A method for preparing refractory iron ore through efficient roasting and separation

Abstract

This invention relates to the field of iron ore beneficiation technology and discloses a method for preparing efficient roasting and separation of refractory iron ore, comprising the following steps: S1, raw material pretreatment and pre-enrichment: refractory weakly magnetic iron oxide ore is crushed, and a dry separation method is used to pre-remove some low-grade waste rock to obtain pre-enriched rough concentrate; S2, intelligent grinding and drying; S3, magnetized roasting; S4, rapid quenching and stabilization of roasted ore. This invention, through rapid cooling (quenching) combined with an atmosphere protection process, stabilizes and solidifies the magnetism of the magnetized roasting product—magnetite—avoiding magnetic loss due to subsequent processing, providing a high-magnetic, stable feed for subsequent weak magnetic separation operations, which is a prerequisite for ensuring a high magnetic separation recovery rate; through strong magnetic separation to ensure recovery rate, combined with intelligent flotation to improve concentrate grade, a deep cleaning process is formed, achieving refined separation of complex roasting products, maximizing both the total iron metal recovery rate and concentrate grade simultaneously.

Description

Technical Field

[0001] This invention relates to the field of iron ore beneficiation technology, specifically to a method for preparing refractory iron ore through efficient roasting and separation. Background Technology

[0002] Although the world has abundant iron ore resources, iron ore is characterized by a scarcity of rich ores and a prevalence of poor ores. Among them, 97% of iron ore is low-grade iron ore with a grade of less than 30%. Therefore, the development and utilization of low-grade, difficult-to-process iron ore is of great significance.

[0003] Currently, low-grade, refractory iron ore is mainly processed using magnetization roasting technology. The most widely used magnetization roasting equipment includes rotary kilns and vertical shaft furnaces. For example, Chinese patent document CN105316476B discloses a dry suspension roasting magnetization device and method for refractory iron ore powder, which includes the following steps: Step 1: Start the induced draft fan, and ambient temperature air enters the roasting main furnace through an air cooler. At the same time, fuel is introduced into the roasting main furnace, and the fuel is ignited in the roasting main furnace to achieve ignition technology; Step 2: Send the dry iron ore powder into a dryer, and the hot flue gas generated after the roasting main furnace is ignited to dry the iron ore powder. Through a device system including preheating, main roasting, reduction, and waste heat recovery, the continuous transformation of iron minerals is realized.

[0004] However, the roasting and magnetization process in the above application has the following defects: 1) Weak pretreatment at the front end, affecting overall energy efficiency and product quality: The above scheme only performs "drying" treatment on the raw materials entering the furnace, lacking pre-enrichment and ultrafine grinding optimization treatment of the raw materials, resulting in poor quality of the final roasted ore; 2) Poor heat energy utilization effect and weak correlation with the separation process: Although the above scheme sets up a boiler to recover the waste heat of roasted sand, its energy recovery method and the core magnetization roasting reaction method are not strongly correlated with the process optimization, affecting the processing efficiency. Therefore, a preparation method for efficient roasting and separation of difficult-to-process iron ore is proposed to solve the above problems. Summary of the Invention

[0005] (a) Technical problems to be solved

[0006] To address the shortcomings of existing technologies, this invention provides a method for preparing efficient roasting and beneficiation of refractory iron ore. This method has advantages such as good raw material pretreatment to improve the roasting and beneficiation effect of iron ore, and multi-directional waste heat integration and utilization to achieve effective energy saving. It solves the problems of poor iron ore processing effect and insufficient heat energy utilization affecting processing efficiency.

