Process for producing iron concentrate by low-grade siderite rotary kiln magnetization roasting

Abstract

The present application relates to a kind of low-grade siderite rotary kiln magnetization roasting production iron concentrate process, to solve the existing siderite in rotary kiln magnetization roasting is produced in over-reduction, make the iron grade and metal recovery rate of the iron concentrate powder produced reduce, while solve the problem of rotary kiln body ring, take the first siderite and reduction coal after crushing and particle size classification, then particle ore is added to oxidation roasting rotary kiln, rotary kiln is carried out oxidation roasting with pulverized coal as fuel, can remove the carbon in siderite while improving the oxidation degree of roasting ore;High-temperature oxidation roasting ore obtained by roasting and normal temperature powder ore are added to the reduction rotary kiln without heating heat source, with high-temperature oxidation roasting ore itself as heat source, particle coal as reducing agent to carry out magnetization roasting, so that the iron oxide in oxidation roasting ore is converted into Fe3O4.Reduced roasting ore is cooled by atomizing cooler, ground by ball mill and magnetically separated by magnetic separator, and iron concentrate powder with iron grade of more than 62% and metal recovery rate of more than 86% can be obtained.

Description

Technical Field

[0001] This invention belongs to the field of metallurgy and mineral processing technology, specifically relating to a process for producing iron concentrate by rotary kiln magnetization roasting of low-grade siderite. Background Technology

[0002] Difficult-to-process low-grade siderite typically contains 26-35% iron and has a density of 3.7-4.0 t / m³. 3 The specific magnetic susceptibility is 35–150 × 10⁻⁶. -9 m 3 The mineral has weak magnetism, fine grain size, complex composition, and low iron grade, making it a difficult-to-process iron ore resource. The theoretical iron grade of siderite is 48.2%, but some siderites have lower iron content due to Mg content. 2+ and Mn 2+ The substitution of iron ions forms magnesium and manganese siderite, resulting in a theoretical iron grade that is typically between 25% and 48%.

[0003] Currently, the main methods for utilizing low-grade siderite that is difficult to process are: (1) Direct reduction method. In view of the characteristics of siderite with high content of fine ore and large difference in mineral particle size during mining and crushing, in order to make the roasting quality of siderite uniform, iron ore is generally ground and then the ore powder is made into 8-16mm pellets. After drying, the pellets are mixed with reducing coal in a certain proportion and then fed into the reduction furnace for reduction roasting to obtain metallized pellets, which are then supplied to the blast furnace for utilization. The main problems with this method of utilizing siderite are: all siderite needs to be ground, pelletized and dried before reduction, the production process is complicated and the cost is high, which limits the promotion and application of this method. (2) Magnetization roasting method: After the siderite is magnetized and roasted to improve its magnetic properties, the magnetic material is ground and magnetically separated to obtain iron concentrate. The iron concentrate is then sintered in a sintering machine to produce oxidized sinter or pelletized and then oxidized and roasted to produce oxidized pellets, which can then be used in blast furnaces. The production process also has the problems of high energy consumption, complex process flow and high production cost. (3) Oxidation sintering method: In view of the problems of poor permeability of siderite powder, low thermal conductivity during high temperature heating and low strength after roasting of lump ore, iron ore is generally ground and magnetically separated to make iron concentrate into 3-5 mm pellets. The pellets are then added to a sintering machine for sintering. This utilization method also has the problems of complex production process flow and high production cost. (4) Gravity separation and strong magnetic separation: This method generally requires siderite to go through multiple gravity separation, grinding and strong magnetic separation processes to obtain iron concentrate with iron grade that meets the requirements of blast furnace use. In addition, the iron concentrate powder needs to go through sintering or pelletizing oxidation process before it can be added to the blast furnace for use. In the production process, there are problems such as low iron grade, low metal recovery rate and high production cost.

[0004] Because FeCO3 in siderite decomposes directly into magnetic Fe3O4 during the high-temperature roasting process, no reducing agent is needed to achieve the purpose of magnetization roasting in the siderite magnetization roasting process.

