A ferrosilicon alloy prepared based on silicon powder and semi-coke regeneration and application thereof in magnesium smelting

Abstract

The application discloses a silicon-iron alloy prepared based on silicon powder and low-quality coke regeneration and application of the silicon-iron alloy in magnesium smelting, and belongs to the technical field of metal smelting. The application discloses a silicon-iron alloy prepared based on silicon powder and low-quality coke regeneration and application of the silicon-iron alloy in magnesium smelting. A four-in-one reaction system of a silicon source, a carbon source, a pore-forming agent and a flux is constructed through the synergic compatibility design of boron mud and phosphogypsum. The pore structure is accurately controlled by using SO2 gas generated by the thermal decomposition of the phosphogypsum, and the reduction temperature is significantly reduced by the low-temperature eutectic phase formed by the boron mud. The low-temperature and high-efficiency forming of the alloy particles is realized by using a specially modified PVA binder. The method significantly reduces the energy consumption and pollution of the traditional process, realizes the efficient resource utilization of industrial solid wastes, and the prepared silicon-iron alloy has unique bimodal pore structure and excellent interface bonding performance, so that the reaction efficiency can be greatly improved and the energy consumption can be reduced in the magnesium smelting application.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of advanced non-ferrous metal technology, more particularly, to a ferrosilicon alloy prepared based on silicon powder and semi-coke regeneration and its application in magnesium smelting. BACKGROUND

[0002] As an important metallurgical raw material, ferrosilicon alloy has a wide application in steel and magnesium smelting industry. Traditional ferrosilicon alloy is mainly produced by electric furnace method, using silica, coke and steel scrap as raw materials, and is prepared by reduction at a high temperature above 1600℃. This method has problems such as high energy consumption (about 8000-9000 kWh of electricity is consumed per ton of product), high raw material cost, and serious environmental pollution. In recent years, with the increasing requirements of resource recycling and energy saving and emission reduction, the preparation of ferrosilicon alloy from industrial solid waste has become an important research direction.

[0003] The current technology mainly has the following defects: (1) poor adaptability of raw materials, the existing process is difficult to handle multiple industrial waste at the same time; (2) the reduction temperature still needs to be above 1400℃, and the energy consumption is limited; (3) the pore structure of the product is uncontrollable, which affects the subsequent application effect. In particular, the collaborative utilization of phosphogypsum and boron mud, two typical industrial wastes, has not been broken through, and the impurity elements (such as P, F) in phosphogypsum and the radioactive substances (U, Th) in boron mud will seriously affect the quality of the alloy.

[0004] The existing improvement directions include: (1) developing new type of composite flux to reduce the reaction temperature; (2) optimizing the raw material pretreatment process to control the impurity content; (3) adjusting the pore structure of the product to improve the performance. However, in the existing technology, the problems such as poor compatibility of waste materials, complex process and unstable product performance have not been solved, and it is urgent to develop a new method for preparing ferrosilicon alloy which can collaboratively handle multiple industrial solid wastes, is low-temperature and high-efficiency, and has controllable product performance. SUMMARY

[0005] The purpose of the present application is to provide a ferrosilicon alloy prepared based on silicon powder and semi-coke regeneration and its application in magnesium smelting, which significantly reduces the energy consumption and pollution of the traditional process, realizes the efficient resource utilization of industrial solid waste, and the prepared ferrosilicon alloy has a unique bimodal pore structure and excellent interface bonding performance, which can greatly improve the reaction efficiency and reduce the energy consumption in magnesium smelting application.

[0006] A ferrosilicon alloy prepared based on silicon powder and semi-coke regeneration, comprising the following steps:

[0007] S1, raw material preparation:

[0008] S1.1, silicon powder: the silicon powder is obtained by wet ball milling and acid washing purification, SiO2≥92wt%, Al2O3≤3wt%, Fe2O3≤1wt%, D50=2-10um;

[0009] S1.2, the low temperature dry distillation product of long flame coal, fixed carbon ≥ 82wt%, ash ≤ 10wt%, volatile matter ≤ 8wt%;

[0010] S1.3, phosphogypsum: by-product of wet-process phosphoric acid, pretreated by water washing and lime neutralization, CaSO4·2H2O ≥ 85wt%, P2O5≤ 1.2wt%, F - ≤ 0.5wt%;

[0011] S1.4, boron mud: waste residue of boric acid production, treated by hydrochloric acid washing, Mg2B2O5≥ 60wt%, B2O3≥ 15wt%, U ≤ 10ppm;

[0012] S1.5, iron source: at least one selected from steel chips, cast iron chips, iron scale, and iron powder, with Fe content ≥ 90wt%;

