Micro-carbon chromium iron ore field classification and impurity removal and densification treatment method

Abstract

This invention discloses a method for the classification, impurity removal, and densification of micro-carbon ferrochrome powder in a field, comprising the following steps: S1: pretreatment and crushing of the raw ore; S2: multi-stage precise classification and particle size statistical control; S3: gravity separation for coarse-grained materials; S4: magnetic separation for medium-coarse-grained materials; S5: flotation for medium-fine-grained materials; S6: centrifugal classification and statistical optimization for fine-grained materials; S7: multi-stage material merging and homogenization; S8: pre-compression densification; S9: high-temperature densification and calculus model control; S10: cooling and crushing / shaping; and S11: finished product testing, packaging, and storage. This method realizes the entire process from raw ore to densified micro-carbon ferrochrome powder, and has the advantages of high purification efficiency and high resource utilization.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically relating to a method for the field classification, impurity removal, and densification treatment of micro-carbon ferrochrome powder. Background Technology

[0002] Microcarbon ferrochrome powder is a core raw material for high-end stainless steel, high-temperature alloys, and wear-resistant weld overlay materials. Its carbon content must be controlled between 0.03% and 0.15%, with stringent requirements for impurity content, particle size distribution, and density. Currently, global microcarbon ferrochrome powder production capacity is regionally distributed. South Africa, Kazakhstan, and India dominate the high-end market due to their high-grade ore resources. China's production capacity in 2024 was approximately 650,000 tons, but the proportion of ultra-low carbon grade (C≤0.06%) was less than 30%, insufficient to meet the demand of downstream high-end sectors. The industry's mainstream production processes are mainly the submerged arc furnace oxygen-enriched injection reduction method and the vacuum carbothermal reduction method, while the hydrogen-based direct reduction process is in the pilot stage. The ore processing stage, as the primary step in raw material purification, directly determines subsequent production efficiency and product quality. Currently, most mines adopt a crude processing model of "single crushing + simple magnetic separation," lacking a systematic design for graded impurity removal and densification, resulting in high energy consumption in subsequent smelting stages and difficulty in achieving product purity and density standards. With the advancement of the "dual carbon" strategy and the implementation of the EU's carbon border adjustment mechanism, the industry has put forward higher requirements for the purity, carbon footprint, and comprehensive performance of micro-carbon ferrochrome powder. Upgrading mine pretreatment technology has become the key to breaking through the bottleneck of industry development.

[0003] Existing micro-carbon ferrochrome powder processing technologies face numerous intractable challenges, severely hindering the industry's high-quality development. First, classification precision is insufficient. Current processes mostly employ single-level screening, failing to perform fine classification based on ore particle size differences. This results in fine-grained micro-carbon ferrochrome powder mixing with coarse-grained impurities, significantly increasing the difficulty of subsequent impurity removal. Furthermore, fine-grained powder is easily lost, leading to low resource utilization. Second, impurity removal methods are limited. Most mines rely solely on magnetic or gravity separation, failing to efficiently remove complex impurities from the raw materials, especially aluminosilicates, iron-titanium minerals, and trace non-metallic impurities with similar magnetic properties and density to micro-carbon ferrochrome powder. This results in product purity failing to meet high-end application standards, leading to persistently high export return rates. Third, densification treatment is disconnected from classification and impurity removal. Existing processes often perform densification treatment in the subsequent smelting stage, neglecting densification control during the mine pretreatment phase. This results in high powder particle porosity and poor flowability, easily causing cracking and delamination during subsequent molding and sintering. Fourth, process control lacks precision. The absence of professional statistical and calculus models for parameter optimization, with processing parameters set entirely based on experience, leads to significant fluctuations in product quality, high standard deviations in carbon and impurity content, and difficulty in improving first-pass yield. Fifth, environmental protection and efficiency are difficult to balance. Traditional impurity removal processes often employ chemical agents, easily generating wastewater and waste residue pollution, while purely physical impurity removal processes suffer from low efficiency and high energy consumption, failing to meet the demands of green and large-scale production. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for the field classification, impurity removal, and densification of micro-carbon ferrochrome powder, which can effectively solve the aforementioned problems.

[0005] This invention provides a method for the field classification, impurity removal, and densification treatment of micro-carbon ferrochrome powder, comprising the following steps:

[0006] S1: Steps for pre-treatment and crushing of raw ore;

[0007] S2: Steps for performing multi-level precise grading and granular statistical control;

[0008] S3: The step of performing gravity separation to remove impurities from coarse-grained materials;

[0009] S4: The step of magnetic separation to remove impurities from medium and coarse-grained materials;

[0010] S5: The step of flotation to remove impurities from medium and fine-grained materials;

[0011] S6: Steps for centrifugal classification and impurity removal of fine-particle materials and statistical optimization;

[0012] S7: Steps for multi-stage material merging and homogenization;

[0013] S8: Step for performing pre-compression densification treatment;

[0014] S9: Steps for high-temperature densification treatment and calculus model control;

[0015] S10: The steps of cooling and crushing / shaping;

[0016] S11: Steps for finished product inspection, packaging, and storage;

[0017] Through the above steps, the present invention achieves a closed-loop process from raw ore to densified micro-carbon ferrochrome powder.

[0018] The advantages of this method are as follows:

[0019] Compared to existing micro-carbon ferrochrome powder ore processing technologies, this method offers significant advantages, specifically as follows: First, it improves product quality and performance. Through four-level precise grading and multi-dimensional impurity removal processes, various impurities are effectively removed, ensuring the product's carbon content is controlled at 0.03%~0.15%, chromium content ≥65%, and total impurity content ≤1.0%, resulting in a significant improvement in purity. In-situ densification at the ore site further enhances the product's density to ≥90%, porosity ≤10%, compressive strength ≥40MPa, and particle size uniformity, meeting the stringent requirements of high-end stainless steel, high-temperature alloys, and wear-resistant weld overlay materials. Second, it improves resource utilization. Fine grading prevents the loss of fine-grained micro-carbon ferrochrome powder, while simultaneously recovering and utilizing iron and titanium impurities, increasing resource utilization to over 95%, a 10%~15% improvement compared to existing processes. Third, it reduces energy consumption and production costs. In-situ densification at the mine reduces the forming and sintering steps in subsequent smelting processes, lowering the overall energy consumption per ton of product by 20%–25%. Simultaneously, it reduces the use of chemical reagents and material transportation costs, lowering the production cost per ton of product by 15%–20%. Fourth, it achieves green and environmentally friendly production. Primarily using physical impurity removal, the flotation process employs environmentally friendly flotation agents, resulting in no wastewater or waste residue pollution. Dust emissions meet national environmental standards, while carbon emissions are reduced, with a carbon footprint as low as 0.15 tons of CO2e / ton, complying with the "dual carbon" strategy requirements. Fifth, it improves production efficiency and quality stability. Automated grading, impurity removal, and densification equipment enables continuous production, increasing production efficiency by 30%–40%. Combined with statistical and calculus models for precise parameter control, product quality fluctuations are minimized, with the standard deviation of carbon and impurity content reduced to ≤0.005%, and the first-pass yield increased to over 98%. Sixth, the process is highly innovative, significantly different from existing publicly available technologies. Its core innovations lie in multi-level precise grading and multi-dimensional impurity removal synergy, in-situ densification treatment at the ore site, and precise control using statistical and calculus models. This breaks through existing technological bottlenecks and provides a new technical path for the processing of micro-carbon ferrochrome powder at the ore site. Seventh, it is highly adaptable. Grading parameters, impurity removal processes, and densification parameters can be adjusted according to the characteristics of different ore sources, adapting to micro-carbon ferrochrome ore of different grades and particle sizes. It has a wide range of applications and is easy to promote and apply industrially. Eighth, it enhances the market competitiveness of the product. The micro-carbon ferrochrome powder produced by this method meets international high-end standards in various performance indicators, can replace imported products, break the foreign market monopoly, reduce export return rates, and enhance the international market recognition of domestically produced micro-carbon ferrochrome powder. Attached Figure Description

[0020] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, use the same reference numerals to denote the same or similar parts. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0021] Figure 1 A schematic diagram of a process for classifying, removing impurities, and densifying micro-carbon ferrochrome powder according to an embodiment of this application is shown. Detailed Implementation

[0022] Step 1: Raw ore pretreatment and crushing

[0023] Pre-treatment and crushing of the raw ore are fundamental to the entire processing flow. The core purpose is to remove large impurities, soil, and moisture from the raw ore, crushing it to a uniform particle size to provide a basis for subsequent grading and impurity removal. During operation, high-grade micro-carbon ferrochrome ore with a Cr2O3 content ≥48% and an Fe / Cr ratio ≤1.2 is first selected and conveyed at a uniform speed to the raw material cleaning platform using a belt conveyor. Through a combination of manual screening and high-pressure spraying, soil, weeds, and large non-metallic impurities adhering to the surface of the raw ore are removed. The spraying water pressure is controlled at 0.3~0.5MPa, and the spraying time is 3~5 minutes per batch of raw material, ensuring that no visible impurities adhere to the surface of the raw ore. After cleaning, the raw ore is fed into a jaw crusher for coarse crushing. The discharge port size is adjusted to 80~100mm, and the feed rate is controlled at 2~3t / h during crushing to avoid overloading the crusher or insufficient crushing due to excessive feeding speed. The coarsely crushed material is conveyed by a belt conveyor to a cone crusher for medium crushing. The discharge opening size for medium crushing is adjusted to 30-40mm. During medium crushing, the crusher's vibration dust collector is activated to reduce dust pollution. The medium-crushed material is then fed into an impact crusher for fine crushing. The discharge opening size for fine crushing is adjusted to 5-10mm. During fine crushing, the crusher speed is controlled at 1200-1500 r / min, employing the principle of layered crushing to ensure uniform particle size and prevent over-crushing. After crushing, the material is fed into a vibrating feeder for uniform conveying to the next step. Simultaneously, the moisture content of the material is monitored, ensuring it is controlled between 8% and 12%. If the moisture content is too high, a hot air drying device is activated, with the drying temperature controlled at 80-100℃ for 20-30 minutes, until the moisture content meets the standard.

[0024] The working principle is to gradually reduce the particle size of the raw ore through multi-stage crushing, thereby breaking the binding state between the raw ore and impurities. At the same time, it removes surface-attached impurities and excess moisture, providing raw materials with uniform particle size and low impurity content for subsequent classification and impurity removal. This avoids large impurities from damaging subsequent equipment, while controlling the moisture content can prevent fine-grained materials from agglomerating and ensure classification accuracy.

[0025] Step Two: Multi-level Precise Grading and Granularity Statistical Control

[0026] Multi-stage precision grading is the core step in achieving refined impurity removal. Grading is based on differences in material particle size, and statistical and calculus models are introduced to achieve precise control of grading parameters, solving the problems of insufficient grading accuracy and uneven particle size distribution in existing methods. During operation, the material crushed in step one is fed into a multi-stage vibrating screen, employing a four-stage grading mode with screen apertures set to 10mm, 5mm, 2mm, and 0.5mm, corresponding to four grades of material: coarse (5~10mm), medium-coarse (2~5mm), medium-fine (0.5~2mm), and fine (<0.5mm). During each grading stage, the vibration frequency of the vibrating screen is controlled at 20~30Hz, and the amplitude at 5~8mm. The feed speed is kept consistent with the vibrating feeder in step one to ensure uniform material distribution on the screen and prevent screen clogging. After grading, samples of each grade of material are taken for testing. A laser particle size analyzer is used to determine the particle size distribution of each grade of material. At the same time, statistical models and calculus formulas are introduced to quantitatively evaluate the grading effect and optimize the parameters.

[0027] The statistical model used is based on the probability density function of particle size distribution, combined with calculus to calculate the grading efficiency. The specific formula is as follows:

[0028] ;

[0029] In formula (1), the meanings of each symbol are as follows: η is the grading efficiency, with a value range of 0~1. The closer to 1, the better the grading effect; d is the particle size of the material, in mm; d is the minimum particle size of the grade, in mm; d is the maximum particle size of the grade, in mm; f(d) is the probability density function of the particle size distribution of the material, which satisfies the condition that its value is obtained by fitting the detection data of the laser particle size analyzer; C1 is the pass / follow constant, with a value of 0.0023, which characterizes the dynamic correction coefficient of particle size change during the grading process; is the average particle size of the material in this grade, in mm; t is the grading time, in min; is the rate of change of the average particle size with grading time, in mm / min, which is obtained by differential calculation of the average particle size detection values ​​at different time points;

[0030] The grading efficiency of each grade of material is calculated according to formula (1). If the grading efficiency of a certain grade is lower than 0.92, the screen aperture, vibration frequency or feed speed of that grade is adjusted, and grading is repeated until the grading efficiency meets the standard. At the same time, the uniformity of particle size distribution of each grade of material is calculated by integration to ensure that the particle size deviation of coarse particles is ≤1.2mm, medium-coarse particles are ≤0.8mm, medium-fine particles are ≤0.3mm, and fine particles are ≤0.1mm.

[0031] The working principle is to utilize the difference in the passage of materials of different particle sizes through the vibrating screen to achieve multi-level classification. The classification effect is quantified by statistical models and calculus formulas, and the classification parameters are precisely controlled to avoid mixing of fine-grained micro-carbon ferrochrome powder with coarse-grained impurities. At the same time, it ensures that the particle size of each grade of material is uniform, which provides a basis for subsequent targeted impurity removal and improves the efficiency and accuracy of impurity removal.

[0032] Step 3: Gravity separation to remove impurities from coarse-grained materials

[0033] The coarse-grained material mainly contains coarse particles of micro-carbon ferrochrome powder and non-metallic impurities such as quartz sand and feldspar. These impurities have a significant density difference from the micro-carbon ferrochrome powder, and can be efficiently removed using gravity separation, providing qualified coarse-grained raw materials for subsequent processing. During operation, the coarse-grained material obtained from step two is fed into a spiral chute gravity separator. The spiral chute diameter is 1.5m, the pitch is 300mm, the number of turns is 5, the slurry concentration is adjusted to 30%~35%, and the slurry flow rate is controlled at 1.2~1.5m / s. During the gravity separation process, coarse-grained materials are mixed with water in a certain proportion to form a slurry, which is then pumped at a constant speed into the top of the spiral sluice. Under the action of gravity and centrifugal force, the slurry flows downward along the spiral blades. The micro-carbon ferrochrome powder has a higher density (4.3~4.8 g / cm³) and a faster settling velocity, sliding along the inner side of the spiral blades and finally falling into the concentrate collection tank at the bottom of the sluice. The impurities such as quartz sand and feldspar have a lower density (2.6~2.8 g / cm³) and a slower settling velocity, sliding along the outer side of the spiral blades and falling into the tailings collection tank, thus achieving the separation of coarse-grained materials and impurities.

[0034] After gravity separation, the coarse-grained micro-carbon ferrochrome powder in the concentrate collection tank is cleaned using high-pressure water spraying, with the water pressure controlled at 0.2~0.4MPa and the spraying time at 1~2 minutes, to remove fine impurities and slurry adhering to the surface. After cleaning, the coarse-grained micro-carbon ferrochrome powder is sent to a hot air dryer, with the drying temperature controlled at 100~120℃ and the drying time at 30~40 minutes, ensuring that the moisture content is reduced to below 5%. At the same time, the impurity content of the coarse-grained micro-carbon ferrochrome powder is tested. If the impurity content is higher than 1.5%, it is sent back to the spiral chute for secondary gravity separation until the impurity content meets the standard.

[0035] The working principle is based on the density difference between micro-carbon ferrochrome powder and non-metallic impurities. The combined effect of gravity and centrifugal force causes them to settle in layers within the slurry, thus achieving impurity removal. Coarse-grained materials have larger particles, resulting in significant differences in settling velocities during gravity separation, leading to high impurity removal efficiency. Furthermore, no chemical reagents are required, meeting green production requirements. Simultaneously, the washing and drying steps further remove surface impurities and excess moisture, laying the foundation for subsequent fine crushing and densification processes.

[0036] Step 4: Magnetic separation to remove impurities from medium and coarse-grained materials

[0037] The medium-to-coarse particle size contains coarse particles of micro-carbon ferrochrome powder, a small amount of iron-titanium magnetic impurities, and incompletely removed non-metallic impurities. The micro-carbon ferrochrome powder has strong magnetism, while the iron-titanium impurities have weak magnetism, and the non-metallic impurities are non-magnetic. High-gradient magnetic separation can achieve precise separation, solving the problem that existing magnetic separation processes cannot effectively separate weakly magnetic impurities. During operation, the medium-to-coarse particle size obtained in step two is fed into a high-gradient magnetic separator. The separator uses a neodymium iron boron permanent magnet system, with the magnetic field strength adjusted to 12000~15000 Gauss, the magnetic field gradient to 500~600 T / m, the feed rate controlled at 1.5~2 t / h, and the drum speed at 30~40 r / min. During the magnetic separation process, medium and coarse particles are uniformly introduced into the magnetic field area of ​​the magnetic separator. Micro-carbon ferrochrome powder, as a strongly magnetic material, is strongly adsorbed onto the surface of the drum by the magnetic field. As the drum rotates, it moves to the non-magnetic field area and falls into the concentrate collection hopper under the action of gravity. Iron-titanium magnetic impurities are weakly magnetic and are slightly adsorbed by the magnetic field. As the drum rotates, they move to the weak magnetic field area, are scraped off by the scraper, and fall into the weak magnetic impurity collection hopper. Non-metallic impurities are non-magnetic and are not affected by the magnetic field force. They fall into the tailings collection hopper under the action of gravity and centrifugal force, thus achieving the separation of the three.

[0038] After magnetic separation, samples of medium- and coarse-grained micro-carbon ferrochrome powder in the concentrate collection hopper are taken for testing, with a focus on detecting the content of iron and titanium impurities. If the iron and titanium impurity content is higher than 0.8%, the magnetic field strength and drum speed are adjusted, and magnetic separation is repeated until the iron and titanium impurity content meets the standard. At the same time, the iron and titanium impurities in the weakly magnetic impurity collection hopper are collected separately for recycling, improving resource utilization.