[0005] In high-temperature neutral roasting of siderite without the addition of reducing agents, FeCO3 in the ore begins to decompose at 400℃ and is completely decomposed at 560℃. The CO and CO2 released from the decomposition of FeCO3 escape from the ore, which can improve the iron grade and magnetic properties of the iron ore. In actual production, siderite is generally heated to 800-850℃ and held for 60 minutes. The roasted ore is then cooled to below 100℃ without secondary oxidation. The room-temperature roasted ore is then ground in a ball mill to a particle size of -200 mesh (80-85%). The ground material is then magnetically separated using a magnetic separator with a magnetic field strength of 1200-1800 Oe to obtain iron concentrate. During the magnetic separation process of roasted ore, under the condition of controlling the iron grade of iron concentrate at 52-55%, the iron recovery rate in the beneficiation can only reach a maximum of 60-70%, indicating that the quality of siderite after high-temperature neutral roasting is poor. The reason for this is as follows: At a high temperature of 800-850℃, the chemical reaction equation for the decomposition of FeCO3 in siderite is: 3FeCO3 = Fe3O4 + 2CO2 + CO. It can be seen that during the high-temperature decomposition of siderite, while generating Fe3O4, CO reducing gas is also released. The concentration of the reducing gas reaches about 33%, which is the reduction concentration of CO gas for the newly generated Fe3O4. Thus, the newly generated Fe3O4 is further reduced by CO gas to FeO at high temperature, causing some of the newly generated magnetic iron to be over-reduced. The chemical reaction equation is: Fe3O4 + CO = 3FeO + CO2. After some FeO appears during the high-temperature roasting of siderite, this part of non-magnetic FeO cannot be recovered by magnetic separation, resulting in a decrease in the magnetic properties of the roasted ore. Currently, many research institutions consider the two reaction processes mentioned above together when conducting high-temperature decomposition analysis of siderite, and believe that the chemical reaction equation for the high-temperature decomposition of FeCO3 is: FeCO3=FeO+2CO2.

[0006] Currently, in the magnetic roasting of siderite in rotary kilns, iron ore is generally fed into the kiln in a full-size format with a particle size of 25-35mm or less. The 0-1mm fine ore particles in the ore heat up rapidly at the high temperatures inside the kiln and easily adhere to the kiln walls. When the rotary kiln uses pulverized coal for heating, the fine fly ash produced after combustion also easily adheres to the kiln walls. Simultaneously, after FeO is produced during the reduction process, it combines with SiO2 in the ore to form low-melting-point ferrosilicon, which is even more likely to adhere to the kiln walls at high temperatures. Due to these factors, the problem of kiln ring formation frequently occurs in rotary kiln production.

[0007] It can be seen that the main problem with producing iron concentrate from siderite through high-temperature magnetization roasting, compared to the process of producing iron concentrate from ordinary magnetite, is that the siderite roasting process results in the formation of some FeO in the roasted ore, leading to over-reduction and a decrease in the magnetic properties of the roasted ore. In subsequent grinding and magnetic separation, the non-magnetic FeO cannot be recovered, resulting in a decrease in the iron grade and metal recovery rate of the iron concentrate. Furthermore, existing rotary kilns also suffer from kiln ring formation during iron ore magnetization roasting. Summary of the Invention

[0008] This invention addresses the problems of over-reduction and kiln ring formation in the high-temperature magnetization roasting of siderite without the addition of reducing agents, which result in the presence of some FeO in the roasted ore. To improve the metal recovery rate and iron grade of siderite after rotary kiln magnetization roasting and to solve the kiln ring formation problem, a process for producing iron concentrate from low-grade siderite by rotary kiln magnetization roasting is proposed.

[0009] Therefore, the present invention adopts the following technical solution: A rotary kiln magnetized roasting process for producing iron concentrate from low-grade siderite, the specific process includes: (1) Siderite with a particle size of less than 250mm mined from iron ore mines is crushed to a particle size of less than 30mm using a jaw crusher. The crushed material is then classified into 0-1mm powder and 1-30mm granules using a mechanical vibrating screen with a screen size of 1mm.

[0010] (2) The reducing coal is crushed to a particle size of less than 20mm using a jaw crusher. The crushed material is then graded into 0-1mm pulverized coal and 1-20mm granular coal using a mechanical vibrating screen with a screen size of 1mm.

[0011] (3) After 0-1mm pulverized coal is ground to -200 mesh or more by a coal mill, it is injected into the burner by pneumatic conveying. At the same time, the 3-5KPa ambient temperature combustion air blown in by the blower is introduced into the burner. After the combustion air and pulverized coal are fully mixed in the burner, it is injected into the oxidizing roasting rotary kiln from the discharge end of the rotary kiln. Under the high temperature heating effect in the rotary kiln, the temperature of pulverized coal and combustion air rises rapidly. When the pulverized coal reaches the ignition temperature, it will burn and release heat under the action of high temperature air, and heat the materials and gas in the kiln.

[0012] (4) Add 1-30mm ore particles from the feed end of the rotary kiln into the oxidative roasting rotary kiln. The inclined rotary kiln continuously moves from the feed end to the discharge end as the ore particles inside the kiln are spirally turned. It also radiates and convects heat with the high-temperature flue gas flowing in the opposite direction from the kiln. As the ore temperature increases, the flue gas temperature gradually decreases.

