Method for preparing high-carbon ferrochrome by smelting chromite in electric furnace

Abstract

The invention discloses a method for preparing high-carbon ferrochrome by smelting chromite in an electric furnace, which comprises the following steps: proportioning first chromite powder, a calcium flux, a magnesium flux, a siliceous flux, slag and fuel as raw materials, uniformly mixing, granulating, distributing, igniting, sintering, crushing, cooling and screening to obtain chromite fluxed sintered ore; fine grinding the second chromite powder, mixing the second chromite powder with a binder and water for pelletizing to obtain chromite green pellets, and drying, preheating and roasting the chromite green pellets to obtain chromite pellets; and adding the chromite fluxed sintered ore, the chromite pellets and a reducing agent into an electric furnace for smelting, and separating slag from iron to obtain high-carbon ferrochrome and slag. The method improves the distribution state of the flux in the electric furnace, improves the alkalinity of the slag, increases the content of low-melting-point phases in the slag, reduces the melting temperature and viscosity of the slag, and has the advantages of stabilizing the production operation of the electric furnace, reducing the smelting temperature, shortening the smelting time, improving the chromium recovery rate and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of chromite smelting, and particularly relates to a method for preparing high-carbon ferrochrome by electric furnace smelting chromite. BACKGROUND

[0002] High-carbon ferrochrome is a main alloy additive for producing stainless steel, and the C content is 4%-10%. The high-carbon ferrochrome is mainly produced by an electric furnace method. Since the melting point of chromium compounds is high, the smelting temperature of ferrochrome needs to be above 1700 DEG C, and the electric consumption is large. The affinity between Cr and C is large, and the chromium carbide is first formed in the reduction process, and then decarburization is performed with the increase of temperature. Meanwhile, the smelting of ferrochrome generates 1.1-1.5 times of slag of iron, which is much higher than the conventional slag amount, and the slag flowability is poor. The natural slag melting point is above 1750 DEG C, and the smelting temperature needs to be above 1700 DEG C by adding flux to adjust the slag composition to reduce the viscosity. The smelting has the disadvantages of high energy consumption, high carbon emission and the like.

[0003] It is one of important measures for efficiently and energy-saving producing high-carbon ferrochrome by the electric furnace method to prepare high-quality high-carbon ferrochrome smelting furnace charge by using low-cost chromite powder by sintering and pelletizing. The sinter is a man-made block ore obtained by a series of complex physical and chemical reactions at high temperature, and has good strength and metallurgical properties. However, the chromite sinter needs higher sintering temperature to be solidified, which shows that the fuel ratio needs to be higher, and the fuel ratio is usually required to be greater than 7.0%. In addition, there are problems of poor product quality and low yield. In addition, the existing electric furnace smelting high-carbon ferrochrome mainly uses the structure of "chromite + flux + reducing agent" as the furnace charge. The furnace charge can determine the smelting effect and is the main component of the smelting cost. The high-carbon ferrochrome production process has high requirements for the permeability, melting speed and reducibility of the furnace charge. In the current production, the smelting of the electric furnace smelting process is directly put into the furnace in the form of slag flux. Since the raw flux is directly put into the furnace for smelting, on the one hand, the raw flux can participate in slagging only after the decomposition in the furnace, and on the other hand, it is not conducive to the uniform distribution of the flux in the furnace, which not only affects the uniformity of slagging, but also reduces the utilization efficiency of the flux, and is one of the main reasons for the problems of high electric energy consumption and unstable operation in the process of electric furnace smelting high-carbon ferrochrome.

[0004] In general, the chromite powder sintering has problems of high sintering temperature, high energy consumption and low yield. In the process of electric furnace smelting high-carbon ferrochrome, the chromite furnace charge, flux and reducing agent are added separately, which causes uneven distribution in the furnace, large difference in resistance of different furnace charges, large fluctuation of furnace conditions, and large difficulty in electric furnace smelting operation. In addition, the existing chromite slag system is mainly Al2O3-SiO2-MgO ternary slag system, and the slag system has high melting temperature, high smelting temperature, high electric energy consumption and low element recovery rate. SUMMARY

[0005] The technical problem solved by the present application is to overcome the deficiencies of the prior art, especially for the high sintering temperature, high energy consumption, low yield, and uneven distribution of chromium ore in the furnace due to the separate addition of chromium ore charge, flux, and reducing agent in the process of smelting high-carbon ferrochrome in the electric furnace, which causes large fluctuations in the furnace condition, large resistance difference between different charges, and large difficulty in electric furnace smelting operation, and the problems of high smelting temperature, high energy consumption, and low element recovery rate in the existing chromium ore smelting process, and to provide a method for preparing high-carbon ferrochrome from chromium ore by electric furnace smelting.

