Flux pre-reduced chromite pellet and preparation method thereof

Abstract

The preparation 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 according to the proportion, then pelletizing is conducted, and chromite fluxed green pellets are obtained; and the chromite fluxed green pellets are dried, preheated and oxidized, chromite fluxed pre-oxidized pellets are obtained, a reducing agent is additionally arranged on the chromite fluxed pre-oxidized pellets for reduction roasting, and chromite fluxed pre-reduced pellets are obtained. According to the method, the flux required by slagging of the electric furnace is added into the pellets, so that the flux completes pre-slagging in the pre-reduction stage, the reduction performance of chromite can be improved, the reduction temperature can be reduced, and the pre-reduced pellets produced by adopting the reduction process of the external reducing agent are stable in reduction degree and stable in carbon content; the adverse effect on the stability of electric furnace smelting operation caused by unstable residual carbon generated when the chromite pellets are reduced by carbon can be avoided.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of comprehensive utilization of chromite, and particularly relates to a chromite fluxing pre-reduced pellet and a preparation method thereof. BACKGROUND

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

[0003] The smelting method of high-carbon chromium-iron includes an electric furnace method and a converter smelting reduction method, and at present, the electric furnace method is mainly used. The main furnace charge structure for smelting high-carbon chromium-iron by the electric furnace method is "chromite + flux + reducing agent". The furnace charge can determine the smelting effect and the cost of smelting. At present, the chromite lump product, the slag-forming flux and the reducing agent are added at the electric furnace charging position in the smelting process of high-carbon chromium-iron, and after a period of smelting, the high-carbon chromium-iron and the slag are discharged. The smelting process has problems such as great operation difficulty, unstable furnace condition and high production cost. The slag composition used in the smelting of high-carbon chromium-iron at present is mainly a MgO-Al2O3-SiO2 ternary slag system, which is located in the magnesium-aluminum spinel phase region. The viscosity and melting temperature of the slag system are high, which leads to high smelting temperature, high energy consumption, high carbon emission, difficult separation of slag and iron, and low recovery rate of valuable elements.

[0004] The pre-reduction-electric furnace method smelts chromite by adding carbon reducing agent into the pellet and obtaining metallized pellets by roasting and pre-reducing the pellet, which can effectively reduce energy consumption and improve the recovery rate of chromium. At present, the representative methods for preparing reducing pellets include SRC and DRC methods. The SRC method adds a certain amount of carbon reducing agent into the pellet, and uses a rotary kiln to pre-reduce the chromite pellet. The carbon content is 70-100% of the theoretical amount of Cr2O3, FeO and Fe2O3 in the reduced ore, the smelting coke consumption is reduced by 45%, and the chromium recovery rate is increased by 1%-2%. The DRC method uses a rotary hearth furnace to pre-reduce the chromite pellet. The process uses combustible gas to provide heat. The Canadian International Metal Recovery Company uses this process to pre-reduce the pellet. The reduction degree of the pellet obtained by the DRC process is in the range of 30%-75%, but the comprehensive energy consumption of the DRC process is higher than that of the SRC method. In addition to the above two pre-reduction processes, in the early 21st century, China successfully developed an external heating shaft furnace production process. The process is to make pellets by mixing chromite powder, coke and bentonite in a certain proportion, and then pre-reduce the pellets in an external heating shaft furnace to obtain a pre-reduced product.

[0005] However, at present, the internal fixed process is used to produce chromite pre-reduced pellets at home and abroad, and the production process is to add carbon-containing reducing agent into the pellets to prepare carbon-containing chromite pellets. Due to different reaction degrees of the reducing agent carbon in the pellets during the production process, the residual carbon content in the pre-reduced products fluctuates greatly (±3% or more), and at the same time, the pellet reduction degree fluctuates greatly (±10% or more), the quality of the pellets is unstable, which leads to the difficulty in controlling the reducing agent addition amount in the subsequent electric furnace smelting process, and the unstable problem of the electric furnace smelting. The reduction temperature of the pre-reduced pellets produced by the internal reducing agent production process of chromite pre-reduced pellets is more than 1350℃, and the reduction time is more than 3 hours, the reduction temperature is high, the time is long, the energy consumption is high, and the reduction process is unstable. The metalization rate and residual carbon of the pellets. The preheating and roasting method of chromite concentrate pellets disclosed in Chinese patent document CN104831056A also uses internal carbon for pellet production. Therefore, it is necessary to develop new technologies to solve these problems. SUMMARY

