Method for recovering ultra-fine materials from iron ore processing for the production of micro-pellets

Abstract

The present invention relates to a method for recovering ultra-fine materials from iron ore processing for the production of micro-pellets for use in steelmaking, comprising: collecting the ultra-fine material in the form of pulp after the desliming stage of the iron ore processing method; sending the ultra-fine material to a wet magnetic concentration stage; dewatering the ultra-fine concentrate in a filter press to obtain a pellet feed; sending the ultra-fine pellet feed to a mixing stage, adding the necessary inputs for the agglomeration and hardening stage; subjecting the ultra-fine pellet feed to an agglomeration stage forming micro-pellets; subjecting the micro-pellets produced in the previous stage to a hot hardening stage in mobile grate furnaces.

Description

[0001] “PROCESS FOR RECOVERING ULTRAFINE MATERIALS FROM IRON ORE PROCESSING FOR MICROPELLET PRODUCTION”

[0002] TECHNICAL FIELD

[0003]

[0001] The present invention belongs to the technical field of ore treatment, agglomeration or granulation processes. More specifically, the present invention aims to use the ultrafine material resulting from the iron ore beneficiation process to obtain micro agglomerates, called micropellets, which can be used in the steel industry as a replacement for natural sinter feed.

[0004] STATE OF THE TECHNIQUE

[0005]

[0002] Iron ore concentration processes are basically composed of unit operations of comminution, flotation, classification (desliming) and thickening. In the desliming stage, this ultrafine fraction, rich in iron, is separated and normally disposed of in a dam or pit.

[0006]

[0003] Consequently, in order to take advantage of these ultrafines in an economically and environmentally sustainable manner, there is a need to treat such waste, which leads companies in the mining sector to seek alternative processing technologies, aiming to increase the iron content through magnetic concentration processes.

[0007]

[0004] In this search for the use of discarded iron slurry tailings, consequently of the treatment of ultrafine material, in the range of 70% passing in 10 pm, one of the possible destinations is in the field of steelmaking. Usually, the natural sinter feed product is used as raw material in the sintering process, which comprises materials with approximate particle sizes between 0.1 and 6.3 mm, and is subsequently subjected to a granulation stage with the application of additives and hardening in sintering furnaces, to form the resulting material called sinter, with particle sizes between 10 and 50 mm, used as a source of iron in blast furnaces in the steelmaking industry.

[0008]

[0005] Furthermore, PASCOAL, Aline da Luz et al (Study of the production of sinter feed and pellet feed according to particle size - Rev. Bras. Apl. Vac., Campinas, Vol. 35, No. 3, pp. 151-154, Sept. - Dec., 2016) mentions the importance of the production of iron ore fines that currently require greater recovery, which is related to the low Fe contents related to the scarcity of deposits and also intrinsic to the growing demand of the steel industry for adequate Fe contents, particle size and metallurgical performance in blast furnaces. It also mentions that the particle size required for the production of pellet feed and sinter feed is a very important variable for concentrates, since to feed the reduction furnaces, concentrates with lower particle sizes necessarily have to undergo an agglomeration process.

[0009]

[0006] The article by PINTO, PF; JUNIOR, HD Recovery of pellet feed from tailings dams, Mining, REM, Int. Eng. J. 72 (3), Jul-Sep 2019 deals with the recovery of iron content present in tailings dams with a view to adapting it as a material for pellet production.

[0010]

[0007] Publications in patent documents such as US2012260772, WO201 3138889 and BR102012008340-0 describe means of recovering iron mud waste resulting from iron ore beneficiation processes.

[0011]

[0008] Patent document BR102012008758 describes a process for separating iron ore contained in waste from the extraction and processing of iron ore and its use in steel mills.

[0012]

[0009] Document US20090169413 describes specific temperature and heating time conditions required in the hardening process of pellets obtained from the use of waste in the steel industry. Specific temperature conditions are also described by document US20160168654, which describes a process for producing agglomerates from particulate iron materials, also citing the problem of the prior art in which it is extremely difficult to apply usual granulation processes aimed at using slurry tailings as iron raw material, since the iron particles are extremely fine.