[0006] To solve the above technical problems, the present application adopts the following technical solutions.

[0007] A method for preparing high-carbon ferrochrome from chromium ore by electric furnace smelting, comprising the following steps:

[0008] (1) Chromium ore flux sinter preparation: the first chromium ore powder, calcium flux, magnesium flux, silicon flux, slag, and fuel are used as raw materials for batching, mixing, granulating, distributing, igniting, sintering, crushing, cooling, and screening to obtain chromium ore flux sinter; wherein the addition amount of the calcium flux is added according to the mass ratio of CaO to SiO2 in the composition of the chromium ore flux sinter is 0.4-1.5:1, the addition amount of the magnesium flux is added according to the mass ratio of MgO to Al2O3 in the composition of the chromium ore flux sinter is 0.8-2.4:1, the addition amount of the silicon flux is added according to the mass ratio of SiO2 / (CaO+SiO2+MgO+Al2O3) in the composition of the chromium ore flux sinter is 0.3-0.6, the addition amount of the slag is 2%-10% of the total mass of the raw materials, and the mass of the fuel is 5.5%-7.0% of the total mass of the raw materials;

[0009] (2) Chromium ore pellet preparation: the second chromium ore powder is ground and mixed with a binder and water to form balls, and the green chromium ore balls are dried, preheated, and calcined to obtain chromium ore pellets; wherein the mass ratio of the second chromium ore powder, the binder, and water is 87-94:1-3:5-10;

[0010] (3) Electric furnace smelting: the chromium ore flux sinter and the chromium ore pellets are added to the electric furnace as mixed charge for smelting, wherein the mass ratio of (chromium ore flux sinter+chromium ore pellets) to reducing agent is 80-90:10-20, the mass ratio of the chromium ore flux sinter to the chromium ore pellets is 10-90:10-90, the smelting temperature is 1600-1700°C, and the smelting time is 60-120 min, and after slag-iron separation, high-carbon ferrochrome and slag are obtained.

[0011] In the method for smelting chromite to prepare high-carbon ferrochrome by using an electric furnace, preferably, in step (1), the fuel comprises coke powder and / or coal powder, the calcareous flux comprises one or more of limestone, dolomite, slaked lime, quicklime and high-calcium slag, the mass fraction of CaO in the high-calcium slag is ≥40%, the magnesian flux comprises one or more of dolomite, magnesite, serpentine and magnesian slag, the mass fraction of MgO in the magnesian slag is ≥30%, and the siliceous flux comprises one or more of silica, diatomite, serpentine and siliceous slag, the mass fraction of SiO2 in the siliceous slag is ≥40%.

[0012] The particle size of the fuel is ≤5 mm, wherein the particle size of -3 mm is not more than 70%, and the particle size of the calcareous flux, the magnesian flux and the siliceous flux is controlled to be ≥90% of -3 mm.

[0013] The particle size of the slag is ≤5 mm, wherein the particle size of -3 mm is not more than 70%.

[0014] In the method for smelting chromite to prepare high-carbon ferrochrome by using an electric furnace, preferably, in step (1), the raw material further comprises returned ore, the addition amount of the returned ore accounts for 20%-25% of the total mass of the raw material, and the returned ore is sintered ore with a particle size of -5 mm obtained after sintering of chromite powder, i.e., sintered ore with a particle size of -5 mm obtained after sintering of chromite powder and then crushing and screening, which cannot be added into the electric furnace for smelting.

[0015] In the method for smelting chromite to prepare high-carbon ferrochrome by using an electric furnace, preferably, in step (1), water is added to adjust the moisture content of the mixture to 6wt%-12wt% during the mixing and granulating process, the ignition temperature is 1050°C-1150°C, the ignition time is 1 min-2 min, the holding time is 1.0 min-2.0 min, the ignition negative pressure is 5 kPa-6 kPa, the sintering negative pressure is 8 kPa-10 kPa, the cooling negative pressure is 4 kPa-8 kPa, and the cooling time is 2 min-5 min.

[0016] In the method for smelting chromite to prepare high-carbon ferrochrome by using an electric furnace, preferably, in step (2), the drying temperature is 200°C-400°C, the drying time is 3 min-5 min, the preheating temperature is 800°C-1100°C, the preheating time is 5 min-30 min, the roasting temperature is 1150°C-1300°C, and the roasting time is 5 min-30 min.