[0039] The working principle is based on the magnetic differences between different substances. A high-gradient magnetic field generates strong adsorption forces to accurately separate micro-carbon ferrochrome powder, weakly magnetic impurities, and non-metallic impurities. The high-gradient magnetic field enhances the adsorption capacity for weakly magnetic impurities, preventing them from mixing into the micro-carbon ferrochrome powder. Simultaneously, the strongly magnetic micro-carbon ferrochrome powder can be efficiently adsorbed and recovered, reducing resource waste. The magnetic separation process involves no chemical reagents, making it environmentally friendly and highly efficient. It is suitable for impurity removal from medium to coarse-grained materials, providing qualified raw materials for subsequent crushing and grading.

[0040] Step 5: Flotation removal of medium and fine-grained materials

[0041] Medium and fine-grained materials have small particle sizes, and the density and magnetic properties of micro-carbon ferrochrome powder and non-metallic impurities such as aluminosilicates are similar, resulting in poor impurity removal effects from gravity separation and magnetic separation. Therefore, flotation is employed to remove impurities by adding a specialized flotation agent, creating a difference in surface properties between the micro-carbon ferrochrome powder and the impurities, thereby achieving efficient impurity removal. During operation, the medium and fine-grained material obtained from step two is fed into the flotation machine. First, water is added to adjust the pulp concentration to 25%–30%. Then, sodium hydroxide is added as a modifier to adjust the pulp pH to 9–10. The mixture is stirred evenly at a speed of 150–200 rpm for 5–8 minutes. The modifier alters the surface electrical properties of the micro-carbon ferrochrome powder and the impurities, making the surface of the micro-carbon ferrochrome powder hydrophobic and the surface of the impurities hydrophilic. Subsequently, sodium oleate, a collector, is added at a rate of 200-300 g / t of material, and the stirring time is 3-5 minutes. The collector selectively adsorbs onto the surface of the micro-carbon ferrochrome powder, enhancing its hydrophobicity and making it easier to adhere to the bubble surface. Finally, pine oil, a frother, is added at a rate of 50-80 g / t of material, and the stirring time is 2-3 minutes. The frother generates a large number of uniform bubbles in the slurry, providing a carrier for the flotation of the micro-carbon ferrochrome powder.

[0042] During the flotation process, the aeration device of the flotation machine is turned on, and the aeration rate is controlled at 0.3~0.5 m³ / (m²·min). The flotation time is 15~20 minutes. Due to its hydrophobic surface, the micro-carbon ferrochrome powder adheres to the surface of the bubbles and rises to the surface of the slurry with the bubbles, forming a frothy product, which is scraped into the concentrate collection tank by a scraper. Impurities such as aluminosilicates remain in the slurry due to their hydrophilic surface and are eventually discharged from the bottom of the flotation machine into the tailings collection tank. After flotation, the medium and fine-grained micro-carbon ferrochrome powder in the concentrate collection tank is de-treated by washing with clean water 3~4 times, with each washing lasting 5~8 minutes, to ensure that the residual flotation reagent is less than 50 mg / kg. After de-treatment, the powder is sent to a hot air dryer, with the drying temperature controlled at 90~110℃ and the drying time at 25~35 minutes, until the moisture content is reduced to below 5%.

[0043] The working principle is to modify the surface properties of micro-carbon ferrochrome powder and impurities by adding modifiers, collectors, and frothers. Utilizing the buoyancy of air bubbles, the hydrophobic micro-carbon ferrochrome powder rises with the bubbles, while the hydrophilic impurities remain in the slurry, achieving separation and impurity removal. The flotation process can effectively remove fine non-metallic impurities from medium- and fine-grained materials, compensating for the shortcomings of gravity and magnetic separation, ensuring the purity of medium- and fine-grained micro-carbon ferrochrome powder, and providing qualified raw materials for subsequent merging and densification treatment with fine-grained materials.

[0044] Step Six: Centrifugal Classification and Statistical Optimization of Fine-Grained Materials

[0045] Fine-grained materials are characterized by their small particle size, easy agglomeration, and high content of fine impurities. Centrifugal classification, combined with statistical and calculus models, enables precise classification and impurity removal of fine-grained materials, addressing the problems of incomplete impurity removal and easy loss in existing methods. During operation, the fine-grained material obtained in step two is fed into a high-speed centrifugal classifier. The centrifugal classifier's speed is adjusted to 3000~3500 r / min, the feed rate is controlled at 1~1.2 t / h, and clean water is used as the classification medium, with the medium temperature controlled at 25~30℃. During centrifugal classification, fine-grained materials are mixed with water to form a slurry, which is then fed into the drum of the centrifugal classifier. The high-speed rotation of the drum generates centrifugal force, the magnitude of which is proportional to the particle mass. The fine particles of micro-carbon ferrochrome powder have a larger mass and are subjected to a greater centrifugal force, so they are thrown against the inner wall of the drum and discharged through the discharge port as the drum rotates, falling into the concentrate collection tank. The fine impurity particles have a smaller mass and are subjected to a smaller centrifugal force, so they are discharged from the overflow port with the slurry and fall into the tailings collection tank, thus achieving the separation of fine-grained materials and fine impurities.

[0046] After centrifugal classification, fine-grained micro-carbon ferrochrome powder in the concentrate collection tank was sampled and tested. A laser particle size analyzer was used to determine its particle size distribution and impurity content. Simultaneously, a statistical model and calculus formulas were introduced to optimize the centrifugal classification parameters, ensuring stable classification and impurity removal effects. The statistical model used focuses on the impurity removal rate of centrifugal classification, and combines calculus to calculate the optimal centrifugal speed. The specific formula is as follows:

[0047] ;

[0048] In formula (2), the meanings of each symbol are as follows: ξ is the impurity removal rate, with a value range of 0~1. The closer to 1, the better the impurity removal effect; m0 is the mass of impurities in the fine-particle material before centrifugation, in kg; m1 is the mass of impurities in the fine-particle material after centrifugation, in kg; ρ is the slurry density, in kg / m³; ω is the angular velocity of the centrifugal classifier drum, in rad / s; r is the distance from a point inside the drum to the center of rotation, in m; R is the drum radius, in m; S(r) is the cross-sectional area at point r inside the drum, in m²; C2 is the constant of rotation, with a value of 0.0018, representing the correction coefficient for the change of angular velocity during centrifugation; t is the centrifugation time, in min; is the rate of change of the drum angular velocity over time, in rad / (s·min); is the integral of the effect of centrifugal force on the slurry, representing the contribution of centrifugal force to impurity separation; is the integral of the change of angular velocity, representing the influence of dynamic adjustment of centrifugal speed on the impurity removal rate;

[0049] The impurity removal rate is calculated according to formula (2). If the impurity removal rate is lower than 0.95, the centrifugal speed, feed rate or slurry concentration is adjusted, and centrifugation is repeated until the impurity removal rate meets the standard. At the same time, the degree of agglomeration of fine-grained micro-carbon ferrochrome powder is calculated by integration to ensure that the particle size of agglomerated particles is ≤1mm. If the degree of agglomeration is too high, polyacrylamide dispersant is added at a rate of 100~150g / t of material. After stirring evenly, centrifugation is repeated.

[0050] The working principle is to use centrifugal force to separate fine-grained micro-carbon ferrochrome powder from fine impurities due to their mass difference. By combining statistical models and calculus formulas to quantify the impurity removal effect, the centrifugal parameters are precisely controlled to avoid the loss of fine-grained micro-carbon ferrochrome powder. At the same time, it solves the problem of incomplete impurity removal caused by the agglomeration of fine-grained materials, ensuring the purity and particle size uniformity of fine-grained micro-carbon ferrochrome powder, and providing a foundation for subsequent material merging and densification treatment.

[0051] Step 7: Multi-stage material merging and homogenization treatment

[0052] Multi-stage material merging and homogenization involves combining the qualified micro-carbon ferrochrome powders from steps three, four, five, and six. Homogenization ensures uniform particle size distribution and composition, providing a homogeneous raw material for subsequent densification and resolving the problem of uneven mixing leading to poor densification. During operation, the coarse-grained micro-carbon ferrochrome powder from step three, the medium-coarse-grained micro-carbon ferrochrome powder from step four, the medium-fine-grained micro-carbon ferrochrome powder from step five, and the fine-grained micro-carbon ferrochrome powder from step six are fed into a twin-shaft mixing homogenizer via belt conveyors. They are mixed at a mass ratio of coarse:medium-coarse:medium-fine:fine = 2:3:3:2, with a mixing time of 40-60 minutes and a stirring speed of 120-150 r / min. During the homogenization process, samples were taken every 10 minutes. The particle size distribution of the mixture was determined using a laser particle size analyzer, and the composition of the mixture was detected using an X-ray fluorescence spectrometer. This ensured that the average particle size of the mixture was controlled within 1~3 mm, the particle size deviation was ≤0.5 mm, the chromium content deviation was ≤0.8%, the carbon content was controlled within 0.03%~0.15%, and the total impurity content was ≤1.0%.

[0053] If the particle size distribution or composition of the mixture does not meet the requirements, adjust the stirring speed, mixing time, or mixing ratio of each stage of material, and continue homogenization until the requirements are met. After homogenization, the mixture is sent to a storage silo with a conical structure and a vibrating discharge device at the bottom to prevent material from clumping. At the same time, the stirring device inside the silo is turned on and stirred every 30 minutes to ensure that the material remains uniform during storage.

[0054] The working principle involves mixing qualified micro-carbon ferrochrome powder of various grades in a reasonable ratio. The shearing and impact forces of the biaxial mixing shaft break up the agglomeration of material particles, ensuring uniform mixing. Simultaneously, real-time monitoring and parameter adjustment ensure consistent particle size and composition. This homogenization process eliminates performance differences between grades, providing uniform raw materials for subsequent densification. It prevents uneven density and cracking in the densified product due to material inhomogeneity, and provides a stable material basis for subsequent parameter control.

[0055] Step 8: Pre-compression densification treatment

[0056] Pre-compression densification is a core step in in-situ densification at the mine. Through pressure, it reduces the porosity of the mixture, increasing its initial density and laying the foundation for subsequent high-temperature densification. This addresses the problems of high energy consumption and insufficient product density caused by the lagging densification process in existing technologies. During operation, the homogenized mixture from step seven is fed into a hydraulic pre-compressor. The pre-compressor's die size is 500mm × 500mm × 100mm, and the feed rate is controlled at 50-60kg per batch to ensure uniform material distribution within the die, without voids or agglomerates. During pre-compression, a staged pressurization mode is used. The initial pressure is adjusted to 10-15MPa and maintained for 5-10 minutes to allow the material to initially form. The pressure is then increased to 30-40MPa and maintained for 15-20 minutes to further reduce material porosity. Finally, the pressure is increased to 50-60MPa and maintained for 10-15 minutes to complete the pre-compression densification process. During the pre-compression process, the temperature of the compression mold is controlled at 50~60℃, and the temperature is evenly distributed to avoid local overheating that could lead to material oxidation.

[0057] After pre-pressing, the pressed blank is removed from the mold, and its density, compressive strength, and porosity are tested. The density should reach 65%~75%, the compressive strength ≥15MPa, and the porosity ≤30%. If the test indicators do not meet the requirements, the pre-pressing pressure, pressing time, or mold temperature is adjusted, and the pre-pressing densification treatment is repeated until the standards are met. At the same time, the surface of the pre-pressed blank is cleaned to remove loose particles and impurities, ensuring that the blank surface is flat and undamaged.

[0058] The working principle utilizes hydraulic pressure to compress and tightly contact the particles of the mixture, expelling air between the particles, reducing porosity, and increasing density and compressive strength. The staged pressurization mode avoids cracking of the billet caused by a single high-pressure application, while temperature control prevents oxidation of the micro-carbon ferrochrome powder, ensuring billet quality. The pre-compression densification treatment is completed at the mine, reducing the number of forming steps in subsequent smelting processes, lowering energy consumption, and improving the efficiency and effectiveness of subsequent high-temperature densification.

[0059] Step Nine: High-Temperature Densification Treatment and Calculus Model Adjustment

[0060] High-temperature densification is a key step in improving the density of micro-carbon ferrochrome powder. Through high temperatures, it promotes particle diffusion and sintering, further reducing porosity and improving product density and overall performance. Simultaneously, statistical and calculus models are introduced to achieve precise control of high-temperature parameters, solving the problem of existing high-temperature densification parameters being set based on experience and resulting in large fluctuations in product quality. During operation, the pre-pressed green body from step eight is fed into a continuous high-temperature sintering furnace. The furnace is heated by natural gas, and nitrogen is introduced into the furnace chamber as a protective gas. The nitrogen purity is ≥99.99%, and the flow rate is controlled at 5~8 m³ / h to prevent oxidation of the micro-carbon ferrochrome powder. The high-temperature densification process adopts a staged heating mode. The specific heating process is as follows: heating from room temperature to 300℃ at a heating rate of 5℃ / min and holding for 30 minutes to remove residual moisture in the green body; heating from 300℃ to 800℃ at a heating rate of 8℃ / min and holding for 60 minutes to remove residual flotation agent and trace impurities in the green body; heating from 800℃ to 1200~1300℃ at a heating rate of 10℃ / min and holding for 90~120 minutes to complete the high-temperature densification sintering; and finally cooling from 1200~1300℃ to room temperature at a cooling rate of 6℃ / min to avoid cracking of the green body due to excessively rapid cooling.

[0061] During the high-temperature densification process, a calculus model is introduced to quantify the density change during sintering and precisely control the heating rate and holding time. The specific formula is as follows:

[0062] ;

[0063] In formula (3), the meanings of each symbol are as follows: ρ(t) is the compaction density of the billet at time t, with a value range of 0~1; ρ0 is the initial compaction density of the billet after pre-pressing; k is the sintering rate constant, with the unit being min. -1 , with a value of 0.0085; E is the sintering activation energy, in J / mol, with a value of 280000; R is the ideal gas constant, in J / (mol·K), with a value of 8.314; T(t) is the temperature inside the furnace at time t, in K; τ is the integral variable, in min; C3 is the constant of the sintering process, with a value of 0.0009, representing the correction coefficient of temperature change on density; is the rate of change of temperature over time, in K / min; is the integral of density increment during sintering, representing the contribution of sintering time and temperature to density; is the integral of temperature change, representing the effect of heating rate on density;

[0064] Calculate the bulk density at different time points according to formula (3). If the bulk density at time t does not reach the target value (≥90%), adjust the heating rate or holding time to ensure that after high-temperature densification, the bulk density is ≥90%, the porosity is ≤10%, and the compressive strength is ≥40MPa.

[0065] The working principle is to promote atomic diffusion on the surface of micro-carbon ferrochrome powder particles through high temperature, forming a strong bond between the particles, expelling residual air and impurities, further reducing porosity, and improving density and mechanical properties. Nitrogen protection prevents oxidation of the micro-carbon ferrochrome powder, and staged heating and cooling prevents cracking of the billet. Combined with a calculus model to precisely control parameters, the high-temperature densification effect is ensured to be stable, and the product density meets the standard. At the same time, in-situ high-temperature densification at the mine can reduce the transfer and secondary processing in subsequent processes, reducing energy consumption and pollution.

[0066] Step 10: Cooling and Crushing / Shaping

[0067] Cooling and crushing / shaping involves cooling the high-temperature densified billet and then crushing it into the required particle size to provide qualified products for subsequent screening and packaging. This process ensures uniform particle size and prevents breakage, addressing the problems of billet cracking and uneven particle size distribution caused by improper cooling methods in existing processes. During operation, the high-temperature densified billet from step nine is removed from the high-temperature sintering furnace and placed in a slow cooling chamber. The chamber is protected by nitrogen, with the nitrogen flow rate consistent with that of the sintering furnace. The slow cooling temperature is gradually increased from room temperature to 500℃ to match the initial temperature of the billet, and then reduced to room temperature at a rate of 3℃ / min for 120-150 minutes. During slow cooling, the billet temperature is monitored in real time to ensure a uniform temperature decrease and prevent excessive local temperature differences that could lead to cracking.

[0068] After slow cooling, the billet is fed into an impact crusher for crushing and shaping. The crusher speed is adjusted to 1000~1200 r / min, and the discharge port size is adjusted to 0.5~2 mm. During the crushing process, a vibration dust collector is activated to reduce dust pollution. After crushing and shaping, the material is fed into a vibrating screen with screen apertures of 0.5 mm, 1 mm, and 2 mm to classify it into three particle sizes of micro-carbon ferrochrome powder: fine (0.5~1 mm), medium (1~2 mm), and coarse (around 2 mm), ensuring that the particle size deviation of each product is ≤0.2 mm. During the crushing and shaping process, the density and impurity content of the product are tested. If they do not meet the requirements, the crushing and shaping process is repeated or the previous steps are returned.

[0069] The working principle is that the slow cooling process can eliminate the thermal stress inside the billet and avoid cracking, and nitrogen protection can prevent oxidation of the billet during the cooling process; the impact crushing and shaping can crush the billet into uniform particle size while avoiding over-crushing, and the grading and screening can ensure that the product particle size meets the needs of different application scenarios, providing qualified products for subsequent packaging and storage.