[0006] The technical problem to be solved by the present application is to overcome the shortcomings of the prior art, and in particular to solve the problems of high reduction temperature, long time, high energy consumption, unstable pellet metallization rate and residual carbon, uneven distribution of different furnace charges in the electric furnace smelting process, and unstable furnace resistance, which affects the electric furnace operation, etc. in the internal carbon rotary kiln reduction process of the chromite pre-reduction-electric furnace smelting process in the prior art, and to provide a chromite flux pre-reduced pellet with stable reduction degree and carbon content, high furnace stability, reduced electric furnace smelting operation difficulty, reduced production cost and improved production efficiency, and a preparation method thereof.

[0007] To solve the above technical problems, the following technical solutions are adopted in the present application.

[0008] A preparation method of a chromite flux pre-reduced pellet, comprising the following steps:

[0009] (1) After the chromite, calcium flux, magnesium flux and additives are pretreated by grinding, they are fully mixed with the binder and water in proportion, and then balling is performed to obtain chromite flux green balls; wherein the mass ratio of (chromite + calcium flux + magnesium flux) : additive : binder : water is = 82-93.9 : 0.1-5 : 1-3 : 5-10, the addition amount of the calcium flux and the magnesium flux is added according to the composition (CaO + MgO) / Al2O3 mass ratio of 1.0-1.5:1 of the chromite flux pre-reduced pellet, and the addition amount of the calcium flux is added according to the mass ratio of CaO to MgO of 0.2-0.5:1 of the chromite flux pre-reduced pellet;

[0010] (2) drying and preheating and oxidizing the chromite fluxing green pellets to obtain chromite fluxing pre-oxidized pellets, and reducing and roasting the chromite fluxing pre-oxidized pellets with an external reducing agent, wherein the temperature of the reducing and roasting is 1100-1300 DEG C, to obtain chromite fluxing pre-reduced pellets.

[0011] Preferably, in step (1), the additive comprises one or more of active silicon, borax, boron mud and chromium-containing smelting slag, the chromium content of the chromium-containing smelting slag is 3-15%, and the particle size of the additive after the pre-treatment of grinding is greater than or equal to 80% of -200 mesh.

[0012] Preferably, 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 greater than or equal to 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 greater than or equal to 30%, and the particle size of the chromite, the calcareous flux and the magnesian flux after the pre-treatment of grinding is greater than or equal to 80% of -200 mesh.

[0013] Preferably, in step (1), the particle size of the chromite fluxing green pellets is 8-20 mm, the drop strength of the chromite fluxing green pellets is greater than 3.0 times / (0.5 m·piece), and the compressive strength of the chromite fluxing green pellets is greater than 10 N / piece.

[0014] Preferably, in step (2), the reducing agent comprises one or more of coke powder, anthracite, bituminous coal, biomass charcoal and semi-coke, the particle size of the reducing agent is greater than or equal to 80% of 5-30 mm, and the adding amount of the reducing agent is 0.5-2.0 in terms of the mass ratio of C / Fe, wherein C is the C in the reducing agent, and Fe is the Fe in the chromite fluxing pre-reduced pellets.

[0015] Preferably, in step (2), the time of the reducing and roasting is 1-3 h, and the reducing and roasting adopts a rotary kiln reduction process.

[0016] Preferably, in step (2), the average compressive strength of the obtained chromite fluxing pre-reduced pellets is greater than or equal to 2000 N / piece, and the average reduction degree is 50-70%.

[0017] Preferably, in the step (2), the drying temperature is 200-400℃, the drying time is 2-20 minutes, the pre-oxidation is carried out in air atmosphere, the pre-oxidation temperature is 800-1100℃, the pre-oxidation time is 5-60 minutes, and the average compressive strength of the chromite fluxing pre-oxidized pellets is not less than 500 N / pellet.

