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

Abstract

The invention discloses a method for producing high-carbon ferro-chrome through chromite fluxed pellet prereduction-electric furnace smelting. The method comprises the steps that chromite, a calcium flux, a magnesium flux and an additive are subjected to ore grinding pretreatment and then fully and evenly mixed with a binder and water, and pelletizing is conducted; and the obtained chromite fluxed pellet green pellets are dried, preheated and oxidized, a first reducing agent is added for reduction roasting, the obtained chromite fluxed pre-reduced pellets, a second reducing agent and a silicon-containing flux are put into an electric furnace for smelting, and high-carbon ferrochrome and slag are obtained through slag-gold separation. The fluxed pre-reduced pellets are prepared by adopting an internal flux and an external reducing agent, the reduction performance of chromite can be improved, the reduction temperature can be reduced, meanwhile, the reduction degree and residual carbon of the prepared fluxed pre-reduced pellets are stable, the smelting time can be effectively shortened by adopting the fluxed pre-reduced pellets to be matched with the reducing agent for electric furnace smelting, and the production cost is reduced. And the smelting power consumption is reduced, the chromium recovery rate is improved, the production stability is improved, and the production cost is remarkably reduced.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of comprehensive utilization of chromite, and particularly relates to a method for producing high-carbon ferrochrome by using chromite fluxed pellet pre-reduction-electric furnace smelting. BACKGROUND

[0002] Ferrochrome alloy is the main alloy additive for producing stainless steel and tool steel, and is divided into high-carbon ferrochrome, medium-carbon ferrochrome, low-carbon ferrochrome and micro-carbon ferrochrome according to the carbon content. Among them, the high-carbon ferrochrome alloy has a chromium content of about 52% to 60% and a C content of 4% to 10%, is the main product of ferrochrome alloy, can be used as a raw material for producing other ferrochrome products such as medium-carbon ferrochrome, low-carbon ferrochrome and micro-carbon ferrochrome, and accounts for more than 90% of the total ferrochrome output. With the development of market and economy, the demand for stainless steel is increasing, and the demand for high-carbon ferrochrome alloy is also increasing.

[0003] The smelting method of high-carbon ferrochrome includes electric furnace method and converter smelting reduction method, and at present, the electric furnace method is mainly used. The main furnace charge structure for smelting high-carbon ferrochrome by electric furnace is "chromite + flux + reducing agent". The furnace charge can determine the smelting effect and the cost of smelting. The process of electric furnace smelting high-carbon ferrochrome has high requirements for the permeability, melting speed and reducibility of the furnace charge. Generally, the chromite powder needs to be processed into blocks. The common block-making methods include sintering method, pelletizing method and briquetting method. The pelletizing method has the characteristics of high utilization rate, low energy consumption, high single-machine production capacity and great production flexibility. At present, in the smelting process of high-carbon ferrochrome, the chromite block product, the slag-making flux and the reducing agent are added into the electric furnace charging port, and after a period of smelting, high-carbon ferrochrome and slag are discharged. The smelting process has problems of great operation difficulty, unstable furnace condition and high production cost.

[0004] The production of high-carbon ferrochrome by pre-reduction-electric furnace method has been industrialized and applied. This method is to add carbonaceous reducing agent into the pellets to obtain metallized pellets by pelletizing and pre-reduction, which can effectively reduce the energy consumption of electric furnace smelting and improve the recovery rate of chromium. At present, the representative methods for preparing reducing pellets include SRC and DRC methods. Among them, the SRC method is to add a certain amount of carbonaceous reducing agent into the pellets, and to use a grate-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. The coke consumption of electric furnace smelting is reduced by 45%, the chromium recovery rate is 93-94%, the reduction degree of the product obtained by this process is 55%, the electric energy consumption of electric furnace smelting is about 2100 kWh / t, and the chromium content in the slag is about 3%. However, the SRC method needs to solve the problem of ring formation caused by the pulverization of carbon-containing pellets in the rotary kiln. The DRC method uses a rotary hearth furnace to pre-reduce chromite pellets. This process uses carbon-containing pellets as reducing agent and uses combustible gas to provide heat. The preferred fuel is natural gas with high calorific value, and coke oven gas can also be used. The International Metals Recovery Company in Canada uses this process to pre-reduce pellets, but in China, solid carbon is still used as reducing agent, and the heat generated by the combustion of solid carbon is used for pre-reduction. The reduction degree of the pellets obtained by the DRC process is in the range of 30-75%, which effectively avoids the problems of ring formation and pulverization in the rotary kiln method. However, the comprehensive energy consumption of DRC (1548 kg / t) is higher than that of SRC (1336 kg / t). In addition to the above two pre-reduction processes, in the early 21st century, China successfully developed an external heating shaft furnace production process. This process is to mix chromite powder, coke and bentonite into pellets according to a certain proportion, and then pre-reduce them in an external heating shaft furnace. The reduction degree of the product is improved.

