Method for comprehensive utilization of rare earth silicon-iron smelting waste slag in stages

Abstract

This invention discloses a method for the comprehensive utilization of rare earth ferrosilicon smelting waste slag through a tiered resource system, belonging to the field of metallurgical solid waste resource utilization. Addressing the challenges of difficult recovery of large amounts of rare earth and magnesium residues in rare earth magnesium ferrosilicon alloy production waste slag, and the high environmental risks associated with their storage, this invention provides an integrated solution of "reduction smelting targeted enrichment – ​​selective phase decomposition – tiered separation – cross-industry collaborative utilization": The waste slag is subjected to reduction smelting with a reducing agent, enriching rare earth and magnesium in the alloy phase to obtain rare earth-rich magnesium ferrosilicon alloy and primary tailings; then, selective phase decomposition of the alloy is performed to achieve efficient separation of rare earth from iron and magnesium, yielding rare earth enrichment and iron-magnesium alloy products respectively; finally, the primary tailings are activated and co-prepared with coal gangue and fly ash to produce foamed ceramics. This invention achieves a total rare earth recovery rate of ≥90%, a magnesium recovery rate of ≥85%, and a waste slag comprehensive utilization rate approaching 100%, is compatible with existing equipment, and provides a green and efficient path for the resource utilization of rare earth smelting waste slag.

Description

Technical Field

[0001] This invention relates to the field of metallurgical solid waste resource utilization and rare earth secondary resource recycling technology, specifically to a comprehensive utilization method for rare earth ferrosilicon smelting waste residue, and more particularly to a cascade resource utilization method for preparing building materials through targeted enrichment by reduction smelting, selective phase decomposition and cascade separation, and synergistic utilization of tailings. Background Technology

[0002] Rare earth magnesium ferrosilicon alloys are key spheroidizing agents in the production of ductile iron, and their production process generates a large amount of silicothermic reduction slag. Statistics show that approximately 0.8-1.2 tons of smelting waste slag are generated for every ton of rare earth ferrosilicon alloy or rare earth magnesium ferrosilicon alloy produced. The main chemical composition of these waste slags includes: REO 5-15%, MgO 6-15%, CaO 25-35%, SiO2 20-30%, Al2O3 3-8%, and FeO 2-5%. The residual rare earth and magnesium content in the waste slag is even close to or exceeds that of some low-grade raw ores, indicating significant secondary resource recovery value.

[0003] However, the resource utilization of rare earth ferrosilicon smelting waste has long faced the following industrial challenges: 1. Difficulty in recovering valuable elements leads to "secondary resource dormancy." Rare earth elements and magnesium in waste residue mainly exist in complex mineral phases such as silicates and aluminates, exhibiting high chemical stability, making them difficult to effectively enrich using conventional physical beneficiation methods. Although some studies have attempted to extract rare earth elements using acid leaching, problems such as high acid consumption, low leaching rate, and difficulty in treating secondary wastewater exist, resulting in poor economic viability and hindering industrialization.

[0004] 2. High environmental risks associated with waste residue storage. The waste residue contains small amounts of soluble fluorides and heavy metals, and long-term open-air storage, coupled with rainwater leaching, may cause soil and water pollution. With increasingly stringent environmental policies, the harmless treatment and resource utilization of waste residue have become a rigid constraint on the survival and development of enterprises.

[0005] 3. Lack of high-value utilization pathways and low added value of existing utilization methods. Currently, some enterprises simply process waste residue and use it as cement admixtures or road construction materials. However, this method fails to recover high-value elements such as rare earth elements and magnesium from the residue, resulting in a huge waste of resources. This is considered "low-value" rather than "high-value" utilization.

[0006] 4. Lack of cross-industry collaborative utilization technology. The chemical composition of the waste residue is similar to that of raw materials in industries such as ceramics and building materials, but there is a lack of targeted compatibility technologies and product development, making it difficult to achieve large-scale cross-industry utilization.

