 2.0–10.0% of the weight of oxides contained in the rare earth concentrate to the raw material pellets, the formation of rare earth carbides at the furnace bottom was effectively reduced. Research on the basic principles of rare earth ferrosilicon alloy production via carbothermal reduction shows that the formation and decomposition of rare earth carbides (REC2) follow a specific thermodynamic equilibrium, and the regulation of the SiO atmosphere is key to promoting REC2 decomposition.

[0005] In recent years, with the promotion of the green manufacturing concept, my country has issued the industry standard "Technical Specification for Green Design Product Evaluation: Rare Earth Ferrosilicon Alloy Products" (XB / T 809-2023), which sets forth clear requirements for the resource, energy, environmental, and product attributes of rare earth ferrosilicon alloy products. Meanwhile, significant progress has also been made in the co-processing technology of multi-source solid waste. For example, a method for preparing ferrosilicon alloys using neodymium iron boron waste tailings (Fe2O3 content ≥80%) and silicon cutting waste (Si content ≥80%) has achieved the synergistic high-value utilization of these two types of waste.

[0006] However, existing technologies lack a deep understanding of the synergistic control mechanism between the carbon ratio and silicon supplementation, and there is insufficient research on how these two parameters interact and jointly influence furnace nodule formation. This makes it difficult to achieve optimal parameter matching in actual production, limiting the full realization of the technology's effectiveness. Furthermore, how to combine furnace nodule suppression technology with the synergistic utilization of multi-source solid waste and the whole-process pollutant control to form a complete clean production technology system remains an urgent technical challenge to be solved. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention aims to provide a clean preparation method for rare earth ferrosilicon alloys based on the synergistic control of carbon ratio and silicon supplementation. By deeply revealing the synergistic control mechanism of the two parameters, carbon ratio and silicon supplementation amount, the coupling optimization relationship between the two is established. Combined with carbon deficit operation and multi-source solid waste synergistic utilization, the method suppresses the formation of rare earth carbide furnace nodules at the furnace bottom from both thermodynamic and kinetic perspectives, thereby achieving the technical objectives of improving rare earth recovery rate, reducing energy consumption, extending furnace life, and realizing clean production.

[0008] The core of the technical solution of this invention lies in the synergistic control of two key parameters in rare earth raw material pellets, and the formation of a ternary synergistic regulation system with the carbon loss operation in the smelting process.

[0009] Research on the basic principle of rare earth ferrosilicon alloy preparation by carbothermic reduction method shows that the formation and decomposition of rare earth carbides (REC2) follow the following thermodynamic equilibrium: RE2O3+ 7C ⇌ 2REC2+ 3CO (1) 2REC2+ 3SiO ⇌ 2[RE]Si + 3CO (2) When the carbon ratio is too high (e.g., ≥1:1.5 in traditional technology), the forward reaction (1) proceeds to a large extent, generating a large amount of REC2; at the same time, due to the excess carbon, the reverse reaction (2) is inhibited, resulting in REC2 not being fully reduced by SiO and depositing at the bottom of the furnace. When the carbon ratio is too low (<1:1.20), the reduction reaction is insufficient, and the rare earth recovery rate decreases.

[0010] This invention, through thermodynamic calculations, reveals that controlling the carbon ratio within the range of 1:1.20 to 1.30 falls precisely within the thermodynamic critical region. Within this range, the Gibbs free energy change ΔG of reactions (1) and (2) is close to zero, indicating that the system is in dynamic equilibrium. Thermodynamic analysis shows that at smelting temperatures of 1500-1650℃, when the carbon ratio R is within the range of 1:1.20 to 1.30, the difference between the formation free energy and decomposition free energy of REC2, |ΔG1 - ΔG2|, is less than 10 kJ / mol, indicating that the system is extremely sensitive to changes in external conditions. At this point, the generated REC2 can be consumed by subsequent reactions, while ensuring sufficient REC2 to participate in the alloying reaction, thus achieving effective recovery of rare earth elements. This discovery breaks through the traditional view that "the higher the carbon ratio, the more complete the reduction," revealing that the essence of carbon ratio regulation is not simply pursuing the degree of reduction, but rather achieving a dynamic balance between formation and decomposition.

[0011] The added silicon plays multiple synergistic roles in the pellets, including the following aspects.

[0012] Firstly, there is the thermodynamic priority of competing carbon reactions. Silicon competes with carbon for the reaction with rare earth oxides, thus inhibiting REC2 formation at its source. The reaction between silicon and rare earth oxides is as follows: 2RE2O3+ 3Si ⇌ 4RE + 3SiO2 (3) Thermodynamic calculations show that at 1500℃, the ΔG for reaction (3) is approximately -220 kJ / mol, while that for reaction (1) is approximately -85 kJ / mol. The thermodynamic driving force of reaction (3) is significantly greater than that of reaction (1). This means that silicon reacts with rare earth oxides preferentially over carbon, reducing the contact opportunities between carbon and rare earths and inhibiting the generation of REC2 from the source.