[0005] However, at present, both domestic and foreign production of chromite pre-reduction pellets uses internal fixed process. The production process is to add carbonaceous reducing agent into the pellets to prepare carbon-containing chromite pellets. Due to the different reaction degrees of the reducing agent carbon in the pellets during the production process, the residual carbon content in the pre-reduction product fluctuates greatly (±3% or more), and the pellet reduction degree also fluctuates greatly (±10% or more). The quality of the pellets is unstable. At present, the internal carbon production process of chromite pre-reduction pellets has the problems of unstable reduction process pellet metallization rate and residual carbon, which leads to unstable furnace charge specific resistance, thereby affecting the stability of the electric furnace smelting process operation, and has the problems of high operation difficulty, high smelting energy consumption and high production cost. SUMMARY

[0006] The technical problem solved by the present application is to overcome the deficiencies of the prior art, particularly the problems of the prior art, such as large fluctuation of reduction degree of pre-reduced pellets, unstable residual carbon, non-uniformity of flux addition, etc., leading to large operation difficulty, long smelting period, low production efficiency, and poor economic benefit in the electric furnace smelting process, and to provide a method for producing high-carbon chromium iron by pre-reducing fluxed chromite pellets in an electric furnace.

[0007] To solve the above technical problems, the present application adopts the following technical solutions.

[0008] A method for producing high-carbon chromium iron by pre-reducing fluxed chromite pellets in an electric furnace, comprising the following steps:

[0009] (1) Preparation of green fluxed chromite pellets: After grinding and pretreatment of chromite, calcium flux, magnesium flux, and additives, mix them with a binder and water in a certain proportion, then ball them to obtain green fluxed chromite pellets; wherein the mass ratio of (chromite + calcium flux + magnesium flux) : additives : binder : water is 82-93.9 : 0.1-5 : 1-3 : 5-10, the addition amount of calcium flux and magnesium flux is added according to the mass ratio of (CaO + MgO) / Al2O3 of 1.0-1.5 : 1 in the composition of fluxed pre-reduced pellets, and the addition amount of calcium flux is added according to the mass ratio of CaO to MgO of 0.2-0.5 : 1 in the composition of fluxed pre-reduced pellets;

[0010] (2) Pre-reduction of fluxed chromite pellets: dry and preheat the green fluxed chromite pellets obtained in the above step, then add a first reducing agent to reduce and roast them to obtain fluxed pre-reduced pellets;

[0011] (3) Electric furnace smelting of fluxed pre-reduced pellets: load the fluxed pre-reduced pellets, a second reducing agent, and a silicon-containing flux into an electric furnace for smelting, the addition amount of the second reducing agent is 5-15% of the mass of the fluxed pre-reduced pellets, the smelting temperature is 1600-1700℃, and after slag-gold separation, high-carbon chromium iron and slag are obtained.

[0012] The above method for producing high-carbon chromium iron by pre-reducing fluxed chromite pellets in an electric furnace, preferably, in step (3), the second reducing agent includes one or more of coke powder, anthracite, and semi-coke, and the particle size of the second reducing agent is 10-50mm > 90%.

[0013] The method for producing high-carbon ferrochrome by using chromite fluxed pellets pre-reduction-electric furnace smelting, preferably, in step (3), the silicon-containing flux includes one or more of silica, serpentine, quartz sand and silicon-containing slag, the SiO2 content in the silicon-containing slag is ≥ 35%, and the silicon-containing flux is added according to the mass ratio of SiO2 / Al2O3 in the slag composition being 1.0-2.0:1.