[0013] (5) By controlling the time siderite is in the rotary kiln for oxidative roasting to 50-60 min and the roasting temperature in the high-temperature section to 800-850℃, the siderite is oxidized and roasted in the rotary kiln, and the resulting oxidized roasted ore is discharged from the discharge end of the rotary kiln. The water in siderite is divided into free water and crystal water. Free water includes surface adsorbed water and pore water. When the temperature of siderite is raised to 105℃, the free water in siderite can be removed. Crystal water is structural water in the mineral lattice, which exists in the form of chemical bonds. When the temperature is raised to 200-500℃, the crystal water is removed. When the temperature of siderite rises to 490-600℃, the FeCO3 contained in the siderite begins to decompose, generating Fe3O4 and releasing CO and CO2 gases. The CO reacts with the O2 in the flue gas in the kiln to burn and release heat, which then supplies heat to the kiln. When the temperature of the siderite rises to 600-850℃, the newly formed Fe3O4 in the ore reacts with O2 in the flue gas in the kiln to generate γ-Fe2O3 and α-Fe2O3 while releasing heat. When the temperature of the siderite reaches 800-850℃ and it moves to the discharge end of the rotary kiln, the FeCO3 contained in the siderite is decomposed. At the same time, more than 90% of the newly formed Fe3O4 in the material is oxidized to generate γ-Fe2O3 and α-Fe2O3. The resulting oxidized roasted ore is discharged from the discharge end of the rotary kiln.

[0014] (6) The high-temperature oxidized roasted ore discharged from the oxidized roasting rotary kiln is directly added to the feed end of the reduction rotary kiln, and at the same time, room temperature powder ore with a particle size of 0-1mm and room temperature reducing coal with a particle size of 1-20mm are fed from the feed end of the reduction rotary kiln. During the rotation of the rotary kiln, the high-temperature oxidized roasted ore is fully mixed with 0-1mm room-temperature powdered ore and 1-20mm room-temperature reducing coal, so that the temperature of the mixture reaches above 600-650℃.

[0015] (7) In the reduction rotary kiln, the concentration of reducing gas during magnetization roasting of the oxidized roasted ore is controlled to be 25-30%. By controlling the time of the mixed material in the kiln to be 30-40 minutes, the oxidized roasted ore is magnetized roasted. The metallurgical gas produced in the reduction of the roasted ore in the reduction rotary kiln is returned to the burner for utilization. High-temperature oxidative roasted ore is thoroughly mixed with 0-1mm room-temperature fine ore and 1-20mm room-temperature reducing coal, allowing the mixture temperature to reach above 600-650℃. At 200-300℃, the reducing coal removes free water and water of crystallization. At 350-600℃, volatile matter, tar, and naphthalene are released from the reducing coal. Further pyrolysis of these substances at high temperatures in the kiln yields H2 and CO. H2 and CO can react with γ-Fe2O3 and α-Fe2O3 in the oxidative roasted ore. The reduction of Fe2O3 produces Fe3O4 while emitting H2O and CO2 gases. The H2O and CO2 gases then react with the semi-coke obtained from coal dry distillation at high temperature to produce new H2 and CO. The new H2 and CO then reduce γ-Fe2O3 and α-Fe2O3 in the oxidized roasted ore, thereby achieving better magnetization roasting of the oxidized roasted ore. The metallurgical gas produced in the reduction of roasted ore in the rotary kiln is returned to the burner for utilization.

[0016] (8) When the mixed material in the reduction rotary kiln reaches the discharge end, the low-temperature magnetized roasted ore with a temperature of 400-450℃ is discharged from the reduction rotary kiln.

[0017] (9) The low-temperature magnetized roasted ore discharged from the kiln is rapidly cooled by water mist atomized by an atomizer with a pressure of 0.2-0.3MPa. This allows the magnetized roasted ore to be cooled to below 100℃ without oxidation, thus obtaining room temperature magnetized roasted ore.

[0018] (10) Dust-laden flue gas with a temperature of 200-250℃ discharged from the feed end of the oxidative roasting rotary kiln enters the gravity settling chamber. After the flue gas is cooled and coarse dust particles settle, low-temperature flue gas with a temperature of 150-180℃ is obtained. The low-temperature flue gas is then removed by a bag filter. The clean flue gas is then pressurized by a flue gas exhaust fan and desulfurized by a desulfurization device before being discharged.

[0019] (11) The room temperature magnetized roasted ore is added into the ball mill for grinding. The grinding concentration of the ball mill is controlled at 60-83%. A slurry with a particle size of -200 mesh accounting for more than 80% and a concentration of 25-35% can be obtained. The slurry is then transported to a magnetic separator with a magnetic field strength of 1200-1800 Oe for magnetic separation. Iron concentrate with an iron grade of more than 62% and a metal recovery rate of more than 86% can be obtained. The iron concentrate can be supplied to the blast furnace for use. At the same time, tailings slurry with an iron grade of 5-8% is obtained.