[0018] Preferably, in the step (1), the ore grinding pre-treatment method comprises one or more of ball milling, roller milling, wet milling and vertical milling; and the binder comprises one or more of inorganic binder and organic binder, and the inorganic binder comprises bentonite.

[0019] As a general technical concept, the present application also provides the chromite fluxing pre-reduced pellets prepared by the above-mentioned method.

[0020] Compared with the prior art, the present application has the following advantages:

[0021] In the method for preparing the chromite fluxing pre-reduced pellets, the flux required for electric furnace slagging is added into the pellets, so that the chromite and the flux are uniformly distributed, and the problems such as unstable furnace condition caused by uneven distribution of the chromite and the flux during the electric furnace smelting process can be avoided. Meanwhile, the reduction is carried out by using the external reduction agent, so that the reduction degree and the carbon content of the produced pre-reduced pellets are stable, the adverse effects of the unstable metallization rate and residual carbon of the carbon-reduced chromite pellets on the stability of the electric furnace smelting operation can be avoided, the difficulty of the electric furnace smelting operation is reduced, the production stability is improved, and the production efficiency is improved. In the pellet roasting process, the flux and the additive react with the chromite in solid phase, on the one hand, the crystal lattice structure of the chromite can be destroyed, the reduction performance of the chromite can be improved, the reduction temperature can be reduced, and the reduction time can be shortened, and on the other hand, the flux reacts with the chromite to generate a low-melting-point compound, which plays a role of pre-slaging, and the smelting time can be saved, and the production cost is significantly reduced. DETAILED DESCRIPTION

[0022] 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 by the following embodiments. The materials and instruments used in the following embodiments are commercially available.

[0023] The main components of the chromite furnace charge used in the following embodiments are shown in Table 1, wherein TFe means total iron content.

[0024] Table 1: Main chemical components of chromite (unit: wt%)

[0025] TFe SiO2 CaO MgO Al2O3 Cr2O3 21.16 3.98 0.38 9.70 13.73 43.92

[0026] Example 1

[0027] A preparation method of the chromite fluxing pre-reduced pellet of the present application comprises the following steps:

[0028] (1) After crushing and ball milling treatment of chromite, limestone, magnesite, and additive chromium-containing smelting slag (chromium content is 5.58%) to ≥80% of -200 mesh, the mixture is uniformly mixed with bentonite and water and balling to obtain chromite fluxing green pellets. Among them, the total proportion of chromite, limestone and magnesite is 88% by mass fraction, the proportion of additive chromium-containing smelting slag is 2%, the proportion of bentonite is 2.0%, and the proportion of moisture is 8.0%. The limestone and magnesite are added according to the mass ratio of (CaO+MgO) / Al2O3 of the chromite fluxing pre-reduced pellet composition is 1.0, and the limestone is added according to the mass ratio of CaO to MgO of the chromite fluxing pre-reduced pellet composition is 0.2:1. The chromite fluxing green pellets with a drop strength greater than 3.0 times / 0.5 m·piece and a compressive strength greater than 10 N / piece are prepared. The particle size of the chromite fluxing green pellets is 8 mm to 20 mm.

[0029] (2) The qualified chromite fluxing green pellets are dried at a drying temperature of 200℃ for 10 min, and then preheating oxidation is carried out in an air atmosphere. The preheating oxidation temperature is 800℃, and the preheating oxidation time is 60 min. The chromite fluxing pre-oxidized pellets are obtained. The average compressive strength of the chromite fluxing pre-oxidized pellets is 531 N / piece. The chromite fluxing pre-oxidized pellets are externally provided with a reducing agent for reduction roasting treatment in a rotary kiln. The reduction roasting temperature is 1300℃, the reduction roasting time is 1 hour, the reducing agent is coke powder, the particle size of the coke powder is 5 mm to 30 mm ≥80%, and the addition amount of the coke powder is added according to the mass ratio of C / Fe is 1.5, wherein C is the C content in the coke powder, and Fe is the Fe content in the chromite fluxing pre-reduced pellet. After reduction roasting, the chromite fluxing pre-reduced pellet is obtained. Through testing, the average compressive strength of the chromite fluxing pre-reduced pellet is 2235 N / piece, the average reduction degree is 66.8%, the reduction degree fluctuation range of the chromite fluxing pre-reduced pellet is ±3.6%, the average carbon content of the pellet is 1.65%, and the carbon content fluctuation range of the pellet is ±0.25%.