[0013]

[0010] Document BR102019025276-6 describes a process for producing iron ore concentrate and pellets, with the addition of waste generated during the beneficiation stage, called desliming, with the generation of fine and ultrafine waste, called “sludge”, by mixing and subsequent agglomeration of these materials, followed by heat treatment.

[0014] SUMMARY OF THE INVENTION

[0015] Technical problem

[0016]

[0011] The usual iron ore concentration processes annually generate millions of tons of an ultrafine iron-rich material that are discarded due to the flotation process's inability to process it.

[0017]

[0012] Several prior art documents seek to utilize and separate iron ore contained in residues from iron ore processing, and sometimes even mention its use in steel mills. However, there remains a need for a technical solution that provides a process with stages for collecting the ultrafine materials contained in the iron slurry tailings, dewatering to obtain an ultrafine pellet feed with specific moisture content, agglomerating them into micropellets of predefined dimensions, and hardening the micropellets in a specific furnace, maintaining a controlled thermal cycle and a predefined particle size distribution, so that the micropellets resulting from this process meet the necessary requirements to be used as a replacement for natural sinter feed in the sintering process of the steel industry.

[0018]

[0013] Natural sinter feed, as the name suggests, is a material extracted from nature, presenting greater variability in its chemical and particle size composition, which can be minimized with a few concentration steps. The main processing steps are crushing and particle size classification into the desired ranges. The ideal particle size distribution of iron ores for sintering follows the Astier curve shown in Figure 1. This curve establishes that the ores should be limited to the mesh sizes of 6.35 mm to 0.105 mm, and approximately 50%.

[0019]

[0014] The depletion of iron mineral reserves, combined with the thinning of commercially available sinter feed, has resulted in increasingly lower sintering process yields. To correct the chemical composition, companies use pellet feed, a material obtained from a concentration process that typically contains higher iron and lower contaminant levels. However, these materials are too fine for the sintering process.

[0020]

[0015] On the other hand, some thermally processed materials are being used in the sintering mix to promote better sintering machine performance by improving bed permeability. One of the products is pellet screening (material from the screening of iron ore pellets), which has high iron contents and larger particle sizes than those offered on the market for sinter feed.

[0021]

[0016] Given the scenario of sinter feed thinning and reduction in iron content, there is a need to create a product with controlled particle size distribution and chemical composition, to adjust the sintering process

[0017] The use of waste to obtain micropellets through current processes is not possible and the particle size of the ultrafine material is not suitable for the existing circuit.

[0022] TECHNICAL SOLUTION

[0023]

[0018] To solve the technical problem, the present application proposes a new and inventive process for recovering ultrafine materials from the beneficiation of iron ore for the production of micropellets for use in the steel industry, as well as a new and inventive micropellet for use in the steel industry produced from the recovery of ultrafine materials from the beneficiation of iron ore.

[0024]

[0019] The process for recovering ultrafine materials from the beneficiation of iron ore for the production of micropellets for use in the steel industry is characterized by (a) collecting the ultrafine material in the form of pulp after the desliming stage of the iron ore beneficiation process, in which the ultrafine material is classified as being in the range of 70% passing 10 pm and having iron contents of the order of 45 to 55% and a specific surface area between 8,000 and 12,000 cm 2 / g; (b) send the ultrafine material to a wet magnetic concentration stage, in which the magnetic concentration adopts a matrix of 1.0-3.0 mm and a field of 4,000-12,000 Gauss, obtaining as a product an ultrafine concentrate with iron contents of the order of 56% and 62% iron, mass recovery between 20% and 50% and specific surface area between 4,000 and 8,000 cm 2 / g; (c) dewater the ultrafine concentrate in a filter press to obtain an ultrafine feed pellet with residual moisture between 12.0 and 14.0%; (d) send the ultrafine feed pellet to a mixing step, adding the necessary inputs for the agglomeration and hardening step, including at least a dosage of bentonite between 0.3% and 0.7%; (e) subject the ultrafine feed pellet to an agglomeration step, forming raw or green micropellets, with a resulting particle size range between 1.0 and 6.3 mm, with 65% above 1.0 mm and an average diameter of 4.0 mm; (f) subject the micropellets produced in the previous step to a hot hardening step in moving grate furnaces, controlling the thermal cycle, gas flow rates and appropriate pressures.