[0007] To address the aforementioned issues, existing patent literature has proposed methods for producing rare earth magnesium ferrosilicon alloys from rare earth ferrosilicon smelting waste. These methods employ a one-step silicon thermal process to prepare the alloy, achieving partial recovery of rare earth and magnesium from the waste. However, this method primarily focuses on alloying utilization and fails to address the issue of full utilization of the waste, with room for improvement in the recovery rate of rare earth and magnesium from the slag. Other studies have explored technologies for recovering rare earth from various rare earth solid wastes, but a systematic solution for the tiered separation and cross-industry collaborative utilization of silicon thermal reduction slag—a specific type of waste—has not yet been reported.

[0008] Therefore, developing a tiered resource utilization method that can simultaneously achieve "efficient recovery of valuable elements" and "full utilization of waste residue" has become a technological direction that urgently needs to be broken through in this field. Summary of the Invention

[0009] The present invention aims to overcome the shortcomings of the prior art and solve the following technical problems: (1) the problem of efficient targeted enrichment and separation of rare earth and magnesium elements in rare earth ferrosilicon smelting waste residue; (2) the integrated problem of recovery of valuable elements in waste residue and harmless disposal of tailings; (3) the technical bottleneck of cross-industry high-value utilization of waste residue, and provides a tiered resource utilization method with rare earth recovery rate ≥90%, magnesium recovery rate ≥85%, and waste residue comprehensive utilization rate close to 100%.

[0010] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for the comprehensive utilization of rare earth ferrosilicon smelting waste slag through a tiered resource recovery process, characterized by comprising the following steps: Step 1: Waste residue pretreatment and batching The silicothermic reduction slag generated during the production of rare earth magnesium ferrosilicon alloys is collected, crushed to a particle size ≤5mm, and magnetically separated to remove metallic iron particles. Its chemical composition is analyzed. According to the target enrichment requirements, a reducing agent, flux, and modifier are added to the pretreated slag and mixed uniformly to obtain the reduction furnace charge. The reducing agent is selected from one or more of ferrosilicon powder, silicon carbide, and coke. The flux is selected from one or more of limestone and fluorite, used to adjust the slag basicity and fluidity. The modifier is selected from one or more of iron oxide scale and rolled steel scale, used to adjust the iron oxide content of the slag and promote the reduction and enrichment of rare earth and magnesium.

[0011] Step 2: Reduction smelting and targeted enrichment Add the reduction charge prepared in step 1 to a submerged arc furnace or electric arc furnace for reduction smelting; control the smelting temperature at 1550-1650℃ and the smelting time at 60-120 minutes, so that the rare earth oxides and magnesium oxide in the waste slag are selectively reduced by the reducing agent and enter the alloy phase; the reduction reaction formula is: RE₂O₃ + 3[Si] → 2RE + 3SiO₂ 2MgO + [Si] → 2Mg↑ + SiO2 During the reaction, stirring is intensified to promote the kinetics of the reduction reaction; after smelting, the power is turned off and the mixture is left to stand for 20-30 minutes to allow the alloy phase and slag phase to fully separate; rare earth-rich magnesium-iron alloy and primary tailings are obtained respectively.

[0012] Step 3: Selective phase decomposition of rare earth-rich magnesium-iron alloys The rare earth-rich magnesium-iron alloy obtained in step 2 is crushed to a particle size ≤3mm and placed in a phase decomposition reactor. A phase decomposition agent is added, and the reaction temperature is controlled at 300-600℃ for 2-4 hours to carry out selective phase decomposition treatment. The phase decomposition agent is selected from one or more of dilute hydrochloric acid, dilute sulfuric acid, and ammonium chloride solution, and the concentration is controlled at 5-15%. During the phase decomposition process, the rare earth elements in the alloy selectively dissolve into the liquid phase, while iron, magnesium, and other elements mainly remain in the solid phase. After the reaction is completed, solid-liquid separation is performed to obtain a rare earth-containing solution and iron-rich magnesium solid phase residue.