[0020] (12) After the tailings slurry is pumped into the thickening tank through the pipeline for sedimentation, concentrated ore and tailings water can be obtained. The concentrated ore is then filtered through a filter to obtain dry tailings with a water content of 10-12%. The tailings can be used as building materials. The water obtained from the concentrated and filtered tailings slurry can be recycled to supply the grinding mill for grinding.

[0021] Furthermore, the raw materials are selected as follows: (1) Siderite is selected from low-grade, difficult-to-process iron ore with an iron grade of 25-35% and a particle size of less than 250mm; (2) Reduced coal is selected from lignite with a fixed carbon content of 45-50%, a volatile matter content of 35-45%, and an ash content of less than 8%.

[0022] Selection of Siderite Particle Size: To improve the internal heat transfer rate during the roasting of massive siderite and avoid uneven oxidation or reduction during oxidative and magnetized roasting, the particle size of the siderite cannot be too large. Simultaneously, to reduce the generation of excessive 0-1mm fine ore particles during crushing, the particle size cannot be too small. Therefore, this invention controls the siderite particle size to below 30mm. For siderite mined with a particle size below 250mm, it needs to be crushed to below 30mm before roasting.

[0023] Furthermore, the selection of reducing coal particle size: In this invention, the proportion of reducing coal added to the siderite is relatively low. If the reducing coal particle size is too large, it will be difficult to mix the reducing coal and iron ore evenly in the reduction rotary kiln, resulting in uneven iron ore magnetization roasting quality. If the reducing coal particle size is too small, iron ore and granular coal segregation will occur during the flow of the reducing coal in the reduction rotary kiln, also affecting the magnetization roasting of the iron ore. Therefore, this invention controls the reducing coal particle size to below 20mm. Simultaneously, considering the high volatile matter content in the reducing coal, which can decompose into a reducing atmosphere at relatively low temperatures, and the short duration of large-scale volatile matter release, a reducing coal particle size of 1-20mm is used to ensure that the reducing coal can uniformly and continuously release reducing gas within the reduction rotary kiln.

[0024] Furthermore, this invention can install an external combustion chamber at the discharge end of the oxidative roasting rotary kiln. A gas-solid two-phase flow, after the combustion air and pulverized coal are fully mixed in the burner, is injected into the external combustion chamber. This allows the pulverized coal to burn completely within the external combustion chamber, and the resulting 900-950°C high-temperature flue gas is then fed back into the rotary kiln from the discharge end to heat the materials. The fly ash produced after pulverized coal combustion in this invention has a high temperature rise rate and fine particle size, making it prone to adhering to the kiln wall and causing ring formation in the rotary kiln. To solve this problem, by installing an external combustion chamber at the discharge end of the oxidative roasting rotary kiln, the fly ash produced after pulverized coal combustion settles to the bottom of the external combustion chamber and is discharged outside the kiln, thus preventing the fly ash from being carried into the kiln after combustion of the pulverized coal.

[0025] During normal combustion of pulverized coal, the highest temperature of the furnace gas can reach 1200-1300℃. In order to reduce the combustion temperature of pulverized coal in the burner, this invention controls the introduction of excessive combustion air during the combustion process of pulverized coal, which can reduce the highest temperature of the furnace gas to 900-950℃, while keeping the O2 content in the furnace gas above 8-10%.

[0026] Furthermore, in this invention, when adding 0-1mm fine ore into the reduction rotary kiln, to ensure that the 0-1mm fine ore at room temperature is incorporated into the high-temperature material at 800-850℃, while simultaneously controlling the temperature of the mixture at 600-650℃, the amount of 0-1mm fine ore added is controlled to not exceed 20-25% of the total siderite content. In this invention, when adding 1-20mm particle size reducing coal into the reduction rotary kiln, to control the reducing gas concentration during magnetization roasting of the oxidized roasted ore to 25-30%, the particle size of the reducing coal is controlled to be 1-20mm, and the amount of reducing coal added is 2-5% of the total siderite content.

[0027] This invention involves adding 0-1mm fine ore to a reduction rotary kiln for magnetized roasting without oxidative roasting. Since the highest temperature inside the reduction rotary kiln is below 650℃, at this temperature, the minimum concentration of CO reducing Fe3O4 to FeO is 40%, while the CO concentration in the gas released during the high-temperature decomposition of siderite is approximately 33%. Therefore, over-reduction will not occur during the magnetized roasting of 0-1mm fine ore in the reduction rotary kiln.