[0025]

[0020] Micropellets for use in the steel industry produced from the recovery of ultrafine materials from the beneficiation of iron ore are characterized by (a) having an iron content of 58% to 62%; (b) having a particle size range between 1.0 and 6.3 mm, with 65% above 1.0 mm and an average diameter of 4.0 mm; (c) having silica between 8.0% and 12.0%; (d) having alumina between 2.5% and 3.5%; (e) having phosphorus between 0.090% and 0.100%. ADVANTAGEOUS EFFECTS

[0026]

[0021] The development of micropellets from iron sludge generated in the concentration, previously considered as process waste, increases the overall metal recovery of the entire iron ore processing chain, significantly reducing the need for area for waste disposal, thus increasing the sustainability and reducing business risks.

[0027]

[0022] Furthermore, the present inventive concept involves using a production process line to produce a final product for the steel market where the only raw material is ultrafine material from desliming, which is not possible using the processes described in the prior art or their combination. Therefore, all the physical, chemical, and metallurgical characteristics of the product must be achieved with the established production process. For example, the combination of the processes described in patent document BR102019025276-6 and in the scientific article "Recovery of pellet feed from tailings dams" cited in the prior art would lead a person skilled in the art to simply add the ultrafine materials according to the proposed parameters in a conventional pellet production process with a conventional raw material base, with characteristics suitable for pellet production, and only adding ultrafines to this base.The complexity of adding a material to an already defined base is much less, as the base offers all the stability that the process demands and creates operational opportunities to make adjustments to both the base and the added ultrafine and proportions.

[0028]

[0023] Finally, the inventive process defended in the present application is to develop a process capable of delivering a product with the only raw material containing the metal of interest, iron, being the ultrafine from desliming, which is contrary to what is proposed by the prior art. This also means an exceptionally advantageous gain in scale in terms of taking advantage of the recovery of ultrafine materials from the beneficiation of iron ore.

[0029]

[0024] The micropellets obtained from the processing of ultrafine materials resulting from the beneficiation of iron ore can be used to partially or completely replace the natural sinter feed offered on the market, with some advantages, including the fact that they do not have loss on ignition, due to their exposure to a controlled thermal cycle during the hardening process, defined and narrow chemical composition, predefined particle size distribution within a narrow range of variation, essential for the permeability of the bed and productivity of the sintering machine.

[0030]

[0025] The particle size distribution of the micropellets allows the addition of fine materials to the blend, such as concentrated pellet feeds, which have a higher iron content and lower gangue content (they are concentration products), to correct the chemical composition, without compromising the permeability of the sintering bed. Thus, the productivity of the sinter machine increases with the addition of the micropellets of the present invention.

[0031] BRIEF DESCRIPTION OF THE DRAWINGS

[0032]

[0026] Hereinafter, the present invention will be described in combination with the figures and embodiments. The accompanying drawings are not necessarily shown to scale. In the drawings, some identical or nearly identical components illustrated in several figures may be represented by a corresponding number. For purposes of clarity, not all components are identified in each drawing.

[0033]

[0027] Figure 01 shows the ideal particle size distribution of iron ores for sintering according to the Astier curve.

[0034]

[0028] Figure 02 presents a diagram of the usual iron ore beneficiation process, more specifically it presents the desliming stage of a concentrator circuit.

[0029] Figure 03 presents a graph with the particle size distribution of the iron slurry particles processed in the present invention compared to a common pellet feed.

[0035]

[0030] Figure 04 presents a simplified flowchart of the micropellet production process of the present invention.

[0036]

[0031] Figure 05 shows a graph with the particle size distribution of the ultrafine material in natura and ultrafine concentrated material.