[0030] Example 2

[0031] A preparation method of the chromite fluxing pre-reduced pellet of the present application comprises the following steps:

[0032] (1) crush and grind chromite, slaked lime, dolomite, and additive active silicon to -200 mesh ≥80%, then mix with bentonite and water to form balls, to obtain chromite fluxing green balls. Among them, the total content of chromite, slaked lime and dolomite is 91% by mass fraction, the content of additive active silicon is 0.2%, the content of bentonite is 1%, and the moisture content is 7.8%. The mass ratio of CaO+MgO / Al2O3 in the composition of chromite pellets is 1.2, the mass ratio of CaO / MgO in the composition of chromite pellets is 0.3:1, and the slaked lime is added. The chromite fluxing green balls prepared have a drop strength greater than 3.0 times / 0.5 m·piece and a compressive strength greater than 10 N / piece, and the particle size of the chromite fluxing green balls is 8 mm-20 mm.

[0033] (2) dry the qualified chromite fluxing green balls at a drying temperature of 300℃ for 5 min, then preheat and oxidize in an air atmosphere, the preheating and oxidizing temperature is 900℃, the preheating and oxidizing time is 45 min, to obtain chromite fluxing pre-oxidized pellets, the average compressive strength is 625 N / P. The chromite fluxing pre-oxidized pellets are externally provided with a reducing agent and subjected to reduction roasting treatment in a rotary kiln, the reduction roasting temperature is 1200℃, the reduction roasting time is 2 hours, the reducing agent is bituminous coal, the particle size of the bituminous coal is 5 mm-30 mm ≥80%, the addition amount of the bituminous coal is 1.0 according to the mass ratio of C / Fe, C is the C content in the bituminous coal, and Fe is the Fe content in the chromite fluxing pre-reduced pellets, to obtain chromite fluxing pre-reduced pellets with an average compressive strength of 2035 N / P and an average reduction degree of 54.8%. The reduction degree of the pre-reduced pellets fluctuates in the range of ±2.8%, the average carbon content of the pellets is 1.52%, and the carbon content of the pellets fluctuates in the range of ±0.22%.

[0034] Example 3

[0035] A preparation method of the chromite fluxing pre-reduced pellets of the present application, comprising the following steps:

[0036] (1) crush and grind chromite, limestone, serpentine, and additive borax to -200 mesh ≥80%, then mix with bentonite and water to form balls, to obtain chromite fluxing green balls. Among them, the total content of chromite, limestone, and serpentine is 89.5% by mass fraction, the content of additive borax is 1%, the content of bentonite is 1.5%, and the moisture content is 8.0%. The mass ratio of CaO+MgO / Al2O3 in the composition of chromite fluxing pre-reduced pellets is 1.3, the mass ratio of CaO / MgO in the composition of chromite fluxing pre-reduced pellets is 0.4:1, and the limestone is added. The chromite fluxing green balls prepared have a drop strength greater than 3.0 times / 0.5 m·piece and a compressive strength greater than 10 N / piece, and the particle size of the chromite fluxing green balls is 8 mm-20 mm.

[0037] (2) The qualified chromite fluxing green balls are dried at a drying temperature of 300°C for 5 min, and then pre-oxidized under an air atmosphere, the pre-oxidation temperature is 1000°C, and the pre-oxidation time is 30 min, to obtain chromite fluxing pre-oxidized pellets with an average compressive strength of 762 N / P. The chromite fluxing pre-oxidized pellets are externally provided with a reducing agent and subjected to a reduction roasting treatment in a rotary kiln, the reduction roasting temperature is 1300°C, the reduction roasting time is 3 hours, the reducing agent is anthracite, the particle size of the anthracite is 5 mm-30 mm≥80%, and the addition amount of the anthracite is added according to a C / Fe mass ratio of 2.0, to obtain chromite fluxing pre-reduced pellets with an average compressive strength of 2935 N / P and an average reduction degree of 69.8%, the reduction degree fluctuation range of the pre-reduced pellets is ±3.8%, the average carbon content of the pellets is 1.84%, and the carbon content fluctuation range of the pellets is ±0.25%.