[0013] Step 4: Cascaded separation and recovery of rare earth elements and iron-magnesium The rare earth-containing solution obtained in step 3 is neutralized and precipitated by adjusting the pH value to 8-10, so that the rare earth precipitates in the form of rare earth hydroxides. After filtration, washing and drying, a rare earth enrichment (REO content ≥85%) is obtained, which can be recycled as raw material for rare earth smelting plants. The iron-magnesium-rich solid residue obtained in step 3 is washed and dried, and can be used as an additive for iron-magnesium alloys to adjust the composition of molten iron in the casting industry.

[0014] Step 5: Activation treatment of primary tailings The primary tailings obtained in step 2 are mechanically activated by grinding them with a ball mill until the specific surface area is ≥400m² / kg. 0.5-2 parts by weight of activator are added to the activated primary tailings and mixed evenly. The activator is selected from one or more of sodium sulfate, sodium hydroxide, and water glass, and is used to activate the gelling activity of the tailings.

[0015] Step 6: Cross-industry collaborative utilization in the preparation of building materials The activated tailings from step 5 are mixed with raw materials such as coal gangue, fly ash, and clay in a specific ratio and mixed evenly. The ratio, by weight, is: 30-60 parts activated tailings, 20-40 parts coal gangue, 10-30 parts fly ash, and 1-3 parts foaming agent. The mixture is placed in a foaming ceramic kiln and sintered and foamed at 1100-1200℃ for 1-2 hours. After cooling, it is cut to obtain foamed ceramic panels. Alternatively, the activated tailings can be mixed with cement, sand, and gravel in a specific ratio to prepare concrete admixtures or roadbed materials.

[0016] As a preferred technical solution: The preferred chemical composition of the waste residue in step 1 is: REO 8-15%, MgO 8-15%, CaO 25-35%, SiO2 20-30%, Al2O3 3-8%, FeO 2-5%.

[0017] In step 1, the amount of reducing agent added is 10-25% of the weight of the waste residue, the amount of flux added is 5-15%, and the amount of modifier added is 3-8%.

[0018] The preferred reduction melting temperature in step 2 is 1580-1620℃, and the preferred melting time is 80-100 minutes.

[0019] The phase decomposition agent mentioned in step 3 is preferably an 8-12% dilute hydrochloric acid solution, the reaction temperature is preferably 400-500℃, and the reaction time is preferably 2.5-3.5 hours.

[0020] The amount of activator added in step 5 is preferably 1-1.5 parts; the specific surface area of ​​the activated tailings is preferably 450-500 m² / kg.

[0021] The foaming agent mentioned in step 6 is selected from one or more of silicon carbide, calcium carbonate, and sodium carbonate, with a particle size ≤0.074mm.

[0022] Secondly, the present invention provides a rare earth enrichment obtained according to the above preparation method, characterized in that the rare earth enrichment has an REO content of ≥85% and a total rare earth recovery rate of ≥90%.

[0023] Thirdly, the present invention provides an iron-magnesium alloy additive obtained according to the above preparation method, characterized in that the iron content in the iron-magnesium alloy additive is 60-75%, the magnesium content is 8-15%, the balance is silicon and unavoidable impurities, and the magnesium recovery rate is ≥85%.

[0024] Fourthly, the present invention provides a foamed ceramic material obtained according to the above preparation method, characterized in that the bulk density of the foamed ceramic material is 0.4-0.8 g / cm³, the compressive strength is ≥2.5 MPa, and the thermal conductivity is ≤0.15 W / (m·K).

[0025] The principle of the technical solution of this invention is as follows: 1. Chemical principles of targeted enrichment in reduction smelting Rare earth elements and magnesium in rare earth ferrosilicon smelting waste mainly exist as complex mineral phases such as silicates (e.g., RE2Si2O7, MgSiO3) and aluminates (e.g., REAlO3, MgAl2O4), exhibiting high chemical stability and making them difficult to separate using simple physical methods. This invention utilizes the strong affinity of silicon for oxygen by adding reducing agents such as ferrosilicon under a high-temperature reducing atmosphere to reduce rare earth oxides and magnesium oxide from silicate minerals. RE₂O₃ (in silicates) + 3[Si] → 2[RE] + 3SiO₂ 2MgO (in silicates) + [Si] → 2Mg↑ + SiO2 The rare earth elements and magnesium generated during reduction enter the alloy phase, achieving targeted enrichment from a "dispersed state" to an "enriched state." Simultaneously, the added iron oxide scale and other modifiers increase the iron oxide content in the slag, improve slag fluidity, and promote the kinetics of the reduction reaction.