[0037]

[0032] Figure 06 shows the results obtained in the pilot scale tests for the ultra-thin material.

[0038]

[0033] Figure 07 shows the results obtained in the pilot scale tests for the ultrafine material in natura and concentrated.

[0039]

[0034] Figure 08 shows the particle size results obtained on a pilot scale for raw micropellets produced in a pelletizing disc and in an intensive mixer.

[0040]

[0035] Figure 09 shows the typical thermal profile for the hardening of micropellets in a moving grate furnace.

[0041]

[0036] Figure 10 shows a comparison of the particle size distribution of micropellets obtained in intensive mixers versus pelletizing discs.

[0042] DETAILED DESCRIPTION OF THE BEST EXECUTION MODES

[0043]

[0037] This invention is not limited in its application to the construction details and arrangement of components set forth in the following description or illustrated in the drawings. The invention is feasible with other configurations and may be practiced or executed in various ways. Furthermore, the phraseology and terminology used herein are for descriptive purposes and should not be considered restrictive. The use of "including," "comprising," "having," "containing," or "involving," and variants of these terms, is intended to encompass the items listed after said terms and their equivalents, as well as additional items.

[0044]

[0038] To solve the technical problem, the present application proposes a new and inventive process for recovering ultrafine materials from the beneficiation of iron ore for the production of micropellets for use in the steel industry, as well as a new and inventive micropellet for use in the steel industry produced from the recovery of ultrafine materials from the beneficiation of iron ore.

[0045]

[0039] The process for recovering ultrafine materials from the beneficiation of iron ore for the production of micropellets for use in the steel industry is characterized by (a) collecting the ultrafine material in the form of pulp in the desliming stage of the iron ore beneficiation process, with iron contents of the order of 45 to 50% and with a specific surface area between 8,000 and 12,000 cm 2 / g; (b) send the ultrafine material to a wet magnetic concentration stage, obtaining as a product an ultrafine concentrate with iron contents of the order of 56% and 62% iron, mass recovery between 30% and 40% and specific surface area between 4,000 and 8,000 cm 2 / g; (c) dewater the ultrafine concentrate in a filter press to obtain an ultrafine feed pellet with residual moisture between 12.0 and 14.0%; (d) send the ultrafine feed pellet to a mixing step, adding the necessary inputs for the agglomeration and hardening step, including at least a dosage of bentonite between 0.3% and 0.7%; (e) subject the ultrafine feed pellet to an agglomeration step, forming raw or green micropellets, with a resulting particle size range between 1.0 and 6.3 mm, with 65% above 1.0 mm and an average diameter of 4.0 mm; (f) subject the micropellets produced in the previous step to a hot hardening step in moving grate furnaces, controlling the thermal cycle, gas flow rates and appropriate pressures.

[0046]

[0040] Micropellets for use in the steel industry produced from the recovery of ultrafine materials from iron ore beneficiation are characterized by (a) having an iron content of 58% to 62%; (b) having a particle size range between 1.0 and 6.3 mm, with 65% above 1.0 mm and an average diameter of 4.0 mm; (c) having silica between 8.0% and 12.0%; (d) having alumina between 2.5% and 3.5%; (e) having phosphorus between 0.090% and 0.100%.

[0041] The diagram of the usual iron ore beneficiation process, in Figure 02, shows the process steps. The material (ROM) from the mine goes through a particle size classification step. The coarse fractions are crushed until the desired particle size is reached for primary grinding, in ball mills.The material leaving the ball mills undergoes a cyclone classification stage, with the coarse material returning to the mill, while the fine material is sent to the desliming circuit, where ultrafines are removed from the production process, as they compromise subsequent flotation stages. This ultrafine material, referred to as iron sludge, is the target of this application. It is commonly presented in the form of a pulp, with a solids concentration of approximately 5% by weight and an actual solids density of approximately 4.0 g / cm3. This pulp is thickened to a solids concentration of between 30 and 35% by weight and deposited in dams for future use, with the development of a processing technique underway to adapt its chemical and physical characteristics for application in steelmaking processes.