[0013] S2, raw material mixing: the above raw materials, silicon powder: long flame coal: phosphogypsum: boron mud: iron source, are mixed in a mass ratio of 100: 50-80: 5-15: 3-8: 20-40;

[0014] S3, low temperature reduction: under argon atmosphere, the temperature is raised to 1100-1250℃ at a rate of 10-15℃ / min, and the temperature is maintained for 1-3 hours, the SO2 gas generated by the thermal decomposition of phosphogypsum is used to increase the porosity of the alloy to 20-40%, the total pressure of the reaction system is maintained at 0.1-0.3MPa by adjusting the argon flow, the volume concentration of SO2 is 30-50% (monitored in real time by an online infrared gas analyzer, with a data sampling frequency ≥ 1Hz), under the synergistic action of the SO2 reduction atmosphere and the CaO-B2O3-MgO liquid phase formed by the boron mud, low temperature carbothermic reduction of silicon-iron oxides is realized to prepare a porous silicon-iron alloy;

[0015] S4, post-treatment: 0.8-1.2wt% polyvinyl alcohol binder is added to the reduction product, the polyvinyl alcohol has a degree of polymerization of 500-2000 and an alcoholysis degree of 85-89%, the polyvinyl alcohol binder is added in the form of a 5-10wt% aqueous solution, the spraying pressure is 0.2-0.5MPa, the atomizing angle is 60-90°, the solution temperature is 40-60℃, the atomized particle size is 50-100um, the distance between the nozzle and the material is maintained at 20-30cm, after drying at 80-120℃ for 2-4 hours, the modified porous silicon-iron alloy is obtained by pressing at 160-200℃ and 50-150MPa, and the compressive strength of the alloy after pressing is ≥ 30MPa.

[0016] Preferably, the chemical composition of the porous silicon-iron alloy is Si: 60-75 wt%, Fe: 15-25 wt%, Ca: 1-5 wt%, B: 0.1-1.5 wt%, with the remainder being unavoidable impurities, and the Fe / Si molar ratio is 0.3-0.5, and the bimodal pore size distribution is 0.1-10 um, wherein the 0.1-1 um pores account for 40-60%, and the 5-10 um pores account for 20-40%, the pores have a three-dimensional interconnected structure, the tortuosity is ≤1.8, and the specific surface area is 6-10 m 2 / g.

[0017] Preferably, the preparation method of the silicon powder is as follows: the silicon powder is ball milled with deionized water at a mass ratio of 1:2-3 for 12-24 hours, then treated with 15-20 wt% hydrochloric acid at 80-90°C for 4-6 hours, followed by treatment with 5-8 wt% hydrofluoric acid, washed with deionized water until neutral, ultrasonic assisted (frequency 40 kHz, power 300 W) dispersion for 30-60 minutes, and spray drying (inlet temperature 190-210°C, outlet temperature 85-95°C) to obtain the silicon powder.

[0018] Preferably, the pretreatment method of the semi-coke is as follows: the semi-coke is crushed and sieved to a particle size of 0.5-3 mm, calcined at 300-400°C for 2-3 hours, soaked in a 10-15 wt% NaOH solution to remove impurities, neutralized with a 5-10 wt% hydrochloric acid solution to a pH of 6.5-7.5, and activated in a rotary kiln at a rotation speed of 2-5 rpm at 550-750°C for 1-2 hours, and cooled to room temperature under nitrogen protection to obtain active semi-coke with a specific surface area of ≥150 m 2 / g.

[0019] Preferably, the pretreatment method of the phosphogypsum is as follows: the wet-process phosphoric acid by-product phosphogypsum is mixed with deionized water at a mass ratio of 1:3.5-4.5, centrifuged after 30 minutes of circular washing at a stirring speed of 150-250 rpm, treated with a 5-8 wt% sulfuric acid solution at 55-65°C for 1.5-2.5 hours, added with 0.1-0.3 wt% sodium dodecyl benzene sulfonate, adjusted to a pH of 6.5-7.5 with lime milk, controlled to a conductivity of ≤500 uS / cm, added with an aluminum sulfate solution to react at 75-85°C for 50-70 minutes to remove fluorine, the addition amount of the aluminum sulfate is controlled to an Al / F molar ratio of 1.2:1, ultraviolet light catalytic oxidation degradation of organic matter is performed for 1.5-2.5 hours at a wavelength of 254 nm and a power of 300 W, dewatered with a belt filter press at a pressure of 0.8-1.2 MPa, and dried in a fluidized bed at 170-190°C to a moisture content of ≤8 wt%, to finally obtain purified phosphogypsum with CaSO4·2H2O ≥85 wt%, P2O5 ≤1.2 wt%, and F - ≤0.5 wt%.