[0026] 2. Separation mechanism of selective phase decomposition In rare-earth-rich magnesium-iron alloys, the chemical differences between rare earth elements and iron and magnesium are the basis for achieving selective separation. This invention uses dilute acid as a phase decomposition agent, taking advantage of the fact that rare earth elements are readily soluble in dilute acid, while iron and magnesium have lower dissolution rates under appropriate conditions, to achieve selective phase decomposition. By controlling the acid concentration and reaction temperature, rare earth elements can selectively enter the liquid phase, while iron and magnesium mainly remain in the solid phase, thereby achieving efficient separation of rare earth elements from iron and magnesium.

[0027] 3. The compatibility principle of tailings activation and synergistic utilization of building materials The main components of primary tailings are calcium silicate and calcium aluminosilicate, which possess potential cementing activity, but this activity is low when unactivated. This invention increases the specific surface area through mechanical grinding, while simultaneously adding chemical activators such as sodium sulfate to disrupt the glassy structure and stimulate hydration activity. The activated tailings are then combined with siliceous and aluminous raw materials such as coal gangue and fly ash. At high temperatures, a foaming agent decomposes to generate gas, forming a closed-cell structure and producing lightweight, high-strength foamed ceramic materials. This process achieves cross-industry collaborative utilization of waste residue, transforming industrial solid waste into high-value-added green building materials.

[0028] Compared with the prior art, the present invention has the following beneficial effects: 1. High rare earth and magnesium recovery rates enable efficient utilization of secondary resources: Through targeted enrichment by reduction smelting, the total recovery rate of rare earth is ≥90% and the recovery rate of magnesium is ≥85%, which is far higher than the 70-80% of existing technologies, transforming the "dormant resources" in waste residue into reusable secondary raw materials.

[0029] 2. The cascade separation process is scientifically designed and produces high added value: After selective phase decomposition, rare earth-rich magnesium-iron alloys are respectively obtained as rare earth enrichment with REO≥85% and iron-magnesium alloy additives with magnesium content of 8-15%. Both can be directly returned to the rare earth smelting and casting production process, realizing a closed-loop cycle of "waste residue-raw material".

[0030] 3. Full utilization of waste residue to completely eliminate environmental risks: After activation, the tailings are used to prepare building materials such as foamed ceramics. The comprehensive utilization rate of waste residue is close to 100%, eliminating the environmental pollution risks caused by waste residue storage from the source.

[0031] 4. Cross-industry collaborative utilization to expand waste disposal pathways: Metallurgical waste slag is used in conjunction with other industrial solid wastes such as coal gangue and fly ash to prepare building materials, realizing a green circular model of "treating waste with waste and cross-industry collaboration".

[0032] 5. Highly compatible with existing equipment and low industrial promotion cost: The submerged arc furnace / electric arc furnace, ball mill, and reaction vessel used in this invention are all mature industrial equipment. They can be technically upgraded based on existing rare earth alloy production enterprises, with small investment, quick results, and conditions for large-scale promotion and application. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the process flow for the cascaded resource utilization method of rare earth ferrosilicon smelting waste slag according to the present invention. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below with reference to specific embodiments. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention. Example 1

[0035] This embodiment provides a method for the cascaded resource utilization of rare earth ferrosilicon smelting waste.

[0036] Step 1: Waste residue pretreatment and batching The slag from the silicothermic reduction process of a rare earth magnesium ferrosilicon alloy production enterprise was crushed to ≤5mm and magnetically separated to remove metallic iron particles. Its chemical composition was analyzed to be: REO 12.5%, MgO 9.8%, CaO 28.6%, SiO2 23.4%, Al2O3 4.8%, FeO 3.1%. The following parts by weight were used to prepare the mixture: 100 parts slag, 18 parts 75# ferrosilicon powder (reducing agent), 8 parts limestone (flux), and 5 parts iron oxide scale (modifier). The mixture was thoroughly mixed.