[0017] The method for smelting chromite in an electric furnace to prepare high-carbon ferrochrome, preferably, in step (2), the method for drying, preheating and roasting the chromite green balls comprises one of a grate-kiln method, a belt method and a shaft furnace method.

[0018] The method for smelting chromite in an electric furnace to prepare high-carbon ferrochrome, preferably, in step (1), the mass fraction of Cr2O3 in the first chromite powder is 30% to 60%, and the mass fraction of chromium in the slag is 3% to 15%; in step (2), the mass fraction of Cr2O3 in the second chromite powder is 30% to 60%, and the particle size of the ground second chromite powder is controlled to be greater than or equal to 80% of 0.074 mm.

[0019] The method for smelting chromite in an electric furnace to prepare high-carbon ferrochrome, preferably, in step (2), the binder is one or more of inorganic binders and organic binders, and the inorganic binder comprises bentonite.

[0020] The method for smelting chromite in an electric furnace to prepare high-carbon ferrochrome, preferably, in step (3), the reducing agent comprises one or more of coke powder, anthracite and semicoke.

[0021] Compared with the prior art, the method has the advantages that:

[0022] Because the melting point of chromite spinel is high, the amount of liquid phase generated is only about 20% of the solidified phase, which is significantly lower than the 30%-40% of ordinary sinter. Small-scale sintering tests of chromite show that liquid phase can be observed when the sintering temperature is higher than 1350℃, and when the temperature reaches 1400℃ or above, the chromite sinter begins to stick together, which makes it difficult to generate low-melting-point liquid phase in the chromite sintering process, and the chromite powder has poor granulation performance, high sintering temperature, high fuel ratio, large production fluctuation, high energy consumption, and low product yield. The present application mixes fluxes required for high-carbon ferrochrome electric furnace smelting with chromite to prepare chromite flux sinter, adjusts the composition and addition amount of flux, and the flux mineralizes with chromite during the sintering process to generate low-melting-point compounds, thereby promoting the increase of liquid phase amount in the chromite sintering process, improving the quality of chromite sinter, and achieving the effect of energy saving and consumption reduction; the produced chromite flux sinter has uniform distribution of flux, which can avoid the problems of electric furnace condition fluctuation and difficult operation control caused by separate addition of chromite and flux, and the flux completes pre-slagging during the sintering process, which can shorten the electric furnace smelting time. In addition, the calcium flux is added to the flux to increase the basicity (CaO / SiO2) of the slag, and the slag composition is adjusted by adding chromite pellets during the electric furnace smelting process, so that the content of low-melting-point phases such as augite and calcium magnesium olivine in the slag increases, the melting temperature and viscosity of the slag decrease, the element diffusion conditions are improved, which helps to reduce the smelting temperature, shorten the smelting time, and reduce the slag amount, thereby reducing the energy consumption and carbon emission, and the chromium recovery rate during the smelting process is increased from below 93% to above 98%. DETAILED DESCRIPTION

[0023] The present application will be further described below in combination with specific preferred embodiments, but the protection scope of the present application is not limited thereby. The materials and instruments used in the following examples are all commercially available.

[0024] Example 1

[0025] A method for preparing high-carbon ferrochrome by electric furnace smelting chromite according to the present application, comprising the following steps:

[0026] (1) Chromite fluxed sinter preparation: South African chromite powder with Cr2O3 of 44.28wt% as raw material, and return fines, flux, chromium-containing slag and coke powder are added. Limestone, dolomite and silica are used as fluxes, and the particle sizes of the three are all controlled to be 90% or more of -3mm. The limestone is added according to the mass ratio of CaO to SiO2 in the composition of the chromite fluxed sinter of 0.4:1. The dolomite is added according to the mass ratio of MgO to Al2O3 in the composition of the chromite fluxed sinter of 0.8:1. The silica is added according to the mass ratio of SiO2 / (CaO+SiO2+MgO+Al2O3) in the composition of the chromite fluxed sinter of 0.3. The particle sizes of the calcareous flux, the magnesian flux and the siliceous flux are all controlled to be 90% or more of -3mm. The chromium-containing slag is added in an amount of 5% of the total mass of the raw materials. The particle size of the slag is controlled to be 0 < slag particle size ≤ 5mm, of which -3mm is not more than 70%. The chromium content in the slag is 5.69%. The mass of the coke powder is 7.0% of the total mass of the raw materials. The particle size of the coke powder is controlled to be 0 < coke powder particle size ≤ 5mm, of which -3mm is not more than 70%. The mass of the return fines is 20% of the total mass of the raw materials. The return fines are sintered fines with a size of -5mm. The raw materials are mixed and granulated into sintering mixtures with a size of 0.5mm to 8mm. The moisture content of the mixture is 10.5%. The mixture is laid out with a layer thickness of 500mm. Then ignition, sintering, crushing and cooling are carried out. The ignition temperature is 1100±20℃, the ignition time is 2min, the holding time is 1min, the ignition negative pressure is 5kPa, the sintering exhaust negative pressure is 8kPa, and the cooling negative pressure is adjusted to 6kPa after sintering is completed. The cooling time is 4min. After screening, the chromite fluxed sinter is obtained. The sinter yield is 82.22%, the drum strength is 64.86%, and the utilization coefficient is 1.209t / (h·m 2 ).