[0014] The method for producing high-carbon ferrochrome by using chromite fluxed pellets pre-reduction-electric furnace smelting, preferably, in step (3), the smelting time is 30 min-90 min, and the Cr2O3 content in the slag is less than 1.0%.

[0015] The method for producing high-carbon ferrochrome by using chromite fluxed pellets pre-reduction-electric furnace smelting, preferably, in step (1), the calcareous flux includes 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 includes one or more of dolomite, magnesite, magnesium silicate, serpentine and magnesian slag, the mass fraction of MgO in the magnesian slag is ≥ 30%; and the additive includes one or more of active silicon, borax and chromium-containing smelting slag, the chromium content in the chromium-containing smelting slag is 3%-15%.

[0016] The method for producing high-carbon ferrochrome by using chromite fluxed pellets pre-reduction-electric furnace smelting, preferably, in step (2), the method for reduction roasting includes one of a rotary kiln method and a shaft furnace method; the reduction roasting temperature is 1100°C-1300°C, the reduction roasting time is 1 h-3 h, and the reduction degree of the chromite fluxed pre-reduction pellets is 50%-70%.

[0017] The method for producing high-carbon ferrochrome by using chromite fluxed pellets pre-reduction-electric furnace smelting, preferably, in step (2), the first reducing agent includes one or more of coke powder, anthracite, bituminous coal, semi-coke and biomass charcoal, the particle size of the first reducing agent is ≥ 80% of 5 mm-30 mm, and the first reducing agent is added in a C / Fe mass ratio of 0.5-2.0, wherein C is the C in the first reducing agent, and Fe is the Fe in the chromite fluxed pre-reduction pellets.

[0018] The method for producing high-carbon ferrochrome by using chromite fluxed pellets pre-reduction-electric furnace smelting, preferably, in step (2), the chromite fluxed pellet green balls are dried, preheated and oxidized, the drying temperature is 200°C-400°C, the drying time is 2 min-20 min, the preheating and oxidizing is performed in an air atmosphere, the preheating and oxidizing temperature is 800°C-1100°C, and the preheating and oxidizing time is 5 min-60 min.

[0019] Preferably, in step (1), the particle size of the chromite, calcareous flux, magnesian flux and additives after the grinding pretreatment is ≥80% of -200 mesh.

[0020] Preferably, in step (1), the grinding pretreatment method comprises one or more of ball milling, roller milling, wet milling and vertical milling; the binder is one or more of inorganic binders and organic binders, and the inorganic binder comprises bentonite.

[0021] The alumina in the chromite is usually 5% to 25%.

[0022] Compared with the prior art, the method has the advantages that:

[0023] The present application provides a method for producing high-carbon ferrochrome by chromite flux pellet pre-reduction-electric furnace smelting. The method comprises the following steps: preparing chromite flux pellet green balls, reducing the chromite flux pellet green balls by using solid carbon reducing agent, and then smelting the obtained flux pre-reduction pellets in an electric furnace to produce high-carbon ferrochrome. The method uses flux to prepare flux pellets, so that the chromite and the flux are uniformly distributed, avoiding the problem of uneven distribution caused by separate addition of the chromite and the flux during electric furnace smelting, and at the same time, the flux, the additives and the chromite undergo solid phase reaction during the oxidation roasting of the pellets, which can destroy the lattice structure of the chromite, improve the reduction performance of the chromite, and reduce the reduction temperature. The present application also uses a reduction process in which the external reducing agent and the chromite flux pellet green balls are separately fed into the kiln, so that the reduction degree and the residual carbon of the produced pre-reduction pellets are stable, the difficulty of electric furnace smelting operation is reduced, and the production stability is improved.

[0024] The flux is added to the pellets, so that the flux and the chromite play a role in pre-slagging, which can shorten the smelting time, significantly reduce the production cost, increase the calcium flux and the additives in the balling process, develop low-melting-point phases in the slag, reduce the melting temperature and viscosity of the slag, compared with the current electric furnace smelting slagging system, which is conducive to reducing the smelting temperature and separating the slag and the iron, improving the conditions for the diffusion of chromium elements into molten iron, and improving the recovery rate of chromium elements in the chromite.