[0047]

[0042] The mineralogical characterizations by X-ray diffraction of this ultrafine material in natura are found in Table I and the particle size distribution of the iron mud particles are found in Figure 03.

[0048] Table I: Mineralogical characterization of ultrafine

[0049]

[0043] Table II shows an example of a typical composition of the ultrafine material resulting from the desliming step. Table II: Characterization of the ultrafine material in natura

[0050]

[0044] Fig. 04 shows a simplified flowchart of the micropellet production process of the present invention. The ultrafine material from desliming, with iron contents between 45 and 55%, with a specific surface area between 8,000 and 12,000 cm 2 / g, is sent to a wet magnetic concentration stage. After processing, the resulting product, called ultrafine concentrate, is an ultrafine iron ore concentrate with iron contents between 56% and 62% and a specific surface area between 8,000 and 12,000 cm 2 / g, with a mass recovery between 20% and 50%. In magnetic concentration, the iron content will determine the mass recovery of the material.

[0051]

[0045] Table III presents the characterization of the concentrated ultrafine material according to the comparative details of Figure 05 with the particle size distribution of the in natura ultrafine material and concentrated ultrafine material. The graph in Figure 06 shows the results obtained in one of the pilot scale tests for the ultrafine material.

[0052] Table III: Characterization of concentrated ultrafine material

[0046] The ultrafine concentrate is directed to a thickener to increase its solids percentage from x% to y% and is then stored in a homogenization tank. In the next step, the ultrafine concentrate produced in the magnetic concentration process undergoes a dewatering stage in a filter press, generating a pellet feed with residual moisture between 12% and 15%. The graph in Figure 07 shows the results obtained in the pilot-scale tests for the ultrafine material in natura and concentrated.

[0053]

[0047] The necessary inputs for the agglomeration and hardening stage will be added to the concentrated ultrafine material in the following proportions: limestone dosage between 0% and 3%; anthracite dosage between 0% and 1.2%, and bentonite dosage between 0.3% and 0.7%.

[0054]

[0048] The agglomeration process can be carried out in two different routes. One possible route would be the use of intensive mixers, in which the ultrafine pellet feed with the inputs necessary for the process is sent to the intensive mixers, and by adjusting the mixer process variables (feed rate, bowl rotation, tool rotation and residence time) the raw / green micropellets are formed, with the predefined particle size distribution in a narrow range of variation, with a minimum of 65% of the micropellets between 1.0 and 6.3 mm.

[0055]

[0049] Alternatively, it is possible to adopt a route with pelletizing discs, in which the ultrafine pellet feed with the inputs necessary for the process are sent to the horizontal mixers and after the mixing and homogenization process, the mixture is sent to the pelletizing discs, with the appropriate adjustments (position of the scrapers, useful height, rotation, inclination and feed rate) for the production of raw / green micropellets, with the predefined particle size distribution in a narrow range of variation, with a minimum of 65% of the micropellets between 1.0 and 6.3 mm;

[0056]

[0050] Figure 08 shows the particle size results obtained on a pilot scale for raw micropellets produced in a pelletizing disc and in an intensive mixer.

[0051] For hardening, the micropellets undergo a hot hardening stage in moving grate furnaces, controlling the thermal cycle, gas flow rates and pressures appropriate to the new product, with the particle size distribution predefined in a narrow range of variation, with a minimum of 65% of the micropellets between 1.0 and 6.3 mm. Some modifications and adaptations will be necessary to allow heat transfer between the hot gases and the micropellets, without causing a rupture of the bed in the grate car.The main parameters include: grate lining layer with a thickness of between 5 and 10 cm; total bed height (raw pellets + lining layer) between 30 and 40 cm; total firing cycle time: 30 to 40 minutes; maximum firing temperature: 1200 to 1250°C; pressures in the various regions of the furnace: 350 to 500 mmca. Changes in the design of the grate bars for support may also be necessary, modifying the gap between the bars in conventional pelletizing, which is on the order of 8.0 mm.