[0027] (2) Chromite pellet preparation: The chromite powder (with a mass fraction of Cr2O3 of 42.56%) is finely ground to 80% or more of -0.074mm. Then the chromite powder, bentonite and water are mixed in a mass ratio of 89:2:9. After mixing, the chromite green balls that meet the requirements (falling strength greater than 3 times / (0.5m·piece), and compressive strength greater than 10N / piece) are dried, preheated and roasted. The process can use one of chain grate-rotary kiln method, belt machine method and shaft furnace method, but is not limited thereto. The drying temperature is 400℃, the drying time is 3min, the preheating temperature is 800℃, the preheating time is 30min, and the roasting temperature is 1300℃. The roasting time is 5min. The compressive strength of the obtained chromite pellets is 2580N / P.

[0028] (3) Electric furnace smelting: the chromite flux sinter, chromite pellet, and coke powder are added into the electric furnace according to the proportion for smelting, wherein the mass ratio of (chromite flux sinter + chromite pellet) : coke powder is 90:10, and the mass ratio of chromite flux sinter: chromite pellet is 90:10, the smelting temperature is 1700℃, the smelting time is 60 min, after slag-iron separation, high-carbon ferrochrome and chromium-containing slag are obtained, and the chromium element recovery rate reaches 98.6%.

[0029] Example 2

[0030] A method for preparing high-carbon ferrochrome by electric furnace smelting chromite according to the present application, comprising the following steps:

[0031] (1) Chromite flux sinter preparation: taking chromite powder with Cr2O3 of 44.28% as raw material, and additionally adding return ore, flux, chromium-containing slag, and coke powder, taking slaked lime, magnesite, and silica as flux, and controlling the particle size of the three to be-3mm≥90%, adding slaked lime according to the mass ratio of CaO to SiO2 in the composition of chromite flux sinter of 0.6:1, adding magnesite according to the mass ratio of MgO to Al2O3 in the composition of chromite flux sinter of 1.2:1, and adding silica according to the mass ratio of SiO2 / (CaO+SiO2+MgO+Al2O3) in the composition of chromite flux sinter of 0.4, controlling the particle size of the calcium flux, magnesium flux, and silica flux to be-3mm≥90%, taking the total mass of all raw materials as the basis, the chromium-containing slag is 2%, the particle size of the slag is controlled to be 0<slag particle size≤5mm, wherein-3mm does not exceed 70%, the mass fraction of chromium in the slag is 10.25%, the mass fraction of coke powder is 6.0%, the particle size of the coke powder is controlled to be 0<coke powder particle size≤5mm, wherein-3mm does not exceed 70%, the mass fraction of return ore is 20%, and the return ore is sinter under-5mm. The raw materials are mixed and granulated into 0.5-8mm sintered mixture, and the moisture content of the mixture is 9.5%. The mixture is distributed, ignited, sintered, crushed, and cooled, the layer thickness is 500mm, the ignition temperature is 1100±20℃, the ignition time is 1.5min, the holding time is 1min, the ignition negative pressure is 5kPa, the sintering negative pressure is 8kPa, after sintering, the cooling negative pressure is adjusted to 5kPa, and the cooling time is 3min. After screening, the chromite flux sinter is obtained, the finished product rate of the sinter is 80.26%, the drum strength is 64.42%, and the utilization coefficient is 1.193t / (h·m 2 ).