[0025] In summary, the method of the present application is beneficial to solve the adverse effects of the instability of the metalization rate and the residual carbon of the pre-reduction pellets on the stability of the electric furnace smelting operation, can improve the stability of the electric furnace production, and can also solve the problem of unstable furnace and ore caused by uneven distribution of flux in the current pre-reduction-electric furnace smelting process, especially the flux completes pre-slagging, which can significantly shorten the smelting time, improve the efficiency of electric furnace smelting, reduce the power consumption of smelting, improve the chromium recovery rate of electric furnace smelting, and has important significance for energy saving and consumption reduction in high-carbon ferrochrome production. DETAILED DESCRIPTION

[0026] The present application will be further described in connection with specific preferred embodiments, but the scope of the present application is not limited by the following examples. The materials and instruments used in the following examples are commercially available.

[0027] The main components of the chromite furnace charge used in the following examples are shown in Table 1 below, wherein TFe means total iron content.

[0028] Table 1 Main chemical composition table of chromite (unit: wt%)

[0029] TFe SiO2 CaO MgO Al2O3 Cr2O3 21.16 3.98 0.38 9.70 13.73 43.92

[0030] Example 1

[0031] A method for producing high-carbon chromium iron by smelting of chromite fluxed pellets pre-reduction-electric furnace according to the present application, comprising the following steps:

[0032] (1) Preparation of chromite fluxed pellet green balls: after crushing and high-pressure roller grinding the chromite, limestone, magnesite and chromium-containing smelting slag (chromium content of 9.45%) to -200 mesh ≥80%, adding bentonite and water in proportion to mix uniformly and then balling, chromite fluxed pellet green balls are obtained; wherein, according to the mass fraction, the total proportion of chromite, limestone, magnesite and additives is 90%, the proportion of bentonite is 1.0%, the proportion of moisture is 9.0%, the proportion of chromium-containing smelting slag is 5%, the addition amount of limestone and magnesite is added according to the mass ratio of (CaO+MgO) / Al2O3 of 1.5:1 in the composition of chromite fluxed pre-reduction pellets, and the addition amount of limestone is added according to the mass ratio of CaO to MgO of 0.5:1 in the composition of chromite fluxed pre-reduction pellets; the qualified chromite fluxed pellet green balls with green ball drop strength greater than 3.0 times / 0.5 m·piece and compressive strength greater than 10 N / P are prepared, and the particle size of the chromite fluxed green balls is 8 mm-20 mm.

[0033] (2) Chromite fluxed pellet pre-reduction: qualified chromite fluxed pellet green ball is dried (preferably using chain grate machine), preheated and oxidized in air atmosphere, and reduced and roasted in a rotary kiln with an external reducing agent. The drying temperature is 200°C, the drying time is 15 min, the preheating and oxidizing temperature is 1000°C, the preheating and oxidizing time is 20 min, the reducing and roasting temperature is 1150°C, the reducing and roasting time is 1.5 hours, the reducing agent is coke powder, the coke powder particle size is 5mm-30mm≥80%, and the addition amount of coke powder in the reducing and roasting process is 0.8 according to the mass ratio of C / Fe, wherein C is the C content in the reducing agent, and Fe is the Fe content in the chromite fluxed pre-reduction pellet. The chromite fluxed pre-reduction pellet with a reduction degree of 55.4% is obtained. The reduction degree of the chromite fluxed pre-reduction pellet fluctuates in the range of ±3.4%, the average carbon content of the pellet is 2.32%, and the carbon content of the pellet fluctuates in the range of ±0.41%.

[0034] (3) Chromite fluxed pellet pre-reduction electric furnace smelting: the chromite fluxed pre-reduction pellet is hot charged into an electric furnace, coke powder is added as a reducing agent, the particle size of the coke powder is 10mm-50mm>90%, the addition amount of the coke powder is 10% of the mass of the chromite fluxed pre-reduction pellet, and silica is added according to the mass ratio of SiO2 / Al2O3 in the high-carbon chromium iron smelting slag composition is 1.5:1. The smelting temperature is 1600°C, and the smelting time is 60 min. High-carbon chromium iron and chromium-containing slag are obtained, the chromium element recovery rate of the high-carbon chromium iron reaches 98.3%, and the Cr2O3 content in the slag is about 0.66%.