[0038] Example 4

[0039] A preparation method of the chromite fluxing pre-reduced pellets of the present application, comprising the following steps:

[0040] (1) Chromite, limestone, high-magnesium slag, and additive chromium-containing smelting slag (chromium content of 15.00%) are broken and ball milled to -200 mesh≥80%, and then mixed with bentonite and water to obtain chromite fluxing green balls. Among them, the high-magnesium slag contains 30.24wt% of MgO, the total mass fraction of the chromite, limestone and high-magnesium slag accounts for 90%, the mass fraction of the additive chromium-containing smelting slag accounts for 0.5%, the mass fraction of the bentonite accounts for 1.5%, and the water content accounts for 8.0%. The limestone and high-magnesium slag are added according to the mass ratio of (CaO+MgO) / Al2O3 of the chromite fluxing pre-reduced pellet composition of 1.5, and the limestone is added according to the mass ratio of CaO to MgO of 0.5:1, to prepare chromite fluxing green balls with a drop strength greater than 3.0 times / 0.5 m·piece and a compressive strength greater than 10 N / piece. The particle size of the chromite fluxing green balls is 8 mm-20 mm.

[0041] (2) The qualified chromite fluxing green balls are dried at a drying temperature of 400°C for 3 min, and then pre-oxidized under an air atmosphere, the pre-oxidization temperature is 1100°C, and the pre-oxidization time is 20 min, to obtain chromite fluxing pre-oxidized pellets with an average compressive strength of 565 N / P. The chromite fluxing pre-oxidized pellets are externally provided with a reducing agent and subjected to a reduction roasting treatment in a rotary kiln, the reduction roasting temperature is 1100°C, the reduction roasting time is 3 hours, the reducing agent is coke powder, the coke powder particle size is 5 mm-30 mm≥80%, and the addition amount of the coke powder is added according to a C / Fe mass ratio of 0.5, to obtain chromite fluxing pre-reduced pellets with an average compressive strength of 2011 N / P and an average reduction degree of 53.5%, the reduction degree fluctuation range of the pre-reduced pellets is ±2.1%, the average carbon content of the pellets is 1.35%, and the carbon content fluctuation range of the pellets is ±0.21%.

[0042] Example 5

[0043] A preparation method of the chromite fluxing pre-reduced pellets of the present application, comprising the following steps:

[0044] (1) The chromite, quicklime, magnesite, and additive chromium-containing smelting slag (chromium content of 9.45%) are crushed and ground to -200 mesh≥80% by high-pressure roller grinding and wet grinding, and then mixed with bentonite and water to obtain chromite fluxing green balls. The total proportion of the chromite, quicklime, and magnesite is 85% by mass fraction, the proportion of the additive chromium-containing smelting slag is 5%, the proportion of bentonite is 2.0%, and the moisture content is 8.0%. The dolomite and magnesite are added according to a (CaO+MgO) / Al2O3 mass ratio of 1.2 in the composition of the chromite fluxing pre-reduced pellets, and the quicklime is added according to a CaO / MgO mass ratio of 0.3:1 in the composition of the chromite fluxing pre-reduced pellets. Qualified chromite fluxing green balls with a drop strength greater than 3.0 times / 0.5 m·piece and a compressive strength greater than 10 N / piece are prepared, and the particle size of the chromite fluxing green balls is 8 mm-20 mm.

[0045] (2) The qualified chromite fluxing green balls are dried at a drying temperature of 400°C for 3 min, and then pre-oxidized under an air atmosphere, the pre-oxidation temperature is 1050°C, the pre-oxidation time is 15 min, and chromite fluxing pre-oxidized pellets with an average compressive strength of 632 N / P are obtained. The chromite fluxing pre-oxidized pellets are externally matched with a reducing agent for reduction roasting treatment in a rotary kiln, the reduction roasting temperature is 1200°C, the reduction roasting time is 3 hours, the reducing agent is semicoke, the particle size of the semicoke is 5mm-30mm≥80%, and the addition amount of the semicoke is added according to the mass ratio of C / Fe of 2.0, and chromite fluxing pre-reduced pellets with an average compressive strength of 2236 N / P and an average reduction degree of 58.6% are obtained. The reduction degree of the pre-reduced pellets fluctuates in the range of ±2.5%, the average carbon content of the pellets is 1.55%, and the carbon content of the pellets fluctuates in the range of ±0.23%.