[0032] (2) Chromite pellet preparation: After the chromite powder (mass fraction of Cr203 is 42.56%) is crushed and ground to -0.074 mm≥80%, the chromite powder, bentonite and water are mixed in a mass ratio of 89.5:1.5:9, and then the mixture is balling. The qualified chromite green balls (falling strength is greater than 3 times / (0.5 m. piece), and the compressive strength is greater than 10 N / piece) are dried, preheated and roasted. The drying temperature is 200°C, the drying time is 5 min, the preheating temperature is 900°C, the preheating time is 15 min, the roasting temperature is 1250°C, and the roasting time is 8 min. The compressive strength of the obtained chromite pellet is 2276 N / P.

[0033] (3) Electric furnace smelting: The chromite flux sinter, chromite pellet and anthracite are added into an electric furnace in a certain proportion for smelting. The mass ratio of (chromite flux sinter + chromite pellet) to anthracite is 88:12, and the mass ratio of chromite flux sinter to chromite pellet is 70:30. The smelting temperature is 1650°C, and the smelting time is 90 min. After slag-iron separation, high-carbon chromite and chromium-containing slag are obtained, and the chromium element recovery rate reaches 98.2%.

[0034] Example 3

[0035] A method for preparing high-carbon chromite by electric furnace smelting according to the present application comprises the following steps:

[0036] (1) Chromite fluxed sinter preparation: with Cr2O3 as 42.26% chromite powder as raw material, and adding return fines, coke powder, chromium-containing slag and flux, with quicklime, serpentine and quartz sand as flux, the particle size of the three is controlled at -3mm≥90%, the addition amount of quicklime is added according to the mass ratio of CaO to SiO2 in the composition of chromite fluxed sinter is 0.8:1, the addition amount of serpentine is added according to the mass ratio of MgO to Al2O3 in the composition of chromite fluxed sinter is 1.6:1, the addition amount of quartz sand is added according to the mass ratio of SiO2 / (CaO+SiO2+MgO+Al2O3) in the composition of chromite fluxed sinter is 0.45, the particle size of calcium flux, magnesium flux and silicon flux is controlled at -3mm≥90%, based on the total mass of all raw materials, the chromium-containing slag is 7%, the particle size of the slag is controlled at 0<slag particle size≤5mm, wherein -3mm is not more than 70%, the mass fraction of chromium in the slag is 14.89%, the mass fraction of coke powder is 6.0%, the particle size of coke powder is controlled at 0<coke powder particle size≤5mm, wherein -3mm is not more than 70%, the mass fraction of return fines is 20%, and the return fines are -5mm sinter. The raw materials are mixed and granulated into 0.5-8mm sintering mixture, and the moisture content of the mixture is 11%. The mixture is distributed, ignited, sintered and cooled, the layer thickness is 500mm, the ignition time is 1min, the holding time is 1min, the ignition temperature is 1100±20℃, the ignition negative pressure is 5kPa, the sintering exhaust negative pressure is 8kPa, and after sintering, the cooling negative pressure is adjusted to 5kPa, the cooling time is 3min, and after screening, the chromite fluxed sinter is obtained, the sinter product yield is 81.14%, the drum strength is 64.85%, and the utilization coefficient is 1.202t / (h·m 2 )。

[0037] (2) Chromite pellet preparation: after crushing and grinding the chromite powder to -0.074mm≥80%, the mass ratio of chromite powder, bentonite and water is 90.5:1.5:8, and the mixture is uniformly mixed and then balling, the qualified (falling strength is greater than 3 times / (0.5m·piece), and the compression strength is greater than 10N / piece) chromite green balls are dried, preheated and roasted, the drying temperature is 400℃, the drying time is 3min, the preheating temperature is 1000℃, the preheating time is 10min, the roasting temperature is 1150℃, and the roasting time is 30min, the compression strength of the obtained chromite pellet is 2170N / P.

[0038] (3) Electric furnace smelting: the chromite flux sinter, chromite pellet, and coking coal are added into the electric furnace for smelting, wherein the mass ratio of (chromite flux sinter + chromite pellet) : coking coal is 80:20, the mass ratio of chromite flux sinter: chromite pellet is 50:50, the smelting temperature is 1600℃, the smelting time is 120 min, after slag-iron separation, high-carbon ferrochrome and chromium-containing slag are obtained, wherein the chromium element recovery rate reaches 98.3%.

