Method for producing high-carbon ferrochrome through chromite pellet prereduction-electric furnace smelting

Abstract

The invention belongs to the field of comprehensive utilization of chromite, and particularly relates to a method for producing high-carbon ferrochrome through chromite pellet prereduction-electric furnace smelting. According to the method, a reduction method that a reducing agent and chromite pellets are fed into a kiln separately is adopted, chromite oxidized pellets are prepared firstly and then reduced through a rotary kiln solid carbon reducing agent, and the obtained pre-reduced pellets are subjected to electric furnace smelting with a calcium flux and a magnesium flux as slagging fluxes to prepare the high-carbon ferro-chrome. The problem that according to an existing method, the metallization rate of the pre-reduced pellets and the adverse effect on electric furnace smelting caused by unstable carbon residues are solved, the production stability of the electric furnace can be improved, and meanwhile the electric furnace smelting temperature can be increased. The method is simple, controllable, low in energy consumption, high in efficiency, high in stability, low in production cost and convenient for industrial application.

Description

Technical Field

[0001] This invention belongs to the field of comprehensive utilization of chromite, specifically relating to a method for producing high-carbon ferrochrome by pre-reduction of chromite pellets and electric furnace smelting. Background Technology

[0002] Ferrochrome alloys are the main alloying additives used in the production of stainless steel and tool steel. They are classified according to carbon content into high-carbon ferrochrome, medium-carbon ferrochrome, low-carbon ferrochrome, and low-carbon ferrochrome. High-carbon ferrochrome alloys, with a chromium content of approximately 52%-60% and a carbon content of 4%-10%, are the main ferrochrome alloy products and can be used as raw materials for the production of other ferrochrome products such as medium, low, and low-carbon ferrochrome. Their production accounts for over 90% of the total ferrochrome output. With market and economic development, the demand for stainless steel and high-carbon ferrochrome alloys is increasing.

[0003] The smelting methods for high-carbon ferrochrome include the electric arc furnace (EAF) method, the vertical shaft furnace (blast furnace) method, the plasma method, and the smelting reduction method. Currently, the EAF method is the main method. The main charge structure for EAF smelting of high-carbon ferrochrome is "chromite + flux + reducing agent". The charge determines both the smelting effect and the smelting cost. The EAF smelting process for high-carbon ferrochrome requires high permeability, melting rate, and reducibility of the charge. Generally, chromite powder needs to be agglomerated. Common agglomeration methods include sintering, pelletizing, and briquetting. The pelletizing method has the advantages of high utilization rate, low energy consumption, high single-unit capacity, and high production flexibility. Currently, in the high-carbon ferrochrome smelting process, chromite agglomerated products, slag-forming flux, and reducing agent are added at the EAF charge outlet. After a period of smelting, the high-carbon ferrochrome and slag are removed. The smelting process has problems such as high operational difficulty, unstable furnace conditions, and high production costs.

[0004] The pre-reduction-electric furnace method for smelting chromite ore to produce high-carbon ferrochrome has been industrially applied. This method involves adding a carbon reducing agent to the pellets and then roasting and pre-reducing the pellets to obtain metallized pellets, which can effectively reduce energy consumption and improve chromium recovery. Currently, representative methods for preparing reducing pellets include the SRC and DRC methods. The SRC method involves adding a certain amount of carbon reducing agent to the pellets and using a chain grate-rotary kiln to pre-reduce the chromite pellets. The carbon content is 70-100% of the theoretical amount of Cr2O3, FeO, and Fe2O3 in the reducing ore. This reduces smelting coke consumption by 45% and increases chromium recovery by 1%-2%. The product obtained by this method has a reduction degree of 55%, and the chromium content in the electric furnace smelting slag is only 3%. However, the SRC method needs to address the problem of internal carbon-added pellet pulverization leading to ring formation in the rotary kiln. The DRC method uses a rotary hearth furnace for the pre-reduction of chromite pellets. This method employs internally compounded carbon pellets and uses combustible gas to provide heat, typically high-calorific-value natural gas, although coke oven gas can also be used. Internationally, companies like International Metals Recycling Canada use this method for pellet pre-reduction, but domestically, internally compounded fixed carbon is still used as the reducing agent, with the heat generated from the combustion of solid carbon used for pre-reduction. The DRC method achieves a reduction degree of 30%-75% in pellets, effectively avoiding problems such as ring agglomeration and pulverization that occur with the rotary kiln method. However, the overall energy consumption of the DRC method (1548 kg / t) is higher than that of the SRC method (1336 kg / t). In addition to the above two pre-reduction methods, in the early 21st century, my country successfully developed an externally heated vertical shaft furnace production method. This method involves preparing chromite powder, coke, and bentonite into pellets in a certain proportion, and then pre-reducing them in an externally heated vertical shaft furnace, ultimately obtaining a product with a reduction degree of 60%-70%.