[0070] Step 11: Finished Product Inspection and Packaging Storage

[0071] Finished product testing and packaging / storage is the final step in the entire process. Comprehensive testing ensures product quality meets standards, and standardized packaging and storage methods prevent oxidation, moisture absorption, or contamination, ensuring stable product performance and addressing the existing problems of incomplete finished product testing and improper packaging / storage leading to product quality degradation. During operation, samples of the three particle sizes after crushing and shaping in step ten are taken for testing. Test items include carbon content, chromium content, impurity content, density, particle size distribution, and compressive strength. Carbon content testing uses a high-frequency infrared carbon-sulfur analyzer to ensure carbon content is controlled between 0.03% and 0.15%; chromium content testing uses an X-ray fluorescence spectrometer to ensure chromium content is ≥65%; impurity content testing uses an inductively coupled plasma atomic emission spectrometer to ensure total impurity content is ≤1.0%, with iron-titanium impurities ≤0.5% and silicon-aluminum impurities ≤0.3%; density testing uses the water displacement method to ensure density is ≥90%; particle size distribution testing uses a laser particle size analyzer to ensure particle size deviation is ≤0.2mm; and compressive strength testing uses a universal testing machine to ensure compressive strength is ≥40MPa.

[0072] After all testing items meet the standards, packaging is carried out. Double-layer packaging is used: an inner aluminum foil bag and an outer woven bag, with a packaging size of 25kg / bag. During packaging, argon gas with a purity of ≥99.99% is injected into the aluminum foil bag to ensure no air is present inside and prevent product oxidation. After packaging, the product name, particle size specification, production date, and test qualification mark are labeled on the woven bag. The packaged products are then sent to a dedicated storage warehouse. The warehouse is kept dry and well-ventilated, with relative humidity controlled below 30% and temperature controlled between 10~25℃. The product stacking height does not exceed 10 layers to avoid crushing and damage. Simultaneously, a product traceability system is established, with each batch of products numbered and all parameters and test results recorded during the production process to ensure product quality traceability.

[0073] The working principle is to ensure that the product quality meets high-end application standards through comprehensive testing, double-layer packaging and argon protection can prevent product oxidation and moisture, standardized storage conditions can ensure stable product performance, and the product traceability system can facilitate quality control and problem investigation, providing downstream customers with reliable micro-carbon ferrochrome powder products.

[0074] Example

[0075] Example 1

[0076] This embodiment uses the method to classify, remove impurities, and densify imported South African micro-carbon ferrochrome ore. The ore has a Cr2O3 content of 48%, an Fe / Cr ratio of 1.1, a carbon content of 0.12%, and a total impurity content of 3.2%, including 1.5% quartz sand, 1.0% aluminosilicate, and 0.7% iron-titanium impurities. The ore particle size is 50~200mm, and the moisture content is 10%.

[0077] Step 1: Raw Ore Pretreatment and Crushing. The selected raw ore is conveyed at a constant speed to the raw material cleaning platform using a belt conveyor. Surface dirt, weeds, and large non-metallic impurities are removed through a combination of manual screening and high-pressure spraying. The spraying water pressure is controlled at 0.4 MPa, and the spraying time is 4 minutes per batch. After cleaning, the ore is fed into a jaw crusher for coarse crushing. The discharge opening size is adjusted to 90 mm, and the feed speed is controlled at 2.5 t / h. The coarsely crushed material is then fed into a cone crusher for medium crushing. The discharge opening size is adjusted to 35 mm, and the vibration dust collector is activated. The medium-crushed material is then fed into an impact crusher for fine crushing. The discharge opening size is adjusted to 7 mm, and the crusher speed is controlled at 1350 r / min. After crushing, the material is fed into a vibrating feeder. The moisture content is measured to be 10%, requiring no drying, and the material is directly conveyed to the next step.

[0078] Step 2: Multi-level Precision Grading and Particle Size Statistical Control. The crushed material is fed into a multi-level vibrating screen, using a four-level sieving mode with screen apertures of 10mm, 5mm, 2mm, and 0.5mm, a vibration frequency of 25Hz, an amplitude of 6.5mm, and a feeding speed consistent with the vibrating feeder. After grading, samples are taken to test the particle size distribution of each grade of material. The grading efficiency is calculated using formula (1). The grading efficiency for coarse particles (5~10mm) is 0.93, for medium-coarse particles (2~5mm) it is 0.94, for medium-fine particles (0.5~2mm) it is 0.93, and for fine particles (<0.5mm) it is 0.95, all meeting the requirement of ≥0.92. The particle size deviations for each grade of material are 1.0mm for coarse particles, 0.7mm for medium-coarse particles, 0.25mm for medium-fine particles, and 0.08mm for fine particles, all meeting the requirements, and proceeding to the next step.

[0079] Step 3: Gravity Separation and Impurity Removal of Coarse-Grained Material. The coarse-grained material is fed into a spiral sluice gravity separator. The spiral sluice has a diameter of 1.5m, a pitch of 300mm, and 5 turns. The slurry concentration is adjusted to 32%, and the slurry flow rate is controlled at 1.35m / s. The coarse-grained material is mixed with water to form a slurry, which is then fed to the top of the spiral sluice. Micro-carbon ferrochrome powder falls into the concentrate collection tank, while impurities such as quartz sand fall into the tailings collection tank. After gravity separation, the material is sprayed with 0.3MPa high-pressure water for 1.5 minutes and then sent to a hot air dryer at 110℃ for 35 minutes, reducing the moisture content to 4.5%. The impurity content is measured at 1.2%, meeting the requirements, and the process proceeds to the next step.

[0080] Step 4: Magnetic separation for medium and coarse-grained materials. The medium and coarse-grained materials are fed into a high-gradient magnetic separator. The magnetic field strength is adjusted to 13500 Gauss, the magnetic field gradient is 550 T / m, the feed rate is controlled at 1.75 t / h, and the drum speed is 35 r / min. During the magnetic separation process, micro-carbon ferrochrome powder falls into the concentrate collection hopper, iron and titanium impurities fall into the weakly magnetic impurity collection hopper, and non-metallic impurities fall into the tailings collection hopper. The iron and titanium impurity content is detected to be 0.6%, which meets the requirements. The iron and titanium impurities are collected and recovered separately and proceed to the next step.

[0081] Step 5: Flotation and impurity removal of medium and fine-grained materials. Feed the medium and fine-grained materials into the flotation machine. Add water to adjust the pulp concentration to 27%, and add sodium hydroxide to adjust the pulp pH to 9.5. Stir at 175 rpm for 6.5 minutes. Add sodium oleate collector at a rate of 250 g / t of material, and stir for 4 minutes. Add pine oil frother at a rate of 65 g / t of material, and stir for 2.5 minutes. Turn on the aeration device at a rate of 0.4 m³ / (m²·min). Flotation time is 17 minutes. The micro-carbon ferrochrome powder forms a frothy product that falls into the concentrate collection tank, while impurities fall into the tailings collection tank. After flotation, wash three times with water for 6.5 minutes each time, reducing the residual flotation agent to 42 mg / kg. Send the material to a hot air dryer at 100℃ for 30 minutes, reducing the moisture content to 4.8%, and proceed to the next step.

[0082] Step Six: Centrifugal Classification and Statistical Optimization of Fine-Grained Materials. The fine-grained material was fed into a high-speed centrifugal classifier, with the rotation speed adjusted to 3250 r / min and the feed rate controlled at 1.1 t / h. The classification medium was 27℃ clean water. During the centrifugal classification process, micro-carbon ferrochrome powder fell into the concentrate collection tank, while fine impurities fell into the tailings collection tank. The impurity removal rate was calculated to be 0.96 using formula (2), meeting the requirement of ≥0.95. The particle size of the agglomerated particles was detected to be 0.8 mm, meeting the requirements, and proceeding to the next step.

[0083] Step Seven: Multi-stage Material Consolidation and Homogenization. The processed materials from each stage are fed into a twin-shaft mixer at a mass ratio of coarse:medium-coarse:medium-fine:fine = 2:3:3:2. The mixing time is 50 minutes, and the mixing speed is 135 rpm. Samples are taken every 10 minutes for testing. The average particle size of the mixture is 2 mm, the particle size deviation is 0.4 mm, the chromium content deviation is 0.6%, the carbon content is 0.10%, and the total impurity content is 0.8%, all meeting the requirements. The mixture is then transferred to a storage silo, and the bottom vibrating discharge device and the in-silo mixing device are activated, stirring once every 30 minutes before proceeding to the next step.

[0084] Step 8: Pre-compression densification treatment. The homogenized mixture is fed into a hydraulic pre-compressor. The die size is 500mm × 500mm × 100mm, with a batch size of 55kg. A staged compression mode is used: initial pressure 12MPa, maintained for 7.5 minutes; pressure increased to 35MPa, maintained for 17.5 minutes; finally increased to 55MPa, maintained for 12.5 minutes. The die temperature is controlled at 55℃. After pre-compression, the blank is removed, and the density is tested to be 70%, compressive strength 18MPa, and porosity 28%, all meeting the requirements. After surface cleaning, proceed to the next step.

[0085] Step Nine: High-Temperature Densification Treatment and Integral Model Control. The pre-pressed green body is fed into a continuous high-temperature sintering furnace, and nitrogen gas with a purity of 99.99% is introduced at a flow rate of 6.5 m³ / h. A staged heating mode is adopted: from room temperature to 300℃, the heating rate is 5℃ / min and held for 30 minutes; from 300℃ to 800℃, the heating rate is 8℃ / min and held for 60 minutes; from 800℃ to 1250℃, the heating rate is 10℃ / min and held for 105 minutes; finally, the temperature is lowered to room temperature at a cooling rate of 6℃ / min and a slow cooling time of 135 minutes. The density at different time points is calculated using formula (3). The final density of the green body is 92%, the porosity is 8%, and the compressive strength is 45 MPa, which meets the requirements and proceeds to the next step.

[0086] Step 10: Cooling and Crushing / Shaping. The high-temperature densified billet is sent to a slow cooling chamber under nitrogen protection. The temperature is raised from room temperature to 500℃ and then lowered to room temperature at a rate of 3℃ / min for 135 minutes. After slow cooling, it is fed into an impact crusher at 1100 rpm with a discharge opening size of 1.2mm. After crushing and shaping, it is sent to a vibrating screen with screen apertures of 0.5mm, 1mm, and 2mm to grade three particle sizes. The particle size deviation of each particle size is 0.15mm, which meets the requirements and proceeds to the next step.

[0087] Step 11: Finished Product Testing and Packaging Storage. Samples of the three particle sizes were taken for testing. The results showed a carbon content of 0.09%, a chromium content of 66.2%, a total impurity content of 0.7% (including 0.4% iron and titanium impurities and 0.2% silicon and aluminum impurities), a density of 92%, uniform particle size distribution, and a compressive strength of 45 MPa. All test items met the standards. Double-layer packaging was used: an inner aluminum foil bag filled with 99.99% argon gas, and an outer woven bag, 25 kg / bag, with relevant information labeled. The products were then placed in a dedicated warehouse at a relative humidity of 25% and a temperature of 20℃, stacked 8 layers high, with a product traceability system established.

[0088] After processing in this embodiment, all performance indicators of the product meet the standards for high-end applications, with a resource utilization rate of 95.5%, a 22% reduction in comprehensive energy consumption per ton of product, an 18% reduction in production costs, a first-pass yield of 98.2%, and no wastewater or waste residue pollution, meeting the requirements for green production.

[0089] Example 2

[0090] This embodiment uses the method described above to classify, remove impurities, and densify micro-carbon ferrochrome ore from a mine in Inner Mongolia, China. The ore has a Cr2O3 content of 50%, an Fe / Cr ratio of 1.0, a carbon content of 0.08%, and a total impurity content of 2.8%, including 1.2% quartz sand, 0.9% aluminosilicate, and 0.7% iron-titanium impurities. The ore particle size is 40~180mm, and the moisture content is 11%.

[0091] Step 1: Raw Ore Pretreatment and Crushing. The selected raw ore is conveyed at a constant speed to the raw material cleaning platform using a belt conveyor. Surface soil, weeds, and large non-metallic impurities are removed through a combination of manual screening and high-pressure spraying. The spraying water pressure is controlled at 0.35 MPa, and the spraying time is 3.5 minutes per batch. After cleaning, the ore is fed into a jaw crusher for coarse crushing. The discharge opening size is adjusted to 85 mm, and the feed speed is controlled at 2.2 t / h. The coarsely crushed material is then fed into a cone crusher for medium crushing. The discharge opening size is adjusted to 32 mm, and the vibration dust collector is activated. The medium-crushed material is then fed into an impact crusher for fine crushing. The discharge opening size is adjusted to 6 mm, and the crusher speed is controlled at 1250 r / min. After crushing, the material is fed into a vibrating feeder. The moisture content is measured to be 11%, requiring no drying, and it is directly conveyed to the next step.

[0092] Step 2: Multi-level Precision Grading and Particle Size Statistical Control. The crushed material is fed into a multi-level vibrating screen, using a four-level sieving mode with screen apertures of 10mm, 5mm, 2mm, and 0.5mm, a vibration frequency of 22Hz, an amplitude of 5.5mm, and a feeding speed consistent with the vibrating feeder. After grading, samples are taken to test the particle size distribution of each grade. The grading efficiency is calculated using formula (1). The grading efficiency for coarse particles (5~10mm) is 0.94, for medium-coarse particles (2~5mm) it is 0.95, for medium-fine particles (0.5~2mm) it is 0.94, and for fine particles (<0.5mm) it is 0.96, all meeting the requirement of ≥0.92. The particle size deviations for each grade are 0.9mm for coarse particles, 0.6mm for medium-coarse particles, 0.2mm for medium-fine particles, and 0.07mm for fine particles, all meeting the requirements, and proceeding to the next step.

[0093] Step 3: Gravity Separation and Impurity Removal of Coarse-Grained Material. The coarse-grained material is fed into a spiral sluice gravity separator. The spiral sluice has a diameter of 1.5m, a pitch of 300mm, and 5 turns. The slurry concentration is adjusted to 31%, and the slurry flow rate is controlled at 1.25m / s. The coarse-grained material is mixed with water to form a slurry, which is then fed to the top of the spiral sluice. Micro-carbon ferrochrome powder falls into the concentrate collection tank, while impurities such as quartz sand fall into the tailings collection tank. After gravity separation, the material is sprayed with 0.25MPa high-pressure water for 1.2 minutes and then sent to a hot air dryer at 105℃ for 32 minutes, reducing the moisture content to 4.2%. The impurity content is measured at 1.1%, meeting the requirements, and the process proceeds to the next step.

[0094] Step 4: Magnetic separation for medium and coarse-grained materials. The medium and coarse-grained materials are fed into a high-gradient magnetic separator. The magnetic field strength is adjusted to 12500 Gauss, the magnetic field gradient is 520 T / m, the feed rate is controlled at 1.6 t / h, and the drum speed is 32 r / min. During the magnetic separation process, micro-carbon ferrochrome powder falls into the concentrate collection hopper, iron and titanium impurities fall into the weakly magnetic impurity collection hopper, and non-metallic impurities fall into the tailings collection hopper. The iron and titanium impurity content is detected to be 0.5%, which meets the requirements. The iron and titanium impurities are collected and recovered separately and proceed to the next step.

[0095] Step 5: Flotation and impurity removal of medium and fine-grained materials. Feed the medium and fine-grained materials into the flotation machine. Add water to adjust the pulp concentration to 26%, and add sodium hydroxide to adjust the pulp pH to 9.2. Stir at 160 rpm for 6 minutes. Add sodium oleate collector at a rate of 220 g / t of material, and stir for 3.5 minutes. Add pine oil frother at a rate of 55 g / t of material, and stir for 2.2 minutes. Turn on the aeration device at a rate of 0.35 m³ / (m²·min), and float for 16 minutes. The micro-carbon ferrochrome powder forms a frothy product that falls into the concentrate collection tank, while impurities fall into the tailings collection tank. After flotation, wash three times with water for 6 minutes each time, reducing the residual flotation agent to 38 mg / kg. Send the material to a hot air dryer at 95℃ for 28 minutes, reducing the moisture content to 4.5%, and proceed to the next step.

[0096] Step 6: Centrifugal Classification and Statistical Optimization of Fine-Grained Materials. The fine-grained material was fed into a high-speed centrifugal classifier, with the rotation speed adjusted to 3100 r / min and the feed rate controlled at 1.05 t / h. The classification medium was 26℃ clean water. During the centrifugal classification process, the fine-grained material and clean water were mixed in proportion to form a slurry, which was fed into the centrifugal classifier drum at a uniform speed. The centrifugal force generated by the high-speed rotation of the drum caused the fine particles of micro-carbon ferrochrome powder to be thrown to the inner wall of the drum and discharged from the discharge port with the rotation of the drum, falling into the concentrate collection tank. Due to their small mass, the fine impurity particles were subjected to weak centrifugal force and were discharged from the overflow port with the slurry, falling into the tailings collection tank, thus achieving efficient separation of fine-grained material and fine impurities. After the centrifugal classification was completed, the fine-grained micro-carbon ferrochrome powder in the concentrate collection tank was sampled and tested. The particle size distribution and impurity content were determined by a laser particle size analyzer. At the same time, the impurity removal rate was calculated by formula (2), and the result was 0.97, which is much higher than the requirement of 0.95. The particle size of the agglomerated particles was found to be 0.7 mm, which meets the standard of ≤1 mm. No dispersant needs to be added, and the process can proceed directly to the next step.

[0097] Step Seven: Multi-stage Material Consolidation and Homogenization. The coarse-grained micro-carbon ferrochrome powder from Step Three, the medium-coarse-grained micro-carbon ferrochrome powder from Step Four, the medium-fine-grained micro-carbon ferrochrome powder from Step Five, and the fine-grained micro-carbon ferrochrome powder from Step Six are fed into a twin-shaft mixing homogenizer at a uniform mass ratio of coarse:medium-coarse:medium-fine:fine = 2:3:3:2 via a belt conveyor. The mixing time is set to 45 minutes, and the stirring speed is 130 r / min. During homogenization, samples are taken every 10 minutes. The particle size distribution of the mixture is determined using a laser particle size analyzer, and the composition of the mixture is detected using an X-ray fluorescence spectrometer. The results show that the average particle size of the mixture is 1.8 mm, the particle size deviation is 0.35 mm, the chromium content deviation is 0.5%, the carbon content is 0.07%, and the total impurity content is 0.75%. All indicators meet the requirements. The homogenized mixture is fed into a storage silo with a conical structure and a vibrating discharge device at the bottom to prevent material clumping. At the same time, the mixing device inside the silo is activated and stirred every 30 minutes to ensure that the material remains uniform during storage, providing a stable raw material for subsequent pre-compression densification treatment.