[0028] This invention uses refractory low-grade siderite as an example to illustrate the process of producing iron concentrate by rotary kiln magnetization roasting of low-grade siderite. The raw materials processed by this process can also be extended to the processing of two or more refractory low-grade mixed iron ores containing siderite, limonite, magnetite and hematite.

[0029] The reducing agent for magnetized roasting of siderite in this invention is illustrated using lignite as an example. The reducing agent can also be extended to semi-coke with a volatile matter content of 11-15%, an ash content of less than 10-11%, and a fixed carbon content of 72-78%, as well as tempered coal made by blending lignite and semi-coke in a certain proportion.

[0030] The basic principle of the present invention for producing iron concentrate by magnetized roasting of siderite in rotary kiln is as follows: (1) In the rotary kiln of oxidative roasting, the siderite is heated from room temperature to 800-850℃ in an aerobic roasting environment. The FeCO3 oxidation decomposition process can be represented as: FeCO3→Fe3O4→γ-Fe2O3→α-Fe2O3. For massive siderite, at temperatures above 490-600℃, when decomposition begins, FeCO3 directly transforms into Fe3O4, while CO gas escapes from the interior of the ore. Since the outer surface of the ore is in direct contact with O2 in the environment, the O2 diffuses and permeates from the surface into the interior, coming into contact with the CO gas and causing it to burn, thus mitigating or preventing over-reduction of Fe3O4. As the temperature of the ore rises to 600-850℃, the Fe3O4 on the surface oxidizes to form γ-Fe2O3 and α-Fe2O3. However, for powdered siderite, due to its larger surface area, the ore heats up very quickly, causing the Fe3O4 generated during high-temperature decomposition to be rapidly oxidized to γ-Fe2O3, which then re-oxidizes with increasing temperature. The transformation into α-Fe2O3, Fe3O4 and γ-Fe2O3 are stable in a certain temperature range. From the high-temperature oxidation decomposition process of siderite, it can be seen that siderite will release CO and CO2 during high-temperature decomposition, and at the same time generate Fe3O4, γ-Fe2O3 and α-Fe2O3; (2) The high-temperature roasted ore discharged from the oxidative roasting rotary kiln at a temperature of 800-850℃ enters the reduction rotary kiln. By controlling the amount of reducing coal added to 2-5% of the total iron ore, the concentration of CO+H2 in the reducing gas is controlled to be 20-30%, which can reduce γ-Fe2O3 and α-Fe2O3 in the oxidative roasted ore to Fe3O4. At the same time, the newly generated Fe3O4 will not be over-reduced, thereby improving the magnetic properties of the roasted ore produced in the magnetized roasting of siderite.

[0031] The beneficial effects of this invention are as follows: 1. This invention addresses the problem that during the neutral magnetization roasting of siderite, the CO gas produced by the high-temperature decomposition of FeCO3 over-reduces some of the iron ore, reducing the magnetic properties of the roasted ore and consequently lowering the iron grade and metal recovery rate of the iron concentrate in subsequent grinding and magnetic separation processes. The invention employs a method of first oxidizing and roasting the siderite in an oxidizing roasting rotary kiln. This removes carbon from the siderite while simultaneously increasing the degree of oxidation roasting. High-temperature oxidized roasted ore, 0-1mm room-temperature powder ore, and reducing agent granules are added in a specific ratio to the reduction rotary kiln for magnetization roasting. This process completely converts iron oxides into Fe3O4, thereby improving the magnetic properties of the roasted ore.

[0032] 2. In this invention, when siderite is oxidized and roasted in an oxidizing rotary kiln, the high-temperature roasting of siderite will not generate FeO, and FeO will not combine with SiO2 contained in the ore to form low-melting-point iron silicate. The softening temperature of the oxidized ore is relatively high. At the same time, the 0-1mm powdered ore in the siderite does not enter the oxidizing rotary kiln for roasting, and there is no phenomenon of powdery material adhering to the kiln wall. The problem of kiln ring formation will not occur in the oxidizing rotary kiln, which can enable the oxidizing rotary kiln to work stably for a long time. In the reduction rotary kiln, since there is no high-temperature zone for fuel combustion in the kiln, the highest working temperature in the kiln is below 650℃, which does not reach the softening temperature of the material, so the reduction rotary kiln can also work stably for a long time.

[0033] 3. This invention addresses the common problem of kiln ring formation during the roasting of siderite, limonite, and hematite in magnetizing rotary kilns. It solves this problem by installing an external combustion chamber at the discharge end of the oxidizing rotary kiln, restricting the entry of 0-1mm fine iron ore into the kiln, preventing fly ash from entering the kiln after pulverized coal combustion, lowering the maximum furnace gas temperature in the oxidizing rotary kiln to below 950℃, and controlling the maximum reduction temperature in the reduction rotary kiln to below 650℃. These measures resolve the kiln ring formation problem that has hindered the long-term stable operation of magnetizing rotary kilns.