[0037] Step 2: Reduction smelting and targeted enrichment The ingredients were added to a 1.5t electric arc furnace and smelted under power. The smelting temperature was controlled at 1600℃, and the smelting time was 90 minutes. Stirring was intensified during the smelting process. After the reaction was completed, the power was turned off and the furnace was allowed to stand for 25 minutes to allow the alloy phase and slag phase to fully separate. Rare earth-rich magnesium-iron alloy (approximately 35 parts) and primary tailings (approximately 78 parts) were obtained.

[0038] Step 3: Selective phase decomposition of rare earth-rich magnesium-iron alloys Rare earth-rich magnesium-iron alloy was crushed to ≤3mm and placed in a phase decomposition reactor. A 10% dilute hydrochloric acid solution was added, with a solid-liquid ratio of 1:5. The reaction temperature was controlled at 450℃ for 3 hours to perform selective phase decomposition. After the reaction, solid and liquid were separated to obtain a rare earth-containing solution and a magnesium-rich iron-phase residue.

[0039] Step 4: Cascaded separation and recovery of rare earth elements and iron-magnesium The pH of the rare earth-containing solution was adjusted to 9, causing the rare earth elements to precipitate as hydroxides. The precipitate was filtered, washed, and dried to obtain a rare earth concentrate with an REO content of 87.3%. The iron-magnesium-rich solid residue was washed and dried to obtain an iron-magnesium alloy additive with an iron content of 68.5% and a magnesium content of 11.2%.

[0040] Step 5: Activation treatment of primary tailings The tailings were ball-milled to a specific surface area of ​​450 m² / kg. 1.2 parts by weight of activator (sodium sulfate) were added and mixed thoroughly.

[0041] Step 6: Cross-industry collaborative utilization in the preparation of foamed ceramics The ingredients are prepared according to the following weight proportions: 45 parts activated tailings, 30 parts coal gangue, 20 parts fly ash, and 2 parts silicon carbide (foaming agent). After mixing evenly, the mixture is placed in a foaming ceramic kiln and sintered at 1150℃ for 1.5 hours. After cooling, the foamed ceramic slabs are cut to obtain the final product.

[0042] According to the test results, the total rare earth recovery rate in this embodiment was 91.2%, and the magnesium recovery rate was 86.5%; the bulk density of the foamed ceramic was 0.62 g / cm³, the compressive strength was 3.2 MPa, and the thermal conductivity was 0.12 W / (m·K). Example 2

[0043] This embodiment provides another method for the cascaded resource utilization of rare earth ferrosilicon smelting waste.

[0044] Step 1: Waste residue pretreatment and batching Take 100 parts of waste residue (composition: REO 10.2%, MgO 11.5%, CaO 30.1%, SiO2 22.8%, Al2O3 5.2%, FeO 2.6%), 22 parts of silicon carbide (reducing agent), 6 parts of fluorite (flux), and 6 parts of rolled steel scale (modifier), and mix them evenly.

[0045] Step 2: Reduction smelting and targeted enrichment Melting temperature 1580℃, melting time 100 minutes, and standing time 20 minutes.

[0046] Step 3: Selective phase decomposition of rare earth-rich magnesium-iron alloys A 12% dilute sulfuric acid solution was used, the reaction temperature was 400℃, and the reaction time was 3.5 hours.

[0047] Step 4: Cascaded separation and recovery of rare earth elements and iron-magnesium The rare earth enrichment (REO) content is 86.5%; the iron content in the iron-magnesium alloy additive is 65.8%, and the magnesium content is 12.5%.

[0048] Step 5: Activation treatment of primary tailings Ball mill to a specific surface area of ​​480 m² / kg, and add 1.0 part of activator (water glass).