[0020] Preferably, the pretreatment method of the boron mud is as follows: the boron acid production waste residue is treated with 15-20wt% hydrochloric acid at 70-80 DEG C for 2.5-3.5 hours, 0.2wt% sodium hexametaphosphate is added, the pH is adjusted to 2.5-3.0 for selective dissolution, the Mg 2+ Concentration ≤ 50 g / L, 0.5-1wt% tributyl phosphate is added at 45-55 DEG C for three-stage extraction to remove uranium, 2-3wt% sodium carbonate solution is used for back extraction to recover rare earth, calcination is carried out in a muffle furnace at 600-700 DEG C for 1.5-2.5 hours, CO2 is introduced at a flow rate of 1-2L / min to reconstruct the crystal form, and airflow with a pressure of 0.8-1.0MPa is used for crushing to obtain a powder with D50=5-15um, and finally Mg2B2O5 ≥ 60wt%, B2O3 ≥ 15wt%, U ≤ 10ppm boron mud is obtained.

[0021] Preferably, the pretreatment method of the iron source is as follows: the iron source is soaked and cleaned with 5-10wt% sodium carbonate solution at 60-80 DEG C for 15-30 minutes to remove surface oil stains, then washed with clean water, then pickled with 10-15wt% hydrochloric acid solution at room temperature for 5-15 minutes to remove the surface oxide layer, then washed with deionized water until neutral, finally dried at 100-120 DEG C for 2-4 hours, and crushed and sieved to a powder with a particle size ≤ 0.5mm to obtain clean iron source raw material.

[0022] Preferably, the SO2 gas generated in the reduction process of step S3 is recycled and absorbed by 5-10wt% Na2CO3 solution at 40-60 DEG C, the byproduct is Na2SO3, and the SO2 absorption rate is ≥ 95%.

[0023] An application of silicon-iron alloy prepared based on silicon powder and semi-coke regeneration in magnesium smelting, the modified porous silicon-iron alloy is mixed with magnesium oxide at a mass ratio of 1:1.5-2.5, and metal magnesium is prepared by reduction at a vacuum degree of 10-100Pa and a temperature of 1200-1300 DEG C, the reduction time is shortened by more than 30%, and the system air leakage rate is ≤ 0.5Pa / min.

[0024] Preferably, the reduction slag generated in the magnesium smelting process has a CaO / B2O3 mass ratio of 1.5-3.5, an alkalinity CaO / SiO2 of 0.8-1.2, contains a Ca3B2O6 phase, has a slag melting point of 900-1000 DEG C, and has a viscosity ≤ 5Pa·s at 1200 DEG C.

[0025] Compared with the prior art, the application has the following advantages:

[0026] (1) Low-temperature and high-efficiency reduction performance

[0027] By the synergistic combination of boron mud and phosphogypsum, a five-in-one reaction system of "silicon source-carbon source-pore former-fluxing agent-iron source" is constructed, and a low-melting-point CaO-B2O3-MgO liquid phase is formed at the micro level. This liquid phase can encapsulate silicon powder, carbon source, and iron source at 1100-1250℃, significantly improving the mass transfer conditions at the solid-solid reaction interface. First-principle calculations show that the B2O3 component in the liquid phase reduces the activation energy barrier of the SiO2 reduction reaction, making the reduction temperature 300-400℃ lower than that of traditional processes, and the energy consumption reduced by more than 40%. At the same time, the controlled release of SO2 gas creates a dynamic reduction atmosphere, and by adjusting the local oxygen partial pressure, the silicon reduction efficiency is improved to 92-95%.

[0028] (2) Optimized hierarchical pore structure

[0029] At the mesoscale, SO2 gas generated by the decomposition of phosphogypsum reacts with carbon to form a bimodal pore distribution: micron-sized macropores (5-10um) as the main diffusion channel for magnesium vapor, while sub-micron-sized small pores (0.1-1um) provide a large specific surface area. Molecular dynamics simulations show that this special structure controls the tortuosity of the magnesium vapor diffusion path to below 1.8, with a 2-order-of-magnitude increase in diffusion coefficient. Experimental measurements show that during the magnesium smelting process, the reduction rate of metallic magnesium is increased by 50-80%, and the reaction time is shortened by more than 30%.

[0030] (3) Excellent mechanical properties

[0031] The PVA binder forms a nanoscale gradient structure during pressing: the near-interface region exhibits a highly oriented crystalline state (65% crystallinity), while the bulk region has a flexible network structure. High-resolution transmission electron microscopy observations show that this special structure forms a strong interfacial bond between the binder phase and the alloy matrix, reducing the interfacial energy. At the same time, the segregation of B elements at the grain boundaries forms Fe2B nanophases, producing a significant pinning effect. These micro characteristics work together to make the compressive strength of the material exceed 35MPa, about 40% higher than that of traditional ferrosilicon alloys.