[0005] However, the aforementioned pre-reduced chromite pellets are all produced using the internal carbon addition method. Currently, the internal carbon addition method for producing pre-reduced chromite pellets suffers from unstable pellet metallization rate and residual carbon during the reduction process, which leads to unstable resistivity of the furnace charge and instability in the electric furnace smelting process. This results in problems such as high operational difficulty, high smelting energy consumption, and high production costs.

[0006] To address the aforementioned problems, this invention employs a reduction method that separately feeds the reducing agent and chromite pellets into the kiln. First, chromite oxide pellets are prepared, then reduced using a rotary kiln solid carbon reducing agent. Because the reducing agent is externally supplied, the pellets do not contain carbon internally. Compared to current reduction methods that use internally supplied carbon reducing agents, the resulting pre-reduced product does not exhibit unstable residual carbon due to reduction temperature and time. During the electric furnace smelting process, calcareous, magnesian, and siliceous fluxes are used as slag-forming fluxes to develop low-melting-point phases in the slag, such as pyroxene and calcium magnesium olivine, thereby reducing the slag melting temperature and viscosity. Compared to current electric furnace smelting slag-forming systems, this method is beneficial for reducing smelting temperature and slag-iron separation, improving the conditions for chromium diffusion into the molten iron, and increasing the recovery rate of chromium in chromite. This invention helps to solve the adverse effects of unstable metallization rate and residual carbon of pre-reduced pellets on electric furnace smelting in existing methods. It can improve the stability of electric furnace production, while also reducing the pre-reduction temperature and electric furnace smelting temperature, reducing smelting energy consumption and improving production efficiency. It is of great significance for energy saving and consumption reduction in high-carbon ferrochrome production. Summary of the Invention

[0007] The existing electric arc furnace (EAF) process for smelting high-carbon ferrochrome from chromite pre-reduction involves problems such as large fluctuations in the reduction degree of pre-reduced pellets, unstable residual carbon, difficult EAF operation, low production efficiency, and poor economic benefits. The purpose of this invention is to provide a method for producing high-carbon ferrochrome from chromite pellets through EAF smelting, thereby improving upon existing methods, reducing smelting energy consumption, lowering costs, and increasing production efficiency.

[0008] This invention provides the following technical solution: a method for producing high-carbon ferrochrome by pre-reduction of chromite pellets and electric furnace smelting, comprising the following steps:

[0009] Preparation of S1 chromite pellets: Chromite pre-treated by grinding, binder and water are mixed thoroughly in a certain proportion and then pelletized to obtain chromite pellets.

[0010] S2 Chromite Pellet Pre-reduction: Qualified chromite pellets are dried and preheated to obtain chromite oxide pellets, which are then reduced and roasted with an external reducing agent to obtain chromite pre-reduced pellets. The amount of external reducing agent added is 30-60% of the mass of the dried chromite pellets, preferably 30-50%.