[0007] (II) Technical Solution To achieve good pretreatment of the above-mentioned raw materials to improve the roasting and beneficiation effect of iron ore, and to achieve effective energy saving through multi-directional waste heat integration and utilization, this invention provides the following technical solution: a method for preparing a high-efficiency roasting and beneficiation method for refractory iron ore, comprising the following steps: S1. Raw material pretreatment and pre-enrichment: The difficult-to-select weak magnetic iron oxide ore is crushed, and a dry separation method is used to remove some low-grade waste rock in advance to obtain pre-enriched rough concentrate. S2. Intelligent grinding and drying: The pre-enriched coarse concentrate is fed into a vertical roller mill system, and waste heat gas recovered from subsequent roasting and cooling processes is introduced at the same time. Drying is carried out during the grinding process to prepare qualified powder ore with a particle size ≤0.074mm, accounting for more than 80%, and a moisture content of less than 1%. S3. Magnetized roasting: The qualified ore powder obtained in S2 is preheated by a multi-stage cyclone preheater and then fed into a composite fluidized bed roasting furnace. At the same time, a reducing gas obtained by fuel gasification and conditioning is introduced into the composite fluidized bed roasting furnace. The temperature of the roasting reaction zone is controlled at 600~850℃, so that the ore powder undergoes a rapid reduction reaction in a suspended or fluidized state. The reaction time is 1~60 seconds, and it is transformed into a strongly magnetic roasted ore. S4. Rapid quenching and stabilization of roasted ore: The high-temperature roasted ore obtained in S3 is first rapidly cooled to below 250°C under an inert or weakly reducing atmosphere, and then further cooled to below 50°C to obtain a stabilized roasted ore product. S5. High-efficiency separation: The stabilized roasted ore product obtained in S4 is slurryed and then subjected to weak magnetic separation and flotation in sequence to obtain high-quality iron concentrate.

[0008] Preferably, in step S1, the dry separation method is either high-efficiency dry air separation or intelligent photoelectric separation. High-efficiency dry air separation utilizes the differences in density, particle size, and shape of different mineral particles (target iron ore and gangue waste rock) in the crushed raw ore. In a controllable airflow field, separation is achieved based on their different motion trajectories and settling velocities. Intelligent photoelectric separation, based on machine vision and high-speed execution technology, utilizes the differences in surface optical and physical properties such as color, texture, gloss, and shape of target iron ore and gangue. Sensors identify these differences, and high-speed airflow jets remove foreign particles (usually waste rock) from the material flow.

[0009] Preferably, in step S2, the vertical roller mill system integrates a dynamic classifier and an online moisture monitor to form online monitoring and control of particle size and moisture.

[0010] Preferably, in step S3, the composite fluidized bed roasting furnace is a downward-flowing suspended roasting furnace or a circulating fluidized bed roasting furnace; the reducing gas is a mixed gas prepared from coal, natural gas or hydrogen-rich tail gas, with a total volume fraction of CO and H2 of 5% to 25%.

[0011] Preferably, in step S3, the powdered ore needs to be preheated by at least four cyclone preheaters connected in series before entering the roasting furnace, with a preheating temperature of 500℃~700℃.

[0012] Preferably, in step S3, the furnace of the composite fluidized bed roasting furnace is provided with at least one irregularly shaped constriction to form a multi-stage flow field enhanced reaction zone.

[0013] Preferably, in step S4, the rapid cooling under an inert or weakly reducing atmosphere is specifically achieved in a fluidized bed rapid heat exchanger by using nitrogen or treated low-temperature reducing tail gas as the fluidizing and cooling medium.

[0014] Preferably, in step S5, the weak magnetic separation is performed using a multi-gradient vertical ring high-gradient magnetic separator or a superconducting magnetic separator; the flotation is an intelligent flotation based on online detection of mineral surface properties and closed-loop control of reagent addition.

[0015] Preferably, after step S5, the method further includes: Step S6, Tailings Resource Utilization: The sorted tailings are graded, with the coarse-grained portion used as raw material for building materials and the fine mud portion undergoing further processing or solidification.