[0035] Example 2

[0036] A method for producing high-carbon chromium iron by chromite fluxed pellet pre-reduction-electric furnace smelting according to the present application, comprising the following steps:

[0037] (1) Chromite fluxed pellet green ball preparation: chromite, quicklime, serpentine and chromium-containing smelting slag (chromium content is 4.86%) are crushed and high-pressure roller ground to -200 mesh≥80%, then bentonite and water are added and mixed uniformly according to the proportion to form balls, and chromite fluxed pellet green balls are obtained; wherein, according to the mass fraction, the total proportion of chromite, quicklime, serpentine and additive is 89.5%, the proportion of bentonite is 1.5%, the proportion of moisture is 9.0%, and the proportion of chromium-containing smelting slag is 2%. The addition amount of quicklime and serpentine is added according to the mass ratio of (CaO+MgO) / Al2O3 in the composition of chromite fluxed pre-reduction pellet is 1.4:1, and the addition amount of quicklime is added according to the mass ratio of CaO to MgO in the composition of chromite fluxed pre-reduction pellet is 0.4:1. Qualified chromite fluxed pellet green balls with a ball drop strength greater than 3.0 times / (0.5m·piece) and a compressive strength greater than 10N / piece are prepared. The particle size of the chromite fluxed green ball is 8mm-20mm.

[0038] (2) Chromite fluxed pellet pre-reduction: qualified chromite fluxed pellet green pellets are dried, preheated and oxidized in air atmosphere, and reduced and roasted in a rotary kiln with an external reducing agent. The drying temperature is 250°C, the drying time is 12 min, the preheating and oxidizing temperature is 900°C, the preheating and oxidizing time is 25 min, the reducing and roasting temperature is 1200°C, the reducing and roasting time is 2 hours, the reducing agent is anthracite, the anthracite particle size is 5mm-30mm≥80%, and the anthracite addition amount in the reducing and roasting process is added according to the mass ratio of C / Fe of 1.2. Chromite fluxed pre-reduced pellets with a reduction degree of 60.8% are obtained. The reduction degree of the chromite fluxed pre-reduced pellets fluctuates in the range of ±3.6%, the average carbon content of the pellets is 2.52%, and the carbon content of the pellets fluctuates in the range of ±0.46%.

[0039] (3) Chromite fluxed pre-reduced pellet electric furnace smelting: the chromite fluxed pre-reduced pellets are hot charged into an electric furnace, and coke powder is added as a reducing agent. The particle size of the coke powder is 10mm-50mm>90%, the addition amount of the coke powder is 9% of the mass of the chromite fluxed pre-reduced pellets, and silica is added according to the mass ratio of SiO2 / Al2O3 in the high-carbon chromium iron smelting slag composition of 1.5:1. The smelting temperature is 1650°C, the smelting time is 30 min, high-carbon chromium iron and chromium-containing slag are obtained, and the chromium element recovery rate reaches 98.2%, and the Cr2O3 content in the slag is about 0.73%.

[0040] Example 3

[0041] A method for producing high-carbon chromium iron by chromite fluxed pellet pre-reduction-electric furnace smelting according to the present application, comprising the following steps:

[0042] (1) Chromite fluxed pellet green pellet preparation: chromite, slaked lime, magnesite and additive active silicon are crushed and high-pressure roller milled to -200 mesh≥80%, then bentonite and water are added and mixed uniformly to form pellets, and chromite fluxed pellet green pellets are obtained. According to the mass fraction, the total proportion of chromite, slaked lime, magnesite and additive is 90%, the proportion of bentonite is 1.0%, the proportion of moisture is 9.0%, the proportion of additive active silicon is 0.1%, the addition amount of slaked lime and magnesite is added according to the mass ratio of (CaO+MgO) / Al2O3 in the composition of chromite fluxed pre-reduced pellets of 1.5:1, and the addition amount of slaked lime is added according to the mass ratio of CaO to MgO in the composition of chromite fluxed pre-reduced pellets of 0.3:1. Qualified chromite fluxed pellet green pellets with a drop strength greater than 3.0 times / (0.5m·piece) and a compressive strength greater than 10N / piece are prepared. The particle size of the chromite fluxed green pellets is 8mm-20mm.