[0011] S3 chromite pre-reduction pellet electric furnace smelting: Chromite pre-reduction pellets, slag-forming flux, and reducing agent are charged into an electric furnace for smelting. The slag-forming flux includes calcium flux, magnesium flux, and silicon flux. During the smelting process, silicon flux is added according to the slag composition SiO2 / Al2O3 mass ratio of 1.0-2.0:1, preferably 1.0-1.5:1; calcium flux and magnesium flux are added according to the slag composition (CaO+MgO) / Al2O3 mass ratio of 1.0-1.5:1, preferably 1.0-1.4:1; and the CaO to MgO mass ratio is 0.2-0.5:1. The amount of reducing agent added is 10-20 wt% of the mass of the pre-reduction pellets, preferably 10-15 wt%. The smelting temperature is 1600-1700℃. High-carbon ferrochrome and slag can be obtained by slag-metal separation.

[0012] Furthermore, the grinding pretreatment method described in S1 includes, but is not limited to, one or more of the following methods: ball milling, high-pressure roller milling, wet milling, vertical milling, etc.

[0013] Furthermore, the chromite particle size after grinding pretreatment described in S1 is ≥80% of -200 mesh.

[0014] Furthermore, the adhesive described in S1 is one or more of bentonite, organic adhesives, and composite adhesives.

[0015] Furthermore, in the chromite pellets, the mass ratio of chromite, binder, and water is chromite:binder:water = 85-92:1-3:7-12.

[0016] Furthermore, the reduction roasting method for chromite pellets described in S2 includes rotary kiln method, vertical shaft furnace method, tunnel kiln method, etc. The reduction roasting temperature is 1100℃~1400℃, and the reduction roasting time is 1h~5h.

[0017] Furthermore, the reducing agent used in the reduction roasting of the chromite pellets described in S2 has a particle size of 5-30mm and >80%.

[0018] Furthermore, the degree of reduction of the chromite pellet pre-reduced pellets described in S2 is 50-70%.

[0019] The reducing agent is applied in two external processes (including pre-reduction external application and electric furnace smelting external application). The pellets do not contain carbon. Compared with the current reduction method that uses carbon reducing agent internally, the pre-reduced product will not have problems with unstable metallization rate and residual carbon due to reduction temperature and time. The pre-reduced pellets produced have stable metallization rate and stable residual carbon, reducing the difficulty of electric furnace smelting operation.

[0020] Furthermore, in the preparation of the chromite oxide pellets described in S2, the drying temperature of the green pellets is 200℃~400℃, the drying time is 2min~20min, the preheating oxidation is carried out in an air atmosphere, the preheating oxidation temperature is 700℃~1200℃, and the preheating oxidation time is 5min~60min.

[0021] Furthermore, the reduction roasting temperature in S2 is 1300–1400℃, and the reduction roasting time is 90–150 min.

[0022] Furthermore, the calcium flux described in S3 includes, but is not limited to, one or more calcium-containing substances such as limestone, dolomite, quicklime, and high-calcium slag.

[0023] Furthermore, the magnesium flux described in S3 includes, but is not limited to, one or more magnesium-containing substances such as dolomite, magnesite, serpentine, and magnesium-containing slag.

[0024] Furthermore, the silicon flux described in S3 includes, but is not limited to, one or more silicon-containing substances such as silica, serpentine, quartz sand, and silicon-containing slag.

[0025] Furthermore, the reducing agents used in the reduction roasting and electric furnace smelting include, but are not limited to, one or more of coke powder, anthracite, and semi-coke.

[0026] This invention achieves effective chromium recovery of over 97% even when smelting at 1600–1650℃. Furthermore, the average power consumption can be reduced to 2000 kW·h / t.

[0027] The slag production of this invention is only 680-720 kg per ton of the target alloy produced. The slag production is low and stable.