[0032] (4) Environmentally friendly characteristics

[0033] At the atomic scale, by selective extraction with tributyl phosphate and calcination in a CO2 atmosphere, radioactive elements such as uranium are stably fixed in the [BO3] 3- network structure. X-ray absorption fine structure spectroscopy confirms that uranium forms a stable complex with the boron-oxygen triangle in the form of UO2 2+ , with an leaching concentration of less than 0.01ppm. At the same time, the fluorine in the phosphogypsum reacts with aluminum to form AlF6 3- complexes into the slag phase, making the product fluorine content less than 0.5wt%. These micro mechanisms ensure the environmental safety of the entire process.

[0034] (5) Byproduct high-value utilization

[0035] The Ca3B2O6 crystal phase formed in the reduction slag (verified by XRD) has a special layered structure, [BO3] 3- planes alternately arrange with [CaO6] octahedrons. This structure enables it to precisely control the initial setting time in the range of 120-480 minutes by regulating the release rate of Ca 2+ when used as a cement retarder. The glassy network structure of the slag phase also endows it with excellent grinding performance, with a specific surface area of 400-500 m 2 2 / g, significantly improving its application value in the building materials field.

[0036] These beneficial effects are derived from the precise regulation of the invention on multiple scales: optimizing the interface electronic structure at the atomic scale, constructing functional phase distribution at the nanoscale, and designing the pore network at the micrometer scale. The synergistic effect of the effects at various scales ultimately achieves significant improvement in performance, providing a new paradigm for the high-value utilization of industrial solid waste. DETAILED DESCRIPTION

[0037] S1, Raw material preparation:

[0038] (1) Silicon micro powder: Ball mill the silicon micro powder with deionized water at a mass ratio of 1:2-3 for 12-24 hours, then treat it with 15-20wt% hydrochloric acid at 80-90°C for 4-6 hours, followed by treatment with 5-8wt% hydrofluoric acid, wash with deionized water until neutral, ultrasonic assisted dispersion (frequency 40kHz, power 300W) for 30-60 minutes, spray drying (inlet temperature 190-210°C, outlet temperature 85-95°C) to obtain silicon micro powder with SiO2≥92wt%, Al2O3≤3wt%, Fe2O3≤1wt%, D50=2-10um;

[0039] (2) Blue coal: Crush and sieve the blue coal to a particle size of 0.5-3mm, calcine it at 300-400°C for 2-3 hours, soak it in a 10-15wt% NaOH solution to remove impurities, neutralize the residual alkali solution with a 5-10wt% hydrochloric acid solution to pH=6.5-7.5, activate it in a rotary kiln at a rotation speed of 2-5rpm at 550-750°C for 1-2 hours, cool it to room temperature under nitrogen protection, and obtain active blue coal with a specific surface area of 150m 2 2 / g, fixed carbon≥82wt%, ash content≤10wt%, volatile matter≤8wt%;

[0040] (3) Phosphogypsum: The by-product phosphogypsum of wet-process phosphoric acid is mixed with deionized water at a mass ratio of 1:3.5-4.5, and after 30 minutes of circulating washing at a stirring speed of 150-250 rpm, centrifugal separation is performed, a 5-8 wt% sulfuric acid solution is used for treatment at 55-65 °C for 1.5-2.5 hours, 0.1-0.3 wt% sodium dodecyl benzene sulfonate is added, lime milk is added to adjust the pH to 6.5-7.5, the conductivity is controlled to be ≤500 uS / cm, aluminum sulfate solution is added to remove fluorine at 75-85 °C for 50-70 minutes, the addition amount of aluminum sulfate is controlled to be Al / F molar ratio 1.2:1, the organic matter is degraded by ultraviolet light catalytic oxidation at a wavelength of 254 nm and a power of 300 W for 1.5-2.5 hours, dehydration is performed by a belt filter with a pressure of 0.8-1.2 MPa, and fluidized bed drying is performed at 170-190 °C until the moisture content is ≤8 wt%, finally, purified phosphogypsum with CaSO4·2H2O≥85 wt%, P2O5≤1.2 wt%, F - ≤0.5 wt% is obtained;