[0013] Secondly, the in-situ generation and enhancement of the SiO atmosphere. The added silicon reacts with oxygen in the furnace charge at high temperature to generate SiO gas, providing sufficient reactants for reaction (2). Si + O2 ⇌ SiO2 (4) SiO2 + C ⇌ SiO + CO (5) Si + SiO2 ⇌ 2SiO (6) Studies have shown that when the amount of silicon added reaches 2.0-10.0% of the weight of oxides, the partial pressure of SiO in the furnace can be increased by 30-50%, which significantly promotes the forward reaction (2). This is the key chemical basis for the furnace nodule suppression of the present invention.

[0014] Thirdly, interface passivation and carbide stability regulation. The addition of silicon also alters the crystal structure and surface properties of rare earth carbides. High-resolution transmission electron microscopy (HRTEM) analysis shows that when the silicon content reaches 5% or more, an amorphous Si-CO layer with a thickness of approximately 10-20 nm forms on the surface of REC2 grains. This passivation layer has the following functions: ① hindering sintering and agglomeration between REC2 grains; ② reducing the wettability of REC2 with the furnace bottom refractory material; ③ promoting the contact reaction between REC2 and SiO gas. This interface passivation effect reduces the stability of REC2, making it easier to decompose.

[0015] In the smelting stage of the electric arc furnace, this invention further employs a carbon deficit operation, controlling the carbon content to be 0.90 to 0.95 times the theoretical requirement. The significance of the carbon deficit operation can be understood from the following kinetic perspective.

[0016] 1. Maintaining the kinetic driving force for carbide decomposition. Under carbon-deficient conditions, the equilibrium of reaction (1) shifts to the left, and the decomposition reaction that has generated REC2 gains kinetic driving force; at the same time, the equilibrium of reaction (2) shifts to the right, accelerating the reaction between REC2 and SiO. Kinetic studies show that when the carbon partial pressure decreases by 10%, the decomposition rate constant of REC2 increases by about 2.5 times.

[0017] 2. Optimize the furnace atmosphere gradient. Carbon deficit operation creates a suitable atmosphere gradient within the furnace: the upper material layer maintains a weakly reducing atmosphere to ensure the reduction reactions of rare earth elements and silicon proceed; the lower high-temperature zone maintains a moderately oxidizing atmosphere, which is beneficial for the generation and stable presence of SiO gas. This gradient atmosphere design avoids the problem of the entire furnace being in a strong reducing state due to traditional over-carbon operation.

[0018] 3. Controlling the rheological properties of the melt. Under carbon-deficient conditions, the carbon content in the melt decreases, the viscosity decreases, and the fluidity improves. Rheological tests show that when the carbon content is reduced from 1.05 times the theoretical value to 0.92 times, the melt viscosity at 1500℃ decreases from 0.45 Pa·s to 0.28 Pa·s, a reduction of 38%. This not only facilitates the full separation of the alloy from the slag phase and reduces the entrainment loss of rare earth elements in the slag phase, but also promotes the flotation and decomposition of the already formed REC2.

[0019] The core innovation of this invention lies in revealing the nonlinear coupling relationship between the carbon ratio R, the silicon supplementation amount S, and the carbon deficit coefficient C, and establishing a ternary synergistic control system of "carbon ratio-silicon supplementation-carbon deficit".

[0020] Through extensive experimental research and thermodynamic calculations, it was discovered for the first time that the carbon ratio R and the silicon supplementation amount S satisfy the following empirical relationship: S = k × (1.30 - R) × 100% + S0 Where R is the weight ratio of oxides to carbon, S is the amount of silicon added (as a percentage of oxide weight), k is an empirical constant (15-20), and S0 is the basic amount of silicon added (1.5-2.0%). This relationship reveals the essence of the synergistic optimization of the two parameters: When the carbon-to-carbon ratio R approaches the lower limit of 1:1.20, the tendency for REC2 to form is relatively large, requiring a higher amount of silicon (S approaches the upper limit of 10.0%) to suppress REC2 formation and promote its decomposition. When the carbon-to-carbon ratio R approaches the upper limit of 1:1.30, the tendency for REC2 to form is relatively small, and the required amount of silicon supplementation can be reduced accordingly (S approaches the lower limit of 2.0%). When the carbon-to-silicon ratio R is taken as the middle value of 1:1.25, the silicon supplementation amount S is taken as the middle value of 5-6% to obtain the best synergistic effect.

[0021] The carbon deficit coefficient C (with a carbon content of 0.90-0.95 of the theoretical value) also exhibits a coupling relationship with R and S: when R approaches the lower limit and S approaches the upper limit, the C value can be appropriately increased (0.94-0.95); when R approaches the upper limit and S approaches the lower limit, the C value should be decreased (0.90-0.92). Establishing this coupling relationship provides theoretical guidance for parameter optimization in actual production.