[0028] The advantages of this invention are:

[0029] This invention proposes a method for producing high-carbon ferrochrome through pre-reduction of chromite pellets and electric arc furnace smelting. The pre-reduction pellet production process employs a reduction method where the reducing agent and chromite pellets are fed separately into the kiln. First, chromite oxide pellets are prepared, then reduced using a rotary kiln with a solid carbon reducing agent. Because the reducing agent is externally supplied, the pellets do not contain carbon internally. Compared to current reduction methods that use internally supplied carbon reducing agents, the resulting pre-reduced product does not suffer from unstable metallization rate and residual carbon due to reduction temperature and time. The produced pre-reduced pellets exhibit stable metallization rate and residual carbon, reducing the difficulty of electric arc furnace smelting operations. During the electric arc furnace smelting process, calcareous, magnesian, and siliceous fluxes are used as slag-forming fluxes to develop low-melting-point phases in the slag, such as pyroxene and calcium magnesium olivine, thereby reducing the slag melting temperature and viscosity. Compared to current electric arc furnace slag-forming systems, this method is beneficial for reducing smelting temperature and slag-iron separation, improving the conditions for chromium diffusion into the molten iron, and increasing the recovery rate of chromium from chromite. This invention addresses the adverse effects of unstable metallization rate and residual carbon in pre-reduced pellets on electric arc furnace smelting, which are present in existing methods. It improves the stability of electric arc furnace production, lowers smelting temperature, reduces energy consumption, increases production efficiency, and significantly reduces production costs. Furthermore, the designed slag system further enhances chromium recovery. Detailed Implementation

[0030] The specific embodiments of the present invention will be further illustrated below, but the specific embodiments of the present invention are not limited to the following embodiments.

[0031] The main components of the chromite furnace charge used in this embodiment are shown in Table 1 below.

[0032] Table 1. Main chemical components of chromite (wt%)

[0033]

[0034] Example 1

[0035] A method for producing high-carbon ferrochrome by pre-reduction of chromite pellets and electric furnace smelting includes the following steps:

[0036] After crushing and grinding chromite to -200 mesh ≥80%, bentonite and water are added in a certain proportion and mixed evenly to form pellets, resulting in qualified green pellets. The qualified green pellets are in the following mass ratio: chromite: bentonite: water = 90:2:8.

[0037] The qualified green pellets were dried, preheated (drying temperature was 300℃, drying time was 12 min, preheating oxidation was carried out in air atmosphere, preheating oxidation temperature was 700℃, preheating oxidation time was 60 min), and reduced roasting was performed. The amount of coke powder added during the reduced roasting process was 30% of the mass of the dried green pellets, resulting in chromite pre-reduced pellets with a reduction degree of 52.1%, an average carbon content of 1.15%, and a carbon content fluctuation range of ±0.11%. The reduced roasting temperature was 1100℃ and the reduced roasting time was 1.5 h.

[0038] Pre-reduced chromite pellets were charged into an electric furnace, with coke powder added as a reducing agent (the amount of coke powder added was 20% of the mass of the pre-reduced pellets). Limestone, magnesite, and silica were added as slag-forming fluxes. Silica was added according to a slag composition SiO2 / Al2O3 mass ratio of 1.0:1, and limestone and magnesite were added according to a slag composition (CaO+MgO) / Al2O3 mass ratio of 1.3:1 and a CaO to MgO mass ratio of 0.5:1. The smelting temperature was 1650℃ and the smelting time was 60 min, yielding high-carbon ferrochrome and chromium-containing slag. The chromium content in the resulting ferrochrome molten metal was 52.35%, with a chromium recovery rate of 98.3%.

[0039] Example 2

[0040] A method for producing high-carbon ferrochrome by pre-reduction of chromite pellets and electric furnace smelting includes the following steps:

[0041] After crushing and grinding chromite to -200 mesh ≥80%, bentonite and water are added and mixed evenly in a certain proportion to form pellets; qualified green pellets are obtained. The qualified green pellets are in the following mass ratio: chromite: bentonite: water = 92:1:7.