[0034] 4. The present invention produces iron concentrate from siderite through oxidative roasting, reduction roasting, grinding and magnetic separation. The iron grade can reach more than 62%, the metal recovery rate can reach more than 86%, and the P and S contents are less than 0.03% and less than 0.2%, respectively, which improves the iron grade of iron concentrate and the metal recovery rate in the beneficiation process.

[0035] 5. In view of the current problem that it is difficult to effectively utilize the large reserves of siderite and mixed iron ore containing siderite, the promotion and application of this process plays an important role in the development and utilization of these difficult-to-process low-grade iron ores. Attached Figure Description

[0036] Figure 1 Flowchart of the process for producing iron concentrate by rotary kiln magnetization roasting of low-grade siderite. Detailed Implementation

[0037] The present invention will be further described below with reference to the accompanying drawings and specific embodiments: The raw materials, energy media, and products involved in this process include: reducing coal, low-grade siderite, water, iron concentrate, tailings slurry, tailings, and flue gas; the equipment involved includes: jaw crusher, mechanical vibrating screen, blower, coal mill, burner, external combustion chamber, oxidative roasting rotary kiln, reduction rotary kiln, atomizer, atomizing cooler, grinding mill, magnetic separator, thickener, filter, gravity settling chamber, bag filter, exhaust fan, and desulfurization device.

[0038] The specific implementation method is as follows: (1) Siderite with a particle size of less than 250mm mined from iron ore mines is crushed to a particle size of less than 30mm using a jaw crusher. The crushed material is then classified into 0-1mm powder and 1-30mm granules using a mechanical vibrating screen with a screen size of 1mm.

[0039] (2) The reducing coal is crushed to a particle size of less than 20mm using a jaw crusher. The crushed material is then graded into 0-1mm pulverized coal and 1-20mm granular coal using a mechanical vibrating screen with a screen size of 1mm.

[0040] (3) The 0-1mm pulverized coal is ground to -200 mesh (85%) using a coal mill and then injected into the burner using pneumatic conveying. At the same time, the 3KPa ambient temperature combustion air blown in by the blower is introduced into the burner. After the combustion air and pulverized coal are fully mixed in the burner, they are injected into the rotary kiln from the discharge end. Under the high temperature heating effect in the rotary kiln, the temperature of the pulverized coal and the combustion air rises rapidly. When the pulverized coal reaches the ignition temperature, it will burn and release heat under the action of the high temperature air, and heat the materials and gas in the kiln.

[0041] (4) Add 1-30mm ore particles into the rotary kiln from the feed end. The inclined rotary kiln continuously moves from the feed end to the discharge end as the ore particles inside the kiln are spirally turned. It also radiates and convects heat with the high-temperature flue gas flowing in the opposite direction from the kiln. As the ore temperature increases, the flue gas temperature gradually decreases.

[0042] (5) By controlling the time of siderite in the rotary kiln for oxidative roasting to 50-60 min and the roasting temperature in the high-temperature section to 800-850℃, the siderite is oxidized and roasted in the rotary kiln, and the resulting oxidized roasted ore is discharged from the discharge end of the rotary kiln.

[0043] The water in siderite is divided into free water and crystal water. Free water includes surface adsorbed water and pore water. When the temperature of siderite is raised to 105℃, the free water in siderite can be removed. Crystal water is structural water in the mineral lattice, which exists in the form of chemical bonds. When the temperature is raised to 200-500℃, the crystal water is removed.

[0044] When the temperature of siderite rises to 490-600℃, the FeCO3 contained in the siderite begins to decompose, generating Fe3O4 and releasing CO and CO2 gases. The CO reacts with the O2 in the flue gas in the kiln to burn and release heat, which then supplies heat to the kiln.

[0045] When the temperature of the siderite rises to 600-850℃, the newly formed Fe3O4 in the ore reacts with O2 in the flue gas in the kiln to generate γ-Fe2O3 and α-Fe2O3 while releasing heat. When the temperature of the siderite reaches 800-850℃ and it moves to the discharge end of the rotary kiln, the FeCO3 contained in the siderite is decomposed. At the same time, 95% of the newly formed Fe3O4 in the material is oxidized to generate γ-Fe2O3 and α-Fe2O3. The resulting oxidized roasted ore is discharged from the discharge end of the rotary kiln.

[0046] (6) The high-temperature oxidized roasted ore discharged from the oxidized roasting rotary kiln is directly added to the feed end of the reduction rotary kiln. At the same time, 0-1mm room temperature powder ore and 1-20mm room temperature reducing coal are added from the feed end of the reduction rotary kiln. During the rotation of the reduction rotary kiln, the high-temperature oxidized roasted ore is fully mixed with 0-1mm room temperature powder ore and 1-20mm room temperature reducing coal, so that the temperature of the mixture reaches above 600-650℃.