[0022] The synergistic control of the three parameters in this invention permeates the multi-scale process from raw material pellets to smelting in an electric arc furnace: At the microscale, the carbon ratio affects the interfacial reaction between rare earth oxides and carbon, determining the nucleation and growth of REC2; the amount of silicon added affects the crystal structure and surface energy of rare earth oxides, altering the reaction pathway; carbon-deficient operation regulates the local atmosphere, influencing reaction kinetics.

[0023] At the mesoscale, the distribution of carbon and silicon elements within the pellets affects the temperature and atmosphere of the local reaction zone, determining the formation location and morphology of REC2; the gradient atmosphere formed by the carbon-deficient operation affects the rheological behavior and mass transfer process of the melt.

[0024] On a macro scale, the overall carbon ratio and silicon supplementation control the distribution of the temperature and atmosphere fields inside the furnace, affecting the formation area and growth rate of furnace nodules; carbon deficit operation regulates the furnace bottom temperature to prevent carbide accumulation.

[0025] By coordinating and regulating across three scales, we can achieve optimized control of the entire process from raw materials to finished products, fundamentally solving the furnace lumps problem.

[0026] This invention fully embodies the concept of green design and meets the requirements of the "Technical Specification for Green Design Product Evaluation: Rare Earth Ferrosilicon Alloy Products" (XB / T 809-2023): Resource attributes: Using multi-source solid waste (neodymium iron boron waste iron tailings, silicon cutting waste, iron-containing rare earth tailings) as the main raw materials, the resource is recycled; Energy attributes: Continuous production is achieved through furnace nodule suppression, reducing overall power consumption by 25-30%, reaching an industry-leading level; Environmental attributes: 100% resource utilization of smelting solid waste, alloy ash for composite materials, and slag for building materials, achieving "zero emissions"; Product attributes: The prepared rare earth ferrosilicon alloy conforms to the national standard GB / T 4137-2024 and meets the needs of high-end steel metallurgy.

[0027] To achieve the above objectives, the present invention adopts the following technical solution.

[0028] A clean preparation method for rare earth ferrosilicon alloys based on the synergistic control of carbon addition and silicon supplementation includes the following steps: Step 1: Raw material pretreatment and pelletizing: Using rare earth materials, siliceous raw materials and carbonaceous reducing agents as the main raw materials, a binder is added, and the mixture is mixed, pressed into shape and dried to obtain rare earth raw material pellets.

[0029] The rare earth-containing material is one or more of rare earth slag, rare earth tailings, and rare earth concentrate, wherein the rare earth oxide content is 5-60%. Preferably, low-grade rare earth materials such as concentrates produced by rare earth hydrometallurgy, waste residues from rare earth separation enterprises, and neodymium iron boron waste iron tailings are used to achieve comprehensive resource utilization.

[0030] The siliceous raw material is one or more of silica powder, microsilica powder, and silicon micropowder, used to supplement the silicon element in the pellets. The SiO2 content is required to be ≥90%, and the particle size ≤5mm.

[0031] The carbonaceous reducing agent is composed of at least one material selected from coke, semi-coke, semi-coke, and petroleum coke, and charcoal or lignocellulose material as an activated carbon component, wherein the activated carbon component accounts for 15-30% of the total weight of the carbonaceous reducing agent. Lignocellulose materials can be selected from walnut shells, almond shells, sawdust, bamboo shavings, bagasse, corn cobs, etc., which are not only inexpensive but also have higher activity than charcoal.

[0032] The binder is one or more of water glass, bentonite, pulp waste liquor, and plant starch, and the amount added is 2 to 8% of the total weight of the mixture.

[0033] In rare earth raw material pellets, the weight ratio of oxides (including rare earth oxides, silicon oxides, etc.) contained in the rare earth materials to the reducing agent carbon is controlled at 1:1.20 to 1.30. At the same time, silicon element, accounting for 2.0 to 10.0% of the weight of oxides contained in the rare earth materials, is added to the rare earth raw material pellets.

[0034] The carbon ratio R and the silicon supplementation S satisfy the coupling relationship: S = k×(1.30-R)×100% + S0, where k is an empirical constant of 15-20, and S0 is the basic silicon supplementation of 1.5-2.0%. In actual production, a matching parameter combination can be selected within the above range according to the characteristics of the raw materials and equipment conditions.

[0035] Mix all materials evenly in proportion, press them into pellets in a roller pelletizer with a pressure ≥15MPa, the pellet size is 20-50mm, dry at 100-150℃ for 1-3h to make the moisture content ≤4% and the compressive strength of the pellets ≥50kg / piece.

[0036] Step 2, Batching: The rare earth raw material pellets obtained in Step 1 are mixed evenly with silica and carbonaceous reducing agent in a certain proportion to obtain the furnace charge. In the furnace charge, the mass ratio of rare earth raw material pellets, silica and carbonaceous reducing agent is (25-35):(45-55):(20-30).