[0042] The qualified green pellets were dried, preheated (drying temperature was 400℃, drying time was 5 min, preheating oxidation was carried out in air atmosphere, preheating oxidation temperature was 1100℃, preheating oxidation time was 30 min), and reduced roasting was performed. The amount of coke powder added during the reduced roasting process was 40% of the mass of the dried green pellets, resulting in chromite pre-reduced pellets with a reduction degree of 59.6%, an average carbon content of 1.45%, and a carbon content fluctuation range of ±0.26%. The reduced roasting temperature was 1200℃ and the reduced roasting time was 2 h.

[0043] Pre-reduced chromite pellets were charged into an electric furnace, with coke powder added as a reducing agent (18% of the mass of the pre-reduced pellets). Steel slag, ferronickel slag, and silica were added as slag-forming fluxes. Silica was added according to a SiO2 / Al2O3 mass ratio of 1.1:1, and steel slag and ferronickel slag were added according to a (CaO+MgO) / Al2O3 mass ratio of 1.4:1 and a CaO / MgO mass ratio of 0.4:1. The smelting temperature was 1650℃ and the smelting time was 60 minutes to obtain high-carbon ferrochrome and chromium-containing slag. The chromium content in the resulting ferrochrome molten metal was 52.14%, with a chromium recovery rate of 98.2%.

[0044] Example 3

[0045] A method for producing high-carbon ferrochrome by pre-reduction of chromite pellets and electric furnace smelting includes the following steps:

[0046] After crushing and grinding chromite to -200 mesh ≥80%, bentonite and water are added and mixed evenly in a certain proportion to form pellets; qualified green pellets are obtained. The qualified green pellets are in the following mass ratio: chromite: bentonite: water = 88:3:9.

[0047] The qualified green pellets were dried, preheated (drying temperature was 200℃, drying time was 20 min, preheating oxidation was carried out in air atmosphere, preheating oxidation temperature was 900℃, preheating oxidation time was 45 min), and reduced roasting was performed. The amount of coke powder added during the reduced roasting process was 60% of the mass of the dried green pellets, resulting in chromite pre-reduced pellets with a reduction degree of 66.1%, an average carbon content of 1.82%, and a carbon content fluctuation range of ±0.32%. The reduced roasting temperature was 1300℃, and the reduced roasting time was 3 h.

[0048] Pre-reduced chromite pellets were charged into an electric furnace, with coke powder added as a reducing agent (15% of the mass of the pre-reduced pellets). Dolomite, serpentine, and silica were added as slag-forming fluxes. Silica was added according to a SiO2 / Al2O3 mass ratio of 1.2:1, and dolomite and serpentine were added according to a (CaO+MgO) / Al2O3 mass ratio of 1.3:1 and a CaO / MgO mass ratio of 0.2:1. The smelting temperature was 1700℃, and the smelting time was 60 min, yielding high-carbon ferrochrome and chromium-containing slag. The chromium content in the resulting ferrochrome molten metal was 52.08%, with a chromium recovery rate of 97.1%.

[0049] Example 4

[0050] A method for producing high-carbon ferrochrome by pre-reduction of chromite pellets and electric furnace smelting includes the following steps:

[0051] After crushing and grinding chromite to -200 mesh ≥80%, bentonite and water are added in a certain proportion and mixed evenly to form pellets; qualified green pellets are obtained. The qualified green pellets are in the following mass ratio: chromite: bentonite: water = 85:3:12.

[0052] The qualified green pellets were dried, preheated (drying temperature was 350℃, drying time was 15 min, preheating oxidation was carried out in air atmosphere, preheating oxidation temperature was 1000℃, preheating oxidation time was 25 min), and reduced roasted. The amount of coke powder added during the reduced roasting process was 50% of the mass of the dried green pellets, resulting in chromite pre-reduced pellets with a reduction degree of 62.2%, an average carbon content of 1.64%, and a carbon content fluctuation range of ±0.25%. The reduction roasting temperature was 1300℃, and the reduction roasting time was 2.5 h.