[0043] (2) Chromite fluxed pellet pre-reduction: qualified chromite fluxed pellet green pellets are dried, preheated and oxidized in air atmosphere, and reduced and roasted in a shaft furnace with an external reducing agent. The drying temperature is 300°C, the drying time is 10 min, the preheating and oxidizing temperature is 800°C, the preheating and oxidizing time is 30 min, the reducing and roasting temperature is 1100°C, the reducing and roasting time is 3 hours, the reducing agent is bituminous coal, the particle size of the bituminous coal is 5mm-30mm≥80%, the addition amount of the bituminous coal in the reducing and roasting process is 1.5 according to the mass ratio of C / Fe, and the reduction degree of the chromite fluxed pre-reduced pellets obtained is 51.8%. The reduction degree of the chromite fluxed pre-reduced pellets fluctuates in the range of ±2.6%, the average carbon content of the pellets is 1.72%, and the carbon content of the pellets fluctuates in the range of ±0.35%.

[0044] (3) Chromite fluxed pellet pre-reduction electric furnace smelting: the chromite fluxed pellet pre-reduced pellets are hot charged into an electric furnace, and coke is added as a reducing agent. The particle size of the coke is 10mm-50mm>90%, the addition amount of the coke is 15% of the mass of the chromite fluxed pellet pre-reduced pellets, quartz sand is added according to the mass ratio of SiO2 / Al2O3 in the composition of the high-carbon chromium iron smelting slag being 1.0:1, the smelting temperature is 1700°C, and the smelting time is 60min. High-carbon chromium iron and chromium-containing slag are obtained, and the chromium element recovery rate reaches 98.6%, and the Cr2O3 content in the slag is about 0.61%.

[0045] Example 4

[0046] A method for producing high-carbon chromium iron by chromite fluxed pellet pre-reduction-electric furnace smelting according to the present application, comprising the following steps:

[0047] (1) Preparation of chromite fluxed pellet green pellets: chromite, dolomite, magnesite and additive borax are crushed and high-pressure roller-milled to -200 mesh≥80%, then bentonite and water are added and mixed uniformly to form pellets, and chromite fluxed pellet green pellets are obtained. According to the mass fraction, the total amount of chromite, dolomite, magnesite and additive accounts for 89.5%, the amount of bentonite accounts for 1.5%, the amount of moisture accounts for 9.0%, and the amount of additive borax accounts for 0.1%. The addition amount of dolomite and magnesite is added according to the mass ratio of (CaO+MgO) / Al2O3 in the composition of the chromite fluxed pre-reduced pellet being 1.0:1, and the addition amount of dolomite is added according to the mass ratio of CaO to MgO in the composition of the chromite fluxed pre-reduced pellet being 0.2:1. The prepared chromite fluxed pellet green pellets have a drop strength greater than 3.0 times / (0.5m·piece) and a compressive strength greater than 10N / piece, and are qualified. The particle size of the chromite fluxed green pellets is 8mm-20mm.

[0048] (2) Chromite fluxed pellet pre-reduction: The qualified chromite fluxed pellet green ball is dried, preheated and oxidized in air atmosphere, and then reduced and roasted in a rotary kiln with an external reducing agent. The drying temperature is 350°C, the drying time is 8 min, the preheating and oxidizing temperature is 1100°C, the preheating and oxidizing time is 10 min, the reducing and roasting temperature is 1250°C, the reducing and roasting time is 1 hour, the reducing agent is anthracite, the anthracite particle size is 5mm-30mm≥80%, and the anthracite addition amount is 1.5 times of the mass ratio of C / Fe. The chromite fluxed pre-reduced pellet with a reduction degree of 60.8% is obtained. The reduction degree of the chromite fluxed pre-reduced pellet fluctuates in the range of ±3.3%, and the average carbon content of the pellet is 2.22%, with a fluctuation range of ±0.39%.

[0049] (3) Chromite fluxed pellet pre-reduction electric furnace smelting: The chromite fluxed pre-reduced pellet is hot charged into an electric furnace with anthracite as the reducing agent, the anthracite particle size is 10mm-50mm>90%, the anthracite addition amount is 12% of the mass of the chromite fluxed pre-reduced pellet, and the silicon-containing slag is added according to the mass ratio of SiO2 / Al2O3 in the high-carbon chromium iron smelting slag (final slag) composition of 1.3:1. The SiO2 content in the silicon-containing slag is 35.8%, the smelting temperature is 1650°C, and the smelting time is 90 min. The high-carbon chromium iron and chromium-containing slag are obtained, and the chromium element recovery rate reaches 98.8%, and the Cr2O3 content in the slag is about 0.53%.