[0041] (4) Boron mud: The waste slag of boric acid production is treated with 15-20 wt% hydrochloric acid at 70-80 °C for 2.5-3.5 hours, 0.2 wt% sodium hexametaphosphate is added, the pH is adjusted to 2.5-3.0 for selective dissolution, the Mg 2+ concentration is controlled to be ≤50 g / L, 0.5-1 wt% tributyl phosphate is added for three-stage extraction to remove uranium at 45-55 °C, 2-3 wt% sodium carbonate solution is used for back extraction to recover rare earth, calcination is performed in a muffle furnace at 600-700 °C for 1.5-2.5 hours, CO2 is introduced at a flow rate of 1-2 L / min for crystal structure reconstruction, and airflow crushing is performed at a pressure of 0.8-1.0 MPa to obtain a powder with D50=5-15 um, finally, boron mud with Mg2B2O5≥60 wt%, B2O3≥15 wt%, U≤10 ppm is obtained;

[0042] (5) Iron source: The iron source is soaked and cleaned with 5-10 wt% sodium carbonate solution at 60-80 °C for 15-30 minutes to remove surface oil stains, then washed with clean water, then pickled with 10-15 wt% hydrochloric acid solution at room temperature for 5-15 minutes to remove the surface oxide layer, then washed with deionized water until neutral, finally dried at 100-120 °C for 2-4 hours, and crushed and sieved to a powder with a particle size of ≤0.5 mm, to obtain clean iron source raw material;

[0043] S2, raw material mixing: The above-mentioned raw materials, silicon powder: semi-coke: phosphogypsum: boron mud: iron source, are mixed at a mass ratio of 100:50-80:5-15:3-8:20-40;

[0044] S3, low-temperature reduction: under an argon atmosphere, the temperature is raised to 1100-1250°C at a rate of 10-15°C / min, and the alloy porosity is increased to 20-40% by SO2 gas generated by thermal decomposition of phosphogypsum, and the total pressure of the reaction system is maintained at 0.1-0.3 MPa by adjusting the argon flow rate, wherein the volume concentration of SO2 is 30-50% (monitored in real time by an online infrared gas analyzer, with a data sampling frequency of ≥1 Hz), and under the synergistic action of the SO2 reduction atmosphere and the CaO-B2O3-MgO liquid phase formed by the boron mud, low-temperature carbothermic reduction of silicon-iron oxides is realized to prepare a porous silicon-iron alloy;

[0045] S4, post-treatment: 0.8-1.2wt% polyvinyl alcohol binder is added to the reduction product, the polyvinyl alcohol has a degree of polymerization of 500-2000 and an alcoholysis degree of 85-89%, the polyvinyl alcohol binder is added in the form of a 5-10wt% aqueous solution, the spraying pressure is 0.2-0.5 MPa, the atomization angle is 60-90°, the solution temperature is 40-60°C, the spraying atomization particle size is 50-100um, and the distance between the nozzle and the material is maintained at 20-30cm, after drying at 80-120°C for 2-4 hours, the alloy is pressed into shape at 160-200°C and 50-150MPa, and the compressive strength of the alloy after pressing is ≥30MPa, thereby obtaining a modified porous silicon-iron alloy;

[0046] S5, magnesium smelting: the modified porous silicon-iron alloy is mixed with magnesium oxide at a mass ratio of 1:1.5-2.5, and metal magnesium is prepared by reduction at a vacuum degree of 10-100Pa and a temperature of 1200-1300°C, the reduction time is shortened by more than 30%, and the system air leakage rate is ≤0.5Pa / min;

[0047] The chemical composition of the porous silicon-iron alloy is Si: 60-75wt%, Fe: 15-25wt%, Ca: 1-5wt%, B: 0.1-1.5wt%, and the balance is unavoidable impurities, and the Fe / Si molar ratio is 0.3-0.5, the bimodal pore size distribution is 0.1-10um, wherein the 0.1-1um pores account for 40-60%, and the 5-10um pores account for 20-40%, the pores have a three-dimensional interconnected structure, the tortuosity is ≤1.8, and the specific surface area is 6-10m 2 / g;

[0048] The SO2 gas generated during the reduction process of step S3 is recycled and absorbed by a 5-10wt% Na2CO3 solution at 40-60°C, and the byproduct is Na2SO3, and the SO2 absorption rate is ≥95%;

[0049] The reduction slag generated in the magnesium smelting process has a mass ratio of CaO / B2O3 of 1.5-3.5, a basicity CaO / SiO2 of 0.8-1.2, contains a Ca3B2O6 phase, and has a melting point of 900-1000 DEG C and a viscosity of 5 Pa s or less at 1200 DEG C.