[0047] (7) In the reduction rotary kiln, the concentration of reducing gas during magnetization roasting of the oxidized roasted ore is controlled to be 25-30%. By controlling the time of the mixed material in the kiln to be 30-40 minutes, the oxidized roasted ore is magnetized roasted. The metallurgical gas produced by the reduction rotary kiln in the reduction of roasted ore is returned to the burner for utilization.

[0048] High-temperature oxidative roasted ore is thoroughly mixed with 0-1mm room-temperature fine ore and 1-20mm room-temperature reducing coal, allowing the mixture temperature to reach above 600-650℃. At 200-300℃, the reducing coal removes free water and water of crystallization. At 350-600℃, volatile matter, tar, and naphthalene are released from the reducing coal. Further pyrolysis of these substances at high temperatures in the kiln yields H2 and CO. H2 and CO can react with γ-Fe2O3 and α-Fe2O3 in the oxidative roasted ore. The reduction of Fe2O3 produces Fe3O4 while emitting H2O and CO2 gases. The H2O and CO2 gases then react with the semi-coke obtained from coal dry distillation at high temperature to produce new H2 and CO. The new H2 and CO then reduce γ-Fe2O3 and α-Fe2O3 in the oxidized roasted ore, thereby achieving better magnetization roasting of the oxidized roasted ore. The metallurgical gas produced in the reduction of roasted ore in the rotary kiln is returned to the burner for utilization.

[0049] (8) When the mixed material in the reduction rotary kiln reaches the discharge end, the low-temperature magnetized roasted ore with a temperature of 400-450℃ is discharged from the reduction rotary kiln.

[0050] (9) The low-temperature magnetized roasted ore discharged from the kiln is rapidly cooled by water mist atomized by an atomizer with a pressure of 0.25MPa. This allows the magnetized roasted ore to be cooled to 50℃ without oxidation, thus obtaining room temperature magnetized roasted ore.

[0051] (10) Dust-laden flue gas with a temperature of 200-250℃ discharged from the feed end of the oxidative roasting rotary kiln enters the gravity settling chamber. After the flue gas is cooled and coarse dust particles settle, low-temperature flue gas with a temperature of 150-180℃ is obtained. The low-temperature flue gas is then removed by a bag filter. The clean flue gas is then pressurized by a flue gas exhaust fan and desulfurized by a desulfurization device before being discharged.

[0052] (11) The room temperature magnetized roasted ore is added into the ball mill for grinding. The grinding concentration of the ball mill is controlled at 70%. A slurry with a particle size of -200 mesh accounting for 85% and a concentration of 30% can be obtained. The slurry is then transported to a magnetic separator with a magnetic field strength of 1800 Oe for magnetic separation. Iron concentrate with an iron grade of 62.5% and a metal recovery rate of 88% can be obtained. The iron concentrate can be supplied to the blast furnace for use. At the same time, tailings slurry with an iron grade of 7% is obtained.

[0053] (12) After the tailings slurry is pumped into the thickening tank through the pipeline for sedimentation, concentrated ore and tailings water can be obtained. The concentrated ore is then filtered through a filter to obtain dry tailings with a water content of 11%. The tailings can be used as building materials. The water obtained from the concentrated and filtered tailings slurry can be recycled to supply the grinding mill for grinding.

Claims

1. A rotary kiln magnetized roasting process for producing iron concentrate from low-grade siderite, characterized in that, Specifically, it includes: Difficult-to-process low-grade siderite and reducing coal are crushed by a crusher and classified by a vibrating screen into granular ore, fine ore, granular coal and fine coal. The granular ore is then added to an oxidative roasting rotary kiln, and the fine coal powder obtained by grinding the coal powder is used as the heating fuel. In the oxidative roasting rotary kiln, the carbon in the granular ore is removed from the siderite, and the degree of oxidation of the roasted ore is increased, resulting in high-temperature oxidized roasted ore. High-temperature oxidized roasted ore, room-temperature powdered ore, and room-temperature granular coal are added in proportion to a reduction rotary kiln without a heating source. The high-temperature oxidized roasted ore is used as a heat source by its own heat storage and the granular coal is used as a reducing agent to carry out magnetization roasting of the oxidized roasted ore, so that the iron oxide in the iron ore is converted into Fe3O4. The low-temperature roasted ore obtained by reducing roasting the high-temperature oxidized roasted ore is then cooled by an atomizing cooler, ground by a ball mill, and magnetically separated by a magnetic separator to obtain iron concentrate with an iron grade of over 62% and a metal recovery rate of over 86%.