[0049] Step 6: Cross-industry collaborative utilization in the preparation of foamed ceramics 50 parts activated tailings, 25 parts coal gangue, 22 parts fly ash, and 2.5 parts calcium carbonate (foaming agent) were sintered and foamed at 1180℃.

[0050] According to the test results, the total rare earth recovery rate in this embodiment was 90.8%, and the magnesium recovery rate was 87.2%; the bulk density of the foamed ceramic was 0.58 g / cm³, the compressive strength was 2.9 MPa, and the thermal conductivity was 0.11 W / (m·K). Comparative Example 1

[0051] Rare earth elements in waste residue were recovered using a traditional acid leaching method. The same waste residue was leached for 2 hours at a hydrochloric acid concentration of 15%, a liquid-to-solid ratio of 4:1, and a temperature of 80℃. After filtration, the residue was neutralized and precipitated.

[0052] Tests showed that the rare earth leaching rate was only 72.5%, and magnesium was basically not recovered. A large amount of acidic waste liquid was generated that needed to be treated, making it uneconomical. Comparative Example 2

[0053] Existing patented technology allows waste residue to be directly used in the production of rare earth magnesium ferrosilicon alloy. The waste residue is mixed with raw materials such as ferrosilicon and magnesium ingots, and then reduced and smelted in an electric arc furnace to obtain the rare earth magnesium ferrosilicon alloy.

[0054] Tests showed that the total rare earth recovery rate was 82.3%, the magnesium recovery rate was 76.8%, and about 40% of secondary waste residue was still generated, failing to achieve full utilization. Comparative Example 3

[0055] Foamed ceramics are prepared by directly mixing unactivated primary tailings with coal gangue.

[0056] Testing revealed that the foamed ceramic had a bulk density of 0.85 g / cm³ and a compressive strength of 1.8 MPa, indicating uneven foaming and poor product quality.

[0057] The performance comparison is shown in the table below.

[0058] project Rare earth recovery rate (%) Magnesium recovery rate (%) Comprehensive utilization rate of waste residue (%) Compressive strength (MPa) of foamed ceramics Example 1 91.2 86.5 98.5 3.2 Example 2 90.8 87.2 98.2 2.9 Comparative Example 1 72.5 - - - Comparative Example 2 82.3 76.8 60.0 - Comparative Example 3 - - 85.0 1.8 As can be seen from the above comparison, the method of the present invention has significant advantages in terms of rare earth and magnesium recovery rate, comprehensive utilization rate of waste residue, and performance of recycled products, realizing the high-value utilization of waste residue through tiered resource utilization.

[0059] This invention's method can be directly integrated into existing rare earth magnesium-silicon-iron alloy production processes: hot waste slag generated during alloy production can be directly fed into a reduction smelting furnace (step 2) for processing, utilizing waste heat for energy saving; the separated rare earth enrichment is returned to the rare earth smelting process, the iron-magnesium alloy additive is returned to the casting process, and the foamed ceramics are sold as building materials. This "closed-loop + cross-industry collaboration" model achieves 100% resource utilization of waste slag and is highly compatible with existing equipment.

[0060] The tiered resource utilization method provided by this invention has the following industrialization advantages: (1) Significant resource recovery benefits—for every 10,000 tons of waste residue processed, approximately 1,000 tons of rare earth (REO) and 800 tons of magnesium can be recovered, resulting in huge economic value; (2) Outstanding environmental benefits—completely eliminating pollution from waste residue stockpiling and assisting enterprises in green transformation; (3) Diversified products—three major products, namely rare earth enrichment, iron-magnesium alloy additives, and foamed ceramics, cover the rare earth, casting, and building materials industries; (4) High policy compatibility—meets the requirements of the national "zero-waste city" construction and "dual-carbon" strategy. Once this technology is promoted and applied, it will open up a new industrialization path for the resource utilization of rare earth smelting waste residue in my country.