[0050] Example 1 (optimal embodiment):

[0051] Raw material ratio: 100 kg of silicon powder (SiO2 93.2%, D50=4.8 um), 65 kg of semi-coke (fixed carbon 83.5%), 10 kg of phosphorus gypsum (P2O5 1.1%), 5 kg of boron mud (B2O3 16.2%), and 30 kg of iron source (Fe content 91.7%);

[0052] Process parameters:

[0053] Reduction stage: argon flow 15 L / min, temperature rise to 1150 DEG C at 12 DEG C / min, SO2 partial pressure 0.12 MPa, and holding time 2 h;

[0054] Post-processing: 1.0 wt% PVA solution (viscosity 20 cP) spraying and 180 DEG C / 100 MPa pressing.

[0055] Example 2 (lower limit of parameters):

[0056] Raw material ratio: 100 kg of silicon powder (SiO2 92.1%), 50 kg of semi-coke, 5 kg of phosphorus gypsum, 3 kg of boron mud, and 20 kg of iron source (Fe content 90.1%);

[0057] Process parameters:

[0058] Reduction stage: argon flow 10 L / min, temperature rise to 1100 DEG C at 10 DEG C / min, SO2 partial pressure 0.05 MPa, and holding time 3 h;

[0059] Post-processing: 0.8 wt% PVA solution (15 cP) spraying and 160 DEG C / 50 MPa pressing.

[0060] Example 3 (upper limit of parameters):

[0061] Raw material ratio: 100 kg of silicon powder, 80 kg of semi-coke, 15 kg of phosphorus gypsum, 8 kg of boron mud, and 40 kg of iron source;

[0062] Process parameters:

[0063] Reduction stage: argon flow 20 L / min, temperature rise to 1250 DEG C at 15 DEG C / min, SO2 partial pressure 0.15 MPa, and holding time 1 h;

[0064] Post-processing: 1.2wt% PVA solution (25cP) spray, 200°C / 150MPa pressing.

[0065] Comparative Example 1 (No Boron Sludge):

[0066] No boron sludge was added in the raw materials, and the rest was the same as Example 1.

[0067] Comparative Example 2 (Traditional Phosphogypsum):

[0068] Unprocessed phosphogypsum (P2O52.8%, F - 1.2%), and the rest was the same as Example 1.

[0069] Comparative Example 3 (Conventional Binder):

[0070] Phenolic resin (1.5wt%) was used instead of PVA, and the rest was the same as Example 1.

[0071] Comparative Example 4 (Single Pore Size):

[0072] Mechanical porosity was used instead of SO2 porosity (porosity 35%), and the rest was the same as Example 1.

[0073] Performance Test

[0074] The modified porous ferrosilicon alloys obtained in Examples 1-3 and Comparative Examples 1-4 were tested for performance, and the specific test types and methods were as follows:

[0075] 1. Pore structure analysis:

[0076] Mercury intrusion method: Micromeritics AutoPore V, pressure 0.1-400MPa;

[0077] Micro-CT: ZEISS Xradia 520, resolution 0.7um;

[0078] 2. Mechanical property test:

[0079] Compressive strength: Instron 5982, loading rate 1mm / min;

[0080] Three-point bending: span 30mm, loading head radius 5mm;

[0081] 3. Metallurgical property test:

[0082] Magnesium reduction experiment: vacuum induction furnace, 10Pa, 1250°C;

[0083] Slag phase viscosity: high temperature rotary viscometer (1700°C);

[0084] 4. Microscopic characterization:

[0085] TEM: FEI Talos F200X, equipped with EDS;

[0086] XPS: Thermo K-Alpha, Al Kα radiation;

[0087] Test data are shown in the following table:

[0088]

[0089] This experimental design is fully demonstrated by multi-scale and multi-angle test verification:

[0090] 1. The key role of boron mud-phosphogypsum synergy in reducing the reduction temperature (comparative example 1 vs. comparative example 1)

[0091] 2. The key role of phosphogypsum pretreatment in reaction efficiency and environmental performance (example 1 vs. comparative example 2)

[0092] 3. The irreplaceability of PVA binder in interface strengthening (example 1 vs. comparative example 3) (see mechanical property data)

[0093] 4. The decisive influence of SO2 partial pressure control on pore structure (comparative example 1 vs. comparative example 4)

[0094] Finally, it should be noted that the above examples are only typical representatives of the technical solutions of the present application, which are used to clearly demonstrate the core innovative points and implementation paths of the present application, and are not a limitation on the scope of application of the technical solutions. Based on the design principles of the present application, those skilled in the art can reasonably extend in the following aspects:

[0095] Raw material adaptability adjustment: within the framework of phosphogypsum (P2O5≤1.2%) and boron mud (B2O3≥15%) synergy, the pretreatment process parameters can be adjusted according to the characteristics of different regional industrial waste;

[0096] Process parameter optimization: according to the specifications of production equipment, key parameters such as SO2 partial pressure (0.05-0.15 MPa) and reduction temperature (1100-1250°C) can be combined in a gradient within the scope of the claims;

[0097] Application scenario extension: the bimodal pore structure design principle of the present application can be extended to other metal reduction fields, such as the preparation of silicon-calcium alloy and silicon-manganese alloy;

[0098] Equipment matching improvement: the gas monitoring system can use equivalent alternative technical solutions (such as mass spectrometer instead of infrared analyzer), which still belongs to the protection scope of the present application.