[0053] Pre-reduced chromite pellets were charged into an electric furnace, with coke powder added as a reducing agent (10% of the mass of the pre-reduced pellets). Limestone, serpentine, and silica were added as slag-forming fluxes. Silica was added according to a SiO2 / Al2O3 mass ratio of 1.5:1, and limestone and serpentine were added according to a (CaO+MgO) / Al2O3 mass ratio of 1.0:1 and a CaO / MgO mass ratio of 0.2:1. The smelting temperature was 1600℃, and the smelting time was 60 min, yielding high-carbon ferrochrome and chromium-containing slag. The chromium content in the resulting ferrochrome molten metal was 52.34%, with a chromium recovery rate of 98.5%.

[0054] Example 5

[0055] A method for producing high-carbon ferrochrome by pre-reduction of chromite pellets and electric furnace smelting includes the following steps:

[0056] After crushing and grinding chromite to -200 mesh ≥80%, bentonite and water are added and mixed evenly in a certain proportion to form pellets; qualified green pellets are obtained. The qualified green pellets are in the following mass ratio: chromite: bentonite: water = 90:1:9.

[0057] The qualified green pellets were dried, preheated (drying temperature was 400℃, drying time was 8 min, preheating oxidation was carried out in air atmosphere, preheating oxidation temperature was 1150℃, preheating oxidation time was 20 min), and reduced roasted. The amount of coke powder added during the reduced roasting process was 30% of the mass of the dried green pellets, resulting in chromite pre-reduced pellets with a reduction degree of 52.1%, an average carbon content of 1.06%, and a carbon content fluctuation range of ±0.12%. The reduction roasting temperature was 1300℃, and the reduction roasting time was 2 hours.

[0058] Pre-reduced chromite pellets were charged into an electric furnace, with semi-coke added as a reducing agent (the amount of semi-coke added was 10% of the mass of the pre-reduced pellets). Dolomite, magnesite, and silica were added as slag-forming fluxes. Silica was added according to a slag composition SiO2 / Al2O3 mass ratio of 1.3:1, and dolomite and magnesite were added according to a slag composition (CaO+MgO) / Al2O3 mass ratio of 1.3:1 and a CaO to MgO mass ratio of 0.3:1. The smelting temperature was 1650℃ and the smelting time was 60 minutes to obtain high-carbon ferrochrome and chromium-containing slag. The chromium content in the resulting ferrochrome molten metal was 52.05%, with a chromium recovery rate of 97.3%.

[0059] Example 6

[0060] A method for producing high-carbon ferrochrome by pre-reduction of chromite pellets and electric furnace smelting includes the following steps:

[0061] After crushing and grinding chromite to -200 mesh ≥80%, bentonite and water are added and mixed evenly in a certain proportion to form pellets; qualified green pellets are obtained. The qualified green pellets are in the following mass ratio: chromite: bentonite: water = 89:2:9.

[0062] The qualified green pellets were dried, preheated (drying temperature was 250℃, drying time was 8 min, preheating oxidation was carried out in air atmosphere, preheating oxidation temperature was 800℃, preheating oxidation time was 40 min), and reduced roasted. The amount of coke powder added during the reduced roasting process was 50% of the mass of the dried green pellets, resulting in chromite pre-reduced pellets with a reduction degree of 64.6%, an average carbon content of 1.75%, and a carbon content fluctuation range of ±0.36%. The reduction roasting temperature was 1200℃, and the reduction roasting time was 4 hours.

[0063] Pre-reduced chromite pellets were charged into an electric furnace, with semi-coke added as a reducing agent (the amount of semi-coke added was 10% of the mass of the pre-reduced pellets). Dolomite, magnesite, and silica were added as slag-forming fluxes. Silica was added according to a slag composition with a SiO2 / Al2O3 mass ratio of 1.4:1, and steel slag and ferronickel slag were added according to a slag composition with a (CaO+MgO) / Al2O3 mass ratio of 1.4:1 and a CaO / MgO mass ratio of 0.4:1. The smelting temperature was 1625℃, and the smelting time was 30 minutes. High-carbon ferrochrome and chromium-containing slag were obtained. The chromium content in the resulting ferrochrome molten metal was 52.23%, with a chromium recovery rate of 97.7%.