[0098] Step 8: Pre-compression densification treatment. The homogenized mixture is fed into a hydraulic pre-compressor. The die size is 500mm×500mm×100mm, and the batch feed is controlled at 52kg to ensure uniform material distribution within the die, without voids or lumps. The pre-compression process uses a staged pressurization mode. The initial pressure is adjusted to 11MPa and maintained for 6 minutes to allow the material to initially form and expel some air. The pressure is then increased to 32MPa and maintained for 16 minutes to further reduce material porosity. Finally, the pressure is increased to 52MPa and maintained for 11 minutes to complete the pre-compression densification treatment. During pre-compression, the die temperature is controlled at 52℃ to ensure uniform temperature distribution and prevent localized overheating that could lead to oxidation of the micro-carbon ferrochrome powder. After pre-compression, the pressed blank is removed from the die, and the surface is cleaned to remove loose particles and impurities, ensuring a smooth and undamaged surface. The green body was tested and found to have a density of 68%, a compressive strength of 17 MPa, and a porosity of 29%, all of which meet the requirements of a density of 65%~75%, a compressive strength of ≥15 MPa, and a porosity of ≤30%. The process then proceeds to the next step.

[0099] Step Nine: High-Temperature Densification Treatment and Integral Model Control. The pre-pressed billet is fed into a continuous high-temperature sintering furnace. The sintering furnace is heated by natural gas, and nitrogen gas with a purity ≥99.99% is introduced into the furnace as a protective gas. The nitrogen flow rate is controlled at 6 m³ / h to prevent the micro-carbon ferrochrome powder from oxidizing at high temperatures. The high-temperature densification process adopts a staged heating mode. The specific heating process is as follows: heating from room temperature to 300℃ at a heating rate of 5℃ / min and holding for 30 minutes to completely remove residual moisture from the billet; heating from 300℃ to 800℃ at a heating rate of 8℃ / min and holding for 60 minutes to remove residual flotation agent and trace impurities from the billet; heating from 800℃ to 1220℃ at a heating rate of 10℃ / min and holding for 100 minutes to complete the high-temperature densification sintering; finally, cooling from 1220℃ to room temperature at a cooling rate of 6℃ / min to avoid cracking of the billet due to excessively rapid cooling. During the high-temperature densification process, the density of the green body at different time points is calculated by formula (3), and the heating rate and holding time are adjusted in real time to ensure that the final green body density reaches 91%, porosity 9%, and compressive strength 42MPa, which meets the requirements of various indicators, and then proceeds to the next step.

[0100] Step 10: Cooling and Crushing / Shaping. The densified billet is removed from the high-temperature sintering furnace and immediately placed in a slow cooling chamber. The chamber is protected by nitrogen, with the nitrogen flow rate matching that of the sintering furnace. The cooling temperature is gradually increased from room temperature to 500℃, matching the initial temperature of the billet. It is then cooled to room temperature at a rate of 3℃ / min for 130 minutes. During slow cooling, the billet temperature is monitored in real time to ensure a uniform temperature decrease, eliminating internal thermal stress and preventing cracking. After slow cooling, the billet is fed into an impact crusher for crushing and shaping. The crusher speed is adjusted to 1050 r / min, and the discharge port size is adjusted to 1.0 mm. A vibration dust collector is activated during crushing to reduce dust pollution and prevent environmental contamination. After crushing and shaping, the material is fed into a vibrating screen with screen apertures of 0.5mm, 1mm, and 2mm. The screen is graded into three grades of micro-carbon ferrochrome powder: fine (0.5~1mm), medium (1~2mm), and coarse (around 2mm). The particle size deviation of each grade is 0.14mm, which meets the requirement of ≤0.2mm, and the material proceeds to the next step.

[0101] Step 11: Finished Product Testing and Packaging Storage. Samples of the finished products in three particle sizes were taken and tested, covering key indicators such as carbon content, chromium content, impurity content, density, particle size distribution, and compressive strength. Specifically, carbon content was measured using a high-frequency infrared carbon-sulfur analyzer, with a result of 0.07%; chromium content was measured using X-ray fluorescence spectrometry, with a result of 67.5%; impurity content was measured using inductively coupled plasma atomic emission spectrometry, with a total impurity content of 0.65%, including 0.35% iron-titanium impurities and 0.18% silicon-aluminum impurities; density was measured using the water displacement method, with a result of 91%; particle size distribution was measured using a laser particle size analyzer, showing uniform distribution; and compressive strength was measured using a universal testing machine, with a result of 42 MPa. All test items met high-end application standards. A double-layer packaging method was used: an inner aluminum foil bag and an outer woven bag, with a packaging specification of 25 kg / bag. During packaging, argon gas with a purity of ≥99.99% was filled into the aluminum foil bag to ensure no air inside the packaging and prevent product oxidation. After packaging, the product name, particle size specification, production date, inspection certificate, and batch number are clearly labeled on the woven bags. The packaged products are then placed in a dedicated storage warehouse, which is kept dry and well-ventilated, with relative humidity controlled at 28% and temperature at 18℃. Products are stacked no more than eight layers high to prevent crushing and damage. Simultaneously, a comprehensive product traceability system is established, with detailed records of production parameters and test results for each batch to ensure product quality traceability.

[0102] After processing in this embodiment, all performance indicators of the product meet the requirements for use in high-end stainless steel and high-temperature alloy fields, with a resource utilization rate of 96.2%, an improvement of 12% compared to existing processes; comprehensive energy consumption per ton of product is reduced by 23%, and production costs are reduced by 17%; the production process achieves continuous operation, increasing production efficiency by 35%, and the first-pass yield of products reaches 98.5%; the entire processing mainly uses physical impurity removal, and the flotation process uses environmentally friendly flotation agents, resulting in no wastewater or waste residue pollution, dust emissions that meet national environmental protection standards, and a carbon footprint as low as 0.14 tons of CO2e / ton, fully complying with the "dual carbon" strategy requirements. At the same time, it realizes the recycling of iron and titanium impurities, further improving resource utilization efficiency, and has significant economic, environmental and social benefits.

[0103] Example 3

[0104] This embodiment uses the method described above to classify, remove impurities from, and densify imported micro-carbon ferrochrome ore from Kazakhstan. The ore has a Cr2O3 content of 52%, an Fe / Cr ratio of 0.9, a carbon content of 0.06%, and a total impurity content of 2.5%, including 1.0% quartz sand, 0.8% aluminosilicates, and 0.7% iron-titanium impurities. The ore particle size is 60~220mm, and the moisture content is 9%.

[0105] Step 1: Raw Ore Pretreatment and Crushing. The aforementioned high-grade, low-carbon ferrochrome raw ore is selected and conveyed at a constant speed to the raw material cleaning platform using a belt conveyor. A combination of manual screening and high-pressure spraying is used to remove surface dirt, weeds, and large non-metallic impurities. The spraying water pressure is controlled at 0.45 MPa, and the spraying time is 4.5 minutes per batch of raw material, ensuring no visible impurities adhere to the surface of the raw ore. After cleaning, the raw ore is fed into a jaw crusher for coarse crushing. The discharge opening size is adjusted to 95 mm, and the feed speed is controlled at 2.8 t / h to avoid overloading the crusher or insufficient crushing due to excessive feeding speed. The coarsely crushed material is then conveyed via belt conveyor to a cone crusher for medium crushing. The discharge opening size is adjusted to 38 mm. During the medium crushing process, the crusher's vibration dust removal device is activated to reduce dust pollution and ensure the production environment meets standards. The medium-crushed material is then fed into an impact crusher for fine crushing. The discharge port size is adjusted to 8mm, and the crusher speed is controlled at 1400r / min. The principle of layered crushing is used to ensure uniform particle size and prevent over-crushing or excessive particle size. After crushing, the material is fed into a vibrating feeder. The moisture content is tested and found to be 9%, meeting the requirement of 8%~12%. No drying treatment is required; the material is directly and uniformly conveyed to the next step.

[0106] Step Two: Multi-stage Precision Grading and Particle Size Statistical Control. The material crushed in Step One is fed into a multi-stage vibrating screen, employing a four-stage grading mode. The screen apertures are set to 10mm, 5mm, 2mm, and 0.5mm, respectively, resulting in four grades: coarse (5~10mm), medium-coarse (2~5mm), medium-fine (0.5~2mm), and fine (<0.5mm). During each grading stage, the vibration frequency of the vibrating screen is controlled at 28Hz, the amplitude at 7mm, and the feeding speed is kept consistent with that of the vibrating feeder in Step One. This ensures uniform material distribution on the screen, prevents screen clogging, and improves grading efficiency. After grading, samples of each grade of material were taken for testing. A laser particle size analyzer was used to determine the particle size distribution of each grade of material. At the same time, formula (1) was introduced to calculate the grading efficiency. The calculation showed that the grading efficiency of coarse particles was 0.95, that of medium-coarse particles was 0.96, that of medium-fine particles was 0.95, and that of fine particles was 0.97, all of which met the requirement of ≥0.92. The particle size deviation of each grade of material was also detected. The deviations were 0.8 mm for coarse particles, 0.5 mm for medium-coarse particles, 0.18 mm for medium-fine particles, and 0.06 mm for fine particles, all of which met the particle size deviation control requirements, and the process proceeded to the next step.

[0107] Step 3: Gravity Separation and Impurity Removal of Coarse-Grained Material. The coarse-grained material obtained in Step 2 is fed into a spiral sluice gravity separator. The spiral sluice diameter is 1.5m, the pitch is 300mm, the number of turns is 5, the slurry concentration is adjusted to 34%, and the slurry flow rate is controlled at 1.4m / s. During the gravity separation process, the coarse-grained material is mixed with water in a certain proportion to form a slurry, which is then uniformly fed into the top of the spiral sluice by a submersible pump. Under the combined action of gravity and centrifugal force, the slurry flows downward along the spiral blades. Due to the high density of the micro-carbon ferrochrome powder (4.3~4.8g / cm³), it settles quickly, sliding along the inner side of the spiral blades and eventually falling into the concentrate collection tank at the bottom of the sluice. Non-metallic impurities such as quartz sand and feldspar have lower densities (2.6~2.8g / cm³), settle slowly, and slide along the outer side of the spiral blades, falling into the tailings collection tank, thus achieving efficient separation of coarse-grained material and impurities. After gravity separation, the coarse-grained micro-carbon ferrochrome powder in the concentrate collection tank is subjected to high-pressure water spray cleaning. The water pressure is controlled at 0.35 MPa, and the spraying time is 1.8 minutes to remove fine impurities and slurry adhering to the surface. After cleaning, the coarse-grained micro-carbon ferrochrome powder is sent to a hot air dryer. The drying temperature is controlled at 115℃, and the drying time is 38 minutes to ensure that the moisture content is reduced to below 4.0%. The impurity content of the coarse-grained micro-carbon ferrochrome powder is tested to be 1.0%, which meets the requirement of ≤1.5%, and proceeds to the next step.

[0108] Step 4: Magnetic separation to remove impurities from medium and coarse particles. The medium and coarse particles obtained in Step 2 are fed into a high-gradient magnetic separator. The separator uses a neodymium iron boron permanent magnet system, with the magnetic field strength adjusted to 14,000 Gauss, the magnetic field gradient to 580 T / m, the feed rate controlled at 1.9 t / h, and the drum rotation speed at 38 r / min. During the magnetic separation process, the medium and coarse particles enter the magnetic field area of ​​the separator evenly. Micro-carbon ferrochrome powder, as a strongly magnetic material, is strongly adsorbed onto the drum surface by the magnetic field and falls into the concentrate collection hopper under gravity as the drum rotates to the non-magnetic field area. Iron-titanium magnetic impurities are weakly magnetic and are slightly adsorbed by the magnetic field. They rotate to the weak magnetic field area and are scraped off by the scraper, falling into the weak magnetic impurity collection hopper. Non-metallic impurities are non-magnetic and not affected by the magnetic field force. They fall into the tailings collection hopper under the action of gravity and centrifugal force, achieving precise separation of the three. After magnetic separation, samples of medium- and coarse-grained micro-carbon ferrochrome powder in the concentrate collection hopper were taken for testing, with a focus on detecting the content of iron and titanium impurities. The test result was 0.45%, meeting the requirement of ≤0.8%. The iron and titanium impurities in the weakly magnetic impurity collection hopper were collected separately for subsequent recycling to further improve resource utilization before proceeding to the next step.

[0109] Step 5: Flotation and Impurity Removal of Medium and Fine-Grained Materials. The medium and fine-grained materials obtained in Step 2 are fed into a flotation machine. First, water is added to adjust the pulp concentration to 28%. Then, sodium hydroxide is added as a modifier to adjust the pulp pH to 9.8. The mixture is stirred evenly at a speed of 185 rpm for 7 minutes. The modifier alters the surface charge of the micro-carbon ferrochrome powder and impurities, making the micro-carbon ferrochrome powder hydrophobic and the impurities hydrophilic, thus laying the foundation for subsequent flotation separation. Next, sodium oleate is added as a collector at a rate of 280 g / t of material, and the stirring time is 4.5 minutes. The collector selectively adsorbs onto the surface of the micro-carbon ferrochrome powder, enhancing its hydrophobicity and making it easier to adhere to the bubble surface. Finally, pine oil, a frother, is added at a rate of 75 g / t of material, and the stirring time is 2.8 minutes. The frother generates a large number of uniform bubbles in the pulp, providing a stable carrier for the flotation of the micro-carbon ferrochrome powder. During the flotation process, the aeration device of the flotation machine is turned on, and the aeration rate is controlled at 0.45 m³ / (m²·min). The flotation time is 18 minutes. Due to its hydrophobic surface, the micro-carbon ferrochrome powder adheres to the surface of the bubbles and rises with the bubbles to the surface of the slurry, forming a frothy product, which is scraped into the concentrate collection tank by a scraper. Impurities such as aluminosilicates remain in the slurry due to their hydrophilic surface and are eventually discharged from the bottom of the flotation machine into the tailings collection tank. After flotation, the medium and fine-grained micro-carbon ferrochrome powder in the concentrate collection tank undergoes de-reagent treatment by washing it four times with clean water, each time for 7 minutes, to ensure that the residual flotation reagent is reduced to below 35 mg / kg. After de-reagent treatment, the powder is sent to a hot air dryer, where the drying temperature is controlled at 105℃ and the drying time is 32 minutes, reducing the moisture content to 4.3%, before proceeding to the next step.

[0110] Step Six: Centrifugal Classification and Statistical Optimization of Fine-Grained Materials. The fine-grained material obtained in Step Two is fed into a high-speed centrifugal classifier. The speed of the centrifugal classifier is adjusted to 3400 r / min, the feed rate is controlled at 1.15 t / h, and 28℃ clean water is used as the classification medium to ensure stable classification results. During the centrifugal classification process, the fine-grained material is mixed with clean water to form a slurry, which is fed into the drum of the centrifugal classifier. The high-speed rotation of the drum generates a strong centrifugal force. The magnitude of the centrifugal force is directly proportional to the particle mass. The fine particles of micro-carbon ferrochrome powder have a larger mass and are subjected to a greater centrifugal force, so they are thrown to the inner wall of the drum and discharged through the discharge port with the rotation of the drum, falling into the concentrate collection tank. The fine impurity particles have a smaller mass and are subjected to a smaller centrifugal force, so they are discharged from the overflow port with the slurry and fall into the tailings collection tank, achieving complete separation of fine-grained materials and fine impurities. After centrifugal classification, fine-grained micro-carbon ferrochrome powder in the concentrate collection tank was sampled and tested. Its particle size distribution and impurity content were determined using a laser particle size analyzer. At the same time, the impurity removal rate was calculated using formula (2), and the result was 0.98, which meets the requirement of ≥0.95. The particle size of the agglomerated particles was found to be 0.6 mm, which meets the standard of ≤1 mm. No dispersant was required, and the process proceeded to the next step.

[0111] Step Seven: Multi-stage Material Consolidation and Homogenization. The coarse-grained micro-carbon ferrochrome powder from Step Three, the medium-coarse-grained micro-carbon ferrochrome powder from Step Four, the medium-fine-grained micro-carbon ferrochrome powder from Step Five, and the fine-grained micro-carbon ferrochrome powder from Step Six are fed into a twin-shaft mixing homogenizer via belt conveyors at a mass ratio of coarse:medium-coarse:medium-fine:fine = 2:3:3:2. The mixing time is controlled at 55 minutes, and the mixing speed is 140 r / min. During homogenization, samples are taken every 10 minutes. The particle size distribution of the mixture is determined using a laser particle size analyzer, and the composition of the mixture is detected using an X-ray fluorescence spectrometer. The average particle size of the mixture is controlled at 2.2 mm, the particle size deviation is 0.45 mm, the chromium content deviation is 0.7%, the carbon content is controlled at 0.06%, and the total impurity content is 0.7%, all meeting the requirements. After homogenization, the mixture is sent to the storage silo, which has a conical structure and a vibrating discharge device at the bottom to prevent the material from clumping. At the same time, the stirring device inside the silo is turned on and stirred once every 30 minutes to ensure that the material remains uniform during storage before proceeding to the next step.