2. The process for producing iron concentrate from low-grade siderite by rotary kiln magnetization roasting according to claim 1, characterized in that, The production process includes the following steps: (1) Siderite with a particle size of less than 250mm is crushed to a particle size of less than 30mm, and the crushed material is then screened into powder ore with a particle size classification of 0-1mm and granular ore with a particle size of 1-30mm. (2) The reducing coal is crushed to a particle size of less than 20 mm, and the crushed material is then screened into 0-1 mm pulverized coal and 1-20 mm granular coal. (3) After grinding 0-1mm pulverized coal to a density of over 80% of -200 mesh, burn the 0-1mm pulverized coal in the burner to heat the oxidative roasting rotary kiln; (4) Add 1-30mm ore particles into the rotary kiln for oxidation roasting from the feed end; (5) By controlling the time siderite is in the rotary kiln for oxidative roasting to 50-60 min and the roasting temperature in the high-temperature section to 800-850℃, the siderite is oxidized and roasted in the rotary kiln, and the resulting oxidized roasted ore is discharged from the discharge end of the rotary kiln. (6) The high-temperature oxidized roasted ore discharged from the oxidized roasting rotary kiln is directly added to the feed end of the reduction rotary kiln, and at the same time, room temperature powder ore with a particle size of 0-1mm and room temperature reducing coal with a particle size of 1-20mm are fed from the feed end of the reduction rotary kiln. During the rotation of the rotary kiln, the high-temperature oxidized roasted ore is fully mixed with 0-1mm room-temperature powder ore and 1-20mm room-temperature reducing coal, so that the temperature of the mixture reaches above 600-650℃. (7) In the reduction rotary kiln, the concentration of reducing gas during magnetization roasting of the oxidized roasted ore is controlled to be 25-30%. By controlling the time of the mixed material in the kiln to be 30-40 minutes, the oxidized roasted ore is magnetized roasted. The metallurgical gas produced in the reduction of the roasted ore in the reduction rotary kiln is returned to the burner for utilization. (8) When the mixture in the reduction rotary kiln reaches the discharge end, the low-temperature magnetized roasted ore with a temperature of 400-450℃ is discharged from the reduction rotary kiln. (9) The low-temperature magnetized roasted ore discharged from the kiln is rapidly cooled by water mist, so that the magnetized roasted ore is cooled to below 100°C without oxidation, and room temperature magnetized roasted ore is obtained. (10) Dust-laden flue gas with a temperature of 200-250℃ discharged from the feed end of the rotary kiln of oxidation roasting enters the gravity settling chamber. After settling, the low-temperature flue gas is removed from the dust and then discharged after being pressurized by the exhaust fan and desulfurized by the desulfurization device. (11) The room temperature magnetized roasted ore from step (9) is added to a ball mill for grinding. The grinding concentration of the ball mill is controlled to be 60-83%, and a slurry with a particle size of -200 mesh accounting for more than 80% and a concentration of 25-35% can be obtained. The slurry is then transported to a magnetic separator with a magnetic field strength of 1200-1800 Oe for magnetic separation to obtain iron concentrate with an iron grade of more than 62% and a metal recovery rate of more than 86%. The iron concentrate can be supplied to the blast furnace for use, and tailings slurry with an iron grade of 5-8% is obtained at the same time. (12) After the tailings slurry is pumped into the thickening tank through the pipeline for sedimentation, concentrated ore and tailings water can be obtained. The concentrated ore is then filtered through a filter to obtain dry tailings with a water content of 10-12%. The water obtained from the concentrated and filtered tailings slurry can be recycled to supply the grinding mill for grinding.

3. The process for producing iron concentrate from low-grade siderite by rotary kiln magnetization roasting according to claim 2, characterized in that, In step (1), the siderite is selected from low-grade, difficult-to-process iron ore with an iron grade of 25-35% and a particle size of less than 250mm; in step (2), the reducing coal is selected from lignite with a fixed carbon content of 45-50%, a volatile matter content of 35-45%, and an ash content of less than 8%.

4. The process for producing iron concentrate from low-grade siderite by rotary kiln magnetization roasting according to claim 2, characterized in that, By controlling the amount of combustion air added to the pulverized coal during combustion in the burner, the maximum temperature of the furnace gas is reduced to 900-950℃, while the O2 content in the furnace gas is controlled at 8-10% or higher.

5. The process for producing iron concentrate from low-grade siderite by rotary kiln magnetization roasting according to claim 2, characterized in that, In step (6), the weight of 0-1mm fine ore added shall not exceed 20-25% of the total siderite; the weight of 1-20mm reducing coal added shall be 2-5% of the total siderite.

Images