[0064] Industrial application experiments:

[0065] A smelting test was conducted at a high-carbon ferrochrome smelter in the country to verify the effectiveness of the invention.

[0066] Comparative Example 1

[0067] (1) Preparation of green chromite pellets: Chromite (composition shown in Table 1) and coke powder are ground to -200 mesh ≥80%, then bentonite and water are added and mixed evenly in proportion to form green chromite pellets; wherein, by mass fraction, chromite accounts for 79.5%, coke powder accounts for 10%, bentonite accounts for 1.5%, and water accounts for 9.0%. Green chromite carbon-containing pellets are qualified with a drop strength greater than 3.0 times / 0.5m·p pellet and a compressive strength greater than 10N / p pellet.

[0068] (2) Pre-reduction of carbon-containing chromite pellets: qualified carbon-containing chromite pellets are dried, preheated and oxidized, and then reduced and roasted in a rotary kiln. The drying temperature is 400℃ and the drying time is 8min. The preheating temperature is 1150℃ and the preheating time is 20min. The reduction roasting temperature is 1350℃ and the reduction roasting time is 2 hours, resulting in pre-reduced chromite pellets with a reduction degree of 39.2%.

[0069] (3) Electric furnace smelting of pre-reduced chromite pellets: Pre-reduced chromite pellets are hot-charged into the electric furnace, and coke powder is added as a reducing agent. The particle size of the coke powder is 10mm~50mm>90%, and the amount of coke powder added is 10% of the mass of the pre-reduced pellets. Block silica, magnesite, and limestone (flux particle size 10-50mm) are added to the electric furnace to adjust the composition of the slag (the slag composition is shown in Table 2). The on-site electric furnace smelting parameters and effects are shown in Table 2.

[0070] Example 7

[0071] (1) Preparation of green chromite pellets: Chromite (composition shown in Table 1) and coke powder were ground to -200 mesh ≥80%, and then chromite, bentonite, and water were mixed evenly in a mass ratio of chromite:bentonite:water = 90:1:9 to obtain green chromite pellets. Qualified chromite pellets are those with a drop strength greater than 3.0 times / 0.5m·pellet and a compressive strength greater than 10N / pellet.

[0072] (2) Pre-reduction of chromite pellets: After drying and preheating oxidation of qualified green chromite pellets, coke powder of 50% of the mass of the dried green pellets is added and the pellets are reduced and roasted in a rotary kiln. The drying temperature is 400℃ and the drying time is 8min. The preheating temperature is 1150℃ and the preheating time is 20min. The reduction roasting temperature is 1350℃ and the reduction roasting time is 2 hours, resulting in chromite pre-reduced pellets with a reduction degree of 39.2%.

[0073] (3) Electric furnace smelting of pre-reduced chromite pellets: Pre-reduced chromite pellets are hot-charged into the electric furnace, and coke powder is added as a reducing agent. The particle size of the coke powder is 10mm~50mm>90%, and the amount of coke powder added is 10% of the mass of the pre-reduced pellets. Block silica, magnesite, and limestone (flux particle size 10-50mm) are added to the electric furnace to adjust the composition of the slag. The on-site electric furnace smelting parameters and effects are shown in Table 2.