[0039] Example 4

[0040] A method for preparing high-carbon ferrochrome by electric furnace smelting chromite according to the present application, comprising the following steps:

[0041] (1) Chromite flux sinter preparation: taking chromite powder with Cr2O3 of 40.18% as raw material, and additionally adding return ore, coke powder, chromium-containing slag, and flux, taking high-calcium slag (CaO content 42.5%), magnesite, and silica as flux, the particle size of the three is controlled to be -3mm≥90%, the addition amount of high-calcium slag is added according to the mass ratio of CaO to SiO2 of 1.0:1 in the composition of chromite flux sinter, the addition amount of magnesite is added according to the mass ratio of MgO to Al2O3 of 1.8:1 in the composition of chromite flux sinter, the addition amount of silica is added according to the mass ratio of SiO2 / (CaO+SiO2+MgO+Al2O3) of 0.5 in the composition of chromite flux sinter, the particle size of calcareous flux, magnesian flux, and siliceous flux is controlled to be -3mm≥90%, taking the total mass of all raw materials as the basis, the chromium-containing slag is added in a proportion of 10%, the particle size of the slag is controlled to be 0<slag particle size≤5mm, wherein -3mm does not exceed 70%, the mass fraction of chromium in the slag is 8.46%, the mass ratio of coal powder is 6.5%, the particle size of the coal powder is controlled to be 0<focal powder particle size≤5mm, wherein -3mm does not exceed 70%, the mass ratio of return ore is 20%, and the return ore is sinter under-5mm. The raw materials are mixed and granulated into 0.5-8mm sintered mixture, and the moisture content of the mixture is 9%. The mixture is distributed, ignited, sintered, crushed, and cooled, the layer thickness is 500mm, the ignition time is 2min, the holding time is 1min, the ignition temperature is 1100±20℃, the ignition negative pressure is 5kPa, the sintering exhaust negative pressure is 8kPa, after sintering is completed, the cooling negative pressure is adjusted to 5kPa, and the cooling time is 2min. The sintered product yield is 80.13%, the drum strength is 62.45%, and the utilization coefficient is 1.122t / (h·m 2 ).

[0042] (2) Chromite pellet preparation: After the chromite powder (mass fraction of Cr203 is 45.69%) is crushed and ground to 80% of -0.074 mm, the chromite powder, bentonite and water are mixed in a mass ratio of 90:1:9, and then the mixture is balling. The qualified chromite green balls (falling strength is greater than 3 times per 0.5 m, and the compressive strength is greater than 10 N per ball) are dried, preheated and roasted. The drying temperature is 200°C, the drying time is 5 min, the preheating temperature is 1100°C, the preheating time is 5 min, the roasting temperature is 1250°C, and the roasting time is 15 min. The compressive strength of the obtained chromite pellets is 2510 N / P.

[0043] (3) Electric furnace smelting: The chromite flux sinter, chromite pellets, anthracite and coke powder are added into an electric furnace for smelting, wherein the mass ratio of (chromite flux sinter + chromite pellets) : anthracite : coke powder is 85:10:5, and the mass ratio of chromite flux sinter : chromite pellets is 30:70. The smelting temperature is 1650°C, and the smelting time is 90 min. After slag-iron separation, high-carbon chromite and chromium-containing slag are obtained, and the chromium element recovery rate reaches 98.5%.

[0044] Example 5

[0045] A method for preparing high-carbon chromite by electric furnace smelting according to the present application, comprising the following steps:

[0046] (1) Chromite fluxed sinter preparation: take the chromite powder with Cr2O3 of 44.28% as raw material, add return fines, coke powder, chromium-containing slag and flux, take limestone, dolomite and silica as flux, the particle size of the three is controlled to be -3mm≥90%, the limestone is added according to the mass ratio of CaO to SiO2 of 1.5:1 in the composition of the chromite fluxed sinter, the dolomite is added according to the mass ratio of MgO to Al2O3 of 2.4:1 in the composition of the chromite fluxed sinter, the silica is added according to the mass ratio of SiO2 / (CaO+SiO2+MgO+Al2O3) of 0.6 in the composition of the chromite fluxed sinter, the particle size of the calcareous flux, the magnesian flux and the siliceous flux is controlled to be -3mm≥90%, the chromium-containing slag is added in an amount of 5% based on the total mass of all raw materials, the particle size of the slag is controlled to be 0<slag particle size≤5mm, wherein -3mm is not more than 70%, the chromium content in the slag is 6.52%, the coke powder accounts for 5.5% of the mass, the particle size of the coke powder is controlled to be 0<coke powder particle size≤5mm, wherein -3mm is not more than 70%, the return fines account for 20% of the mass, and the return fines are sinter under -5mm. The raw materials are mixed and granulated into 0.5-8mm sintering mixture with a moisture content of 10%. The mixture is distributed, ignited, sintered, crushed and cooled, the layer thickness is 500mm, the ignition time is 1.5min, the holding time is 1min, the ignition temperature is 1100±20℃, the ignition negative pressure is 6kPa, the sintering exhaust negative pressure is 10kPa, the cooling negative pressure is adjusted to 8kPa after sintering is completed, and the cooling time is 2min. After screening, the chromite fluxed sinter is obtained, the sinter yield is 80.86%, the drum strength is 62.48%, and the utilization coefficient is 1.195t / (h·m 2 )。