[0057]

[0052] Figure 09 shows the typical thermal profile for the hardening of micropellets in a mobile grate furnace, so that they acquire physical resistance for handling and transportation to steel plants.

[0058]

[0053] The resulting product, called micropellets, has a particle size distribution according to Figure 10, which compares the particle size distribution obtained in intensive mixers versus pelletizing discs.

[0059]

[0054] Table IV presents the main chemical elements of the micropellets, which may present small variations. As it is a thermally processed material, it does not have PPC.

[0060] Table IV: Chemical composition of burned micropellets

[0061]

[0055] The micropellets produced will be used to partially or completely replace the natural sinter feeds offered on the market, with the advantage of not having loss on ignition due to their exposure to a controlled thermal cycle during the hardening process, defined and narrow chemical composition, predefined particle size distribution in a narrow range of variation. In the sintering process, the micropellets can be used with particles to increase the permeability of the sinter bed, enabling increased process productivity, even if fine concentrates (pellet feeds) are added to it.

[0062]

[0056] Although the invention has been disclosed by this specification, including the examples and figures therein, various equivalents, modifications, and improvements will become apparent to one skilled in the art. The following claims are also intended to encompass such equivalents, modifications, and improvements.

Claims

CLAIMS 01. Process for recovering ultrafine materials from the beneficiation of iron ore for the production of micropellets for use in the steel industry characterized by (a) collect the ultrafine material in the form of pulp after the desliming stage of the iron ore beneficiation process, in which the ultrafine material is classified as being in the range of 70% passing 10 pm and having iron contents of the order of 45 to 55% and a specific surface area between 8,000 and 12,000 cm 2 / g; (b) send the ultrafine material to a wet magnetic concentration stage, in which the magnetic concentration adopts a matrix of 1.0-3.0 mm and a field of 4,000-12,000 Gauss, obtaining as a product an ultrafine concentrate with iron contents of the order of 56% and 62% iron, mass recovery between 20% and 50% and specific surface area between 4,000 and 8,000 cm 2 / g; (c) dewater the ultrafine concentrate in a filter press to obtain an ultrafine feed pellet with residual moisture between 12.0 and 14.0%; (d) send the ultrafine pellet feed to a mixing stage adding the necessary inputs for the agglomeration and hardening stage, including at least a dosage of bentonite between 0.3% and 0.7%; (e) subject the ultrafine pellet feed to an agglomeration step forming raw or green micropellets, with a resulting particle size range between 1.0 and 6.3 mm, with 65% above 1.0 mm and an average diameter of 4.0 mm; (f) subject the micropellets produced in the previous step to a hot hardening step in moving grate furnaces.

02. Process for recovering ultrafine materials from the processing of iron ore for the production of micropellets for use in the steel industry according to claim 01, characterized in that the agglomeration step is carried out in an intensive mixer.

03. Process for recovering ultrafine materials from the processing of iron ore for the production of micropellets for use in the steel industry according to claim 01, characterized in that the agglomeration stage is carried out in a horizontal mixer and after the mixing and homogenization process, the resulting pellet feed is sent to the pelletizing discs.

04. Process for recovering ultrafine materials from the processing of iron ore for the production of micropellets for use in the steel industry according to claim 01, characterized in that the inputs required for the agglomeration and hardening stage include a limestone dosage of up to 3%.

05. Process for recovering ultrafine materials from the processing of iron ore for the production of micropellets for use in the steel industry according to claim 01, characterized in that the inputs required for the agglomeration and hardening stage include an anthracite dosage of up to 1.2%.

06. Micropellet for use in the steel industry produced from the process defined in claim 01 characterized by (a) have an iron content of 58% to 62%; (b) have a particle size range between 1.0 and 6.3 mm, with 65% above 1.0 mm and an average diameter of 4.0 mm; (c) have silica between 8.0% and 12.0%; (d) have alumina between 2.5% and 3.5%; (e) have phosphorus between 0.090% and 0.100%.

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