[0074] Table 2 Results of a Smelting Test at a Certain Plant

[0075]

[0076]

Claims

1. A method for producing high-carbon ferrochrome by pre-reduction of chromite pellets and electric furnace smelting, characterized in that: Preparation of S1 chromite green pellets: Chromite pre-treated by grinding, binder and water are mixed thoroughly in a certain proportion and then pelletized to obtain chromite green pellets. S2 Chromite Pellet Pre-reduction: Qualified chromite green pellets are dried and preheated to obtain chromite oxide pellets, which are then reduced and roasted with an external reducing agent to obtain chromite pre-reduced pellets; the amount of external reducing agent added is 30-60% of the mass of the dried chromite pellets. S3 chromite pre-reduction pellet electric furnace smelting: Chromite pre-reduction pellets, slag-forming flux, and reducing agent are charged into the electric furnace for smelting. The slag-forming flux includes calcium flux, magnesium flux, and silicon flux. During the smelting process, silicon flux is added according to the slag composition SiO2 / Al2O3 mass ratio of 1.0 to 2.0:1, and calcium flux and magnesium flux are added according to the slag composition (CaO+MgO) / Al2O3 mass ratio of 1.0 to 1.5:1 and the CaO to MgO mass ratio of 0.2 to 0.5:

1. The amount of reducing agent added is 10-20 wt% of the mass of the pre-reduction pellets. The smelting temperature is 1600-1700℃. High-carbon ferrochrome and slag can be obtained by slag-metal separation.

2. The method for producing high-carbon ferrochrome by electric furnace smelting of chromite ore according to claim 1, characterized in that: The grinding pretreatment method described in S1 includes, but is not limited to, one or more of the following methods: ball milling, high-pressure roller milling, wet milling, vertical milling, etc.; the chromite particle size after grinding pretreatment is -200 mesh ≥80%.

3. The method for producing high-carbon ferrochrome by electric furnace smelting of chromite ore according to claim 1, characterized in that: The binder described in S1 is one or more of bentonite, organic binders, and composite binders.

4. The method for producing high-carbon ferrochrome by electric furnace smelting of chromite ore according to claim 1, characterized in that: In the chromite pellets, the mass ratio of chromite, binder and water is chromite:binder:water = 85-92:1-3:7-12.

5. The method for producing high-carbon ferrochrome by electric furnace smelting of chromite ore according to claim 1, characterized in that: The reduction roasting method for chromite pellets described in S2 includes rotary kiln method, vertical shaft furnace method, tunnel kiln method, etc. The reduction roasting temperature is 1200℃~1350℃, and the reduction roasting time is 1h~5h.

6. The method for producing high-carbon ferrochrome by electric furnace smelting of chromite ore according to claim 1, characterized in that: The reducing agent in the S2 chromite pellet reduction roasting process has a particle size of 5-30mm and a reduction rate of >80%, and the pre-reduced chromite pellets in the S2 process have a reduction rate of 50-70%. The preparation of chromite oxide pellets as described in S2 involves drying green pellets at a temperature of 200℃~400℃ for 2min~20min, and preheating oxidation in an air atmosphere at a temperature of 800℃~1100℃ for 5min~60min.

7. The method for producing high-carbon ferrochrome by electric furnace smelting of chromite ore according to claim 1, characterized in that: The calcium flux described in S3 includes, but is not limited to, one or more calcium-containing substances such as limestone, dolomite, quicklime, and high-calcium slag.

8. The method for producing high-carbon ferrochrome by electric furnace smelting of chromite ore according to claim 1, characterized in that: The magnesium flux described in S3 includes, but is not limited to, one or more magnesium-containing substances such as dolomite, magnesite, magnesium silicate, serpentine, and magnesium-containing slag.

9. The method for producing high-carbon ferrochrome by electric furnace smelting of chromite ore according to claim 1, characterized in that: The silicon-based flux described in S3 includes, but is not limited to, one or more silicon-containing substances such as silica, serpentine, quartz sand, and silicon-containing slag.

10. The method for producing high-carbon ferrochrome by electric furnace smelting of chromite ore according to claim 1, characterized in that: The reducing agents used in the reduction roasting and electric furnace smelting include, but are not limited to, one or more of coke powder, anthracite, and semi-coke.

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