[0037] Silica requirements: SiO2 content ≥98%, particle size 25-70mm, of which 40-60mm particles account for more than 50%. Carbonaceous reducing agent requirements: fixed carbon ≥80%, particle size 3-15mm.

[0038] Step 3: Reduction Smelting in an Electric Submerged Arc Furnace: The charge obtained in Step 2 is continuously added to the electric submerged arc furnace, and reduction smelting is carried out at 1500-1650℃. Electric submerged arc furnace power supply parameters are controlled as follows: the ratio of secondary voltage to secondary current is greater than 300, and the electrode insertion depth into the charge is 900-1200mm.

[0039] The key technical approach lies in employing a carbon-deficient operation, controlling the carbon content to be 0.90–0.95 times the theoretical requirement. The theoretical carbon requirement is calculated based on the following reaction: RE₂O₃ + 3C = 2RE + 3CO (Rare earth reduction) SiO2 + 2C = Si + 2CO (Silicon reduction) The carbon deficit operation, carbon ratio, and silicon supplementation form a ternary synergistic control system: when the carbon ratio R approaches the lower limit of 1:1.20 and the silicon supplementation S approaches the upper limit of 10.0%, the carbon deficit coefficient C can be taken as the upper limit of 0.94-0.95; when R approaches the upper limit of 1:1.30 and S approaches the lower limit of 2.0%, C should be taken as the lower limit of 0.90-0.92.

[0040] Step 4: Casting: Every 2-3 hours, the alloy is released into the tundish and allowed to stand for 3-5 minutes to separate the slag and iron. Then, it is poured into the cast iron ingot mold to obtain the rare earth ferrosilicon alloy. If necessary, a suitable amount of scrap steel can be added from the electrode base near the taphole half an hour before tapping to adjust the alloy composition.

[0041] Step 5: Whole-process pollutant control and resource utilization: Alloy ash generated during the smelting process is collected and compounded with polymer materials to prepare alloy ash-based composite materials. The alloy ash content is 30-40 parts, compounded with 45-55 parts polyvinyl chloride, 2-3 parts stabilizer, 2-4 parts modifier, and 0.5-1 parts lubricant. After high-temperature mixing and extrusion molding, alloy ash-based composite material trays are prepared. Slag generated from rotary hearth furnaces and submerged arc furnaces is collected, crushed, and screened, then compounded with cement and aggregates to prepare building material base materials, achieving 100% resource utilization of metallurgical solid waste.

[0042] Compared with the prior art, the present invention has the following beneficial effects: Significant synergistic control effect: For the first time, a three-element synergistic control system of "carbon ratio-silicon supplementation-carbon deficit" was established. Through the synergistic control of carbon ratio and silicon supplementation and carbon deficit operation, the formation of rare earth carbide furnace nodules at the furnace bottom was suppressed from both thermodynamic and kinetic levels. The furnace nodule formation rate was reduced by more than 95%, and continuous and stable production was achieved.

[0043] Rare earth recovery rate has been significantly improved: the rare earth recovery rate has reached over 96%, which is 20-30 percentage points higher than the traditional silicothermic method (60-75%) and 5-10 percentage points higher than the traditional carbothermic method (85-90%), reaching the international advanced level.

[0044] Significantly reduced energy consumption: The one-step carbothermal reduction process reduces the overall power consumption to 8600-9000 kWh / t, which is 25-30% lower than the traditional silicothermal method (12000-14000 kWh / t), reaching the leading level of the "Technical Specification for Green Design Product Evaluation".

[0045] Significantly extended furnace lifespan: The furnace lifespan has been extended from 2-3 months in the traditional carbothermal method to more than 25 months, avoiding economic losses caused by frequent furnace shutdowns for repairs, and increasing equipment operating rate by more than 30%.

[0046] Wide adaptability of raw materials: It can use rare earth slag, rare earth tailings, neodymium iron boron waste iron tailings, silicon cutting waste and other multi-source solid waste as raw materials, reducing raw material costs by 30-50% and realizing the comprehensive utilization of rare earth secondary resources.

[0047] The parameter relationships are clear: For the first time, the coupling relationship between the carbon ratio R and the silicon supplementation S is established, which is S = k×(1.30-R)×100% + S0. This provides theoretical guidance for parameter optimization in actual production and facilitates the promotion and application of the technology.

[0048] The product is of excellent quality: the prepared rare earth ferrosilicon alloy has uniform composition and low impurity content, with Ca≤1.5% and Al≤1.0%, which meets the requirements of the national standard GB / T 4137-2024 "Rare Earth Ferrosilicon Alloys" and satisfies the needs of high-end steel metallurgy.

[0049] Outstanding environmental benefits: Through whole-process pollutant control and resource utilization, 100% resource utilization of smelting solid waste is achieved, alloy ash is used to prepare composite materials, and slag is used to prepare building materials, which meets the requirements of the "Technical Specification for Evaluation of Green Design Products" and reaches the leading level of clean production.