[0046] Example 6

[0047] A preparation method of the chromite fluxing pre-reduced pellets of the present application, comprising the following steps:

[0048] (1) The chromite, limestone, magnesite and additive active silicon are crushed, and then ground by high-pressure roller grinding-wet grinding to-200 mesh≥80%, and then mixed with bentonite and water to obtain chromite fluxing green balls. Among them, the total mass fraction of chromite, limestone and magnesite accounts for 85.5%, the mass fraction of additive active silicon accounts for 5%, the mass fraction of bentonite accounts for 1.5%, and the mass fraction of water accounts for 8.0%. The magnesite and limestone are added according to the mass ratio of (CaO+MgO) / Al2O3 of the chromite fluxing pre-reduced pellet composition of 1.0, and the limestone is added according to the mass ratio of CaO to MgO of 0.2:1 of the chromite fluxing pre-reduced pellet composition. Qualified chromite fluxing green balls with a drop strength greater than 3.0 times / 0.5 m·piece and a compressive strength greater than 10 N / piece are prepared, and the particle size of the chromite fluxing green balls is 8mm-20mm.

[0049] (2) The qualified chromite fluxed green pellets are dried at a drying temperature of 250°C for 7 min, and then pre-oxidized in an air atmosphere, the pre-oxidizing temperature is 1100°C, and the pre-oxidizing time is 5 min, to obtain chromite fluxed pre-oxidized pellets with an average compressive strength of 931 N / P. The chromite fluxed pre-oxidized pellets are treated by reduction roasting in a rotary kiln, the reduction roasting temperature is 1300°C, the reduction roasting time is 2 hours, the reducing agent is bituminous coal, the particle size of the bituminous coal is 5 mm-30 mm≥80%, and the addition amount of the bituminous coal is added according to a C / Fe mass ratio of 1.5, to obtain chromite fluxed pre-reduced pellets with an average compressive strength of 2635 N / P and an average reduction degree of 66.5%. The reduction degree fluctuation range of the pre-reduced pellets is ±3.5%, the average carbon content of the pellets is 1.78%, and the carbon content fluctuation range of the pellets is ±0.24%.

[0050] Comparative Example 1

[0051] A preparation method of chromite pre-reduced pellets is basically the same as that of Example 1, the only difference is that no flux and additives are added in step (1), i.e. no limestone, magnesite and chromium-containing smelting slag are added. Finally, chromite pre-reduced pellets with an average compressive strength of 1435 N / P and an average reduction degree of 44.7% are obtained, the reduction degree fluctuation range of the pre-reduced pellets is ±4.6%, the average carbon content of the pellets is 2.43%, and the carbon content fluctuation range of the pellets is ±0.65%.

[0052] Comparative Example 2

[0053] A preparation method of chromite pre-reduced pellets is basically the same as that of Example 1, the only difference is that 15% of coke powder is internally added in step (1), and the coke powder is crushed and ball milled to -200 mesh≥80% before being added into the mixture for pelletizing; no reducing agent is externally added in step (2), and the drying, pre-oxidizing and roasting systems are the same as those of Example 1, during which chromite fluxed pre-oxidized pellets with a compressive strength of 223 N / P are obtained, finally, chromite pre-reduced pellets with an average compressive strength of 1568 N / P and an average reduction degree of 52.9% are obtained, the reduction degree fluctuation range of the chromite pre-reduced pellets is ±9.6%, the average carbon content of the pellets is 4.22%, and the carbon content fluctuation range of the pellets is ±4.15%.

[0054] Comparative Example 3

[0055] A preparation method of chromite pre-reduced pellets is basically the same as that of example 1, the only difference is 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 into the mixture for pelletizing; in step (2), no reducing agent is added, the drying and preheating oxidation system is the same as that of example 1, the roasting temperature needs to be increased to 1400℃, and the time is extended to 5 hours, thereby obtaining the chromite pre-reduced pellets with a roasting ball compressive strength of 2123N / P, an average reduction degree of 58.4%, a reduction degree fluctuation range of the chromite pre-reduced pellets of ±10.3%, an average carbon content of the pellets of 4.15%, and a carbon content fluctuation range of the pellets of ±3.82%.