[0112] Step 8: Pre-compression densification treatment. The homogenized mixture from Step 7 is fed into a hydraulic pre-compressor. The pre-compressor's die dimensions are 500mm × 500mm × 100mm, and the feed rate is controlled at 58kg per batch to ensure uniform material distribution within the die, without voids or lumps. During pre-compression, a staged pressurization mode is used. The initial pressure is adjusted to 14MPa and maintained for 9 minutes to allow the material to initially form; then the pressure is increased to 38MPa and maintained for 19 minutes to further reduce material porosity; finally, the pressure is increased to 58MPa and maintained for 14 minutes to complete the pre-compression densification treatment. During pre-compression, the die temperature is controlled at 58℃, ensuring uniform temperature distribution and preventing localized overheating that could lead to material oxidation. After pre-pressing, the pressed blank is removed from the mold and its density, compressive strength and porosity are tested. The density is 73%, the compressive strength is 19MPa and the porosity is 26%, all of which meet the requirements. The surface of the blank is cleaned to remove loose particles and impurities, ensuring that the surface of the blank is flat and undamaged, and then proceeds to the next step.

[0113] Step Nine: High-Temperature Densification Treatment and Integral Model Control. The pre-pressed billet from Step Eight is fed into a continuous high-temperature sintering furnace. The furnace is heated by natural gas, and nitrogen gas with a purity ≥99.99% is introduced into the furnace as a protective gas. The nitrogen flow rate is controlled at 7.5 m³ / h to prevent oxidation of the micro-carbon ferrochrome powder. The high-temperature densification process adopts a staged heating mode. The specific heating process is as follows: heating from room temperature to 300℃ at a heating rate of 5℃ / min and holding for 30 minutes to remove residual moisture from the billet; heating from 300℃ to 800℃ at a heating rate of 8℃ / min and holding for 60 minutes to remove residual flotation agent and trace impurities from the billet; heating from 800℃ to 1280℃ at a heating rate of 10℃ / min and holding for 115 minutes to complete the high-temperature densification sintering; finally, cooling from 1280℃ to room temperature at a cooling rate of 6℃ / min to avoid cracking of the billet due to excessively rapid cooling. During the high-temperature densification process, formula (3) is introduced to quantify the density change during sintering, and the heating rate and holding time are precisely controlled. The density of the green body at different time points is calculated according to the formula to ensure that the final green body density is ≥90%. After testing, the final green body density is 93%, porosity is 7%, and compressive strength is 48MPa, which meets the requirements and proceeds to the next step.

[0114] Step 10: Cooling and Crushing / Shaping. The high-temperature densified billet is removed from the high-temperature sintering furnace and placed in a slow cooling chamber for slow cooling. The chamber is protected by nitrogen, with the nitrogen flow rate consistent with that of the sintering furnace. The cooling temperature is gradually increased from room temperature to 500℃ to match the initial temperature of the billet, then reduced to room temperature at a rate of 3℃ / min for 145 minutes. During slow cooling, the billet temperature is monitored in real time to ensure a uniform temperature decrease, eliminating internal thermal stress and preventing cracking. After slow cooling, the billet is fed into an impact crusher for crushing and shaping. The crusher speed is adjusted to 1150 r / min, and the discharge port size is adjusted to 1.5 mm. A vibration dust collector is activated during crushing to reduce dust pollution. After crushing and shaping, the material is fed into a vibrating screen with screen apertures of 0.5mm, 1mm, and 2mm. The screens are graded into three particle sizes of micro-carbon ferrochrome powder: fine (0.5~1mm), medium (1~2mm), and coarse (around 2mm). The particle size deviation of each particle size product is 0.16mm, which meets the requirement of ≤0.2mm, and the material proceeds to the next step.

[0115] Step 11: Finished Product Testing and Packaging Storage. Samples of the three particle sizes were taken and tested separately. Tests included carbon content, chromium content, impurity content, density, particle size distribution, and compressive strength. Carbon content was tested using a high-frequency infrared carbon-sulfur analyzer, with a result of 0.06%; chromium content was tested using X-ray fluorescence spectrometry, with a result of 68.8%; impurity content was tested using inductively coupled plasma atomic emission spectrometry, with a total impurity content of 0.6%, including 0.3% iron-titanium impurities and 0.15% silicon-aluminum impurities; density was tested using the water displacement method, with a result of 93%; particle size distribution was tested using a laser particle size analyzer, showing uniform distribution; and compressive strength was tested using a universal testing machine, with a result of 48 MPa. All test items met high-end application standards and exceeded expectations. Double-layer packaging was used: an inner aluminum foil bag and an outer woven bag, with a packaging size of 25 kg / bag. During packaging, argon gas with a purity of ≥99.99% was filled into the aluminum foil bag to ensure no air was inside the packaging and to prevent product oxidation. After packaging, the product name, particle size specification, production date, inspection certificate, batch number, and other information are labeled on the woven bags. The packaged products are then placed in a dedicated storage warehouse, which is kept dry and well-ventilated, with relative humidity controlled at 22% and temperature at 15℃. The products are stacked no more than seven layers high to prevent crushing and damage. Simultaneously, a product traceability system is established to record detailed production process parameters and test results for each batch of products, ensuring product quality traceability and providing downstream customers with reliable high-end micro-carbon ferrochrome powder products.

[0116] After processing in this embodiment, all performance indicators of the product meet the international high-end micro-carbon ferrochrome powder standards, and it can be directly used in the production of high-end stainless steel and high-temperature alloys. The resource utilization rate reaches 96.8%, which is 13% higher than the existing process. The comprehensive energy consumption per ton of product is reduced by 24%, and the production cost is reduced by 19%. The production efficiency is increased by 38%, and the first-pass yield rate of the product reaches 99.0%. There is no wastewater or waste residue pollution in the production process, and the dust emission meets the national environmental protection standards. The carbon footprint is as low as 0.13 tons of CO2e / ton, which meets the requirements of the "dual carbon" strategy. At the same time, the iron and titanium impurities are recycled and utilized, which further improves the economic benefits and resource utilization efficiency, and has extremely strong industrial promotion value.

[0117] Example 4

[0118] This embodiment uses the method described above to classify, remove impurities from, and densify micro-carbon ferrochrome ore from a mine in Xinjiang, China. The ore has a Cr2O3 content of 49%, an Fe / Cr ratio of 1.15, a carbon content of 0.10%, and a total impurity content of 3.0%, including 1.3% quartz sand, 0.9% aluminosilicates, and 0.8% iron-titanium impurities. The ore particle size is 45~190mm, and the moisture content is 12%.

[0119] Step 1: Raw Ore Pretreatment and Crushing. The aforementioned low-carbon ferrochrome ore is selected and conveyed at a constant speed to the raw material cleaning platform using a belt conveyor. A combination of manual screening and high-pressure spraying is used to remove surface dirt, weeds, and large non-metallic impurities. The spraying water pressure is controlled at 0.3 MPa, and the spraying time is 3 minutes per batch of raw material, ensuring no visible impurities adhere to the ore surface. After cleaning, the ore is fed into a jaw crusher for coarse crushing. The discharge opening size is adjusted to 80 mm, and the feed rate is controlled at 2 t / h to avoid overloading the crusher or insufficient crushing due to excessive feeding speed. The coarsely crushed material is then conveyed via belt conveyor to a cone crusher for medium crushing. The discharge opening size is adjusted to 30 mm. During the medium crushing process, the crusher's vibration dust removal device is activated to reduce dust pollution. The medium-crushed material is then fed into an impact crusher for fine crushing. The discharge port size for fine crushing is adjusted to 5mm, and the crusher speed is controlled at 1200r / min during fine crushing. The principle of layered crushing is used to ensure uniform particle size of the crushed material, with no excessively large particles or over-crushing. After crushing, the material is fed into a vibrating feeder. The moisture content of the material is tested and found to be 12%, meeting the requirement of 8%~12%. Therefore, there is no need to turn on the hot air drying device; the material is directly and uniformly conveyed to the next step.

[0120] Step Two: Multi-stage Precision Grading and Particle Size Statistical Control. The material crushed in Step One is fed into a multi-stage vibrating screen, employing a four-stage screening mode. The screen apertures are set to 10mm, 5mm, 2mm, and 0.5mm, respectively, resulting in four grades: coarse (5~10mm), medium-coarse (2~5mm), medium-fine (0.5~2mm), and fine (<0.5mm). During each screening stage, the vibration frequency of the vibrating screen is controlled at 20Hz, the amplitude at 5mm, and the feeding speed is kept consistent with that of the vibrating feeder in Step One, ensuring uniform material distribution on the screen and preventing screen clogging. After grading, samples of each grade of material were taken for testing. The particle size distribution of each grade of material was determined using a laser particle size analyzer. At the same time, the grading efficiency was calculated using formula (1). The grading efficiency for coarse particles was 0.92, for medium-coarse particles it was 0.93, for medium-fine particles it was 0.92, and for fine particles it was 0.95, all of which met the requirement of ≥0.92. The particle size deviation of each grade of material was tested. The deviations were 1.2 mm for coarse particles, 0.8 mm for medium-coarse particles, 0.3 mm for medium-fine particles, and 0.1 mm for fine particles, all of which met the particle size deviation control requirements, and the process proceeded to the next step.

[0121] Step 3: Gravity Separation and Impurity Removal of Coarse-Grained Material. The coarse-grained material obtained in Step 2 is fed into a spiral sluice gravity separator. The spiral sluice diameter is 1.5m, the pitch is 300mm, the number of turns is 5, the slurry concentration is adjusted to 30%, and the slurry flow rate is controlled at 1.2m / s. During the gravity separation process, the coarse-grained material is mixed with water in a certain proportion to form a slurry, which is then uniformly pumped into the top of the spiral sluice. Under the action of gravity and centrifugal force, the slurry flows downward along the spiral blades. The micro-carbon ferrochrome powder has a higher density and a faster settling velocity, sliding along the inner side of the spiral blades and falling into the concentrate collection tank. The impurities such as quartz sand and feldspar have a lower density and a slower settling velocity, sliding along the outer side of the spiral blades and falling into the tailings collection tank, thus achieving the separation of coarse-grained material from impurities. After the gravity separation is completed, the coarse-grained micro-carbon ferrochrome powder in the concentrate collection tank is washed with high-pressure water spray. The water pressure is controlled at 0.2MPa, and the spraying time is 1 minute to remove the fine-grained impurities and slurry adhering to the surface. After cleaning, the coarse-grained micro-carbon ferrochrome powder is fed into a hot air dryer. The drying temperature is controlled at 100℃, and the drying time is 30 minutes to ensure that the moisture content is reduced to below 5%. The impurity content of the coarse-grained micro-carbon ferrochrome powder is tested and found to be 1.5%, which meets the requirement of ≤1.5%, and proceeds to the next step.

[0122] Step 4: Magnetic separation to remove impurities from medium and coarse particles. The medium and coarse particles obtained in Step 2 are fed into a high-gradient magnetic separator. The separator uses a neodymium iron boron permanent magnet system, with the magnetic field strength adjusted to 12,000 Gauss, the magnetic field gradient to 500 T / m, the feed rate controlled at 1.5 t / h, and the drum rotation speed at 30 r / min. During the magnetic separation process, the medium and coarse particles enter the magnetic field area of ​​the separator evenly. Micro-carbon ferrochrome powder, as a strongly magnetic material, is strongly adsorbed onto the drum surface by the magnetic field and rotates with the drum to the non-magnetic field area, falling into the concentrate collection hopper under the action of gravity. Iron-titanium magnetic impurities have weaker magnetism and are slightly adsorbed by the magnetic field. They rotate with the drum to the weak magnetic field area, are scraped off by the scraper, and fall into the weak magnetic impurity collection hopper. Non-metallic impurities are non-magnetic and are not affected by the magnetic field force, falling into the tailings collection hopper, thus achieving the separation of the three. After magnetic separation, the medium and coarse-grained micro-carbon ferrochrome powder in the concentrate collection hopper is sampled and tested. The iron and titanium impurity content is 0.8%, which meets the requirement of ≤0.8%. The weakly magnetic impurities are collected and recovered separately and proceed to the next step.

[0123] Step 5: Flotation and impurity removal of medium and fine-grained materials. The medium and fine-grained materials obtained in Step 2 are fed into the flotation machine. First, water is added to adjust the pulp concentration to 25%. Then, sodium hydroxide is added to adjust the pH of the pulp to 9. The mixture is stirred evenly at a speed of 150 r / min for 5 minutes. Next, sodium oleate is added as a collector at a rate of 200 g / t of material, and the mixture is stirred for 3 minutes. The collector selectively adsorbs onto the surface of the micro-carbon ferrochrome powder, enhancing its hydrophobicity. Finally, pine oil is added as a frother at a rate of 50 g / t of material, and the mixture is stirred for 2 minutes. The frother generates a large number of uniform bubbles in the pulp. During the flotation process, the aeration device is turned on, and the aeration rate is controlled at 0.3 m³ / (m²·min). The flotation time is 15 minutes. The micro-carbon ferrochrome powder adheres to the surface of the bubbles and rises with them to form a frothy product, which is scraped into the concentrate collection tank. Impurities remain in the pulp and are discharged from the bottom of the flotation machine. After flotation, the concentrate undergoes de-reagent treatment by washing it three times with clean water for 5 minutes each time, reducing the residual flotation reagent to 48 mg / kg. After de-reagent treatment, the concentrate is sent to a hot air dryer at a temperature controlled at 90℃ for 25 minutes, reducing the moisture content to below 5%, before proceeding to the next step.

[0124] Step Six: Centrifugal Classification and Statistical Optimization of Fine-Grained Materials. The fine-grained materials obtained in Step Two are fed into a high-speed centrifugal classifier. The rotation speed is adjusted to 3000 r / min, the feed rate is controlled at 1 t / h, and 25℃ clean water is used as the classification medium. During the centrifugal classification process, the fine-grained materials are mixed with clean water to form a slurry, which is fed into the drum. The high-speed rotation of the drum generates centrifugal force, and the fine particles of micro-carbon ferrochrome powder are thrown to the inner wall of the drum and fall into the concentrate collection tank. Fine impurities are discharged from the overflow port with the slurry and fall into the tailings collection tank. After the centrifugal classification is completed, samples are taken for testing. The impurity removal rate is calculated using formula (2) to be 0.95, which meets the requirements. The particle size of the agglomerated particles is 1.0 mm, which meets the standard of ≤1 mm, and the process proceeds to the next step.

[0125] Step Seven: Multi-stage Material Consolidation and Homogenization. The materials processed in Steps Three, Four, Five, and Six are combined at a mass ratio of coarse:medium-coarse:medium-fine:fine = 2:3:3:2 and fed into a twin-shaft mixer homogenizer. The mixing time is controlled at 40 minutes, and the mixing speed is 120 rpm. During homogenization, samples are taken every 10 minutes for testing. The average particle size of the mixture is 1 mm, the particle size deviation is 0.5 mm, the chromium content deviation is 0.8%, the carbon content is 0.09%, and the total impurity content is 1.0%, all meeting the requirements. After homogenization, the mixture is transferred to a storage silo. The bottom vibrating discharge device and the in-silo mixing device are activated, and the mixture is stirred every 30 minutes to ensure uniformity before proceeding to the next step.

[0126] Step 8: Pre-compression densification treatment. The homogenized mixture is fed into a hydraulic pre-compressor. The die size is 500mm × 500mm × 100mm, with a batch size of 50kg. A staged pressurization mode is used: initial pressure 10MPa, maintained for 5 minutes; pressure increased to 30MPa, maintained for 15 minutes; finally increased to 50MPa, maintained for 10 minutes. The die temperature is controlled at 50℃. After pre-compression, the blank is removed, and the density is tested to be 65%, compressive strength 15MPa, and porosity 30%, all meeting the requirements. After surface cleaning, proceed to the next step.

[0127] Step Nine: High-Temperature Densification Treatment and Integral Model Control. The pre-pressed green body is fed into a continuous high-temperature sintering furnace, and nitrogen gas with a purity of 99.99% is introduced at a flow rate of 5 m³ / h. A staged heating mode is adopted: from room temperature to 300℃, the heating rate is 5℃ / min and held for 30 minutes; from 300℃ to 800℃, the heating rate is 8℃ / min and held for 60 minutes; from 800℃ to 1200℃, the heating rate is 10℃ / min and held for 90 minutes; and the temperature is lowered to room temperature at a cooling rate of 6℃ / min. The density is calculated using formula (3). The final density of the green body is 90%, the porosity is 10%, and the compressive strength is 40 MPa, which meets the requirements. Proceed to the next step.

[0128] Step 10: Cooling and Crushing / Shaping. The high-temperature densified billet is sent to a slow cooling chamber under nitrogen protection. The slow cooling temperature is raised from room temperature to 500℃, then lowered to room temperature at a rate of 3℃ / min for 120 minutes. After slow cooling, it is fed into an impact crusher at 1000 rpm with a discharge port size of 0.5mm. After crushing and shaping, it is sent to a vibrating screen with screen apertures of 0.5mm, 1mm, and 2mm to classify the product into three particle sizes. The particle size deviation of each particle size is 0.2mm, which meets the requirements, and the process proceeds to the next step.

[0129] Step 11: Finished Product Testing and Packaging Storage. Samples of the three particle sizes were taken for testing. The results showed a carbon content of 0.08%, a chromium content of 65.5%, a total impurity content of 1.0% (including 0.5% iron and titanium impurities and 0.3% silicon and aluminum impurities), a density of 90%, uniform particle size distribution, and a compressive strength of 40 MPa. All test items met the standards. Double-layer packaging was used: an inner aluminum foil bag filled with 99.99% argon gas, and an outer woven bag, 25 kg / bag, with relevant information labeled. The products were then placed in a dedicated warehouse with a relative humidity of 30%, a temperature of 10℃, and a stacking height of 10 layers. A product traceability system was established.

[0130] After processing in this embodiment, all performance indicators of the product meet the high-end application standards, with a resource utilization rate of 95.0%, a 20% reduction in comprehensive energy consumption per ton of product, a 15% reduction in production costs, a 98.0% first-pass yield, and no wastewater or waste residue pollution. It meets the requirements of green production, is suitable for the processing needs of medium- and high-grade raw ore in China, and has strong practicality and promotion value.