[0099] Any improvement scheme obtained by equivalent replacement, parameter adjustment or process combination under the guidance of the technical concept of the present application shall be deemed to fall within the protection scope defined by the claims of the present application. The right to explain the embodiments of the specification belongs to the applicant.

Claims

1. A ferrosilicon alloy based on silicon fines and low-quality coke, characterized in that, The method comprises the following steps: S1, raw material preparation: S1.1, silicon powder: the silicon powder is obtained by wet ball milling and acid washing purification, SiO2≥92wt%, Al2O3≤3wt%, Fe2O3≤1wt%, D50=2-10um; S1.2, coke: long flame coal low-temperature dry distillation product, fixed carbon≥82wt%, ash≤10wt%, volatile matter≤8wt%; S1.3, phosphogypsum: by-product of wet-process phosphoric acid, pretreated by washing with water, neutralization with lime, CaS04-2H20 > 85 wt%, P205< 1.2 wt%, F - < 0.5 wt%; S1.4, boron mud: boron acid production waste residue, treated by hydrochloric acid washing, Mg2B2O5≥60wt%, B2O3≥15wt%, U≤10ppm; S1.5, iron source: at least one selected from steel chips, cast iron chips, iron scale, and iron powder, with Fe content≥90wt%; S2, raw material mixing: the above-mentioned raw materials silicon powder: coke: phosphogypsum: boron mud: iron source are mixed in a mass ratio of 100:50-80:5-15:3-8:20-40; S3, low-temperature reduction: under argon atmosphere, heated to 1100-1250℃ at a rate of 10-15℃ / min, and kept for 1-3 hours, the alloy porosity is increased to 20-40% by SO2 gas generated by thermal decomposition of phosphogypsum, the total pressure of the reaction system is maintained at 0.1-0.3MPa by adjusting the argon flow, wherein the volume concentration of SO2 is 30-50%, under the synergistic action of SO2 reduction atmosphere and CaO-B2O3-MgO liquid phase formed by boron mud, low-temperature carbothermal reduction of silicon-iron oxides is realized to prepare porous silicon-iron alloy; S4, post-treatment: 0.8-1.2wt% polyvinyl alcohol binder is added to the reduction product, the degree of polymerization of polyvinyl alcohol is 500-2000, the alcoholysis degree is 85-89%, the polyvinyl alcohol binder is added in the form of 5-10wt% aqueous solution, the spraying pressure is 0.2-0.5MPa, the atomizing angle is 60-90°, the solution temperature is 40-60℃, the atomized particle size is 50-100um, the distance between the nozzle and the material is kept at 20-30cm, after drying at 80-120℃ for 2-4 hours, the alloy is pressed and formed at 160-200℃ and 50-150MPa, the compressive strength of the alloy after pressing is≥30MPa, and a modified porous silicon-iron alloy is obtained. The chemical composition of the porous silicon-iron alloy is Si: 60-75 wt%, Fe: 15-25 wt%, Ca: 1-5 wt%, B: 0.1-1.5 wt%, the balance being inevitable impurities, and the molar ratio of Fe / Si is 0.3-0.5, the bimodal pore size distribution is 0.1-10 um, wherein the 0.1-1 um pore accounts for 40-60%, the 5-10 um pore accounts for 20-40%, the pores have a three-dimensional interconnected structure, the tortuosity is ≤1.8, the specific surface area is 6-10 m 2 / g.

2. The ferrosilicon alloy based on silicon powder and blue- carbon regeneration according to claim 1, characterized in that: The preparation method of the silicon powder is as follows: the silicon powder and deionized water are ball milled at a mass ratio of 1:2-3 for 12-24 hours, then treated with 15-20wt% hydrochloric acid at 80-90℃ for 4-6 hours, followed by treatment with 5-8wt% hydrofluoric acid, washed with deionized water until neutral, ultrasonic dispersed, and then spray dried to obtain the silicon powder.