[0056] The above description is only the 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 the 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 solution of the present application, or modify it into equivalent embodiments with equivalent changes, without departing from the spirit and technical solution 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 solution of the present application, still falls within the protection scope of the technical solution of the present application.

Claims

1. A method for preparing flux-induced pre-reduced chromite pellets, characterized in that, Includes the following steps: (1) After grinding and pretreatment, chromite, calcium flux, magnesium flux, and additives are thoroughly mixed with binder and water in a certain proportion, and then pelletized to obtain chromite flux-based green pellets; wherein, the mass ratio of (chromite + calcium flux + magnesium flux): additive: binder: water is 82~93.9:0.1~5:1~3:5~10, the amount of calcium flux and magnesium flux added is added according to the mass ratio of (CaO+MgO) / Al2O3 of the chromite flux-based pre-reduced pellets is 1.0~1.5:1, and the amount of calcium flux added is added according to the mass ratio of CaO to MgO of the chromite flux-based pre-reduced pellets is 0.2~0.5:1; (2) Dry and preheat oxidize the chromite flux green pellets to obtain chromite flux pre-oxidized pellets. Add a reducing agent to the chromite flux pre-oxidized pellets and reduce roast at a temperature of 1100℃~1300℃ to obtain chromite flux pre-reduced pellets.

2. The method for preparing chromite flux-induced pre-reduced pellets according to claim 1, characterized in that, In step (1), the additive includes one or more of activated silicon, borax, borax mud and chromium-containing smelting slag, wherein the chromium content in the chromium-containing smelting slag is 3% to 15%, and the particle size of the additive after grinding pretreatment is -200 mesh ≥ 80%.

3. The method for preparing chromite flux-induced pre-reduced pellets according to claim 1, characterized in that, In step (1), 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, magnesium silicate, serpentine, and magnesian slag, wherein the mass fraction of MgO in the magnesian slag is ≥30%; and the particle size of the chromite, calcareous flux, and magnesian flux after grinding pretreatment is ≥80% -200 mesh.

4. The method for preparing chromite flux-induced pre-reduced pellets according to claim 1, characterized in that, In step (1), the particle size of the chromite flux green pellets is 8mm to 20mm, the drop strength of the chromite flux green pellets is greater than 3.0 times / (0.5m·pellet), and the compressive strength is greater than 10N / pellet.

5. The method for preparing chromite flux-induced pre-reduced pellets according to any one of claims 1 to 4, characterized in that, In step (2), the reducing agent includes one or more of coke powder, anthracite, bituminous coal, biochar and semi-coke, the particle size of the reducing agent is 5mm to 30mm ≥80%, and the amount of the reducing agent added is 0.5 to 2.0 according to the C / Fe mass ratio, where C is C in the reducing agent and Fe is Fe in the chromite flux pre-reduced pellets.

6. The method for preparing chromite flux-induced pre-reduced pellets according to any one of claims 1 to 4, characterized in that, In step (2), the reduction roasting time is 1h to 3h, and the reduction roasting adopts a rotary kiln reduction process.

7. The method for preparing chromite flux-induced pre-reduced pellets according to any one of claims 1 to 4, characterized in that, In step (2), the average compressive strength of the obtained chromite flux pre-reduced pellets is ≥2000N / pellet, and the average degree of reduction is 50% to 70%.

8. The method for preparing chromite flux-induced pre-reduced pellets according to any one of claims 1 to 4, characterized in that, In step (2), the drying temperature is 200℃~400℃, the drying time is 2min~20min, the preheating oxidation is carried out in an air atmosphere, the preheating oxidation temperature is 800℃~1100℃, the preheating oxidation time is 5min~60min, and the average compressive strength of the chromite flux pre-oxidized pellets is not less than 500N / piece.

9. The method for preparing chromite flux-induced pre-reduced pellets 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 binder and organic binder, and the inorganic binder includes bentonite.

10. A chromite flux-reduced pre-reduced pellet prepared by the method described in any one of claims 1 to 9.