[0050] Comparative Example 1

[0051] A method for producing high-carbon chromium iron by chromite fluxed pellet pre-reduction-electric furnace smelting is basically the same as Example 1, except that no flux and additives are added in step (1), i.e. no limestone, magnesite and chromium-containing smelting slag are added. Step (2) can obtain chromite pre-reduced pellets with an average reduction degree of 37.8%, and the pre-reduced pellet reduction degree fluctuates in the range of ±4.9%, the average carbon content of the pellet is 2.56%, and the carbon content of the pellet fluctuates in the range of ±0.76%. Step (3) uses bulk silicon stone, magnesite, limestone and other fluxes (flux particle size 10-50mm) to adjust the composition of the slag in the electric furnace, and the smelting effect is shown in Table 1.

[0052] Comparative Example 2

[0053] A method for producing high-carbon ferrochrome by pre-reducing chromite fluxed pellets in an electric furnace, which is basically the same as that of Example 1, with the exception that in step (1) no flux and additives are added, i.e. no limestone, magnesite and chromium-containing smelting slag is added; step (2) is the same as that of Example 1, and chromite pre-reduced pellets with an average reduction degree of 37.8% are obtained, the pre-reduced pellet reduction degree fluctuation range is ±4.9%, the average carbon content of the pellets is 2.56%, and the carbon content of the pellets fluctuation range is ±0.76%. In step (3), lump silicon stone, magnesite, limestone and the like (flux particle size 10-50 mm) are added to the electric furnace to adjust the composition of the slag, with reference to the existing ternary slag composition MgO / Al203=1.3 and Si02=30%, the smelting temperature and time are the same as those of Example 1, and the smelting effect is shown in Table 1.

[0054] Comparative Example 3

[0055] A method for producing high-carbon ferrochrome by pre-reducing chromite fluxed pellets in an electric furnace, which is basically the same as that of Example 1, with the exception that in step (1) 15% of coke powder is added, and the coke powder is crushed and ball milled to -200 mesh ≥80% before being added to the mixture for pelletizing; no reducing agent is added in step (2), and the drying, preheating oxidation and roasting system are the same as those of Example 1, finally obtaining chromite pre-reduced pellets with an average reduction degree of 53.7%, the reduction degree fluctuation range of the chromite pre-reduced pellets is ±9.2%, the average carbon content of the pellets is 4.11%, and the carbon content fluctuation range of the pellets is ±4.02%. Step (3) is the same as that of Example 1, and the smelting effect is shown in Table 1.

[0056] Table 1 Smelting test effect table of Example 1 and Comparative Examples 1-3

[0057] Cr recovery / % Slag amount / kg / t alloy Electricity consumption kw·h Example 1 98.3 600-650 1900 Comparative Example 1 95.6 700-750 2000 Comparative Example 2 89.5 750-850 2100 Comparative Example 3 97.2 650-700 1950

[0058] The above description is only a preferred embodiment of the present application, and does not limit the present application in any form. Although the present application has been disclosed as above with a preferred embodiment, it is not intended to limit the present application. Any skilled person in the art can make many possible changes and modifications to the technical solutions of the present application, or modify equivalent embodiments with equivalent changes, without departing from the spirit and technical solutions of the present application. 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, all still belong to the protection scope of the technical solutions of the present application.

Claims

1. A process for the production of high-carbon ferrochrome by a chromite fluxed pellet pre-reduction-electric furnace smelting, characterised in that, The method comprises the following steps: (1) Preparation of chromite fluxed green pellets: chromite, calcareous flux, magnesian flux, additives are pretreated by grinding, then mixed with binder and water in proportion, and then pelletized to obtain chromite fluxed green pellets; wherein the mass ratio of (chromite + calcareous flux + magnesian flux) : additives : binder : water is 82-93.9: 0.1-5: 1-3: 5-10, the addition amount of the calcareous flux and the magnesian flux is added according to the mass ratio of (CaO + MgO) / Al2O3 of 1.0-1.5: 1 in the composition of the chromite fluxed pre-reduced pellets, and the addition amount of the calcareous flux is added according to the mass ratio of CaO to MgO of 0.2-0.5: 1 in the composition of the chromite fluxed pre-reduced pellets; (2) Pre-reduction of chromite fluxed pellets: the above-mentioned chromite fluxed green pellets are dried, preheated and oxidized, then reduced by adding a first reducing agent to obtain chromite fluxed pre-reduced pellets; (3) Electric furnace smelting of chromite fluxed pre-reduced pellets: the above-mentioned chromite fluxed pre-reduced pellets, a second reducing agent and a silicon-containing flux are loaded into an electric furnace for smelting, the addition amount of the second reducing agent is 5%-15% of the mass of the chromite fluxed pre-reduced pellets, the smelting temperature is 1600-1700 DEG C, and high-carbon ferrochrome and slag are obtained after slag-gold separation.