[0061] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., 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 method for the tiered resource utilization of rare earth ferrosilicon smelting waste slag, characterized in that, Includes the following steps: Step 1: Waste slag pretreatment and batching - After crushing the rare earth ferrosilicon smelting waste slag, add reducing agent, flux and modifier, mix evenly to obtain reducing furnace charge; Step 2: Reduction smelting and targeted enrichment - The reduction furnace charge obtained in Step 1 is added to a submerged arc furnace or electric arc furnace for reduction smelting, so that the rare earth oxides and magnesium oxide in the waste slag are reduced into the alloy phase. After smelting, the mixture is allowed to stand and separate into layers to obtain rare earth-rich magnesium-iron alloy and primary tailings. Step 3: Selective phase decomposition - After crushing the rare earth-rich magnesium-iron alloy obtained in Step 2, a phase decomposition agent is added to carry out selective phase decomposition treatment, so that rare earth selectively enters the liquid phase, while iron and magnesium elements mainly remain in the solid phase. After the reaction is completed, solid and liquid are separated to obtain a rare earth-containing solution and iron-rich magnesium solid phase residue. Step 4: Cascade separation and recovery - The rare earth-containing solution obtained in Step 3 is neutralized and precipitated to obtain rare earth enrichment; the iron-magnesium-rich solid residue obtained in Step 3 is washed and dried to obtain iron-magnesium alloy additive. Step 5: Tailings activation treatment - The tailings obtained in Step 2 are mechanically activated by adding an activator to obtain activated tailings; Step 6: Cross-industry collaborative utilization - The activated tailings obtained in Step 5 are mixed with coal gangue, fly ash and foaming agent in a certain proportion, and foamed ceramic materials are prepared by sintering and foaming.

2. The comprehensive utilization method according to claim 1, characterized in that, The reducing agent in step 1 is selected from one or more of ferrosilicon powder, silicon carbide, and coke, and the amount added is 10-25% of the weight of the waste residue; the flux is selected from one or more of limestone and fluorite, and the amount added is 5-15%; the modifier is selected from one or more of iron oxide scale and rolled steel scale, and the amount added is 3-8%.

3. The comprehensive utilization method according to claim 1, characterized in that, The reduction melting temperature in step 2 is 1550-1650℃, and the melting time is 60-120 minutes.

4. The comprehensive utilization method according to claim 1, characterized in that, The phase decomposition agent in step 3 is selected from one or more of dilute hydrochloric acid, dilute sulfuric acid, and ammonium chloride solution, with a concentration of 5-15%; the reaction temperature for selective phase decomposition is 300-600℃, and the reaction time is 2-4 hours.

5. The comprehensive utilization method according to claim 1, characterized in that, The pH value of the neutralization precipitation in step 4 is controlled at 8-10; the REO content in the rare earth enrichment is ≥85%.

6. The comprehensive utilization method according to claim 1, characterized in that, The iron-magnesium alloy additive mentioned in step 4 contains 60-75% iron and 8-15% magnesium.

7. The comprehensive utilization method according to claim 1, characterized in that, The mechanical activation treatment described in step 5 involves ball milling the primary tailings to a specific surface area ≥ 400 m² / kg; the activator is selected from one or more of sodium sulfate, sodium hydroxide, and water glass, and the amount added is 0.5-2% of the weight of the activated tailings.

8. The comprehensive utilization method according to claim 1, characterized in that, The mixing ratio mentioned in step 6 is as follows by weight: 30-60 parts activated tailings, 20-40 parts coal gangue, 10-30 parts fly ash, and 1-3 parts foaming agent; the foaming agent is selected from one or more of silicon carbide, calcium carbonate, and sodium carbonate.

9. The comprehensive utilization method according to any one of claims 1-8, characterized in that, The chemical composition of the rare earth ferrosilicon smelting waste slag includes: REO 8-15%, MgO 8-15%, CaO 25-35%, SiO2 20-30%, Al2O3 3-8%, FeO 2-5%.

10. The comprehensive utilization method according to any one of claims 1-8, characterized in that, The method achieves a total rare earth recovery rate of ≥90%, a magnesium recovery rate of ≥85%, and a waste residue comprehensive utilization rate of ≥95%.

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