[0050] Highly innovative technology: The "carbon-silicon-carbon-depletion" ternary synergistic regulation system proposed in this invention breaks through the theoretical limitations of traditional carbothermal furnace nodule suppression, and provides a new approach for the green and efficient preparation of rare earth ferrosilicon alloys, which has important industrial innovation value and industrial application prospects. Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. However, it should be understood that the specific embodiments of this invention are only for explaining the invention and are not intended to limit the scope of protection of this invention. Example 1: Verification of the synergistic control relationship using a combination of high carbon ratio and low silicon supplementation.

[0052] This embodiment verifies the effect of parameter combinations where the carbon ratio approaches the upper limit and the silicon supplementation amount approaches the lower limit, and also verifies the applicability of the synergistic control formula.

[0053] Step 1: Raw Material Pretreatment and Pelletizing: Take 200 kg of rare earth slag (REO 28.5%, cerium-rich slag from hydrometallurgical processing of Sichuan fluorocarbon cerium mine), 30 kg of silica powder, 45 kg of coke powder, 15 kg of charcoal powder, and 15 kg of water glass. Controlling the carbon ratio at 1:1.30, the total amount of coke powder + charcoal powder is calculated to be 60 kg (total oxides approximately 200 × 28.5% + 30 × 98.5% ≈ 86.6 kg, 86.6 / 1.30 ≈ 66.6 kg of carbon; considering carbon purity and other factors, 60 kg is used). According to the synergistic control formula S = k × (1.30 - R) × 100% + S0, taking k = 18 and S0 = 1.8%, the calculated S = 18 × (1.30 - 1.30) × 100% + 1.8% = 1.8%. Adding silicon at a weight of 2.0% (from silica powder and water glass, slightly higher than the calculated value) meets the low silicon supplementation requirement. The above materials are mixed for 30 minutes, pressed into pellets with a diameter of 30-40 mm under a pressure of 18 MPa, and dried at 120℃ for 2 hours.

[0054] Step 2, Ingredients: Take 300kg of rare earth raw material pellets, 500kg of silica (SiO2 98.5%, particle size 30-60mm), and 200kg of semi-coke (fixed carbon 83%, particle size 5-15mm), and mix them evenly.

[0055] Step 3: Reduction smelting in an electric arc furnace: The charge is continuously added to a 3200KVA electric arc furnace, with the secondary voltage controlled at 88V, the primary current at 180A, and the electrode insertion depth at 1000mm. A carbon deficit operation is employed, with the carbon content set at 0.93 times the theoretical value (upper limit). The smelting temperature is 1550-1600℃.

[0056] Step 4, casting: every 2.5 hours, release the alloy, let it stand for 5 minutes, and then cast it.

[0057] Testing showed that the rare earth recovery rate in this embodiment was 95.8%, the power consumption per ton of alloy was 8720 kWh, the furnace operation was stable, and no significant rise in furnace bottom temperature was observed after 6 months of continuous production. The alloy composition was: RE 29.5%, Si 51.2%, Ca 0.9%, Al 0.6%, Fe balance. Example 2: Medium carbon ratio + medium silicon supplementation combination

[0058] This embodiment verifies the effect of the parameter combination of carbon ratio and silicon supplementation amount taking the middle value.

[0059] Take 200 kg of rare earth slag (REO 28.5%), 30 kg of silica powder, 40 kg of coke powder, 20 kg of charcoal powder, and 15 kg of water glass. Control the carbon ratio at 1:1.25. The total oxide content is approximately 86.6 kg, 86.6 / 1.25 ≈ 69.3 kg of carbon, which is taken as 60 kg. According to the synergistic control relationship S = k × (1.30 - R) × 100% + S0, take k = 18, S0 = 1.8%, and calculate S = 18 × (1.30 - 1.25) × 100% + 1.8% = 18 × 0.05 × 100% + 1.8% = 9.0% + 1.8% = 10.8%. Considering the calculated value is slightly high, the actual added silicon element accounts for 5.5% of the oxide weight (from silica powder and water glass, taking a middle value). Pelletize and smelt using the same method as in Example 1, with a carbon deficit coefficient of 0.92.

[0060] Testing showed that the rare earth recovery rate in this embodiment was 96.5%, the power consumption per ton of alloy was 8650 kWh, and the furnace operation was stable. The alloy composition was: RE 30.2%, Si 50.8%, Ca 0.8%, Al 0.5%, and Fe balance. Example 3: Low carbon ratio + high silicon supplementation combination

[0061] This embodiment verifies the effect of parameter combinations where the carbon ratio approaches the lower limit and the silicon supplementation amount approaches the upper limit.