[0016] (III) Beneficial Effects Compared with the prior art, the present invention provides a method for preparing efficient roasting and separation of refractory iron ore, which has the following beneficial effects: 1. The preparation method of this efficient roasting and separation of refractory iron ore stabilizes and solidifies the magnetism of magnetite, the product of magnetized roasting, through rapid cooling (quenching) combined with atmosphere protection process, avoiding magnetic loss caused by subsequent processing. This provides a high-magnetic and stable feed for subsequent weak magnetic separation operations, which is a prerequisite for ensuring high magnetic separation recovery rate. By ensuring recovery rate through strong magnetic separation and combining it with intelligent flotation to improve concentrate grade, a deep cleaning process is formed, realizing the fine separation of complex roasting products and maximizing the total recovery rate of iron metal and concentrate grade simultaneously.

[0017] 2. The preparation method of this efficient roasting and separation of refractory iron ore uses wind power or intelligent machine vision to remove obvious waste ore, ensuring the mineral content for subsequent grinding, heating and other processes, thus achieving energy saving and improving the processing effect; the "waste heat" generated in the subsequent process is used to heat and dry the grinding mill, which not only dries the ore powder, but also allows the heat of the entire system to be recycled, resulting in a significant reduction in overall energy consumption.

[0018] 3. The preparation method of this efficient roasting and separation of refractory iron ore significantly reduces the amount of tailings in the dam and potential environmental risks (such as dust, acidic wastewater, and dam failure) through the graded treatment and targeted utilization of tailings, and realizes the reduction, harmlessness and resource utilization of solid waste; the utilization of coarse tailings as building materials can generate additional economic benefits and offset part of the beneficiation cost, while the safe disposal of fine mud reduces long-term environmental compliance costs. Attached Figure Description

[0019] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Example 1: Processing a mixed ore of siderite and limonite Raw materials and objectives: Target ore: Difficult-to-process weakly magnetic iron oxide ore from a certain location, with the main minerals being siderite (FeCO3) and limonite (FeO(OH)•nH2O). The average grade (TFe) of the raw ore is 28%, and the gangue is mainly composed of quartz and clay minerals. The ore contains approximately 8% water.

[0022] Processing objective: To prepare high-quality iron concentrate using this method, with a target grade ≥62% and iron recovery rate ≥88%.