[0131] Example 5

[0132] This embodiment uses the method described above to classify, remove impurities from, and densify imported Indian micro-carbon ferrochrome ore. The ore has a Cr2O3 content of 51%, an Fe / Cr ratio of 0.95, a carbon content of 0.07%, and a total impurity content of 2.7%, including 1.1% quartz sand, 0.8% aluminosilicates, and 0.8% iron-titanium impurities. The ore particle size is 55~210mm, and the moisture content is 8%.

[0133] Step 1: Raw Ore Pretreatment and Crushing. The selected raw ore is conveyed at a constant speed to the raw material cleaning platform using a belt conveyor. A combination of manual screening and high-pressure spraying is used to remove surface dirt, weeds, and large non-metallic impurities. The spraying water pressure is controlled at 0.5 MPa, and the spraying time is 5 minutes per batch of raw material, ensuring no visible impurities adhere to the surface of the raw ore. After cleaning, the raw ore is fed into a jaw crusher for coarse crushing. The discharge opening size is adjusted to 100 mm, and the feed speed is controlled at 3 t / h to avoid overloading the crusher or insufficient crushing due to excessive feeding speed. The coarsely crushed material is then conveyed to a cone crusher for medium crushing via a belt conveyor. The discharge opening size is adjusted to 40 mm. During the medium crushing process, the crusher's vibration dust removal device is activated to reduce dust pollution. The material after medium crushing is then fed into an impact crusher for fine crushing. The discharge port size for fine crushing is adjusted to 10mm, and the crusher speed is controlled at 1500r / min during fine crushing. The principle of layered crushing is adopted to ensure uniform particle size of the crushed material, with no excessively large particles or over-crushing. After crushing, the material is fed into a vibrating feeder. The moisture content of the material is tested and found to be 8%, meeting the requirement of 8%~12%. No drying is required, and it is directly conveyed to the next step.

[0134] Step Two: Multi-stage Precision Grading and Particle Size Statistical Control. The material crushed in Step One is fed into a multi-stage vibrating screen, employing a four-stage screening mode. The screen apertures are set to 10mm, 5mm, 2mm, and 0.5mm, respectively, resulting in four grades: coarse (5~10mm), medium-coarse (2~5mm), medium-fine (0.5~2mm), and fine (<0.5mm). During each screening stage, the vibration frequency of the vibrating screen is controlled at 30Hz, the amplitude at 8mm, and the feeding speed is kept consistent with that of the vibrating feeder in Step One, ensuring uniform material distribution on the screen and preventing screen clogging. After grading, samples of each grade of material were taken for testing. The particle size distribution of each grade of material was determined using a laser particle size analyzer. At the same time, the grading efficiency was calculated using formula (1). The grading efficiency for coarse particles was 0.95, for medium-coarse particles it was 0.96, for medium-fine particles it was 0.95, and for fine particles it was 0.97, all of which met the requirement of ≥0.92. The particle size deviation of each grade of material was tested. The deviations were 0.8 mm for coarse particles, 0.5 mm for medium-coarse particles, 0.2 mm for medium-fine particles, and 0.06 mm for fine particles, all of which met the requirements, and the process proceeded to the next step.

[0135] Step 3: Gravity Separation and Impurity Removal of Coarse-Grained Material. The coarse-grained material obtained in Step 2 is fed into a spiral sluice gravity separator. The spiral sluice diameter is 1.5m, the pitch is 300mm, the number of turns is 5, the slurry concentration is adjusted to 35%, and the slurry flow rate is controlled at 1.5m / s. During the gravity separation process, the coarse-grained material is mixed with water in a certain proportion to form a slurry, which is then uniformly pumped into the top of the spiral sluice. Under the action of gravity and centrifugal force, the slurry flows downward along the spiral blades. The micro-carbon ferrochrome powder has a higher density and a faster settling velocity, sliding along the inner side of the spiral blades and falling into the concentrate collection tank. Impurities such as quartz sand and feldspar have a lower density and a slower settling velocity, sliding along the outer side of the spiral blades and falling into the tailings collection tank, thus achieving the separation of coarse-grained material from impurities. After the gravity separation is completed, the coarse-grained micro-carbon ferrochrome powder in the concentrate collection tank is subjected to high-pressure water spray cleaning. The water pressure is controlled at 0.4MPa, and the spraying time is 2 minutes to remove the fine-grained impurities and slurry adhering to the surface. After cleaning, the coarse-grained micro-carbon ferrochrome powder is fed into a hot air dryer. The drying temperature is controlled at 120℃, and the drying time is 40 minutes to ensure that the moisture content is reduced to below 5%. The impurity content of the coarse-grained micro-carbon ferrochrome powder is tested and found to be 0.9%, which meets the requirement of ≤1.5%, and proceeds to the next step.

[0136] Step 4: Magnetic separation to remove impurities from medium and coarse particles. The medium and coarse particles obtained in Step 2 are fed into a high-gradient magnetic separator. The separator uses a neodymium iron boron permanent magnet system, with the magnetic field strength adjusted to 15,000 Gauss, the magnetic field gradient to 600 T / m, the feed rate controlled at 2 t / h, and the drum rotation speed at 40 r / min. During the magnetic separation process, the medium and coarse particles enter the magnetic field area of ​​the separator evenly. Micro-carbon ferrochrome powder, as a strongly magnetic material, is strongly adsorbed onto the drum surface by the magnetic field and rotates with the drum to the non-magnetic field area, falling into the concentrate collection hopper under the action of gravity. Iron-titanium magnetic impurities have weaker magnetism and are slightly adsorbed by the magnetic field. They rotate with the drum to the weak magnetic field area, are scraped off by the scraper, and fall into the weak magnetic impurity collection hopper. Non-metallic impurities are non-magnetic and are not affected by the magnetic field force, falling into the tailings collection hopper, thus achieving the separation of the three. After magnetic separation, the medium and coarse-grained micro-carbon ferrochrome powder in the concentrate collection hopper is sampled and tested. The iron and titanium impurity content is 0.4%, which meets the requirement of ≤0.8%. The weakly magnetic impurities are collected and recovered separately and proceed to the next step.

[0137] Step 5: Flotation and impurity removal of medium and fine-grained materials. The medium and fine-grained materials obtained in Step 2 are fed into the flotation machine. First, water is added to adjust the pulp concentration to 30%. Then, sodium hydroxide is added to adjust the pH of the pulp to 10. The mixture is stirred evenly at a speed of 200 rpm for 8 minutes. Next, sodium oleate is added as a collector at a rate of 300 g / t of material, and the mixture is stirred for 5 minutes. The collector selectively adsorbs onto the surface of the micro-carbon ferrochrome powder, enhancing its hydrophobicity. Finally, pine oil is added as a frother at a rate of 80 g / t of material, and the mixture is stirred for 3 minutes. The frother generates a large number of uniform bubbles in the pulp. During the flotation process, the aeration device is turned on, and the aeration rate is controlled at 0.5 m³ / (m²·min). The flotation time is 20 minutes. The micro-carbon ferrochrome powder adheres to the surface of the bubbles and rises with them to form a frothy product, which is scraped into the concentrate collection tank. Impurities remain in the pulp and are discharged from the bottom of the flotation machine. After flotation, the concentrate is de-reacted by washing it four times with clean water for eight minutes each time, reducing the residual flotation reagent to 32 mg / kg. After de-reacting, the concentrate is sent to a hot air dryer at 110℃ for 35 minutes, reducing the moisture content to 4.2%, before proceeding to the next step.

[0138] Step Six: Centrifugal Classification and Statistical Optimization of Fine-Grained Materials. The fine-grained materials obtained in Step Two were fed into a high-speed centrifugal classifier. The rotation speed was adjusted to 3500 r / min, the feed rate was controlled at 1.2 t / h, and 30℃ clean water was used as the classification medium. During the centrifugal classification process, the fine-grained materials were mixed with clean water to form a slurry, which was fed into the drum. The high-speed rotation of the drum generated centrifugal force, and the fine particles of micro-carbon ferrochrome powder were thrown to the inner wall of the drum and fell into the concentrate collection tank. Fine impurities were discharged from the overflow port with the slurry and fell into the tailings collection tank. After the centrifugal classification was completed, samples were taken for testing. The impurity removal rate was calculated using formula (2) to be 0.98, which met the requirements. The particle size of the agglomerated particles was found to be 0.5 mm, which met the standard of ≤1 mm, and the process proceeded to the next step.

[0139] Step Seven: Multi-stage Material Consolidation and Homogenization. The materials processed in Steps Three, Four, Five, and Six are combined at a mass ratio of coarse:medium-coarse:medium-fine:fine = 2:3:3:2 and fed into a twin-shaft mixer homogenizer. The mixing time is controlled at 60 minutes, and the mixing speed is 150 rpm. During homogenization, samples are taken every 10 minutes for testing. The average particle size of the mixture is 3 mm, the particle size deviation is 0.5 mm, the chromium content deviation is 0.7%, the carbon content is 0.07%, and the total impurity content is 0.65%, all meeting the requirements. After homogenization, the mixture is transferred to a storage silo. The bottom vibrating discharge device and the in-silo mixing device are activated, and the mixture is stirred every 30 minutes to ensure uniformity before proceeding to the next step.

[0140] Step 8: Pre-compression densification treatment. The homogenized mixture is fed into a hydraulic pre-compressor. The die size is 500mm × 500mm × 100mm, and the feed rate is 60kg per batch. A staged compression mode is used: initial pressure 15MPa, maintained for 10 minutes; pressure increased to 40MPa, maintained for 20 minutes; finally increased to 60MPa, maintained for 15 minutes. The die temperature is controlled at 60℃. After pre-compression, the blank is removed, and the density is tested to be 75%, compressive strength 20MPa, and porosity 25%, all meeting the requirements. After surface cleaning, proceed to the next step.

[0141] Step Nine: High-Temperature Densification Treatment and Integral Model Control. The pre-pressed green body is fed into a continuous high-temperature sintering furnace, and nitrogen gas with a purity of 99.99% is introduced at a flow rate of 8 m³ / h. A staged heating mode is adopted: from room temperature to 300℃, the heating rate is 5℃ / min and held for 30 minutes; from 300℃ to 800℃, the heating rate is 8℃ / min and held for 60 minutes; from 800℃ to 1300℃, the heating rate is 10℃ / min and held for 120 minutes; and the temperature is reduced to room temperature at a rate of 6℃ / min. The density is calculated using formula (3). The final density of the green body is 94%, the porosity is 6%, and the compressive strength is 50 MPa, which meets the requirements. Proceed to the next step.

[0142] Step 10: Cooling and Crushing / Shaping. The high-temperature densified billet is sent to a slow cooling chamber under nitrogen protection. The slow cooling temperature is raised from room temperature to 500℃, then lowered back to room temperature at a rate of 3℃ / min for 150 minutes. After slow cooling, it is fed into an impact crusher at 1200 rpm with a discharge opening size of 2mm. After crushing and shaping, it is sent to a vibrating screen with screen apertures of 0.5mm, 1mm, and 2mm to grade three particle sizes. The particle size deviation of each particle size is 0.15mm, which meets the requirements, and the process proceeds to the next step.

[0143] Step 11: Finished Product Testing and Packaging Storage. Samples of the three particle sizes were taken for testing. The results showed a carbon content of 0.06%, a chromium content of 68.2%, a total impurity content of 0.6% (including 0.3% iron and titanium impurities and 0.16% silicon and aluminum impurities), a density of 94%, uniform particle size distribution, and a compressive strength of 50 MPa. All test items met or exceeded high-end application standards. Double-layer packaging was used: an inner aluminum foil bag filled with 99.99% argon gas, and an outer woven bag, 25 kg / bag, with relevant information labeled. The products were then placed in a dedicated warehouse at a relative humidity of 20% and a temperature of 25℃, stacked 7 layers high, with a product traceability system established.

[0144] After processing in this embodiment, the product's performance indicators reach the international leading level, and it can replace imported high-end micro-carbon ferrochrome powder. The resource utilization rate is 97.0%, the comprehensive energy consumption per ton of product is reduced by 25%, the production cost is reduced by 20%, the first-pass yield is 99.2%, there is no wastewater or waste residue pollution, and the carbon footprint is as low as 0.12 tons of CO2e / ton, which meets the requirements of the "dual carbon" strategy. At the same time, it achieves efficient recovery of iron and titanium impurities, with significant economic and environmental benefits and extremely high industrial promotion value.

[0145] Comparative Example 1: Existing single crushing + simple magnetic separation process

[0146] This comparative example uses the mainstream "single crushing + simple magnetic separation" extensive process in the industry to process the same imported South African micro-carbon ferrochrome ore as in Example 1. The ore has a Cr2O3 content of 48%, an Fe / Cr ratio of 1.1, a carbon content of 0.12%, and a total impurity content of 3.2%, including 1.5% quartz sand, 1.0% aluminosilicate, and 0.7% iron-titanium impurities. The ore particle size is 50~200mm, and the moisture content is 10%. The processing target is the same as in Example 1, that is, to obtain a micro-carbon ferrochrome powder product with a carbon content of 0.03%~0.15%, a total impurity content of ≤1.0%, and a density of ≥90%.

[0147] The specific processing steps are as follows: Step 1, raw ore pretreatment and single crushing. The above-mentioned raw ore is selected, and large surface impurities are removed by manual screening. High-pressure spray washing is not required; the ore is directly fed into a jaw crusher for single crushing. The discharge port size is adjusted to 5-10mm, and the crusher speed is controlled at 1350r / min. The vibration dust collector is not activated during crushing. After crushing, the material moisture content is measured to be 10%, and it proceeds directly to the next step. Step 2, simple magnetic separation for impurity removal. The crushed material is directly fed into a conventional magnetic separator. The magnetic field strength is adjusted to 8000 Gauss, the feed rate is controlled at 2.5t / h, and the drum speed is 35r / min. Only one magnetic separation is performed; no grading is performed. After magnetic separation, the micro-carbon ferrochrome powder falls into the concentrate collection hopper, and impurities fall into the tailings collection hopper. Weakly magnetic impurities are not collected separately. Step 3, simple drying and packaging. The magnetically separated concentrate is fed into a hot air dryer at a drying temperature of 110℃ for 35 minutes, reducing the moisture content to 4.5%. Without densification, it is directly fed into a crusher to be crushed to 0.5~2mm. Then, it is sampled, tested, and packaged in single-layer woven bags without protective gas filling, and stored in a regular warehouse.

[0148] After processing, the product underwent comprehensive testing. The results are as follows: carbon content was 0.13%, which, although within the range of 0.03% to 0.15%, is close to the upper limit; chromium content was 64.8%, lower than the requirement of ≥65%; total impurity content was 1.8%, far exceeding the requirement of ≤1.0%, with iron-titanium impurities at 0.9% and silicon-aluminum impurities at 0.6%, both failing to meet standards; due to the lack of densification treatment, the product density was only 58%, porosity was 42%, and compressive strength was only 10 MPa, far below the requirements of ≥90%, ≤10%, and ≥40 MPa; particle size distribution was uneven, with a particle size deviation of 0.8 mm, exceeding the ≤0.2 mm limit. The standard is as follows: resource utilization rate is only 82%, and a large amount of fine-grained micro-carbon ferrochrome powder is lost with impurities; the comprehensive energy consumption per ton of product is 22% higher than that of Example 1, and the production cost is 18% higher; the dust removal device is not turned on during the production process, resulting in serious dust pollution, and the tailings generated after magnetic separation are not properly treated, posing a potential environmental pollution hazard; the first-pass yield of the product is only 75%, with large quality fluctuations, and the standard deviation of carbon content and impurity content is 0.012%, which is much higher than 0.005% in Example 1; the packaging is not filled with protective gas, and some products are oxidized during storage, resulting in a decline in product performance, which cannot meet the needs of high-end applications and can only be used for the production of low-end wear-resistant materials.

[0149] The core difference between this comparative example and Example 1 lies in the absence of the four-level precise grading, multi-dimensional impurity removal, in-situ densification at the mine, and statistical and calculus model control employed in this method. Instead, it uses single crushing and simple magnetic separation, resulting in a crude process that leads to product quality, resource utilization, energy consumption, and environmental friendliness that are far inferior to Example 1. Specifically, the single crushing without grading results in the mixing of fine-grained micro-carbon ferrochrome powder with coarse-grained impurities, increasing the difficulty of impurity removal and causing incomplete removal. The simple magnetic separation has a low magnetic field strength and lacks grading, failing to effectively remove weakly magnetic and non-metallic impurities, leading to excessive impurity content. The lack of densification treatment results in product density and compressive strength that fail to meet standards. The absence of statistical and calculus models means that processing parameters are set based on experience, leading to large fluctuations in product quality. Furthermore, the lack of environmentally friendly processing methods results in dust pollution and resource waste. Therefore, it can be seen that the multi-level precise grading, multi-dimensional impurity removal, densification synergy, and parameter model-based control of this method can effectively solve many drawbacks of the existing single crushing + simple magnetic separation process, significantly improve product quality and production efficiency, and reduce energy consumption and environmental pollution.

[0150] Furthermore, the production efficiency of this comparative example is 30% lower than that of Example 1. Due to the lack of continuous production and the need for secondary processing of substandard products, the production cycle is extended. Simultaneously, due to substandard product quality, the export return rate is as high as 15%, far exceeding the less than 0.5% of Example 1, resulting in weak market competitiveness. In summary, the existing single crushing + simple magnetic separation process cannot meet the production needs of high-end micro-carbon ferrochrome powder, while this method can effectively overcome the bottleneck of this process and achieve green, efficient, and high-quality production.

[0151] Comparative Example 2: Process without densification treatment

[0152] This comparative example uses a "grading and impurity removal + non-densification treatment" process to process a low-carbon chromite ore from a mine in Inner Mongolia, China, similar to Example 2. The ore has a Cr2O3 content of 50%, an Fe / Cr ratio of 1.0, a carbon content of 0.08%, and a total impurity content of 2.8%, including 1.2% quartz sand, 0.9% aluminosilicate, and 0.7% iron-titanium impurities. The ore particle size is 40-180 mm, and the moisture content is 11%. The treatment objective is the same as in Example 2, but the pre-compression densification and high-temperature densification steps of this method are not used. The remaining steps are basically the same as in Example 2 (the grading method and impurity removal process are the same as in Example 2, but statistical and calculus model control parameters are not introduced).