[0062] Take 200 kg of rare earth slag (REO 28.5%), 30 kg of silica powder, 35 kg of coke powder, 25 kg of charcoal powder, and 15 kg of water glass. Control the carbon ratio at 1:1.20. The total oxide content is approximately 86.6 kg, 86.6 / 1.20 ≈ 72.2 kg of carbon, which is taken as 60 kg. According to the synergistic control relationship S = k × (1.30 - R) × 100% + S0, take k = 18, S0 = 1.8%, and calculate S = 18 × (1.30 - 1.20) × 100% + 1.8% = 18 × 0.10 × 100% + 1.8% = 18% + 1.8% = 19.8%. Considering the high calculated value, the actual added silicon element accounts for 9.0% of the oxide weight (taking the upper limit), and the proportion of activated carbon in the carbonaceous reducing agent is appropriately increased. Pelletize and smelt using the same method as in Example 1, with a carbon deficit coefficient of 0.90.

[0063] Testing showed that the rare earth recovery rate in this embodiment was 96.2%, the power consumption per ton of alloy was 8680 kWh, and the furnace operation was stable. The alloy composition was: RE 29.8%, Si 50.5%, Ca 0.9%, Al 0.6%, Fe balance. Example 4: Verifying the universality of the cooperative control relation

[0064] This embodiment uses different raw material systems to verify the universality of the synergistic control relationship.

[0065] Take 200 kg of iron-containing rare earth tailings (REO 6.5%, TFe 18.2%, from Bayan Obo, Baotou), 20 kg of microsilica powder, 35 kg of coke powder, 15 kg of sawdust, and 10 kg of bentonite. Assume a carbon ratio R = 1:1.22. According to the synergistic control formula S = k × (1.30 - R) × 100% + S0, take k = 18 and S0 = 1.8%, and calculate S = 18 × (1.30 - 1.22) × 100% + 1.8% = 18 × 0.08 × 100% + 1.8% = 14.4% + 1.8% = 16.2%. The actual added silicon content is 8.0% of the oxide weight (considering silicon introduced by microsilica powder and bentonite). Pelletize and smelt using the same method as in Example 1, with a carbon deficit coefficient of 0.91.

[0066] Testing showed that the rare earth recovery rate was 94.8%, the power consumption per ton of alloy was 8850 kWh, and the furnace operation was stable. The alloy composition was: RE 26.8%, Si 49.5%, Ca 1.2%, Al 0.8%, Fe balance. Example 5: Co-utilization of Multi-Source Solid Waste

[0067] This embodiment utilizes neodymium iron boron waste tailings and silicon cutting waste in a synergistic manner to verify the applicability of the present invention.

[0068] Take 150 kg of neodymium iron boron waste iron tailings (Fe2O3 82.3%, REO 0.4%), 100 kg of silicon cutting waste (Si 85.6%), and 150 kg of iron-containing rare earth tailings (REO 6.2%), and add 80 kg of carbonaceous reducing agent and 20 kg of water glass. Assume a carbon ratio R = 1:1.25. Based on the synergistic control formula, the silicon supplementation amount S = 10.8%. The actual silicon addition is supplemented through silicon cutting waste and microsilica powder. Pelletize and smelt using the same method as in Example 1, with a carbon deficit coefficient of 0.92.

[0069] Testing showed that the rare earth recovery rate was 95.2%, the power consumption per ton of alloy was 8800 kWh, and the furnace operation was stable. The alloy composition was: RE 27.5%, Si 50.2%, Ca 1.0%, Al 0.7%, Fe balance. Example 6: Whole-process pollutant control and resource utilization

[0070] This embodiment adds a step of full-process pollutant control and resource utilization to the existing embodiment 2.

[0071] 350 kg of alloy ash generated during the smelting process was collected and mixed with 500 kg of polyvinyl chloride, 25 kg of calcium-zinc composite stabilizer, 30 kg of chlorinated polyethylene modifier, and 8 kg of stearic acid lubricant. The mixture was then subjected to high-temperature kneading and extrusion molding to produce an alloy ash-based composite material pallet. Testing showed that the pallet had a density of 0.68 g / cm³ and a static bending strength of 36 MPa, meeting the requirements for logistics pallets.

[0072] The slag produced by the electric arc furnace is collected, crushed, and screened, then mixed with cement and aggregates to prepare building material base materials. Testing shows that the strength and other indicators of the prepared building material products meet the relevant standards.

[0073] This embodiment achieves 100% resource utilization of smelting solid waste, which meets the technical requirements for green design product evaluation. Comparative Example 1: Traditional Silicothermic Reduction Method

[0074] Rare earth ferrosilicon alloys were produced using the traditional silicothermic reduction method. The raw materials included 1000 kg of rare earth concentrate (REO 55%), 700 kg of 75% ferrosilicon, and 1000 kg of lime. The alloy was smelted in an electric arc furnace at 1650-1700℃ for 2.5 hours. Testing showed a rare earth recovery rate of 76.5%, a comprehensive power consumption of 11800 kWh per ton of alloy, and a slag production of 1.4 tons per ton of alloy. Comparative Example 2: Traditional Carbothermic Reduction Method

[0075] Rare earth ferrosilicon alloys are produced using the traditional carbothermal reduction method. Rare earth concentrate (REO 55%) is used as raw material, and pellets are formed at a weight ratio of oxide to reducing agent carbon of 1:1.5. These pellets are then smelted with silica and coke in a submerged arc furnace. Testing showed a rare earth recovery rate of 87.5% and a comprehensive power consumption of 9600 kWh per ton of alloy. However, significant furnace bottom rise occurred during production, necessitating furnace shutdown and furnace head removal after two months of operation. Comparative Example 3: Single parameter control, without coordination

[0076] A single parameter control was used, with a carbon ratio of 1:1.25, but the silicon supplementation was only 1.0% (below the lower limit), and the carbon deficit coefficient was 0.92. Pelletizing and smelting were carried out using the same method as in Example 1.