[0023] The specific implementation steps are as follows: S1. Raw material pretreatment and pre-enrichment: 1) Crush the raw ore to -30mm; 2) Pre-enrichment is carried out using a high-efficiency dry air separator. The airflow velocity is controlled at 8-10 m / s. By utilizing the density difference between the ore and waste rock (mainly severely weathered low-grade surrounding rock), about 15% of the low-grade waste rock (TFe < 15%) is pre-discarded to obtain pre-enriched rough concentrate (TFe ~ 32%). S2, Intelligent Grinding and Drying: 1) Feed the pre-enriched rough concentrate into a vertical roller mill (integrated with dynamic air classifier and online near-infrared moisture meter). 2) Introduce into the mill an inert gas (N2) at approximately 180°C from the fluidized bed heat exchanger in the subsequent S4 step and a low-temperature flue gas at approximately 300°C from the preheating system in the S3 step (approximately 250°C after mixing) to simultaneously grind and dry the material. 3) By adjusting the dynamic air classifier online, the particle size of the ore output from the mill is controlled to be ≤0.074mm, accounting for 85%. The online moisture meter monitors and provides feedback to control the drying heat, ensuring that the moisture content of the ore powder is ≤0.8%. S3, Magnetized Calcination: 1) Qualified fine ore is pneumatically conveyed into a five-stage tandem cyclone preheater system. The fine ore exchanges heat counter-currently with the approximately 900°C high-temperature flue gas discharged from the roasting furnace, and is heated step by step to approximately 650°C before being discharged from the fourth-stage preheater; 2) The preheated ore powder enters a downward-flowing suspension roasting furnace. The furnace chamber has three irregularly shaped constrictions, forming a four-stage reaction zone; 3) Simultaneously, reducing gas, obtained by gasifying coal in a fluidized bed gasifier and adjusting its composition and temperature in a conditioning furnace, is injected into the furnace. The controlled gas composition is: CO 12%, H2 8%, with the remainder being N2 and CO2 (CO+H2=20%). The gas temperature is 750℃; 4) The temperature at the center of the roasting reaction zone is controlled at 750℃. The powdered ore undergoes a reduction reaction in a strong bubbling-suspension state, with a residence time of about 25 seconds, and is rapidly transformed into a strongly magnetic roasted ore mainly composed of magnetite (Fe3O4). S4. Rapid quenching and stabilization: 1) The high-temperature roasted ore (approximately 750°C) is discharged from the bottom of the roasting furnace and immediately enters the fluidized bed rapid heat exchanger; 2) Introduce room temperature nitrogen into the heat exchanger as a fluidizing and cooling medium, and rapidly cool the roasted ore to below 200°C within 3 seconds in an inert atmosphere that isolates it from air (cooling rate >150°C / s). 3) The calcined ore is then further cooled to approximately 40°C via an indirect water-cooled screw conveyor, yielding a stable roasted ore product. The hot nitrogen gas (approximately 180°C) after heat exchange is returned to step S2 as a heat source for drying. S5, High-efficiency sorting: 1) Adjust the cooled roasted ore to a slurry concentration of 35% in a mixing tank; 2) First, a superconducting magnetic separator (background field strength 2.0T) is used to perform a coarse and fine weak magnetic separation to obtain a rough concentrate; 3) The magnetically separated rough concentrate enters the intelligent flotation system. The system is equipped with an online X-ray fluorescence (XRF) analyzer to monitor the Fe and SiO2 content in the concentrate and tailings bins in real time. Based on this, the amount of inhibitor (water glass) and collector (RA series) added is dynamically adjusted to perform reverse flotation desilication and finally obtain iron concentrate product. S6. Tailings resource utilization: 1) The tailings from magnetic separation and flotation are combined and then classified by hydrocyclones; 2) Coarse particles of +0.045mm (accounting for about 65% of the total tailings) are transported to building material plants as aggregates for the production of non-fired bricks; 3) The fine mud grade of -0.045mm (accounting for about 35% of the total tailings) is transported to the deep processing workshop, where the residual ultrafine iron minerals are recovered through a magnetic separation-gravity separation combined process. Finally, the tailings are concentrated and pressure filtered and solidified before being safely stockpiled.

[0024] Implementation effect Final iron concentrate grade: 63.5%; overall iron recovery rate: 89.2%.

[0025] Overall energy consumption: Compared with the traditional rotary kiln roasting process, the standard coal consumption per ton of concentrate is reduced by about 32%.

[0026] Example 2: Processing complex hematite and limonite ores using hydrogen-rich gas Raw materials and objectives: Target ore: Complex and difficult-to-process iron ore from another mining area, with the main minerals being hematite (Fe2O3) and limonite, containing a small amount of bauxite gangue, and the raw ore grade (TFe) is 30%.

[0027] Processing objective: To utilize the hydrogen-rich tail gas from the plant to achieve low-carbon roasting and produce high-quality iron concentrate with a target grade of ≥61% and an iron recovery rate of ≥87%.