[0153] The specific processing steps are as follows: Steps one to seven are basically the same as in Example 2, namely, completing the pretreatment and crushing of the raw ore, four-level precise classification, corresponding impurity removal of each level of material (gravity separation, high-gradient magnetic separation, flotation, centrifugal classification), and merging and homogenization of multiple levels of materials. However, statistical and calculus models were not introduced in the classification and impurity removal process, and the processing parameters were set based on experience without precise control. Steps eight to nine omit the pre-compression densification and high-temperature densification treatments. After simple drying (drying temperature 100℃, drying time 30 minutes, moisture content reduced to 4.5%), the homogenized mixture directly enters step ten, cooling and crushing and shaping. Steps ten to eleven are basically the same as in Example 2, but no densification-related index testing was performed after crushing and shaping. The packaging and storage methods are the same as in Example 2.

[0154] After processing, the product underwent comprehensive testing. The results are as follows: carbon content 0.07%, chromium content 67.2%, total impurity content 0.7%, including 0.38% iron-titanium impurities and 0.20% silicon-aluminum impurities. All these indicators meet the requirements for high-end applications. This is because the same graded impurity removal process as in Example 2 was used, effectively removing various impurities and ensuring product purity. However, due to the lack of pre-compression densification and high-temperature densification treatment, the product density is only 62%, porosity 38%, and compressive strength only 14 MPa, far lower than the 91%, 9%, and 42 MPa of Example 2, respectively. This fails to meet the stringent requirements for material density and mechanical properties in high-end stainless steel and high-temperature alloys. Although the particle size distribution is basically uniform with a particle size deviation of 0.16 mm, meeting the standard, the high porosity and poor flowability of the particles will affect subsequent molding and sintering. Cracking and delamination are prone to occur during the process; the resource utilization rate is 95.8%, slightly lower than 96.2% in Example 2, mainly because impurities in the densification process were not further precipitated and recovered; the comprehensive energy consumption per ton of product is 23% higher than in Example 2, although lower than in Comparative Example 1, but due to the lack of in-situ densification treatment at the mine, the subsequent smelting process requires additional forming and sintering steps, resulting in an overall increase in energy consumption and a 17% higher production cost; although the production process achieves green and environmentally friendly results, the product quality stability is slightly poor, with a standard deviation of 0.008% for carbon content and impurity content, higher than 0.005% in Example 2, and a first-pass yield of 96.5%, lower than 98.5% in Example 2; when the product is subsequently used in the production of high-end alloys, the forming pass rate is only 78%, far lower than the 99% or more in Example 2, making it impossible to achieve large-scale high-end applications.

[0155] The core difference between this comparative example and Example 2 lies in the omission of the in-situ pre-compression densification and high-temperature densification steps in this method, and the absence of statistical and calculus model control parameters. This results in a significant decrease in product density, mechanical properties, and production efficiency. Specifically, densification is crucial for improving the density and mechanical properties of micro-carbon ferrochrome powder. Omitting this step prevents the formation of a strong bond between material particles, resulting in high porosity, insufficient compressive strength, and difficulty in meeting the molding and usage requirements of high-end applications. The lack of statistical and calculus models, with processing parameters set empirically, while ensuring purity through graded impurity removal, leads to insufficient quality stability and reduced first-pass yield and subsequent molding pass rates. Furthermore, the absence of in-situ densification necessitates additional molding and sintering processes in subsequent smelting stages, increasing energy consumption and production costs, extending the production cycle, and reducing production efficiency.

[0156] Furthermore, due to insufficient product density and high particle porosity, the product is prone to moisture absorption and oxidation during storage and transportation, leading to a further decline in product performance. Upon export, the return rate is approximately 8% due to substandard mechanical properties, higher than the 0.5% or less in Example 2. In summary, the synergistic effect of densification treatment and graded impurity removal is one of the core advantages of this method. Without densification treatment, even with a reasonable graded impurity removal process, it is impossible to achieve high-end production of micro-carbon ferrochrome powder. This further confirms the scientific validity and necessity of the design principles of "precise grading, diversified impurity removal, synergistic densification, and parameter modeling" in this method.

[0157] Comparative Example 3: Process Control without Statistical Analysis and Calculus Model

[0158] This comparative example uses a process of "grading and impurity removal + densification treatment + parameterless model control" to process imported Kazakhstani micro-carbon ferrochrome ore, the same as in Example 3. The ore has a Cr2O3 content of 52%, an Fe / Cr ratio of 0.9, a carbon content of 0.06%, and a total impurity content of 2.5%, including 1.0% quartz sand, 0.8% aluminosilicate, and 0.7% iron-titanium impurities. The ore particle size is 60~220mm, and the moisture content is 9%. The treatment objectives are the same as in Example 3, using the grading and impurity removal and densification steps of this method. However, no statistical or calculus model is introduced. The key parameters for grading, centrifugal impurity removal, and high-temperature densification are all set based on experience and have not been precisely optimized.

[0159] The specific processing steps are as follows: Steps one to eleven are basically the same as in Example 3, including raw ore pretreatment and crushing, four-level precise grading, material removal at each level, material merging and homogenization, pre-compression densification, high-temperature densification, cooling, crushing and shaping, and finished product testing and packaging. However, in step two, the grading process did not use formula (1) to calculate the grading efficiency, and the grading effect was judged only by visual observation and simple sampling. In step six, the centrifugal grading process did not use formula (2) to calculate the impurity removal rate, and parameters such as centrifugal speed and feeding speed were set based on experience. In step nine, the high-temperature densification process did not use formula (3) to control the density, and the heating rate and holding time were fixed and not adjusted according to the real-time density changes.

[0160] After processing, the product underwent comprehensive testing. The results are as follows: carbon content 0.07%, chromium content 68.5%, total impurities 0.7%, density 88%, porosity 12%, compressive strength 45 MPa. The density and porosity did not meet the standards of 93% and 7% respectively in Example 3, slightly below the minimum requirements for high-end applications (density ≥90%). The particle size distribution was uneven, with a coarse particle size deviation of 1.0 mm and agglomerated particle size of 1.2 mm in fine particles, exceeding the 0.8 mm and 0.6 mm requirements of Example 3 and the standard requirements. The resource utilization rate was 95.2%, lower than 96.8% in Example 3. The loss of fine-grained micro-carbon ferrochrome powder was 1.6% higher than in Example 3; the comprehensive energy consumption per ton of product was 8% higher than in Example 3, mainly due to insufficient grading efficiency and incomplete centrifugal impurity removal, which required secondary processing of some materials, increasing energy consumption; the product quality fluctuated greatly, with a standard deviation of 0.010% for carbon content and impurity content, which was twice that of Example 3, and a first-pass yield of 95.0%, which was lower than 99.0% in Example 3; during the production process, the parameter adjustment frequency of grading, centrifugal impurity removal, and high-temperature densification was 40% higher than in Example 3, and unqualified products were more likely to occur due to improper parameter adjustment, resulting in a production efficiency 15% lower than in Example 3.

[0161] Compared with Example 3, the core difference of this comparative example is that the statistical and calculus model of this method was not introduced. It is impossible to accurately control the key parameters of grading, centrifugal impurity removal and high-temperature densification, resulting in a decrease in product quality stability, production efficiency and resource utilization. Specifically, the core role of the statistical and calculus model is to quantify the processing effect, optimize parameters in real time, and avoid the deviation caused by setting parameters based on experience: the grading efficiency was not calculated using formula (1) during the grading process, so the grading effect could not be accurately judged, resulting in some fine-grained materials being mixed with coarse-grained impurities, increasing the difficulty of impurity removal, and increasing the loss of fine-grained materials; the impurity removal rate was not calculated using formula (2) during centrifugal impurity removal, so the centrifugation parameters could not be accurately controlled, resulting in incomplete impurity removal and some fine impurities remaining; the density was not controlled using formula (3) during high-temperature densification, so the heating rate and holding time could not be adjusted according to the real-time density of the green body, resulting in the final density not meeting the standard and the porosity being too high.

[0162] Furthermore, due to inaccurate parameter control, defective products are prone to occur during the production process, requiring secondary processing. This not only prolongs the production cycle but also increases energy consumption and production costs. When the product is subsequently used in the production of high-end high-temperature alloys, its performance fluctuates significantly, making it difficult to guarantee product consistency, and its market acceptance is lower than that of the product in Example 3. In summary, the introduction of statistical and calculus models is the key innovation of this method in achieving precise control and improving product quality stability and production efficiency. Without this control mechanism, even with the combined process of graded impurity removal and densification, the process advantages cannot be fully utilized, making it difficult to achieve stable mass production of high-end micro-carbon ferrochrome powder.

[0163] This method addresses several challenges in existing micro-carbon ferrochrome powder ore classification, impurity removal, and densification technologies, achieving breakthroughs in multiple aspects and effectively solving the following existing technical problems: First, it solves the problems of insufficient classification accuracy and uneven particle size distribution. Existing processes often use single-level sieving without fine classification, resulting in the mixing of fine powder with coarse impurities, making impurity removal difficult and reducing resource utilization. This method employs four-level precise classification, combining statistical and calculus models to quantify the classification effect, precisely controlling classification parameters to ensure uniform particle size at each level, preventing the loss of fine-particle micro-carbon ferrochrome powder, and improving resource utilization. Second, it solves the problems of single and incomplete impurity removal methods in existing processes. Existing processes often use single magnetic separation or gravity separation, which cannot efficiently remove complex impurities, especially fine impurities and weakly magnetic impurities. This method, tailored to the characteristics of materials with different particle sizes, employs four impurity removal processes: gravity separation, high-gradient magnetic separation, flotation, and centrifugal classification, achieving multi-dimensional and comprehensive impurity removal. This effectively removes various impurities such as quartz sand, aluminosilicates, and iron-titanium impurities, ensuring product purity meets standards. Third, this method addresses the problems of disconnect between densification treatment and graded impurity removal, resulting in high energy consumption. Existing processes often perform densification treatment in subsequent smelting stages, neglecting densification control during the pre-treatment stage at the ore mine, leading to high energy consumption and insufficient product density. This method achieves in-situ pre-compression densification and high-temperature densification in synergistic processing at the ore mine, reducing subsequent transfer and secondary processing, lowering energy consumption, and simultaneously improving product density and mechanical properties. Fourth, this method solves the problems of insufficient precision in existing process control and large fluctuations in product quality. Existing process parameters are set entirely based on experience, resulting in large fluctuations in carbon content and impurity content, and low first-pass yield. This method introduces statistical and calculus models into the three key steps of grading, centrifugal impurity removal, and high-temperature densification, combined with generalized constants, to achieve precise parameter control and ensure stable product quality. Fifth, it solves the problem of balancing environmental protection and efficiency in existing processes. Traditional impurity removal processes often use chemical reagents, which are prone to pollution, and purely physical impurity removal is inefficient. This method primarily uses physical impurity removal, employs environmentally friendly flotation agents in the flotation process, and improves efficiency through multi-stage impurity removal while reducing the amount of chemical reagents used, achieving green and efficient production. Sixth, it solves the problem that existing products cannot meet the needs of high-end applications. The purity, density, and particle size uniformity of existing products are insufficient to meet the requirements of high-end stainless steel and high-temperature alloys. This method, through refined grading, all-round impurity removal, and precise densification control, enables all performance indicators of the product to meet high-end application standards, breaking the monopoly of foreign high-end products and enhancing the market competitiveness of domestically produced micro-carbon ferrochrome powder.

Claims

1. A method for field classification, impurity removal, and densification treatment of micro-carbon ferrochrome powder, characterized in that, Includes the following steps: S1: Pre-treatment and crushing of raw ore; S2: Multi-stage precision grading and particle size statistical control; S3: Gravity separation for removing impurities from coarse-grained materials; S4: Magnetic separation for removing impurities from medium-coarse-grained materials; S5: Flotation for removing impurities from medium-fine-grained materials; S6: Centrifugal grading for removing impurities from fine-grained materials and statistical optimization; S7: Multi-stage material merging and homogenization; S8: Pre-compression densification; S9: High-temperature densification and calculus model control; S10: Cooling, crushing and shaping; S11: Finished product testing, packaging and storage.

2. The method according to claim 1, characterized in that, In step S1, the pretreatment and crushing of the raw ore is the foundation of the entire process. Its core purpose is to remove large impurities, soil, and moisture from the raw ore, crushing it to a uniform particle size to provide a basis for subsequent grading and impurity removal. During operation, high-grade micro-carbon ferrochrome raw ore with a Cr2O3 content ≥48% and an Fe / Cr ratio ≤1.2 is first selected and conveyed at a uniform speed to the raw material cleaning platform using a belt conveyor. Soil, weeds, and large non-metallic impurities adhering to the surface of the raw ore are removed through a combination of manual screening and high-pressure spraying. The spraying water pressure is controlled at 0.3~0.5MPa, and the spraying time is 3~5 minutes per batch of raw material to ensure that no visible impurities adhere to the surface of the raw ore. After cleaning, the raw ore is fed into a jaw crusher for coarse crushing. The discharge port size is adjusted to 80~100mm, and the feeding speed is controlled at 2~3t / h during the crushing process to avoid excessively fast feeding. This can lead to overloading or insufficient crushing of the crusher. The coarsely crushed material is then conveyed via belt conveyor to a cone crusher for medium crushing. The discharge opening size for medium crushing is adjusted to 30-40mm. During medium crushing, the crusher's vibration dust collector is activated to reduce dust pollution. The medium-crushed material is then fed into an impact crusher for fine crushing. The discharge opening size for fine crushing is adjusted to 5-10mm. During fine crushing, the crusher speed is controlled at 1200-1500 r / min, employing the principle of layered crushing to ensure uniform particle size and avoid over-crushing or excessively large particles. After crushing, the material is fed into a vibrating feeder for uniform conveying to the next step. Simultaneously, the material's moisture content is monitored, ensuring it is controlled between 8% and 12%. If the moisture content is too high, a hot air drying device is activated, with the drying temperature controlled at 80-100℃ for 20-30 minutes, until the moisture content meets the standard.

3. The method according to claim 1, characterized in that, In step S2, multi-stage precise grading is the core step for achieving refined impurity removal. Grading is based on differences in material particle size, and statistical and calculus models are introduced to achieve precise control of grading parameters, solving the problems of insufficient grading accuracy and uneven particle size distribution in existing methods. During operation, the material crushed in step one is fed into a multi-stage vibrating screen, employing a four-stage grading mode with screen apertures set to 10mm, 5mm, 2mm, and 0.5mm, corresponding to four grades of material: coarse particles (5-10mm), medium-coarse particles, and... The particle size distribution is as follows: 2-5mm, medium-fine particle size 0.5-2mm, fine particle size <0.5mm. During each screening process, the vibration frequency of the vibrating screen is controlled at 20-30Hz, the amplitude is 5-8mm, and the feeding speed is consistent with that of the vibrating feeder in step one to ensure that the material is evenly distributed on the screen and avoid screen clogging. After the grading is completed, samples of each grade of material are taken for testing. A laser particle size analyzer is used to determine the particle size distribution of each grade of material. At the same time, statistical models and calculus formulas are introduced to quantitatively evaluate the grading effect and optimize the parameters. The statistical model used is based on the probability density function of particle size distribution, combined with calculus to calculate the grading efficiency. The specific formula is as follows: ； In formula (1), the meanings of each symbol are as follows: η is the classification efficiency, with a value range of 0~1. The closer to 1, the better the classification effect; d is the particle size of the material, in mm; d is the minimum particle size of the classification level, in mm; d is the maximum particle size of the classification level, in mm; f(d) is the probability density function of the particle size distribution of the material, which satisfies the condition that its value is obtained by fitting the detection data of the laser particle size analyzer; C1 is the pass / follow constant, with a value of 0.0023, which characterizes the dynamic correction coefficient of particle size change during the classification process; and is the average particle size of the material in this level, in mm. t is the grading time in minutes; t is the rate of change of average particle size with grading time in mm / min, which is obtained by differentiating the average particle size detection values ​​at different time points. The grading efficiency of each grade of material is calculated according to formula (1). If the grading efficiency of a certain grade is lower than 0.92, the screen aperture, vibration frequency or feeding speed of that grade is adjusted and the grading is repeated until the grading efficiency meets the standard. At the same time, the uniformity of particle size distribution of each grade of material is calculated by integration to ensure that the particle size deviation of coarse particles is ≤1.2mm, medium-coarse particles are ≤0.8mm, medium-fine particles are ≤0.3mm, and fine particles are ≤0.1mm.

4. The method according to claim 1, characterized in that, In step S3, the coarse-grained material mainly contains coarse particles of micro-carbon ferrochrome powder and non-metallic impurities such as quartz sand and feldspar. These impurities have a significant density difference from the micro-carbon ferrochrome powder and can be efficiently removed using gravity separation, providing qualified coarse-grained raw materials for subsequent processing. During operation, the coarse-grained material obtained in step two is fed into a spiral chute gravity separator. The spiral chute diameter is 1.5m, the pitch is 300mm, the number of turns is 5, the slurry concentration is adjusted to 30%~35%, and the slurry flow rate is controlled at 1.2~1.5m / s. During the process, coarse-grained materials are mixed with water in a certain proportion to form a slurry, which is then pumped at a constant speed into the top of the spiral sluice. Under the action of gravity and centrifugal force, the slurry flows downward along the spiral blades. The micro-carbon ferrochrome powder has a higher density of 4.3~4.8 g / cm³, and its settling speed is fast. It slides along the inner side of the spiral blades and finally falls into the concentrate collection tank at the bottom of the sluice. The impurities such as quartz sand and feldspar have a lower density of 2.6~2.8 g / cm³, and their settling speed is slow. They slide along the outer side of the spiral blades and fall into the tailings collection tank, thus achieving the separation of coarse-grained materials and impurities. After gravity separation, the coarse-grained micro-carbon ferrochrome powder in the concentrate collection tank is cleaned by high-pressure water spraying, with the water pressure controlled at 0.2~0.4MPa and the spraying time at 1~2 minutes, to remove fine impurities and slurry adhering to the surface. After cleaning, the coarse-grained micro-carbon ferrochrome powder is sent to a hot air dryer, with the drying temperature controlled at 100~120℃ and the drying time at 30~40 minutes, to ensure that the moisture content is reduced to below 5%. At the same time, the impurity content of the coarse-grained micro-carbon ferrochrome powder is tested. If the impurity content is higher than 1.5%, it is sent back to the spiral chute for secondary gravity separation until the impurity content meets the standard.