[0047] (2) Chromite pellet preparation: the chromite powder (the mass fraction of Cr2O3 is 41.85%) is crushed and ground to -0.074mm≥80%, then the chromite powder, bentonite and water are mixed uniformly in a mass ratio of 89:2:9, and the qualified (the falling strength is greater than 3 times / (0.5m·piece), and the compression strength is greater than 10N / piece) chromite green balls are dried, preheated and roasted, the drying temperature is 300℃, the drying time is 4min, the preheating temperature is 900℃, the preheating time is 15min, the roasting temperature is 1250℃, and the roasting time is 12min. The compression strength of the obtained chromite pellet is 2390N / P.

[0048] (3) Electric furnace smelting: the chromite fluxed sinter, chromite pellet, coke powder and semi-coke are added into the electric furnace according to the proportion, wherein the mass ratio of (chromite fluxed sinter + chromite pellet) : coke powder : semi-coke is 80:10:10, the mass ratio of chromite fluxed sinter : chromite pellet is 10:90, the smelting temperature is 1700℃, the smelting time is 60 min, and after slag-iron separation, high-carbon ferrochrome and chromium-containing slag are obtained, wherein the chromium element recovery rate reaches 98.8%.

[0049] Comparative Example 1

[0050] A method for preparing high-carbon ferrochrome by electric furnace smelting chromite, which is basically the same as Example 1, the only difference is that no flux is added in step (1), the sinter yield is 63.35%, the drum strength is 50.56%, and the utilization coefficient is 1.014 t / (h·m2). The flux added in step (1) is in the form of blocks (flux particle size 10-50 mm) and is added in step (3), and the amount is consistent with Example 1. The electric furnace smelting effect is shown in Table 1.

[0051] Comparative Example 2

[0052] A method for preparing high-carbon ferrochrome by electric furnace smelting chromite, which is basically the same as Example 1, the only difference is that no chromite fluxed sinter is added in step (3), only the pellet obtained in step (2) is added, the flux added in step (1) is in the form of blocks (flux particle size 10-50 mm) and is added in step (3). The electric furnace smelting effect is shown in Table 1.

[0053] Comparative Example 3

[0054] A method for preparing high-carbon ferrochrome by electric furnace smelting chromite, which is basically the same as Example 1, the only difference is that no flux is added in step (1), the flux added in step (1) is in the form of blocks (flux particle size 10-50 mm) and is added in step (3) according to the final slag MgO / Al2O3=1.3, SiO2 content=30%, and the electric furnace smelting effect is shown in Table 1.

[0055] Table 1 Comparison of smelting test effects of Example 1 and Comparative Examples 1-3

[0056] Charge type Cr recovery / % Slag quantity / kg / t alloy Average electricity consumption of electric furnace / kw·h Example 1 98.6 630-680 3000 Comparative Example 1 95.2 680-720 3100 Comparative Example 2 94.3 700-750 3150 Comparative Example 3 89.2 750-800 3300

[0057] The above merely describes preferred embodiments of the present application, and is not intended to limit the present application in any form. Although the present application has been disclosed with the preferred embodiments as above, it is not intended to limit the present application. Any person skilled in the art, without departing from the spirit and technical solutions of the present application, can make many possible changes and modifications to the technical solutions of the present application, or modify equivalent embodiments with equivalent changes. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments according to the technical essence of the present application, without departing from the technical solutions of the present application, still belongs to the protection scope of the technical solutions of the present application.