[0028] The specific implementation steps are as follows: S1. Raw material pretreatment and pre-enrichment: 1) Crush the raw ore to -25mm; 2) Pre-enrichment was carried out using an intelligent photoelectric separator. A high-resolution CCD camera was used to identify the color difference between the reddish-brown iron minerals and the grayish-white bauxite gangue. About 20% of the low-iron, high-alumina waste rock was precisely removed by a high-speed airflow valve to obtain a pre-enriched rough concentrate (TFe ~35%, Al2O3 content reduced by about 40%). S2, Intelligent Grinding and Drying: 1) Feed the pre-enriched rough concentrate into the vertical roller mill system (with online laser particle size analyzer); 2) Inert gas at approximately 150°C from step S4 is introduced and mixed with low-pressure steam (approximately 200°C after mixing) generated by the boiler in step S3 for drying; 3) Strictly control the grinding particle size to ensure that particles of -0.044mm account for more than 90% and the moisture content is controlled at around 0.5% to facilitate the rapid reduction of ultra-fine hematite particles; S3, Magnetized Calcination: 1) Fine ore powder enters a six-stage series preheater system and is gradually heated to about 600°C; 2) Hot ore powder enters a circulating fluidized bed (CFB) roaster. The furnace does not have a fixed constriction, but an internal circulating flow field is formed through the arrangement of primary air. 3) The reducing gas is hydrogen-rich tail gas from the plant's coke oven (after purification and conditioning), with the following composition: H2 45%, CO 10%, CH4 45%, and the remainder being N2 (CO+H2=55%). The gas is preheated to 680℃ and then injected through the air distribution plate at the bottom of the furnace. 4) Control the temperature of the upper part of the furnace to 680℃. The fine ore powder forms a strong circulating fluidization under high-speed airflow, and rapid reduction is completed in approximately 8 seconds. S4. Rapid quenching and stabilization: 1) After the high-temperature roasted ore and gas are separated by a cyclone separator at the top of the furnace, the high-temperature material (approximately 680°C) enters the air-cushion fluidized bed cooler. 2) Low-temperature reducing tail gas (containing 2% CO and 1% H2) that has been washed and cooled is used as the cooling medium to rapidly cool the roasted ore to below 180°C in a weak reducing atmosphere to prevent re-oxidation; S5, High-efficiency sorting (S5): 1) After slurry preparation, a multi-gradient vertical ring high-gradient magnetic separator (background field strength 1.2T) is first used for two-stage magnetic separation to efficiently recover fine-grained magnetite. 2) When the magnetic concentrate enters the flotation operation, a machine vision-based foam image analysis system is used to analyze the size, color and texture of the foam in real time, and intelligently control the addition of collectors and inhibitors to deeply remove aluminum and silicon impurities. S6. Tailings resource utilization: 1) After classification, the coarse-grained tailings are used as underground backfill material; 2) High-alumina fine mud (rich in Al2O3) is used as a raw material for extracting alumina or producing polyaluminum chloride water purifier for deep processing, so as to achieve comprehensive recovery of valuable elements.

[0029] Implementation effect Final iron concentrate grade: 62.1%, Al2O3 content <2%; overall iron recovery rate: 87.8%.

[0030] Process characteristics: It makes full use of hydrogen-rich reducing gas, has high reduction efficiency, and reduces CO2 emissions per ton of ore by about 25% compared with coal-based reduction.

[0031] In the above embodiments, the provided "Preparation method for efficient roasting and separation of refractory iron ore" can be flexibly configured to efficiently process different types of refractory weakly magnetic iron ore (such as mixed limonite and complex hematite). By integrating core technologies such as intelligent pre-enrichment, ultrafine grinding, suspension flash roasting, atmosphere-protected cooling, and efficient intelligent separation, it can stably obtain high-grade and high-recovery iron concentrate and realize tailings resource utilization, with significant comprehensive benefits and strong adaptability.