3. The ferrosilicon alloy based on silicon powder and semicoke regeneration according to claim 1, characterized by the fact that: The pre-treatment method of the semi-coke is as follows: the semi-coke is crushed and sieved to a particle size of 0.5-3 mm, calcined at 300-400℃ for 2-3 hours, soaked in a 10-15wt% NaOH solution to remove impurities, neutralized to pH=6.5-7.5 with a 5-10wt% hydrochloric acid solution, activated in a rotary kiln at a rotation speed of 2-5 rpm at 550-750℃ for 1-2 hours, and cooled to room temperature under nitrogen protection to obtain activated semi-coke with a specific surface area of ≥150m 2 / g.

4. The ferrosilicon alloy prepared based on silicon powder and blue- carbon regeneration according to claim 1, characterized in that: The pretreatment method of the phosphogypsum is as follows: the wet-process phosphoric acid by-product phosphogypsum is mixed with deionized water at a mass ratio of 1:3.5-4.5, centrifuged after circulating washing at a stirring speed of 150-250 rpm for 30 minutes, treated with a 5-8 wt% sulfuric acid solution at 55-65°C for 1.5-2.5 hours, 0.1-0.3 wt% sodium dodecyl benzene sulfonate is added, lime milk is added to adjust the pH to 6.5-7.5, the conductivity is controlled to be ≤500 uS / cm, aluminum sulfate solution is added to remove fluorine at 75-85°C for 50-70 minutes, the addition amount of aluminum sulfate is controlled to be Al / F molar ratio 1.2:1, the organic matter is catalytically oxidized and degraded by ultraviolet light with a wavelength of 254 nm and a power of 300 W for 1.5-2.5 hours, dewatered by a belt filter press with a pressure of 0.8-1.2 MPa, and dried in a fluidized bed at 170-190°C until the moisture content is ≤8 wt%, finally, the purified phosphogypsum with CaSO4·2H2O≥85 wt%, P2O5≤1.2 wt%, F - ≤0.5 wt% is obtained. - ≤0.5 wt% is obtained.

5. The ferrosilicon alloy based on silicon powder and blue- carbon regeneration according to claim 1, characterized by the fact that: The pretreatment method of the boron mud is as follows: the boron acid production waste residue is treated with 15-20wt% hydrochloric acid at 70-80℃ for 2.5-3.5 hours, 0.2wt% sodium hexametaphosphate is added, the pH is adjusted to 2.5-3.0 for selective dissolution, the Mg 2+ concentration≤50g / L, 0.5-1wt% tributyl phosphate is added for three-stage extraction to remove uranium at 45-55℃, 2-3wt% sodium carbonate solution is used for back extraction to recover rare earth, calcination is carried out in a muffle furnace at 600-700℃ for 1.5-2.5 hours, CO2 is introduced at a flow rate of 1-2L / min to reconstruct the crystal form, airflow with a pressure of 0.8-1.0MPa is used for crushing to obtain powder with D50=5-15um, and finally Mg2B2O5≥60wt%, B2O3≥15wt%, U≤10ppm boron mud is obtained.

6. The ferrosilicon alloy based on silicon powder and blue- carbon regeneration according to claim 1, characterized by the fact that: The pretreatment method of the iron source is as follows: the iron source is soaked and cleaned with 5-10wt% sodium carbonate solution at 60-80℃ for 15-30 minutes to remove surface oil stains, then rinsed with clean water, then acid washed with 10-15wt% hydrochloric acid solution at room temperature for 5-15 minutes to remove the surface oxide layer, then washed with deionized water until neutral, finally dried at 100-120℃ for 2-4 hours, and crushed and sieved into powder with a particle size of≤0.5mm to obtain clean iron source raw material.

7. The ferrosilicon alloy based on silicon powder and semicoke regeneration according to claim 1, characterized by the fact that it contains: The SO2 gas produced in the step S3 reduction process is recycled and absorbed by 5-10wt% Na2CO3 solution at 40-60℃, the by-product is Na2SO3, and the SO2 absorption rate is ≥95%.

8. The application of ferrosilicon alloy prepared based on silicon powder and low-quality coke in magnesium smelting according to any one of claims 1-7, characterized in that: The modified porous ferrosilicon alloy is mixed with magnesium oxide at a mass ratio of 1:1.5-2.5, and then reduced at a vacuum degree of 10-100 Pa and a temperature of 1200-1300℃ to prepare magnesium, and the reduction time is shortened by more than 30%, and the system air leakage rate is ≤0.5 Pa / min.

9. The application of ferrosilicon alloy prepared based on silicon powder and semi-coke regeneration in magnesium smelting according to claim 8, characterized in that: The reduction slag produced in the magnesium smelting process has a CaO / B2O3 mass ratio of 1.5-3.5, an alkalinity CaO / SiO2 of 0.8-1.2, contains a Ca3B2O6 phase, a slag melting point of 900-1000℃, and a viscosity of ≤5 Pa·s at 1200℃.

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