Claims

1. A method of smelting chromite in an electric furnace to produce high carbon ferrochrome, characterised in that, Includes the following steps: (1) Preparation of chromite flux sinter: Using first chromite powder, calcium flux, magnesium flux, silicon flux, slag and fuel as raw materials, the mixture is batched, mixed, granulated, distributed, ignited, sintered, crushed, cooled and screened to obtain chromite flux sinter; wherein, the amount of calcium flux added is based on the mass ratio of CaO to SiO2 in the composition of chromite flux sinter being 0.4 to 1.5:1, the amount of magnesium flux added is based on the mass ratio of MgO to Al2O3 in the composition of chromite flux sinter being 0.8 to 2.4:1, the amount of silicon flux added is based on the mass ratio of SiO2 / (CaO+SiO2+MgO+Al2O3) in the composition of chromite flux sinter being 0.3 to 0.6, the amount of slag added accounts for 2% to 10% of the total mass of raw materials, and the mass of fuel accounts for 5.5% to 7.0% of the total mass of raw materials; (2) Preparation of chromite pellets: The second chromite powder is ground and then mixed with binder and water to form pellets, which are then dried, preheated and roasted to obtain chromite pellets; wherein the mass ratio of the second chromite powder, binder and water is 87-94:1-3:5-10. (3) Electric furnace smelting: The fluxed sintered chromite, the chromite pellets, and the reducing agent are added to the electric furnace for smelting. The fluxed sintered chromite and the chromite pellets are used as mixed furnace charge for electric furnace smelting. The mass ratio of (fluxed sintered chromite + chromite pellets) to reducing agent is 80-90:10-20, and the mass ratio of fluxed sintered chromite to chromite pellets is 10-90:10-90. The smelting temperature is 1600℃-1700℃, and the smelting time is 60-120 minutes. After slag-iron separation, high-carbon ferrochrome and slag are obtained.

2. The method of smelting chromite to produce high carbon ferrochrome in an electric furnace according to claim 1, characterised in that, In step (1), the fuel includes coke powder and / or coal powder; the calcareous flux includes one or more of limestone, dolomite, hydrated lime, quicklime, and high-calcium slag, wherein the mass fraction of CaO in the high-calcium slag is ≥40%; the magnesian flux includes one or more of dolomite, magnesite, serpentine, and magnesian slag, wherein the mass fraction of MgO in the magnesian slag is ≥30%; and the siliceous flux includes one or more of silica, diatomite, serpentine, quartz sand, and siliceous slag, wherein the mass fraction of SiO2 in the siliceous slag is ≥40%. The particle size of the fuel is ≤5mm, of which -3mm does not exceed 70%, and the particle size of the calcium flux, magnesium flux, and silicon flux is controlled to be ≥90% of -3mm; The slag has a particle size of ≤5mm, of which -3mm does not exceed 70%.

3. The method of smelting chromite to produce high carbon ferrochrome in an electric furnace as claimed in claim 1 characterised in that, In step (1), return ore is also added to the raw materials. The amount of return ore added accounts for 20% to 25% of the total mass of the raw materials. The return ore is the sintered ore that is screened through a -5mm sieve in step (1).

4. The method of smelting chromite to produce high carbon ferrochrome in an electric furnace according to claim 1 characterised in that, In step (1), the mixing and granulating process is carried out by adding water to adjust the moisture content of the mixture to 6wt%-12wt%, the ignition temperature is 1050°C-1150°C, the ignition time is 1min-2min, the holding time is 1.0min-2.0min, the ignition negative pressure is 5kPa-6kPa, the sintering negative pressure is 8kPa-10kPa, the cooling negative pressure is 4kPa-8kPa, and the cooling time is 2min-5min.

5. The method of smelting chromite to produce high carbon ferrochrome in an electric furnace as claimed in claim 1, wherein, In step (2), the drying temperature is 200°C-400°C, the drying time is 3min-5min, the preheating temperature is 800°C-1100°C, the preheating time is 5min-30min, the calcining temperature is 1150°C-1300°C, and the calcining time is 5min-30min.

6. The method of smelting chromite to produce high carbon ferrochrome in an electric furnace according to any one of claims 1 to 5, characterised in that, In step (2), the drying, preheating and calcining of the chromite green balls are carried out by one of the following methods: chain grate-rotary kiln method, belt method and shaft furnace method.

7. The method of smelting chromite to produce high carbon ferrochrome in an electric furnace according to any one of claims 1 to 5, characterised in that, In step (1), the mass fraction of Cr2O3 in the first chromite powder is 30%-60%, and the mass fraction of chromium in the slag is 3%-15%; in step (2), the mass fraction of Cr2O3 in the second chromite powder is 30%-60%, and the particle size of the ground second chromite powder is controlled to be ≥80% of-0.074mm.

8. The method of smelting chromite to produce high carbon ferrochrome in an electric furnace according to any one of claims 1 to 5, characterised in that, In step (2), the binder is one or more of inorganic binders and organic binders, and the inorganic binder includes bentonite.

9. The method of smelting chromite to produce high carbon ferrochrome in an electric furnace according to any one of claims 1 to 5, characterised in that, In step (3), the reducing agent includes one or more of coke powder, anthracite and semicoke.