5. The method according to claim 1, characterized in that, In step S4, the medium-coarse particle size material contains coarse particles of micro-carbon ferrochrome powder, a small amount of iron-titanium magnetic impurities, and non-metallic impurities that have not been completely removed. The micro-carbon ferrochrome powder has strong magnetism, while the iron-titanium impurities have weak magnetism, and the non-metallic impurities are non-magnetic. High-gradient magnetic separation can achieve precise separation, solving the problem that existing magnetic separation processes cannot effectively separate weakly magnetic impurities. During operation, the medium-coarse particle size material obtained from step two is fed into a high-gradient magnetic separator. The separator uses a neodymium iron boron permanent magnet system, with the magnetic field strength adjusted to 12000~15000 Gauss and the magnetic field gradient to 500~600 T / m. The speed is controlled at 1.5~2t / h, and the drum rotation speed is 30~40r / min. During the magnetic separation process, medium and coarse particles are uniformly introduced into the magnetic field area of ​​the magnetic separator. Micro-carbon ferrochrome powder, as a strongly magnetic material, is strongly adsorbed by the magnetic field on the surface of the drum. As the drum rotates, it moves to the non-magnetic field area and falls into the concentrate collection hopper under the action of gravity. Iron-titanium magnetic impurities are weakly magnetic and are slightly adsorbed by the magnetic field. As the drum rotates, they move to the weak magnetic field area, are scraped off by the scraper, and fall into the weak magnetic impurity collection hopper. Non-metallic impurities are non-magnetic and are not affected by the magnetic field force. They fall into the tailings collection hopper under the action of gravity and centrifugal force, thus achieving the separation of the three. After magnetic separation, the medium and coarse-grained micro-carbon ferrochrome powder in the concentrate collection hopper is sampled and tested, with a focus on testing the iron and titanium impurity content. If the iron and titanium impurity content is higher than 0.8%, the magnetic field strength and drum speed are adjusted, and magnetic separation is repeated until the iron and titanium impurity content meets the standard. At the same time, the iron and titanium impurities in the weak magnetic impurity collection hopper are collected separately for recycling, thereby improving resource utilization.

6. The method according to claim 1, characterized in that, In step S5, the medium-fine particles are small, and the density and magnetic properties of micro-carbon ferrochrome powder and non-metallic impurities such as aluminosilicates are similar, resulting in poor removal effects from gravity separation and magnetic separation. Therefore, a flotation process is employed to remove impurities. By adding a special flotation agent, the surface properties of the micro-carbon ferrochrome powder and the impurities are differentiated, thereby achieving efficient impurity removal. During operation, the medium-fine particles obtained from step two are fed into a flotation machine. First, water is added to adjust the pulp concentration to 25%–30%. Then, sodium hydroxide is added to adjust the pH of the pulp to 9–10. The mixture is stirred evenly at a speed of 150–200 r / min. The stirring time is 5-8 minutes. The modifier changes the surface charge of the micro-carbon ferrochrome powder and impurities, making the surface of the micro-carbon ferrochrome powder hydrophobic and the surface of the impurities hydrophilic. Then, sodium oleate collector is added at a dosage of 200-300 g / t of material, and the stirring time is 3-5 minutes. The collector can selectively adsorb onto the surface of the micro-carbon ferrochrome powder, enhancing its hydrophobicity and making it easier to adhere to the surface of air bubbles. Finally, pine oil frother is added at a dosage of 50-80 g / t of material, and the stirring time is 2-3 minutes. The frother can generate a large number of uniform air bubbles in the slurry, providing a carrier for the flotation of micro-carbon ferrochrome powder. During the flotation process, the aeration device of the flotation machine is turned on, and the aeration rate is controlled at 0.3~0.5m³ / m²·min. The flotation time is 15~20 minutes. Due to the hydrophobicity of the surface, the micro-carbon ferrochrome powder will adhere to the surface of the bubbles and rise to the surface of the slurry with the bubbles to form a foam product, which is scraped into the concentrate collection tank by the scraper. Impurities such as aluminosilicates remain in the slurry due to their hydrophilic surface and are eventually discharged from the bottom of the flotation machine into the tailings collection tank. After flotation, the medium and fine-grained micro-carbon ferrochromium powder in the concentrate collection tank is de-treated by washing with clean water 3 to 4 times, with each washing lasting 5 to 8 minutes, to ensure that the residual flotation agent is less than 50 mg / kg. After de-treatment, the powder is sent to a hot air dryer, with the drying temperature controlled at 90 to 110°C and the drying time at 25 to 35 minutes, reducing the moisture content to below 5%.

7. The method according to claim 1, characterized in that, In step S6, the fine-particle material is small, easily agglomerates, and contains a large number of fine impurities. A centrifugal classification process is used to remove impurities, combining statistical and calculus models to achieve precise classification and impurity removal of the fine-particle material, solving the problems of incomplete impurity removal and easy loss in existing methods. During operation, the fine-particle material obtained in step two is fed into a high-speed centrifugal classifier. The speed of the centrifugal classifier is adjusted to 3000~3500 r / min, the feed rate is controlled at 1~1.2 t / h, and clean water is used as the classification medium. The temperature is controlled at 25~30℃. During the centrifugal classification process, fine-particle materials are mixed with water to form a slurry, which is then fed into the drum of the centrifugal classifier. The high-speed rotation of the drum generates centrifugal force, which is proportional to the particle mass. The fine particles of micro-carbon ferrochrome powder have a larger mass and are subjected to a greater centrifugal force, so they are thrown against the inner wall of the drum and discharged through the discharge port as the drum rotates, falling into the concentrate collection tank. The fine impurity particles have a smaller mass and are subjected to a smaller centrifugal force, so they are discharged from the overflow port with the slurry and fall into the tailings collection tank, thus achieving the separation of fine-particle materials and fine impurities. After centrifugal classification, fine-grained micro-carbon ferrochrome powder in the concentrate collection tank was sampled and tested. A laser particle size analyzer was used to determine its particle size distribution and impurity content. Simultaneously, statistical models and calculus formulas were introduced to optimize the centrifugal classification parameters, ensuring stable classification and impurity removal effects. The statistical model used focused on the impurity removal rate of centrifugal classification, and combined with calculus to calculate the optimal centrifugal speed. The specific formula is as follows: ； In formula (2), the meanings of each symbol are as follows: ξ is the impurity removal rate, with a value range of 0~1. The closer to 1, the better the impurity removal effect; m0 is the mass of impurities in the fine-particle material before centrifugation, in kg; m1 is the mass of impurities in the fine-particle material after centrifugation, in kg; ρ is the slurry density, in kg / m³; ω is the angular velocity of the centrifugal classifier drum, in rad / s; r is the distance from a point inside the drum to the center of rotation, in m; R is the drum radius, in m; S(r) is the cross-sectional area at point r inside the drum, in m²; C2 is the constant of rotation, with a value of 0.0018, representing the correction coefficient for the change of angular velocity during centrifugation; t is the centrifugation time, in min; is the rate of change of the drum angular velocity over time, in rad / (s·min); is the integral of the effect of centrifugal force on the slurry, representing the contribution of centrifugal force to impurity separation; is the integral of the change of angular velocity, representing the influence of dynamic adjustment of centrifugal speed on the impurity removal rate; According to formula (2), the impurity removal rate is calculated. If the impurity removal rate is lower than 0.95, the centrifugal speed, feed rate or slurry concentration is adjusted, and centrifugation is carried out again until the impurity removal rate meets the standard. At the same time, the degree of agglomeration of fine-grained micro-carbon ferrochrome powder is calculated by integration to ensure that the particle size of agglomerated particles is ≤1mm. If the degree of agglomeration is too high, the dispersant polyacrylamide is added at a rate of 100~150g / t of material. After stirring evenly, centrifugation is carried out again.

8. The method according to claim 1, characterized in that, In step S7, the multi-stage material merging and homogenization process combines the qualified micro-carbon ferrochrome powders from steps three, four, five, and six. Through homogenization, the particle size distribution and composition of the materials are ensured to be uniform, providing a uniform raw material for subsequent densification and solving the problem of poor densification effect caused by uneven mixing of existing materials. During operation, the coarse-grained micro-carbon ferrochrome powder from step three, the medium-coarse-grained micro-carbon ferrochrome powder from step four, the medium-fine-grained micro-carbon ferrochrome powder from step five, and the fine-grained micro-carbon ferrochrome powder from step six are respectively fed into a twin-shaft mixing homogenizer via belt conveyors. The mixture was prepared according to a mass ratio of coarse:medium-coarse:medium-fine:fine = 2:3:3:2, with a mixing time of 40-60 minutes and a stirring speed of 120-150 r / min. During homogenization, samples were taken every 10 minutes. The particle size distribution of the mixture was determined using a laser particle size analyzer, and the composition of the mixture was detected using an X-ray fluorescence spectrometer. The aim was to ensure that the average particle size of the mixture was controlled within 1-3 mm, the particle size deviation was ≤0.5 mm, the chromium content deviation was ≤0.8%, the carbon content was controlled within 0.03%-0.15%, and the total impurity content was ≤1.0%. If the particle size distribution or composition of the mixture does not meet the requirements, adjust the stirring speed, mixing time, or mixing ratio of each stage of material, and continue the homogenization process until the standard is met. After homogenization, send the mixture into the storage silo. The storage silo adopts a conical structure and is equipped with a vibrating discharge device at the bottom to prevent material from clumping. At the same time, turn on the stirring device in the silo and stir once every 30 minutes to ensure that the material remains in a uniform state during storage.

9. The method according to claim 1, characterized in that, In step S8, the pre-compression densification treatment is the core step of in-situ densification in the mine. Through pressure, the porosity of the mixture is reduced, and the initial density of the material is increased, laying the foundation for subsequent high-temperature densification. This solves the problems of high energy consumption and insufficient product density caused by the lag in the densification process in existing technologies. During operation, the homogenized mixture from step seven is fed into a hydraulic pre-compressor. The pre-compressor's die size is 500mm × 500mm × 100mm, and the feed rate is controlled at 50-60kg per batch to ensure the material is properly compressed. The material is evenly distributed within the mold, without voids or lumps. During pre-compression, a staged pressurization mode is adopted. The initial pressure is adjusted to 10~15MPa and maintained for 5~10 minutes to allow the material to initially form. Then, the pressure is increased to 30~40MPa and maintained for 15~20 minutes to further reduce the porosity of the material. Finally, the pressure is increased to 50~60MPa and maintained for 10~15 minutes to complete the pre-compression densification process. During pre-compression, the mold temperature is controlled at 50~60℃, and the temperature is evenly distributed to avoid local overheating that could lead to material oxidation. After pre-pressing, the pressed blank is removed from the mold and its density, compressive strength, and porosity are tested. The density should reach 65%~75%, the compressive strength should be ≥15MPa, and the porosity should be ≤30%. If the test indicators do not meet the requirements, the pre-pressing pressure, pressing time, or mold temperature should be adjusted, and the pre-pressing densification treatment should be repeated until the standards are met. At the same time, the surface of the pre-pressed blank is cleaned to remove loose particles and impurities, ensuring that the blank surface is flat and undamaged.

10. The method according to claim 1, characterized in that, In step S9, the high-temperature densification treatment is a key step in improving the density of micro-carbon ferrochrome powder. Through high temperature, the diffusion and sintering of material particles are promoted, further reducing porosity and improving product density and overall performance. Simultaneously, statistical and calculus models are introduced to achieve precise control of high-temperature parameters, solving the problem of existing high-temperature densification parameters being set based on experience and resulting in large fluctuations in product quality. During operation, the pre-pressed billet from step eight is fed into a continuous high-temperature sintering furnace. The sintering furnace is heated by natural gas, and nitrogen is introduced into the furnace as a protective gas. The nitrogen purity is ≥99.99%, and the flow rate is controlled at 5~8 m³ / h to prevent oxidation of the micro-carbon ferrochrome powder. The high-temperature densification process adopts a staged heating mode. The specific heating process is as follows: heating from room temperature to 300℃ at a heating rate of 5℃ / min and holding for 30 minutes to remove residual moisture in the green body; heating from 300℃ to 800℃ at a heating rate of 8℃ / min and holding for 60 minutes to remove residual flotation agent and trace impurities in the green body; heating from 800℃ to 1200~1300℃ at a heating rate of 10℃ / min and holding for 90~120 minutes to complete the high-temperature densification sintering; finally, cooling from 1200~1300℃ to room temperature at a cooling rate of 6℃ / min to avoid cracking of the green body due to excessively rapid cooling. In step S10, cooling and crushing / shaping involves cooling the high-temperature densified billet and then crushing it into particles of the required size to provide qualified products for subsequent screening and packaging. This ensures uniform particle size and prevents breakage, addressing the problems of billet cracking and uneven particle size caused by improper cooling methods in existing systems. During operation, the high-temperature densified billet from step nine is removed from the high-temperature sintering furnace and placed in a slow-cooling chamber. The chamber is protected by nitrogen, with the nitrogen flow rate matching that of the sintering furnace. The slow-cooling temperature is gradually increased from room temperature to 500°C to match the initial temperature of the billet, and then reduced to room temperature at a rate of 3°C / min for 120-150 minutes. During the slow-cooling process, the billet temperature is monitored in real time to ensure a uniform temperature decrease and prevent excessive local temperature differences that could lead to billet cracking. In step S11, finished product testing and packaging storage is the final step in the entire processing flow. Comprehensive testing ensures product quality meets standards, and standardized packaging and storage methods prevent oxidation, moisture absorption, or contamination, ensuring stable product performance and addressing the existing problems of incomplete finished product testing and improper packaging and storage leading to product quality degradation. During operation, samples of the three particle sizes after crushing and shaping in step ten are taken for testing. Testing items include carbon content, chromium content, impurity content, density, particle size distribution, and compressive strength. Carbon content testing uses a high-frequency infrared carbon-sulfur analyzer to ensure carbon content is controlled between 0.03% and 0.15%; chromium content testing uses an X-ray fluorescence spectrometer to ensure chromium content ≥ 65%; impurity content testing uses an inductively coupled plasma atomic emission spectrometer to ensure total impurity content ≤ 1.0%, with iron-titanium impurities ≤ 0.5% and silicon-aluminum impurities ≤ 0.3%; density testing uses the water displacement method to ensure density ≥ 90%; particle size distribution testing uses a laser particle size analyzer to ensure particle size deviation ≤ 0.2 mm; and compressive strength testing uses a universal testing machine to ensure compressive strength ≥ 40 MPa. During the high-temperature densification process, a calculus model is introduced to quantify the density change during sintering and precisely control the heating rate and holding time. The specific formula is as follows: ； In formula (3), the meanings of each symbol are as follows: ρ(t) is the compaction density of the billet at time t, with a value range of 0~1; ρ0 is the initial compaction density of the billet after pre-pressing; k is the sintering rate constant, with the unit being min. -1 , with a value of 0.0085; E is the sintering activation energy, in J / mol, with a value of 280000; R is the ideal gas constant, in J / (mol·K), with a value of 8.314; T(t) is the temperature inside the furnace at time t, in K; τ is the integral variable, in min; C3 is the constant, with a value of 0.0009, representing the correction coefficient for the effect of temperature change on density; is the rate of change of temperature over time, in K / min; is the integral of the density increment during the sintering process, representing the contribution of sintering time and temperature to density; The integral of the temperature change characterizes the effect of the heating rate on the density. Calculate the bulk density at different time points according to formula (3). If the bulk density at time t does not reach the target value of ≥90%, adjust the heating rate or holding time to ensure that after high-temperature densification, the bulk density is ≥90%, the porosity is ≤10%, and the compressive strength is ≥40MPa. After slow cooling, the billet is fed into an impact crusher for crushing and shaping. The crusher speed is adjusted to 1000~1200 r / min, and the crushing discharge port size is adjusted to 0.5~2 mm. During the crushing process, a vibration dust removal device is turned on to reduce dust pollution. After crushing and shaping, the material is fed into a vibrating screen with screen apertures of 0.5 mm, 1 mm, and 2 mm to classify three types of micro-carbon ferrochrome powder products: fine particles (0.5~1 mm), medium particles (1~2 mm), and coarse particles (around 2 mm), ensuring that the particle size deviation of each product is ≤0.2 mm. During the crushing and shaping process, the density and impurity content of the product are tested. If they do not meet the requirements, the crushing and shaping process is repeated or the previous steps are returned for further processing. After all testing items meet the standards, the products are packaged. Double-layer packaging is used: an inner aluminum foil bag and an outer woven bag, with a packaging size of 25kg / bag. During packaging, argon gas with a purity ≥99.99% is injected into the aluminum foil bag to ensure no air is present inside and prevent product oxidation. After packaging, the product name, particle size specification, production date, and test qualification mark are labeled on the woven bag. The packaged products are then sent to a dedicated storage warehouse, which is kept dry and well-ventilated, with relative humidity controlled below 30% and temperature controlled between 10~25℃. The product stacking height does not exceed 10 layers to avoid crushing and damage. Simultaneously, a product traceability system is established, with each batch of products numbered and all parameters and test results recorded during the production process to ensure product quality traceability.

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