2. The process for production of high carbon ferro-chrome by chromite fluxed pellet pre-reduction-electric furnace smelting as claimed in claim 1 wherein, In step (3), the second reducing agent comprises one or more of coke powder, anthracite and semi-coke, and the particle size of the second reducing agent is 10-50 mm > 90%.

3. The process for production of high carbon ferro-chrome by chromite fluxed pellet pre-reduction-electric furnace smelting as claimed in claim 1 wherein, In step (3), the silicon-containing flux comprises one or more of silica, serpentine, quartz sand and silicon-containing slag, the SiO2 content in the silicon-containing slag is ≥ 35%, and the silicon-containing flux is added according to the mass ratio of SiO2 / Al2O3 in the slag composition of 1.0-2.0:

1.

4. The process for production of high carbon ferro-chrome by chromite fluxed pellet pre-reduction-electric furnace smelting as claimed in claim 1 wherein, In step (3), the smelting time is 30-90 min, and the Cr2O3 content in the slag is less than 1.0%.

5. The process for the production of high-carbon ferrochromium by the chromite fluxed pellet direct-reduction- electric furnace smelting according to any one of claims 1 to 4, characterized in that, In step (1), 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, magnesium silicate, serpentine and magnesian slag, the mass fraction of MgO in the magnesian slag is ≥ 30%; and the additives comprise one or more of active silicon, borax and chromium-containing smelting slag, the chromium content in the chromium-containing smelting slag is 3%-15%.

6. The process for the production of high-carbon ferrochromium by the chromite fluxed pellet direct-reduction- electric furnace smelting according to any one of claims 1 to 4, characterized in that, In step (2), the method for reduction roasting comprises one of a rotary kiln method and a shaft furnace method; the reduction roasting temperature is 1100-1300 DEG C, the reduction roasting time is 1-3 h, and the reduction degree of the chromite fluxed pre-reduced pellets is 50%-70%.

7. The process for the production of high-carbon ferrochromium by the chromite fluxed pellet direct-reduced- electric furnace smelting according to any one of claims 1 to 4, characterized in that, In step (2), the first reducing agent includes one or more of coke breeze, anthracite, bituminous coal, semi-coke and biomass char, the particle size of the first reducing agent is 5mm-30mm≥80%, and the first reducing agent is added in a C / Fe mass ratio of 0.5-2.0, wherein C is the C in the first reducing agent and Fe is the Fe in the chromite fluxing pre-reduced pellets.

8. The process for production of high carbon ferro-chrome by pre- reduction of chromite fluxed pellets-electric furnace smelting according to any one of claims 1 to 4, characterized in that, In step (2), the chromite fluxing green pellets are dried and preheated and oxidized, the drying temperature is 200-400°C, the drying time is 2-20min, the preheating and oxidizing is performed in an air atmosphere, the preheating and oxidizing temperature is 800-1100°C, and the preheating and oxidizing time is 5-60min.

9. The process for production of high carbon ferro-chrome by pre- reduction of chromite fluxed pellets-electric furnace smelting according to any one of claims 1 to 4, characterized in that, In step (1), the particle size of the chromite, calcareous flux, magnesian flux and additives after the grinding pretreatment is all-200 mesh≥80%.

10. The process for production of high carbon ferro-chrome by pre- reduction of chromite fluxed pellets-electric furnace smelting according to any one of claims 1 to 4, characterized in that, In step (1), the grinding pretreatment method includes one or more of ball milling, roller milling, wet milling and vertical milling; the binder is one or more of inorganic binders and organic binders, and the inorganic binder includes bentonite.