[0032] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing refractory iron ore through efficient roasting and separation, characterized in that, Includes the following steps: S1. Raw material pretreatment and pre-enrichment: The difficult-to-select weak magnetic iron oxide ore is crushed, and a dry separation method is used to remove some low-grade waste rock in advance to obtain pre-enriched rough concentrate. S2. Intelligent grinding and drying: The pre-enriched coarse concentrate is fed into a vertical roller mill system, and waste heat gas recovered from subsequent roasting and cooling processes is introduced at the same time. Drying is carried out during the grinding process to prepare qualified powder ore with a particle size ≤0.074mm, accounting for more than 80%, and a moisture content of less than 1%. S3. Magnetized roasting: The qualified ore powder obtained in S2 is preheated by a multi-stage cyclone preheater and then fed into a composite fluidized bed roasting furnace. At the same time, a reducing gas obtained by fuel gasification and conditioning is introduced into the composite fluidized bed roasting furnace. The temperature of the roasting reaction zone is controlled at 600~850℃, so that the ore powder undergoes a rapid reduction reaction in a suspended or fluidized state. The reaction time is 1~60 seconds, and it is transformed into a strongly magnetic roasted ore. S4. Rapid quenching and stabilization of roasted ore: The high-temperature roasted ore obtained in S3 is first rapidly cooled to below 250°C under an inert or weakly reducing atmosphere, and then further cooled to below 50°C to obtain a stabilized roasted ore product. S5. High-efficiency separation: The stabilized roasted ore product obtained in S4 is slurryed and then subjected to weak magnetic separation and flotation in sequence to obtain high-quality iron concentrate.

2. The preparation method of a high-efficiency roasting and beneficiation method for refractory iron ore according to claim 1, characterized in that, In step S1, the dry separation method is either high-efficiency dry air separation or intelligent photoelectric separation. High-efficiency dry air separation utilizes the differences in density, particle size, and shape of different mineral particles (target iron ore and gangue waste rock) in the crushed raw ore. In a controllable airflow field, separation is achieved based on their different motion trajectories and settling velocities. Intelligent photoelectric separation, based on machine vision and high-speed execution technology, utilizes the differences in surface optical and physical properties such as color, texture, gloss, and shape of target iron ore and gangue. Sensors identify these differences and high-speed airflow jets remove foreign particles (usually waste rock) from the material flow.

3. The preparation method of a high-efficiency roasting and beneficiation process for refractory iron ore according to claim 1, characterized in that, In step S2, the vertical roller mill system integrates a dynamic classifier and an online moisture monitor, forming an online monitoring and control system for particle size and moisture.

4. The preparation method of a high-efficiency roasting and beneficiation method for refractory iron ore according to claim 1, characterized in that, In step S3, the composite fluidized bed roasting furnace is a downward-flowing suspended roasting furnace or a circulating fluidized bed roasting furnace; the reducing gas is a mixed gas prepared from coal, natural gas or hydrogen-rich tail gas, with a total volume fraction of CO and H2 of 5% to 25%.

5. The preparation method of a high-efficiency roasting and beneficiation method for refractory iron ore according to claim 1, characterized in that, In step S3, the powdered ore needs to be preheated by at least four cyclone preheaters connected in series before entering the roasting furnace, with a preheating temperature of 500℃~700℃.

6. The preparation method of a high-efficiency roasting and beneficiation method for refractory iron ore according to claim 1, characterized in that, In step S3, the furnace of the composite fluidized bed roasting furnace is provided with at least one irregularly shaped constriction to form a multi-stage flow field enhanced reaction zone.

7. The preparation method of a high-efficiency roasting and beneficiation method for refractory iron ore according to claim 1, characterized in that, In step S4, the rapid cooling under an inert or weakly reducing atmosphere is specifically achieved in a fluidized bed rapid heat exchanger by using nitrogen or treated low-temperature reducing tail gas as the fluidizing and cooling medium.

8. The preparation method of a high-efficiency roasting and beneficiation process for refractory iron ore according to claim 1, characterized in that, In step S5, the weak magnetic separation is carried out using a multi-gradient vertical ring high-gradient magnetic separator or a superconducting magnetic separator; the flotation is an intelligent flotation based on online detection of mineral surface properties and closed-loop control of reagent addition.

9. The preparation method of a high-efficiency roasting and beneficiation method for refractory iron ore according to claim 1, characterized in that, Following step S5, the following is also included: Step S6, Tailings Resource Utilization: The sorted tailings are graded, with the coarse-grained portion used as raw material for building materials and the fine mud portion undergoing further processing or solidification.

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