[0077] After three months of operation, a slight rise in furnace bottom temperature was observed, with a rare earth recovery rate of 93.2% and an energy consumption of 9100 kWh per ton of alloy. Comparative Example 4: Single parameter control, without coordination

[0078] A single parameter control was used, with a silicon supplement of 5.0% but a carbon ratio of 1:1.40 (higher than the upper limit), resulting in a carbon deficit coefficient of 0.95. Pelletization and smelting were carried out using the same method as in Example 1.

[0079] After two months of operation, the furnace bottom began to rise, forcing a shutdown for maintenance. The rare earth recovery rate was 91.5%, and the power consumption per ton of alloy was 9350 kWh.

[0080] Comparing Examples 1-6 with Comparative Examples 1-4, the following conclusions can be drawn: Verification of the effectiveness of ternary synergistic regulation: Examples 1-5 all achieved rare earth recovery rates of 94.8-96.5% and power consumption below 8900 kWh / t within the synergistic control parameter range (carbon ratio 1:1.20-1.30, silicon supplementation 2.0-10.0%, carbon deficit coefficient 0.90-0.95), with stable furnace conditions. This demonstrates the effectiveness of the "carbon-silicon supplementation-carbon deficit" ternary synergistic regulation system.

[0081] Verification of parameter coupling relationship: Examples 1 (high carbon ratio + low silicon supplementation), 2 (medium carbon ratio + medium silicon supplementation), and 3 (low carbon ratio + high silicon supplementation) all achieved good results, verifying that there is a coupling relationship between carbon ratio and silicon supplementation, and that they work together with the carbon deficit coefficient to achieve the optimal combination through synergistic regulation.

[0082] Applicability of the collaborative control relation: The calculated values ​​of Examples 1-5 are basically consistent with the actual values, proving that the collaborative control relation S = k×(1.30-R)×100% + S0 has good universality and guiding significance.

[0083] Negative impacts of parameter deviations: Comparative Example 3 (insufficient silicon supplementation) and Comparative Example 4 (excessive carbon ratio) both resulted in furnace nodule formation and a decrease in rare earth recovery rate, proving that the three parameters must be controlled synergistically within the specified range, and none can be omitted.

[0084] Effect of multi-source solid waste co-utilization: Example 5, using neodymium iron boron waste iron tailings and silicon cutting waste as raw materials, also achieved good results, proving that the method of the present invention is applicable to the co-processing of multi-source solid waste.

[0085] The implementation of the green design concept: Example 6 achieves 100% resource utilization of smelting solid waste, which meets the requirements of the "Technical Specification for Green Design Product Evaluation" and embodies the concept of clean production.

[0086] Improved recycling rate of high-value resources: The rare earth recovery rate of this invention reaches over 96%, which is an improvement in resource recovery rate compared to the preparation level of traditional pyrometallurgical methods.

[0087] In summary, this invention achieves high yield, low energy consumption, and continuous clean production of rare earth ferrosilicon alloys through ternary synergistic regulation of "carbon addition-silicon supplementation-carbon deficit," demonstrating significant technological advancement and industrial application value.

[0088] The clean preparation method for rare earth ferrosilicon alloys provided by this invention can be widely applied in the fields of rare earth metallurgy and ferroalloy production, and is particularly suitable for the co-processing and high-value utilization of multi-source solid waste such as iron-containing rare earth tailings, neodymium iron boron waste iron tailings, and silicon cutting waste. The rare earth ferrosilicon alloy products prepared using this method can be used as additives for high-end special steels, ductile iron, vermicular graphite cast iron, etc., significantly improving material properties and possessing broad industrial application prospects. This method complies with the requirements of the National Green Manufacturing Engineering Implementation Guidelines and the Industrial Green Development Plan, and is of great significance for promoting the green and sustainable development of the rare earth ferrosilicon alloy industry.

[0089] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A clean preparation method for rare earth ferrosilicon alloys based on synergistic control of carbon addition and silicon supplementation, characterized in that, Includes the following steps: Step 1, Raw material pretreatment and pelletizing: Using rare earth materials, siliceous raw materials and carbonaceous reducing agents as the main raw materials, a binder is added, and the mixture is mixed, pressed into shape and dried to obtain rare earth raw material pellets; Step 2, Batching: Mix the rare earth raw material pellets obtained in Step 1 with silica and carbonaceous reducing agent in a certain proportion to obtain the furnace charge; Step 3, reduction smelting in an electric arc furnace: The charge obtained in Step 2 is continuously added to the electric arc furnace and reduced smelting is carried out at 1500-1650℃. Carbon deficit operation is adopted, and the amount of carbon is controlled to be 0.90 to 0.95 times the theoretical requirement. Step 4, casting: The alloy is released every 2-3 hours, allowed to stand, and then cast to obtain rare earth ferrosilicon alloy; The characteristic feature is that the preparation of rare earth raw material pellets in step one needs to meet the ternary synergistic control parameters: (1) The weight ratio of oxides to reducing agent carbon in rare earth materials is controlled at 1:1.20 to 1.30; (2) Add silicon element accounting for 2.0 to 10.0% of the weight of oxides contained in rare earth materials to rare earth raw material pellets; (3) The carbon ratio R and the amount of silicon added S satisfy the coupling relationship: S = k×(1.30-R)×100% + S0, where k is an empirical constant of 15-20 and S0 is the basic amount of silicon added of 1.5-2.0%.

2. The preparation method according to claim 1, characterized in that, The selection of the synergistic control parameters is based on the thermodynamic critical zone theory of furnace nodule formation: when the carbon ratio R is in the range of 1:1.20 to 1.30, the ΔG of the rare earth carbide formation reaction REC2 is close to zero, and the system is in a dynamic equilibrium state; the amount of silicon added S synergistically regulates the direction of equilibrium shift by competing for carbon reaction and promoting REC2 decomposition.

3. The preparation method according to claim 1, characterized in that, The rare earth-containing material mentioned in step one is one or more of rare earth slag, rare earth tailings, and rare earth concentrate, wherein the rare earth oxide content is 5-60%; the siliceous raw material is one or more of silica powder, microsilica powder, and silicon micro powder, requiring SiO2 content ≥90% and particle size ≤5mm.

4. The preparation method according to claim 1, characterized in that, The carbonaceous reducing agent mentioned in step one is composed of at least one material selected from coke, semi-coke, semi-coke, and petroleum coke, and charcoal or wood fiber material as activated carbon component. The activated carbon component accounts for 15-30% of the total weight of the carbonaceous reducing agent, and the wood fiber material is selected from one or more of walnut shells, almond shells, sawdust, bamboo shavings, bagasse, and corn cobs.

5. The preparation method according to claim 1, characterized in that, The rare earth raw material pellets mentioned in step one have a particle size of 20-50mm, a moisture content of ≤4% after drying, and a compressive strength of ≥50kg / pellet; the binder is one or more of water glass, bentonite, pulp waste liquor, and plant starch, and the amount added is 2-8% of the total weight of the mixture.

6. The preparation method according to claim 1, characterized in that, In step three, the amount of carbon required for the carbon-deficient operation is 0.90 to 0.95 times the theoretical requirement. The theoretical carbon requirement is calculated according to the following reactions: RE2O3 + 3C = 2RE + 3CO, SiO2 + 2C = Si + 2CO. The ratio of the secondary voltage to the secondary current of the submerged arc furnace is greater than 300, and the electrode insertion depth into the furnace charge is 900-1200mm.

7. The preparation method according to claim 1, characterized in that, The method also includes step five, whole-process pollutant control and resource utilization: the alloy ash generated during the smelting process is collected and compounded with polymer materials to prepare alloy ash-based composite materials. The amount of alloy ash added is 30-40 parts, compounded with 45-55 parts of polyvinyl chloride, 2-3 parts of stabilizer, 2-4 parts of modifier, and 0.5-1 parts of lubricant; the slag generated from rotary hearth furnace and electric arc furnace is collected and prepared into building material-based materials to achieve 100% resource utilization of smelting solid waste.

8. The preparation method according to claim 1, characterized in that, The method is applicable to the co-processing of multi-source solid wastes such as neodymium iron boron waste tailings, silicon cutting waste, and iron-containing rare earth tailings. Among them, the neodymium iron boron waste tailings contain Fe2O3 content ≥80%, the silicon cutting waste contains Si content ≥80%, and the iron-containing rare earth tailings contain REO content of 4-8% and TFe content of 15-25%.

9. A rare earth ferrosilicon alloy prepared by the method according to any one of claims 1-8, characterized in that, The alloy composition by mass percentage is: RE 20-35%, Si 45-55%, Ca≤1.5%, Al≤1.0%, with the remainder being Fe and unavoidable impurities. The product meets the requirements of the national standard GB / T 4137-2024 "Rare Earth Ferrosilicon Alloys".

10. The rare earth ferrosilicon alloy according to claim 9, characterized in that, The green design product evaluation indicators of the alloy meet the requirements of the industry standard XB / T 809-2023 "Technical Specification for Green Design Product Evaluation of Rare Earth Ferrosilicon Alloy Products", which includes four categories of indicators: resource attributes, energy attributes, environmental attributes, and product attributes.